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Astrocytes are a major target in thiamine deficiency and Wernicke's encephalopathy
Abstract
Thiamine deficiency (TD) is the underlying cause, and an established model, of Wernicke's encephalopathy (WE). Although the neurologic dysfunction and brain damage that results from TD has been well-described, the precise mechanisms that lead to the selective histological lesions characteristic of this disorder remain a mystery. Over the course of many years, various processes have been proposed that could lead to focal neuronal cell death in this disorder. But despite a concerted effort to relate these processes to a clear sequelae of events culminating in development of the focal neuropathology, little success has resulted. In recent years, however, a role for astrocytes in the pathophysiology of TD has been emerging. Here, alterations in glutamate uptake, and levels of the astrocytic glutamate transporters EAAT1 and EAAT2 in TD and WE, are discussed in terms of an excitotoxic event, along with the GABA transporter subtype GAT-3, and changes in other astrocytic proteins including GFAP and glutamine synthetase. Lactic acidosis, changes in the water channel protein AQP-4 and brain edema are also a focus of attention in relation to astrocyte dysfunction, while involvement of oxidative stress and inflammatory processes, along with white matter injury in terms of excitotoxicity are other key issues considered. In summary, a new appraisal of the extent of involvement of astrocytes in TD and WE is presented, with the evidence suggesting these cells represent a major target for damage during the disease process.
... Levels of astroglial transporters EAAT1 and EAAT2 in cortical samples from human tissues obtained from confirmed cases of the disease are reduced by 60-70 per cent. A similar profound decrease in astroglial glutamate transporters has been found in the rat thiamine deficiency model of the disease (Hazell, 2009;Hazell et al., 2009). The failure of astroglial glutamate uptake causes severe neuronal excitotoxicity and subsequent tissue lesions. ...
... The failure of astroglial glutamate uptake causes severe neuronal excitotoxicity and subsequent tissue lesions. In addition, a significant decrease in expression of GFAP, astrocytic glutamine synthetase and astrocytic GAT-3 GABA transporter, all indicative of astroglial dystrophy, have been observed in the thalamus of thiamine deficient rats (Hazell, 2009;Hazell et al., 2009). 10.8.4 Fronto-temporal, thalamic, HIV-associated and other non-Alzheimer's type dementias ...
... In these cases, severe neurological symptoms correlate with macroscopically apparent, substantial degeneration of GM or WM in cerebellum, thalamus, mammillary bodies or cerebral cortex (Phillips et al., 1990;Kril and Harper, 2012). Interestingly, although neurons and oligodendrocytes are considered major targets of nutritional and metabolic disturbances, such as thiamine deficiency, astrocytes can be also critically affected by the same disturbances (Hazell, 2009). In addition, acute ethanol exposure of cultured astrocytes causes extensive gene expression changes that resemble the heat shock response (Pignataro et al., 2013). ...
... These roles include the regulation of neuroinflammatory processes, calcium signaling, balance of excitatory and inhibitory neurotransmission, water balance/cell volume regulation, as well as the regulation of dopamine-dependent behavioral processes in brain reward circuits (Adermark and Bowers, 2016). In addition, acute or prolonged exposure of astrocytes to alcohol may substantially modify the efficacy of connections between brain areas by disturbing the maintenance of myelin (Hazell, 2009) and the buffering of ions in the proximity of nodes Ranvier. Altering ion buffering and the osmotic regulation that results from astrocyte interactions with oligodendrocytes around NR causes abnormal action potential propagation in WM and myelinated portions of GM (Gankam Kengne et al., 2011). ...
Postmortem studies reveal structural and molecular alterations of astrocytes and oligodendrocytes in both the gray and white matter (GM and WM) of the prefrontal cortex (PFC) in human subjects with chronic alcohol abuse or dependence. These glial cellular changes appear to parallel and may largely explain structural and functional alterations detected using neuroimaging techniques in subjects with alcohol use disorders (AUDs). Moreover, due to the crucial roles of astrocytes and oligodendrocytes in neurotransmission and signal conduction, these cells are very likely major players in the molecular mechanisms underpinning alcoholism-related connectivity disturbances between the PFC and relevant interconnecting brain regions. The glia-mediated etiology of alcohol-related brain damage is likely multifactorial since metabolic, hormonal, hepatic and hemodynamic factors as well as direct actions of ethanol or its metabolites have the potential to disrupt distinct aspects of glial neurobiology. Studies in animal models of alcoholism and postmortem human brains have identified astrocyte markers altered in response to significant exposures to ethanol or during alcohol withdrawal, such as gap-junction proteins, glutamate transporters or enzymes related to glutamate and gamma-aminobutyric acid (GABA) metabolism. Changes in these proteins and their regulatory pathways would not only cause GM neuronal dysfunction, but also disturbances in the ability of WM axons to convey impulses. In addition, alcoholism alters the expression of astrocyte and myelin proteins and of oligodendrocyte transcription factors important for the maintenance and plasticity of myelin sheaths in WM and GM. These changes are concomitant with epigenetic DNA and histone modifications as well as alterations in regulatory microRNAs (miRNAs) that likely cause profound disturbances of gene expression and protein translation. Knowledge is also available about interactions between astrocytes and oligodendrocytes not only at the Nodes of Ranvier (NR), but also in gap junction-based astrocyte-oligodendrocyte contacts and other forms of cell-to-cell communication now understood to be critical for the maintenance and formation of myelin. Close interactions between astrocytes and oligodendrocytes also suggest that therapies for alcoholism based on a specific glial cell type pathology will require a better understanding of molecular interactions between different cell types, as well as considering the possibility of using combined molecular approaches for more effective therapies.
... The resulting metabolic disruption leads to oxidative stress, inflammation, excitotoxicity, blood brain barrier dysfunction, cytotoxic edema, and apoptotic cell death [12,14,15]. Many effects of TD-induced metabolic disruption occur in astrocytes [16,17]. TD disrupts neuron-astrocyte metabolic trafficking and induces focal lactic acidosis that further contributes to neurological damage [16]. ...
... Many effects of TD-induced metabolic disruption occur in astrocytes [16,17]. TD disrupts neuron-astrocyte metabolic trafficking and induces focal lactic acidosis that further contributes to neurological damage [16]. Additionally, astrocyte-specific morphological changes are an early marker of TDinduced damage [18,19]. ...
Thiamine is an essential enzyme cofactor required for proper metabolic function and maintenance of metabolism and energy production in the brain. In developed countries, thiamine deficiency (TD) is most often manifested following chronic alcohol consumption leading to impaired mitochondrial function, oxidative stress, inflammation and excitotoxicity. These biochemical lesions result in apoptotic cell death in both neurons and astrocytes. Comparable histological injuries in patients with hypoxia/ischemia and TD have been described in the thalamus and mammillary bodies, suggesting a congruency between the cellular responses to these stresses. Consistent with hypoxia/ischemia, TD stabilizes and activates Hypoxia Inducible Factor-1α (HIF-1α) under physiological oxygen levels. However, the role of TD-induced HIF-1α in neurological injury is currently unknown. Using Western blot analysis and RT-PCR, we have demonstrated that TD induces HIF-1α expression and activity in primary mouse astrocytes. We observed a time-dependent increase in mRNA and protein expression of the pro-apoptotic and pro-inflammatory HIF-1α target genes MCP1, BNIP3, Nix and Noxa during TD. We also observed apoptotic cell death in TD as demonstrated by PI/Annexin V staining, TUNEL assay, and Cell Death ELISA. Pharmacological inhibition of HIF-1α activity using YC1 and thiamine repletion both reduced expression of pro-apoptotic HIF-1α target genes and apoptotic cell death in TD. These results demonstrate that induction of HIF-1α mediated transcriptional up-regulation of pro-apoptotic/inflammatory signaling contributes to astrocyte cell death during thiamine deficiency.
... Microglia undergoes activation in PD associated with high secretion of cytokines; activated microglia is generally believed to produce neurotoxicity and contribute to the demise of dopaminergic neurones. Activated microglial cells are often clustered around degenerating dopaminergic neurones [28][29][30][31] Wernicke encephalopathy Major (~70-80%) decrease in expression of astroglial plasmalemmal l-glutamate transporters represents the key pathological step in neurotoxicity and neuronal atrophy [32,33] (continued) superoxide dismutase 1 (Tg(SOD1*G93A)1Gur mice), the occurrence of atrophic astrocytes seems to be the earliest pathological signature [12,14]. The ability of these atrophic astrocytes to remove l-glutamate is compromised, which is thought to result in the accumulation of extracellular l-glutamate with ensuing excitotoxicity [48]. ...
... The importance of astrocytes in ALS pathogenesis is further corroborated by the observation that silencing of ALS-related mutant SOD1 gene in astrocytes delayed the appearance of clinical symptoms in the transgenic mouse model [15]. Astroglial degeneration and loss of function also assumes a pathological proportion in Wernicke encephalopathy, a thalamo-cortical neurodegeneration, which represents the substrate for Korsakoff syndrome; significant down-regulation of astroglial l-glutamate transporters results in prominent excitotoxicity [32,33]. Similarly, in Huntington disease (HD), a decreased astroglial l-glutamate uptake as well as an aberrant release of L-glutamate from astrocytes contributes to neurotoxicity. ...
The most notable finding in neurodegenerative diseases is the progressive death of neurones cells. Yet, neuroglial changes can precede and facilitate neuronal loss. This is perhaps expected because astroglial cells maintain the brain homoeostasis, and are responsible for defence and regeneration, so that their malfunction manifested as degeneration or asthenia together with reactivity contribute to pathophysiology. Neuroglia may represent a novel target for therapeutic intervention, be that prevention, slowing progression of or possibly curing neurodegenerative diseases.
... Growing research on this topic suggests that astrocytes have a role in the pathophysiology of thiamine deficiency. The excitotoxic event is discussed in terms of the gamma-aminobutyric acid (GABA) transporter subtype GABA transporter 3 (GAT-3), changes in other astrocytic proteins, such as glial fibrillary acidic protein (GFAP) and glutamine synthetase, and changes in glutamate uptake and levels of the astrocytic glutamate transporters excitatory amino acid transporters (EAATs) 1 and 2 in thiamine deficiency and Wernicke's encephalopathy [4]. The patients who are alcohol dependent have lower thiamine levels. ...
Korsakoff syndrome and Wernicke's encephalopathy (WE) show neurological and cognitive deficits. Wernicke-Korsakoff syndrome (WKS) is a compound neurological condition. The cause of this neurological condition could be the consumption of alcohol regularly for a chronic duration. A tailored rehabilitation protocol that focuses on cognitive and physical deficiencies was implemented along with thiamine supplementation for managing a case of a 49-year-old male patient who had a history of high alcohol consumption and was exhibiting typical signs of WKS. After planning a proper physiotherapy plan, it is necessary to look after the patient's progress along with re-evaluation, which reveals notable gains in cognitive function, memory, and functional independence. There is a dearth of research on the impact of physical therapy in managing WKS. The above case report reflects the benefits of combining physiotherapy, cognitive rehabilitation, and balance training to improve patient functionality and independence. Tailored rehabilitation interventions like the Benson relaxation method (BRM), brain gym exercises, Frenkel's exercise, electrical stimulation, sensorimotor training, basic body awareness therapy (BBAT), and gait training can be used to enhance a patient's quality of life. Addressing individual needs is essential in managing WKS, focusing on the importance of comprehensive care beyond cognitive rehabilitation alone.
... It contributes as a cofactor for enzymes necessary for the Krebs cycle, such as pyruvate dehydrogenase and alpha-ketoglutarate. Thus, thiamine deficiency causes thiamine-dependent enzymes to function less efficiently, which in turn causes impaired cerebral energy utilization and neuronal damage [5]. ...
Abstract
Background: Wernicke’s encephalopathy is a metabolic
disorder caused by thiamine deficiency, and is characterized
by acute mental confusion, ophthalmoplegia and ataxia. Its
due to nutritional deficiency arising from prolonged illness
affecting nutrition of the patient or requiring parenteral
nutrition for prolonged duration, debilitating chronic
illnesses like solid organ and lymphoid malignancies. It has
been commonly seen chronic alcoholics who have poor oral
intake. It is a rare neurologic complication in the setting of
hematopoietic stem cell transplantation (HSCT). So, a high
index of suspicion should be kept in HSCT patients as delay
in early identification may lead to permanent neurologic
disability or even mortality.
Material and methods: We report a case of wernickes
encephalopathy in post-transplant patient who had poor
oral intake and prolonged hospitalization for different
complications post-transplant. Based on the review of
literature and our experience, it’s prudent to have an
early radiologic investigation done in suspected patients
as clinical features along with typical MRI (magnetic
resonance imaging) findings of brain are highly suggestive
of Wernicke’s encephalopathy following HSCT.
Results: A 55-year-old hypertensive, obese, non-diabetic
female, case of relapse acute myeloid leukemia underwent
allogeneic stem cell transplant from a matched unrelated
donor [MUD], since she had no human leucocyte antigen
(HLA) matched siblings. Post-transplant, on day +66 she
was evaluated for complaints of severe loss of appetite
and vomiting and was suspected to have acute GVHD.
She was admitted and immediately started on parenteral
methylprednisolone at 1 mg/kg. On day +75 post-transplants,
the patient complained of extreme fatigue, dizziness, gait
disturbance, and restlessness and soon became bedbound.
Neurological examination revealed mild confusion, bilateral
horizontal gaze nystagmus, bilateral lower limb ataxia, and
truncal ataxia and tremors. Power on examination was 5/5
in all limbs. Based on neurological signs and MRI imaging
features, she was diagnosed as Wernicke’s encephalopathy
secondary to malnutrition. The patient was given a high
dosage of intravenous thiamine, 500 mg three times a day,
as well as a steadily rising high-calorie and protein meal
through a ryles tube feeding. After three days, the patient
responded to the treatment with a noticeably improved gait,
consciousness, and the absence of tremors and nystagmus.
By day 10 of thiamine therapy, ryles tube was removed
and patient began active oral feeding. She was able to do
activities of self-care.
Conclusion: We report a post HSCT patient with Wernicke’s
encephalopathy who had poor oral intake and prolonged
hospitalization for several post-transplant complications.
Poor oral nutrition or prolonged TPN without the addition of
thiamine post HSCT might undoubtedly result in WE even
though it is an unusual complication of HSCT, therefore,
addition of IV thiamine is essential for the patients.
Keywords
Wernicke’s encephalopathy, Thiamine deficiency, Stem cell
transplant, AML
... An almost 80% decrease in expression of astrocytic glutamate transporters, with associated severe excitotoxicity and massive neuronal death, is a leading cause of Wernicke-Korsakoff encephalopathy. 96 Deficits in astroglial glutamate clearance as well as failure in the glutamate (GABA)-glutamine shuttle are likely responsible for abnormal neurotransmission as well as excitotoxic neuronal death that underlie psychotic symptoms. 97 Morphological atrophy of astrocytes together with decreased glutamate clearance is a common feature of many addictive disorders, with astrocytic glutamate transporters being considered as promising drug targets. ...
