Treatment of hyperhomocysteinemia in renal transplant recipients. A randomized, placebo-controlled trial

BACKGROUND: Stable renal transplant recipients have an excess prevalence of hyperhomocysteinemia, which is a risk factor for arteriosclerosis. OBJECTIVE: To determine the effect of treatment with 1) vitamin B6 or 2) folic acid plus vitamin B12 on fasting and post-methionine-loading plasma total homocysteine levels in renal transplant recipients. DESIGN: Block-randomized, placebo-controlled, 2 x 2 factorial study. SETTING: University-affiliated transplantation program. PATIENTS: 29 clinically stable renal transplant recipients. INTERVENTION: Patients were randomly assigned to one of four regimens: placebo (n = 8); vitamin B6, 50 mg/d (n = 7); folic acid, 5 mg/d, and vitamin B12, 0.4 mg/d (n = 7); or vitamin B6, 50 mg/d, folic acid, 5 mg/d, and vitamin B12, 0.4 mg/d (n = 7). MEASUREMENTS: Fasting and 2-hour post-methionine-loading plasma total homocysteine levels. RESULTS: Vitamin B6 treatment resulted in a 22.1% reduction in geometric-mean post-methionine-loading increases in plasma total homocysteine levels (P = 0.042), and folic acid plus vitamin B12 treatment caused a 26.2% reduction in geometric-mean fasting plasma total homocysteine levels (P = 0.027). These results occurred after adjustment for age; sex; and pretreatment levels of total homocysteine, B vitamins, and creatinine. CONCLUSIONS: Vitamin B6 should be added to the combination of folic acid and vitamin B12 for effective reduction of both post-methionine-loading and fasting plasma total homocysteine levels in renal transplant recipients.     

Vitamin requirements for the treatment of hyperhomocysteinemia in humans

We have previously shown that a modest vitamin supplement containing folic acid, vitamin B-12 and vitamin B-6 is effective in reducing elevated plasma homocysteine concentrations. The effect of supplementation of the individual vitamins on moderate hyperhomocysteinemia has now been investigated in a placebo-controlled study. One hundred men with hyperhomocysteinemia were randomly assigned to five groups and treated with a daily dose of placebo, folic acid (0.65 mg), vitamin B-12 (0.4 mg), vitamin B-6 (10 mg) or a combination of the three vitamins for 6 wk. Folic acid supplementation reduced plasma homocysteine concentrations by 41.7% (P < 0.001), whereas the daily vitamin B-12 supplement lowered homocysteine concentrations by 14.8% (P < 0.01). The daily pyridoxine dose did not reduce significantly plasma homocysteine concentrations. The combination of the three vitamins reduced circulating homocysteine concentrations by 49.8%, which was not significantly different (P = 0.48) from the reduction achieved by folate supplementation alone. Our results indicate that folate deficiency may be an important cause of hyperhomocysteinemia in the general population.     

Effects of folic acid and combinations of folic acid and vitamin B-12 on plasma homocysteine concentrations in healthy, young women

BACKGROUND: Elevated plasma homocysteine concentrations are considered to be a risk factor for vascular disease and fetal malformations such as neural tube defects. Recent studies have shown that plasma homocysteine can be lowered by folic acid in amounts corresponding to 1-2 times the recommended dietary allowance. Preliminary evidence indicates that vitamin B-12 may be beneficial when included in supplements or in a food-fortification regimen together with folic acid. OBJECTIVE: We aimed to compare the homocysteine-lowering potential of a folic acid supplement with that of 2 supplements containing different doses of vitamin B-12 in addition to folic acid. DESIGN: Female volunteers of childbearing age (n = 150) received a placebo for 4 wk followed by a 4-wk treatment with either 400 microg folic acid, 400 microg folic acid + 6 microg vitamin B-12, or 400 microg folic acid + 400 microg vitamin B-12. RESULTS: Significant reductions (P < 0.001) in plasma homocysteine were observed in all groups receiving vitamin treatment. The effect observed with the combination of folic acid + 400 microg vitamin B-12 (total homocysteine, -18%) was significantly larger than that with a supplement containing folic acid alone (total homocysteine, -11%) (P < 0.05). Folic acid in combination with a low vitamin B-12 dose (6 microg) affected homocysteine as well (-15%). CONCLUSIONS: These results suggest that the addition of vitamin B-12 to folic acid supplements or enriched foods maximizes the reduction of homocysteine and may thus increase the benefits of the proposed measures in the prevention of vascular disease and neural tube defects.     

