Protection of retinal pigment epithelium from oxidative injury by glutathione and precursors.

PURPOSE This study was performed to examine the effect of exogenous glutathione (GSH) or its precursor amino acids on oxidative injury in cultured human retinal pigment epithelium (RPE). METHODS Cultured human RPE cells were suspended in Krebs-Henseleit medium, and 150 microM t-butylhydroperoxide was added. Cell viability was assessed by 0.2% trypan blue exclusion 30, 60, and 120 minutes after the addition of GSH or its amino acid precursors. RESULTS Added GSH provided protection at concentrations of 0.01 mM and higher. The amino acid precursors for GSH, glutamate, cysteine, and glycine also protected against injury, but this required at least 0.1 mM of each amino acid. Inhibition of intracellular GSH synthesis by inclusion of 1 mM buthionine sulfoximine eliminated the protection by added amino acids but did not alter the protection by added GSH. CONCLUSIONS These results indicate that protection by the amino acid precursors is mediated through synthesis of GSH, and they also show that exogenous GSH can provide protection against oxidative injury.