Effect of sulfinpyrazone on homocysteine-induced endothelial injury and arteriosclerosis in baboons

Homocysteine metabolism in diabetes

An increase in the plasma level of Hcy (homocysteine), an intermediate in the catabolism of methionine, has been identified as a risk factor for many diseases including CVD (cardiovascular disease). CVD is the major cause of death in patients with diabetes mellitus. Therefore the study of Hcy metabolism in diabetes mellitus has been a major focus of current research. Studies conducted in our laboratory were able to show that in both Type 1 and Type 2 diabetes with no renal complications, the plasma Hcy levels were lower than in controls. In Type 1 diabetes, increased activities of the trans-sulfuration enzymes were the major cause for the reduction in plasma Hcy. In Type 2 diabetes, BHMT (betaine:homocysteine methyltransferase) was also observed to play a major role in the increased catabolism of Hcy in addition to the trans-sulfuration enzymes. We were also able to demonstrate the direct effect of insulin and the counter-regulatory hormones on the regulation of cystathionine beta-synthase and BHMT, which accounts for the changes in the activities of these two enzymes seen in diabetes mellitus.

Homocysteine in the prevention of ischemic heart disease, stroke and venous thromboembolism: therapeutic target or just another distraction?

PURPOSE OF REVIEW

Homocysteine has been proposed as a potentially modifiable risk factor for arterial and venous vascular disease. This notion is supported by a large body of literature derived from observations in patients with rare inborn errors of metabolism associated with homocystinuria, experimental studies, which show that homocysteine promotes atherogenesis and thrombosis and epidemiological studies, which in general suggest a graded and independent relationship between homocysteine and atherothrombotic vascular risk.

RECENT FINDINGS

The current review briefly summarizes observational studies with emphasis on new meta-analyses linking homocysteine to ischemic heart disease, stroke, and venous thromboembolism. These data support weak associations between homocysteine and vascular risk. A number of recent large randomized controlled trials failed to demonstrate benefit for homocysteine lowering with B vitamin supplements in the prevention of cardiovascular events and venous thrombosis. These studies, however, may have been insufficiently powered to detect modest but clinically important treatment benefits. Therefore, completion of ongoing large randomized trials is essential.

SUMMARY

At present, the status of homocysteine as a target for intervention in the prevention of atherothrombotic arterial and venous disease is uncertain. Current evidence does not support the use of B vitamin supplements to reduce vascular risk. Ongoing large randomized trials will provide further clarity on this subject.

Should hyperhomocysteinemia be treated in patients with atherosclerotic disease?

Numerous retrospective and prospective observational studies support an association between elevated homocysteine and increased risk for myocardial infarction, stroke, and peripheral vascular disease. Although folic acid therapy substantially reduces homocysteine levels, recent large, randomized controlled trials failed to translate folic acid-induced homocysteine reduction into clinical benefit for the secondary prevention of cardiovascular events. These studies are compelling and have generated some newfound skepticism regarding a clinical role for folic acid therapy. Because these intervention trials have been limited to patients with mild hyperhomocysteinemia, the results of the trials imply that folic acid therapy may be best suited for individuals with more robustly elevated homocysteine levels. Furthermore, the potential benefit of folic acid therapy for primary prevention in individuals at low- or intermediate-risk for atherothrombotic disease has not been studied to date. Thus, at this time, folic acid therapy for borderline or mild hyperhomocysteinemia is not recommended. However, the role of folic acid therapy in patients with intermediate or severe hyperhomocysteinemia, or for primary prevention of cardiovascular diseases, remains unresolved.

Homocysteine and abdominal aortic aneurysms

There is evidence to suggest that increased levels of homocysteine play a significant role in vascular disease. It has been suggested that lowering homocysteine levels by dietary folate supplementation may reduce the risk of stroke and coronary heart disease. It is plausible that homocysteine may also play a role in the pathogenesis of abdominal aortic aneurysms (AAA) and that patients with this disease may benefit from folate supplementation. Our objective was to review the published work with regard to the role of homocysteine in the pathogenesis of AAA. Searches were carried out in published work in English with the keywords 'abdominal aortic aneurysm' and 'homocysteine'. There is evidence from in vitro and animal model studies that activation of metalloproteinases by homocysteine can influence aortic wall structure. Several case-control studies report an association between increased levels of homocysteine and the presence of an AAA. There are conflicting genotypic data concerning the association between methylenetetrahydrofolate reductase gene variants and AAA. Although there is evidence for an association between homocysteine and AAA, it is not strong enough to conclude that it plays a causal role in the pathogenesis of AAA. Further research is needed, given the potential benefit that simple vitamin supplementation may have for patients with AAA.

Hyperhomocysteinemia and thrombosis: an overview

CONTEXT

Homocysteine, a sulfur-containing amino acid, absent in natural diets, is a metabolic intermediary in transmethylation and transsulfuration reactions. Such reactions are essential to normal cellular growth, differentiation, and function. Excess homocysteine is associated with vascular disease and related disorders.

OBJECTIVE

To review homocysteine metabolism, the pathogenesis and classification of hyperhomocysteinemia, and the published literature investigating the association of homocysteine and methylenetetrahydrofolate reductase defects with arterial and venous thromboembolism and related disorders. The role of vitamin supplementation in patients with hyperhomocysteinemia is addressed.

DATA SOURCES

Published medical and scientific literature. Articles addressing the objectives were selected and reviewed. Pertinent studies and conclusions were summarized, grouped, and contrasted.

CONCLUSIONS

The association of hyperhomocysteinemia and arterial and venous thrombosis is controversial. Severe hyperhomocysteinemia is associated with atherosclerosis. The effect of mild hyperhomocysteinemia is less certain. Coinheritance of methylenetetrahydrofolate reductase defects and factor V Leiden is likely to increase the risk of venous thromboembolism. The association of methylenetetrahydrofolate reductase defects combined with no additional thrombophilic risk factors with venous thrombosis is less clear. High doses of folic acid to lower homocysteine levels might not be necessary.

Protective effect of hydrogen sulfide on balloon injury-induced neointima hyperplasia in rat carotid arteries

Endogenous hydrogen sulfide (H(2)S), generated from homocysteine metabolism mainly catalyzed by cystathionine gamma-lyase (CSE), possesses important functions in the cardiovascular system. In this study, we investigated the role of H(2)S during the pathogenesis of neointimal formation induced by balloon injury in rats. CSE mRNA levels were reduced by 86.5% at 1 week and 64.0% at 4 weeks after balloon injury compared with the uninjured controls. CSE activity was also correspondingly reduced. Endogenous production of H(2)S in the injured carotid artery was significantly inhibited at 1 week and 4 weeks after balloon injury. Treatment with NaHS (a donor of H(2)S) enhanced methacholine-induced vasorelaxation of balloon-injured artery. More importantly, treatment with NaHS significantly inhibited neointima formation (0.15 +/- 0.01 mm(2) versus 0.21 +/- 0.01 mm(2), P < 0.001) of the balloon-injured carotid arteries and reduced the intima/media ratio (1.05 +/- 0.07 versus 1.43 +/- 0.06, P < 0.001). A significant decrease in vascular smooth muscle cell proliferation was demonstrated by bromodeoxyuridine incorporation at day 7 after injury. In conclusion, CSE expression and H(2)S production are reduced during the development of balloon injury-induced neointimal hyperplasia, and treatment with NaHS significantly reduces neointimal lesion formation.

Lowering homocysteine with B vitamins has no effect on blood pressure in older adults

An elevated circulating homocysteine concentration is associated with the risk of cardiovascular disease. The mechanism by which an elevated homocysteine increases cardiovascular risk is unclear but may be mediated in part by elevating blood pressure. It is well established that supplements containing folate, vitamins B-12, and B-6 lower homocysteine concentrations. However, the effect of homocysteine-lowering vitamins on blood pressure has not been well studied. We sought to determine whether lowering homocysteine with B vitamins lowers blood pressure in healthy older people with elevated homocysteine concentrations. Two hundred seventy-six healthy older participants (> or = 65 y) with a homocysteine > or = 13 micromol/L were randomized to receive a daily supplement containing folate (1 mg), vitamin B-12 (500 microg), and vitamin B-6 (10 mg), or a placebo, for 2 y. Plasma homocysteine was lower in the Vitamins group than the Placebo group at both 1 [-4.3 micromol/L (95% CI; -4.9, -3.7)] and 2 y [-4.4 micromol/L (95% CI: -5.3, -3.6)]. Systolic and diastolic blood pressures as well as pulse pressure in the Vitamins group did not differ from the Placebo group over the duration of the trial. The mean differences in blood pressures, adjusted for baseline values, did not exceed 1 mm Hg. Supplemental B-vitamins lowered plasma homocysteine but had no effect on blood pressure in older people with elevated baseline homocysteine concentrations.

Antioxidant supplementation with or without B-group vitamins after acute ischemic stroke: a randomized controlled trial

BACKGROUND

Evidence shows that there is a rapid increase in the production of markers of oxidative damage immediately after acute ischemic stroke and that endogenous antioxidant defenses are rapidly depleted, thus permitting further tissue damage. Several studies point to an antioxidant effect of B-group vitamins and a pro-oxidant effect of elevated total plasma homocysteine (tHcy).

