Reactions between hydroxyl-radical-induced 7,8-dihydro-8-oxo-2'-deoxyguanosine precursor and the spin trap alpha-phenyl-N-tert-butylnitrone

An N2O-saturated aqueous solution containing 2'-dG and the spin trap agent PBN was examined by ESR and HPLC-ECD methods after X irradiation. ESR examination showed that the ESR spectrum obtained consisted of signals due to the PBN-OH and PBN-H adducts. The signal intensity of PBN-H adducts was larger in the presence of 2'-dG than in the absence of 2'-dG, while that of PBN-OH adducts was smaller in the presence of 2'-dG than in the absence of 2'-dG. When the OH-radical-induced 8-oxodG was measured by HPLC-ECD, the yield of 8-oxodG was found to be enhanced about twofold in the presence of PBN. By contrast, usual OH-radical scavengers (DMSO, sodium formate and mannitol) inhibited the formation of 8-oxodG beyond expectation. The enhancement of the yield of PBN-H adducts by 2'-dG and the enhancement of the 8-oxodG formation by PBN were explained by the electron transfer and subsequent proton transfer reactions from OH-radical-induced guanine-N7 radicals to PBN to form 8-oxodG and PBN-H. The present study led us to conclude that PBN reacted with the precursor radical of 8-oxodG to accelerate the formation of 8-oxodG, while OH-radical scavengers reacted with it to diminish the formation of 8-oxodG.