S-nitrosoglutathione inhibits SOD/H₂O₂-dependent lipid peroxidation

The peroxidase activity of superoxide dismutase (SOD) has been attributed to the increased lipid peroxidation observed during the reaction between linoleic acid, SOD and H₂O₂. The copper-bound hydroxyl radical was proposed to abstract an hydrogen atom from linoleate and initiate lipid peroxidation. To better understand the mechanism of SOD/H₂O₂-catalyzed lipid peroxidation, we have used S-nitrosoglutathione (GSNO) as an antioxidant probe. Addition of H₂O₂ (1 mM) to an incubation mixture containing egg phosphatidylcholine liposomes (250 μg/ml) and SOD (200 μg/ml) caused an increase in the formation of conjugate diene which was inhibited by the addition of diethylenetriaminepentaacetic acid (DTPA). Addition of GSNO caused a dose-dependent increase in time-lag for conjugate diene formation. Nitric oxide released from GSNO in the presence of SOD and H₂O₂ was measured by electron spin resonance spectroscopy. We attribute the increase in lipid peroxidation caused by SOD and H₂O₂ to the copper ions released from SOD that subsequently catalyzes the lipid hydroperoxide-dependent oxidation. The antioxidant activity of GSNO is attributed to the copper ion dependent release of nitric oxide, which acts as a chain breaking antioxidant. We conclude that GSNO can act as a potent antioxidant in biological systems where free copper ions released from metalloproteins catalyze peroxidation of lipid.