Plasma total homocysteine and risk of angina pectoris with subsequent coronary artery bypass surgery

Design and statistical issues in the homocysteinemia in kidney and end stage renal disease (HOST) study

The Homocysteine Study (HOST) Veterans Affairs Cooperative Studies Program No. 453, is a prospective, randomized, two arm, double blind study of patients with end stage renal disease (ESRD) or advanced chronic kidney disease (ACKD, defined as an estimated creatinine clearance of 30 ml/min or less). Its primary objective is to determine whether administration of high doses of three vitamins, folic acid, vitamin B6 and vitamin B12, to lower the high plasma homocysteine levels, will reduce all cause mortality. The secondary objectives are to examine whether the treatment lowers the incidence of myocardial infarction, stroke, amputation of a lower extremity, a composite of death and the foregoing three events, the plasma homocysteine level, and, in ESRD patients undergoing hemodialysis, thrombosis of the vascular access. A unique feature of this trial is that after initial evaluation at enrollment and one return visit the follow up is exclusively by phone (or, if necessary, by mail). The subject is contacted every three months throughout the duration of the study from a central location. The study drug is shipped to the patient from a central location rather supplied locally. In a two year enrollment period, 2006 patients are to be enrolled. The duration of the observation period is four to six years. Data will be stored and analyzed at a coordinating center. The study design has the power to detect a reduction in all cause mortality rate of 17%. Issues related to the unique features of the design of this study are discussed.

Management of hyperhomocysteinemia

Hyperhomocysteinemia is an established risk factor for cardiovascular disease. The modification of traditional cardiovascular risk factors has resulted in better morbidity and mortality outcomes, so the treatment of hyperhomocysteinemia is explored for a similar benefit. Vitamin B(6), vitamin B(12) and folate, as co-factors in the metabolism of homosyteine, are used in the treatment of hyperhomocysteinemia. Betaine, a methyl-donor in a separate homocysteine metabolism pathway, is also used to treat hyperhomocysteinemia. These supplements have been used in various doses and combinations for different periods of time, with favorable outcomes. There is still no concensus whether hyperhomocysteinemia can be treated with folic acid alone, or in combination with vitamin B(6) and vitamin B(12). The dose of the supplements required to normalize fasting homocysteine remains to be determined, especially in diabetic nephropathy, hemodialysis and renal transplant patients. The benefits from lowering homocysteine levels have mainly been demonstrated in surrogate cardiovascular outcomes. The treatment of hyperhomocysteinemia cannot be firmly advocated until there are trials that demonstrate a beneficial clinical endpoint. In patients who have cardiovascular disease in the absence of more established risk factors, investigation and treatment of hyperhomocysteinemia should be considered.

Fasting total homocysteine (tHcy) concentration and mortality in older Mexican Americans

OBJECTIVES

This study examines the association between tHcy on cardiovascular and noncardiovascular mortality.

DESIGN

Longitudinal study of 1,633 Mexican Americans age>60 years recruited in 1998.

SETTING

Sacramento, California.

MEASUREMENTS

Cox proportional models were used to estimate the effects of tHcy on mortality rate in the total sample and in a subgroup of subjects without a history of cardiovascular disease at baseline.

RESULTS

About half of the cohort was born in Mexico. Among Mexican-born participants, high tHcy (>11.0 micromol/L) was associated with a higher rate of cardiovascular mortality compared to those with low tHcy concentration

CONCLUSIONS

The effect of tHcy on cardiovascular mortality is nearly 40% stronger among the immigrant group. tHcy might be an early marker of subclinical vascular pathology amongst the Mexican-born group, despite their apparently healthy profile at baseline.

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Key Words

• homocysteine
• cardiovascular mortality
• mexican americans
• nutritional biomarkers
• elderly

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MESH Headings

• Aged
• Aged, 80 and over
• Biomarkers/blood
• California/epidemiology
• Cardiovascular Diseases/ethnology
• Cardiovascular Diseases/mortality
• Female
• Homocysteine/blood
• Humans
• Longitudinal Studies
• Male
• Mexican Americans
• Mexico/ethnology
• Middle Aged
• Proportional Hazards Models

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Grants

• 1R24HD047861 NICHD NIH HHS
• P60 DK20572 NIDDK NIH HHS
• R01 DK060753 NIDDK NIH HHS
• AG12975 NIA NIH HHS
• R24 HD047861 NICHD NIH HHS
• DK60753 NIDDK NIH HHS
• R01 DK060753-03 NIDDK NIH HHS
• R03 AG033751 NIA NIH HHS
• R01 AG012975 NIA NIH HHS
• P60 DK020572-30 NIDDK NIH HHS
• P30 DK092926 NIDDK NIH HHS
• R01 AG012975-11 NIA NIH HHS
• P60 DK020572 NIDDK NIH HHS
• RWJ04823 PHS HHS

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Affiliation(s)

V Colon Lopez Department of Epidemiology, University of Michigan, School of Public Health, Ann Arbor, MI, USA.
M N Haan
A E Aiello
D Ghosh

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Homocysteine level and coronary heart disease incidence: a systematic review and meta-analysis

OBJECTIVE

To determine whether an elevated homocysteine level is an independent risk factor for the development of coronary heart disease (CHD) to aid the US Preventive Services Task Force in its evaluation of novel risk factors for incident CHD.

METHODS

Studies of homocysteine and CHD were identified by searching MEDLINE (1966 through March 2006). We obtained additional articles by reviewing reference lists from prior reviews, original studies, editorials, and Web sites and by consulting experts. We included prospective cohort studies that measured homocysteine and Framingham risk factors and the incidence of CHD in the general adult population without known CHD. Each study was quality rated using criteria developed by the US Preventive Services Task Force. We conducted a meta-analysis using a random-effects model to determine summary estimates of the risk of major CHD associated with each 5-micromol/L increase in homocysteine level. The systematic review and meta-analysis were conducted between January 25, 2005, and September 17, 2007.

RESULTS

We identified 26 articles of good or fair quality. Most studies found elevations of 20% to 50% in CHD risk for each increase of 5 micromol/L in homocysteine level. Meta-analysis yielded a combined risk ratio for coronary events of 1.18 (95% confidence interval, 1.10-1.26) for each increase of 5 micromol/L in homocysteine level. The association between homocysteine and CHD was similar when analyzed by sex, length of follow-up, outcome, study quality, and study design.

CONCLUSION

Each increase of 5 micromol/L in homocysteine level increases the risk of CHD events by approximately 20%, independently of traditional CHD risk factors.

Homocysteine as a risk factor for cardiovascular and related disease: nutritional implications

The objectives were firstly to assess the evidence that homocysteine is a significant and independent risk factor for vascular disease with special reference to cardiovascular disease, and secondly to evaluate the evidence that a food staple fortified with folic acid will reduce this problem on a population basis.

The structure of plasma homocysteine (tHcy) is described. Homocysteine, a highly reactive compound, is synthesized from the amino acid, methionine, and is metabolized by two pathways, the catabolic transsulphuration routeviacystathionine β-synthase (EC 4.2.1.22) and the remethylation path using 5-methyltetrahy-drofolate polyglutamate, the product of 5,10-methylenetetrahydrofolate reductase (MTHFR; EC 1.1.1.171),viathe cobalamin dependent enzyme, methionine synthase (MS; EC 2.1.1.13).

