IN-VITRO REVERSE CHOLESTEROL TRANSPORT FROM THP-1-DERIVED MACROPHAGE-LIKE CELLS WITH SYNTHETIC HDL PARTICLES CONSISTING OF PROAPOLIPOPROTEIN A1 OR APOLIPOPROTEIN A1 AND PHOSPHATIDYLCHOLINE

The human monocytic leukaemia cell line THP-1 was induced to different iate to macrophage-like cells by the addition of phorbol myristoyl ace tate (PMA). Subsequently, the cells were enriched in cholesterol and t hese cholesterol laden cells were used to study the capability of reco nstituted discoidal complexes (RDCs), consisting of either human apoli poprotein A1 (apo A1) or recombinant human proapolipoprotein A1 (proap o A1) and phosphatidylcholine (PC), to promote cholesterol efflux. RDC s containing apo A1 and proapo A1 were both effective in the mobilizat ion of intracellular cholesterol, whether this was measured by intrace llular cholesterol mass or by the appearance of radiolabelled choleste rol in the supernatant. Using the radiolabelling technique, the activi ty was saturable and followed Michaelis-Menten kinetics. For both type s of complexes and for native HDL the maximum rate of cholesterol remo ved was approximately 0.5 nmol h(-1) per 10(6) cells. For RDCs of proa po A1 and apo A1 and for native HDL the K-m values were 3.7, 2.9 and 6 4.8 mu g ml(-1) respectively. A significant in vitro cholesterol efflu x could only be achieved with protein-lipid complexes; no significant export was observed with either free proapo A1 or multilamellar PC lip osomes without apolipoprotein. Both RDCs were found to be more active in the mobilization of intracellular cholesterol than HDL isolated fro m human plasma. The combined results demonstrate that synthetic comple xes consisting either of apo A1 or proapo A1 and PC are both active in the in vitro reverse transport of cholesterol.