title: Uremic toxins inhibit transport by breast cancer resistance protein and multidrug resistance protein 4 at clinically relevant concentrations.
abstract: During chronic kidney disease (CKD), there is a progressive accumulation of toxic solutes due to inadequate renal clearance. Here, the interaction between uremic toxins and two important efflux pumps, viz. multidrug resistance protein 4 (MRP4) and breast cancer resistance protein (BCRP) was investigated. Membrane vesicles isolated from MRP4- or BCRP-overexpressing human embryonic kidney cells were used to study the impact of uremic toxins on substrate specific uptake. Furthermore, the concentrations of various uremic toxins were determined in plasma of CKD patients using high performance liquid chromatography and liquid chromatography/tandem mass spectrometry. Our results show that hippuric acid, indoxyl sulfate and kynurenic acid inhibit MRP4-mediated [(3)H]-methotrexate ([(3)H]-MTX) uptake (calculated Ki values: 2.5 mM, 1 mM, 25 µM, respectively) and BCRP-mediated [(3)H]-estrone sulfate ([(3)H]-E1S) uptake (Ki values: 4 mM, 500 µM and 50 µM, respectively), whereas indole-3-acetic acid and phenylacetic acid reduce [(3)H]-MTX uptake by MRP4 only (Ki value: 2 mM and IC(50) value: 7 mM, respectively). In contrast, p-cresol, p-toluenesulfonic acid, putrescine, oxalate and quinolinic acid did not alter transport mediated by MRP4 or BCRP. In addition, our results show that hippuric acid, indole-3-acetic acid, indoxyl sulfate, kynurenic acid and phenylacetic acid accumulate in plasma of end-stage CKD patients with mean concentrations of 160 µM, 4 µM, 129 µM, 1 µM and 18 µM, respectively. Moreover, calculated Ki values are below the maximal plasma concentrations of the tested toxins. In conclusion, this study shows that several uremic toxins inhibit active transport by MRP4 and BCRP at clinically relevant concentrations.
authors.affiliation: Department of Pharmacology and Toxicology, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.
authors.forename: Henricus A M
authors.initials: HA
authors.lastname: Mutsaers
authors.forename: Lambertus P
authors.initials: LP
authors.lastname: van den Heuvel
authors.forename: Lauke H J
authors.initials: LH
authors.lastname: Ringens
authors.forename: Anita C A
authors.initials: AC
authors.lastname: Dankers
authors.forename: Frans G M
authors.initials: FG
authors.lastname: Russel
authors.forename: Jack F M
authors.initials: JF
authors.lastname: Wetzels
authors.forename: Joost G
authors.initials: JG
authors.lastname: Hoenderop
authors.forename: Rosalinde
authors.initials: R
authors.lastname: Masereeuw
mesh_terms: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004970:Estrone / Q000031:analogs & derivatives / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood; D008727:Methotrexate / Q000378:metabolism; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D014118:Toxins, Biological / Q000097:blood / Q000633:toxicity*; D014511:Uremia / Q000378:metabolism*
chemical_list: D000070997:ATP Binding Cassette Transporter, Subfamily G, Member 2; D018528:ATP-Binding Cassette Transporters; D004970:Estrone; D008727:Methotrexate; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D009363:Neoplasm Proteins; D014118:Toxins, Biological; C073492:ABCC4 protein, human; C116614:ABCG2 protein, human; C017296:estrone sulfate