The mechanisms whereby hyper-tHcy is produced include both increased rates of synthesis and decreased metabolism. The latter may occur owing to nutritional deficiency of the vitamin cofactors which are necessary for the normal function of the metabolic enzymes. In particular, folate is required for methylene reductase, pyridoxal phosphate for cystathionine synthase and cobalamin for methionine synthase. When these vitamins are deficient hyper-tHcy is induced and this occurs especially in the elderly. Alternatively, a variant form of methylene reductase has recently been described which occurs in nearly 10% of the normal population. This variant is associated with hyper-tHcy, especially in situations associated with a low folate nutritional status.

Meta-analysis of both retrospective case-control studies, nested prospective case-control surveys and a secondary trial of mortality in postmyocardial infarct patients have shown that the association of hyper-tHcy with vascular disease is beyond doubt. This has been further supported by direct assessments of the degree of vascular disease in the carotid brachial and aortic arteries in relation to tHcy levels. Furthermore, treatment with a cocktail of the vitamin cofactors has produced lowering of tHcy levels and regression of the vascular disease in the carotid arteries of affected individuals.

Suggested pathogenic mechanisms in vascular disease induced by hyper-tHcy include vascular endothelial cell dysfunction, smooth muscle proliferation and derangements of normal intravascular regulation mechanisms. A variety of clinical conditions are known to be associated with a high incidence of thromboembolic complications. Some of these are associated with hyper-tHcy.

Low physiological doses of folic acid, as well as pharmocological doses, lower tHcy. However, because of the poor bioavailability of food folate (50%) and the considerable chemical instability of the naturally occurring reduced forms of folate, in most people it would require unacceptably high consumption of green vegetables to accomplish the necessary increase in intracellular folate and reduction in tHcy. Accordingly, folic acid, the nonreduced synthetic form of the vitamin, which is 100% bioavailable and chemically extremely stable, should be added to a food staple such as flour to ensure maximum protection for most of the population.

Plasma concentrations of C-reactive protein and total homocysteine in relation to the severity and risk factors for cerebrovascular disease

Higher C-reactive protein (CRP) and plasma homocysteine (tHcy) concentrations have been shown to indicate increased risk of coronary heart disease and cerebrovascular disease (CVD), but the mechanisms by which they increase the risk of atherothrombotic disease are under investigation. This study evaluates the associations of high-sensitivity C-reactive protein (hs-CRP) and tHcy with the risk factors, severity, and outcome on discharge in patients with CVD. hs-CRP, fasting tHcy, and lipid profile were determined in 50 patients with CVD and 20 healthy control subjects. Clinical data, National Institutes of Health stroke scale (NIHSS) on admission and disability Rankin scale on discharge, were recorded. Based on epidemiologic studies, cutoff points of 1.5 mg/L (hs-CRP) and 15mumol/L (tHcy) were used to indicate increased risk. Univariate and multivariate logistic regression analyses were used to relate tHcy with other CVD risk factors, NIHSS on admission and the disability Rankin scale on discharge. Overall, 38% of patients had increased hs-CRP and 26% had elevated tHcy. hs-CRP (P = 0.005) and tHcy (P < 0.0001) concentrations were significantly higher in patients compared with controls, and these differences remained significant after correction for age and sex. tHcy showed significant correlations with hs-CRP (rs = 0.35; P = 0.003) and low-density lipoprotein-cholesterol (LDL-C; rs = 0.49; P = 0.005). Logistic regression analysis with CVD as the dependent variable showed significant association with hs-CRP (P = 0.01) and tHcy (P < 0.0001) after adjustment for potential confounders. hs-CRP showed increased trend with disease severity and significant association with the disability Rankin scale (P = 0.033). These data support 4 main conclusions: (1) Elevation of hs-CRP and tHcy are common in CVD; (2) the significant relationship between tHcy and hs-CRP suggests that the association of tHcy with CVD risk may be dependent on inflammation-related mechanisms; (3) increased hs-CRP and tHcy show that patients with CVD may be at greater risk of subsequent coronary heart disease; and (4) admission hs-CRP could be used as an indicator of prognosis.

Homocysteine and cardiovascular disease: a review of the evidence

Elevated homocysteine (HCY) levels can be caused by a number of factors, including folate and B-vitamin deficiency, pre-existing atherosclerotic disease, diabetes and various drugs. Epidemiological evidence, as well as data from retrospective and prospective studies, supports an association between elevated HCY levels and increased risk of cardiovascular disease (CVD). However, whether lowering HCY levels by administration of folate and vitamins B6 and B12 is associated with any significant decrease in vascular risk remains the subject of ongoing debate. Although the major studies that have reported to date show that vitamin supplementation was associated with a decrease in HCY levels, this failed to have any significant effect on cardiovascular risk. Furthermore, although some lipid-modifying treatments have been shown to increase HCY levels, there is no evidence that this attenuates or compromises the beneficial effects of such treatments on cardiovascular risk. Taken together, these data suggest that HCY is a marker, rather than a cause, of CVD and therefore do not provide support for routine screening for and treatment of elevated HCY to prevent CVD. Data from ongoing clinical trials are awaited to clarify this issue.

Progressive glycosylation of albumin and its effect on the binding of homocysteine may be a key step in the pathogenesis of vascular damage in diabetes mellitus

The majority of diabetes research to date has rightly focussed on the direct effects of hyperglycaemia on tissues and a number of theories relating to the pathogenesis of vascular disease have been proposed. This research is important as until methods are found to achieve glycaemic control in all diabetic patients, prophylactic interventions to prevent vasculopathy will be required. One of the major blood proteins, human albumin is known to be covalently modified by extended incubation with glucose, leading to an impairment of ligand binding. One of the important ligands bound by albumin is homocysteine. There is increasing and compelling clinical, experimental and epidemiological evidence that homocysteine, and in particular the free unbound fraction, is vasculotoxic. If homocysteine binding to albumin is impaired by increasing glycosylation of albumin then either drugs which reduce homocysteine levels (pyridoxine, folic acid and cobalamin) or inhibit glycosylation (aminoguanidines) may be of benefit in the prevention of vascular damage in diabetic patients.

Homocysteine and coronary heart disease risk in the PRIME study

INTRODUCTION

Despite recent meta-analyses suggesting that homocysteine is an independent predictor of coronary heart disease (CHD), there is debate regarding whether elevated homocysteine may be deleterious only in the presence of other risk factors, with which it acts synergistically to exert a multiplicative effect on CHD risk, emerging only as a CHD predictor in patients with pre-existing risk factors. The Prospective Epidemiological Study of Myocardial Infarction (PRIME) Study is a multicentre prospective study of 10593 men from France and Northern Ireland, investigating cardiovascular risk factors. We investigated: (1) whether higher homocysteine is associated with increased CHD risk in the PRIME case-control cohort; (2) whether homocysteine interacts synergistically with pre-existing CHD risk factors.

METHODS

Homocysteine was measured in 323 participants who had developed CHD at 5-year follow-up and in 638 matched controls.

