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.
- Hexose monophosphate shunt