Total homocysteine and cardiovascular disease

Changes in basal and postmethionine load concentrations of total homocysteine and cystathionine after B vitamin intervention

BACKGROUND

Vitamin B-6 is necessary for the metabolism of homocysteine and is often used in combination with folic acid and vitamin B-12 in clinical trials that investigate whether the lowering of plasma total homocysteine (tHcy) can prevent vascular disease.

OBJECTIVE

We compared the effects of vitamin B-6 with the effects of folic acid and vitamin B-12, as used in the Western Norway B-vitamin Intervention Trial (WENBIT), on basal and postmethionine load (PML) tHcy and cystathionine concentrations.

DESIGN

Ninety patients with suspected coronary artery disease were randomly assigned to 1 of 4 groups to receive daily oral treatment with 1) 0.8 mg folic acid, 0.4 mg vitamin B-12, and 40 mg vitamin B-6 (group A); 2) 0.8 mg folic acid and 0.4 mg vitamin B-12 (group B); 3) 40 mg vitamin B-6 (group C); or 4) placebo (group D). For the first 2 wk, groups A and B received additional folic acid (5 mg/d). A methionine-loading test was performed at baseline and after 3 mo.

RESULTS

Treatment with folic acid and vitamin B-12 caused a rapid and significant lowering of basal (31%) and PML tHcy concentrations (22%), with no effect on cystathionine. Vitamin B-6 did not change basal tHcy and had a significant but limited effect on PML tHcy concentrations. However, vitamin B-6 treatment markedly lowered basal and PML cystathionine by 31% and 42%, respectively.

CONCLUSION

The folic acid and vitamin B-12 combination applied in WENBIT provides rapid, substantial, and long-term tHcy-lowering effects, whereas the effect of vitamin B-6 on tHcy was relatively small and confined to PML tHcy. However, vitamin B-6 treatment caused a marked reduction in plasma cystathionine. Cystathionine could be a useful marker for assessment of the vitamin B-6 effect and should, together with tHcy, be related to clinical outcome in ongoing trials.

Serum folate and homocysteine and the incidence of acute coronary events: the Kuopio Ischaemic Heart Disease Risk Factor Study

BACKGROUND

Several, but not all, prospective studies have shown that low folate intakes, low circulating folate concentrations, or high plasma total homocysteine (tHcy) concentrations are associated with an increased risk of coronary artery disease (CAD).

OBJECTIVE

We examined the relations of both serum folate and serum tHcy concentrations with acute coronary events in middle-aged men from eastern Finland who had no CAD at baseline.

DESIGN

In a population-based prospective cohort study, 1027 men aged 46-64 y were examined in 1991-1993 as part of the Kuopio Ischaemic Heart Disease Risk Factor Study. During an average follow-up of 7.7 y (7900 person-years of follow-up), 114 acute coronary events were observed in 61 men who had no previous history of CAD (n = 810).

RESULTS

In a Cox model, compared with men whose serum folate concentrations were in the lowest tertile, those whose concentrations were in the highest tertile had a risk factor-adjusted relative risk of acute coronary events of 0.35 (95% CI: 0.17, 0.73; P = 0.005). Serum tHcy concentrations were not significantly associated with the risk of acute coronary events (for the highest tertile compared with the lowest, adjusted relative risk = 1.03; 95% CI: 0.57, 1.87; P = 0.932).

CONCLUSIONS

The results of this prospective cohort study do not support the hypothesis that a high circulating tHcy concentration is a risk factor for acute coronary events in a male population free of prior heart disease. However, they do suggest that moderate-to-high serum folate concentrations are associated with a greatly reduced incidence of acute coronary events.

Acute negative inotropic effects of homocysteine are mediated via the endothelium

Previous studies have shown that chronic hyperhomocysteinemia is associated with an adverse cardiac remodeling and heart failure. This study, which utilized coronary-perfused hearts and superfused papillary muscle, was designed to determine whether homocysteine acts acutely to alter cardiac contractile function. Left ventricular developed pressure was used as a measure of systolic function in the Langendorff-perfused heart, whereas isometric developed tension was used in papillary muscle. All preparations were bathed in physiological buffer and paced electrically. Initial results showed that homocysteine elicits a relatively rapid onset (maximum effect observed within 5 min), concentration-dependent (10-300 microM), and moderate negative inotropic action (maximum decrease in tension was approximately 15% of control values) in Langendorff-perfused hearts but not in papillary muscle. In contrast, effluent from homocysteine-treated hearts decreased contractility in papillary muscle, and all inotropic actions were largely eliminated when brief Triton X-100 treatment was utilized to inactivate the coronary endothelium in the intact heart. The homocysteine-induced decrease in contractile function was not antagonized by N(omega)-nitro-l-arginine, a nitric oxide synthase inhibitor, or the cyclooxygenase inhibitor indomethacin. Thus data suggest that pathophysiological concentrations of homocysteine elicit an acute negative inotropic effect on ventricular myocardium that is mediated by a coronary endothelium-derived agent other than nitric oxide or products of cyclooxygenase. Future studies are required to elucidate the mechanism by which homocysteine acts to elicit the release of the proposed endothelial mediator, the identity of the proposed paracrine agent, and the mechanism of its negative inotropic action.

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.

Serum homocysteine in relation to mortality and morbidity from coronary heart disease: a 24-year follow-up of the population study of women in Gothenburg

BACKGROUND

Elevated serum total homocysteine (tHcy) is an established risk factor for cardiovascular disease (CVD), especially in men. However, there are few prospective population studies on female cohorts, and none of these has been longer than 13 years.

METHODS AND RESULTS

The Population Study of Women in Gothenburg began in 1968/1969, at which time a representative population-based cohort of women aged 38, 46, 50, 54, and 60 years was recruited. The present cohort is a prospective follow-up of 1368 women in the original cohort for whom blood samples were stored and who were free of previous acute myocardial infarction (AMI) at the 1968/1969 baseline. Homocysteine was analyzed in 2001 with frozen serum from the baseline study and related to AMI incidence and mortality during 24 years of follow-up. Cox regression analyses were used with adjustment for age, traditional risk factors, and tHcy modifiers. For the fifth tHcy quintile, relative risk was 1.86 (95% CI 1.06 to 3.26) for AMI and 5.14 (95% CI 2.22 to 11.92) for death due to AMI. Age-standardized Kaplan-Meier plots for the fifth tHcy quintile versus others showed significant differences both for AMI and for death due to AMI that were apparent after 15 years of follow-up.

CONCLUSIONS

Homocysteine in middle-aged women is an independent risk factor for myocardial infarction and in particular mortality due to myocardial infarction. The study illustrates that long-term prospective studies might be necessary to show effects of homocysteine levels on AMI morbidity and mortality in women.

Population-based differences in frequency of the transcobalamin II Pro259Arg polymorphism

OBJECTIVE

A common polymorphism of the transcobalamin II (TC-II) gene, Pro250Arg, has been implicated as a possible genetic factor in population-based differences in vitamin B(12) metabolism. Our objective was to determine whether the prevalence of TC-II Pro259Arg polymorphism differs significantly between Caucasian, Asian and African-American groups.

METHODS

Genomic DNA was available on 187 Caucasians and 43 Asians from the Toronto area, and 51 African-Americans from Northeastern United States. A mutagenically separated PCR method was employed to genotype these groups for the TC-II Pro259Arg polymorphism (776C-->G).

RESULTS

The frequency of the Arg 259 allele varied significantly among the three groups studied (0.439 in Caucasian, 0.558 in Asian and 0.363 in African; P = 0.022). The Asian group had a significantly higher frequency of the Arg 259 allele compared to the Caucasian (P = 0.030) and the African-American group (P = 0.006). The frequency of the Arg 259 allele in the Caucasian and African-American groups was not significantly different (P = 0.103).

CONCLUSION

Population-based differences in TC-II Pro259Arg frequency are significant and could be a contributor to ethnic variation in susceptibility to vitamin B(12) deficiency, a common and persistent problem.

