Relationship between total plasma homocysteine, polymorphisms of homocysteine metabolism related enzymes, risk factors and coronary artery disease in the Australian hospital-based population

The association between homocysteine and ischemic stroke subtypes in Chinese: A meta-analysis

BACKGROUND

The findings on the association between elevated plasma homocysteine levels and the risk of the trial of org 10172 in acute stroke treatment (TOAST) of ischemic stroke have been inconsistent in Chinese. So far, there is no meta-analysis about the association between Hcy and the TOAST subtypes of ischemic stroke in Chinese. This study; therefore, aimed to evaluate whether elevated homocysteine levels are associated with the TOAST subtypes of ischemic stroke using a meta-analysis.

MATERIALS AND METHODS

A systematic search of electronic databases were conducted for studies reporting homocysteine levels in ischemic stroke and the TOAST of ischemic stroke to April 18, 2018. The data were extracted after the application of inclusion and exclusion criteria. All the data were analyzed using Stata software version 9.0 (Stata Corp LP, College Station, TX). The standardized mean difference (SMD) and 95% confidence interval (CI) were used to compare continuous variables.

RESULTS

Thirteen studies comprising 3114 participants (2243 patients and 871controls) met the eligibility criteria and were included in the meta-analysis. The meta-analysis revealed that the ischemic stroke group had significantly higher levels of homocysteine than controls (SMD = 1.15, 95% CI = 0.85-1.45, P < .05). The subgroup analyses suggested that the groups of patients with large-artery atherosclerosis, small-vessel occlusion, cardioembolism, stroke of other determined etiology and stroke of undetermined etiology had significantly higher levels of homocysteine compared to those in the control group (large-artery atherosclerosis: SMD = 2.12, 95% CI = 1.40-2.84, P < .05; small-vessel occlusion: SMD = 1.10, 95% CI = 0.72-1.48, P < .05; CE: SMD = 1.17, 95% CI = 0.64-1.71, P < .05; stroke of other determined etiology: SMD = 0.88, 95% CI = 0.53-1.24, P < .05; stroke of undetermined etiology: SMD = 1.50, 95% CI = 0.66-2.33, P < .05, respectively).

CONCLUSION

This meta-analysis found that ischemic stroke patients and the TOAST of ischemic stroke patients in Chinese had significantly higher homocysteine levels than the controls, suggesting that serum homocysteine levels may be a risk factor for ischemic stroke and the TOAST subtypes of ischemic stroke in Chinese.

50 bp deletion in promoter superoxide dismutase 1 gene and increasing risk of cardiovascular disease in Mashhad stroke and heart atherosclerotic disorder cohort study

Cardiovascular disease (CVD), one of the main mortality causes worldwide is considered to be affected by general oxidative stress and inadequacy antioxidant system. Superoxide dismutase 1 (SOD1), a cytosolic antioxidant enzyme has a key role in neutralizing the excessive prooxidant by scavenging the super oxide anions. SOD1 polymorphic variants exhibit the altered activity properties. In the current study, we are aimed to investigate the association between the SOD1 polymorphism and CVD prevalence. A 6-years case control follow up study was designed to genotype the 526 participants (311 controls and 215 cases) for studying the 50 bp INS/DEL polymorphism at SOD1 promoter gene and analyze their blood lipid profile and anthropometric characteristics. Among the two possible alleles of the SOD1 gene (Wild [W] and Mutant [M]) the meaningful association was detected between the Mutants' frequency and the prevalence of CVD patients (p-value <.001). The W and M allele refer to inserted and deleted 50 bp in the polymorphic site of the SOD1 promoter, respectively. The WM and MM genotypes' frequency which indicate the wild heterozygotes and Mutant homozygotes, respectively, were significantly correlated with the prevalence of cardiovascular disease (p-value <.001). The present study has the potential to introduce the 50 bp INS/DEL polymorphism of SOD1 genotyping as a novel unique diagnostic approach for screening the high risk CVD.

Potential Links between Impaired One-Carbon Metabolism Due to Polymorphisms, Inadequate B-Vitamin Status, and the Development of Alzheimer's Disease

Alzheimer's disease (AD) is the major cause of dementia and no preventive or effective treatment has been established to date. The etiology of AD is poorly understood, but genetic and environmental factors seem to play a role in its onset and progression. In particular, factors affecting the one-carbon metabolism (OCM) are thought to be important and elevated homocysteine (Hcy) levels, indicating impaired OCM, have been associated with AD. We aimed at evaluating the role of polymorphisms of key OCM enzymes in the etiology of AD, particularly when intakes of relevant B-vitamins are inadequate. Our review indicates that a range of compensatory mechanisms exist to maintain a metabolic balance. However, these become overwhelmed if the activity of more than one enzyme is reduced due to genetic factors or insufficient folate, riboflavin, vitamin B6 and/or vitamin B12 levels. Consequences include increased Hcy levels and reduced capacity to synthetize, methylate and repair DNA, and/or modulated neurotransmission. This seems to favor the development of hallmarks of AD particularly when combined with increased oxidative stress e.g., in apolipoprotein E (ApoE) ε4 carriers. However, as these effects can be compensated at least partially by adequate intakes of B-vitamins, achieving optimal B-vitamin status for the general population should be a public health priority.

Protective effect of quercetin on homocysteine-induced oxidative stress

OBJECTIVE

The aim of this study was to evaluate whether quercetin (QUER) treatment could have a protective effect against oxidative stress induced by homocysteinemia in rats.

MATERIALS AND METHODS

Thirty-two male Sprague-Dawley rats (adult) were assigned randomly to four groups: the control group was given physiological saline (PS; 1.5 mL/d); the QUER group was given QUER (50 mg/kg body weight [BW] daily) in distilled water and 0.25 mL PS; the homocysteine (HCY) group was given HCY (1 mg/kg BW daily) in distilled water and 1.25 mL PS; and the QUER + HCY group was given QUER 1 h before the administration of HCY. QUER, HCY, and PS were injected intraperitoneally every other day for 30 d. Plasma malondialdehyde (MDA), carbonyl, erythrocyte-reduced glutathione (GSH), plasma sulphydril (-SH) levels, erythrocyte catalase (CAT), and superoxide dismutase (SOD) activities were determined.

RESULTS

Plasma CAT levels in the QUER group were found to be significantly higher than in the control group, whereas plasma MDA levels in the QUER group significantly decreased compared with the control group. In the HCY group, plasma MDA and carbonyl levels significantly increased and GSH and SOD levels significantly decreased compared with the control group. Plasma MDA levels significantly decreased and GSH and CAT levels significantly increased in the QUER + HCY group compared with the HCY group. Plasma -SH levels were significantly lower in the HCY group than in the control group. Plasma -SH levels were higher in the QUER + HCY group than in the HCY group, but they were not significant.

CONCLUSION

The exposure of rats to HCY leads to oxidative stress reflected in increased MDA and decreased antioxidant enzyme levels. Administration of QUER might attenuate oxidative damage induced by HCY or have a protective effect against it.

A Fast Multiple-Kernel Method With Applications to Detect Gene-Environment Interaction

Kernel machine (KM) models are a powerful tool for exploring associations between sets of genetic variants and complex traits. Although most KM methods use a single kernel function to assess the marginal effect of a variable set, KM analyses involving multiple kernels have become increasingly popular. Multikernel analysis allows researchers to study more complex problems, such as assessing gene-gene or gene-environment interactions, incorporating variance-component based methods for population substructure into rare-variant association testing, and assessing the conditional effects of a variable set adjusting for other variable sets. The KM framework is robust, powerful, and provides efficient dimension reduction for multifactor analyses, but requires the estimation of high dimensional nuisance parameters. Traditional estimation techniques, including regularization and the "expectation-maximization (EM)" algorithm, have a large computational cost and are not scalable to large sample sizes needed for rare variant analysis. Therefore, under the context of gene-environment interaction, we propose a computationally efficient and statistically rigorous "fastKM" algorithm for multikernel analysis that is based on a low-rank approximation to the nuisance effect kernel matrices. Our algorithm is applicable to various trait types (e.g., continuous, binary, and survival traits) and can be implemented using any existing single-kernel analysis software. Through extensive simulation studies, we show that our algorithm has similar performance to an EM-based KM approach for quantitative traits while running much faster. We also apply our method to the Vitamin Intervention for Stroke Prevention (VISP) clinical trial, examining gene-by-vitamin effects on recurrent stroke risk and gene-by-age effects on change in homocysteine level.

