Accelerative effect of leflunomide on recovery from hepatic fibrosis involves TRAIL-mediated hepatic stellate cell apoptosis

Aims: Hepatic fibrosis is reversible, associated with apoptosis of activated hepatic stellate cells (HSCs) as injury subsides, thus providing potential targets for therapy. Little is known, however. about the course of this condition. The objective of this study was to elucidate the mechanism by which Kupffer cells regulate HSC biology during regression of hepatic fibrosis and the effect of leflunomide on this process. Main methods: We harvested Kupffer cells from rats during spontaneous recovery from liver fibrosis induced by carbon tetrachloride (CCl4) and prepared recovery Kupffer cell conditioned medium (KCCM). Culture-activated HSCs were pretreated in the absence or presence of A771726, the active metabolite of leflunomide, and then stimulated with recovery KCCM. Key findings: Following stimulation with recovery KCCM, HSCs showed a decrease in proliferation and an increase in apoptosis by a caspase-dependent mechanism. Furthermore, pretreatment with A771726 markedly enhanced these effects. Real-time quantitative PCR (Q-PCR) analysis showed increased expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in Kupffer cells during the spontaneous recovery phase. The pro-apoptotic function of KCCM prepared from TRAIL siRNA-treated Kupffer cells was obviously decreased, suggesting that TRAIL played an important role in recovery from hepatic fibrosis. Moreover, A771726 enhanced recovery KCCM-induced apoptosis of HSCs by a mechanism involving the inhibition of nuclear factor-kappa B (NF-kappa B) activation. Significance: Our results showed the role of TRAIL in the apoptosis of activated HSCs that is induced by Kupffer cells prepared from livers recovering from CCl4-induced fibrosis and provided insights into the resolution of fibrosis and the mechanisms by which leflunomide might act upon liver fibrosis. (C) 2009 Elsevier Inc. All rights reserved.