Differences in the metabolism of oxidatively modified low density lipoprotein and acetylated low density lipoprotein by human endothelial cells: inhibition of cholesterol esterification by oxidatively modified low density lipoprotein.
The rate of degradation of oxidatively modified low density lipoprotein (Ox-LDL) by human endothelial cells was similar to that of unmodified low density lipoprotein (LDL), and was approximately 2-fold greater than the rate of degradation of acetylated LDL (Ac-LDL). While LDL and Ac-LDL both stimulated cholesterol esterification in endothelial cells, Ox-LDL inhibited cholesterol esterification by 34%, demonstrating a dissociation between the degradation of Ox-LDL and its ability to stimulate cholesterol esterification. Further, while LDL and Ac-LDL resulted in a 5- and 15-fold increase in cholesteryl ester accumulation, respectively, Ox-LDL caused only a 1.3-fold increase in cholesteryl ester mass. These differences could be accounted for, in part, by the reduced cholesteryl ester content of Ox-LDL. However, when endothelial cells were incubated with Ac-LDL in the presence and absence of Ox-LDL, Ox-LDL led to a dose-dependent inhibition of cholesterol esterification without affecting the degradation of Ac-LDL. This inhibitory effect of Ox-LDL on cholesteryl ester synthesis was also manifest in normal human skin fibroblasts incubated with LDL and in LDL-receptor-negative fibroblasts incubated with unesterified cholesterol to stimulate cholesterol esterification. Further, the lipid extract from Ox-LDL inhibited cholesterol esterification in LDL-receptor negative fibroblasts. These findings suggest that the inhibition of cholesterol esterification by oxidized LDL is independent of the LDL and scavenger receptors and may be a result of translocation of a lipid component of oxidatively modified LDL across the cell membrane.
Jialal
I
I
Department of Medicine, University of Washington, Seattle 98195.
Chait
A
A
D000107:Acetylation; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism*; D004587:Electrophoresis, Agar Gel; D004730:Endothelium, Vascular / Q000378:metabolism*; D006801:Humans; D008077:Lipoproteins, LDL / Q000378:metabolism*; D010084:Oxidation-Reduction; D011973:Receptors, LDL / Q000378:metabolism
D002788:Cholesterol Esters; D008077:Lipoproteins, LDL; D011973:Receptors, LDL; D002784:Cholesterol