RESULTS

There was no significant difference in homocysteine between cases and controls (p=0.18). Homocysteine was significantly higher in current smokers (geometric mean mumol/l (interquartile range mumol/l) 9.45 (7.43, 11.75)) compared with non-smokers (8.90 (7.32, 10.70); p=0.007). There was a significant interaction between homocysteine, smoking and CHD risk (chi2=10.29, d.f.=2, p=0.006).

CONCLUSIONS

These findings suggest that elevated homocysteine is significantly associated with CHD risk in current smokers.

Is homocysteine important as risk factor for coronary heart disease?

AIM

Homocysteine (Hcy), a sulfur-containing amino acid product of methionine metabolism, may play an important role in the development of cardiovascular disease. In this paper we review available knowledge on the pathways leading to synthesis and degradation of Hcy, as well as on the genetic and environmental factors affecting its plasma levels, focussing on its potential role in the development of coronary heart disease.

DATA SYNTHESIS

Hyperhomocysteinemia (HHcy) is determined by genetic and environmental factors and represents a modifiable cardiovascular risk factor since vitamin supplementation has been shown to effectively lower plasma homocysteine levels. While case-control and cross-sectional studies consistently showed an association of HHcy with cardiovascular disease, prospective studies have given conflicting results. Thus, the role of HHcy in the development of coronary heart disease is still under debate. Furthermore, it remains unclear which patients should be screened for HHcy and treated to correct HHcy.

CONCLUSIONS

Available information collectively suggests that although HHcy can be regarded as a minor risk factor for coronary heart disease, it interacts with other risk factors in triggering new events in patients with known CAD. Thus, the treatment of mild HHcy with folate supplementation is appropriate in particular in high risk patients or patients with established CAD who do not present with the "traditional" risk factors.

Associations of plasma homocysteine and the methylenetetrahydrofolate reductase C677T polymorphism with carotid intima media thickness among South Asian, Chinese and European Canadians

BACKGROUND

Few studies have evaluated the associations of plasma homocysteine concentration, the methylenetetrahydrofolate reductase (MTHFR) C677T genotype and B vitamin concentration with intima media thickness (IMT) in multiethnic populations.

METHODS

In the Study of Health Assessment and Risk in Ethnic groups (SHARE), we measured carotid IMT, fasting serum folate, serum B12, plasma pyridoxal-5'-phosphate (PLP) and plasma homocysteine and determined the MTHFR C677T genotype in a cross-sectional study of 818 South Asian, Chinese and European Canadians without previous history of CVD, cancer or diabetes during 1996-1998.

RESULTS

Plasma homocysteine was inversely related to serum folate, serum B12, plasma PLP, B vitamin supplement use and Chinese ethnicity, and was positively associated with hypertension, smoking, IMT, MTHFR 677T/T genotype and South Asian ethnicity. Although ethnicity was not a statistically significant modifier, among carriers of the MTHFR 677T/T genotype with serum folate < or =14 nmol/L compared to >14 nmol/L, plasma homocysteine was significantly higher among South Asians (50.9% increase, P < 0.001) and Europeans (52.4% increase, P < 0.001) but not Chinese (11.0% increase, P > 0.05). Plasma homocysteine > 11.7 micromol/L was associated with a 5.9% (95% CI: 1.9%, 10.0%) increase in IMT (approximately 0.04 mm) in the pooled-data analyses with similar increases noted in the ethnic-specific analyses. The 677T/T genotype was not associated with a significant change in IMT in the pooled-data analyses (2.7%; 95% CI: -1.7%, 7.2%) nor in ethnic-specific analyses compared to other genotypes, although there were only 63 677T/T homozygotes.

CONCLUSION

The combination of lower serum folate and the MTHFR 677T/T genotype is associated with increased plasma homocysteine among South Asians and Europeans, but the association is not evident among Chinese possibly because their serum folate may not have been low enough to compromise MTHFR activity. Plasma homocysteine > 11.7 micromol/L appears to be associated with a clinically important increase in IMT.

Total plasma homocysteine and primary open-angle glaucoma

PURPOSE

To evaluate total plasma homocysteine (tHcy) levels in patients diagnosed with primary open-angle glaucoma (POAG) and normal subjects.

DESIGN

Case-control study.

METHODS

This study involved 55 POAG patients, 16 patients with secondary open-angle glaucoma or angle-closure glaucoma (non-POAG group), and 39 control healthy subjects undergoing ocular surgery. All glaucoma patients had characteristic glaucomatous optic disk damage and visual field loss. Fasting tHcy concentrations of all study participants were determined using high-performance liquid chromatography. Analysis of variance was used to compare homocysteine levels among the three diagnostic groups, and multivariate analysis was conducted to assess the associations between tHcy and diagnostic group, age, gender, smoking status, systemic hypertension, hyperlipidemia, and cardiovascular or cerebrovascular disease.

RESULTS

Mean +/- standard deviation of tHcy levels in POAG individuals, non-POAG patients and control subjects was 14.90 +/- 6.45 micromol/l, 14.30 +/- 4.35 micromol/l, and 14.81 +/- 4.56 micromol/l, respectively (P =.93; ANOVA). No statistically significant difference was found in the proportion of patients with abnormal tHcy levels among the three diagnostic groups. In multivariate analysis, only age and positive smoking status were significantly correlated with total plasma homocysteine levels.

CONCLUSION

No significant difference was found in plasma homocysteine levels among POAG patients and normal control individuals.

The nested case-control study in cardiology

BACKGROUND

The nested case-control study is an efficient epidemiological design whereby a case-control approach is employed within an established cohort. The large number of recent prospective studies and randomized trials conducted in cardiology provide cohorts within which the nested case-control approach is increasingly used.

METHODS

This paper describes the design of the nested case-control study, and evaluates its role in cardiology by reviewing all such studies indexed in Medline from 1966 to 2000. The example of homocysteine is used to illustrate how discrepancies between results of nested case-control and case-control studies played an important role in the decisions and recommendations of national and international organizations.

RESULTS

Seventy-seven nested case-control studies in cardiology were reviewed. The number of studies per year has been increasing since the first publication in 1987. The majority (96%) of studies evaluated potential risk factors for cardiovascular disease while the remainder evaluated drugs with cardiac adverse effects. In studies of homocysteine and coronary artery disease, nested case-control studies did not confirm the strong association suggested by early case-control studies that may have been influenced by bias (eg, selection, publication, or reverse causality). This led national and international organizations to advise against routine screening.

CONCLUSIONS

The nested case-control study is increasingly used to study causal relationships in cardiology. The large cohorts of cardiac patients created by prospective studies, clinical trials, and administrative databases should be exploited using this methodology to assess potential cardiac risk factors and other causal relationships that cannot be studied in randomized trials.

Plasma total homocysteine levels and prognosis in patients with previous premature myocardial infarction: a 10-year follow-up study

OBJECTIVES

To explore plasma total homocysteine (tHcy) as a predictor of long-term prognosis after premature myocardial infarction (MI).

DESIGN

Prospective cohort study.

SETTINGS

Akershus University Hospital.

SUBJECTS

A total of 247 patients (193 men and 54 women) in stable clinical phase after premature MI (males: first MI at age < or =55; females < or =60).

MAIN OUTCOME MEASURES

The primary end-point was total mortality and the secondary end-point was cardiac death. The third end-point was major cardiac events: a combination of cardiac death, MI and cardiac arrest.

