Drug- and estrogen-induced cholestasis through inhibition of the hepatocellular bile salt export pump (Bsep) of rat liver

Background & Aims: Drug-induced cholestasis is a frequent form of acquired liver disease. To elucidate the molecular pathogenesis of drug-induced chol estasis, we investigated the effects of prototypic cholestatic drugs on the canalicular bile salt export pump (Bsep) of rat liver. Methods: Vesicles w ere isolated from Bsep-, Mrp2-, and Bsep/Mrp2-expressing Sf9 cells. Canalic ular plasma membrane (cLPM) vesicles from rat liver and Sf9 cell vesicles w ere used to study adenosine triphosphate (ATP)-dependent solute uptake by a rapid filtration technique. Results: Bsep-expressing Sf9 cell vesicles sho wed ATP-dependent transport of numerous monoanionic bile salts with similar Michaelis constant values as in cLPM vesicles, whereas several known subst rates of the multispecific organic anion transporter Mrp2 were not transpor ted by Bsep. Cyclosporin A, rifamycin SV, rifampicin, and glibenclamide cis -inhibited Bsep-mediated bile salt; transport to similar extents as ATP-dep endent taurocholate transport in cLPM vesicles. In contrast, the cholestati c estrogen metabolite estradiol-17 beta-glucuronide inhibited ATP-dependent taurocholate transport only in normal cLPM and in Bsep/Mrp2-coexpressing S f9 cell vesicles, but not in Mrp2-deficient cLPM or in selectively Bsep-exp ressing Sf9 cell vesicles, indicating that it trans-inhibits Bsep only afte r its secretion into bile canaliculi by Mrp2. Conclusions: These results pr ovide a molecular basis for previous in vivo observations and identify Bsep as an important target for induction of drug- and estrogen-induced cholest asis in mammalian liver.