Metabolic consequences of genetic heterogeneity of lipoprotein composition (lipoprotein heterogeneity)

Segregation analysis of plasma apolipoprotein B levels in familial combined hyperlipidemia

Familial combined hyperlipidemia (FCH) is a heritable lipid disorder that is associated with an increased risk of premature cardiovascular disease. An elevated plasma apolipoprotein (apo) B concentration is reported to be a diagnostic feature of the disorder. Recently we demonstrated a strong relation between plasma apoB concentrations and the cholesterol concentration in VLDL plus LDL, both elevated in FCH families. Therefore, examination of the inheritance of elevated plasma apoB levels in FCH families may reveal important information about the mechanism responsible for the aggregation of elevated plasma lipids in FCH. This study included 663 Dutch family members in 40 families ascertained through FCH probands. Plasma apoB concentration correlated significantly with apoB-related cholesterol both in the probands and the relatives (r=.83 and r=.90, respectively). Adjustment for age, sex, body mass index, and smoking habits accounted for 35.7% of the variation in apoB levels, and there was strong familial aggregation in adjusted apoB levels in these families. Complex segregation analysis was performed to determine the mechanism of inheritance behind this familial aggregation. The aggregation of elevated apoB levels was best explained by a major gene effect inherited by a codominant mechanism. Estimated mean apoB levels for the three supposed genotypes AA, AB, and BB were 111.5, 126.7, and 165.7 mg/dL, respectively, with relative frequencies of 43.5%, 44.9%, and 11.6%, respectively. In conclusion, despite assumed metabolic and genetic heterogeneity of FCH, there is clear evidence for a single gene effect on apoB concentrations in families ascertained through FCH. Linkage studies based on this analysis may further clarify the molecular basis of the apoB regulation in these families.

Autoantibodies against malondialdehyde-modified LDL are elevated in subjects with an LDL subclass pattern B

Small low density lipoproteins (LDL) are more susceptible to in vitro oxidation than larger LDL. To study whether this leads to more oxidation of small LDL in vivo, we determined the level of autoantibodies against malondialdehyde-modified LDL (MDA-LDL) in subjects with small or large LDL (LDL subclass pattern B or A) by ELISA. The study group consisted of 92 subjects with coronary heart disease without severe hypercholesterolemia (mean total plasma cholesterol 5.9 +/- 0.8 mM), 46 with an LDL subclass pattern A and 46 with an LDL subclass pattern B. In the subjects with LDL subclass pattern B the titre of autoantibodies of the IgM class against MDA-LDL was 29% higher than in the subjects with LDL subclass pattern A (P < 0.0001). The concentration of the anti-MDA-LDL autoantibodies of the IgM class was 58% higher in the patients with the pattern B than in the patients with the pattern A (P < 0.0001). There was no statistically significant difference in the titre or concentration of autoantibodies of the IgG class between subjects with LDL subclass patterns A and B. Besides plasma triglyceride and HDL cholesterol, the titre and concentration of the IgM autoantibodies were found to be independent predictors of the LDL subclass pattern. These results show that small LDL are associated with higher autoantibody levels than large LDL. Based on the assumption that the level of autoantibodies against MDA-LDL represents the rate of LDL oxidation in vivo, we conclude that in vivo small LDL is more readily oxidised than larger LDL.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic lipase and lipoprotein lipase are not major determinants of the low density lipoprotein subclass pattern in human subjects with coronary heart disease

The influence of hepatic lipase (HL) and lipoprotein lipase (LPL) activity on the low density lipoprotein (LDL) subclass pattern was studied in a population of males with coronary heart disease and without severe hypercholesterolemia. LDL subclass patterns, lipases and plasma lipoproteins were determined in 326 patients. In part of the study population, fasting insulin and glucose levels were also determined. The LDL subclass pattern was determined by gradient gel electrophoresis (GGE) and classified according to Austin et al. (J. Am. Med. Assoc. 260 (1988) 1917 (predominantly large LDL = A-pattern, predominantly small LDL = B-pattern). An LDL subclass A-pattern was exhibited by 199 subjects; 108 exhibited a B-pattern. In 19 subjects no distinctive A- or B-pattern was present (A/B-pattern). Hepatic and lipoprotein activities differed significantly between patients with the A- or B-pattern. The median hepatic lipase activity was lower (384 vs. 417 mU/ml, P = 0.006), and the lipoprotein lipase activity higher (122 vs. 101 mU/ml, P = 0.001) in the A-pattern subjects than in the B-pattern subjects. In subjects with the A/B pattern the lipase activities were intermediate between the values in the A- and B-pattern subjects (HL 408 +/- 87 mU/ml, LPL 115 +/- 55 mU/ml). Plasma triglyceride, very low density lipoprotein (VLDL)-triglyceride, intermediate density lipoprotein (IDL)-triglyceride and LDL-triglyceride were higher in the patients with a B-pattern (+84%, +171%, +10% and +16%, respectively). Total plasma cholesterol was not different between A- and B-pattern subjects. VLDL- and IDL-cholesterol were higher in the B-pattern group (+174% and +66%, respectively), while LDL- and HDL-cholesterol were higher in the A-pattern group (+2 and +24%, respectively). In univariate analysis HL, LPL, plasma (and VLDL) triglyceride, HDL-cholesterol and IDL-cholesterol were each significantly associated with the LDL subclass pattern. In multivariate analysis plasma triglyceride (or VLDL-triglyceride) and HDL-cholesterol appeared to be independently associated with the LDL subclass pattern. No additional discriminative value of HL or LPL was found. Similar results were obtained if the patients with or without beta blocker were evaluated separately. An estimate of insulin resistance (EIR), calculated from plasma insulin and glucose in part of the study population (n = 145), was significantly higher in the subjects with a B-pattern than in those with an A-pattern (3.12 vs. 2.00, P < 0.003). EIR correlated positively with plasma triglyceride (P < 0.0001), but not with HL or LPL.(ABSTRACT TRUNCATED AT 400 WORDS)