RESULTS

After 10 years, 44 patients had died, 36 from cardiac causes. Major cardiac event occurred in 70 patients. The relative risk for death of all causes increased 1.43 (95% CI, 1.08-1.88) per tHcy quartile (P for trend = 0.01), and was only modestly reduced after adjustment for age, ejection fraction, total cholesterol, C-reactive protein, fibrinogen, smoking and hypertension to 1.37 (95% CI, 1.04-1.80) (P for trend = 0.03). Similar results were observed when cardiac death was used as the end-point, but we observed no association between tHcy and the end-point major cardiac event.

CONCLUSIONS

Total homocysteine was an independent predictor of total and cardiac mortality in stable patients following premature MI. tHcy had no effect on major cardiac event in contrast to most other risk factors in this study. Thus, the mechanism(s) underlying the effects of homocysteine on coronary heart disease may differ from other risk factors.

Thermolabile methylenetetrahydrofolate reductase, homocysteine, and cardiovascular disease risk: the European Concerted Action Project

BACKGROUND

Homozygotes for the thermolabile mutation (TT genotype) of the methylenetetrahydrofolate reductase (MTHFR; EC 1.5.1.20) enzyme have elevated plasma concentrations of the cardiovascular disease risk factor homocysteine, particularly if folate depleted.

OBJECTIVE

We examined the relations between thermolabile MTHFR, plasma homocysteine, plasma folate, and vascular disease risk.

DESIGN

This was a case-control comparison in 711 vascular disease cases and 747 controls from 9 European countries.

RESULTS

The TT genotype was associated with higher homocysteine and lower plasma folate than the CC and CT genotypes in both cases and controls and a nonsignificant increase in vascular disease risk (1.26; 95% CI: 0.88, 1.81; P = 0.20). The frequency of the TT genotype in cases was not significantly different from that in controls (12.8% compared with 10.8%). After adjustment for traditional risk factors, the TT genotype was associated with an odds ratio of 1.48 (1.0, 2.20) for risk of vascular disease. This risk was attenuated after further adjustment for homocysteine. In subgroups with homocysteine concentrations >or= 9 micro mol/L, risk tended to be higher in CC than in TT subjects. However, CC subjects were characterized by a higher prevalence of the conventional risk factors associated with both elevated plasma homocysteine and serum creatinine. After adjustment, the risk of vascular disease associated with each genotype was not significantly different.

CONCLUSIONS

There was a strong graded association between homocysteine and vascular risk in all genotypes. MTHFR genotype is a key determinant of plasma total homocysteine concentrations. The initially nonsignificant risk estimate associated with the TT genotype was strengthened after adjustment for conventional cardiovascular disease risk factors but was attenuated after adjustment for plasma folate and total homocysteine. The modest risk increase conferred by the TT genotype is mediated mainly by increased total homocysteine and low plasma folate concentrations.

Prognostic value of tryptophan load test followed by serum kynurenine determination. Its comparison with pyridoxal-5-phosphate, kynurenine, homocysteine and neopterin amounts

Tryptophan load test followed by serum kynurenine determination at fasting state and after L-tryptophan loading, as well as serum pyridoxal-5-phosphate (P-5-P), homocysteine and neopterin concentrations at fasting state have been examined in 30 healthy individuals and 87 patients with coronary heart disease (CHD), verified by coronary angiography. Received results have shown that low serum P-5-P concentration as well as P-5-P deficiency identified by tryptophan load test have been found in 78% of CHD patients, while increased homocysteine concentration above 15 micromol/L in 31.8%, and elevated neopterin concentration above 8.7 nmol/L in 32.1% of cases. It allows to conclude that a lot of CHD patients have P-5-P deficiency. Moreover P-5-P deficiency is an earlier indicator of CHD than increased homocysteine level above 15 micromol/L. Elevated serum neopterin concentration above 8.7 nmol/L may be a marker of coronary disease activity rather than a marker of the presence of CHD.

Increased serum homocysteine and sudden death resulting from coronary atherosclerosis with fibrous plaques

INTRODUCTION

Modest elevations of total homocysteine have been associated with increased risk for coronary atherosclerosis but correlation between elevated homocysteine and plaque morphology has not been described in humans.

METHODS

We determined serum homocysteine at postmortem from 87 men with coronary thrombus (62 of whom were diagnosed as acute), from 35 men with severe coronary disease without thrombus, and from 46 controls. In coronary deaths, atherosclerotic plaques at the sites of maximal luminal narrowing of the four epicardial coronary arteries were classified as fibrous plaques, fibrous cap atheromas, thin-cap atheromas, and healed ruptures, and macrophage infiltration was assessed semiquantitatively.

RESULTS

Median serum homocysteine postmortem as a result of acute thrombus was 10.4 micro mol/L (P=0.4 versus controls), 12.1 micro mol/L in men with organized thrombi (P=0.1 versus controls), 15.6 micro mol/L in men without thrombus (P=0.007 versus controls), and 9.8 micro mol/L in controls. The median homocysteine was 12.1 micro mol/L in 65 men with healed infarcts (P=0.03 versus controls). The number of fibrous plaques was associated with log-normalized homocysteine (P=0.004), independent of age, albumin, smoking, hypertension, and serum cholesterol. Homocysteine levels in the upper tertile (>15 micromol/L) were associated with sudden death without acute or organized thrombus (odds ratio 3.8, P=0.03) independent of age and other risk factors; the coexistence of diabetes increased the association (odds ratio 25.1, P=0.009, versus lowest tertile < or =8.5 micromol/L).

CONCLUSIONS

Increased serum homocysteine is associated with sudden death in the absence of acute coronary thrombosis, especially with concomitant diabetes, and with the presence of lipid-poor, fibrous plaques.

Relation of plasma total homocysteine to cardiovascular mortality in a French population

Although there is considerable epidemiologic evidence for a relation between plasma homocysteine (HCY) and cardiovascular (CV) disease, the role of HCY as a causal CV risk factor remains controversial, mainly because of the intercorrelation between HCY and other CV risk factors. The goal of the present nested case-control prospective study is to determine the multiadjusted relation between HCY and CV mortality in a large and low CV risk population after a mean follow-up of 14 years. In 1980 and 1981, plasma was saved from 5,000 patients who underwent a systematic health checkup, including clinical and biologic examinations. In 1999, HCY concentration was measured in 110 subjects who died of CV disease (cases) and in 154 randomly matched survivors (control subjects). Statistical analysis was adjusted for CV risk factors. Based on Cox analyses, 3 factors emerged as independent predictors of CV mortality: C-reactive protein, systolic blood pressure, and HCY. The adjusted hazard ratio for CV mortality was 1.22 (95% confidence interval 1.04 to 1.41) per 1 SD (3.9 micromol/L) increment of HCY. Thus, HCY is an independent risk predictor for CV mortality. Because of extensive adjustment procedures, the present study provides additional epidemiologic evidence for a causal relation between HCY and CV disease.