The role of vitamins in the pathogenesis and treatment of hyperhomocyst(e)inaemia

The relation between vitamin nutritional status and circulating plasma homocyst(e)ine concentrations is reviewed. Several studies have shown that plasma concentrations of folate, vitamin B12 and pyridoxal 5'-phosphate are inversely associated with plasma total homocyst(e)ine concentrations. Of the three vitamins mentioned above, folate is the most powerful homocyst(e)ine lowering agent and a daily supplement of 0.65 mg/day is sufficient to normalize moderate hyperhomocyst(e)inaemia in most individuals with normal renal function. In patients with severe renal failure, high doses of folate are required to treat hyperhomocyst(e)inaemia. Folic acid is ineffective in reducing plasma total homocyst(e)ine concentrations in patients with a vitamin B12 deficiency. Vitamin B6 supplementation has no effect on fasting plasma total homocyst(e)ine concentrations, but attenuates the post-methionine load plasma homocyst(e)ine peak. At least one report has shown that some individuals appear to be unable to maintain plasma total homocyst(e)ine concentrations in the normal reference range by a dietary intake of folic acid only. Long-term vitamin supplementation may be indicated in these individuals. However, the clinical benefit of vitamin supplementation has not yet been demonstrated and controlled trials are urgently required.     

Plasma folic acid cutoff value, derived from its relationship with homocyst(e)ine

We established the cutoff value for plasma folic acid, using plasma homocyst(e)ine as the functional marker. To do this, we investigated the relationship of the plasma folic acid of 103 apparently healthy adults with their fasting plasma homocyst(e)ine and with their plasma homocyst(e)ine 6 h after oral methionine challenge (100 mg/kg). We also studied the relationship of their plasma folic acid with the decline of fasting plasma homocyst(e)ine after 7 days of folic acid supplementation (5 mg/day). The three approaches suggested a cutoff value of 10 nmol/L. The chances of individuals to significantly (P <0.05) lower their plasma homocyst(e)ine after folic acid supplementation proved significantly higher at plasma folic acid concentrations < or = 10 nmol/L, as compared with folic acid concentrations above this value (odds ratio, 5.02; 95% confidence interval, 1.87-13.73). We suggest adopting a 10 nmo/L plasma folic acid cutoff value on functional grounds.     

Homocysteine, a risk factor of atherosclerosis

Homocysteine is a sulphurated amino acid which, at high plasma concentrations, predisposes to thrombosis and induces focal arteriosclerosis. These characteristics have been established both in patients with homocystinuria, a genetic disease in which homocysteine accumulates in the blood, and in animals submitted to intravenous infusions of this amino acid. Many recent publications have addressed the problem of whether mild increases in plasma homocysteine predisposed to the development of the usual forms of atherosclerosis. Transverse epidemiological studies have established a correlation between homocysteine levels and atherosclerosis at all its vascular localisations, coronary, carotid and lower limb. Multivariate analysis in several prospective studies have shown plasma homocysteine to be an independent risk factor for cerebrovascular accidents and myocardial infarction. Causes of mild increases in plasma homocysteine are usually dietetic deficiencies in folic acid, vitamin B6 or B12, or genetic by mutation of the methylene-tetrahydrofolate reductase. Renal failure is also associated with a high risk in plasma homocysteine levels. However, the toxicity of homocysteine to the arterial wall at slightly elevated concentration remains speculative.     

