We investigated the effect of tetrahydroswertianolin (THS), a hepatoprotective agent from Swertia japonica, on tumor necrosis factor-alpha (TNF-alpha)-dependent hepatic apoptosis induced by D-galactosamine (D-GalN) (700 mg/kg, i.p.) and lipopolysaccharide (LPS) (10 microg/kg, i.p.) in mice. Apoptotic symptoms were observed at the initial stage of liver damage. By 5 hr after intoxication, hepatic DNA fragmentation had risen to 2123%, with the value in untreated mice set at 100%, without a significant elevation of serum alanine transaminase (ALT) activity. There was a parallel increase in hepatocytes undergoing chromatin condensation and apoptotic body formation. By 8 hr after intoxication, serum ALT activity had risen to 3707 U/L. Pretreatment with THS (50 mg/kg, p.o.) at 18 and 2 hr before intoxication significantly reduced DNA fragmentation to 821% of that in untreated mice and prevented the emergence of chromatin condensation and apoptotic body formation. A significant and dose-dependent reduction in serum ALT activity at 8 hr also was observed with THS pretreatment. These effects of THS were different from those observed from pretreatment with glycyrrhizin (GCR), which is a clinically used hepatoprotective agent with membrane-stabilizing activity. GCR pretreatment (100 mg/kg, p.o.) did not inhibit hepatic DNA fragmentation (1588% of untreated mice), although this compound significantly protected against serum ALT elevation (1463 U/L). These data suggest that an inhibitory effect on the progression of hepatic apoptosis prior to liver injury may be involved in the hepatoprotective mechanisms of THS, whereas it appears that GCR affects the processes after apoptosis. In a separate experiment, we found that the concentration of serum TNF-alpha rose to 2016 pg/mL at 1 hr after intoxication of mice with D-GalN and LPS, but this increase was suppressed by THS pretreatment (10, 50, or 200 mg/kg, p.o.) to 716, 454, or 406 pg/mL, respectively. Further study with a reverse transcriptase-polymerase chain reaction method showed that THS blocked TNF-alpha production at the transcriptional level. Because TNF-alpha is a critical mediator to elicit apoptosis in this model, the property of suppressing TNF-alpha production may be of prime importance for THS inhibition of hepatic apoptosis.