Total plasma homocysteine level and risk of cardiovascular disease: a meta-analysis of prospective cohort studies

The role of homocysteine as a risk factor for cardiovascular disease remains controversial because positive reports from case-control studies may be the consequence of reverse causality bias, and positive and negative results have been reported in cohort studies. This is a meta-analysis of published cohort studies. An average relative risk (ARR) was calculated using fixed and random effect models. The likelihood of publication and selection bias, and the impact of each study on the ARR were also evaluated. Fourteen eligible studies were retrieved. We found no evidence of publication bias (P =.62) nor heterogeneity (P =.56). The ARRs from a fixed effect model were 1.49 (95% CI: 1.31-1.70) for cardiac events, and 1.37 (95% CI: 0.99- 1.99) for ischemic stroke. Duration of follow up and age did not significantly change the ARRs. Hyperhomocysteinemia moderately increases the risk of a first cardiovascular event, regardless of age and follow-up duration.

Hyperhomocysteinemia and thrombosis

Homocysteine (Hcy) is a sulfhydryl amino acid derived from the metabolic conversion of methionine, which is dependent on vitamins (folic acid, B12, and B6) as cofactors or cosubstrates. In 1969, McCully first reported the presence of severe atherosclerotic lesions in patients with severe hyperhomocysteinemia and hypothesized the existence of a pathogenic link between hyperhomocysteinemia and atherogenesis. Several case-control and cross-sectional studies were consistent with the initial hypothesis of McCully, showing that moderate hyperhomocysteinemia is also associated with heightened risk of occlusive arterial disease. Less consistent results have been reported by prospective cohort studies of subjects who were healthy at the time of their enrollment, whereas prospective cohort studies of patients with overt coronary artery disease or other conditions at risk consistently confirmed the association between moderate hyperhomocysteinemia and cardiovascular morbidity and mortality. More recently, an association between moderate hyperhomocysteinemia and heightened risk of venous thromboembolism has been documented, suggesting that hyperhomocysteinemia might be involved not only in atherogenesis, but also in thrombogenesis. The mechanisms by which hyperhomocysteinemia might contribute to atherogenesis and thrombogenesis are incompletely understood. The mainstay of treatment of hyperhomocysteinemia is folic acid, alone or in combination with vitamin B12 and vitamin B6. Although it is quite clear that vitamins effectively reduce the plasma levels of total homocysteine (tHcy), we do not yet know whether they will decrease the risk of vascular disease. The results of ongoing randomized, placebo-controlled, double-blind trials of the effects of vitamins on the thrombotic risk will help in defining whether the relationship between hyperhomocysteinemia and thrombosis is causal, and will potentially have a dramatic effect in the prevention of thromboembolic events.

Homocysteine and atherothrombosis

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

Homocysteine and occlusive arterial disease

BACKGROUND

An increased plasma level of homocysteine has been proposed as an independent risk factor for atherosclerosis; this review examines the evidence.

METHODS

A Medline search was undertaken for English language articles on homocysteine and vascular disease. Further papers were identified by cross-referencing from the reference lists of relevant major articles.

RESULTS

Although much interest has been generated about homocysteine and atherosclerotic disease, contradictory data exist regarding its role in disease progression. There is insufficient current evidence to regard increased homocysteine level as a causative factor in atherosclerotic disease.

CONCLUSION

It is not known whether lowering plasma homocysteine concentration will reduce cardiovascular risk in the long term. Until such data become available, there is no evidence for the widespread use of folic acid therapy to reduce cardiovascular disease risk.

Homocysteine and cardiovascular disease: current evidence and future prospects

Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Despite the well-known effectiveness of vitamin supplementation in reducing homocysteine levels, it is not known whether lowering of homocysteine levels is associated with a reduction in cardiovascular morbidity and mortality. The aim of this review is to discuss the epidemiologic evidence about the relation between homocysteine and cardiovascular disease, the pathophysiologic mechanisms responsible for the deleterious vascular and hemostatic effects of homocysteine, and studies of the potential benefits of homocysteine-lowering therapy.

Hyperhomocysteinemia and the risk of thromboembolic phenomenon in patients with chronic renal failure

Thromboembolic phenomena are a major cause of morbidity and mortality in patients with end-stage renal disease. Studies in patients with chronic renal failure (CRF) have demonstrated an increased relative risk of coronary artery disease (CAD) in association with hyperhomocysteinemia (HHe). However, very little data exist about the causal relationship between HHe and cerebrovascular diseases (CVA) in patients with CRF. We report the results of our observational retrospective study to determine the effect of HHe on CVA and CAD in patients with CRF (defined as creatinine clearance <50 ml/min). One hundred ten male patients were eligible for our study performed at a Veterans Affairs Medical Center. Age range was 36-86 years (median age 67 years). A fasting plasma HC level >15 micromol/l was considered as HHe. Thirty-four patients were on dialysis. Eight patients were postrenal transplantation. Our study results showed that a homocysteine (HC) level greater than 15 micromol/l was an independent predictor of CVA, after adjusting for potential confounders. Adjusted odds ratio (OR) for CVA was 10.9 (CI: 1.8-67.2, p=.01). Although our study results suggest a strong relationship between HHe and CVA, they failed to demonstrate an association between HHe and CAD. There exists a need for larger prospective randomized clinical trials to evaluate the effect of HHe on the incidence of CVA and CAD in patients with CRF.

Homocyst(e)ine and cardiovascular disease: a systematic review of the evidence with special emphasis on case-control studies and nested case-control studies

BACKGROUND

Elevated concentrations of homocyst(e)ine are thought to increase the risk of vascular diseases including coronary heart disease and cerebrovascular disease.

METHODS

We searched MEDLINE (1966-1999), EMBASE (1974-1999), SciSearch (1974- 1999), and Dissertation Abstracts (1999) for articles and theses about homocyst(e)ine concentration and coronary heart disease and cerebrovascular disease.

RESULTS

We included 57 publications (3 cohort studies, 12 nested case-control studies, 42 case-control studies) that reported results on 5518 people with coronary heart disease (11,068 control subjects) and 1817 people with cerebrovascular disease (4787 control subjects) in our analysis. For coronary heart disease, the summary odds ratios (OR) for a 5-micromol/l increase in homocyst(e)ine concentration were 1.06 (95% CI : 0.99-1.13) for 2 publications of cohort studies, 1.23 (95% CI : 1.07-1.41) for 10 publications of nested case-control studies, and 1.70 (95% CI : 1.50-1.93) for 26 publications of case-control studies. For cerebrovascular disease, the summary OR for a 5-micromol/l increase in homocyst(e)ine concentration were 1.10 (95% CI : 0.94-1.28) for 2 publications of cohort studies, 1.58 (95% CI : 1.35-1.85) for 5 publications of nested case-control studies, and 2.16 (95% CI : 1.65-2.82) for 17 publications of case-control studies.

CONCLUSIONS

Prospective studies offer weaker support than case-control studies for an association between homocyst(e)ine concentration and cardiovascular disease. Although other lines of evidence support a role for homocyst(e)ine in the pathogenesis of cardiovascular disease, more information from prospective epidemiological studies or clinical trials is needed to clarify this role.

