Content uploaded by Dragan M. Djuric
Author content
All content in this area was uploaded by Dragan M. Djuric on May 02, 2020
Content may be subject to copyright.
Send Orders for Reprints to reprints@benthamscience.ae
Current Medicinal Chemistry, 2017, 24, 1-13 1
REVIEW ARTICLE
0929-8673/17 $58.00+.00 © 2017 Bentham Science Publishers
Sulfur – Containing Amino Acids in Seizures: Current State of the Art
Dragan Hrnčića, Aleksandra Rašić-Markovića, Đuro Macutb, Dušan Mladenovićc,
Veselinka Šušićd, Dragan Djurića and Olivera Stanojlovića*
aLaboratory of Neurophysiology, Institute of Medical Physiology “Richard Burian”, Faculty of Medicine,
University of Belgrade, 11000 Belgrade, Serbia; bCCS, Faculty of Medicine, University of Belgrade, Bel-
grade, Serbia; cInstitute of Pathophysiology "Ljubodrag Buba Mihailovic", Faculty of Medicine, University
of Belgrade, 11000 Belgrade, Serbia; dSerbian Academy of Sciences and Arts, 11000 Belgrade, Serbia
A R T I C L E H I S T O R Y
Received: November 02, 2016
Revised: May 15, 2017
Accepted: May 24, 2017
DOI:
10.2174/0929867324666170609090613
Abstract: Homocysteine and taurine are non-proteinogenic sulfur-containing amino acids
with numerous important physiological roles. Homocysteine and taurine are considered to
be neurotransmitters and neuromodulators, the first showing clear hyperexcitability role,
while the second is known by its inhibitory and neuroprotective properties.
In this article, we addressed the role of homocysteine and its related metabolite homocys-
teine thiolactone in the development of seizures, focusing on its experimental models in
vivo, potential mechanisms of pro-epileptogenic activity via interactions with glutamater-
gic neurotransmission, sodium pump activity, oxidative stress, cholinergic system and
NO-mediated neuronal signaling, as well as the pharmacological and non-
pharmacological approaches to modulate its proconvulsive activity. Additionally, herein
we will focus on taurine neuroprotective effects linked with its anticonvulsive properties
and mediated by taurine interactions with GABA-ergic and glutamatergic system and
oxidative stress.
Keywords: Homocysteine, taurine, amino acids, sulfur, seizures, epilepsy, oxidative stress, glutamate.
1. INTRODUCTION
Methionine, cysteine, homocysteine, and taurine are
the four common sulfur-containing amino acids, but
only methionine and cysteine are incorporated into pro-
teins [1]. These sulfur-containing amino acids share
common metabolic pathway in which methionine could
be in the top/start, and taurine in the bottom/final part.
Although, homocysteine and taurine are non-
proteinogenic amino acids, they also play numerous,
important, physiological roles [1]. Both homocysteine
and taurine are considered to be neurotransmitters and
neuromodulators, the first showing the clear hyperex-
citability role, while the second is known for its inhibi-
tory and neuroprotective properties.
*Address correspondence to this author at the Institute of Medical
Physiology “Richard Burian”, Belgrade University School of Medi-
cine, Višegradska 26/II, 11000 Belgrade, Serbia; Tel/Fax: ++381-
11-3607-106; E-mail: solja@afrodita.rcub.bg.ac.rs
Physiological blood concentrations of homocysteine
has been considered to be up to 15 µmol/l. Elevated
level of homocysteine has been recognized as an inde-
pendent risk factor for numerous disorders of various
organ systems, such as cardiovascular diseases, disor-
ders connected with the aging brain like cognitive de-
cline, vascular dementia and Alzheimer’s disease, as
well as the cerebrovascular diseases and stroke [2-5].
Taurine is considered to be the most abundant free
amino acid in animal tissues. Namely, taurine ac-
counts for 3% of the free amino acid pool in plasma,
but this percentage is much higher in different tissues
ranging from 19% in the brain, up to 25.50 and 53%
in the liver, kidneys and muscles [1]. Besides its nu-
merous physiological roles related (not only) to cell
volume regulation, formation of bile salts, and ther-
moregulation [1, 6], taurine satisfies many of the cri-
teria for inclusion in the armamentaria of neurotrans-
mitters [7].
2 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
In this article, we will address the role of homocys-
teine and its related metabolites in the development of
seizures, focusing its experimental modeling, potential
mechanisms of pro-epileptogenic activity and pharma-
cological and non-pharmacological approaches to
modulate its proconvulsive activity. Also, herein we
will focus on taurine neuroprotective attributes linked
with its anticonvulsive effects.
2. HOMOCYSTEINE AND SEIZURES: ACUTE
AND CHRONIC EXPERIMENTAL MODELING,
MECHANISMS AND MODULATION
Homocysteine together with its metabolites, primar-
ily homocysteine thiolactone, is one of the excitatory
factors in the framework of new concepts in the devel-
opment of hyperexcitability [8]. Metabolism of homo-
cysteine is closely related to the metabolism of me-
thionine. Briefly, this relationship is as follows (Fig. 1).
Methionine is converted to S-adenosyl methionine
(SAM) which is a donor of methyl groups in numerous
reactions of methylation. SAM is converted to S-
adenosyl homocysteine (SAH), which is converted to
homocysteine after hydrolysis. Further metabolic fate
of homocysteine occurs in two ways: remethylation
and/or transsulfuration. In the process of remethylation,
homocysteine is converted to methionine by a ubiqui-
tously distributed enzyme methionine synthase in the
presence of vitamin B12 or by betaine-homocysteine
methyltransferase (BHMT), distributed in the liver and
kidneys. On the other hand, the transsulfuration process
takes place under the catalytic action of cystathionine -
beta synthase (CBS), and as a result cystathionine and
then cysteine is created. It should be noted that vitamin
B6 is necessary for the performance of the described
process of transsulfuration [9, 10].
One of the most reactive metabolites of homocys-
teine is homocysteine thiolactone, which is believed to
be responsible for many deleterious effects of homo-
cysteine, regardless of the fact that it constitutes up to
1% of the total homocysteine in plasma (0 to 34.8
nmol/l is physiological concentration). Methionyl-
tRNA synthetase is responsible for this conversion
[10], but reconversion of homocysteine thiolactone in
homocysteine is possible by the activity of the enzymes
bleomycin hydrolase and the paraoxonase 1 [11-13].
The brain is particularly vulnerable to high concen-
trations of homocysteine, since it does not possess
BHMT enzyme and therefore betain-remethylation of
homocysteine is not possible. Homocysteine enters
neurons via the Na+-dependent membrane transporter
[14]. Homocysteine thiolactone systemic application
causes neurotoxicity, convulsions and death in experi-
mental animals [15]. In addition, the toxic effect of
homocysteine thiolactone is possible related to its me-
tabolism into homocysteic acid [12].
Kubova et al. [16] reported epileptic phenomenon in
homocysteine thiolactone - treated rats in the form of
flexion seizures, observed in young, but never seen in
25-day-old rats. Homocysteine was revealed to elicit
clonic and generalized tonic-clonic seizures during on-
togenesis in immature rats [16, 17].
Stanojlović et al. [18] have shown that intraperito-
neal administration of homocysteine thiolactone to
adult rats is a suitable model of generalized epilepsy. It
is characterized by well-defined motor phenomena in
the behavior of animals, as well as by the characteristic
bioelectrical phenomena in the EEG. These phenomena
meet, by their characteristics, the criteria of ictal phe-
nomena known as spike-wave discharges (SWD) corre-
lated with the absence type of behavioral manifesta-
tions. Alterations in the neural circuits induced by ho-
mocysteine thiolactone are characterized by coexis-
tence of convulsive and absence seizures in behavior
and SWD in the EEG patterns. All these findings, to-
gether with clinical findings of seizure symptoms in
patients with severe hyperhomocysteinemia, tightly
linked homocysteine and its related compounds with
seizure activity.
2.1. Modeling Experimental Chronic Hyperhomo-
cysteinemia in vivo: Tools for Discovering Underly-
ing Mechanisms
Hyperhomocysteinemia stands for elevated concen-
tration of homocysteine in the blood and is defined as
total homocysteine level greater than 15 µmol/l. Ab-
normalities in the regulatory enzymes (CBS or thermo-
labile methylenetetrahydrofolate reductase - MTHFR)
or cofactors (folate, vitamin B12, vitamin B6) involved
in the metabolism of homocysteine could result in the
development of hyperhomocysteinemia and it is fre-
quently classified as mild (homocysteine in the range
of 15 - 30 µmol/l) moderate (31- 100 µmol/l) and se-
vere (level of homocysteine exceeds 100 µmol/l) [19,
20]. The deficit of folic acid, vitamin B6 and/or vita-
min B12 in diet usually results in mild hyperhomocys-
teinemia, while genetic factors, certain medications,
and renal diseases may also be the contributing factors
[21], while severe hyperhomocysteinemia is a result of
homozygous genetic defects, such as lack of CBS or
MTHFR. Severe hyperhomocysteinemia is rare, while
mild and moderate hyperhomocysteinemia are signifi-
cantly more spread in different populations [19], and
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 3
Fig. (1). The schematic illustration of major metabolic pathways of homocysteine and taurine. Abbreviations are as follow:
BHMT – betaine-homocysteine methyltransferase; CBS – Cysthatione beta synthetase; CDO - cysteine dioxigenase; CγL - cys-
tathione - gamma lyase; CSD - cysteine sulfonic acid decarboxylase; HD - hypotaurine dyhydrogenase ; MRS -Methionyl-
tRNA synthetase; MS – methionine synthase MT – methyl transferases; MTHFR – methylene tetrahydrofolate reductase; PO1
– paraoxonase 1; THF – tetrahydrofolate Details could be find in the text of the article.
are recognized risk factors for development of numer-
ous cardiovascular [5, 22], neurological and other dis-
eases (diabetes, psoriasis and malignant diseases) [23].