Association between the methionine synthase A2756G polymorphism and neural tube defect risk: a meta-analysis

Many studies have accessed the association between methionine synthase (MTR) A2756G polymorphism and neural tube defect (NTD). However, the conclusions are inconsistent. Our study aimed to clarify the nature of the genetic risks contributed by this polymorphism for NTD using meta-analysis. We searched electronic literature from the PubMed, EMBASE, and Medline databases, from which 10 articles were selected according to the inclusion criteria. The meta-analysis was conducted in 3 groups, namely, NTD patients, mothers with NTD offspring and fathers with NTD offspring. Pooled odds ratios (ORs) and 95% confidence intervals were used to evaluate the strength of the association and the result was corrected by multiple testing. To sum up, no associations between the MTR A2756G polymorphism and NTD risk were found among the 3 groups in all genetic models. However, as their sample size is not large enough, this result needs further research.

Methyl deficient diet aggravates experimental colitis in rats

Inflammatory bowel diseases (IBD) result from complex interactions between environmental and genetic factors. Low blood levels of vitamin B12 and folate and genetic variants of related target enzymes are associated with IBD risk, in population studies. To investigate the underlying mechanisms, we evaluated the effects of a methyl-deficient diet (MDD, folate, vitamin B12 and choline) in an experimental model of colitis induced by dextran sodium sulphate (DSS), in rat pups from dams subjected to the MDD during gestation and lactation. Four groups were considered (n= 12–16 per group): C DSS⁻ (control/DSS⁻), D DSS⁻ (deficient/DSS⁻), C DSS⁺ (control/DSS⁺) and D DSS⁺ (deficient/DSS⁺). Changes in apoptosis, oxidant stress and pro-inflammatory pathways were studied within colonic mucosa. In rat pups, the MDD produced a decreased plasma concentration of vitamin B12 and folate and an increased homocysteine (7.8 ± 0.9 versus 22.6 ± 1.2 μmol/l, P < 0.001). The DSS-induced colitis was dramatically more severe in the D DSS⁺ group compared with each other group, with no change in superoxide dismutase and glutathione peroxidase activity, but decreased expression of caspase-3 and Bax, and increased Bcl-2 levels. The mRNA levels of tumour necrosis factor (TNF)-α and protein levels of p38, cytosolic phospolipase A2 and cyclooxygenase 2 were significantly increased in the D DSS⁺ pups and were accompanied by a decrease in the protein level of tissue inhibitor of metalloproteinases (TIMP)3, a negative regulator of TNF-α. MDD may cause an overexpression of pro-inflammatory pathways, indicating an aggravating effect of folate and/or vitamin B12 deficiency in experimental IBD. These findings suggest paying attention to vitamin B12 and folate deficits, frequently reported in IBD patients.

Methionine synthase polymorphisms (MTR 2756 A>G and MTR 2758 C>G) frequencies and distribution in the Jordanian population and their correlation with neural tube defects in the population of the northern part of Jordan

BACKGROUND

The human methionine synthase gene (MTR) is located on chromosome 1q43; it is of 105.24 kb and is made up of 33 exons. Methionine synthase is a cytoplasmic enzyme that requires methylcobalamin for activity and catalyzes the remethylation of homocysteine to methionine. In this reaction, the methyl group of 5-methyltetrahydrofolate is transferred to the enzyme bond cob(I) alamin to generate methylcobalamin, followed by the transfer of the methyl group to homocysteine to reform methionine.

MATERIALS AND METHODS

The frequencies of the polymorphisms of MTR 2756A>G and MTR 2758C>G have been determined in this study in a sample of 491 individuals collected from all regions of Jordan and representing the Jordanian population. The different alleles and genotypes at the two polymorphic sites were identified using the Polymerase Chain Reaction - Restriction Fragment Length Polymorphism (PCR-RFLP) analysis.

RESULTS

Showed that the percentages of the polymorphic alleles at the MTR 2756 position in the north, middle and south regions were 90.38, 92.65 and 83.69%, respectively, for the MTR 2756A allele, and were 9.61, 7.34 and 16.30%, respectively, for the MTR 2756G allele, with overall percentages in the whole Jordanian population of 90.73 and 9.27% for the MTR 2756A and MTR 2756G alleles, respectively. The percentages of the genotype MTR 2756AA were 82.90% in the northern region, 86.72% in the middle region and 71.73% in the southern region, and an overall percentage of MTR 2756AA in the whole Jordanian population was 83.50%. The frequencies of MTR 2756AG genotype in the northern, middle and southern regions were 14.95, 11.84 and 23.91%, respectively, with an overall percentage of 14.46% in the whole Jordanian population. The percentages of the genotype MTR 2756GG in the northern, middle and southern regions were 2.13, 1.42 and 4.34%, respectively, with an overall percentage of 2.04% in the whole Jordanian population. Only the wild type allele (C) of the MTR 2758C>G polymorphism was detected in this study. In addition, the association of MTR 2756A>G and MTR 2758C>G polymorphisms with the development of neural tube defects (NTDs) was examined using 17 cases of mothers from the northern part of Jordan, who gave birth to NTD affected children during the period of this study. Results showed no association between these two examined polymorphisms and the increase in maternal risk for giving birth to NTD children.

CONCLUSION

results of this study recommend that examination should be done on larger populations to arrive at better conclusions. Also, more studies on gene-gene interaction should be done to examine the associations with NTDs.

Association of homocysteine and methylene tetrahydrofolate reductase (MTHFR C677T) gene polymorphism with coronary artery disease (CAD) in the population of North India

The implications of the methylene tetrahydrofolate reductase (MTHFR) gene and the level of homocysteine in the pathogenesis of coronary artery disease (CAD) have been extensively studied in various ethnic groups. Our aim was to discover the association of MTHFR (C677T) polymorphism and homocysteine level with CAD in north Indian subjects. The study group consisted of 329 angiographically proven CAD patients, and 331 age and sex matched healthy individuals as controls. MTHFR (C677T) gene polymorphism was detected based on the polymerase chain reaction and restriction digestion with HinfI. Total homocysteine plasma concentration was measured using immunoassay. T allele frequency was found to be significantly higher in patients than in the control group. We found significantly elevated levels of mean homocysteine in the patient group when compared to the control group (p = 0.00). Traditional risk factors such as diabetes, hypertension, smoking habits, a positive family history and lipid profiles (triglyceride, total cholesterol, HDL-cholesterol, LDL-cholesterol, VLDL-cholesterol), were found significantly associated through univariate analysis. Furthermore, multivariable logistics regression analysis revealed that CAD is significantly and variably associated with diabetes, hypertension, smoking, triglycerides and HDL-cholesterol. Our findings showed that MTHFR C677T polymorphism and homocysteine levels were associated with coronary artery disease in the selected population.

Polymorphism of genes encoding homocysteine metabolism-related enzymes and risk for cardiovascular disease

The aim of this review is to present a general overview of the relationships among homocysteine metabolism, polymorphism of the genes encoding homocysteine metabolism-related enzymes, and the nutrients influencing the plasma homocysteine level. Combining these factors creates a profile of an individual's susceptibility to complex diseases associated with hyperhomocysteinemia. Homocysteine is an amino acid derived from the demethylation of methionine. Hyperhomocysteinemia is associated with an increased risk of several complex diseases, including cardiovascular diseases. The level of plasma homocysteine depends on the combined effects of genetic and environmental factors. Polymorphisms of genes encoding homocysteine metabolism-related enzymes, such as methylenetetrahydrofolate reductase, methionine synthase, methionine synthase reductase, and cystathionine beta-synthase, influence plasma homocysteine concentration and thereby cardiovascular health. On the other hand, homocysteine metabolism may be modulated by dietary intake of the nutrients involved in homocysteine metabolism (ie, folates, vitamin B(6), and vitamin B(12)). Thus, the appropriate health-promoting doses of these nutrients may vary among certain groups of individuals, depending on their genotypes and other risk factors for complex diseases. Better understanding of the relationship between genotype and nutrition influencing the plasma total homocysteine level and cardiovascular health may improve the cardiovascular diagnostic tests (ie, measurement of biologic markers). It could be possible to define the level of progression, severity, and susceptibility to disease much earlier than it is done now. In conclusion, the introduction of combined dietary and pharmacologic treatment would be possible at the initial stages of disease.

