Therapeutic Effects Of Leflunomide On Acute Liver Injury In Mice And Its Mechanism

Leflunomide is a novel immunosuppressive and anti-inflammatory agent.It is metabolized in vivo to its active form,A771726,which exerts the immunosuppressive activity,leflunomide was currently being tested for treatment of autoimmune diseases and transplant rejection.However,our recent studies have provided evidence that leflunomide also protects from T cell-mediated or non-T cell-mediated oxidative cell injury.The aims of the present work were to explore the protective effects of leflunomide against CCl₄ and BCG+LPS induced hepatotoxicity.The main contents are divided into six sections,as follows:1.Protective effect of Leflunomide on hepatocyte damage in acute liver injury induced by CCl₄ or BCG+LPS.Acute liver injury model was successfully established by injection of CCl₄ or BCG+LPS.ALT,AST levels in serum and liver histology was examined at 17 h after Lef administration.ALT,AST levels were elevated in model group compared to normal group(p＜0.01).Lef(5,9mg/kg) and bifendate(50 mg/kg) can significantly decrease the contents of ALT and AST in serum.The hepatocytes in normal group were funicular around the central vein.The hepatocytes in model control group had apparent dropsy and much metamorphic fat. The hepatocytes treated with Lef 5 mg/kg were in normal shape except for a few metamorphic ones,much less severe than that in model group,without metamorphic fat. as well as in the bifendate group.These findings suggest that Lef protect the liver from injury induced by CCl₄ and BCG+LPS.2.Effect of Leflunomide on lipid peroxidationIn chemical liver injury model,we discovered that compared to model group, MDA levels in liver tissue was decreased,and GSH activities increased in Lef(5,9mg/kg) and bifendate group(p＜0.05 or 0.01).Similar results were also obtained in immunological liver injury mice induced by BCG plus LPS.These results suggest that therapteutic effects of Lef on acute liver injury might be associated with its antioxide activity.3.Effect of Leflunomide on Cyt.P450 and Cyt.bs content in acute liver injuryIn acute liver injury mice,administration of CCl₄ or BCG+LPS casuse a significant loss in cytochrome P450s and their dependent substrate pathways.The levels of Cyt.P450 and Cyt.b₅ contents in hepatic microsomal increased following Lef administration(p＜0.05 or 0.01).This study suggest that protective effect of Lef(1,5,9mg/kg) on acute liver injury may be attributed to the induction of CYP450 enzyme.4.Effect of Leflunomide on CYP2E1 mRNA in chemical liver injuryIt has been established that CCl₄ is metabolized by the cytochrome P450 system yielding trichloromethyl radical,which causes direct damage to hepatocytes.In contrast, Lef could dose dependently decreased the P450 2E1 mRNA content in liver issue.These findings suggest that induction of CYP2E1 was the primary mechanism of increased bioactivation-based liver injury of CCl₄ in mice.Administration of Lef could dcreased the CCl₄-related hepatotoxicity.5.Effect of Leflunomide on NO content in serum and iNOS mRNA in liver issue of immunological liver injury miceIn our study,NO content in serum and iNOS mRNA in liver issue of immunological liver injury mice was increased.In contrast,Lef(5,9 mg/kg) administration could decreased NO content and iNOS mRNA expression,which suggested that protective effect of Lef on immunological liver injury may be associated with the ability to reduce NO content.5.Conclusionwe demonstrate that leflunomide protects from acute CCL₄ and BCG+LPS -induced liver injury in mice.The results suggested that its mechanisms of action in chemical or BCG+LPS liver injury might be associated with its anti-oxide activity,ability to regulate liquid metabolism,induction of CYP450,scaveing reactive species formed, suppression CYP2E1 mRNA content,decreasing liver iNOS mRNA content.