TRANSFER OF CHOLESTEROL FROM OB1771 CELLS OR LDL TO RECONSTITUTED, DEFINED HIGH-DENSITY-LIPOPROTEINS

We used defined, reconstituted high density lipoproteins (rHDL) to stu dy the effects of structure and composition of these particles on thei r role as cholesterol accepters from cell membranes or from low densit y lipoproteins (LDL). Three discoidal rHDL and one spherical rHDL with distinct apolipoprotein A-T conformations, diameters, and composition s were used in conjunction with Ob1771 cells to measure the rate of [H -3]cholesterol efflux from the cells, direct binding to the cells, and competition with native HDL(3) for binding. In addition, the same rHD L particles were used to study the kinetics of cholesterol mass transf er from LDL. The results show that the rates of cholesterol transfer d epend on the nature of the donor (t1/2 11-19 min from LDL, and t1/2 5 h from the cells), on the phosphatidylcholine/cholesterol ratio in the accepters (the closer this ratio is to the equilibrium value, the slo wer is the rate), and on the diameter of the accepters (the smallest p articles have the lowest t1/2 for cholesterol uptake from LDL, and are the most effective accepters of [H-3]cholesterol from cells after the ir phospholipid content is taken into account). The cholesterol uptake by the rHDL, both from the cells and from LDL, is determined mostly b y the phospholipid pool available in the accepters. Binding to the cel ls was equivalent for all the rHDL (K-d = 38-67 mu g/ml) and comparabl e to HDL(3), suggesting that the differences in apoA-I conformation ha ve no effect on the binding to cells. Finally we observed that exposur e of rHDL to cells may lead to remodeling of some of the lipoprotein p articles.