... FLIPT would prove to be a useful non-invasive real-time monitoring tool of thiamine in HD models. Moreover, FLIPT may be used to investigate thiamine deficiency's role in astrocyte and synapse dysfunction [75][76][77] in neurodegeneration. ...
Neurodegenerative diseases present a progressive loss of neuronal structure and function, leading to cell death and irrecoverable brain atrophy. Most have disease-modifying therapies, in part because the mechanisms of neurodegeneration are yet to be defined, preventing the development of targeted therapies. To overcome this, there is a need for tools that enable a quantitative assessment of how cellular mechanisms and diverse environmental conditions contribute to disease. One such tool is genetically encodable fluorescent biosensors (GEFBs), engineered constructs encoding proteins with novel functions capable of sensing spatiotemporal changes in specific pathways, enzyme functions, or metabolite levels. GEFB technology therefore presents a plethora of unique sensing capabilities that, when coupled with induced pluripotent stem cells (iPSCs), present a powerful tool for exploring disease mechanisms and identifying novel therapeutics. In this review, we discuss different GEFBs relevant to neurodegenerative disease and how they can be used with iPSCs to illuminate unresolved questions about causes and risks for neurodegenerative disease.
... A reduction in the thiamine-dependent activity of transketolase leads to a lower use of glucose and oxidative stress secondary to endothelial cell dysfunction. This produces cytotoxic and vasogenic edema firstly in astrocytes, then in neurons along with disruption of the blood-brain barrier [10,34] and local petechial hemorrhages [35] in brain areas that are specifically vulnerable to thiamine deficiency [10,[36][37][38]. Subsequently, neuronal DNA fragmentation and lactic acidosis occur in astrocytes and neurons, leading to necrosis and irreversible structural damage [10]. ...
The purpose of this article is to improve recognition and treatment of Wernicke-Korsakoff syndrome. It is well known that Korsakoff syndrome is a chronic amnesia resulting from unrecognized or undertreated Wernicke encephalopathy and is caused by thiamine (vitamin B1) deficiency. The clinical presentation of thiamine deficiency includes loss of appetite, dizziness, tachycardia, and urinary bladder retention. These symptoms can be attributed to anticholinergic autonomic dysfunction, as well as confusion or delirium, which is part of the classic triad of Wernicke encephalopathy. Severe concomitant infections including sepsis of unknown origin are common during the Wernicke phase. These infections can be prodromal signs of severe thiamine deficiency, as has been shown in select case descriptions which present infections and lactic acidosis. The clinical symptoms of Wernicke delirium commonly arise within a few days before or during hospitalization and may occur as part of a refeeding syndrome. Wernicke encephalopathy is mostly related to alcohol addiction, but can also occur in other conditions, such as bariatric surgery, hyperemesis gravidarum, and anorexia nervosa. Alcohol related Wernicke encephalopathy may be identified by the presence of a delirium in malnourished alcoholic patients who have trouble walking. The onset of non-alcohol-related Wernicke encephalopathy is often characterized by vomiting, weight loss, and symptoms such as visual complaints due to optic neuropathy in thiamine deficiency. Regarding thiamine therapy, patients with hypomagnesemia may fail to respond to thiamine. This may especially be the case in the context of alcohol withdrawal or in adverse side effects of proton pump inhibitors combined with diuretics. Clinician awareness of the clinical significance of Wernicke delirium, urinary bladder retention, comorbid infections, refeeding syndrome, and hypomagnesemia may contribute to the recognition and treatment of the Wernicke-Korsakoff syndrome.
... In addition, astrocytic dysfunction, induced by the thiamine deficiency and this increase in oxidative stress, alters its function of reuptake and metabolism of extracellular glutamate, especially with the loss of the glutamate transporters [33,[59][60][61]. Using an animal model of Wernicke-Korsakoff syndrome, in which rats were submitted to a chronic ethanol treatment with or without a thiamine deficiency episode, the glutamate uptake was found to be reduced in the prefrontal cortex by thiamine deficiency, but not by chronic ethanol intake [62]. ...
Alcohol use is a leading cause of mortality, brain morbidity, neurological complications and minor to major neurocognitive disorders. Alcohol-related neurocognitive disorders are consecutive to the direct effect of chronic and excessive alcohol use, but not only. Indeed, patients with severe alcohol use disorders (AUD) associated with pharmacological dependence suffer from repetitive events of alcohol withdrawal (AW). If those AW are not managed by adequate medical and pharmacological treatment, they may evolve into severe AW, or be complicated by epileptic seizure or delirium tremens (DT). In addition, we suggest that AW favors the occurrence of Wernicke’s encephalopathy (WE) in patients with known or unknown thiamine depletion. We reviewed the literature on oxidative stress as a core mechanism in brain suffering linked with those conditions: AW, epileptic seizure, DT and WE. Thus, we propose perspectives to further develop research projects aiming at better identifying oxidative stress brain damage related to AW, assessing the effect of repetitive episodes of AW, and their long-term cognitive consequences. This research field should develop neuroprotective strategies during AW itself or during the periwithdrawal period. This could contribute to the prevention of severe alcohol-related brain damage and cognitive impairments.
... Early le-sions in the brains of thiamine-deficient mice often show edematous swelling of astrocytes, with little or no change in neurons or oligodendrocytes. As the tissue damage progresses, changes are seen in neurons and oligodendrocytes [7] . Diffusion-weighted imaging of brain lesions may or may not be restricted. ...
A 30-year-old woman suffering from an eating disorder and alcoholism presented with a progressively worsening gait disturbance lasting 2 weeks. Her neurological findings included impaired ocular motility and trunk ataxia. Fluid-attenuated inversion recovery imaging of the brain showed hyperintensity in the dorsal brainstem, aqueduct, thalamus, and cerebral cortex. A long hyperintense segment on T2-weighted imaging was visible in the central gray matter of the cervical spinal cord. No restricted diffusion was observed; thus, T2 elongation in the spine was suggested to be due to vasogenic edema. We diagnosed the patient with Wernicke's encephalopathy and initiated vitamin supplementation. Thereafter, her symptoms rapidly improved; magnetic resonance imaging on the 11th day of hospitalization showed normalization of the signals in her brain and spinal cord. As our case demonstrates, Wernicke's encephalopathy can induce vasogenic edema of the spinal cord, which can rapidly improve with early therapeutic intervention.
... Another pathological feature, the astrocytic asthenia, which is manifested by failures of astroglial homeostatic cascades, is also frequently present in diseases of the brain. In particular, severe decrease in glutamate clearance due to ~80% decrease in expression of astrocytic plasmalemmal glutamate transporters is a leading cause of Wernicke-Korsakoff encephalopathy, associated with massive excitotoxic neuronal death (Hazell 2009;Hazell et al. 2009). Deficits in astroglial glutamate clearance and failure in glutamate-glutamine/GABA shuttle are likely responsible for abnormal neurotransmission as well as for excitotoxic neuronal death, both resulting in psychotic symptoms (Sanacora and Banasr 2013). ...
The role of astrocytes in the nervous system pathology was early on embraced by neuroscientists at end of the nineteenth and the beginning of the twentieth century, only to be pushed aside by neurone-centric dogmas during most of the twentieth century. However, the last decade of the twentieth century and the twenty-first century have brought the astroglial “renaissance”, which has put astroglial cells as key players in pathophysiology of most if not all disorders of the nervous system and has regarded astroglia as a fertile ground for therapeutic intervention.
... The fragmented processes of astrocytes in IAE are closely adjacent to synapses on the dendritic spines with fragmentation [31]. The anti-AQP-4 antibody can mediate neurological diseases such as severe brain edema [57][58][59][60]. The brain cell edema rapidly appeared around the pathological microvessels in IANE patients, which might be explained by AQP-4 dysfunction on the astrocyte membrane, but this requires further investigation. ...
Background
Influenza-associated acute necrotizing encephalopathy (IANE) can be lethal and disabling and have a sudden onset and deteriorate rapidly but lacks early diagnostic indicators. We aimed to examine the early clinical diagnostic indicators in children with IANE.
Material/Methods
Acute influenza patients were grouped according to their clinical manifestations: flu alone (FA), flu with febrile seizure (FS), influenza-associated encephalopathy (IAE), and IANE. The clinical features, biomarkers, neuroelectrophysiological results, and neuroimaging examination results were compared.
Results
A total of 31 patients were included (FA (n=4), FS (n=8), IAE (n=14), and IANE (n=5)). The IANE group, whose mean age was 3.7 years, was more likely to show rapid-onset seizure, acute disturbance of consciousness (ADOC), Babinski’s sign, and death/sequela. More patients in the IANE group required tracheal intubation mechanical ventilation and received intravenous immunoglobulins (IVIG) and glucocorticoids. The alanine aminotransferase (ALT), aspartate transaminase (AST), and lactate dehydrogenase (LDH) levels in the IANE group were significantly higher than in the FS and IAE groups. The aquaporin-4 (AQP-4) antibody and malondialdehyde (MDA) levels in the serum and cerebrospinal fluid (CSF) were notably higher in IANE patients in the acute stage compared with FS and IAE patients. All patients in the IANE group had positive neuroimaging findings.
Conclusions
Early clinical warning factors for IANE include rapid-onset seizures in patients under 4 years of age, ADOC, and pathological signs. Increased AQP-4 antibodies and MDA levels in CSF might contribute to early diagnosis. Early magnetic resonance venography (MRV) and susceptibility-weighted imaging (SWI) sequences, or thrombelastography to identify deep vein thrombosis, might indicate clinical deterioration.
... Decreased expression of either one or both glutamate transporters compromises the ability of astrocytes to reuptake the excess of glutamate, and to regulate glutamatergic transmission. This in turn results in severe excitotoxicity that underlies rapid thedevelopment of severe dementia, as shown in Wernicke encephalopathy [86,87]. In AD pathogenesis the situation seems still controversial. ...
This review is focused on the description and discussion of the alterations of astrocytes and microglia interplay in models of Alzheimer’s disease (AD). AD is an age-related neurodegenerative pathology with a slowly progressive and irreversible decline of cognitive functions. One of AD’s histopathological hallmarks is the deposition of amyloid beta (Aβ) plaques in the brain. Long regarded as a non-specific, mere consequence of AD pathology, activation of microglia and astrocytes is now considered a key factor in both initiation and progression of the disease, and suppression of astrogliosis exacerbates neuropathology. Reactive astrocytes and microglia overexpress many cytokines, chemokines, and signaling molecules that activate or damage neighboring cells and their mutual interplay can result in virtuous/vicious cycles which differ in different brain regions. Heterogeneity of glia, either between or within a particular brain region, is likely to be relevant in healthy conditions and disease processes. Differential crosstalk between astrocytes and microglia in CA1 and CA3 areas of the hippocampus can be responsible for the differential sensitivity of the two areas to insults. Understanding the spatial differences and roles of glia will allow us to assess how these interactions can influence the state and progression of the disease, and will be critical for identifying therapeutic strategies.
... This indicates that increased BBB permeability is unlikely to be a major contributor to selective vulnerability in this disorder. Studies indicate the basis of this cerebral vulnerability is likely to be multifactorial in nature resulting from impaired oxidative metabolism (Abdou and Hazell 2015), and involving the targeting of astrocytes in these focal areas of the brain in which several of their important functions are compromised (Hazell 2009). ...
Thiamine deficiency (TD) results in focal lesions in several regions of the rat brain including the thalamus and inferior colliculus. Since alterations in blood-brain barrier (BBB) integrity may play a role in this damage, we have examined the influence of TD on the unidirectional blood-to-brain transfer constant (Ki) of the low molecular weight species α-aminoisobutyric acid (AIB) in vulnerable and non-vulnerable brain regions at different stages during progression of the disorder, and following its reversal with thiamine. Analysis of the regional distribution of Ki values showed early (day 10) increased transfer of [¹⁴C]-AIB across the BBB in the vulnerable medial thalamus as well as the non-vulnerable caudate and hippocampus. At the acute symptomatic stage (day 14), more widespread BBB permeability changes were detected in most areas including the lateral thalamus, inferior colliculus, and non-vulnerable cerebellum and pons. Twenty-four hours following thiamine replenishment, a heterogeneous pattern of increased BBB permeability was observed in which many structures maintained increased uptake of [¹⁴C]-AIB. No increase in the [³H]-dextran space, a marker of intravascular volume, was detected in brain regions during the progress of TD, suggesting that BBB permeability to this large tracer was unaffected. These results indicate that BBB opening i) occurs early during TD, ii) is not restricted to vulnerable areas of the brain, iii) is progressive, iv) persists for at least 24 h following treatment with thiamine, and v) is likely selective in nature, depending on the molecular species being transported.
... It serves as a specific cofactor of certain enzymes involved in energy metabolism of cells and its deficiency may affect enzymes of the TCA cycle (Sharma et al., 2013;Sharma & Bist, 2014). Thiamine deficiency may also be associated with brain degenerative conditions such as Parkinson's and Alzheimer's disease (Hazell & Butterworth, 2009;Hazell, 2009;Karuppagounder et al., 2009;Hirsch &Parott, 2012). Blood is a loose connective tissue which is first to be affected by a stress introduced into the body and therefore proposes an insightful and consistent indicator, which could be effectively used to assess the magnitude of oxidative stress (Lakshmanan et al., 2013). ...
It is known that thiamine deficiency may lead to Alzheimer’s diseases in humans. The present study has thus been conducted to understand the role of thiamine deficiency with respect to alteration in the peripheral blood of Swiss albino mice. For this purpose, adult Swiss albino mice (6–8 week old) were divided into three groups. The first group was control; the second (group II) and the third group (group III) were made thiamine deficient for 08 and 10 days respectively. Thiamine deficiency was induced in mice by injecting pyrithiamine (5 µg/10 g bwt) and feeding a thiamine deficient diet. The erythrocytes, leukocytes count, hemoglobin, hematocrit value, mass cell volume, mean corpuscular hemoglobin in blood of mice were determined by hematoanalyzer. Malondialdehyde (MDA) and reduced glutathione (GSH) level was also determined in serum of treated and non-treated groups. A significant reduction in leukocyte and erythrocyte count was observed in both the thiamine deficient groups as compared to control. Levels of hemoglobin and hematocrit value were also declined in the thiamine deficient groups. Enhancement in mass cell volume (MCV) level and decline in mean corpuscular hemoglobin (MCH) levels were observed in both thiamine deficient groups with respect to control. Inter-group comparison of all parameters also showed a significant value at p <0.01. In comparison with the control group, elevation in MDA and decline in GSH level was observed in both thiamine deficient groups which were statistically significant. These data indicate that thiamine deficiency leads to significant alterations in the hematological parameters as well as in MDA and GSH level.
