Search PubMed⌕ Search

Biomedical subjects

B Stieger

Publications and source records attributed to B Stieger.

At least 19 recordsLinked to original sources
PubMed2006

The organic anion transport polypeptide 1d1 (Oatp1d1) mediates hepatocellular uptake of phalloidin and microcystin into skate liver.

Organic anion transporting polypeptides (rodent Oatp; human OATP) mediate cellular uptake of numerous organic compounds including xenobiotic toxins into mammalian hepatocytes. In the little skate Leucoraja erinacea a liver-specific Oatp (Oatp1d1, also called sOatp) has been identified and suggested to represent an evolutionarily ancient precursor of the mammalian liver OATP1B1 (human), Oatp1b2 (rat), and OATP1B3 (human). The present study tested whether Oatp1d1 shares functional transport activity of the xenobiotic oligopeptide toxins phalloidin and microcystin with the mammalian liver Oatps/OATPs. The phalloidin analogue [(3)H]-demethylphalloin was taken up into skate hepatocytes with high affinity (Km approximately 0.4 microM), and uptake could be inhibited by phalloidin and a variety of typical Oatp/OATP substrates such as bromosulfophthalein, bile salts, estrone-3-sulfate, cyclosporine A and high concentrations of microcystin-LR (Ki approximately 150 microM). When expressed in Xenopus laevis oocytes Oatp1d1 increased uptake of demethylphalloin (Km approximately 2.2 microM) and microcystin-LR (Km approximately 27 microM) 2- to 3-fold over water-injected oocytes, whereas the alternative skate liver organic anion transporter, the dimeric Ostalpha/beta, exhibited no phalloidin and only minor microcystin-LR transport. Also, the closest mammalian Oatp1d1 orthologue, the human brain and testis OATP1C1, did not show any phalloidin transport activity. These results demonstrate that the evolutionarily ancient Oatp1d1 is able to mediate uptake of cyclic oligopeptide toxins into skate liver. The findings support the notion that Oatp1d1 is a precursor of the liver-specific mammalian Oatps/OATPs and that its transport properties are closely associated with certain forms of toxic liver injury such as for example protein phosphatase inhibition by the water-borne toxin microcystin.

Animals↗
PubMed2006

Characterization of two distinct liver progenitor cell subpopulations of hematopoietic and hepatic origins.

Despite extensive studies, the hematopoietic versus hepatic origin of liver progenitor oval cells remains controversial. The aim of this study was to determine the origin of such cells after liver injury and to establish an oval cell line. Rat liver injury was induced by subcutaneous insertion of 2-AAF pellets for 7 days with subsequent injection of CCl(4). Livers were removed 9 to 13 days post-CCl(4) treatment. Immunohistochemistry was performed using anti-c-kit, OV6, Thy1, CK19, AFP, vWF and Rab3b. Isolated non-parenchymal cells were grown on mouse embryonic fibroblast, and their gene expression profile was characterized by RT-PCR. We identified a subpopulation of OV6/CK19/Rab3b-expressing cells that was activated in the periportal region of traumatized livers. We also characterized a second subpopulation that expressed the HSCs marker c-kit but not Thy1. Although we successfully isolated both cell types, OV6/CK19/Rab3b(+) cells fail to propagate while c-kit(+)-HSCs appeared to proliferate for up to 7 weeks. Cells formed clusters which expressed c-kit, Thy1 and albumin. Our results indicate that a bona fide oval progenitor cell population resides within the liver and is distinct from c-kit(+)-HSCs. Oval cells require the hepatic niche to proliferate, while cells mobilized from the circulation proliferate and transdifferentiate into hepatocytes without evidence of cell fusion.

2-Acetylaminofluorene↗
PubMed2003

Effect of ursodeoxycholic acid on the impairment induced by maternal cholestasis in the rat placenta-maternal liver tandem excretory pathway.

