Folate improves endothelial function in coronary artery disease: an effect mediated by reduction of intracellular superoxide?

Effect of folic acid on endothelial function following acute myocardial infarction

The aim of this study was to test the influence of high-dose folic acid (10 mg/d) on endothelial function in patients referred for coronary intervention after an acute myocardial infarction (AMI) and determine its relation to homocysteine levels. Flow-mediated dilation (FMD) of the brachial artery was performed in 40 patients after AMI (16 with normal homocysteine levels and 24 patients with elevated levels [>11 micromol/L]). Subjects were randomized to receive first folic acid (10 mg/day; group A) or placebo (group B) for 6 weeks in a double-blind crossover trial with a 2-week washout. Plasma folate, total homocysteine and its subtypes (oxidized, reduced, and protein-bound), FMD, and nitroglycerin-mediated dilation were assessed at baseline and at 6 and 14 weeks. In group A, folic acid improved FMD from 3.98 +/- 0.35% to 6.44 +/- 0.56% (p <0.001). This effect persisted after the crossover with placebo (5.42 +/- 0.59, p = 0.13). In group B, placebo did not increase FMD (4.01 +/- 0.34% vs 4.46 +/- 0.38, p = 0.38); however, a significant increase was observed in the second active treatment period (6.49 +/- 0.56%, p = 0.005). In both groups, improved FMD neither correlated with basal levels of homocysteine and its subtypes nor with changes induced during the folate treatment. Nitroglycerin-mediated dilation did not change significantly in either group. Folic acid increased FMD in both normo- and hyperhomocysteinanemic groups (p = 0.006 and p <0.001). In conclusion, 6-week treatment with high-dose folic acid improves endothelial function in post-AMI patients, independent from homocysteine status. Folic acid can be recommended to improve postinfarction endothelial dysfunction in patients with normo- and hyperhomocysteinemia.

Mechanism of the Antithrombotic Effect of Dietary Diacylglycerol in Atherogenic Mice

INTRODUCTION

We have shown earlier that diacylglycerol (DAG) but not triacylglycerol (TAG) inhibited thrombus formation. The aim of the present study was to investigate the mechanism of this antithrombotic effect of DAG.

MATERIALS AND METHODS

Four different diets, the (1) Western-style high-fat diet (HFD) containing 20% lipid and 0.05% cholesterol (w/w), (2) TAG-rich and (3) DAG-rich HFDs containing 20% lipid and 0.05% cholesterol, but all lipid replaced by TAG or DAG oil with very similar fatty acid composition and the (4) Japanese-style low-fat diet (LFD) containing 7% oil but no cholesterol were given to apolipoprotein E and low-density lipoprotein (LDL) receptor double-deficient mice. Atherogenicity was assessed by morphology, mapping the whole aorta and measuring the total area of lipid-stained lesions. Endothelial function was measured by the flow-mediated vasodilation test. Platelet reactivity was assessed from native blood sample by a shear-induced platelet function test (hemostatometry). Serum lipoprotein profile was measured by HPLC.

RESULTS

Both the Western-style and the TAG-rich HFDs have accelerated atherosclerosis. In contrast, DAG-rich HFD inhibited the atherosclerotic process to an extent comparable with the Japanese-style LFD. There was no significant difference in platelet and coagulant activity between the studied diet groups. DAG-rich but not the TAG-rich HFD significantly suppressed serum LDL cholesterol level.

CONCLUSIONS

The present findings suggest that the mechanism of antithrombotic and anti-atherogenic effect of DAG may involve the protection of the vascular endothelium from injury and lowered serum LDL cholesterol.

Oster rediscovered--mega-dose folate for symptomatic atherosclerosis

Thirty years ago, Kurt Oster promulgated the avant-garde theory that bovine xanthine oxidase, absorbed intact from homogenized milk, promoted atherogenesis by oxidatively damaging membrane plasmalogens. Under the mistaken impression that folic acid is a xanthine oxidase inhibitor, he administered high-dose folate (80 mg daily) to hundreds of patients afflicted with symptomatic atherosclerosis, and reported marked improvements in angina, intermittent claudication, and wound healing; he also suspected that this regimen was decreasing heart attack risk. The xanthine oxidase theory has since fallen by the wayside, but there is now evidence that folic acid can lessen endothelial oxidative stress by improving the function of "uncoupled" nitric oxide synthase deficient in tetrahydrobiopterin. In light of these new findings, a properly controlled assessment of Oster's mega-dose folate therapy is warranted.

High-dose folate may improve platelet function in acute coronary syndrome and other pathologies associated with increased platelet oxidative stress

Although nitric oxide of endothelial origin plays a major role in warding off inappropriate thrombus formation, platelets also express the "constitutive" isoform of nitric oxide synthase (cNOS). Activation of this enzyme by calcium influx during platelet aggregation provides an important feedback signal that dampens platelet recruitment. Platelets also express a membrane-bound NAD(P)H oxidase complex, activated by collagen receptors, that produces superoxide. Superoxide can directly quench NO; moreover, by giving rise to peroxynitrite, it can oxidize the cNOS cofactor tetrahydrobiopterin (BH4), thereby suppressing cNOS activity and converting it to superoxide generator. In a canine model of acute coronary syndrome, infusion of BH4 has been shown to prevent thrombus formation. Platelets from patients with acute coronary syndrome produce markedly less NO than do control platelets. A reasonable explanation for these findings is that episodic contact with collagen boosts platelet superoxide production, oxidizing BH4. Since 5-methyltetrahydrofolate can reduce oxidized BH4, or otherwise compensate for its deficiency, supplementation with its precursor folic acid may improve platelet function in acute coronary syndrome and possibly reduce risk for coronary thrombosis in other at-risk patients. Other research demonstrates that superoxide production is increased, and nitric oxide production diminished, in platelets of diabetics; the ability of glutathione--a peroxynitrite scavenger--to largely ameliorate these abnormalities, is consistent with a prominent role for BH4 deficiency in diabetic platelet malfunction. Reports that platelet NO production is decreased, and/or superoxide production increased, in patients with disorders associated with insulin resistance syndrome, suggest that BH4 deficiency--potentially remediable with high-dose folate--may likewise contribute to the platelet hyperreactivity noted in these disorders. Supplemental vitamin C and arginine also have the potential to boost platelet production of NO Increased intakes of taurine, magnesium, gamma-tocopherol, fish oil, and garlic may help to stabilize platelets by additional mechanisms. As a complement to the proven benefits of low-dose aspirin, a supplemental regimen emphasizing these nutrients in appropriate doses may act directly on platelets to further diminish risk for thrombotic episodes.

Hyperhomocysteinemia and cardiovascular risk in postmenopausal women: the role of folate supplementation

In the postmenopausal period, cardiovascular diseases are a frequent chronic condition leading to high risk of myocardial infarction and death. Recently hyperhomocysteinemia and even mildly elevated plasma concentrations of homocysteine have been recognized as independent risk factors for vascular damage predisposing to arteriosclerosis. Elevated plasma levels of homocysteine induce vascular endothelial damage and are frequently associated with low folate levels.

In this review we evaluate literature data on some aspects related to menopause and homocysteine metabolism. In particular, we show the effect of folic acid supplementation on homocysteine concentrations and on homocysteine-related thiols, such as cysteine and cysteine-glycine, as well as the relationship with glucose, insulin, and lipidic metabolism in postmenopausal women. We also analyze the influence of folate supplementation on endothelial function, by brachial artery flow-mediated dilatation (endothelium-dependent) and nitroglycerine-induced dilatation (endothelium-independent) before and after a methionine load.

Folate administration in postmenopausal women is able to reduce high plasma homocysteine levels and to modify impaired endothelial function induced by hyperhomocysteinemia.

Clin Chem Lab Med 2007;45:130–5.

High- but not low-dose folic acid improves endothelial function in coronary artery disease

BACKGROUND

While folic acid (FA) reduces plasma homocysteine (Hcy), whether the simultaneous improvement in endothelial function is dependent on Hcy lowering per se is questionable. In the present study the relationship between FA dose, Hcy lowering and endothelial function in patients with coronary artery disease (CAD) was investigated.

MATERIALS AND METHODS

Eighty-four patients with CAD received either 400 microg FA or 5 mg placebo daily for a 6-week treatment period. A further 44 patients with CAD received either 100 mg kg(-1) day(-1) of betaine or placebo for a 6-week treatment period. Flow-mediated dilatation (FMD), a measure of endothelial function, was assessed before and after the 6-week periods. Isometric tension and Western blotting were used to investigate the effect of FA on endothelial function and endothelial nitric oxide synthase (eNOS) dimerization in isolated rabbit aortic rings and cultured porcine aortic endothelial cells (PAEC), respectively.

