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The effect of glucose and insulin on the activity of methylene tetrahydrofolate reductase and cystathionine-β-synthase: Studies in hepatocytes
Abstract
Hyperhomocysteinemia is a well established risk factor for cardiovascular disease, and multiple factors likely lead to abnormal regulation of plasma homocysteine in patients with diabetes. To examine a possible role for insulin and glucose in homocysteine metabolism, we examined the activity of two important enzymes of homocysteine metabolism in hepatocytes. In various tissues of six mice, methylene tetrahydrofolate reductase (MTHFR) activity was present in all tissues tested and the highest concentration (per gram) was in the brain. In contrast, cystathionine beta-synthase (CBS) activity appeared to be present only in the liver and to a small extent in the kidney. Using HEP G2 cells in culture, MTHFR activity was 3.3+/-0.8 nmol/h when the glucose concentration in the medium was 100 mg/dl and fell to 2.3+/-0.3 nmol/h when glucose was increased to 300 mg/dl. MTHFR activity was 3.4+/-0.3 nmol/h when cells were exposed to an insulin concentration of 5 mU/ml and fell to 2.8+/-0.3 nmol/h when insulin concentration was increased to 200 mU/ml (P<0.01). In contrast CBS activity increased from 0.017 to 0.13 U/ml by increasing the glucose concentration in the medium (P<0.01), but decreased from 0.04 to 0.02 (P<0.01) when the insulin concentration was increased from 5 to 200 mU/ml, respectively. We conclude that CBS and MTHFR have different tissue distributions, with CBS being present predominantly in liver and kidney, and MTHFR found in many tissues. In addition, both insulin and glucose affect the activity of the two enzymes when added to hepatocytes in vitro. If such effects occur in humans with hyperglycemia and hyperinsulinemia, then alterations in homocysteine metabolism may contribute to the accelerated macrovascular disease associated with insulin resistance or type 2 diabetes.
... Hcy metabolism is disturbed in subjects with IR and T2DM, and may be modulated by insulin and glucose. 150 Moreover, Hcy levels are determined by the activity of two key enzymes, MTHFR and cystathionine-β-synthase (CBS). 10 It would be expected that subjects with MTHFR gene mutation should be more prone to CVD, but meta-analyses designed to answer this question showed no significant difference, 151 or only a weak association 152 between mutations in MTHFR and CVD. ...
... These abnormalities may have implications for the pathogenesis of premature vascular disease associated with T2DM. 10 CBS is regulated by insulin and is dysfunctional in IR, and patients with IR in the absence of DM could be more likely to demonstrate low levels of CBS and MTHFR. 150 Plasma Hcy concentrations in T2DM patients would be variable, since insulin and glucose levels fluctuate in such patients. 150 Since insulin is secreted following an oral protein load, it is possible that insulin plays a role in decreasing postprandial Hcy levels by modulating CBS activity. ...
... 150 Plasma Hcy concentrations in T2DM patients would be variable, since insulin and glucose levels fluctuate in such patients. 150 Since insulin is secreted following an oral protein load, it is possible that insulin plays a role in decreasing postprandial Hcy levels by modulating CBS activity. 10 Some drugs like troglitazone (no longer available on market) lowered plasma Hcy in insulinresistant animals, and the Hcy-lowering effects of this medication may be mediated in part by an upregulation of hepatic CBS activity. ...
Diabetes mellitus (DM) can lead to the development of macro- and microvascular complications. Homocysteine (Hcy) may play a role in the development of cardiovascular (CV) diseases (CVDs). The role of Hcy in the development of the vascular complications associated with DM is not clearly defined. Despite a strong initial assumption regarding the importance of Hcy in DM and its complications, over time "enthusiasm has waned" because several studies showed unconvincing and occasionally contradictory results. A universal conclusion is not easy to draw given the diversity of studies (e.g. number of patients, design, folic acid and vitamin B status, ethnic differences, genetic background). For some complications, most results encourages further investigation. Impaired renal function is a major independent determinant of high total Hcy (tHcy) levels. However, the role of hyperhomocysteinaemia (HHcy) in the development of diabetic kidney disease (DKD) has yet to be determined. Hcy-lowering therapies can significantly decrease Hcy levels but their effects on CVD risk reduction are conflicting. Further studies are needed to determine the influence of Hcy-lowering therapy on CVD risk reduction, especially in patients with DM.
... Nieman et al. (20) reported that streptozotocin treated rats lacking insulin have increased BHMT and reduced MS. Increases in the insulin concentration leads to significant decrease MTHFR activities in hepatocytes (21). CS-1b promoter activity is decreased by insulin treatment in HepG2 cells (17). ...
... It was reported previously that glucose treatment at 300 mg/dl for 72 h increased CS up to 8-fold in HepG2 cells (21). However, we did not find evidence of elevated homocysteine transsulfuration in glucose-treated cells. ...
... Homocysteine was found to inversely correlate with blood glucose levels in diabetic patients (34), suggesting a potential regulatory mechanism of glucose on homocysteine homeostasis in vivo. MTHFR activity decreased whereas CS activity increased as glucose concentrations increased in HepG2 cells (21). Based on these data, one would predict that high glucose may have enhanced homocysteine clearance mainly via an elevation in transsulfuration. ...
The mechanisms underlying the impact of pathophysiological elevations in insulin or glucose on hepatic cellular homocysteine kinetics is not fully understood. Objective: The objective of the study was to investigate the impact of elevated insulin/glucose on hepatic homocysteine kinetics at the cellular level.
Effects of insulin and glucose on homocysteine remethylation and transsulfuration metabolic fluxes were investigated in a cell model using stable isotopic tracers and gas chromatography/mass spectrometry. The methylation status was assessed by S-adenosylmethionine (adoMet), the adoMet to S-adenosylhomocysteine ratio, DNA methyltransferase activity, and methylated cytidine content of DNA. The expression profile of homocysteine remethylation, transmethylation, and transsulfuration-associated genes was determined.
Insulin increased cellular homocysteine production primarily by its inhibition of transsulfuration. When cells were exposed to elevated insulin and glucose, homocysteine remethylation was enhanced, which consequently increased intracellular adoMet concentrations by inducing adoMet synthase activity. Elevated glucose further enhanced DNA methyltransferase activity that subsequently led to increased global DNA methylation.
We demonstrated the novel finding of a direct promoting effect of high cellular insulin or glucose exposure on homocysteine remethylation, adoMet synthase activity, and adoMet synthesis. We also provided new evidence indicating that when hepatic tissue is exposed to elevated insulin or glucose, the cellular methylation balance can be altered, which may have potential epigenetic impacts gene regulation in diabetic individuals. These findings in a cell line may or may not reflect what happens in humans. In vivo studies on the homocysteine transmethylation fluxes and DNA methylation in diabetic state are underway.
... Even though, interrelationships between biotin, folate and vitamin B 12 have been reported [10][11][12], biotin has not been studied in relation to Hcy yet. Evidence also indicates the importance of macronutrients like protein, carbohydrates and dietary fats in influencing Hcy [13][14][15][16][17][18]. Hcy is synthesized in the liver as a response to the breakdown of the essential dietary amino acid, methionine. ...
... One of the other interactions observed for MTHFR C677T and Hcy was with added sugar as a percentage of energy intake from carbohydrates, where TT genotype carriers presented with a noticeable increase in Hcy concentrations as sugar intake increased. We speculate that sugar poses an additional threat to increasing Hcy concentrations in those with the 677 TT genotype, because both the T allele [53] and higher glucose concentrations per se reduce MTHFR activity [15]. This underscores the potential benefits that may be gained by improving the dietary control of the glycemic milieu and a decreased intake of added sugar. ...
Background:
Elevated homocysteine (Hcy) is associated with several pathologies. Gene-diet interactions related to Hcy might be used to customize dietary advice to reduce disease incidence. To explore this possibility, we investigated interactions between anthropometry, biochemical markers and diet and single-nucleotide polymorphisms (SNPs) in relation to Hcy concentrations. Five SNPs of Hcy-metabolizing enzymes were analyzed in 2010 black South Africans.
Results:
Hcy was higher with each additional methylenetetrahydrofolate reductase (MTHFR) C677T minor allele copy, but was lower in methionine synthase (MTR) 2756AA homozygotes than heterozygotes. Individuals harboring cystathionine β synthase (CBS) 833 T/844ins68 had lower Hcy concentrations than others. No interactive effects were observed with any of the anthropometrical markers. MTHFR C677T and CBS T833C/844ins68 homozygote minor allele carriers presented with lower Hcy as high density lipoprotein cholesterol (HDL-c) increased. Hcy concentrations were negatively associated with dietary protein and animal protein intake in the TT and TC genotypes, but positively in the CC genotype of CBS T833C/844ins68. Hcy was markedly higher in TT homozygotes of MTHFR C677T as added sugar intake increased. In CBS T833C/844ins68 major allele carriers, biotin intake was negatively associated with Hcy; but positively in those harboring the homozygous minor allele.
Conclusions:
The Hcy-SNP associations are modulated by diet and open up the possibility of invoking dietary interventions to treat hyperhomocysteinemia. Future intervention trials should further explore the observed gene-diet and gene-blood lipid interactions.
... Results of study performed on human hepatocyte cell line showed in presence of insulin and glucose, MTHFR and cystathionine-β-synthase activity decrease. These enzymes are responsible for remethylation and transsulfuration reactions respectively and maintain the plasma homocysteine Concentrations [28]. Although the association between Hhcy and C677T polymorphism in the MTHFR gene is inconsistent [13,14,29,30]. ...
... Results of in vivo studies suggested Hhcy could be a factor causing insulin resistance [4,28]. The study of Lee et al showed that Hcy promotes insulin resistance by inducing adipose endoplasmic reticulum stress and downstream inflammation in mice. ...
Background
The insulin resistance syndrome is one of the major contributors of metabolic syndrome, diabetes Type 2 and atherosclerotic cardiovascular disease. A common mutation (677C to T; Ala to Val) in the methylenetetrahydrofolate reductase (MTHFR) gene is associated with decreased specific MTHFR activity and elevation of the homocysteine. The aim of this study is investigation of association between MTHFR 677C > T polymorphism with insulin resistance by using HOMA (Homeostasis Model Assessment) index in nurses who are potentially prone to develop insulin resistance because of unfavorable effects of shift work.
Method
Nursing Unacquainted Related Stress Etiologies Study (Nurse Study) was conducted in five different educational hospitals of Tehran University of Medical Science (TUMS). The nurses aged 22–57 who have been referred by the matron were recruited. A self-administered questionnaire was completed. Anthropometric measurements including weight, height, waist and hip circumference in addition to blood pressure were measured. Insulin resistance and Insulin sensitivity were measured using the homeostatic model assessment (HOMA) and quantitative insulin sensitivity check index (QUICKI) respectively. The detection of MTHFR C677T polymorphism in exon four of MTHFR gene was performed by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis using HINFI restriction enzyme digestion.
Result
A total of 273 subjects were recruited in the study. CT genotype were detected in 51.6% (129) subjects and CC and TT genotype were seen in 9.2% (25) and 35.2% (96) subjects respectively. Participants with TT genotype (9.65 ± 4.00) have significantly lower insulin level than participants with CT genotype (14.12 ± 15.34) (p-value: 0.01). The same significant difference was observed for HOMA index (p-value: 0.03). Result showed that HOMA is lower in subjects who are taking supplements.
Conclusion
Result of this study showed subjects with TT genotype had significantly lower HOMA compare to CT genotype and the same pattern was seen for insulin level. We also found subjects taking supplement have lower HOMA compared to others regardless of their genotype.
... Thus, besides dietary folate, also smoking, alcohol intake and obesity may influence cancer risk, partly through an interference with folate metabolism [14,39,40]. Smoking may inactivate both folate and vitamin B 12 , alcohol is a well-known folate antagonist, and obesity may be associated with a lower consumption of folate enriched foods or an impairment of methionine metabolism because of the underlying insulin-resistance [41][42][43]. ...
... It's note of working that all of these factors have also been reported to modulate the effect of MTHFR genotype on colon cancer risk, although with conflicting results [14,[41][42][43]. However, when we tested these other gene-environment relationships, no significant interactions were demonstrated between MTHFR mutation and smoking, alcohol consumption or obesity in our cohort. ...
Acromegalic patients have a higher risk of developing colorectal tumours (CRT). The common C677T polymorphism in methylenetetrahydrofolate reductase (MTHFR) gene is a well-documented CRT risk factor in the general population, but its role in acromegaly has never been examined.
We investigated the influence of MTHFR C677T polymorphism, folate status and other lifestyle, nutritional and disease-specific variables on CRT risk in acromegaly.
Clinical data were collected from 115 acromegalic patients (25 with active disease) who underwent a complete colonoscopy. C677T MTHFR genotype, homocysteine, vitamin B12, insulin growth factor and insulin levels, as well as metabolic variables were evaluated.
Colorectal tumours were identified in 51 patients (3 adenocarcinomas). MTHFR C677T distribution was in the Hardy-Weinberg equilibrium and similar in patients with or without CRT. There was a correlation between patients with TT genotype and CRT occurrence (Spearman's test: P = 0.03), with an Odds Ratio (OR) of 1.32 (95 % CI 0.522-3.362, P NS). A folate-MTHFR genotype interaction on CRT risk was found (P = 0.037): in the lower folate subgroup, TT patients showed a 2.4 higher OR for CRT (95 % CI 0.484-11.891; P NS) than C-allele carriers. Smoking (P = 0.007), increased HbA1c levels (P = 0.021), dyslipidaemia (P = 0.049), acromegaly control (P = 0.057), and folate-MTHFR genotype interaction (P = 0.088) were associated with CRT at multivariate analysis.
In this cohort of acromegalic patients, CRT risk is increased in 677TT MTHFR patients with low plasma folate levels. Smoking, high HbA1c levels, dyslipidaemia and disease activity were also associated with increased CRT risk.
... Homocysteine has been shown to be inversely correlated with blood glucose concentrations in type 2 diabetic patients (Mazza et al. 2005). It has also been demonstrated that glucose concentration is negatively correlated with the activity of the enzyme methylenetetrahydrofolate reductase, which provides methyl groups for the remethylation of homocysteine (Fig. 2) (Dicker-Brown et al. 2001). Glucose is also positively correlated with the activity of enzymes involved in homocysteine transsulfuration in cultured hepatocytes (Dicker-Brown et al. 2001). ...
