Snyder R D, Lachmann P J
Merrell Dow Research Institute, Cincinnati, Ohio.
Mol Toxicol. 1989 Apr-Jun;2(2):117-28.
We have previously demonstrated that a number of metal salts have the capacity to inhibit the DNA repair process in human cells. In order to determine a role for non-protein thiols (TNPT) in this inhibition, we investigated repair of X-ray damage in metal-treated HeLa cells under normal conditions and conditions in which cellular thiols had been depleted by treatment with buthionine sulfoximine (BSO) and diethyl maleate (DEM). The combination reduced cellular TNPT by 92%, and cells so depleted became sensitized to X-ray-induced killing and exhibited retarded sealing of X-ray-induced DNA single-strand breaks. Thiol depletion also sensitized cells to the cytotoxicity of certain but not all metals tested. The sensitivity to copper was increased over 6000-fold, and significant enhancement of killing was also seen in cells treated with arsenic, lead, and mercury. Smaller effects were observed with cadmium and nickel, and sensitivity to manganese, magnesium, cobalt or zinc was not substantially altered. Enhanced sensitivity to X-ray killing was found in cells treated with nickel, cadmium, zinc, arsenic, and copper under conditions in which thiols were not limiting. In thiol-depleted cells, sensitivity was not further increased in the case of nickel and arsenic but at least additively affected for copper, mercury and zinc. X-Ray-induced single-strand break repair was retarded by treatment of cells with mercury, nickel, zinc, arsenic, and copper in thiol-normal cells. In thiol-depleted cells, repair inhibition by zinc, arsenic, and copper was nearly complete, while little additional effect on repair was seen following mercury and nickel treatment. An examination of the effects of brief metal treatment on cellular TNPT revealed that copper strongly decreased thiol levels whereas the other metals tested either had no effect on TNPT or reduced TNPT levels to no less than 48% under the conditions employed. No simple relationship appears to exist relating loss of cellular thiols and sensitivity of repair in the series of metals tested. Clear, although indirect, evidence exists, however, that sensitivity to X-rays is mediated through thiols and that the interaction of metals and thiols in the cell may be an important factor in modulating the response to irradiation.
我们之前已经证明，多种金属盐有能力抑制人类细胞中的DNA修复过程。为了确定非蛋白硫醇（TNPT）在这种抑制作用中的作用，我们研究了在正常条件下以及用丁硫氨酸亚砜胺（BSO）和马来酸二乙酯（DEM）处理使细胞硫醇耗竭的条件下，金属处理的HeLa细胞中X射线损伤的修复情况。这种联合处理使细胞TNPT减少了92%，如此耗竭的细胞对X射线诱导的杀伤变得敏感，并表现出X射线诱导的DNA单链断裂的封闭延迟。硫醇耗竭也使细胞对某些但不是所有测试金属的细胞毒性变得敏感。对铜的敏感性增加了6000多倍，在用砷、铅和汞处理的细胞中也观察到杀伤作用的显著增强。对镉和镍的影响较小，对锰、镁、钴或锌的敏感性没有实质性改变。在用镍、镉、锌、砷和铜处理的细胞中，在硫醇不缺乏的条件下发现对X射线杀伤的敏感性增强。在硫醇耗竭的细胞中，镍和砷的情况下敏感性没有进一步增加，但铜、汞和锌至少有累加效应。在硫醇正常的细胞中，用汞、镍、锌、砷和铜处理细胞会延迟X射线诱导的单链断裂修复。在硫醇耗竭的细胞中，锌、砷和铜对修复的抑制几乎是完全的，而汞和镍处理后对修复几乎没有额外影响。对短暂金属处理对细胞TNPT的影响进行检查发现，铜强烈降低硫醇水平，而其他测试金属在所用条件下要么对TNPT没有影响，要么使TNPT水平降低不低于48%。在测试的一系列金属中，细胞硫醇的丧失与修复敏感性之间似乎不存在简单的关系。然而，有明确的尽管是间接的证据表明，对X射线的敏感性是通过硫醇介导的，并且细胞中金属和硫醇的相互作用可能是调节对辐射反应的一个重要因素。
