Incidence and localization of sister chromatid exchanges induced by nickel and chromium compounds

Carcinogenic nickel compounds enhanced the incidence of sister chromatid exchanges (SCEs) in a concentration-dependent fashion in intact Chinese hamster ovary cells. There was a preferential induction of these exchanges in the heterochromatic regions of the chromosomes. CaCrO4 also caused a dose-dependent induction of SCEs. However, in contrast to NiCl2, the exchanges induced by CaCrO4 were not localized in any particular chromosomal region. The total incidence of exchanges was higher with CaCrO4 than with NiCl2. CaCrO4, crystalline NiS and NiCl2 enhanced the incidence of SCEs at concentrations below the threshold of DNA damage as detected by the technique of alkaline elution. Additionally, following treatment time intervals of 24-48 h, there was an increase in SCEs at concentrations of NiCl2 or CaCrO4 that produced little disruption of cell cycle progression. These results are consistent with the hypothesis that potently carcinogenic nickel compounds which are not very mutagenic exert selective effects on genetically inactive heterochromatin, while potently mutagenic and carcinogenic chromate do not appear to produce a similar predominance of SCEs in heterochromatic regions.