... It has also been demonstrated that glucose concentration is negatively correlated with the activity of the enzyme methylenetetrahydrofolate reductase, which provides methyl groups for the remethylation of homocysteine (Fig. 2) (Dicker-Brown et al. 2001). Glucose is also positively correlated with the activity of enzymes involved in homocysteine transsulfuration in cultured hepatocytes (Dicker-Brown et al. 2001). The data suggest that changes in homocysteine are due to its metabolism by the transsulfuration pathway. ...
Type 1 diabetes (T1D) is an autoimmune disease that has increased two- to threefold over the past half century by as yet unknown means. It is generally accepted that T1D is the result of gene-environment interactions, but such rapid increases in incidence are not explained by Mendelian inheritance. There have been numerous advances in our knowledge of the pathogenesis of T1D. Indeed, there has been a large number of genes identified that contribute to risk for this disease and several environmental factors have been proposed. The complexity of such interactions is yet to be understood for any major chronic disease. Epigenetic regulation is one way to explain the rapid increase in incidence and could be a central mechanism by which environmental factors influence development of diabetes. However, there is remarkably little known about the contribution of epigenetics to T1D pathogenesis. Here we speculate on various candidate processes and molecules of the immune and endocrine systems that could modify risk for T1D through epigenetic regulation.
... Other factors seem to influence the homocysteine metabolism, such as smoking; intake of alcohol and coffee; age; sex; and body mass index (BMI) [5]. Epidemiological [2,[6][7][8] and case-control [9][10][11][12][13][14][15][16] studies have investigated the relation between Hhcy and IR, but only a few reports have focused on this relationship in subjects with MS, and with variable results [2,6,8,15]. ...
... Consistent with our results, previous studies have shown that hyperinsulinemia associated with MS could affect homocysteine metabolism [2,7,15]. A study performed in vitro using a human hepatocyte cell line reported a decrease in both MTHFR and cystathionine-β-synthase activity [12]. MTHFR and cystathionine-β-synthase are enzymes responsible for remethylation and transsulfuration reactions, respectively, which maintain the plasma homocysteine concentrations [3]. ...
Information on plasma homocysteine concentrations and their associated factors in Brazilian subjects with metabolic syndrome (MS) is nonexistent. Therefore, a cross-sectional study was conducted to investigate the association of homocysteinemia with MS components; folate and cobalamin biochemical and dietary indices of nutritional status; and genetic, anthropometric, and lifestyle factors in Brazilian subjects with MS. Waist circumference; body fat; body mass index; insulin resistance; lipid profiles; glycemia; uricemia; insulinemia; erythrocyte folate and plasma homocysteine; folate and cobalamin concentrations; C677T polymorphism in the methylenetetrahydrofolate reductase (MTHFR) gene; coffee and alcohol intake; and smoking were determined in 63 subjects (24 males and 39 females) with MS. No difference in homocysteine plasma was observed between sexes. Hyperhomocysteinemia (Hhcy) frequency was 49.2% (n = 31) in the group studied. The distribution of MTHFR genotypes was as follows: CC, 64% (n = 42); CT, 32% (n = 19); and TT, 4% (n = 2). No association was found between Hhcy and C677T polymorphism in the MTHFR gene. Plasma homocysteine concentrations showed no association with age; blood pressure; dietary intakes of folate, cobalamin, and pyridoxine; body mass index; waist circumference; body fat; glycemia; lipid profile; insulin resistance; and concentrations of folate erythrocyte and plasma folate and cobalamin. Also, there was no correlation between Hhcy, sex, and lifestyle factors. In this study, the variables uricemia (C = 0.67, chi(2) = 2.23, P = .27) and insulinemia (C = 0.86, chi(2) = 2.98, P = .07) were positively associated with homocysteinemia. In conclusion, our results suggest that high concentrations of serum insulin and uric acid are associated with an increased risk of developing Hhcy in subjects with MS.
... This aspect expands the consideration of associations between these two polymorphisms and the development of diabetic retinopathy, including the possible involvement of epigenetic mechanisms. Moreover, in vitro data and some clinical study results suggest that disturbances to the SAM cycle in these conditions could be enhanced by hyperinsulinemia and insulin resistance, as insulin was found to decrease the expression of MTHFR in cells [33]. It should be noted here also that the retina is one of the most responsive targets of insulin action, where the expression of insulin receptors is higher than in the liver or muscles [34]. ...
Diabetic retinopathy (DR) is renowned as a leading cause of visual loss in working-age populations with its etiopathology influenced by the disturbance of biochemical metabolic pathways and genetic factors, including gene polymorphism. Metabolic pathways considered to have an impact on the development of the disease, as well as genes and polymorphisms that can affect the gene expression, modify the quantity and quality of the encoded product (protein), and significantly alter the metabolic pathway and its control, and thus cause changes in the functioning of metabolic pathways. In this article, the screening of chromosomes and the most important genes involved in the etiology of diabetic retinopathy is presented. The common databases with manuscripts published from January 2000 to June 2023 have been taken into consideration and chosen. This article indicates the role of specific genes in the development of diabetic retinopathy, as well as polymorphic changes within the indicated genes that may have an impact on exacerbating the symptoms of the disease. The collected data will allow for a broader look at the disease and help to select candidate genes that can become markers of the disease.
... 20,21 In the liver, the content of CBS is most abundant in hepatocytes and least in the hepatic stellate cells (HSCs) and Kupffer cells. 22,23 CBS is expressed in all brain regions except the hippocampus, with the highest content present in the cerebellum and cerebral cortex. 24 CBS is also expressed in neural stem cells and regulates their differentiation. ...
Hydrogen sulphide (H 2 S) is a gaseous neurotransmitter that can be self-synthesized by living organisms. With the deepening of research, the pathophysiological mechanisms of endogenous H 2 S in cancer have been increasingly elucidated: (1) promote angiogenesis, (2) stimulate cell bioenergetics, (3) promote migration and proliferation thereby invasion, (4) inhibit apoptosis and (5) activate abnormal cell cycle. However, the increasing H 2 S levels via exogenous sources show the opposite trend. This phenomenon can be explained by the bell-shaped pharmacological model of H 2 S, that is, the production of endogenous (low concentration) H 2 S promotes tumour growth while the exogenous (high concentration) H 2 S inhibits tumour growth. Here, we review the impact of endogenous H 2 S synthesis and metabolism on tumour progression , summarize the mechanism of action of H 2 S in tumour growth, and discuss the possibility of H 2 S as a potential target for tumour treatment.
... Some studies reported that homocysteine levels were decreased after antipsychotic treatment in schizophrenia (31), others found that the homocysteine levels did not change (36). Furthermore, Dicker-Brown et al.'s study demonstrated that glucose and insulin might influence homocysteine metabolism, possibly by affecting the activity of cystathionine-beta-synthase and methylenetetrahydrofolate reductase (37). Therefore, we speculated that the possible explanations for the association between the plasma C OLA and homocysteine levels might be related to the impaired glucose-insulin homeostasis in the OLAtreated patients with schizophrenia. ...
Objectives
The aim of the present study was to investigate a potential relationship between metabolic parameters and steady-state plasma concentrations of olanzapine (OLA) and its metabolite, 4-N'-desmethyl-olanzapine (DMO) in patients with schizophrenia taking therapeutic doses.
Methods
A total of 352 inpatients, diagnosed with schizophrenia according to the DSM-V criteria and treated with OLA, were investigated. The plasma concentrations of OLA and DMO were measured by high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS). Fasting blood samples were measured for insulin, glucose, total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), C-reactive protein (CRP) and homocysteine, and differences in these parameters were investigated in relation to plasma concentrations of OLA and DMO.
Results
Lower plasma DMO concentrations were associated with higher glucose and TG levels and homeostasis model assessment of insulin resistance (HOMA-IR), while higher plasma OLA concentrations were associated with higher CRP and homocysteine levels in the OLA-treated patients with schizophrenia.
Conclusion
These results demonstrate that OLA and its metabolite DMO may have different effects on OLA-induced metabolic abnormalities. DMO might have a counteracting effects on glucose-insulin homeostasis and lipid metabolic abnormalities, which suggests that regular measure of various metabolic parameters and drug monitoring on both OLA and DMO are recommended in OLA-treated patients with schizophrenia.
... Meanwhile, elevated serum homocysteine levels exacerbated insulin resistance by inhibiting insulin receptor kinase activity (40). In vitro cell culture and in vivo animal studies have also shown that insulinresistant states may reduce rather than increase circulating Hcy levels due to enhanced Hcy catabolism (41,42). In addition, HHcy was reported preceding the development of metabolic syndrome features in a fructose-fed animal model (43). ...
Background
Hyperhomocysteinemia (HHcy) and abdominal obesity are risk factors for metabolic syndrome (MetS) and death from cardiovascular disease (CVD). Recent studies have shown a correlation between HHcy and abdominal obesity, suggesting that they may have a combined effect on the risk of MetS and CVD mortality. However, this suspicion remains to be confirmed, particularly in the elderly population. We explored their combined effects on the risk of MetS and CVD mortality among the community population aged 65 and above in China.
Methods and Results
This prospective study enrolled 3,675 Chinese community residents aged 65 and above in May 2013 with 7-year follow-up of all-cause and CVD mortality. HHcy was defined as the blood homocysteine (Hcy) level >15 μmol/L and abdominal obesity as waist circumference (WC) ≥90 cm for men and ≥80 cm for women (HWC). All participants were grouped into four categories by WC and the blood level of Hcy: NWC (normal WC) /HHcy(–), NWC/HHcy(+), HWC/HHcy(–), and HWC/HHcy(+). The relationship of combined HHcy and abdominal obesity with MetS and metabolic profile was evaluated by logistic regression analysis and the association of combined HHcy and abdominal obesity with CVD and all-cause mortality evaluated by Cox regression analysis. The prevalence of HHcy, abdominal obesity and MetS in elderly Chinese community residents was 40.1, 59.3, and 41.4%, respectively. Using group without HHcy and abdominal obesity [NWC/HHcy(–)] as reference, the participants of other three groups had significantly higher risk of MetS and its component abnormalities, with HWC/HHcy(+) group having the highest risk (OR = 13.52; 95% CI = 8.61–14.55). After a median of 6.94 (±1.48) years follow-up, 454 deaths occurred with 135 CVD deaths. Compared with NWC/HHcy(–) group, the risk of 7-year follow-up CVD mortality (HR = 1.75; 95% CI = 1.02–3.03) and all-cause mortality (HR = 1.23; 95% CI = 1.04–2.18) of HWC/HHcy(+) group increased considerably after adjustment for major MetS and CVD risk factors.
Conclusions
There is high prevalence of HHcy, abdominal obesity, and MetS in the elderly Chinese community population. HHcy increases risk of MetS, CVD, and all-cause mortality, especially in the populations with abdominal obesity.
... Homocysteine is a known risk factor for CVD mainly due to its role in endothelial injury (34) , and is known to be modifiable through exposure to dietary factors (35) . Macronutrients, including carbohydrates, are of huge importance in influencing homocysteine levels (36,37) and one potential mechanism is through elevated insulin and glucose that increases homocysteine concentrations via re-methylation (38) . Alternatively, we found that those consuming higher intakes of free sugars had lower intakes of fruit and nuts and seeds which are known to contain homocysteine-lowering nutrients such as folate (39) . ...
Recommendations for free sugar intake in the UK should be no more than 5% of total energy due to increased health risks associated with overconsumption. It was therefore of interest to examine free sugar intakes and associations with health parameters in the UK population. The UK National Diet and Nutrition Survey (NDNS) rolling programme (2008-2017) was used for this study. Dietary intake, anthropometrical measurements and clinical biomarker data collated from 5121 adult respondents aged 19-64 years, were statistically analysed. Compared to the average total carbohydrate intake (48% of energy), free sugars comprised 12.5%, with sucrose 9% and fructose 3.5%. Intakes of these sugars, apart from fructose, were significantly different over collection year ( P <0.001), and significantly higher in males ( P <0.001). Comparing those consuming above or below the UK recommendations for free sugars (5% energy) significant differences were found for BMI ( P <0.001), triglyceride ( P <0.001), HDL ( P =0.006) and homocysteine concentrations ( P =0.028), and significant gender differences were observed (e.g lower blood pressure in females). Regression analysis demonstrated that free sugar intake could predict plasma triglycerides, HDL and homocysteine concentrations ( P <0.0001), consistent with the link between these parameters and cardiovascular disease. We also found selected unhealthy food choices (using the UK Eatwell Guide) to be significantly higher in those that consumed above the recommendations ( P <0.0001) and were predictors of free sugar intakes ( P <0.0001). We have shown that adult free sugar intakes in the UK population are associated with certain negative health parameters that support the necessary reduction in free sugar intakes for the UK population.
... In mammals, CBS mRNA and protein are primarily found in the liver, brain, kidney and pancreas [53,54]. It is well known that CBS is abundant in hepatocytes; however, it is also detected at lower levels in hepatic stellate cells and Kupffer cells [55,56]. In the brain, all regions express CBS in various amounts but hippocampus, cerebellum and cerebral cortex seem to have the highest expression [57]. ...
Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used “CBS inhibitors” (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.
... Patients with diabetes also show HHcy possibly due to insufficient kidney function and the effects of glucose and Frontiers in Physiology | www.frontiersin.org insulin on decreased CBS activity and homocysteine tissue uptake (Fukagawa et al., 1986;Wollesen et al., 1999;Dicker-Brown et al., 2001;Ndrepepa et al., 2008;Ganguly and Alam, 2015). Mild HHcy is an independent risk factor for the development of cardiovascular disease and other pathologies including diabetes, hypertension, and birth defects (Hayden et al., 2004;Singh and Tyagi, 2017). ...
Patients with diabetes, a methionine-rich meat diet, or certain genetic polymorphisms show elevated levels of homocysteine (Hcy), which is strongly associated with the development of cardiovascular disease including diabetic cardiomyopathy. However, reducing Hcy levels with folate shows no beneficial cardiac effects. We have previously shown that a hydrogen sulfide (H2S), a by-product of Hcy through transsulfuration by cystathionine beta synthase (CBS), donor mitigates Hcy-induced hypertrophy in cardiomyocytes. However, the in vivo cardiac effects of H2S in the context of hyperhomocysteinemia (HHcy) have not been studied. We tested the hypothesis that HHcy causes cardiac remodeling and dysfunction in vivo, which is ameliorated by H2S. Twelve-week-old male CBS+/− (a model of HHcy) and sibling CBS+/+ (WT) mice were treated with SG1002 (a slow release H2S donor) diet for 4 months. The left ventricle of CBS+/− mice showed increased expression of early remodeling signals c-Jun and c-Fos, increased interstitial collagen deposition, and increased cellular hypertrophy. Notably, SG1002 treatment slightly reduced c-Jun and c-Fos expression, decreased interstitial fibrosis, and reduced cellular hypertrophy. Pressure volume loop analyses in CBS+/− mice revealed increased end systolic pressure with no change in stroke volume (SV) suggesting increased afterload, which was abolished by SG1002 treatment. Additionally, SG1002 treatment increased end-diastolic volume and SV in CBS+/− mice, suggesting increased ventricular filling. These results demonstrate SG1002 treatment alleviates cardiac remodeling and afterload in HHcy mice. H2S may be cardioprotective in conditions where H2S is reduced and Hcy is elevated.
