Relation of serum homocysteine and lipoprotein(a) concentrations to atherosclerotic disease in a prospective Finnish population based study

Associations between classical cardiovascular risk factors and coronary artery disease in two countries at contrasting risk for myocardial infarction: the PRIME study

PURPOSE

In two countries with contrasting risk for coronary artery disease (CAD)-Northern Ireland and France-a case-control study was performed on baseline data within a cohort study to compare the strength of the associations between CAD prevalence and classical risk factors.

METHOD AND RESULTS

A sample of 9561 men, aged 50-60 years, was studied: 382 had had myocardial infarction or angina, and 9179 were controls. In both countries, variables associated with CAD were age, body mass index, hypertension, diabetes, family history of myocardial infarction (MI), tobacco consumption, triglycerides, HDL-cholesterol, apolipoprotein A-I and B levels. Logistic regression analyses were conducted using standardized odds ratios. The strength of the associations with CAD was rather similar in the two countries (Northern Ireland versus France) for age [1.26 (1.10-1. 45) vs. 1.41 (1.17-1.69)], family history of MI [1.50 (1.04-2.15) vs. 1.83 (0.99-3.37)], hypertension [1.49 (1.13-1.97) vs. 1.67 (1.14-2. 44)], diabetes [5.42 (2.53-11.60) vs. 2.24 (1.06-4.73)], tobacco consumption [1.43 (1.27-1.60) vs. 1.39 (1.22-1.58)], HDL-cholesterol [0.80 (0.68-0.94) vs. 0.86 (0.70-1.06)] and triglyceride levels [1. 17 (1.01-1.36) vs. 1.10 (0.91-1.32)]. Discrepancies concerned lipoprotein(a) [1.22 (1.06-1.40) vs. 0.96 (0.81-1.15), P<0.01], with stronger associations in Northern Ireland than in France.

CONCLUSION

It is concluded that the higher prevalence of CAD in Northern Ireland cannot be explained by major differences in the susceptibility to classical risk factors; the difference in risk of CAD appears mainly related in Northern Ireland to other risk factors including a worse lipid profile and genetic/environmental interactions.

Lipoprotein (a) and stroke

Strokes are one of the most common causes of mortality and long term severe disability. There is evidence that lipoprotein (a) (Lp(a)) is a predictor of many forms of vascular disease, including premature coronary artery disease. Several studies have also evaluated the association between Lp(a) and ischaemic (thrombotic) stroke. Several cross sectional (and a few prospective) studies provide contradictory findings regarding Lp(a) as a predictor of ischaemic stroke. Several factors might contribute to the existing confusion--for example, small sample sizes, different ethnic groups, the influence of oestrogens in women participating in the studies, plasma storage before Lp(a) determination, statistical errors, and selection bias. This review focuses on the Lp(a) related mechanisms that might contribute to the pathogenesis of ischaemic stroke. The association between Lp(a) and other cardiovascular risk factors is discussed. Therapeutic interventions that can lower the circulating concentrations of Lp(a) and thus possibly reduce the risk of stroke are also considered.

Physiologic concentrations of homocysteine inhibit the human plasma GSH peroxidase that reduces organic hydroperoxides

The plasma reduced glutathione (GSH) selenoperoxidase is a highly conserved enzyme. Furthermore, a small clinical study reported that patients with severe atherosclerosis had low peroxidase activities. Together these observations suggest that the peroxidase is important in preventing atherosclerosis. Yet others have reported that when the assay was run in Tris buffer, it was inactive with the concentrations of GSH found in the plasma. Second, it is known that hyperhomocysteinemia increases the rate of atherogenesis. Because there is some homology between homocysteine and the cysteine in GSH, the question is whether the hyperhomocysteinemia effect may be due to inhibition of the peroxidase. We purified the peroxidase from human plasma and determined its activity by a coupled spectrophotometric assay and a substrate disappearance chemiluminescence assay. When the peroxidase activity was determined in phosphate-buffered saline solution (PBS), there was significant activity with the reported plasma GSH concentrations (5 to 20 micromol/L). The peroxidase was exclusively in the HDL fraction. There was no correlation between the peroxidase activity and the HDL or LDL cholesterol concentrations. Finally, at physiologic concentrations of GSH (9 micromol/L), the peroxidase was inhibited by physiologic, free homocysteine concentrations (1 to 5 micromol/L). These data suggest that the peroxidase is active in vivo and may be important in protecting the endothelium from atherosclerosis by preventing oxidant injury. The homocysteine inhibition of the peroxidase suggests a possible biochemical basis for the observed association between hyperhomocysteinemia and cardiovascular disease. Our studies imply that low concentrations of this peroxidase may be an independent risk factor for atherosclerosis.

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.

Association between high homocyst(e)ine and ischemic stroke due to large- and small-artery disease but not other etiologic subtypes of ischemic stroke

BACKGROUND AND PURPOSE

Elevated plasma homocyst(e)ine may be a causal and modifiable risk factor for ischemic stroke, but the results of previous studies have been conflicting. One possible explanation is that homocyst(e)ine may only be associated with certain pathophysiological subtypes of ischemic stroke.

METHODS

We conducted a case-control study of 219 hospital cases with a first-ever ischemic stroke and 205 randomly selected community control subjects stratified by age, sex, and postal code. With the use of established criteria, cases of stroke were classified by etiologic subtype in a blinded fashion. The prevalence of conventional vascular risk factors, fasting plasma homocyst(e)ine levels, vitamin levels, and nucleotide 677 methylene tetrahydrofolate reductase (MTHFR) genotypes were determined in cases and controls.

RESULTS

Increasing homocyst(e)ine was a strong and independent risk factor for ischemic stroke (adjusted OR 2.7, 95% CI 1.4 to 5.1 for a 5-micromol/L increase in fasting plasma homocyst(e)ine from 10 to 15 micromol/L). Compared with the lowest quartile, the highest quartile of homocyst(e)ine was associated with an adjusted OR of ischemic stroke of 2.2 (95% CI 1.1 to 4.2). Mean plasma homocyst(e)ine was significantly higher in cases of ischemic stroke due to large-artery disease (14.1 micromol/L, 95% CI 12.5 to 15.9, P<0.001) and small-artery disease (12.7 micromol/L, 95% CI 11. 4 to 14.1, P=0.004) compared with control subjects (10.5 micromol/L; 95% CI 10.0 to 11.0) but not in cardioembolic or other etiologic subtypes of ischemic stroke. Compared with the lowest quartile of homocyst(e)ine, the upper 3 quartiles were associated with an adjusted OR of ischemic stroke due to large-artery disease of 3.0 (95% CI 0.8 to 10.8) for the second quartile, 5.6 (95% CI 1.6 to 20) for the third quartile, and 8.7 (95% CI 2.4 to 32) for the fourth quartile (P for trend=0.0005). However, despite a clear association between the TT MTHFR genotype and elevated fasting plasma homocyst(e)ine, there was no association between MTHFR genotype and ischemic stroke or subtype of ischemic stroke.

