Inhibition of glutathione synthesis can enhance cycloheximide-induced protection of developing neurons against axotomy.

Developing neurons depend for survival on target-derived trophic substances. These are thought to block the expression of a genetic program of cell death. Nevertheless, it is known that less orderly events such as oxidative stress are involved in neuron death. In vivo, retinal ganglion cell death induced by axotomy can be reduced by antioxidants. In this study, we investigated the effects of inhibiting glutathione synthesis by means of buthionine sulfoximine to characterize the influence of endogenous glutathione-dependent antioxidant systems on ganglion cell death. Moreover, since protein synthesis inhibition by cycloheximide has been shown to enhance glutathione synthesis in vitro, we studied the effects on cell death of intraocular injections of buthionine sulfoximine, cycloheximide and combinations of the two inhibitors. Cycloheximide's protective action did not seem to involve an increase in glutathione synthesis. Surprisingly, buthionine sulfoximine injected before cycloheximide enhanced its protective effects, whereas it inhibited them when injected later. We interpret our results as an interaction between death-promoting effects of glutathione depletion through an elevation of free radical concentrations and cycloheximide-sensitive effects of oxidative stress through the synthesis of both death-inhibiting and death-promoting proteins.