title: Alteration of cadmium-induced mutational spectrum by catalase depletion in Chinese hamster ovary-K1 cells.
abstract: Previously, we have demonstrated that cadmium acetate significantly induces hprt mutation frequency in Chinese hamster ovary (CHO)-K1 and that 3-amino-1,2,4-triazole (3AT), a catalase inhibitor, potentiates the mutagenicity of cadmium [Chem. Res. Toxicol. 9 (1996) 1360-1367]. In this study, we investigate the role of intracellular peroxide in the molecular nature of mutations induced by cadmium. Using 2',7'-dichlorofluorescin diacetate and fluorescence spectrophotometry, we have shown that cadmium dose-dependently increased the amounts of intracellular peroxide and the levels were significantly enhanced by 3AT. Furthermore, we have characterized and compared the hprt mutation spectra in 6-thioguanine-resistant mutants derived from CHO-K1 cells exposed to 4 microM of cadmium acetate for 4h in the absence and presence of 3AT. The mutation frequency induced by cadmium and cadmium plus 3AT was 11- and 16-fold higher than that observed in untreated populations (2.2 x 10(-6)), respectively. A total of 40 and 51 independent hprt mutants were isolated from cadmium and cadmium plus 3AT treatments for mRNA-polymerase chain reaction (PCR), genomic DNA-PCR and DNA sequencing analyses. 3AT co-administration significantly enhanced the frequency of deletions induced by cadmium. Cadmium induced more transversions than transitions. In contrast, 3AT co-administration increased the frequency of GC-->AT transitions and decreased the frequencies of TA-->AT and TA-->GC transversions. Together, the results suggest that intracellular catalase is important to prevent the formation of oxidative DNA damage as well as deletions and GC-->AT transitions upon cadmium exposure.
authors.affiliation: Molecular Carcinogenesis Laboratory, Department of Life Sciences, National Tsing Hua University, Hsinchu 300, Taiwan, ROC.
authors.forename: J I
authors.initials: JI
authors.lastname: Chao
authors.forename: J L
authors.initials: JL
authors.lastname: Yang
mesh_terms: D000085:Acetates / Q000633:toxicity*; D000640:Amitrole / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002104:Cadmium / Q000633:toxicity*; D002374:Catalase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D006224:Cricetinae; D004252:DNA Mutational Analysis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics; D007424:Intracellular Fluid / Q000378:metabolism; D016296:Mutagenesis / Q000187:drug effects*; D009152:Mutagenicity Tests; D009153:Mutagens / Q000633:toxicity*; D010545:Peroxides / Q000378:metabolism; D017354:Point Mutation / Q000187:drug effects; D016133:Polymerase Chain Reaction
chemical_list: D000085:Acetates; D004791:Enzyme Inhibitors; D009153:Mutagens; D010545:Peroxides; D002104:Cadmium; C028031:cadmium acetate; D002374:Catalase; D007041:Hypoxanthine Phosphoribosyltransferase; D000640:Amitrole