Abstract
Midazolam undergoes oxidative hydroxylation by CYP3A to its metabolites, which are excreted mainly as glucuronidated conjugates into the urine. In this study, we examined the glucuronidation of hydroxymidazolam in human liver microsomes (HLMs) and characterized the UDP-glucuronosyltransferases (UGTs) involved in 1′- and 4-hydroxymidazolam glucuronidation. Among the 12 UGT isoforms tested, the O- and N-glucuronidation of 1′-hydroxymidazolam was mediated by UGT2B4/2B7 and 1A4, respectively. In contrast, the glucuronidation of 4-hydroxymidazolam was mediated by UGT1A4. Consistent with these observations, the UGT1A4 inhibitor hecogenin and the UGT2B7 substrate diclofenac potently inhibited the N- and O-glucuronidation of 1′-hydroxymidazolam in HLMs, respectively. A correlation analysis of UGT enzymatic activity and the formation rate of glucuronide metabolites from 1′- and 4-hydroxymidazolam in 25 HLMs showed that hydroxymidazolam glucuronidation is correlated with UGT1A4-mediated lamotrigine glucuronidation and UGT2B7-mediated diclofenac glucuronidation activity. Taken together, these findings indicate that UGT1A4, 2B4, and 2B7 are major isoforms responsible for glucuronide conjugate formation from 1′- and 4-hydroxymidazolam, which are the two major oxidative metabolites of midazolam.
Footnotes
This study was supported by the Korean Health 21 R&D Project, Ministry of Health, Welfare, and Family Affairs [Grant A030001]; and by the Ministry of Education, Science, and Engineering [Korean Science and Engineering Foundation Grant R13-2007-023-00000-0].
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.110.035295.
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ABBREVIATIONS:
- UGT
- UDP-glucuronosyltransferase
- HLM
- human liver microsome
- UDPGA
- uridine diphosphoglucuronic acid
- LC
- liquid chromatography
- MS/MS
- tandem mass spectrometry.
- Received July 5, 2010.
- Accepted August 16, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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