CONCLUSIONS

There is a strong, graded association between increasing plasma homocyst(e)ine and ischemic stroke caused by large-artery atherosclerosis and, to a much lesser extent, small-artery disease, but not cardioembolic or other etiologic subtypes of ischemic stroke. Our results are consistent with the hypothesis that the deleterious effect of high homocyst(e)ine is mediated primarily via a proatherogenic effect.

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.

Hyperhomocysteinemia increases risk of death, especially in type 2 diabetes : 5-year follow-up of the Hoorn Study

BACKGROUND

A high serum total homocysteine (tHcy) concentration is a risk factor for death, but the strength of the relation in patients with type 2 (non-insulin-dependent) diabetes mellitus compared with nondiabetic subjects is not known. A cross-sectional study suggested that the association between tHcy and cardiovascular disease is stronger in diabetic than in nondiabetic subjects. We therefore prospectively investigated the combined effect of hyperhomocysteinemia and type 2 diabetes on mortality.

METHODS AND RESULTS

Between October 1, 1989, and December 31, 1991, serum was saved from 2484 men and women, 50 to 75 years of age, who were randomly selected from the town of Hoorn, The Netherlands. Fasting serum tHcy concentration was measured in 171 subjects who died (cases; 76 of cardiovascular disease) and in a stratified random sample of 640 survivors (control subjects). Mortality risks were calculated over 5 years of follow-up by means of logistic regression. The prevalence of hyperhomocysteinemia (tHcy >14 micromol/L) was 25. 8%. After adjustment for major cardiovascular risk factors, serum albumin, and HbA(1c), the odds ratio (95% CI) for 5-year mortality was 1.56 (1.07 to 2.30) for hyperhomocysteinemia and 1.26 (1.02 to 1. 55) per 5-micromol/L increment of tHcy. The odds ratio for 5-year mortality for hyperhomocysteinemia was 1.34 (0.87 to 2.06) in nondiabetic subjects and 2.51 (1.07 to 5.91) in diabetic subjects (P=0.08 for interaction).

CONCLUSIONS

Hyperhomocysteinemia is related to 5-year mortality independent of other major risk factors and appears to be a stronger (1.9-fold) risk factor for mortality in type 2 diabetic patients than in nondiabetic subjects.

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.

Correlation between Plasma Total Homocysteine and Copper in Patients with Peripheral Vascular Disease

Background: Increased concentrations of both plasma total homocysteine and copper are separately associated with cardiovascular disease. Correlations between plasma total homocysteine, trace elements, and vitamins in patients with peripheral vascular disease have not been investigated.

Methods: The concentrations of trace elements in plasma were determined by the multielement analytical technique of total-reflection x-ray fluorescence spectrometry. Plasma total homocysteine was determined by HPLC.

Results: In the univariate and multivariate regression analyses, copper was positively correlated with plasma total homocysteine in all subjects (coefficient ± SE, 0.347 ± 0.113; P = 0.0026 and coefficient ± SE, 0.422 ± 0.108; P = 0.0002, respectively), and in patients with peripheral vascular disease (coefficient ± SE, 0.370 ± 0.150; P = 0.016; and coefficient ± SE, 0.490 ± 0.151; P = 0.0025, respectively). Correlation between copper and plasma total homocysteine was not detected in healthy control subjects. The concentration of calcium in plasma (67.5 vs 80.8 μg/g) was significantly lower in the patients than in the control subjects (P = 0.02). When the patients were divided into groups, the patients with suprainguinal lesions had significantly higher copper concentrations (P = 0.04) and significantly lower selenium and calcium concentrations (P = 0.01 and 0.008, respectively) than the healthy subjects. Patients had higher concentrations of autoantibodies against oxidized LDL and concentrations of thiobarbituric acid-reactive substance than the healthy subjects (P &lt;0.0001 and P = 0.001, respectively). The concentrations of plasma total homocysteine and α-tocopherol were significantly higher, and the concentrations of vitamin B6 and β-carotene were lower in the patients than the healthy subjects.

Conclusion: Our findings suggest that the atherogenicity of homocysteine may be related to copper-dependent interactions.

Effect of homocysteine-lowering treatment with folic acid plus vitamin B6 on progression of subclinical atherosclerosis: a randomised, placebo-controlled trial

BACKGROUND

A high plasma homocysteine concentration is associated with increased risk of atherothrombotic disease. We investigated the effects of homocysteine-lowering treatment (folic acid plus vitamin B6) on markers of subclinical atherosclerosis among healthy siblings of patients with premature atherothrombotic disease.

METHODS

We did a randomised, placebo-controlled trial among 158 healthy siblings of 167 patients with premature atherothrombotic disease. 80 were assigned placebo and 78 were assigned 5 mg folic acid and 250 mg vitamin B6 daily for 2 years. The primary endpoint was the development or progression of subclinical atherosclerosis as estimated from exercise electrocardiography, the ankle-brachial pressure index, and carotid and femoral ultrasonography.

FINDINGS

Ten participants in the treatment group, and 14 in the placebo group dropped out. Vitamin treatment, compared with placebo, was associated with a decrease in fasting homocysteine concentration (from 14.7 to 7.4 micromol/L vs from 14.7 to 12.0 micromol/L), and in postmethionine homocysteine concentration (from 64.9 to 34.9 micromol/L vs from 64.8 to 50.3 micromol/L). It was also associated with a decreased rate of abnormal exercise electrocardiography tests (odds ratio 0.40 [0.17-0.93]; p=0.035). There was no apparent effect of vitamin treatment on ankle-brachial pressure indices (0.87 [0.56-1.33]), or on carotid and peripheral-arterial outcome variables (1.02 [0.26-4.05] and 0.86 [0.47-1.59], respectively).

INTERPRETATION

Homocysteine-lowering treatment with folic acid plus vitamin B6 in healthy siblings of patients with premature atherothrombotic disease is associated with a decreased occurrence of abnormal exercise electrocardiography tests, which is consistent with a decreased risk of atherosclerotic coronary events.

Homocysteine and endothelial dysfunction: a link with cardiovascular disease

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

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.

