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

Apolipoprotein(a) isoforms and coronary heart disease in men: a nested case-control study

The objective of the present study was to examine the possible associations between low molecular weight (LMW) apolipoprotein(a) (apo(a)) isoforms (F,B,S1,S2) and coronary heart disease (CHD). We conducted a nested case-control (prospective) study of five cohorts of white men: The 1936 cohort (baseline 1976, n = 548) and four cohorts from MONICA I born in 1923 (n = 463), 1933 (n = 491), 1943 (n = 504) and 1953 (n = 448) studied at baseline in 1983. At follow up in 1991, 52 subjects had developed a first myocardial infarction and 22 had been hospitalized with angina pectoris. Plasma samples obtained at baseline were stored frozen until 1993-94, when case samples (n = 74) were analyzed together with samples from matched (disease free) controls (n = 190). In a statistical model (conditional logistic regression) including all age groups, cholesterol (or apo B) level (P < 0.01), systolic blood pressure (P = 0.05) and smoking (P = 0.02) predicted CHD. In the statistical model Lp(a) interacted significantly with age (OR = 5.7; 95% CI: 1.4-23.6; P = 0.016), and high Lp(a) (over 45 mg/dl) was associated with significantly increased risk in subjects under 60 years (OR = 3.82; 95% CI: 1.47-9.96), but not in older men (OR = 0.67; 95% CI: 0.235-1.89). Therefore, we studied the impact of Lp(a)/apo(a) and other variables in subjects who had been under 60 years when they became cases. Among the younger subjects the presence of LMW apo(a) isoforms significantly predicted the development of CHD (OR = 3.83; 95% CI: 1.18-12.4). The increased risk pertained to high Lp(a) (above versus below 45 mg/dl: OR = 3.68; 95% CI: 1.03-13.10), and to Lp(a) concentrations when entered into the model as a continuous variable (P = 0.04). Cholesterol or apo B (P < 0.01), smoking (P = 0.02), systolic blood pressure (P = 0.05) and low alcohol consumption (under nine drinks/week) (P = 0.04) were also significant predictors of CHD. We conclude that LMW apo(a) isoforms are significantly associated with increased risk of CHD in men under 60 years.

Relationship between lipoprotein (a) and both stroke and carotid atheroma

In vitro studies provide mechanisms by which elevated lipoprotein (a) [Lp(a)] concentrations may promote both thrombosis and atherogenesis. Case-control studies have reported raised Lp(a) concentrations in patients with stroke, but prospective studies have failed to confirm the association. A potential confounding factor is that Lp(a) may rise acutely after stroke. We determined Lp(a) concentrations in 164 patients studied at least 21 days after stroke or transient ischaemic attack, and in 91 controls. In the patient group we correlated Lp(a) concentrations with both the degree of carotid stenosis estimated on duplex ultrasonography, and with stroke subtype (large vessel disease, lacunar infarction, and cardioembolic and unknown pathogenesis). There was no difference between Lp(a) concentration in cases and controls [median (quartiles) 0.10 (0.04, 0.39) versus 0.12 (0.04, 0.30) g/L, P = 0.34]. There was no difference in the proportion of cases compared with controls with a markedly elevated Lp(a) of > 0.4 g/L (21.3 versus 16.5%, P = 0.34). There was non-significant trend towards higher median Lp(a) concentrations in women [median (quartiles) 0.16 (0.04, 0.32) g/L versus 0.12 (0.04, 0.28) g/L, P = 0.3]. In view of this trend we analysed the differences between cases and controls for each sex separately. Lp(a) concentrations in men were median (quartiles) 0.08 (0.04, 0.26) g/L in the 101 cases and 0.12 (0.04, 0.28) g/L in the 43 controls (P = 0.6). Lp(a) concentrations in women were median (quartiles) 0.25 (0.04, 0.44) g/L in the 63 cases, and 0.16 (0.04, 0.32) g/L in the 48 controls (P = 0.16). Within the patient group there was no difference between Lp(a) concentrations in the different stroke subgroups. There was no relationship between Lp(a) concentrations and mean percentage carotid stenosis (rs = 0.14, P = 0.07). Our results suggest that in an unselected population of men studied more than 3 weeks post event there is no relationship between lipoprotein(a) concentrations and either stroke/transient ischaemic attack, or carotid atheroma. The relationship in women requires further study.