RESULTS

Both 400 micro g day(-1) and 5 mg day(-1) FA significantly increased plasma folate and decreased plasma Hcy. The FMD improved significantly after 6 weeks' treatment of 5 mg day(-1) FA but did not correlate with the reduction in Hcy. There was no change in FMD in either the 400 micro g FA or placebo group. In a subgroup analysis of 11 patients in the betaine group, despite a reduced Hcy, a significant impairment in FMD was observed. In the in vitro studies FA, but not betaine, reversed methionine-induced endothelial dysfunction. Moreover, the FA promoted eNOS dimerization in cultured PAEC.

CONCLUSIONS

These data suggest that FA dose-dependently improves endothelial function in CAD via a mechanism independently of Hcy lowering. It may involve promotion of eNOS dimerization.

The effects of folic acid and nitric oxide synthase inhibition on coronary flow and oxidative stress markers in isolated rat heart

The aim of this study was to assess the effects of folic acid on coronary flow and oxidative stress markers with or without non-specific inhibition of nitric oxide synthase by L-NAME in isolated rat hearts. The hearts of male Wistar albino rats (n = 12, age 8 weeks, body mass 180-200 g) were retrograde perfused according to the Langendorff technique at gradually increased constant perfusion pressure (40-120 cmH2O). Coronary flow and markers of oxidative stress: nitrite outflow, superoxide anion production, and index of lipid peroxidation (by measuring thiobarbituric acid reactive substances) in coronary effluent were calculated. The experiments were performed during control conditions and in presence of folic acid (100 microM) alone or folic acid (100 microM) plus L-NAME (30 microM). Control values of coronary flow varied in range from 4.37 +/- 0.10 ml/min/g wt at 40 cmH2O to 12.05 +/- 0.42 ml/min/g wt at 120 cmH2O. Nitrite outflow varied from 1.68 +/- 0.17 nmol/min/g wt at 40 cmH2O to 3.56 +/- 0.17 nmol/min/g wt at 120 cmH2O and was parallel with coronary perfusion pressure-coronary flow curve. Folic acid significantly increased coronary flow (40-120 cmH2O, 5.63 +/- 0.10 ml/min/g wt and 15.2 +/- 0.42 ml/min/g wt, respectively) and was accompanied by significant increase in nitrite outflow (2.28 +/- 0.29 nmol/min/g wt at 40 cmH2O to 6.66 +/- 0.50 nmol/min/g wt at 120 cmH2O). In addition, folic acid significantly decreased superoxide anion production especially at upper coronary perfusion pressure values (60% at 120 cmH2O) and increased index of lipid peroxidation (37.16% at 120 cmH2O), respectively. Folic acid plus L-NAME did not change control values of coronary flow significantly. However, folic acid plus L-NAME increased nitrite outflow especially at upper coronary perfusion pressure values (43.05% at 120 cmH2O) and did not change significantly superoxide anion production or index of lipid peroxidation versus control values, respectively. The results clearly showed that on isolated rat hearts at gradually increased constant perfusion pressure, folic acid increased coronary flow, increased nitrite outflow, decreased superoxide anion production, and increased index of lipid peroxidation. These effects were reversed or blocked by L-NAME thus demonstrating mediation or at least participation of NO in the mechanism of the folic acid-induced effects.

Folic acid supplementation delays atherosclerotic lesion development in apoE-deficient mice

Folic acid is a vitamin that when used as a dietary supplementation can improve endothelial function. To assess the effect of folic acid on the development of atherosclerosis, male apolipoprotein E-deficient mice fed a standard chow diet received either water (control group) or an aqueous solution of folic acid that provided a dose of 75 microg/kg/day, for ten weeks. At the time of sacrifice, blood was drawn and the heart removed. The study measured plasma homocysteine, lipids, lipoproteins, low-density lipoprotein (LDL) oxidation, isoprostane, paraoxonase, and apolipoproteins, and aortic atherosclerotic areas. In folic acid-treated animals, total cholesterol, mainly carried in very low-density and low-density lipoproteins, increased significantly, and homocysteine, HDL cholesterol, paraoxonase, and triglyceride levels did not change significantly. Plasma isoprostane and apolipoprotein (apo) B levels decreased. The resistance of LDL to oxidization and plasma apoA-I and apoA-IV levels increased with a concomitant decrease in the area of atherosclerotic lesions. The administration of folic acid decreased atherosclerotic lesions independently of plasma homocysteine and cholesterol levels, but was associated with plasma levels of apolipoproteins A-I, A-IV and B, and decreased oxidative stress.

Novel therapies targeting vascular endothelium

Endothelial dysfunction has been identified as a major mechanism involved in all the stages of atherogenesis. Evaluation of endothelial function seems to have a predictive role in humans, and therapeutic interventions improving nitric oxide bioavailability in the vasculature may improve the long-term outcome in healthy individuals, high-risk subjects, or patients with advanced atherosclerosis. Several therapeutic strategies are now available, targeting both the synthesis and oxidative inactivation of nitric oxide (NO) in human vasculature. Statins seem to be currently the most powerful category of these agents, improving endothelial function and decreasing cardiovascular risk after long-term administration. Other cardiovascular agents improving endothelial function in humans are angiotensin-converting enzyme inhibitors/angiotensin receptors blockers, which increase NO bioavailability by modifying the rennin-angiotensin-aldosterone system. Newer therapeutic approaches targeting endothelial dysfunction in specific disease states include insulin sensitizers, L-arginine (the substrate for endothelial NO synthase [eNOS]) as well as substances that target eNOS "coupling," such as folates or tetrahydrobiopterin. Although there are a variety of strategies to improve NO bioavailability in human endothelium, it is still unclear whether they have any direct benefit at a clinical level.

Differential effects of low and high dose folic acid on endothelial dysfunction in a murine model of mild hyperhomocysteinaemia

The exact mechanism(s) by which hyperhomocysteinaemia promotes vascular disease remains unclear. Moreover, recent evidence suggests that the beneficial effect of folic acid on endothelial function is independent of homocysteine-lowering. In the present study the effect of a low (400 microg/70 kg/day) and high (5 mg/70 kg/day) dose folic acid supplement on endothelium-dependent relaxation in the isolated perfused mesenteric bed of heterozygous cystathionine beta-synthase deficient mice was investigated. Elevated total plasma homocysteine and impaired relaxation responses to methacholine were observed in heterozygous mice. In the presence of N(G)-nitro-L-arginine methyl ester relaxation responses in wild-type tissues were reduced, but in heterozygous tissues were abolished. Clotrimazole and 18alpha-glycyrrhetinic acid, both inhibitors of non-nitric oxide/non-prostanoid-induced endothelium-dependent relaxation, reduced responses to methacholine in wild-type but not heterozygous tissues. The combination of N(G)-nitro-L-arginine methyl ester and either clotrimazole or 18alpha-glycyrrhetinic acid completely inhibited relaxation responses in wild-type tissues. Both low and high dose folic acid increased plasma folate, reduced total plasma homocysteine and reversed endothelial dysfunction in heterozygous mice. A greater increase in plasma folate in the high dose group was accompanied by a more significant effect on endothelial function. In the presence of N(G)-nitro-L-arginine methyl ester, a significant residual relaxation response was evident in tissues from low and high dose folic acid treated heterozygous mice. These data suggest that the impaired mesenteric relaxation in heterozygous mice is largely due to loss of the non-nitric oxide/non-prostanoid component. While low dose folic acid may restore this response in a homocysteine-dependent manner, the higher dose has an additional effect on nitric oxide-mediated relaxation that would appear to be independent of homocysteine lowering.

Serum homocysteine, folate and risk of stroke: Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study

BACKGROUND

Homocysteine and folate have been suggested to have opposite effects on the risk of stroke, although the results are controversial.

DESIGN AND METHODS

The purpose of this study was to assess the effects of serum total homocysteine (tHcy) and serum folate levels on the risk of stroke in a prospective cohort study. The subjects were 1015 men aged 46-64 years and free of prior stroke, examined in 1991-1993 in the Kuopio Ischaemic Heart Disease Risk Factor (KIHD) Study.

RESULTS

At baseline the mean serum tHcy concentration was 10.9 micromol/l (SD 3.4). During an average follow-up time of 9.6 years, 49 men experienced a stroke, of which 34 were ischaemic. In Cox proportional hazards models, men in the highest tHcy third had a risk factor-adjusted hazard rate ratio (RR) of 2.77 [95% confidence interval (CI): 1.23-6.24] for any stroke and 2.61 (95% CI: 1.02-6.71) for ischaemic stroke, compared with men in the lowest third. The mean baseline serum folate concentration was 10.4 nmol/l (SD 4.1). Men in the highest third of serum folate (>11.2 nmol/l) had an adjusted RR for any stroke of 0.35 (95% CI: 0.14-0.87) and for ischaemic stroke of 0.40 (95% CI: 0.15-1.09), compared with men in the lowest third.

