Glutathione modifies the toxicity of triethyltin and trimethyltin in C6 glioma cells

Abstract

It has been demonstrated that exposure to mercury or cadmium compounds causes alterations in the glutathione system in a model glial cell line, C6. Here we report that two organic tin compounds, triethyltin (TET) and trimethyltin (TMT), are also toxic to these cells with EC₅₀ values for cell death of c. 0.02 μM and 0.8 μM respectively. Exposure for 24 h to either of these compounds at sub-toxic concentrations caused increases in the amount of reduced glutathione (GSH) per cell. Increases in glutathione-S-transferase enzyme activity were also demonstrated after TET or TMT exposure. This suggests that glutathione increases occur in glial cells after toxic insults below that required to cause cell death, possibly acting as a protective mechanism. To test whether GSH plays a role in organotin-induced cell death we manipulated GSH in the culture media or via intracellular GSH and looked at the effects on sensitivity to TET or TMT toxicity. Adding GSH to the culture media did not protect the cells. Depletion of intracellular GSH with buthionine-[S,R] sulphoximine did not alter cytotoxicity of TET or TMT. However, pre-treatment with (−)-2-oxo-4-thiazolidine carboxylic acid (OTC), which increases intracellular GSH levels, protected the cells against both compounds. The EC₅₀ for TMT was increased from 0.77 to 1.8 μM, a 2.3-fold shift, whereas the EC₅₀ for TET was increased >20-fold, from 0.022 to 0.47 μM. One interpretation of these results is that GSH protects cells against the toxicity of organic tin compounds without reacting directly with them to any significant extent. Under conditions where GSH is depleted, additional protective mechanisms may be active.