Effect of diethylmaleate and other glutathione depletors on protein synthesis

The alpha, beta-unsaturated carbonyl compound diethylmaleate (DEM) depletes glutathione (GSH) from liver and other tissues, and for this reason it is often used in toxicological research to study the GSH-mediated metabolism of xenobiotics. In addition to GSH depletion, however, DEM has been shown to have other nonspecific effects, such as alteration of monooxygenase activities or glycogen metabolism. In this study we found that DEM (1 ml/kg) inhibited protein synthesis in brain and liver, following in vivo administration to mice. Protein synthesis was measured as the incorporation of [3H]valine into trichloroacetic acid-precipitable material. Administration of DEM also decreased body temperature by 2-3 degrees. By increasing the environmental temperature from 22 degrees to 35 degrees the hypothermic effect of DEM was prevented, without affecting its ability to deplete GSH from brain and liver. Furthermore, when mice were maintained at 35 degrees, DEM still caused a significant decrease in protein synthesis, suggesting that this effect was only partially due to hypothermia. To test whether inhibition of protein synthesis was related to GSH depletion, groups of animals were dosed with the alpha, beta-unsaturated carbonyl phorone (diisopropylidenacetone) or the specific inhibitor of GSH synthesis, buthionine sulfoximine (BSO). Phorone decreased GSH in liver and brain; however, it had no effect on protein synthesis. BSO decreased GSH levels in liver and kidney, but not in brain, and did not have any effect on protein synthesis in any of these tissues, nor did it cause any hypothermia. Furthermore, when hepatic GSH content was decreased by in vivo administration of DEM or BSO, there was no inhibition of protein synthesis measured in vitro. These results indicate that, at the dose normally used to deplete GSH from various tissues. DEM also exerts an inhibitory effect on protein synthesis, which appears to be only partially due to its hypothermic effect, and is independent from GSH depletion. BSO, which, in our experimental conditions, lacks this and other nonspecific effects, might be a good alternative for studies aimed at characterizing the role of GSH in the metabolism and toxicity of chemicals.