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

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We recently reported the photomutagenic property of thiabendazole [2-(4-thiazolyl)-1H-benzimidazole, TBZ], a post harvest fungicide, in bacterial and mammalian cells. In the present study we investigated its photomutagenic potential along with several of its structurally-related pesticides including benomyl, mefenacet, tricyclazole, and imazalil. None of the compounds except TBZ showed photomutagenicity with UVA-irradiation in S. typhimurium TA100, TA98, or E. coli WP2uvrA/pKM101. Since TBZ consists of thiazole and benzimidazole rings, we then investigated photomutagenic potential of thiazole, benzimidazole, and 2-phenylbenzimidazole. Only 2-phenylbenzimidazole showed very weak photomutagenicity with UVA-irradiation. These results indicate both benzimidazole ring and thiazole ring are necessary for UVA-activation of TBZ. We measured 8-hydroxydeoxyguanosine (8-OHdG) in salmon sperm DNA exposed to TBZ and UVA by HPLC-ECD, and found that 8-OHdG was not responsible for the photomutagenesis of TBZ.