Non-pharmacological management of type 2 diabetes

Major studies have demonstrated an association between poor glycaemic control and the development of micro - and macrovascular complications in type 2 diabetes. Optimized metabolic control, including treatment of hyperglycaemia and other risk factors, reduces the risk of complications. Current strategies aiming at achieving the best possible control include a non-pharmacological approach consisting of lifestyle intervention using physical exercise and modification of nutrition intakes in the early stage of type 2 diabetes, or in later stages, combined with pharmacotherapy. Such an approach is also efficient in preventing type 2 diabetes in patients with impaired glucose tolerance. The purpose of this review is to analyse, in a clinical practice perspective, the current recommendations with respect to lifestyle modifications.

Facts and Recommendations about Total Homocysteine Determinations: An Expert Opinion

Background: Measurement of plasma total homocysteine has become common as new methods have been introduced. A wide range of disorders are associated with increased concentrations of total homocysteine. The purpose of this review is to provide an international expert opinion on the practical aspects of total homocysteine determinations in clinical practice and in the research setting and on the relevance of total homocysteine measurements as diagnostic or screening tests in several target populations.

Methods: Published data available on Medline were used as the basis for the recommendations. Drafts of the recommendations were critically discussed at meetings over a period of 3 years.

Outcome: This review is divided into two sections: (a) determination of homocysteine (methods and their performance, sample collection and handling, biological determinants, reference intervals, within-person variability, and methionine loading test); and (b) risk assessment and disease diagnosis (homocystinuria, folate and cobalamin deficiencies, cardiovascular disease, renal failure, psychiatric disorders and cognitive impairment, pregnancy complications and birth defects, and screening of elderly and newborns). Each of these subsections concludes with a separate series of recommendations to assist the clinician and the research scientist in making informed decisions. The review concludes with a list of unresolved questions.

Homocysteine and its relation to B-vitamins in Graves' disease before and after treatment: effect modification by smoking

OBJECTIVES

To investigate plasma total homocysteine levels and its relation to B-vitamins and smoking in Graves' disease before and after antithyroid therapy.

DESIGN

A longitudinal study taking place at four hospitals in Norway.

METHODS AND SUBJECTS

Plasma total homocysteine, serum folate, serum cobalamin and riboflavin, flavin mononucleotide and flavin adenine dinucleotide in plasma were investigated in 182 patients with hyperthyroidism before treatment. The same parameters were reinvestigated in 112 of these patients after attaining euthyroid state.

RESULTS

In hyperthyroidism, plasma total homocysteine was low, and inversely related to folate, cobalamin and riboflavin, and positively related to serum creatinine and age. Following antithyroid therapy, total homocysteine increased and the concentration of folate, cobalamin, riboflavin, flavin mononucleotide and flavin adenine dinucleotide decreased significantly. The most pronounced reduction (35%) was observed for flavin mononucleotide. In the hyperthyroid state, smokers had lower levels of folate and flavin mononucleotide than non-smokers. After restoration of euthyroidism, both folate and riboflavin were significantly lower in smokers than non-smokers. Plasma total homocysteine increased according to decreasing quartiles of B-vitamins. For riboflavin, this relation was confined to smokers.

CONCLUSION

Plasma total homocysteine changes according to thyroid status. These changes may be partly attributable to altered folate, cobalamin but also riboflavin status, particularly in smokers.

Randomized, placebo-controlled trial of intramuscular vitamin B12for the treatment of hyperhomocysteinaemia in dialysis patients

BACKGROUND

Plasma homocysteine is elevated in patients with end-stage renal disease (ESRD) and is a risk factor for cardiovascular disease. Folic acid has been shown to partially reduce homocysteine levels in dialysis patients. It is not known whether vitamin B12 reduces homocysteine independent of folic acid in patients who are not vitamin B12 deficient.

AIM

To determine whether 1 mg vitamin B12 lowers homocysteine in stable, chronic, haemodialysis patients independent of folic acid.

METHODS

Twenty-eight haemodialysis patients were randomized to receive three doses of 1 mg vitamin B12 or 1 mL saline placebo in a double-blind fashion at 1-month intervals. Fasting plasma total homocysteine, folic acid, red-cell folate, vitamin B12 and haemoglobin levels were determined prior to each dose and 4 weeks after the final injection. The study was powered to detect a 30% reduction in homocysteine over the 3 months.

RESULTS

Both the two groups were well matched with respect to total homocysteine levels, folic acid, red-cell folate and vitamin B12 levels. Serum vitamin B12 levels were significantly higher in the treatment group compared to placebo (217.7 pmol/L; 95% confidence interval (CI) 103.0-332.5; P < 0.001) at the end of the trial but homocysteine levels were not significantly different (3.08 micromol/L; 95% CI -4.44-10.61; P= 0.406).

CONCLUSIONS

The administration of intramuscular vitamin B12 over a 3-month period does not result in any reduction of plasma homocysteine levels in haemo-dialysis patients independent of folate status, however reductions of <30% cannot be excluded by the present study. High-dose folic acid remains the treatment of choice in reducing homocysteine, but whether this results in a reduction in cardiovascular events remains to be determined.

Insulin resistance syndrome in children : pathophysiology and potential management strategies

The simultaneous presence of various cardiovascular risk factors in the same individual is not rare, even in the pediatric age group. The clustering of risk factors can be termed insulin resistance syndrome (IRS) because of the putative central role of tissue insulin insensitivity in the background of the inter-related metabolic disturbances. Fasting hyperinsulinemia, impaired glucose tolerance, dyslipidemia, and hypertension are considered to represent the basic abnormalities of IRS. The most prevalent related disturbances are increased plasma levels of plasminogen activator inhibitor-1, fibrinogen, uric acid, homocysteine, and C-reactive protein, as well as visceral adiposity, microalbuminuria, disturbed essential fatty acid metabolism, low availability of lipid-soluble antioxidant vitamins, and enhanced expression of tumor necrosis factor-alpha in adipose tissues. Certain genetic abnormalities have been associated with IRS, but explain only a small part of the variability in insulin resistance. The exact prevalence of IRS in children remains to be defined; it was found to be 9% in one survey among children with obesity seeking medical attention. Modification of lifestyle, i.e. reduction of energy intake and enhancement of physical activity, are unquestionable prerequisites for long-term success in the management of IRS. In at least two randomized controlled studies, metformin proved to be clinically effective in increasing insulin sensitivity in hyperinsulinemic, nondiabetic adolescents. Thiazolidinediones have been successfully tested for the treatment of insulin resistance in adults, but not in children as yet. Prevention of the development of IRS in children is obviously of great significance for the health status of the community. However, the efficacy of various preventive approaches should be investigated further in carefully designed controlled trials.

Comparative effects of atorvastatin, simvastatin, and fenofibrate on serum homocysteine levels in patients with primary hyperlipidemia

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disease. Lipid-lowering agents, such as fibrates, can modify homocysteine levels. However, less is known about the effect of statin therapy on homocysteine. The authors compared the effects of atorvastatin (40 mg/day), simvastatin (40 mg/day), and micronized fenofibrate (200 mg/day) on the serum concentrations of total homocysteine, vitamin B12, and folic acid in patients with primary hyperlipidemia. A total of 128 patients with primary hyperlipidemia (total cholesterol > 240 mg/dL and triglycerides < 350 mg/dL) were assigned to atorvastatin, simvastatin, or fenofibrate. Serum lipid and metabolic parameters were measured at baseline and at 6 and 12 weeks of treatment. Homocysteine correlated positively with serum creatinine and uric acid levels and inversely with serum folic acid levels. All treatment modalities reduced total, low-density lipoprotein (LDL) cholesterol, and triglyceride concentrations. High-density lipoprotein (HDL) cholesterol levels significantly increased only in the fenofibrate-treated patients (47.9 +/- 12.5 vs. 50.7 +/- 12.6 vs. 51.2 +/- 12.8 mg/dL, p < 0.01). Atorvastatin and fenofibrate treatment resulted in a significant reduction of serum uric acid levels (5.3 +/- 1.6 vs. 4.9 +/- 1.4 vs. 4.8 +/- 1.4 mg/dL, p < 0.0001 for atorvastatin; 5.6 +/- 1.6 vs. 4.3 +/- 1.4 vs. 4.4 +/- 1.4 mg/dL, p < 0.0001 for fenofibrate). Homocysteine levels were significantly increased only by fenofibrate (10.3 +/- 3.3 vs. 14.1 +/- 3.8 vs. 14.2 +/- 3.6 microU/L, p < 0.001) but did not change from baseline following statin treatment. Neither statins nor fenofibrate had any effect on serum vitamin B12 and folic acid levels. In contrast to fenofibrate, therapeutic dosages of atorvastatin and simvastatin have a neutral effect on serum homocysteine levels, which is in favor of their "cardioprotective" properties.

