The influence of apolipoproteins on the structure and function of spheroidal, reconstituted high density lipoproteins

Abstract

This study investigates the influence of apolipoproteins on the structure and function of spheroidal, reconstituted high density lipoproteins (rHDL). Spheroidal rHDL containing apolipoprotein (apo) A-I, (A-I)rHDL, were prepared by incubating discoidal rHDL with low density lipoproteins and lecithin:cholesterol acyltransferase. Spheroidal rHDL containing apoA-II, (A-II)rHDL, were prepared by displacing apoA-I from (A-I)rHDL with apoA-II. When the (A-I)rHDL were subjected to agarose gel electrophoresis, their migration was retarded relative to native HDL. The (A-II)rHDL migrated slower than either the (A-I)rHDL or native HDL. Spectroscopic studies showed that the packing order of the rHDL phospholipids was independent of apolipoprotein composition and that the polarity, or hydration, of the lipid-water interface of the (A-I)rHDL was greater than that of the (A-II)rHDL. When the rHDL were incubated with very low density lipoproteins (VLDL) and cholesteryl ester transfer protein, comparable amounts of cholesteryl ester (CE) were transferred from (A-I)rHDL and (A-II)rHDL to VLDL. The transfer of triglyceride (TG) from VLDL to (A-I)rHDL and (A-II)rHDL was also comparable. Similar results were obtained when Intralipid was substituted for VLDL. It is concluded that (i) apolipoproteins influence the surface charge of spheroidal rHDL, (ii) the hydration of the lipid-water interface of (A-I)rHDL is greater than that of (A-II)rHDL and (ii) cholesteryl ester transfer protein-mediated transfers of CE and TG between spheroidal rHDL and TG-rich particles are independent of rHDL apolipoprotein composition.