Antibacterial activity of bovine lactoferrin and its peptides against enterohaemorrhagic Escherichia coli O157:H7

OBJECTIVES: To assess the long term effects of small increases in dietary folic acid on the concentration of plasma homocysteine, an independent risk factor for occlusive vascular disease, in a general population. DESIGN: A randomized double-blind placebo-controlled intervention study. SUBJECTS: One hundred and nineteen healthy volunteers, whose intake of fortified or supplemental folic acid was low, were recruited by letter from the patient register of a large inner-city group general practice. METHODS: Volunteers were randomized to receive unfortified cereals, or cereals fortified with 200 microg of folic acid per portion, with or without other vitamins. Blood samples were taken presupplement and at 4, 8 and 24 weeks on treatment and analysed for plasma homocysteine, cysteine and vitamin B12 and serum and red cell folate. Ninety-four subjects completed the study providing blood samples on all four occasions. RESULTS: There were no significant changes in any measured parameter in those eating unfortified cereals. Overall, folic acid fortification of cereals led to significant increases (P < 0.001) in serum folate (66%), and red cell folate (24%), and a decrease in plasma homocysteine (10%; P < 0.001). There were no changes in vitamin B12 or cysteine. The homocysteine decrease persisted until the end of the study and was primarily seen in those who initially had the highest plasma homocysteine or the lowest serum folate. CONCLUSIONS: If homocysteine is found to be a causative risk factor in occlusive vascular disease, food fortification with physiological levels of folic acid should have a significant impact on the prevalence of the disease in the general population.     

An Arabidopsis mutant missing one acid phosphatase isoform

BACKGROUND: A high plasma homocysteine concentration is a risk factor for atherosclerosis and thrombosis, which are major causes of morbidity and mortality in heart transplant patients. High homocysteine concentrations may be caused by lower folate and vitamin B6 levels. We hypothesized that these patients might have high homocysteine concentrations and low levels of folate and vitamin B6, which could contribute to the development of vascular complications. METHODS: Total fasting plasma homocysteine was measured in 189 cardiac transplant recipients and in healthy controls, as were concentrations of folate, vitamin B12, vitamin B6, and creatinine. RESULTS: Homocysteine concentrations were higher in recipients than controls (19.1+/-13.0 vs. 11.0+/-3.0 micromol/L, P<0.01), and hyperhomocysteinemia (>90th percentile for controls, 14.6 micromol/L) was seen in 68% of recipients (P<0.01). Folate and vitamin B6 concentrations were lower (5.9+/-4.2 vs. 7.9+/-4.2 pmol/L and 40+/-25 vs. 84+/-77 nmol/L, respectively; P<0.01 for both). Folate and vitamin B6 deficiencies were seen in 10.8% and 17.91% of recipients, respectively (P<0.01). Hyperhomocysteinemia was more frequent in patients with vascular complications after transplantation than in those without (79.2% vs. 63.8%, P<0.05). CONCLUSIONS: Elevated plasma homocysteine and deficiencies of folate and vitamin B6 are common in transplant recipients. A high homocysteine concentration was more common in patients with vascular complications. Prospective studies are now required to evaluate the role of these abnormalities as risk factors for the atherothrombotic complications of transplantation.     

Methylenetetrahydrofolate reductase polymorphism affects the change in homocysteine and folate concentrations resulting from low dose folic acid supplementation in women with unexplained recurrent miscarriages