CONCLUSION

Elevated serum tHcy is associated with increased risk of all strokes and ischaemic strokes in middle-aged eastern Finnish men free of prior stroke. On the other hand, high serum folate concentration may protect against stroke.

Folate and vitamin B6 rapidly normalize endothelial dysfunction in children with type 1 diabetes mellitus

BACKGROUND

Endothelial dysfunction, a precursor of vascular disease, begins early in type 1 diabetes mellitus and is associated with folate status.

METHODS

A randomized, double-blind, placebo-controlled study of folate (5 mg daily) and vitamin B6 (100 mg daily) in 124 children with type 1 diabetes determined the immediate and 8-week effects of these vitamins, alone and in combination, on endothelial function. Endothelial function, assessed as flow-mediated dilation and glyceryltrinitrate-induced dilation with high-resolution ultrasound of the brachial artery, was measured at baseline, at 2 and 4 hours after the first dose (n = 35), and at 4 and 8 weeks of treatment (n = 122).

RESULTS

Flow-mediated dilation normalized in all treatment groups. From baseline to 8 weeks, flow-mediated dilation improved with folate from 2.6% +/- 4.3% (mean +/- SD) to 9.7% +/- 6.0%, with vitamin B6 from 3.5% +/- 4.0% to 8.3% +/- 4.2%, and with folate/vitamin B6 from 2.8% +/- 3.5% to 10.5% +/- 4.4%. This improvement in flow-mediated dilation occurred within 2 hours and was maintained at 8 weeks for each treatment. Flow-mediated dilation in the placebo group, and glyceryltrinitrate-induced dilation in all groups, did not change. Increases in serum folate, red cell folate, and serum vitamin B6 levels related to increases in flow-mediated dilation. Improvement in flow-mediated dilation was independent of changes in total plasma homocyst(e)ine, glucose, hemoglobin A1c, and high-sensitivity C-reactive protein levels. Baseline red cell folate levels and baseline diastolic blood pressure were related inversely to improvement in flow-mediated dilation. Serum triglyceride and low-density lipoprotein cholesterol inversely related to baseline flow-mediated dilation.

CONCLUSIONS

High-dose folate and vitamin B6 normalized endothelial dysfunction in children with type 1 diabetes. This effect was maintained over 8 weeks, with no additional benefit from combination treatment.

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.

Hyperhomocysteinemia induces liver injury in rat: Protective effect of folic acid supplementation

Hyperhomocysteinemia, a condition of elevated blood homocysteine level, is an independent risk factor for cardiovascular diseases. Hyperhomocysteinemia is also found in patients with liver diseases. However, the direct effect of homocysteine on liver injury is not well known. Folic acid supplementation is a promising approach for improving endothelial function in patients with hyperhomocysteinemia. The aim of this study was to investigate the direct effect of hyperhomocysteinemia on liver injury and whether folic acid could offer any protective effect to the liver. Hyperhomocysteinemia was induced in rats fed a high-methionine diet for 4 weeks. There was a significant increase in the serum aspartate aminotransferase and alanine aminotransferase activities reflecting liver injury in hyperhomocysteinemic rats. Hepatic NAD(P)H oxidase was activated during hyperhomocysteinemia leading to increased superoxide anion production and peroxynitrite formation in the liver. As a consequence, the level of lipid peroxides was significantly elevated in livers of hyperhomocysteinemic rats. Folic acid supplementation effectively inhibited NAD(P)H oxidase-mediated superoxide anion production leading to reduced lipid peroxidation in the liver. Folic acid supplementation also alleviated hyperhomocysteinemia-induced liver injury. These results suggest that hyperhomocysteinemia can cause liver injury and supplementation of folic acid offers a hepatoprotective effect.

Effect of folic acid and betaine supplementation on flow-mediated dilation: a randomized, controlled study in healthy volunteers

OBJECTIVES

We investigated whether lowering of fasting homocysteine concentrations, either with folic acid or with betaine supplementation, differentially affects vascular function, a surrogate marker for risk of cardiovascular disease, in healthy volunteers. As yet, it remains uncertain whether a high concentration of homocysteine itself or whether a low folate status--its main determinant--is involved in the pathogenesis of cardiovascular disease. To shed light on this issue, we performed this study.

DESIGN

This was a randomized, placebo-controlled, double-blind, crossover study.

SETTING

The study was performed at Wageningen University in Wageningen, the Netherlands.

PARTICIPANTS

Participants were 39 apparently healthy men and women, aged 50-70 y.

INTERVENTIONS

Participants ingested 0.8 mg/d of folic acid, 6 g/d of betaine, and placebo for 6 wk each, with 6-wk washout in between.

OUTCOME MEASURES

At the end of each supplementation period, plasma homocysteine concentrations and flow-mediated dilation (FMD) of the brachial artery were measured in duplicate.

RESULTS

Folic acid supplementation lowered fasting homocysteine by 20% (-2.0 micromol/l, 95% confidence interval [CI]: -2.3; -1.6), and betaine supplementation lowered fasting plasma homocysteine by 12% (-1.2 micromol/l; -1.6; -0.8) relative to placebo. Mean (+/- SD) FMD after placebo supplementation was 2.8 (+/- 1.8) FMD%. Supplementation with betaine or folic acid did not affect FMD relative to placebo; differences relative to placebo were -0.4 FMD% (95%CI, -1.2; 0.4) and -0.1 FMD% (-0.9; 0.7), respectively.

CONCLUSIONS

Folic acid and betaine supplementation both did not improve vascular function in healthy volunteers, despite evident homocysteine lowering. This is in agreement with other studies in healthy participants, the majority of which also fail to find improved vascular function upon folic acid treatment. However, homocysteine or folate might of course affect cardiovascular disease risk through other mechanisms.

Acute effect of folic acid, betaine, and serine supplements on flow-mediated dilation after methionine loading: a randomized trial

OBJECTIVES

We investigated whether reducing post-methionine homocysteine concentrations via various treatments other than folic acid affects vascular function, as measured through flow-mediated dilation (FMD) of the brachial artery. High fasting and post-methionine homocysteine concentrations are associated with cardiovascular disease risk, but homocysteine might be a surrogate marker for low folate status.

DESIGN

This was a randomized, placebo-controlled, double-blind, crossover study.

SETTING

The study took place at Wageningen University in Wageningen in the Netherlands.

PARTICIPANTS

Participants were 39 apparently healthy men and women, aged 50-70 y.

INTERVENTIONS

Participants ingested 10 mg of folic acid, 3 g of betaine, 5 g of serine, and placebo together with an oral methionine load. Each supplement was tested on two different days.

OUTCOME MEASURES

On each of the eight treatment days, plasma homocysteine concentrations and FMD were measured before (t = 0 h, fasting) and 6 h (t = 6 h) after methionine loading.

RESULTS

The mean (+/- SD) fasting homocysteine concentrations averaged over the eight test days were 9.6 +/- 2.1 micromol/l. Mean fasting FMD was 3.1 +/- 2.4 FMD%. A methionine load with placebo increased homocysteine concentrations by 17.2 +/- 9.3 micromol/l at 6 h after loading, similar to the increase following methionine loading with folic acid. A methionine load together with betaine and with serine increased homocysteine by 10.4 +/- 2.8 micromol/l (p < 0.001 relative to placebo) and by 12.1 +/- 8.2 micromol/l (p < 0.001 relative to placebo), respectively. Methionine loading with placebo did not affect FMD, and neither did methionine loading with folic acid, betaine, or serine; differences relative to placebo were +0.7 FMD% (95%CI, -0.6; 1.9), +0.2 FMD% (-1.0; 1.3), and +0.3 FMD% (-0.8; 1.4), respectively.

CONCLUSIONS

Experimentally induced acute changes in homocysteine concentrations did not affect FMD in healthy volunteers. This implies that potential adverse effects of high homocysteine concentrations on the cardiovascular system are not mediated through vascular function. However, homocysteine or folate may affect cardiovascular disease risk through other mechanisms.

Endothelial function and cerebrovascular disease: Implications for diagnosis and treatment

Cerebrovascular disease remains one of the most common causes of morbidity and mortality in the United States. There is strong evidence to implicate endothelial dysfunction in the initiation and progression of atherosclerosis and its complications. It is now well known that endothelial dysfunction represents a systemic syndrome involving multiple vascular beds, including the cerebral vasculature. Currently, no gold standard treatment for endothelial dysfunction exists. Nonetheless, several treatment strategies have been found to be helpful in improving endothelial function. A few of these strategies have been implicated in stroke risk reduction as well, adding another line of evidence to the relationship between endothelial function and cerebrovascular disease.

