title: P-glycoprotein (MDR1) functional activity in human alveolar epithelial cell monolayers.
abstract: The distribution of the P-glycoprotein (P-gp/MDR1) efflux transporter at mucosal barriers has defined it as a functionally important element in limiting drug absorption into the systemic circulation. However, little is known about the distribution and functionality of P-gp/MDR1 in the human lung. Here, the presence of P-gp/MDR1 was investigated immunohistochemically in distal human lung tissue and at mRNA and protein levels in human alveolar epithelial cells (hAEpC) in primary culture. We studied the presence and activity of P-gp/MDR1 in hAEpC monolayers by Western blotting, by immunofluorescence microscopy and by conducting bi-directional transport studies employing a P-gp substrate (rhodamine 123) with and without a P-gp inhibitor (verapamil). The flux of fluorescein sodium was also examined as a paracellular transport marker. Alveolar tissue specimens showed P-gp localised at the luminal membranes of type I pneumocytes. Reverse transcription-polymerase chain reaction revealed the presence of mRNA encoding for P-gp/MDR1 in freshly isolated (i.e. type II) hAEpC and in monolayers of hAEpC cultured for 8 days (i.e. type I-like morphology). At the protein level, P-gp could be detected in hAEpC monolayers after 8 days in culture but not in freshly isolated type II pneumocytes. The flux of rhodamine 123 across hAEpC monolayers on day 8 in culture exhibited net secretion, which disappeared in the presence of verapamil. Fluorescein sodium fluxes showed no distinct directionality. Our findings indicate that P-gp is functionally active in the human alveolar airspace and that hAEpC monolayers might provide a suitable in vitro model for studying P-gp function mechanistically in the distal human lung.
authors.affiliation: School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Sibylle
authors.initials: S
authors.lastname: Endter
authors.forename: Ulrich
authors.initials: U
authors.lastname: Becker
authors.forename: Nicole
authors.initials: N
authors.lastname: Daum
authors.forename: Hanno
authors.initials: H
authors.lastname: Huwer
authors.forename: Claus-Michael
authors.initials: CM
authors.lastname: Lehr
authors.forename: Mark
authors.initials: M
authors.lastname: Gumbleton
authors.forename: Carsten
authors.initials: C
authors.lastname: Ehrhardt
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D021381:Protein Transport / Q000187:drug effects; D011650:Pulmonary Alveoli / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020112:Rhodamine 123 / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D012333:RNA, Messenger; D020112:Rhodamine 123