Low-density lipoprotein augments interleukin-1-induced vascular adhesion molecule expression in human endothelial cells.

In this study, the effect of low density lipoproteins (LDL) on the ability of the vascular endothelium to respond to vascular cell adhesion molecule 1 (VCAM-1) activation by a cytokine was investigated. After a 4-day pre-exposure to 240 mg/dl of LDL, human umbilical vein endothelial cells (HUVECs) were hyperresponsive to minute amounts of interleukin 1 alpha (IL-1 alpha) as demonstrated by an augmentation of VCAM-1 gene expression. Furthermore, in response to LDL exposure, endothelial recruitment of monocytes induced by minute amounts of IL-1 alpha was increased. This enhancing effect was blocked by an anti-VCAM antibody. The increased response appears not to be due to changes in IL-1 binding affinity or induction of endogenous IL-1 alpha. Transient transfection of HUVECs with a reporter driven by the VCAM promoter showed that LDL increased cellular response to IL-1 alpha by 46%. LDL itself does not increase NF-kappa B binding in endothelial cells (ECs). However, after a 2-day LDL incubation, NF-kappa B binding could be induced by over 63% with a very low dose of IL-1 alpha. IL-1 alpha at this dose (which activates NF-kappa B, but not AP-1) also enhanced LDL-activated AP-1 binding. This cross-enhanced effect may be an important intracellular signaling mechanism for EC activation. The results from this study provide new clues to understanding the mechanisms governing combined risk factors for atherosclerosis.