Effect of Homocysteine Lowering by 5-Methyltetrahydrofolate on Redox Status in Hyperhomocysteinemia

The endothelial dysfunction induced by hyperhomocysteinemia can be reversed by 5-methyltetrahydrofolate (5-MTHF) via homocysteine (Hcy) lowering. An additive antioxidant action of 5-MTHF has been suggested to ameliorate endothelial dysfunction through increased nitric oxide production and superoxide radical scavenging, independent of Hcy lowering. The aim of the study was to assess whether 5-MTHF affects the redox state in hyperhomocysteinemia. We examined the effect of 3 months of oral 5-MTHF treatment (15 mg/day) on the redox pattern in 48 hyperhomocysteinemic subjects compared to 24 untreated hyperhomocysteinemic subjects. By analysis of variance with repeated measures in the 72 subjects, 5-MTHF markedly decreased plasma total Hcy (p-tHcy; P = 0.0001) and blood-total glutathione (GSH; b-tGSH; P = 0.002). By multivariate linear regression in the treated subjects, p-tHcy changes from baseline to 3 months (adjusted by baseline p-tHcy levels) correlated only with changes in reduced cysteinylglycine (P = 0.001). The effects of treatment on Hcy lowering and GSH metabolism were greater in medium than in moderate hyperhomocysteinemia. In conclusion, high-dose 5-MTHF treatment for 3 months ensures marked Hcy lowering to normal values even in subjects with high Hcy levels, and should be the treatment of choice in medium hyperhomocysteinemia. Furthermore, 5-MTHF shows a favorable interaction with GSH metabolism.

Effects of folinic acid on forearm blood flow in patients with end-stage renal disease

BACKGROUND

Abnormalities of endothelial function are likely to contribute to the accelerated atherosclerotic risk in subjects with end-stage renal disease (ESRD). While folates can improve endothelial function, their role in ESRD has not been fully studied. The objective was to determine the acute and 12 week-effect of folinic acid on endothelium-dependent vasodilation in subjects with ESRD.

METHODS

Forearm blood flow (FBF) was assessed by strain gauge plethysmography at baseline and after 12 weeks in 34 ESRD patients (57 +/- 14 years). Vascular function was assessed with acetylcholine (ACh), and sodium nitroprusside (SNP). Patients were randomized to receive folinic acid (50 mg i.v. once weekly) or a matching placebo. A subset of 25 subjects also received folinic acid (500 microg/min intra-arterially) or placebo to determine the acute effect on ACh and SNP mediated dilation at the time of the baseline vascular study.

RESULTS

Folinic acid acutely improved the maximum change in ACh mediated FBF (10.0 +/- 2.4 to 12.8 +/- 2.2 ml/min/100 ml, P = 0.017), but did not change SNP responses. Chronic active therapy did not change ACh or SNP-mediated increases in FBF. Folinic acid resulted in a non-significant decrease in homocysteine (21 +/- 6 vs 28 +/- 18 micromol/l, P = 0.16) and diastolic blood pressure was significantly reduced (P = 0.05).

CONCLUSIONS

The present study demonstrated that folinic acid acutely improved endothelium-dependent vasodilatation in patients with ESRD suggesting a direct vascular effect. Chronic treatment with folinic acid did not show benefit in endothelial function, but did lower diastolic blood pressure. Further work is required to determine the optimal regime to protect vascular health in subjects with ESRD.

Folic acid pretreatment prevents the reduction of Na+,K+‐ATPase and butyrylcholinesterase activities in rats subjected to acute hyperhomocysteinemia

The main objective of the present study was to evaluate the effect of folic acid pretreatment on parietal cortex Na(+),K(+)-ATPase and serum butyrylcholinesterase activities in rats subjected to acute hyperhomocysteinemia. Animals were pretreated daily with an intraperitoneal injection of folic acid (5 mg/kg) or saline from the 22th to the 28th day of age. Twelve hours after the last injection of folic acid or saline, the rats received a single subcutaneous injection of homocysteine (0.6 micromol/g of weight body) or saline and were killed 1h later. Serum was collected and the brain was quickly removed and parietal cortex dissected. Results showed that acute homocysteine administration significantly decreased the activities of Na(+),K(+)-ATPase and butyrylcholinesterase on parietal cortex and serum, respectively. Furthermore, folic acid pretreatment totally prevented these inhibitory effects. We also evaluated the effect of acute homocysteine administration on some parameters of oxidative stress, namely thiobarbituric acid-reactive substances and total thiol content in parietal cortex of rats. No alteration of these parameters were observed in parietal cortex of homocysteinemic animals, indicating that these oxidative stress parameters were probably not responsible for the reduction of Na(+),K(+)-ATPase and butyrylcholinesterase activities. The presented results confirm previous findings that acute hyperhomocysteinemia produces an inhibition of Na(+),K(+)-ATPase and butyrylcholinesterase activities and that pretreatment with folic acid prevents such effects. Assuming that homocysteine might also reduce the activities of these enzymes in human beings, our results support a new potential therapeutic strategy based on folic acid supplementation to prevent the neurological damage found in hyperhomocysteinemia.

Folic acid reverses endothelial dysfunction induced by inhibition of tetrahydrobiopterin biosynthesis

While folic acid has been shown to reverse endothelial dysfunction, the exact underlying mechanism remains elusive. Here, folic acid reversed both the endothelial dysfunction and increased production of superoxide following depletion of rabbit aortic ring tetrahydrobiopterin (BH4) levels with 2,4-diamino-6-hydroxy-pyrimidine (DAHP) and N-acetyl-5-hydroxy-tryptamine (NAS). Incubation with l-nitroarginine methyl ester also attenuated the production of superoxide. DAHP and NAS reduced BH4 concentrations in both aorta and cultured porcine aortic endothelial cells. Folic acid had no effect on BH4 concentrations in either preparation. The superoxide anion scavenger Tiron but not folic acid reversed the endothelial dysfunction produced in aortic rings by inhibition of copper-zinc superoxide dismutase with diethyldithiocarbamic acid. Neither folic acid nor its metabolite 5-methyltetrahydrofolate prevented the in vitro oxidation of BH4. This study demonstrates that folic acid reverses the endothelial dysfunction induced by BH4 depletion independently of either the regeneration or stabilization of BH4 or an antioxidant effect.

Plasma homocysteine and markers for oxidative stress and inflammation in patients with coronary artery disease--a prospective randomized study of vitamin supplementation

BACKGROUND

Elevated plasma levels of total homocysteine (tHcy) are associated with an increased risk of developing occlusive vascular diseases. To better illustrate the relationship between plasma tHcy concentration, oxidative stress, and inflammation in patients with coronary artery disease (CAD), we measured plasma 8-isoprostane-prostaglandin F 2 (Iso-P), plasma malondialdehyde (MDA), and several markers of inflammation. We also aimed to demonstrate the effects of vitamin supplementation on these markers.

METHODS

A total of 93 patients with ischemic heart disease were investigated. Of these, 34 had plasma tHcy < or =8 micromol/L, while 59 had plasma tHcy > or = 15.0 micromol/L. The 59 patients were randomized to open therapy with folic acid, 5 mg, pyridoxine, 40 mg, and cyancobalamin, 1 mg once daily for 3 months (n = 29) or to no vitamin treatment (n = 30). Blood samples were obtained from both groups before randomization and 3 months later. A sample was also obtained from the remaining 34 patients.

RESULTS

Plasma Iso-P, serum amyloid A (S-AA), and plasma intercellular adhesion molecule-1 (ICAM-1) concentrations were higher in patients with high plasma tHcy levels than in patients with low to normal tHcy levels. Plasma levels of P-, L-, E-selectins, MDA, C-reactive protein (CRP), and orosomucoid did not differ between the groups. Vitamin therapy reduced plasma tHcy from 17.4 (15.3/20.1) to 9.2 (8.3/10.3) micromol/L (25th and 75th percentiles in parentheses) (p<0.0001). Plasma levels of Iso-P remained unchanged and, of all inflammatory markers, only the S-AA concentrations were slightly reduced by the vitamin treatment, from 5.3 (2.2/7.0) ng/L at baseline to 4.6 (2.1/6.9) ng/L (p<0.05) after 3 months of vitamin supplementation.

CONCLUSION

Patients with CAD and high plasma tHcy levels had elevated plasma levels of Iso-P. The increase remained unaffected by plasma tHcy-lowering therapy, suggesting that homocysteine per se does not cause increased lipid peroxidation. Levels of plasma ICAM-1 and S-AA were increased in patients with high plasma tHcy, suggesting an association between homocysteinemia and low-grade inflammation.

