title: The role of different P-glycoproteins in hepatobiliary secretion of fluorescently labeled short-chain phospholipids.
abstract: Class III P-glycoproteins (Pgps) mediate biliary phosphatidylcholine (PC) secretion. Recent findings that class I P-glycoproteins are able to transport several short-chain phospholipid analogues raises questions about the role of these Pgps in physiological lipid transport. We investigated the biliary secretion of C6-7-nitro-2,1, 3-benzoxadiazol-4-yl (NBD)-labeled ceramide and its metabolites in Mdr1a/b and Mdr2 knockout mice compared to control mice. Biliary secretion of these NBD-lipids was unaffected in Mdr1a/b -/- mice. Thus neither Mdr1a nor Mdr1b Pgp mediates biliary secretion of these lipids. In contrast, secretion of all three NBD-labeled short-chain phospholipids was significantly reduced in Mdr2 -/- mice. As in vitro studies revealed that Mdr2 Pgp is not able to translocate these lipid analogues, we hypothesized that Mdr2 -/- mice had a reduced PC content of the exoplasmic canalicular membrane leaflet so that extraction of the short-chain lipid probes from this membrane by canalicular bile salts was impaired. To investigate this possibility we studied the bile salt-mediated extraction of natural sphingomyelin (SM) and NBD-labeled short-chain SM from small unilamellar vesicles of different lipid composition. Natural SM could be extracted by the bile salt tauroursodeoxycholate from vesicles containing PC, cholesterol (CHOL), and SM (1:2:2) but not from vesicles containing only SM and CHOL (3:2). NBD-labeled short-chain SM could be extracted from vesicles containing PC while its extraction from pure SM:CHOL vesicles was reduced by 65%. These data confirm that the efficiency of NBD-SM extraction depends on the lipid composition and suggest that the canalicular membrane outer leaflet of Mdr2 -/- mice has a reduced PC content.
authors.affiliation: Departments of Gastrointestinal and Liver Diseases and Clinical Chemistry, Academic Medical Center, FO-221, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
authors.forename: C M
authors.initials: CM
authors.lastname: Frijters
authors.forename: C J
authors.initials: CJ
authors.lastname: Tuijn
authors.forename: R
authors.initials: R
authors.lastname: Ottenhoff
authors.forename: B N
authors.initials: BN
authors.lastname: Zegers
authors.forename: A K
authors.initials: AK
authors.lastname: Groen
authors.forename: R P
authors.initials: RP
authors.lastname: Elferink
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism; D018435:ATP Binding Cassette Transporter, Subfamily B / Q000494:pharmacology*; D000418:Albumins / Q000378:metabolism; D000818:Animals; D001646:Bile / Q000737:chemistry / Q000187:drug effects; D001648:Bile Canaliculi / Q000378:metabolism; D001659:Biliary Tract / Q000187:drug effects / Q000378:metabolism*; D002352:Carrier Proteins; D002518:Ceramides / Q000378:metabolism; D005456:Fluorescent Dyes; D019450:Genes, MDR; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008566:Membranes / Q000737:chemistry / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010477:Perfusion; D010743:Phospholipids / Q000032:analysis / Q000378:metabolism; D013109:Sphingomyelins / Q000032:analysis; D013657:Taurodeoxycholic Acid / Q000494:pharmacology; D014580:Ursodeoxycholic Acid / Q000494:pharmacology
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D000418:Albumins; D002352:Carrier Proteins; D002518:Ceramides; D005456:Fluorescent Dyes; C041065:N-4-nitrobenzo-2-oxa-1,3-diazoleaminocaproyl sphingosylphosphorylcholine; D010743:Phospholipids; D013109:Sphingomyelins; D013657:Taurodeoxycholic Acid; D014580:Ursodeoxycholic Acid; C037974:N-(7-(4-nitrobenzo-2-oxa-1,3-diazole))-6-aminocaproyl sphingosine; D009327:4-Chloro-7-nitrobenzofurazan