title: Almokalant glucuronidation in human liver and kidney microsomes: evidence for the involvement of UGT1A9 and 2B7.
abstract: 1. Almokalant, a class III antiarrythmic drug, is metabolized to form isomeric glucuronides identified in human urine. Synthesis of the total glucuronide was studied in human liver and kidney microsomes. Recombinant UDP-glucuronosyltransferases (UGTs) were screened for activity and kinetic analysis was performed to identify the isoform(s) responsible for the formation of almokalant glucuronide in man. 2. From a panel of recombinant isoforms used, both UGT1A9 and 2B7 catalysed the glucuronidation of almokalant. The Km values in both instances were similar with 1.06 mM for the 1A9 and 0.97 mM for the 2B7. Vmax for 1A9 was fourfold higher than that measured for UGT2B7, 92 compared with 21 pmol min(-1) mg(-1), respectively, but UGT1A9 was expressed at approximately twofold higher level than the UGT2B7 in the recombinant cell lines. Therefore, the contribution of UGT2B7 to almokalant glucuronidation could be as significant as that of UGT1A9 in man. 3. Liver and kidney microsomes displayed similar Km values to the cloned expressed UGTs, with the liver and kidney microsomes at 1.68 and 1.06 mM almost identical to the 1A9. 4. The results suggest a significant role for UGT1A9 and 2B7 in the catalysis of almokalant glucuronidation.
authors.affiliation: Department of Molecular and Cellular Pathology, Ninewells Medical School, University of Dundee DD1 9SY, UK.
authors.forename: B K
authors.initials: BK
authors.lastname: Gaiser
authors.forename: D J
authors.initials: DJ
authors.lastname: Lockley
authors.forename: A G
authors.initials: AG
authors.lastname: Staines
authors.forename: C
authors.initials: C
authors.lastname: Baarnhielm
authors.forename: B
authors.initials: B
authors.lastname: Burchell
mesh_terms: D000328:Adult; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000378:metabolism*; D016466:CHO Cells; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D006224:Cricetinae; D003720:Densitometry; D020719:Glucuronides / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D013058:Mass Spectrometry; D008861:Microsomes / Q000378:metabolism*; D008862:Microsomes, Liver / Q000378:metabolism*; D008875:Middle Aged; D011412:Propanolamines / Q000378:metabolism*; D000090264:UDP-Glucuronosyltransferase 1A9
chemical_list: D000889:Anti-Arrhythmia Agents; D020719:Glucuronides; D007527:Isoenzymes; D011412:Propanolamines; C000715591:UGT1A9 protein, human; C491474:UGT2B7 protein, human; D014453:Glucuronosyltransferase; D000090264:UDP-Glucuronosyltransferase 1A9; C074334:almokalant