title: Interaction of rat kidney P-glycoprotein with a urinary component and various drugs including cyclosporin A.
abstract: The interaction of rat renal P-glycoprotein with various drugs and a hydrophobic component found in rat urine was studied to gain an understanding of both its transport function in kidney and its potential role in drug secretion and drug-induced nephrotoxicity. Rat kidney brush-border membranes (BBM) were photolabeled with [3H]azidopine, a calcium-channel blocker that covalently labeles P-glycoprotein. P-glycoprotein was immunoprecipitated with a rabbit polyclonal antibody against the human MDR1 protein (multidrug resistance gene class 1). The amount of [3H]azidopine incorporated into P-glycoprotein was quantitated following gel electrophoresis and fluorography. Photolabeling inhibition assays were conducted with a panel of drugs known to interact with P-glycoprotein in multidrug-resistant cells. Verapamil or quinidine [half-maximal inhibition constant (K0.5) = 1 microM], vinblastine (K0.5 = 3 microM), and doxorubicin or daunomycin (K0.5 = 10 microM) all blocked [3H]azidopine photolabeling of renal P-glycoprotein. Of the drugs tested, the immunosuppressant drug, cyclosporin A, interacted with kidney P-glycoprotein with the highest affinity (K0.5 = 50 nM). However, the cardiac glycoside, digoxin, failed to inhibit P-glycoprotein photolabeling. A hydrophobic rat urine extract prepared by reverse-phase chromatography also blocked photolabeling of renal P-glycoprotein. Our current hypothesis is that various drugs may inhibit urinary excretion of an endogenous substrate by virtue of their ability to bind with high affinity to P-glycoprotein. A hypothesis of drug-induced nephrotoxicity based on the interaction of various compounds like cyclosporin A with P-glycoprotein is presented.
authors.affiliation: Department of Medicine, University of Toronto, Ontario, Canada.
authors.forename: J H
authors.initials: JH
authors.lastname: Charuk
authors.forename: T W
authors.initials: TW
authors.lastname: Loo
authors.forename: D M
authors.initials: DM
authors.lastname: Clarke
authors.forename: R A
authors.initials: RA
authors.lastname: Reithmeier
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000818:Animals; D001386:Azides; D002352:Carrier Proteins / Q000302:isolation & purification / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology*; D004095:Dihydropyridines; D004347:Drug Interactions; D004351:Drug Resistance / Q000502:physiology; D005260:Female; D007672:Kidney Cortex / Q000737:chemistry*; D008297:Male; D008562:Membrane Glycoproteins / Q000302:isolation & purification / Q000494:pharmacology*; D008871:Microvilli / Q000737:chemistry; D011233:Precipitin Tests; D051381:Rats; D014316:Tritium; D014556:Urine / Q000737:chemistry*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D001386:Azides; D002352:Carrier Proteins; D004095:Dihydropyridines; D008562:Membrane Glycoproteins; D014316:Tritium; C041130:azidopine; D016572:Cyclosporine