ATHEROGENIC LEVELS OF LOW-DENSITY-LIPOPROTEIN INCREASE HYDROGEN-PEROXIDE GENERATION IN CULTURED HUMAN ENDOTHELIAL-CELLS - POSSIBLE MECHANISM OF HEIGHTENED ENDOCYTOSIS

Cultured human umbilical vein endothelial cells (EC) exposed to athero genic low-density lipoprotein (LDL) levels have augmented reactive oxy gen species generation. Confluent EC were incubated with 30-330 mg/dl LDL cholesterol and cellular hydrogen peroxide (H2O2) generation measu red. EC incubated with 30 and 90 mg/dl LDL cholesterol showed similar low level H2O2 production. In contrast, EC exposed to 180 and 330 mg/d l LDL cholesterol have a marked, dose-related elevation in H2O2 genera tion. Subsequent studies have explored if direct EC exposure to H2O2 p romotes cellular functional changes similar to those induced by high L DL levels (>160 mg/dl cholesterol). Confluent EC were incubated with 0 .1 - 10 mM H2O2 for 30 minutes and endocytosis measured and cytoskelet al structure examined. H2O2 exposure (0.5 and 1 mM) promoted heightene d EC endocytosis, which similarly occurs with high LDL exposure. Likew ise, cytoskeletal examination of EC perturbed with 1 mM H2O2 reveals s tructural remodeling with a marked increase in stress fibers, which si milarly happens with high LDL levels. The above observations that high LDL levels cause increased EC H2O2 production, and direct H2O2 exposu re promotes cellular functional changes similar to those induced by hi gh LDL concentrations, suggest a modulatory role for reactive oxygen s pecies. Thus LDL-induced reactive oxygen species generation may contri bute mechanistically to endothelial perturbation, which has been hypot hesized to be a major contributing factor in the pathogenesis Of ather osclerosis. (C) 1996 Wiley-Liss, Inc.