... Homocysteine converts to methionine by receiving one methyl group from 5-methyltetrahydrofolate, which also plays a role in the biosynthesis of Sadenosyl methionine (11). Earlier studies have established that insulin plasma levels affect homocysteine metabolism through the effective activation of enzymes involved in homocysteine metabolism, such as MTHFR (12,13). rs1801133 (677C>T, MAF=0.31) and rs1801131 (1298A/C, MAF=0.29) are two common polymorphisms located within MTHFR (14). ...
Aims: Type 2 diabetes mellitus (T2D) is determined by high levels of blood glucose. DNA methylation has been linked to the development and progression of multiple disorders including T2D since increased DNA Methylation was found in patients with this metabolic disease. One substantial enzyme involved in DNA methylation pathway is methylene tetra hydro folate reductase (MTHFR). This study was designed to evaluate the association between rs1801133 and rs1801131 polymorphisms, located in the MTHFR gene, and T2D in a sample of the Iranian population.
Methods: Blood samples from 151 patients with T2D and 136 healthy individuals were collected and DNA extraction was performed using the salting out method. Genotyping of variants was done using amplification tetra-refractory mutation system-polymerase chain reaction analysis. The data were analyzed via independent sample t-test and x2 tests.
Results: rs1801131 A/C polymorphism significantly increased the risk of T2D in codominant heterozygous AC (p=0.008), homozygous CC (p=0.01), and recessive CC (p=0.001) genotypes while in codominant heterozygous TC (p=0.001), homozygote CC (p=0.001) and recessive CC (p=0.0001) genotypes, dramatic correlation were found concerning rs1801133 T/C gene polymorphisms and the risk of T2D. The presence of the C allele is a potential risk factor for T2D in rs1801133 T/C (p=0.001) and rs1801131 A/C (p=0.04) polymorphisms.
Conclusion: Both The rs1801133 T/C and rs1801131 A/C MTHFR gene polymorphisms significantly increased the risk of T2D in our population. Further studies in other ethnicities are necessary to verify our findings.
... Some studies suggested that hyperhomocysteinemia may induce insulin resistance [15,29]. However, other studies showed that hyperinsulinemia can cause elevated plasma Hcy by impairing the activity of Hcy metabolizing enzymes [30,31]. After 48 weeks of administration of methionine, the rats had significantly increased levels of plasma cholesterol and triglycerides. ...
Hyperhomocysteinemia, a risk factor for vascular disease, is associated with metabolic syndrome. Our study was aimed at exploring the effect of long-term hyperhomocysteinemia with metabolic disturbances on vascular remodeling. We also studied oxidative stress and expression of PPAR γ in the coronary arteriole as a possible mechanism underlying vascular remodeling. Rats were treated with standard rodent chow (Control) or diet enriched in methionine (Met) for 48 weeks. Plasma homocysteine, blood glucose, serum lipids, malondialdehyde (MDA), superoxide dismutase (SOD), and nitric oxide (NO) levels were measured. Coronary arteriolar and carotid arterial remodeling was assessed by histomorphometric techniques and the expression of PPAR γ in vessel wall was investigated. In Met group, an increase in the level of fasting blood glucose, serum triglyceride, total cholesterol, MDA, and NO, a decline in the serum SOD level, and increased collagen deposition in coronary and carotid arteries were found. Moreover, we detected decreased expression of PPAR γ in the coronary arterioles in Met group. In summary, our study revealed metabolic disturbances in this model of long-term hyperhomocysteinemia together with vascular remodeling and suggested that impaired oxidative stress, endothelium dysfunction, and decreased PPAR γ expression in the vessel wall could be underlying mechanisms.
... The positive association between HHcy and elevated insulin resistance or hyperinsulinemia might be caused by the insulin-mediated reduction in the activity of key enzymes which govern the remethylation pathway or control the transsulfuration pathway [20,21]. Additionally, Hcy thiolactone has been documented to repress insulin signaling through elevating oxidative stress [22]. ...
Background
Impaired glucose tolerance (IGT) is characterized by insulin resistance and causes atherosclerosis. Hyperhomocysteinemia is associated with insulin resistance and predicts cardiovascular diseases. In this study, we assessed the possible association between homocysteine and IGT.
Material/Methods
This was a cross-sectional study of 118 consecutive subjects with IGT (IGT group) and 128 consecutive subjects with normal glucose tolerance (NGT group). Homocysteine and clinical characteristics were measured.
Results
The IGT group had higher homocysteine than the NGT group [18.00 (14.00, 22.25) vs. 12.50 (9.00, 15.00) μmol/L, p<0.001]. Homocysteine was positively associated with body mass index (BMI) (r=0.178, p=0.005), triglycerides (r=0.306, p<0.001), fasting blood glucose (FBG) (r=0.312, p<0.001), 2-hour postchallenge glucose (2hPG) (r=0.363, p<0.001), fasting insulin (FINS) (r=0.655, p<0.001), and homeostasis model assessment for insulin resistance (HOMA-IR) (r=0.643, p<0.001), and was negatively correlated with high-density lipoprotein cholesterol (HDL-C) (r=−0.250, p<0.001). After controlling for confounders, hyperinsulinemia (β=7.430, p<0.001) was independently related to hyperhomocysteinemia. In a logistic regression analysis, high triglycerides (OR=1.177, p<0.001) and homocysteine (OR=1.508, p=0.007), and low HDL-C (OR=0.315, p=0.026) were associated with IGT.
Conclusions
Patients with IGT have higher homocysteine levels compared with subjects with normal glucose tolerance, and hyperhomocysteinemia might be correlated with IGT.
... Pterins belong to a family of compounds represented by tetrahydrofolate [1], tetrahydrobiopterin (BH 4 ) and its oxidized forms, dihydrobiopterin (BH 2 ) and biopterin [2,3]. All these molecules are involved in essential metabolic reactions in mammals, therefore their deficiency or excess can produce biochemical alterations that lead to serious diseases [4]. ...
Tetrahydrobiopterin (BH4) has become a potential therapeutic tool to treat cardiovascular diseases, since it is an essential cofactor of nitric oxide synthase. In order to quantify the amount of BH4 and its related biopterins, a procedure that involves differential oxidation is currently used, which measures biopterin (the product of the oxidation of BH4 and BH2) at two different pH conditions to calculate the quantity of BH2 and BH4, using high performance liquid chromatography (HPLC). In this work, a method was established in order to quantify BH4 and BH2 by adapting previously described procedures. Several chromatographic conditions were evaluated to define the most convenient methodology. Four types of mobile phases and two different analytical columns were used for HPLC. Additionally, calibration curves were made in acid and basic pH compatible with the differential oxidation method. Each method was suitable for quantification purposes, but the choice was based on an economic factor. The selected condition was a mobile phase of 95% water/5% methanol using a C18 column at 35°C at a flow rate of 0.9mL/min. Then, it was calculated the recovery rate, which was about 80% using the chosen method. The aim of this work was to establish a simplified method of differential oxidation, compatible with matrixes such as cardiac tissue in order to facilitate the assessment of the BH4/BH2 ratio in biological samples.
... These results strongly suggest a regulatory role of insulin in the hepatic trans-sulfuration pathway that metabolizes Hc. In vitro studies conducted on cultured hepatocytes also demonstrated an increased activity of CBS [34]. ...
Background
Elevated homocysteine (Hc) levels have a well-established and clear causal relationship to epithelial damage leading to coronary artery disease. Furthermore, it is strongly associated with other metabolic syndrome variables, such as hypertension, which is correlated with type II diabetes mellitus (T2DM). Studies on T2DM in relation to Hc levels have shown both positive and negative associations. The aim of the present study is to examine the relationship between Hc levels and risk of T2DM in the Lebanese population. Methods
We sought to identify whether Hc associates positively or negatively with diabetes in a case–control study, where 2755 subjects enrolled from patients who had been catheterized for coronary artery diagnosis and treatment. We further sought to identify whether the gene variant MTHFR 667C>T is associated with T2DM, and how Hc and MTHFR 667C>T also impact other correlates of T2DM, including the widely used diuretics in this study population. ResultsWe found that Hc levels were significantly reduced among subjects with diabetes compared to those without diabetes when adjusted for all potential confounders (OR 0.640; 95% CI [0.44–0.92]; p = 0.0200). The associations between Hc levels and other variates contradicted the result: hypertension associates positively with high Hc levels, and with T2DM. The MTHFR 667C>T only associated significantly with high Hc levels. Conclusion
These results suggest population-specific variations among a range of mechanisms that modulate the association of Hc and T2DM, providing a probe for future studies.
... Cystathionine β-synthase in the liver was determined according to the method described by Dicker-Brown et al. [5]. This method utilised 14 C-serine which reacted with homocysteine forming cysteine in the presence of the enzyme. ...
Oxidative stress plays an important role in cardiovascular diseases. The study investigated the effects of dietary palm tocotrienol-rich fraction on homocysteine metabolism in rats fed a high-methionine diet. Forty-two male Wistar rats were randomly assigned to six groups. Five groups were fed with high-methionine diet (1 %) for 10 weeks. Groups 2 to 5 were also given dietary folate (8 mg/kg) and three doses of palm tocotrienol-rich fraction (30, 60 and 150 mg/kg) from week 6 to week 10. The last group was only given basal rat chow. High-methionine diet increased plasma homocysteine after 10 weeks, which was prevented by the supplementations of folate and high-dose palm tocotrienol-rich fraction. Hepatic S-adenosyl methionine (SAM) content was unaffected in all groups but S-adenosyl homocysteine (SAH) content was reduced in the folate group. Folate supplementation increased the SAM/SAH ratio, while in the palm tocotrienol-rich fraction groups, the ratio was lower compared with the folate. Augmented activity of hepatic cystathionine β-synthase and lipid peroxidation content by high-methionine diet was inhibited by palm tocotrienol-rich fraction supplementations (moderate and high doses), but not by folate. The supplemented groups had lower hepatic lipid peroxidation than the high-methionine diet. In conclusion, palm tocotrienol-rich fraction reduced high-methionine-induced hyperhomocysteinaemia possibly by reducing hepatic oxidative stress in high-methionine-fed rats. It may also exert a direct inhibitory effect on hepatic cystathionine β-synthase.
... One possibility, is that changes in expression may be due to elevated blood insulin (Fonseca et al., 2000). This hypothesis is supported by increases in MTHFR activity in human hepatocyte cell lines when administered insulin (Dicker-Brown et al., 2001). Regardless of the mechanism, this finding allows for speculation that the increase in MTHFR mRNA transcripts in PF dams may be secondary to increased levels of insulin due to relatively higher levels of maltose- (Guerri & Sanchis, 1985) outlines a possible mechanism through which the fetus may be buffered from the detrimental effects of ethanol exposure. ...
... Hyperhomocysteinemia in these animal models may be associated with high insulin level. Indeed, insulin reduces CBS activity in the liver (16,17). Streptozotocin-induced diabetes -the state of insulin deficiency -is characterized by high CBS and CSE activities in the liver and low plasma homocysteine level, and insulin supplementation corrects these abnormalities (18). ...
Homocysteine (Hcy) is a non-protein aminoacid which is an intermediate of methionine metabolism. Elevated homocysteine level (hyperhomocysteinemia) is a risk factor of cardiovascular diseases. In addition, obesity and metabolic syndrome are associated with greater prevalence of atherosclerosis. The purpose of this article is to discuss the relationship between adipose tissue and Hcy metabolism. All enzymes involved in the synthesis and metabolism of Hcy are expressed in adipose tissue, and recent studies suggest that adipose tissue may be an important source of circulating homocysteine. The effect of obesity on Hcy level is controversial, however, most experimental and clinical studies indicate that Hcy is elevated in the metabolic syndrome in the absence of diabetes. Homocysteine elevation in the metabolic syndrome may result from either hyperinsulinemia or the impairment of renal function. In contrast, plasma Hcy is reduced in both type 1 and type 2 diabetes if renal function is normal, but becomes elevated when diabetic nephropathy develops. Leptin, which is markedly elevated in obese patients, has no effect on total plasma Hcy, but increases the level of homocysteine thiolactone - a cyclic thioester of homocysteine which plays an important role in complications of hyperhomocysteinemia. The effect of leptin is accounted for by the inhibition of paraoxonase 1 (PON1) - the HDL-associated esterase, which hydrolyzes homocysteine thiolactone to Hcy. In addition, recent studies indicate that homocysteine may induce insulin resistance in adipose tissue by promoting endoplasmic reticulum stress and/or disrupting adipokine production; e.g. enhancing resistin and suppressing adiponectin.
... 17,18 Also, glucocorticoids and glucagon, hormones whose concentrations are increased in DM, decrease Hcy and increase activities of cyastathionin beta-synthase and cystathionine gamma-lyase. 19 The importance elevated serum Hcy as an independent cardiovascular risk factor in type 2 DM remained unclear. ...
Plasma homocysteine (Hcy) is considered to be a marker of endothelial dysfunction and a predictor of cardiovascular disease (CVD). Arterial stiffness measured by brachial-ankle pulse wave velocity (baPWV) is not only a marker of vascular damage but a significant predictor of CVD. Previous studies about the effect of high plasma Hcy levels on arterial stiffness have yielded inconsistent results. We therefore assessed the association between Hcy and baPWV in a relatively large number of subjects with type 2 diabetes mellitus (DM).
... Studies in cultured hepatoma cells indicated that Hcy thiolactone inhibit insulin signaling and it's action by increasing oxidative stress (97, 98). In a separate study using mouse hepatocytes indicated that hyperinsulinemia causes HHcy by decreasing activity of Hcy metabolizing enzymes such as MTHFR and CBS (99,100). Furthermore, in a study using rats fed with high fat and sucrose diet, has developed obesity which is associated with hyperinsulinemia, IR, and HHcy, along with changes in CBS and MTHFR enzymes in liver (101). These studies suggest that HHcy may cause IR, or vice versa, and that this HHcy and IR connection play important role in the development of CVD. ...
