Abstract 239: Augmented Cardiac Pyruvate Dehydrogenase Complex Flux During Hypoxia Increases Post-hypoxic Damage

Abstract

Modulation of cardiac pyruvate dehydrogenase complex (PDC) flux is known to alter post-ischemic myocardial injury. Hypoxia is intrinsic to ischemia, but its specific role in cardiac injury is unknown. We hypothesized that post-hypoxic cardiac injury would be attenuated with activation of the PDC complex during hypoxia. Mouse hearts were isolated and Langendorff perfused with 0.4mM palmitate and 11mM glucose. Following 30min of normoxia, hearts were subjected to 30min hypoxia (20% of normoxic pO2) followed by 30min of reoxygenation. PDC flux was increased by infusion of 1mM dichloroacetate (DCA), either from onset of hypoxia, or with onset of reoxygenation. Cardiac function was measured using an IV balloon, and fatty acid β-oxidation determined via 3H-labelling. Lactate efflux was assayed from timed buffer collections. Hearts were frozen at end-normoxia, end-hypoxia and end-reoxygenation, and assayed for PDC flux, and phosphate metabolites. Reactive oxygen species formation was assessed by Western blotting of protein carbonyls. End-hypoxic cardiac PDC flux fell to 41±5% of pre-hypoxic values (0.96 of 2.37 μmol/gdwt, p<0.001) with β-oxidation also lower (25±11%, 0.06 of 0.24 μmol/min/gwwt, p<0.025). Lactate efflux increased 2.3-fold (4.7 to 10.6 μmol/min/gwwt, p<0.028) and AMP/ATP ratio 5.3-fold (0.04 to 0.21 p<0.002). DCA infusion increased end-hypoxic PDC flux (170±16%, 1.64 of 0.96 μmol/gdwt, p<0.003), reducing lactate efflux (47±8%, 5 of 11 μmol/min/gwwt, p<0.021) and AMP/ATP ratio (43±12%, 0.09 of 0.21, p<0.025). Control hearts were damaged by hypoxia, final recovery being 63±7% of pre-hypoxic function (18 of 29 bpm.mmHg.103). Hypoxic DCA infusion impaired recovery (49±4%, 15 of 31 bpm.mmHg.103), compared to DCA infusion during reoxygenation (63±3%, 19 of 30 bpm.mmHg.103, p<0.023). Reactive oxygen species formation was not altered. Increasing PDC flux during hypoxia significantly modified myocardial substrate metabolism. In contrast to the reported beneficial effects of augmented PDC flux during ischemia, increasing PDC flux in the hypoxic heart exacerbated myocardial injury. These results indicate that the potentially therapeutic effects of increasing PDC flux are not dependent on the hypoxic aspect of myocardial ischemia.