Mechanism of hepatobiliary transport of a novel thromboxane A2 receptor antagonist, [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335), and its xenobiotic taurine conjugate (Z-335-Tau) in rats

Abstract We investigated the mechanism of hepatobiliary transport of a novel thromboxane A 2 receptor antagonist, [2-(4-chlorophenylsulfonylaminomethyl)indan-5-yl]acetate (Z-335), and its taurine conjugate (Z-335-Tau) in normal Sprague-Dawley rats (SDRs) and Eisai hyperbilirubinemic rats (EHBRs). The biliary excretion rate/unbound concentration in the cytosol (ν bile / C u,cyt ) of Z-335 was markedly decreased in EHBRs, whereas ν bile / C u,cyt values for Z-335-Tau did not differ significantly between EHBRs and SDRs. These results suggest that biliary excretion of Z-335 involves mrp2, whereas Z-335-Tau is excreted by other transporters. The effects of inhibitors on the biliary excretion of Z-335 and Z-335-Tau were also examined in SDRs. After infusion of bromosulfophthalein (BSP), the ν bile / C u,cyt of Z-335 was significantly decreased, whereas that of Z-335-Tau decreased to 50% of control values by infusion of indocyanine green (ICG) or taurocholate. However, biliary excretion of Z-335-Tau was maintained at a highly concentrative. In conclusion, the biliary excretion of Z-335 involves mrp2, whereas Z-335-Tau is excreted into the bile by active transport systems that remain intact in EHBRs. The mdr2 and/or BSEP/spgp might contribute to a part of total biliary excretion of Z-335-Tau, however, these transporters have not played a major role in the biliary excretion of Z-335-Tau.