Hepatocellular response to chemical stress in CD-1 mice: Induction of early genes and gamma-glutamylcysteine synthetase

Exposure of cells to toxic chemical species can result in reduced glutathio ne (GSH) depletion, generation of free radicals, and/or binding to critical cell determinants. Chemical stress is usually followed by a concerted cell ular response aimed at restoring homeostasis, although the precise initial stimulus for the response is unclear. We have focused on one component of t his stress response, the up-regulation of gamma-glutamylcysteine synthetase (gamma-GCS) and the preceding molecular events involved in its regulation in an in vivo mouse model. Male CD-1 mice received buthionine sulphoximine (BSO; 7.2 mmol/kg), diethyl maleate (DEM; 4.2 mmol/kg), paracetamol (APAP; 3.5 and 1.0 mmol/kg), or carbon tetrachloride (CCl4; 1.0 and 0.2 mmol/kg). Biochemical (serum transaminase and hepatic GSH levels) and molecular (c-ju n and c-fos messenger RNA [mRNA] levels and activator protein 1 [AP-1] DNA binding activity) parameters were measured, as well as the consequent effec ts on gamma-GCS levels and activity. All compounds produced GSH depletion, but only the higher doses of APAP and CCl4 caused liver damage. DEM, APAP, and CCl4 increased c-jun and c-fos mRNA levels, together with an increase i n AP-1 binding; BSO failed to induce AP-1 despite an increase in c-fos. Int erestingly, the effects on gamma-GCS varied markedly according to the compo und: BSO and DEM increased gamma-GCS enzyme activity, although only DEM, bu t not BSO, resulted in an increase in gamma-GCS(h) mRNA and protein. In con trast, APAP and CCl4 both increased gamma-GCS(h) mRNR and protein; however, there was a marked dose-dependent decrease in gamma-GCS activity. These da ta indicate that the effect of chemical stress on the liver is compound spe cific and is not merely dependent on depletion of GSH.