Plasma homocysteine levels in obese and non-obese subjects with or without hypertension; its relationship with oxidative stress and copper

OBJECTIVES

The relationship between plasma total Homocysteine (tHcy) and oxidative stress and plasma levels of lipids, insulin and copper levels were investigated in obese and nonobese hypertensives.

DESIGN AND METHODS

Plasma tHcy levels were determined by an enzyme immunoassay method. Plasma lipid peroxidation levels were measured as thiobarbituric acid reactive substances (TBARS) by spectrophotometric methods. Plasma levels of copper and insulin were measured by atomic absorption spectrophotometer and electrochemiluminescence method, respectively.

RESULTS

Plasma tHcy, copper and insulin levels did not differ in nonobese hypertensives compared to nonobese normotensives. Plasma TBARS levels were significantly increased in nonobese hypertensives when compared to nonobese normotensives (p < 0.001). Plasma tHcy, TBARS, copper and fasting insulin levels were significantly higher in obese normotensives and hypertensives than in nonobese normotensives and hypertensives, respectively (for each comparison; p < 0.001). There was a significant difference in plasma tHcy, TBARS and copper levels between obese subjects with or without hypertension (for each comparison p < 0.01). The univariate analyses demonstrated a significant positive correlation between tHcy and TBARS (coefficient +/- SE, 0.411 +/- 0.115, p < 0.01) and copper (coefficient +/- SE, 0.425 +/- 0.135, p < 0.01) in obese subjects. In a multivariate regression analysis in obese subjects tHcy was positively correlated with TBARS (coefficient +/- SE, 0.480 +/- 0.155, p < 0.01) and copper (coefficient +/- SE, 0.486 +/- 0.140, p < 0.01).

CONCLUSIONS

We hypothesize that in the presence of other traditional risk factors, Hcy may have a permissive role in the endothelium damage even within the normal range and this role may be related to free radical generating systems. Therefore, modest elevation of plasma Hcy may causally be involved in the pathogenesis of atherosclerosis and/or cardiovascular disease.

Hyperhomocysteinaemia is not associated with increased levels of asymmetric dimethylarginine in patients with ischaemic heart disease

BACKGROUND

Elevated plasma total homocysteine appears to be related to endothelial dysfunction and impaired nitric oxide production. We aimed to investigate [1] whether elevated levels of plasma total homocysteine are associated with high plasma levels of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthase, and [2] whether reduction of plasma total homocysteine levels by folate and vitamin B supplementation lowers plasma concentration of asymmetric dimethylarginine.

MATERIALS AND METHODS

Sixty patients with ischaemic heart disease and with plasma total homocysteine levels of 15.0 micromol L-1 were randomized to open therapy with folic acid, pyridoxine and cyancobalamin for 3 months (n = 30) or to no treatment (n = 30). Samples were also obtained from 34 patients with plasma total homocysteine levels of 8.0 micromol L-1 on admission.

RESULTS

Plasma asymmetric dimethylarginine concentrations in patients with elevated total homocysteine levels were not significantly higher (0.68 +/- 0.19 micromol L-1) than in patients with low total homocysteine levels (0.61 +/- 0.10 micromol L-1; P = 0.08). Plasma asymmetric dimethylarginine level in the vitamin supplemented group was 0.65 +/- 0.12 micromol L-1 before, and 0.64 +/- 0.12 micromol L-1 after 3 months of vitamin supplementation (NS). Plasma asymmetric dimethylarginine levels were correlated with serum cystatin C levels (P < 0.001).

CONCLUSION

A nonsignificant trend to increased plasma levels of asymmetric dimethylarginine in patients with high plasma total homocysteine levels may be explained by concomitant subtle renal dysfunction. Substantial reduction of plasma total homocysteine did not affect the level of plasma asymmetric dimethylarginine.

The effect of methylenetetrahydrofolate reductase C677T common variant on hypertensive risk is not solely explained by increased plasma homocysteine values

The C677T transition of methylenetetrahydrofolate reductase (MTHFR) gene causes a moderate increase in total plasma homocysteine (tHcy). We studied the effect of MTHFR TT homozygosity and mild hyperhomocysteinemia on arterial hypertension. Normotensive controls (n = 223) and hypertensive subjects (n = 235) were matched for age, gender, and history of cardiovascular disease. Homocysteine levels were measured by a polarization immunoassay method. Methylenetetrahydrofolate reductase we determined by polymerase chain reaction and restriction fragment analysis. Hypertensives showed elevated tHcy compared to normotensive group in men (P = 0.039). Homocysteine values higher than 15 micromol/L were associated with increased hypertensive risk in the male population [odds ratios (OR) = 1.63; 95% confidence interval (CI) = 1.06-2.52; P = 0.027]. In multivariate analysis, TT genotype was associated with an increased risk of hypertension in males (OR = 2.27; 95% CI = 1.12-4.60; P = 0.022) An increased hypertensive risk was observed in those TT males with tHcy levels higher than 15 micromol/L (OR = 2.78; 95% CI = 1.05-7.3; P = 0.032) but not in those non-TT males with tHcy levels higher than 15 micromol/L (P = 0.33). Our findings do not support the possibility that mild hyperhomocysteinemia my solely account for the hypertensive risk associated to the TT genotype.

Nutrient involvement in preeclampsia

Preeclampsia is a pregnancy-specific condition that increases maternal and infant mortality and morbidity. It is diagnosed by new-onset increased blood pressure and proteinuria during gestation; for many years these markers were the sole targets for study. More recently, increased attention to the multisystemic nature of the syndrome with involvement of almost all organs, activation of coagulation and increased sensitivity to pressor agents has expanded understanding of the disorder. The epidemiology of preeclampsia, being more common in poor women, long ago suggested that nutrients might be involved in the disorder. Numerous conflicting hypotheses were advanced but the testing of these hypotheses has either been done poorly or not at all. Review of the available data indicates very few studies that provide useful insights. In many studies the syndrome is poorly defined and in most studies nutritional data (questionnaires or biomarkers) are obtained on women with the clinical syndrome. In overtly preeclamptic women it is impossible to decipher cause from effect. Nonetheless, current concepts of the genesis of preeclampsia that include endothelial dysfunction, inflammatory activation, oxidative stress and predisposing maternal factors provide targets for well-designed nutritional investigation. In this review the current concepts of the pathogenesis of preeclampsia are reviewed and available data are assessed in light of these concepts. Targets for nutritional investigation based on the current knowledge of pathophysiology are suggested.

Folate and cobalamin levels as determinants of plasma homocysteine in different age groups of healthy controls and psychogeriatric patients

Homocysteine (Hcy) is the demethylated derivate of methionine and can be metabolized by two pathways. It is either catabolized by the transulfuration pathway to cysteine or remethylated to methionine mainly by the folate- and cobalamin-dependent enzyme methionine synthase. Previous findings suggest that folate is the most important vitamin determinant of plasma total homocysteine (tHcy) concentration but also that the relation between plasma tHcy levels and levels of cobalamin and folate in the circulation might differ in different populations. In the present study, we have analyzed these parameters in different age groups of healthy subjects and psychogeriatric patients, who are known to have increased plasma tHcy. The present study shows that serum cobalamin concentration is a more important determinant of plasma tHcy concentration than blood folate concentration in the age groups <65 years in both psychogeriatric patients and control subjects, whereas with increasing age blood folate concentration becomes the most important vitamin determinant. The findings of increased plasma tHcy with folate being the main vitamin determinant in the oldest age groups of patients and controls, suggest that tissue levels of folate in elderly subjects are too low and that vitamin supplementation should be given.