According to Sener et al. [24], some antiepileptic drugs
have potential to induce hyperhomocysteinemia.
Namely, classic antiepileptic drugs such as phenytoin,
carbamazepine and valproate reduced the concentration
of folate levels and produced increased homocysteine
levels. The capability of these drugs to raise homocys-
teine levels might actually contribute to the poor sei-
zure control, as well as to the hyperhomocysteinemia –
linked diseases in these patients. Therefore, the rela-
tionship between homocysteine and epileptogenesis has
been emphasized by these findings, especially when we
have in mind that antiepileptic pharmacotherapy is the
long-lasting one.
The significant impetus of hyperhomocysteinemia
proved in clinical practice and experimental studies in
different branches of medicine was the main reason to
create and develop several experimental models of
chronic hyperhomocysteinemia. These models differ in
type and gender of experimental subjects, applied sub-
stances, ways of its administration, duration of the ex-
periment and others [8]. Therefore, several experimen-
tal models of hyperhomocysteinemia have been estab-
lished [25]. Nutritional alterations, such as diets low in
folate and/or vitamin B12 [26], enriched with me-
thionine [27, 28] or a combination of vitamin B com-
plex deficiency and increased content of methionine
[28] are the most common ways to establish the ex-
perimental model of mild hyperhomocysteinemia. Se-
vere hyperhomocysteinemia is developed in CBS
4 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
knock-out mice [29]. A common way of experimental
chronic hyperhomocysteinemia generation is the ex-
ogenous application of homocysteine or its metabolites
[30]. Wistar rats [25, 30, 31] and Spregue -Dawley rats
[32-34] are the most commonly used, regardless of be-
ing males [31] or females [25, 27]. Ways of a drug de-
livery vary from intraperitoneal and subcutaneous in-
jections to modifications in the rat chaw and water con-
tent. The length of the experimental intervention is also
variable, from 7 days to 3 months [8]. Therefore, from
our standpoint, that differences in the observed effects
of these interventions [25] could be consequences of
above-mentioned variations (described in details else-
where [8]).
Hrnčić et al. [35] developed a model of chronic
moderate hyperhomocysteinemia by methionine nutri-
tional overload. For this purpose, we used Wistar al-
bino rats, males, and methionine - enriched food (7.7
g/kg, double content of methionine comparing to stan-
dard rat chaw provided to control animals) during one
month. We believe that genetically intact animals on
hypermethionine diet are equivalent to the methionine-
rich diet in the general human population; thus the use
of diet with high content of methionine might be a
good choice in inducing chronic hyperhomocysteine-
mia in the translational studies.
2.2. Pro-epileptic Mechanisms of Homocysteine and
Related Metabolites
Shedding the light on the relationship between ho-
mocysteine and the CNS dysfunction is vital for
improving the treatment of neurological disorders
whose mechanisms include homocysteine [4]. The role
of homocysteine and its derivatives in the development
of neurotoxicity and hyperexcitability requires further
investigations. The accumulation of homocysteine in
the brain increases intracellular levels of SAH, a potent
inhibitor of many methylation reactions, while the im-
pairment of methylation processes could result in in-
creased permeability of the blood-brain barrier [36].
Homocysteine deleterious neuronal effects have been
linked to the increased glutamatergic neurotransmis-
sion [4]. Beside this mechanism we will further discuss
the involvement of sodium pump activity, oxidative
stress, cholinergic system and NO-mediated signaling
in the homocysteine effects related to its epileptiform
activity (Fig. 2).
2.2.1. Homocysteine via Glutamatergic Receptors
Homocysteine has been reported to activate
ionotropic glutamate receptors [37], but also to activate
the groups I and III of metabotropic glutamate recep-
tors [12, 38]. The metabolic products of homocysteine
are also very potent neurotoxins acting as agonists of
these receptors [39], which are expressed in hippocam-
pal pyramidal cells and may be directly responsible for
excitotoxic cell death. However, NMDA receptors are
not exclusively expressed in neurons, since cardiomyo-
cytes as well as endothelial cells from cerebral tissue
contain this receptor complex. Our studies [40] on ex-
perimental model of homocysteine seizures, dealing
with MK-801 as NMDA antagonist, and ifenprodil (as
NR2B-selective NMDA antagonist), confirmed in-
volvement of these mechanisms in homocysteine
thiolactone - induced epileptogenesis. We demon-
strated that MK-801 administered prior to homocys-
teine thiolactone significantly decreased the number
and the intensity of convulsive episodes, and even de-
creased lethality 90 min after homocysteine injection.
However, the effects of homocysteine on NMDA
receptors have been described as dual and dependent
on glycine concentration [37, 41]. Namely, in condi-
tions of increased concentrations of glycine, even small
concentrations of homocysteine could be excitotoxic.
On the other side, at low concentrations of glycine,
homocysteine acts as a partial antagonist at glycine site
and inhibits the NMDA receptor, preventing deleteri-
ous effects in normohomocysteinaemia. It is also be-
lieved that homocysteine indirectly potentiate gluta-
mate-induced neurotoxicity, since the initial Ca2+ influx
through NMDA receptors stimulates the release of glu-
tamate, which further activates metabotropic glutamate
receptors and leads to a secondary Ca2+ ion influx, re-
sulting in excitotoxicity [41]. Moreover, homocysteine
was reported to affect turnover of other endogenous
excitatory amino acids [17]. Ethanol has been shown to
inhibit NMDA-induced Ca2+ influx and cyclic GMP
production, as well as to affect other neurotransmitter
systems, primarily glutamate and GABA [42]. Rašić-
Marković A. et al. [43] reported alterations in the total
spectral power density upon ethanol and homocysteine
thiolactone treatments in rats. Indeed, we found that
ethanol action on electrographic pattern is biphasic,
with potentiation of epileptiform activity in one dose
range and depression in another one.
2.2.2. The Role of the Na+/K+-ATPase Activity in Ho-
mocysteine Seizures
Alterations in the Na+/K+-ATPase activity have
been recognized as a mechanism implicated in seizure
generation [44], since it is one of the main enzymes
included in maintaining the high gradients of Na+ and
K+ ions across the cell membrane [45]. Also, it is be-
lieved that impaired Na+/K+-ATPase activity affects the
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 5
Fig. (2). The role of homocysteine and taurine in seizures. Potential mechanisms by which homocysteine and taurine affect
seizures are illustrated. These mechanisms are discussed in details in 2.2, 3.1 and 3.2 sections of the article.
release of GABA and glutamate, what could be a pos-
sible way of evoking hyperexcitability [44].
The effects of homocysteine and related compounds
on the activity of Na+/K+-ATPase have been studied
both in vitro and in vivo. Homocysteine in vitro led to
the inhibition of Na+/K+-ATPase activity in the rat parie-
tal, prefrontal, and cingulated cortex, while chronic hy-
perhomocysteinemia decreased the activity of this en-
zyme in the parietal cortex, but increased it in the pre-
frontal cortex, and had no effect on Na+/K+-ATPase ac-
tivity in the cingulated cortex [46]. Strong inhibition of
the hippocampal Na+/K+-ATPase was observed on ho-
mocysteine application in high dose to immature rats
[47]. The congruent results were reported for the parietal
cortex upon subcutaneous injection of homocysteine
[48]. In an in vivo study, we explored the effects of ho-
mocysteine thiolactone applied in the same dose that
provoked seizures, as well as equimolar concentration of
homocysteine on the Na+/K+-ATPase activity in the
brain cortex, the hippocampus and the brain stem of
adult male rats [49]. We demonstrated a moderate inhi-
bition of the rat hippocampal Na+/K+-ATPase activity by
homocysteine without a significant effect on the cortex
and the brain stem Na+/K+-ATPase activity, in contrast
to homocysteine thiolactone which strongly inhibited
Na+/K+-ATPase activity in all of these brain regions
[49]. It was supposed that the homocysteine - induced
impairment of the Na+/K+-ATPase activity could be a
consequence of the oxidation of thiol groups within this
enzyme and that homocysteine inhibits in a non-
competitive manner Na+/K+-ATPase with ATP [50].
Acute application of folic acid and L-arginine pre-
vented the inhibitory effect of homocysteine thiolac-
tone on the Na+/K+-ATPase activity what we demon-
strated in studies from our laboratory [51, 52]. Re-
cently, we reported that subchronic supplementation
with folic acid and L-arginine per se increased the
Na+/K+-ATPase activity. However, folic acid and L-
arginine were able to prevent the inhibitory effect of
homocysteine thiolactone and even increase Na+/K+-
ATPase activity [53].