... In acute excitotoxic neurodegeneration of Wernicke type, massive neuronal death results from functional astroglial degeneration manifested by downregulation of expression of astroglial glutamate transporters. This compromises the ability of astrocytes to remove the excess of glutamate and to regulate glutamatergic transmission, which in turn results in severe excitotoxicity that underlies rapid development of severe dementia with prominent psychotic components [51,52]. ...
... The pathological mechanism of Korsakoff-W-ernicke syndrome is primarily associated with acute failure in astroglial glutamate uptake resulting from ~60 to 70% decrease in expression of EAAT1 and EAAT2 glutamate transporters. This remarkable decrease in plasmalemmal glutamate transporters expression has been identified in postmortem human samples, as well as in the rat thiamine deficiency model of the disease [104,105]. In addition to decrease in EAAT1/2 expression, astrocytes demonstrated signs of atrophy including decrease in GFAP morphological profiles, as well as decrease in expression of glutamine synthetase (GS) and GAT-3 GABA transporter. ...
Alzheimer’s disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer’s disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer’s disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.
... In acute excitotoxic neurodegeneration of Wernicke type, massive neuronal death results from functional astroglial degeneration manifested by downregulation of expression of astroglial glutamate transporters. This compromises the ability of astrocytes to remove the excess of glutamate and to regulate glutamatergic transmission, which in turn results in severe excitotoxicity that underlies rapid development of severe dementia with prominent psychotic components [51,52]. ...
Astrocytes, a class of morphologically and functionally diverse primary homeostatic neuroglia, are key keepers of neural tissue homeostasis and fundamental contributors to brain defence in pathological contexts. Failure of astroglial support and defence facilitate the evolution of neurological diseases, which often results in aberrant synaptic transmission, neurodegeneration and death of neurones. In Alzheimer’s disease (AD), astrocytes undergo complex and multifaceted metamorphoses ranging from atrophy with loss of function to reactive astrogliosis with hypertrophy. Astroglial asthenia underlies reduced homeostatic support and neuroprotection that may account for impaired synaptic transmission and neuronal demise. Reactive astrogliosis which mainly develops in astrocytes associated with senile plaque is prominent at the early to moderate stages of AD manifested by mild cognitive impairment; downregulation of astrogliosis (reflecting astroglial paralysis) is associated with late stages of the disease characterised by severe dementia. Cell-specific therapies aimed at boosting astroglial supportive and defensive capabilities and preventing astroglial paralysis may offer new directions in preventing, arresting, or even curing AD-linked neurodegeneration.
... Moreover, a number of studies indicate that acidosis is involved in ROS-induced intestinal inflammatory diseases [25][26][27]. In turn, the acidosis associated with inflammatory conditions produces oxidative stress and/or amplifies its effects [6,23,[28][29][30]. In vivo and in vitro studies indicate that at an acidotic pH, the response of the gut to an insult is magnified [31]. ...
We investigated the effects of creatine treatment on jejunal phenotypes in a rat model of oxidative stress induced by acidosis. In particular, the activities of some antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase, and glutathione reductase), the level of lipid peroxidation, the expression of heat shock proteins (HSP70), and the expression of the major carriers of the cells (Na+/K+-ATPase, sodium-glucose Transporter 1—SGLT1, and glucose transporter 2—GLUT2) were measured under control and chronic acidosis conditions. Creatine did not affect the activity of antioxidant enzymes in either the control or acidosis groups, except for catalase, for which the activity was reduced in both conditions. Creatine did not change the lipid peroxidation level or HSP70 expression. Finally, creatine stimulated (Na+/K+)-ATPase expression under both control and chronic acidosis conditions. Chronic acidosis caused reductions in the expression levels of GLUT2 and SGLT1. GLUT2 reduction was abolished by creatine, while the presence of creatine did not induce any strengthening effect on the expression of SGLT1 in either the control or chronic acidosis groups. These results indicate that creatine has antioxidant properties that are realized through direct interaction of the molecule with reactive oxygen species. Moreover, the administration of creatine seems to determine a functional strengthening of the tissue, making it more resistant to acidosis.
... Acidosis promotes lipid peroxidation or other manifestations of oxidant-mediated damage in various cell types [21][22][23][24]; moreover, a number of studies indicate acidosis to be involved in ROS-induced intestinal inflammatory diseases [25][26][27]. Acidosis associated with inflammatory conditions, in turn, produces oxidative stress and/or amplifies its effects [6,23,[28][29][30]; in vivo and in vitro studies indicate that at an acidotic pH, the response of the gut to an insult is magnified [31]. ...
The protective effect of creatine supplementation on the jejunal epithelium of rats under conditions of oxidative stress induced by chronic acidosis was investigated. In particular, we measured the activities of the main antioxidant enzymes (superoxide dismutase, glutathione peroxidase, catalase, glutathione reductase), the level of lipid peroxidation, the expression of heat shock proteins (HSP70), and the expression of the major carriers of the cells (Na+/K+-ATPase, SGLT1 and GLUT2) in control and chronic acidosis conditions. Creatine did not affect the activity of antioxidant enzymes, nor in control, neither in acidosis, except for catalase, which activity was reduced in both conditions. Creatine did not change the level of lipid peroxidation and the expression of HSP70. Finally, creatine stimulated the expression of (Na+/K+)-ATPase both in control and in chronic acidosis. Chronic acidosis caused a reduction in the expression of GLUT2 and SGLT1. GLUT2 reduction was abolished by creatine, while the presence of creatine did not induce any strengthening effect on the expression of SGLT1, neither in control nor in chronic acidosis. These results indicate that creatine has antioxidant properties that would be realized through direct interaction of the molecule with reactive oxygen species. Moreover, the administration of creatine seems to determine a functional strengthening of the tissue making the tissue more resistant to acidosis.
... Several factors can be associated to GSH depletion in the retinal tissue, including the generation of local oxidative stress conditions [73]. Studies reveal that oxidant damage in retinal tissue are closely associated to glutamatergic system alterations [74][75][76], including the hyperstimulation of NMDA glutamate receptors which evoke excitotoxicity in retinal cells [77][78][79]. This excitotoxic pathway culminates in ROS production and intense consumption of intracellular GSH. ...
Background
Cerebral malaria (CM) is a severe complication resulting from Plasmodium falciparum infection. This condition has usually been associated with cognitive, behavioural and motor dysfunctions, being the retinopathy the most serious consequence resulting from the disease. The pathophysiological mechanisms underlying this complication remain incompletely understood. Several experimental models of CM have already been developed in order to clarify those mechanisms related to this syndrome. In this context, the present work has been performed to investigate which possible electrophysiological and neurochemistry alterations could be involved in the CM pathology.
Methods
Experimental CM was induced in Plasmodium berghei-infected male and female C57Bl/6 mice. The survival and neurological symptoms of CM were registered. Brains and retina were assayed for TNF levels and NOS2 expression. Electroretinography measurements were recorded to assessed a- and b-wave amplitudes and neurochemicals changes were evaluated by determination of glutamate and glutathione levels by HPLC.
Results
Susceptible C57Bl/6 mice infected with ≈ 10⁶ parasitized red blood cells (P. berghei ANKA strain), showed a low parasitaemia, with evident clinical signs as: respiratory failure, ataxia, hemiplegia, and coma followed by animal death. In parallel to the clinical characterization of CM, the retinal electrophysiological analysis showed an intense decrease of a- and-b-wave amplitude associated to cone photoreceptor response only at the 7 days post-infection. Neurochemical results demonstrated that the disease led to a decrease in the glutathione levels with 2 days post inoculation. It was also demonstrated that the increase in the glutathione levels during the infection was followed by the increase in the ³H-glutamate uptake rate (4 and 7 days post-infection), suggesting that CM condition causes an up-regulation of the transporters systems. Furthermore, these findings also highlighted that the electrophysiological and neurochemical alterations occurs in a manner independent on the establishment of an inflammatory response, once tumour necrosis factor levels and inducible nitric oxide synthase expression were altered only in the cerebral tissue but not in the retina.
Conclusions
In summary, these findings indicate for the first time that CM induces neurochemical and electrophysiological impairment in the mice retinal tissue, in a TNF-independent manner.
... Secondary astrocytopathy with inhibition of glutamate transport occurs in thiamine deficiency and Wernicke-Korsakoff encephalopathy (173,174), and after poisoning with heavy metals (451). ...
Astrogliopathy refers to alterations of astrocytes occurring in diseases of the nervous system, and it implies the involvement of astrocytes as key elements in the pathogenesis and pathology of diseases and injuries of the central nervous system. Reactive astrocytosis refers to the response of astrocytes to different insults to the nervous system, whereas astrocytopathy indicates hypertrophy, atrophy/degeneration and loss of function and pathological remodeling occurring as a primary cause of a disease or as a factor contributing to the development and progression of a particular disease. Reactive astrocytosis secondary to neuron loss and astrocytopathy due to intrinsic alterations of astrocytes occur in neurodegenerative diseases, overlap each other, and, together with astrocyte senescence, contribute to disease-specific astrogliopathy in aging and neurodegenerative diseases with abnormal protein aggregates in old age. In addition to the well-known increase in glial fibrillary acidic protein and other proteins in reactive astrocytes, astrocytopathy is evidenced by deposition of abnormal proteins such as β-amyloid, hyper-phosphorylated tau, abnormal α-synuclein, mutated huntingtin, phosphorylated TDP-43 and mutated SOD1, and PrPres, in Alzheimer's disease, tauopathies, Lewy body diseases, Huntington's disease, amyotrophic lateral sclerosis and Creutzfeldt-Jakob disease, respectively. Astrocytopathy in these diseases can also be manifested by impaired glutamate transport; abnormal metabolism and release of neurotransmitters; altered potassium, calcium and water channels resulting in abnormal ion and water homeostasis; abnormal glucose metabolism; abnormal lipid and, particularly, cholesterol metabolism; increased oxidative damage and altered oxidative stress responses; increased production of cytokines and mediators of the inflammatory response; altered expression of connexins with deterioration of cell-to-cell networks and transfer of gliotransmitters; and worsening function of the blood brain barrier, among others. Increased knowledge of these aspects will permit a better understanding of brain aging and neurodegenerative diseases in old age as complex disorders in which neurons are not the only players.
... Administration of glutamate to experimental animals and humans [9,10], led to the development of depression and anxiety in the form of imbalance of mood and emotions, abnormalities of limbic system structures [11], and disruption of the hypothalamic pituitary adrenal axis [12]. Glutamate was linked to many diseases such as Alzheimer's disease, Huntington's disease and Wernicke's encephalopathy [13,14], as well as retinal ischemia leading to loss of ganglion cells [15]. In vitro studies of MSG (20 mM) on astrocyte culture cells revealed increased a liberation of reactive oxygen species and apoptotic cell death [16]. ...
The phytochemical constituents of Carob (Ceratonia siliqua L) showed therapeutic medical importance
especially concerning neurotoxicity which represents the major public health problem. Neurodegenerative
disorders are developed from different metabolic diseases and chemical component such as monosodium
glutamate. It is the widely used chense sodium salt of the non-essential glutamic amino acid. It is one of the
most popular fl avor enhancer. Monosodium glutamate is excitatory neurotransmitter in brain, increased the
perception of wetness and saltiness as a taste sensation UMAMI. Treatment with the carob extract or their
phytochemical constituents either protect or ameliorates these diseases which is promising.
... The importance of astrocytes in ALS pathogenesis is further corroborated by the observation that silencing the ALS-related mutant SOD1 gene specifically in astrocytes delayed the appearance of disease symptoms in the transgenic mouse model [60]. Astroglial degeneration with loss of function characterized by a significant down-regulation of astroglial glutamate transporters resulting in prominent excitotoxicity is manifest in Wernicke encephalopathy, a thalamo-cortical neurodegeneration that represents the morphological substrate of Korsakoff syndrome [61,62]. Similarly, in Huntington disease (HD), a decreased astroglial glutamate uptake as well as an aberrant release of glutamate from astrocytes contributes to neurotoxicity [63]. ...
Although the central nervous system (CNS) consists of highly heterogeneous populations of neurones and glial cells, clustered into diverse anatomical regions with specific functions, there are some conditions, including alertness, awareness and attention that require simultaneous, coordinated and spatially homogeneous activity within a large area of the brain. During such events, the brain, representing only about two percent of body mass, but consuming one fifth of body glucose at rest, needs additional energy to be produced. How simultaneous energy procurement in a relatively extended area of the brain takes place is poorly understood. This mechanism is likely to be impaired in neurodegeneration, for example in Alzheimer’s disease, the hallmark of which is brain hypometabolism. Astrocytes, the main neural cell type producing and storing glycogen, a form of energy in the brain, also hold the key to metabolic and homeostatic support in the central nervous system and are impaired in neurodegeneration, contributing to the slow decline of excitation-energy coupling in the brain. Many mechanisms are affected, including cell-to-cell signalling. An important question is how changes in cellular signalling, a process taking place in a rather short time domain, contribute to the neurodegeneration that develops over decades. In this review we focus initially on the slow dynamics of Alzheimer’s disease, and on the activity of locus coeruleus, a brainstem nucleus involved in arousal. Subsequently, we overview much faster processes of vesicle traffic and cytosolic calcium dynamics, both of which shape the signalling landscape of astrocyte-neurone communication in health and neurodegeneration.
... In fact, these two disorders are so closely related that the patients are commonly diagnosed with Wernicke-Korsakoff syndrome , also called wet brain, which is a thiamine (vitamin B 1 ) defi ciency associated with a severe excitotoxic damage secondary to alcoholism. The Wernicke encephalopathy is a primary astrogliopathy; the key pathogenetic step is a prominent down-regulation (by ~ 70 %) of the expression of astroglial plasmalemmal glutamate transporters, which leads to impaired glutamate transmission and glutamate excitotoxicity (Hazell 2009 ;Hazell et al. 2009 ). ...
Astrocytes are primary homeostatic cells of the central nervous system. They regulate glutamatergic transmission through the removal of glutamate from the extracellular space and by supplying neurons with glutamine. Glutamatergic transmission is generally believed to be significantly impaired in the contexts of all major neuropsychiatric diseases. In most of these neuropsychiatric diseases, astrocytes show signs of degeneration and atrophy, which is likely to be translated into reduced homeostatic capabilities. Astroglial glutamate uptake/release and glutamate homeostasis are affected in all forms of major psychiatric disorders and represent a common mechanism underlying neurotransmission disbalance, aberrant connectome and overall failure on information processing by neuronal networks, which underlie pathogenesis of neuropsychiatric diseases.
... Pathological suppression of astroglial glutamate uptake also plays the leading role in the development of Wernicke encephalopathy, a thalamo-cortical neurodegeneration, which represents the substrate for Korsakoff syndrome. Expression of astroglial glutamate transporters decreases by~70% resulting in massive glutamate excitotoxicity [85,86]. In Huntington disease (HD) the hampered astroglial glutamate uptake is concomitant with an aberrant release of glutamate from astrocytes, both processes instigating excitotoxic damage to neurones [87]. ...