... The reduced Hcy level may be explained by an influence of hyperglycemia on acceleration in the hepatic transsulfuration pathway due to insulin disorder [12], subsequently, elevated glucocorticoids decreased Hcy level [55]. Cell culture and animal studies also showed that the diabetic status may reduce rather than increase the circulating Hcy level due to enhanced Hcy catabolism [55,56]. However, it should be emphasized that this data was derived from animal models of experimental diabetes and cannot provide solid evidence that a similar relationship between diabetic status and Hcy level exists in patients with diabetes. ...
We tested the hypothesis that elevated homocysteine (Hcy) level is causally associated with increased risk of type 2 diabetes mellitus (T2DM).
The meta-analysis and Mendelian randomization analysis were performed among 4011 cases and 4303 controls. The absolute pooled mean Hcy concentration in subjects with MTHFR 677TT was 5.55 mumol/L (95% CI, 1.33 to 9.77) greater than that in subjects with MTHFR 677CC in T2DM. Overall, the T allele of the MTHFR 677 C > T conferred a greater risk for T2DM [Random effect (RE) OR = 1.31(1.17-1.64), I2 = 41.0%, p = 0.055]. The random effect (RE) pooled OR associated with T2DM for MTHFR 677TT relative to the 677CC was [RE OR = 1.38(1.18-1.62)]. The fixed-effect pooled OR of the association for the MTHFR 677 TT vs CT was 1.29 (95% CI, 1.09-1.51). MTHFR 677 TT showed a significantly higher risk for T2DM compared with MTHFR 677 CC + CT [Fixed effect (FE) OR = 1.32(1.14-1.54), I2 = 0.0%, p = 0.686]. The absolute pooled mean Hcy concentration in individuals with T2DM was 0.94 mumol/L (95% CI, 0.40-1.48) greater than that in control subjects. The estimated causal OR associated with T2DM was 1.29 for 5 mumol/L increment in Hcy.
Our findings provided strong evidence on the causal association of Hcy level with the development of T2DM.
... The mean homocysteine level for the currently recruited patients with schizophrenia was very similar to the results of two previous studies [15,45]. Glucose and insulin seem to influence the metabolism of homocysteine, possibly through affecting the activity of key enzymes in homocysteine metabolism, includingmethylenetetrahydrofolate reductase and cystathionine-b-synthase [46]. Patients with schizophrenia and impaired fasting glucose had higher homocysteine levels than those with normal fasting glucose [47]; however, it is noteworthy that, in our study, the mean values of serum homocysteine in both genders were lower than 15 mmol/ L, which is a cut-off point for hyperhomocysteinaemia, and only 8/48 patients had an abnormal serum homocysteine. ...
Olanzapine (OLZ) is one of the most prescribed atypical antipsychotic drugs but its use is associated with unfavorable metabolic abnormalities. N-desmethyl-olanzapine (DMO), one of the OLZ metabolites by CYP1A2, has been reported to have a normalizing action on metabolic abnormalities, but this remains unclear. Our aim was to explore the correlation between the concentrations of OLZ or DMO with various metabolic parameters in schizophrenic patients.
The chromatographic analysis was carried out with a solvent delivery system coupled to a Coulochem III coulometric detector to determine OLZ and DMO simultaneously in OLZ-treated patients. The correlation between the concentration of OLZ or DMO and the metabolic parameters was analyzed by the Spearman rank order correlation method (r s).
The established analytical method met proper standards for accuracy and reliability and the lower limitation of quantification for each injection of DMO or OLZ was 0.02 ng. The method was successfully used for the analysis of samples from nonsmoking patients (n = 48) treated with OLZ in the dosage range of 5-20 mg per day. There was no correlation between OLZ concentrations and tested metabolic parameters. DMO concentrations were negatively correlated with glucose (r s = -0.45) and DMO concentrations normalized by doses were also negatively correlated with insulin levels (r s = -0.39); however, there was a marginally positive correlation between DMO and homocysteine levels (r s = +0.38).
The observed negative correlations between levels of DMO and glucose or insulin suggest a metabolic normalization role for DMO regardless of its positive correlation with a known cardiovascular risk factor, homocysteine. Additional studies of the mechanisms underlying DMO's metabolic effects are warranted.
... [27][28] While, cell culture have demonstrated that insulin mediates a decrease in the activities of MTHFR and CBS in HepG2 cells. [28][29] Ndrepepa et al. showed that circulating levels of folate and vitamin B 12 continue to be independent predictors of Hcy levels in T2DM. 6 Therefore, elevated Hcy levels in T2DM cannot be explained by the influence of diabetes itself, more attention should be focused on the influence of the diabetes-associated risk factors on Hcy metabolism. ...
The main aim of the present study was to investigate the plasma phospholipids (PL) fatty acids status and its association with plasma Hcy in patients with type 2 diabetes mellitus (T2DM). One hundred and four T2DM (aged 57.3±13.4 y) and 150 healthy subjects (aged 48.4±8.7 y) were recruited. Plasma Hcy and PL fatty acids were determined by standard methods. Plasma Hcy concentration in T2DM was significantly higher than that in healthy subjects (p<0.001). The prevalence of hyperhomocysteinemia was significantly higher in T2DM (36.54%) than that in healthy subjects (17.32%) (p=0.012). Plasma PL 20:4n-6 (r=0.303, p=0.012), 22:5n-3 (r=0.312, p=0.01), total PUFA (r=0.303, p=0.012), n-6 PUFA (r=0.261, p=0.032) were significantly positively associated with plasma Hcy concentration in T2DM. While, plasma PL n-3:n-6 PUFA (r=-0.400, p=0.046) was negatively associated with plasma Hcy in T2DM. In healthy subjects, plasma PL 22:6n-3 (r=-0.201, p=0.042) was negatively associated with plasma Hcy. In addition, plasma PL 22:6n-3 (r=0.193, p=0.044) and 22:5n-6 (r=0.234, p=0.038) were significantly negatively associated with plasma vitamin B-12 in healthy subjects. Our results suggested that increased plasma Hcy levels in T2DM associated with low n-3:n-6 ratio intake. We suggest that T2DM increase their long chain n-3 PUFA intake from fish or fish oil while decrease n-6 PUFA intake.
... It has been demonstrated that glucagon decreases homocysteine concentrations by reducing the export of homocysteine by cells and by increasing the activity of enzymes responsible for the transsulfuration pathway, namely, cystathionine beta-synthase (CBS) and cystathionine lyase (CL) (House et al., 1999; Jacobs et al., 2001). Insulin seems to exert an opposite effect, as it increases homocysteine concentration by decreasing the activity of these same enzymes, as well as by acting on the remethylation pathway modifying the activity of the enzyme methylenetetrahydrofolate reductase (House et al., 1999; Dicker-Brown et al., 2001). In this context it is interesting to note that the same effect observed here with restraint stress had been previously observed in humans. ...
Homocysteine levels are affected by diet factors such as vitamin deficiencies, non-diet factors such as genetic disorders, and stress exposure. Hyperhomocysteinemia has been implicated in several disorders, including cardiovascular disease, depression, schizophrenia, Alzheimer's and Parkinson's disease. Since sex differences play a role both in stress responses and in susceptibility to various diseases, the objective of this study was to evaluate possible alterations in homocysteine metabolism including cysteine, folate, and vitamin B6, and oxidative stress markers in female rats exposed to different types of acute stress. Female rats were randomly distributed into eight groups according to stress manipulation (restraint, swimming, cold and control) and estrous cycle (diestrus and estrus). In general no significant differences were seen between rats in estrus and diestrus. Restraint stress was the only type of stress that altered homocysteine concentrations (+ 33% relative to controls). An increase in levels of thiobarbituric acid reactive substances (TBARS) and a decrease in total glutathione (GSHt) concentration were also observed in animals subjected to restraint and swimming stress, suggesting the possibility of oxidative damage. Thus, both the homocysteine results and the oxidative stress data indicated that restraint stress was the most powerful stress manipulation in female rats, as previously observed in male rats.These findings indicate that hormonal and gonadal differences do not interfere with stress responses related to homocysteine metabolism and suggest that putative gender-related differences in homocysteine responses are probably not involved in the differential prevalence of some diseases in human males and females.
... This study suggested that prolonged folate administration decreases Hcy and reduces insulin levels, thereby improving IR. (97,98). In a separate study using mouse hepatocytes indicated that hyperinsulinemia causes HHcy by decreasing activity of Hcy metabolizing enzymes such as MTHFR and CBS (99,100). Furthermore, in a study using rats fed with high fat and sucrose diet, has developed obesity which is associated with hyperinsulinemia, IR, and HHcy, along with changes in CBS and MTHFR enzymes in liver (101). These studies suggest that HHcy may cause IR, or vice versa, and that this HHcy and IR connection play important role in the development of CVD. ...
Atherosclerosis, a pathological process that underlies the development of cardiovascular disease, is the primary cause of morbidity and mortality in patients with type 2 diabetes mellitus (T2DM). T2DM is characterized by hyperglycemia and insulin resistance (IR), in which target tissues fail to respond to insulin. Systemic IR is associated with impaired insulin signaling in the metabolic tissues and vasculature. Insulin receptor is highly expressed in the liver, muscle, pancreas, and adipose tissue. It is also expressed in vascular cells. It has been suggested that insulin signaling in vascular cells regulates cell proliferation and vascular function. In this review, we discuss the association between IR, metabolic stress, and atherosclerosis with focus on 1) tissue and cell distribution of insulin receptor and its differential signaling transduction and 2) potential mechanism of insulin signaling impairment and its role in the development of atherosclerosis and vascular function in metabolic disorders including hyperglycemia, hypertension, dyslipidemia, and hyperhomocysteinemia. We propose that insulin signaling impairment is the foremost biochemical mechanism underlying increased cardiovascular morbidity and mortality in atherosclerosis, T2DM, and metabolic syndrome.
... Insulin and glucose can affect methionine metabolism [179]. Hyperinsulinemia decreases MTHFR activity [180] and CβS-1b promoter activity [181] in hepatocytes; when cells are exposed to elevated insulin and glucose, homocysteine (Hcy) remethylation; hence, intracellular SAM concentrations are increased, due to SAM synthase activity [182]. Elevated glucose further enhances DNA methyltransferase activity that subsequently led to increased global DNA methylation [182]. ...
Type 2 Diabetes Mellitus (T2DM) is a metabolic disorder influenced by interactions between genetic and environmental factors. Epigenetics conveys specific environmental influences into phenotypic traits through a variety of mechanisms that are often installed in early life, then persist in differentiated tissues with the power to modulate the expression of many genes, although undergoing time-dependent alterations. There is still no evidence that epigenetics contributes significantly to the causes or transmission of T2DM from one generation to another, thus, to the current environment-driven epidemics, but it has become so likely, as pointed out in this paper, that one can expect an efflorescence of epigenetic knowledge about T2DM in times to come.
H 2 S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H 2 S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H 2 S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H 2 S and oxidative posttranscriptional modification of proteins, the effect of H 2 S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H 2 S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H 2 S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H 2 S in various cell types and organ systems are overviewed. Finally, the role of H 2 S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H 2 S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H 2 S in the physiological regulation of all organ functions emerges from this review.
Le complicanze cardiovascolari (CVD) rappresentano la principale causa di morte nei soggetti affetti da diabete mellito. L’iperomocisteinemia moderata potrebbe rappresentare un fattore di rischio indipendente di CVD tanto nella popolazione generale quanto in quella con diabete. Tuttavia, a causa dei risultati deludenti di alcuni trial clinici di intervento, l’ipotesi di un’associazione causale tra iperomocisteinemia e rischio di complicanze CVD è molto dibattuta. Gli studi condotti nella popolazione diabetica non hanno riportato dati univoci circa l’associazione tra elevati livelli plasmatici di omocisteina e malattia diabetica, e anche gli studi che hanno indagato l’associazione tra iperomocisteinemia e macroangiopatia hanno riportato risultati contrastanti. Sembra però che l’iperomocisteinemia sia un forte predittore della mortalità in questi pazienti. Sulla base delle conflittuali evidenze attualmente disponibili non sembra opportuno consigliare il dosaggio (e/o il trattamento) sistematico dei livelli di omocisteina nei soggetti con diabete mellito.
Objective:
To examine the association between dietary intake of choline and betaine with the risk of type 2 diabetes.
Research design and methods:
Among 13,440 Atherosclerosis Risk in Communities (ARIC) study participants, the prospective longitudinal association between dietary choline and betaine intake and the risk of type 2 diabetes was assessed using interval-censored Cox proportional hazards and logistic regression models adjusted for baseline potential confounding variables.
Results:
Among 13,440 participants (55% women, mean age 54 [SD 7.4] years), 1,396 developed incident type 2 diabetes during median follow-up of 9 years from 1987 to 1998. There was no statistically significant association between every 1-SD increase in dietary choline and risk of type 2 diabetes (hazard ratio [HR] 1.01 [95% CI 0.87, 1.16]) nor between dietary betaine intake and the risk of type 2 diabetes (HR 1.01 [0.94, 1.10]). Those in the highest quartile of dietary choline intake did not have a statistically significant higher risk of type 2 diabetes than those in the lowest choline quartile (HR 1.09 [0.84, 1.42]); similarly, dietary betaine intake was not associated with the risk of type 2 diabetes comparing the highest quartile to the lowest (HR 1.06 [0.87, 1.29]). Among women, there was a higher risk of type 2 diabetes, comparing the highest to lowest dietary choline quartile (HR 1.54 [1.06, 2.25]), while in men, the association was null (HR 0.82 [0.57, 1.17]). Nevertheless, there was a nonsignificant interaction between high choline intake and sex on the risk of type 2 diabetes (P = 0.07). The results from logistic regression were similar.
Conclusions:
Overall and among male participants, dietary choline or betaine intakes were not associated with the risk of type 2 diabetes. Among female participants, there was a trend for a modestly higher risk of type 2 diabetes among those with the highest as compared with the lowest quartile of dietary choline intake. Our study should inform clinical trials on dietary choline and betaine supplementation in relationship with the risk of type 2 diabetes.
