Native LDL increases endothelial cell adhesiveness by inducing intercellular adhesion molecule-1

Native LDL (n-LDL) increased human umbilical vein endothelial cell (EC) adherence of mononuclear cells. Such phenotypic changes suggest that n-LDL alters the usual expression of cell adhesion molecules to enhance the adhesive properties of the endothelium. To investigate n-LDL mechanisms governing adherence, ECs were exposed to n-LDL in concentrations up to 240 mg/dL for 2 and 4 days. n-LDL-treated ECs bound nearly threefold more phorbol myristate acetate (PMA)-stimulated U937 cells than control ECs but did not bind unstimulated U937 cells. Anti-cellular adhesion molecule-1 (ICAM-1) antibodies blocked PMA-stimulated U937 cell binding to control and n-LDL-treated ECs by more than 80%, suggesting that increases in ICAM-1 may be involved in this increased adherence. Although increases in PMA-stimulated U937 cell binding developed with respect to time and concentration, statistically significant increases were achieved only when n-LDL concentrations exceeded 180 mg cholesterol/dL at day 4. n-LDL increased endothelial adherence of freshly isolated human monocytes more than twofold and neutrophils by almost twofold. Fluorescent-linked immunoassays revealed that n-LDL increased ICAM-1 protein expression by twofold, which corresponded with increased ICAM-1 message levels. n-LDL also appeared to increase E-selectin and vascular cell adhesion molecule-1 message levels, but these changes did not translate into statistically significant differences in protein levels. Taken together, these data indicate that n-LDL increases ICAM-1 expression to enhance the adhesive properties of the endothelium. Such perturbations in EC function likely represent a proinflammatory response to protracted n-LDL exposure and one of the early steps in atherogenesis.