Abstract
Plasma triglyceride (TG) -rich lipoproteins, chylomicrons and VLDL, vary in lipid composition during their metabolism : specifically their cholesterol content in the surface and cholesteryl oleate (CO) in the core. Using lipid emulsions of defined composition as model particles, we investigated the effects of the lipid composition on the surface and core structures and the binding of apolipoproteins to the emulsion surface. We have demonstrated that an increase in surface cholesterol of emulsions causes the acyl chain condensation of surface phospholipids, resulting in the significant decrease in the binding of apolipoproteins such as apoA-I and C-II. We have also shown that the physical states of not only surface but also core lipids affect the binding behavior of apolipoproteins, such that replacing core TG with CO significantly decreases the mobility of core lipids and the binding of apoE. In addition, replacing core TG with CO is found to cause the relocation of cholesterol in the emulsion surface layers and thereby modulates the surface properties. As a result, exchangeable apolipoproteins such as apoC-II and apoE will dissociate from the cholesterol-enriched, CO-core emulsions that represent the lipid composition of LDL. These results suggest that the binding behavior of exchangeable apolipoproteins may closely correlate with the location of surface cholesterol and the mobility of core lipids.