Plasma total homocysteine, B vitamins, and risk of coronary atherosclerosis

Epidemiological research has shown that elevated plasma total homocysteine (tHcy) is a risk factor for atherosclerotic disease. In the present case-control study, we investigated whether fasting or postmethionine-loading tHcy was a stronger predictor of risk of severe coronary atherosclerosis. Furthermore, we studied levels of B vitamins, which are involved in homocysteine metabolism. Subjects were recruited from men and women, aged 25 to 65 years, who underwent coronary angiography between June 1992 and June 1994 in a hospital in Rotterdam, The Netherlands. Cases (n=131) were defined as those with > or =90% occlusion in one and > or =40% occlusion in a second coronary artery, while control subjects (n=88) had <50% occlusion in only one coronary vessel. In addition, a population-based control group free from clinical cardiovascular disease (n=101) was studied. Coronary patients were studied at least 2.5 months after angiography or other acute illness, such as myocardial infarction. After adjusting for age and sex differences between the groups, cases had 9% (P=.01) higher geometric mean fasting and 7% (P=.04) higher geometric mean postload tHcy than the combined control groups. Despite higher levels of tHcy for cases, their geometric mean levels of red cell folate and pyridoxal 5'-phosphate were higher than for control subjects, whereas plasma vitamin B12 was only slightly lower in cases. The frequency distribution of tHcy values in cases was slightly shifted toward the right, across the entire range, compared with the distribution in the combined control group. This was somewhat more obvious for fasting than postload tHcy levels. The odds ratio (OR) for severe coronary atherosclerosis (case status) for each 1 SD increase in fasting tHcy (5 micromol/L) was 1.3 (95% confidence interval [CI], 1.0-1.6), similar to the OR for each 1 SD increase (12 micromol/L) in postmethionine-loading tHcy (1.3 [95 CI, 1.0-1.7]), after adjustment for sex, age, and other potential confounders. Furthermore, there was a significant linear trend of increasing fasting tHcy with increasing number of occluded arteries (P=.01), correcting for sex, age, and other potential confounders. Our data show a positive association between plasma tHcy and risk of severe coronary atherosclerosis, of similar strength for fasting and postload tHcy levels. The data suggest that the association exists over a wide range of tHcy levels, without a clear cutoff point below which there is no increased risk.

Clinical chemistry and molecular biology of homocysteine metabolism: an update

OBJECTIVE

To summarize recent developments in our understanding of homocysteine as a clinically relevant and independent predictor of vaso-occlusive disease (including atherosclerosis and thromboembolism), as an early indicator of folate or cobalamin deficiency, and as a key factor in the pathogenesis of neural tube defects.

METHODS AND RESULTS

To determine total homocysteine, plasma or serum must be separated shortly after collection and subjected to chemical reduction. Reference intervals should take into account the prevalence of physiological hyperhomocystinemia. A common cause of hyperhomocystinemia is a genetic predisposition caused by a polymorphic substitution in the methylenetetrahydrofolate reductase (MTHFR) gene, which can be readily detected by molecular means.

CONCLUSION

Determination of homocysteine and MTHFR testing should be limited to laboratories with relevant expertise and ability to maintain the high degree of precision required for reliable interpretation. Assays should be offered in selected cases with clinical features or laboratory findings suggestive of hyperhomocystinemia, since treatment is simple and may be highly effective.

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

In the Physicians' Health Study, we prospectively investigated the relation between plasma total homocysteine levels and risk of angina pectoris leading to coronary artery bypass surgery, among 149 case control pairs, matched for age and smoking. Plasma total homocysteine was unrelated to risk of disease overall as well as within the strata of major coronary risk factors.

Urinary apo(a) discriminates coronary artery disease patients from controls

Increased plasma lipoprotein (a) (Lp(a)) levels are associated with premature cardiovascular diseases and stroke. Since Lp(a) immune reactivity is found in urine we compared urinary apolipoprotein (a) (apo(a)) with plasma Lp(a) levels in 116 patients suffering from angiographically proven coronary artery diseases with that of 109 controls. Urinary apo(a) investigated by immuno blotting, revealed a distinct apo(a) fragmentation pattern with molecular weights between 50 and 160 kDa. Apolipoprotein B however was not secreted into urine. Lp(a) and apo(a) were measured by a fluorescence immuno assay. Within single individuals, urinary apo(a) levels correlated significantly with creatinine (Rho, 0.98; P < 0.0005). Medians and 25/75 percentiles of urinary apo(a) in coronary artery disease (CAD) patients were 5.70, 3.25 and 10.35 microg/dl and in controls 2.64, 1.43 and 3.50 microg/dl respectively. At cut-off levels of 30 mg/dl for plasma Lp(a) and 10 microg/dl of urinary apo(a) respectively, both paramenters showed comparable sensitivities (33.8% vs. 26.7%), yet the specificity (76.1% vs. 91.7%) and the positive predictive value (60.0% vs.76.4%) of urinary apo(a) were much higher. In receiver-operating characteristic plots, urinary apo(a) was much more sensitive at high specificities i.e. greater than 60% as compared to Lp(a). Urinary secretion of apo(a) fragments normalized to creatinine is stable in a given individual and significantly associated with coronary artery disease.

