Mechanism of metal-mediated DNA damage induced by metabolites of carcinogenic 2-nitropropane

Abstract

2-Nitropropane (2-NP), a widely used industrial solvent, is carcinogenic to rats. To clarify the mechanism of carcinogenesis by 2-NP, we investigated DNA damage by 2-NP metabolites, N-isopropylhydroxylamine (IPHA) and hydroxylamine- O-sulfonic acid (HAS), using 32 P -5′-end-labelled DNA fragments obtained from genes that are relevant to human cancer. In the presence of Fe(III) EDTA, both IPHA and HAS caused DNA damage at every nucleotide position without marked site preference. The damage was inhibited by free hydroxyl radical ( OH) scavengers, catalase and deferoxamine mesilate, an iron chelating agent. These results suggest that the DNA damage was caused by OH generated via H 2O 2 by both IPHA and HAS. In contrast, in the presence of Cu(II), IPHA frequently caused DNA damage at thymine. The Cu(II)-mediated DNA damage caused by IPHA was inhibited by catalase, methional and bathocuproine, a Cu(I)-specific chelator, suggesting the involvement of H 2O 2 and Cu(I). These results suggest that the DNA damage induced by IPHA in the presence of Cu(II) was caused by a reactive oxygen species like the Cu(I)–hydroperoxo complex. On the other hand, HAS most frequently induced DNA damage at 5′- T G-3′, 5′-GG-3′ and 5′-GGG-3′ sequences. Catalase and methional only partly inhibited the Cu(II)-mediated DNA damage caused by HAS, suggesting that the reactive oxygen species and another reactive species participate in this process. Formation of 8-oxodG by IPHA or HAS increased in the presence of metal ions. This study suggests that metal-mediated DNA damage caused by 2-NP metabolites plays an important role in the mutagenicity and the carcinogenicity of 2-NP.