Title: Identification of Human UGT2B7 as the Major Isoform Involved in the<i>O</i>-Glucuronidation of Chloramphenicol
Abstract: Chloramphenicol (CP), a broad spectrum antibiotic, is eliminated in humans by glucuronidation. The primary UGT enzymes responsible for CP <i>O</i>-glucuronidation remain unidentified. We have previously identified the 3-<i>O</i>-CP (major) and 1-<i>O</i>-CP (minor) glucuronides by β-glucuronidase hydrolysis, liquid chromatography-tandem mass spectrometry, and 1D/2D H NMR. Reaction phenotyping for the glucuronidation of CP with 12 expressed human liver UGT isoforms has identified UGT2B7 as having the highest activity for 3-<i>O</i>- and 1-<i>O</i>-CP glucuronidation with minor contributions from UGT1A6 and UGT1A9. The kinetics of CP 3-<i>O</i>-glucuronidation by pooled human liver microsomes (HLMs) exhibited biphasic Michaelis-Menten kinetics with the apparent high-affinity <i>K</i><sub>m1</sub> and low-affinity <i>K</i><sub>m2</sub> values of 46.0 and 1027 μM, whereas expressed UGT2B7 exhibited Michaelis-Menten kinetics with the apparent <i>K</i><sub>m</sub> value of 109.1 μM. The formation of 1-<i>O</i>-CP glucuronide by pooled HLM and expressed UGT2B7 exhibited substrate inhibition kinetics with apparent <i>K</i><sub>m</sub> values of 408.2 and 115.0 μM, respectively. Azidothymidine (AZT) and hyodeoxycholic acid (substrates of UGT2B7) inhibited 3-<i>O</i>- and 1-<i>O</i>-CP glucuronidation in pooled HLMs. In 10 donor HLM preparations, both CP 3-<i>O</i>- and CP 1-<i>O</i>-glucuronidation showed a significant correlation with AZT glucuronidation (UGT2B7) (<i>r</i><sub>s</sub> = 0.85 and <i>r</i><sub>s</sub> = 0.83, respectively) at 30 μM CP, whereas no significant correlation was observed between CP 3-<i>O</i>-glucuronidation and serotonin glucuronidation (UGT1A6) or propofol glucuronidation (UGT1A9) at this CP concentration. These results suggest that UGT2B7 is the primary human hepatic UDP-glucuronosyltransferase isoform catalyzing 3-<i>O</i>- and 1-<i>O</i>-CP glucuronidation with minor contributions from UGT1A6 and UGT1A9.
Publication Year: 2009
Publication Date: 2009-12-11
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 41
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