Effect of inhibition of gamma-glutamyltranspeptidase by AT-125 (acivicin) on glutathione and cysteine levels in rat brain and plasma.

AT-125 (Acivicin) is an inhibitor of gamma-glutamyltranspeptidase (gamma-GTP) which initiates glutathione catabolism to cysteine. We measured plasma and brain glutathione and cysteine in rats treated with AT-125. Six h after AT-125 treatment, plasma glutathione had increased 6-fold and plasma cysteine had fallen significantly. Brain cysteine fell after 24 h of AT-125 treatment, and brain glutathione had also decreased 18%. AT-125 pretreatment inhibited brain uptake of 35S when it was given as 35S-GSH but had no effect when it was given as 35S-cysteine. These results suggest that plasma glutathione is catabolized by gamma-GTP, and cysteine derived from it is taken up by the brain. N-acetylcysteine was administered to AT-125 treated rats in an attempt to supply cysteine to the brain in the face of gamma-GTP inhibition. N-acetylcysteine supported brain glutathione levels, suggesting that it can serve as a source of cysteine under these conditions.