Reduced glutathione depletion causes necrosis and sensitization to tumor necrosis factor-α-induced apoptosis in cultured mouse hepatocytes

The effect of reduced glutathione (GSH) depletion by acetaminophen (A-PAIP), diethylmaleate (DEM), or phorone on the mode of cell death and susceptibility to tumor necrosis factor (TNF)-induced cell death was studied in cultured mouse hepatocy-tes. Dose-dependent necrosis was the exclusive mode of cell death with APAP alone, but the addition of TNF-alpha induced a switch to about half apoptosis without changing total loss of viability. This effect was seen at 1 and 5 mmol/L but was inhibited at 10 and 20 mmol/L APAP. The switch to apoptosis was associated with increased caspase activities, release of cytochrome c, and DNA laddering and was inhibited by caspase inhibitors. DEM and phorone also induced dose-dependent necrosis. Treatment with TNF-a under these conditions lead to incremental cell death in the form of apoptosis at 0.25 and 0.5 mmol/L DEM and 0.1 and 0.2 mmol/L phorone. At 1.0 and 2.0 mmol/L DEM and 0.5 mmol/L phorone, 90% to 100% necrosis was observed with resistance to TNF-a effects. The apoptosis with TNF-a plus DEM was confirmed by DNA laddering and inhibition by caspase inhibitors. However, in the presence of caspase inhibitors, the increment in cell death induced by TNF-alpha persisted as an increase in necrosis. A combination of antioxidants, vitamin E, and butylated hydroxytoluene (BHT) markedly inhibited necrosis induced by APAP or DEM alone, but the sensitization to TNF-alpha-induced apoptosis was unaffected. GSH monoethylester (GSH-EE) protected against necrosis and apoptosis. In conclusion, depletion of GSH by A.PA.P, DEM, or phorone causes oxidative stress-induced necrosis and sensitizes to an oxidative stress independent TNF-alpha-induced apoptosis.