title: Metabolism and renal elimination of gaboxadol in humans: role of UDP-glucuronosyltransferases and transporters.
abstract: Gaboxadol, a selective extrasynaptic agonist of the delta-containing gamma-aminobutyric acid type A (GABAA) receptor, is excreted in humans into the urine as parent drug and glucuronide conjugate. The goal of this study was to identify the UDP-Glucuronosyltransferase (UGT) enzymes and the transporters involved in the metabolism and active renal secretion of gaboxadol and its metabolite in humans.Methods. The structure of the glucuronide conjugate of gaboxadol in human urine was identified by LC/MS/MS. Human recombinant UGT isoforms were used to identify the enzymes responsible for the glucuronidation of gaboxadol. Transport of gaboxadol and its glucuronide was evaluated using cell lines and membrane vesicles expressing human organic anion transporters hOAT1 and hOAT3, organic cation transporter hOCT2, and the multidrug resistance proteins MRP2 and MRP4.Results. Our study indicated that the gaboxadol-O-glucuronide was the major metabolite excreted in human urine. UGT1A9, and to a lesser extent UGT1A6, UGT1A7 and UGT1A8, catalyzed the O-glucuronidation of gaboxadol in vitro. Gaboxadol was transported by hOAT1, but not by hOCT2, hOAT3, MRP2, and MRP4. Gaboxadol-O-glucuronide was transported by MRP4, but not MRP2.Conlusion. Gaboxadol could be taken up into the kidney by hOAT1 followed by glucuronidation and efflux of the conjugate into urine via MRP4.
authors.affiliation: DMPK Global Technologies, Merck & Co, Rahway, New Jersey, 07065, USA. xiaoyan_chu@merck.com
authors.forename: Xiao-Yan
authors.initials: XY
authors.lastname: Chu
authors.forename: Yuexia
authors.initials: Y
authors.lastname: Liang
authors.forename: Xiaoxin
authors.initials: X
authors.lastname: Cai
authors.forename: Karla
authors.initials: K
authors.lastname: Cuevas-Licea
authors.forename: Ronda K
authors.initials: RK
authors.lastname: Rippley
authors.forename: Kelem
authors.initials: K
authors.lastname: Kassahun
authors.forename: Magang
authors.initials: M
authors.lastname: Shou
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Braun
authors.forename: George A
authors.initials: GA
authors.lastname: Doss
authors.forename: M Reza
authors.initials: MR
authors.lastname: Anari
authors.forename: Raymond
authors.initials: R
authors.lastname: Evers
mesh_terms: D000284:Administration, Oral; D000818:Animals; D001711:Biotransformation; D016466:CHO Cells; D002853:Chromatography, Liquid; D006224:Cricetinae; D003412:Cricetulus; D018755:GABA Agonists / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes; D007555:Isoxazoles / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000652:urine; D007668:Kidney / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008862:Microsomes, Liver / Q000201:enzymology; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000378:metabolism; D027362:Organic Anion Transport Protein 1 / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D053719:Tandem Mass Spectrometry; D014162:Transfection; D000090264:UDP-Glucuronosyltransferase 1A9
chemical_list: D018755:GABA Agonists; D020719:Glucuronides; D014453:Glucuronosyltransferase; D007527:Isoenzymes; D007555:Isoxazoles; D026901:Membrane Transport Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D027362:Organic Anion Transport Protein 1; D011994:Recombinant Proteins; D000090264:UDP-Glucuronosyltransferase 1A9; C073492:ABCC4 protein, human; C000715591:UGT1A9 protein, human; C110655:UDP-glucuronosyltransferase, UGT1A6; C454320:UDP-glucuronosyltransferase, UGT1A8; C524630:UGT1A7 protein, human; C015542:gaboxadol