We investigated the effects of ursodeoxycholic acid (UDCA; 60 microg/day/100 g b.wt.) on the impairment induced by maternal obstructive cholestasis during pregnancy (OCP) in the rat placenta-maternal liver tandem excretory pathway. A blunted catheter was implanted in the common bile duct on day 14 of pregnancy, and the tip was cut on day 21. [(14)C]Glycocholate (GC) was then administered through the umbilical artery of "in situ" perfused placenta (placental transfer test) or through the maternal jugular vein (biliary secretion test), and GC bile output was measured. OCP impaired both GC placental transfer and maternal biliary secretion. UDCA moderately improved the latter but had a more marked beneficial effect on GC placental transfer. Histological examination revealed trophoblast atrophy and structural alterations, e.g., loss of apical membrane microvilli in OCP placentas. Gene expression level was investigated by real-time quantitative reverse transcription-polymerase chain reaction and Western blot analysis. OCP reduced both placental lactogen II (a trophoblast-specific gene) mRNA and the functional amount of epithelial tissue, determined by transplacental diffusion of antipyrin. Using a rapid filtration technique, impairment in the ATP-dependent GC transport across trophoblast apical plasma membranes obtained from OCP placentas was found. UDCA partially prevented all these changes. The expression level of organic anion transporters Oatp1, Oatp2, and Oatp4, and multidrug resistance-associated proteins Mrp1, Mrp2, and Mrp3 in whole placenta were not affected or were moderately affected by OCP but greatly enhanced by UDCA. In summary, UDCA partially prevents deleterious effects of OCP on the rat placenta-maternal liver tandem excretory pathway, mainly by preserving trophoblast structure and function.

Animals↗
PubMed2003

Hepatocyte performance on different crystallographic faces of rutile.

The influence of crystallographic orientation of polished rutile single crystal surfaces of the (100), (110) and (111) orientation on hepatocyte performance was tested in cell culture over 3 days. Cell adhesion was observed on the titanium dioxide surfaces and their performance was measured by means of cell number attached (protein mass), cell viability (neutral red assays) and metabolic activity (thiazolyl tetrazolium bromide assay). Titanium dioxide displays no cytotoxic effects on hepatocytes, and shows a performance in the range of standard collagen-coated tissue culture polystyrene dish. The number of hepatocytes adhered on the different rutile surfaces were not significantly different to those on dense rutile polycrystalline ceramic. These findings suggest that hepatocytes do not recognize the specific differences of differently orientated rutile crystal surfaces.

Animals↗
PubMed2002

Functional analysis of candidate ABC transporter proteins for sitosterol transport.

Two ATP-binding cassette (ABC) proteins, ABCG5 and ABCG8, have recently been associated with the accumulation of dietary cholesterol in the sterol storage disease sitosterolemia. These two 'half-transporters' are assumed to dimerize to form the complete sitosterol transporter which reduces the absorption of sitosterol and related molecules in the intestine by pumping them back into the lumen. Although mutations altering ABCG5 and ABCG8 are found in affected patients, no functional demonstration of sitosterol transport has been achieved. In this study, we investigated whether other ABC transporters implicated in lipid movement and expressed in tissues with a role in sterol synthesis and absorption, might also be involved in sitosterol transport. Transport by the multidrug resistance P-glycoprotein (P-gp; Abcb1), the multidrug resistance-associated protein (Mrp1; Abcc1), the breast cancer resistance protein (Bcrp; Abcg2) and the bile salt export pump (Bsep; Abcb11) was assessed using several assays. Unexpectedly, none of the candidate proteins mediated significant sitosterol transport. This has implications for the pathology of sitosterolemia. In addition, the data suggest that otherwise broad-specific ABC transporters have acquired specificity to exclude sitosterol and related sterols like cholesterol presumably because the abundance of cholesterol in the membrane would interfere with their action; in consequence, specific transporters have evolved to handle these sterols.

3T3 Cells↗
PubMed2002

Bile salt transporters.

Bile salts are the major organic solutes in bile and undergo extensive enterohepatic circulation. Hepatocellular bile salt uptake is mediated predominantly by the Na(+)-taurocholate cotransport proteins Ntcp (rodents) and NTCP (humans) and by the Na(+)-independent organic anion-transporting polypeptides Oatp1, Oatp2, and Oatp4 (rodents) and OATP-C (humans). After diffusion (bound by intracellular bile salt-binding proteins) to the canalicular membrane, monoanionic bile salts are secreted into bile canaliculi by the bile salt export pump Bsep (rodents) or BSEP (humans). Both belong to the ATP-binding cassette (ABC) transporter superfamily. Dianionic conjugated bile salts are secreted into bile by the multidrug-resistance-associated proteins Mrp2/MRP2. In bile ductules, a minor portion of protonated bile acids and monomeric bile salts are reabsorbed by non-ionic diffusion and the apical sodium-dependent bile salt transporter Asbt/ASBT, transported back into the periductular capillary plexus by Mrp3/MRP3 [and/or a truncated form of Asbt (tAsbt)], and subjected to cholehepatic shunting. The major portion of biliary bile salts is aggregated into mixed micelles and transported into the intestine, where they are reabsorbed by apical Oatp3, the apical sodium-dependent bile salt transporter (ASBT), cytosolic intestinal bile acid-binding protein (IBABP), and basolateral Mrp3/MRP3 and tAsbt. Transcriptional and posttranscriptional regulation of these enterohepatic bile salt transporters is closely related to the regulation of lipid and cholesterol homeostasis. Furthermore, defective expression and function of bile salt transporters have been recognized as important causes for various cholestatic liver diseases.

