Mutagenicity and NO formation from UVA irradiated N-nitrosoproline, and characterization of photoproduct formed in UVA-irradiated mixture of N-nitrosoproline with 2-′deoxyguanosine in neutral solution

Earlier studies in our laboratory showed that UVA-irradiated N-nitrosoproline (NPRO) could produce mutagenic compounds and strand breaks in treated DNA with the release of nitric oxide and active oxygen species. In the present study, we investigated the phosphate-dependence of photomutagenicity and solvent effects on nitric oxide release from irradiated NPRO. We also investigated the UVA-driven reaction of NPRO with 2′-deoxyguanosine (dG) in neutral solution, and identified the chemical structure of the photoproduct. A mixture of NPRO and dG dissolved in neutral solution was irradiated with UVA at 320-400 nm for 6 h, and the solution was then subjected to HPLC analysis. The photoproduct isolated from the NPRO and dG mixture in neutral buffer was identified as 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG). We propose a photoreaction mechanism involving the absorption of UVA photons by NPRO followed by UVA-driven photolysis of NPRO, and subsequent production of active oxygen radicals that generate 8-oxodG.