Different Effects of Subclasses of HDL Containing ApoA-I but Not ApoA-II (LpA-I) on Cholesterol Esterification in Plasma and Net Cholesterol Efflux From Foam Cells

Abstract

Abstract We investigated the effects of subclasses of plasma LpA-I (HDL containing apoA-I but not apoA-II) on cholesterol esterification in plasma and net cholesterol efflux from foam cells. LpA-I was composed of particles of three diameters: large (11.1 nm; Lg–LpA-I), medium (8.8 nm; Md–LpA-I), and small (7.7 nm; Sm–LpA-I). Plasma concentrations of LpA-I were positively correlated only with the level of Lg–LpA-I. Plasma concentrations of Lg–LpA-I were inversely correlated with the rate of cholesterol esterification in plasma and VLDL- and LDL-depleted plasma. Plasma concentrations of Md–LpA-I and Sm–LpA-I did not correlate with the rate of cholesterol esterification in plasma or VLDL- and LDL-depleted plasma. When macrophage foam cells were incubated with Md– and Sm–LpA-I, cellular cholesterol mass was reduced by approximately 70%. In contrast, the cellular cholesterol–reducing capacity of Lg–LpA-I was negligible. Lg–LpA-I inhibited net cholesterol removal from foam cells that was mediated by Md– and Sm–LpA-I and cholesteryl ester production with these particles. These results suggest that Md– and Sm–LpA-I may actively participate in cellular cholesterol removal and cholesterol esterification in plasma and HDL, while Lg–LpA-I may regulate these functions of Md– and Sm–LpA-I.