2.2.3. The Role of the Cholinergic System in Deleteri-
ous Effects of Homocysteine
The cholinergic system has been investigated as one
of the possible targets of homocysteine, specifically the
enzyme acetylcholinesterase, which basic physiological
role is to terminate the acetylcholine action on mus-
carinic and nicotinic receptors. However, acetylcho-
linesterase may have other non-enzymatic functions,
like trophic effects, effects on cell proliferation and
differentiation, as well as the response to various stim-
uli, including stress [54]. Inhibition of the acetylcho-
linesterase activity is partly responsible for the neuro-
toxic effects of lindane [55], as well as some other pes-
ticides. The seizure model induced by soman is devel-
oped by irreversible inhibition of acetylcholinesterase
with the consequent hyperactivity of cholinergic sys-
tem [56]. Acetylcholine potentiates the NMDA-
induced frequency of interictal discharges in the hippo-
campus via activation of muscarinic receptors [57].
Activation of the cholinergic system could suppress
excitation processes by increasing the release of GABA
from the interneuron terminals [58]. The link between
cholinergic system dysregulation and epileptogenesis
could also involve the immune system [59].
It has been shown that hyperhomocysteinemia de-
creases the acetylcholinesterase activity in vitro; with
6 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
oxidative stress being accused as a major mediator
[60]. On the other hand, in vitro studies have shown
that methionine has no effect, and homocysteine inhib-
its butyrylcholinesterase [61] in a manner of competi-
tive inhibition. Studies in vivo and in vitro showed that
acute hyperhomocysteinemia inhibits the activity of
cholinesterase in the serum of humans and rats. Acute
application of homocysteine thiolactone decreased the
acetylcholinesterase activity in the brain and heart tis-
sue, without affecting this enzyme in the rat blood [62].
We have shown the effects of chronic mild hyper-
homocysteinemia induced by methionine nutritional
overload in rats on the activity of acetylcholinesterase
in different brain regions. Results of this study showed
that hyperhomocysteinemia, elicited by methionine
nutritional overload over 30 days, decreased the acetyl-
cholinesterase activity in the cortex, hippocampus,
thalamus, and nc. caudatus, but the observed inhibition
was statistically significant only in the cortex [35]. It is
known that acetylcholinesterase exists in different iso-
forms due to post-translational modifications. This fact
may be potential reason for the selective vulnerability
of different brain regions proved in the mentioned
study. The cortex has shown the greatest sensitivity to
hyperhomocysteinemia induced by hypermethionine
diet in our reported study.
2.2.4. Implications of NO-mediated Signaling in Ho-
mocysteine-induced Epileptic Activity
NO-mediated signaling in epileptogenesis has been
one of the challenging issues in shedding more lights
on underling mechanism of epileptic activity [63], but
also in functioning of other organ systems, like gastro-
intestinal system [64]. The role of NO in epileptogene-
sis is highly ambiguous. Namely, numerous studies
indicated anticonvulsive activity of NO in different
experimental models of epileptic activity, while others
reported proconvulsive role for NO. These issues have
been reviewed in more details elsewhere [63].
We have investigated the role of NO in the homo-
cysteine epileptic activity by using L-arginine and L-
NAME as modulators of NO production [35]. Namely,
NO is synthesized from L-arginine by the activity of
the family of enzymes known as NO synthases (NOS).
Our results showed that the systemic administration of
L-arginine significantly decreased the seizure incidence
and the number of seizure episodes and prolonged la-
tency time to the first seizure elicited by the convulsive
dose of homocysteine thiolactone. On the contrary, L-
NAME increased the seizure incidence and severity
and shortened the latency time to the first seizure fol-
lowing homocysteine application in the subconvulsive
dose. Moreover, EEG analysis showed that L-arginine
decreased, while L-NAME increased the number of
SWD per rat. These results showed the functional in-
volvement of NO in the homocysteine-induced convul-
sive activity.
The effects of NO could be related to the type of
NOS involved in its production. Namely, neural
(nNOS), endothelial NOS (eNOS) and inducible NOS
(iNOS) have been identified, so far [65]. Therefore, we
further investigated contribution of nNOS and iNOS in
functional role of NO in homocysteine-mediated sei-
zures. nNOS is found to be expressed in the hippocam-
pus, cerebral cortex, corpus striatum and cerebellum
[66]. Pharmacological inhibition of nNOS by 7-
nitroindazole has been used to investigate the involve-
ment of nNOS in the model of homocysteine thiolac-
tone seizures [67]. In this study, 7-nitroindazole
showed tendency to increase seizure incidence, de-
crease latency time to first seizure, increase number of
seizure episodes per rat and increase severity of these
seizures. It is believed that iNOS is a major contributor
to the CNS inflammatory/degenerative conditions via
excessive NO production [68]. Its overexpression has
been reported in brains of epilepsy patients and some
spontaneously epileptic mice [69, 70]. We have dem-
onstrated the involvement of iNOS-derived NO in ho-
mocysteine -mediated seizures by using aminogua-
nidine, a selective iNOS inhibitor [71]. In this study we
observed that treatment with aminoguanidine increased
behavioral seizure properties. Quantitative analysis of
ictal activity in EEG showed congruent results.
The anticonvulsive properties of NO derived by
nNOS and iNOS in epileptic activity elicited by homo-
cysteine thiolactone has been proposed to be a result of
several possible mechanisms, as well as the interplay
between NO and HCT on various levels, i.e. interaction
at NMDA and GABA receptors, including the relation-
ship of NO with NMDA and GABA receptors, neu-
rodegeneration and cytoprotection and oxidative stress
[63, 72].
2.2.5. Implications of Brain Oxidative Stress in Dele-
terious Effects of Homocysteine: Link with Folic Acid
Oxidative stress is one of the mechanisms believed
to be responsible for various damages caused by homo-
cysteine [73], especially in the CNS where response to
oxidative stress is not uniform [74] and the brain being
particularly vulnerable to oxidative stress for several
reasons [75].
We recently reported the effects of chronic hyper-
homocysteinemia induced by methionine nutritional
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 7
overload on the oxidative stress in different brain struc-
tures [76]. Results of that study showed that lipid per-
oxidation was significantly increased in the cortex and
nc. caudatus of rats developing hyperhomocysteinemia,
and that there was no significant alterations in the level
of lipid peroxidation in the hippocampus and thalamus.
Other studies also showed an increase of oxidative
stress in the brain as a consequence of hyperhomocys-
teinemia [73]. In our study, hyperhomocysteinemia
didn't affect significantly activity of the superoxide
dismutase (SOD) in the brain. Catalase (CAT) activity
was significantly increased in the cortex and hippo-
campus, and highly significantly increased in the
thalamus by hyperhomocysteinemia. Content of glu-
tathione (GSH) was significantly increased in the
thalamus and nc. caudatus, and prominently in the hip-
pocampus. Glutathione peroxidase (GPx) activity was
significantly increased in the cortex and thalamus by
hyperhomocysteinemia. Different brain regions had
different response to oxidative stress: the cortex and nc.
caudate showed a higher sensitivity compared to the
hippocampus and thalamus. We hypothesized that
lower sensitivity of the thalamus and hippocampus to
oxidative damage may be explained, at least in part, by
increased activity of SOD and significant rise in activ-
ity of CAT and GPx, as well as significant rise in the
content of GSH in these brain areas. We believed that
increase in the activity of these enzymes may be an
adaptive response of brain cells to the neurotoxic ef-
fects of homocysteine. On the other hand, the cortex
and nc. caudatus were less and non-uniformly protected
by these mechanisms.
Folic acid prevented homocysteine-induced oxida-
tive stress in the central nervous and cardiovascular
system [77, 78]. Namely, folic acid decreased the
level of malondialdehyde [77, 79] and superoxide an-
ion [78]. Also, it prevented hyperhomocysteinemia-
provoked reduction of antioxidant enzymes in the rat
brain [77, 75]. Folic acid has been shown to reduce
blood homocysteine concentrations both in humans
and rats [80, 81], thus ameliorating the risk of hyper-
homocysteinemia [82]. At the same time, the link be-
tween epilepsy and folic acid is complex: it aggra-
vates or diminishes seizures (discussed elsewhere, see
[83, 84]).
We showed that high dose of folic acid (15 mg/kg,
i.p.) significantly decreased seizure incidence and pro-
longed the latency of the seizures induced by homocys-
teine thiolactone. In the same study from our labora-
tory, EEG analyses showed that acute folic acid de-
creased the mean total power spectral density and the
amplitude of spikes during ictal period in dose depend-
ent manner [85]. On the other hand, we also demon-
strated that subchronic supplementation with folic acid
(5 mg/kg) did not exacerbate behavioral seizure mani-
festations in a model of homocysteine seizures, without
significant alterations in spectral power densities of
ictal episodes [52]. Moreover, in our further study on
the supplementation with folic acid and L-arginine, we
concluded that subchronic supplementation with folic
acid and L-arginine had an antiepileptic effect.
Namely, behavioral characteristics of seizures in this
homocysteine model were not exacerbated, while the
EEG spectral power densities and amplitudes during
ictal periods were significantly decreased in rats sup-
plemented with folic acid and L-arginine compared
with the homocysteine group [53].
