LIGHT ACTIVATION OF A COMPLEX MIXTURE: EFFECTS OF UV EXCISION REPAIR ON THE MODULATION OF GENOTOXIC AND MOLECULAR EVENTS IN CHINESE HAMSTER CELLS

Abstract— An aqueous effluent produced during the retorting of oil shale has been shown to induce a significant genotoxic response in cultured Chinese hamster (CHO) cells following activation by near ultraviolet light (UVA). In this report the light-activated responses induced by this complex mixture were compared between two DNA excision repair deficient mutants and their parental strain, CHO-AA8-4. The mutants, UV-5 and UV-135, were hypersensitive to both the cytotoxic and mutagenic effects of concurrent exposures to the retort process water and UVA. Repair proficiency appeared to render AA8-4 relatively insensitive to low doses of UVA treatment, whereas in the two mutants a linear dose-response in the induction of 6-thioguanine resistant (6TG^®) mutations was observed even at the lower UVA doses examined. Filter DNA alkaline elution methods were utilized to demonstrate that both single-strand breaks and DNA-DNA interstrand crosslinks were induced in CHO DNA following process water and UVA treatment. Results were also obtained which indicated that the inability to repair DNA-DNA crosslinks contributed significantly to the hypersensitive response seen in the excision repair mutants following the photoactivation of this complex mixture.