Remodeling of HDL containing apoA-I but not apoA-II (LpA-I) by lipoprotein-deficient plasma and hepatic lipase: its effect on the structure and cellular cholesterol-reducing capacity of LpA-I.

We investigated the effects of lipoprotein-deficient plasma (LDP) and hepatic lipase (HL) on the structure and cellular cholesterol-reducing capacity of subclasses of LpA-I (HDL containing apoA-I but not apoA-II). LpA-I is composed of large (11.1 nm; L-LpA-I), medium (8.8 nm: M-LpA-I) and small (7.7 nm: S-LpA-I) particles. L-LpA-I and M- and S-LpA-I combined (MS-LpA-I) were incubated with lipoprotein-deficient plasma and HL in the presence of very low density lipoprotein (VLDL). After incubation of L-LpA-I, the proportions of cholesteryl esters and phospholipids decreased and as a result, the proportion of protein increased. The remodeled L-LpA-I particles were generally smaller (spherical: 7.8-8.8 nm) in diameter. A small number of disc-shaped particles were also found in electron photomicrographs. These changes coincided with a slower electrophoretic mobility of remodeled L-LpA-I. In the case of MS-LpA-I, only the proportion of free cholesterol increased after incubation, and MS-LpA-I particles did not change in size. The cholesterol-reducing capacities of remodeled L-LpA-I and MS-LpA-I from macrophage foam cell were slightly higher and lower than their respective original counterparts, although neither of these differences was statistically significant. These results suggest that LDP and HL mainly contribute to the remodeling of L-LpA-I particles, and may not affect the cellular cholesterol-reducing capacity of these particles.