To determine the effects of daily supplementation of 0.5 mg folic acid on homocysteine and folate concentrations, we investigated 49 women with a history of unexplained recurrent miscarriages. A methionine loading test (including the vitamin concentrations of concern) was used preceding and after 2 mo of folic acid intake. Subsequently, these effects were studied after stratification for C677T 5,10-methylenetetrahydrofolate reductase (MTHFR) polymorphism. Folic acid supplementation (for 2 mo) reduced the median fasting and delta (after-load minus fasting) total plasma homocysteine (tHcy) concentrations 27% (P < 0.001) and 14% (P < 0.05), respectively. Median serum and red cell folate concentrations increased 275 and 70%, respectively (P < 0.01). The homocysteine-lowering effect was most marked in women with the highest tHcy concentrations at baseline. All MTHFR-genotypes (homozygous T/T, n = 8; heterozygous T/C, n = 23; wild type C/C, n = 18) had a different response to the supplementation. After 2 mo, homozygous women showed the greatest decline in median fasting (-41%; P < 0.01) tHcy concentrations, but the lowest absolute increase in serum folate concentration (+26 nmol/L; P < 0.05). In conclusion, 2 mo of daily supplementation of 0. 5 mg folic acid in women with a history of unexplained recurrent miscarriages caused, in general, substantially reduced tHcy concentrations. This effect was most distinct in women with the highest tHcy concentrations at baseline and in women homozygous for the 677 C-->T mutation of the MTHFR-gene.     

High plasma homocysteine: a risk factor for vascular disease in the elderly

Homocysteine is an intermediate compound formed during the metabolism of methionine. Several studies have shown that plasma homocysteine concentrations rise with age. Overt or borderline deficiencies of folate, vitamin B12 or B6 and possibly age-related kidney dysfunction are the major causes of homocysteine elevation in the elderly population. Multiple case-control and prospective studies have shown that a high plasma homocysteine concentration is an independent risk factor for cardiovascular diseases; this association persists in the elderly. Supplementation with folic acid either alone or with vitamins B12 and B6 can lower plasma homocysteine. Intervention studies to assess the effects (if any) of such treatment on prognosis are now in progress in patients with vascular disease.     

Effects of B vitamin injections on plasma B vitamin concentrations of feed-restricted beef calves infected with bovine herpesvirus-1

For nonruminants, stress and disease greatly increase requirements for vitamin B6, folic acid, pantothenic acid, and ascorbate. The effects of feed restriction, virus infection, and vitamin injections on plasma concentrations of B vitamins critical to the immune response were evaluated. Twelve beef steer calves, 6 to 8 mo of age, were fed below maintenance for 17 d and deprived of food for 3 d during a 20-d period after weaning. They then were inoculated intranasally with live attenuated bovine herpesvirus-1 (BHV-1). Six calves received saline injections and six received injections of a B vitamin mixture and ascorbate every 48 h for 14 d before and 14 d after inoculation. A mild respiratory infection developed in all calves 4 to 5 d after inoculation. In control calves, restricted intake and food deprivation decreased plasma vitamin B6 and pantothenate and increased vitamin B12 but did not affect folic acid and ascorbate concentrations. Vitamin injections increased plasma concentrations of vitamin B6, folic acid, vitamin B12, pantothenic acid, and ascorbate (P < .002). Plasma concentrations of vitamin B6, vitamin B12, pantothenic acid, and ascorbate, but not folic acid, were markedly reduced in all calves during the BHV-1 infection (P = .001). The vitamin B6, pantothenic acid, vitamin B12, and ascorbate status of stressed calves may affect their immune response to vaccination or infection.     

Vitamin nutrition status and homocysteine: an atherogenic risk factor

In an epidemiologic survey, a marginal status of folic acid, vitamin B12, and vitamin B6 was shown to be associated with hyperhomocysteinemia. In a case-control study, a low plasma folate concentration was associated with increased coronary heart disease risk. This phenomenon appears to be mediated by folate's effect on homocysteine metabolism. Both studies offer further perspectives on homocysteine as an atherogenic risk factor.     

