Differential effects of HDL subpopulations on cellular ABCA1- and SR-BI-mediated cholesterol efflux

Our objective was to evaluate the associations of individual apolipoprotein A-I (apoA-I)-containing HDL subpopulation levels with ABCA1- and scavenger receptor class B type I (SR-BI)-mediated cellular cholesterol efflux. HDL subpopulations were measured by nondenaturing two-dimensional gel electrophoresis from 105 male subjects selected with various levels of apoA-I in pre-beta-1, alpha-1, and alpha-3 HDL particles. ApoB-containing lipoprotein-depleted serum was incubated with [(3)H]cholesterol-labeled cells to measure efflux. The difference in efflux between control and ABCA1-upregulated J774 macrophages was taken as a measure of ABCA1-mediated efflux. SR-BI-mediated efflux was determined using cholesterol-labeled Fu5AH hepatoma cells. Fractional efflux values obtained from these two cell systems were correlated with the levels of individual HDL subpopulations. A multivariate analysis showed that two HDL subspecies correlated significantly with ABCA1-mediated efflux: small, lipid-poor pre-beta-1 particles (P=0.0022) and intermediate-sized alpha-2 particles (P=0.0477). With regard to SR-BI-mediated efflux, multivariate analysis revealed significant correlations with alpha-2 (P=0.0004), alpha-1 (P=0.0030), pre-beta-1 (P=0.0056), and alpha-3 (P=0.0127) HDL particles. These data demonstrate that the small, lipid-poor pre-beta-1 HDL has the strongest association with ABCA1-mediated cholesterol even in the presence of all other HDL subpopulations. Cholesterol efflux via the SR-BI pathway is associated with several HDL subpopulations with different apolipoprotein composition, lipid content, and size.