Neuroglial contribution to Alzheimer's disease (AD) is pathologically relevant and highly heterogeneous. Reactive astrogliosis and activation of microglia contribute to neuroinflammation, whereas astroglial and oligodendroglial atrophy affect synaptic transmission and underlie the overall disruption of the central nervous system (CNS) connectome. Astroglial function is tightly integrated with the intracellular ionic signalling mediated by complex dynamics of cytosolic concentrations of free Ca(2+) and Na(+). Astroglial ionic signalling is mediated by plasmalemmal ion channels, mainly associated with ionotropic receptors, pumps and solute carrier transporters, and by intracellular organelles comprised of the endoplasmic reticulum and mitochondria. The relative contribution of these molecular cascades/organelles can be plastically remodelled in development and under environmental stress. In AD astroglial Ca(2+) signalling undergoes substantial reorganisation due to an abnormal regulation of expression of Ca(2+) handling molecular cascades.
... Moreover, ablation of astrocytes in the prefrontal cortex (by injection of specific toxin L-aaminoadipic acid) was sufficient to induce depression-like symptoms in adult rats [143]. The leading mechanism of Wernicke encephalopathy (clinically expressed as Korsakoff syndrome) is directly associated with profound downregulation of astroglial glutamate transporters with ensuing excitotoxic neuronal death [151,152]. Astrocytes therefore are increasingly considered as a legitimate target for cellspecific therapy in various neuropsychiatric conditions [153,154]. ...
Evolution of the nervous system progressed through cellular diversification and specialization of functions. Conceptually, the nervous system is composed from electrically excitable neuronal networks connected with chemical synapses and non-excitable glial cells that provide for homeostasis and defence. Astrocytes are integrated into neural networks through multipartite synapses; astroglial perisynaptic processes closely enwrap synaptic contacts and control homeostasis of the synaptic cleft, supply neurons with glutamate and GABA obligatory precursor glutamine and contribute to synaptic plasticity, learning and memory. In neuropathology, astrocytes may undergo reactive remodelling or degeneration; to a large extent, astroglial reactions define progression of the pathology and neurological outcome.
This article is part of the themed issue ‘Evolution brings Ca ²⁺ and ATP together to control life and death’.
... These heavy metals (such as mercury, lead or aluminium) are specifically accumulated by astroglia, where they disrupt astrocytic glutamate uptake, with secondary excitotoxic neuronal damage (Verkhratsky et al., 2013). Similarly, a profound inhibition of astroglial glutamate transport underlie neuronal death in Wernicke-Korsakoff encephalopathy (Hazell, 2009; Hazell et al., 2009). Astrocytes are also primary targets in hepatoencephalopathy, which arises from the liver failure with subsequent hyperammoniemia; astrocytes accumulate ammonia that interferes with glutamine synthetase, incapacitates astroglial homeostatic cascades responsible for K + , Na + , pH and Ca 2+ homeostasis and induces pathological release of glutamate (Kelly et al., 2009; Haack et al., 2014; Liang et al., 2014; Montana et al., 2014). ...
The common denominator of neurodegenerative diseases, which mainly affect humans, is the progressive death of neural cells resulting in neurological and cognitive deficits. Astroglial cells are the central elements of the homoeostasis, defence and regeneration of the central nervous system, and their malfunction or reactivity contribute to the pathophysiology of neurodegenerative diseases. Pathological remodelling of astroglia in neurodegenerative context is multifaceted. Both astroglial atrophy with a loss of function and astroglial reactivity have been identified in virtually all the forms of neurodegenerative disorders. Astroglia may represent a novel target for therapeutic strategies aimed at preventing and possibly curing neurodegenerative diseases.
... It is well known that astrocytes (cells of the nerve tissue) possess the maximum sensitivity to thiamine deficiency; dysfunction of these cells under conditions of В 1 deficit plays the leading role in the pathophysiological processes accompanying the development of avitaminosis [125]. Within the symptomatic stages of thiamine deficiency (9 to 14 days), the level of GFAP remains unchanged [126] or tends to increase [127]. Overexpression of GFAP was observed against the background of a significant decrease in the number of neurons, which was estimated by the neuronal marker NeuN. ...
Glial fibrillary acidic protein (GFAP) is the main component of intermediate filaments of the cytoskeleton of astrocytes. Over more than four decades of fundamental and applied studies, GFAP achieved the status of the classical marker for astroglia. Our review deals with the analysis and systematization of the literature data describing the peculiarities of the structural organization of the molecules of this protein, its isoform composition, and changes in expression of the GFAP gene in the course of CNS ontogenesis; the hierarchical principle of the formation of glial intermediate filaments is also described. A great deal of information about key reactions of post-translational modifications of GFAP and their role in the functioning of the above-mentioned protein is conveyed. Based on the modern literature data, the limited proteolysis of GFAP is considered not only a stage of catabolic transformation of this protein but also a mechanism underlying regulation of the dynamic properties of the cytoskeleton in astroglial cells. It is believed that the main functions of GFAP are the maintenance of specific morphology of astrocytes, control of migration of these cells, and maintenance of the stability of their processes; however, more and more findings are indicative of the involvement of this protein in the processes of cellular signalling and modulation of neuron-to-glia interactions. GFAP as a component of intermediate filaments of the cytoskeleton plays a key role in the development of reactive astrocytosis, i.e., of a typical response of the CNS to injury. Overexpression of GFAP or suppression of its biosynthesis reflect modifications of the functional activity of astrocytes related to damage to the nerve tissue, metabolic abnormalities, and development of neurodegenerative states. Quantitative estimation of GFAP and of its breakdown products, as well as that of anti-GFAP autoantibodies in biological fluids, are at present used as significant criteria in the diagnostics of neurodegenerative pathologies. Non-canonical functions of GFAP, which it fulfills in non-astrocyte units, are indicative of functional polymorphism of this protein and need further investigations.
... A reduced Cho peak is observed in patients with disturbed energy metabolism (Bluml et al. 1998) and may be relevant to the primary biochemical lesion in thiamine deficiency (Lee et al. 2001;Murata et al. 1999). On the other hand, reduced Cho may reflect disrupted osmoregulation (Hazell 2009;Hazell and Butterworth 2009) as glycerophosphocholine, one of the compounds included in the Cho signal, plays an important role in peripheral osmotic regulation (Gallazzini and Burg 2009). Changes in osmoregulation may also disrupt white matter integrity, as reported in thiamine deficiency (He et al. 2007;Langlais and Savage 1995;Langlais and Zhang 1997) and liver failure (Rovira et al. 2008(Rovira et al. , 2002. ...
Rationale
Serious neurological concomitants of alcoholism include Wernicke’s encephalopathy (WE), Korsakoff’s syndrome (KS), and hepatic encephalopathy (HE).
Objectives
This study was conducted in animal models to determine neuroradiological signatures associated with liver damage caused by carbon tetrachloride (CCl4), thiamine deficiency caused by pyrithiamine treatment, and nonspecific nutritional deficiency caused by food deprivation.
Methods
Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were used to evaluate brains of wild-type Wistar rats at baseline and following treatment.
Results
Similar to observations in ethanol (EtOH) exposure models, thiamine deficiency caused enlargement of the lateral ventricles. Liver damage was not associated with effects on cerebrospinal fluid volumes, whereas food deprivation caused modest enlargement of the cisterns. In contrast to what has repeatedly been shown in EtOH exposure models, in which levels of choline-containing compounds (Cho) measured by MRS are elevated, Cho levels in treated animals in all three experiments (i.e., liver damage, thiamine deficiency, and food deprivation) were lower than those in baseline or controls.
Conclusions
These results add to the growing body of literature suggesting that MRS-detectable Cho is labile and can depend on a number of variables that are not often considered in human experiments. These results also suggest that reductions in Cho observed in humans with alcohol use disorder (AUD) may well be due to mild manifestations of concomitants of AUD such as liver damage or nutritional deficiencies and not necessarily to alcohol consumption per se.
... In several acquired neuropsychiatric disorders such as hepatic encephalopathy, Wernicke encephalopathy and heavy metals encephalopathy astrocytes are the primary affected cells (Rönnbäck and Hansson, 1992;Hazell, 2009;Rama Rao and Norenberg, 2014). Their dysfunction is believed to determine neuronal injury and eventually death through glutamate toxicity. ...
Along the last years it has been demonstrated that non-neural cells play a major role in the pathogenesis of the Primary Degenerative Disorders (PDD) of the human central nervous system. Among them, astrocytes coordinate and participate in many different and complex metabolic processes, in close interaction with neurons. Moreover, increasing experimental evidence hints an early astrocytic dysfunction in these diseases. In this mini review we summarize the astrocytic behavior in PDDs, with special consideration to the experimental observations where astrocytic pathology precedes the development of neuronal dysfunction. We also suggest a different approach that could be consider in human investigations in Alzheimer’s and Parkinson's disease. We believe that the study of PDDs with human brain samples may hold the key of a paradigmatic physiopathological process in which astrocytes might be the main players.
... The loss of astroglial function is manifested by compromised glutamate homeostasis following down-regulation of astroglial glutamate transporters EAAT1 and EAAT2. Failure in glutamate homeostasis instigates neuronal excitotoxicity and severe brain lesions characteristic for the disease [72,73]. Similarly in Huntington´s and Parkinson´s diseases, loss of astroglial glutamate uptake, an increase in astroglial glutamate, release contribute to neurodegenerative progression [74][75][76][77][78]. ...
Glial cells and their association with neurones are fundamental for brain function. The emergence of complex neurone-glial networks assures rapid information transfer, creating a sophisticated circuitry where both types of neural cells work in concert, serving different activities. All glial cells, represented by astrocytes, oligodendrocytes, microglia and NG2-glia, are essential for brain homeostasis and defence. Thus, glia are key not only for normal central nervous system (CNS) function, but also to its dysfunction, being directly associated with all forms of neuropathological processes. Therefore, the progression and outcome of neurological and neurodegenerative diseases depend on glial reactions. In this review, we provide a concise account of recent data obtained from both human material and animal models demonstrating the pathological involvement of glia in neurodegenerative processes, including Alzheimer's disease (AD), as well as physiological ageing.
... In Wernicke's encephalopathy a profound (60e70%) down-regulation of astroglial glutamate transporters EAAT1 and EAAT2 expression occurs, which causes severe deficiency of glutamate uptake and excitotoxicity. Similar down-regulation of these transporters is responsible for nutritional thiamine deficiency that causes the beriberi disease (Hazell, 2009; Hazell et al., 2009). ...
Neuroglia, represented by astrocytes, oligodendrocytes, NG glia and microglia are homeostatic, myeli-nating and defensive cells of the brain. Neuroglial cells express various combinations of purinoceptors, which contribute to multiple intercellular signalling pathways in the healthy and diseased nervous system. Neurological diseases are invariably associated with profound neuroglial remodelling, which is manifest by reactive gliosis, pathological remodelling and functional atrophy of various types of glial cells. Gliopathology is disease and region specific and produces multiple glial phenotypes that may be neuroprotective or neurotoxic. In this review we summarise recent knowledge on the role of glial purinergic signalling in cognitive-related neurological diseases.
... Decrease in the astroglial numbers as well as astroglial atrophy has been detected in schizophrenia, in temporal lobe epilepsy, and in major depressive disorders and loss of astrocyte-dependent control over glutamatergic transmission is considered as one of the principal mechanisms of abnormal synaptic connectivity in these major psychiatric disorders [15,156,182,238]. Astrodegeneration and downregulation of astroglial glutamate uptake plays a leading role in excitotoxicity in amyotrophic lateral sclerosis, in Korsakoff-Wernicke syndrome and in toxic encephalopathies [86,189,238]. Atrophic changes in astroglia are observed in several types of neurodegenerative disorders. ...
The neurone-centred view of the past disregarded or downplayed the role of astroglia as a primary component in the pathogenesis of neurological diseases. As this concept is changing, so is also the perceived role of astrocytes in the healthy and diseased brain and spinal cord. We have started to unravel the different signalling mechanisms that trigger specific molecular, morphological and functional changes in reactive astrocytes that are critical for repairing tissue and maintaining function in CNS pathologies, such as neurotrauma, stroke, or neurodegenerative diseases. An increasing body of evidence shows that the effects of astrogliosis on the neural tissue and its functions are not uniform or stereotypic, but vary in a context-specific manner from astrogliosis being an adaptive beneficial response under some circumstances to a maladaptive and deleterious process in another context. There is a growing support for the concept of astrocytopathies in which the disruption of normal astrocyte functions, astrodegeneration or dysfunctional/maladaptive astrogliosis are the primary cause or the main factor in neurological dysfunction and disease. This review describes the multiple roles of astrocytes in the healthy CNS, discusses the diversity of astroglial responses in neurological disorders and argues that targeting astrocytes may represent an effective therapeutic strategy for Alexander disease, neurotrauma, stroke, epilepsy and Alzheimer's disease as well as other neurodegenerative diseases.
Astroglia are a broad class of neural parenchymal cells primarily dedicated to homoeostasis and defence of the central nervous system (CNS). Astroglia contribute to the pathophysiology of all neurological and neuropsychiatric disorders in ways that can be either beneficial or detrimental to disorder outcome. Pathophysiological changes in astroglia can be primary or secondary and can result in gain or loss of functions. Astroglia respond to external, non-cell autonomous signals associated with any form of CNS pathology by undergoing complex and variable changes in their structure, molecular expression, and function. In addition, internally driven, cell autonomous changes of astroglial innate properties can lead to CNS pathologies. Astroglial pathophysiology is complex, with different pathophysiological cell states and cell phenotypes that are context-specific and vary with disorder, disorder-stage, comorbidities, age, and sex. Here, we classify astroglial pathophysiology into (i) reactive astrogliosis, (ii) astroglial atrophy with loss of function, (iii) astroglial degeneration and death, and (iv) astrocytopathies characterised by aberrant forms that drive disease. We review astroglial pathophysiology across the spectrum of human CNS diseases and disorders, including neurotrauma, stroke, neuroinfection, autoimmune attack and epilepsy, as well as neurodevelopmental, neurodegenerative, metabolic and neuropsychiatric disorders. Characterising cellular and molecular mechanisms of astroglial pathophysiology represents a new frontier to identify novel therapeutic strategies.
Wernicke's encephalopathy is responsible for an acute neuropsychiatric syndrome that is associated with significant morbidity and mortality. It is most frequently due to alcoholism but can also be the result of chronic diseases, mainly systemic tumours, leading to thiamine deficiency. In the non-thiamine treated patients Korsakoff’s syndrome is the residual complication of the encephalopathy. The clinical diagnosis of Wernicke encephalopathy in alcoholics requires two of the following four signs: dietary deficiencies, eye signs, cerebellar dysfunction, and either disturbed mental state or mild memory impairment. These symptoms are less specific in the non-alcoholic patients. Korsakoff's syndrome is the residual condition in none thiamine treated patients. It is predominantly characterized by global amnesia, and in the more severe cases also by cognitive and behavioral dysfunction. Magnetic resonance imaging of the brain can detect the specific lesions and be helpful for the diagnosis. Treatment with 2500 mg thiamine intravenously is recommended as soon as possible.
