title: Microvilli Morphology Can Affect Efflux Active P-Glycoprotein in Confluent MDCKII -hMDR1-NKI and Caco-2 Cell Monolayers.
abstract: From fits of drug transport kinetics across confluent MDCKII-hMDR1-NKI and Caco-2 cell monolayers we estimated the levels of efflux active P-glycoprotein (P-gp) in these two cell lines (companion paper). In the present work, we compared the efflux active P-gp number to the total P-gp level, using liquid chromatography-tandem mass spectrometry, and showed that in Caco-2 cells total P-gp is about 10-fold greater than efflux active P-gp, whereas in MDCKII-hMDR1-NKI cells these values are within twofold. We further visualized the microvilli in MDCKII-hMDR1-NKI and Caco-2 cells using three-dimensional structured illumination super-resolution microscopy and found that the microvilli in Caco-2 cells are taller and more densely packed than those in MDCK-hMDR1-NKI cells. We hypothesized over 10 years ago that only P-gp at the tips of the microvilli contribute significantly to efflux activity, whereas the remaining P-gp are involved in a futile cycle of efflux of amphipathic drugs from the microvillus membrane, followed by their reabsorption into the same or nearby microvillous membranes. The difference between the levels of total and efflux active P-gp in Caco-2 cells can be explained by the more densely packed microvilli in Caco-2 cells, which would lead to a substantial fraction of P-gp not contributing to final release of drug into the apical chamber. Our results suggest that the effect of microvilli morphology differences between in vitro and in vivo systems must be considered when scaling transporter activity for efflux transporters of amphipathic compounds, for example, P-gp.
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.).
authors.forename: Zhou
authors.initials: Z
authors.lastname: Meng
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.).
authors.forename: Sylvain
authors.initials: S
authors.lastname: Le Marchand
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.).
authors.forename: Deep
authors.initials: D
authors.lastname: Agnani
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.).
authors.forename: Matthew
authors.initials: M
authors.lastname: Szapacs
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.).
authors.forename: Harma
authors.initials: H
authors.lastname: Ellens
authors.affiliation: Department of Biology, Drexel University, Philadelphia, Pennsylvania (Z.M., S.L.M., D.A., J.B.); and Drug Metabolism and Pharmacokinetics, GlaxoSmithKline Pharmaceuticals, King of Prussia, Pennsylvania (Z.M., M.S., H.E.) bentzj@drexel.edu.
authors.forename: Joe
authors.initials: J
authors.lastname: Bentz
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism* / Q000648:ultrastructure*; D002853:Chromatography, Liquid; D018920:Coculture Techniques; D004285:Dogs; D006801:Humans; D021621:Imaging, Three-Dimensional; D007150:Immunohistochemistry; D061985:Madin Darby Canine Kidney Cells; D008853:Microscopy; D008871:Microvilli / Q000378:metabolism* / Q000648:ultrastructure*; D053719:Tandem Mass Spectrometry
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1