title: Hepatobiliary disposition of 3alpha,6alpha,7alpha,12alpha-tetrahydroxy-cholanoyl taurine: a substrate for multiple canalicular transporters.
abstract: Tetrahydroxy bile acids become major biliary bile acids in Bsep(-/-) mice and Fxr(-/-) mice fed cholic acid; we characterized disposition of these novel bile acids that also occur in patients with cholestasis. We investigated mouse Mrp2 (mMrp2) and P-glycoprotein [(P-gp) mMdr1a]-mediated transport of a tetrahydroxy bile acid, 6α-OH-taurocholic acid (6α-OH-TC), and its biliary excretion in wild-type and Mrp2(-/-) mice in the presence or absence of N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918), a P-gp and breast cancer resistance protein inhibitor. 6α-OH-TC was rapidly excreted into bile of wild-type mice (78% recovery); coinfusion of GF120918 had no significant effect. In Mrp2(-/-) mice, biliary excretion was decreased (52% recovery) and coinfusion of GF120918 further decreased these values (34% recovery). In wild-type, but not Mrp2(-/-), mice, 6α-OH-TC increased bile flow 2.5-fold. Membrane vesicle transport studies of 6α-OH-TC (0.05-0.75 mM) yielded saturation kinetics with a higher apparent affinity for mMrp2 (K(m) = 0.13 mM) than for mMdr1a (K(m) = 0.33 mM); mBsep transported 6α-OH-TC with positive cooperativity (Hill slope = 2.1). Human multidrug resistance-associated protein (MRP) 2 and P-gp also transported 6α-OH-TC but with positive cooperativity (Hill slope = 3.6 and 1.6, respectively). After intraileal administration, the time course of 6α-OH-TC biliary recovery was similar to that of coinfused taurocholate, implying that 6α-OH-TC can undergo enterohepatic cycling. Thus, Mrp2 plays a key role in 6α-OH-TC biliary excretion, whereas P-glycoprotein plays a secondary role; Bsep likely mediates excretion of 6α-OH-TC in the absence of Mrp2 and P-gp. In Bsep(-/-) mice, efficient synthesis of tetrahydroxy bile acids that are Mrp2 and P-gp substrates can explain the noncholestatic phenotype.
authors.affiliation: University of Kentucky, Graduate Center for Toxicology, Lexington, KY 40536-0305, USA.
authors.forename: Vandana
authors.initials: V
authors.lastname: Megaraj
authors.forename: Takashi
authors.initials: T
authors.lastname: Iida
authors.forename: Paiboon
authors.initials: P
authors.lastname: Jungsuwadee
authors.forename: Alan F
authors.initials: AF
authors.lastname: Hofmann
authors.forename: Mary
authors.initials: M
authors.lastname: Vore
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D000166:Acridines / Q000494:pharmacology; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001648:Bile Canaliculi / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010477:Perfusion; D013379:Substrate Specificity; D013656:Taurocholic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D044005:Tetrahydroisoquinolines / Q000494:pharmacology
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D000166:Acridines; D001647:Bile Acids and Salts; D000089762:Multidrug Resistance-Associated Protein 2; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D013656:Taurocholic Acid; D044005:Tetrahydroisoquinolines; C555837:3alpha,6alpha,7alpha,12alpha-tetrahydroxy-cholanoyl taurine; C000715087:ABCC2 protein, human; C095122:multidrug resistance protein 3; C083501:Elacridar