L'influence de l'hypothèse de la programmation fœtale sur la stéato-hépatite non-alcoolique (NASH) n’a pas été suffisamment étudiée. La carence en donneurs de méthyles pendant la grossesse et l'allaitement est fréquente dans la population et est un modèle expérimental de programmation fœtale. Dans ce modèle, elle entraîne une stéatose hépatique chez les ratons de 21 jours, résultant notamment d'une déficience de l'oxydation des acides gras. Nous avons évalué les effets de la programmation fœtale sur la NASH chez des rats Wistar nés de mères recevant soit un régime standard, soit un régime carencé en donneurs de méthyles (iMDD), pendant la gestation et l'allaitement. Les ratons sevrés ont ensuite reçu un régime standard (D21 à D50), puis une partie de ces rats devenus adultes ont ensuite été soumis à un régime hyper-énergétique (HF) (D50 à D185). Les animaux ont été sacrifiés à D50 et D185. Nous avons observé une augmentation de la graisse abdominale et du rapport ASAT/ALAT, mais aucune anomalie histologique hépatique chez les rats D50 iMDD. En revanche, les rats D185 iMDD/HF ont développé une NASH, avec les caractéristiques d'une insulino-résistance ainsi qu'une augmentation de l'expression de nombreux gènes et protéines impliqués dans l'inflammasome, l'activation des cellules étoilées hépatiques, la fibrose et le remodelage tissulaire, incluant l'AngII, TGFβ1 et NFκB. En conclusion, la carence en donneurs de méthyles pendant la gestation et l'allaitement produit une NASH chez des animaux soumis ultérieurement à un régime hyper-énergétique à l'âge adulte, malgré le retour préalable à une alimentation standard. Ces résultats suggèrent qu'une carence gestationnelle en donneurs de méthyles est un facteur de risque de NASH chez les individus exposés ultérieurement à un régime hyper-énergétique.
Background
There are large differences between men and women of child-bearing age in the expression level of 5 key enzymes in one-carbon metabolism almost certainly caused by the sex hormones. These male-female differences in one-carbon metabolism are greatly accentuated during pregnancy. Thus, understanding the origin and consequences of sex differences in one-carbon metabolism is important for precision medicine.
Results
We have created a mathematical model of hepatic one-carbon metabolism based on the underlying physiology and biochemistry. We use the model to investigate the consequences of sex differences in gene expression. We give a mechanistic understanding of observed concentration differences in one-carbon metabolism and explain why women have lower S-andenosylmethionine, lower homocysteine, and higher choline and betaine. We give a new explanation of the well known phenomenon that folate supplementation lowers homocysteine and we show how to use the model to investigate the effects of vitamin deficiencies, gene polymorphisms, and nutrient input changes.
Conclusions
Our model of hepatic one-carbon metabolism is a useful platform for investigating the mechanistic reasons that underlie known associations between metabolites. In particular, we explain how gene expression differences lead to metabolic differences between males and females.
Electronic supplementary material
The online version of this article (doi:10.1186/s12918-018-0621-7) contains supplementary material, which is available to authorized users.
Background
Metabolic syndrome (MS) is a construct used to separate “healthy” from “unhealthy” obese patients, and is a major risk factor for type 2 diabetes (T2D) and cardiovascular disease. There is controversy over whether obese “metabolically well” persons have a higher morbidity and mortality than lean counterparts, suggesting that MS criteria do not completely describe physiologic risk factors or consequences of obesity. We hypothesized that metabolomic analysis of plasma would distinguish obese individuals with and without MS and T2D along a spectrum of obesity-associated metabolic derangements, supporting metabolomic analysis as a tool for a more detailed assessment of metabolic wellness than currently used MS criteria.
Methods
Fasting plasma samples from 90 adults were assigned to groups based on BMI and ATP III criteria for MS: (1) lean metabolically well (LMW; n = 24); (2) obese metabolically well (OBMW; n = 26); (3) obese metabolically unwell (OBMUW; n = 20); and (4) obese metabolically unwell with T2D (OBDM; n = 20). Forty-one amino acids/dipeptides, 33 acylcarnitines and 21 ratios were measured. Obesity and T2D effects were analyzed by Wilcoxon rank-sum tests comparing obese nondiabetics vs LMW, and OBDM vs nondiabetics, respectively. Metabolic unwellness was analyzed by Jonckheere-Terpstra trend tests, assuming worsening health from LMW → OBMW → OBMUW. To adjust for multiple comparisons, statistical significance was set at p < 0.005. K-means cluster analysis of aggregated amino acid and acylcarnitine data was also performed.
Results
Analytes and ratios significantly increasing in obesity, T2D, and with worsening health include: branched-chain amino acids (BCAAs), cystine, alpha-aminoadipic acid, phenylalanine, leucine + lysine, and short-chain acylcarnitines/total carnitines. Tyrosine, alanine and propionylcarnitine increase with obesity and metabolic unwellness. Asparagine and the tryptophan/large neutral amino acid ratio decrease with T2D and metabolic unwellness. Malonylcarnitine decreases in obesity and 3-OHbutyrylcarnitine increases in T2D; neither correlates with unwellness. Cluster analysis did not separate subjects into discreet groups based on metabolic wellness.
Discussion
Levels of 15 species and metabolite ratios trend significantly with worsening metabolic health; some are newly recognized. BCAAs, aromatic amino acids, lysine, and its metabolite, alpha-aminoadipate, increase with worsening health. The lysine pathway is distinct from BCAA metabolism, indicating that biochemical derangements associated with MS involve pathways besides those affected by BCAAs. Even those considered “obese, metabolically well” had metabolite levels which significantly trended towards those found in obese diabetics. Overall, this analysis yields a more granular view of metabolic wellness than the sole use of cardiometabolic MS parameters. This, in turn, suggests the possible utility of plasma metabolomic analysis for research and public health applications.
Les folates (vitamine B9) et la vitamine B12 interviennent comme cofacteurs dans le métabolisme des monocarbones qui régule les réactions de transméthylation impliquées dans les mécanismes épigénétiques. Un déficit en folates et/ou B12 réduit la production de méthionine à partir de l'homocystéine, un acide aminé toxique dont l'accumulation a été associée à la survenue de pathologies du système nerveux central aux différents stades de la vie (spina bifida, maladie d'Alzheimer...). Afin d'explorer les mécanismes cellulaires et moléculaires impliqués dans la réponse à la carence en ces micronutriments, nous avons développé deux nouveaux modèles cellulaires. Ainsi, nous avons étudié les effets d'une déficience en folate sur la prolifération, la différenciation et la plasticité neuronale de progéniteurs neuronaux issus de l'hippocampe d'embryons de rat, la lignée H19-7. Le second modèle correspond à un projet innovant visant à obtenir une déplétion cellulaire en B12 par séquestration membranaire. Il a été obtenu par transfection stable de la lignée de neuroblastome murin NIE-115 dans le but d'induire l'expression d'une protéine chimère contenant le transporteur plasmatique de la vitamine B12, la transcobalamine II, et une protéine d'ancrage membranaire. L'ensemble de ces travaux montre que les altérations du métabolisme des monocarbones associées aux carences répriment la neurogenèse et induisent des troubles de la différentiation neuronale. Ceci suggère l'existence de mécanismes précis par lesquels le déficit en folates, en vitamine B12 et/ou l'homocystéine peuvent affecter le fonctionnement du cerveau et sa plasticité.
Aim:
Methylenetetrahydrofolate reductase (MTHFR) is a regulatory enzyme of homocysteine metabolism. The C677T and A1298C polymorphism of the MTHFR gene has been reported to be associated with elevated plasma homocysteine in patients with Diabetic nephropathy. This study aimed to investigate the influence of the C677T and A1298C polymorphisms on the progression chronic kidney disease in diabetic nephropathy of south Indian population.
Methods:
We genotyped 145 DN cases and 100 controls for the C677T and A1298C polymorphisms using PCR-RFLP based protocols, and all diabetic nephropathy cases divided into two groups based on CKD stages: 60 DN cases were early stage (CKD1 to CKD3) and 85 DN cases were advanced stage (CKD4 and CKD5). Association χ2 and univariate analysis were performed.
Results:
The C677T (OR=4.2; 95% CI=2.31-7.64 and p=0.001) and A1298C (OR=2.8; 95% CI=1.05-7.57 and p=0.033) polymorphism was shown that the significant association between the cases and control. Furthermore, the MTHFR gene polymorphism C677T (OR=2.48; 95% CI=1.25-4.9 and p=0.008) was observed that the significant contribution of the progression of CKD in DN.
Conclusion:
These findings suggest that the C677T and A1298C polymorphism of MTHFR gene was associated with diabetic nephropathy in south Indian population. Furthermore, the present study provides evidence that the C677T polymorphism was associated with CKD progression in DN.
Background: The relationship between serum homocysteine levels and cardiovascular diseases has been elucidated since many years ago. In this study, the association between serum levels of homocysteine, folic acid, and vitamin B12 with the pulse wave velocity and Buckberg index or subendocardial viability ratio was assessed in individuals with diabetes and also non-diabetic subjects.
Methods: In this cross-sectional study, 58 individuals with type 2 diabetes and 36 non-diabetic people, from April to October 2013 were enrolled in Dr. Shariati Hospital affiliated to Tehran University of Medical Sciences. Anthropometric and blood pressure measurements were performed with standard methods. Fasting serum glucose, total cholesterol, low density lipoprotein cholesterol, high density lipoprotein cholesterol, Triglyceide, A1C, vitamin B12, folic acid and serum homocysteine levels as well as, highly sensitive complement-reactive protein (hs-CRP) were measured. Artherial stiffness was assessed by calculating pulse wave velocity and aortic agumentation index via Sphygmocor. In addition, Buckberg index (Subendocardial viability ratio) was assessed by dividing myocardial oxygen supply to dimand expressed as percent. The normality of distributions was evaluated by Kolmogorov-Smirnov test and linear regression models were utilized to detect associations.
Results: Diabetic and non-diabetic subjects differed in terms of age, history of hypertension, serum levels of homocysteine, and LDL-C (P< 0.05). The pulse wave velocity in subjects with diabetes and without diabetes were 60.91 m/s and 41.91 m/s, respectively (P= 0.01). After adjustment for confounding factors in multivariate regression analysis pulse wave velocity was associated with age and homocysteine levels in non-diabetic group, (β equal to 0.441 and 0.345, respectively), and it was related to age, diastolic blood pressure and serum levels of c-reactive protein in subject with diabetes (β= 0.417, 0.302, and 0.262, respectively).
Conclusion: Homocysteine levels in non-diabetic individuals were associated to sub-clinical atherosclerosis markers but we could not find this association in diabetic participants.
Introduction
Hydrogen sulfide (H2S) is an endogenous gasotransmitter. The levels of H2S-generating enzyme expression and endogenous H2S production in diabetic rats with erectile dysfunction (ED) remain unknown. The aim of this study was to investigate the expression of the H2S-generating enzymes and endogenous production of H2S in penile tissues of diabetic ED rats.
Methods
Experimental rats were randomly divided into normal control group, apomorphine (APO)-positive group and APO-negative group. Primary rat corpus cavernosum smooth muscle cells (CCSMCs) and aortic endothelial cells (AECs) were isolated and cultured in vitro under 3 different conditions: normal glucose (NG) condition, high glucose (HG) condition, and osmotic control (OC) condition.
Main Outcome Measures
Erectile function; H2S concentrations in plasma or penile tissues; expression of H2S-generating enzymes and endogenous H2S production in penile tissues, CCSMCs, and AECs.
Results
Erectile function was significantly decreasedin the APO-negative group. In addition to significantly decreased expression of cysteine aminotransferase (CAT), d-amino acid oxidase (DAO), and 3-mercaptopyruvate sulfurtransferase (3-MST), the H2S concentrations in plasma and penile tissues and endogenous H2S production were significantly decreased in the APO-negative group. Endogenous H2S production by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) decreased to the same levels in the APO-negative and APO-positive groups as that in the normal control group. However, CBS and CSE expression remained unchanged in the 3 groups. Under HG conditions, H2S-generating enzyme expression in AECs did not change, while CAT, DAO, and 3-MST expression in CCSMCs was significantly decreased. In both cell types, H2S production by these enzymes was decreased in the HG group.
Conclusion
Endogenous H2S production was significantly decreased in the diabetic ED rats' penile tissues due to downregulated expression of the CAT/3-MST and DAO/3-MST pathways and low activities of CBS and CSE.
Objective: To explore the influence of homocysteine (Hcy) on liver cystathionine-β-synthase (CBS) and methylenetetrahydrofolate reductase (MTHFR) system in apoE-/- mice, and determine the effects of atorvastatin and/or folate/vitamin B12 on liver CBS and MTHFR system. Methods: Eighty male 6-week-old apoE-/- mice were randomly divided into two groups: 65 mice were fed with a chow diet containing 2% (wt/vol) L-methionine (homomethionine group) and 15 mice were fed with normal saline (control group). Two months later, the 60 mice survived in homomethionine group were subdivided into four groups: group I (untreated), II (3 mg/kg atorvastatin), III (3 mg/kg atorvastatin + 2 mg/kg folate + 30 μg/kg vitamin B12) and IV (2 mg/kg folate + 30 μg/kg vitamin B12). After one month, Western blotting was performed to detect the liver CBS and MTHFR system protein expression in each group. Results: The relative expression of liver CBS and MTHFR was significantly lower in group I than in control group (P < 0.01), while that of liver CBS in group II, III and IV was significantly higer than in group I (P < 0.05), and that of liver CBS and MTHFR in group IV almost recovered to normal level. After drug treatment, there was no significant difference in the relative expression of MTHFR between group I and group II, while that in group III and IV was significantly higher than in group I (P < 0.01). Conclusion: It was demonstrated for the first time that atorvastatin and folate/vitamin B12 therapy had favourable effects on liver CBS in mice. Folate and vitamin B12 can improve liver MTHFR, while atorvastatin can not.
Objective: To investigate the risk factors of ischemic stroke(IS) patients with increased ho-mocysteine(Hcy). Methods: Eighty hospitalized patients of IS with Hcy > 8 mg/L and 138 control subjects without clinical and instrumental evidence of atherosclerosis diseases were enrolled. All traditional risk factors for IS and biochemical indexes were recorded. Several statistically significant risk factors were screened out with univariate non-conditional logistic regression analysis, then independent risk factors were determined with multivariate stepwise non-conditional logistic regression analysis. Results: Univariate non-conditional logistic regression analysis showed that male, hypertension, heart disease, diabetes, smoking, alcohol abuse, familiar stroke history, SBP, LDL and CRP were positively correlated with Hcy increasing in patients with IS (P < 0.05). Regular liftstyle and HDL were negatively correlated with increasing in Hcy in patients with IS. Multivariate stepwise non-conditional logistic regression analysis showed that male, hypertension history, diabetes history and smoking were the independent risk factors of increasing in Hcy in patients with IS. Conclusion: Healthy lifestyle was protective factors against increasing in Hcy in patients with IS: hypertension, diabetes and smoking were independent risk factors for increasing in Hcy in patients with IS. Interventional treatment on related risk factors is necessary to ischemic stroke patients with increased Hcy.
