DAMAGE, REPAIR, AND MUTAGENESIS IN NUCLEAR GENES AFTER MOUSE FOREBRAIN ISCHEMIA-REPERFUSION

To determine whether oxidative stress after cerebral ischemia-reperfus ion affects genetic stability in the brain, we studied mutagenesis aft er forebrain ischemia-reperfusion in Big Blue transgenic mice (male C5 7BL/6 strain) containing a reporter lad gene, which allows detection o f mutation frequency. The frequency of mutation in this reporter lad g ene increased from 1.5 to 7.7 (per 100,000) in cortical DNA after 30 m in of forebrain ischemia and 8 hr of reperfusion and remained elevated at 24 hr reperfusion. Eight DNA lesions that are characteristic of DN A damage mediated by free radicals were detected. Four mutagenic lesio ns (2,6-diamino-4-hydroxy-5-formamidopyrimidine 8-hydroxyadenine, 5-hy droxycytosine, and 8-hydroxyguanine) examined by gas chromatography/ma ss spectrometry and one corresponding 8-hydroxy-2'-deoxyguanosine by a method of HPLC with electrochemical detection increased in cortical D NA two- to fourfold (p < 0.05) during 10-20 min of reperfusion. The da mage to gamma-actin and DNA polymerase-beta genes was detected within 20 min of reperfusion based on the presence of formamidopyrimidine DNA N-glycosylase-sensitive sites. These genes became resistant to the gl ycosylase within 4-6 hr of reperfusion, suggesting a reduction in DNA damage and presence of DNA repair in nuclear genes. These results sugg est that nuclear genes could be targets of free radicals.