Plasma total homocysteine levels in subjects with hyperinsulinemia

OBJECTIVES

Hyperhomocysteinemia as well as insulin resistance are considered to be risk factors for the development of coronary artery disease. This study was aimed at determining whether any relationship between plasma insulin and glucose levels and total plasma homocysteine (tHcy) concentrations exists in a population based survey performed 10 years apart.

DESIGN AND SETTING

A cross-sectional study was undertaken during the years 1986-87 to examine risk factors for diabetes and for coronary artery disease (CAD) in the Jewish population of Jerusalem. Ten years later two groups of individuals were invited for re-examination.

SUBJECTS

Two groups of individuals were examined: the first one consisted of nondiabetic subjects (n = 86), who had hyperinsulinemia 10 years previously (at the first visit), the second group consisted of normoinsulinemic nondiabetic individuals (n = 265) who had initially normal glucose and insulin levels.

MAIN OUTCOME MEASURES

Metabolic, biochemical and anthropomorphic features were determined. Fasting and post load glucose, as well as insulin concentrations on fasting and 2 h post glucose load were measured at the first and second visits. Plasma tHcy and folic acid were determined only at the second visit.

RESULTS

The results demonstrated a significant negative correlation between plasma tHcy levels and insulin levels at the second visit. No difference was found in folic acid levels between these two groups.

CONCLUSIONS

In general, hyperinsulinemia and hyperhomocysteinemia are both related to an increased incidence of CAD. In our population most of the subjects examined had tHcy levels within the normal range and only a few demonstrated very high levels. However, negative association between insulin levels and tHcy concentrations was found. Possible explanations for this finding are discussed.

The relation of plasma total homocysteine levels to prevalent cardiovascular disease in older patients with ischemic stroke

The objectives of this study were to describe the distribution of serum levels of total homocysteine (HCys) in a sample of older patients consecutively admitted following acute ischemic cerebral stroke, as compared with healthy controls, and to test for possible relationships of HCys levels to some of the prevalent cardiovascular diseases in these stroke patients. One hundred and thirty-seven stroke patients and 132 healthy controls (age > or =60) participated in this study. HCys levels were determined by HPLC method with fluorescence detection. Correlates of HCys levels and clinical data were examined. The results showed that stroke patients (mean age 74.6+/-9.2) had higher HCys levels as compared with controls (13.8 and 9.8 respectively, p<0.001). Advanced age, male gender, absence of diabetes and a positive history of previous myocardial infarction were the factors associated with HCys levels higher than 10 mmol/L (Odds ratio 2.72, 2.54, 3.12, 3.55, respectively). We conclude that hyperhomocysteinemia is prevalent in older patients with acute ischemic stroke. Few factors associated with increased risk for hyperhomocysteinemia in these stroke patients were identified. The study supports earlier observations regarding elevated HCys levels in stroke patients and increased prevalence of associated cardiovascular disease.

Homocysteine and lipoprotein(a) interact to increase CAD risk in young men and women

A biochemical link between homocysteine (tHcy) and lipoprotein(a) [Lp(a)] related to fibrin binding has been proposed. This hypothesis has not been specifically examined in human subjects. We sought to determine in a clinical setting whether these risk factors would interact to increase coronary artery disease (CAD) risk. We performed a cross-sectional analysis of 750 men and 403 women referred to a preventive cardiology clinic at the Cleveland Clinic Foundation, in whom baseline tHcy and Lp(a) data were available. Logistic regression after adjusting for standard cardiovascular risk factors was used to estimate the relative risk of CAD in patients with an Lp(a) >/=30 mg/dL and a tHcy >/=17 micromol/L. Neither isolated high tHcy (odds ratio [OR]=1.06, P=0.89) nor isolated high Lp(a) (OR=1.15, P=0.60) appeared to be associated with CAD in women. However, strong evidence of an association was seen when both risk factors were present (OR=4.83, P=0.003). Moreover, this increased risk showed evidence of an interactive effect beyond that attributable to either additive or multiplicative effects of tHcy and Lp(a) (P=0.03). In contrast, both elevated tHcy (OR=1.93, P=0. 05) and elevated Lp(a) (OR=1.87, P=0.01) showed evidence of being independent risk factors for CAD in men. The presence of both risk factors in men did not appear to confer additional risk (OR=2.00, P=0.09), even though ORs as high as 12.4 were observed within specific age intervals. Consistent with prior studies, tHcy and Lp(a) are risk factors, either independently or in concert, for CAD in this clinical population. More significantly, we found evidence that when both risk factors were present in women, the associated risk was greater than what would be expected if the 2 risks were simply acting independently. The absence of such an interactive effect in men may be due to the confounding effects of age manifested as "survivor bias." These clinical findings provide insights into the potential roles of both tHcy and Lp(a) in the pathogenesis of atherosclerosis.

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.

Methionine synthase D919G polymorphism is a significant but modest determinant of circulating homocysteine concentrations

Elevation in plasma homocysteine concentration has been associated with vascular disease and neural tube defects. Methionine synthase is a vitamin B(12)-dependent enzyme that catalyses the remethylation of homocysteine to methionine. Therefore, defects in this enzyme may result in elevated homocysteine levels. One relatively common polymorphism in the methionine synthase gene (D919G) is an A to G transition at bp 2,756, which converts an aspartic acid residue believed to be part of a helix involved in co-factor binding to a glycine. We have investigated the effect of this polymorphism on plasma homocysteine levels in a working male population (n = 607) in which we previously described the relationship of the C677T "thermolabile" methylenetetrahydrofolate reductase (MTHFR) polymorphism with homocysteine levels. We found that the methionine synthase D919G polymorphism is significantly (P = 0.03) associated with homocysteine concentration, and the DD genotype contributes to a moderate increase in homocysteine levels across the homocysteine distribution (OR = 1.58, DD genotype in the upper half of the homocysteine distribution, P = 0.006). Unlike thermolabile MTHFR, the homocysteine-elevating effects of the methionine synthase polymorphism are independent of folate and B(12) levels; however, the DD genotype has a larger homocysteine-elevating effect in individuals with low B(6) levels. This polymorphism may, therefore, make a moderate, but significant, contribution to clinical conditions that are associated with elevated homocysteine.

