HUMAN UDP-GLUCURONOSYLTRANSFERASES: ISOFORM SELECTIVITY AND KINETICS OF 4-METHYLUMBELLIFERONE AND 1-NAPHTHOL GLUCURONIDATION, EFFECTS OF ORGANIC SOLVENTS, AND INHIBITION BY DICLOFENAC AND PROBENECID

• DOI: 10.1124/dmd.32.4.413
• Publication Date: 2004-03-23T22:08:14Z
• Authors: Verawan Uchaipichat; Peter I. Mackenzie; Xiao-Hui Guo; Dione Gardner-Ste...; Aleksandra Galetin; J. Brian Houston; John O. Miners
• Keywords: Probenecid; Diclofenac

The glucuronidation kinetics of the prototypic substrates 4-methylumbelliferone (4MU) and 1-naphthol (1NP) by human UDP-glucuronosyltransferases (UGT) 1A1, 1A3, 1A4, 1A6, 1A7, 1A8, 1A9, 1A10, 2B7, 2B15, 2B17 were investigated. Where activity was demonstrated, inhibitory effects diclofenac, probenecid, solvents acetone, acetonitrile, dimethyl sulfoxide, ethanol, methanol characterized. All isoforms except UGT1A4 glucuronidated 4MU, whereas all but UGT metabolized 1NP. However, kinetic models varied with substrate (for same isoform) from isoform to (with substrate). Hyperbolic (Michaelis-Menten), inhibition, sigmoidal variably observed for both 4MU 1NP various UGTs. <i>K</i>_m or <i>S</i>₅₀ (sigmoidal kinetics) <i>V</i>_max values 525- (8–4204 μM) 5535-fold, respectively, glucuronidation, 1360- (1.3–1768 560-fold, glucuronidation. use a two-site model proved useful those reactions exhibiting non-Michaelis-Menten kinetics. organic generally had relatively minor effect on activity. most susceptible presence solvent, although solvent-selective inhibition occasionally other isoforms. Diclofenac probenecid inhibited isoforms, precluding these compounds reaction phenotyping xenobiotic pathways in tissues. <i>K</i>_i values, determined selected ranged 11 60 μM 96 2790 μM, respectively. Overall, results emphasize need careful design interpretation studies