Niacin (nicotinic acid) in non-physiological doses causes hyperhomocysteineaemia in Sprague-Dawley rats

Niacin (nicotinic acid) in its non-physiological dose level is known to be an effective lipid-lowering agent; its potential risk as a therapeutic agent, however, has not been critically considered. Since niacin is excreted predominantly as methylated pyridones, requiring methionine as a methyl donor, the present study was undertaken to examine whether metabolism of the amino acid is altered in the presence of large doses of niacin. Male Sprague-Dawley rats were given a nutritionally adequate, semi-synthetic diet containing niacin at a level of either 400 or 1000mg/kg diet (compared to 30mg/kg in the control diet) for up to 3 months. Supplementation with niacin (1,000 mg/kg diet) for 3 months resulted in a significant increase in plasma and urinary total homocysteine levels; this increase was further accentuated in the presence of a high methionine diet. The hyperhomocysteineaemia was accompanied by a significant decrease in plasma concentrations of vitamins B6 and B12, which are cofactors for the metabolism of homocysteine. The homocysteine-raising action of niacin, in particular, has an important toxicological implication, as hyperhomocysteineaemia is considered to be an independent risk factor for arterial occlusive disease. The niacin-associated change in homocysteine status may be an important limiting factor in the use of this vitamin as a lipid-lowering agent.

Homocyst(e)ine and coronary heart disease: pharmacoeconomic support for interventions to lower hyperhomocyst(e)inaemia

Homocyst(e)ine, a sulphur-containing amino acid, is an intermediate formed during the metabolism of the essential amino acid methionine. Biological and epidemiological evidence suggest that elevated plasma levels of homocyst(e)ine are a risk factor for atherosclerosis and coronary heart disease (CHD). In the general US population, hyperhomocyst(e)inaemia is common and most often due to mild nutritional deficiencies in the B vitamins (folic acid, vitamin B(12) and vitamin B(6)). While high homocyst(e)ine levels can be effectively lowered using folic acid and other B vitamins, it is unknown whether such vitamin therapy will lead to clinical benefits. Given that strategies for homocyst(e)ine-lowering are safe and inexpensive, however, even small reductions in CHD risk will be highly cost effective. Thus, it may be prudent for patients to ensure an adequate daily intake of dietary folic acid and other B vitamins and for physicians to screen high-risk adults such as those with established CHD as we await definitive results from ongoing clinical trials.

Homocysteine and cardiovascular disease in diabetes mellitus

BACKGROUND

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

METHODS

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

RESULTS

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

DISCUSSION

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

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

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

An MTHFR variant, homocysteine, and cardiovascular comorbidity in renal disease

BACKGROUND

It is unclear whether total serum homocysteine (tHcy) and the C677T mutation of methylenetetrahydrofolate reductase (MTHFR) are associated with cardiovascular disease (CVD) in patients with end-stage renal disease (ESRD).

METHODS

A cross-sectional sample of 459 patients with ESRD on chronic dialysis was assessed to determine whether tHcy and the C677T mutation are associated with CVD prevalence in multiple logistic regression. As CVD mortality is high, we examined the relationship between homozygosity and duration of dialysis.

RESULTS

Mean tHcy was higher in patients without a history of CVD (35.2 micromol/L vs. 30.4 micromol/L, P = 0.02). In multivariate models, CVD was negatively associated with tHcy and positively associated with TT genotype, male gender, and body mass index. Mean tHcy levels were higher among those with the TT genotype compared with those with the CC genotype when adjusted for age, folate, creatinine, and albumin (37.9 micromol/L vs. 31.9 micromol/L, P = 0.005). Among whites, the prevalence of the TT genotype was higher in those having undergone less than one year of dialysis (P = 0.002).

CONCLUSIONS

The C677T genotype of MTHFR is associated with CVD in ESRD and may be a more meaningful marker than tHcy for abnormal homocysteine metabolism in ESRD. Prospective data from ongoing clinical trials are needed to improve our understanding of these findings. Screening for this polymorphism may help guide prevention measures.

Heterogeneity of the association between plasma homocysteine and atherothrombotic disease: insights from studies of vascular structure and function

Among individuals with severe hyperhomocysteinaemia, there is a striking heterogeneity in the severity of the clinical features. This observation demonstrates that factors must exist that modulate the relationship between hyperhomocysteinaemia and clinical disease. Investigations of the association between mild-to-moderate hyperhomocysteinaemia and atherothrombotic disease also suggest heterogeneity in the association between plasma homocysteine levels and 1) clinical disease; 2) angiographic and echographic estimates of the extent of atherosclerosis; 3) arterial stiffness; 4) endothelial function; and 5) procoagulant status. The commonly held view that homocysteine is a vasculotoxic substance that promotes atherogenesis by causing endothelial damage is incomplete, because it cannot explain this heterogeneity. I suggest that homocysteine may have both prothrombotic and proatherogenic properties, but that there are strong, as yet unidentified enhancing and protective factors, the prevalence of which may differ among populations. This concept could account for some of the observed heterogeneity. Identifying these factors would be of major clinical importance and would provide crucial mechanistic insights.

Homocysteine and coronary heart disease in the Caerphilly cohort: a 10 year follow up

OBJECTIVE

Prospective assessment of the risk of coronary heart disease associated with total serum homocyst(e)ine (homocysteine) concentration.

DESIGN

Nested case-control study.

SETTING

Caerphilly and surrounding villages in south Wales, UK.

PARTICIPANTS

2290 men who participated in phase II of the study in 1984. After a mean follow up of 10 years, 312 men developed coronary heart disease and were compared with 1248 randomly selected, age frequency matched controls.

MAIN OUTCOME MEASURE

Acute myocardial infarction or death from coronary heart disease.

RESULTS

The geometric mean serum homocysteine concentration was higher in cases (12.2 micromol/l, 95% confidence interval (CI) 11.8 to 12.6 micromol/l) than in controls (11.8 micromol/l, 95% CI 11.3 to 12.5 micromol/l) (p = 0.09). There was a graded increase in the odds ratio of coronary heart disease across quintiles of the homocysteine concentration distribution compared with the first (p = 0.04), which was attenuated when adjusted for confounding variables (p = 0.4). There was a small but non-significant increase in the adjusted odds ratio of coronary heart disease per standard deviation change in the log distribution of homocysteine concentration (OR = 1.07 (95% CI.93 to 1.24), p = 0.34). Comparing the top quintile of the homocysteine concentration with the remaining 80%, the adjusted odds ratio of coronary heart disease was 1.03 (95% CI 0.73 to 1.45) (p = 0.8) and comparing the top 5% with the remaining 95% it was 1.05 (95% CI 0.56 to 1.95) (p = 0.9).

CONCLUSIONS

These findings do not support the hypothesis that a raised homocysteine concentration is a strong independent risk factor for coronary heart disease. Randomised controlled trials of homocysteine lowering treatment such as folic acid are needed before generalizing the early positive results of observational studies.

Diagnosis and treatment of hyperhomocysteinemia

Hyperhomocysteinemia has emerged as an important risk factor for cardiovascular disease. However, its place in clinical practice is somewhat unclear, due to the lack of clinical trials documenting the benefit of treatment on reducing cardiovascular events. Vitamin therapy, particularly with folic acid, reduces plasma homocysteine significantly and improves other surrogate markers of cardiovascular risk such as endothelial function. Although a consensus is lacking on the right approach to diagnosis and treatment of this risk factor, we have suggested an algorithm based on data from clinical studies. We are optimistic that such an approach will be helpful for the clinician until clinical trials, with cardiovascular events as endpoints, are completed.

