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 (APAP), 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 hepatocytes. 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-alpha 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-alpha effects. The apoptosis with TNF-alpha 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 APAP, DEM, or phorone causes oxidative stress-induced necrosis and sensitizes to an oxidative stress independent TNF-alpha-induced apoptosis.