Plasma homocysteine levels in acute coronary syndromes

Hyperhomocysteinemia is currently regarded as an independent and modifiable risk factor for ischemic vascular diseases and thrombosis. We measured fasting plasma total homocysteine levels by HPLC with fluorescence detection in 30 patients presenting with acute coronary syndromes and 30 age and sex-matched control subjects. Demographic data, classical risk factors (systolic blood pressure, diabetes mellitus, smoking, ethanol intake, family history of ischaemic heart disease) and life-style habits were recorded. Lipid fractions including total cholesterol, triglycerides, HDL-cholesterol, total cholesterol/HDL-cholesterol ratio, serum creatinine, LDL-cholesterol and vitamins involved in the metabolism of homocysteine, folic acid and vitamin B12 were also assessed. Total fasting homocysteine concentrations were significantly higher in the patient group (12.2 +/- 1.01 micromol/l) than in the control subjects (7.05 +/- 0.36 micromol/l; p < 0.0001). Homocysteine correlated positively with age (r = 0.617; p < 0.01) and serum creatinine (r = 0.457; p < 0.01) in the patient group. Hyperhomocysteinemia was not associated with vitamin B12 or folate deficiency states. Vitamin B12 concentration was 273 +/- 16.4 ng/l in the control group and 284.3 +/- 32.2 ng/l in the patient group (p = NS). Serum folate concentration also was not significantly different between controls and patients; 7.57 +/- 0.58 microg/l and 8.05 +/- 0.72 microg/l, respectively. Since no significant difference was observed in the lipid parameters between patients and controls, the hyperhomocysteinemia in the patient group supports the view that homocysteine is an independent risk factor for cardiovascular diseases. Our results strongly suggest that elevated homocysteine levels are among the interacting factors in the complex, multifactorial pathophysiology of ischemic heart disease.

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.

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.

International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Standardization Project for the Measurement of Lipoprotein(a). Phase 2: selection and properties of a proposed secondary reference material for lipoprotein(a)

The International Federation of Clinical Chemistry and Laboratory Medicine Working Group for the Standardization of Lipoprotein(a) Assays has initiated a project to select a secondary reference material for lipoprotein(a) that can standardize the measurement of this lipoprotein. Most of the analytical problems with lipoprotein(a) assays are due to apolipoprotein(a) kringle 4 type 2 reactive antibodies and values being expressed in mg/l mass units rather than as nmol/l of apolipoprotein(a) particles. In Phase 2, four manufactured materials were compared for analytical performance, commutability properties and method harmonization in 27 lipoprotein(a) test systems. Results of precision and linearity testing were comparable for all materials whereas testing for the harmonization effect resulted in an among-assay coefficient of variation for corrected lipoprotein(a) values of between 11% and 22%. The material that gave maximum harmonization achieved a variation of < 8% for 18 immunonephelometric and immunoturbidimetric assay systems. It can be hypothesized that this residual variation in part takes into account the inaccuracy of lipoprotein(a) measurement due to apolipoprotein(a) size polymorphism. On the basis of acceptable analytical performance, maximal harmonization effect and documented stability, a lyophilized material has been selected as the common calibrator for lipoprotein(a) to be used in a value transfer procedure by diagnostic companies.

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.

Serum total homocysteine and coronary heart disease: prospective study in middle aged men

OBJECTIVES

To examine the prospective relation between total homocysteine and major coronary heart disease events.

DESIGN

A nested case-control study carried out within the British regional heart study, a prospective investigation of cardiovascular disease in men aged 40-59 years at entry. Serum total homocysteine concentrations were analysed retrospectively and blindly in baseline samples from 386 cases who had a myocardial infarct during 12.8 years of follow up and from 454 controls, frequency matched by age and town.

RESULTS

Geometric mean serum total homocysteine was slightly higher in cases (14.2 micromol/l) than in controls (13.5 micromol/l), a proportional difference of 5.5% (95% confidence interval (CI) -0.02% to 10.8%, p = 0.06). Age adjusted risk of myocardial infarction increased weakly with log total homocysteine concentration; a 1 SD increase in log total homocysteine (equivalent to a 47% increase in total homo cysteine) was associated with an increase in odds of myocardial infarction of 1.15 (95% CI 1.00 to 1. 32; p = 0.05). The relation was particularly marked in the top fifth of the total homocysteine distribution (values >16.5 micromol/l), which had an odds ratio of 1.77 (95% CI 1.28 to 2.42) compared with lower levels. Adjustment for other risk factors had little effect on these findings. Total homocysteine concentrations more than 16.5 micromol/l accounted for 13% of the attributable risk of myocardial infarction in this study population. Serum total homocysteine among control subjects varied between towns and was correlated with town standardised mortality ratios for coronary heart disease (r = 0.43, p = 0.08).

CONCLUSIONS

Serum total homocysteine is prospectively related to increased coronary risk and may also be related to geographical variation in coronary risk within Britain. These results strengthen the case for trials of total homocysteine reduction with folate.

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.

Potential new cardiovascular risk factors: left ventricular hypertrophy, homocysteine, lipoprotein(a), triglycerides, oxidative stress, and fibrinogen

The 1996 Bethesda Conference acknowledged left ventricular hypertrophy, hyperhomocysteinemia, lipoprotein(a) excess, hypertriglyceridemia, oxidative stress, and hyperfibrinogenemia as possible new cardiac risk factors. This review summarizes the current literature that supports these conditions as cardiac risk factors. Left ventricular hypertrophy is an independent risk factor for vascular disease. Improvement or progression of left ventricular hypertrophy influences subsequent cardiovascular complications. Clinical trials are under way to assess the potential benefit of decreasing homocysteine levels. The role of lipoprotein(a) excess in vascular disease is controversial. The atherogenic potential of lipoprotein(a) seems to be neutralized by effective reduction of low-density lipoprotein cholesterol levels. Increasing evidence supports an independent role of hypertriglyceridemia in cardiovascular disease and a possible clinical benefit from decreasing triglyceride levels. Among antioxidant micronutrients, supplementation with vitamin E has been shown to be beneficial in primary and secondary prevention studies. Data supporting the use of other antioxidants are much weaker. Preliminary evidence suggests that reducing fibrinogen levels in patients with high baseline levels and coronary disease may be beneficial. Despite the potential relation between new risk factors and cardiovascular disease, routine clinical application of these conditions as cardiovascular risk factors would be premature. Evidence is needed that these conditions extend prognostic ability beyond conventional risk factors and that modification of these conditions can reduce the risk for cardiovascular events.

Nonfasting plasma total homocysteine levels and stroke incidence in elderly persons: the Framingham Study

BACKGROUND

Total homocysteine levels are associated with arteriosclerotic outcomes.

OBJECTIVE

To determine whether total homocysteine levels predict incident stroke in elderly persons.

DESIGN

Prospective population-based cohort study with 9.9 years of follow-up.

SETTING

Framingham, Massachusetts.

PATIENTS

1947 Framingham Study participants (1158 women and 789 men; mean age +/- SD, 70 +/- 7 years).

MEASUREMENTS

Baseline total homocysteine levels and 9.9-year stroke incidence.

