ENHANCEMENT BY L-HISTIDINE OF NICKEL(II)-INDUCED DNA PROTEIN CROSS-LINKING AND OXIDATIVE DNA-BASE DAMAGE IN THE RAT-KIDNEY

Formation of DNA-protein cross-links and oxidatively damaged DNA bases was investigated with the use of alkaline elution and gas chromatography/mass spectrometry techniques in the nuclei from kidneys of rats 3 and 18 h after a single iv injection of the Ni(II)(His)2 complex (NiHis), nickel(II) acetate (NiAcet), or L-histidine (His). Administration of 20 mumol of NiHis/kg body wt caused the formation of DNA-protein cross-links and significantly increased levels of oxidatively damaged DNA bases, including 2,6-diamino-4-hydroxy-5-formamidopyrimidine (FapyGua; 3.5-fold vs the control value) 3 h postinjection and 8-oxoguanine (2.6-fold), cytosine glycol (2.5-fold), 8-oxoadenine (2-fold), and FapyGua (1.9-fold) 18 h postinjection. Injection of 20 mumol of NiAcet/kg body wt enhanced the cross-linking to a lesser extent than NiHis and did not significantly increase the amounts of modified DNA bases over the control levels. Forty micromoles of His per kilogram body wt alone caused a marked DNA-protein cross-linking effect and increased the amount of 4,6-diamino-5-formamidopyrimidine (2-fold vs the control) 3 h, but not 18 h, after treatment. The DNA base derivatives found were typical products of hydroxyl radical (.OH) attack on DNA. Formation of the cross-links may also be attributed to .OH, although other mechanisms, e.g., formation of ternary complexes of Ni(II), cannot be excluded. The present in vivo study confirms the conclusion of our former in vitro experiments that His enhances Ni(II)-mediated oxidative damage to DNA and chromatin. Since His is the major low molecular weight tissue carrier of Ni(II), this enhancement may be responsible, at least in part, for nickel genotoxicity and carcinogenicity.