2.3. Non -pharmacological Approaches to Modulate
Homocysteine Epileptiform Activity
Sleep is a cyclic vital physiological process consist-
ing of REM and NON-REM sleep and it makes one-
third of human life. Nearly 20% of the world’s popula-
tion is affected by different sleep impairments due to
sleep disorders or lifestyle alterations. The effects of
selective REM sleep deprivation on epileptiform activ-
ity of homocysteine thiolactone have been reported in
our earlier study [86]. In this study we used a platform
method to deprive REM (s. paradoxical) sleep in rats.
Results of that study showed that this kind of sleep
modulation increased the incidence and number of sei-
zure episodes per rat induced by subconvulsive dose of
homocysteine thiolactone. Behavioral analysis showed
that REM-sleep-deprived rats exhibited shorter latency
time to seizures, as well as significant lethality upon
homocysteine treatment without significant changes in
seizure severity. The number and duration of SWD
were significantly increased, while latency of SWD
appearance was decreased in EEG of REM-sleep-
deprived rats receiving homocysteine treatment there-
after. Based on these behavioral and EEG findings, it
was concluded that selective REM sleep deprivation
aggravated process of epileptogenesis in the model of
homocysteine seizures. We assumed that those altera-
tions observed upon REM sleep deprivation are par-
tially due to an imbalance in the neurotransmitter sys-
tems, like generalized down regulation of muscarinic
receptors, up-regulation of postsynaptic dopamine re-
ceptors and excitatory amino acid levels [87, 88, 89].
Regular physical activity has been proven as a bene-
ficial non-pharmacological intervention for different
diseases, from a cardiovascular to the CNS disorders
[90-92]. We investigated the effects of regular physical
activity on epileptic activity induced by homocysteine
8 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
thiolactone using experimental paradigm of aerobic
physical activity on treadmill [93]. The results obtained
in that study [93] showed that the rats subjected to the
regular physical exercise training on treadmill during
30 consecutive days had significantly prolonged the
latency time in developing their first seizure sign. Fur-
thermore, significantly lower the number of seizure
episodes per rat induced by homocysteine thiolactone
was observed comparing with rats being sedentary dur-
ing the same period of time. Analysis of SWD appear-
ance in EEG showed significantly lower number of
SWDs in rats subjected to regular physical activity
comparing to sedentary mates. In the same study, we
showed that applied physical activity partially pre-
vented elevation of lipid peroxidation after homocys-
teine thiolactone administration, and prevented de-
crease of SOD and CAT activity. These findings al-
lowed us to conclude that physical activity decreased
susceptibility of rats for homocysteine epileptiform
activity, as well as to hypothesize that those effects
could be, at least in part, a consequence of improved
antioxidant enzymes activity. Moreover, physical activ-
ity may ameliorate some oxidative stress parameters in
the brain in a model of chronic hyperhomocysteinemia.
The roles of synaptic plasticity, neurogenesis, level of
neurotrophic factors and melatonin have been proposed
to contribute to the effects of physical activity, while
involvement of other mechanisms in observed effects
of physical activity have to be further investigated [72,
93].
3. NEUROPROTECTIVE EFFECTS OF
TAURINE: LINK WITH ANTICONVULSIVE
PROPERTIES
Although, homocysteine and taurine share some
common metabolic pathway features, they have distinct
roles in the homeostasis of the brain excitability. The
major route for the biosynthesis of taurine is from me-
thionine and cysteine via cysteine sulfinic acid decar-
boxylase (CSD), and typically requires oxidation of
hypotaurine to taurine as the final step [94]. CSD is
considered to be the rate-limiting enzyme in the bio-
synthesis of taurine [95]. It is expressed in the liver,
kidneys and the brain. It should be pointed out that
neurons can only produce taurine from hypotaurine
whereas glia can generate the whole synthesis [96]. For
details on taurine metabolic pathways see elsewhere
[97, 98].
Relationship between taurine and epilepsy has been
subject of research for a long time [99], but results are
not consistent, especially when it comes to translation
from animal models to clinical trials, as well as among
studies within each of these groups. These discrepan-
cies and possible reasons for them has been discussed
[99], underlying the lack of specific taurine antagonist
as tool for our better understanding of taurine link with
epileptic activity. However, taurine anticonvulsive ac-
tivity has been widely reported in the literature, espe-
cially when we have in mind results obtained in ex-
perimental animals. Namely, its anticonvulsive effects
have been proved in epilepsy models in different
strains from mice and rats to dogs and cats [7, 99]. Re-
cently, acute taurine has been reported to have anticon-
vulsive property in two similar mouse model of kainate
-induced seizures [100, 101]. At the same time, chronic
supplementation of 0.05% taurine in drinking water
increased the animal susceptibility to seizures. It should
be also pointed out that epileptic kindling in rats, as
well as the other epileptiform events, could affect the
level of taurine in brain regions known to be implicated
in epileptogenesis [102]. On the other hand, prelimi-
nary experiments in humans with epilepsy confirmed
the taurine antiepileptic attributes, but these studies
were small producing non - robust and inconsistent re-
sults [99].
Taurine interactions with GABA-ergic and glutama-
tergic system, as well as its antioxidative properties are
considered as major mediators of its anticonvulsive
effects (Fig. 2).
3.1. Glutamatergic and GABA-ergic System as Tar-
gets of Taurine Action
Taurine molecular structure is very similar to
GABA, and it has been shown that taurine affects the
opening of Cl- channels by interactions primarily with
GABAA receptors [103]. Namely, taurine has been
shown to hyperpolarize neurons in the hippocampus
[104]. Taurine is, therefore, considered to be an inhibi-
tory agent in the brain, causing hyperpolarization and
inhibition of neurons firing and cell membrane stabili-
zation [99, 105]. It is generally believed that taurine
protects neurons against glutamate - induced neurotox-
icity by preventing glutamate-induced membrane depo-
larization, excitotoxicity, elevation of intracellular free
calcium, mitochondrial energy failure, activation of
calpain, reduction of bcl-2 levels, and apoptosis [106,
107]. The downstream events by which taurine may
prevent glutamate-induced apoptosis has been summa-
rized by Ye et al. [107] and it includes ability of taurine
to prevent the glutamate-induced increase in intracellu-
lar free calcium.
Direct effects of taurine on NMDA receptors have
been proposed [108]. Namely, Chan et al. [108], using
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 9
electrophysiological and receptor binding approaches,
showed that taurine directly interact with NMDA recep-
tors via different mechanisms. In a further study they
showed that chronic taurine intraperitoneal application
increased expression of the NMDA GluN2B, but not
GluN1, subunit and decreased expression of the AMPA
GluR2 subunit in rat frontal cortex, suggesting GluN2B
subunit to be a major target for taurine action [109].
3.2. Taurine ameliorates oxidative stress
Taurine has been considered to be a potent antioxi-
dant agent [110]. This has been proved by its role in
stabilization of mitochondrial electron transport chain
and suppression of the reactive oxygen species genera-
tion [111]. This antioxidant property of taurine has
been considered from different clinical aspects [6, 98],
while the exact mechanisms for its antioxidant activity
has not been completely elucidated.
In a recent study, Han et al. [112] demonstrated that
taurine exerted protective effects against NMDA-
induced neuronal injury and suppressed the production
of reactive oxygen species, especially superoxide ani-
ons. In this study, taurine inhibited NMDA-induced
NADP oxidases activity by decreasing the protein ex-
pression and calcium influx. Therefore, they suggested
involvement of NAPDH oxidase inhibition in taurine
antioxidative action [112]. However, Noor et al. [113]
reported that daily taurine pretreatment for 3 days
failed to show any significant effect on the oxidative
stress induced in the hippocampus examined in a pilo-
carpine model of status epilepticus. On the contrary,
taurine prevented the hippocampal acetylcholinesterase
activity reduction during pilocarpine - induced status
epilepticus in that study. Zhu et al. [114] demonstrated
significant neuroprotective effect of taurine in amelio-
ration of hypoxic-ischemic brain damage in neonatal
rats. Namely, in this study taurine remarkably reduced
infarct volume, suppressed cell death, and ameliorated
histopathology injury. At the same time, antioxidant
enzyme activities were increased and lipid peroxidation
was decreased.
4. OTHER SULFUR - CONTAINING AMINO AC-
IDS RELEVANT FOR SEIZURES
Beside homocysteine and taurine, as a non-
proteinogenic sulfur containing amino acids with the
most relevant roles in seizure induction and control, we
should also take into account the effects of L-cysteine
and N-acetyl-L-cysteine (NAC). The roles of other de-
rived sulfur-containing amino acids are scarcely re-
ported in the literature.
NAC is known for its antioxidant properties by free-
radical scavenging and increased levels of glutathione
in different tissues, including the central nervous sys-
tem [115]. Its role in seizure control has been investi-
gated in several experimental studies showing positive
effects in convulsive behavior ameliorations, however
dependent on the dose and route of administration.
Namely, NAC in dose of 200 mg/kg, but not in 100
mg/kg prolonged latency time to aminophylline- in-
duced seizures in mice [116]. NAC also showed good
properties to be add-on drug in seizure control, what
was shown with phenytoin and valproate in the ex-
perimental model of seizures in mice induced by
maximal electroshock [117]. Recently, Zaeri et al.