Folic Acid Does Not Limit Endothelial Dysfunction Induced by Ischemia and Reperfusion

Nitric oxide synthase (NOS) uncoupling is a condition of increased production of superoxide anion associated with a decreased production of nitric oxide (NO) by this enzyme. Folic acid can prevent and/or reverse NOS uncoupling in the setting of diabetes, smoking, hypercholesterolemia, and nitrate tolerance. Whereas animal studies showed a protective effect of folic acid in ischemia and reperfusion (IR) injury, no study tested whether folic acid administration limits IR-induced endothelial dysfunction in humans. In a double-blind, parallel study, 20 healthy young male volunteers were randomized to receive folic acid, 10 mg/d for 7 days, or matching placebo. At the end of the treatment period, endothelium-dependent, flow-mediated dilation (FMD) of the radial artery was measured before and after IR injury (15 minutes of ischemia at the level of the brachial artery followed by 15 minutes of reperfusion). There was no difference at baseline between groups in any variable. In the placebo group, IR significantly blunted FMD (before IR, 6.7+/-1.0%; after IR, 1.5+/-1.3%, P<0.01). A similar effect was observed in the folic acid group (before IR, 6.3+/-1.1%; after IR, 2.1+/-1.0%, P=ns compared with placebo). As opposed to animal studies, high-dose folic acid does not protect the vascular endothelium from IR injury in humans.

Reduced in vivo oxidative stress following 5-methyltetrahydrofolate supplementation in patients with early-onset thrombosis and 677TT methylenetetrahydrofolate reductase genotype

The protective role of folate in vascular disease has been related to antioxidant effects. In 45 patients with previous early-onset (at age <50 years) thrombotic episodes and the 677TT methylenetetrahydrofolate reductase genotype, we evaluated the effects of a 28 d-course (15 mg/d) of 5-methyltetrahydrofolate (MTHF) on homocysteine metabolism and on in vivo generation of 8-iso-prostaglandin F2alpha (8-iso-PGF2alpha), a reliable marker of oxidative stress. At baseline, patients' fasting total homocysteine (tHcy) was 11.5 micromol/l (geometric mean) and urinary excretion of 8-iso-PGF2alpha was 304 pg/mg creatinine, with the highest metabolite levels in the lowest quartile of plasma folate distribution (P < 0.05). After 5-MTHF supplementation, plasma folate levels increased approximately 13-fold (P < 0.0001 versus baseline); tHcy levels (6.7 micromol/l, P < 0.0001) and urinary 8-iso-PGF2alpha (254 pg/mg creatinine, P < 0.001) were both significantly lowered, their reduction being proportional to baseline values (r = 0.98 and r = 0.77, respectively) and maximal in patients with the lowest pre-supplementation folate levels (P < 0.05). The effects on folate (P < 0.0001) and tHcy (P = 0.0004) persisted for at least up to 2 months after withdrawing 5-MTHF. In parallel with long-lasting tHcy-lowering effects, a short-course 5-MTHF supplementation reduces in vivo formation of 8-iso-PGF2alpha in this population, supporting the antioxidant protective effects of folate in vascular disease.

Association of red blood cell 5-methyltetrahydrofolate and severity of coronary artery disease: a cross-sectional study from Shiraz, southern Iran

In this study we tested the hypothesis that red blood cell 5-methyltetrahydrofolate, a long-term marker of the folate status, is associated with the severity of coronary artery disease and whether this association is independent of homocysteine, vitamin B12, plasma 5-methyltetrahydrofolate, 5,10-methyltetrahyrofolate reductase C677T genotype, and other cardiovascular risk factors. Two hundred and fifty-one angiographically documented patients aged <70 years with single, double, or triple coronary artery disease were investigated. Red blood cell 5-methyltetrahydrofolate concentrations were significantly decreased with the increasing number of diseased vessels (analysis of variance, P < 0.001). Red blood cell 5-methyltetrahydrofolate was also inversely and significantly correlated with the number of diseased vessels (r = -0.36, P < 0.001). Stepwise multiple regression analysis showed that red cell 5-methyltetrahydrofolate was a strong predictor of number of diseased vessels independent of plasma total homocysteine, 5,10-methyltetrahyrofolate reductase C677T genotype, and all other coronary artery risk factors (beta = -0.002, P < 0.001, r2 = 0.128). The results of this study suggest that low red blood cell 5-methyltetrahydrofolate is associated with the severity of coronary artery disease independent from plasma homocysteine and other cardiovascular risk factors.

Vascular dysfunction produced by hyperhomocysteinemia is more severe in the presence of low folate

Earlier we reported that dietary folate depletion causes hyperhomocysteinemia (HHcy) and arterial dysfunction in rats (Symons JD, Mullick AE, Ensunsa JL, Ma AA, and Rutledge JC. Arterioscler Thromb Vasc Biol 22: 772-780, 2002). Both HHcy and low folate (LF) are risk factors for cardiovascular disease. Therefore, the dysfunction we observed could have resulted from HHcy, LF, and/or their combination (HHcy + LF). We tested the hypothesis that HHcy-induced vascular dysfunction is more severe in the presence of LF. Four groups of rats consumed diets for approximately 10 wk that produced plasma homocysteine (microM) and liver folate (microg folate/g liver) concentrations, respectively, of 7 +/- 1 and 15 +/- 1 (Control; Con; n = 16), 17 +/- 2 and 15 +/- 2 (HHcy; n = 17), 10 +/- 1 and 8 +/- 1 (LF; n = 14), and 21 +/- 2 and 8 +/- 1 (HHcy + LF; n = 18). We observed that maximal ACh-evoked vasorelaxation was greatest in aortas and mesenteric arteries from Con rats vs. all groups. While the extent of dysfunction was similar between LF and HHcy animals, it was less severe compared with arteries from HHcy + LF rats. Maximal ACh-evoked vasorelaxation in coronary arteries was not different between Con and LF rats, but both were greater than HHcy + LF animals. In segments of aortas, 1) ACh-evoked vasorelaxation was similar among groups after incubation with the nonenzymatic intracellular O2(-) scavenger Tiron, 2) vascular O2(-) estimated using dihydroethidium staining was greatest in HHcy + LF vs. all groups, and 3) tension development in response to nitric oxide (NO) synthase inhibition was greatest in Con vs. all other groups. We conclude that HHcy + LF evokes greater dysfunction than either HHcy alone (aortas, mesentery) or LF alone (aortas, mesentery, coronary), likely by producing more O2(-) within the vasculature and thereby reducing NO bioavailability.

Association of Low Red Blood Cell Folate Concentrations with Coronary Artery Disease in Iranians: A Matched Case-Control Study

BACKGROUND

It is not fully established whether the increasing risk of coronary artery disease (CAD) is associated with high plasma homocysteine levels or components of the homocysteine remethylation pathway, e.g. vitamin B(12) or 5-methyltetrahydrofolate (5-MTHF) in plasma and red blood cells (RBC). In this study, we tested the hypothesis that 5-MTHF in RBC, which represents the long-term folate status of individuals, may be a more reliable marker of homocysteine remethylation pathway disturbances, and its deficiency may be associated with CAD in Iranians.

METHODS

Plasma total homocysteine (tHcy), vitamin B(12), and plasma and RBC 5-MTHF were measured in 200 angiographically documented patients and 200 controls matched for sex and age.

RESULTS

In the plasma, tHcy levels were significantly higher in cases compared to controls (geometric mean 12.9 +/- 6.5 vs. 10.6 +/- 5.6 micromol/l, p = 0.04). However, RBC 5-MTHF (527.2 +/- 185.9 vs. 461.3 +/- 117.9 nmol/l, p = 0.007) and vitamin B(12) (254.2 +/- 132.8 vs. 182.2 +/- 110.4 pmol/l, p = 0.04) were significantly higher in controls than patients. RBC 5-MTHF was a strong and independent predictor of plasma tHcy (beta = -0.01, p = 0.003, r(2) = 0.19). Subjects in the lowest quartile of red-cell 5-MTHF had a 2.5-fold increased prevalence of CAD compared to subjects in the highest quartile. The association of CAD in the first quartile with red-cell 5-MTHF remained significant when adjusted for plasma tHcy, vitamin B(12), hypertension and hypercholesterolemia (odds ratio, OR 2.3, confidence interval: 1.1-3.9, p = 0.01). However, the association between CAD in the highest quartile and plasma tHcy decreased and became insignificant when adjusted for red-cell 5-MTHF, vitamin B(12), hypertension and hypercholesterolemia (OR 1.27, confidence interval: 0.96-1.69, p = 0.11).