Type 1 diabetes (T1D) results from the immune-mediated destruction of insulin-secreting β-cells that reside in the pancreatic Islets of Langerhans. Genetic susceptibility is necessary but not sufficient for the development of autoimmune diabetes, indicating a key role for risk modification by environmental factors. Epigenetic mechanisms could mediate the effect of specific environmental factors and could therefore explain, at least in part, non-genetic susceptibility to Type 1 diabetes. Exposure to variable nutrition or infection in early life, including in utero experiences can modify T1D susceptibility, which may occur via epigenetic means. T1D is characterized by autoimmune destruction of pancreatic insulin-secreting β-cells and their aberrant development and function of β-cells; these pathogenic mechanisms are also subject to epigenetic regulation. Furthermore, the diabetic state, characterized by fluctuations in insulin and glucose, can influence genomic methylation profiles and gene expression, which can potentially impact susceptibility to co-morbidities of T1D. This chapter identifies potential epigenetic mechanisms that may modify T1D risk and describes study designs that can be implemented to determine the role played by epigenetics in disease pathogenesis. © 2012 Springer Science+Business Media B.V. All rights reserved.
Accumulation of oxidized-matrix (fibrosis) between the endothelium (the endothelial cells embedded among the myocytes) and cardiomyocytes is a hallmark of diabetes mellitus and causes diastolic impairment. In diabetes mellitus, elevated levels of homocysteine activate matrix metalloproteinase and disconnect the endothelium from myocytes. Extracellular matrix functionally links the endothelium to the cardiomyocyte and is important for their synchronization. However, in diabetes mellitus, a disconnection is caused by activated metalloproteinase, with subsequent accumulation of oxidized matrix between the endothelium and myocyte. This contributes to endothelial-myocyte uncoupling and leads to impaired diastolic relaxation of the heart in diabetes mellitus. Elevated levels of homocysteine in diabetes are attributed to impaired homocysteine metabolism by glucose and insulin and decreased renal clearance. Homocysteine induces oxidative stress and is inversely related to the expression of peroxisome proliferators activated receptor (PPAR). Several lines of evidence suggest that ablation of the matrix metalloproteinase (MMP-9) gene ameliorates the endothelial-myocyte uncoupling in diabetes mellitus. Homocysteine competes for, and decreases the PPARγ activity. In diabetes mellitus, endothelial-myocyte uncoupling is associated with matrix metalloproteinase activation and decreased PPARγ activity. The purpose of this review is to discuss the role of endothelial-myocyte uncoupling in diabetes mellitus and increased levels of homocysteine, causing activation of latent metalloproteinases, decreased levels of thioredoxin and peroxiredoxin, and cardiac tissue inhibitor of metalloproteinase (CIMP) in response to antagonizing PPARγ.
Homocysteine is an independent risk factor for atherosclerosis, plausibly through induction of endothelial dysfunction and smooth muscle cell proliferation. Under oxidative stress and inflammatory stimuli, vascular smooth muscle cells may undergo osteogenic differentiation, which leads to coronary artery calcification. This study evaluated the association between plasma homocysteine and coronary artery calcification.
Coronary artery calcium scores (CACSs) and plasma homocysteine concentrations were measured in 21,235 men (42 ± 6.5 years) who participated in the Kangbuk Samsung Health Study between 2010 and 2011. Subjects were grouped by quartile of plasma homocysteine.
The prevalence of coronary artery calcification (CAC) among the 21,235 men was 13.5%. In the first to fourth homocysteine quartiles, CAC(+) prevalence rates were 12.1%, 12.6%, 13.9%, and 15.3%, respectively. The CAC(+) group had unfavorable cardiometabolic and lipid profiles. In multivariate regression analysis after adjusting for variables with a univariate relationship (p < 0.20), the odds ratio (OR) for the presence of CAC was higher for the highest homocysteine quartile than for the lowest quartile group (OR (95% confidence interval (CI)), 1.275 (1.027, 1.583)), and presence of CAC was positively associated with quartile of homocysteine (p for trend = 0.009). Moreover, absolute plasma homocysteine concentration was positively and significantly related to presence of CAC and to CACS, respectively (OR (95% CI) 1.399 (1.089, 1.796): standardized β = 0.040, p < 0.001).
This study shows that plasma homocysteine is independently related to coronary artery calcification in Korean men, suggesting that plasma homocysteine concentration may serve as a marker for CAC.
This thesis demonstrates that in a system with relatively low biological diversity, such as the Baltic Sea, abiotic (physical/chemical) perturbation can in general manifest itself, along with biological control mechanisms, in a considerable impact on functional and structural biodiversity in the marine ecosystem. However, the control effect largely depends on the trophic level, as well as on species-specific response. Moreover, through biological control mechanisms these effects can forward chain-of-event consequences in succeeding trophic levels above or below. It also demonstrates that during the last decades the characteristics of macrozoobenthic communities in the Archipelago Sea have mainly been modified by eutrophication (chemical stress) and subsequent bottom-up control, but locally also by physical (e.g.dredging) or chemical (e.g. pollution, oxygen depletion) processes. If the recent favourable progress in water quality continues, macrozoobenthic communities in the middle and outer Archipelago Sea will not generally become decisively impoverished in the near future but will remain more or less stable Naturally this is above all spatially scale-dependent; however, the large-scale pattern can also be considerably influenced by many thus far poorly recognised elements, such as possible lags before effects become evident or internal processes in nutrient dynamics. This thesis reveals for the first time the large potential of remote climatic control of the Baltic Sea pelagic ecosystem. I demonstrate that seawater salinity, which practically controls the composition and abundance of the biota in the Baltic Sea, is ultimately controlled by North Sea weather conditions and their resulting effects on the Baltic Sea oceanography. If the recent change towards a higher NAO index due to the enhanced greenhouse effect proves correct, freshwater organisms in the Baltic pelagic biota will probably become increasingly predominant in the future due to increased precipitation and less frequent major inflows into the Baltic Sea. This, however depends on the relative significance of the changes in variability of climatic processes versus changes in the average boundary conditions and their importance in the Baltic Sea hydrography. In any case, the recent large-scale decrease of large neritic copepods and the subsequent consequences for succeeding higher trophic levels are evident, for instance in the unfavourable change in the staple food composition of the Baltic herring. Although differences in the abundances of Antarctic copepod species were found during the period studied, the reasons for the change whether physical or biological, and their possible consequences for the function of the pelagic ecosystem, were not found. This implies that the outcomes of control effects may depend on many factors – among them a weakening cascade effect, species-specific responses, resource availability or interspecific competition – which may also induce a coincidental contrasting effect and thus confuse interpretations. The intention of this thesis was to focus only on relatively simple systems, where a single chemical, physical or biological disturbance can have a considerable effect on the existing ecosystem, and which therefore can be isolated, observed and described. When we investigate just one factor in a more complicated system, without taking into account the increased heterogeneity and more complicated abiotic/biotic interactions and functions, there is the risk of being easily led to oversimplified conclusions about the controlling mechanisms. Thus we need to be aware that ecological models constructed and proved correct for ‘frames’ within one system are not necessarily appropriate or valid in another.
Hydrogen sulfide (H2S) is synthesized from l-cysteine by cystathionine β-synthase (CBS) or cystathionine γ-lyase (CSE), and is enzymatically metabolized in mitochondria by sulfide:quinone oxidoreductase (SQR). Recent studies have indicated that H2S is synthesized by CSE in perivascular adipose tissue (PVAT), and is responsible for the anticontractile effect of PVAT on adjacent vessels. The lipophilic statin atorvastatin increases PVAT-derived H2S by suppressing its mitochondrial oxidation; the effect that results from statin-induced depletion of ubiquinone. Experimental obesity induced by a highly palatable diet has a time-dependent effect on H2S in PVAT. Adipose tissue hypoxia suppresses H2S oxidation and increases its level in short-term obesity not associated with insulin resistance. In contrast, in long-term obesity, insulin resistance and (or) hyperinsulinemia result in the down-regulation of CSE and H2S deficiency, which is corrected by treatment with the insulin sensitizer rosiglitazone. In addition, cannabinoid CB1 receptor agonist administered for 2 weeks increases H2S by impairing mitochondria biogenesis. This indicates that the rate of mitochondrial H2S oxidation plays an important role in the regulation of H2S level in PVAT. Up-regulation of H2S signaling in short-term obesity and (or) by elevated endocannabinoids may be a compensatory mechanism that maintains vascular tone, despite endothelial dysfunction.
Hydrogen sulfide (H(2)S) is now considered a member of a group of signaling molecules termed 'gasotransmitters'. H(2)S has been shown to be generated in the endocrine and reproductive organs and elicits various actions. H(2)S modulates insulin secretion in pancreatic islets. Adipose tissues have the ability to produce H(2)S, which regulates the local insulin sensitivity and vascular responsiveness. H(2)S also acts on the hypothalamic-pituitary-adrenal axis and is involved in stress responses. The effects of H(2)S on male and female reproductive function have also attracted great interest for their potential therapeutic implications in reproductive disorders. Alterations of H(2)S biosynthesis are associated with various endocrine disorders, and hormones can be important factors in the regulation of H(2)S production. Understanding the regulatory mechanisms for H(2)S synthesis pathways may help develop new therapeutic strategies.
This study was conducted to evaluate the analytical performance of a new colorimetric assay for plasma homocysteine (Hcy) and to determine the influence of the method used on the frequency of hyperhomocysteinemia and on the association between Hcy and biological parameters in diabetic patients. Plasma Hcy was measured in 160 diabetic patients by high performance liquid chromatography (HPLC) in parallel with an automated colorimetric assay (DiaSys Diagnostic Systems GmbH) using the Olympus AU640 and Abbott C8000 analyzers. Plasma glucose, creatinine, folates, vitamin B(12), high-sensitivity C-reactive protein (hs-CRP), and blood hemoglobin A1c (HbA1c) concentrations were measured by routine methods. The Hcy concentrations obtained with the HPLC (x) and colorimetric methods (y) were highly correlated (y = 1.032x - 0.65, r(2) = 0.884 for AU640; y = 1.028x + 0.87, r(2) = 0.934 for C8000). The frequency of Hcy >15 micromol/L was 41.9% by HPLC assay and there was no statistically significant difference using the colorimetric method. Patients with Hcy >15 micromol/L compared to < or =15 micromol/L using HPLC had significantly lower glycemia (p <0.001), lower HbA1c (p <0.001), lower estimated glomerular filtration rate (GFR) (p <0.0001), and lower vitamin B(12) levels (p <0.001). All these relationships were also noted when using the colorimetric assay on the Olympus AU640 or Abbott C8000 analyzers. In summary, this study shows that the DiaSys colorimetric assay is suitable for plasma Hcy determinations in routine clinical biochemistry.
To assess the association of genetic polymorphisms related to cardiovascular disease (CVD) risk with anthropometric parameters and indices of androgenicity in healthy postmenopausal women.
Cross-sectional study in a University Menopause Clinic.
The following polymorphisms were assessed in 84 healthy postmenopausal women: glycoprotein IIIa Leu33Pro, apolipoprotein E2/E3/E4, methylenetetrahydrofolate reductase (MTHFR) Ala222Val, apolipoprotein B Arg3500Gln, paraoxonase 1 Gln192Arg, plasminogen activator inhibitor 1 4G/5G, cholesterol-7 alpha-hydroxylase A-204C, and cholesterol ester transfer protein (TaqIB) B1/B2. Hormonal assays included FSH, LH, 17-beta-estradiol, testosterone, sex hormone-binding globulin (SHBG), DHEA sulfate, Delta-4-androstenedione (Delta4A), free androgen index (FAI), free estrogen index (FEI), and homocysteine (Hcy). The anthropometric components were body mass index (BMI) and waist-to-hip ratio (WHR).
MTHFR Ala222Val polymorphism was positively associated with testosterone, FAI, and FEI (P=0.001, P=0.0004, and P=0.014 respectively) and negatively with SHBG (P=0.047). Furthermore, women bearing this polymorphism had higher BMI and WHR compared with women with the wild-type variant (P=0.027 and P=0.044 respectively).
MTHFR Ala222Val polymorphism is associated with increased androgenicity and elevated BMI and WHR in healthy postmenopausal women. The significance of this association with respect to the CVD risk of postmenopausal women remains to be elucidated in future studies.
Vascular disease is the leading cause of death and disability in the Western World: atherosclerosis is responsible for the majority of deaths in virtually all westernized societies; pulmonary embolism, a complication of deep venous thrombosis, is the leading cause of morbidity and mortality, resulting in approximately 50,000 deaths per year in the United States; approximately 1.5 million acute myocardial infarcts occur each year, each infarction bearing a 30% mortality rate; and strokes represent the third leading cause of death in developed countries (1). While the adverse effects of hypertension, hypercholesterolemia, diabetes, and smoking on the vascular system have received widespread publicity, another important risk factor for vascular disease--less well-known outside the medical community but recently gaining increasing attention in the literature is an elevated plasma level of the amino acid homocysteine. Bolstered by findings of an association between hyperhomocysteinemia and a variety of vascular disorders, theories implicating homocysteine in the pathogenesis of these disorders have inspired researchers to explore novel approaches in the prevention and treatment of vascular disease. With the biochemistry of homocysteine metabolism already well understood, vitamin supplementation has emerged as a promising strategy for reduction of plasma homocysteine levels, with consequent arrest or reversal of the postulated pathogenic mechanisms involved in homocysteine-associated disorders of the vasculature, and, thus, potential prevention and treatment of vascular disease in hyperhomocysteinemic patients.
The discovery of hyperhomocysteinemia as a major factor in the pathogenesis of arteriosclerosis offers new strategies and opportunities for prevention and treatment.
Considering that elevated blood levels of homocyst(e)ine represent a known independent risk factor for macrovascular disease, we assessed the link between hyperhomocyst(e)inemia and diabetic microvascular complications.
Homocyst(e)ine and thrombomodulin plasma levels, a marker of endothelial cell damage, were measured before and 3 h after oral methionine loading in 75 patients with stable, well-controlled IDDM and 40 healthy control subjects matched for sex and age. Exclusion criteria were hyperlipidemia, hypertension, smoking, or positive family history for cardiovascular disease.
