Molecular Mechanism Of Biliary Excretion Of Cefditoren And The Effects Of Cefditoren On The Expression Levels Of Hepatic Transporters

Objective: The important role of transport proteins in drug metabolism and disposition process, tend to gain more and more attention together with liver drug enzymes. Mrp2 and Bcrp are the members of ATP-binding cassette (ABC) superfamily on canalicular membrane of hepatocyte. They transport a great deal of endogenous substances and xenobiotics, such as drugs which may regulate the expression levels of these transporters. Cefditoren, a fourth generation cephalosporin antibiotics, has been used in clinic extensively. Determining which transport protein on the hepatocyte canalicular membrane is involved in cefditoren biliary excretion is important for the prediction of potential cefditoren-related drug-drug interactions and may contribute to our understanding of the mechanisms of biliary excretion ofβ-lactam antibio- tics.We used in situ and in vivo methods to investigate the role of transporters involved in biliary excretion of cefditoren and the effects of cefditoren on expression levels of hepatic transporters.Methods: Perfused rat livers were performed to investigate whether Mrp2,Bcrp and P-gp were involved in the biliary excretion of cefditoren. We used RT-PCR and Western blot to study the alteration of expression levels of relative hepatic transporters. (1) The hepatobiliary disposition of cefditoren (1μΜ) was examined with probenecid (20μΜ), novobiocin (20μΜ) and verapamil (20μΜ) as the inhibitor of Mrp2, Bcrp and P-gp respectively in the perfused rat liver. The concentration of cefditoren in perfusate and bile were determined by HPLC. Then compare the hepatic extraction ratio and cumu- lative biliary excretion rates in control and experimental group; (2) 16mg/kg, 50mg/kg, 100mg/kg of cefditoren and physiological saline as control were administered twice a day. After one week, the expression levels of Mrp2, Bcrp, P-gp, Oct1 and Oat2 mRNA were examined by RT-PCR; (3) The expre- ssion of Mrp2 was investigated by Western blot to observe the dose- dependence.Results: (1) The hepatic extraction ratio showed no statistically significant differences, whereas cumulative biliary excretion rates were sig- nificantly reduced to 43.78% and 79.52% over 25 min in the perfused probenecid and novobiocin group, respectively. The cumulative biliary excre- tion rates in perfused verapamil group had no change compared with control; (2) One week after oral administration of cefditoren, the expression levels of Mrp2, Bcrp and Oat2 mRNA were markedly up-regulated, while P-gp and Oct1 mRNA were down-regulated; (3) In accordance with RT-PCR results, the Mrp2 expression was increased by Western blot. After administration of 100 mg/kg, the Mrp2 levels were markedly up-regulated to 1.70 fold of the control, while the Mrp2 expression levels in 16 mg/kg group increased to 1.32 fold over the control.Conclusions: (1) Mrp2 is the major protein of efflux transport into bile, while Bcrp is also involved in the biliary excretion of cefditoren, and P-gp has no contribution to this process. (2) Mrp2, Bcrp and Oat2 mRNA are up- regulated, and P-gp and Oct1 mRNA are down-regulated after administration of cefditoren. (3) Cefditoren increases expression levels of Mrp2. These results provide important data for drug-drug interactions.