THE PROTECTIVE ROLE OF HIGH-DENSITY-LIPOPROTEIN ON OXDIZED-LOW-DENSITY-LIPOPROTEIN-INDUCED U937 ENDOTHELIAL CELL-INTERACTIONS/

The adherence of monocytes to the endothelium is an early event in ath erogenesis. We have investigated this process by examining whether nat ive and oxidized low-density and high-density lipoproteins could modul ate this process. Only oxidized low-density lipoprotein caused a signi ficant dose-dependent and time-dependent increase in U937 monocyte-lik e cell line binding to human endothelial cells, by a process which req uired de novo protein synthesis. Interestingly, E-selectin, intercellu lar 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 mo nocyte-like cells in response to oxidized low-density Lipoprotein. Hig h-density lipoprotein completely suppressed oxidized low-density-lipop rotein-induced adhesion of U937 cells to the endothelial monolayer, wh ile 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.