Pharmacogenetic Research: The Effect Of Bifendate On The Pharmacokinetics Of Cyclosporine And It's Potential Mechanism

Pharmacogenetics studies indicate that activity change of drug-metabolizing enzymes and transporter is the major mechanism for clinical drug-drug interactions,which is also the key point for the process of bio-transformation and transporting.The inherited variation in activities of drug-metabolizing enzymes and transporters results in interindividual difference in drug metabolism,disposition and efficacy. CyA is a calcineurin inhibitor,which is developed for the treatment of many immune-mediated diseases,especially for the prevention of allograft rejection after the solid organ transplantation.Leukocytes, special helper CD4+ lymphocytes are the main therapeutic targets of this drug.It is regarded as a highly effective in preventing acute rejection, whereas also characterized by a narrow therapeutic index and variable pharmacokinetic characteristics.The process of biotransformation and transporting of cyclosporine is especially via CYP3A4 and P-gp,on which much attention have been paid.The CYP system is consisted of more than 50 isozymes,by which many exogenous agents and drug are metabolized.Expressed both in liver and small intestine,CYP3A subfamily is found to metabolize about 50%-60%drugs,which is the most abundant CYPs.The variations in the oral bioavailability and the systemic clearance of CYP3A substrates may result from the great interindividual differences in their activity.The studies have found that the variation of CYP3A4 activity does result in the cyclosporine related drug-drug interaction.As the major enzyme involved in the metabolism of drugs,the expressing level of CYP3A4 varies up to 40-fold in the human population,which include inducible and constitute levels.CYP3A4~*18B was speculated to be associated with an increase level of CYP3A4 activity,which could increase the metabolism of cyclosporine.P-gp is the ATP-binding ex-pumper,which is expressed in liver, small intestine,and kidney and encoded by MDR1.The P-gp played an important role in the process of drug absorption,disposition and elimination.The variation of P-gp activity may lead to the inter-individual difference in the concentration of cyclosporine.Nuclear receptors PXR and CAR have become hotpoints for pharmacological research by involving in transcriptional regulation of several drug-metabolizing enzymes and transpoters mentioned above. Due to the dual key roles played by PXR and CAR ligands medicated in pharmagology efficacy as well as herb-drug interactions,finding significantly induction of PXR or CAR targeted CYP450 enzymes and drug transporters through activating PXR or CAR using PXR or CAR expressed dual luciferase reporter gene platform becomes crutial in drug development and clinical pharmacology research.Bifendateis a synthetic intermediate of schisandrin C,which is widely used for the treatment of chronic hepatitis,by lowering alanine transaminase(ALT) in patients. Following the intake of bifendate in rats,it was observed to improve liver function by increasing the detoxification process,reducing pathological lesion,accelerating the hepatocyte regeneration.Bifendate can also function as a membrane-stabilizing agent to prevent the cell from the impairment.After the treatment of bifendate,the protein metabolism process of the hepatitis patients was improved,with serum albumin level increased and globulin level decreased.In China,the combined therapy of bifendate with CyA on the patients with renal transplant is found to decrease the side effect of hepatotoxicity induced by CyA,which is also accompanied by the decreased concentration of cyslosporine.Based on above information,our study was aimed to find effects of bifendate on the activity of CYP3A4 and P-gp,and the mechanism of drug-drug interaction between bifendate and cyclosporine.The effects of bifendate on transcription of CYP3A4 and P-g have been explored by dual-luciferase activity dection.In strictly designed clinical experiment, the effect of bifenate on the pharmacokinetic of cyclosporine in relation to CYP3A4~*18B was evaluated.Using talinolol and midazolam as the substrate drugs,the potential impact of bifendate on CYP3A4 and P-gp have been clarified.Thepresent study may provide molecular mechanism for the bifendate-cyclosporine interaction,theoretic guidance for combination use of bifendate with cyclosporine,and also the explanation for the bifendate-cyclosporine interaction.The present series of studies have found that:1.Bifendate(0.1uM) can significantly increase promoter activities of CYP3A4,MDR1 when cotransfected with PXR-expressed plasmid and dual-luciferase reporter plasmid while bifendate can not significantly increase promoter activities of CYP3A4,MDR1 when cotransfected with CAR-expressed plasmid and dual-luciferase reporter plasmid.2.Bifendate can decrease the cyclosporine concentration in the CYP3A4~*18B gene dependent manner.3.Bifendate significantly decreases plasma concentrations and oral bioavailability of talinolol in all subjects,indicating that bifendate can significantly induce P-gp activity in human.4.Bifendate can decrease significantly decrease the plasma concentration of midazolam and 1-OH-midazolam.The variance of AUC(0-24), AUC(0-∞) and Cmax decreased in the CYP3A4~*18B gene dependent manner.5.Screening the frequency of PXR 1207 C＞T in Chinese healthy subjects, no mutation of 1207 C＞T was found. The present study has provided explanation for the bifendate-cyclosporine interaction from gene transcription and clinical investigation and offered the experimental and theoretic guidance for combination use of bifendate with cyclosporine,β-receptor antagonist talinolol and midazolam as well as similar drugs.