The 844ins68 polymorphism of the cystathionine beta-synthase gene is associated with schizophrenia

A subtle genetic defect in homocysteine metabolism is thought to play an etiologic role in schizophrenia. Cystathionine-beta-synthase (CBS) is a key enzyme related to homocysteine levels. The aim of the present study was to search for association between the 844ins68 polymorphism of the CBS gene and schizophrenia in a large Russian sample using case-control and family-based designs. The sample comprised 1135 patients, 626 controls and 172 families. There was a trend for association between the 844ins68 polymorphism and schizophrenia in the case-control study, with higher frequency of the insertion in the control group. The FBAT revealed a statistically significant difference in transmission of alleles from parents to the affected proband, with preferential transmission of the variant without insertion. When the sample of patients was stratified by sex and forms of schizophrenia, the significantly lower frequency of insertion was observed in the group of female patients with chronic schizophrenia (n=180) as compared to psychiatrically well women. The insertion variant has been reported earlier to be related to decreased levels of homocysteine and thus thought to play a protective role. In conclusion, our study revealed a possible relation of the CBS 844ins68 polymorphism to schizophrenia.

Association between the 2756A> G variant in the gene encoding methionine synthase and myocardial infarction in Tunisian patients

BACKGROUND

Elevated plasma total homocysteine (tHcy), a risk factor for coronary artery disease (CAD), is due to defects in genes encoding for enzymes involved in tHcy metabolism or from inadequate status of vitamins involved in tHcy disposal. Methionine synthase (MS), a vitamin B(12)-dependent enzyme, catalyses the remethylation of homocysteine to methionine using a methyl group donated by 5-methyltetra-hydrofolate, which is the major circulating form of folate in the body. Functional genetic variants of the MS may alter tHcy as well as folate levels which are independent risk factors for CAD. The influence of a common genetic polymorphism 2756A>G of the MS gene (MTR) on plasma tHcy, folate and vitamin B(12) levels and its relation to the risk of myocardial infarction (MI) in a Tunisian case-control study was investigated.

METHODS

A total of 321 Tunisian patients with MI and 343 healthy controls were included in the study. The 2756A>G variant of the MTR was determined by polymerase chain reaction-restriction fragment length polymorphism analysis. Plasma tHcy was assessed with a fluorescent polarising immunoassay method. Plasma vitamin B(12) and folate were determined by microparticular enzyme immunoassay and ion-capture, respectively.

RESULTS

A significant difference in genotype distribution and allele frequency was observed between patients and controls. Patients with MI had a frequency of 1.9% for the GG genotype, 26.2% for the AG genotype and 72% for the AA genotype. Controls had a frequency of only 0.9% for the GG genotype, 18.7% for the AG genotype and 80.5% for the AA genotype (chi(2)=6.97, p=0.03). The MI patient group showed a significant higher frequency of the G allele compared to controls (0.149 vs. 0.101; OR 1.55; 95% CI 1.10-2.18; p=0.008). The association between the 2756A>G variant in the gene encoding MS and MI was no longer significant after adjustment for other well-established risk factors. When clinical and laboratory values were compared amongst genotypes in the study groups, no significant differences were noted.

CONCLUSIONS

The present study showed a significant but not independent association between the 2756A>G polymorphism of the MTR (presence of G allele) and MI in the Tunisian population.

Polymorphisms of methionine metabolism and susceptibility to meningioma formation: laboratory investigation

OBJECT

Functionally relevant polymorphisms of methionine and folate metabolism have been shown to be associated with various human cancer entities including cerebral lymphoma and glioblastoma multiforme. The authors investigated the association of 7 functional polymorphisms of methionine metabolism with meningioma formation.

METHODS

This case-controlled, monocenter association study included 290 patients of Caucasian origin undergoing surgical resection for intracranial meningioma (World Health Organization [WHO] Grade I, 190 cases; WHO Grade II, 82 cases; WHO Grade III, 18 cases) and 287 age- and sex-matched local controls. The authors analyzed the following genetic variants: dihydrofolate reductase c.594+59del19, 5,10-methylenetetrahydrofolate reductase c.677C > T and c.1298A > C, 5-methyltetrahydrofolate-homocysteine S-methyltransferase (MTR) c.2756A > G, reduced folate carrier 1 c.80G > A, cystathionine beta-synthase (CBS) c.844_855ins68 and transcobalamin 2 c.776C > G.

RESULTS

The variant CBS c.844_855ins68 -- that is, the allele carrying the insertion ("ins" or "i") as opposed to the wild-type allele designated as deletion ("del" or "d") -- was significantly overrepresented in meningioma patients (dd/ id/ii: 0.81/0.18/0.01) in comparison with the controls (dd/id/ii: 0.88/0.12/0; 2 df, chi-square 8.97, p = 0.011; multiple nominal regression with age and sex as covariables). In addition, explorative analyses revealed an association of the MTR c.2756A > G variant with meningioma WHO Grade III (AA/AG/GG: patients, 1.0/0/0; controls, 0.64/0.32/0.04; 2 df, chi-square 14.44, p = 0.001).

CONCLUSIONS

The results of this study suggest that genetic variants of methionine metabolism are associated with meningioma formation.

Influence of the cystathionine beta-synthase 844ins68 and methylenetetrahydrofolate reductase 677C>T polymorphisms on folate and homocysteine concentrations

A high homocysteine, low folate phenotype is a feature of many diseases. The effect of the cystathionine beta-synthase (CBS) 844ins68 polymorphism on homocysteine and folate concentrations was examined alone and in the context of the 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism in a Northwestern European male population. The MTHFR 677TT genotype is known to be associated with increased homocysteine and decreased folate relative to CT heterozygotes and CC homozygotes in this and other populations. MTHFR 677TT homozygotes who were also CBS 844ins68 carriers had homocysteine and folate concentrations similar to those of individuals with the MTHFR 677CT and CC genotypes. Homocysteine levels in MTHFR 677TT subjects carrying the CBS 844ins68 allele were 24.1% lower than in non-carriers (6.66 vs 8.77 micromol/l, P=0.045), and serum folate levels were 27.7% higher (11.16 vs 8.74 nmol/l, P=0.034). These findings suggest that the CBS 844ins68 allele 'normalizes' homocysteine and folate levels in MTHFR 677TT individuals.

[Evaluation of MTHFR C677T gene polymorphism and homocysteine level in coronary atherosclerotic disease]

OBJECTIVE

The aim of this study is to determine the prevalence of C677T methylenetetrahydrofolate reductase (MTHFR) polymorphism and correlate it with plasma homocysteine levels in coronary artery disease (CAD).

METHODS

Ninety-three patients with documented CAD from Hospital Universitário Oswaldo Cruz (Recife, PE, Brazil) and 108 healthy controls were evaluated. Homocysteine and folate levels were determined by HPLC and chemoluminescence, respectively, and lipid profile was considered. Genotyping was done by RFLP/PCR.

RESULTS

The groups were homogeneous for the C677T polymorphisms. The homocysteine level in cases (11.7 micromol/L) was statistically different from that observed in controls (8.84 micromol/L, p< 0.05). It was also observed that 72% of the patients had homocysteine values above 12 micromol/L while the control group presented only 32% in this range. There was no relationship between homozygosity for the C677T polymorphism and the homocysteine level (p= 0.634). We noticed statistical differences between folate levels from patients and controls (6.22 and 7.69 ng/dL, p< 0.05, respectively). However, there was no correlation between homocysteine and folate concentrations in the entire group (r= -0.202). Comparing cases and controls, the odds ratio (OR) when homocysteine is high and folate is low was OR= 11.9; CI 95%= 4.16-34.42, p< 0.01.

CONCLUSION

A lack of correlation between C677T mutation and homocysteine level suggests that environmental factors and others genetic factors seem to exert more influence on homocysteine level in this population.

Association of MTRR 66A>G polymorphism with superoxide dismutase and disease activity in patients with Crohn's disease

OBJECTIVES

The aim of this study was to evaluate the association of nutritional (folate, vitamin B12) and genetic (MTHFR, MTR, MTRR, TCN) determinants of homocysteine metabolism and of superoxide dismutase with Crohn's disease (CD).

METHODS

One hundred forty patients with CD were compared with 248 matched healthy controls.

RESULTS

Plasma homocysteine levels were higher in CD patients than controls (11.8 vs 10.4 micromol/L, P= 0.0004). Vitamin B12 and folate levels were lower in CD subjects compared to controls (207 vs 255 pmol/L, P= 0.0082, and 8.6 vs 11 nmol/L, P= 0036, respectively). Patients with a personal history of ileal resection, ileitis, or colectomy had significantly lower vitamin B12 levels. In multivariate analysis, vitamin B12 and MTHFR 677 TT carriers were the two significant independent factors of plasma homocysteine >15 micromol/L in CD patients (P= 0.0187 and 0.0048, respectively). The significant association between homocysteine and vitamin B12 levels remained significant only in patients with the highest superoxide dismutase values (P < 0.0001). The MTRR AA genotype was a significant independent predictor of CD risk (odds ratio 3.7, 95% CI 1.218-11.649, P= 0.0213). The level of superoxide dismutase was significantly higher (P= 0.0143) and was correlated with Crohn's Disease Activity Index (CDAI) scores (P for trend = 0.0276) in patients carrying MTRR AA genotype.