News and views on folate and elderly persons

Elderly persons are especially exposed to folate deficiency, where normal/subnormal folate levels do not exclude tissue deficiency. Accompanying diseases, medication, and lifestyle factors may contribute to/cause deficiency. Symptoms of deficiency can be hematological, neurological, or neuropsychiatric, but it is likely that there are also cardiovascular manifestations as well as associations with malignancies. The physician should make an individualized investigation to establish the probable cause. Among the available determinants of the folate/cobalamin state, plasma homocysteine (Hcy) is a swift and sensitive marker and has the strongest connection to cognitive function. The association is generally stronger between Hcy levels and symptoms than between vitamin-related levels and symptoms. The duration as well as the severity of symptoms are of importance in terms of the improvement of neurological and neuropsychiatric symptoms when substitution is performed. The issue of general folate fortification of flour is complex, and there are as many pros and cons as there are countries in which it is considered to be launched. It is important to bear in mind that in our modern society, deficiency of folate/cobalamin--overt or latent--mainly is a problem of the elderly and a challenge to the doctor.

Modulation of extracellular homocysteine concentration in human cell lines

BACKGROUND

Despite the growing evidence that plasma homocysteine is a cardiovascular risk factor, the mechanism behind the vascular injuries is still unknown. Information about the metabolism of homocysteine is, therefore, essential for an understanding of its role in atherogenesis, thereby enabling a modulation of that risk.

METHODS

In the present study, we have examined the modulation of extracellular homocysteine in HeLa and hepatoma cell cultures in relation to a changed extracellular thiol redox status and in the presence of specific inhibitors of amino acid transporters.

RESULTS

The findings in the present study show that a changed thiol redox status by copper ions, copper chelator or the monothiol, N-acetylcysteine (NAC), affects extracellular homocysteine in the same way in hepatoma cell cultures, but not to the same extent as observed in HeLa cell cultures. However, the dithiols, dithiothreitol (DTT) and alpha-lipoic acid (LA), which lowered extracellular homocysteine concentration in HeLa cell cultures, increased the extracellular total homocysteine concentration in hepatoma cell cultures, probably mainly as a result of increased release of homocysteine extracellularly. Studies with specific inhibitors of amino acid transporters in HeLa cell cultures showed that homocysteine uptake occurred mainly by system A and glutamate transporters. Hepatoma cells seemed to have a much smaller uptake capacity of homocysteine compared to HeLa cells.

CONCLUSION

The lack of uptake capacity of homocysteine in hepatoma cells indicates that hepatocytes only play a small role in the elimination of homocysteine from circulation. Intracellular metabolism, cellular export and the complex pattern of homocysteine uptake in different cells are important to examine further in order to possibly be able to lower plasma homocysteine levels.

Plasma homocysteine concentration is decreased by dietary intervention

High plasma total homocysteine (tHcy) concentration is reported to be a risk factor for vascular diseases. We investigated the extent to which serum folate and plasma tHcy respond to a high intake of natural folate from food. Thirty-seven healthy females volunteered t o participate in a crossover dietary intervention. The study included a baseline period and two 5-week diet periods (low- and high-folate diets) with a 3-week washout in between. The low-folate diet contained one serving of both vegetables and fruit/d, while during the high-folate diet the subjects ate at least seven servings of vegetables, berries, and citrus fruit/d. Serum and erythrocyte (RBC) folate, serum vitamin B (12), and plasma tHcy concentrations were measured at the base-line and at the end of each diet period. The mean concentrations of serum and RBC folate were 11.0 (SD 3.0) nmol/l and 412 (SD 120) nmol/l at the end of the low-folate diet and 78 (95 % CI 62, 94) % and 14 (95 % CI 8, 20) % higher in response to the high-folate diet (P< 0.001). The serum concentration of vitamin B12 remained unchanged during the intervention. The mean plasma tHcy concentration was 8.0 pmol/ at the end of the low-folate diet and decreased by 13 (95% CI 9, 18) % in response to the high-folate diet (P<0.001). In conclusion, a diet high in fresh berries, citrus fruit, and vegetables effectively increases serum and RBC folate and decreases plasma homocysteine.

Homocysteine during the menstrual cycle in depressive women

BACKGROUND

Two possible factors that may have a causal relation with both depressive disorder and cardiovascular disease are elevated homocysteine and steroid hormones. Our previous study found significant changes in the plasma homocysteine concentration during the menstrual cycle in healthy women. The purpose of this study therefore was to test homocysteine in depressive women treated with fluoxetine during the menstrual cycle.

MATERIALS AND METHODS

Thirteen premenopausal women suffering from mixed anxiety-depressive disorder and a control group of 15 healthy women were enrolled in this study. The homocysteine concentration was determined by high-performance liquid chromatography with fluorescence detection, and estradiol, progesterone and cortisol by RIA methods.

RESULTS

We found significantly higher plasma homocysteine concentrations in the follicular phase than in the luteal phase of the menstrual cycle in both the depressive group (P < 0.003) and the controls (P < 0.0009). Moreover, the patient values of total homocysteine were significantly higher in the follicular phase (P < 0.03) and also in the luteal phase (P < 0.007) than the values of the controls. Estradiol and cortisol were significantly higher in the follicular phase of the patients compared with the control group.

CONCLUSION

According to our results, women suffering from mixed anxiety-depressive disorder have not only significantly different concentrations of homocysteine in the follicular and luteal phase of the menstrual cycle but also higher plasma homocysteine compared with healthy women. More elevated homocysteine in the depressive than in the healthy premenopausal women points to the notion that psychological factors might be important when considering the homocysteine concentration.

Inhibitory effects of melatonin on neural lipid peroxidation induced by intracerebroventricularly administered homocysteine

Melatonin, the main secretory product of the pineal gland, has been shown to be potentially effective in prevention of numerous types of neurodegenerative disorders in which free radical processes are involved. Homocysteine (Hcy), an independent risk factor for atherosclerosis, undergoes auto-oxidation and generates reactive oxygen species. The purpose of this study was to test whether intracerebroventricular (ICV) injection of Hcy leads to neural lipid peroxidation and also to investigate the protective effects of melatonin on the brain tissue from oxidative stress of Hcy. Adult male Wistar rats under anaesthesia were injected ICV with Hcy at a dose of 143 microg/kg. Melatonin was administered intraperitoneally to a group of rats for three consecutive days before Hcy injection. The rats were decapitated and brain tissues were removed and hippocampus, cortex and cerebellum were dissected. There was a significant development of oxidative stress as indicated by an increase in malondialdehyde in hippocampus, cortex and cerebellum of rats injected with Hcy, whereas melatonin prevented the elevation of lipid peroxidation. Furthermore, melatonin significantly increased glutathione levels and glutathione peroxidase activity in all brain regions. The present study demonstrates that Hcy, in high levels, may be a causal factor in generation of free radicals in the brain and it may be one of the mechanisms which cause neurodegeneration in elderly people. It also shows that melatonin could potentially be beneficial in prevention of neurodegeneration caused by hyperhomocysteinemia.

Predictors of change in plasma total cysteine: longitudinal findings from the Hordaland homocysteine study

BACKGROUND

Total cysteine (tCys) in plasma has recently been linked to cardiovascular risk and is also associated with cardiovascular risk factors, including body mass index (BMI) and cholesterol. Changes and predictors of change in tCys concentrations over a mean follow-up time of 6.0 (5.2-7.2) years were assessed in this study.