RESULTS

The quartiles of nonfasting total homocysteine levels were as follows: quartile 1, 4.13 to 9.25 micromol/L; quartile 2, 9.26 to 11.43 micromol/L; quartile 3, 11.44 to 14.23 micromol/L; quartile 4, 14.24 to 219.84 micromol/L. During follow-up, 165 incident strokes occurred. In proportional hazards models adjusted for age, sex, systolic blood pressure, diabetes, smoking, and history of atrial fibrillation and coronary heart disease, relative risk (RR) estimates comparing quartile 1 with the other three quartiles were as follows: quartile 2 compared with quartile 1--RR, 1.32 (95% CI, 0.81 to 2.14); quartile 3 compared with quartile 1--RR, 1.44 (CI, 0.89 to 2.34); quartile 4 compared with quartile 1--RR, 1.82 (CI, 1.14 to 2.91). The linear trend across the quartiles was significant (P < 0.001).

CONCLUSION

Nonfasting total homocysteine levels are an independent risk factor for incident stroke in elderly persons.

Homocyst(e)ine and cardiovascular disease: a critical review of the epidemiologic evidence

PURPOSE

To review epidemiologic studies on the association between homocyst(e)ine level and risk for cardiovascular disease and the potential benefits of homocysteine-decreasing therapies.

DATA SOURCES

Computerized and manual searches of the literature on total homocysteine levels and cardiovascular disease.

STUDY SELECTION

Prospective studies and major retrospective epidemiologic studies evaluating the association between homocyst(e)ine levels and cardiovascular disease and the association between blood levels or dietary intake of folate, vitamin B6, and vitamin B12 and cardiovascular disease.

DATA EXTRACTION

Relevant data on patient population, plasma homocyst(e)ine levels, duration of follow-up, and main results were extracted from studies that met the inclusion criteria.

DATA SYNTHESIS

The designs and results of studies included in this review are summarized. A formal meta-analysis was not performed because the studies were heterogeneous in method and design.

CONCLUSIONS

Results of epidemiologic studies suggest that moderately elevated plasma or serum homocyst(e)ine levels are prevalent in the general population and are associated with an increased risk for cardiovascular disease, independent of classic cardiovascular risk factors. Simple, inexpensive, nontoxic therapy with folic acid, vitamin B6, and vitamin B12 reduces plasma homocyst(e)ine levels. Although the association between homocyst(e)ine levels and cardiovascular disease is generally strong and biologically plausible, the data from the prospective studies are less consistent. In addition, epidemiologic observations of an association between hyperhomocyst(e)inemia and cardiovascular risk do not prove the existence of a causal relation. Therefore, the effectiveness of folate, vitamin B6, and vitamin B12 in reducing cardiovascular morbidity and mortality requires rigorous testing in randomized clinical trials. Several such trials are under way; their results may greatly affect cardiovascular morbidity and mortality, given the simplicity and low cost of vitamin therapy.

Cysteine is a cardiovascular risk factor in hyperlipidemic patients

Several studies have reported that moderate hyperhomocysteinemia is related to an increased risk for atherosclerosis, but few data are available with regard to any other thiol compound having a potential vascular toxicity. Therefore, we measured both total cysteine and homocysteine plasma levels in patients with hyperlipidemia (242 males and 147 females, 41-65 years old). Homocysteine was higher in males than in females, 13.2+/-4.1 versus 11.1+/-3.4 micromol/l (P<0.0001). The mean cysteine level was 243.3+/-45.7 micromol/l in the whole study population. The subjects were split in two groups, symptomatic patients with cardiovascular disease (n = 106) and asymptomatic subjects (n = 283). Blood pressure, smoking status, total cholesterol, LDL-cholesterol and triglycerides did not statistically differ between groups, but the mean HDL-cholesterol level was lower in symptomatic patients (1.24+/-0.38 versus 1.42+/-0.41, P<0.0001). Cysteine levels were higher in patients with cardiovascular disease than in asymptomatic patients, respectively 254.7+/-47.7 versus 239.1+/-44.3 micromol/l (P = 0.003). A similar result was found for homocysteine, respectively 13.1+/-4.3 versus 12.2+/-3.9 micromol/l (P = 0.05). To analyse whether cysteine levels were related to atherosclerosis independently of age, adjusted levels were compared between asymptomatic patients with normal carotid arteries (n = 176), carotid atherosclerosis (n = 107) and symptomatic patients (n = 106). Age adjusted cysteine levels differed significantly between groups (P = 0.027) while the P-value was of borderline significance for homocysteine (P = 0.09). Odds ratios for having symptomatic cardiovascular disease were 1.81 (95% CI, 1.02-3.21) and 2.05 (95% CI, 1.16-3.60) for the mid and highest tertiles of cysteine using the lowest as the reference. After adjustment in a multivariate model including age, sex, and creatinine, the odds ratio for disease remained significant between the highest tertile versus the lowest (OR = 1.89). Adjusted odds ratios were found to be weaker when homocysteine tertiles were compared. Our data suggest that plasma total cysteine is a risk factor for atherosclerosis in hyperlipidemic patients.

Total homocysteine is associated with nephropathy in non-insulin-dependent diabetes mellitus

Non-insulin-dependent diabetes mellitus (NIDDM) and hyperhomocysteinemia are both associated with premature vascular disease. We tested the hypothesis that homocysteine is associated with vascular disease and other diabetic complications in patients with NIDDM. The current investigation is a cross-sectional analysis of baseline variables for participants in the Appropriate Blood Pressure Control in Diabetes (ABCD) Trial. Men and women aged 40 to 74 years with NIDDM and a mean diastolic blood pressure (BP) of 80 mm Hg or higher were eligible. We measured serum levels of total homocysteine (tHcy), cystathionine, and methylmalonic acid (MMA) and correlated these values with clinical and other laboratory measures of the complications of diabetes mellitus in 452 subjects. tHcy was higher in males than in females and correlated with the duration of hypertension and systolic BP. tHcy was significantly correlated with MMA (r = .35, P < .0001) and cystathionine (r = .53, P < .0001) levels and inversely correlated with serum B12 (r = -.23, P < .0001) and folate (r = -.18, P < .0001). It was significantly correlated with serum creatinine (r = .28, P < .0001 for males and r = .39, P < .0001 for females) and inversely correlated with creatinine clearance (r = -.19, P < .005 for males and r = -.30, P < .0001 for females). tHcy was not increased in subjects with cardiovascular disease or retinopathy, but it was increased in those with neuropathy (10.3 v 9.3 micromol/L, P < .05) and macroalbuminuria (11.0 v 9.2 micromol/L, P < .005). Of these subjects, 2.2% met the criteria for vitamin B12 deficiency and 1% met the criteria for folate deficiency. We conclude that elevations of tHcy in this population appear to be the result of a combination of vitamin deficiency and decreased renal function and do not appear to be a predictor of cardiovascular disease.