Animals↗
PubMed2002

Identification of a novel human organic anion transporting polypeptide as a high affinity thyroxine transporter.

Transport of various amphipathic organic compounds is mediated by organic anion transporting polypeptides (OATPs in humans, Oatps in rodents), which belong to the solute carrier family 21A (SLC21A/Slc21a). Several of these transporters exhibit a broad and overlapping substrate specificity and are expressed in a variety of different tissues. We have isolated and functionally characterized OATP-F (SLC21A14), a novel member of the OATP family. The cDNA (3059 bp) contains an open reading frame of 2136 bp encoding a protein of 712 amino acids. Its gene containing 15 exons is located on chromosome 12p12. OATP-F exhibits 47-48% amino acid identity with OATP-A, OATP-C, and OATP8, the genes of which are clustered on chromosome 12p12. OATP-F is predominantly expressed in multiple brain regions and Leydig cells of the testis. OATP-F mediates high affinity transport of T(4) and reverse T(3) with apparent K(m) values of approximately 90 nM and 128 nM, respectively. Substrates less well transported by OATP-F include T(3), bromosulfophthalein, estrone-3-sulfate, and estradiol-17beta-glucuronide. Furthermore, OATP-F-mediated T(4) uptake could be cis-inhibited by L-T(4) and D-T(4), but not by 3,5-diiodothyronine, indicating that T(4) transport is not stereospecific, but that 3',5'-iodination is important for efficient transport by OATP-F. Thus, in contrast to most other family members, OATP-F has a more selective substrate preference and may play an important role in the disposition of thyroid hormones in brain and testis.

Amino Acid Sequence↗
PubMed2001

Metabolism of amiodarone. II. High-performance liquid chromatographic assay for mono-N-desethylamiodarone hydroxylation in liver microsomes.

Amiodarone (AMI) is a potent antiarrhythmic drug. In vivo and in vitro, AMI is biotransformed to mono-N-desethylamiodarone (MDEA). Recently, it was observed that MDEA was further hydroxylated to n-3'-hydroxybutyl-MDEA (3'OH-MDEA). The performance of a HPLC-UV assay being developed for the quantification of the new compound was investigated. Liver microsomes isolated from rabbit, rat and human biotransformed MDEA to 3'OH-MDEA. Their estimates of Michaelis-Menten parameters were Km=6.39, 25.2, 19.4 microM; Vmax=560, 54, 17.3 pmol/mg protein/min), respectively. Thus, hydroxylase activity in mammals may be the origin of the species dependence observed in the AMI metabolism.

Amiodarone↗
PubMed2001

Functional analysis and androgen-regulated expression of mouse organic anion transporting polypeptide 1 (Oatp1) in the kidney.

Mouse Oatp1 was recently identified as a new murine member of the organic anion transporting polypeptide (Oatp) family and suggested to represent the counterpart of rat Oatp1. Northern blot analysis detected expression of several mouse Oatp-transcripts predominantly in liver and kidney. In the present study we describe the strict androgen-dependent expression of mouse Oatp1 mRNA in kidney and obtained further information about its substrate specificity using Xenopus oocytes. In addition to the previously reported estrone-3-sulfate, we demonstrate that mouse Oatp1 mediates sodium-independent uptake of the anionic steroid conjugates dehydroepiandrosterone sulfate (K(m) approximately 8 microM) and estradiol-17-glucuronide (K(m) approximately 5 microM) and also of the prostaglandin PGE(2).

3' Untranslated Regions↗
PubMed2001

Localization of organic anion transporting polypeptide 4 (Oatp4) in rat liver and comparison of its substrate specificity with Oatp1, Oatp2 and Oatp3.