[118] showed that NAC exerts a dose-dependent anti-
convulsant effect in acute and chronic uses, with no
muscle relaxant activity, and they proposed NAC to be
used as a prophylactic treatment for absence seizure in
human. For further details of NAC in neurological and
psychiatric disorders, refer to recent review papers
[119,120].
Beside involvement in seizure promotion or control,
sulfur-containing amino acids are considered as bio-
markers of epilepsy with L-cysteine being especially
promising in this allay. Namely, recently Ling and
Patel [121] reported that the decreased cysteine and
ratio of cysteine/cystine in plasma could potentially
serve as redox biomarkers in temporal lobe epilepsy.
CONCLUSION
It is clear that homocysteine and taurine play nu-
merous, important, physiological and pathological
roles. They could be considered as neurotransmitters
and neuromodulators. Homocysteine and taurine stands
on the opposite sights, the first showing hyperexcitabil-
ity role, while the second has inhibitory and neuropro-
tective properties. Potential mechanisms of pro-
epileptogenic activity of homocysteine are mediated
via interactions with glutamatergic neurotransmission,
sodium pump activity, oxidative stress, cholinergic sys-
tem and NO-mediated neuronal signaling.
However, this puzzle mosaic of different pro-
epileptogenic mechanisms of homocysteine still miss-
ing many pieces in order to create a complete coherent
model. Taurine’s neuroprotective effects linked with its
anticonvulsive characteristics are mediated by its inter-
actions with GABA-ergic and glutamatergic system
and oxidative stress. Homocysteine and taurine medi-
ated effects in the CNS require further investigations in
order to explore its potential implications in pharma-
cotherapy.
10 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
CONSENT FOR PUBLICATION
Not applicable.
CONFLICT OF INTEREST
The authors declare no conflict of interest, financial
or otherwise.
ACKNOWLEDGEMENTS
This work was supported by the Ministry of Educa-
tion, Science and Technological Development of Ser-
bia (grant #175032).
REFERENCES
[1] Brosnan, J.T.; Brosnan, M.E. The sulfur-containing amino
acids: an overview. J. Nutr., 2006, 136(6), 1636-1640.
[2] Smith, A.D.; Refsum, H. Homocysteine, B Vitamins, and
Cognitive Impairment. Annu. Rev. Nutr., 2016, 36, 211-239.
[3] Refsum, H.; Ueland, P.M.; Nygård, O.; Vollset, S.E. Ho-
mocysteine and cardiovascular disease. Annu. Rev. Med.,
1998, 49, 31-62.
[4] Stanojlović, O.; Hrnčić, D.; Rašić-Marković, A.; Djuric, D.
Homocysteine: neurotoxicity and mechanisms of induced
hyperexcitability. Serb. J. Exp. Clin. Res., 2011, 12, 3–9.
[5] Djuric, D.; Jakovljević, V.; Rašić-Marković, A.; Đurić, A.;
Stanojlović, A. Homocystein e, folic acid and coronary ar-
tery disease: possible impact on prognosis and therapy. In-
dian J. Chest. Di. Allied. Sci., 2008, 50, 39–48.
[6] Sirdah, M.M. Protective and therapeutic effectiveness of
taurine in diabetes mellitus: a rationale for antioxidant sup-
plementation. Diabetes Metab. Syndr., 2015, 9(1), 55-64.
[7] Ripps, H.; Shen, W. Review: taurine: a "very essential"
amino acid. Mol. Vis., 2012, 18, 2673-2686.
[8] Hrncic, D. Sleep, nutrition and physical activity in regula-
tion of brain hyperexcitability: translational viewpoint. 1st
ed; Andrejevic Endw: Belg rade, 2015
[9] Hoffer, L.J. Homocysteine remethylation and trans-
sulfuration. Metabolism, 2004, 53(11), 1480–1483.
[10] Jakubowski, H.; Głowacki, R. Chemical biology of homo-
cysteine thiolactone and related metabolites. Adv. Clin.
Chem., 2011, 55, 81–103.
[11] Jakubowski, H. Homocysteine Thiolactone: Metabolic Ori-
gin and Protein Homocysteinylation in Humans. J. Nutr.,
2000, 130, 377–381.
[12] Jakubowski, H. Molecular b asis of homocysteine toxicity in
humans. Cell. Mol. Life Sci., 2004, 61, 470–487.
[13] Perła-Kaján, J.; Jakubowski, H. Paraoxonase 1 and homo-
cysteine metabolism . Amino Acids, 2012, 43(4), 1405-1417.
[14] Bleich, S.; Degner, D.; Sperling, W.; Bönsch, D.; Thürauf,
N.; Kornhuber, J. Homocysteine as a neurotoxin in chronic
alcoholism. Prog. Neuropsychopharmacol. Biol. Psychia-
try, 2004, 28(3), 453-464.
[15] Spence, A.M.; Rasey, J.S.; Dwyer-Hansen, L.; Grunbaum,
Z.; Livesey, J.; Chin, L.; Nelson, N.; Stein, D.; Krohn,
K.A.; Ali-Osman, F. Toxicity, biodistribution and adiopro-
tective capacity of L-homocysteine thiolactone in CNS tis-
sues and tumors in rodents: comparison with prior results
with phosphorothioates. Radiother. Oncol., 1995, 35, 216-
226.
[16] Kubova, H.; Folbergova, J.; Mareš, P. Seizures induced by
homocysteine in rats during ontogenesis. Epilepsia, 1995,
36, 750-756.
[17] Folbergrova, J. Anticonvulsant action of both NMDA and
non-NMDA receptor antagonists against seizures induced
by homocysteine in immature rats. Exp. Neurol., 1997, 145,
442-450.
[18] Stanojlović, O.; Rašić–Marković, A.; Hrnčić, D.; Šušić, V.;
Macut, Đ.; Radosavljević, T.; Djuric, D. Two types of sei-
zures in homocysteine thiolactone – treated adult rats, be-
havioral and encephalographic study. Cell. Mol. Neurobiol.,
2009, 29, 329-239.
[19] De Bree, A.; Verschuren, W.M.; Kromhout, D.; Kluijtmans,
L.A.; Blom, H.J. Homocysteine determinants and the evi-
dence to what extent homocysteine determines the risk of
coronary heart disease. Pharmacol. Rev., 2002, 54(4),599-
618.
[20] Troen, A.M.; Shea-Budgell, M.; Shukitt-Hale, B.; Smith,
D.E.; Selhub, J.; Rosenberg, I.H. B-vitamin deficiency
causes hyperhomocysteinemia and vascular cognitive im-
pairment in mice. Proc. Natl. Acad. Sci. USA., 2008;
105(34), 12474-12479.
[21] Selhub, J.; Jacques, P.F.; Wilson, P.W.; Rush, D.; Rosen-
berg, I.H. Vitamin status and intake as primary determi-
nants of homocysteinemia in an elderly population. JAMA .,
1993; 270(22), 2693–2698.
[22] Sharma, M.; Rai, S.K.; Tiwari, M.; Chandra, R. Effect of
hyperhomocysteinemia on cardiovascular risk factors and
initiation of atherosclerosis in Wistar rats. Eur. J. Pharma-
col., 2007, 574(1), 49-60.
[23] Herrmann, W.; Obeid, R. Homocysteine: a biomarker in
neurodegenerative diseases. Clin. Chem. Lab. Med., 2011,
49(3), 435-441.
[24] Sener, U.; Zorlu, Y.; Karaguzel, O.; Ozdamar, O.; Coker, I.;
Topbas, M. Effects of common anti-epileptic drug mono-
therapy on serum levels of homocysteine, vitamin B12, fo-
lic acid and vitamin B6. Seizure, 2006, 15(2), 79-85.
[25] Pexa, A.; Herrmann, M.; Taban-Shomal, O.; Henle, T.;
Deussen, A. Experimental hyperhomocysteinaemia: differ-
ences in tissue metabolites between homocystine and me-
thionine feeding in a rat model. Acta. Physiol (Oxf)., 2009,
197(1), 27-34.
[26] Blaise, S.A.; Nédélec, E.; Schroeder, H.; Alberto, J.M.;
Bossenmeyer-Pourié, C.; Guéant, J.L.; Daval, J.L. Gesta-
tional vitamin B deficiency lead s to homocysteineassoci ated
brain apoptosis and alters neurobehavioral development in
rats. Am. J. Pathol., 2007, 170(2), 667-679.
[27] De Vriese, A.S.; Blom, H.J.; Heil, S.G.; Mortier, S.;
Kluijtmans, L.A.; Van de Voorde, J.; Lameire, N.H. Endo-
thelium-derived hyperpolarizing factor m ediated renal
vasodilatory response is impaired during acute and chronic
hyperhomocysteinemia. Circulation, 2004, 109(19), 2331-
2336.
[28] Fukada, S.; Shimada, Y.; Morita, T.; Sugiyama, K. Sup-
pression of methionine induced hyperhomocysteinemia by
glycine and serine in rats. Biosci. Biotechnol. Biochem.,
2006, 70(10), 2403-2409.
[29] Dayal, S.; Arning, E.; Bottiglieri, T.; Böger, R.H.; Sig-
mund, C.D.; Faraci, F.M.; Lentz, S.R. Cerebral vascular
dysfunction mediated by superoxide in hyperhomocys-
teinemic mice. Stroke, 2004, 35(8), 1957-1962.