Hyperhomocysteinaemia

Homocysteine is a sulphur-containing amino acid that is derived primarily from protein of animal origin. Classical homocystinuria is an inherited metabolic disorder that arises from defects in either the re-methylation or trans-sulphuration pathways of homocysteine metabolism and leads to skeletal abnormalities, mental retardation and a high risk of vascular disease. In contrast, moderate hyperhomocysteinaemia is associated with an increased risk of both arterial and venous thrombotic disease but no other abnormalities. This increased risk appears to be independent of other conventional risk factors. Many cases of hyperhomocysteineaemia have been attributed to defects in the enzyme cystathionine-beta-synthase (CBS) but this accounts for less than 1.5% of cases. A thermolabile variant of the enzyme methylenetetrahydrofolate reductase (MTHFR) arises from a C --> T transition at nucleotide 677 in the MTHFR gene resulting in an alanine-to-valine substitution. While the mutation does not appear to be associated with an increased risk of vascular disease, it results in excessively high homocysteine levels in response to a low or low-normal serum folate. Supplementation of the diet with folate, B6 and B12 can reduce homocysteine levels and this is the mainstay of treatment. Supplementation of grain with folate is undertaken in the USA to reduce the risk of neural tube defects in pregnant women. However, by reducing plasma homocysteine levels, it is estimated that this will save up to 50,000 lives per annum.

Homocysteine: cholesterol of the 90s?

Homocysteine is a sulfur-containing amino acid generated through the demethylation of methionine. It is largely catabolized by trans-sulfuration to cysteine but it may also be remethylated to methionine. Dubbed 'the cholesterol of the 90s' by the lay press, homocysteine is thought to be thrombophilic and to damage the vascular endothelium. Total plasma homocysteine (tHcy) is now established as a clinical risk factor for coronary artery disease, as well as other arterial and venous occlusive disease in adult populations. Regulation of homocysteine is dependent on nutrient intake, especially folate, vitamins B6 and B12. It is also controlled by common genetic variations (polymorphisms) in how vitamins are utilized as cofactors in the reactions controlling homocysteine metabolism. Moreover, concentrations are age- and sex-dependent and are altered by renal function, hormonal status, drug intake and a variety of other common clinical factors. Considerable care must be taken in assaying tHcy. Plasma should be separated shortly after collection, to avoid artifactual increases due to synthesis by blood cells in vitro. Reference methods have not been validated and criteria for establishing reference ranges should take into account the variable prevalence of physiological hyperhomocysteinemia. Determination of tHcy should probably be limited to centres with relevant expertise and ability to maintain the high degree of precision required for reliable interpretation. Molecular testing for the genetic polymorphisms is still in the research phase but the ease and reliability of molecular diagnosis will speed its introduction into clinical laboratory practice--particularly in relation to diagnosis of thrombophilic disorders. Clinical research initiatives are being driven by the benefit that should be achieved by correction with vitamin supplements, particularly folate and B vitamins, but it must be recognized that prospective controlled studies to validate clinical benefit are only now being initiated. At the moment, it is safe to say that hyperhomocysteinemia is one of the few prevalent biochemical risk factors for thromboembolic disease that might be corrected by vitamin supplements. Such a possibility lies behind the growing momentum to recommend increased supplements of folate and B vitamins to at-risk population and patient groups today.

Homocysteine

Homocysteine is a sulfur-containing amino acid generated through the demethylation of methionine. It is largely catabolized by trans-sulfuration to cysteine, but it may also be remethylated to methionine. Regulation of homocysteine is dependent on nutrient intake, especially folate, vitamins B6 and B12. It is also controlled by individual genetic differences in how vitamins are utilized as cofactors in the reactions controlling homocysteine metabolism. In excess quantities, homocysteine is thought to be thrombophilic and to damage the vascular endothelium. Total plasma homocysteine (tHcy) is now established as a clinical risk factor for coronary artery disease, as well as other arterial and venous occlusive disease in adult populations. These effects are probably related to its role as a teratogen in the pathogenesis of neural tube defects--genetic variants causing hyperhomocysteinemia are associated with both neural tube defects in susceptible pregnancies and with risks for vaso-occlusive disease in later years. Considerable care must be taken in assaying tHcy. Plasma should be separated shortly after collection to avoid artifactual increases due to synthesis by blood cells in vitro. tHcy concentrations must be interpreted in light of the fact that serum albumin, urate, creatinine, and vitamin concentrations may be important analytical covariates. Moreover, concentrations are age- and sex-dependent and are altered by renal function, hormonal status, drug intake, and a variety of other common clinical factors. Why then is homocysteine now of such great clinical and scientific interest? If the homocysteine moiety itself is important in the pathogenesis of vaso-occlusive disease, then simple treatment of hyperhomocysteinemia with vitamins should lead to a significant reduction in disease risk. Such a possibility lies behind the growing momentum to recommend increased supplements of folate and B vitamins to at-risk populations and patient groups today.

Homocyst(e)ine and risk of cerebral infarction in a biracial population : the stroke prevention in young women study

BACKGROUND AND PURPOSE

Genetic enzyme variation and vitamin intake are important determinants of blood homocyst(e)ine levels. The prevalence of common genetic polymorphisms influencing homocyst(e)ine levels varies by race, and vitamin intake varies by socioeconomic status. Therefore, we examined the effect of vitamin intake, race, and socioeconomic status on the association of homocyst(e)ine with stroke risk.

METHODS

All 59 hospitals in the greater Baltimore-Washington area participated in a population-based case-control study of stroke in young women. One hundred sixty-seven cases of first ischemic stroke among women aged 15 to 44 years were compared with 328 controls identified by random-digit dialing from the same region. Risk factor data were collected by standardized interview and nonfasting phlebotomy. Plasma homocyst(e)ine was measured by high-performance liquid chromatography and electrochemical detection.

RESULTS

Blacks and whites did not differ in median homocyst(e)ine levels, nor did race modify the association between homocyst(e)ine and stroke. After adjustment for cigarettes per day, poverty status, and regular vitamin use, a plasma homocyst(e)ine level of >/=7.3 micromol/L was associated with an odds ratio for stroke of 1.6 (95% CI, 1.1 to 2.5).

CONCLUSIONS

The association between elevated homocyst(e)ine and stroke was independent not only of traditional vascular risk factors but also of vitamin use and poverty status. The degree of homocyst(e)ine elevation associated with an increased stroke risk in young women is lower than that previously reported for middle-aged men and the elderly and was highly prevalent, being present in one third of the control group.

