Manganese Superoxide Dismutase Deficiency Exacerbates Cerebral Infarction After Focal Cerebral Ischemia/Reperfusion in Mice Implications for the Production and Role of Superoxide Radicals

Abstract

BACKGROUND AND PURPOSE: Superoxide anion radicals (O2*-) are implicated in ischemia/reperfusion injury, although a direct relationship has not been elucidated. Recently, a specific method of hydroethidine (HEt) oxidation by O2*- was developed to detect O2*- production in a variety of experimental brain injury models. To clarify the role of O2*- in the mechanism of ischemia/reperfusion, we investigated O2*- production after ischemia/reperfusion and ischemia/reperfusion injury in mutant mice deficient in mitochondrial manganese superoxide dismutase (MnSOD) and in wild-type littermates. METHODS: Ischemia/reperfusion was performed for 60 minutes using intraluminal suture blockade of the middle cerebral artery in the mutant or wild-type mice. We evaluated fluorescent kinetics of HEt or ethidium, the oxidized form of HEt, in brains after an intravenous injection of HEt, followed by measurement of cellular O2*- production using specific HEt oxidation by O2*- before and after ischemia/reperfusion. Furthermore, we compared O2*- production and subsequent infarct volume in the mice using triphenyltetrazolium chloride after ischemia/reperfusion. RESULTS: HEt oxidation to ethidium is primarily a result of mitochondrially produced O2*- under physiological conditions. Cerebral ischemia/reperfusion produced O2*- prominently in neurons shortly after reperfusion, followed by a delayed increase in endothelial cells. A deficiency in MnSOD in mutant mice increased mitochondrial O2*- production and exacerbated cerebral infarction, worsening neurological deficits after ischemia/reperfusion. CONCLUSION: These results suggest that mitochondrial O2*- production may be a critical step underlying the mechanism of ischemia/reperfusion injury and that MnSOD may protect against ongoing oxidative cell death after ischemia/reperfusion.