[30] Scherer, E.B.; da Cunha, A.A.; Kolling, J.; da Cunha, M.J.;
Schmitz, F.; Sitta, A.; Lima, D.D.; Delwing, D.; Vargas,
C.R.; Wyse, A.T. Development of an animal model for
chronic mild hyperhomocyst einemia and its response to
oxidative damage. Int. J. Dev. Neurosci., 2011, 29(7), 693-
699.
[31] Setoue, M.; Ohuchi, S.; Morita, T.; Sugiyama, K. Hyper-
homocysteinemia induced by guanidinoacetic acid is effec-
tively suppressed by choline and betain e in rats. Biosci. Bio-
technol. Biochem., 2008, 72(7), 1696-1703.
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 11
[32] Guo, Y.H.; Chen, F.Y.; Wang, G.S.; Chen, L.; Gao, W.
Diet-induced hyperhomocysteinemia exacerbates vascular
reverse remodeling of balloon injured arteries in rat. Chin.
Med. J (Engl)., 2008, 121(22), 2265-2271.
[33] Hansrani, M.; Stansby, G. The use of an in vivo model to
study the effects of hyperhomocysteinaemia on vascular
function. J. Surg. Res., 2008; 145(1), 13-18.
[34] Morita, H.; Kurihara, H.; Yoshida, S.; Saito, Y.; Shindo, T.;
Oh-Hashi, Y.; Kurihara, Y.; Yazaki, Y.; Nagai, R. Diet-
induced hyperhomocysteinemia exacerbates neointima for-
mation in rat carotid arteries after balloon injury. Circula-
tion, 2001, 103(1), 133-139.
[35] Hrnčić, D.; Rašić-Marković, A.; Stojković, T.; Velimirović,
M.; Puškaš, N.; Obrenović, R.; Macut, Đ.; Šušić, V.;
Jakovljević, V.; Djuric, D.; Petronijević, N.; Stanojlović, O.
Hyperhomocysteinemia induced by methionine dietary nu-
tritional overload modulates acetylcholinesterase actvity in
the rat brain. Mol. Cell. Biochem., 2014, 396(1–2), 99-105.
[36] Kamath, A.F.; Chauhan, A.K.; Kisucka, J.; Do le, V.S.;
Loscalzo, J.; Handy, D.E.; Wagner, D.D. Elevated levels of
homocysteine compromise blood-brain barrier integrity in
mice. Blood, 2006, 107(2), 591-593.
[37] Lipton, S.A.; Kim, W.K.; Choi, Y.B.; Kumar, S.; D’Emilia,
D.M.; Rayudy, P.V.; Arnelle, D.R.; Stamler, J.S. Neurotox-
city associated with dual actions of Homocysteine at the N-
methyl-D-aspartate receptor. Proc. Natl. Acad. Sci. USA.,
1997, 94, 5923-5928.
[38] Lazarewicz, J.W.; Ziembowicz, A.; Matyja, E.; Stafiej, A.;
Zieminska, E. Homocysteine-evoked Ca release in the rab-
bit hippocampus is mediated by both NMDA and group I
metabotropic glutamate receptors: in vivo microdialysis
study. Neurochem. Res., 2003, 28, 259-269.
[39] Shi, Q.S.; Savage, J.E.; Hufeisen, S.J.; Rauser, L.;
Grajkowska, E.; Ernsberger, P. L-Homocysteine sulfinic
acid and other acid ic homocysteine derivates are potent and
selective metabotropic glutamate receptor agonists. J.
Pharmacol. Exp. Ther., 2003, 305, 131-142.
[40] Rašić-Marković, A.; Hrnčić, D.; Djuric, D.; Macut, Đ.;
Lončar-Stevanović, H.; Stanojlović, O. The effect of N-
methyl-D-aspartate receptor antagonists on D,L-
homocysteine thiolactone induced seizures in adult rats.
Acta. Physiol. Hung., 2011, 98(1), 17–26.
[41] Ho, P.I.; Ortiz, D.; Rogers, E.; She, T.B. Multiple aspects of
homocysteine neurotoxicity: glutamate excitotoxicity,
kinase hyperactivation and DNA damage. J. Neurosci. Res.,
2002, 70, 694-702.
[42] Simson, P.E.; Criswell, H.E.; Johnson, K.B.; Hicks, R.E.;
Breese, G.R. Ethanol inhibits NMDA-evoked electrophysi-
ological activity in vivo. J. Pharmacol. Exp. Ther., 1991,
257, 225-231.
[43] Rašić-Marković, A.; Djuric, D.; Hrnčić, D.; Lončar-
Stevanović, H.; Vučević, D.; Mladenović, D.; Brkić, P.;
Macut, Đ.; Stanojević, I.; Stanojlović, O. High dose of
ethanol decreases total spectral power density in seizures
induced by D,L- homocysteine thiolactone in adult rats.
Gen. Physiol. Biophys., 2009, 28, 25-32.
[44] Vaillend, C.; Mason, S.E.; Cuttle, M.F.; Alger, B.E.
Mechanisms of neuronal hyperexcitability caused by partial
inhibition of Na+-K+-ATPases in the rat CA1 hippocampal
region. J. Neurophysiol., 2002, 88(6), 2963-2978.
[45] Rodrigez, L.A.; Arnaiz, G.; Pena, C. Characterization of
Na+/K+-ATPase. Neurochem. Int., 1995, 27, 319-327.
[46] Matte, C.; Monteiro, S.C.; Calcagnotto, T.; Bavaresco, C.S.;
Netto, C.A.; Wyse, A.T. In vivo and in vitro effects of ho-
mocysteine on Na+, K+-ATPase activity in parietal, prefron-
tal and cingulated cortex of young rats. Int. J. Dev. Neuro-
sci., 2004, 22, 185-190.
[47] Wyse, A.T.; Zugno, A.I.; Streck, E.L.; Matté, C.; Calcag-
notto, T.; Wannmacher, C.M.; Wajner, M. Inhibition of
Na(+), K(+)-ATPase activity in hippocampus of rats sub-
jected to acute administration of homocysteine is prevented
by vitamins E and C treatment. Neurochem. Res., 2002, 27,
1685-1689.
[48] Matte, C.; Durigon, E.; Stefanello, F.M.; Cipriani, F.; Wa-
jner, M.; Wyse, A.T. Folic acid pretreatment prevents the
reduction of Na(+),K(+)-ATPase and butyrylcholinesterase
activities in rats subjected to acute hyperhomocysteinemia.
Int. J. D ev. Neurosci., 2006, 24, 3-8.
[49] Rašić-Marković, A.; Stanojlović, O.; Hrnčić, D.; Krstić, D.;
Čolović, M.; Šusić, V.; Radosavljević, T.; Djuric, D. The
activity of erythrocyte and brain Na+/K+ and Mg2+-
ATPases in rats subjected to acute homocysteine and homo-
cysteine thiolactone administration. Mol. Cell. Biochem.,
2009, 327, 39-45
[50] Streck, EL.; Zugno, A.I.; Tagliari, B.; Sarkis, J.J.; Wajner,
M.; Wannmacher, C.M.; Wy se, A.T. On the mechanism of
the inhibition of Na(+), K(+)-ATPase activity caused by
homocysteine. Int. J. Dev. Neurosci., 2002, 20(2), 77-81.
[51] Hrnčić, D.; Rašić-Marković, A.; Krstić, D.; Macut, D.;
Djuric, D.; Stanojlović, O. The Role of Nitric Oxide in
Homocysteine Thiolactone-Induced Seizures in Adult R ats.
Cell. Mol. Neurobiol., 2010, 30, 219-31.
[52] Rašić-Marković, A.; Rankov-Petrović, B.; Hrnčić, D.;
Krstic, D.; Čolović, M.; Macut, Đ.; Djuric, D.; Stanojlović,
O. The effect of subchronic supplementation with folic acid
on homocysteine induced seizures. Acta Physiol. Hung.,
2015, 120(2), 151-162.
[53] Rašić-Marković, A.M.; Hrnčić, D.; Krstić, D.; Čolović, M.;
Đurić, E.; Rankov-Petrović, B.; Šusić, V.; Stanojlović, O.;
Djuric, D. The effect of subchronic supplementation with
folic acid and l-arginine on homocysteine-induced seizures.
Can. J. Physiol. Pharmacol., 2016, 94(10), 1083-1089.
[54] Gralewicz, S. Possible consequences of acetylcholinesterase
inhibition in organophosphate poisoning. Discussion con-
tinued. Med. Pr., 2006, 57(3), 291-302.
[55] Vučević, D.; Petronijević, N.; Radonjić, N.; Rašić-
Marković, A.; Mladenović, D.; Radosavljević, T.; Hrnčić,
D.; Djuric, D.; Sušić, V.; Macut, Đ.; Stanojlović, O. Ace-
tylcholinesterase as a potential target of acute neurotoxic ef-
fects of lindane in rats. Gen. Physiol. Bioph., 2009, 28, 18-
24.
[56] de Araujo Furtado, M.; Rossetti, F.; Chanda, S.; Yourick,
D. Exposure to nerve agents: from status epilepticus to neu-
roinfl ammation, brain damage, neurogenesis and epilepsy.
