Bromate induces loss of heterozygosity in the thymidine kinase gene of L5178Y/Tk(+/-)-3.7.2C mouse lymphoma cells.
Potassium bromate (KBrO(3)) induces DNA damage and tumors in mice and rats, but is a relatively weak mutagen in microbial assays and the in vitro mammalian Hprt assay. Concern that there may be a human health risk associated with bromate, a disinfectant by-product of ozonation, has accompanied the increasing use of ozonation as an alternative to chlorination for treatment of drinking water. In this study, we have evaluated the mutagenicity of KBrO(3) and sodium bromate (NaBrO(3)) in the Tk gene of mouse lymphoma cells. In contrast to the weak mutagenic activity seen in the previous studies, bromate induced a mutant frequency of over 100 x 10(-6) at 0.6mM with minimal cytotoxicity (70-80% survival) and over 1300 x 10(-6) at 3mM ( approximately 10% survival). The increase in the Tk mutant frequency was primarily due to the induction of small colony of Tk mutants. Loss of heterozygosity (LOH) analysis of 384 mutants from control and 2.7 mM KBrO(3)-treated cells showed that almost all (99%) bromate-induced mutants resulted from LOH, whereas in the control cultures 77% of the Tk mutants were LOH. Our results suggest that bromate is a potent mutagen in the Tk gene of mouse lymphoma cells, and the mechanism of action primarily involves LOH. The ability of the mouse lymphoma assay to detect a wider array of mutational events than the microbial or V79 Hprt assays may account for the potent mutagenic response.
National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, NC 27709, USA.
Karen
K
Harrington-Brock
Deborah D
DD
Collard
Tao
T
Chen
D000818:Animals; D001959:Bromates; D002273:Carcinogens; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D006579:Heterozygote; D019656:Loss of Heterozygosity / Q000187:drug effects*; D008223:Lymphoma / Q000188:drug therapy* / Q000235:genetics*; D051379:Mice; D009153:Mutagens; D009154:Mutation; D010100:Oxygen / Q000378:metabolism; D013937:Thymidine Kinase / Q000235:genetics*; D014407:Tumor Cells, Cultured
D001959:Bromates; D002273:Carcinogens; D009153:Mutagens; C019536:potassium bromate; D013937:Thymidine Kinase; D010100:Oxygen