Kortenkamp A, Ozolins Z, Beyersmann D, O'Brien P
Universität Bremen, F.R.G.
Mutat Res. 1989 Feb;216(1):19-26. doi: 10.1016/0165-1161(89)90019-8.
The carcinogen chromate is efficiently taken up and reduced to chromium(III) compounds by various biological systems. To test the possible DNA damage induced in the course of chromium(VI) reduction, we used a combination of chromate with the reductant glutathione (GSH) as well as a green complex of chromium(V), which is formed in the reaction of chromate with GSH. The combination of chromate and glutathione was found to cause single-strand breaks in supercoiled circular DNA of the bacteriophage PM2. The green chromium(V) complex Na4(GSH)4Cr(V).8H2O, prepared from chromate and glutathione, also cleaved supercoiled PM2 DNA. No DNA-degrading effects were observed with either chromate or the final product of the reaction with GSH, a purple anionic chromium(III) GSH complex. The nature of the buffering agents revealed a strong influence on the extent of DNA strand breaks produced by chromate and GSH. A variation of the GSH concentration in the reaction with chromate and PM2 DNA, performed in sodium phosphate-buffered solutions showed an initial increase in the number of strand breaks at GSH concentrations up to 1 mM followed by a decline at higher GSH concentrations. Since neither chromate, when administered individually, nor the final product of chromium(VI) reduction, the purple chromium(III) GSH complex, produced any detectable DNA cleavage, the critical steps leading to DNA strand breaks occur in the course of the conversion of chromium(VI) to chromium(III) by GSH, the most abundant intracellular low molecular thiol. Moreover, the demonstration that DNA cleavage is induced in the presence of the chromium(V) complex identifies chromium(V) as the oxidation state of the metal, which is involved in the steps leading to DNA-damaging effects of chromate.
致癌物铬酸盐能被各种生物系统有效摄取并还原为铬（III）化合物。为了测试在铬（VI）还原过程中可能诱导的DNA损伤，我们将铬酸盐与还原剂谷胱甘肽（GSH）结合使用，以及铬（V）的绿色络合物，该络合物是在铬酸盐与GSH的反应中形成的。发现铬酸盐和谷胱甘肽的组合会导致噬菌体PM2的超螺旋环状DNA出现单链断裂。由铬酸盐和谷胱甘肽制备的绿色铬（V）络合物Na4（GSH）4Cr（V）·8H2O也能切割超螺旋PM2 DNA。铬酸盐或与GSH反应的最终产物——紫色阴离子铬（III）GSH络合物均未观察到DNA降解作用。缓冲剂的性质显示出对铬酸盐和GSH产生的DNA链断裂程度有很大影响。在磷酸钠缓冲溶液中进行的铬酸盐与PM2 DNA反应中，改变GSH浓度，结果显示在GSH浓度高达1 mM时，链断裂数量最初增加，随后在更高GSH浓度下下降。由于单独施用铬酸盐时以及铬（VI）还原的最终产物——紫色铬（III）GSH络合物均未产生任何可检测到的DNA切割，导致DNA链断裂的关键步骤发生在细胞内最丰富的低分子硫醇GSH将铬（VI）转化为铬（III）的过程中。此外，在铬（V）络合物存在下诱导DNA切割的证明表明铬（V）是金属的氧化态，它参与了导致铬酸盐产生DNA损伤作用的步骤。