Organic anion transporting polypeptides (rodents: Oatps; human: OATPs) are involved in the absorption and elimination of a wide variety of structurally unrelated amphipathic organic compounds. Several members of this protein family mediate the uptake of substrates across the basolateral membrane of hepatocytes as the first step in hepatic elimination. In contrast to the well-characterized Oatp1 and Oatp2, the localization and substrate specificity of the recently cloned Oatp4 have not been investigated in detail. Therefore, we raised an antibody against the C-terminal end of Oatp4 and localized this 85-kDa protein to the basolateral membrane of rat hepatocytes. Similar to Oatp1 and Oatp2, Oatp4 is a multispecific transporter with high affinities for bromosulfophthalein, dehydroepiandrosterone sulfate, leukotriene C4, and anionic peptides. In addition, we compared the substrate specificity of Oatp4 to that of Oatp3, which so far has mainly been shown to mediate intestinal bile acid transport. Oatp3 had a similar broad substrate specificity, but in general much lower affinities than Oatp4. Thus, while Oatp4 seems to work in concert with Oatp1 and Oatp2 in the basolateral membrane of rat hepatocytes, Oatp3 is a multispecific transport system in the small intestine.

Animals↗
PubMed2001

Effect of phenobarbital on the expression of bile salt and organic anion transporters of rat liver.

BACKGROUND/AIMS: The hepatic clearance of drugs and cholephilic organic anions is stimulated by phenobarbital (PB). Our aim was to analyze the effects of PB on the expression of hepatocellular bile salt and organic anion transporters. METHODS: Male Sprague-Dawley rats were treated intraperitoneally with PB (80 mg/kg/d) or saline for 5 days. Transporter expression was quantified by northern and western blot analysis and initial uptake rates of bromosulphophthalein (BSP) and digoxin were measured in isolated hepatocytes. RESULTS: Compared to control rats, PB treatment increased expression of the organic anion transporting polypeptide 2 (Oatp2; Slc21aS) more than 2-fold on the RNA (P < 0.05) and protein (P < 0.001) levels. Expression of Oatpl (Slc21al), Oatp4 (Slc21a6) and the Na+-taurocholate cotransporting polypeptide (Ntcp; Slc10a1) was unaltered. At the canalicular pole, expression of the bile salt export pump (Bsep; ABCB11) and of the multidrug resistance proteins 2 (Mrp2; ABCC2) and 6 (Mrp6; ABCC6) was not significantly changed. Whereas hepatocellular BSP uptake was unaffected by PB, digoxin uptake was stimulated 4-fold. CONCLUSIONS: The induction of digoxin uptake by PB correlates with Oatp2 expression. In contrast, the lack of increase of Oatpl and Oatp4 expression is in accordance with unchanged BSP uptake. These data challenge the previously held view that PB induces hepatocellular BSP uptake systems.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Organic anion-transporting polypeptide B (OATP-B) and its functional comparison with three other OATPs of human liver.

BACKGROUND & AIMS: Hepatic uptake of cholephilic organic compounds is mediated by members of the organic anion-transporting polypeptide (OATP) family. We aimed to characterize the novel OATP-B with respect to tissue distribution and hepatocellular localization and to compare its substrate specificity with those of OATP-A, OATP-C, and OATP8. METHODS: Tissue distribution and hepatocellular localization of OATP-B were analyzed by Northern blotting and immunofluorescence, respectively. Transport of 16 substrates was measured for each individual human OATP in complementary RNA-injected Xenopus laevis oocytes. RESULTS: Expression of OATP-B was most abundant in human liver, where it is localized at the basolateral membrane of hepatocytes. OATP-B, OATP-C, and OATP8 mediated high-affinity uptake of bromosulphophthalein (K(m), approximately 0.7, 0.3, and 0.4 micromol/L, respectively). OATP-B also transported estrone-3-sulfate but not bile salts. Although OATP-A, OATP-C, and OATP8 exhibit broad overlapping substrate specificities, OATP8 was unique in transporting digoxin and exhibited especially high transport activities for the anionic cyclic peptides [D-penicillamine(2,5)]enkephalin (DPDPE; opioid-receptor agonist) and BQ-123 (endothelin-receptor antagonist). CONCLUSIONS: OATP-B is the third bromosulphophthalein uptake system localized at the basolateral membrane of human hepatocytes. OATP-B, OATP-C, and OATP8 account for the major part of sodium-independent bile salt, organic anion, and drug clearance of human liver.

