Effect of pyruvate on oxidant injury to isolated and cellular DNA

Drawing upon the capacity of pyruvate to detoxify H₂O₂, we demonstrate that pyruvate (i) protects against H₂O₂-dependent, hydroxyl radical mediated degradation of isolated DNA; (ii) reduces the amount of 8-hydroxy- 2-deoxyguanosine detected following oxidative injury to isolated DNA and (iii) diminishes the amounts of detectable hydroxyl radical generated by a H₂O₂-dependent system. Compared to mannitol, pyruvate protects weakly against oxidative degradation of DNA induced by a H₂O₂-independent, hydroxyl radical-generating system. The protective effects of pyruvate against H₂O₂-instigated DNA damage were also evinced in cells in culture exposed to H₂O₂. In contrast to its protective effects against H₂O₂- dependent injury to DNA, pyruvate failed to offer convincing protection to another intracellular, H₂O₂-vulnerable target, glyceraldehyde-3-phosphate dehydrogenase. The protection conferred by pyruvate to intracellular H₂O₂- vulnerable targets is thus influenced by the nature of the target exposed to H₂O₂. Pyruvate was markedly protective in a model of cytotoxicity induced by the concomitant depletion of cellular glutathione and inhibition of catalase activity; pyruvate can thus function as an intracellular antioxidant and in this latter model, no evidence of DNA damage was observed. Pyruvate, in contrast to catalase, is a potent protector against cytotoxicity induced by organic peroxides, a finding that cannot be explained by the scavenging of organic peroxides, differences in glutathione content or attenuation in oxidative injury to DNA. We conclude that while DNA damage is a key pathogenetic event in oxidative stress induced by H₂O₂, such nuclear changes may not universally subserve a critical role in models of H₂O₂- dependent cell death. We also conclude that the antioxidant capabilities of pyruvate extend beyond scavenging of H₂O₂ to include potent protection against cytotoxicity induced by organic peroxides.