METHODS

Baseline data from the Hordaland Homocysteine Study recorded in 1992-1993 included tCys, total homocysteine (tHcy), and various lifestyle and cardiovascular risk factors. In 1998-1999, the same measurements were repeated in 3,732 individuals born in 1950-1951 and 3,339 individuals born in 1925-1927. Most of the statistical analyses were done separately in the four age and sex groups.

RESULTS

The overall mean values of tCys were higher at follow-up [mean (SD), 296 (41) micro mol/L] than at baseline [278 (36.5) micro mol/L]; P <0.0001. The mean percentage of increase in tCys in the different age and sex groups ranged from 4.9% to 8.5%. There was a significant correlation between the tCys values measured on the two occasions (Spearman correlation coefficient, 0.55-0.59 in the different age and sex groups; P <0.0001). The change in tCys correlated with changes in BMI, cholesterol, and diastolic blood pressure in the younger age group, whereas only changes in BMI predicted changes in tCys in the older age group.

CONCLUSIONS

tCys increased in the 6 years between the two measurements. Factors related to the baseline tCys values, including BMI and the change in BMI, predicted the tCys changes over time.

Hyperhomocysteinemia leads to adverse cardiac remodeling in hypertensive rats

Hyperhomocysteinemia (Hhe), linked to cardiovascular disease by epidemiological studies, may be an important factor in adverse cardiac remodeling in hypertension. Specifically, convergence of myocardial and vascular alterations promoted by Hhe and hypertension may exacerbate cardiac remodeling and myocardial dysfunction. We studied male spontaneously hypertensive rats fed one of three diets: control, intermediate Hhe inducing, or severe Hhe inducing. After 10 wk of dietary intervention, cardiac function was assessed in vitro, and cardiac and coronary arteriolar remodeling were monitored by histomorphometric, immunohistochemical, and biochemical techniques. Results showed that Hhe induced diastolic dysfunction, as characterized by the diastolic pressure-volume curve, without significant changes in baseline systolic function. Perivascular collagen levels were increased by Hhe, and there was an increase in left ventricular hydroxyproline levels. Myocyte size was not affected. Coronary arteriolar wall thickness increased with Hhe due to smooth muscle hyperplasia. Mast cells increased in parallel with Hhe and collagen accumulation. In summary, 10 wk of Hhe caused coronary arteriolar remodeling, myocardial collagen deposition, and diastolic dysfunction in hypertensive rats.

Comparing different methods for homocysteine determination

Slightly elevated values of homocysteine are commonly associated with thromboembolic diseases, while high values can be found in patients with congenital metabolic defects or nutritional problems. The clinical use of homocysteine as an independent marker of cardiovascular disease was limited in the past by technical problems with its measurement, the instrumentation (HPLC, radioenzymatic assays, gas chromatography-mass spectrometry, etc.) and the necessary skills required. Commercially available immunoassays now permit a simpler and more rapid measurement of homocysteine, that is more suitable for routine clinical laboratories; in this paper we analyze the results obtained by using three fully automated methods for homocysteine determination (Abbott IMx immunoassay, Abbott AxSYM immunoassay and Immulite 2000 homocysteine immunoassay) and their correlation with the widely used HPLC method. The results clearly indicate that all three automated immunochemical methods correlate well with the HPLC method (slope 0.97-1.03; intercept 0.95-1.91 with a recovery above 95% for all three methods).

Optimal use of markers for cobalamin and folate status in a psychogeriatric population

BACKGROUND

Cobalamin/folate deficiency is common in elderly subjects and may lead to psychiatric symptoms, but even more often it increases the severity of other organic and non-organic mental diseases. It is therefore of importance to evaluate the optimal use of different markers of cobalamin/folate status in a psychogeriatric population.

METHODS

We measured serum cobalamin, blood folate, plasma homocysteine (tHcy) and serum methylmalonic acid (MMA) in 475 well-defined psychogeriatric patients.

RESULTS

The findings in the present study showed that many (41%) of the patients with normal levels of serum MMA (< 0.41 micromol/l) had pathological values of at least one of the other markers for cobalamin/folate status, whereas only 17% of patients with normal plasma tHcy (< 19.9 micromol/l) had pathological levels of other markers. If patients with decreased levels of serum cobalamin and/or blood folate were also excluded from these patients, only nine patients with slightly elevated levels of serum MMA remained. In the present study different upper reference limits were also tested for both serum MMA and plasma tHcy. However, the use of these limits did not cause any diagnostic improvement in the evaluation of cobalamin-folate status. Plasma tHcy was increased in almost all diagnosis groups of the psychogeriatric patients, whereas serum MMA was increased in only some groups. The distribution of the two common polymorphisms of the methylenetetrahydrofolate reductase gene (C677T and A1298C) was similar in patients with elevated and normal plasma tHcy.

CONCLUSIONS

The findings in the present study suggest the use of plasma tHcy, serum cobalamin and blood folate to evaluate cobalamin-folate status in psychogeriatric patients and to omit the use of serum MMA.

Methods for measuring sulfur amino acid metabolism

PURPOSE OF REVIEW

The importance of sulfur amino acid metabolism has become increasingly apparent in recent years. Methionine and cysteine are precursors of glutathione, which plays an important role in intracellular antioxidant/free radical defenses. Homocysteine is a non-protein-bound sulfur amino acid strongly implicated in the pathogenesis of several diseases. Both glutathione and homocysteine are affected by abnormalities in sulfur amino acid metabolism that occur in the clinical setting.

RECENT FINDINGS

The Storch-Young model, which determines methionine turnover and homocysteine remethylation by means of a tracer methionine infusion, has been improved by using plasma homocysteine (rather than methionine) enrichment in the model. A complex new tracer method involving the use of tracer serine, methionine, and leucine has been described to determine the effects of folate or pyridoxine deficiency on sulfur amino acid-methyl transfer reactions in humans. The etiology of hyperhomocysteinemia in chronic renal failure is controversial; new concepts in this area are described. There is new interest in the subspecies of homocysteine in the circulation. A new method is described for measuring the extremely low plasma concentrations of reduced homocysteine, using gas chromatography-mass spectrometry. Plasma S-adenosylhomocysteine, measured by fluorescence high-performance liquid chromatography, has been suggested as being superior to homocysteine as a predictor of the risk of vascular disease.

SUMMARY

This review highlights and critiques the above recent developments, and points out some of the complexities and pitfalls in designing and interpreting human metabolic studies involving the sulfur amino acids.

Transcobalamin II 775G>C polymorphism and indices of vitamin B12 status in healthy older adults

A common polymorphism (775G>C) in the vitamin B12 transport protein, transcobalamin II (TCII), has been identified in which proline replaces arginine at codon 259. We determined the influence of TCII genotype on indices of B12 status, including total serum B12, the amount of B12 bound to TCII (holoTCII), methylmalonic acid, and homocysteine, in 128 healthy older adults (ages 40-88 years). Mean total B12 and homocysteine concentrations were not significantly different among the 3 genotypes. Mean holoTCII concentration was significantly higher in those subjects homozygous for the proline form of TCII (PP) compared with those homozygous for the arginine form (RR) and heterozygotes (PR) (P <or=.006). In addition, mean methylmalonic acid concentrations were significantly lower in the PP and PR groups compared with the RR group (P <or=.02). The PP genotype may be more efficient in delivering B12 to tissues, resulting in enhanced B12 functional status. TCII genotype may thus influence susceptibility to B12 deficiency.

Evidence of poor vitamin status in coeliac patients on a gluten-free diet for 10 years

BACKGROUND

Patients with coeliac disease are advised to keep to a lifelong gluten-free diet to remain well. Uncertainty still exists as to whether this gives a nutritionally balanced diet.

AIM

To assess the vitamin nutrition status of a series of coeliac patients living on a gluten-free diet for 10 years.

