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 catabolism of glutathione (GSH) by gamma-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 polyunsaturated 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 diethylnitrosamine (DEN) followed by 0.1% or 0.25% phenobarbital (PB) in the diet. Cryostat sections were examined histochemically 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 triaminopentaacetic 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.

Gamma-glutamyltransferase: an effect modifier in the association between age and hypertension in a 4-year follow-up study

“…Alternatively, we are interested in the possibility that body iron storage plays a role in this interaction between GGT and age, because the cellular role of GGT differs depending on iron storage. [8][9][10][11] In this study, among young subjects who probably had low body iron storage, 18 GGT showed no relationship with hypertension, whereas among old age subjects who probably had high body iron storage, 18 GGT was a strong risk factor for hypertension.…”

“…GGT is a key enzyme for transport of glutathione into cells. Furthermore, recent experimental studies [8][9][10][11] indicated that under physiological conditions, especially in the presence of iron, GGT is involved directly in reactive oxygen species generation as a pro-oxidant. Thus, it may be that GGT plays an antioxidant or pro-oxidant role, depending on the presence of iron or similar oxidative stress.…”

“…[5][6][7] Paradoxically, recent studies [8][9][10][11] have shown that GGT is itself able to play a pro-oxidant role, particularly in the presence of iron.…”

Prospective study of the association of gamma‐glutamyltransferase with cancer incidence in women

“…Thus, serum GGT might increase with increasing exposure to xenobiotics which need to be conjugated to GSH. 24,25 In an experiment with carcinogen-treated rats, Stark and coworkers 42 found 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.…”

ReviewIs Serum Gamma Glutamyltransferase a Marker of Oxidative Stress?

“…Specifically, cysteinylglycine, which is one of the products of GGT action, has a strong ability to reduce Fe 3þ to Fe 2þ , which again promotes generation of free radical species. A GGT-mediated oxidative stress has been repeatedly reported, capable of inducing oxidation of lipids, [7,8] oxidation of protein thiols, [10] alterations of the normal protein phosphorylation patterns, [11] and biological effects such as the activation of transcription factors. [12,13] …”