Differential Inhibition of Rat and Human Na⁺-Dependent Taurocholate Cotransporting Polypeptide (NTCP/SLC10A1)by Bosentan: A Mechanism for Species Differences in Hepatotoxicity

Abstract

Bile acid accumulation in hepatocytes due to inhibition of the canalicular bile salt export pump (BSEP/ABCB11) has been proposed as a mechanism for bosentan-induced hepatotoxicity. The observation that bosentan does not induce hepatotoxicity in rats, although bosentan has been reported to inhibit rat Bsep and cause elevated serum bile acids, challenges this mechanism. The lack of hepatotoxicity could be explained if bosentan inhibited hepatocyte uptake as well as canalicular efflux of bile acids. In the current study, bosentan was found to be a more potent inhibitor of Na ϩ -dependent taurocholate uptake in rat (IC 50 5.4 M) than human (IC 50 30 M) suspended hepatocytes. In addition, bosentan was a more potent inhibitor of taurocholate uptake by rat Na ϩ -dependent taurocholate cotransporting polypeptide (Ntcp/Slc10a1) (IC 50 0.71 M) than human NTCP (SLC10A1) (IC 50 24 M) expressed in HEK293 cells. Thus, bosentan is a more potent inhibitor of Ntcp than NTCP, and this should result in less intrahepatocyte accumulation of bile acids in rats during bosentan treatment. To begin characterization of this species difference, two chimeric molecules were generated and expressed in HEK293 cells; NTCP 1-140 /Ntcp 141-362 and Ntcp 1-140 /NTCP 141-349 . The mode of bosentan inhibition was noncompetitive for Ntcp, and competitive for NTCP (K i 18 M) and NTCP 1-140 / Ntcp 141-362 (K i 1.7 M); bosentan affected both the K m and V max of Ntcp 1-140 /NTCP 141-349 (K i 7.0 M). The carboxyl portions of NTCP and Ntcp were found to confer species differences in basal taurocholate transport V max . In conclusion, differential inhibition of Ntcp and NTCP may represent a novel mechanism for species differences in bosentaninduced hepatotoxicity.

An In Vitro Assay to Assess Transporter-Based Cholestatic Hepatotoxicity Using Sandwich-Cultured Rat Hepatocytes

“…Bosentan and troglitazone demonstrated similar effects on the hepatobiliary disposition of d 8 dmd.aspetjournals.org inhibition of the efflux of d 8 -TCA into bile. These results are consistent with the findings of Leslie et al (2007) in which bosentan was identified as a potent inhibitor of rat Ntcp. Furthermore, Kemp et al (2005) also observed inhibition of hepatic uptake and biliary efflux of TCA by troglitazone coadministration in SCRH.…”

Modulation of trabectedin (ET-743) hepatobiliary disposition by multidrug resistance-associated proteins (Mrps) may prevent hepatotoxicity

“…Covalent adduct formation, immunotoxicity, and disruption of cellular bioenergetics have been considered previously as mechanisms underlying hepatotoxicity, but more recent data suggest that hepatic transport proteins may be an important site of toxic interactions (Fattinger et al, 2001;Funk et al, 2001;Leslie et al, 2007). The objective of this study was to evaluate the capability of sandwich-cultured primary rat hepatocytes (SCRH), which more closely mimic the metabolic and transport capabilities of the intact liver, to predict the hepato-protective effect of DEX against trabectedin-mediated hepatotoxicity.…”

Stereoselective Recognition of Amethopterin Enantiomers by the Rat Proton-Coupled Folate Transporter

“…The Na + -dependent taurocholate cotransporting polypeptide (NTCP, SLC10A1), which is a major transporter of bile acids in hepatocytes, showed species differences in terms of its inhibition by bosentan. 26) Taurocholate uptake was inhibited in a competitive manner by bosentan in the human NTCP with a K i value of 18 µM, whereas the uptake of taurocholate was inhibited in a noncompetitive manner by bosentan in the rat NTCP. Multidrug resistance-associated protein 2 (MRP2, ABCC2) transports a variety of different drug molecules and metabolites, including glutathione, glucuronide, and sulfate conjugates, across extraand intracellular membranes.…”