A prospective case-control study of lipoprotein(a) levels and apo(a) size and risk of coronary heart disease in Stanford Five-City Project participants

Lipoprotein(a) [Lp(a)] is formed by the assembly of LDL particles and a carbohydrate-rich protein, apolipoprotein(a) [apo(a)], which has a high degree of structural homology with plasminogen. While the majority of retrospective studies have found an association between Lp(a) level and cardiovascular disease (CVD), the few prospective studies to date have reported contradictory results. We conducted a nested case-control study using the participants in the Stanford Five-City Project, a long-term CVD prevention trial. Participants with an incident possible or definite myocardial infarction or coronary death were matched to a single control subject for age, sex, ethnicity, residence in a treatment or control city, and time of survey. This process yielded 134 case-control pairs, 90 male and 44 female, for whom plasma was available for analysis of Lp(a). Lp(a) values in nanomoles per liter were determined by an enzyme-linked immunoassay that measures Lp(a) independently of apo(a) size polymorphism. Apo(a) size isoforms were determined by SDS-agarose gel electrophoresis. Median Lp(a) level in male cases was almost double that in control subjects (41.8 versus 21.2 nmol/L; P < .01); in female cases, median Lp(a) was 34% higher than in control subjects (32.5 versus 21.2 nmol/L), but this difference was not statistically significant. Among the male cases, there was an increased frequency of small apo(a) isoforms, while no significant difference was found in apo(a) size between female cases and control subjects. The association between Lp(a) level and case-control status in men was independent of total, HDL, and non-HDL cholesterol levels, as well as apo(a) size isoform, cigarette smoking, blood pressure, and obesity. In men, the most efficient threshold value of Lp(a) concentration for separating cases and control subjects was 35 nmol/L; the odds ratio for being a case above this level compared with below was 2.84 (95% confidence interval: 1.53-5.27, P < .001). This study provides strong evidence that Lp(a) level is a prospective, independent risk factor for developing coronary artery disease in men and indicates that the size of apo(a) may also play a role. The lack of a significant association in women deserves further evaluation in larger studies.

Lipoprotein(a) in stored plasma samples and the ravages of time. Why epidemiological studies might fail

Prospective case-control studies investigating lipoprotein(a) [Lp(a)] as a risk factor for atherosclerosis have measured Lp(a) in samples stored frozen up to nearly 20 years. We therefore prospectively examined the influence of long-term plasma sample storage on measured values, depending on the molecular weight of apolipoprotein(a) [apo(a)] isoforms. Apo(a) phenotyping was performed in 310 plasma samples, and Lp(a) was measured after 3 and 28 months of storage at -80 degrees C. The values of both measurements correlated significantly for both low- and high-molecular-weight apo(a) phenotypes (r = .97 and r = .98, respectively, P < .001). Nevertheless, we detected on average a small decrease of 4.83% from mean +/- SD (median) 21.24 +/- 23.54 (11.10) mg/dL to 20.02 +/- 21.72 (10.55) mg/dL, which was statistically significant (P < .001). The absolute and relative Lp(a) decrease over time became larger with a decreasing number of kringle IV repeats of apo(a) (P < .05), and Lp(a) decreased markedly more in subjects with low-molecular-weight compared with those with high-molecular-weight apo(a) isoforms (-3.26 versus -0.46 mg/dL, P < .05). More than 70% of the absolute Lp(a) decrease in the total sample was caused by samples with low-molecular-weight apo(a) isoforms, which represented only 27% of the sample. Low-molecular-weight apo(a) isoforms are reportedly more frequent in patients with atherothrombotic disease compared with control subjects. Measurement of Lp(a) in several-year-old frozen samples is therefore likely to result in a preferential decrease and false lower Lp(a) concentrations in patient groups compared with control groups. The negative results of some prospective studies with retrospective measurement of Lp(a) may be caused by such an artifact.

Risk of primary and recurrent acute myocardial infarction from lipoprotein(a) in men and women

OBJECTIVES

This study sought to examine whether lipoprotein(a) concentrations were risk factors for a first acute and recurrent myocardial infarction.

