Yuji Mano1, Takashi Usui, Hidetaka Kamimura. 1. Drug Metabolism Research Laboratories, Astellas Pharma Inc, 1-8, Azusawa 1-Chome, Itabashi-ku, Tokyo, 174-8511, Japan. yuuji.mano@jp.astellas.com
Abstract
PURPOSE: To assess the uridine diphosphate (UDP)-glucuronosyltransferase (UGT) isozymes involved in the glucuronidation of niflumic acid in human liver. METHODS: The glucuronidation activity of niflumic acid was determined in liver microsomes and recombinant UGT isozymes by incubation of niflumic acid with UDP-glucuronic acid (UDPGA). RESULTS: Incubation of niflumic acid with liver microsomes and UDPGA produced one peak, which was identified as a glucuronide from mass spectrometric analysis. A study involving a panel of recombinant human UGT isozymes showed that glucuronidation activity was highest in UGT1A1 among the isozymes investigated. The glucuronidation in human liver microsomes (HLMs) followed Michaelis-Menten kinetics with a Km value of 16 microM, which is similar to that found with recombinant UGT1A1. The glucuronidation activity of niflumic acid in microsomes from eight human livers significantly correlated with UGT1A1-catalyzed estradiol 3beta-glucuronidation activity (r=0.78, p<0.05). Beta-estradiol inhibited niflumic acid glucuronidation with an IC50 of 25 microM in HLMs, comparable to that for UGT1A1. CONCLUSIONS: These findings indicate that UGT1A1 is the main isozyme involved in the glucuronidation of niflumic acid in the human liver.
PURPOSE: To assess the uridine diphosphate (UDP)-glucuronosyltransferase (UGT) isozymes involved in the glucuronidation of niflumic acid in human liver. METHODS: The glucuronidation activity of niflumic acid was determined in liver microsomes and recombinant UGT isozymes by incubation of niflumic acid with UDP-glucuronic acid (UDPGA). RESULTS: Incubation of niflumic acid with liver microsomes and UDPGA produced one peak, which was identified as a glucuronide from mass spectrometric analysis. A study involving a panel of recombinant humanUGT isozymes showed that glucuronidation activity was highest in UGT1A1 among the isozymes investigated. The glucuronidation in human liver microsomes (HLMs) followed Michaelis-Menten kinetics with a Km value of 16 microM, which is similar to that found with recombinant UGT1A1. The glucuronidation activity of niflumic acid in microsomes from eight human livers significantly correlated with UGT1A1-catalyzed estradiol 3beta-glucuronidation activity (r=0.78, p<0.05). Beta-estradiol inhibited niflumic acid glucuronidation with an IC50 of 25 microM in HLMs, comparable to that for UGT1A1. CONCLUSIONS: These findings indicate that UGT1A1 is the main isozyme involved in the glucuronidation of niflumic acid in the human liver.
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