A meta-analysis of cerebrovascular disease and hyperhomocysteinaemia

Hyperhomocysteinaemia has been identified as a risk factor for stroke and cerebrovascular disease in several studies. To evaluate the evidence we performed a meta-analysis. We found 21 studies searching Medline from 1966-July 1999 using the key words homocysteine, homocystine and cerebrovascular disease or stroke combined with a search of Embase, Science Citation Index and Biological Abstract. In 17 of these studies the populations were comparable. The studies were divided into two groups, cross-sectional studies and longitudinal studies where a pre-insult plasma or serum total homocysteine was used. The reports on 8 cross-sectional and 4 longitudinal studies gave data on the mean and standard deviations of plasma or serum homocysteine for both cases and controls, and these studies were included in the meta-analysis. The results of the 5 excluded studies all pointed to a positive relationship between hyperhomocysteinaemia and cerebrovascular disease. For each study, the expected fractions of the cases with total homocysteine higher than the 95-percentile for the controls were calculated, using the means and standard deviations, assuming a log-normal distribution, and the odds-ratios for disease with total homocysteine above the 95-percentile were computed. The overall weighted odds-ratio for disease with a concentration of homocysteine in plasma or serum above the 95-percentile (95% confidence interval) for the cross-sectional studies was 4.12 (2.94-5.77), for the longitudinal studies 3.74 (2.53-5.54), and for all 12 studies 3.97 (3.07-5.12). In conclusion, the results support the case for a strong relation between hyperhomocysteinaemia and cerebrovascular disease.

Plasma total homocysteine levels in postmenopausal women with unstable coronary artery disease

An elevated plasma total homocysteine (tHcy) level is considered a risk factor for coronary artery disease (CAD), but the relationship between plasma tHcy and well-defined CAD in women is still unclear. Plasma tHcy concentrations and the covariates serum folate, vitamin B12, and creatinine were analysed in 157 angiographically examined postmenopausal women with unstable CAD and in 101 healthy controls. At coronary angiography, 16% had normal vessels and 84% had coronary atherosclerosis. Mean plasma tHcy concentration (micromol/l, 95% confidence interval) did not differ in patients compared to controls (13.1 (12.3-13.8) vs. 12.5 (11.6-13.5)) or in patients with or without coronary atherosclerosis (13.3 (12.4-14.1) vs. 12.0 (10.8-13.2)). A trend to an increasing plasma tHcy with increasing degree of coronary atherosclerosis was attenuated after adjustment for age and the previous mentioned covariates. Odds ratio for the risk of coronary artery disease and coronary atherosclerosis in hyperhomocysteinemic patients (> or =90th percentile in controls) was approximately 3. However, the confidence interval included unity in half of the groups and the significance was therefore difficult to judge. Receiver operating characteristics showed age to be the only variable with a significant discriminatory ability regarding the presence of coronary atherosclerosis (area 0.77). Mild hyperhomocysteinemia seems not to be related to the risk of unstable CAD in postmenopausal women. The trend towards higher plasma tHcy with increasing degree of coronary atherosclerosis may be a marker of the disease. In future studies adjustment for age and the other three covariates should be considered.

Blood levels of homocysteine and atherosclerotic vascular disease

In contrast to cross-sectional and case-control studies, which tend to report strong positive associations between plasma homocysteine and vascular risk, many prospective epidemiologic studies indicate modest associations at most, whereas other prospective studies report no evidence of association. Thus, while homocysteine may represent a causal factor in atherothrombosis, it is also possible that homocysteine is a marker of preclinical disease, or a consequence of other factors more closely linked to risk. Randomized trials are necessary to test reliably whether lowering homocysteine levels will decrease risks of atherosclerotic vascular disease. Current guidelines from the American College of Cardiology and the American Heart Association do not support population-based homocysteine screening to determine cardiovascular risk.

Nutritional aspects and possible pathological mechanisms of hyperhomocysteinaemia: an independent risk factor for vascular disease

Numerous case-control and prospective studies have identified elevated plasma homocysteine as a strong independent risk factor for cerebovascular, cardiovascular and peripheral vascular disease. Homocysteine is formed as a result of the breakdown of the dietary amino acid methionine. Once formed, homocysteine is either remethylated to methionine, or undergoes a trans-sulfuration reaction to form cysteine. The re-methylation of homocysteine to methionine is dependent on three B-vitamins, i.e. riboflavin, vitamin B12 and folate. The second pathway of homocysteine metabolism is the trans-sulfuration pathway which requires both vitamin B6 and riboflavin for its activity. Thus, up to four B-vitamins are required for intracellular homocysteine metabolism. Many studies have noted strong inverse relationships between homocysteine levels and the status of both vitamin B12 and folate. However, the relationship between vitamin B6 status and homocysteine is still uncertain. Similarly, numerous intervention studies have demonstrated effective lowering of homocysteine levels as a result of folate and vitamin B12 supplementation, while the homocysteine-lowering ability of vitamin B6 is unclear. Even though riboflavin plays a crucial role in both the trans-sulfuration and remethylation pathways of homocysteine metabolism, the relationship between riboflavin status and homocysteine levels has not been investigated. The exact mechanism that explains the vascular toxicity of elevated homocysteine levels is unknown at present, studies indicate that it is both atherogenic and thrombogenic. To date, no randomized clinical trial has demonstrated that lowering of homocysteine levels is beneficial in terms of reducing the prevalence of vascular disease. It is probable, however, that optimal B-vitamin status is important in the prevention of vascular disease.

Clinical relevance of hyperhomocysteinaemia in atherothrombotic disease

High fasting plasma homocysteine levels (> 12 to 15 mumol/L) are commonly encountered in clinical practice and are associated with increased risk of atherothrombotic disease. Treatment with folic acid (1 to 5 mg/day) is inexpensive and effective in normalising plasma homocysteine levels. High plasma homocysteine levels after methionine loading (> 40 to 50 mumol/L) are also common and can be treated with pyridoxine-based regimens (50 to 250 mg/day). As compared with fasting plasma homocysteine levels, the association between high postmethionine loading plasma homocysteine levels and atherothrombotic disease has been less extensively studied. There is reasonable, but not clearly definitive, evidence that high plasma homocysteine levels are causally related to atherothrombotic disease. Results of randomised trials of homocysteine-lowering treatment with clinical end-points will be available in 4 to 6 years. At present, a reasonable policy for the practising clinician would be to consider homocysteine-lowering treatment in individuals at very high risk of atherothrombotic disease, such as patients with clinically manifest atherothrombotic disease with onset before 55 years of age, patients with end stage renal disease, and healthy subjects with a strong family history of early-onset atherothrombotic disease. Such a policy should be reassessed as the results of randomised trials become available.

Agreement among Four Homocysteine Assays and Results in Patients with Coronary Atherosclerosis and Controls

Background: Hyperhomocysteinemia has been associated with coronary atherosclerosis in many, but not all, prospective and retrospective studies. Some on these inconsistencies may be attributed to methodological variabilities.

