Abstract
The goal of this study was to evaluate the specific contribution of individual UDP-glucuronosyltransferase (UGT) isoforms in the metabolism of buprenorphine (BUP) and norbuprenorphine (Nor-BUP), as well as the impact of their genetic variations. The glucuronidation of BUP and Nor-BUP was examined using human liver microsomes (HLMs) and heterologously expressed UGTs. The individual contribution of UGT isoforms was estimated using enzyme kinetic experiments combined with the relative activity factor (RAF). Phenotype-genotype relationships were investigated in a bank of 52 HLMs. Among the six hepatic UGT isoforms tested, UGT1A1, UGT1A3, and UGT2B7 metabolized BUP and Nor-BUP. Using the RAF approach, we found that UGT1A1 and UGT2B7 accounted for approximately 10 and 41% of BUP glucuronidation, respectively. Nor-BUP glucuronidation involved predominantly UGT1A3 (approximately 63%) and UGT1A1 (34%), whereas UGT2B7 had only a minor role. The UGT1A1 promoter (TA)6/7TAA mutation (UGT1A1*28) resulted in a 28% decrease of BUP glucuronidation Vmax in pooled HLMs but was not statistically associated with glucuronidation rate in 52 individual HLMs. The presence of the UGT2B7 promoter (G–842A) mutation resulted in higher BUP glucuronidation Vmax in pooled HLMs (+80% on average) and in a significant higher glucuronidation rate in noncarriers (but not in carriers) of the UGT1A1*28 allele (P = 0.0352). This study represents a functional basis for further clinical pharmacogenetic studies.
Footnotes
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.029546
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- BUP
- buprenorphine
- Nor-BUP
- norbuprenorphine
- P450
- cytochrome P450
- UGT
- UDP-glucuronosyltransferase
- HEK
- human embryonic kidney
- SNP
- single nucleotide polymorphism
- HLM
- human liver microsome
- ETO
- etoposide
- MPA
- mycophenolic acid
- UDPGA
- UDP-glucuronic acid
- AcMPAG
- mycophenolic acid acyl-glucuronide
- AZT
- 3′-azido-3′-deoxythymidine
- Clmax
- maximal clearance
- Vmax
- maximal velocity
- LC/MS/MS
- liquid chromatography/tandem mass spectrometry
- RAF
- relative activity factor.
- Received July 20, 2009.
- Accepted October 15, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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