Characterization of nickel-induced mutations

A Chinese hamster ovary cell line (designated AS52) has been used to test the mutagenicity of nickel compounds. This line lacks the endogenous gene for hypoxanthine phosphoribosyl transferase (HPRT) but contains an inserted bacterial gene coding for the enzyme guanine-hypoxanthine phosphoribosyl transferase (gpt) which is the targeted locus for selection. Isolated mutants were clonally expanded and analysed utilizing the polymerase chain reaction (PCR) following exposure to ethyl methanesulfonate (EMS), Ni3S2, Ni(OH)2, NiSO4, and control conditions. Amplification of the gpt locus in normal AS52 cells results in the generation of two distinct bands, both of which have been characterized by restriction enzyme analysis and nucleotide sequencing. The smaller band represents the gpt gene. The larger band contains a large insert of bacterial origin and is non-functional. Analysis of mutants revealed three distinct patterns: (1) both PCR bands remain intact; (2) the smaller DNA band is deleted; (3) both bands are deleted. Mutant analysis was performed with two unique sets of DNA amplification primers with identical results. When compared to spontaneous or EMS induced mutants, those generated by exposure to nickel compounds exhibited an increase in gene deletions relative to point mutations; the extent of which was compound specific: NiSO4 > Ni(OH)2 > Ni3S2. These results clearly suggest that a variety of genotoxicological mechanisms are involved in the mutagenic activity of nickel compounds.