Studies on the lipid and apolipoprotein compositions of two species of apoA-I-containing lipoproteins in normolipidemic males and females

Two species of apoA-I-containing lipoproteins (A-ILp), lipoprotein containing apoA-I and apoA-II (LpA-I/A-II) and lipoprotein containing apoA-I but no apoA-II (LpA-I), have been isolated from 20 normolipidemic adults (10 males and 10 females) by immunoaffinity chromatography. We have characterized the lipid and apolipoprotein compositions in these lipoproteins, and found sex differences. In A-ILp, the levels of lipids, except triglyceride, and the level of apoE were significantly higher in females than in males. In LpA-I/A-II, sex differences were found only in the levels of apoA-I and apoE. In LpA-I, the levels of all lipids, except triglyceride, and the level of apoA-I were significantly higher in females than in males. Therefore, sex differences observed in A-ILp appear to be due primarily to the differences found in LpA-I. Of considerable significance is our finding that the ratio of cholesteryl ester to total cholesterol in LpA-I was significantly lower than that in LpA-I/A-II in both males and females. This might suggest that LpA-I could be a carrier of free cholesterol.