Background:
Osmotic demyelination syndrome (ODS) is non inflammatory demyelination in response to an osmotic challenge. It can be pontine or extrapontine in presentation AIM: Retrospective review of cases involving ODS and define the spectrum of causes, risk factors, clinical and radiological presentations, and functional outcomes.
Results:
The study utilized data from 15 patients with a mean age of 53.6 years. Malnutrition 9 (60%) and chronic alcoholism 10 (66.7%) were the most common associated disorders. 2 patients (13.3%) had severe hyponatremia (<120 mmol/L). The average highest single-day change was 5.1mmol/L. Radiologically, 14 (93.3%) had pontine and 6 (60%) had extra-pontine lesions. Hypokalemia 14 (93.3%) and hypophosphatemia 9 (60%) were commonly associated. Common clinical manifestations include altered consciousness/encephalopathy 9 (60%), dysphagia 4 (26.7%) and limb weakness 4 (26.7%). At 3 months, 2 (14.3%) had died and 6 (42.9%) were functionally independent (modified Rankin scale 0-2).
Conclusion:
We found that ODS occurred despite appropriate correction rates of hyponatremia. Factors such as malnutrition, chronic alcoholism, hypokalemia, and hypophosphatemia are thought to play a role in its pathogenesis. Approximately half of the patients survived and became functionally independent. This article is protected by copyright. All rights reserved.
Changes induced in the morphology and the multiplicity of functional roles played by astrocytes in brain regions critical to the establishment and maintenance of alcohol abuse suggest that they make an important contribution to the vulnerability to alcohol use disorders. The understanding of the relevant mechanisms accounting for that contribution is complicated by the fact that alcohol itself acts directly on astrocytes altering their metabolism, gene expression, and plasticity, so that the ultimate result is a complex interaction of various cellular pathways, including intracellular calcium regulation, neuroimmune responses, and regulation of neurotransmitter and gliotransmitter release and uptake. The recent years have seen a steady increase in the characterization of several of the relevant mechanisms, but much remains to be done for a full understanding of the astrocytes’ contribution to the vulnerability to alcohol dependence and abuse and for using that knowledge in designing effective therapies for AUDs.
Alcohol is globally a major component of daily life and nutrition. Presently, about 61% of US adults are current drinkers. Due to its metabolic characteristics, alcohol as a function of the absolute amount consumed, consumption frequency, genetic factors etc., has a high potential to affect most metabolic pathways and cell and organ function including the metabolism and nutriture of all macro- and micronutrients. In this chapter, the present knowledge of the effects of alcohol on selected nutrients as well as health and disease burden will be summarized.
Possible otoprotective properties of cocarboxylase were studied on the model of amikacin-induced ototoxicity in immature rabbits. Auditory function was evaluated by the short-latency auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) tests. Administration of cocarboxylase after modeling of amikacin-induced ototoxicity resulted in a decrease in the ABR peak I threshold and prevented damage to the outer hair cells.
Several studies have reported on the beneficial effects of memantine on behavioral and psychological symptoms of dementia (BPSD) in patients with Alzheimer's disease. However, the effects of memantine on BPSD-like behaviors in animals have not been well addressed. Here, the effects of memantine on memory disturbance and BPSD-like behaviors were evaluated in thiamine-deficient (TD) mice. Memantine (3 and 10 mg/kg, b.i.d.) was orally administered to ddY mice fed a TD diet for 22 days. During the treatment period, the forced swimming test, elevated plus-maze test, passive avoidance test, and locomotor activity test were performed. Neurotransmitter levels in the brain were analyzed after the treatment period. Daily oral administration of memantine ameliorated the memory disturbances, anxiety-like behavior, and depression-like behavior observed in TD mice. Memantine did not have a significant effect on monoamine levels, but increased glutamate levels in the hippocampus in TD mice. These results suggest that memantine prevents or suppresses the progression of BPSD-like behaviors that develop due to TD. This effect may be mediated in part by the enhancement of glutamatergic neuron activity in the hippocampus.
Vitamin B1, or thiamine is a critical enzyme cofactor required for metabolic function and energy production. Thiamine deficiency (TD) is common in various diseases, and results in severe neurological complications due to diminished mitochondrial function, oxidative stress, excitotoxicity and inflammation. These pathological sequelae result in apoptotic cell death in both neurons and astrocytes in distinct regions, in particular the thalamus and mammillary bodies. Comparable histological injuries in patients with hypoxia/ischemia (H/I) have also been described, suggesting a congruency between the cellular responses to these stresses. Analogous to H/I, TD stabilizes and activates Hypoxia Inducible Factor-1α (HIF-1α) even without changes in physiological oxygen levels. However, the mechanism of HIF-1α stabilization in TD is currently unknown. Using a pyruvate assay, we have demonstrated that TD induces pyruvate accumulation in mouse primary astrocytes which correlates to an increase in HIF-1α expression. Additionally, we utilized an enzymatic assay for pyruvate dehydrogenase to demonstrate a reduction in catalytic activity during TD due to lack of available thiamine pyrophosphate cofactor, resulting in the observed pyruvate accumulation. Finally, a pyruvate kinase inhibitor which limited pyruvate accumulation was utilized to demonstrate the role of pyruvate accumulation in HIF-1α stabilization during TD. These results reveal that stabilization of HIF-1α protein in TD centralizes on pyruvate accumulation in mouse primary astrocytes due to metabolic disruption of PDH.
Astrocytes, a subtype of glial cells, come in variety of forms and functions. However, overarching role of these cell is in the homeostasis of the brain, be that regulation of ions, neurotransmitters, metabolism or neuronal synaptic networks. Loss of homeostasis represents the underlying cause of all brain disorders. Thus, astrocytes are likely involved in most if not all of the brain pathologies. We tabulate astroglial homeostatic functions along with pathological condition that arise from dysfunction of these glial cells. Classification of astrocytes is presented with the emphasis on evolutionary trails, morphological appearance and numerical preponderance. We note that, even though astrocytes from a variety of mammalian species share some common features, human astrocytes appear to be the largest and most complex of all astrocytes studied thus far. It is then an imperative to develop humanized models to study the role of astrocytes in brain pathologies, which is perhaps most abundantly clear in the case of glioblastoma multiforme.
Thiamine (vitamin B1), a water-soluble vitamin, is an essential factor in cellular metabolism
and fundamental cofactor in important biochemical cycles. Thiamine deficiency is a wellknown
cause of neurological and cardiologic disorders, especially in patients with alcohol
dependence. Recently, several researchers have studied the role of thiamine deficiency in
critically ill patients and the link between thiamine supplementation and changes in lactate
levels in septic shock patients. The role of thiamine in this group of patients is still unclear;
however, thiamine supplementation does not cause toxic side effects or increase morbidity
or mortality. In this review, we discuss the most common conditions associated with thiamine
deficiency and the limited literature available on thiamine supplementation in critically ill
patients.
Vitamin В1 deficiency was modeled in rats; their daily diet during 6 weeks contained about 20% of the necessary amount of thiamine. Under these conditions, the total content of vitamin В1 (thiamine) in the liver was, on average, 18.3% of the control, while the content of thiamine diphosphate (ТDP) in the blood and cerebral tissues was 40%. General indices of the redox balance (levels of reactive oxygen species, ROSs, and of free SH groups) were also smaller. The activity of thiamine pyrophosphokinase (TPK) in the brain homogenate of animals with thiamine deficiency (TD) was 35% higher than that in the control. In three cerebral structures, the cortex, cerebellum, and hippocampus, we measured the contents of proteins involved in thiamine metabolism, namely thiamine transporter (ТHTR) and TPK. In TD, directions of alterations of these indices for the above-mentioned proteins were opposite; the TPK content in all cerebral structures increased, while the THTR content in the cerebellum and hippocampus decreased. After single injections of 2.0 mg/kg thiamine into animals with TD 24 h before the completion of the experiment, the content of TPK in all cerebral structures increased. As to ТHТR, such effect was observed only in the cortex, while the reactions to thiamine injections in the cerebellum and hippocampus were not clearly manifested. We also estimated the content of glial fibrillary acidic protein (GFAP), an astrocyte marker, in all examined cerebral structures. In TD, this index was stably lower in all structures but returned to nearly control levels after single thiamine injection. Possible relations between alterations in the content of key proteins involved in thiamine metabolism and the supply of the organism with this vitamin are discussed.
Recent clinical trials suggest that patients with myelofibrosis can develop Wernicke’s encephalopathy (WE) when treated with fedratinib, a specific Janus kinase-2 (JAK-2) inhibitor. To investigate this issue, we have examined (1) if fedratinib can produce or alter the course of this disorder, (2) its effects on thiamine-dependent enzyme activity and thiamine status, and (3) its influence on the uptake of thiamine. Animals administered fedratinib for 28 days at a comparable dose used to treat human cases of myelofibrosis showed no evidence of clinical signs of thiamine deficiency (TD). Rats treated with a combination of fedratinib and made thiamine-deficient exhibited no neurological differences in their progress to the symptomatic stage when compared to thiamine-deficient animals only. Treatment with the JAK-2 inhibitor did not compromise erythrocyte transketolase activity in the absence or presence of thiamine diphosphate, and thus thiamine status was not affected in a major way when compared to animals with TD. In addition, treatment of cultured astrocytes with fedratinib did not diminish the uptake of thiamine into these cells. Our findings suggest that treatment with fedratinib does not lead to or alter the progress of TD and thus do not support the notion that administration of this JAK-2 inhibitor directly results in the development of WE due to inhibition of thiamine transport. Known adverse effects of fedratinib involving compromised gastrointestinal function may be an important indirect contributing factor to previously reported cases of WE in patients with myelofibrosis.
Glutamate, the major excitatory neurotransmitter in brain, is almost exclusively intracellular due to the action of the glutamate transporters in the plasma membranes. To study the localization and properties of these proteins, we have raised antibodies specifically recognizing parts of the sequences of two cloned rat glutamate transporters, GLT-1 (Pines et al., 1992) and GLAST (Storck et al., 1992). On immunoblots the antibodies against GLT-1 label a broad heterogeneous band with maximum density at around 73 kDa, while the antibody against GLAST labels a similarly broad band at around 66 kDa in the cerebellum and a few kilodaltons lower in other brain regions. GLT-1 is expressed at the highest concentrations in the hippocampus, lateral septum, cerebral cortex, and striatum, while GLAST is preferentially expressed in the molecular layer of the cerebellum. However, both transporters are present throughout the brain, and have roughly parallel distributions in the cerebral hemispheres and brainstem. Preembedding light and electron microscopical immunocytochemistry shows that both GLT-1 and GLAST are restricted to astrocytes, which appear to express both proteins concomitantly, but in different proportions in different parts of the brain. Nerve terminal labeling was not observed. Both the amino and carboxyl terminals of GLT- 1 and GLAST are located intracellularly, indicating an even number of transmembrane segments. Antibodies against a synthetic peptide corresponding to amino acid residues 2–11 of the proposed sequence of GLT-1 recognize the native rat brain GLT-1 protein, confirming that the translation initiation site is at the first ATG.
We examined the role of glutamatergic mechanisms in acute injury to rat spinal cord white matter. Compound action potentials (CAPs) were recorded from isolated dorsal column segments in vitro . Under control conditions (Ringer’s solution), the CAPs decreased to 71.4 ± 2.0% of preinjury values after compression injury with a clip exerting a closing force of 2 g . The combination of the NMDA receptor blocker APV (50 μ m ) and the AMPA/kainate (KA) receptor blocker CNQX (10 μ m ) resulted in significantly improved recovery of CAP amplitude postinjury; however, the NMDA receptor antagonist APV alone did not enhance postinjury recovery, and infusion of NMDA (10 μ m ) did not affect recovery of the CAPs. In contrast, the AMPA/KA receptor blockers NBQX (10 μ m ) or CNQX (10 μ m ) significantly enhanced the recovery of CAP amplitude postinjury. The agonists AMPA (100 μ m ) or KA (100 μ m ) resulted in significant attenuation of CAP amplitude postinjury. Coapplication of AMPA/KA plus NBQX and CNQX was also associated with improved functional recovery. After incubation with AMPA and KA, Co ²⁺ -positive glia were visualized in spinal cord white matter. Similar results were seen after compressive injury but not in control cords. Immunohistochemistry and Western blot analysis demonstrated AMPA (GluR4)- and KA (GluR6/7 and KA2)-positive astrocytes in spinal cord white matter. In summary, non-NMDA ionotropic glutamate receptors seem to be involved in the pathophysiology of traumatic spinal cord injury. The presence of AMPA (GluR4) and KA (GluR6/7 and KA2) receptors on periaxonal astrocytes suggests a role for these cells in glutamatergic white matter injury.
Little is known of the molecular mechanisms that trigger oligodendrocyte death and demyelination in many acute central nervous system insults. Since oligodendrocytes express functional alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate-type glutamate receptors, we examined the possibility that oligodendrocyte death can be mediated by glutamate receptor overactivation. Oligodendrocytes in primary cultures from mouse forebrain were selectively killed by low concentrations of AMPA, kainate or glutamate, or by deprivation of oxygen and glucose. This toxicity could be blocked by the AMPA/kainate receptor antagonist 6-nitro-7-sulfamoylbenzo(f)quinoxaline-2,3-dione (NBQX). In vivo, differentiated oligodendrocytes in subcortical white matter expressed AMPA receptors and were selectively injured by microstereotaxic injection of AMPA but not NMDA. These data suggest that oligodendrocytes share with neurons a high vulnerability to AMPA/kainate receptor-mediated death, a mechanism that may contribute to white matter injury in CNS disease.
An acute bout of pyrithiamine-induced thiamine deficiency (PTD) produces pathologic lesions within thalamus, mammillary body, and periventricular regions of rat brain. The biological bases for these pathologic changes and their selective distribution within the brain are unclear. The type of tissue damage observed within the thalamus of PTD rats closely resembles that observed following anoxic-ischemic insults and suggests the involvement of excitotoxic amino acids in its pathogenesis. The effects of the N-methyl-D-aspartate receptor antagonist MK-801 (3 mg/kg, i. p.) on brain lesions and amino acid changes have been assessed in rats killed during the late acute stages of PTD. A marked loss of neurons within midline intralaminar nuclei and the posterior nuclear group of the thalamus were observed in the early acute stage of PTD treatment. In the late acute stage, these changes were present throughout the entire thalamus and extended caudally to the periacqueductal gray and mesencephalic tegmentum. Hemorrhagic lesions were observed only in the late acute group and were the primary lesion within the mammillary body and medial and lateral geniculates. No pathologic changes were observed in hippocampus, amygdala, and cortex. MK-801 administered during the late stages resulted in a marked attenuation of necrotic damage to thalamus and periacqueductal gray and a reduction in the number and size of hemorrhagic lesions. Significant reductions of aspartate and glutamate and increases of glycine were observed in 5 regions of thalamus, the hippocampus, hypothalamus, and mammillary bodies of both the early and late acute PTD groups. Levels of GABA and taurine in caudal areas were significantly elevated in the early acute stage but were unchanged from controls in the late acute group. These amino acid changes were reduced in the MK-801 treated late acute group. These observations suggest that NMDA receptors are involved the pathogenesis of PTD-induced brain lesions and that nuclei of the intralaminar and posterior nuclear groups are most vulnerable to PTD effects.
