A case-control study of lipoprotein particles in two populations at contrasting risk for coronary heart disease. The ECTIM Study

Biochemical characterization of the three major subclasses of lipoprotein A-I preparatively isolated from human plasma

Apolipoprotein (apo) A-I is the major protein constituent of plasma high-density lipoproteins (HDL). HDL consist of two major classes of apoA-I-containing lipoproteins: LpA-I and LpA-I:A-II. LpA-I includes heterogeneous lipoprotein particles that differ in size and hydrated density. LpA-I was isolated by immunoaffinity chromatography from the fasting plasma of 24 normal human subjects and separated by gel filtration chromatography. Three major subclasses of LpA-I were eluted: large (Lg-LpA-I), medium (Md-LpA-I), and small LpA-I (Sm-LpA-I). By nondenaturing gradient PAGE, Lg-LpA-I, Md-LpA-I, and Sm-LpA-I had mean Strokes diameters of 10.8 +/- 0.5, 8.9 +/- 0.5, and 7.5 +/- 0.3 nm, respectively. The lipid/protein ratios were 1.25 +/- 0.12 for Lg-LpA-I, 0.75 +/- 0.10 for Md-LpA-I, and 0.38 +/- 0.08 for Sm-LpA-I. Lg-LpA-I was relatively lipid and cholesteryl ester rich compared with Md-LpA-I and Sm-LpA-I. Sm-LpA-I contained phospholipids as the major lipid component. ApoA-I was the major apolipoprotein in all LpA-I subfractions, whereas apoE was present only in Lg-LpA-I and apoA-IV was associated with both Md-LpA-I and Sm-LpA-I. All three LpA-I subclasses exhibited predominantly alpha mobility on agarose electrophoresis. Lg-LpA-I migrated as a diffuse band in the fast alpha position, whereas Md-LpA-I and Sm-LpA-I migrated to the slow alpha position.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for linkage of the apolipoprotein A-II locus to plasma apolipoprotein A-II and free fatty acid levels in mice and humans

Although it has been hypothesized that the synteny between mouse and human genes provides an approach to the localization of genes that determine quantitative traits in humans, this has yet to be demonstrated. We tested this approach with two quantitative traits, plasma apolipoprotein A-II (apoAII) and free fatty acid (FFA) levels. ApoAII is the second most abundant protein of high density lipoprotein particles, but its function remains largely unknown. We now show that, in a backcross between strains Mus spretus and C57BL/6J, apoAII levels correlate with plasma FFA concentrations on both chow (P < 0.0001) and high-fat (P < 0.0003) diets and that apoAII levels are linked to the apoAII gene (P < 0.0002). To test whether variations of the apoAII gene influence plasma lipid metabolism in humans, we studied 306 individuals in 25 families enriched for coronary artery disease. The segregation of the apoAII gene was followed by using an informative simple sequence repeat in the second intron of the gene and two nearby genetic markers. Robust sib-pair linkage analysis was performed on members of these families using the SAGE linkage programs. The results suggest linkage between the human apoAII gene and a gene controlling plasma apoAII levels (P = 0.03). Plasma apoAII levels were also significantly correlated with plasma FFA levels (P = 0.007). Moreover, the apoAII gene exhibited linkage with a gene controlling FFA levels (P = 0.003). Evidence for nonrandom segregation was seen with markers as far as 6-12 centimorgans from the apoAII structural locus. These data provide evidence, in two species, that the apoAII gene is linked to a gene that controls plasma apoAII levels and that apoAII influences, by an unknown mechanism, plasma FFA levels. The results illustrate the utility of animal studies for analysis of complex traits.

Parental history of early myocardial infarction is associated with decreased levels of lipoparticle AI in adolescents