Animals↗
PubMed2001

Effects of ursodeoxycholic and cholic acid feeding on hepatocellular transporter expression in mouse liver.

BACKGROUND AND AIMS: Cholestasis is associated with retention of potentially toxic bile acids and alterations in hepatocellular transporter expression. Conversely, nontoxic ursodeoxycholic acid (UDCA) stimulates bile secretion and counteracts cholestasis. This study aimed to determine the effects of UDCA and cholic acid (CA) on the expression of hepatocellular transporters for bile acids (Ntcp, Bsep), organic anions (Oatp1, Mrp2), organic cations (Mdr1a/b), and phospholipids (Mdr2) in mouse liver. METHODS: Bile flow/composition was analyzed in UDCA- or CA-fed mice. Transporter expression was studied by reverse-transcription polymerase chain reaction, Western blotting, and immunofluorescence microscopy. RESULTS: UDCA had no effect on basolateral Ntcp and down-regulated Oatp1, whereas canalicular Bsep and Mrp2 were up-regulated. CA down-regulated basolateral Ntcp and Oatp1, whereas canalicular Bsep, Mrp2, and Mdr1a/b were up-regulated. Neither UDCA nor CA affected Mdr2 expression. Both UDCA and CA stimulated biliary bile acid and glutathione excretion, although only CA increased phospholipid and cholesterol excretion. CONCLUSIONS: Down-regulation of basolateral and up-regulation of canalicular transporters in response to CA may represent a defense mechanism, in an attempt to prevent hepatocellular accumulation of potentially toxic bile acids. The therapeutic effects of UDCA may be caused in part by stimulation of canalicular transporter expression in the absence of hepatocellular toxicity.

Administration, Oral↗
PubMed2001

Hepatic uptake of cholecystokinin octapeptide by organic anion-transporting polypeptides OATP4 and OATP8 of rat and human liver.

BACKGROUND & AIMS: Cholecystokinin (CCK) is a major gastrointestinal peptide hormone that is released postprandially from the small intestine and exerts marked effects on gallbladder and gastrointestinal motility. The smaller isoforms CCK-8 and CCK-4 are rapidly taken up into hepatocytes, metabolized, and excreted into bile. Our aim was to identify and characterize the hepatocellular CCK-8 uptake system. METHODS: CCK-8 uptake was measured in Xenopus laevis oocytes expressing the organic anion-transporting polypeptides of rat liver (Oatp1, Oatp2, Oatp3, or Oatp4) and of human liver (OATP-A, OATP-B, OATP-C, or OATP8) and in primary cultured rat hepatocytes. RESULTS: Rat Oatp4 and human OATP8 efficiently mediated CCK-8 uptake in oocytes, with Michaelis constant (Km) values of 14.9 +/- 2.9 micromol/L and 11.1 +/- 2.9 micromol/L, respectively. CCK-8 uptake by hepatocytes was also saturable, with a Km of 6.7 +/- 2.1 micromol/L. The Km value in rat hepatocytes is consistent with Oatp4-mediated transport. CONCLUSIONS: CCK-8 is selectively transported by rat Oatp4 and human OATP8, both of which are exclusively expressed at the basolateral membrane of hepatocytes. These 2 transporters are the first and probably the predominant hepatic uptake systems for CCK-8 and may be critical for the rapid clearance of this hormone from the circulation.

Animals↗
PubMed2001

Differential regulation of hepatic bile salt and organic anion transporters in pregnant and postpartum rats and the role of prolactin.