CONCLUSION

In this study, the association between CAD and low RBC 5-MTHF was stronger than with plasma 5-MTHF and plasma tHcy levels, indicating that RBC 5-MTHF may be a more stable parameter to study disturbances in the homocysteine remethylation pathway in Iranians.

Supplemental arginine and high-dose folate may promote bone health by supporting the activity of endothelial-type nitric oxide synthase in bone

The endothelial isoform of NO synthase promotes maintenance of bone density by stimulating osteoblastic activity while inhibiting bone catabolism; it appears to be a key mediator of the anabolic effects of mechanical loading, estrogens, and statin therapy on bone. This enzyme is susceptible to competitive inhibition by elevated systemic levels of asymmetric dimethylarginine (ADMA) encountered in vascular disorders associated with endotheliopathy; it may not be coincidental that reduced bone density has been observed in subjects afflicted with many of these disorders. Supplemental arginine has the potential to offset this adverse effect of ADMA. Superoxide production by osteoclasts may also impair bone NO synthase activity by oxidizing its cofactor tetrahydrobiopterin; high-dose folate has been shown to compensate for endothelial deficiency of this cofactor by effectively "pinch hitting" for it. These considerations suggest that supplementation with arginine as well as high-dose folate might aid maintenance of bone density by helping to preserve optimal NO synthase activity in bone cells.

Assessment of tailor-made prevention of atherosclerosis with folic acid supplementation: randomized, double-blind, placebo-controlled trials in each MTHFR C677T genotype

This study aimed at assessing the effect of folic acid supplementation quantitatively in each MTHFR C677T genotype and considered the efficiency of tailor-made prevention of atherosclerosis. Study design was genotype-stratified, randomized, double-blind, placebo-controlled trials. The setting was a Japanese company in the chemical industry. Subjects were 203 healthy men after exclusion of those who took folic acid or drugs known to effect folic acid metabolism. Intervention was folic acid 1 mg/day p.o. for 3 months. The primary endpoint was plasma total homocysteine level (tHcy). In all three genotypes, there were significant tHcy decreases. The greatest decrease was in the TT homozygote [6.61 (3.47-9.76) micromol/l] compared with other genotypes [CC: 2.59 (1.81-3.36), CT: 2.64 (2.16-3.13)], and there was a significant trend between the mutated allele number and the decrease. The tHcy were significantly lowered in all the genotypes, but the amount of the decrease differed significantly in each genotype, which was observed at both 1 and 3 months. Using these time-series data, the largest benefit obtained by the TT homozygote was appraised as 2.4 times compared with the CC homozygote. Taking into account the high allele frequency of this SNP, this quantitative assessment should be useful when considering tailor-made prevention of atherosclerosis with folic acid.

High-dose folic acid acutely improves coronary vasodilator function in patients with coronary artery disease

OBJECTIVES

We investigated the acute effect of orally administered high-dose folic acid on coronary dilator function in humans.

BACKGROUND

Folic acid and its active metabolite, 5-methyltetrahydrofolate, increase endothelium-dependent vasodilation in human peripheral circulation. However, the acute effect on coronary circulation is not known.

METHODS

Fourteen patients with ischemic heart disease, age 62 +/- 12 years (mean +/- SD), were enrolled in a double-blind, placebo-controlled crossover trial. Basal and adenosine-stimulated myocardial blood flow (MBF) were determined by positron emission tomography, and myocardial flow reserve was calculated. Each patient was studied after ingestion of placebo and after ingestion of 30 mg folic acid. Myocardial zones were prospectively defined physiologically as "normal" versus "abnormal" on the basis of MBF response to adenosine 140 microg/kg/min (normal = MBF >1.65 ml/min/g). Abnormal and normal zones were analyzed separately in a patient-based analysis.

RESULTS

Folate was associated with a reduction in mean arterial pressure (100 +/- 12 mm Hg vs. 96 +/- 11 mm Hg, placebo vs. folate, p < 0.03). Despite the fall in mean arterial pressure, folic acid significantly increased the MBF dose response to adenosine (p < 0.001 using analysis of variance) in abnormal zones, whereas MBF in normal zones did not change. In abnormal segments, folic acid increased peak MBF by 49% (1.45 +/- 0.59 ml/min/g vs. 2.16 +/- 1.01 ml/min/g, p < 0.02). Furthermore, folate increased dilator reserve by 83% in abnormal segments (0.77 +/- 0.59 vs. ml/min/g 1.41 +/- 1.08 ml/min/g, placebo vs. folate, p < 0.05), whereas dilator reserve in normal segments remained unchanged (2.00 +/- 0.61 ml/min/g vs. 2.12 +/- 0.69 ml/min/g, placebo vs. folate, p = NS).

CONCLUSIONS

The data demonstrate that high-dose oral folate acutely lowers blood pressure and enhances coronary dilation in patients with coronary artery disease.

Folic acid reverses hyper-responsiveness of LPS-induced chemokine secretion from monocytes in patients with hyperhomocysteinemia

Our previous study demonstrated that homocysteine (Hcy) mediated the expression and secretion of MCP-1 and IL-8 in human monocytes. In the present study, we investigated whether the responsiveness of isolated monocytes to lipopolysaccharide (LPS)-induced chemokine secretion was enhanced in patients with hyperhomocysteinemia (HHcy), and if so, whether this enhanced response could be inhibited by folic acid treatment. We studied 38 control subjects and 40 patients with HHcy. The results showed that MCP-1 secretion from isolated monocytes in response to low-dose LPS in patients with HHcy was significantly higher than that in controls. After patients with HHcy underwent low-dose folic acid treatment (0.8 mg/d) for 6 months, plasma Hcy levels were decreased and the hyper-responsiveness of MCP-1 and IL-8 secreted by isolated monocytes was significantly reversed. Furthermore, folic acid treatment at high concentrations (5 microM) significantly reduced the elevated levels of reactive oxygen species, NADPH oxidase activity and chemokines in response to Hcy in cultured human monocytes. HHcy may contribute to atherogenesis through enhancing the responsiveness of monocytes to inflammatory stimuli and promoting leukocyte recruitment into atherosclerotic plaque. In addition to lowering the plasma levels of Hcy, low-dose folic acid treatment exerts beneficial effects on patients with HHcy by inhibiting pro-inflammatory responses such as chemokine secretion from human monocytes.

Effect of homocysteine, folates, and cobalamin on endothelial cell- and copper-induced LDL oxidation

Oxidation of LDL contributes to endothelial dysfunction and atherosclerosis. This process could be associated with hyperhomocysteinemia, a condition that can be reduced after folic acid treatment. Because a reduction in LDL oxidation may improve endothelial function, we studied the effect of some vitamins (folic acid, 5-methyltetrahydrofolic acid, and vitamin B-12) on LDL oxidation, either in the presence or absence of homocysteine. For this purpose, two in vitro systems were used: an endothelial cell-catalyzed LDL oxidation system and a cell-free copper-initiated LDL oxidation system. The kinetics of copper-catalyzed LDL oxidation was determined by continuous monitoring of the production of conjugated dienes in the reaction medium. TBARS production, a parameter of lipid peroxidation, was also evaluated. In both in vitro systems, only 5-methyltetrahydrofolic acid was able to decrease TBARS production in a concentration-dependent manner, independently of the presence or absence of homocysteine. In the copper-induced LDL oxidation system, vitamin B-12 and 5-methyltetrahydrofolic acid increased the lag time of conjugated diene production by 25 and 47%, respectively, suggesting that both vitamins in this system had antioxidant properties. Folic acid was unable to show antioxidant properties when included in either in vitro system. The results demonstrate that 5-methyltetrahydrofolic acid and vitamin B-12 are important protective agents against LDL oxidative modifications.

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.

Assessing endothelial function as a risk factor for cardiovascular disease

The vascular endothelium plays a key role in the prevention of atherosclerosis. Endothelial dysfunction is an antecedent of clinical cardiovascular disease and can be viewed as the final pathway between coronary risk factors and the development of atherosclerosis. The development of a noninvasive method of assessing endothelial health (ie, measurement of flow- mediated dilation of the brachial artery) has enabled investigators to evaluate the effects of dietary patterns on vascular function. Emerging evidence indicates that dietary fats may acutely impair endothelial function, but this effect is dependent on the type of fat and on the other nutrients consumed. Although inconclusive, studies in cohorts of modest size suggest that antioxidants, L-arginine, and folic acid may modulate endothelial function. Additional research is needed to define the impact of complex, long-term dietary patterns on the vascular endothelium.

