Regulation of 3,3′,4,4′-Tetrachlorobiphenyl Induced Cytochrome P450 Metabolism by Thiols in Tissues of Rainbow Trout

We observed that glutathione (GSH) status regulates the Ah receptor inducible cytochrome P4501A (CYP1A) gene expression and catalytic activity in 3,3′,4,4′-tetrachlorobiphenyl (TCB) exposed rainbow trout. Tissue GSH status of TCB (1 mg/kg body weight, in corn oil) injected fish was manipulated by a) injecting (i.p.) GSH (0.25 g/kg), b) arresting GSH synthesis by l-buthionine-[S,R]-sulfoximine (BSO; 6 mmol/kg) injection for 3 and 6 days. Our attempt to manipulate GSH levels by lipoate supplementation (16 mg/kg) was not productive. Both BSO- and lipoate-supplemented fish maintained a low tissue redox (GSSG/GSH) ratio. Activities of glutathione peroxidase and glutathione reductase were elevated following 3 days of GSH supplementation in GSH rich tissues. Low activities of these enzymes were observed in BSO treated GSH deficient tissues. TCB injection markedly induced hepatic and renal CYP1A catalytic (ethoxyresorufin O-deethylase [EROD]) activities. This effect was further potentiated (3-fold) in GSH-supplemented fish tissues. In contrast, EROD induction by TCB was markedly suppressed in GSH deficient (BSO-treated) and lipoate-supplemented fish. The suppression of CYP1A catalytic activities in GSH deficient and lipoate-supplemented fish was consistently associated with a suppression of TCB induced CYP1A mRNA and protein expressions in these groups. In glutathione-supplemented fish, TCB induced CYP1A protein expression was markedly higher following 3 days of GSH supplementation. Results of our study suggest that tissue thiol status modulates cytochrome P450 CYP1A gene expression and catalytic activity.