We characterized expression and activity of the bile salt transporters Na(+)/taurocholate (TC) cotransporting polypeptide (Ntcp), and bile salt export pump (Bsep), and the expression of organic anion transporting polypeptides 1 and 2 (Oatp1 and 2) and multidrug resistance associated protein-2 (Mrp2) in pregnancy and throughout lactation in rats. The V(max) for Na(+)/TC cotransport in basolateral liver plasma membrane was increased 1.7-fold in 2 days postpartum relative to control and pregnant rats. This correlated well with an increase in Ntcp messenger RNA (mRNA) and a 2-fold increase in Ntcp protein. Ntcp mRNA remained significantly elevated until 14 days postpartum but had begun to decline by 21 days postpartum. The maximal secretory rate (nmol/min/g liver) for TC in the single pass isolated perfused liver was also increased by 10%, 31%, and 24% at 2, 14, and 21 days postpartum and correlated with increased expression of Ntcp and Bsep mRNA and protein. Infusion of ovine prolactin (oPRL) to ovariectomized rats increased expression of both Ntcp and Bsep mRNA and protein. These data indicate a coordinate increased expression of bile salt transporters postpartum and by PRL. Mrp2 mRNA was stable in pregnancy and postpartum, whereas Mrp2 protein expression decreased significantly in pregnancy, but returned to control levels postpartum. Organic anion transporting polypeptide 2 (Oatp2) mRNA was decreased in pregnancy and increased postpartum, but changes in Oatp2 protein were not significant. Oatp1 mRNA and protein were unchanged in pregnancy and postpartum.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

Cholestatic expression pattern of sinusoidal and canalicular organic anion transport systems in primary cultured rat hepatocytes.

To maintain ongoing vectorial bile secretion, hepatocytes localize distinct transport systems at their basolateral and canalicular membrane domains. Here we compare the expression of the basolateral Na(+)-taurocholate cotransporter (Ntcp) and organic anion transporting polypeptides 1 and 2 (Oatp1, Oatp2) and the canalicular bile salt export pump (Bsep) and multidrug resistance-associated protein 2 (Mrp2) in primary cultured rat hepatocytes. During 72 hours of culturing time the messenger RNA (mRNA) and protein levels of Ntcp and Oatp1 decreased in parallel to 2% to 7% of initial values at 3 hours. Although Oatp2 mRNA exhibited a similar down-regulation to 4%, Oatp2 protein and function were maintained at 25% to 47% of initial values. Furthermore, Bsep and Mrp2 protein levels were maintained at about 50%, while the Mrp2 mRNA showed a transient up-regulation to 154% at 24 and 48 hours. Also, induction of Mrp1 mRNA and protein was observed starting after 24 hours. These results indicate transcriptional down-regulation or decreased mRNA stability of Ntcp and Oatp1, transcriptional and posttranslational regulation of Oatp2, Bsep, and Mrp2 and transcriptional up-regulation of Mrp1 in primary cultured hepatocytes. Furthermore, and most importantly, the observed changes in transporter expression closely resemble the altered transporter phenotypes of cholestatic and proliferating hepatocytes in vivo, thus indicating that primary cultured hepatocytes acquire a cholestatic phenotype, and that the transporter expression might be a suitable differentiation marker for maintenance of hepatocytes in vitro.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2001

The endothelin antagonist bosentan inhibits the canalicular bile salt export pump: a potential mechanism for hepatic adverse reactions.

BACKGROUND: During clinical trials bosentan, the first orally active endothelin receptor antagonist, caused asymptomatic transaminase elevations in some patients. In this study we investigated whether inhibition of the hepatocanalicular bile salt export pump (rodents, Bsep; humans, BSEP ABCB11) could account for bosentan-induced liver injury. METHODS: We reanalyzed the safety database of the bosentan trials for cholestatic liver injury, determined the cholestatic potency of bosentan in the rat, and studied the effects of bosentan and its metabolites on Bsep-mediated taurocholate transport in vitro. RESULTS: Bosentan caused dose-dependent and reversible liver injury in 2% to 18% of patients and caused a significant increase of serum bile salt levels (P <.01). Concomitant administration of glyburide (INN, glibenclamide) enhanced the cholestatic potency of bosentan. Similar effects were seen in rats, in which serum bile salt levels were increased by glyburide less than by bosentan, which increased the levels less than a combination of bosentan and glyburide. In vitro, Bsep-mediated taurocholate transport was inhibited by bosentan (inhibition constant, approximately 12 micromol/L) and metabolites (inhibition constant, approximately 8.5 micromol/L for metabolite Ro 47-8634). CONCLUSIONS: These results indicate that bosentan-induced liver injury is mediated, at least in part, by inhibition of Bsep/BSEP-causing intracellular accumulation of cytotoxic bile salts and bile salt induced liver cell damage. The data further emphasize the pathophysiologic importance of drug-Bsep interactions in acquired forms of cholestatic liver injury.

ATP Binding Cassette Transporter, Subfamily B, Mem↗