Effect of pyruvate on oxidant injury to isolated and cellular DNA

Effect of pyruvate on oxidant injury to isolated and cellular DNA. Drawing upon the capacity of pyruvate to detoxify H 2 O 2 , we demonstrate that pyruvate (i) protects against H 2 O 2 -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 H 2 O 2 -dependent system. Compared to mannitol, pyruvate protects weakly against oxidative degradation of DNA induced by a H 2 O 2 -independent, hydroxyl radical-generating system. The protective effects of pyruvate against H 2 O 2 -instigated DNA damage were also evinced in cells in culture exposed to H 2 O 2 . In contrast to its protective effects against H 2 O 2 -dependent injury to DNA, pyruvate failed to offer convincing protection to another intracellular, H 2 O 2 -vulnerable target, glyceraldehyde-3-phosphate dehydrogenase. The protection conferred by pyruvate to intracellular H 2 O 2 -vulnerable targets is thus influenced by the nature of the target exposed to H 2 O 2 . 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 H 2 O 2 , such nuclear changes may not universally subserve a critical role in models of H 2 O 2 -dependent cell death. We also conclude that the antioxidant capabilities of pyruvate extend beyond scavenging of H 2 O 2 to include potent protection against cytotoxicity induced by organic peroxides.