A family history of coronary heart disease (CHD) is a known risk factor for CHD. To investigate the possible role of lipoprotein particles in the relationship between family history of CHD and risk of CHD, we performed a case-control study in a sample of adolescents. The case group consisted of 97 adolescents whose parents had suffered a verified myocardial infarction before the age of 55 years. The control group was composed of 194 subjects without any family history of CHD. One case patient was matched to two control subjects for gender, age, and body mass index. In both groups, plasma lipid variables were measured, including total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C) low-density lipoprotein cholesterol, apolipoprotein (apo)AI, apoB, apoAI-containing lipoprotein particles without apoAII (LpAI) and with apoAII, and apoB-containing lipoprotein particles with apoE and with apoCIII. Adolescents with a family history of early myocardial infarction had lower plasma levels of HDL-C (P < .0001), apoAI (P < .01), and LpAI (P < .0001) than control subjects (adjusted for gender, age, body mass index, smoking habits, and oral contraceptive use). No other differences were statistically significant between case and control subjects. The analysis was repeated separately for male and female subjects. In young men, the best predictor of family history of early myocardial infarction was the LpAI plasma level, whereas in young women it was the HDL-C plasma level. Decreased levels of HDL-C and LpAI lipoprotein particles explain part of the relationship between parental history of early myocardial infarction and CHD risk.

Increased production of apolipoprotein A-I associated with elevated plasma levels of high-density lipoproteins, apolipoprotein A-I, and lipoprotein A-I in a patient with familial hyperalphalipoproteinemia

Familial hyperalphalipoproteinemia (FHA) is a heritable trait associated with elevated plasma concentrations of high-density lipoprotein (HDL) cholesterol and possibly with longevity and protection against coronary heart disease (CHD). The metabolic basis and molecular etiology of FHA have not been established in most kindreds. The proband of a kindred with FHA and possible longevity was found to have elevated plasma levels of HDL cholesterol, apolipoprotein (apo) A-I, and lipoproteins containing apo A-I without apo A-II (Lp A-I), but normal levels of apo A-II and lipoproteins containing apo A-I with apo A-II (Lp A-I:A-II). The in vivo kinetics of apo A-I and apo A-II were studied in the FHA proband and in control subjects using both exogenous radiotracer (125I-apo A-I and 131I-apo A-II) and endogenous stable isotope (primed constant infusion of 13C6-phenylalanine) labeling techniques. The production rate (PR) of apo A-I was markedly increased in the FHA subject (28.9 mg/kg.d) compared with the control subjects (12.0 +/- 2.1 mg/kg.d), whereas the apo A-II PR was not substantially increased. The primary sequence of the proband's apo A-I gene, including 1.2 kb of the 5'-flanking sequence, was normal. We conclude that a selective upregulation of apo A-I production is one metabolic cause of FHA, and results in high plasma concentrations of HDL cholesterol, apo A-I, and Lp A-I and possibly in protection from atherosclerotic CHD.

Distribution of lipid variables in subjects in Belfast, Northern Ireland and Taiyuan, P R China

To compare the plasma lipid, lipoprotein and apolipoprotein profiles of people of Chinese and European origin, a sample of 151 male Chinese subjects was selected from Taiyuan, Shanxi Province, P R China to 202 broadly age-matched subjects in Belfast who were selected as controls in a case-control study of myocardial infarction. Mean total cholesterol (TC) was 6.15 mmol/l in Belfast and 4.28 mmol/l in Taiyuan. Low density lipoprotein cholesterol (LDL) was much higher in Belfast. High density lipoprotein cholesterol (LDL) was also higher in Belfast than in Taiyuan but the ratio of HDL to TC was lower in Belfast than Taiyuan. Triglyceride (TG) levels were similar and this was reflected in the relatively high level of apolipoprotein E (apo E) in the Chinese sample.

Genetic variation at the beta-fibrinogen locus in relation to plasma fibrinogen concentrations and risk of myocardial infarction. The ECTIM Study

Increased plasma fibrinogen concentration is a major cardiovascular risk factor. Conflicting results on genetic variations in plasma fibrinogen levels have been reported. Furthermore, whether fibrinogen genotype is associated with the risk of ischemic heart disease has not been studied so far. An HaeIII restriction fragment length polymorphism of the beta-fibrinogen gene was used in a case-control study to investigate the genetic variation at this locus in relation to plasma fibrinogen concentrations and the risk of myocardial infarction (MI). Five hundred thirty-three male patients aged 27-66 years and 648 control subjects were recruited from four World Health Organization MONICA centers in Northern Ireland and in France. The absence of the HaeIII cutting site (H2 allele) was associated with a significant rise in fibrinogen concentrations in both patients and control subjects. The effect of the HaeIII polymorphism on plasma fibrinogen levels did not significantly differ between centers. Fibrinogen levels were higher in smokers than in nonsmokers. The difference between the two groups was larger in subjects with the genotype H2H2 than in those with either genotype H1H1 or H1H2, regardless of the case-control status. However, there was no significant interaction between smoking status and genotype in their effects on variance in fibrinogen levels, whereas fibrinogen levels. HaeIII genotype accounted for approximately 1% of the total variance in fibrinogen levels, whereas smoking and age together explained 7% and 5% in control subjects and patients, respectively. The frequency of the H2 allele was 0.21 in control subjects and 0.19 in patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Lipoprotein metabolism and renal failure