Methods: In the present study, three newly commercially available assays and one in-house HPLC assay for total homocysteine (tHcy) were utilized in 99 subjects with angiographically documented atherosclerosis and in 91 community controls matched by age, gender, and smoking history. The in-house assay, a modified Fortin and Genest HPLC method, was compared with the Bio-Rad HPLC assay, the Abbott IMx® fluorescence polarization immunoassay, and a Bio-Rad enzyme-linked immunoassay (EIA) microtiter method.

Results: Correlation coefficient values between the in-house HPLC assay and the Bio-Rad HPLC, the Abbott IMx, and the Bio-Rad EIA assays were 0.95, 0.96 and 0.90, respectively. Although tHcy concentrations were higher in cases compared with controls by all four methods, the difference reached statistical significance only with the in-house HPLC procedure (median, 13.5 ± 6.7 μmol/L in cases vs 10.9 ± 4.8 μmol/L in controls; P &lt;0.01, adjusting for covariates), where it was an independent predictor of case or control status, along with hypertension, total cholesterol, and triglycerides. The tHcy distributions in cases and controls demonstrated significant overlap. The number of atherosclerotic major coronary vessels was associated with significantly higher tHcy (P &lt;0.01 for trend) in all four methods.

Conclusions: The three commercial assays for tHcy differed in analytical and clinical performance. Analytically, the Abbott IMx method showed the best comparability with the in-house assay, but clinically, the three commercial methods were similar and did not distinguish cases from controls.

Homocysteine, B vitamins, and coronary artery disease

This article discusses the metabolism of homocysteine, factors affecting its plasma level, and the evidence for its role in the pathogenesis of vascular disease. The treatment of hyperhomocysteinemia and its possible impact on vascular disease prevention and progression are described also.

Total homocysteine and cardiovascular disease

Recent data have shown that an elevated plasma level of the amino acid homocysteine (Hcy) is a common, independent, easily modifiable and possibly causal risk factor for cardiovascular disease (CVD) which may be of equal importance to hypercholesterolemia, hypertension and smoking. This paper reviews the biochemical, clinical, epidemiological and experimental data underlying this conclusion and is critically questioning whether elevated tHcy is a causal factor.

Betaine in wine: answer to the French paradox?

In France, a diet high in saturated fat and cholesterol is associated with low coronary artery disease mortality and it may be that drinking wine is protective against ischemic heart disease. Recent studies suggest that high plasma homocysteine concentrations are an independent risk factor for coronary, cerebral and peripheral arterial occlusive diseases. One of several routes for metabolism of homocysteine involves methylation using betaine as the methyl donor. Betaine is often added to less expensive wine when beet sugar is used to increase alcohol content. We found that many commercial wines contain betaine; an average glass of wine contains approximately 3 mg betaine. This small amount is less than the dose used to lower homocysteine in patients with genetic forms of hyperhomocysteinemia, but we do not know whether humans with modest elevations of homocysteine would be influenced by this dose.

Plasma homocysteine as a cardiovascular risk factor: causal, consequential, or of no consequence?

Elevated plasma total homocysteine may be causally related to the risk of atherosclerotic cardio-vascular diseases. Many significant studies indicate an effect by elevated homocysteine on cardiovascular disease occurrence, progression, and recurrence that is independent of traditional risk factors. However, recent data have cast doubt on the veracity of the relationship between elevated plasma total homocysteine and the incidence of cardiovascular disease. In general, a stronger relationship has been found in cross-sectional and retrospective case-control studies than in nested case-control or prospective studies. The issues of study design, bias, and confounding are critical to an analysis of this putative relationship, and their effects can only be avoided by randomized controlled trials of homocysteine-lowering therapy (folic acid). While awaiting the outcome of these trials, there may already be sufficient evidence to prescribe homocysteine-lowering therapy in subjects deemed to be at high risk of cardiovascular disease.

Plasma homocysteine, aortic stiffness, and renal function in hypertensive patients

Hyperhomocysteinemia has been associated with both vascular structure alterations and vascular clinical end points. To assess the relation between plasma homocysteine, structure and function of large arteries, and the presence of clinical vascular disease, we investigated a population of 236 hypertensive patients. We estimated arterial stiffness by measuring the carotid-femoral pulse wave velocity. Total plasma homocysteine was determined by fluorometric high-performance liquid chromatography. The presence of cardiovascular disease was defined on the basis of clinical events, including coronary heart disease, cerebrovascular disease, and peripheral vascular disease. In this population, pulse wave velocity was positively correlated with homocysteine, even after adjustments for age, mean blood pressure, extent of atherosclerosis, and creatinine clearance (P=0.016). Analysis of variance showed statistically significant differences between the mean values of homocysteine, creatinine clearance, and pulse wave velocity according to the extent of atherosclerosis, with an increase in these 3 parameters concomitant with an increase in the number of vascular sites involved with atherosclerosis. In conclusion, in hypertensive patients the levels of homocysteine are strongly and independently correlated to arterial stiffness measured by aortic pulse wave velocity. Plasma homocysteine, creatinine clearance, and aortic pulse wave velocity are higher in patients presenting with clinical vascular disease. These results suggest that the evaluation of aortic distensibility and homocysteine levels can help in cardiovascular risk assessment in hypertensive populations.

Nonfasting plasma total homocysteine level and mortality in middle-aged and elderly men and women in Jerusalem

BACKGROUND

Elevated plasma total homocysteine level has been associated with cardiovascular disease in many studies, mostly in Europe and North America. Data on persons from other areas and on associations with overall mortality are sparse.

OBJECTIVE

To determine the relation of plasma homocysteine level to all-cause and cause-specific mortality.

DESIGN

Prospective observational study with 9- to 11-year follow-up.

SETTING

A free-living, multiethnic Jewish population in western Jerusalem, Israel.

PARTICIPANTS

1788 residents of Jerusalem (808 men and 980 women) who were at least 50 years of age and were examined between 1985 and 1987 as part of the Kiryat Yovel Community Health Study.

MEASUREMENTS

Nonfasting plasma homocysteine level was determined in frozen stored samples. Deaths during follow-up were identified by linkage with the national population registry.

RESULTS

Plasma homocysteine levels exceeded 14 micromol/L in 28% of men and 20% of women. During the study period, 405 deaths occurred. In multivariate Cox models that controlled for possible confounders, a nonmonotonic increase in mortality hazard ratios was associated with ascending quintile of homocysteine level: 1.0, 1.4, 1.3, 1.5, and 2.0 (P < 0.001 for trend). The relation was similar for cardiovascular and noncardiovascular causes of death (excluding cancer). The association was weaker when deaths that occurred during the first 5 years of follow-up were excluded; corresponding hazard ratios for ascending quintile of homocysteine level were 1.0, 1.0, 1.2, 1.1, and 1.6 (P = 0.063 for trend). Age- and sex-adjusted percentages of deaths "attributable" to elevated plasma homocysteine level (> or = 14 micromol/L) were 12.5% (95% CI, 6.7% to 18.8%) for all deaths, 16.0% (CI, 7.2% to 25.6%) for deaths during the first 5 years of follow-up, and 8.3% (CI, 1.5% to 16.1%) for later deaths.

CONCLUSIONS

A mildly to moderately elevated nonfasting plasma homocysteine level is a substantial risk marker for death from all causes. The association seems to be stronger during the first 5 years of follow-up.