Tachon P, Deflandre A, Giacomoni P U
Laboratoire de Recherche Avancée de l'Oréal, Clichy, France.
Carcinogenesis. 1994 Aug;15(8):1621-6. doi: 10.1093/carcin/15.8.1621.
The mechanism by which L-histidine modulates H2O2-induced damage to DNA has been investigated by alkaline and neutral gel electrophoresis of cellular DNA, by measuring the conversion of purified supercoiled DNA to its relaxed and linear forms and by the ESR spin-trapping technique. L-Histidine greatly increased the amount of H2O2-mediated DNA single-strand breaks. DNA double-strand breaks were produced only in cells exposed to H2O2 and L-histidine. The addition of a cell permeable chelator such as o-phenanthroline (unlike EDTA, DTPA and desferrioxamine) prevented both DNA single- and double-strand breakage induced by H2O2 plus L-histidine. In vitro, the profile of the dose-response curve for the ferrous iron-mediated, H2O2-dependent DNA nicking was modified by the addition of L-histidine. At low H2O2 concentrations, corresponding to the maximum extent of DNA cleavage, L-histidine was protective. At higher H2O2 concentrations L-histidine enhanced the formation of DNA single-stand breaks and produced DNA double-strand breaks. The increase in H2O2-mediated DNA nicking by L-histidine depended on the L-histidine:Fe(II) ratio, the maximal rate occurring at a molar ratio of 10(3):1 and being independent of the concentration of DNA. Thus, it appeared that intracellular iron mediated both DNA single- and double-strand breaks induced by H2O2 plus L-histidine. Results of ESR experiments seemed to rule out the involvement of the hydroxyl radical by itself in DNA cleavage mediated by the L-histidine:Fe(II):H2O2 system.
通过细胞DNA的碱性和中性凝胶电泳、测量纯化的超螺旋DNA向其松弛和线性形式的转化以及ESR自旋捕获技术，研究了L-组氨酸调节H2O2诱导的DNA损伤的机制。L-组氨酸大大增加了H2O2介导的DNA单链断裂的数量。DNA双链断裂仅在暴露于H2O2和L-组氨酸的细胞中产生。添加一种细胞可渗透的螯合剂，如邻菲罗啉（与EDTA、DTPA和去铁胺不同），可防止H2O2加L-组氨酸诱导的DNA单链和双链断裂。在体外，添加L-组氨酸可改变亚铁离子介导的、H2O2依赖性DNA切口的剂量反应曲线。在对应于DNA切割最大程度的低H2O2浓度下，L-组氨酸具有保护作用。在较高的H2O2浓度下，L-组氨酸增强了DNA单链断裂的形成并产生了DNA双链断裂。L-组氨酸增加H2O2介导的DNA切口取决于L-组氨酸与Fe(II)的比例，最大速率出现在摩尔比为10(3):1时，且与DNA浓度无关。因此，似乎细胞内铁介导了H2O2加L-组氨酸诱导的DNA单链和双链断裂。ESR实验结果似乎排除了羟自由基本身参与L-组氨酸:Fe(II):H2O2系统介导的DNA切割的可能性。
