Copper-zinc superoxide dismutase prevents the early decrease of apurinic/apyrimidinic endonuclease and subsequent DNA fragmentation after transient focal cerebral ischemia in mice

Background and Purpose-DNA damage and its repair mechanism are thought to b e involved in ischemia/reperfusion injury in the brain. We have previously shown that apurinic/apyrimidinic endonuclease (APE/Ref-1), a multifunctiona l protein in the DNA base excision repair pathway, rapidly decreased after transient focal cerebral ischemia (FCI) before the peak of DNA fragmentatio n. To further investigate the role of reactive oxygen species in APE/Ref-1 expression in vivo, we examined the expression of APE/Ref-1 and DNA damage after FCI in wild-type and transgenic mice overexpressing copper-zinc super oxide dismutase, Methods-Transgenic mice overexpressing copper-zinc superoxide dismutase and wild-type littermates were subjected to 60 minutes of transient FCI by int raluminal blockade of the middle cerebral artery, APE/Ref-1 protein express ion was analyzed by immunohistochemistry and Western blot analysis. DNA dam age was evaluated by gel electrophoresis and terminal deoxynucleotidyl tran sferase-mediated uridine 5'-triphosphate-biotin nick end-labeling (TUNEL), Results-A similar level of APE/Ref-1 was detected in the control brains fro m both groups. APE/Ref-1 was significantly reduced 1 hour after transient F CI in both groups, whereas the transgenic mice had less reduction than that seen in wild-type mice 1 and 4 hours after FCI, DNA laddering was detected 24 hours after FCI and was decreased in transgenic mice. Double staining w ith APE/Ref-1 and TUNEL showed that the neurons that lost APE/Ref-1 immunor eactivity became TUNEL positive. Conclusions-These results suggest that reactive oxygen species contribute t o the early decrease of APE/Ref- I and thereby exacerbate DNA fragmentation after transient FCI in mice.