CHOLESTERYL ESTERS FROM OXIDIZED LOW-DENSITY LIPOPROTEINS ARE IN-VIVO RAPIDLY HYDROLYZED IN RAT KUPFFER CELLS AND TRANSPORTED TO LIVER PARENCHYMAL-CELLS AND BILE

Human low-density lipoprotein was labeled in its cholesteryl ester moiety with [H-3]cholesteryl oleate or [H-3]cholesteryl oleoyl ether and oxidized by exposure to 10 mu mol/L of cupric sulfate. The in vivo metabolism of cholesteryl esters of oxidized low-density lipoprotein was determined after injection into rats. When oxidized low density lipoprotein was labeled with [H-3]cholesteryl oleoyl ether, a nonhydrolyzabIe analog of cholesteryl oleate, Kupffer cells contributed to 55.1% +/- 4.1% of the total liver uptake 10 min after injection. When [H-3]cholesteryl oleate-labeled oxidized low-density lipoprotein was injected, the radiolabeled cholesterol esters were nearly completely hydrolyzed within 1 hr of injection. Within this time, the Kupffer cell-associated radioactivity declined to 32% of the maximal uptake value. In serum, the highest specific resecreted [H-3]cholesteryl (esters) were associated with the serum high-density lipoprotein fraction, suggesting a role for high-density lipoprotein as an in vivo cholesterol acceptor. The kinetics of biliary secretion were studied in rats equipped with catheters in the bile duct, duodenum and heart. One hour after injection of [H-3]cholesteryl oleate-labeled oxidized low-density lipoprotein, 4.15% +/- 0.67% of the injected dose was secreted in the bile, mainly as bile acids. Six hours after injection, this value was 19.2% +/- 1.2%. These values are three times higher than those for injected [H-3]cholesteryl oleate-labeled acetylated low-density lipoprotein, which is initially mainly taken up by liver endothelial cells. The rapid processing of cholesteryl esters derived from oxidized low-density lipoprotein to bile acids indicates that Kupffer cells form an efficient protection system against the atherogenic action of oxidized low-density lipoprotein in the blood compartment.