Photosensitized DNA damage induced by NADH: Site specificity and mechanism

Abstract

Increasing evidence reveals the carcinogenicity of UVA radiation. We demonstrated that UVA-irradiated NADH induced damage to ³²P-labeled DNA fragments obtained from the p53 gene in the presence of Cu(II). Formamidopyrimidine glycosylase (Fpg)-sensitive lesions were formed at guanine residues, whereas piperidine-labile lesions occurred frequently at thymine residues. Formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), upon UVA exposure in the presence of Cu(II), increased depending on NADH concentration. Catalase and bathocuproine, a Cu(I)-specific chelator, inhibited the DNA damage, suggesting the involvement of reactive species derived from H₂O₂ and Cu(I). UVA-irradiated riboflavin induced DNA cleavage through electron transfer at 5′ guanine of the 5′-GG-3′ sequence with both Fpg and piperidine treatments; Fpg induced less cleavage at the guanine residues than piperidine. These results imply that NADH may participate as an endogenous photosensitizer in UVA carcinogenesis via H₂O₂ generation, producing metal-mediated mutagenic lesions such as 8-oxodG.

• NADH
• DNA damage
• 8-oxo-7,8-dihydro-2′-deoxyguanosine
• UVA
• hydrogen peroxide