title: Acyl glucuronidation and glucosidation of a new and selective endothelin ET(A) receptor antagonist in human liver microsomes.
abstract: Compound A [(+)-(5S,6R,7R)-2-isopropylamino-7-[4-methoxy-2-((2R)-3-methoxy-2-methylpropyl)-5-(3,4-methylenedioxyphenyl) cyclopenteno [1,2-b] pyridine 6-carboxylic acid] is a new and selective endothelin ET(A) receptor antagonist. It underwent significant acyl glucuronidation and acyl glucosidation in human liver microsomes supplemented with UDP-glucuronic acid (UDPGA) and UDP-glucose (UDPG). These two conjugations were observed in a panel of human liver microsomal samples (n = 16) that gave rise to varying activities but with no significant correlation with each other in the native and activator-treated microsomal preparations (r(2) <or= 0.4, p > 0.05). The lack of correlation may be explained by the involvement of multiple UDP-glucuronosyltransferases (UGTs; UGT1A1, 1A3, 1A9, 2B7 and 2B15) in the glucuronidation but essentially solely UGT2B7 in the glucosidation. Both reactions conformed to monophasic Michaelis-Menten kinetics in human liver microsomes. The glucuronidation reaction exhibited apparent K(m) values (mean +/- S.E.) for compound A and UDPGA of 8.4 +/- 0.6 and 605 +/- 35 microM, respectively, whereas the values for the glucosidation reaction were 10.2 +/- 1.5 and 670 +/- 120 microM, respectively. In both pooled human liver microsomes and expressed UGT2B7, UDPG and UDPGA competitively inhibited their counterpart conjugations with K(i) values close to their K(m) values, indicating a comparable affinity of the enzyme toward these two nucleotide sugars. We herein report a drug acyl glucoside formed in human liver microsomes at a considerable turnover rate and provide the evidence for a UGT isoform (UGT2B7) capable of transferring both glucuronic acid and glucose from UDPGA and UDPG to an aglycone.
authors.affiliation: Department of Drug Metabolism, West Point, Pennsylvania 19486-0004, USA. cuyue_tang@merck.com
authors.forename: Cuyue
authors.initials: C
authors.lastname: Tang
authors.forename: Jerome H
authors.initials: JH
authors.lastname: Hochman
authors.forename: Bennett
authors.initials: B
authors.lastname: Ma
authors.forename: Raju
authors.initials: R
authors.lastname: Subramanian
authors.forename: Kamlesh P
authors.initials: KP
authors.lastname: Vyas
mesh_terms: D065128:Endothelin Receptor Antagonists; D005960:Glucosides / Q000737:chemistry / Q000378:metabolism*; D020723:Glucuronic Acid / Q000737:chemistry / Q000378:metabolism; D020719:Glucuronides / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008862:Microsomes, Liver / Q000378:metabolism*; D020033:Protein Isoforms / Q000737:chemistry / Q000378:metabolism; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin / Q000378:metabolism; D014532:Uridine Diphosphate Glucose / Q000737:chemistry / Q000378:metabolism; D014535:Uridine Diphosphate Glucuronic Acid / Q000737:chemistry / Q000378:metabolism
chemical_list: D065128:Endothelin Receptor Antagonists; D005960:Glucosides; D020719:Glucuronides; D020033:Protein Isoforms; D044022:Receptor, Endothelin A; D017466:Receptors, Endothelin; D014535:Uridine Diphosphate Glucuronic Acid; D020723:Glucuronic Acid; D014532:Uridine Diphosphate Glucose