Walther U I, Wilhelm B, Walther S, Mückter H, Fichtl B
Walther Straub-Institut für Pharmakologie und Toxikologie der Ludwig-Maximilians Universität München, Germany.
Biol Trace Elem Res. 2000 Winter;78(1-3):163-77. doi: 10.1385/BTER:78:1-3:163.
In a previous work, it was shown that in cells after a decrease of cellular glutathione content, toxic zinc effects, such as protein synthesis inhibition or GSSG (glutathione, oxidized form) increases, were enhanced. In this study, zinc toxicity was determined by detection of methionine incorporation as a parameter of protein synthesis and GSSG increase in various lung cell lines (A549, L2, 11Lu, 16Lu), dependent on enhanced GSSG reductase activities and changed glutathione contents. After pretreatment of cells with DL-buthionine-[R,S]-sulfoximine (BSO) for 72 h, cellular glutathione contents were decreased to 15-40% and GSSG reductase activity was increased to 120-135% in a concentration-dependent manner. In BSO pretreated cells, the IC50 values of zinc for methionine incorporation inhibition were unchanged as compared to cells not pretreated. The GSSG increase in BSO pretreated cells by zinc was enhanced in L2, 11Lu, and 16Lu cells, whereas in A549 cells, the GSSG increase by zinc was enhanced only after pretreatment with the highest BSO concentration. Inhibition of GSSG reductase in alveolar epithelial cells was observed at lower zinc concentrations than needed for methionine incorporation inhibition, whereas in fibroblastlike cells, inhibition of GSSG reductase occurred at markedly higher zinc concentrations as compared to methionine incorporation inhibition. These results demonstrate that GSSG reductase is an important factor in cellular zinc susceptibility. We conclude that reduction of GSSG is reduced in zinc-exposed cells. Therefore, protection of GSH oxidation by various antioxidants as well as enhancement of GSH content are expected to be mechanisms of diminishing toxic cellular effects after exposure to zinc.
在之前的一项研究中发现，细胞内谷胱甘肽含量降低后，细胞对锌的毒性作用更加敏感，例如蛋白质合成受抑制或氧化型谷胱甘肽（GSSG）含量增加。在本研究中，通过检测甲硫氨酸掺入量（作为蛋白质合成的参数）以及不同肺细胞系（A549、L2、11Lu、16Lu）中GSSG含量的增加来确定锌的毒性，这取决于GSSG还原酶活性的增强和谷胱甘肽含量的变化。用DL-丁硫氨酸-[R,S]-亚砜亚胺（BSO）预处理细胞72小时后，细胞内谷胱甘肽含量降低至15%-40%，GSSG还原酶活性以浓度依赖的方式增加至120%-135%。在BSO预处理的细胞中，与未预处理的细胞相比，锌抑制甲硫氨酸掺入的IC50值没有变化。在L2、11Lu和16Lu细胞中，锌导致BSO预处理细胞中GSSG增加，而在A549细胞中，仅在最高BSO浓度预处理后，锌导致的GSSG增加才增强。与抑制甲硫氨酸掺入所需的锌浓度相比，在较低的锌浓度下即可观察到肺泡上皮细胞中GSSG还原酶受到抑制，而在成纤维样细胞中，与抑制甲硫氨酸掺入相比，GSSG还原酶受到抑制时的锌浓度明显更高。这些结果表明，GSSG还原酶是细胞对锌敏感性的一个重要因素。我们得出结论，在锌暴露的细胞中，GSSG的还原作用减弱。因此，通过各种抗氧化剂保护谷胱甘肽氧化以及提高谷胱甘肽含量有望成为减少锌暴露后细胞毒性作用的机制。