CONCLUSIONS

Vitamin B12 and MTHFR 677 TT genotype are the main determinants of hyperhomocysteinemia in CD patients. The association of MTRR 66A>G polymorphism with oxidant stress and disease activity provides rationale for screening vitamin deficiencies in these patients.

Vascular oxidant stress and inflammation in hyperhomocysteinemia

Elevated plasma levels of homocysteine are a metabolic risk factor for atherosclerotic vascular disease, as shown in numerous clinical studies that linked elevated homocysteine levels to de novo and recurrent cardiovascular events. High levels of homocysteine promote oxidant stress in vascular cells and tissue because of the formation of reactive oxygen species (ROS), which have been strongly implicated in the development of atherosclerosis. In particular, ROS have been shown to cause endothelial injury, dysfunction, and activation. Elevated homocysteine stimulates proinflammatory pathways in vascular cells, resulting in leukocyte recruitment to the vessel wall, mediated by the expression of adhesion molecules on endothelial cells and circulating monocytes and neutrophils, in the infiltration of leukocytes into the arterial wall mediated by increased secretion of chemokines, and in the differentiation of monocytes into cholesterol-scavenging macrophages. Furthermore, it stimulates the proliferation of vascular smooth muscle cells followed by the production of extracellular matrix. Many of these events involve redox-sensitive signaling events, which are promoted by elevated homocysteine, and result in the formation of atherosclerotic lesions. In this article, we review current knowledge about the role of homocysteine on oxidant stress-mediated vascular inflammation during the development of atherosclerosis.

Relation between plasma homocysteine, gene polymorphisms of homocysteine metabolism-related enzymes, and angiographically proven coronary artery disease

BACKGROUND

Hyperhomocyteinemia (HHcy) is a risk factor for coronary artery disease (CAD), and methylenetetrahydrofolate reductase (MTHFR), methionine synthase (MTR), and methionine synthase reductase (MTRR) polymorphisms may contribute to plasma total homocysteine (tHcy) variation. We investigated the association of polymorphisms 1298A-->C in the MTHFR gene, 2756A-->G in the MTR gene, and 66A-->G in the MTRR gene with tHcy levels and with CAD in patients undergoing coronary angiography.

METHODS

CAD patients (n=151) and control subjects (n=79) were compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.

RESULTS

The mean tHcy concentration was significantly higher in CAD patients than in control subjects (P<0.001). HHcy (tHcy>/=15 mumol/l) conferred an OR of CAD of 4.1 (95% CI 2.2-7.5, P<0.001). In both cases and controls, smokers had a higher tHcy level than non-smokers and demonstrated a markedly increased risk for CAD (OR=2.5, 95% CI 1.7-3.3, P<0.001). The allele frequencies of the MTHFR 1298A-->C, MTR 2756A-->G, and MTRR 66A-->G mutations were 36.7%, 15.7%, and 36.6%, respectively. The 1298C allele frequency was significantly higher in the CAD group than in controls (P<0.05) and showed a significant association with CAD in heterozygote carriers. There was no statistically significant difference between cases and controls in the frequencies of the A2756G alleles/genotypes in the MTR gene and of the A66G alleles/genotypes in the MTRR gene. The contributions to tHcy levels of the three common mutations were statistically significant. The heterozygosity of the MTHFR 1298AC genotype, MTR 2756G allele, and MTRR 66G allele yielded an OR of 3.4, 2.0, and 2.1, respectively, for having HHcy.

CONCLUSION

We suggest that HHcy confers a risk for CAD, and smokers with tHcy are at a greatly increased risk. Our finding supports an important role of the MTHFR gene in CAD and provides evidence of polygenic regulation of tHcy.

A CBS haplotype and a polymorphism at the MSR gene are associated with cardiovascular disease in a Spanish case–control study

OBJECTIVES

The aim of this study was to evaluate the association of polymorphisms present in genes related to homocysteine (Hcy) metabolism with coronary artery disease (CAD).

DESIGN AND METHODS

We examined 8 polymorphisms in the cystathionine beta-synthase (CBS), glutamate carboxypeptidase II (GCPII), methionine synthase (MS), methionine synthase reductase (MSR) and methylenetetrahydrofolate reductase (MTHFR) genes in 140 CAD patients and 113 controls, by means of Chi-square, logistic regression, ANOVA and the Mann-Whitney U test.

RESULTS

The c.66 G allele of MSR conferred an odds-ratio for CAD of 1.76 (95% CI 1.12-2.77), while a CBS haplotype [c.699C-c.844wt-c.1080C] was found over-represented in CAD [OR of 2.16 (1.29-3.63)].

CONCLUSIONS

Our results not only highlight the involvement of the MSR and CBS genes in the etiology of cardiovascular disease, but also emphasize the strength of haplotype analyses in association studies.

Genetic polymorphisms in folate metabolism and the risk of stomach cancer

Folate deficiency has been implicated in the etiology of stomach cancer through abnormal DNA methylation and disrupted DNA synthesis and repair. Enzyme-coding genes involved in folate metabolism are often polymorphic. In a population-based study of 305 cases and 427 controls in Warsaw, Poland, we evaluated the risk of stomach cancer in relation to polymorphisms in folate-metabolizing genes, including MTHFR (Ex5+79C>T and Ex8-62A>C), MTR (Ex26-20A>G), and MTRR (Ex2-64A>G, Ex5+123C>T, Ex15+572C>T, Ex15-405A>T, Ex9-85C>T, Ex15-526G>A, and Ex14+14C>T). Polymorphisms in the MTHFR gene were not associated with stomach cancer risk. No notable effect was found for polymorphisms in MTR or MTRR either, although MTR Ex26-20 A>G and MTRR Ex5+123C>T polymorphisms were associated with a borderline increased risk of stomach cancer (MTR Ex26-20A>G, AG/GG versus AA: odds ratio, 1.35; 95% confidence interval, 0.96-1.90; MTRR Ex5+123C>T, CT/TT versus CC: odds ratio, 1.30; 95% confidence interval, 0.93-1.82). We did not find significant interactions between polymorphisms in MTHFR, MTR, and MTRR genes and dietary folate and alcohol consumption. Our study did not identify strong genetic determinants in the folate metabolism pathway for stomach cancer risk.

Hydrogen sulfide: neurochemistry and neurobiology

Current evidence suggests that hydrogen sulfide (H2S) plays an important role in brain functions, probably acting as a neuromodulator as well as an intracellular messenger. In the mammalian CNS, H2S is formed from the amino acid cysteine by the action of cystathionine beta-synthase (CBS) with serine (Ser) as the by-product. As CBS is a calcium and calmodulin dependent enzyme, the biosynthesis of H2S should be acutely controlled by the intracellular concentration of calcium. In addition, it is also regulated by S-adenosylmethionine which acts as an allosteric activator of CBS. H2S, as a sulfhydryl compound, has similar reducing properties as glutathione. In neurons, H2S stimulates the production of cAMP probably by direct activation of adenylyl cyclase and thus activate cAMP-dependent processes. In astrocytes, H2S increases intracellular calcium to an extent capable of inducing and propagating a "calcium wave", which is a form of calcium signaling among these cells. Possible physiological functions of H2S include potentiating long-term potentials through activation of the NMDA receptors, regulating the redox status, maintaining the excitatory/inhibitory balance in neurotransmission, and inhibiting oxidative damage through scavenging free radicals and reactive species. H2S is also involved in CNS pathologies such as stroke and Alzheimer's disease. In stroke, H2S appears to act as a mediator of ischemic injuries and thus inhibition of its production has been suggested to be a potential treatment approach in stroke therapy.

Influence of combined methionine synthase (MTR 2756A > G) and methylenetetrahydrofolate reductase (MTHFR 677C > T) polymorphisms to plasma homocysteine levels in Korean patients with ischemic stroke

PURPOSE

Methionine synthase (MTR) and 5,10-methylenetetrahydrofolate reductase (MTHFR) are the main regulatory enzymes for homocysteine metabolism. The present case- control study was conducted to determine whether there is an association between the MTR 2756A > G or MTHFR 677C > T polymorphism and plasma homocysteine concentration in Korean subjects with ischemic stroke.