Neurotoxicology, 2012, 33(6), 1476-1490.
[57] Mikroulis, C. Endogenous ACh effects on NMDA-induced
interictal-like discharges along the septotemporal hippo-
campal axis of adult rats and their modulation by an early
life generalized seizure. Epilepsia, 2012, 53(5), 879-887.
[58] Pitler, T.A.; Alger, B.E. Cholinergic excitation of
GABAergic interneurons in the rat hippocampal slice. J.
Physiol., 1992, 450, 127-142.
[59] Gnatek, Y.; Zimmerman, G.; Goll, Y.; Najami, N.; Soreq,
H.; Friedman, A. Acetylcholinesterase loosens the brain’s
cholinergic anti-infl ammatory response and promotes epi-
leptogenesis. Front. Mol. Neurosci., 2012, 5, 66.
[60] Schulpis, K.; Kalimeris, K.; Bakogiannis, C.; Tsakiris, T.;
Tsakiris, S. The effect of in vitro homocystinuria on the
suckling rat hippocampal acetylcholinesterase. Metab.
Brain. Dis., 2006, 21(1), 21-28.
[61] Stefanello, F.M.; Zugno, A.I.; Wannmacher, C.M.; Wajner,
M.; Wyse, A.T. Homocysteine inhibits butyrylcho-
linesterase activity in rat serum. Metab. Brain Dis., 2003,
18(3), 187-194.
12 Current Medicinal Chemistry, 2017, Vol. 24, No. 00 Hrnčić et al.
[62] Petrović, M.; Fufanović, I.; Elezović, I.; Čolović, M.;
Krstić, D.; Jakovljević V, Djuric D. Efekti homocistein tio-
laktona n a aktivnost acetilholinesteraze u mozgu, krvi i srcu
pacova. Serb. J. Exp. Clin. Res., 2010; 11(1), 19–22.
[63] Hrnčić, D.; Rašić-Marković A.; Krstić, D.; Bjekić-Macut,
J.; Šušić V.; Mladenović, D.; Djuric, D.; Stanojlović, O.
Gaseous neurotransmitter nitric oxide: its role in experi-
mental models of epilepsy. Arch. Biol. Sci., 2012;
64(3):1207-16.
[64] Stojanović, M.; Šćepanović, Lj.; Hrnčić, D.; Rašić-
Marković, A.; Djuric, D.; Stanojlović, O. Multidisciplinary
approach to nitric oxide signaling: focus on gastrointestinal
and nervous system. Vojnosanit. Pregl., 2015, 72(7), 619-
624.
[65] Elfering, S.L.; Sarkela, T.M.; Giulivi, C. Biochemistry of
mitochondrial nitric-oxide synthase. J. Biol. Chem., 2002,
277, 38079-38086.
[66] Zhou, L.; Zhu, D. Neuronal nitric oxide synthase: Structure,
subcellular localization, regulation, and clinical implica-
tions. Nitric Oxide, 2009, 20, 223-230.
[67] Hrnčić, D.; Rašić-Marković, A.; Krstić, D .; Macut , Đ.;
Šušić, V.; Djuric, D.; Stanojlović, O. Inhibition of the neu-
ronal nitric oxide synthase potentiates homocysteine
thiolacton e-induced seizures in adult rats. Med. Chem.,
2012, 8(1), 59-64.
[68] Pannu, R.; Singh, I. Pharmacological strategies for the regu-
lation of inducible nitric oxide synth ase: neurodegenerative
versus neuroprotective mechanisms. Neurochem. Int., 2006;
49, 170-182.
[69] González-Hernández, T.; García-Marín, V.; Pérez-Delgado,
M.M.; González-González, M.L.; Rancel-Torres, N.; Gon-
zález-Feria, L. Nitric oxide synthase expression in the cere-
bral cortex of patients with epilepsy. Epilepsia, 2000, 41,
1259-1268.
[70] Murashima, Y.L.; Yoshii, M.; Suzuki, J. Role of nitric ox-
ide in the epileptogenesis of EL mice. Epilepsia, 2000, 41,
1951-99.
[71] Hrnčić, D.; Rašić-Marković, A.; Macut, Đ.; Šušić, V.;
Djuric, D.; Stanojlović, O. Homocysteine thiolactone-
induced seizures in adult rats are aggravated by inhibiton of
inducible nitric oxide synthase. Hum. Exp. Toxicol., 2014;
33(5), 496-503.
[72] Hrnčić, D.; Rašić-Marković, A.; Sušić, V.; Djuric, D.;
Stanojlović, O. Modulation of epileptic activity in rats: fo-
cus on sleep , physical exercise and nitric oxide-mediated
neurotransmission in a model of homocysteine thiolactone-
induced seizures. Serb. J. Exp. Clin. Res., 2014, 15(1), 3-10.
[73] Makhro, A.V.; Mashkina, A.P.; Solenaya, O.A.; Trunova,
O.A.; Kozina, L.S.; Arutyunian, A.V.; Bulygina, E.R. Pre-
natal hyperhomocysteinemia as a model of oxidative stress
of the brain. Bull. Exp. Biol. Med., 2008, 146(1), 33-35.
[74] Wang, X.; Michaelis, E.K. Selective neuronal vulnerability
to oxidative stress in the brain. Front. Aging Neurosci.,
2010, 2:12.
[75] Matté, C.; Mackedanz, V.; Stefanello, F.M.; Scherer, E.B.;
Andreazza, A.C.; Zanotto, C.; Moro, A.M.; Garcia, S.C.;
Gonçalves, C.A.; Erdtmann, B.; Salvador, M.; Wyse, A.T.
Chronic hyperhomocysteinemia alters antioxidant defenses
and increases DNA dam age in brain and blood of rats: p ro-
tective effect of folic acid. Neurochem. Int., 2009, 54(1), 7-
13.
[76] Hrnčić, D.; Mikić, J.; Rašić-Marković, A.; Velimirović, M.;
Stojković, T.; Obrenović, R.; Rankov-Petrović, B.; Šušić,
V.; Djuric, D.; Petronijević, N.; Stanojlovic, O. Anxiety-
related behavior in hyperhomocysteinemia induced by me-
thionine nutritional overload in rats: role of the brain oxida-
tive stress. Can. J. Physiol. Pharmacol., 2016, 30, 1-9.
[77] Singh, R.; Kanwar, S.S.; Sood, P.K.; Nehru, B. Beneficial
effects of folic acid on enhan cement of memo ry and anti-
oxidant status in aged rat brain. Cell. Mol. Neurobiol., 2011,
31, 83–91.
[78] Djuric, D.; Vusanović, A.; Jakovljević, V. The effects of
folic acid and nitric oxide synthase inhibition on coronary
flow and oxidative stress m arkers in isolated rat heart. Mol.
Cell. Biochem., 2007, 300, 177–183.
[79] Racek, J.; Rusnakova, H.; Trefil, L.; Siala, K.K. The influ-
ence of folate and antioxidants on homocysteine levels and
oxidative stress in patients with hyperlipidemia and hyper-
homocysteinemia. Physiol. Res., 2005, 54, 87–95.
[80] Lamers, Y.; Prinz-Langenohl, R.; Moser, R.; Pietrzik, K.
Supplementation with [6S]-5-methyltetrahydrofolate or fo-
lic acid equally reduces plasma total homocysteine concen-
trations in healthy wom en. Am. J. Clin. Nutr., 2004, 79,
473-478.
[81] Rydlewicz, A.; Simpson, J.A.; Taylor, R.J.; Bond, C.M.;
Golden, M.H. The effect of folic acid supplementation on
plasma homocysteine in an elderly population. Quart. J.
Med., 2002, 95, 27–35.
[82] Tagliari, B.; Zamin, L.; Salbego, C.G.; Netto, C.A.; Wyse,
A.T. Hyperhomocysteinemia increases damage on brain
slices exposed to in vitro model of oxygen and glucose dep-
rivation: prevention by folic acid. Int. J. Dev. Neurosci.,
2006, 24(4), 285-291.
[83] Reynolds, E.H. Benefits and risks of folic acid to the nerv-
ous system. J. Neurol. Neurosu rg. Psychiatry., 2002, 72,
567-571.
[84] Apeland, T.; Mansoor, M.A.; Pentieva, K.; McNulty, H.;
Seljeflot, I.; Strandjord, R.E. The effect of B-vitamins on
hyperhomocysteinemia in patients on antiepileptic drugs.
Epilepsy Res., 2002, 51, 237-247.
[85] Rašić-Marković, A.; Hrnčić, D.; Macut, Đ.; Stanojlović, O.;
Djuric, D. Anticonvulsive Effect of Folic Acid in Homocys-
teine Thiolactone-Induced Seizu res. Cell. Mol. Neurobiol.,
2011, 31(8), 1221-1228.
[86] Hrnčić, D.; Rašić-Marković, A.; Macut-Bjekic, J.; Šušić,
V.; Djurić, D.; Stanojlović, O. Paradoxical sleep depriva-
tion potentiates epilepsy induced by homocysteine thiolac-
tone in rats. Exp. Biol. Med. (Maywood), 2013, 238(1), 77-
83.
[87] McCarley, R.W. Neurobiology of REM and NREM sleep.
