Ian F. W. McDowell

Neutrophil superoxide anion--generating capacity, endothelial function and oxidative stress in chronic heart failure:effects of short- and long-term vitamin C therapy

OBJECTIVES First, we sought to study the effects of short- and long-term vitamin C therapy on oxidative stress and endothelial dysfunction in chronic heart failure (CHF), and second, we sought to investigate the role of neutrophils as a cause of oxidative stress in CHF. BACKGROUND Oxidative stress may contribute to endothelial dysfunction in CHF. Vitamin C ameliorates endothelial dysfunction in CHF, presumably by reducing oxidative stress, but this is unproven. METHODS We studied 55 patients with CHF (ischemic and nonischemic etiologies) and 15 control subjects. Flow-mediated dilation (FMD) in the brachial artery was measured by ultrasound wall-tracking, neutrophil superoxide anion (O2-) generation by lucigenin-enhanced chemiluminescence and oxidative stress by measurement of free radicals (FRs) in venous blood using electron paramagnetic resonance (EPR) spectroscopy and plasma thiobarbituric acid reactive substances (TBARS). Measurements were performed at baseline in all subjects. The effects of short-term (intravenous) and long-term (oral) vitamin C therapy versus placebo were tested in patients with nonischemic CHF. RESULTS At baseline, FRs were higher in patients with CHF than in control subjects (p < 0.01), TBARS were greater (p < 0.005), neutrophil O2- -generating capacity was enhanced (p < 0.005) and FMD was lower (p < 0.0001). Compared with placebo, short-term vitamin C therapy reduced FR levels (p < 0.05), tended to reduce TBARS and increased FMD (p < 0.05), but did not affect neutrophil O2- -generating capacity. Long-term vitamin C therapy reduced FR levels (p < 0.05), reduced TBARS (p < 0.05) and improved FMD (p < 0.05), but also reduced neutrophil O2- -generating capacity (p < 0.05). Endothelial dysfunction was not related to oxidative stress, and improvements in FMD with vitamin C therapy did not relate to reductions in oxidative stress. CONCLUSIONS Oxidative stress is increased in ischemic and nonischemic CHF, and neutrophils may be an important cause. Vitamin C reduces oxidative stress, increases FMD and, when given long term, decreases neutrophil O2- generation, but the lack of a correlation between changes in endothelial function and oxidative stress with vitamin C implies possible additional non-antioxidant benefits of vitamin C.

Homocysteine and Endothelial Dysfunction: A Link with Cardiovascular Disease

The nature of the link between homocysteine and cardiovascular disease has not yet been clearly established. Impaired endothelium-independent vasodilatation is an early feature of vascular disease. In human studies, methionine loading, which acutely elevates plasma homocysteine, induces endothelial dysfunction. Folate therapy, which lowers homocysteine, enhances endothelial function. This is consistent with, but not proof of, homocysteine toxicity to endothelium in vivo. Homocysteine, in high concentration, can induce endothelial dysfunction in vitro. This is accompanied by increased superoxide production, which when inhibited, restores normal endothelial function. These observations suggest that homocysteine may induce vascular endothelial dysfunction by a mechanism involving reactive oxygen species.

Effect of riboflavin status on the homocysteine-lowering effect of folate in relation to the MTHFR (C677T) genotype.

BACKGROUND Riboflavin (vitamin B(2)) is the precursor for FAD, the cofactor for methylenetetrahydrofolate reductase (MTHFR). MTHFR catalyzes the formation of 5-methyltetrahydrofolate, which acts as a methyl donor for homocysteine remethylation. Individuals with the MTHFR 677C-->T mutation have increased plasma total homocysteine (tHcy) concentrations, particularly in association with low folate status. It has been proposed that riboflavin may act together with folate to lower plasma tHcy, particularly in individuals with the thermolabile MTHFR T variant. METHODS We measured B-vitamin status and plasma tHcy in 126 healthy individuals 20-63 years of age (42 CC, 42 CT, and 42 TT MTHFR genotypes) at baseline and after three interventions (4 months): placebo plus natural diet; daily 400 microg folic acid supplement plus natural diet; and increased dietary folate to 400 microg/day. RESULTS At baseline and after nutritional intervention, lower riboflavin status was associated with increased plasma tHcy concentrations. Plasma tHcy was 2.6 micromol/L higher in the lowest plasma riboflavin quartile compared with the highest (P <0.02) and was 4.2 micromol/L higher in the highest erythrocyte glutathione reductase activation coefficient (EGRAC) quartile compared with the lowest (P <0.001). This effect was not restricted to those with the T allele. Folic acid given as a 400 microg/day supplement appeared to exacerbate a tendency toward riboflavin deficiency, as suggested by an increase in the proportion of individuals with EGRAC > or =1.4 from 52% to 65% after supplementation (P <0.05). CONCLUSIONS Folate and riboflavin interact to lower plasma tHcy, possibly by maximizing the catalytic activity of MTHFR. The effect may be unrelated to MTHFR genotype.

Folate, homocysteine, endothelial function and cardiovascular disease. What is the link?

Elevated plasma homocysteine concentrations are associated with an increased risk of cardiovascular disease, but the relationship has not been proven to be causal. Folate is the strongest nutritional and pharmacological determinant of plasma homocysteine concentrations, which also interact with the genetic variation in methylenetetrahydrofolate reductase (MTHFR). Endothelial dysfunction due to reduced nitric oxide bioavailability is an early feature of vascular pathology. This can be assessed noninvasively by measurement of flow-mediated dilatation. Human studies on folic acid, homocysteine and endothelial function are reported. It is proposed that folic acid in high doses may have beneficial effects on endothelial function, which are independent of homocysteine lowering.

Lowering plasma homocysteine with folic acid in cardiovascular disease: what will the trials tell us?

