Immunogenetic polymorphism of apolipoprotein B in humans: studies with a monoclonal anti-Ag(c) antibody

The effect of six polymorphisms in the Apolipoprotein B gene on parameters of lipid metabolism in a Danish population

Lipoproteins are vehicles for the distribution of plasma lipids and polymorphisms in the genes for apolipoproteins could influence the amount of lipid in plasma. We examined the effect of six single nucleotide polymorphisms in codons 71, 591, 2488, 2712, 3611, and 4154 of the apolipoprotein B gene on fasting levels of triglyceride, VLDL-, LDL-, HDL- and total cholesterol and on body mass index (BMI) in a cohort of 2656 Danes aged 40-70 years using a linear model correcting for the effects of gender, age, BMI, smoking, alcohol consumption and physical activity. The codon 2488 polymorphism was the most influential of the tested polymorphisms, significantly influencing triglyceride (P = 0.002), LDL-cholesterol (P < or = 0.0004), VLDL-cholesterol (P = 0.006) and total cholesterol (P = 0.0001). The codon 2712 polymorphism had an impact on triglyceride (P = 0.007) and VLDL-cholesterol (P = 0.001), while the codon 71 polymorphism influenced LDL- and total cholesterol (P = 0.04 and P = 0.02, respectively). An interaction between smoking and codon 591 (P = 0.03) and smoking and codon 3611 (P = 0.02) on BMI was observed, as well as modest interactions between codon 3611 and codons 2488 and 2712 on lipid parameters. All polymorphisms were in close linkage disequilibrium. The population was not in Hardy-Weinberg equilibrium in four of the six polymorphisms but the lack of equilibrium was restricted mainly to the 60-year olds.

Relation between sex hormones and serum lipoprotein and lipoprotein(a) concentrations in premenopausal obese women

Lipoprotein(a) (Lp[a]) is generally considered to be a risk factor for the development of cardiovascular disease, but little is known about the possible influence of obesity on the circulating levels of this lipoprotein. The present study was undertaken to examine this aspect in 136 menstrually active women by comparing the serum concentrations of Lp(a) between 72 obese and 64 age-matched nonobese women. Since an adverse effect of androgens and a protective effect of estrogens have been described for plasma lipoprotein profiles in obese women, the relation between the circulating levels of Lp(a) and those of these other hormones was also investigated in obese patients. In addition, other lipoproteins, anthropometric parameters (body mass index and waist-to-hip ratio), and insulin were evaluated. The levels of Lp(a) were not significantly different (Mann-Whitney U test chi 2, 3.59; p = 0.0582 [NS]) between obese (rank sum, 5,367) and control (rank sum, 3,949) women; in addition, the percentage of patients with high Lp(a) levels (cutoff defined at 30 mg/dL) did not differ between the two groups (obese women, 30%; control, 21.8%; chi 2, 0.90; two-sided p = 0.341 [NS]). Moreover, no correlation was found between Lp(a) and body mass index. Lastly, when the Lp(a) prevalence odds ratio for obesity was examined by adjusting the levels of this lipoprotein for age, triglycerides, total cholesterol, and high density lipoprotein cholesterol, the probability value (0.88) was far from significant. In obese women, no correlation was found between the logarithmically transformed Lp(a) concentrations and all the other variables evaluated in the study. In conclusion, the present study shows that the circulating levels of Lp(a) are not influenced by body weight and cardiovascular risk factors commonly associated with obesity, such as enhanced androgenic activity, hyperinsulinemia, adverse lipoprotein profile, and abdominal fat accumulation.

Role of plasma lipoproteins in the pathogenesis of atherosclerotic disease, with special reference to sex hormone effects

Plasma lipoproteins constitute a complex lipid transport system. Very low-density lipoproteins transport triglycerides to peripheral tissues, whereas low-density lipoproteins are the main carriers of cholesterol. Cholesterol transport in low-density lipoprotein enters body cells by way of "low-density lipoprotein receptor pathway" but may also be taken up by macrophages by way of the "scavenger pathway." Excessive influx of cholesterol by way of the "scavenger pathway" may result in deposition of cholesterol in arterial walls and atheroma formation. In a yet incompletely known process of "reverse cholesterol transport," cholesterol is carried away from the tissues to the liver by high-density lipoproteins. The above-mentioned transport processes are regulated by a well-synchronized system that involves several enzymes and lipid transport proteins. Under normal conditions, the lipoprotein system is able to balance the flow of cholesterol and other lipids in both directions between the liver and peripheral tissues. This delicate balance may be disturbed by many factors, including contraceptive steroids. The metabolic steps influenced by administration of contraceptive steroids are summarized.

Relationships between DNA and protein polymorphisms of apolipoprotein B

The associations between four restriction fragment length polymorphisms (RFLPs) of the gene for human apolipoprotein B (apo B) and five antigen group (Ag) protein-polymorphisms of apo B have been investigated in 24 unrelated Finnish individuals. In this sample a complete correlation exists between the EcoRI RFLP and the Ag(t/z) polymorphism. There is strong association between the alleles of the XbaI RFLP and Ag(c/g) and a weaker one of the same XbaI site with Ag(x/y). Linkage disequilibrium is observed between the PvuII RFLP and the Ag(a1/d) polymorphism. These associations confirm that the Ag variants are true protein sequence polymorphisms of apo B.

Association between epitopes detected by monoclonal antibody BIP-45 and the XbaI polymorphism of apolipoprotein B

An epitope of Apolipoprotein B (ApoB), recognised by a monoclonal antibody BIP-45, is associated with the development of ischaemic heart disease (Duriez et al. 1988). We have examined the genetic relationships between this epitope and three Restriction Fragment Length Polymorphisms (RFLPs) of the gene for ApoB detected with the enzymes EcoRI, PvuII and XbaI in a sample of 53 unrelated individuals from France. There is an association between binding affinity to BIP-45 and the XbaI RFLP; the 8.6 kb XbaI allele (absence of cutting site) being associated with low-affinity binding to BIP-45. In this sample of individuals there is no significant association between serum cholesterol levels and BIP-45 binding affinity, but there is a significant correlation between serum cholesterol levels and XbaI genotype, with individuals of the genotype X1X1 having the highest and those with the genotype X2X2 having the lowest levels of serum cholesterol. This suggests that variation at the ApoB locus may be involved independently in the determination of serum lipid levels and in the development of ischaemic heart disease.