MATERIALS AND METHODS

DNA samples of 237 patients who had an ischemic stroke and 223 age and sex-matched controls were studied. MTR 2756A > G and MTHFR 677C > T genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

Frequencies of mutant alleles for MTR and MTHFR polymorphisms were not significantly different between the controls and cases. The patient group, however, had significantly higher homocysteine concentrations of the MTR 2756AA and MTHFR 677TT genotypes than the control group (p=0.04 for MTR, p=0.01 for MTHFR). The combined MTR 2756AA and MTHFR 677TT genotype (p= 0.04) and the homocysteine concentrations of the patient group were also higher than those of the controls. In addition, the genotype distribution was significant in the MTHFR 677TT genotype (p=0.008) and combined MTR 2756AA and MTHFR 677TT genotype (p=0.03), which divided the groups into the top 20% and bottom 20% based on their homocysteine levels.

CONCLUSION

The results of the present study demonstrate that the MTR 2756A > G and MTHFR 677C > T polymorphisms interact with elevated total homocysteine (tHcy) levels, leading to an increased risk of ischemic stroke.

Impact of methionine synthase gene and methylenetetrahydrofolate reductase gene polymorphisms on the risk of sudden sensorineural hearing loss

Idiopathic sudden sensorineural hearing loss (SSNHL) represents a frequently encountered otological disease of unknown etiology. In recent years, several inherited risk factors have been found in the pathogenesis of vascular diseases. In the present study, we determined whether specific polymorphism or the combination of polymorphisms in folate-dependent homocysteine metabolism genes can act as predisposing inherited vascular risk factors in the development of SSNHL. We conducted a prospective case-control study using DNA samples extracted from 81 patients diagnosed as suffering from SSNHL and 264 healthy control subjects. Three functional polymorphisms were analyzed by polymerase chain reaction amplification, restriction enzyme digestion, and DNA fragment separation by electrophoresis: methylenetetrahydrofolate reductase (MTHFR) C677T, MTHFR A1298C, and methionine synthase (MTR) A2756G polymorphisms. The prevalence of the homozygous genotype of MTR 2756GG in the SSNHL patients (9%) was significantly higher than in the control group (4%) (p = 0.011). The allelic frequency of the G allele of the MTR A2756G polymorphism among SSNHL patients (12.5%) was also significantly higher than in the control group (5%) (p = 0.033). The prevalence of patients possessing two polymorphisms (31%) and three polymorphisms (17%) in the SSNHL group was significantly higher than in the control group (23 and 9%, respectively; p = 0.019). The frequency of patients with a very high rank risk (double homozygous) was significantly higher in the SSNHL group, MTHFR 677TT/MTR 2675GG--7%, than the frequency of patients in the control group, MTHFR 677TT/MTR 2675GG--3% (p = 0.030). Certain polymorphisms in genes encoding enzymes in the folate-dependent homocysteine metabolism are associated with SSNHL. In our case-control study, a significant association between MTR 2756GG genotype and SSNHL was found which may represent an inherited vascular risk factor in the pathogenesis of SSNHL.

Gene-gene, gene-environment & multiple interactions in colorectal cancer

This review comprehensively evaluates the influence of gene-gene, gene-environment and multiple interactions on the risk of colorectal cancer (CRC). Methods of studying these interactions and their limitations have been discussed herein. There is a need to develop biomarkers of exposure and of risk that are sensitive, specific, present in the pathway of the disease, and that have been clinically tested for routine use. The influence of inherited variation (polymorphism) in several genes has been discussed in this review; however, due to study limitations and confounders, it is difficult to conclude which ones are associated with the highest risk (either individually or in combination with environmental factors) to CRC. The majority of the sporadic cancer is believed to be due to modification of mutation risk by other genetic and/or environmental factors. Micronutrient deficiency may explain the association between low consumption of fruit/vegetables and CRC in human studies. Mitochondrial modulation by dietary factors influences the balance between cell renewal and death critical in colon mucosal homeostasis. Both genetic and epigenetic interactions are intricately dependent on each other, and collectively influence the process of colorectal tumorigenesis. The genetic and environmental interactions present a good prospect and a challenge for prevention strategies for CRC because they support the view that this highly prevalent cancer is preventable.

The effect of MTHFR(C677T) genotype on plasma homocysteine concentrations in healthy children is influenced by gender

OBJECTIVE

To explore the influence of gender, together with folate status, on the relation between the common methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and plasma total homocysteine (tHcy) concentrations in healthy children.

DESIGN

Cross-sectional study by face-to-face interview.

SETTING AND SUBJECTS

A total of 186 sixth-grade students participated from twelve randomly selected primary schools in Volos, Greece.

METHODS

Fasting tHcy, folate, and vitamin B(12) were measured in plasma. The MTHFR genotypes were determined. Anthropometric and dietary intake data by 24-h recall were collected.

RESULTS

Geometric means for plasma tHcy, plasma folate and energy-adjusted dietary folate did not differ between females and males. The homozygous mutant TT genotype was associated with higher tHcy only in children with lower plasma folate concentrations (<19.9 nmol/l, P = 0.012). As a significant gender interaction was observed (P = 0.050), we stratified the lower plasma folate group by gender and found that the association between the genotype and tHcy was restricted to males (P = 0.026). Similar results were obtained when folate status was based on estimated dietary folate. Specifically, only TT males that reported lower dietary folate consumption (<37 microg/MJ/day) had tHcy that was significantly higher than tHcy levels of C-allele carriers (P = 0.001).

CONCLUSIONS

Under conditions of lower folate status (as estimated by either plasma concentration or reported dietary consumption), gender modifies the association of the MTHFR(C677T) polymorphism with tHcy concentrations in healthy children.

SPONSORSHIP

Kellog Europe.

Thymidylate synthase promoter tandem repeat and MTHFD1 R653Q polymorphisms modulate the risk for migraine conferred by the MTHFR T677 allele

There is growing evidence that folate metabolism is involved in migraine pathophysiology, mainly in migraine with aura. Even though folate metabolism is regulated by a number of enzymes, only two functional polymorphisms have been tested in association studies with migraine. Here, we have explored the possible role in migraine of other folate-metabolizing enzymes which are in close interdependency with 5',10'-methylenetetrahydrofolate reductase analyzing functional polymorphisms of these enzymes in a case-control study. Individually, thymidylate synthase (TS), methenyltetrahydrofolate cyclohydrolase formyltetrahydrofolate synthase (MTHFD1), or methionine synthase (MS) polymorphisms did not modify the general risk for suffering migraine. Nevertheless, we observed a strong interaction between TS and MTHFR mutated genotypes, which increased over 8-fold the risk for experiencing aura among migraineurs; MTHFD1 and MTHFR mutated genotypes also increased together the risk for migraine in general (OR = 3.08; 95% CI = 1.3-7.4). We conclude that the pathogenetic role of the MTHFR T677 allele in migraine is modulated by functional polymorphisms of TS and MTHFD1.

Endothelial function markers in parkinsonian patients with hyperhomocysteinemia

Hyperhomocysteinemia is considered a risk factor for vascular disease causing endothelial damage and consequently atherogenesis. The purpose of this study was to investigate the effect of elevated homocysteine on certain biochemical markers of endothelial function in patients with idiopathic Parkinson's disease (PD). Blood homocysteine levels were assessed in 57 PD patients and 40 matched normal controls. Investigation of the C677T 5,10 methylenetetrahydrofolate reductase (MTHFR) genotype was also performed in 43 PD patients. The following markers of endothelial function were assessed: superoxide dismutase (SOD), nitric oxide (NO), sICAM-1 and sE-selectin. Homocysteine levels were found mildly elevated in PD patients particularly in those treated with L-Dopa. MTHFR genotype did not influence significantly this finding. SOD activity was found reduced but it was not correlated to homocysteine levels. All other parameters measured were normal and were not related to hyperhomocysteinemia. Our findings indicate that mild hyperhomocysteinemia in PD patients was not associated with endothelial dysfunction.

[Polymorphisms in cystathionine beta-synthase and methylenetetrahydrofolate reductase genes as risk factors for cerebral vascular disease]

BACKGROUND AND OBJECTIVE

High plasma total homocysteine (tHcy), low dietary intake of folate and other B vitamins, and genetic polymorphisms related to the metabolism of homocysteine may interactively contribute to the risk of cerebral vascular disease (CVD). We explored interrelations between total homocysteine levels and mutations in genes for the two key enzymes in methionine-homocysteine metabolism.