Plasma homocysteine, a risk factor for cardiovascular disease, is lowered by physiological doses of folic acid

Elevated plasma homocysteine, an independent risk factor for cardiovascular disease (CVD) can be lowered by administration of pharmacological doses of folic acid. The effect of lower doses in apparently normal subjects is currently unknown but is highly relevant to the question of food fortification. Healthy male volunteers (n = 30) participated in a chronic intervention study (26 weeks). Folic acid supplements were administered daily at doses increasing from 100 micrograms (6 weeks), to 200 micrograms (6 weeks), to 400 micrograms (14 weeks). Fasting blood samples collected before, during and 10 weeks post intervention were analysed for plasma homocysteine, serum and red-cell folate levels. Results, expressed as tertiles of baseline plasma homocysteine concentration, showed significant (p < or = 0.001) homocysteine lowering in the top (10.90 +/- 0.83 mumol/l) and middle (9.11 +/- 0.49 mumol/l) tertiles only. In the low tertile, where the mean baseline homocysteine level was 7.07 +/- 0.84 mumol/l, no significant response was observed. Of the three folic acid doses, 200 micrograms appeared to be as effective as 400 micrograms, while 100 micrograms was clearly not optimal. There is thus a minimal level of plasma homocysteine below which folic acid has no further lowering effect, probably because an optimal folate status has been reached. A dose as low as 200 micrograms/day of folic acid is effective in lowering plasma homocysteine concentrations in apparently normal subjects. Any public health programme for lowering homocysteine levels, with the goal of diminishing CVD risk, should not be based on unnecessarily high doses of folic acid.     

Deregulation of homocysteine metabolism and consequences for the vascular system

The link between vascular disease and elevated homocysteine levels has been recognized for more than 30 years, and association with moderately elevated levels has been suspected for 20 years. Homocysteine is a sulfhydryl-containing amino acid that is formed by the demethylation of methionine. It is normally catalysed to cystathionine by cystathionine beta-synthase a pyridoxal phosphate-dependent enzyme. Homocysteine is also remethylated to methionine by methionine synthase, a vitamin B12 dependent enzyme and by methylenetetrahydrofolate reductase. Environmental factors such as folate, or vitamin B12, or vitamin B6 deficiencies and genetic defects such as cystathionine beta-synthase or abnormality of methylene-tetrahydrofolate reductase or some vitamin B12 metabolism defects may contribute to increasing plasma homocysteine levels. Normal fasting levels of homocysteine lie within the range 6-16 mumol/l. Apart from differences in assay methods, age, sex and nutritional status may affect the plasma levels. Though it is now well known that homocysteine is an independent risk factor for premature vascular disease, the pathogenesis of homocysteine-induced vascular damage is, for the most part, unknown. It may be multifactorial, including direct homocysteine damage to the endothelium, an enhanced low-density lipoprotein peroxidation, an increase of platelet thromboxane A2, or a decrease of protein C activation.     

Homocysteine: a new risk factor for atherosclerosis

The accumulating evidence for the role of homocysteine as a risk factor for atherosclerosis is persuasive. A high plasma homocysteine concentration induces pathologic changes in the arterial wall and thus is strongly associated with an increased risk of atherosclerosis, manifested as cardiovascular, cerebrovascular and peripheral vascular events. Studies are being conducted to determine whether lowering homocysteine levels prevents occlusive events. At present, testing for elevated homocysteine concentrations should be considered in patients with premature atherosclerosis or a strong family history of atherosclerosis, since hyperhomocysteinemia is a common risk factor in these patients. Treatment of hyperhomocysteinemia is straightforward and associated with minimal risk. This disorder is usually correctable with vitamin supplements containing folic acid.     