BACKGROUND

There is conflicting evidence concerning the risk of acute myocardial infarction from lipoprotein(a). No studies have examined the risk of recurrent acute myocardial infarction from lipoprotein(a), and few have addressed the risk in women.

METHODS

This was a population-based case-control study of 893 men and women 35 to 69 years old participating in the World Health Organization Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) Project in Newcastle, Australia in 1993 to 1994. Case and control patients were classified into those with and without a previous myocardial infarction, and median lipoprotein(a) concentrations were compared after adjusting for other variables. Quintiles of lipoprotein(a) concentration were also examined.

RESULTS

Compared with control subjects without a previous myocardial infarction, median lipoprotein(a) concentrations increased from case patients with a first myocardial infarction (15 mg/liter higher, 95% confidence interval [CI] -36 to 60) to control patients with a previous myocardial infarction (159 mg/ liter higher, 95% CI 40 to 278) and case patients with a previous myocardial infarction (60 mg/liter higher, 95% CI -16 to 136, p < 0.01, test for trend). Women had significantly higher lipoprotein(a) concentrations than men (median 71 mg/liter higher, 95% CI 23 to 118). The highest quintile of lipoprotein(a) (>550 mg/liter) was a significant risk factor for a first acute myocardial infarction (odds ratio [OR] 1.77, 95% CI 1.03 to 3.03); but in those with a previous myocardial infarction, the highest quintile was not associated with recurrent myocardial infarction (OR 0.84, 95% CI 0.30 to 2.37).

CONCLUSIONS

High lipoprotein(a) concentrations may be a marker of vascular or tissue injury or may be associated with other genetic or environmental factors that cause acute myocardial infarction. Currently, lipoprotein(a) measurement cannot be recommended for assessment of risk for acute myocardial infarction.

Lipoprotein(a) and its correlates in Japanese and U.S. population samples

To examine whether serum levels of lipoprotein(a) [Lp(a)], a potential coronary risk factor, are higher in Caucasian-Americans than in Japanese, a circumstance that would correspond to the higher mortality from coronary heart disease in the United States than in Japan, we analyzed serum Lp(a) levels in 300 nonsmoking men and women aged 47-69 years. Participants were drawn from two population-based samples: rural Japanese living in Akita and Caucasians living in Minneapolis-St. Paul, MN. Geometric mean and median serum Lp(a) concentrations were higher (P < 0.05) in Japanese than in Caucasians for both men (difference in geometric mean = 3.2 mg/dL) and women (difference = 5.3 mg/dL). There was however, no racial difference in the proportion of elevated Lp(a) concentrations (i.e., > or = 30 mg/dL) in either sex. Alcohol intake was inversely correlated with Lp(a) levels in Japanese men, who had a high average alcohol intake, but not in other sex and racial groups. Serum Lp(a) was nonsignificantly but consistently correlated with plasma fibrinogen and LDL-cholesterol for all sex and racial groups. With adjustment for alcohol intake, LDL-cholesterol, and plasma fibrinogen, the Japanese-Caucasian difference in geometric mean Lp(a) values was even larger for men and was not changed for women. Results of the present study do not support the hypothesis that racial differences in Lp(a) concentrations contribute to the higher mortality rate from coronary heart disease in the United States than in Japan.

Correlation of toddlers' serum lipoprotein(a) concentration with parental values and grandparents' coronary heart disease: the STRIP baby study

The correlation between lipoprotein(a) (Lp(a)) concentrations in children aged 7-24 months and their family members was determined and the association between the Lp(a) values of the children and a family history of coronary heart disease (CHD) was assessed. The Lp(a) values of the children correlated strongly with midparent Lp(a) values as early as at 7 months of age (r = 0.54 to 0.59, p < 0.0001). This correlation was stronger than the correlation of serum total cholesterol and total cholesterol corrected for Lp(a)-cholesterol between children and parents. None of the parents had CHD. The median Lp(a) concentration of the parents with a family history of CHD was significantly higher than that of parents with no such history (111 vs 87 mg/1, p = 0.024). However, the children's Lp(a) levels were not associated with CHD in their grandparents. The genetic dependence of the Lp(a) concentration is already evident in infancy. The Lp(a) concentration in young parents, but not in their 24-month-old children, is associated with CHD in grandparents. This may be explained by a dilution of the genetic influence on Lp(a) over two generations.