PATIENTS AND METHOD

We analyzed two polymorphisms, C677T in the MTHFR gene and 844ins68 in the CBS gene. We assessed their association with fasting homocysteine in 64 patients with CVD, and in 159 controls.

RESULTS

No differences in CBS and MTHFR genotype frequencies between cases and controls were found (C677T p = 0.87 and 844ins68 p = 0.63), nor was a particular CBS and MTHFR genotype associated with an elevated risk of CVD. None of the genotypes defined by the CBS and MTHFR variants studied showed an association with elevated fasting homocysteine concentrations (C677T p = 0.07 and 844ins68 p = 0.47).

CONCLUSIONS

We did not find any indication that genetic variation in the CBS and MTHFR genes are associated with homocysteine-related risk of CVD, hence needing further investigation. The contributions to total plasma homocysteine levels of the common mutations of genes coding for the enzymes controlling homocysteine metabolism are modest.

Prevalence of myocardial infarction is related to hyperhomocysteinemia but not influenced by C677T methylenetetrahydrofolate reductase and A2756G methionine synthase polymorphisms in diabetic and non-diabetic subjects

BACKGROUND

Hyperhomocysteinemia has emerged as a novel risk factor for myocardial infarction (MI). Some mechanisms proposed to explain its relationship with coronary events are also shared by major coronary risk factors. We examined whether C677T methylenetetrahydrofolate reductase and A2756G methionine synthase polymorphisms could affect the relative risk for MI.

METHODS

A sample of 196 individuals was divided into four groups (diabetics with MI, n=43; diabetics without MI, n=50; non-diabetics with MI, n=47; non-diabetics without MI, n=56) and compared regarding the prevalence of the polymorphisms, risk factors, and biochemical parameters.

RESULTS

Higher prevalence of hyperhomocysteinemia was found in MI patients (p<0.05 vs. non-MI subjects), in males (p<0.001 vs. female) and in those > or = 65 years (p=0.01 vs. <65 years). Homocysteine was negatively associated with HDL-C (p<0.05) and glucose, although results did not reach significance (p=0.06). Similar distribution of studied polymorphisms was seen in all groups, which presented normal folate and vitamin B12 serum levels.

CONCLUSIONS

Higher homocysteinemia was predominantly observed in men, presenting low HDL-C, and at advancing age. Methylenetetrahydrofolate reductase and methionine synthase polymorphisms did not contribute to risk assessment in diabetic and non-diabetic subjects presenting normal folate levels.

Gene-gene and gene-environment interactions in mild hyperhomocysteinemia

Mild/moderate hyperhomocysteinemia (HHcy), a highly prevalent condition, is independently associated with an increased risk of arterial and venous thromboembolic diseases. Early reports of the association of mild/moderate HHcy with juvenile venous thromboembolism have shown familiarity for HHcy in relatives of index cases with thrombosis. Similar to inherited thrombophilia defects, inheritance of the HHcy phenotype was accordingly retained important for the definition of HHcy as an independent risk factor for thrombosis. A number of common polymorphisms in genes coding for methylenetetrahydrofolate reductase(MTHFR), methionine-synthase, methionine-synthase reductase and cysthationine beta-synthase (CBS) have been explored for their association with homocysteine levels, fasting and post-methionine load, and with thrombotic diseases. MTHFR thermolability accounts for a 10-fold increase in the risk of mild/moderate HHcy. With the possible exception of the CBS844ins68 insertion, there is no evidence for an increased risk of HHcy for any of these polymorphisms, isolated or in association with MTHFR thermolability. Environmental factors and MTHFR thermolability are main determinants of the HHcy phenotype.If mild/moderate HHcy is a pathogenetic risk factor for thrombosis, intervention aimed to improve the vitamin status appears of major importance, irrespective of common gene polymorphisms of the homocysteine metabolism.

Methionine synthase D919G polymorphism, folate metabolism, and colorectal adenoma risk

Methionine synthase [5-methyltetrahydrofolate-homocysteine S-methyltransferase (MTR)] is involved in folate-mediated one-carbon metabolism, a pathway known to play a role in colorectal carcinogenesis. We investigated whether the MTR D919G polymorphism was associated with risk of colorectal adenoma in a colonoscopy-based study of 513 cases and 609 controls from Minneapolis, MN. Adenoma risk appeared nonsignificantly increased among women with DG or GG genotype [adjusted odds ratio (OR) versus DD, 1.4; 95% confidence interval (CI), 0.9-2.1] but not men (OR, 1.0; 95% CI, 0.7-1.5). An interaction with methionine intake was observed among women, such that low versus high intake was associated with a 2.3-fold increased risk only among those with DG or GG genotype (95% CI, 1.1-4.9; P for interaction = 0.05). Similarly, risk associated with alcohol intake was not elevated among women with the DD genotype; however, consumption of >7 g of alcohol/day versus none was associated with an increased risk among women with DG or GG genotype (adjusted OR, 2.5; 95% CI, 1.4-4.4; P for interaction = 0.03). An interaction between MTR D919G and the thymidylate synthase (TS or TYMS) 3'-untranslated region polymorphism 1494del6 was also observed among women (P for interaction = 0.007). No evidence of interaction with intake of folate, vitamin B(12), or vitamin B(6) or with genotype at MTHFR C677T or the TS enhancer region 28-bp repeat polymorphism was seen. These findings add to what is known about the complexities of genetic variations in one-carbon-metabolizing enzymes in relation to colorectal carcinogenesis.

Influence of hyperhomocysteinemia on the cellular redox state--impact on homocysteine-induced endothelial dysfunction

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. An increasing body of evidence has implicated oxidative stress as being contributory to homocysteine's deleterious effects on the vasculature. Elevated levels of homocysteine may lead to increased generation of superoxide by a biochemical mechanism involving nitric oxide synthase, and, to a lesser extent, by an increase in the chemical oxidation of homocysteine and other aminothiols in the circulation. The resultant increase in superoxide levels is further amplified by homocysteine-dependent alterations in the function of cellular antioxidant enzymes such as cellular glutathione peroxidase or extracellular superoxide dismutase. One direct clinical consequence of elevated vascular superoxide levels is the inactivation of the vasorelaxant messenger nitric oxide, leading to endothelial dysfunction. Scavenging of superoxide anion by either superoxide dismutase or 4,5-dihydroxybenzene 1,3-disulfonate (Tiron) reverses endothelial dysfunction in hyperhomocysteinemic animal models and in isolated aortic rings incubated with homocysteine. Similarly, homocysteine-induced endothelial dysfunction is also reversed by increasing the concentration of the endogenous antioxidant glutathione or overexpressing cellular glutathione peroxidase in animal models of mild hyperhomocysteinemia. Taken together, these findings strongly suggest that the adverse vascular effects of homocysteine are at least partly mediated by oxidative inactivation of nitric oxide.

Age and Gender Affect the Relation between Methylenetetrahydrofolate Reductase C677T Genotype and Fasting Plasma Homocysteine Concentrations in the Framingham Offspring Study Cohort

The C677T variant of methylenetetrahydrofolate reductase (MTHFR), a key enzyme in the remethylation of homocysteine to methionine, is a frequent genetic cause of mild hyperhomocysteinemia among individuals with low folate status. However, little is known about the influence of subject characteristics, such as age and sex, on the relation between the C677T MTHFR polymorphism and fasting plasma total homocysteine (tHcy) concentrations. The aim of the present study was to explore the influence of age and gender, together with folate status, on the association between the C677T polymorphism and tHcy concentrations. The C677T genotype was determined for 1820 participants from the fifth examination of the Framingham Offspring Study. Mean age of the participants was 56 y (range 28-82 y). The allelic distribution was not different from the Hardy-Weinberg equilibrium, with a TT frequency comparable in men and women (14%). Geometric mean tHcy was 15% higher in men than in women (P < 0.001), and women had significantly higher plasma folate levels (P < 0.001). Geometric mean tHcy was significantly higher in TT participants (P = 0.001) than in participants with the CC and CT genotypes among those with plasma folate <12.5 nmol/L, but not among those with higher folate status. Because of a significant age and sex interaction (P = 0.02), we further stratified the low folate group by age and sex, and observed that the association between genotype and tHcy was confined to men <55 y old (P < 0.001). Our results suggest that age and sex modify the contribution of the MTHFR C677T mutation to fasting tHcy concentrations.