Correlates of plasma total homocysteine in patients with hyperlipidaemia

The study sought to define the relation of plasma total homocysteine to biological and clinical variables and to serum vitamin concentrations in patients with primary hyperlipidaemia. Fasting plasma total homocysteine was measured in 219 men and 159 women; vitamin concentrations were available for about 60% of the sample. Men had significantly higher plasma total homocysteine than women [median (25th, 75th percentiles) 9.4 (8.2, 11.5) mumol L-1 vs. 8.5 (7.0, 10.2) mumol L-1; P = 0.0001]. Plasma total homocysteine was lower in women taking lipid-lowering drugs than in women who were not taking drugs. Serum folate and vitamin B12 concentrations were normal for all but one and four subjects respectively. Correlations (P < or = 0.06) were found between plasma total homocysteine and age, triglyceride concentration in women, uric acid concentration in men, serum folate, vitamin B12 and creatinine concentrations. In multiple regression analysis, the association between plasma total homocysteine and sex and between plasma total homocysteine and use of lipid-lowering drugs disappeared when creatinine concentration was entered into the analysis. This study shows that plasma total homocysteine is related to vitamin concentrations within the normal range, suggesting that plasma total homocysteine may be modifiable by diet in hyperlipidaemic subjects with normal vitamin nutrition. Sex-related differences appear to be related to men's higher creatinine concentration. Whether lipid-lowering drugs interact with total homocysteine concentration requires further study.     

Treatment of mild hyperhomocysteinemia in vascular disease patients

Mild hyperhomocysteinemia is recognized as a risk factor for premature arteriosclerotic disease. A few vitamins and other substances have been reported to reduce blood homocysteine levels, but normalization of elevated blood homocysteine concentrations with any of these substances has not been reported. Therefore, we screened 421 patients suffering from premature peripheral or cerebral occlusive arterial disease by oral methionine loading tests for the presence of mild hyperhomocysteinemia. Thirty-three percent of patients with peripheral and 20% of patients with cerebral occlusive arterial disease were identified with mild hyperhomocysteinemia (14% of the men, 34% of the premenopausal women, and 26% of the postmenopausal women). Mildly hyperhomocysteinemic patients were administered vitamin B6 250 mg daily. After 6 weeks methionine loading tests were again assessed to evaluate the effect of treatment. Patients with nonnormalized homocysteine concentrations were further treated with vitamin B6 250 mg daily and/or folic acid 5 mg daily and/or betaine 6 g daily, solely or in any combination. Vitamin B6 treatment normalized the afterload homocysteine concentration in 56% of the treated patients (71% of the men, 45% of the premenopausal women, and 88% of the postmenopausal women). Further treatment resulted in a normalization of homocysteine levels in 95% of the remaining cases. Thus, mild hyperhomocysteinemia, which is frequently encountered in patients with premature arteriosclerotic disease, can be reduced to normal in virtually all cases by safe and simple treatment with vitamin B6, folic acid, and betaine, each of which is involved in methionine metabolism.     

Blood folic acid and vitamin B12 in relation to neural tube defects

OBJECTIVE: To determine the relation between blood folic acid and serum vitamin B12 in neural tube defect pregnancies using data from the MRC Vitamin Study and a literature review of all studies. DESIGN: Stored blood samples collected as part of a randomised trial of vitamin supplementation in the prevention of neural tube defects were retrieved from affected pregnancies (cases) and unaffected pregnancies (controls). Four controls were matched with each case by centre, maternal age and duration of storage of the blood sample. The samples had been collected from women at entry to the trial, immediately before the women became pregnant, and at around 12 weeks of pregnancy. Our results were combined with those already published from other studies to obtain an overall assessment of blood folic acid and vitamin B12 in relation to neural tube defects. SETTING: Blood samples were collected as part of the MRC Vitamin Study. The collaborating centres were in the United Kingdom, Hungary, Israel, Australia, Canada and Russia. PARTICIPANTS: Twenty-seven women with neural tube defect pregnancies and 108 matched controls with unaffected pregnancies. RESULTS: Serum and red cell folic acid and serum vitamin B12 levels were lower in the cases than in controls at each of the three occasions when blood samples were collected, but no comparison was significant (P > 0.05). A systematic review of all studies from the literature showed that on average, during the 1st trimester of pregnancy, serum folic acid was 0.6 ng/ml lower in neural tube defect pregnancies (P < 0.01), red cell folic acid was 77 ng/ml lower (P < 0.001) and serum vitamin B12 was 38 ng/l lower (P < 0.001). A logistic regression showed no association between serum B12 and neural tube defects after allowing for serum folic acid. CONCLUSION: our results are consistent with other evidence that folic acid and vitamin B12 levels are lower in women with neural tube defect pregnancies and consistent with evidence from randomised trials which showed that folic acid is protective.     