METHODS

To test whether supplementary antioxidants with or without B-group vitamins during this critical period enhance antioxidant capacity or mitigate oxidative damage, ninety-six acute ischemic stroke patients within 12 hours of symptom onset were randomly assigned to receive either daily oral 800 IU (727 mg) vitamin E and 500 mg vitamin C (n = 24), or B-group vitamins (5 mg folic acid, 5 mg vitamin B(2), 50 mg vitamin B(6), and 0.4 mg of vitamin B(12); n = 24), both vitamins together (n = 24), or no supplementation (n = 24) for 14 days. Treatment groups and controls were matched for stroke subtype and age. Blood was obtained before treatment, at day 7, and day 14 for measurements of plasma or blood vitamin status, plasma total antioxidant capacity (TAOC), malondialdehyde (MDA), tHcy and C-reactive protein (CRP).

RESULTS

Supplementation with antioxidant vitamins and B-group vitamins separately or together significantly increased the plasma concentration of vitamin C, E, pyridoxal phosphate (B(6) status), red blood cell folate, and improved a measure of B(2) status (red cell glutathione reductase activation coefficient [EGRAC]), compared with the control group. Plasma TAOC increased significantly in the antioxidant treatment groups compared with the nonsignificant decline seen in the control group. tHcy concentrations decreased in subjects who received B-group vitamins and the control group compared with the rise seen in those who received antioxidants alone. There was a significant reduction in plasma MDA concentration in the 3 treatment groups, in contrast to the increase seen in the control group; however, the changes were most evident in antioxidant groups. CRP concentrations (a marker of tissue inflammation) were significantly lower in the 3 treatment groups compared with the control group. There were no additive or synergistic effects of antioxidants and B-group vitamins together on any outcome measure.

CONCLUSIONS

Antioxidants supplementation with or without B-group vitamins enhances antioxidant capacity, mitigates oxidative damage, and may have an anti-inflammatory effect immediately postinfarct in stroke disease.

Pathophysiological consequences of homocysteine excess

Elevated level of the nonprotein amino acid homocysteine (Hcy) is a risk factor for cardiovascular diseases, neurodegenerative diseases, and neural tube defects. However, it is not clear why excess Hcy is harmful. To explain Hcy toxicity, the "Hcy-thiolactone hypothesis" has been proposed. According to this hypothesis, metabolic conversion of Hcy to a chemically reactive metabolite, Hcy-thiolactone, catalyzed by methionyl-tRNA synthetase is the first step in a pathway that contributes to Hcy toxicity in humans. Plasma Hcy-thiolactone levels are elevated in human subjects with hyperhomocysteinemia caused by mutations in CBS or MTHFR genes. Plasma and urinary Hcy-thiolactone levels are also elevated in mice fed a high-methionine diet. Hcy-thiolactone can be detrimental because of its intrinsic ability to form N-Hcy-protein adducts, in which a carboxyl group of Hcy is N-linked to epsilon-amino group of a protein lysine residue. This article reviews recent studies of Hcy-thiolactone and N-Hcy-protein in the human body, including their roles in autoimmune response, cellular toxicity, and atherosclerosis. Potential utility of Hcy-thiolactone, N-Hcy-protein, or anti-N-Hcy-protein autoantibodies as markers of Hcy excess is discussed.

Homocysteine lowering with folic acid and B vitamins in vascular disease

BACKGROUND

In observational studies, lower homocysteine levels are associated with lower rates of coronary heart disease and stroke. Folic acid and vitamins B6 and B12 lower homocysteine levels. We assessed whether supplementation reduced the risk of major cardiovascular events in patients with vascular disease.

METHODS

We randomly assigned 5522 patients 55 years of age or older who had vascular disease or diabetes to daily treatment either with the combination of 2.5 mg of folic acid, 50 mg of vitamin B6, and 1 mg of vitamin B12 or with placebo for an average of five years. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, and stroke.

RESULTS

Mean plasma homocysteine levels decreased by 2.4 micromol per liter (0.3 mg per liter) in the active-treatment group and increased by 0.8 micromol per liter (0.1 mg per liter) in the placebo group. Primary outcome events occurred in 519 patients (18.8 percent) assigned to active therapy and 547 (19.8 percent) assigned to placebo (relative risk, 0.95; 95 percent confidence interval, 0.84 to 1.07; P=0.41). As compared with placebo, active treatment did not significantly decrease the risk of death from cardiovascular causes (relative risk, 0.96; 95 percent confidence interval, 0.81 to 1.13), myocardial infarction (relative risk, 0.98; 95 percent confidence interval, 0.85 to 1.14), or any of the secondary outcomes. Fewer patients assigned to active treatment than to placebo had a stroke (relative risk, 0.75; 95 percent confidence interval, 0.59 to 0.97). More patients in the active-treatment group were hospitalized for unstable angina (relative risk, 1.24; 95 percent confidence interval, 1.04 to 1.49).

CONCLUSIONS

Supplements combining folic acid and vitamins B6 and B12 did not reduce the risk of major cardiovascular events in patients with vascular disease. (ClinicalTrials.gov number, NCT00106886; Current Controlled Trials number, ISRCTN14017017.).

Rationale, design and baseline characteristics of a large, simple, randomized trial of combined folic acid and vitamins B6 and B12 in high-risk patients: the Heart Outcomes Prevention Evaluation (HOPE)-2 trial

BACKGROUND

Epidemiological studies suggest that mild to moderate elevation in plasma homocysteine concentration is associated with increased risk of atherothrombotic cardiovascular (CV) disease. Simple, inexpensive and nontoxic therapy with folic acid and vitamins B6 and B12 reduces plasma homocysteine levels by approximately 25% to 30% and may reduce CV events. Therefore, a large, randomized clinical trial--the Heart Outcomes Prevention Evaluation (HOPE)-2 study--is being conducted to evaluate this therapy in patients at high risk for CV events.

OBJECTIVES

To evaluate whether long-term therapy with folic acid and vitamins B6 and B12 reduces the risk of major CV events in a high-risk population. The primary study outcome is the composite of death from CV causes, myocardial infarction and stroke.

METHODS

A total of 5522 patients aged 55 years or older with pre-existing CV disease or with diabetes and additional risk factor(s) at 145 centres in 13 countries were randomly assigned to daily therapy with combined folic acid 2.5 mg, vitamin B6 50 mg and vitamin B12 1 mg, or to placebo. Follow-up will average five years, to be completed by the end of 2005.

RESULTS

The patients' baseline characteristics confirmed their high-risk status. Baseline homocysteine levels varied between countries and regions. HOPE-2 is one of the largest trials of folate and vitamins B6 and B12 and is expected to significantly contribute to the evaluation of the role of homocysteine lowering in CV prevention.

Hyperhomocysteinemia inhibits post-injury reendothelialization in mice

OBJECTIVE

Hyperhomocysteinemia (HHcy) is a risk factor for cardiovascular disease and has been reported to inhibit endothelial cell (EC) growth. Notwithstanding, precisely how HHcy regulates EC growth in vivo remains unknown. In this study, we established a mouse model of endothelial injury and reendothelialization and examined the role and mechanism of HHcy in endothelial repair.

METHODS AND RESULTS

A mouse model of carotid artery air-dry endothelium denudation and reendothelialization was established and used to evaluate post-injury endothelial repair in mice with the gene deletion of cystathionine-beta-synthase (CBS). Moderate and severe HHcy were induced in CBS+/+ and CBS-/+ mice through a high-methionine diet. Post-injury reendothelialization, which correlated with increased post-injury neointima formation, was impaired in severe HHcy mice. To elucidate the underlying mechanism, we examined circulating endothelial progenitor cells (EPC) in HHcy mice and studied the effect of homocysteine (Hcy) on proliferation, migration, and adhesion of human umbilical vein endothelial cells (HUVEC). The peripheral EPC population was not significantly altered in HHcy mice. Hcy had a profound inhibitory effect on EC proliferation and migration at physiologically relevant concentrations and inhibited EC adhesion at concentrations of 200 microM and higher.

CONCLUSION

We have established a convenient and accurate mouse model of carotid injury in which the reendothelialization process can be precisely quantified. In addition, we have observed impaired reendothelialization and increased neointimal formation in severe HHcy mice. The capacity of Hcy to inhibit proliferation and migration of EC may be responsible for impaired reendothelialization and contribute to arteriosclerosis in HHcy.

Hyperhomocyst(e)inemia impairs angiogenesis in a murine model of limb ischemia

Hyperhomocyst(e)inemia (HH) is an established independent risk factor for coronary, cerebral and peripheral vascular diseases. Recent studies have indicated that certain cardiovascular risk factors, including diabetes and hypercholesterolemia, impair expression of vascular endothelial growth factor (VEGF) and endogenous angiogenesis. In this study, we investigate the impact of moderate HH on angiogenesis and VEGF pathway in a mouse model of hindlimb ischemia. Upon induction of unilateral hindlimb ischemia, endogenous angiogenesis, expression of VEGF, and phosphorylation of the VEGF receptor Flk-1 were evaluated in mice heterozygous for a deletion of the cystathionine beta-synthase gene (CBS) and compared with those observed in CBS+/+ mice. CBS+/- mice exhibit moderate HH, as demonstrated by measuring plasma total homocyst(e)ine (tHcy) levels, which were significantly higher in these animals compared with CBS+/+ mice (4.77 +/- 0.82 vs 2.10 +/- 0.28, p < 0.01). Twenty-eight days after induction of ischemia, hindlimb blood flow was significantly reduced in CBS+/- mice compared with CBS+/+ animals (0.49 +/- 0.03, n = 12 vs 0.71 +/- 0.09, n = 10; p < 0.05). In addition, there was a significant negative correlation between plasma homocyst(e)ine levels and the laser Doppler perfusion ratio in CBS+/- mice (p = 0.0087, r = -0.7171). While VEGF expression and Flk-1 phosphorylation were not impaired in the ischemic muscles of CBS+/- mice, phosphorylation of the endothelial cell survival factor Akt was significantly inhibited by homocyst(e)ine in a dose-dependent manner in human umbilical vein endothelial cell (HUVECs) in vitro. In conclusion, our findings demonstrate that endogenous angiogenesis is inversely related to plasma levels of homocyst(e)ine in genetically engineered, heterozygous mice with moderate HH. This impairment, however, is not dependent on reduced expression of VEGF or impaired phosphorylation of its receptor Flk-1. In contrast, our data suggest that impaired Akt phosphorylation mediates the impairment of angiogenesis associated with HH.