Homocysteine and coronary atherosclerosis

Homocysteine is increasingly recognized as a risk factor for coronary artery disease. An understanding of its metabolism and of the importance of vitamins B6 and B12 and folate as well as enzyme levels in its regulation will aid the development of therapeutic strategies that, by lowering circulating concentrations, may also lower risk. Possible mechanisms by which elevated homocysteine levels lead to the development and progression of vascular disease include effects on platelets, clotting factors and endothelium. This review presents the clinical and basic scientific evidence supporting the risk and mechanisms of vascular disease associated with elevated homocysteine concentrations as well as the results of preliminary therapeutic trials.

Lipoprotein composition and serum cholesterol ester fatty acids in nonwesternized Melanesians

In this study, the relationships between dietary fat [as measured by serum cholesterol ester fatty acids (CE-FA)], age, smoking, body mass index, and serum lipids were analyzed in 151 subsistence horticulturalists, aged 20-86 yr, from Kitava, Trobriand Islands, Papua New Guinea. Their diet consists of tubers, fruit, coconut, fish, and vegetables with a negligible influence of western food and alcohol. Total fat intake is low [21% of energy (en%)], while saturated fat intake from coconuts is high (17 en%, mainly lauric and myristic acid). In multivariate analysis, 11-43% of the variation of the serum lipoprotein composition was explained by CE-FA, age, and smoking habits. The proportion of CE20:5n-3 explained much of the variation of triglycerides (TG, negative relation) and high density lipoprotein-cholesterol (HDL-C, positive) in both sexes and serum apolipoprotein A1 (ApoA1, positive) in the males. CE16:0 was positively related to TG and negatively related to HDL-C and ApoA1 in both sexes, and in males it related negatively to total cholesterol (TC) and low density lipoprotein-cholesterol (LDL-C). In males, negative relationships were present between CE18:2n-6 and TC and between CE14:0 and serum lipoprotein(a). Smoking was independently associated with lower ApoA1 in both sexes and with lower HDL-C and higher TG, TC, LDL-C, and apolipoprotein B in males. In conclusion, marine n-3 fatty acids and linoleic acid showed the same potentially beneficial relationships with lipoproteins and apolipoproteins as in western populations. The relations of palmitic acid to serum lipids may be explained in terms of endogenous fat synthesis at a low-fat intake, rather than reflecting its relative intake.

Genetic and nongenetic factors for moderate hyperhomocyst(e)inemia

To assess the risk for homocyst(e)ine-associated vascular disease, overt hyperhomocyst(e)inemia should be demonstrated. In nonhomocystinuric subjects, clinical vascular disease must have developed after 40 or more years of persistent hyperhomocyst(e)inemia which may not be present without a genetic defect(s). Nongenetic factors, however, may amplify or mask phenotypic expression of a genetic defect, causing difficulties for the evaluation of hyperhomocyst(e)inemia based on plasma homocyst(e)ine concentration alone. Therefore, the search for genetic defects seems as important as the determination of plasma homocyst(e)ine concentration in evaluating the relationship between hyperhomocyst(e)inemia and the development of vascular disease. If genetic defect, such as heterozygous cystathionine synthase deficiency or thermolabile methylenetetrahydrofolate reductase is not detected, post-methionine homocyst(e)ine determination is a suitable means to identify genetic susceptibility to hyperhomocyst(e)inemia when the environmental factors are similar in the control and study groups.

[Homocysteine: relations to ischemic cardiovascular diseases]

Homocysteine, a sulfur-containing amino acid, is an intermediate metabolite of methionine. Patients with homocystinuria and severe hyperhomocysteinemia develop premature arteriosclerosis and arterial thrombotic events, and venous thromboembolism. Studies suggest that moderate hyperhomocysteinemia can be considered as an independent risk factor in the development of premature cardiovascular disease. In vitro, homocysteine has toxic effects on endothelial cells. Homocysteine can promote lipid peroxidation and damage vascular endothelial cells. Moreover, homocysteine interferes with the natural anticoagulant system and the fibrinolytic system. Homocysteinemia should be known in patients with premature vascular diseases, especially in subjects with no risk factors. Folic acid, vitamin B6 can lower homocysteine levels.

