Effects of Cold Injury–Induced Trauma in Manganese Superoxide Dismutase–Deficient Mice

Abstract

Manganese superoxide dismutase (Mn-SOD, SOD2) is an inducible antioxidant localized to the mitochondria, which have been shown to be both the sites of superoxide anion (O₂ ^.-) production and the target of free radical attacks. Knock-out mice with targeted disruption of Sod2 (SOD2-KO) are more susceptible to ischemic damage than their wild-type (WT) counterparts, showing increased loss of mitochondrial cytochrome c after trauma, but less apoptotic cell death in the first 24 h following controlled cortical injury. In this study, we sought to investigate whether oxidative stress plays a significant role in the development of secondary brain damage following cold injury-induced brain trauma (CIBT), a model of vasogenic edema. We first measured the levels of O₂ ^.- production 2 h after CIBT by means of in situ hydroethidine oxidation. We then examined lesion size, brain swelling, apoptosis by morphology and TUNEL-staining, neutrophil infiltration, and hemorrhage rates in both SOD2-KO and WT mice at 1, 3, and 7 days post-CIBT. We found no significant differences between SOD2-KO and WT littermates in any of the paradigms or endpoints studied. There was, however, a significant increase in hemorrhagic transformations in all animals that paralleled a robust inflammatory response at 3 days post insult compared with the 24-h endpoint. In the CIBT model used in this study, a 50% reduction in SOD2 activity did not appear to alter the injury response, suggesting that accumulation of free radicals does not play a significant role in secondary brain damage as previously thought with this particular model.