Induction of Oxidative DNA Damage in the Peri‐Infarct Region After Permanent Focal Cerebral Ischemia

To address the role of oxidative DNA damage in focal cerebral ischemia lacking reperfusion, we investigated DNA base and strand damage in a rat model of permanent middle cerebral artery occlusion (MCAO). Contents of 8‐hydroxyl‐2′‐deoxyguanosine (8‐OHdG) and apurinic/apyrimidinic abasic sites (AP sites), hallmarks of oxidative DNA damage, were quantitatively measured in nuclear DNA extracts from brains obtained 4‐72 h after MCAO. DNA single‐ and double‐strand breaks were detected on coronal brain sections using in situ DNA polymerase I‐mediated biotin‐dATP nick‐translation (PANT) and terminal deoxynucleotidyl transferase‐mediated dUTP nick end‐labeling (TUNEL), respectively. Levels of 8‐OHdG and AP sites were markedly elevated 16‐72 h following MCAO in the frontal cortex, representing the peri‐infarct region, but levels did not significantly change within the ischemic core regions of the caudateputamen and parietal cortex. PANT‐ and TUNEL‐positive cells began to be detectable 4‐8 h following MCAO in the caudate‐putamen and parietal cortex and reached maximal levels at 72 h. PANT‐ and TUNEL‐positive cells were also detected 16‐72 h after MCAO in the lateral frontal cortex within the infarct border, where many cells also showed colocalization of DNA single‐strand breaks and DNA fragmentation. In contrast, levels of PANT‐positive cells alone were transiently increased (16 h after MCAO) in the medial frontal cortex, an area distant from the infarct zone. These data suggest that within peri‐infarct brain regions, oxidative injury to nuclear DNA in the form of base and strand damage may be a significant and contributory cause of secondary expansion of brain damage following permanent focal ischemia.