Mechanisms of homocysteine-induced atherothrombosis

Elevation of plasma homocysteine level is a risk factor for cardiovascular disease, stroke, and venous thromboembolism. It is still uncertain, however, whether hyperhomocysteinemia is a causative factor or a marker of vascular disease. The strongest evidence that homocysteine plays a causal role in atherothrombosis has been provided by studies using animal models. In the past decade, considerable progress in defining the vascular effects of hyperhomocysteinemia was achieved through the use of genetic and dietary approaches to induce hyperhomocysteinemia in experimental animals. A key vascular phenotype observed in hyperhomocysteinemic animals is endothelial dysfunction, manifested by decreased bioavailability of endothelium-derived nitric oxide. Impairment of endothelial function may be mediated by either accelerated oxidative inactivation of nitric oxide or inhibition of nitric oxide production caused by the endogenous nitric oxide synthase inhibitor, asymmetric dimethylarginine. Hyperhomocysteinemia also increases susceptibility to arterial thrombosis and accelerates the development of atherosclerosis in susceptible models such as the apolipoprotein E-deficient mouse. Mechanisms of atherothrombosis may include homocysteine-induced thiolation or acylation of plasma or endothelial proteins and endoplasmic reticulum stress, which activates signal transduction pathways leading to inflammation and apoptosis.

Plasma homocysteine concentration and blood pressure in healthy Iranian adults: the Tehran Homocysteine Survey (2003–2004)

Hypertension is a modifiable risk factor for cardiovascular disease, but its aetiology has not been fully elucidated. Recently, attention has been focused on the direct relations of plasma homocysteine (Hcy) to blood pressure (BP). The purpose of this study was to determine the relationship of Hcy with BP and other cardiovascular disease risk factors. This population-based study was a part of the Cardiovascular Risk Factors Survey and has been designed and conducted based on the methodology of the MONICA/WHO Project. A total of 1214 people aged 25-64 years were recruited using cluster sampling and assessed regarding standardized methods. BP was measured in seated position after a 10-min rest period. Blood samples were gathered and analysed according to standard methods. Variables were assessed in 1191 participants (416 men; 775 women). Mean age was higher in hypertensives compared to normotensives (P < 0.001). Mean Hcy was higher in hypertensives, but significant only in men (P < 0.031). Concurrent effects of Hcy, folate and vitamin B12 on hypertension indicated that Hcy acts as a risk factor and folate and vitamin B12 as protective factors; however, after adjustment, just vitamin B12 remained as a protective factor. Although we detected a simple correlation of Hcy with BP in Iranian adults, this relationship was no longer significant after applying an adjustment. In light of our observations, it is likely that the increased Hcy levels reported in hypertensive persons are concomitant rather than a precursor of hypertension.

Helicobacter pylori eradication lowers serum homocysteine level in patients without gastric atrophy

AIM

To determine whether Helicobacter pylori (H pylori)infection caused hyperhomocysteinemia by altering serum vitamin B(12), serum folate and erythrocyte folate levels and whether eradication of this organism decreased serum homocysteine level.

METHODS

The study involved 73 dyspeptic H pylori-positive patients, none of them had gastric mucosal atrophy based on rapid urease test and histology. Out of 73 patients, 41 (56.2%) showed a successful eradication of H pylori 4 wk after the end of treatment. In these 41 patients, fasting serum vitamin B(12), folate and homocysteine levels, and erythrocyte folate levels before and 4 wk after H pylori eradication therapy were compared.

RESULTS

The group with a successful eradication of H pylori had significantly higher serum vitamin B(12) and erythrocyte folate levels in the post-treatment period compared to those in pre-treatment period (210+/-97 pg/mL vs 237+/-94 pg/mL, P<0.001 and 442+/-212 ng/mL vs 539+/-304 ng/mL, P = 0.024, respectively), but showed no significant change in serum folate levels (5.6+/-2.6 ng/mL vs 6.0+/-2.4 ng/mL, P = 0.341). Also, the serum homocysteine levels in this group were significantly lower after therapy (13.1+/-5.2 micromol/L vs 11.9+/-6.2 micromol /L, P = 0.002). Regression analysis showed that serum homocysteine level was positively correlated with age (P = 0.01) and negatively with serum folate level before therapy (P = 0.003).

CONCLUSION

Eradication of H pylori decreases serum homocysteine even in patients who do not exhibit gastric mucosal atrophy. It appears that the level of homocysteine in serum is related to a complex interaction among serum vitamin B(12), serum folate and erythrocyte folate levels.

Nitric Oxide Inhibition of Homocysteine-induced Human Endothelial Cell Apoptosis by Down-regulation of p53-dependent Noxa Expression through the Formation of S-Nitrosohomocysteine

Hyperhomocysteinemia is believed to induce endothelial dysfunction and promote atherosclerosis; however, the pathogenic mechanism has not been clearly elucidated. In this study, we examined the molecular mechanism by which homocysteine (HCy) causes endothelial cell apoptosis and by which nitric oxide (NO) affects HCy-induced apoptosis. Our data demonstrated that HCy caused caspase-dependent apoptosis in cultured human umbilical vein endothelial cells, as determined by cell viability, nuclear condensation, and caspase-3 activation and activity. These apoptotic characteristics were correlated with reactive oxygen species (ROS) production, lipid peroxidation, p53 and Noxa expression, and mitochondrial cytochrome c release following HCy treatment. HCy also induced p53 and Noxa expression and apoptosis in endothelial cells from wild type mice but not in the p53-deficient cells. The NO donor S-nitroso-N-acetylpenicillamine, adenoviral transfer of inducible NO synthase gene, and antioxidants (alpha-tocopherol and superoxide dismutase plus catalase) but not oxidized SNAP, 8-Br-cGMP, nitrite, and nitrate, suppressed ROS production, p53-dependent Noxa expression, and apoptosis induced by HCy. The cytotoxic effect of HCy was decreased by small interfering RNA-mediated suppression of Noxa expression, indicating that Noxa up-regulation plays an important role in HCy-induced endothelial cell apoptosis. Overexpression of inducible NO synthase increased the formation of S-nitroso-HCy, which was inhibited by the NO synthase inhibitor N-monomethyl-l-arginine. Moreover, S-nitroso-HCy did not increase ROS generation, p53-dependent Noxa expression, and apoptosis. These results suggest that up-regulation of p53-dependent Noxa expression may play an important role in the pathogenesis of atherosclerosis induced by HCy and that an increase in vascular NO production may prevent HCy-induced endothelial dysfunction by S-nitrosylation.

Homocysteine induces DNA synthesis and proliferation of vascular smooth muscle cells by interfering with MAPK kinase pathway

Hyperhomocysteinemia has been identified as an important and independent risk factor for cerebral, coronary and peripheral atherosclerosis. However the mechanisms by which homocysteine promote atherosclerotic plaque formation are not clearly defined. Earlier reports have suggested that homocysteine exert its effect via the H2O2 produced during its metabolism. To evaluate which signalling molecules are involved in homocysteine induced atherosclerotic changes during the pathogenesis of vascular diseases, we examined homocysteine induced smooth muscle cell proliferation in the presence of different signal transduction inhibitors. We show that MAPK kinase pathway is involved in homocysteine induced DNA synthesis and proliferation of vascular smooth muscle cells in the presence of the peroxide scavenging enzyme, catalase. Our data suggest that homocysteine induces smooth muscle cell growth through a pathway that is independent of H2O2, that involves MAPK kinase activation, and that results in accelerated atherosclerosis.

B-group vitamin supplementation mitigates oxidative damage after acute ischaemic stroke

Evidence shows that there is a rapid increase in the production of markers of oxidative damage immediately following acute stroke and that endogenous antioxidant defences are rapidly depleted, thus permitting further tissue damage. Several studies point to an antioxidant effect of B-group vitamins and a pro-oxidant effect of elevated plasma tHcy (total homocysteine). In the present study, we assessed whether supplementary B-group vitamins during this critical period will enhance antioxidant capacity and mitigate oxidative damage. Forty-eight patients with acute ischaemic stroke within 12 h of symptom onset were assigned to receive daily oral supplements of B-group vitamins comprising 5 mg of folate, 5 mg of vitamin B2, 50 mg of vitamin B6 and 0.4 mg of vitamin B12 (n=24) or no supplements (n=24) for 14 days. The treatment group and controls were matched for stroke subtype and age. Blood samples were obtained before intervention and also at 7 and 14 days post-recruitment for measurement of the following biomarkers: red cell folate (whole blood folate corrected with haematocrit), erythrocyte glutathione reductase activity coefficient (EGRAC; measure of vitamin B2 status), plasma pyridoxal phosphate (vitamin B6 status), plasma vitamin B12, plasma alpha-tocopherol, plasma ascorbic acid, plasma TAOC (total antioxidant capacity), plasma MDA (malondialdehyde), plasma tHcy and CRP (C-reactive protein). Supplementation for 14 days with B-group vitamins significantly increased the plasma concentrations of pyridoxal phosphate and red blood cell folate and improved a measure of B2 status compared with the control group (P<0.05). Plasma tHcy decreased in both groups albeit less in the control group, but differences in cumulative changes were not significant. There was, however, a decrease in plasma MDA concentration in the treatment group, in contrast with the increase seen in the control group and these differences were significant (P=0.05). CRP concentration, a marker of tissue inflammation, was significantly lower in the treatment group compared with controls (P<0.05). In conclusion, B-group vitamin supplementation immediately post-infarct may have antioxidant and anti-inflammatory effects in stroke disease independent of a homocysteine-lowering effect.

