Increased rate of hemorrhage in SOD2-deficient mice following transient focal cerebral ischemia
The development of knock-out (KO) mice with targeted disruption of the inducible manganese superoxide dismutase (SOD2) provided a model for investigating the effects of free radicals by perturbing the enzymatic machinery responsible for their metabolism. Previous research in our laboratory showed that heterozygous SOD2-KO mutants exhibited a 50% decrease in SOD2 activity. These animals were also more susceptible to ischemic damage than their wild-type (WT) counterparts and had a 30% mortality at 24 h following 1 h of focal ischemia. Mortality among SOD2-KO mice was increased when the reperfusion period was extended to 72 h. Therefore, animals in this study (SOD2-KO n=7; WT n=7) were subjected to 30 min of middle cerebral artery occlusion (MCAO), using the intraluminal suture method, which was sufficient to cause extensive and reproducible infarcts at 3 days post-insult as measured from H&E stained sections. Our results showed that 7 out of 7 SOD2-KO animals had hemorrhagic transformations (HT) at 72 h post-MCAO, while only 3 out of 7 WT animals exhibited HT (p=0.02 by Mann-Whitney U-test). Interestingly, the rate of HT did not always correlate with the size or anatomical distribution of the lesion. Hemorrhagic transformations were observed in the ischemic core and ischemic penumbra of both WT and SOD2-KO animals, however the latter also showed HT in histologically undamaged tissue. Three additional animals per group were also injected with Evan’s blue at 64 h post-insult and were perfusion-fixed at 72 h. Fifty μm coronal sections examined under fluorescence showed that SOD2-KO animals had extensive extravasation of the dye compared with their WT counterparts. Previous studies by our group did not show a significant increase in HT in SOD2-KO animals at 24 h post-insult compared with WT controls. This suggests that SOD2-KO animals undergo delayed disruption of the blood-brain barrier integrity and may serve as an ideal model for studying the effects of free radical mediated injury to the vascular endothelium.