Folate, homocysteine, endothelial function and cardiovascular disease

Evidence reported from numerous clinical studies over the past decade has revealed an association between increased plasma total homocysteine (tHcy) concentrations and cardiovascular disease (CVD). In addition, epidemiological studies have identified an inverse association between blood folate concentrations, folate intake and cardiovascular endpoints, that are independent of homocysteine. Folic acid supplementation can lower plasma tHcy concentrations safely and inexpensively. Furthermore, folic acid can reverse endothelial dysfunction observed in patients with CVD. This reversal in endothelial dysfunction with folic acid has been shown to be independent of plasma tHcy lowering, suggesting that folate has pleiotropic effects on the vasculature other than homocysteine lowering. In vitro evidence demonstrates that 5-methyltetrahydrofolate (5MeTHF) the main circulating metabolite of folate, can increase nitric oxide production and can directly scavenge superoxide radicals. The potential beneficial role of folic acid supplements on vascular disease are currently being tested in randomized placebo controlled studies.

Solid-phase extraction-electrospray ionization mass spectrometry for the quantification of folate in human plasma or serum

The measurement of 5-methyltetrahydrofolic acid (5 MT) blood levels is one of several factors used to diagnose folate deficiency in humans. 5 can be selectively purified from either human plasma or human serum via solid-phase extraction procedures and specifically detected and quantified in the extracts with liquid chromatography/isotope-dilution electrospray-ionization mass spectrometry. Two different, yet complementary, solid-phase extraction-liquid chromatography/mass spectrometry methods have been developed and applied to the quantification of 5 MT from such extracts. One method utilizes the high-affinity folate-binding protein from cow's milk coupled with multiple-reaction-monitoring-mode tandem mass spectrometry while the other method utilizes reversed-phase C(18) extraction followed by selected-ion-monitoring-mode mass spectrometry. The accuracy of each method is assessed through a comparative determination of 5 MT levels in homogenous plasma and serum pools. Additionally, each method is compared and evaluated against the "total folate" results provided by routine radioassay and microbiological assay determinations. On the basis of the experimental data presented in this report, it is suggested that both methods have the capacity to serve as potential reference methods for the quantification of circulating 5MT in plasma or serum.

Short-term high-dose folic acid does not alter markers of endothelial cell damage in patients with coronary heart disease

BACKGROUND AND OBJECTIVE

Endothelial dysfunction is an early, pre-clinical manifestation of coronary heart disease and is associated with increased plasma levels of von Willebrand factor (vWF), soluble E-selectin, and thrombomodulin, markers of endothelial cell damage/activation and reduced nitric oxide bioavailability. Homocysteine is associated with an increased risk of cardiovascular disease and mortality. High-dose folic acid treatment lowers plasma homocysteine by 25% and improves nitric oxide bioavailability; however, the effects on other indices of endothelial cell activation/damage has not been examined in patients with coronary heart disease and normal renal function.

DESIGN AND METHODS

In a randomised, double-blind, cross-over study in 50 patients with coronary heart disease and normal serum creatinine, folic acid (5 mg/daily) was administered for 6 weeks and blood was analysed for von Willebrand factor, soluble E-selectin, and thrombomodulin. Endothelial nitric oxide bioavailability was assessed by flow-mediated dilatation.

RESULTS

Plasma folate levels increased (9.1+/-3.4 vs. 310+/-235 microg/l; p<0.001) and nitric oxide bioavailability improved (47+/-35 vs. 110+/-43 microm; p<0.001) following active treatment. However, markers of endothelial cell injury were not significantly influenced (von Willebrand factor 118+/-33 vs. 119+/-34%; E-selectin 52+/-17 vs. 51+/-16 microg/l; thrombomodulin 3.94+/-1.81 vs. 3.94+/-1.51 microg/l; p=NS comparing post-placebo with post-folate). No correlation was observed between improvement in flow-mediated dilatation and change in endothelial marker proteins.

INTERPRETATION AND CONCLUSION

These data suggest that endothelial markers are not useful surrogates of endothelial nitric oxide bioavailability in coronary heart disease and may be a less sensitive marker of endothelial function than nitric oxide.

Oxidative stress in childhood obesity

OBJECTIVE

To measure products of free radical damage in childhood obesity.

METHODS

Plasma free radicals were assayed in 24 children with exogenous obesity and 24 non-obese healthy controls. A new colorimetric method was used that measures the generation of peroxy radicals (D-Roms), first products of the reaction between free radicals and oxygen.

RESULTS

D-Roms levels were higher in the obese children than in the non-obese group (33.3+/-10.1 mg% of H2O2 vs 22.8+/-2.8 mg% of H2O2; p <0.001). Moreover, D-Roms levels were higher in children with hyperlipidemia than in children with normolipidemia (49.6+/-3.1 mg% of H2O2 vs 27.8+/-3.2 mg% of H2O2; p <0.001). D-Roms level was positively correlated with waist-hip ratio, serum total cholesterol, serum triglycerides, serum low-density lipoprotein-cholesterol, systolic blood pressure, diastolic blood pressure and fasting blood glucose in obese children. In a multivariate regression model for obese children, the independent correlates for D-Roms level were systolic blood pressure (p <0.001) and serum total cholesterol (p <0.001), with the total variance explained being 82%.

CONCLUSION

Our study demonstrates for the first time that there was increased D-Roms levels in obese children and adolescents and suggests that increased systolic blood pressure associated with hyperlipidemia may independently contribute to increased oxidative stress in childhood obesity.

Hyperhomocysteinemia in healthy young men and elderly men with normal serum folate concentration is not associated with poor vascular reactivity or oxidative stress

The mechanism by which homocysteine (Hcy) causes endothelial dysfunction is probably mediated by oxidative stress. The aim of this study was to evaluate the effect of oxidative stress on endothelial function in young and elderly hyperhomocysteinemic (HHcy) men. A total of 35 HHcy (Hcy > 15 micro mol/L), young (n = 15; 20-40 y) and elderly men (n = 20; > 65 y) and 33 normohomocysteinemic (NHcy; controls) young (n = 14) and elderly (n = 19) men (Hcy < 13 micro mol/L), without classic cardiovascular risk factors were recruited. Serum Hcy, folate, and vitamin B-12, whole-blood glutathione, plasma total antioxidants status, TBARS, and 8-F(2alpha) isoprostanes were determined. Noninvasive ultrasound measurements of endothelium-dependent (EDVR) and -independent dilatation (EIVR) were performed. EDVR, EIVR, and markers of oxidative stress did not differ among the groups. Folate concentrations were higher in elderly than in young men (P < 0.001), independent of Hcy concentrations. Vitamin B-12 concentrations were lower in HHcy than in NHcy elderly men (P < 0.045). EDVR was correlated with folate concentrations in young men (r = 0.40, P = 0.04) and negatively with BMI in elderly men (r = -0.52, P = 0.002). In the present study, HHcy with normal serum folate concentrations was not associated with poor EDVR or oxidative stress in healthy young and elderly men.

Homocysteine and cardiovascular disease: biological mechanisms, observational epidemiology, and the need for randomized trials

Basic research indicates that homocysteine causes endothelial dysfunction and damage, accelerates thrombin formation, inhibits native thrombolysis, promotes lipid peroxidation through free radical formation, and induces vascular smooth muscle proliferation and monocyte chemotaxis. Most, but not all, observational epidemiological studies indicate that individuals with higher homocysteine levels have increased risks of cardiovascular disease. The magnitude ranges from approximately 20% in prospective studies to approximately 80% in retrospective case-control studies. In all observational epidemiological studies, however, the amount of uncontrolled and uncontrollable confounding is as large as the postulated small to moderate effect size. Thus, the totality of evidence should include randomized trials of sufficient sample size and duration with clinical end points. Folic acid reduces levels of homocysteine, but at present, despite several plausible biological mechanisms and a large body of observational epidemiological data, it is unclear whether supplementation will reduce risks of cardiovascular disease. It is also unclear whether any benefit of folic acid is attributable to lowering homocysteine levels. The current evidence is necessary, but not sufficient to judge causality. Such judgments await the availability of data from large-scale randomized trials. The availability of such data would permit rational clinical decision-making for individual patients and policy decisions for the health of the general public.

Assessment of atherosclerotic risk factors and endothelial function in children and young adults with pediatric-onset systemic lupus erythematosus

OBJECTIVE

To characterize atherosclerotic risk factors and endothelial function in pediatric-onset systemic lupus erythematosus (SLE).

METHODS

Lipoproteins, oxidized state, and autoantibodies to oxidized low-density lipoprotein (Ox-LDL) were assessed. Endothelial function was evaluated using brachial artery reactivity.