Homocysteine and vascular disease

For more than 20 years, moderately raised concentrations of total homocysteine (tHcy) have been associated with an increased risk of atherothrombotic vascular events but only recently has evidence mounted to suggest that the association may be causal. The association is independent of other factors, it is fairly consistent across many studies, it is strong and dose-related, and it is biologically plausible. However, the evidence needs to be strengthened by a systematic review of all comparable studies and the demonstration, in randomised trials, that lowering tHcy is followed by a significant reduction in atherothrombotic vascular disease. In addition, the measurement of tHcy needs to be standardised. If these can be achieved then tHcy measurement will become another useful marker of vascular risk, multivitamin therapy will be another therapeutic option for people at risk of atherothrombotic vascular disease, and fortification of food with folic acid will rise high on the political and public health agenda.

Lipoprotein(a)-Cholesterol and Coronary Heart Disease in the Framingham Heart Study

Background: Increased plasma lipoprotein(a) [Lp(a)] concentrations have been reported to be an independent risk factor for coronary heart disease (CHD) in some prospective studies, but not in others. These inconsistencies may relate to a lack of standardization and the failure of some immunoassays to measure all apolipoprotein(a) isoforms equally.

Methods: We measured plasma Lp(a)-cholesterol [Lp(a)-C] in a Caucasian population of offspring and spouses of the Framingham Heart Study participants, using a lectin-based assay (LipoproTM). We compared the prevalence of increased Lp(a)-C to the presence of sinking pre-β-lipoprotein (SPB). We also related Lp(a)-C concentrations to the prevalence of CHD risk in the entire population.

Results: The mean (± SD) Lp(a)-C concentration in the Framingham population (n = 3121) was 0.186 ± 0.160 mmol/L, with no significant gender or age differences. The mean Lp(a)-C concentrations in the absence or presence of SPB were 0.158 ± 0.132 mmol/L and 0.453 ± 0.220 mmol/L, respectively (P &lt;0.0001). The mean Lp(a)-C concentration in men with CHD (n = 156) was 0.241 ± 0.204 mmol/L, which was significantly (P &lt;0.001) higher, by 34%, than in controls. The odds ratio for CHD risk in men with Lp(a)-C ≥0.259 mmol/L (≥10 mg/dL), after adjusting for age, HDL-cholesterol, LDL-cholesterol, smoking, diabetes, blood pressure, and body mass index, was 2.293 (confidence interval, 1.55–3.94; P &lt;0.0005). Lp(a)-C values correlated highly with a Lp(a)-mass immunoassay [ApotekTM Lp(a); r = 0.832; P &lt;0.0001; n = 1000].

Conclusions: An increased Lp(a)-C value ≥0.259 mmol/L (≥10 mg/dL) is an independent CHD risk factor in men with a relative risk of more than 2, but was inconclusive in women. Lp(a)-C measurements offer an alternative to Lp(a)-mass immunoassays and can be performed on automated analyzers.

Homocysteine as a novel risk factor for atherosclerosis

Homocysteine is a sulfhydryl amino acid formed during metabolism of methionine. Increasing evidence suggests that homocyst(e)ine may act as an independent risk factor for ischemic heart disease, cerebrovascular disease, and peripheral arterial disease. Recent prospective data have shown that homocyst(e)ine levels in the top 20% of the population increase the risk for ischemic heart disease by approximately twofold. Homocyst(e)ine seems to promote the progression of atherosclerosis by causing endothelial dysfunction, increasing oxidant stress, and promoting vascular smooth muscle growth. Recent human studies using methionine loading to experimentally induce moderate hyperhomocyst(e)inemia have demonstrated rapid and profound impairment of resistance and conduit artery endothelial function. No data are available from randomized, controlled trials of the effects of lowering plasma homocyst(e)ine on atherosclerotic vascular events; however, screening for hyperhomocyst(e)inemia should be actively considered in individuals with progressive and unexplained atherosclerosis. Both fasting and postmethionine load homocyst(e)ine levels should be measured. B vitamins, including folic acid and vitamins B6 and B12 are the mainstay of treatment of patients with hyperhomocyst(e)inemia. Primary prevention strategies await the completion of long-term, randomized, prospective studies.

Sequence polymorphisms in the apolipoprotein(a) gene and their association with lipoprotein(a) levels and myocardial infarction. The ECTIM Study

Lp(a) concentrations are largely determined by apo(a) isoform size, but several studies have shown that apo(a) isoforms could not entirely explain the increase of Lp(a) levels observed in patients with coronary heart disease (CHD). Since up to 90% of the variance in Lp(a) levels has been suggested to be attributable to the apo(a) locus, the hypothesis that polymorphisms of the apo(a) gene other than size could contribute to the increase of Lp(a) levels in CHD patients must be considered. This hypothesis was tested in the ECTIM Study comparing 594 patients with myocardial infarction and 682 control subjects in Northern Ireland and France. In addition to apo(a) phenotyping, five previously described polymorphisms of the apo(a) gene were genotyped: a (TTTTA)n repeat at position -1400 from the ATG, a G/A at -914, a C/T at -49, a G/A at -21 and a Met/Thr affecting amino acid 4168. As reported earlier [Parra HJ, Evans AE, Cambou JP, Amouyel P, Bingham A, McMaster D, Schaffer P, Douste-Blazy P, Luc G, Richard JL, Ducimetiere P, Fruchart JC, Cambien F. A case-control study of lipoprotein particles in two populations at contrasting risk for coronary heart disease. The ECTIM study. Arterioscler Thromb 1992; 12:701-707], mean Lp(a) levels were higher in cases than in controls (20.7 vs 14.6 mg/dl in Belfast, 17.2 vs 8.9 mg/dl in France, P < 0.001 for case-control and population differences). In the present study, mean apo(a) isoform size differed significantly between cases and controls (25.7 vs 26.6 kr in Belfast, 25.9 vs 27.4 kr in France, P < 0.001 for case-control and P = 0.13 for population difference). After adjustment for apo(a) isoforms, Lp(a) levels remained significantly higher in cases than in controls (difference, 4.6 mg/dl; P < 0.001). Genotype and allele frequencies did not differ significantly between cases and controls for any of the five polymorphisms studied. The five polymorphisms were in strong linkage disequilibrium and had a combined heterozygosity of 0.83. In multivariate regression analysis adjusted for apo(a) isoforms, only the (TTTTA)n polymorphism was significantly associated with Lp(a) levels; it explained 4.5% of Lp(a) variability in cases and 3.1% in controls. The Lp(a) case/control difference was not reduced after taking into account the (TTTTA)n effect. We conclude that the increase of Lp(a) levels observed in MI cases, and which was not directly attributable to apo(a) size variation, was not related to the five polymorphisms of the apo(a) gene considered.

