title: Role of organic anion-transporting polypeptides, OATP-A, OATP-C and OATP-8, in the human placenta-maternal liver tandem excretory pathway for foetal bilirubin.
abstract: Recent functional studies have suggested that, in addition to simple diffusion, carrier-mediated transport may play an important role in foetal unconjugated bilirubin (UCB) uptake by the placenta. We have investigated the role of organic anion-transporting polypeptides (OATPs) in UCB transport by the placenta-maternal liver tandem. RNA was obtained from human liver (hL), human placenta (hPl) at term, and purified (> 80%) cytokeratin-7-positive mononucleated human trophoblast cells (hTCs). By analytical reverse transcription (RT)-PCR, agarose gel electrophoresis separation and sequencing, the mRNA of OATP-A ( SLC21A3 ) and OATP-8 ( SLC21A8 ) was identified in hL, hPl and hTCs, whereas that of OATP-C ( SLC21A6 ) was detectable only in hL. Real-time quantitative RT-PCR revealed that in hL the abundance of mRNA was OATP-8 > OATP-C >> OATP-A, whereas in hPl and hTCs this was OATP-8 >> OATP-A >> OATP-C. Expression levels for these OATPs were hL >> hTCs > hPl. Injection of mRNA of OATP-A, OATP-C or OATP-8 or RNA from hL, hPl or hTCs into Xenopus laevis oocytes conferred on them the ability to take up [(3)H]17 beta-D-glucuronosyl oestradiol ([(3)H]E(2)17 beta G) and [(3)H]UCB, although in the case of OATP-A mRNA, the induced uptake of [(3)H]UCB was very low. Cis -inhibition of [(3)H]E(2)17 beta G and [(3)H]UCB uptake by both unlabelled E(2)17 beta G and UCB was found in all cases. The affinity and efficiency of [(3)H]UCB transport was OATP-C > OATP-8. Kinetic parameters for [(3)H]UCB uptake induced by RNA from hTCs resembled most closely those of OATP-8. In conclusion, our results suggest that OATP-8 may play a major role in the carrier-mediated uptake of foetal UCB by the placental trophoblast, whereas both OATP-8 and OATP-C may substantially contribute to UCB uptake by adult hepatocytes.
authors.affiliation: Department of Physiology and Pharmacology, University of Salamanca, Salamanca 37007, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Briz
authors.forename: Maria A
authors.initials: MA
authors.lastname: Serrano
authors.forename: Rocio I R
authors.initials: RI
authors.lastname: MacIas
authors.forename: Javier
authors.initials: J
authors.lastname: Gonzalez-Gallego
authors.forename: Jose J G
authors.initials: JJ
authors.lastname: Marin
mesh_terms: D000818:Animals; D001483:Base Sequence; D001663:Bilirubin / Q000378:metabolism*; D001692:Biological Transport; D017931:DNA Primers; D005260:Female; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D027361:Organic Anion Transporters / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014327:Trophoblasts / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D017931:DNA Primers; D027361:Organic Anion Transporters; D001663:Bilirubin