Is serum ferritin an additional cardiovascular risk factor for all postmenopausal women?

BACKGROUND

Most of the studies on cardiovascular disease (CVD) risk factors in menopause have focused on serum lipid(lipoprotein) abnormalities and were conducted in populations which were not well controlled for several important influential factors.

METHODS

Two homogenous groups of 30 apparently healthy Caucasian premenopausal women and 3-5 years postmenopausal women who were nonobese, nonsmoking and not using estrogen were compared in a well-controlled cross-sectional design. Fasting serum ferritin and plasma total homocysteine (tHcy) were evaluated concomitantly to classical serum lipid(lipoprotein) risk factors. Relationships between risk factors and the influence of other contributing variables such as diet and body weight were also examined.

RESULTS

Serum total cholesterol (p < 0.01), low-density lipoproteins (LDL; p < 0.05) and triglycerides (p < 0.05) of postmenopausal women were greater than that of their menstruating counterparts, even though they ate a CVD-preventive diet, had similar body weight and body fat distribution. Their serum ferritin was almost 3-fold greater (p < 0.0001) but was still within normal limits, except for the 38.5% of postmenopausal women who exhibited values above the 80 mug/l limit that has been associated with sharp increases in the rate of heart disease in either gender. Serum ferritin was low in one third of the postmenopausal group (as low as in the premenopausal control group, whose dietary iron intake was slightly below the nutritional recommendation). The mean plasma tHcy of the postmenopausal group was almost twice as elevated (p < 0.0001). Both ferritin and tHcy were found to be linked to serum cholesterol. The correlation between tHcy and triglycerides was also significant.

CONCLUSION

Early menopause is not associated with blood iron overload and CVD risk factor in an important proportion of women.

Homocysteine-thiolactone and S-nitroso-homocysteine mediate incorporation of homocysteine into protein in humans

Indirect pathways, involving homocysteine (Hcy)-thiolactone and S-nitroso-Hcy, allow incorporation of Hcy into protein. Hcy-thiolactone, synthesized by methionyl-tRNA synthetase in all organisms investigated, including human, modifies proteins post-translationally by forming adducts in which Hcy is linked by amide bonds to epsilon-amino group of protein lysine residues. S-Nitroso-Hcy, synthesized in human vascular endothelial cells, is incorporated translationally into peptide bonds in protein at positions normally occupied by methionine. Hcy-N-hemoglobin and Hcy-N-albumin constitute a major pool of Hcy in human blood. Hcy-thiolactone is present in human plasma. Modification with Hcy-thiolactone leads to protein damage. Hcy-thiolactone is detoxified by Hcy-thiolactonase/paraoxonase present in a subset of high-density lipoprotein particles in humans.

Restenosis in Intervened Coronaries with Hyperhomocysteinemia (RICH)

BACKGROUND

Controversy exists regarding the contribution made by elevated serum homocysteine evels in raising the risk of restenosis after percutaneous coronary interventions. The objective of this study was to determine whether elevated homocysteine evels increase the risk of restenosis.

METHODS

Two hundred and two consecutive patients undergoing percutaneous coronary intervention with stents on previously nonintervened native coronary arteries were eligible for enrollment in the study. Before the percutaneous coronary intervention, a fasting serum homocysteine evel was drawn. Patients were followed-up by their primary cardiologists for recurrence of symptoms. Those patients who had a recurrence of anginal symptoms consistent with clinical restenosis were referred for a repeat angiogram. All other patients were followed-up medically. The homocysteine evels of the patients who had repeat angiography for recurrent symptoms were compared to those who were followed-up medically.

RESULTS

Age, stent ength, stent diameter, and homocysteine evels were all associated with an increased risk of restenosis in the univariate analysis. In the multiple ogistic regression model, the only variable that remained significant in relation to an increased risk of restenosis was homocysteine. There was a significant difference in the mean homocysteine evels between the restenosis group (13.7 micromol/L) and those without restenosis (9.6 micromol/L; P <.0001). A homocysteine evel > or =11.1 micromol/L was identified as the best threshold for an increased risk of restenosis with a sensitivity of 75.0% and specificity of 76.9% (OR 6.5, CI 2.3-18.6; P =.0004).

CONCLUSION

This study demonstrates that elevated homocysteine evels strongly correlate with an increased risk of restenosis.

Menopause, the Cardiovascular Risk Factor Homocysteine, and the Effects of Treatment

Since the identification of homocysteine (Hcy) as a risk factor for cardiovascular disease, it has been the subject of much research. As with other cardiovascular risk factors, a gender difference exists for Hcy. Plasma levels are lower in women of reproductive age than in men and postmenopausal women. This has led to the hypothesis that the increased risk of cardiovascular disease documented in postmenopausal women may be related to the increase in Hcy levels. Factors affecting total plasma levels of Hcy include genetic factors, nutritional factors, and lifestyle. Many studies appear to support the ability of estrogen replacement therapy to significantly lower both basal levels of Hcy and levels following methionine loading. A mean reduction of 10-15% in Hcy levels after 6 months of hormone therapy has been reported. Similarly, raloxifene and tamoxifen and low-dose folic acid administration induce reductions in plasma Hcy levels of the same degree observed for hormone therapy. The reduction occurs after a few months of therapy and is sustained, suggesting the potential for cardioprotective effects. Although there is a positive effect of estrogen therapy and hormone therapy on Hcy levels, recent studies do not recommend the use of estrogen or hormone replacement therapy for the primary or secondary prevention of cardiovascular disease. Further research is therefore needed to identify strategies to maximize the efficacy of hormone replacement therapy, while minimizing the risks.

Brain energy metabolism is compromised by the metabolites accumulating in homocystinuria

Homocystinuria is an inborn error of metabolism caused by severe deficiency of cystathionine beta-synthase activity. It is biochemically characterized by tissue accumulation of homocysteine (Hcy) and methionine (Met). Homocystinuric patients present a variable degree of neurological dysfunction whose pathophysiology is poorly understood. In the present study, we investigated the in vitro effect of Hcy and Met on some parameters of energy metabolism in hippocampus of rats. CO(2) production from [U-14C] acetate, glucose uptake and lactate release were assessed by incubating hippocampus prisms from 28-day-old rats in Krebs-Ringer bicarbonate buffer, pH 7.4, in the absence (controls) or presence of Hcy (10-500 microM) or Met (0.2-2.0mM). Hcy and Met decreased CO(2) production in a dose-dependent manner and increased lactate release. In contrast, glucose uptake was not altered by the metabolites. The effect of Hcy and Met on cytochrome c oxidase activity was also studied. It was observed that Met did not alter this enzyme activity, in contrast with Hcy, which significantly inhibited cytochrome c oxidase activity. It is suggested that impairment of brain energy metabolism caused by the metabolites accumulating in homocystinuria may be related to the neurological symptoms present in homocystinuric patients.

Isoprenylcysteine carboxyl methyltransferase activity modulates endothelial cell apoptosis

Extracellular ATP, adenosine (Ado), and adenosine plus homocysteine (Ado/HC) cause apoptosis of cultured pulmonary artery endothelial cells through the enhanced formation of intracellular S-adenosylhomocysteine and disruption of focal adhesion complexes. Because an increased intracellular ratio of S-adenosylhomocysteine/S-adenosylmethionine favors inhibition of methylation, we hypothesized that Ado/HC might act by inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT). We found that N-acetyl-S-geranylgeranyl-L-cysteine (AGGC) and N-acetyl-S-farnesyl-L-cysteine (AFC), which inhibit ICMT by competing with endogenous substrates for methylation, caused apoptosis. Transient overexpression of ICMT inhibited apoptosis caused by Ado/HC, UV light exposure, or tumor necrosis factor-alpha. Because the small GTPase, Ras, is a substrate for ICMT and may modulate apoptosis, we also hypothesized that inhibition of ICMT with Ado/HC or AGGC might cause endothelial apoptosis by altering Ras activation. We found that ICMT inhibition decreased Ras methylation and activity and the activation of the downstream signaling molecules Akt, ERK-1, and ERK-2. Furthermore, overexpression of wild-type or dominant active H-Ras blocked Ado/HC-induced apoptosis. These findings suggest that inhibition of ICMT causes endothelial cell apoptosis by attenuation of Ras GTPase methylation and activation and its downstream antiapoptotic signaling pathway.

Effects of long-term administration of methionine on vascular endothelium in rabbits

BACKGROUND AND AIM

We studied the effects of long-term methionine administration on the vascular endothelium of Japanese white rabbits.

