Peroxynitrite-induced secondary oxidative lesions at guanine nucleobases: Chemical stability and recognition by the Fpg DNA repair enzyme

Synthetic oligodeoxynucleotides containing secondary oxidative lesions at g uanine nucleobases have been prepared by the site-specific oxidation by ONO O- of oligomers containing 8-oxoguanine (8-oxo-G). The oligomers have been tested for their stability to the standard hot piperidine treatment that is commonly used to uncover oxidized DNA lesions. While DNA containing oxalur ic acid and oxazolone was cleaved at the site of modification under hot pip eridine conditions, the corresponding cyanuric acid and 8-oxo-G lesions wer e resistant to piperidine. The recognition of the oxidative lesions by form amidopyrimidine glycosylase (Fpg enzyme) was examined in double-stranded ve rsions of the synthetic oligodeoxynucleotides. Fpg efficiently excised 8-ox o-G and oxaluric acid and to some extent oxazolone, but not cyanuric acid. These data suggest that some DNA lesions formed via ONOO- exposures (cyanur ic acid) are not repaired by Fpg and are not uncovered by assays based on p iperidine cleavage at the site of lesion. Our results indicate that cryptic secondary and tertiary oxidation products arising from 8-oxo-G may contrib ute to the overall mutational spectra arising from oxidative stress.