HYDROPEROXIDE-INDUCED OXIDATIVE STRESS IMPAIRS HEART-MUSCLE CELL CARBOHYDRATE-METABOLISM

Hydrogen peroxide (H2O2) may incite cardiac ischemia-reperfusion injur y. We evaluate herein the influence of H2O2-induced oxidative stress o n heart muscle hexose metabolism in cultured neonatal rat cardiomyocyt es, which have a substrate preference for carbohydrate. Cardiomyocyte exposure to 50 mu M-1.0 mM bolus H2O2 transiently activated the pentos e phosphate cycle and thereafter inhibited cellular glucose oxidation and glycolysis. These metabolic derangements were nonperoxidative in n ature (as assessed in alpha-tocopherol-loaded cells) and occurred with out acute change in cardiomyocyte hexose transport or glucose/glycogen reserves. Glycolytic inhibition was supported by the rapid, specific inactivation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The degree of GAPDH inhibition correlated directly with the magnitude of t he oxidative insult and was independent of both metal-catalyzed H2O2 r eduction to free radicals and lipid peroxidation. Severe GAPDH inhibit ion was required for a rate-limiting effect on glycolytic flux. Cardio myocyte pyruvate dehydrogenase was also inhibited by H2O2 overload, bu t to a lesser degree than GAPDH such that entry of hexose-derived acet yl units into the tricarboxylic acid cycle was not as restrictive as G APDH inactivation to glycolytic ATP production. An increase in phospho fructokinase activity accompanied GAPDH inactivation, leading to the p roduction and accumulation of glycolytic sugar phosphates at the expen se of ATP equivalents. Cardiomyocyte treatment with iodoacetate or 2-d eoxyglucose indicated that GAPDH inactivation/glycolytic blockade coul d account for similar to 50% of the maximal ATP loss following H2O2 ov erload. Partial restoration of GAPDH activity after a brief H2O2 ''pul se'' afforded some ATP recovery. These data establish that specific as pects of heart muscle hexose catabolism are H2O2-sensitive injury targ ets. The biochemical pathology of H2O2 overload on cardiomyocyte carbo hydrate metabolism has implications for postischemic cardiac bioenerge tics and function.