Evaluation of the endothelin receptor antagonists ambrisentan, darusentan, bosentan, and sitaxsentan as substrates and inhibitors of hepatobiliary transporters in sandwich-cultured human hepatocytesThis article is one of a selection of papers published in the two-part special issue entitled 20 Years of Endothelin Research.

Abstract

To evaluate potential mechanisms of clinical hepatotoxicity, 4 endothelin receptor antagonists (ERAs) were examined for substrate activity and inhibition of hepatic uptake and efflux transporters in sandwich-cultured human hepatocytes. The 4 transporters studied were sodium-dependent taurocholate cotransporter (NTCP), organic anion transporter (OATP), bile salt export pump (BSEP), and multidrug resistance-associated protein 2 (MRP2). ERA transporter inhibition was examined using the substrates taurocholate (for NTCP and BSEP), [(3)H]estradiol-17beta-D-glucuronide (for OATP), and [2-D-penicillamine, 5-D-penicillamine]enkephalin (for MRP2). ERA substrate activity was evaluated using probe inhibitors ritonavir (OATP and BSEP), bromosulfalein (OATP), erythromycin (P-glycoprotein), probenecid (MRP2 and OATP), and cyclosporin (NTCP). ERAs were tested at 2, 20, and 100 micromol*L-1 for inhibition and at 2 micromol*L-1 as substrates. OATP, NTCP, or BSEP transport activity was not reduced by ambrisentan or darusentan. Bosentan and sitaxsentan attenuated NTCP transport at higher concentrations. Only sitaxsentan decreased OATP transport (52%), and only bosentan reduced BSEP transport (78%). MRP2 transport activity was unaltered. OATP inhibitors decreased influx of all ERAs. Darusentan influx was least affected (84%-100% of control), whereas bosentan was most affected (32%-58% of control). NTCP did not contribute to influx of ERAs. Only bosentan and darusentan were shown as substrates for both BSEP and P-glycoprotein efflux. All ERAs tested were substrates for at least one hepatic transporter. Bosentan and sitaxsentan, but not ambrisentan and darusentan, inhibited human hepatic transporters, which provides a potential mechanism for the increased hepatotoxicity observed for these agents in the clinical setting.

Assessment of the Roles of P-glycoprotein and Cytochrome P450 in Triptolide-induced Liver Toxicity in Sandwich-Cultured Rat Hepatocyte Model

“…Ritonavir is not only a P-gp inhibitor but also inhibits CYP3A (Hartman et al, 2010;Ye et al, 2010), whereas tariquidar is a potent P-gp inhibitor with negligent effect on CYP (Pusztai et al, 2005). Our data showed tariquidar seemed to be a more potent inhibitor toward the biliary clearance of TP compared with ritonavir but caused less toxicity that may indicate the involvement of CYP in the disposition of TP in SCRH.…”

Multiple Compound-Related Adverse Properties Contribute to Liver Injury Caused by Endothelin Receptor Antagonists

“…BSEP inhibition by sitaxentan and ambrisentan has been less widely studied, as have the effects of all three compounds on MRP2 activity. Modest inhibition of BSEP-mediated biliary efflux of radiolabeled taurocholate from isolated sandwich-cultured human hepatocytes was observed in the presence of 100 mM sitaxentan or bosentan, but not ambrisentan (Hartman et al, 2010). In the same study, ambrisentan did not affect MRP2-mediated biliary Covalent binding to protein was determined following incubation of bosentan (10 mM), ambrisentan (10 mM), and sitaxsentan (10 mM) with pooled cryopreserved human hepatocytes for 4 hours.…”

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“…62 Liver function of patients with portopulmonary hypertension should be monitored closely during endothelin receptor antagonist therapy because these agents have been associated with hepatotoxicity in unselected patients with idiopathic PAH. 63 …”