Abstract 328: Critical Role For Intra-mitochondrial NADPH Generation For Survival After Cardiac Arrest: Studies In The Nicotinamide Nucleotide Transhydrogenase Deficit Mouse

Abstract

INTRODUCTION: The loss of the mitochondrial nicotinamide nucleotide transhydrogenase (NNT) reduces antioxidant capacity within the mitochondrial compartment, is associated with cardiovascular, endocrine, and inflammatory disease states, but has not been evaluated for a role in reperfusion injury following cardiac arrest. The NNT-/- deficient mutant mouse becomes NADPH depleted during stress and provides an ideal model for studying stress induced antioxidant deficiency during reperfusion after cardiac arrest. HYPOTHESIS: Due to oxidant stress during reperfusion of initially successfully resuscitated NNT-/- mice, there will be rapid cardiovascular deterioration mimicking reperfusion injury, and evidence of impaired metabolism and activation of injury cascades. METHODS: Using a well described mouse hyperkalemic cardiac arrest model, we induced arrest for 8 min followed by attempted resuscitation in C57BL6N NNT+/+ wild type (N=8) and NNT-/- (N=9) mice. Our primary outcome was survival to 240 min. Tissue and plasma samples were obtained after the 240 minutes or at death. Additional animals were studied at 100 min post arrest to provide time-matched comparisons. Assays were performed for lactate, total antioxidant capacity, circulating Cytochrome c, cleaved caspase-3, and Parkin protein levels. RESULTS: All animals were initially resuscitated but significant differences in 240-min survival rate were observed for NNT+/+ (8/8) versus NNT-/- (3/9) mice; p<0.005. Early accelerated death was seen in the NNT-/- mice. Elevations in lactate and circulating Cytochrome c were observed in all animals. However, in the NNT-/- mice total antioxidant capacity was decreased and cleaved caspase-3 and Parkin protein was increased. Conclusions: NNT-/- deficiency creates a phenotype of signifcant early death during reperfusion, associated with increased apoptosis, Parkin protein, and decreased antioxidant capacity. This reperfusion accelerated death mimics hemondynamic collapse seen in patients who initially survive cardiac arrest but progress to death. Diminished NADPH generation within the mitochondrial compartment may be one pathway for reperfusion mediated injury and provides a potential new target for therapies after ischemia.