During pyrithiamine-induced thiamine deficiency (PTD), specific regions of the brain develop histological damage. The basis of this selective vulnerability is unknown but the mechanism may involve a glutamate-mediated excitotoxic process in affected structures, leading to alterations in membrane potential and disturbances in calcium homeostasis, In this study, we have examined the volume of distribution of [H-3]nimodipine, an L-type voltage-sensitive calcium channel (VSCC) antagonist, in the brain of the PTD rat. An increase in specific binding of [H-3]nimodipine was detected only in the posterior thalamus at the symptomatic stage, immediately following the loss of righting reflexes (P < 0.0001), There was also an increase in nonspecific binding in the medial geniculate and inferior colliculi, Replenishment with thiamine at the symptomatic stage returned [H-3]nimodipine binding to normal levels. These findings provide evidence that depolarization and activation of L-type VSCCs occur in the posterior thalamus and may contribute to the appearance of histological lesions in this structure during experimental thiamine deficiency. (C) 1998 Wiley-Liss, Inc.
Prior studies have demonstrated that a transformation in neuronal structural responses occurs during the reperfusion period following complete cerebral ischemia (CCI)10,11,12,14. ThE homo-geneous pattern of neuronal injury seen with permanent CCI is modified into a heterogeneous pattern of “selectively vulnerable” neuronal responses with recirculation10,11. The events which cause this transformation remain poorly understood. In addition to such neuronal responses, the glial population of the brain also displays characteristic structural changes, Oligodendrocytes are resistent to significant structural change compared to neurons, but astrocy-tes show an early enlargement of perineuronal and perivascular pro-cesses10,11,12,14,15,8. The anatomical relationships which exist between the neuronal, astrocytic and vascular compartments make any enlargement in the astrocytic compartment a factor of potential importance2,3,17,16. Yet, few morphological studies have attempted to quantify astrocytic changes or relate such alterations to neuronal responses following CCI. Perivascular glial swelling has been implicated as one of the causes of reperfusion defects following CCI4,13,1,9. but subsequent experimental evidence has not confirmed this view5,7,6. Recent studies have proposed that even in the absence of any direct vascular effect, astrocytic swelling may increase the critical diffusion pathway for substrate, metabolite and gas exchange between the vascular and neuronal compartments2,3,16. The purpose of the present investigation was to quantify the distribution of the above neuronal and astrocytic responses after various durations of CCI and postischemic recirculation. Additionally, plasma or blood substitute reperfusion following CCI was evaluated to determine the effect of electrolyte, fluid and oxygen restitution upon the completely ischemic brain.
The relative etiologic roles of ethanol and thiamine deficiency in the cortical atrophy and loss of cerebral white matter in chronic alcoholics are uncertain. The present study examined the distribution of degenerating axons within cortical and subcortical tracts 1 week after recovery from early to late symptomatic stages of thiamine deficiency in the absence of ethanol in Sprague-Dawley rats. The brains of rats exposed to an early symptomatic stage of pyrithiamine-induced thiamine deficiency, 12–13 days of treatment, contained degenerating axons in corpus callosum, anterior commissure, external and internal capsules, optic and olfactory tracts, and fomix and mammillothalamic tracts. A dense pattern of degenerating axons was evident in layers Ill-IV of frontal and parietal cortex. Less intense and more evenly distributed degenerating axons were present in layers IV-VI of frontal, parietal, cingulate, temporal, retrosplenial, occipital, and granular insular cortex. Neuronal counts in mamrnillary body nuclei and areal measurements of the mammillary body were unchanged from controls and the thalamus was relatively undamaged. In animals reversed at later and more advanced symptomatic stages of thiamine deficiency, 14–15 days of treatment, degenerating axons were found in other cortical regions and hippocampus and there was extensive neuronal loss and gliosis within mammillary body and medial thalamus. These results demonstrate that a single episode of thiamine deficiency can selectively damage cortical white matter tracts while sparing the thalamus and mammillary body and may be a critical factor responsible for the pathological and behavioral changes observed in alcoholics without Wernicke's encephalopathy.
(1) The effects of thiamine deficiency as produced by pyrithiamine injections have been studied in the weanling mouse. Selected metabolites were measured in extracts from brain and liver of quick-frozen animals. Pyruvate and α-oxoglutarate dehydrogenases and transketolase were also measured.
(2) In deficient brain, pyruvate and α-oxoglutarate levels were greatly increased. Xylulose-5-P and 6-P-gluconate were more than doubled. Lactate, glucose-6-P, glucose and P-creatine were moderately elevated, and ATP was increased a little. Glutamate was depressed.
(3) In deficient liver, α-oxoglutarate was much increased and ATP was twice normal. Glycogen, glucose, glucose-6-P, 6-P-gluconate, pyruvate, and glutamate were not different from the controls. Lactate was depressed.
(4) Pyruvate dehydrogenase activity was reduced to 25 per cent or less in brain and liver. Transketolase and α-oxoglutarate dehydrogenase activities were reduced to 50 per cent in both organs.
(5) Thiamine treatment, within 5 hr, largely reversed the metabolite changes brought on by pyrithiamine in brain. At the same time pyruvate and α-oxoglutarate dehydrogenase activities were increased 60 per cent or more in both brain and liver. Transketolase activity in liver was only increased 20 per cent at this time, however, and in brain was unchanged.
(6) The results are interpreted to indicate that inhibition of pyruvate and α-oxoglutarate dehydrogenases in brain is sufficient to depress in vivo function. The same seems true for the inhibition of α-oxoglutarate dehydrogenase in liver. However, the changes seen in brain 6-P-gluconate and xyluIose-5-P probably depend on factors other than, or in addition to, the decrease in transketolase activity. It seems worthy of emphasis that in spite of the partial metabolic blocks high-energy phosphate stores were actually increased.
Rapid removal of glutamate from the extracellular space is required for the survival and normal function of neurons. Although glutamate transporters are expressed by all CNS cell types, astrocytes are the cell type primarily responsible for glutamate uptake. Astrocyte glutamate uptake also plays a role in regulating the activity of glutamatergic synapses. Lastly, release of glutamate from astrocytes, via transporter reversal and other routes, can contribute to glutamate receptor activation. This review examines the mechanisms of astrocyte glutamate uptake and release, with particular focus on high-affinity Na+-dependent transporters. Transporter regulation, energetics, and physiological roles are discussed. GLIA 32:1–14, 2000. Published 2000 Wiley-Liss, Inc.
The water channel protein aquaporin (AQP) may play roles in the homeostasis of water content in the brain and brain edema. One possible mechanism of brain edema is glial swelling due to lactic acidosis associated with ischemia. Here, we investigated the effect of lactic acid on the expression and cellular distribution of AQP 4 in cultured rat astrocytes. After 24 h of incubation, the AQP4 expression level increased maximally with 35 mM lactic acid. The AQP4 expression levels also increased with hydrochloric acid or acetic acid. In contrast, with sodium lactate, the AQP4 levels did not increase. The increase in AQP4 expression level occurred without a significant increase in AQP4 mRNA expression level by lactic acid. Under the conditions of de novo protein synthesis inhibition with cycloheximide, lactic acid increased the AQP4 expression level. Furthermore, lactic acid increased the AQP4 expression level on the cell surface of the astrocytes, as determined by a cell surface biotinylation assay and immunocytochemical examination. The increase in AQP4 expression level on the cell membrane of astrocytes induced by lactic acid may be a new regulation mechanism of AQP4 in the brain.
Abnormalities in oxidative metabolism and reductions of thiamine-dependent enzymes accompany many age-related neurodegenerative diseases. Thiamine deficiency (TD) produces a cascade of events including mild impairment of oxidative metabolism, activation of microglia, astrocytes and endothelial cells that leads to neuronal loss in select brain regions. The earliest changes occur in a small, well-defined brain region, the submedial thalamic nucleus (SmTN). In the present study, a micropunch technique was used to evaluate quantitatively the selective regional changes in mRNA and protein levels. To test whether this method can distinguish between changes in vulnerable and non-vulnerable regions, markers for neuronal loss (NeuN) and endothelial cells (eNOS) and inflammation (IL-1beta, IL-6 and TNF-alpha) in SmTN and cortex of control and TD mice were assessed. TD significantly reduced NeuN and increased CD11b, GFAP and ICAM-1 immunoreactivity in SmTN as revealed by immunocytochemistry. When assessed on samples obtained by the micropunch method, NeuN protein declined (-49%), while increased mRNA levels were observed for eNOS (3.7-fold), IL-1beta (43-fold), IL-6 (44-fold) and TNF-alpha (64-fold) in SmTN with TD. The only TD-induced change that occurred in cortex with TD was an increase in TNF-alpha (22-fold) mRNA levels. Immunocytochemical analysis revealed that IL-1beta, IL-6 and TNF-alpha protein levels increased in TD brains and colocalized with glial markers. The consistency of these quantitative results with immunocytochemical measurements validates the micropunch technique. The results demonstrate that TD induces quantitative, distinct inflammatory responses and oxidative stress in vulnerable and non-vulnerable regions that may underlie selective vulnerability.
During a four year peirod, 51 cases of Wernicke's encephalopathy were diagnosed at necropsy, an incidence of 1.7% of all necropsies performed at the Royal Perth Hospital and by the Perth City coroner. Only seven had been diagnosed during life. Many of the patients died suddenly and unexpectedly, apparently as a result of haemorrhagic brainstem lesions, typical of acute Wernicke's encephalopathy, since no other cause of death was found. There was a high incidence of epilepsy and four patients were hypothermic. The diagnosis of Wernicke's encephalopathy may be missed at necropsy unless the brain is examined histologically. Cerebral atrophy and ventricular dilatation were common findings. This is a more common disease than is generally recognised, one which can be readily treated and, more importantly, prevented by adequate nutrition.
Acute thiamine-deficient encephalopathy was produced in mice by the administration of pyrithiamine in conjuction with a thiamine-deficient diet. Clinically, the encephalopathy occurred abruptly on Day 10, frequently with tonic seizures during which many mice died. The survivors developed peculiar neurological signs manifested by ataxia, rigid tail movement, impaired righting reflex, and the Woolley-White sign. With additional malaise and anorexia, the animals died within 4 days. In the brain, there were symmetrically distributed lesions in the thalamus, tegmentum of the fourth ventricle, mammillary body, and periaqueductal gray matter, in order of incidence of involvement. Histologically, the lesion consisted of petechial hemorrhage and/or edematous necrosis of the brain tissue. Electron microscopically, mild petechial lesions were characterized by intact endothelial cells, intact smooth muscle cells and pericytes, a widened Virchow-Robin space associated with erythrocyte infiltration, and an occasional fibrin or platelet clot in the lumen. Among the brain cells, the astrocytes were most severely damaged, showing edematous swelling at the early stage of the illness and necrosis by cytoplasmic fragmentation in the advanced lesions. Moderate edema was also present in the oligodendroglia. Myelin sheaths were often swollen due to edema which occurred most severely at the inner loop. In spite of marked cytoplasmic edema, neuronal cells showed less degenerative alterations than did the glial cells. These ultrastructural changes are similar to the lesions in diet-induced thiamine deficiency in rats, which have been reported by others. It is concluded that pyrithiamine-induced acute thiamine-deficient encephalopathy is an easily reproducible animal model for the human Wernicke-Korsakoff syndrome.
Pyrithiamine induced acute thiamine deficient encephalopathy in the mouse is one of the possible animal models of human Wernicke-Korsakoff syndrome. In this experiment, the adult male Swiss Mice, treated with a daily subcutaneous injection of pyrithiamine in conjunction with a thiamine deficient diet, abruptly developed unique encephalopathic signs on day 10. In the animals sacrificed immediately after the onset of the disease, the gross examination of the brains revealed a small number of minute hemorrhagic lesions in the thalamus, mammilary bodies and pontine tegmentum, including the medial and lateral vestibular nuclei. When spared the hemorrhage, these regions appear intact grossly and in paraffin sections, but were found to be significantly altered in Epon sections. In semithin Epon sections of the pontine tegmentum, there was edematous swelling of all the astrocytes and oligodendrocytes and occasional myelin sheaths. By electron microscopy, the edema of astrocytes involved both nucleus and cytoplasm extensively. The oligodendroglial edema was severe in the peripheral cytoplasm, particularly in the inner loops of the myelin sheaths and only moderately in the nuclei, perinuclear cytoplasm and outer loops. Disintegration of the myelin lamellae occurred when edema of the inner loops had advanced. The axis cylinders surrounded by the edematous loops were essentially intact. In contrast to such glial cell damage, the nerve cells and blood vessels were not altered. These findings suggest that (1) astroglia and oligodendroglia are the cells most sensitive to thiamine deficiency and (2) the resultant glial cell injury is the initial change of thiamine deficient encephalopathy in man and in experimental animals.
Acute dietary deficiency of thiamine was produced in immature female rats. Uptake of glucose by brainstem nuclei was determined by autoradiographic examination of tissue concentrations of 14-C-3-O-methyl-d-glucose following a test dose, and compared with levels in normal and isocaloric control animals. The experiment showed that glucose uptake was depressed in the lesions of thiamine deficiency as compared with the controls, that the depression occurred with the occurrence of morphologic evidence of tissue edema, and that the depression was temporally independent of the breakdown of the blood-brain barrier to protein which is found in the late, necrotic lesions.
Abstract— Thiamine deficiency produced by administration of pyrithiamine to rats maintained on a thiamine-deficient diet resulted in a marked disturbance in amino acid and glucose levels of the brain.
In the two pyrithiamine-treated groups of rats (Expt. A and Expt. B) there was a significant decrease in the levels of glutamate (23%, 9%) and aspartate (42%, 57%), and an increase in the levels of glycine (26%, 27%) in the brain, irrespective of whether the animals showed signs of paralysis (Expt. A) or not (Expt. B). as a result of thiamine deficiency. A significant decrease in the levels of γ-aminobutyrate (22%) and serine (28%) in the brain was also observed in those pyrithiamine-treated rats which showed signs of paralysis (Expt. A). Threonine content increased by 57% in Expt. A and 40% in Expt. B in the brain of pyrithiamine-treated rats, but these changes were not statistically significant.
