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

From the Departments of Biochemistry (X.F., A.A.S.), Internal Medicine (N.L.W., C.D.R., D.A.C., D.D.H., A.A.S.), Pharmacology (D.D.H.), and the Radiation Research Laboratory (L.W.O., T.Y.), University of Iowa College of Medicine, Iowa City, and the Institute for Human Gene Therapy (R.M.Z., J.F.E.), University of Pennsylvania Medical Center, Philadelphia.

Correspondence to Arthur A. Spector, MD, Department of Biochemistry, 4-403 BSB, University of Iowa, Iowa City, IA 52242.

Abstract—Oxidation of LDL in the subendothelial space has been proposed to play a key role in atherosclerosis. Endothelial cells produce superoxide anions (O₂^.-) and oxidize LDL in vitro; however, the role of O₂^.- 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; P<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 O₂^.- 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 O₂^.- 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.

Key Words: low density lipoprotein • superoxide anion • superoxide dismutase • gene transfection • endothelial cell

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