The protective role of high-density lipoprotein on oxidized-low-density-lipoprotein-induced U937/endothelial cell interactions

The adherence of monocytes to the endothelium is an early event in atherogenesis. We have investigated this process by examining whether native and oxidized low-density and high-density lipoproteins could modulate this process. Only oxidized low-density lipoprotein caused a significant dose-dependent and time-dependent increase in U937 monocyte-like cell line binding to human endothelial cells, by a process which required de novo protein synthesis. Interestingly, E-selectin, intercellular adhesion molecule-1, vascular cell-adhesion molecule or P-selectin induction was not apparent in this system suggesting the presence of an alternative system for the interaction of endothelial cells with monocyte-like cells in response to oxidized low-density lipoprotein. High-density lipoprotein completely suppressed oxidized low-density-lipoprotein-induced adhesion of U937 cells to the endothelial monolayer, while oxidized high-density lipoprotein did not. These data suggest that the balance between native and oxidized lipoproteins may play a role in the formation of the atherosclerotic lesion by modulating monocyte endothelial interactions.