METHODS

Thirty adults with coeliac disease (mean age, 55 years; range, 45-64 years; 60% women), in biopsy-proven remission following 8-12 years of dietary treatment, were studied. We measured the total plasma homocysteine level, a metabolic marker of folate, vitamin B-6 and vitamin B-12 deficiency, and related plasma vitamin levels. The daily vitamin intake level was assessed using a 4-day food record. Normative data were obtained from the general population of the same age.

RESULTS

Coeliac patients showed a higher total plasma homocysteine level than the general population, indicative of a poor vitamin status. In accordance, the plasma levels of folate and pyridoxal 5'-phosphate (active form of vitamin B-6) were low in 37% and 20%, respectively, and accounted for 33% of the variation of the total plasma homocysteine level (P < 0.008). The mean daily intakes of folate and vitamin B-12, but not of vitamin B-6, were significantly lower in coeliac patients than in controls.

CONCLUSIONS

Half of the adult coeliac patients carefully treated with a gluten-free diet for several years showed signs of a poor vitamin status. This may have clinical implications considering the linkage between vitamin deficiency, elevated total plasma homocysteine levels and cardiovascular disease. The results may suggest that, when following up adults with coeliac disease, the vitamin status should be reviewed.

Contributions of active site residues to the partial and overall catalytic activities of human S-adenosylhomocysteine hydrolase

Residues glutamate 156 (E156), aspartate 190 (D190), asparagine 181 (N181), lysine 186 (K186), and asparagine 191 (N191) in the active site of S-adenosylhomocysteine (AdoHcy) hydrolase have been mutated to alanine (A). AdoHcy hydrolase achieves catalysis of AdoHcy hydrolysis to adenosine (Ado) and homocysteine (Hcy) by means of a redox partial reaction (3'-oxidation of AdoHcy at the beginning and 3'-reduction of Ado at the end of the catalytic cycle) spanning an elimination/addition partial reaction (elimination of Hcy from the oxidized substrate and addition of water to generate the oxidized product), with the enzyme in an open NAD(+) form in the ligand-free state and in a closed NADH form during the elimination/addition partial reaction. Mutation K186A reduces the rate of a model enzymatic reaction for the redox partial reaction by a factor of 280000 and the rate of a model reaction for the elimination/addition partial reaction by a factor of 24000, consistent with a primary catalytic role in both partial reactions as a proton donor/acceptor at the 3'-OH/3'-keto center. Secondary roles for N181 and N191 in localizing the flexible side chain of K186 in a catalytically effective position are supported by rate reduction factors for N181A of 2500 (redox) and 240 (elimination/addition) and for N191A of 730 (redox) and 340 (elimination/addition). A role of D190 in orienting the substrate for effective transition-state stabilization is consistent with rate reduction factors of 1300 (redox) and 30 (elimination/addition) for D190A. Residue E156 may act to maintain K186 in the desired protonation state: rate deduction factors are 1100 (redox) and 70 (elimination/addition). The mutational increases in free energy barriers for k(cat)/K(M) are described by a linear combination of the effects for the partial reactions with the coefficients equal to the fractional degree that each partial reaction determines the rate for k(cat)/K(M). A similar linear equation for k(cat) overestimates the barrier increase by a uniform 5 kJ/mol, probably reflecting reactant-state stabilization by the wild-type enzyme that is abolished by the mutations.

Upregulation of smooth muscle cell collagen production by homocysteine-insight into the pathogenesis of homocystinuria

Patients with untreated homocystinuria have widespread premature atherosclerosis with intimal thickening and collagen-rich, fibrous plaques. We previously demonstrated that homocysteine (Hcy) upregulates collagen synthesis and accumulation by arterial smooth muscle cells (SMCs) [A. Majors, L.A. Ehrhart, E.H. Pezacka, Arterioscler. Thromb. Vasc. Biol. 17 (1997) 2074-2081] but the underlying mechanisms are not known. Since many of the effects of Hcy on intact vessels and vascular cells are thought to involve reactive oxygen species generated from Hcy oxidation, we investigated the role of reactive oxygen species in the upregulation of collagen production by Hcy. Treatment of SMCs with 300 microM l-Hcy increased collagen accumulation 2-3-fold. When added to culture medium containing serum, the exogenous Hcy was rapidly oxidized with a half-life of approximately 1 h but only very low amounts of H(2)O(2) (up to 2 microM) were detected. Three lines of evidence demonstrate that the increased accumulation of collagen was not mediated by reactive oxygen species generated from Hcy oxidation: (1) catalase in the medium did not block the accumulation of collagen in Hcy-treated cultures; (2) the addition of xanthine/xanthine oxidase, a system that generates superoxide and H(2)O(2), did not increase collagen accumulation; and (3) the direct addition of H(2)O(2) did not substantially enhance collagen accumulation. In contrast, heparin, a potent modulator of SMC function, significantly blocked the accumulation of collagen in Hcy-treated cultures. Together, these results demonstrate that the increase in collagen accumulation in Hcy-treated cultures involves alternate mechanisms not involving H(2)O(2).

Vitamin supplementation normalizes total plasma homocysteine concentration but not plasma homocysteine redox status in patients with acute coronary syndromes and hyperhomocysteinemia

Despite the growing evidence that elevated total homocysteine (tHcy) in plasma is a cardiovascular risk factor, the mechanism underlying the vascular injury is still unknown. Studies are difficult due to the fact that little is known about the formation of different homocysteine species in vivo. In the present study we have investigated the different fractions of tHcy in 21 patients with acute coronary syndromes and elevated concentration of plasma tHcy. A subgroup of the patients (n=16) was investigated before and after a 3 months study period with or without vitamin supplementation (folic acid 5 mg, pyridoxine 40 mg and cyanocobalamin 1 mg once daily). A major finding is that these patients had a lowered ratio (0.95%) between the concentration of reduced homocysteine (HcyH) and tHcy compared to controls (1.38%). A low ratio HcyH/tHcy in plasma in combination with elevated plasma tHcy concentrations might reflect increased oxidative activity or decreased reducing capacity in plasma from the patients. Another main finding in the present study is that, although vitamin supplementation of these patients normalized plasma tHcy, the ratio between HcyH and tHcy did not normalize. Since substantial evidence indicates that progression of arteriosclerosis is related to enhanced oxidant activity, the premature vascular disease associated with increased plasma tHcy concentration might be due to increased oxidative activity and the elevated plasma tHcy concentration may only reflect the increased oxidative stress.

Sleep deprivation reduces total plasma homocysteine levels in rats

Hyperhomocysteinemia has been associated with pathological and stressful conditions and is a risk factor for cardiovascular disease. Since sleep deprivation is a stressful condition that is associated with disruption of various physiological processes, we investigated whether it would also be associated with increases in plasma homocysteine levels. Further, since hyperhomocysteinemia may promote oxidative stress, and we had previously found evidence of oxidative stress in brain following sleep deprivation, we also searched for evidence of systemic oxidative stress by measuring glutathione and thiobarbituric acid reactive substance levels. Rats were sleep deprived for 96 h using the platform technique. A group was killed after sleep deprivation and another two groups were allowed to undergo sleep recovery for 24 or 48 h. Contrary to expectation, plasma homocysteine was reduced in sleep-deprived rats as compared with the control group and did not revert to normal levels after 24 or 48 h of sleep recovery. A trend was observed towards decreased glutathione and increased thiobarbituric acid reactive substance levels in sleep-deprived rats. It is possible that the observed decreases in homocysteine levels may represent a self-correcting response to depleted glutathione in sleep-deprived animals, which would contribute to the attenuation of the deleterious effects of sleep deprivation.

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.

