Reverse cholesterol transport: relationship between free cholesterol uptake and HDL3 in normolipidaemic and hyperlipidaemic subjects

Abstract

High density lipoproteins (HDL) are responsible for the Reverse Cholesterol Transport (RCT). The role of the composition of the HDL particle in RCT, involving free cholesterol (chol) uptake from cell membranes, is not completely understood. We have therefore studied the uptake capacity from subjects with a wide variety of plasma HDL cholesterol concentrations in an HDL-receptor free model consisting of bovine heart mitochondrial membranes labeled with [14C]cholesterol. HDL were isolated by molecular sieve chromatography from fresh plasma samples of eight subjects with low plasma HDL chol concentrations (< or equal to 1.0 mmol L-1) and 15 subjects with normal HDL chol concentrations. The latter were subdivided into an intermediate (HDL chol: 1.0-1.4 mmol L-1; n =9) and a high HDL chol group (> or equal to 1.4 mmol L-1; n = 6). In the HDL fractions isolated by chromatography (cHDL), total chol and apolipoprotein (apo) AI were measured. Free chol uptake was significantly decreased by 32% in the tertile with the lowest plasma HDL chol (49.1 +/- 15.8 arbitrary units; mean +/- SD), compared to the tertile with high HDL chol (72.1 +/- 16.6 au). Linear regression analysis showed a positive correlation between the free chol uptake and plasma HDL3 concentrations (r = 0.61; P < 0.01), HDL chol (r = 0.56; P < 0.01), HDL associated apo AI (R = 0.46; P < 0.05), cHDL apo AI (r = 0.56; P < 0.05) and cHDL chol (r = 0.46; P < 0.05) in all subjects combined. Stepwise multiple-regression analysis confirmed the association of [14C] cholesterol uptake with plasma HDL3 concentrations (beta, 0.61; P = 0.004). No correlations were found between free chol uptake and total plasma apo AI (r = 0.26. ns) or HDL2 (r = 0.27; ns). After an oral fat load in four FCH patients, free chol uptake paralleled the changes in plasma HDL 3 chol concentrations. We conclude that HDL3 is involved in the early steps of RCT and low HDL 3 levels may result in less efficient RCT in hypertriglyceridemia.