The utilization of [U-14C]glucose into amino acids decreased and accumulation of glucose and [U-14C]glucose increased significantly in the brain after injection of [U-14C]glucose to pyrithiamine-treated rats which showed abnormal neurological symptoms (Expt. A). The decrease in 14C-content of amino acids was due to decreased conversion of [U-14C]glucose into alanine, glutamate, glutamine, aspartate and γ-aminobutyrate. The flux of [14C]glutamate into glutamine and γ-aminobutyrate also decreased significantly only in the brain of animals paralysed on treatment with pyrithiamine.
The decrease in the labelling of, amino acids was attributed to a decrease in the activities of pyruvate dehydrogenase and α-oxoglutarate dehydrogenase in the brain of pyrithiamine-treated rats. The measurement of specific radioactivity of glucose, glucose-6-phosphate and lactate also indicated a decrease in the activities of glycolytic enzymes in the brain of pyrithiamine-treated animals in Expt. A only. It was suggested that an alteration in the rate of oxidation in vivo of pyruvate in the brain of thiamine-deficient rats is controlled by the glycolytic enzymes, probably at the hexokinase level.
The lack of neurotoxic effect and absence of significant decrease in the metabolism of [U-14C]glucose in the brain of pyrithiamine-treated animals in Expt. B were probably due to the fact that animals in Expt. B were older and weighed more than those in Expt. A, both at the start and the termination of the experiments.
Evidence is accumulating that interactions between different cell types are of paramount importance for CNS function, for example, release of the excitatory transmitter glutamate from neurons and its preferential uptake into astrocytes. Some information is also available about energy metabolism in different cell types, or more often in models of different cell types (e.g., synaptosomes, cultured neurons, cultured astrocytes). In this review an attempt is made not only to correlate information obtained with different cell models but also to integrate this information with in vivo data, with histochemical observations, and with results obtained using brain slices. The emerging patterns indicate that neurons, synaptosomes, and astrocytes are all capable of complete glycolysis and oxidation of glucose. Elevated extracellular concentrations of potassium, known to occur in vivo, enhance energy metabolism by mechanisms that differ between neurons and astrocytes and to a large extent serve to reaccumulate extracellular potassium ions into adjacent cells. Monoaminergic agonists also stimulate energy metabolism, but mainly or exclusively in astrocytes. Profound differences are found between the effects of excess potassium and of aminergic transmitters, suggesting that high potassium concentrations enhance neuronal-astrocytic interactions, whereas the monoamines may tend to dissociate metabolic events in neurons and in astrocytes.
Polyclonal antibodies were generated against the major polypeptide (73,000 mol. wt) present in a highly purified preparation of the [Na+ + K+]coupled L-glutamate transporter from rat brain. These antibodies were able to selectively immunoprecipitate the 73,000 mol. wt polypeptide as well as most of the L-glutamate transport activity--as assayed upon reconstitution--from crude detergent extracts of rat brain membranes. The immunoreactivity in the various fractions obtained during the purification procedure [Danbolt et al. (1990) Biochemistry 29, 6734-6740] closely correlated with the L-glutamate transport activity. Immunoblotting of a crude sodium dodecyl sulphate brain extract, separated by two-dimensional isoelectric focusing-sodium dodecyl sulphate-polyacrylamide gel electrophoresis, showed that the antibodies recognized one 73,000 mol. wt protein species only. Deglycosylation of the protein gave a 10,000 reduction in molecular mass, but no reduction in immunoreactivity. These findings establish that the 73,000 mol. wt polypeptide represents the L-glutamate transporter or a subunit thereof. The antibodies also recognize a 73,000 mol. wt polypeptide and immunoprecipitate L-glutamate transport activity in extracts of brain plasma membranes from rabbit, pig, cow, cat and man. Using the antibodies, the immunocytochemical localization of the transporter was studied at the light and electron microscopic levels in rat central nervous system. In all regions examined (including cerebral cortex, caudatoputamen, corpus callosum, hippocampus, cerebellum, spinal cord) it was found to be located in glial cells rather than in neurons. In particular, fine astrocytic processes were strongly stained. Putative glutamatergic axon terminals appeared non-immunoreactive. The uptake of glutamate by such terminals (for which there is strong previous evidence) therefore may be due to a subtype of glutamate transporter different from the glial transporter demonstrated by us.
Alterations of excitatory amino acids in brain may be of pathophysiological significance in thiamine-deficiency encephalopathy. The present study was undertaken to evaluate the effects of thiamine deficiency induced by the central thiamine antagonist, pyrithiamine, on the glutamate content of glutamatergic nerve terminals. Electrically-stimulated, Ca(2+)-dependent release of glutamate from hippocampal slices obtained from symptomatic pyrithiamine-treated rats was significantly decreased compared to pair-fed controls. Possible explanations for the decreased "neurotransmitter pool" of glutamate in thiamine-deficient rat brain include decreased synthesis of glutamate as a result of decreased activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase or increased release of glutamate per se. There is evidence to suggest that the latter mechanism with ensuing excitotoxic neuronal damage could be involved in the pathogenesis of selective neuronal death in thiamine deficiency. Similar mechanisms could be implicated in Wernicke's encephalopathy in humans.
Several neuropathological reports in the last 5 years have described brain lesions characteristic of Wernicke's Encephalopathy in patients with AIDS. Using the erythrocyte transketolase activation assay, we now report biochemical evidence of thiamine deficiency in 9/39 (23%) of patients with AIDS or AIDS-related complex. In no cases was there history of alcohol abuse nor were there clinical signs of Wernicke's Encephalopathy. Thiamine deficiency in these patients most likely results from the cachexia and catabolic state characteristic of AIDS. In view of (i) the confirmed neuropathological evidence of Wernicke's Encephalopathy in AIDS patients, (ii) the significant thiamine deficiency in these patients and (iii) the difficulties of clinical diagnosis of Wernicke's Encephalopathy, it is recommended that dietary thiamine supplementation be initiated in all newly diagnosed cases of AIDS or AIDS-related complex.
In this article, David Nicholls and David Attwell describe recent advances in our understanding of the mechanisms by which excitatory amino acids are released from cells, and of the way in which a low extracellular glutamate concentration is maintained. Glutamate can be released from cells by two mechanism: either by Ca2(+)-dependent vesicular release or, in pathological conditions, by reversal of the plasma membrane uptake carrier. The contrasting pharmacology and ionic dependence of the glutamate uptake carriers in the vesicle membrane and in the plasma membrane explain how glutamate (but probably not aspartate) can function as a neurotransmitter, and why the extracellular glutamate concentration rises to neurotoxic levels in brain anoxia.
There has been much interest in the biochemical and biophysical processes that couple extracellular signals to alterations in gene expression. While many early events associated with the treatment of cells with growth factors have been described (for example, ion flux and protein phosphorylation), it has proved difficult to establish biochemical links to gene expression. Recently, the study of such genomic control signals has been facilitated by the demonstration that the c-fos proto-oncogene is rapidly and transiently induced by treatment of several cell types with polypeptide growth factors and other growth modulating substances. In one particular system it has been shown that nerve growth factor (NGF) causes a transient induction of c-fos in the phaeochromocytoma cell line PC12, within 15 min. Furthermore, the magnitude of this induction can be modulated with pharmacological agents such as peripheral-type benzodiazepines (BZDs). Thus, the study of c-fos expression in PC12 cells could yield valuable clues to the coupling mechanisms linking cell surface activation to genomic events. Here we demonstrate that c-fos is induced in PC12 cells either by receptor-ligand interaction or by agents or conditions that effect voltage-dependent calcium channels.
Dietary thiamine deficiency, enhanced by pyrithiamine administration in adult rats, produces overt lesions in the brain that are especially prominent in the thalamus. The present study was undertaken to determine whether the thalamic lesions could be correlated with alterations in the physiological properties of neurons in the thalamus and somatosensory cortex. The regimen for experimentally inducing thiamine deficiency produced large lesions in the thalamus of every case; the lesions included most, if not all, of the neurons in the intralaminar thalamic nuclei. The extent of the lesion in the intralaminar thalamus was highly correlated with the loss of bilaterally synchronous spontaneous activity in the cerebral cortex. This correlation was seen in animals analyzed as early as 1–18 hr after the appearance of opisthotonus, the crisis state of thiamine deficiency, and as late as 2–9 weeks of recovery following thiamine replacement therapy. The loss of bilateral synchronous bursting neuronal activity following intralaminar thalamic lesions is consistent with the proposed role of the intralaminar thalamus as a pacemaker for rhythmic cortical activity (Armstrong-Jameset al.,Exp. Brain Res., 1985; Fox and Armstrong-James,Exp. Brain Res.
63: 505–518, 1986). The location and size of the central lesions within the thalamus suggest that the observed neuronal loss could result from a nonhemorrhagic infarction in the ventromedial branches of the superior cerebellar arteries. Experimental thiamine deficiency also produced alterations in the receptive field properties of the somatosensory cortex neurons in all animals examined. Changes in cortical receptive field properties were correlated with the destruction of sensory relay neurons in the thalamic ventrobasal complex. The loss of the central lateral thalamic input to the cortex and the loss of somatosensory relay neurons in the ventrobasal thalamus in experimental thiamine deficiency produce alterations in cortical function which may contribute to deficits in memory and cognition analogous to those which characterize Korsakoff's psychosis in humans.
A set of early response genes has been identified whose transcription in fibroblasts is rapidly induced in response to growth factors. Prototype members of this group, c-fos and c-jun, encode products that form a heterodimer and have been implicated in the regulation of gene expression and cell growth. It is thought that other early response genes also encode critical mediators of the cell's response to external stimuli. We have used PC12 pheochromocytoma cells as a model system to test the hypothesis that different extracellular signals induce distinct patterns of expression of early response genes. Our results indicate that membrane depolarization, induced either by potassium chloride or by the neurotransmitter analog nicotine, activates a program of gene expression distinct from that activated by nerve growth factor or epidermal growth factor. Notably, c-fos and c-jun activation can be dissociated; whereas c-jun is coinduced with c-fos and jun-B after growth factor stimulation, membrane depolarization activates c-fos and jun-B without stimulating c-jun. Fos may therefore form transcription complexes with alternative cofactors under different stimulation conditions. nur/77 and zif/268, which encode putative transcription factors, also show markedly different responses to growth factors and depolarization. We conclude that multiple nonconvergent signal transduction pathways control early response gene expression. Our findings also indicate that the diversity and specificity of cellular response to environmental change can be accounted for by the differential combinatorial induction of a relatively small number of early response genes.
In a 5-year autopsy material constituting 6,964 autopsies, there were 52 cases of Wernicke's encephalopathy of which 12 (23%) occurred in non-alcoholics. Among 18 cases with active (acute) disease, 7 cases (39%) were found in non-alcoholics. Only 4 cases of active Wernicke's disease were diagnosed clinically, all of them in alcoholics. The predominant clinical symptoms were disorientation and depressed levels of consciousness, whereas eye symptoms were recorded in only 3 cases. None of the non-alcoholics were given specific thiamine therapy, whereas some alcoholics received large doses of the vitamin as a routine procedure. However, the thiamine therapy was often instituted too late. It is concluded that active Wernicke's encephalopathy should be considered in all patients with prolonged malnutrition and that disorientation and depressed levels of consciousness may be the predominating symptoms of the disease. Even the slightest suspicion of Wernicke's encephalopathy should prompt immediate administration of large doses of thiamine parenterally.
Treatment of rats with the central thiamine antagonist, pyrithiamine, results in severe neurological symptoms such as loss of righting reflex. Measurement of gamma-aminobutyric acid (GABA) content of brain tissue from symptomatic pyrithiamine-treated (PT) rats revealed significant reductions in thalamus, cerebellum, and pons. GABA content of cerebral cortex, however, was unaltered. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase (alpha KGDH) were reduced in parallel with the GABA changes. On the other hand, activities of the GABA-synthetic enzyme glutamic acid decarboxylase (GAD) remained within normal limits, with the exception of a small but significant decrease in thalamus of symptomatic PT rats. Affinities and densities of high-affinity [3H]muscimol binding sites on crude cerebral membrane preparations from symptomatic PT rats were unchanged. Thiamine administration to symptomatic animals resulted in correction of abnormal righting reflexes and in normalization of decreased GABA levels and reduced alpha KGDH activities in cerebellum and pons. Thalamic GABA levels and alpha KGDH activities, on the other hand, remained significantly lower than normal. These results suggest that the reversible symptoms of pyrithiamine treatment may result from imparied GABA synthesis in cerebellum and pons of these animals. Similar mechanisms may play a role in the pathogenesis of the reversible symptoms of Wernicke's encephalopathy in man.
The intracellular water content of astrocytes in primary cultures shows a biphasic swelling pattern on exposure to various increased external K+ concentrations over the range of 1.5-100 mM. The two phases (physiological, 1.5-12 mM K+; pathological, 25-100 mM K+) are based on two different mechanisms. Both can be blocked by low Cl- solutions and involve intensive net uptake of K+. However, the physiological phase consists of the activation of a KCl + NaCl carrier, while the Na+ in turn is pumped out by Na+-K+ ATPase, with a resultant net accumulation of KCl. At pathological K+ concentrations the KCl + NaCl carrier is less active because the Na+ driving force, its energy source, is reduced (owing to depolarization by K+). However, the Donnan equilibrium across the cell membrane is heavily disturbed, which leads to passive KCl accumulation. The results suggest that volume changes in cultured glial cells during exposure to high K+ should be taken into consideration since they disguise K+ accumulation when only ion activity is measured.
We have studied the potassium uptake using 86Rb+ into monolayers of secondary cultures of human astrocytes prepared from cerebral hemispheres of a 4-month-old fetus. With the use of inhibitors we could attribute 30-40% of the 86Rb+ uptake to an Na+,K+-ATPase, 50-60% to an anion-cation co-transporter and 10% to potassium leak channels. The anion-cation co-transporter was dependent on the simultaneous presence of both sodium and chloride in the incubation medium and is therefore most likely an Na+,K+,Cl- co-transporter. This is the first evidence of such an Na+,K+,Cl- co-transport in human astrocytes.
