Increase in γ-Glutamyltransferase by Glutathione Depletion in Rat Type II Pneumocytes

The purpose of our study was to investigate the effect of oxidative stress or intracellular glutathione (GSH) depletion on γ-glutamyltransferase (γ-GT) activity in cultured type II pneumocytes. Twenty-four hours after isolation, primary cultures of rat type II pneumocytes were preincubated with one of four compounds: 15, 30, 60, 125, 250 μM l-buthionine-[SR]-sulfoximine (BSO) for 3 h; 100, 200, 400, 800 μM tertiary-butylhydroperoxide (t-BOOH) for 45 min; 10, 25, 50, 100 μM menadione for 15 min; 100, 1000 μM paraquat for 1 h. GSH levels, H2O2 and O2·− generation were measured immediately after the incubation, γ-GT activity and GSH levels also up to 24 h or 48 h later. Exposure to BSO led to a persistent GSH depletion without increase in H2O2 or O2·− production, together with a dose- and time-dependent increase (doubling) of γ-GT activity with a nonsignificant increase in γ-GT mRNA expression 24 h after exposure to BSO. Exposure to 100 μM menadione, which increased H2O2 production, decreased γ-GT activity. t-BOOH or paraquat did not give rise to a measurable increase in H2O2 or O2·−. Paraquat did not affect initial GSH levels, but increased GSH and decreased γ-GT activity 24 h later. t-BOOH (400 and 800 μM) initially decreased GSH, and tended to increase GSH 24 h later, 100 and 200 μM increased γ-GT activity 24 h later, but 800 μM decreased it. Restoration of intracellular GSH levels by addition of GSH to the culture medium completely prevented the increase in γ-GT activity by BSO, while the addition of catalase or DMTU had no effect. We conclude that at least two effects are operating upon γ-GT activity: GSH depletion seems to increase γ-GT activity, while exposure to compounds generating oxidative stress correlates with a decrease in γ-GT activity. Copyright © 1996 Elsevier Science Inc.