IDDM patients had higher pre- and postload homocyst(e)ine plasma levels than did healthy control subjects (12.0 vs. 7.7 mumol/l and 27.6 vs. 16.0 mumol/l; P < 0.001). Of 75 IDDM patients, 26 had homocyst(e)ine plasma levels above the normal range (defined as mean +2 SD of values obtained in the control group). The IDDM patients with hyperhomocyst(e)inemia had higher thrombomodulin plasma levels (62.2 vs. 38.2 ng/ml; P < 0.001), higher albumin excretion rates (485 vs. 115 mg/l; P < 0.005), and a higher prevalence of late diabetic complications (nephropathy, 76 vs. 33%; retinopathy, 69 vs. 51%; neuropathy, 57 vs. 41%; macroangiopathy, 57 vs. 33%) compared with IDDM patients with normal plasma homocyst(e)ine. In vitro experiments with human umbilical vein cells show an increased release of thrombomodulin into the culture supernatant only when endothelial cells were pretreated with advanced glycation end product (AGE)-albumin before L-homocystine was added. A synergistic action of homocyst(e)ine and AGEs might contribute to vascular complications of patients with diabetes.
Hyperhomocyst(e)inemia is common in nephropathic diabetic patients and may contribute to the enhanced morbidity and mortality from cardiovascular diseases characteristically observed in IDDM patients with diabetic nephropathy.
An elevation in the concentration of total plasma homocysteine is known to be an independent risk factor for the development of vascular disease. Alterations in homocysteine metabolism have also been observed clinically in diabetic patients. Patients with either type 1 or type 2 diabetes who have signs of renal dysfunction tend to exhibit elevated total plasma homocysteine levels, whereas type 1 diabetic patients who have no clinical signs of renal dysfunction have lower than normal plasma homocysteine levels. The purpose of this study was to investigate homocysteine metabolism in a type 1 diabetic animal model and to examine whether insulin plays a role in its regulation. Diabetes was induced by intravenous administration of 100 mg/kg streptozotocin to Sprague-Dawley rats. We observed a 30% reduction in plasma homocysteine in the untreated diabetic rat. This decrease in homocysteine was prevented when diabetic rats received insulin. Transsulfuration and remethylation enzymes were measured in both the liver and the kidney. We observed an increase in the activities of the hepatic transsulfuration enzymes (cystathionine beta-synthase and cystathionine gamma-lyase) in the untreated diabetic rat. Insulin treatment normalized the activities of these enzymes. The renal activities of these enzymes were unchanged. These results suggest that insulin is involved in the regulation of plasma homocysteine concentrations by affecting the hepatic transsulfuration pathway, which is involved in the catabolism of homocysteine.
Epidemiological studies performed over the past 40 years have shown that the prevalence of diagnosed diabetes has increased dramatically in the U.S. and that a substantial proportion of the population has undiagnosed diabetes, impaired fasting glucose, and impaired glucose tolerance. Diabetes is most prevalent in minority populations, such as African-Americans, Native Americans, and Mexican Americans. Increasing prevalence of diabetes has led to increases in microvascular complications such as blindness, end-stage renal disease, and lower limb amputations. Poor glycemic control contributes to the high incidence of these complications, yet community-based studies of diabetic patients show their mean fasting plasma glucose concentration is generally >180 mg/dl compared with 100 mg/dl for nondiabetic individuals. In people with diabetes, risk factors for cardiovascular disease including elevated fasting plasma glucose, blood pressure, total cholesterol, triglycerides, and obesity partly explain the high proportion of deaths (60-70%) caused by cardiovascular disease in people with diabetes. More intensive diabetes management and improved glycemic control could minimize long-term complications of the disease and would be expected to reduce the morbidity, mortality, and costs associated with diabetes.
Resistance to insulin-stimulated glucose uptake is present in the majority of patients with impaired glucose tolerance (IGT) or non-insulin-dependent diabetes mellitus (NIDDM) and in ∼25% of nonobese individuals with normal oral glucose tolerance. In these conditions, deterioration of glucose tolerance can only be prevented if the β-cell is able to increase its insulin secretory response and maintain a state of chronic hyperinsulinemia. When this goal cannot be achieved, gross decompensation of glucose homeostasis occurs. The relationship between insulin resistance, plasma insulin level, and glucose intolerance is mediated to a significant degree by changes in ambient plasma free-fatty acid (FFA) concentration. Patients with NIDDM are also resistant to insulin suppression of plasma FFA concentration, but plasma FFA concentrations can be reduced by relatively small increments in insulin concentration.Consequently, elevations of circulating plasma FFA concentration can be prevented if large amounts of insulin can be secreted. If hyperinsulinemia cannot be maintained, plasma FFA concentration will not be suppressed normally, and the resulting increase in plasma FFA concentration will lead to increased hepatic glucose production. Because these events take place in individuals who are quite resistant to insulinstimulated glucose uptake, it is apparent that even small increases in hepatic glucose production are likely to lead to significant fasting hyperglycemia under these conditions. Although hyperinsulinemia may prevent frank decompensation of glucose homeostasis in insulin-resistant individuals, this compensatory response of the endocrine pancreas is not without its price. Patients with hypertension, treated or untreated, are insulin resistant, hyperglycemic, and hyperinsulinemic. In addition, a direct relationship between plasma insulin concentration and blood pressure has been noted. Hypertension can also be produced in normal rats when they are fed a fructose-enriched diet, an intervention that also leads to the development of insulin resistance and hyperinsulinemia. The development of hypertension in normal rats by an experimental manipulation known to induce insulin resistance and hyperinsulinemia provides further support for the view that the relationship between the three variables may be a causal one. However, even if insulin resistance and hyperinsulinemia are not involved in the etiology of hypertension, it is likely that the increased risk of coronary artery disease (CAD) in patients with hypertension and the fact that this risk if not reduced with antihypertensive treatment are due to the clustering of risk factors for CAD, in addition to high blood pressure, associated with insulin resistance. These include hyperinsulinemia, IGT, increased plasma triglyceride concentration, and decreased high-density lipoprotein cholesterol concentration, all of which are associated with increased risk for CAD. It is likely that the same risk factors play a significant role in the genesis of CAD in the population as a whole. Based on these considerations the possibility is raised that resistance to insulin-stimulated glucose uptake and hyperinsulinemia are involved in the etiology and clinical course of three major related diseases— NIDDM, hypertension, and CAD.
In 1969, McCully made the clinical observation linking elevated plasma homocyst(e)ine concentrations with vascular disease.1 He reported autopsy evidence of extensive arterial thrombosis and atherosclerosis in two children with elevated plasma homocyst(e)ine concentrations and homocystinuria. On the basis of this observation, he proposed that elevated plasma homocyst(e)ine (hyperhomocyst(e)inemia) can cause atherosclerotic vascular disease. The term “homocyst(e)ine” is used to define the combined pool of homocysteine, homocystine, mixed disulfides involving homocysteine, and homocysteine thiolactone found in the plasma of patients with hyperhomocyst(e)inemia. Subsequent investigations have confirmed McCully's hypothesis, and it has recently become clear that hyperhomocyst(e)inemia is an independent risk factor . . .
Elevated plasma homocysteine enhances the risk of thrombosis and premature arteriosclerosis. We have assessed the activity of the 3 prime enzymes of homocysteine metabolism in cultured human venous endothelial cells, in a study of their possible protective roles. In cells from 4 individuals, cultured in Dulbecco's modified Eagle medium, the mean activity +/- S.D. of cystathionine beta-synthase (nmol of product/h per mg of cell protein, at 37 degrees C) was 3.58 +/- 3.11 at pH 8.6. The assay used was our newly developed amino acid analyser-based procedure. The activity of 5-methyltetrahydrofolate:homocysteine methyltransferase at pH 7.4 was 4.12 +/- 1.25 and betaine:homocysteine methyltransferase (BHMT) was undetectable (< 1.4 nmol/h per mg protein). Cells were also cultured in a medium aimed at stimulating methionine biosynthesis, containing methionine-deficient Dulbecco's modified Eagle medium to which L-homocystine (100 mumol/l) and methylcobalamin (1 mumol/l) had been added. In these cells 5-methyltetrahydrofolate:homocysteine methyltransferase activity increased to 7.95 +/- 1.45, P < 0.001, there was a non-significant decrease in cystathionine beta-synthase activity to 2.16 +/- 1.52 and BHMT activity was still undetectable. These cells were more resistant to in vitro homocysteine-induced detachment than were cells from the same line cultured in Dulbecco's modified Eagle medium alone. Our findings establish that human endothelial cells express 2 of the 3 primary enzymes of homocysteine catabolism. They suggest that persons who are deficient in cystathionine beta-synthase or 5-methyltetrahydrofolate:homocysteine methyltransferase activity may not only develop homocysteinemia, but also have vascular endothelium which is more susceptible to damage by homocysteine than persons with normal enzyme levels.
Publisher Summary Cystathionine β-synthase (L-serine hydro-lyase [adding homocysteine]) is a pyridoxal 5’-phosphate-dependent enzyme in the transsuifuration pathway of higher eukaryotes which catalyzes the condensation of serine and homocysteine to form cystathionine. This chapter describes a purification procedure starting with an "aged" liver homogenate in which synthase molecules have been converted to the smaller, more active, and more stable form. In assays of cystathionine β-synthase from extracts of cultured human skin fibroblasts, the following concentrations of reagents are used: lm M pyridoxal 5'-phosphate, up to 700 μg extract protein, 2.5 m M [ 14 C]serine (3,000 cpm/nmol), and 15 m M L-homocysteine. Incubations are at 37° for 4 hr. The rapid colorimetric assay is useful for monitoring purification. The enzyme is assayed under conditions identical to the radioisotopic assay except for omission of the 14 C label. The reaction is stopped by addition of 3.3 ml of ninhydrin reagent. The mixture is heated for 5 min in a boiling water bath and then cooled in an ice bath for 2 min. After 20 min at room temperature, the absorbance at 453 nm is determined, and the enzyme-free blank is subtracted. The amount of cystathionine formed is determined relative to a standard reaction containing 0.5 μmol of L-cystathionine, without enzyme.
The ability of insulin to stimulate glucose uptake can vary substantially in non-obese individuals with no apparent disease (10). In addition, differences in either degree of obesity or level of habitual physical activity can also modulate in vivo insulin action (18,24). In an apparent attempt to maintain glucose homeostasis, the compensatory response to a decrease in insulin-stimulated glucose up take is an increase in plasma insulin concentration. A defect in the ability of insulin-stimulated glucose uptake has also been demonstrated (21) in patients with either impaired glucose tolerance (IGT) or non-insulin dependent diabetes mellitus (NIDDM). It has been suggested that the degree to which glucose tolerance deteriorates in these individuals is a function of the level of compensatory hyperinsulinemia that they can maintain, and the appearance of severe fasting hyperglycemia marks the failure of the pancreatic beta cell to sustain the necessary increase in insulin secretory response (21).
Premature arteriosclerosis and thromboembolic events are well-known complications of homozygous homocystinuria due to cystathionine synthase deficiency. It is unknown whether heterozygosity for homocystinuria predisposes to premature vascular disease. We explored the frequency of excessive homocysteine accumulation after standardized methionine loading in 75 patients presenting with clinical signs of ischemic disease before the age of 50:25 with occlusive peripheral arterial disease, 25 with occlusive cerebrovascular disease, and 25 with myocardial infarction. In seven patients in each of the first two groups but in none of the patients in the third group, heterozygosity for homocystinuria was established on the basis of pathological homocysteinemia after methionine loading and cystathionine synthase deficiency in skin fibroblast cultures. Because the frequency of heterozygosity for homocystinuria in the normal population is 1 in 70 at the most, we conclude that this condition predisposes to the development of premature occlusive arterial disease, causing intermittent claudication, renovascular hypertension, and ischemic cerebrovascular disease.
A new type of homocystinuria is described. A variety of evidence indicates that patients with this type of homocystinuria are not deficient in cystathionine synthase activity. Fibroblasts from these patients were unable to grow as rapidly as control fibroblasts if homocystine replaced methionine in the culture medium. N5-Methyltetrahydrofolate-homocysteine methyltransferase activity in these cells was not markedly decreased, whereas methylenetetrahydrofolate reductase activity was significantly below normal. A deficiency of this reductase activity can explain the biochemical abnormalities in these patients.
Homocysteine is a thiol‐containing amino acid resulting from demethylation of methionine. The free and protein‐bound forms of the amino acid derived disulfides are called homocyst(e)ine [H(e)]. Multiple studies have shown elevated H(e) levels in patients with coronary, cerebrovascular, or peripheral arterial diseases; this association is frequent and independent of most other risk factors for atherosclerosis. In the 1993 Frontiers in Medicine Symposium* investigators discussed the genetic, physiological, nutritional, and pharmacological mechanisms involved in the regulation of plasma H(e), the association of H(e) with arterial occlusive diseases, and the relationships of H(e) with nitric oxide and haemostasis.
High plasma H(e) levels usually can be reversed with vitamin supplements. Whether vitamin supplements will affect the evolution of arterial occlusive diseases needs to be established in prospective, placebo‐controlled, randomized, clinical trials.
Hyperinsulinemia, hypertension, hypertriglyceridemia and obesity are all risk factors for atherosclerosis. The clustering of these risk factors in the same individual greatly increases the risk for atherosclerosis and has been termed 'Syndrome X' or 'The Deadly Quartet' The purpose of the present study was to investigate the effects of diet on these risk factors in inbred, female Fischer 344 rats. Animals were raised on ad lib diets consisting of high-fat, sucrose (HFS) or low-fat, complex-carbohydrate (LFCC). After 2 years, the HFS rats were obese (38% +/- 1% vs. 15% +/- 1% body fat), hypertensive (140 +/- 3 vs. 123 +/- 3 mmHg), hyperinsulinemic (439 +/- 118 vs. 98 +/- 10 pmol/l), and hypertriglyceridemic (1.1 +/- 0.2 vs. 0.4 +/- 0.07 mmol/l). The HFS rats also exhibited enhanced clotting and impaired fibrinolytic response to streptokinase. All these differences between the two groups were statistically significant (P < 0.05). Insulin was significantly correlated with body weight (r = 0.71), triglycerides (r = 0.48), and systolic blood pressure (r = 0.70). Total cholesterol was slightly, but not significantly higher, in the HFS group (2.8 +/- 0.3 vs 2.2 +/- 0.1 mmol/l) while HDL-cholesterol was unchanged. These results show that many risk factors for atherosclerosis can be induced in inbred rats by feeding a HFS diet. Aggregation of risk factors was found in the HFS group but not in the LFCC group. In fact, most of the rats on the LFCC diet developed no risk factors after 2 years, indicating that the development of risk factors is not an aging phenomenon.