Chronic heart failure in the United States: a manifestation of coronary artery disease

BACKGROUND: Hyperhomocysteinemia occurs in renal failure and may increase the risk for cardiovascular disease, possibly by damaging the endothelium. Folic acid and betaine are required in two separate homocysteine conversion pathways and may therefore lower plasma homocysteine. OBJECTIVE: To study the therapeutic role of betaine and the effect on endothelial function of long-term homocysteine-lowering therapy with folic acid, in peritoneal dialysis (PD) patients. PATIENTS AND DESIGN: Thirty PD patients were randomized to a 12-week treatment with 5 mg folic acid and 4 g betaine daily, or to 5 mg folic acid alone daily. They were then rerandomized to treatment with 1 or 5 mg folic acid daily for 40 weeks. MEASUREMENTS: At baseline and after 52 weeks, endothelial function was assessed by determination of endothelium-dependent vasodilatation and biochemical markers. RESULTS: Plasma total homocysteine (tHcy) was elevated at baseline: 42.6 (5.8) micromol/L. Only 1 patient (3%) had a normal plasma homocysteine (i.e., < or = 15 micromol/L) before therapy. Normalization of plasma homocysteine occurred in 39% of the patients at 12 weeks. Betaine had no additional homocysteine-lowering effect. Plasma tHcy levels were similar during treatment with 1 or 5 mg folic acid daily. Endothelial function was impaired at baseline and had not improved after 52 weeks of treatment. CONCLUSIONS: Peritoneal dialysis patients have hyperhomocysteinemia, which can be normalized with folic acid alone in about 40% of patients. Betaine does not further lower plasma homocysteine. A maintenance dose of 1 or 5 mg folic acid daily results in equivalent plasma homocysteine levels. Long-term reduction in plasma homocysteine did not result in improvement of endothelial function as assessed by our methods.     

Consequences of hyperhomocyst(e)inemia on vascular function in atherosclerotic monkeys

Moderate elevation of plasma homocyst(e)ine is associated with increased risk for atherosclerotic vascular disease. In a previous study, we observed impaired vascular function in nonatherosclerotic monkeys with moderate hyperhomocyst(e)inemia. In this study, we tested the hypothesis that dietary intervention to lower plasma homocyst(e)ine corrects vascular dysfunction in atherosclerotic monkeys. Cynomolgus monkeys were fed an atherogenic diet that produces both hypercholesterolemia and moderate hyperhomocyst(e)inemia. After 17 months, the atherogenic diet was supplemented with B vitamins (5 mg folic acid, 400 micrograms vitamin B-12, and 20 mg vitamin B-6 daily) for 6 months. Total plasma homocyst(e)ine decreased from 12.8 +/- 2.8 to 3.5 +/- 0.3 mumol/L (n = 9; mean +/- SE; P < .01) after vitamins were added to the diet, but plasma cholesterol remained elevated (522 +/- 63 versus 514 +/- 41 mg/dL; P > .05). In response to intra-arterial infusion of collagen, blood flow to the leg decreased by 30 +/- 3% and 38 +/- 5%, respectively, before and after vitamin supplementation (P > .05). In vivo responses of resistance vessels to endothelium-dependent vasodilators (acetylcholine or ADP) were impaired at baseline and did not improve after vitamin supplementation. In carotid artery studied ex vivo, relaxation to low doses of acetylcholine improved after vitamin supplementation, but maximal relaxation remained impaired. Ex vivo thrombomodulin anticoagulant activity was threefold higher in monkeys fed the atherogenic diet (with or without B vitamins) than in normal monkeys (P < .05). We conclude that normalization of plasma homocyst(e)ine is insufficient to restore normal vascular function in atherosclerotic monkeys with persistent hypercholesterolemia and that atherosclerosis, with or without hyperhomocyst(e)inemia, is associated with elevated thrombomodulin activity.