Pyruvate restores contractile function and antioxidant defenses of hydrogen peroxide-challenged myocardium

Purpose: Pyruvate, a natural energy-yielding fuel in myocardium, neutralizes peroxides by a direct decarboxylation reaction, and indirectly augments the glutathione (GSH) antioxidant system by generating NADPH reducing power via citrate formation. The possibility that pyruvate's antioxidant actions could mediate its enhancement of contractile performance in prooxidant-challenged myocardium was investigated in isolated working guinea-pig hearts reversibly injured by hydrogen peroxide. Methods: Hearts were challenged by 10 min perfusion with 100 μM H₂O₂, followed by 90 min H₂O₂-free perfusion. Metabolic and antioxidant treatments (each 5 mM) were administered at 30-90 min post-H₂O₂. Phosphocreatine phosphorylation state, GSH/glutathione disulfide redox potential (GSH/GSSG) and key enzyme activities were measured in snap-frozen myocardium. Results: H₂O₂ exposure depleted myocardial energy and antioxidant reserves and produced marked contractile impairment that persisted throughout the H₂O₂ washout period. Relative to untreated post-H₂O₂ myocardium, pyruvate restored contractile performance, increased GSH/GSSG 52% and maintained phosphocreatine phosphorylation state: in contrast, lactate lowered cardiac performance and phosphorylation state. Neither the pharmacological antioxidant N-acetylcysteine (NAC) nor the pyruvate analog α-ketobutyrate increased cardiac function; both treatments increased GSH/GSSG but lowered phosphocreatine potential. H₂O₂ partially inactivated aconitase, creatine kinase and glyceraldehyde 3-phosphate dehydrogenase (GAPDH), but all three enzymes spontaneously recovered during H₂O₂ washout. Pyruvate did not further activate these enzymes and unexpectedly inhibited GAPDH by 60-70%. Conclusion: Pyruvate promoted robust contractile recovery of H₂O₂-challenged myocardium by the combination of citrate-mediated antioxidant mechanisms and maintenance of myocardial energy reserves.