Cytotoxicity of metals in isolated fish cells: Importance of the cellular glutathione status

Abstract

The study investigates the importance of glutathione (GSH) for protection of fish cells against heavy metal stress. The cytotoxicities of six metal salts to the continuous rainbow trout cell line RTG-2 were determined by means of the neutral red (NR) uptake inhibition assay. The rank order of metal cytotoxicities (in terms of NR50 values) were Hg>Cd>Zn>Cu>Pb>Ni. The importance of GSH in determining metal toxicity was assessed by inhibition of its synthesis. A 20 h pretreatment of RTG-2 cells with 1 mM buthionine sulfoxime caused sustained reduction of cellular GSH level to ≈30% of the control value. The effect of GSH depletion on metal cytotoxicity was found to be related to the chemical softness parameter of the metal cations: Cytotoxicities of the ‘soft’ metals Hg, Cu and Cd were significantly increased in GSH-depleted cells, whereas cytotoxicities of the ‘hard’ metals Zn, Ni and Pb were not significantly altered. Since chemical softness is a determinant for binding of metal ions to sulfhydryl groups as being present in GSH, the findings of this study suggest that the metal-protective effect of GSH in fish cells is, at least partly, due to its action as an intracellular metal chelator.