Lipoprotein metabolism is altered in the majority of patients with renal insufficiency and renal-failure, but may not necessarily lead to hyperlipidemia. The dyslipoproteinemia of renal disease has characteristic abnormalities of the apolipoprotein (apo) profile and lipoprotein composition. It develops during the asymptomatic stages of renal insufficiency and becomes more pronounced as renal failure advances. The qualitative characteristics of renal dyslipoproteinemia are not modified substantially by dialysis treatment. Patients with chronic renal disease may therefore be exposed to dyslipoproteinemia for long periods of time. The characteristic plasma lipid abnormality is a moderate hypertriglyceridemia. The alterations of lipoprotein metabolism affect both the apoB-containing very low-density and intermediate-density, and low-density lipoproteins and the apoA-containing high-density lipoproteins. The main underlying abnormality of lipoprotein transport is a decreased catabolism of the apoB-containing lipoproteins caused by decreased activity of lipolytic enzymes and altered lipoprotein composition. There is an increase of intact or partially metabolized, triglyceride-rich, apoB-containing lipoproteins with a disproportionate elevation of apoC-III and, to a lesser extent, apoE, resulting in a marked increase of the intermediate-density lipoproteins and an enrichment of triglycerides, apoC-III, and apoE in the low-density lipoproteins. In high-density lipoproteins there are decreases in the concentrations of cholesterol, apolipoproteins A-I and A-II, and the high-density lipoprotein-2 to high-density lipoprotein-3 ratio. These abnormalities result in a characteristic decrease of the apoA-I to apoC-III ratio and anti-atherogenic index apoA-I/apoB. The pathophysiologic links between the renal insufficiency and the abnormalities of lipoprotein transport are still poorly defined. Changes in the action of insulin on lipolytic enzymes, possibly mediated via increased levels of parathyroid hormone, have been suggested to play a contributory role. The clinical consequences of a defective lipoprotein transport may be related to the atherogenic character of lipoprotein abnormalities. Renal dyslipoproteinemia may contribute to the development of atherosclerotic vascular disease and progression of glomerular and tubular lesions with subsequent deterioration of renal function. Dietary and/or pharmacologic intervention may ameliorate the uremic dyslipoproteinemia, but the long-term clinical effects of such treatment have yet to be established.

Deletion polymorphism in angiotensin-converting enzyme gene associated with parental history of myocardial infarction

In a European study an insertion (I)/deletion (D) polymorphism in the angiotensin converting enzyme (ACE) gene has been shown to be associated with the risk of myocardial infarction (MI). In the same study, we investigated the association of the polymorphism with a parental history of fatal MI. There was an excess of both DD (odds ratio 2.6, p = 0.02) and ID (odds ratio = 1.9, p = 0.08) genotypes among those having a parental history of MI, confirming that genetic variation in the ACE locus could be involved in the risk of MI.

Deletion polymorphism in the gene for angiotensin-converting enzyme is a potent risk factor for myocardial infarction

Factors involved in the pathogenesis of atherosclerosis, thrombosis and vasoconstriction contribute to the development of coronary heart disease. In a study comparing patients after myocardial infarction with controls, we have explored a possible association between coronary heart disease and a variation found in the gene encoding angiotensin-converting enzyme (ACE). The polymorphism ACE/ID is strongly associated with the level of circulating enzyme. This enzyme plays a key role in the production of angiotensin II and in the catabolism of bradykinin, two peptides involved in the modulation of vascular tone and in the proliferation of smooth muscle cells. Here we report that the DD genotype, which is associated with higher levels of circulating ACE than the ID and II genotypes, is significantly more frequent in patients with myocardial infarction (n = 610) than in controls (n = 733) (P = 0.007), especially among subjects with low body-mass index and low plasma levels of ApoB (P < 0.0001). The ACE/ID polymorphism seems to be a potent risk factor of coronary heart disease in subjects formerly considered to be at low risk according to common criteria.