Kortenkamp A, Casadevall M, Faux S P, Jenner A, Shayer R O, Woodbridge N, O'Brien P
Department of Toxicology, School of Pharmacy, University of London, United Kingdom.
Arch Biochem Biophys. 1996 May 15;329(2):199-207. doi: 10.1006/abbi.1996.0209.
Although well-established as carcinogens, the way in which chromium (VI) compounds exert their carcinogenic, mutagenic, and DNA-damaging potential remains obscure. It is clear that inside cells chromium(VI) is activated to its ultimate carcinogenic form by reducing agents including glutathione (GSH). The present study is intended to clarify if Fenton mechanisms are likely to be important in the formation of DNA lesions by chromium(VI) in combination with GSH. In buffer solutions which were 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 arising from chromate/GSH, unless activated by oxygen, appeared to be unreactive 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/mass 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 hydroxyl radical attack on DNA. Experimental conditions which readily induced SSB gave rise to the formation of chromium-DNA adducts, clearly demonstrating that the generation of these two DNA lesions is not mutually exclusive. We conclude that models which ascribe the induction of chromium-DNA adducts to chromium(V) and the generation of oxidative DNA damage including SSB to hydrogen peroxide are oversimplistic. It is not necessary to invoke a mechanism requiring the presence of added hydrogen peroxide to account for the ability of Cr(VI)/GSH to cause SSB. Our findings suggest that the combination of GSH, molecular oxygen, and chromium(VI) can damage DNA via non-Fenton pathways.
尽管铬（VI）化合物作为致癌物已广为人知，但其发挥致癌、致突变和破坏DNA潜力的方式仍不清楚。很明显，在细胞内，铬（VI）通过包括谷胱甘肽（GSH）在内的还原剂被激活为其最终致癌形式。本研究旨在阐明芬顿机制在铬（VI）与GSH结合形成DNA损伤过程中是否可能起重要作用。在经过处理以去除芬顿活性金属离子的缓冲溶液以及未进一步纯化的缓冲溶液中，铬酸盐和GSH在分离的PM2 DNA中诱导出相似数量的单链断裂（SSB）。发现分子氧对于SSB的形成至关重要，但铬酸盐/GSH产生的铬（V）物种，除非被氧激活，否则似乎对DNA无反应。向铬（VI）和GSH溶液中加入Mn（II）后，观察到Mn（II）电子自旋共振信号减弱，这有力证明了铬（IV）物种的存在。使用选择性离子监测模式的气相色谱/质谱联用以及电化学检测的高效液相色谱，我们能够表明Cr（VI）/GSH未能诱导出典型的羟基自由基攻击DNA所导致的碱基修饰。容易诱导SSB的实验条件导致了铬-DNA加合物的形成，清楚地表明这两种DNA损伤的产生并非相互排斥。我们得出结论，将铬-DNA加合物的诱导归因于铬（V）以及将包括SSB在内的氧化性DNA损伤的产生归因于过氧化氢的模型过于简单。没有必要援引一种需要添加过氧化氢才能解释Cr（VI）/GSH导致SSB能力的机制。我们的研究结果表明，GSH、分子氧和铬（VI）的组合可以通过非芬顿途径损伤DNA。