RESULTS

Thirty-three SLE patients and 30 controls were studied. SLE subjects had significantly decreased mean high-density lipoprotein (HDL) cholesterol (41 mg/dl versus 51 mg/dl; P = 0.002) and apolipoprotein A-I (97 mg/dl versus 199 mg/dl; P = 0.0004). There was no difference between groups in markers of oxidized state (including nitric oxide metabolites, isoprostanes, and Ox-LDL) or in endothelial function. However, SLE subjects had increased median anti-Ox-LDL IgG (2,480 relative light units [RLU] versus 1,567 RLU; P = 0.0007) and IgG immune complexes with LDL (4,222 RLU versus 2,868 RLU; P = 0.002).

CONCLUSION

Pediatric SLE patients had significantly decreased levels of HDL cholesterol and apolipoprotein A-I and elevated titers of autoantibodies to Ox-LDL. Despite these atherosclerotic risk factors, SLE patients had normal measures of oxidized state and endothelial function.

ADMA and oxidative stress

Elevated plasma concentrations of the endogenous nitric oxide synthase (eNOS) inhibitor asymmetric dimethylarginine (ADMA) represent a novel risk factor for the development of endothelial dysfunction and a predictor for all-cause and cardiovascular mortality. However, it is unknown whether elevated ADMA plasma concentrations may be considered simply as a marker for cardiovascular disease or whether increased ADMA levels per se may predispose to the development of vascular disease. There is experimental and clinical evidence linking endothelial dysfunction to increased production of oxygen-derived free radicals such as superoxide anion. Oxidative stress has been shown to increase the activity of arginine methylating and ADMA degrading enzymes leading to increased ADMA concentrations. Interestingly, the endothelial nitric oxide synthase may become uncoupled in the presence of high ADMA levels further contributing to the vascular oxidative stress burden. It remains to be established to what extent ADMA is able to interact with eNOS in vivo. Possible mechanisms underlying increased oxidative stress in the setting of elevated ADMA concentrations and therapeutic implications will be discussed.

Folic acid improves endothelial function in children and adolescents with type 1 diabetes

OBJECTIVE

To evaluate the effect of folate supplementation on endothelial function in children and adolescents with type 1 diabetes.

STUDY DESIGN

Thirty-six subjects with type 1 diabetes age 13.6+/-2.6 years completed a randomized, double-blind, placebo-controlled crossover trial. Each subject received 8 weeks of oral folic acid (5 mg/d) and 8 weeks of placebo, with an 8-week washout period. Before and after each intervention, we assessed endothelial function by using brachial artery responses to flow (flow-mediated dilatation [FMD]) and glyceryl trinitrate, von Willebrand factor, glucose, hemoglobin A1c, total plasma homocyst(e)ine (tHcy), vitamin B(12), serum folate, and red cell folate (RCF).

RESULTS

Folic acid increased FMD by 2.58 (3.1-5.7) % (95% confidence interval, 1.28-3.88), whereas placebo did not change FMD (-0.42%; 95% confidence interval, -1.67 to 0.83; P<.001). Folic acid increased serum folate by 14 nmol/L (6.2 ng/mL, P<.001) and RCF by 467.2 nmol/L (206 ng/mL, P<.001). Change in FMD was related to change in serum folate (r=0.46, P=.005) and RCF (r=0.39, P=.02). Glyceryl trinitrate responses, von Willebrand factor, tHcy, and hemoglobin A1c were not affected by the intervention.

CONCLUSIONS

Short-term high-dose folic acid improves endothelial function in children and adolescents with type 1 diabetes and normal folate status independently of tHcy.

Nutrition and prevention of ischemic stroke: present knowledge, limitations and future perspectives

Stroke, particularly ischemic stroke, has a major impact on public health due to its high incidence, prevalence and rate of subsequent disability in Italy as in most industrialised countries. Apart from age, many modifiable factors, such as hypertension, smoking, diabetes, dyslipidemia, obesity, physical inactivity, alcohol abuse and hyperhomocysteinemia, have been recognised as playing a role in the pathogenesis of this disease. While appropriate pharmacological therapy has proven effective in the prevention of stroke in particular categories of patients, most of the above mentioned predisposing conditions are amenable to be affected by nutrition. Unequivocal demonstration of a protective or adverse role of single foods and nutrients against the risk of stroke has been however difficult to achieve due to confounding by biological variability, methodological inadequacies in the assessment of individual nutritional habits and difficulty to carry out long-term randomised controlled trials in the nutritional area. Notwithstanding, in several cases, causal relationships could be inferred from case-control and cohort studies in the presence of plausible and reproducible associations, evidence of dose-dependent effects and consistency in the results of different studies. The aim of this paper was to review present knowledge and highlight limitations and future perspectives about the role of nutrition in the prevention of ischemic stroke.

L-Homocysteine and L-homocystine stereospecifically induce endothelial nitric oxide synthase-dependent lipid peroxidation in endothelial cells

Atherothrombotic cardiovascular disease associated with hyperhomocysteinemia has been proposed to result, at least in part, from increased vascular oxidative stress. Here we characterize one mechanism by which homocyteine may induce a vascular cell type-specific oxidative stress. Our results show that L-homocysteine at micromolar levels stereospecifically increases lipid peroxidation in cultured endothelial cells, but not in vascular smooth muscle cells or when medium is incubated in the absence of cells. Consistent with these observations, homocysteine also increases the formation of intracellular reactive oxygen species. The pro-oxidant effect of homocysteine can be fully replicated by an equivalent concentration of homocystine (i.e., an oxidized form of homocysteine), but not with cysteine or glutathione. Homocyst(e)ine-dependent lipid peroxidation is independent of H(2)O(2) and alterations in glutathione peroxidase activity, but dependent on superoxide. Mechanistically, the pro-oxidant effect of homocysteine appears to involve endothelial nitric oxide synthase (eNOS), as it is blocked by the eNOS inhibitor L-N(G)-nitroarginine methyl ester. Thus, homocyst(e)ine actively promotes oxidative stress in endothelial cells via an eNOS-dependent mechanism.

DACH-LIGA homocystein (german, austrian and swiss homocysteine society): consensus paper on the rational clinical use of homocysteine, folic acid and B-vitamins in cardiovascular and thrombotic diseases: guidelines and recommendations

About half of all deaths are due to cardiovascular disease and its complications. The economic burden on society and the healthcare system from cardiovascular disability, complications, and treatments is huge and getting larger in the rapidly aging populations of developed countries. As conventional risk factors fail to account for part of the cases, homocysteine, a "new" risk factor, is being viewed with mounting interest. Homocysteine is a sulfur-containing intermediate product in the normal metabolism of methionine, an essential amino acid. Folic acid, vitamin B12, and vitamin B6 deficiencies and reduced enzyme activities inhibit the breakdown of homocysteine, thus increasing the intracellular homocysteine concentration. Numerous retrospective and prospective studies have consistently found an independent relationship between mild hyperhomocysteinemia and cardiovascular disease or all-cause mortality. Starting at a plasma homocysteine concentration of approximately 10 micromol/l, the risk increase follows a linear dose-response relationship with no specific threshold level. Hyperhomocysteinemia as an independent risk factor for cardiovascular disease is thought to be responsible for about 10% of total risk. Elevated plasma homocysteine levels (>12 micromol/l; moderate hyperhomocysteinemia) are considered cytotoxic and are found in 5 to 10% of the general population and in up to 40% of patients with vascular disease. Additional risk factors (smoking, arterial hypertension, diabetes, and hyperlipidemia) may additively or, by interacting with homocysteine, synergistically (and hence over-proportionally) increase overall risk. Hyperhomocysteinemia is associated with alterations in vascular morphology, loss of endothelial anti-thrombotic function, and induction of a procoagulant environment. Most known forms of damage or injury are due to homocysteine-mediated oxidative stress. Especially when acting as direct or indirect antagonists of cofactors and enzyme activities, numerous agents, drugs, diseases, and lifestyle factors have an impact on homocysteine metabolism. Folic acid deficiency is considered the most common cause of hyperhomocysteinemia. An adequate intake of at least 400 microg of folate per day is difficult to maintain even with a balanced diet, and high-risk groups often find it impossible to meet these folate requirements. Based on the available evidence, there is an increasing call for the diagnosis and treatment of elevated homocysteine levels in high-risk individuals in general and patients with manifest vascular disease in particular. Subjects of both populations should first have a baseline homocysteine assay. Except where manifestations are already present, intervention, if any, should be guided by the severity of hyperhomocysteinemia. Consistent with other working parties and consensus groups, we recommend a target plasma homocysteine level of <10 micromol/l. Based on various calculation models, reduction of elevated plasma homocysteine concentrations may theoretically prevent up to 25% of cardiovascular events. Supplementation is inexpensive, potentially effective, and devoid of adverse effects and, therefore, has an exceptionally favorable benefit/risk ratio. The results of ongoing randomized controlled intervention trials must be available before screening for, and treatment of, hyperhomocysteinemia can be recommended for the apparently healthy general population.