METHODS AND RESULTS

Eleven rabbits were divided into a control group (n = 6) and a methionine-fed group (n = 5), and reared for 22 weeks. Blood samples were collected at baseline and after 22 weeks for the measurement of serum homocysteine and cysteine, serum lipids and serum superoxide dismutase activity. At the end of experiments, the animals were sacrificed, and the thoracic aorta was removed for the measurement of isometric tension and histopathological examination. The blood samples taken from the methionine group in the 22nd week showed slight but significant increases in serum homocysteine and cysteine levels (Hcy: 13.7 +/- 1.4 vs 21.0 +/- 4.9, p < 0.01; Cys: 241.6 +/- 37.8 vs 342.6 +/- 35.0, p < 0.01). In the isometric tension experiments, the methionine group had a significantly decreased (p < 0.01) vasodilatation reaction induced by acetylcholine, an endothelium-dependent vasodilator. The histopathological examination (immunostaining in response to eNOS and tissue factor) showed significant increases in endothelium expression in the methionine group before atherosclerotic changes appeared.

CONCLUSIONS

The above results suggest that vascular endothelial dysfunction played an important role in the atherosclerosis occurring after excess methionine feeding.

Molecular mechanisms of cholesterol or homocysteine effect in the development of atherosclerosis: Role of vitamin E

The development of atherosclerosis is a multifactorial process in which both elevated plasma cholesterol levels and proliferation of smooth muscle cells play a central role. Numerous studies have suggested the involvement of oxidative processes in the pathogenesis of atherosclerosis and especially of oxidized low density lipoprotein. Some epidemiological studies have shown an association between high dietary intake and high serum concentrations of vitamin E and lower rates of ischemic heart disease. Cell culture studies have shown that alpha-tocopherol brings about inhibition of smooth muscle cell proliferation. This takes place via inhibition of protein kinase C activity. alpha-Tocopherol also inhibits low density lipoprotein induced smooth muscle cell proliferation and protein kinase C activity. The following animal studies showed that vitamin E protects development of cholesterol induced atherosclerosis by inhibiting protein kinase C activity in smooth muscle cells in vivo. Elevated plasma levels of homocysteine have been identified as an important and independent risk factor for cerebral, coronary and peripheral atherosclerosis. However the mechanisms by which homocysteine promotes atherosclerotic plaque formation are not clearly defined. Earlier reports have been suggested that homocysteine exert its effect via H2O2 produced during its metabolism. To evaluate the contribution of homocysteine in the pathogenesis of vascular diseases, we examined whether the homocysteine effect on vascular smooth muscle cell growth is mediated by H2O2. We show that homocysteine induces DNA synthesis and proliferation of vascular smooth muscle cells in the presence of peroxide scavenging enzyme, catalase. Our data suggest that homocysteine induces smooth muscle cell growth through the activation of an H2O2 independent pathway and accelerate the progression of atherosclerosis. The results indicate a cellular mechanism for the atherogenicity of cholesterol or homocysteine and protective role of vitamin E in the development of atherosclerosis.

Effects of folate treatment and homocysteine lowering on resistance vessel reactivity in atherosclerotic subjects

Hyperhomocysteinemia is associated with arterial hypertension and endothelial dysfunction in healthy humans. Placebo-controlled vitamin intervention studies cannot distinguish intrinsic actions of homocysteine (tHcy) and folate concentrations on the endothelium. The present two-period crossover study investigates the effects of tHcy lowering through oral folic acid on antioxidant status and resistance vessel reactivity in patients with established coronary artery disease (CAD). We investigated 27 male patients with angiographically documented multivessel CAD aged 50 (range 46-56) years. Resistance vessel reactivity was assessed by measurement of postischemic reactive hyperemia (RH) in the forearm using venous occlusion plethysmography at baseline, after 6 weeks of treatment with 5 mg of oral folic acid, and after a washout period of another 6 weeks. Plasma folate increased 3.49-fold with a mean tHcy reduction of 21.3%. Peak reactivity of resistance vessels improved significantly (18.97-23.60 ml/min(-1) per 100 ml; P = 0.01) with unchanged total antioxidant status (TAS; 0.912-0.944 microM; P = 0.4). This effect was limited to subjects (n = 14) with a tHcy reduction >2 microM (median reduction, 14.4-9.6 microM, P < 0.001). In the 13 subjects with a below-median reduction, tHcy remained unaltered (9.7-9.6 microM, P = 0.88) and TAS increased significantly (0.923-1.055 microM, P = 0.006), whereas RH peak flow was not affected (20.22-22.99 ml/min(-1) per 100 ml, P = 0.28). Homocysteine lowering >2 microM through folic acid supplementation improves resistance vessel reactivity in patients with CAD. Our data support the hypothesis that homocysteine lowering may have intrinsic vasoprotective effects largely independent of folate.

Homocysteine and atherothrombosis

Atherosclerosis with or without thrombosis superimposed is the most frequent cause of ischemic heart disease (IHD), peripheral arterial disease, and a main cause of stroke. Conflicting results have been reported in genetic, observational, and experimental studies on the relationship between homocysteine and these atherothrombotic diseases. Although cardiovascular complications are common in homocystinuric patients (severe hyperhomocysteinemia), IHD, the most frequent manifestation of atherothrombosis in the general population, appears to be rare. On the basis of findings in individuals with hyperhomocysteinemia of genetic origin, there is in fact no clear evidence for a causal role of homocysteine in the pathogenesis of atherothrombotic disease, and the positive association between plasma homocysteine and IHD observed in many, but not all epidemiologic studies does not prove causality. To infer causality from observational studies, there should be a temporal, consistent, strong, independent, graded (dose-response effect), and duration-dependent relationship between exposure and outcomes, and a biologically plausible mechanism should exist. The relationship between plasma homocysteine levels and IHD does not fulfill these criteria beyond reasonable doubt. In the general population, plasma homocysteine levels are to a great extent determined by dietary habits, and plasma homocysteine could be a marker, or a consequence, of atherothrombosis and/or risk-associated behavior (e.g., a diet low in fruits and vegetables) rather than a cause of atherothrombosis. Experimentally, hyperhomocysteinemia is not in itself atherogenic in normal animals with relatively low plasma cholesterol levels. The homocysteine theory of atherosclerosis should be tested more thoroughly in hypercholesterolemic animals that develop atherosclerosis spontaneously to determine whether elevated plasma homocysteine levels are harmful under atherogenic conditions. A causal role of homocysteine in atherothrombotic disease remains to be established.

Differential effects of homocysteine on porcine endothelial and vascular smooth muscle cells

High concentrations of homocysteine damage endothelial cells and lower concentrations increase vascular smooth muscle cell (VSMC) growth. This study investigated the effects of various concentrations of homocysteine on endothelial cells (VECs) and VSMCs in terms of cell survival, proliferation, and function. VECs and VSMCs from porcine thoracic aorta were studied. These cells were exposed to homocysteine in concentrations of 20 microM, 400 microM, and 1 mM every 8 h for 24 h, and its effect on cell survival, proliferation, and function were studied using methylthiazoletetrazolium assay, [3H]-thymidine incorporation test, and 6-keto-prostaglandin F1alpha enzyme-linked immunosorbent assay for VECs, and platelet-derived growth factor (PDGF) enzyme-linked immunosorbent assay for VSMCs, respectively. In VECs, 20 microM of homocysteine reduced the viable cell count to 95 +/- 31%, 400 microM reduced it to 89 +/- 35%, 1,000 microM reduced it to *58 +/- 29% (control = 100 +/- 30%, n = 18, *p < 0.05). In VSMCs, 20 microM of homocysteine slightly increased the viable cell count to 106 +/- 30%, but there was no statistical significance; 400 microM of homocysteine reduced the viable cell count to *74 +/- 29%, 1,000 microM to *50 +/- 24% (control = 100 +/- 28%, n = 18, *p < 0.05). In VECs, 20 microM of homocysteine reduced [3H]-thymidine uptake by 98 +/- 14%, 400 microM reduced it by *82 +/- 17%, 1,000 microM reduced it by *66 +/- 17% (control = 100 +/- 12, n = 6, *p < 0.05), respectively. But in VSMCs, 20 microM of homocysteine significantly increased [3H]-thymidine uptake (*131 +/- 16%), and thereafter, homocysteine decreased VSMCs [3H]-thymidine uptake, 400 microM by *24 +/- 7%, 1,000 microM by *29 +/- 10% (control = 100 +/- 16, n = 6, *p < 0.05), respectively. Homocysteine decreased VEC prostacyclin secretion in a dose-dependent manner, 20 microM by 105 +/- 0.65 pg/100 microl, 400 microM by *100 +/- 2.37 pg/100 microl, 1,000 microM by *93 +/- 2.54 pg/100 microl (control = 107 +/- 1.26 pg/100 microl, n = 6, *p = 0.007). In VSMCs, 20 microM of homocysteine slightly increased PDGF secretion by 62.2 +/- 20.7 pg/100 microl, but there was little statistical significance (p = 0.13); 400 microM of homocysteine reduced PDGF secretion by *28.9 +/- 10.7 pg/100 microl, and 1,000 microM reduced it by *21.3 +/- 4.7 pg/100 microl (control = 54.5 +/- 9.3 pg/100 microl, n = 6, *p < 0.05). High concentrations of homocysteine damaged both VECs and VSMCs with respect to cell survival, proliferation, and function. By increasing exposure to homocysteine, it was shown that physiologic high concentrations of homocysteine enhanced VSMC proliferation.

Homocysteine and arterial disease. Experimental mechanisms

Hyperhomocysteinemia (hH(e)) in the general population is associated with incidence and progression of arterial occlusive disease, although the underlying mechanisms are not well defined. Current research supports a role for homocysteine (H(e))-mediated endothelial damage and endothelial dysfunction. This mechanism appears to be a key factor in subsequent impaired endothelial-dependent vasoreactivity and decreased endothelium thromboresistance. These consequences may predispose hyperhomocysteinemic vessels to the development of increased atherogenesis. Additional mechanisms of H(e)-mediated vascular pathology, including protein homocysteinylation and vascular smooth muscle cell proliferation may also play a role. Continued investigation into the mechanisms contributing to H(e) toxicity will provide further insight into the processes by which hH(e) may increase atherosclerosis.

