Overexpression of Human Superoxide Dismutase Inhibits Oxidation of Low-Density Lipoprotein by Endothelial Cells

<jats:p> <jats:italic>Abstract</jats:italic> —Oxidation of LDL in the subendothelial space has been proposed to play a key role in atherosclerosis. Endothelial cells produce superoxide anions (O <jats:sub>2</jats:sub> <jats:sup>.−</jats:sup> ) and oxidize LDL in vitro; however, the role of O <jats:sub>2</jats:sub> <jats:sup>.−</jats:sup> in endothelial cell–induced LDL oxidation is unclear. Incubation of human LDL (200 μg/mL) with bovine aortic endothelial cells (BAECs) for 18 hours resulted in a 4-fold increase in LDL oxidation compared with cell-free incubation (22.5±1.1 versus 6.3±0.2 [mean±SEM] nmol malondialdehyde/mg LDL protein, respectively; <jats:italic>P</jats:italic> &lt;0.05). Under similar conditions, incubation of LDL with porcine aortic endothelial cells resulted in a 5-fold increase in LDL oxidation. Inclusion of exogenous copper/zinc superoxide dismutase (Cu/ZnSOD, 100 μg/mL) in the medium reduced BAEC-induced LDL oxidation by 79%. To determine whether the intracellular SOD content can have a similar protective effect, BAECs were infected with adenoviral vectors containing cDNA for human Cu/ZnSOD (AdCu/ZnSOD) or manganese SOD (AdMnSOD). Adenoviral infection increased the content and activity of either Cu/ZnSOD or MnSOD in the cells and reduced cellular O <jats:sub>2</jats:sub> <jats:sup>.−</jats:sup> release by two thirds. When cells infected with AdCu/ZnSOD or AdMnSOD were incubated with LDL, formation of malondialdehyde was decreased by 77% and 32%, respectively. Two other indices of LDL oxidation, formation of conjugated dienes and increased LDL electrophoretic mobility, were similarly reduced by SOD transduction. These data suggest that production of O <jats:sub>2</jats:sub> <jats:sup>.−</jats:sup> contributes to endothelial cell–induced oxidation of LDL in vitro. Furthermore, adenovirus-mediated transfer of cDNA for human SOD, particularly Cu/ZnSOD, effectively reduces oxidation of LDL by endothelial cells. </jats:p>