Lowering plasma homocysteine with folic acid in cardiovascular disease: what will the trials tell us? Sagar N. Doshi , Stuart J. Moat *, Ian F.W. McDowell , Malcolm J. Lewis , Jonathan Goodfellow d a Cardiovascular Institute, Mount Sinai School of Medicine, New York, USA b Department of Pharmacology, Cardiovascular Sciences Research Group, Wales Heart Research Institute, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK c Department of Medical Biochemistry, Cardiovascular Sciences Research Group, Wales Heart Research Institute, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK d Department of Cardiology, Cardiovascular Sciences Research Group, Wales Heart Research Institute, University of Wales College of Medicine, Heath Park, Cardiff, CF14 4XN, UK

Homocysteine and endothelial function

See article of Lambert et al. [34] (pages 743–751) in this issue. The hypothesis that homocysteine may cause vascular disease was originally proposed by McCully, following the observation that premature thromboembolism and atherosclerosis was a feature of homocystinuria [1]. In homocystinuria, a rare inborn error of metabolism, plasma homocysteine concentrations are generally 10 to 50 times that found in the healthy population [2]. This led to the hypothesis that mild to moderate elevations of plasma homocysteine may be a risk factor for atherosclerosis in the general population. This hypothesis has generated considerable interest, particularly as simple therapy with oral B group vitamins significantly lowers plasma homocysteine [3]. Homocysteine is a thiol containing amino acid that is metabolised from methionine, an essential amino acid derived from dietary protein. Homocysteine can be metabolised further to cysteine by transsulfuration (using vitamin B6 as cofactor) or remethylated back to methionine using either methyltetrahydrofolate (and Vit B12 as cofactor) or betaine as co-substrate (see Fig. 1). In human plasma, homocysteine exists in several forms. Approximately 70–80% is bound to protein, mainly albumin, by a disulphide bond. The remaining homocysteine oxidises to form dimers (homocystine) or combines with cysteine to form a mixed disulphide. Only a small proportion (<1%) circulates as free homocysteine. A number of techniques are now available for the combined measurement of the multiple forms of plasma homocysteine, which is expressed as total homocysteine (tHcy) [4]. Fig. 1 Metabolism of homocysteine. A ‘normal’ range for tHcy cannot be defined but various studies report fasting levels in the range 5–15 μmol/l in the healthy population. A number of factors, genetic and acquired, can influence the blood levels of tHcy. Genetic factors include the genotype for methylene tetrahydrofolate reductase (MTHFR) C677T mutation, which results in thermolability, reduced activity and consequently fasting hyperhomocysteinaemia, particularly … * Corresponding author. Tel.: +44-1222-744-851; fax: +44-1222-766-276

Decreased circulating plasma lipids in patients with homocystinuria.

Premature vascular disease and thrombosis are recognized complications in homocystinuria. Vascular disease in patients with homocystinuria affects both arterial and venous systems, with venous thrombosis as the major cause of death (Mudd et al 1985). Histologically, the arterial disease is characterized by intimal and medial smooth-muscle hyperplasia, with fibrosis and thickening of the elastic lamina, but lipid deposition is usually not observed (Gibson et al 1964). This contrasts with the classical appearance of atheromatous vascular disease in the general population. Relatively little is known about possible disturbances to lipid metabolism in patients with homocystinuria. We report observations on lipids and lipoproteins in a group of patients being treated and monitored for homocystinuria.

Nutritional advice to increase soluble fibre intake does not change plasma folate or homocysteine in men with angina: a randomised controlled trial

OBJECTIVE To study the effect of advice to increase dietary soluble fibre, including fruit and vegetables, on plasma folate and homocysteine in men with angina. DESIGN Data were collected on a subset of subjects from the Diet and Angina Randomised Trial (DART II). In a randomised (2 x 2) factorial design, subjects received advice on either, neither or both interventions to: (1) increase soluble fibre intake to 8.0 g day(-1) (fruit, vegetables and oats); (2) increase oily fish intake to 2 portions week(-1). Those who received soluble fibre advice were compared with those who did not. Subjects were genotyped for C677T variant 5,10-methylenetetrahydrofolate reductase (MTHFR). SETTING/SUBJECTS Seven hundred and fifty-three male angina patients were recruited from general practice. RESULTS Plasma homocysteine concentrations were at the upper end of the normal range (median 11.5, 25% 9.4, 75% 14.0 micromol l(-1)). Baseline intake of fruit and vegetables was positively correlated with plasma folate (r(s) = 0.29, P < 0.01). Smokers had lower intakes of fruit and vegetables, lower plasma folate and higher homocysteine (all P < 0.01). Homozygotes for variant MTHFR had higher homocysteine concentrations at low plasma folate (P < 0.01). Reported intakes of fruit and vegetables and estimated dietary folate increased in the intervention group (ca. +75 g day(-1), P < 0.01 and ca. +20 g day(-1), P < 0.05, respectively). However, neither plasma folate (baseline/follow-up 4.5 vs. 4.4 microg l(-1), P = 0.40) nor homocysteine (baseline/follow-up 11.7 vs. 11.7 micromol l(-1), P = 0.31) changed. CONCLUSIONS Plasma homocysteine, a cardiovascular risk factor, is influenced by MTHFR genotype, plasma folate and smoking status. Dietary advice successfully led to changes in fruit and vegetable intake, but not to changes in plasma folate or homocysteine, possibly because the fruits and vegetables that were chosen were not those richest in folate.

Approaches to defining the optimal dietary folate intake for cardiovascular health

Looks at the role of dietary folate for cardiovascular health. Considers the hypothesis that a diet poor in folate may lead to accelerated vascular disease. Also looks at the role of some enzymes with regard to cardiovascular disease.