Detection of DNA strand breaks, DNA-protein crosslinks, and telomerase activity in nickel-transformed BALB/c-3T3 cells

Although nickel compounds are known carcinogens, the underlying carcinogenic mechanisms are not fully understood. The objective of this research was to determine if the genotoxic lesions of DNA strand breaks and DNA-protein crosslinks are present in nickel-transformed BALB/c-3T3 cells, and to further elucidate the potential carcinogenesis of insoluble and soluble nickel compounds through telomerase activity in nickel-transformed BALB/c-3T3 cell lines. DNA strand breaks, DNA-protein crosslinks and telomerase activity were investigated by single cell gel electrophoresis (comet assay), I-125-postlabelling techniques, and the TRAP-silver staining assay, respectively. Results showed that both DNA strand breaks and DNA-protein crosslinks were present in nickel-transformed BALB/c-3T3 cells. However, the highest levels of DNA strand breaks and DNA-protein crosslinks were found in insoluble crystalline NiS-transformed cells and high levels of DNA strand breaks and DNA-protein crosslinks were also found in the transformed cells induced by two water-soluble NiCl2 and NiSO4 at moderate concentrations of cytotoxicity. These data suggest that these two genetic endpoints are useful biomarkers and are associated with cell transformation and carcinogensis of insoluble and soluble nickel compounds. Also, we found that the crystalline NiS- and NiCl2-transformed cells possessed a high telomerase activity. A weak telomerase was found in NiSO4-transformed cells. The results seem to indicate that in addition to crystalline NiS, some water-soluble nickel compounds such as NiCl2 are also highly carcinogenic. These results may partly explain the cell transformation and relative carcinogenic potency of insoluble crystalline NiS, soluble NiCl2, and NiSO4. Teratogenesis Carcinog. Mutagen. 21:463-471, 2001. (C) 2001 Wiley-Liss, Inc.