Abstract

We used immortalized human hepatocytes to study the bioactivation of leflunomide and the metabolic degradation to its major metabolic,A77 1726. Both leflunomide and A77 1726 caused a time-and concentration-dependent increase in LDH release. The cytotoxicity of leflunomide,but not that of A77 1726, was prevented by the pan -CYP inhibitor, 1-aminobenzotriazole,indicating that an oxidative metabolite(s) was responsible for the cell injury.LC/MS/MS analysis revealed that leflunomide was rapidly degraded in hepatocytes biphasically(t1/2a=1.5 h,t1/2b > 24h),but much slower in cell-free medium(t1/2 > 24 h).In contrast,the generation of A77 1726 occured at a similar rate in cells and cell-free system s.In conclusion,leflunomide wsa rapidly metabolized in human hepatocytes to A77 1726, but its toxicity was dependent on other ,CYP-dependent intermedietly metabolized in human hepatocytes to A77 1726, but its toxicity was dependent on other ,CYP-dependent intermediidly metabolized in human hepatocytes to A77 1726, but its toxicity was dependent on other,CYP-dependent intermediidly metabolized in human hepatocytes to A77 1726,but its toxicity was dependent intermediates.

Keywords: Leflunomide, A77 1726, human hepatocytes, bioactivation, hepatotoxicity