Zinc toxicity in various lung cell lines is mediated by glutathione and GSSG reductase activity

In a previous work, it was shown that in cells after a decrease of cellular glutathione content, toxic zinc effects, such as protein synthesis inhibit ion or GSSG (glutathione, oxidized form) increases, were enhanced. In this study, zinc toxicity was determined by detection of methionine incorporatio n as a parameter of protein synthesis and GSSG increase in various lung cel l lines (A549, L2, 11Lu, 16Lu), dependent on enhanced GSSG reductase activi ties 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 GSSC reduc tase activity was increased to 120-135% in a concentration-dependent manner . In BSO pretreated cells, the IC50 values of zinc for methionine incorpora tion inhibition were unchanged as compared to cells not pretreated. The GSS G increase in BSO pretreated cells by zinc was enhanced in L2, 11Lu, and 16 Lu cells, whereas in A549 cells, the CSSG increase by zinc was enhanced onl y after pretreatment with the highest BSO concentration, Inhibition of GSSG reductase in alveolar epithelial cells was observed at lower zinc concentr ations than needed for methionine incorporation inhibition, whereas in fibr oblastlike cells, inhibition of GSSG reductase occurred at markedly higher zinc concentrations as compared to methionine incorporation inhibition. These results demonstrate that CSSG reductase is an important factor in cel lular zinc susceptibility. We conclude that reduction of GSSG is reduced in zinc-exposed cells. Therefore, protection of GSH oxidation by various anti oxidants as well as enhancement of GSH content are expected to be mechanism s of diminishing toxic cellular effects after exposure to zinc.