title: Resolution of P-glycoprotein and non-P-glycoprotein effects on drug permeability using intestinal tissues from mdr1a (-/-) mice.
abstract: 1. Intestinal xenobiotic transporters are a significant barrier to the absorption of many orally administered drugs. P-glycoprotein (PGP) is the best known, but several others, including members of the multidrug resistance-associated protein (MRP) family, are also expressed. Definitive information on their precise effect on intestinal drug permeability is scarce due to a lack of specific inhibitors and the difficulty of studying non-PGP activity in the presence of high PGP expression. 2. We have investigated the in vitro use of intestinal tissues from PGP knockout (mdr1a (-/-)) mice as a tool for dissecting the mechanisms of intestinal drug efflux. The permeability characteristics of digoxin (DIG), paclitaxel (TAX) and etoposide (ETOP) were measured in ileum from mdr1a (-/-) and wild-type (FVB) mice mounted in Ussing chambers. 3. DIG and TAX exhibited marked efflux across FVB tissues (B-A : A-B apparent permeability (P(app)) ratio 10 and 17 respectively) which was absent in mdr1a (-/-) tissues, confirming that PGP is the sole route of intestinal efflux for these compounds. The A-B P(app) of both compounds was 3 - 5 fold higher in mdr1a (-/-) than in FVB. 4. Polarized transport of ETOP in FVB tissues was reduced but not abolished in mdr1a (-/-) tissues. Residual ETOP efflux in mdr1a (-/-) tissues was abolished by the MRP inhibitor MK571, indicating involvement of both PGP and MRP. 5. MK571 abolished calcein efflux in mdr1a (-/-) tissues, while quinidine had no parallel effect in FVB tissues, suggesting involvement of MRP but not PGP. 6. Tissues from mdr1a (-/-) mice provide a novel approach for investigating the influence of PGP ablation on intestinal permeability and for resolving PGP and non-PGP mechanisms that modulate drug permeability.
authors.affiliation: Gut Barrier Group, Clinical Division I, University of Manchester, Hope Hospital, Salford, M6 8HD.
authors.forename: R H
authors.initials: RH
authors.lastname: Stephens
authors.forename: C A
authors.initials: CA
authors.lastname: O'Neill
authors.forename: J
authors.initials: J
authors.lastname: Bennett
authors.forename: M
authors.initials: M
authors.lastname: Humphrey
authors.forename: B
authors.initials: B
authors.lastname: Henry
authors.forename: M
authors.initials: M
authors.lastname: Rowland
authors.forename: G
authors.initials: G
authors.lastname: Warhurst
mesh_terms: D018435:ATP Binding Cassette Transporter, Subfamily B / Q000096:biosynthesis / Q000172:deficiency* / Q000235:genetics* / Q000502:physiology; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D000818:Animals; D018432:Drug Resistance, Multiple / Q000235:genetics; D005047:Etoposide / Q000378:metabolism; D007082:Ileum / Q000378:metabolism; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008353:Mannitol / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D010539:Permeability; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D011433:Propranolol / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D018435:ATP Binding Cassette Transporter, Subfamily B; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D004364:Pharmaceutical Preparations; D008353:Mannitol; D005047:Etoposide; C095122:multidrug resistance protein 3; D011433:Propranolol