Hyperhomocysteinemia and hypofibrinolysis in young adults with ischemic stroke

BACKGROUND AND PURPOSE

Data from epidemiological and case-control studies suggest that increased total homocysteine (tHcy) levels are associated with increased risk for thromboembolic disease. The mechanisms by which hyperhomocysteinemia contributes to thrombogenesis are incompletely understood. The main objectives of this study of young ischemic stroke patients were (1) to examine fasting and post-methionine load levels of tHcy, (2) to ascertain the genotype frequency of the C677CT mutation in the methylenetetrahydrofolate reductase gene (TT genotype), and (3) to study the possible interaction between plasma tHcy levels and fibrinolytic factors.

METHODS

This case-control study was based on 80 consecutive patients aged 18 to 44 years admitted between January 1992 and May 1996 as a result of a first-ever ischemic stroke. Forty-one healthy control subjects were recruited. Measurement of fasting tHcy and post-methionine load levels and evaluation of the fibrinolytic system were undertaken at least 3 months (mean, 5.1+/-1. 9 months) after admission. Genotyping of the methylenetetrahydrofolate reductase gene was performed.

RESULTS

Although the increase after methionine loading (ie, postload tHcy minus fasting-level tHcy) was significantly higher among patients, there was no difference in fasting and postload tHcy levels. After adjustment for conventional risk factors, elevated postload increase tHcy levels were associated with a 4.8-fold increased risk of ischemic stroke. There was no difference between patients and control subjects in either TT genotype frequency or T allele frequency. Abnormal response to methionine loading was associated with higher tissue plasminogen activator (tPA) mass concentration, higher plasminogen activator inhibitor-1 levels, and lower tPA activity. After adjustment for age, sex, body mass index, serum cholesterol, and triglycerides, an abnormal increase in postload tHcy levels remained significantly associated with tPA mass concentration levels (P=0.03).

CONCLUSIONS

A moderately elevated increase in tHcy levels after methionine loading was associated with an increased risk for ischemic stroke in young adults. In contrast, fasting tHcy levels did not differ between patients and controls. A moderately elevated increase in tHcy after methionine loading may provide a additional thrombogenic risk mediated in part by interactions with the fibrinolytic system. In young stroke patients, a methionine loading test to detect hyperhomocysteinemia should always be considered in the convalescent phase of the disease.

Plasma homocysteine distribution and its association with parental history of coronary artery disease in black and white children: the Bogalusa Heart Study

BACKGROUND

Elevated homocysteine is associated with increased risk for coronary artery disease (CAD) in adults, but its distribution in children is not well documented. We examined the distribution of homocysteine in children and its relation to parental history of CAD.

METHODS AND RESULTS

A subsample of 1137 children (53% white, 47% black) aged 5 to 17 years in 1992 to 1994 examined in the Bogalusa Heart Study (n=3135), including all with a positive parental history of CAD (n=154), had plasma homocysteine levels measured. Homocysteine correlated positively with age (r=0.16, P=0.001). No race or sex differences in homocysteine levels were observed; geometric mean (GM) levels were 5.8 micromol/L (95% CI, 5.6 to 6.1) among white males, 5.8 micromol/L (95% CI, 5.5 to 6.0) among white females, 5.6 micromol/L (95% CI, 5.4 to 5.8) among black males, and 5.6 micromol/L (95% CI, 5.4 to 5.9) among black females. Children with a positive parental history of CAD had a significantly greater age-adjusted GM homocysteine level (GM, 6.7 micromol/L; 95% CI, 6.4 to 7.1) than those without a positive history (GM, 5.6 micromol/L; 95% CI, 5.4 to 5.7); this relation was observed in each race-sex group.

CONCLUSIONS

Higher homocysteine levels were observed among children with a positive family history of CAD. Additional studies should elucidate the contribution of genetic, dietary, and other factors to homocysteine levels in children.

Homocyst(e)ine and heart disease: pathophysiology of extracellular matrix

Occlusive coronary artery disease is an important factor of cardiovascular morbidity and mortality. The rupture of the thin fibrous cap of the atheroma may be one of the causes of acute coronary syndrome, however, the mechanism of formation of fibrous plaque are poorly understood. Elevation of plasma homocysteine, hyperhomocystinemia, H(e), has emerged as an independent risk factor for hypertension and fibrotic heart disease. The extracellular matrix (ECM) components, particularly fibrillar collagen, are elevated in the atherosclerotic lesions and are the essential integral element in holding the oxidized low density lipoproteins (LDL), homocystine, macrophage and foam cells in milieu, constituting the primary atherosclerotic and secondary restenotic lesions. In vivo and in vitro physiological, morphological, cellular, biochemical and molecular experiments have suggested the role of tissue homocystine in cardiovascular fibrosis and adverse ECM remodeling following H(e). The tissue homocystine induces cardiovascular fibrosis and may lead to heart failure via the redox-receptor pathway. The underlying cause and mechanism of cardiovascular fibrosis associated with arteriosclerosis, atherosclerosis, hypertension and coronary heart disease, involve changes in the levels of tissue redox state.

Effect of Lp(a) on the early functional and structural changes of atherosclerosis

Epidemiologic studies have shown a significant relationship between elevated plasma levels of Lp(a) and increased risk of cardiovascular events; however, the mechanisms by which elevated Lp(a) levels produce this increased risk are not known. To test the hypothesis that high Lp(a) levels might contribute to the development of subclinical atherosclerosis, we examined the influence of Lp(a) levels on early functional and structural atherosclerotic vascular changes. Flow-mediated (endothelium-dependent) and nitrate-mediated (smooth muscle-dependent) arterial dilations were measured by high-resolution ultrasound in 241 normal healthy subjects (aged 15 to 69 years; 116 men). In addition, carotid artery intima-media thickness was measured by ultrasound in 71 subjects. Plasma Lp(a) was measured using a 2-sided immunoradiometric assay (cohort median, 10 mg/dL; interquartile range, 3.9 to 24.4 mg/dL). In these subjects, there were no significant relationships between Lp(a) and arterial endothelial function, smooth muscle responses, or carotid wall thickness (P>0.25). By contrast, other lipid risk factors, such as LDL-cholesterol and LDL-cholesterol/HDL-cholesterol ratio, were significantly correlated with abnormal arterial function and structure (P</=0.01). These data suggest that elevated Lp(a) levels do not confer cardiovascular risk by contributing to the early functional or structural changes of atherosclerosis.