Local CBF (LCBF) was determined in the same rat model and at the same intervals of thiamine deficiency and reversal as in previous studies of local cerebral glucose utilization (LCGU) and pH (LCpH). The results showed that prior to the appearance of the clinical sequelae of thiamine deficiency (opisthotonus, which usually occurs on day 18 of deficiency) cerebral structures such as the mammillary body, vestibular nucleus, inferior colliculus, and thalamus showed significant hyperperfusion, reaching greater than 200% of control values. At opisthotonus, there was a general decline in LCBF, but, in addition, the larger of these structures developed inhomogeneous perfusion with patches of hyperperfusion adjacent to others of low flow. Seven days of thiamine replenishment at opisthotonus resulted in delayed hypoperfusion notably in the mammillary body, inferior colliculus, and thalamic nuclei. Superimposition of the LCBF, LCGU, and LCpH data reveals that structures known to be vulnerable to the development of histological lesions in this model showed an early phase of hyperperfusion uncoupled from declining LCGU and normal LCpH. Then, following a significant but only focal rise in LCGU between days 11 and 14 of deficiency, hyperperfusion persisted while the pH was dropping and LCGU was rapidly declining. The phase of patchy perfusion occurred only in the histologically vulnerable structures when LCGU was very low and acidosis was at its peak, suggesting that it may have resulted from these opposing influences on LCBF. Following replenishment with thiamine, the vulnerable structures showed delayed hypoperfusion coupled to LCGU.(ABSTRACT TRUNCATED AT 250 WORDS)
Brain levels of y-aminobutyric acid (GABA), glutamate and 2-oxoglutarate, activities of glutamate decarboxylase GABA-transaminase plus succinic semiaidehyde dehydrogenase and blood levels of glutamate and 2-oxoglutarate were determined in normal, thiamine-deprived, oxythiamine-treated and pyrithiamine-treated rats. Brain GABA levels were significantly reduced in thiamine-deprived and pyrithiamine-treated rats, but the activities of the enzymes of the GABA shunt pathway were not affected. Brain levels of glutamate were decreased and of 2-oxoglutarate increased in all three types of deficiency. This was associated with similar decreases in glutamate and increases in 2-oxoglutarate in the blood in all three deficient groups. Intraventricular injections of 2-[U-14C] oxoglutarate into the brain in these four groups of rats resulted in some significant differences in distribution of 14C in various TCA-pathway intermediates and satellite compounds in the brain. Increases in 14C-label were observed for glutamine and 2-oxoglutarate in all three deficient groups as compared to controls. The 14C content of succinate, fumarate and aspartate was decreased in the thiamine deprived and PTh-treated groups and [14C]glutamate was decreased in all three deficient groups. The 14C content of GABA was not significantly affected.
The classical clinical picture of the syndrome described by Wernicke1 consists of disturbances of consciousness, ophthalmoplegia, and ataxia. It has been ascribed to thiamine deficiency, although other dietary deficiencies may contribute to its development. The fullblown triad is frequently not present, a confused state often being the only manifestation. This may progress to stupor or coma. The condition has been described in adults with alcoholism, in chronic gastrointestinal disease, in prisoners of war maintained on very precarious diets and in obese patients kept on restricted diets without adequate vitamin supplementation.2
Guerrero3 in 1949 reported two infants with Wernicke's syndrome due to vitamin B deficiency.
In the early brainstem lesions of acute dietary thiamine deficiency in rats, an outstanding feature is the occurrence of edema. This study, using horseradish peroxidase as a marker, confirms and extends our previous observations using fluorescent dye-labeled albumin that vascular permeability to proteins remains essentially intact during this phase, and becomes altered only when necrosis and hemorrhage supervene. In addition, however, although a minor degree of pinocytotic transendothelial transport and pericytic uptake of horseradish peroxidase was found in both normal animals and in the early lesions, in the late lesions there was markedly enhanced pinocytotic transport but no evidence that interendothelial junctions were disrupted. Reaction product was present in the vascular basement membrane regions and in the extracellular spaces of the neuropil, as in other forms of reactive edema. The localized cerebral edema in thiamine deficiency lesions is thus a biphasic phenomenon. It occurs initially in the absence of vascular permeability change and perhaps as the result of defective active transport related to the deficiency state. In contrast, the late edema is the result of gross breakdown of barrier function to protein, with enhanced pinocytotic transport and extracellular accumulation of the marker in the neuropil.
Labeling patterns in the free glutamic acid from brain tissue from rats injected with sodium pyruvate-2-¹⁴C indicate that the blood brain barrier is not functioning normally in thiamine deficiency. This alteration in selectivity permits pyruvic acid to enter the brain. The polyneuritis in deficiency, therefore, might result from altered metabolic pathways in the brain.
Thiamine-deficient encephalopathy is characterized by morphologic lesions in the brainstem and less extensively in the cerebellum, but the early neurologic signs reverse rapidly and fully with thiamine, indicating a metabolic disorder. The suggested causal mechanisms of the encephalopathy involve two thiamine-dependent enzymes: (a) impairment of pyruvate decarboxylase activity with decreased cerebral energy (ATP) synthesis, and (b) reduction of transketolase activity with possible impairment of the hexose monophosphate shunt and subsequent decrease in NADPH formation. The latter may be important in maintaining glutathione in a reduced form (GSH), which apparently functions by keeping enzymes in a reduced (active) conformation. To examine some of these postulated mechanisms, in this study we measured pyruvate decarboxylase and transketolase activity, lactate, ATP and GSH levels in the cerebral cortex, cerebellum, and brainstem, and thiamine concentration in whole brain of rats with diet-induced low thiamine encephalopathy. Pair-fed and normally fed asymptomatic control animals were similarly investigated. To assess the functional importance of some of our results, we repeated the studies in rats, immediately (16-36 hr) after reversal of the neurological signs with thiamine administration. THE DATA OBTAINED LED TO THE FOLLOWING CONCLUSIONS: (a) Brain contains a substantial reserve of thiamine in that thiamine level has to fall to below 20% of normal before the onset of overt encephalopathy and an increase in brain thiamine to only 26% of normal results in rapid reversal of neurologic signs. (b) Both cerebral transketolase and pyruvate decarboxylase activities are impaired in low thiamine encephalopathy and the abnormality in the pyruvate decarboxylase is reflected in a rise in brain lactate. These biochemical abnormalities occur primarily in the brainstem and cerebellum, the sites of the morphologic changes. (c) Although the fall in cerebral transketolase is about twofold greater than that of pyruvate decarboxylase activity during encephalopathy, both enzymes rise on reversal of neurologic signs and the degree of the transketolase rise is slight. Accordingly, this study cannot ascertain the relative functional importance of these two pathways in the induction of the encephalopathy. The data suggest, however, that the depression of transketolase is not functionally important per se, but may only be an index of some other critical aspect of the hexose monophosphate shunt. (d) The normal cerebral ATP concentration and small GSH fall during encephalopathy, with little GSH rise on reversal of neurologic signs, suggest that a depletion of neither substance is instrumental in inducing thiamine-deficient encephalopathy.
This chapter discusses the important roles of glutamate and gamma-aminobutyric acid (GABA) in brain metabolism. The chapter shows the amino acids as excitatory and inhibitory transmitters in the CNS. The inactivation of these transmitters is generally brought about by sodium-dependent high-affinity uptake systems rather than enrymatic degradation. The importance of the different cell types in these processes and the characteristics of the different transport systems are discussed. The quantitative importance of the high-affinity uptake of glutamate and GABA into glial cells is investigated in primary cultures of astrocytes that seem to constitute a valid model for such cells in vivo. From these studies, it can be concluded that astrocytes are quantitatively important for uptake of putative transmitter amino acids. Whether this uptake has to do primarily with the transmitter pools of these amino acids, and hence their inactivation, or the uptake is involved in the metabolic processes remains to be finally elucidated. The fact that the processes of astrocytes control a large surface area around synapses seems to favor a function of such cells in the inactivation of these amino acids.On the other hand, it is undoubtedly correct that these amino acids can be taken up into presynaptic nerve endings through high-affinity transport processes. In the case of GABA, it is even possible to distinguish between these transport mechanisms employing inhibitors that have been shown to be selective for the transport carriers.
To clarify the enzymatic mechanisms of brain damage inthiamin deficiency, glucose oxidation, acetylcholine synthesis, and the activities of the three major thiamin pyrophosphate (TPP) dependent brain enzymes were compared in untreated controls, in symptomatic pyrithiamin-induced thiamin-deficient rats, and in animals in which the symptoms had been reversed by treatment with thiamin. Although brain slices from symptomatic animals produced14CO2 and14C-acetylcholine from [U-14C]glucose at rates similar to controls under resting conditions, their K+-induced-increase declined by 50 and 75%, respectively. In brain homogenates from these same animals, the activities of two TPP-dependent enzymes transketolase (EC 2.2.1.1) and 2-oxoglutarate dehydrogenase complex (EC 1.2.4.2, EC 2.3.1.61, EC 1.6.4.3) decreased 60–65% and 36%, respectively. The activity of the third TPP-dependent enzyme, pyruvate dehydrogenase complex (EC 1.2.4.1, EC 2.3.1.12, EC 1.6.4.3.) did not change nor did the activity of its activator pyruvate dehydrogenase phosphate phosphatase (EC 3.1.3.43). Although treatment with thiamin for seven days reversed the neurological symptoms and restored glucose oxidation, acetylcholine synthesis and 2-oxoglutarate dehydrogenase activity to normal, transketolase activity remained 30–32% lower than controls. The activities of other TPP-independent enzymes (hexokinase, phosphofructokinase, and glutamate dehydrogenase) were normal in both deficient and reversed animals.
Thus, changes in the neurological signs during pyrithiamin-induced thiamin deficiency and in recovery paralleled the reversible damage to a mitochondrial enzyme and impairment of glucose oxidation and acetylcholine synthesis. A more sustained deficit in the pentose pathway enzyme, transketolase, may relate to the anatomical abnormalities that accompany thiamin deficiency.
Work with ion-selective microelectrodes on the retina of the honeybee drone has shown that potassium is released from photoreceptors during activity and enters glial cells. Measurements of the extracellular voltage gradients indicate that, in this preparation, currents flowing through the glial cells in the 'spatial buffer' pattern account for a large fraction of the glial K+ entry in the active region of the tissue.
Regional cerebral pH was determined autoradiographically using carbon 14-labeled dimethyloxazolidinedione in normal rats, following various durations of thiamine deficiency and replenishment with thiamine when the clinical sequelae of the deficiency appeared. In our model the clinical sequelae of thiamine deficiency (opisthotonus) appeared on the average on day 18. Regional cerebral pH on day 12 was comparable to that in controls and ranged between 7.02 +/- 0.03 and 7.09 +/- 0.03 (mean +/- SEM) in gray matter structures. On day 14 the pH in the inferior colliculus was 6.85 +/- 0.08 and relative acidosis also appeared in thalamic structures. At opisthotonus the pH was 6.48 +/- 0.17 in the mamillary body, 6.43 +/- 0.14 in the vestibular nucleus, and 6.36 +/- 0.14 in the medial dorsal nucleus of the thalamus (p less than 0.01). One dose of thiamine replenishment at this stage transiently raised the pH in the inferior colliculus to 7.25 +/- 0.19 and in the medial dorsal nucleus to 7.20 +/- 0.13 (p less than 0.01). Cerebral regions showing significant acidosis during thiamine deficiency coincided largely with those known to be histologically vulnerable and those previously reported to show a focal rise in local cerebral glucose utilization between days 11 and 14 of thiamine deficiency. This focal acidosis shown to occur in thiamine deficiency may be one mechanism contributing to the selective histological vulnerability in this model.
We have examined the extracellular pH (pHe) during spreading depression and complete cerebral ischemia in rat parietal cortex utilizing double-barrelled H+ liquid ion exchanger microelectrodes. The baseline pHe of the parietal cortex was 7.33 at a mean arterial PCO2 of 38 mm Hg. Following spreading depression and cerebral ischemia, highly reproducible triphasic changes in pHe occurred, which were intimately related to the negative deflection in tissue potential (Ve). The changes in pHe for spreading depression (n = 23) were a small initial acidic shift, beginning before the rapid change in Ve, followed by a rapid transient alkaline shift of 0.16 pH units, the onset of which coincided with the negative deflection in Ve. A prolonged acidic shift of 0.42 pH units then occurred. The maximal decrease in pHe was to 6.97 and the mean duration of the triphasic pHe change was 7.8 min. The lactate concentration in brain cortex increased from baseline 1.2 mM to 7.0 mM (n = 6) during the maximal acidic change in spreading depression. In addition, lactate levels correlated well with resolution of the pHe changes during spreading depression. The triphasic pHe changes following complete cerebral ischemia were an initial acidic shift of 0.43 pH units which developed over 2 min, then an alkaline shift of 0.10 pH units coincident with the negative deflection in Ve, and a final acidic shift of 0.26 pH units. The terminal pHe was 6.75. Superfusion of the cortex with inhibitors of carbonic anhydrase (acetazolamide), Na+/H+ counter transport (amiloride), and Cl-/HCO-3 countertransport (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) altered the triphasic pHe changes in a similar fashion for both spreading depression and cerebral ischemia, providing insights into the pHe regulatory mechanisms in mammalian brain.
An unconscious patient had a differential diagnosis of coma. Traumatic, metabolic, and infectious origins were considered, but none explained her condition satisfactorily. Clinical features on examination were compatible with Wernicke-Korsakoff syndrome. Her condition improved with supportive treatment and thiamine hydrochloride administration. A computed tomographic scan showed large, symmetric, low-density thalamic lesions, the condition of which improved after three months.
An intense K+ accumulation in primary cultures of astrocytes, occurring when external K+ was increased from 5.4 to 54 mM, was investigated. This increase resulted in a doubling of the K+ content within 10 s. Thirty percent of the accumulation was inhibited by furosemide (2 mM). This drug had no effect on the unidirectional influx of K+ at 5.4 mM K+, but when the extracellular K+ concentration was increased, there appeared to be a furosemide-sensitive component of the influx. This component increased with increasing external K+ levels, reaching 44% of the total influx at 72 mM. These results show that astrocytes exhibit an intense furosemide-sensitive K+ accumulation which is activated by K+ levels resembling those occurring in the extracellular compartment during pathological events. Previous studies on a furosemide-sensitive Cl- pump in cultured astrocytes suggest that this accumulation might be via KCl cotransport, which in other systems is involved in volume control.
Pyrithiamine-induced acute thiamine-deficient encephalopathy was produced in adult male Wistar rats. Twenty-four hours before the onset of neurological signs the brain showed no morphological abnormalities. Encephalopathic rats had symmetrical lesions of edematous necrosis localized in the thalamus, mammillary body, and pontine tegmentum. Biochemically, encephalopathic rats had brain thiamine levels less than 20% of controls. For the assay of the concentrations of adenosine triphosphate (ATP) and phosphocreatine, the brains were fixed using 5 KW microwave irradiation and were divided into four parts: cerebral cortex, diencephalon, lower brainstem, and cerebellum. In the lower brainstem of the encephalopathic rats ATP concentrations were 89.5% of normal controls. Phosphocreatine levels were lowered to 70% of controls in the diencephalon and to 75% in the lower brainstem. Total high energy phosphate levels were decreased to 89% of controls in the diencephalon and 91% in the lower brainstem before the onset of neurological signs and to 76% and 79%, respectively, after the onset. In the cerebral cortex and cerebellum high energy phosphates were not significantly reduced. Lower high energy phosphate levels and the distribution of edematous lesions were coincident in the brain. These findings suggest that a low energy state is closely related to the formation of edematous lesions in thiamine-deficient encephalopathy.