Effect of metabolic control on homocysteine levels in type 2 diabetic patients: a 3-year follow-up

OBJECTIVES

Hyperhomocysteinaemia has emerged as a novel risk factor for cardiovascular disease. The determinants of total homocysteine (tHcy) levels in type 2 diabetic patients (D2p) have not been studied in detail. We examined prospectively the effect of different degrees of metabolic control on plasma tHcy in D2p with preserved kidney function. SUBJECTS AND MAIN OUTCOME MEASUREMENTS: Ninety-five D2p were studied. Clinical parameters, fasting plasma glucose, HbA1c, serum lipids, blood urea nitrogen (BUN) and creatinine, vitamin B12 and folate and tHcy were measured at the baseline and after 36 months. The methylentetrahydrofolate reductase (MTHFR) C677T polymorphism was also determined. Subjects were categorized according to deltaHbA1c into group A (+/-1 point), B (>1 point increase) or C (>1 point decrease).

RESULTS

Total homocysteine was reduced in subjects whose HbA1c decreased with time, whilst patients showing a worsened metabolic control had an increased tHcy in respect to baseline. A larger response to the improved metabolic control in terms of tHcy reduction was noted in wild type patients versus those homozygous for the mutation. A multivariate analysis revealed MTHFR polymorphism and HbA1c as strong determinants of changes in tHcy with time.

CONCLUSIONS

The findings suggest that in D2p tHcy decreases even with modest improvement of glycaemic control; moreover patients homozygous for the MTHFR C677T mutation show the largest changes in tHcy levels with concomitant changing of HbA1c. These results define a further mechanism through which hyperglycaemia might promote cardiovascular damage in diabetic patients.

Extracellular superoxide dismutase in biology and medicine

Accumulated evidence has shown that reactive oxygen species (ROS) are important mediators of cell signaling events such as inflammatory reactions (superoxide) and the maintenance of vascular tone (nitric oxide). However, overproduction of ROS such as superoxide has been associated with the pathogenesis of a variety of diseases including cardiovascular diseases, neurological disorders, and pulmonary diseases. Antioxidant enzymes are, in part, responsible for maintaining low levels of these oxygen metabolites in tissues and may play key roles in controlling or preventing these conditions. One key antioxidant enzyme implicated in the regulation of ROS-mediated tissue damage is extracellular superoxide dismutase (EC-SOD). EC-SOD is found in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. In addition, EC-SOD is likely to play an important role in mediating nitric oxide-induced signaling events, since the reaction of superoxide and nitric oxide can interfere with nitric oxide signaling. This review will discuss the regulation of EC-SOD and its role in a variety of oxidant-mediated diseases.

Homocysteine as a risk factor for cognitive impairment in stroke patients

BACKGROUND

Elevated total homocysteine (tHcy) levels are associated with an increased risk of cerebrovascular disease. It is uncertain whether tHcy is also an independent risk factor for cognitive impairment.

METHODS

We examined 95 stroke subjects 3 months after their strokes, and 55 healthy comparison subjects, with a detailed neuropsychological assessment, and MRI brain scans in a proportion (n = 97). Baseline measurements of tHcy, serum folate and B(12), creatinine and plasma fibrinogen levels were obtained.

RESULTS

tHcy levels were higher in the stroke subjects by a mean 34%. These levels were significantly correlated with the first factor of a principal component analysis of the neuropsychological data, after controlling for age, folate, B(12) and creatinine levels. The correlation of Hcy levels was particularly significant with frontal-executive functioning and attention. tHcy levels were significantly correlated with number of infarcts and total stroke volume in the stroke group, but not with T(2)-weighted deep white matter hyperintensity scores, after correction for age. In the control group, tHcy levels were significantly correlated with ventricle-to-brain ratios as measures of brain atrophy.

CONCLUSION

This study provides evidence that high tHcy levels are associated with cognitive impairment, in particular that of frontal-executive function. The major component of this association is accounted for by small and large strokes, but non-vascular neurotoxic effects of tHcy also appear to play a role. tHcy must receive greater attention as a risk factor for cognitive impairment.

The 2756A>G variant in the gene encoding methionine synthase: its relation with plasma homocysteine levels and risk of coronary heart disease in a Dutch case-control study

INTRODUCTION

Elevated plasma homocysteine levels have been associated with increased risk of cardiovascular disease. A 2756A>G polymorphism has been found in the gene (MTR) coding for methionine synthase, an enzyme catalyzing remethylation of homocysteine to methionine.

MATERIALS AND METHODS

In a Dutch case-control study comprising 123 cases with coronary heart disease (CHD) and 540 controls, we evaluated whether the MTR 2756A>G polymorphism was associated with plasma homocysteine, vitamin B12, folate concentrations, and CHD risk.

RESULTS AND CONCLUSIONS

The polymorphism was not associated with fasting or post-methionine load homocysteine concentrations. Individuals with the GG genotype had 30% lower vitamin B12 concentrations than individuals with AA or AG genotype (P < 0.05). After adjustment for CHD risk factors, the odds ratio (OR) of CHD was 4.0 (95% CI 1.4-11.6) for the GG genotype and 0.7 (95% CI 0.4-1.2) for the AG genotype, when compared to the AA genotype. In conclusion, despite the absence of an association with plasma homocysteine, the GG genotype represented a four-fold increased risk of CHD when compared to the AA genotype. Before putting effort in additional epidemiological studies, it needs to be established first whether this polymorphism has functional consequences for enzyme activity.

Serum extracellular superoxide dismutase in patients with type 2 diabetes: relationship to the development of micro- and macrovascular complications

OBJECTIVE

The aim of this study was to determine the distribution of serum extracellular superoxide dismutase (EC-SOD) concentrations in patients with type 2 diabetes and to assess whether increased EC-SOD concentration is associated with the development of diabetic vascular complications.

RESEARCH DESIGN AND METHODS

Serum EC-SOD concentrations were determined in 222 patients with type 2 diabetes and 75 healthy control subjects by an enzyme-linked immunosorbent assay. All subjects had the EC-SOD domain genotyped.

RESULTS

The serum EC-SOD concentrations showed a distinct bimodal distribution in both patients with diabetes and control subjects. All subjects with the high-level phenotype carried the Arg213Gly mutation. The frequency of this variant was similar in the diabetes and control groups. Within the group of subjects with the common EC-SOD phenotype, the serum EC-SOD concentration (mean +/- SE) was significantly higher in patients with type 2 diabetes (99.3 +/- 1.3 ng/ml) compared with the control subjects (68.4 +/- 2.3 ng/ml, P < 0.01). Stepwise multiple regression analysis of the data from the diabetic common phenotype group showed a significant relationship between serum EC-SOD concentration and duration of diabetes (F = 5.31), carotid artery intimal-media thickness (F = 8.24), and severity of nephropathy (F = 16.05) and retinopathy (F = 4.43).

CONCLUSIONS

We observed a strong relationship between the serum concentration of EC-SOD and the severity of both micro- and macrovascular diabetic complications. These findings suggest that serum EC-SOD concentration levels may be a marker of vascular injury, possibly reflecting hyperglycemia-induced oxidative injury to the vascular endothelium and decreased binding of EC-SOD to the vascular wall.

Hyperhomocysteinemia and thrombosis

Homocysteine remains an enigmatic marker for vascular disease. Studies have shown hyperhomocysteinemia is a risk factor for VTE, cerebrovascular disease, and coronary artery disease. This relationship, however, has not been consistently corroborated by studies of patients with genetic polymorphisms that alter homocysteine metabolism. Studies at the molecular level reveal interactions between homocysteine, the endothelium, and the clotting system. Further investigation at the basic science level is needed to determine whether homocysteine is a marker of vascular injury and thrombotic potential or whether it plays a pathogenic role. Preliminary trials with vitamins clearly show that safe, inexpensive treatment can lower homocysteine levels. The clinical impact on decreasing vascular disease, however, has yet to be shown. Until there is evidence that treatment improves outcomes, testing for homocysteine and treating hyperhomocysteinemia will be a debatable issue. A series of vitamin intervention trials begun in 1997 will enroll tens of thousands of patients (Table 1) and will, it is hoped, provide the necessary information for developing evidence-based guidelines.