Homocysteine increases monocyte and T-cell adhesion to human aortic endothelial cells

Although hyperhomocysteinemia has been recognized as an independent risk factor for atherosclerosis, its mechanism(s) are not well understood. Because chemotaxis and accumulation of leukocytes such as monocytes and T cells have been demonstrated to be critical events in the initiation and development of atherosclerosis, we investigated the effect of homocysteine (HCY) on U937 monocytic cells- and Jurkat T-cell-human aortic endothelial cell (HAEC) interactions under inflammatory cytokine-stimulated conditions. When HAEC were pretreated with HCY followed by stimulation with IL-1 beta, U937 and Jurkat T-cell adhesion to HAEC increased in a dose-dependent manner. The significant increase in U937 cell adhesion to HAEC was also observed when U937 cells were treated with HCY or when both cell types were treated with HCY. We also demonstrated that HCY increases endothelial surface expression and mRNA level of adhesion molecules, VCAM-1 and E-selectin. Attenuation of Jurkat T-cell and U937 cell adhesion to HAEC by monoclonal antibodies directed to specific adhesion molecules demonstrated that both VCAM-1 and E-selectin are involved in Jurkat T-cell adhesion, and VCAM-1 in U937 cell adhesion. Supplementation of HAEC with vitamin E was effective in preventing HCY-stimulated Jurkat T-cell adhesion and VCAM-1 and E-selectin expression in HAEC. These results indicate that HCY-mediated leukocyte-endothelial cell interaction is one potential mechanism by which homocysteinemia may lead to the development of atherosclerosis under inflammatory conditions. Dietary antioxidants such as vitamin E may attenuate HCY-stimulated activation of the endothelium and may help reduce the risk of vascular disease associated with hyperhomocysteinemia.

Relation of Helicobacter pylori infection to plasma vitamin B12, folic acid, and homocysteine levels in patients who underwent diagnostic coronary arteriography

OBJECTIVE

The aim of this study was to test the hypothesis that chronic atrophic gastritis induced by Helicobacter pylori (H. pylori) causes malabsorption of vitamin B12 and folate in food, leading ultimately to an increase in circulating homocysteine levels.

METHODS

We performed endoscopy with stomach biopsy and measured fasting plasma homocysteine, vitamin B12, and folate levels in 93 patients who underwent diagnostic coronary arteriography. The patients were divided into two groups according to the presence (n = 57) or absence (n = 36) of H. pylori infection. Positive H. pylori infection was defined as positive H. pylori histology of biopsy specimens from the stomach. The extent of atrophic gastritis was endoscopically graded from 0 to 6.

RESULTS

There were no differences in age, sex, or traditional coronary risk factors between the two groups. Atrophy scores of the stomach were greater in patients with H. pylori infection than in patients without (3.9 +/- 1.4 vs 2.2 +/- 1.8, p < 0.0001). Patients with H. pylori infection had lower levels of vitamin B12 (630 +/- 222 vs 747 +/- 259 pg/ml, p = 0.02) and folate (6.2 +/- 2.1 vs 7.4 +/- 2.8, p = 0.046), as well as higher levels of homocysteine (11 +/- 4.9 vs 8.3 +/- 2.1 nmol/ml, p = 0.01), than did patients without H. pylori infection. Plasma homocysteine levels correlated inversely with plasma vitamin B12 and folate levels and positively with atrophic scores.

CONCLUSIONS

This study suggests that H. pylori-induced chronic atrophic gastritis decreases plasma vitamin B12 and folic acid levels, thereby increasing homocysteine levels. However, this effect does not seem to be strong.

Intraperitoneal infusion of homocysteine increases intimal hyperplasia in balloon-injured rat carotid arteries

Hyperhomocysteinemia is a significant risk factor in atherosclerosis and thrombosis. However, its role in the development of intimal hyperplasia after arterial reconstructive procedures remains uncertain. We therefore studied the effect of homocysteine on intimal hyperplasia in a rat model of carotid artery balloon injury. Twenty-four Sprague-Dawley rats were divided into three groups: control (saline infusion), and low dose (0.14 mg/day) and high dose (0.71 mg/day) homocysteine delivered continuously via osmotic pumps implanted intraperitoneally. All animals underwent left common carotid artery balloon denudation with sacrifice after 14 days. Plasma homocysteine levels, intimal hyperplasia, and cell proliferation of rat carotid arteries were determined. In vitro rat smooth muscle cell (SMC) proliferation with homocysteine treatment was also performed. Plasma homocysteine levels at sacrifice were 1.80+/-0.35, 2.65+/-0.05 and 3.50+/-0.22 microM in three groups, respectively. Intimal hyperplasia developed in all balloon-injured arteries in both control and homocysteine-treated animals. The intimal area and intima/media area ratio were increased by 92% (P<0.05) and 105% (P<0.05), respectively, in the high dose-homocysteine-treated animals as compared to the control animals. Homocysteine (high dose) also significantly promoted the intimal cell proliferation (bromodeoxyuridine incorporation) by 2.2-fold as compared to controls. Furthermore, homocysteine treatment in the cell culture study showed a concentration-dependent increase of rat SMC proliferation. These data demonstrate that the continuous intraperitoneal administration of homocysteine significantly increases intimal hyperplasia and SMC proliferation after carotid artery balloon injury in the rat as well as in vitro SMC proliferation. This study suggests that, following arterial reconstructive procedures, elevated plasma homocysteine may increase the complications of clinical restenoses that are associated with intimal hyperplasia.

Activation of JNK and transcriptional repressor ATF3/LRF1 through the IRE1/TRAF2 pathway is implicated in human vascular endothelial cell death by homocysteine

Endothelial cell injury underlies an increased occurrence of thromboembolic vascular disease in hereditary hyperhomocysteinemia. We have previously shown that homocysteine causes activation of c-Jun NH(2)-terminal kinase (JNK) and activating transcription factor 3/liver regenerating factor 1 (ATF3/LRF1) and induces apoptosis in human umbilical vein endothelial cells (HUVECs). In this study, the activation of JNK and ATF3 in HUVECs was mediated by the endoplasmic reticulum (ER) resident transmembrane kinase IRE1alpha and beta, which sense and transduce signal of the accumulationj of unfolded proteins in the ER. Moreover, dominant negative mutants of tumor necrosis factor receptor-associated factor 2 and mitogen-activated kinase kinase 4 and 7, as well as antisense ATF3 cDNA, inhibited cell death by homocysteine. These results indicate that the activation of JNK and ATF3 through the ER stress of homocysteine plays a role in the homocysteine-induced cell death. The JNK-ATF3 pathway may be implicated in endothelial cell injury associated with hereditary hyperhomocysteinemia.

Homocysteine and cardiovascular disease in diabetes mellitus

BACKGROUND

Patients with diabetes mellitus (DM) have 2- to 6-fold increase in the prevalence of cardiovascular disease (CVD) compared to non-DM subjects. Epidemiological data show that DM is synergic with other conventional risk factors. Total plasma homocysteine (tHcy) is an emerging CVD risk factor. We reviewed the literature to explore the relation between tHcy and CVD in patients with DM.

METHODS

We searched the MEDLINE database for articles on homocysteine, DM and CVD published from January 1991 to October 2000.

RESULTS

The mean plasma tHcy level is usually low or normal in DM patients, except when nephropathy is present. Levels in that case tend to be higher than in non-DM patients. An independent association with tHcy and CVD was shown in retrospective studies, for DM patients. Prospective studies showed an association between elevated tHcy and all cause mortality in DM patients. In general, the association between elevated levels of tHcy and the outcome was stronger than in non-DM individuals, for all types of study.

DISCUSSION

To date, there are no prospective work that specifically examined the relationship between levels of tHcy and the presence of CVD in the DM population. Nor are there studies to show that treating elevated tHcy results in a reduction of CVD events. Such studies are ongoing. Nevertheless, since hyperhomocysteinemia is potentially reversible with vitamin therapy, interaction of DM with high levels tHcy on the risk of CVD may have consequences with regard to management of primary and secondary prevention in DM patients who are at particularly high risk of CVD events.

Protein N-homocysteinylation: implications for atherosclerosis

Elevated levels of homocysteine (Hcy) are associated with various human pathologies, including cardiovascular disease. However, it is not exactly known why Hcy is harmful. A plausible hypothesis is that the indirect incorporation of Hcy into protein, referred to as protein N-homocysteinylation, leads to cell damage. A translational pathway involves: 1) reversible S-nitrosylation of Hcy with nitric oxide produced by nitric oxide synthase; 2) aminoacylation of tRNAMet with S-nitroso-Hcy catalyzed by MetRS; and 3) transfer of S-nitroso-Hcy from S-nitroso-Hcy-tRNAMet into growing polypeptide chains at positions normally occupied by methionine. Subsequent transnitrosylation leaves Hcy in the protein chain. A post-translational pathway involves: 1) metabolic conversion of Hcy to thiolactone by methionyl-tRNAsynthetase (MetRS), and 2) acylation of protein lysine residues by Hcy thiolactone. The levels of Hcy thiolactone and N-homocysteinylated protein in human vascular endothelial cells depend on the ratio of Hcy/Met, levels of folic acid, and HDL, factors linked to cardiovascular disease. HDL-associated human serum Hcy thiolactonase/paraoxonase hydrolyzes thiolactone to Hcy, thereby minimizing protein N-homocysteinylation. Variations in Hcy thiolactonase may play an important role in Hcy-associated human cardiovascular disease.

