Enhancement of UV-induced mutagenesis and sister-chromatid exchanges by nickel ions in V79 cells: evidence for inhibition of DNA repair.

With regard to contradictory results concerning the mutagenicity of nickel compounds in short-term assays, especially in bacterial test systems, Chinese hamster V79 cells were used to measure mutagenicity, comutagenicity and the induction of sister-chromatid exchanges (SCEs) by NiCl2. We confirmed the induction of mutations at the HGPRT locus as well as SCEs. In addition, NiCl2 shows a pronounced comutagenic effect towards UV. When using confluent cultures or resting cells due to serum deprivation, where more time is given for repair processes, the comutagenic effect is higher compared to logarithmically growing cells (10 and 4 times, respectively, compared to twice). Hence, we attribute this enhancement in mutagenicity to inhibition of DNA repair. Also the increase in induced SCEs after combined treatment with UV and NiCl2 supports this thesis. Furthermore, NiCl2 enhances the cyto-toxicity of cis-DDP about 12-fold. Since no comutagenic effect is observed in combination with MMS, we suggest that the inhibition of DNA repair by Ni(II) applies to all DNA changes that are repaired by the 'long-patch' excision repair system. This inhibition may occur via replacement of other divalent metal ions essential in repair and regulation processes.