Lipoprotein(a) in health and disease

Lipoprotein(a) [Lp(a)] represents an LDL-like particle to which the Lp(a)-specific apolipoprotein(a) is linked via a disulfide bridge. It has gained considerable interest as a genetically determined risk factor for atherosclerotic vascular disease. Several studies have described a correlation between elevated Lp(a) plasma levels and coronary heart disease, stroke, and peripheral atherosclerosis. In healthy individuals, Lp(a) plasma concentrations are almost exclusively controlled by the apo(a) gene locus on chromosome 6q2.6-q2.7. More than 30 alleles at this highly polymorphic gene locus determine a size polymorphism of apo(a). There exists an inverse correlation between the size (molecular weight) of apo(a) isoforms and Lp(a) plasma concentrations. The standardization of Lp(a) quantification is still an unresolved task due to the large particle size of Lp(a), the presence of two different apoproteins [apoB and apo(a)], and the large size polymorphism of apo(a) and its homology with plasminogen. A working group sponsored by the IFCC is currently establishing a stable reference standard for Lp(a) as well as a reference method for quantitative analysis. Aside from genetic reasons, abnormal Lp(a) plasma concentrations are observed as secondary to various diseases. Lp(a) plasma levels are elevated over controls in patients with nephrotic syndrome and patients with end-stage renal disease. Following renal transplantation, Lp(a) concentrations decrease to values observed in controls matched for apo(a) type. Controversial data on Lp(a) in diabetes mellitus result mainly from insufficient sample sizes of numerous studies. Large studies and those including apo(a) phenotype analysis came to the conclusion that Lp(a) levels are not or only moderately elevated in insulin-dependent patients. In noninsulin-dependent diabetics, Lp(a) is not elevated. Conflicting data also exist from studies in patients with familial hypercholesterolemia. Several case-control studies reported elevated Lp(a) levels in those patients, suggesting a role of the LDL-receptor pathway for degradation of Lp(a). However, recent turnover studies rejected that concept. Moreover, family studies also revealed data arguing against an influence of the LDL receptor for Lp(a) concentrations. Several rare diseases or disorders, such as LCAT- and LPL-deficiency as well as liver diseases, are associated with low plasma levels or lack of Lp(a).

Plasma homocysteine and severity of atherosclerosis in young patients with lower-limb atherosclerotic disease

Elevated plasma homocysteine levels are recognized as an independent risk factor for atherosclerotic disease. It is not known (1) whether the severity of atherosclerotic disease is related to hyperhomocyst(e)inemia or (2) whether any such relation differs between fasting and post-methionine loading plasma homocysteine levels. Therefore, in 171 consecutive patients under 55 years of age with first symptoms of lower-limb disease, we examined the relation between severity of atherosclerosis and plasma homocysteine concentration. Severity of atherosclerotic disease was estimated from the prevalence of coronary artery disease and cerebrovascular disease and from the angiographic extent of lower-limb disease. Plasma homocysteine was measured after a period of fasting and in response to methionine loading (0.1 g/kg). In multivariate analysis, the prevalence of coronary artery disease plus cerebrovascular disease was related to both fasting and postmethionine homocysteine levels (odds ratio [OR] for the upper quartile versus the lower three quartiles, 2.8, 95% confidence interval [CI], 1.1 to 7.5; and OR 3.0, 95% CI, 1.1 to 7.8, respectively). The extent of lower-limb disease was weakly related to the fasting homocysteine level (partial correlation coefficient, .12; P = .17) and more strongly related to the postmethionine homocysteine level (partial correlation coefficient, .25; P = .003). These relations tended to be more pronounced in women than in men. They were independent of age, total serum cholesterol, blood pressure, and smoking habit. We concluded that the severity of atherosclerotic disease in young patients with lower-limb atherosclerotic disease is associated with high postmethionine and fasting homocysteine concentrations.

Prospective study of serum total homocysteine concentration and risk of stroke in middle-aged British men

Moderate hyperhomocysteinaemia is common in the general population and has been linked with cardiovascular disease. However, there are no data from prospective, population-based studies. We examined the association between serum total homocysteine (tHcy) concentration and stroke in a nested case-control study within the British Regional Heart Study cohort. Between 1978 and 1980 serum was saved from 5661 men, aged 40-59 years, randomly selected from the population of one general practice in each of 18 towns in the UK. During follow-up to December, 1991, there were 141 incident cases of stroke among men with no history of stroke at screening. Serum tHcy was measured in 107 cases and 118 control men (matched for age-group and town, without a history of stroke at screening, who did not develop a stroke or myocardial infarction during follow-up). tHcy concentrations were significantly higher in cases than controls (geometric mean 13.7 [95% CI 12.7-14.8] vs 11.9 [11.3-12.6] mumol/L; p = 0.004). There was a graded increase in the relative risk of stroke in the second, third, and fourth quarters of the tHcy distribution (odds ratios 1.3, 1.9, 2.8; trend p = 0.005) relative to the first. Adjustment for age-group, town, social class, body-mass index, hypertensive status, cigarette smoking, forced expiratory volume, packed-cell volume, alcohol intake, diabetes, high-density-lipoprotein cholesterol, and serum creatinine did not attenuate the association. These findings suggest that tHcy is a strong and independent risk factor for stroke.

