ApoA-I dissociated from human HDL retains its acceptor properties in ABCA1-mediated cholesterol efflux from RAW 264.7 macrophages in coronary artery disease

The significance of cholesterol efflux as a predictor of coronary artery disease (CAD) remains controversial. The major pathway of the export of intracellular cholesterol by the ABCA1 transporter includes the acceptance of effluxed cholesterol by lipid-free apolipoprotein A-I and/or high-density lipoproteins (HDL). To separate the contribution of lipid-free and lipid-bound apoA-I with different efficiencies in the total cholesterol efflux and underlying mechanism, we measured apoA-I dissociation concomitant with HDL denaturation, the expression of preselected genes, and the efficiency of cholesterol efflux. HDL preparations from plasma of 63 control and 76 CAD male patients were denatured by 4.25 M urea at the transition midpoint. ApoA-I partitioned 1.5-fold higher into the water phase for HDL from CAD patients relative to controls. The dissociation parameter D was reciprocally correlated with phospholipid and cholesterol levels and PL:apoA-I ratio in HDL from CAD patients. For control patients, the D parameter was positively correlated with CETP and ABCA1 expression level. For CAD patients, the D parameter was negatively correlated with CUBN and ALB expression levels that may be associated with the increased catabolism of lipid-free apoA-I. The apoA-I functionality in ABCA1-mediated cholesterol efflux from RAW 264.7 macrophages to urea-pretreated HDL revealed by V _m , K _m , and V _m /K _m values was similar for HDL from both cohorts. The enrichment of HDL with phospholipid and cholesterol could be involved in the increased apolipoprotein dissociation in CAD. The estimates of the contribution of both lipid-free and lipid-bound apoA-I to total cholesterol efflux are required to accurately describe them as CAD predictors.