Homocysteine plasma levels in young patients with coronary artery disease. Relation to history of acute myocardial infarction and anatomical extent of disease

Although there is considerable epidemiologic evidence for a relationship between plasma homocysteine (Hcy) levels and cardiovascular disease, not all prospective studies have shown such a relationship. Furthermore, data concerning the role of hyperhomocysteinemia in patients with premature coronary artery disease (CAD) are rare. It was the aim of the study to investigate a possible association between Hcy plasma levels in young patients with the extent of CAD and the history of myocardial infarction (MI). A cohort of 94 patients was examined for conventional risk factors and the history of previous transmural MI. Furthermore, coronary angiography was performed to assess the anatomical extent of vessel disease. Plasma Hcy levels were measured by use of a commercial enzyme-linked immunosorbent assay. Only a history of previous MI was significantly associated with hyperhomocysteinemia. There was no relationship between elevated Hcy levels and the anatomical extent of vessel disease in patients with premature CAD. Our data may indicate that hyperhomocysteinemia represents an independent risk factor for acute coronary thrombosis rather than for the development of coronary sclerosis. Thereby, hyperhomocysteinemia may influence the clinical situation after plaque rupture not only by prothrombotic action but also by favouring endothelial dysfunction and vasospasm.

Homocysteine induces programmed cell death in human vascular endothelial cells through activation of the unfolded protein response

Severe hyperhomocysteinemia is associated with endothelial cell injury that may contribute to an increased incidence of thromboembolic disease. In this study, homocysteine induced programmed cell death in human umbilical vein endothelial cells as measured by TdT-mediated dUTP nick end labeling assay, DNA ladder formation, induction of caspase 3-like activity, and cleavage of procaspase 3. Homocysteine-induced cell death was specific to homocysteine, was not mediated by oxidative stress, and was mimicked by inducers of the unfolded protein response (UPR), a signal transduction pathway activated by the accumulation of unfolded proteins in the lumen of the endoplasmic reticulum. Dominant negative forms of the endoplasmic reticulum-resident protein kinases IRE1alpha and -beta, which function as signal transducers of the UPR, prevented the activation of glucose-regulated protein 78/immunoglobulin chain-binding protein and C/EBP homologous protein/growth arrest and DNA damage-inducible protein 153 in response to homocysteine. Furthermore, overexpression of the point mutants of IRE1 with defective RNase more effectively suppressed the cell death than the kinase-defective mutant. These results indicate that homocysteine induces apoptosis in human umbilical vein endothelial cells by activation of the UPR and is signaled through IRE1. The studies implicate that the UPR may cause endothelial cell injury associated with severe hyperhomocysteinemia.

Increasing levels of dietary homocystine with carotid endarterectomy produced proportionate increases in plasma homocysteine and intimal hyperplasia

PURPOSE

The role that homocysteine may play in post-carotid endarterectomy (CEA) restenosis due to intimal hyperplasia is not well understood. This study was designed to investigate the effects of different levels of dietary homocystine on: (1) plasma homocysteine; (2) post-CEA intimal hyperplasia; and (3) levels of the methyl donor S-adenosylmethionine (SAM) and its counterpart S-adenosylhomocysteine (SAH) in the homocysteine pathway.

METHODS

Male rats were fed specialized diets for 2 weeks pre- and post-CEA. Groups included control (0 homocystine added, n=9), 1.5 (1.5 g/kg homocystine added, n=10), 3.0 (3.0 g/kg homocystine added, n=9), and 4.5 (4.5 g/kg homocystine added, n=11). The rats underwent a surgical carotid endarterectomy. Endpoints included; plasma homocysteine, intimal hyperplasia, replicative index using with alpha-SM actin and BrdU, hepatic SAM levels, SAH levels, and the hepatic activities of methylenetetrahydrofolate reductase (MTHFR) and cystathionine beta-synthase (CBS).

RESULTS

Increasing dietary homocystine produced a proportionate increase in plasma homocysteine and an increase in intimal hyperplasia. Regression analysis of plasma homocysteine levels and intimal hyperplasia showed a significant correlation (r=0.71,P=0.003). Plasma homocysteine levels above 15 microM were associated with significant increases in intimal hyperplasia above 6.5% (P=0.04). Elevation of plasma homocysteine levels to moderate levels (5-25 microM) resulted in significant post-CEA intimal hyperplasia. Cellular analysis of the area of intimal hyperplasia in all diet groups showed comparable amounts of cells positive for alpha-SM actin. However, with increasing levels of dietary homocystine and plasma homocysteine there was an increase in replicative index (P<0.001) as determined by BrdU staining. Increasing dietary homocystine increased plasma homocysteine and was followed by increases in the replicative index thus producing increased intimal hyperplasia and lumenal stenosis. In hepatic measurements the 1.5 and 3.0 g/kg homocystine diets caused: increased liver activity of MTHFR (P=0.03) and decreased hepatic levels of SAM, SAH and SAM/SAH ratios compared to controls. Homocystine treatment did not cause significant alterations in CBS levels (P=0.992). These studies also showed no correlation of the MTHFR and CBS enzymes with plasma homocysteine levels or intimal hyperplasia. However, hepatic levels of SAM showed significant negative correlations with plasma homocysteine (r=-0.58; P=0.006) and with BrdU percentages of cellular proliferation (r=-0.69; P=0.06).

CONCLUSION

The degree of post-CEA intimal hyperplasia in a rat model is directly related to the plasma level of homocysteine. The hyperplastic effects of homocysteine may be mediated in part by a physiological insufficiency of methyl donors as shown by decreases in SAM. Thus, increasing levels of plasma homocysteine enhanced and accelerated the smooth muscle cell response after CEA which led to increased intimal hyperplasia and lumenal stenosis.

Efficiency of homocysteine plus copper in inducing apoptosis is inversely proportional to gamma-glutamyl transpeptidase activity

Hyperhomocysteinemia represents an independent risk factor for atherosclerosis, but the mechanisms leading to cellular dysfunctions remain unknown. Using ECV304 cells, we found that homocysteine (Hcy) plus copper (Cu2+) induced cytotoxic effects: loss of cell adhesion, increased permeability to PI, and the occurrence of morphologically apoptotic cells. This form of apoptosis, inhibited by Z-VAD-fmk, was associated with a loss of mitochondrial potential, a cytosolic release of cytochrome c, activation of caspase-3, degradation of poly(ADP-ribose)polymerase, and internucleosomal DNA fragmentation. However, the ability of Hcy plus Cu2+ to induce apoptosis decreased when the pretreatment culture time increased. As a positive correlation was found between the length of time of culture before treatment and the enhancement of gamma-glutamyl transpeptidase (gamma-GT) activity, we asked whether gamma-GT was involved in the control of Hcy plus Cu2+-induced apoptosis. Therefore, ECV304 cells were treated with either acivicin or dexamethasone, inhibiting and stimulating gamma-GT, respectively. In ECV304 cells and human umbilical venous endothelial cells, acivicin favored Hcy plus Cu2+-induced apoptosis whereas dexamethasone counteracted the apoptotic process. As acivicin and dexamethasone were also capable of modulating cell death in ECV304 cells treated with antitumoral drugs, our data emphasize that the involvement of gamma-GT in the control of apoptosis is not restricted to Hcy but also concerns other chemical compounds.

Folate supplementation inhibits intimal hyperplasia induced by a high-homocysteine diet in a rat carotid endarterectomy model

OBJECTIVE

Hyperhomocysteinemia has been implicated as a causative factor in intimal hyperplasia development. The addition of dietary folate in a hyperhomocysteinemia, carotid endarterectomy rat model is postulated to decrease plasma homocysteine levels and, in turn, reduce post-carotid endarterectomy intimal hyperplasia.

METHODS

Each rat was fed one of six diets: (1) lab chow with no folate (n = 7), (2) lab chow with 10 mg/kg folate added (n = 3), (3) lab chow with 25 mg/kg folate added (n = 3), (4) a homocysteine diet with no folate (n = 7), (5) a homocysteine diet with 10 mg/kg folate added (n = 5), or (6) homocysteine diet with 25 mg/kg folate added (n = 5). Each rat then underwent an open carotid endarterectomy. In 2 weeks, intimal hyperplasia in the carotid artery was measured. Plasma homocysteine and folate levels were measured.

RESULTS

Plasma folate levels rose with folate administration. Plasma homocysteine in the lab chow group was 5.4 +/- 0.5 micromol/L and did not change with the addition of folate. In the homocysteine diet group, plasma homocysteine rose 10-fold over the lab chow group (51.9 +/- 6.5 vs 5.4 +/- 0.5, micromol/L, P <.0001). In the group fed a homocysteine diet with 10 mg/kg folate added, a significant decrease in plasma homocysteine was observed (17.5 +/- 8.5 vs 51.9 +/- 6.5, micromol/L, P =.0003). In the group fed a homocysteine diet with 25 mg/kg folate added, plasma homocysteine levels were further reduced to levels seen in the lab chow group (12.6 +/- 2.6 vs 5.4 +/- 0.5, micromol/L, P = not significant). The relationship between plasma folate and homocysteine was inverse (R = 0.39, P =.0036). Luminal stenosis due to intimal hyperplasia was minimal in lab chow groups and unaffected by folate. The homocysteine diet group demonstrated post-carotid endarterectomy luminal stenosis due to intimal hyperplasia (60.9% +/- 9.2%). In the group fed a homocysteine diet with 10 mg/kg folate added, intimal hyperplasia was reduced, compared with the homocysteine diet group (32.6% +/- 7.4% vs 60.9% +/- 9.2%, P =.009). In the group fed a homocysteine diet with 25 mg/kg folate added, intimal hyperplasia was reduced to lab chow group levels (10.8% +/- 0.8% vs 4.8% +/- 1.0%, P = not significant) and was reduced, compared with the group fed a homocysteine diet with 10 mg/kg folate added.