Prospective studies of homocysteine and cardiovascular disease

The link between vascular disease and elevated homocysteine levels has been recognized for more than 30 years, and an association with moderately elevated levels has been suspected for 20 years. The initial investigations were case series, cross-sectional, and case-control studies. Those studies consistently suggest a strong positive relationship between moderate hyperhomocysteinemia and risk of vascular disease. However, a major limitation of these types of study design is that the possibility of elevated homocysteine levels being influenced by the disease or its treatment cannot be ruled out. In case-control studies there is always concern about the appropriateness of the control group. These issues pose much less of a problem in prospective designs. Prospective studies also offer the opportunity to study various manifestations of cardiovascular disease at the same time. However, prospective studies tend to be more expensive and time-consuming, perhaps explaining the smaller number of prospective studies and why the first was not published until 1992. The distinct limitations and advantages of prospective studies are also reviewed.

Higher plasma homocyst(e)ine and increased susceptibility to adverse effects of low folate in early familial coronary artery disease

To examine the graded risks for coronary artery disease (CAD) associated with plasma homocyst(e)ine [H(e)] and to evaluate the extent to which this risk is mediated by altered vitamin status, we measured plasma concentrations of H(e), vitamins B6 and B12, and folate as well as other coronary risk factors in subjects with early familial CAD and in control subjects. We studied 120 male and 42 female patients with early CAD who were unrelated to each other but were from families in which at least one other sibling had early CAD. Control subjects were 85 men and 70 women with the same age range (38 to 68) as the subjects with CAD at screening. Increasing H(e) was associated with graded increased risks of CAD that appeared consistent with a multiplicative model. Relative odds for CAD were approximately 12.8 in women when those with H(e) levels of 9 mumol/L and above were compared with those with H(e) levels of 9 mumol/L or less (P = .007). For men, the same comparison yielded relative odds of 13.8 (P = .0002). Plasma H(e) remained a strong, independent risk factor after adjustment for standard risk factors and plasma vitamin levels in multiple logistic regression (relative odds, 8.1 for a 10-mumol/L increase in H(e); 95% confidence interval, 3.2 to 20.4; P < .0001). In multivariate ANCOVA the slope of H(e) versus folate was much steeper in subjects with CAD than in control subjects (P = .0035). These data suggest that high plasma H(e) is an important, independent contributor to risk for early familial CAD.(ABSTRACT TRUNCATED AT 250 WORDS)

No association between plasma lipoprotein(a) concentrations and the presence or absence of coronary atherosclerosis in African-Americans

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] are associated with coronary atherosclerosis in Caucasians. Although African-Americans have a higher median plasma Lp(a) concentration than Caucasians, they do not have a greater incidence of coronary atherosclerosis. This study was performed to determine whether the plasma concentration of Lp(a) is associated with coronary atherosclerosis in African-Americans. The fasting plasma concentrations of Lp(a) and lipoproteins were measured in 140 African-American subjects (62 men, 78 women, aged 31 to 80 years) 18 +/- 16 months (mean +/- SD) after they underwent coronary angiography: 72 had angiographically normal coronary arteries and 68 had > 70% luminal diameter narrowing of one or more major epicardial coronary arteries. The groups were similar in age, sex, and other risk factors for atherosclerosis. The subjects with coronary artery disease had higher plasma concentrations of total cholesterol, triglycerides, and VLDL and LDL cholesterol (P = .04) and lower concentrations of HDL cholesterol (P = .0001) than subjects without coronary artery disease, but there was no significant difference in the plasma concentration of Lp(a). The distribution of apolipoprotein(a) alleles by size was also not significantly different between the two groups. These results suggest that the plasma concentration of Lp(a) is not an independent risk factor for coronary artery disease in African-Americans.

Serum folate and risk for ischemic stroke. First National Health and Nutrition Examination Survey epidemiologic follow-up study

BACKGROUND AND PURPOSE

A serum folate concentration < or = 9.2 nmol/L has been associated with elevated levels of plasma homocyst(e)ine. Elevated homocyst(e)ine levels have been associated with ischemic stroke in case-control studies; however, the results from prospective studies have been equivocal. We investigated whether a folate concentration < or = 9.2 nmol/L was associated with ischemic stroke in a national cohort.

