Plasma, apolipoprotein A-I and A-II levels in hyperlipidemia
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Some of the component moieties of high denisty lipoproteins (HDL) were analyzed in normal subjects and in patients with hyperlipidemia. Apoproteins A-I and A-II were quantified by radioimmunoassay, HDL cholesterol and triglycerides were assessed on heparin-MnCl2 supernates of fasting plasmas. We found that HDL is enriched in triglycerides in all forms of hyperlipidemia, while the proportion of ApoA-II is unaltered and the proportion of ApoA-I is decreased. Thus, the composition of HDL is altered in hypertriglyceridemia. The molecular associations of ApoA-I and ApoA-II in plasma were also examined by assaying the apoprotein contents of plasma fractions prepared by ultracentrifugation and by gel filtration column chromatography. The ApoA-I contents of d<1.063 fraction increased in hyperlipidemia from <0.5% to ∼2%, but the ApoA-I contents of the d>1.21 fraction remained at <12% of total in plasmas with triglyceride levels <1500 mg/dl. d>1.21 ApoA-I rose to 23% in one plasma with a triglyceride level of >1700 mg/dl. On column chromatography, ApoA-I eluted with the lipoproteins and also in a fraction whose molecular weight (MW) appreared to be ∼50,000 daltons. The proportion of plasma ApoA-I which eluted in the 50,000 MW peak was positively correlated with plasma triglyceride levels, but at triglyceride levels of <1500 mg/dl, <20% of ApoA-I was in the 50,000 MW peak. Between levels of ∼2000 and 12,000 mg/dl, the percentage “50,000 M.W. ApoA-I” was 20–25%. The ApoA-II contents of d<1.063 fractions were also increased in hyperlipidemia, but >95% of ApoA-II was found in the HDL fractions in both normal and hyperlipidemic plasma both by column chromatography and ultracentrifugation. Thus, the molecular association of ApoA-I appears to be altered in hyperlipidemia.
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