title: Differential involvement of Mrp2 (Abcc2) and Bcrp (Abcg2) in biliary excretion of 4-methylumbelliferyl glucuronide and sulfate in the rat.
abstract: The hepatic excretion of hydrophilic conjugates, end products of phase II metabolism, is not completely understood. In the present studies, transport mechanism(s) responsible for the biliary excretion of 4-methylumbelliferyl glucuronide (4MUG) and 4-methylumbelliferyl sulfate (4MUS) were studied. Isolated perfused livers (IPLs) from Mrp2-deficient (TR(-)) Wistar rats were used to examine the role of Mrp2 in the biliary excretion of 4MUG and 4MUS. After a 30-micromol dose of 4-methylumbelliferone, cumulative biliary excretion of 4MUG was extensive in wild-type rat IPLs (25 +/- 3 micromol) but was negligible in TR(-) livers (0.4 +/- 0.1 micromol); coadministration of the Bcrp and P-glycoprotein inhibitor GF120918 [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] had no effect on 4MUG biliary excretion in wild-type rat IPLs. In contrast, biliary excretion of 4MUS was partially maintained in Mrp2-deficient rat IPLs. Recovery of 4MUS in bile was approximately 50 to 60% lower in both control TR(-) (149 +/- 8 nmol) and wild-type IPLs with GF120918 coadministration (176 +/- 30 nmol) relative to wild-type control livers (378 +/- 37 nmol) and was nearly abolished in TR(-) IPLs in the presence of GF120918 (13 +/- 8 nmol). These changes were the result of decreased rate constants governing 4MUG and 4MUS biliary excretion. In vitro assays and perfused livers from Bcrp and P-glycoprotein gene-knockout mice indicated that 4MUS did not interact with P-glycoprotein but was transported by Bcrp in a GF120918-sensitive manner. In the rat liver, Mrp2 mediates the biliary excretion of 4MUG, whereas both Mrp2 and Bcrp contribute almost equally to the transport of 4MUS into bile.
authors.affiliation: University of North Carolina School of Pharmacy, Chapel Hill, NC 27599-7360, USA.
authors.forename: Maciej J
authors.initials: MJ
authors.lastname: Zamek-Gliszczynski
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hoffmaster
authors.forename: Joan E
authors.initials: JE
authors.lastname: Humphreys
authors.forename: Xianbin
authors.initials: X
authors.lastname: Tian
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Nezasa
authors.forename: Kim L R
authors.initials: KL
authors.lastname: Brouwer
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000502:physiology*; D000818:Animals; D001646:Bile / Q000378:metabolism*; D002460:Cell Line; D004285:Dogs; D006923:Hymecromone / Q000031:analogs & derivatives* / Q000378:metabolism; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; C423013:Abcc2 protein, rat; C489249:Abcg2 protein, rat; C019492:4-methylumbelliferyl sulfate; D006923:Hymecromone; C034888:4-methylumbelliferyl glucuronide