Free radicals-mediated induction of oxidized DNA bases and DNA-protein cross-links by nickel chloride

Using the comet assay, we showed that nickel chloride at 250-1000 muM induced. DNA damage in human lymphocytes, measured as the change in comet tail moment, which increased with nickel concentration up to 500 muM and then decreased. Observed increase might follow from the induction of strand breaks or/and alkali-labile sites (ALS) by nickel, whereas decrease from its induction of DNA-DNA and/or DNA-protein cross-links. Proteinase K caused an increase in the tail moment, suggesting that nickel chloride at 1000 muM might cross-link DNA with nuclear proteins. Lymphocytes exposed to NiCl2 and treated with enzymes recognizing oxidized and alkylated bases: endonuclease HI (Endo III), formamidopyrimidine-DNA glycosylase (Fpg) and 3-methyladenine-DNA glycosylase II (AlkA), displayed greater extent of DNA damage than those not treated with these enzymes, indicating the induction of oxidized and alkylated bases by nickel. The incubation of lymphocytes with spin traps, 5,5-dimethyl-pyrroline N-oxide (DMPO) and PBN decreased the extent of DNA damage, which might follow from the production of free radicals by nickel. The pre-treatment with Vitamin C at 10 muM and Vitamin E at 25 muM decreased the tail moment of the cells exposed to NiCl2 at the concentrations of the metal causing strand breaks or/and ALS. The results obtained suggest that free radicals may be involved in the formation of strand breaks or/and ALS in DNA as well as DNA-protein cross-links induced by NiCl2. Nickel chloride can also alkylate DNA bases. Our results support thesis on multiple, free radicals-based genotoxicity pathways of nickel. (C) 2002 Published by Elsevier Science B.V.