Localization of oxidative damage by a glutathione-γ-glutamyl transpeptidase system in preneoplastic lesions in sections of livers from carcinogen-treated rats

Abstract

Previous studies from our laboratories have shown that catabotism of glutathione (GSH) by γ-glutamyl transpeptidase (GGT) in the presence of transition metals leads to oxidative damage (OD). This damage is exemplified in vitro by GGT-dependent GSH mutagenesis which involves reactive oxygen species and by GGT-dependent accumulation of lipid peroxidation (LPO) products in systems containing poly-unsaturated fatty acid and GSH. In order to test whether catabolism of GSH by membranal GGT in enzyme-altered preneoplastic hepatic lesions can induce oxidative damage in situ, and to test whether the OD is localized in these lesions, 21 day old Fischer rats were treated with 12 mg/kg diethyl-nitrosamine (DEN) followed by 0.1% or 0.25% phenobarbital (PB) in the diet. Cryostat sections were examined histo-chemically for GGT-rich hepatic lesions. Adjacent sections were incubated with GSH and iron and examined for areas staining for lipid peroxidation. Distinct LPO-positive areas were shown to correspond well with the GGT-positive hepatic lesions. Promotion with 0.25% PB led to increasing proportions of LPO-positive lesions with time among GGT-positive lesions. The visualization of LPO in GGT-rich hepatic lesions depended on the presence of GSH and iron, and was not observed following chelation of iron by diethyl triaminopen-taacetic acid (DTPA), in the presence of acivicin, an inhibitor of GGT, or in the presence of the radical scavenger butylated hydroxytoluene (BHT). The factors affecting GSH-GGT-dependent LPO in the GGT-rich foci were identical to those affecting GSH-GGT-driven LPO in vitro, and were similar to those affecting oxidative GSH-mutagenesis catalyzed by GGT. The results indicate that metabolism of GSH by GGT in preneoplastic liver foci can initiate an oxidative process leading to a radical-rich environment and to oxidative damage. Such damage may contribute to the processes by which cells within such foci progress to malignancy.