METHODS

We used data from the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study (n = 2006). Cox proportional hazards analyses were used to adjust for differences in follow-up time and covariates. During the 13-year follow-up, 98 ischemic strokes occurred.

RESULTS

After adjusting for age, race, sex, education, diabetes, history of heart disease, systolic blood pressure, body mass index, hemoglobin level, cigarette smoking, and alcohol intake, participants with a folate concentration < or = 9.2 nmol/L were at slightly increased risk for ischemic stroke (relative risk [RR], 1.37; 95% confidence interval [CI], 0.82 to 2.29). There was a folate-race interaction (P = .11 for interaction term). Whites with a folate concentration < or = 9.2 nmol/L had a relative risk of 1.18 (95% CI, 0.67 to 2.08), whereas blacks had a relative risk of 3.60 (95% CI, 1.02 to 12.71).

CONCLUSIONS

These findings suggest that a folate concentration < or = 9.2 nmol/L may be a risk factor for ischemic stroke, especially in blacks. However, given the small number of stroke events, additional studies are needed to assess the role of folate in the epidemiology of ischemic stroke.

Whether, to what degree, and why lipoprotein(a) levels change over time

Our specific aim in this study of 6 +/- 2 serial lipoprotein(a) (Lp(a)) measurements over 1.7 +/- 0.5 years in 145 patients (64 men, 81 women, 135 whites, 10 blacks, mean age 63 years) with high Lp(a) (> or = 25 mg/dl) was to assess whether, to what degree, and why Lp(a) levels change over time. A second specific aim was to study the biological coefficient of variation of Lp(a) (C.V.b). No Lp(a) lowering drugs were given. In the 145 patients, mean (S.D.) and median Lp(a) on entry (70 +/- 34 and 59 mg/dl) did not differ from levels on follow-up (72 +/- 34 and 64 mg/dl) (P > 0.4). Mean (S.D.) C.V.b was 18 +/- 9%, median 17%, minimum 1.7% and maximum 58%. Three or four samples for Lp(a) measurement should be very adequate to establish a 'true' Lp(a) value, since C.V.bs based on three to four samples did not differ (P > 0.1) from those based on five to six, seven, eight, or nine samples. For patients with mean +/- S.D. baseline Lp(a) levels of 39 +/- 3, 49 +/- 3 and 59 +/- 2, 95% of the follow-up values fell in the following ranges: 25-78, 24-93 and 34-104 mg/dl. Lp(a) on study entry was highly correlated with Lp(a) on follow-up (r = 0.84, P = 0.0001) and with Lp(a)'s C.V.b on follow-up (r = 0.24, P = 0.003). Entry Lp(a) was inversely correlated with absolute and percent change in Lp(a) on follow-up (r = -0.38, P = 0.0001 for both).(ABSTRACT TRUNCATED AT 250 WORDS)

Homocysteine and coronary artery disease in French Canadian subjects: relation with vitamins B12, B6, pyridoxal phosphate, and folate

We determined plasma levels of homocysteine in 584 healthy subjects (380 men and 204 women) from a major utility company in the province of Québec, Canada, and in 150 subjects (123 men and 27 women) with angiographically documented coronary artery disease (CAD) (age < 60 years). Plasma levels of vitamins B12, B6, pyridoxal phosphate (a vitamin B6 derivative), and folate were also determined. Mean homocysteine levels were higher (p < 0.05) in the bottom quartiles for folate, vitamin B12, and pyridoxal phosphate. A significant correlation was noted between homocysteine levels and folate and vitamin B12 levels. No significant correlation was found between plasma homocysteine levels and age, lipids and lipoprotein cholesterol, glucose, and the presence of hypertension or cigarette smoking in healthy subjects or in patients with CAD. Control men had higher homocysteine levels than control women (p < 0.005). Men and women with CAD had higher levels of homocysteine than controls (11.7 +/- 5.8 vs 9.7 +/- 4.9 nmol/ml [p < 0.001] and 12.0 +/- 6.3 vs 7.6 +/- 4.1 nmol/ml, p < 0.01, respectively). Women and men with CAD had similar homocysteine levels. The proportion of patients with CAD having homocysteine levels > 90th percentile of controls was 18.1% for men and 44.4% for women (both p < 0.01). Significantly lower pyridoxal phosphate levels were seen in subjects with CAD, men and women combined (27.7 +/- 29.5 vs 42.1 +/- 38.4 ng/ml, p < 0.005). No significant differences were observed for B12, folate, or total B6.(ABSTRACT TRUNCATED AT 250 WORDS)