Renal function exerts only a minor influence on high plasma homocysteine concentrations in patients with acute coronary syndromes

It has been suggested that hyperhomocysteinemia observed in patients with occlusive vascular disease is caused by reduced renal function secondary to renovascular disease. We have therefore used serum cystatin C, a new sensitive marker for glomerular filtration, in 59 patients with acute coronary syndromes and high plasma homocysteine (tHcy) concentration to measure renal function. Samples were also obtained from 34 patients with low-normal plasma tHcy and 50 control subjects. The patients with low-normal plasma tHcy concentration showed decreased concentrations of serum cystatin C and serum creatinine and increased concentrations of blood folate and serum cobalamin compared to the controls and to the patients with high plasma tHcy. There was a large overlap in cystatin C concentrations between patients with high and low-normal plasma tHcy. None of the parameters investigated except plasma tHcy were significantly different in the group of patients with high plasma tHcy concentration compared to the control group. In order to further demonstrate the importance of renal impairment, a subgroup of the patients with high plasma tHcy was supplemented daily with folic acid 5 mg, pyridoxine 40 mg and cyancobalamin 1 mg for 3 months. Vitamin therapy reduced plasma tHcy from 18.3+/-4.6 pmol/l to 9.6+/-2.2 pmol/l (p<0.0001). However, vitamin treatment did not strengthen the correlation between cystatin C and plasma tHcy concentrations. These findings do not support the hypothesis that subtle renal dysfunction is an important cause of high plasma tHcy concentration in patients with acute coronary syndromes.

Correlates of plasma homocysteine, cysteine and cysteinyl-glycine in respondents in the British National Diet and Nutrition Survey of young people aged 4-18 years, and a comparison with the survey of people aged 65 years and over

Plasma total homocysteine (tHcy), cysteine and cysteinyl-glycine were measured in a representative sample of 922 young people aged 4-18 years, participating in the National Diet and Nutrition Survey in mainland Britain in 1997. Both tHcy and cysteine increased markedly with age; cysteinyl-glycine less so. Neither tHcy nor cysteine differed between genders; cysteinyl-glycine was higher in males. tHcy concentrations were lowest in the winter; cysteine and cysteinyl-glycine varied only slightly with season. In respondents aged >15 years, tHcy was higher in smokers, but in respondents aged 7-11 years, tHcy was higher in those whose mothers smoked. tHcy was inversely correlated with serum folate, serum vitamin B12 and vitamin B6 status, but neither cysteine nor cysteinyl-glycine shared these relationships. The relationships between tHcy and B-vitamin status indices ran parallel with those of the 65 years and over survey, but at much lower tHcy concentrations for any given B-vitamin concentration. Age-adjusted tHcy was not correlated with anthropometric indices, blood pressure, haematology, plasma creatinine, urea or cholesterol, but was directly correlated with fasting triacylglycerol. We conclude that disease-risk indices, like tHcy and perhaps cysteine, if established during early life, may be modulated by diet and lifestyle, thereby providing an opportunity for public health intervention.

Relative roles of albumin and ceruloplasmin in the formation of homocystine, homocysteine-cysteine-mixed disulfide, and cystine in circulation

Disulfide forms of homocysteine account for >98% of total homocysteine in plasma from healthy individuals. We recently reported that homocysteine reacts with albumin-Cys(34)-S-S-cysteine to form homocysteine-cysteine mixed disulfide and albumin-Cys(34) thiolate anion. The latter then reacts with homocystine or homocysteine-cysteine mixed disulfide to form albumin-bound homocysteine (Sengupta, S., Chen, H., Togawa, T., DiBello, P. M., Majors, A. K., Büdy, B., Ketterer, M. E., and Jacobsen, D. W. (2001) J. Biol. Chem. 276, 30111-30117). We now extend these studies to show that human albumin, but not ceruloplasmin, mediates the conversion of homocysteine to its low molecular weight disulfide forms (homocystine and homocysteine-cysteine mixed disulfide) by thiol/disulfide exchange reactions. Only a small fraction of homocystine is formed by an oxidative process in which copper bound to albumin, but not ceruloplasmin, mediates the reaction. When copper is removed from albumin by chelation, the overall conversion of homocysteine to its disulfide forms is reduced by only 20%. Ceruloplasmin was an ineffective catalyst of homocysteine oxidation, and immunoprecipitation of ceruloplasmin from human plasma did not inhibit the capacity of plasma to mediate the conversion of homocysteine to its disulfide forms. In contrast, ceruloplasmin was a highly efficient catalyst for the oxidation of cysteine and cysteinylglycine to cystine and bis(-S-cysteinylglycine), respectively. However, when thiols (cysteine and homocysteine) that are disulfide-bonded to albumin-Cys(34) are removed by treatment with dithiothreitol to form albumin-Cys(34)-SH (mercaptalbumin), the conversion of homocysteine to its disulfide forms is completely blocked. In conclusion, albumin mediates the formation of disulfide forms of homocysteine by thiol/disulfide exchange, whereas ceruloplasmin converts cysteine to cystine by copper-dependent autooxidation.

Plasma S-adenosylhomocysteine is a more sensitive indicator of cardiovascular disease than plasma homocysteine

BACKGROUND

Although plasma total homocysteine has been identified as an independent risk factor for vascular disease in a multitude of studies, there is a considerable overlap in values between patients at risk and control subjects. The difference in values can be used to distinguish statistically between the 2 groups, provided each group is large enough; however, discriminating between individual patients at risk and control subjects is difficult.

OBJECTIVE

We investigated whether the precursor of homocysteine, S-adenosylhomocysteine, is a more sensitive indicator of risk.

DESIGN

We measured plasma total homocysteine, S-adenosylhomocysteine, S-adenosylmethionine, creatinine, folate, and vitamin B-12 in 30 patients with proven cardiovascular disease and 29 age- and sex-matched control subjects.

RESULTS

The homocysteine values (+/-SD) were 12.8 +/- 4.9 (95% CI: 11.0, 14.7) micromol/L for patients and 11.0 +/- 3.2 (9.8, 12.2) micromol/L for control subjects. The S-adenosylhomocysteine values were 40.0 +/- 20.6 (32.3, 47.7) nmol/L for patients and 27.0 +/- 6.7 (24.5, 30.0) nmol/L for control subjects (P = 0.0021). The S-adenosylmethionine values were 121.8 +/- 42.9 (105.8, 137.8) nmol/L for patients and 103.9 +/- 21.8 (95.6, 112.2) nmol/L for control subjects (P = 0.0493). The creatinine values were 110 +/- 27 (97, 120) micromol/L for patients and 97 +/- 9 (80, 100) micromol/L for control subjects (P = 0.0025). Values for folate and vitamin B-12 did not differ significantly between groups.

CONCLUSIONS

Plasma S-adenosylhomocysteine appears to be a much more sensitive indicator of the difference between patients with cardiovascular disease and control subjects than is homocysteine. Both plasma total homocysteine and S-adenosylhomocysteine are significantly correlated with plasma creatinine in patients.

Stabilization of blood homocysteine in an epidemiological setting

The major problem in the determination of homocysteine (Hcy), which is thought to be a risk factor in colorectal cancer, is the rise in its concentration if blood is not centrifuged immediately after collection. We assess the interference of 3-deazaadenosine (which inhibits conversion of S-adenosylhomocysteine into Hcy within the erythrocyte), using the fluorescence polarization immunoassay (FPIA) assay, the stabilizing effect of 3-deazaadenosine and the impact of temperature on Hcy stabilization. To assess interference of 3-deazaadenosine, 12 blood samples were extracted; two aliquots were obtained from each and one of them was added 3-deazaadenosine (50 micromol/l). To assess the stabilizing value of 3-deazaadenosine, as well as the effect of temperature, two blood samples were extracted from 24 volunteers. One of the tubes was immediately placed on ice and centrifuged (reference concentration). To the second tube was immediately added 3-deazaadenosine (50 micromol/l), producing six aliquots, three of which were kept at room temperature (25 degrees C) for 1, 4 and 6 hours, the other three kept at 37 degrees C. The mean values (standard deviation) obtained for methodological interference were: 7.32 (3.58) micromol/l without stabilizer, and 7.11 (3.61) micromol/l with stabilizer. There were no statistically significant differences (P = 0.104) and intraclass correlation coefficient was 0.989, suggesting no methodological interference. We did not find any significant differences regarding our reference value in the samples kept at room temperature during the interval studied. A high Pearson correlation coefficient was obtained. Nevertheless, in those samples kept at 37 degrees C, a slight increase was observed in the 4-hour period (P = 0.009). The addition of 3-deazaadenosine may avoid problems in the critical pre-analytical phase in the Hcy measurement. There is no interference with the FPIA assay, nor any dilution effect, and new reference values are not necessary.

