A ROLE FOR MOLECULAR-OXYGEN IN THE FORMATION OF DNA-DAMAGE DURING THEREDUCTION OF THE CARCINOGEN CHROMIUM(VI) BY GLUTATHIONE

Although well-established as carcinogens, the way in which chromium(VI ) compounds exert their carcinogenic, mutagenic, and DNA-damaging pote ntial remains obscure. It is clear that inside cells chromium(VI) is a ctivated to its ultimate carcinogenic form by reducing agents includin g glutathione (GSH). The present study is intended to clarify if Fento n mechanisms are likely to be important in the formation of DNA lesion s by chromium(VI) in combination with GSH. In buffer solutions which w ere treated to remove Fenton-active metal ions as well as in those not further purified, chromate and GSH induced similar numbers of single- strand breaks (SSB) in isolated PM2 DNA. Molecular oxygen was found to be essential for the formation of SSB, but chromium(V) species arisin g from chromate/GSH, unless activated by oxygen, appeared to be unreac tive toward DNA. Upon addition of Mn(II) to solutions of chromium(VI) and GSH a diminution of Mn(II) ESR signals was observed, good evidence for the presence of chromium(IV) species. Using gas chromatography/ma ss spectrometry in selective ion-monitoring mode and high-performance liquid chromatography with electrochemical detection, we were able to show that Cr(VI)/GSH failed to induce base modifications typical of hy droxyl radical attack on DNA. Experimental conditions which readily in duced SSB gave rise to the formation of chromium-DNA adducts, clearly demonstrating that the generation off these two DNA lesions is not mut ually exclusive. We conclude that models which ascribe the induction o f chromium-DNA adducts to chromium(V) and the generation of oxidative DNA damage including SSB to hydrogen peroxide are oversimplistic. It i s not necessary to invoke a mechanism requiring the presence of added hydrogen peroxide to account for the ability of Cr(VI)/GSH to cause SS B. Our findings suggest that the combination of GSH, molecular oxygen, and chromium(VI) can damage DNA via non-Fenton pathways. (C) 1996 Aca demic Press.