CONCLUSION

The use of folate in this hyperhomocysteinemia carotid endarterectomy model and the resultant attenuation of plasma homocysteine elevation and intimal hyperplasia development lend strong support to homocysteine being an independent etiologic factor in post-carotid endarterectomy intimal hyperplasia.

Associations between homocysteine and coagulation factors--a cross-sectional study in two populations of central Europe

Plasma homocysteine has been associated with vascular disease and mortality. Experimental studies and studies on patients with vascular disease have indicated a thrombogenic potential of raised homocysteine levels. Studies on community samples are rare. We investigated the associations between homocysteine levels and selected coagulation factors in population-based random samples of 187 men from Pardubice (Czech Republic) and 147 men from Augsburg (Germany), aged 45 to 64 years. Czech men had higher mean levels of plasma homocysteine (10.3 vs. 8.9 micromol/l, P<.001) and of fibrinogen, von Willebrand factor (vWF), prothrombin fragment 1+2 (F 1+2) and D-Dimer (each P<.05). Plasma homocysteine was positively correlated with fibrinogen (r=.34) and vWF (r=.23, each P<.001) only in Czechs, and with D-Dimer in both Czechs and Germans (r=.26 and.21, respectively). Formal testing for interaction regarding the intercountry differences in the relationship with homocysteine revealed significance only for fibrinogen (P<.01). In multivariate analyses, the association of homocysteine with D-Dimer remained statistically significant after adjustment for indicators of chronic inflammation and fibrinogen. No significant correlation was found with Factor VII (F VII) activity or F 1+2. Homocysteine levels were also unrelated to traditional risk factors. In conclusion, in these cross-sectional studies we found moderate to strong associations between homocysteine and components of the endogenous hemostatic and fibrinolytic systems. The associations were slightly different between Czech and German men. These findings may help to better understand the role of homocysteine in atherothrombotic diseases.

The importance of hyperhomocysteinemia as a risk factor for diseases: an overview

Hyperhomocysteinemia is the result of a disturbed methionine metabolism. It results from enzyme and/or vitamin deficiency. Epidemiological studies have proven, that hyperhomocysteinemia is a risk factor for atherosclerotic cardiovascular diseases, stroke, peripheral arterial occlusive disease and venous thrombosis. Conflicting results come from prospective studies. Trials which are now in progress may clarify the "causality" of high homocysteine concentrations and will assess the value of homocysteine-lowering therapy. The induction of the atherogenic process by hyperhomocysteinemia seems to be associated with an alteration of endothelial and smooth muscle cell function leading to an accelerated formation of reactive oxygen species. An increased endothelial expression of adhesion molecules will then lead to an enhanced deposition of oxidized LDL in the vessel wall with the formation of foam cells. Additionally, hyperhomocysteinemia interferes with the coagulation system and thus also has prothrombotic effects. There is a high prevalence of hyperhomocysteinemia as a sign of a vitamin deficiency in elderly subjects which strongly increases with age. Elderly people have a high frequency of vitamin B12 deficiency which can be diagnosed more reliably by the measurement of serum methylmalonic acid (MMA) level than by serum vitamin B12. Subjects following a strict vegetarian diet also have a high prevalence of hyperhomocysteinemia caused by functional vitamin B12 deficiency (increased MMA level). Last but not least, hyperhomocysteinemia is a factor in the pathogenesis of neural tube defects and pre-eclampsia. An early diagnosis of vitamin B12 deficiency is important for the prevention of neurological damages. Homocysteine should be measured in patients with a history of atherothrombotic vessel diseases, in patients with diabetes or hyperlipidemia, in renal patients, in obese subjects, in elderly people, in postmenopausal women, and in early pregnancy. A specific diagnosis of an underlying vitamin deficiency is important for adequate treatment. Individuals with homocysteine level >12 micromol/l should increase and/or supplement their dietary intake of vitamins.

Hyperhomocyst(e)inaemia, but not MTHFR C677T mutation, as a risk factor for non-arteritic ischaemic optic neuropathy

BACKGROUND/AIMS

Hyperhomocyst(e)inaemia has been identified as a strong risk factor for stroke, myocardial infarction, and deep vein thrombosis. A point mutation of methylene tetrahydrofolate reductase (MTHFR C677T) has been associated with increased plasma homocyst(e)ine levels. To investigate whether hyperhomocyst(e)inaemia and/or MTHFR C677T mutation are associated with non-arteritic ischaemic optic neuropathy (NAION), a case-control study including 59 consecutive patients with NAION and 59 controls matched for age and sex was performed.

METHODS

Fasting plasma homocyst(e)ine levels, MTHFR C677T genotypes, and plasma levels of folate and vitamin B-12 were determined.

RESULTS

Mean plasma homocyst(e)ine levels were significantly higher in patients than in controls (11.8 (SD 5.7) micromol/l v 9.8 (2.5) micromol/l, p = 0.02). The odds ratio for patients with homocyst(e)ine levels exceeding the 95th percentile of control homocyst(e)ine levels was 5.8 (95% CI 1.5-21.4). Mean plasma folate levels were significantly lower in patients than in controls (4.3 (1.7) ng/ml v 5.5 (1.9) ng/ml, p = 0.001), whereas plasma vitamin B-12 levels did not differ significantly. Prevalence of the MTHFR C677T mutation was not significantly increased in patients with NAION compared with controls.

CONCLUSION

These results suggest that hyperhomocyst(e)inaemia, but not MTHFR C677T mutation is associated with NAION. Determination of plasma homocyst(e)ine levels might be of diagnostic value in patients with NAION.

Homocysteine-induced endoplasmic reticulum stress causes dysregulation of the cholesterol and triglyceride biosynthetic pathways

Hepatic steatosis is common in patients having severe hyperhomocysteinemia due to deficiency for cystathionine beta-synthase. However, the mechanism by which homocysteine promotes the development and progression of hepatic steatosis is unknown. We report here that homocysteine-induced endoplasmic reticulum (ER) stress activates both the unfolded protein response and the sterol regulatory element-binding proteins (SREBPs) in cultured human hepatocytes as well as vascular endothelial and aortic smooth muscle cells. Activation of the SREBPs is associated with increased expression of genes responsible for cholesterol/triglyceride biosynthesis and uptake and with intracellular accumulation of cholesterol. Homocysteine-induced gene expression was inhibited by overexpression of the ER chaperone, GRP78/BiP, thus demonstrating a direct role of ER stress in the activation of cholesterol/triglyceride biosynthesis. Consistent with these in vitro findings, cholesterol and triglycerides were significantly elevated in the livers, but not plasmas, of mice having diet-induced hyperhomocysteinemia. This effect was not due to impaired hepatic export of lipids because secretion of VLDL-triglyceride was increased in hyperhomocysteinemic mice. These findings suggest a mechanism by which homocysteine-induced ER stress causes dysregulation of the endogenous sterol response pathway, leading to increased hepatic biosynthesis and uptake of cholesterol and triglycerides. Furthermore, this mechanism likely explains the development and progression of hepatic steatosis and possibly atherosclerotic lesions observed in hyperhomocysteinemia.

The effect on endothelial function of vitamin C during methionine induced hyperhomocysteinaemia

BACKGROUND

Manipulation of total homocysteine concentration with oral methionine is associated with impairment of endothelial-dependent vasodilation. This may be caused by increased oxidative stress. Vitamin C is an aqueous phase antioxidant vitamin and free radical scavenger. We hypothesised that if the impairment of endothelial function related to experimental hyperhomocysteinaemia was free radically mediated then co-administration of vitamin C should prevent this.

METHODS

Ten healthy adults took part in this crossover study. Endothelial function was determined by measuring forearm blood flow (FBF) in response to intra-arterial infusion of acetylcholine (endothelial-dependent) and sodium nitroprusside (endothelial-independent). Subjects received methionine (100 mg/Kg) plus placebo tablets, methionine plus vitamin C (2 g orally) or placebo drink plus placebo tablets. Study drugs were administered at 9 am on each study date, a minimum of two weeks passed between each study. Homocysteine (tHcy) concentration was determined at baseline and after 4 hours. Endothelial function was determined at 4 hours. Responses to the vasoactive substances are expressed as the area under the curve of change in FBF from baseline. Data are mean plus 95% Confidence Intervals.

RESULTS

Following oral methionine tHcy concentration increased significantly versus placebo. At this time endothelial-dependent responses were significantly reduced compared to placebo (31.2 units [22.1-40.3] vs. 46.4 units [42.0-50.8], p < 0.05 vs. Placebo). Endothelial-independent responses were unchanged. Co-administration of vitamin C did not alter the increase in homocysteine or prevent the impairment of endothelial-dependent responses (31.4 [19.5-43.3] vs. 46.4 units [42.0-50.8], p < 0.05 vs. Placebo)

CONCLUSIONS

This study demonstrates that methionine increased tHcy with impairment of the endothelial-dependent vasomotor responses. Administration of vitamin C did not prevent this impairment and our results do not support the hypothesis that the endothelial impairment is mediated by adverse oxidative stress.