Simultaneous determination of several amino acids, including homocysteine, cysteine and glutamic acid, in human plasma by isocratic reversed-phase high-performance liquid chromatography with fluorimetric detection

A method for the simultaneous measurement of two biologically important thiol compounds cysteine and homocysteine and five amino acids including neurotransmitters aspartate and glutamate is reported. This method utilized derivatization of compounds with o-phthalaldehyde in the presence of 2-mercaptoethanol following alkylation of the free sulfydryl group with iodoacetic acid followed by separation using reversed-phase high-performance liquid chromatography. These o-phthalaldehyde-2-mercaptoethanol-labeled compounds were separated within 30 min on a Spherisorb ODS-2 column with isocratic elution using 17% methanol, 0.04 M sodium phosphate buffer (pH 7.0), 0.002 M Na2EDTA and detected fluorimetrically (excitation 340 nm, emission 450 nm). Using this method, the concentrations of homocysteine, cysteine, glutamic acid. aspartic acid, asparagine, serine and glutamine in human plasma were determined.

Plasma total cysteine as a risk factor for vascular disease: The European Concerted Action Project

BACKGROUND

Elevated plasma total homocysteine (tHcy) is a risk factor for cardiovascular disease. Although cysteine is structurally similar and metabolically linked to tHcy, its relation to the risk of cardiovascular disease has received little attention. We studied the relation between plasma total cysteine (tCys) levels and the risk of vascular disease in the coronary, cerebral, and peripheral vessels.

METHODS AND RESULTS

This case-control study included 750 patients with vascular disease and 800 age- and sex-matched control subjects recruited from 19 centers in 9 European countries. Conventional risk factors for cardiovascular disease were recorded. In addition, plasma levels of tCys, tHcy, folate, B(6), B(12), and creatinine were measured. Overall, a U-shaped relationship was observed between tCys and risk of vascular disease. With the middle range of 250 to 275 micromol/L tCys used as the reference category, the adjusted risk of vascular disease at low (</=225 micromol/L) tCys levels was 2.1 (95% CI 1.2 to 3.6), and the risk at high (>300 micromol/L) tCys levels was 1.6 (95% CI 1.1 to 2.3). Different shapes of the dose-response relationship were seen for the 3 vascular disease categories. The relation with peripheral vascular and cerebrovascular disease was U-shaped, whereas a weak positive relation was observed with coronary heart disease.

CONCLUSIONS

Our data show a significant U-shaped relationship between tCys and cardiovascular disease after adjustment for tHcy, creatinine, and other cardiovascular disease risk factors.

Albumin thiolate anion is an intermediate in the formation of albumin-S-S-homocysteine

An elevated concentration of plasma total homocysteine is an independent risk factor for cardiovascular disease. Greater than 80% of circulating homocysteine is covalently bound to plasma protein by disulfide bonds. It is known that albumin combines with cysteine in circulation to form albumin-Cys(34)-S-S-Cys. Studies are now presented to show that the formation of albumin-bound homocysteine proceeds through the generation of an albumin thiolate anion. Incubation of human plasma with l-(35)S-homocysteine results in the association of >90% of the protein-bound (35)S-homocysteine with albumin as shown by nonreduced SDS-polyacrylamide gel electrophoresis. Treatment of the complex with beta-mercaptoethanol results in near quantitative release of the bound l-(35)S-homocysteine, demonstrating that the binding of homocysteine to albumin is through a disulfide bond. Furthermore, using an in vitro model system to study the mechanisms of this disulfide bond formation, we show that homocysteine binds to albumin in two steps. In the first step homocysteine rapidly displaces cysteine from albumin-Cys(34)-S-S-Cys, forming albumin-Cys(34) thiolate anion and homocysteine-cysteine mixed disulfide. In the second step, albumin thiolate anion attacks homocysteine-cysteine mixed disulfide to yield primarily albumin-Cys(34)-S-S-Hcy and to a much lesser extent albumin-Cys(34)-S-S-Cys. The results clearly suggest that when reduced homocysteine enters circulation, it attacks albumin-Cys(34)-S-S-Cys to form albumin-Cys(34) thiolate anion, which in turn, reacts with homocysteine-cysteine mixed disulfide or homocystine to form albumin-bound homocysteine.

Supplementation of atherogenic diet with B vitamins does not prevent atherosclerosis or vascular dysfunction in monkeys

BACKGROUND

Hyperhomocysteinemia is associated with increased risk of atherosclerotic and thrombotic vascular disease. In many patients, hyperhomocysteinemia can be treated or prevented by dietary supplementation with B vitamins, but the clinical benefit of B vitamins for the prevention of vascular disease has not been proven.

METHODS AND RESULTS

Using an atherogenic diet that produces both hyperhomocysteinemia and hypercholesterolemia, we tested the hypothesis that dietary supplementation with B vitamins (folic acid, vitamin B(12), and vitamin B(6)) would prevent hyperhomocysteinemia, vascular dysfunction, and atherosclerotic lesions in monkeys. After 17 months, plasma total homocysteine increased from 3.6+/-0.3 to 11.8+/-1.7 micromol/L in monkeys fed an unsupplemented atherogenic diet (P<0.01) but did not increase in monkeys fed an atherogenic diet supplemented with B vitamins (3.8+/-0.3 micromol/L). Serum cholesterol increased from 122+/-7 to 550+/-59 mg/dL in the unsupplemented group (P<0.001) and from 118+/-5 to 492+/-55 mg/dL in the supplemented group (P<0.001). Responses to endothelium-dependent vasodilators, both in resistance vessels in vivo and in the carotid artery ex vivo, were impaired to a similar extent in groups that did and did not receive vitamin supplements. Anticoagulant responses to the infusion of thrombin were also impaired to a similar extent in both groups. Vitamin supplementation failed to prevent intimal thickening in the carotid or iliac arteries.

CONCLUSIONS

These findings demonstrate that supplementation with B vitamins prevents hyperhomocysteinemia but is not sufficient to prevent the development of vascular dysfunction or atherosclerotic lesions in monkeys with marked hypercholesterolemia, even in the absence of preexisting atherosclerosis.

Plasma reduced homocysteine concentrations are increased in end-stage renal disease

BACKGROUND

Plasma total homocysteine (tHcy) concentrations> 15 micromol/L are associated with an increased risk of cardiovascular disease. This is especially the case in end-stage renal disease (ESRD), in which tHcy concentrations commonly range between 20 and 30 micromol/L. Adverse vascular or prothrombotic effects associated with hyperhomocysteinemia are assumed to be mediated by the free sulfhydryl (reduced) form of the molecule (rHcy), but data based on fluorescence high-pressure liquid chromatography (HPLC) indicate that rHcy concentrations are not increased in ESRD despite two- to threefold elevations in tHcy.

METHODS

We developed a sensitive method for measuring plasma rHcy concentrations in which freshly drawn blood is incubated with sodium iodoacetate, and the resulting S-carboxymethylhomocysteine is analyzed by gas chromatography mass spectrometry.

RESULTS

Unlike with the earlier methodology, we found plasma rHcy concentrations two to four times higher than normal in ESRD. These concentrations were lowered by hemodialysis and were proportional to plasma tHcy over the range of tHcy concentrations that has been associated with increased cardiovascular risk (r2 = 0.39, P < 0.0001).

CONCLUSIONS

These results support the hypothesis that homocysteine could directly mediate vascular disease through mechanisms related to the reactivity of its free sulfhydryl group. It remains to be determined how much of the variability between plasma tHcy and rHcy is due to analytical variation and how much is due to biologic factors that separately influence concentrations of the disease marker, tHcy, and its presumed mediator, rHcy.