The study of nonspecific internalization of cholesteryl esters by the Hep G2 hepatoma cells.

The cholesteryl oleate-POPC dispersions (1:3, mol/mol, mean particle size 110+/-20 nm) were taken up by the human hepatoma line Hep G2 cells via endocytosis. Internalization of the cholesteryl oleate-POPC dispersions by Hep G2 cells was dependent on the incubation time and dispersion concentration. At the cholesteryl oleate concentration 100 microM, its total uptake and internalization were found to be 1.5 nmol and 0.8 nmol per 1 mg of cell protein/24 h, respectively. Intracellular cleavage of the cholesteryl oleate incorporated in dispersions resulted in accumulation of free cholesterol capable of being released into the medium and metabolized to water-soluble polar products, presumably bile acids; oleic acid released is, apparently, involved in biosynthesis of triacylglycerides. The low-density lipoprotein receptor is not involved in internalization of lipid dispersions, and the presence of the cholesteryl oleate-POPC dispersions has no effect on the receptor-dependent internalization of cholesteryl esters of the low-density lipoproteins. The obtained data allow us to consider nonspecific internalization of cholesteryl esters by hepatocytes as a substantial part of the nonpolar lipid clearance.