In the setting of an outpatient diabetic clinic, we determined whether macrovascular disease in patients with diabetes mellitus is associated with hyperhomocysteinemia (elevated plasma homocysteine [H(e)] concentrations) following a methionine load. Methionine-load tests were performed in 18 healthy controls, 11 diabetics without vascular disease (five insulin-dependent [IDDM] and six non-insulin-dependent [NIDDM]); and 17 diabetics with vascular disease (five IDDM and 12 NIDDM). All subjects were male, and there was no significant difference in mean age among the three groups. We measured plasma H(e) concentrations before and 2, 4, 6, 8, and 24 hours after an oral methionine load. Hyperhomocysteinemia (peak plasma H(e) concentration > control mean +/- 2 SD) occurred with significantly greater frequency (seven of 18, 39%) in patients with NIDDM as compared with age-matched controls (7%), being more common in those with macrovascular disease (five of 12, 41%). The area under the curve (AUC) over 24 hours, reflecting the total period of exposure to H(e), was also elevated with greater frequency in patients with NIDDM and macrovascular disease (33%) as compared with controls (0%). We conclude that hyperhomocysteinemia is associated with macrovascular disease in a significant proportion of patients with NIDDM. Further investigation of this association may determine whether hyperhomocysteinemia contributes to the increased frequency and accelerated clinical course of vascular disease in patients with diabetes mellitus.
Results of basal plasma homocyst(e)ine concentrations in patients reported in the literature are reviewed, with emphasis on the series of subjects analyzed by the author. Findings support the hypothesis that plasma homocyst(e)ine is a risk factor for coronary, cerebral and peripheral arterial occlusive diseases, as well as for carotid thickening. Results of four studies show that heritability influences plasma homocyst(e)ine. Moreover, data suggest that a graded risk for atherothrombotic disease is distributed across the entire distribution of plasma homocyst(e)ine levels. Elevated levels of homocyst(e)ine can be decreased effectively by supplementary folate, occasionally requiring the addition of vitamin B-12, vitamin B-6, choline or betaine. Consequently, it is important that placebo-controlled clinical trials be conducted to determine whether the clinical evolution of arterial occlusive diseases is influenced by those supplements.
Fasting plasma total homocysteine (tHcy) concentration was measured in 380 men and 204 women selected for health on the basis of clinical history, physical examination, and normal results of a biochemical profile. We sought to define tHcy reference values in healthy individuals and to determine relations between tHcy and plasma folic acid, vitamin B-12, and pyridoxal phosphate (vitamin B-6) concentrations. Men had significantly higher plasma tHcy than women (9.7 +/- 4.9 compared with 7.6 +/- 4.1 mumol/L, x +/- SD) and lower folate concentrations (8.6 +/- 5.2 compared with 9.8 +/- 6.6 nmol/L, P < 0.05). Significant correlations were found between tHcy and uric acid, creatinine, albumin, folate, and vitamin B-12 concentrations. There was no correlation with age, body mass index, blood pressure, glucose, and total and lipoprotein lipids. When divided in quartiles of vitamin concentrations, subjects with the lowest vitamin B-12 and folate values had significantly higher tHcy concentrations than those in the other three quartiles. Interestingly, after exclusion of subjects in the lowest quartiles of folate and vitamin B-12 concentration, correlations between tHcy and vitamin concentrations were no longer observed, except for vitamin B-12 in men. Stepwise-multiple-regression analyses showed that the sex-specific influence of biological variables on tHcy concentrations was twice as important in healthy women than in healthy men. This study emphasizes the significance of sex-associated differences in the biology of homocysteine and underlines the importance of considering these in the determination of threshold values.
Homocysteine is an important contributing factor to thrombosis, vascular injury, and vascular disease. Mechanisms for homocysteine-induced vascular disease include alterations in coagulation as well as endothelial cell and vessel wall injury. Hyperhomocysteinemia (HH[e]) can occur when homocysteine metabolism is altered by mutations in enzymes responsible for homocysteine metabolism. Characterization of these mutations identifies patient groups at risk for vascular disease. Treatment of HH(e) consists of vitamins and raises the possibility that some forms of vascular disease may be easily, safely, and inexpensively treated.
Most patients with diabetes die from macrovascular complications. Little is known about the pathogenesis of diabetic vascular disease, but recent advances in molecular genetics and oxidation chemistry provide clues to the mystery of diabetes and atherosclerosis. Genetic variants of well-known proteins such as lipoprotein lipase and apolipoprotein E are common. These proteins are suitable candidates for mediating diabetic vascular risk because their variants can produce hypertriglyceridemia, a risk factor for atherosclerosis in diabetes. However, mutations could have different effects on lipoprotein flux across arteries depending on whether expression is dominant in the vascular space or the vascular wall. Lipoproteins retained in the arterial wall are subject to oxidative modification, which could be dependent on glycoxidation, the enzyme myeloperoxidase, or reactive nitrogen species derived from nitric oxide. Accelerated vascular disease in diabetes is likely the result of complex interactions between metabolic derangements such as hyperglycemia, mutations in genes controlling lipid metabolism, and antioxidant defense mechanisms.
A high serum total homocysteine (tHcy) level is an independent risk factor for cardiovascular disease. Because it is not known whether the strength of the association between hyperhomocysteinemia and cardiovascular disease is similar for peripheral arterial, coronary artery, and cerebrovascular disease, we compared the three separate risk estimates in an age-, sex-, and glucose tolerance-stratified random sample (n=631) from a 50- to 75-year-old general white population. Furthermore, we investigated the combined effect of hyperhomocysteinemia and diabetes mellitus with regard to cardiovascular disease. The prevalence of fasting hyperhomocysteinemia (>14.0 micromol/L) was 25.8%. After adjustment for age, sex, hypertension, hypercholesterolemia, diabetes, and smoking, the odds ratios (ORs; 95% confidence intervals) per 5-micromol/L increment in tHcy were 1.44 (1.10 to 1.87) for peripheral arterial, 1.25 (1.03 to 1.51) for coronary artery, 1.24 (0.97 to 1.58) for cerebrovascular, and 1.39 (1.15 to 1.68) for any cardiovascular disease. After stratification by glucose tolerance category and adjustment for the classic risk factors and serum creatinine, the ORs per 5-micromol/L increment in tHcy for any cardiovascular disease were 1.38 (1.03 to 1.85) in normal glucose tolerance, 1.55 (1.01 to 2.38) in impaired glucose tolerance, and 2.33 (1.11 to 4.90) in non-insulin-dependent diabetes mellitus (P=.07 for interaction). We conclude that the magnitude of the association between hyperhomocysteinemia and cardiovascular disease is similar for peripheral arterial, coronary artery, and cerebrovascular disease in a 50- to 75-year-old general population. High serum tHcy may be a stronger (1.6-fold) risk factor for cardiovascular disease in subjects with non-insulin-dependent diabetes mellitus than in nondiabetic subjects.
An association between hyperhomocysteinemia and premature atherosclerosis in patients with non-insulin-dependent diabetes mellitus (NIDDM) has recently been described. Little is known about the role of insulin in homocysteine [H(e)] metabolism. We measured plasma H(e) concentrations in the fasting state and during a hyperinsulinemic-euglycemic clamp in normal subjects and patients with NIDDM. Plasma H(e) decreased significantly from 7.2 +/- 2.6 to 6.0 +/- 2.7 mmol/L (P < .01) in normal subjects, but did not change in patients with NIDDM (6.0 +/- 2.7 to 5.9 +/- 2.5 mmol/L, respectively). These data suggest that plasma H(e) concentrations are regulated by acute hyperinsulinemia in normal subjects, but not in insulin-resistant NIDDM subjects. These abnormalities may have implications for the pathogenesis of premature vascular disease associated with NIDDM.
Epidemiological studies performed over the past 40 years have shown that the prevalence of diagnosed diabetes has increased dramatically in the U.S. and that a substantial proportion of the population has undiagnosed diabetes, impaired fasting glucose, and impaired glucose tolerance. Diabetes is most prevalent in minority populations, such as African-Americans, Native Americans, and Mexican Americans. Increasing prevalence of diabetes has led to increases in microvascular complications such as blindness, end-stage renal disease, and lower limb amputations. Poor glycemic control contributes to the high incidence of these complications, yet community-based studies of diabetic patients show their mean fasting plasma glucose concentration is generally > 180 mg/dl compared with 100 mg/dl for nondiabetic individuals. In people with diabetes, risk factors for cardiovascular disease including elevated fasting plasma glucose, blood pressure, total cholesterol, triglycerides, and obesity partly explain the high proportion of deaths (60-70%) caused by cardiovascular disease in people with diabetes. More intensive diabetes management and improved glycemic control could minimize long-term complications of the disease and would be expected to reduce the morbidity, mortality, and costs associated with diabetes.
The plasma concentrations of total homocysteine (tHcy) and total cysteine (tCys) are determined by intracellular metabolism and by renal plasma clearance, and we hypothesized that glomerular filtration is a major determinant of plasma tHcy and tCys. We studied the relationships between the glomerular filtration rate (GFR) and plasma tHcy and tCys in populations of diabetic patients with particularly wide ranges of GFR.
We measured GFR, urine albumin excretion rate (UAER), plasma tHcy, tCys, methionine, vitamin B12, folate, C-peptide, and routine parameters in 50 insulin-dependent diabetes mellitus (IDDM) and 30 non-insulin-dependent diabetes mellitus (NIDDM) patients. All patients underwent intensive insulin treatment and had a serum creatinine concentration below 115 micromol/liter.
Mean plasma tHcy in diabetic patients (0.1 micromol/liter) was lower than in normal persons (11.1 micromol/liter, P = 0.0014). Mean plasma tCys in diabetic patients (266.1 micromol/liter) was also lower than in normal persons (281.9 micromol/liter, P = 0.0005). Seventy-three percent of the diabetic patients had relative hyperfiltration. Plasma tHcy and tCys were closely and independently associated with GFR, serum folate, and serum B12. However, plasma tHcy was not independently associated with any of the 22 other variables tested, including age, serum creatinine concentration, UAER, total daily insulin dose, and glycemic control.
Glomerular filtration rate is an independent determinant of plasma tHcy and tCys concentrations, and GFR is rate limiting for renal clearance of both homocysteine and cysteine in diabetic patients without overt nephropathy. Declining GFR explains the age-related increase in plasma tHcy, and hyperfiltration explains the lower than normal mean plasma tHcy and tCys concentrations in populations of diabetic patients.
Elevated plasma total homocysteine is an independent risk factor for atherosclerotic vascular disease. Risk rises continuously across the spectrum of homocysteine concentrations and may become appreciable at levels greater than 10 mumol/l. A compelling case can be made for screening all individuals with atherosclerotic disease or at high risk. A reasonable, but unproven, goal for treatment is a plasma total homocysteine concentration less than 10 mumol/l. Folic acid is the mainstay of treatment, but vitamins B12 and B6 may have added benefit in selected patients. The results of ongoing randomized placebo-controlled trials will not be available for several years, but will help determine whether homocysteine lowering reduces the risk of cardiovascular disease.
Hyperhomocysteinemia as well as insulin resistance are considered to be risk factors for the development of coronary artery disease. This study was aimed at determining whether any relationship between plasma insulin and glucose levels and total plasma homocysteine (tHcy) concentrations exists in a population based survey performed 10 years apart.
A cross-sectional study was undertaken during the years 1986-87 to examine risk factors for diabetes and for coronary artery disease (CAD) in the Jewish population of Jerusalem. Ten years later two groups of individuals were invited for re-examination.
Two groups of individuals were examined: the first one consisted of nondiabetic subjects (n = 86), who had hyperinsulinemia 10 years previously (at the first visit), the second group consisted of normoinsulinemic nondiabetic individuals (n = 265) who had initially normal glucose and insulin levels.
Metabolic, biochemical and anthropomorphic features were determined. Fasting and post load glucose, as well as insulin concentrations on fasting and 2 h post glucose load were measured at the first and second visits. Plasma tHcy and folic acid were determined only at the second visit.
The results demonstrated a significant negative correlation between plasma tHcy levels and insulin levels at the second visit. No difference was found in folic acid levels between these two groups.
In general, hyperinsulinemia and hyperhomocysteinemia are both related to an increased incidence of CAD. In our population most of the subjects examined had tHcy levels within the normal range and only a few demonstrated very high levels. However, negative association between insulin levels and tHcy concentrations was found. Possible explanations for this finding are discussed.
Hyperhomocysteinemia (HH) and hyperinsulinemia are both risk factors for cardiovascular disease. To examine the effects of hyperinsulinemia on homocysteine metabolism, we fed rats a high-fat-sucrose (HFS) diet and then measured the hepatic mRNA and activity of 2 key enzymes involved in this metabolic pathway: 5,10-methylenetetrahydrofolate reductase (MTHFR) and cystathionine-beta-synthase (CbetaS). Fischer rats made insulin-resistant by a HFS diet were examined at 6 months and 2 years of age and compared with control rats fed a low-fat, complex-carbohydrate (LFCC) diet. At the end of 6 months, the HFS rats were heavier than the LFCC rats (214 +/- 3.4 v 188 +/- 1.4 g, P < .01). There were no differences in blood glucose between HFS and LFCC rats; however, plasma insulin and homocysteine concentrations were elevated in HFS rats (insulin, 56 +/- 12 v 14.5 +/- 2.9 microU/mL; homocysteine, 10.77 +/- 0.9 v 6.89 +/- 0.34 micromol/L, P < .01). Hepatic CbetaS enzyme activity was significantly lower in HFS compared with LFCC rats (0.45 v 0.64 U/mg, P = .0001), and this decrease was reflected in a decrease of the CbetaS mRNA concentration. In contrast, hepatic MTHFR enzyme activity and mRNA concentration were significantly elevated in the HFS group compared with controls (HFS and LFCC, 8.62 and 4.8 nmol/h/mg protein, respectively, P = .0001). These changes in plasma homocysteine, CbetaS, and MTHFR were significantly correlated with the degree of obesity and hyperinsulinemia. Fasting plasma insulin correlated significantly and positively with plasma homocysteine (r = .51, P < .01) and MTHFR activity (r = .48, P < .01) and negatively with CbetaS activity (r = -.54, P < .001). CbetaS and MTHFR activities were inversely correlated with each other (r = -.58, P < .001). In conclusion, rats fed a HFS diet are hyperinsulinemic, and the hyperinsulinemia is associated with an elevated homocysteine concentration and changes in 2 key enzymes in homocysteine metabolism.
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