Krebs cycle metabolites and preferential succinate oxidation following neonatal hypoxic-ischemic brain injury in mice

BACKGROUND: Reverse electron transport (RET) driven by the oxidation of succinate has been proposed as the mechanism of accelerated production of reactive oxygen species (ROS) in post-ischemic mitochondria. However, it remains unclear whether upon reperfusion, mitochondria preferentially oxidase succinate. METHODS: Neonatal mice were subjected to Rice-Vannucci model of hypoxicischemic brain injury (HI) followed by assessment of Krebs cycle metabolites, mitochondrial substrate preference, and H(2)O(2) generation rate in the ischemic brain. RESULTS: While brain mitochondria from control mice exhibited a rotenonesensitive complex-I-dependent respiration, HI-brain mitochondria, at the initiation of reperfusion, demonstrated complex-II-dependent respiration, as rotenone minimally affected, but inhibition of complex-II ceased respiration. This was associated with a 30-fold increase of cerebral succinate concentration and significantly elevated H(2)O(2) emission rate in HI-mice compared to controls. At sixty minutes of reperfusion, cerebral succinate content and the mitochondrial response to rotenone did not differ from that in controls. CONCLUSION: These data are the first ex-vivo evidence, that at the initiation of reperfusion, brain mitochondria transiently shift their metabolism from complex-I-dependent oxidation of NADH toward complex II-linked oxidation of succinate. Our study provides a critical piece of support for existence of the RET-dependent mechanism of elevated ROS production in reperfusion.