Sleep Med., 2007, 8, 302-330.
[88] Tufik, S.; Troncone, L.R.P.; Braz, S. Does REM sleep dep-
rivation induce subsen sitivity of presynaptic dopamine or
postsynaptic acetylcholine receptors in the rat brain? Eur. J.
Pharmacol., 1987, 140, 215-219.
[89] Mohamed, S.H.; Ezz, H.A.S.; Khadrawy, A.Y.; Noor, A.N.
Neurochemical and electrophysiological changes induced
by paradoxical sleep deprivation in rats. Behav. Brain Res.,
2011, 225, 39-46.
[90] Pimentel, J.; Tojal, R.; Morgado, J. Epilepsy and physical
exercise. Seizure, 2015, 25, 87-94.
[91] Sperling, M.R.; Schilling, C.A.; Glosser, D.; Tracy, J.I.;
Asadi-Pooya, A.A. Self perception of seizure precipitants
and their relation to anxiety level, depression, and health lo-
cus of control in epilepsy. Seizure, 2008, 17(4), 302-307.
[92] Wong, J.; Wirrell, E. Physical activity in children/teens
with epilepsy compared with that in their siblings without
epilepsy. Epilepsia, 2006, 47(3), 631-639.
[93] Hrnčić, D.; Rašić-Marković, A.; Leković, J.; Čolović, M.;
Krstić, D.; Macut, Đ.; Šušić, V.; Djuric, D.; Stanojlović, O.
Exercise decreases susceptibility to homocysteine seizures:
the role of oxidative stress. Inter. J. Sports Med., 2014,
35(7), 544-550.
[94] Stipanuk, M.H. Metabolism of sulfur-containing amino
acids. Annu. Rev. Nutr., 1986, 6, 179-209.
Homocysteine, Taurine and Seizures Current Medicinal Chemistry, 2017, Vol. 24, No. 00 13
[95] Reymond, I.; Sergeant, A.; Tappaz, M. Molecular cloning
and sequence analysis of the cDNA encoding rat liver cys-
teine sulfinate decarboxylase (CSD). Biochim. Biophys.
Acta., 1996, 1307(2), 152-156.
[96] Dominy, J.; Eller, S.; Dawson, R.Jr. Building biosynthetic
schools: reviewing compartmentation of CNS taurine syn-
thesis. Neurochem. Res. , 2004, 29, 97-103.
[97] Huxtable, R.J. Physiological actions of taurine. Physiol.
Rev., 1992, 72, 101-163.
[98] Froger, N.; Moutsimilli, L.; Cadetti, L.; Jammoul, F.;
Wang, Q.P.; Fan, Y.; Gaucher, D.; Rosolen, S.G.; Neveux,
N.; Cynober, L.; Sahel, J.A.; Picaud, S. Taurine: the come-
back of a nutraceutical in the prevention of retinal degen-
erations. Prog. Retin. Eye Res., 2014, 41, 44-63.
[99] Oja, S.S.; Saransaari, P. Taurine and epilepsy. Epilepsy
Res., 2013, 104(3), 187-194.
[100] El Idrissi, A.; Messing, J.; Scalia, J.; Trenkner, E. Preven-
tion of epileptic seizures by taurine. Adv. Exp. Med. Biol.,
2003, 526, 515-525.
[101] Junyent, F.; Utrera, J.; Romero, R.; Pallàs, M.; Camins, A.;
Duque, D.; Auladell, C. Prevention of epilepsy by taurine
treatments in mice experimental model. J. Neurosci. Res.,
2009, 87, 1500-1508.
[102] Maciejak, P.; Szyndler, J.; Turzyńska, D.; Sobolewska, A.;
Bidziński, A.; Kołosowska, K.; Plaźnik, A. Time course of
changes in the concentrations of amino acids in the brain
structures of pentylenetetrazole-kindled rats. Brain Res.,
2010, 1342, 150-159.
[103] Song, N.Y.; Shi, H.B.; Li, C.Y.; Yin, S.K. Interaction be-
tween taurine and GABA(A)/glycine receptors in neurons
of the rat anteroventral cochlear nucleus. Brain Res., 2012,
1472, 1-10.
[104] del Olmo, N.; Bustamante, J.; Martín del Río, R.; Solís,
J.M. Taurine activ ates GABAA, but not GABAB receptors
in rat hippocampal CA1 area. Brain Res., 2000, 864, 298-
307.
[105] Saransaari, P.; Oja, S.S. Taurine and neural cell damage.
Amino Acids, 2000, 19, 509-526.
[106] Wu, J.Y.; Wu, H.; Jin, Y.; Wei, J.; Sha, D.; Prentice, H.;
Lee, H.H.; Lin, C.H.; Lee, Y.H.; Yang, L.L. Mechanism of
neuroprotective function of taurine. Adv. Exp. Med. Biol.,
2009, 643, 169-179.
[107] Ye, H.B.; Shi, H.B.; Yin, S.K. Mechanisms underlying
taurine protection against glutamate-induced neurotoxicity.
Can. J. Neurol. Sci., 2013, 40(5), 628-634.
[108] Chan, C.Y.; Sun, H.S.; Shah, S.M.; Agovic, M.S.; Fried-
man, E.; Banerjee, S.P. Modes of direct modulation by
taurine of the glutamate NMDA receptor in rat cortex.
Eur.J.Pharmacol., 2014, 728, 167–175.
[109] Chan, C.Y.; Singh, I.; Magnuson, H.; Zohaib, M.; Bakshi,
K.P.; Le François, B.; Anazco-Ayala, A.; Lee, E.J.; Tom
A.; Yee Mon, K.; Ragnauth, A.; Friedman, E.; Banerjee,
S.P. Taurine targets the GluN2b-containing NMDA recep-
tor subtype. Adv. Exp. Med. Biol., 2015, 803, 531–544.
[110] Chen, G.; Nan, C.; Tian, J.; Jean-Charles, P.; Li, Y.; Weiss-
bach, H.; Huang, X.P. Protective effects of taurine against
oxidative stress in the heart of MsrA knockout mice. J. Cell.
Biochem., 2012, 113, 3559–3566.
[111] Jong, C.J.; Azuma, J.; Schaffer, S. Mechanism underlying
the antioxidant activity of taurine: preven tion of mitochon-
drial oxidant production. Amino Acids, 2012, 42, 2223-
2232.
[112] Han, Z.; Gao, L.Y.; Lin, Y.H.; Chang, L.; Wu, H.Y.; Luo,
C.X.; Zhu, D.Y. Neuroprotection of taurine against reactive
oxygen species is associated with inhibiting NADPH oxi-
dases. Eur. J. Pharmacol., 2016, 777, 129-135.
[113] Noor, N.A.; Mohammed, H.S.; Khadrawy, Y. A.; Aboul
Ezz H.S.;. Radwan, N. M. Evaluation of the neuroprotective
effect of taurin e and green tea extract ag ainst oxidative
stress induced by pilocarpine during status epilepticus. J.
Bas. Appl. Zool., 2015, 72, 8 -15.
[114] Zhu, X.Y.; Ma, P.S.; Wu, W.; Zhou, R., Hao, Y.J.; Niu, Y.;
Sun, T.; Li, Y.X.; Yu, J.Q. Neuroprotective actions of
taurine on hypoxic-ischemic brain damage in neonatal rats.
Brain Res. Bull., 2016, 124, 295-305.
[115] Arakawa, M.; Ito, Y. N-acety lcysteine and neurodegenera-
tive d iseases: basic and clinical pharmacology. Cerebellum,
2007, 6 , 308–314.
[116] Gulati, K..; Ray, A.; Pal, G.; Vijayan, V.K.. Possible role of
free radicals in theophylline-induced seizures in mice.
Pharmacol. Biochem. Behav., 2005, 82, 241-245.
[117] Devi, P.U.; Saraogi, P.; Manocha, A.; Vohora, D. Pharma-
cological and biochemical analysis of interactions between
N-acetylcysteine and some antiepileptic drugs on experi-
mental seizures in mice. CNS Neurosci. Ther., 2012, 18,
406-413.
[118] Zaeri, S.; Emamghoreishi, M. Acute and Chronic Effects of
N-acetylcysteine on Pentylenetetrazole-induced Seizure and
Neuromuscular Coordination in Mice. Iran. J. Med. Sci.,
2015, 40(2), 118-124.
[119] Bavarsad Shahripour, R., Harrigan, M.R., Alexandrov, A.V.
N-acetylcysteine (NAC) in neurological disorders: mecha-
nisms of action and therapeutic opportunities. Brain Behav.,
2014, 4, 108-122.
[120] Dean, O., Giorlando, F., Berk, M. N-acetylcysteine in psy-
chiatry : current therapeutic eviden ce and potential mecha-
nisms of action. J. Psychiatry. Neurosci., 2011, 36(2),78-
86.
[121] Liang, L.P., Patel, M. Plasma cysteine/cystine redox couple
disruption in animal models of temporal lobe epilepsy. Re-
dox. Biol., 2016, 9, 45-49.
DISCLAIMER: The above article has been published in Epub (ahead of print) on the basis of the materials provided by the author. The
Editorial Department reserves the right to make minor modifications for further improvement of the manuscript.
PMID: 28595553
