Mutations and oxidative DNA damage in phage M13mp2 exposed to N-nitrosomorpholine plus near-ultraviolet light

Abstract

Previously we reported that a direct-acting mutagen can be formed from N-nitrosomorpholine (NMOR) on exposure to near-ultraviolet light (UVA, 320-400 nm). We have now studied the spectrum of mutations caused by NMOR plus UVA. M13mp2 phages suspended in a sodium phosphate buffer were treated with NMOR under UVA irradiation and Escherichia coli NR9099 was then infected with the phage. Mutations induced in the phage DNA lacZ alpha region were analyzed. The majority (approximately 50%) of the induced sequence changes were G to T transversions. This suggested that modifications in guanine residues were responsible for these transversions. We explored the formation of 7,8-dihydro-8-oxodeoxyguanosine (8-oxodG) in the DNA. When the phage were treated with NMOR plus UVA, 8-oxodG/dG in DNA increased up to 12-fold over the value in untreated control. When a mutM-deficient mutant of E. coli CSH50 was used as the host, the mutation level was higher than that observed with CSH50. We conclude that 8-oxodG may be involved in mutations induced by NMOR plus UVA.

Mutation and formation of methyl- and hydroxylguanine adducts in DNA caused by N-nitrosodimethylamine and N-nitrosodiethylamine with UVA irradiation

“…The amounts quantified were similar to those found previously in the DNA of phage M13mp2 treated with N-nitrosomorpholine ϩ UVA (10). At high concentrations of N-nitrosodialkylamine and with longer irradiation periods the amounts of 8-oxodG decreased.…”

“…Since in our present reaction singlet oxygen does not appear to be involved, it is possible that here again oxidation of guanine to form 8-oxodG occurs via a guanine radical cation. In 'N-nitrosomorpholine ϩ UVA' mutagenesis we observed a higher level of mutation of phage M13mp2 in a mutM-deficient host (10). However, in the present experiments no stimulation by mutM deficiency was observed in the NDMA ϩ UVA-induced mutation in E.coli.…”

“…Escherichia coli CC102 (ada -, ogt -) and CC106 (ada -, ogt -) were gifts from Dr K.Ihara (University of Kyushu, Japan). Escherichia coli YG5113 [ara -, ∆(gpt-lac)5, mutM::cat/ FЈ(lacI378, lacZ461, proAB)] was a gift from Dr T.Nohmi (National Institute of Hygienic Sciences, Tokyo), which is a derivative of E.coli CC104 carrying the 8-oxoG DNA glycosylase deficiency (10).…”

“…For NDMA ϩ UVA we have shown that when an aromatic amine is simultaneously present in the reaction mixture, the amine is oxidized into its nitro derivative (9). Furthermore, treatment of DNA with N-nitrosomorpholine ϩ UVA results in formation of 7,8-dihydro-8-oxo-2Ј-deoxyguanosine (8-oxodG) in the DNA (10). These observations suggest that UVA irradiation of N-nitrosodialkylamines generates oxidative species.…”

Analysis of Photomutagenicity of Thiabendazole with UVA Irradiation: Absence of 8-Hydroxyguanosine Formation

“…One likely mutagenic species could be oxygen radicals. The contribution of reactive oxygen species to photomutagenicity has been reported for many chemicals, including methylene blue (4), chlorpromazine (5,6), benzo[a]pyrene (7), and several N-nitroso compounds (8)(9)(10)(11). The second purpose of the present study was to investigate the possibility that 8-hydroxydeoxyguanosine (8-OHdG) is formed in DNA exposed to TBZ and UVA in vitro.…”