Folate Improves Endothelial Function in Patients with Coronary Heart Disease

Elevated plasma homocysteine is associated with increased cardiovascular risk but it remains unproven that the effect is directly causal. Folate and homocysteine metabolism are closely linked such that administration of folic acid in doses ranging from 0.2-10 mg/day lowers plasma total homocysteine (tHcy) by up to 25%. Folic acid has been widely advocated as a therapy which may reduce cardiovascular risk, but the clinical benefit remains as yet unproven and the choice of dose remains unclear. The effect of folic acid on endothelial function has been investigated in patients with proven coronary heart disease (CHD) by measuring flow-mediated dilatation (FMD) in the brachial artery. Oral folic acid (5 mg/day) markedly enhances endothelial function (FMD) and lowers homocysteine. Studies of the acute effects of folic acid have shown that this improvement occurs within the first 2-4 hours following the first dose, at which times there was no significant reduction in plasma tHcy. Administration of 5-methyltetrahydrofolate directly into the brachial artery markedly enhances FMD, an effect that is blocked by monomethyl arginine (LNMMA), suggesting that the effects of folate are mediated by nitric oxide. This Review summarises studies which show that pharmacological doses of folate markedly enhance endothelial function in patients with CHD. The discordance with changes in plasma homocysteine suggests that these effects may occur by mechanisms distinct from homocysteine lowering.

Effects of polymorphisms of methionine synthase and methionine synthase reductase on total plasma homocysteine in the NHLBI Family Heart Study

The metabolism of homocysteine requires contributions of several enzymes and vitamin cofactors. Earlier studies identified a common polymorphism of methylenetetrahydrofolate reductase that was associated with mild hyperhomocysteinemia. Common variants of two other enzymes involved in homocysteine metabolism, methionine synthase and methionine synthase reductase, have also been identified. Methionine synthase catalyzes the remethylation of homocysteine to form methionine and methionine synthase reductase is required for the reductive activation of the cobalamin-dependent methionine synthase. The methionine synthase gene (MTR) mutation is an A to G substitution, 2756A-->G, which converts an aspartate to a glycine codon. The methionine synthase reductase gene (MTRR) mutation is an A to G substitution, 66A-->G, that converts an isoleucine to a methionine residue. To determine if these polymorphisms were associated with mild hyperhomocysteinemia, we investigated subjects from two of the NHLBI Family Heart Study field centers, Framingham and Utah. Total plasma homocysteine concentrations were determined after an overnight fast and after a 4-h methionine load test. MTR and MTRR genotype data were available for 677 and 562 subjects, respectively. The geometric mean fasting homocysteine was unrelated to the MTR or MTRR genotype categories (AA, AG, GG). After a methionine load, a weak positive association was observed between change in homocysteine after a methionine load and the number of mutant MTR alleles (P-trend=0.04), but this association was not statistically significant according to the overall F-statistic (P=0.12). There was no significant interaction between MTR and MTRR genotype or between these genotypes and any of the vitamins with respect to homocysteine concentrations. This study provides no evidence that these common MTR and MTRR mutations are associated with alterations in plasma homocysteine.

Hyperhomocysteinemia due to methionine synthase deficiency, cblG: structure of the MTR gene, genotype diversity, and recognition of a common mutation, P1173L

Mutations in the MTR gene, which encodes methionine synthase on human chromosome 1p43, result in the methylcobalamin deficiency G (cblG) disorder, which is characterized by homocystinuria, hyperhomocysteinemia, and hypomethioninemia. To investigate the molecular basis of the disorder, we have characterized the structure of the MTR gene, thereby identifying exon-intron boundaries. This enabled amplification of each of the 33 exons of the gene, from genomic DNA from a panel of 21 patients with cblG. Thirteen novel mutations were identified. These included five deletions (c.12-13delGC, c.381delA, c.2101delT, c.2669-2670delTG, and c.2796-2800delAAGTC) and two nonsense mutations (R585X and E1204X) that would result in synthesis of truncated proteins that lack portions critical for enzyme function. One mutation was identified that resulted in conversion of A to C of the invariant A of the 3' splice site of intron 9. Five missense mutations (A410P, S437Y, S450H, H595P, and I804T) were identified. The latter mutations, as well as the splice-site mutation, were not detected in a panel of 50 anonymous DNA samples, suggesting that these sequence changes are not polymorphisms present in the general population. In addition, a previously described missense mutation, P1173L, was detected in 16 patients in an expanded panel of 24 patients with cblG. Analysis of haplotypes constructed using sequence polymorphisms identified within the MTR gene demonstrated that this mutation, a C-->T transition in a CpG island, has occurred on at least two separate genetic backgrounds.

Decreased rate of coronary restenosis after lowering of plasma homocysteine levels

BACKGROUND

We have previously demonstrated an association between elevated total plasma homocysteine levels and restenosis after percutaneous coronary angioplasty. We designed this study to evaluate the effect of lowering plasma homocysteine levels on restenosis after coronary angioplasty.

METHODS

A combination of folic acid (1 mg), vitamin B12 (400 microg), and pyridoxine (10 mg)--referred to as folate treatment--or placebo was administered to 205 patients (mean [+/-SD] age, 61+/-11 years) for six months after successful coronary angioplasty in a prospective, double-blind, randomized trial. The primary end point was restenosis within six months as assessed by quantitative coronary angiography. The secondary end point was a composite of major adverse cardiac events.

RESULTS

Base-tine characteristics and initial angiographic results after coronary angioplasty were similar in the two study groups. Folate treatment significantly lowered plasma homocysteine levels from 11.1+/-4.3 to 7.2+/-2.4 micromol per liter (P<0.001). At follow-up, the minimal luminal diameter was significantly larger in the group assigned to folate treatment (1.72+/-0.76 vs. 1.45+/-0.88 mm, P=0.02), and the degree of stenosis was less severe (39.9+/-20.3 vs. 48.2+/-28.3 percent, P=0.01). The rate of restenosis was significantly lower in patients assigned to folate treatment (19.6 vs. 37.6 percent, P=0.01), as was the need for revascularization of the target lesion (10.8 vs. 22.3 percent, P=0.047).

CONCLUSIONS

Treatment with a combination of folic acid, vitamin B12, and pyridoxine significantly reduces homocysteine levels and decreases the rate of restenosis and the need for revascularization of the target lesion after coronary angioplasty. This inexpensive treatment, which has minimal side effects, should be considered as adjunctive therapy for patients undergoing coronary angioplasty.

Gene polymorphisms of homocysteine metabolism-related enzymes in Chinese patients with occlusive coronary artery or cerebral vascular diseases

The mutations in homocysteine (Hcy) metabolism-related enzyme genes including methylenetetrahydrofolate reductase (MTHFR) C677T, cystathionine beta-synthase (CBS) 844ins68, and methionine synthase (MS) A2756G have been identified as genetic risk factors for thromboembolic events. It has been noticed that these gene mutations have heterogeneous distributions among different ethnic groups or geographic areas. The data on the prevalence of the gene mutations in Chinese population is not yet available. In the present study, we have investigated the frequency of the MTHFR C677T, CBS 844ins68, and MS A2756G mutations in 102 patients with ischemic stroke (IS), 73 patients with myocardial infarction (MI) and 100 healthy controls. The distributive frequencies of the gene variations are as follows: In the IS, MI and control groups, the mutant homozygote for MTHFR C677T is 15 (14.7%), 8 (11.7%) and 16 (16.0%), respectively, and the T allele frequency is 37.7%, 33.6% and 39.5%, respectively; the heterozygote for CBS 844ins68 is 1 (1.0%), 1 (1.4%) and 5 (5.0%), respectively; the heterozygote for MS A2756G is 18 (17.6%), 14 (19.2%) and 17 (17.0%), and the G allele frequency is 8.8%, 11.0% and 9.5%, respectively. The carrier of both MS A2756G and MTHFR C677T (combined mutations) is 14 (12.7%), 8(11.0%) and 12(12.0%), respectively. There is no statistically significant difference between the patient groups and the control group in the frequencies of these single mutation or combined mutations. The heterozygosity of CBS 844ins68 yields an odds ratio (OR) of 0.19 (95% confidence interval (CI) 0.02-1.43) for IS and 0.26 (95% CI 0.03-2.31) for MI. The T allele of MTHFR C677T yields an OR of 0.93 for IS (95% CI 0.62-1.39) and 0.77 for MI (95% CI 0.50-1.21). The G allele of MS A2756G yields an OR of 0.92(95% CI 0.47-1.81) for IS and 1.17 (95% CI 0.58-2.37) for MI. Our results suggest that neither single mutation nor combined mutations in MTHFR C677T, CBS 844ins68 and MS A2756G represent an independent risk factor for increasing IS and coronary artery disease risks in Chinese population. However, CBS 844ins68 may be a protective factor against vascular thromboembolic disease. The prevalence of CBS 844ins68 and MS A2756G in Chinese population is obviously lower than in Western Caucasian population.