Cholesterol Efflux, Cholesterol Esterification, and Cholesteryl Ester Transfer by LpA-I and LpA-I/A-II in Native Plasma

Abstract

Abstract HDLs encompass structurally heterogeneous particles that fulfill specific functions in reverse cholesterol transport. Two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) of normal plasma and subsequent immunoblotting with anti–apolipoprotein (apo) A-I antibodies differentiates an abundant particle with electrophoretic α-mobility and less abundant particles with electrophoretic pre-β-mobility (preβ 1 –LpA-I, preβ 2 –LpA-I, preβ 3 –LpA-I). Immunodetection with anti–apoA-II antibodies identifies a single particle with α-mobility. To differentiate α-migrating HDL without apo A-II (α–LpA-I) from those with apoA-II (α–LpA-I/A-II), we combined 2D-PAGGE with immunoadsorption of apoA-II. Incubation of plasma with [ 3 H]cholesterol-labeled fibroblasts in combination with immunosubtracting 2D-PAGGE allowed us to analyze the role of α–LpA-I and α–LpA-I/A-II in the uptake and esterification of cell-derived cholesterol in native plasma. Depending on the duration of incubations with cells, α-LpA-I took up two to four times more [ 3 H]cholesterol than α–LpA-I/A-II. Irrespective of the duration of incubation, two to three times more [ 3 H]cholesteryl esters accumulated in α–LpA-I than in α–LpA-I/A-II. Subsequent incubations in the presence of an inhibitor of lecithin:cholesterol acyltransferase led to preferential accumulation of [ 3 H]cholesteryl esters in α–LpA-I/A-II. In conclusion, our data indicate that α–LpA-I is more effective than α–LpA-I/A-II in both uptake and esterification of cell-derived cholesterol. Moreover, α–LpA-I/A-II appears to accumulate cholesteryl esters, at least partially, from α–LpA-I.