Up-regulation of base excision repair activity for 8-hydroxy-2'-deoxyguanosine in the mouse brain after forebrain ischemia-reperfusion.

The repair enzyme 8-oxoguanine glycosylase/ apyrimidinic/apurinic lyase (OGG) removes 8-hydroxy-2'deoxyguanosine (oh8dG) in human cells. Our goal was to examine oh8dG-removing activity in the cell nuclei of male C57BL/6 mouse brains treated with either forebrain ischemia-reperfusion (FblR) or sham operations. We found that the OGG activity in nuclear extracts, under the condition in which other nucleases did not destroy the oligodeoxynucleotide duplex, excised oh8dG with the greatest efficiency on the oligodeoxynucleotide duplex containing oh8dG/dC and with less efficiency on the heteroduplex containing oh8dG/dT, oh8dG/dG, or oh8dG/dA. This specificity was the same as for the recombinant type 1 OGG (OGG1) of humans. We observed that the OGG1 peptide and its activity in the mouse brain were significantly increased after 90 min of ischemia and 20-30 min of reperfusion. The increase in the protein level and in the activity of brain OGG1 correlated positively with the elevation of FblR-induced DNA lesions in an indicator gene (the c-fos gene) of the brain. The data suggest a possibility that the OGG1 protein may excise oh8dG in the mouse brain and that the activity of OGG1 may have a functional role in reducing oxidative gene damage in the brain after FblR.