No abstract

Human hepatocytes usually are resistant to TNF-α cytotoxicity. In mouse or rat hepatocytes, repression of NF-κB activation is sufficient to induce TNF-α-mediated apoptosis. However, in both Huh-7 human hepatoma cells and Hc human normal hepatocytes, when infected with an adenovirus expressing a mutated form of IκBα (Ad5IκB), which almost completely blocks NF-κB activation, >80% of the cells survived 24 h after TNF-α stimulation. Here, we report that TNF-α activates other antiapoptotic factors, such as sphingosine kinase (SphK), phosphatidylinositol 3-kinase (PI3K), and Akt kinase. Pretreatment of cells with N,N-dimethylsphingosine (DMS), an inhibitor of SphK, or LY 294002, an inhibitor of PI3K that acts upstream of Akt, increased the number of apoptotic cells induced by TNF-α in Ad5IκB-infected Huh-7 and Hc cells. TNF-α-induced activations of PI3K and Akt were inhibited by DMS. In contrast, exogenous sphingosine 1-phosphate, a product of SphK, was found to activate Akt and partially rescued the cells from TNF-α-induced apoptosis. Although Akt has been reported to activate NF-κB, DMS and LY 294002 failed to prevent TNF-α-induced NF-κB activation, suggesting that the antiapoptotic effects of SphK and Akt are independent of NF-κB. Furthermore, apoptosis mediated by Fas ligand (FasL) involving Akt activation also was potentiated by DMS pretreatment in Hc cells. Sphingosine 1-phosphate administration partially protected cells from FasL-mediated apoptosis. These results indicate that not only NF-κB but also SphK and PI3K/Akt are involved in the signaling pathway(s) for protection of human hepatocytes from the apoptotic action of TNF-α and probably FasL.

Serum pro- and anti-inflammatory mediators in patients with acute liver diseases were assessed to clarify the clinical significance of these measurements in relation to disease severity. Concentrations of circulating tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, IL-10, IL-12, and soluble TNF receptors (sTNFR) p55 and p75 were measured at admission in patients with fulminant hepatitis (FH; n=19), severe acute hepatitis (AHS, n=15), or acute hepatitis (AH, n=7). Serum concentrations of TNF-alpha, IL-10, and sTNFR-55 were significantly higher in patients with FH than in those with AHS (P<.05, <.05, and <.01, respectively) or AH (P<.05). Serum IL-10 and TNF-alpha levels were higher in patients who died of FH (n=13) than in FH survivors (n=6; P<.05). The ratios between TNF-alpha and IL-10 and sTNFR-55 or sTNFR-75 were not valuable in predicting mortality and disease severity. However, both proinflammatory cytokine TNF-alpha and anti-inflammatory cytokine IL-10 levels at admission were associated with fatal outcome among patients with FH.

TNF-alpha and IL-6 may be important in the pathogenesis of the clinical symptoms that differentiate fulminant hepatitis from the severe form of acute hepatitis, and plasma exchange removes these inflammatory mediators from the circulation of patients with severe liver disease.