Oxidatively generated DNA damage induced by 3-amino-5-mercapto-1,2,4-triazole, a metabolite of carcinogenic amitrole

Amitrole (3-amino-1,2,4-triazole) is a widely used herbicide. Amitrole induces thyroid and liver tumors in rodents. However, the mechanism of carcinogenesis by amitrole remains to be clarified. To clarify the mechanism of carcinogenesis induced by amitrole, we investigated the formation of 8-oxo-7,8-dihydro-2′-deoxyguanosine (8-oxodG), a characteristic of oxidatively generated DNA damage, by an amitrole metabolite, 3-amino-5-mercapto-1,2,4-triazole (AMT), in the presence of Cu(II). The amount of 8-oxodG was increased by AMT in the presence of Cu(II). AMT-induced 8-oxodG formation was enhanced in deuterium oxide (D2O), which prolongs the half life of singlet oxygen (1O2), more than that in H2O. Sodium azide and 1,4-diazabicyclo[2,2,2]-octane (DABCO), potent and relatively specific scavengers of 1O2, inhibited AMT-mediated 8-oxodG formation. Bathocuproine, a Cu(I) chelator, also inhibited the 8-oxodG formation. On the other hand, typical OH scavengers did not inhibit the generation of 8-oxodG. AMT plus Cu(II) also induced piperidine-labile DNA lesions frequently at every guanine residue. These results suggest that 1O2 and Cu(I) play an important role in DNA damage induced by AMT. It is concluded that oxidatively generated DNA damage induced by AMT via the generation of 1O2 may contribute to carcinogenicity of amitrole.