Document Detail

Effect of aging on glucuronidation of valproic acid in human liver microsomes and the role of UDP-glucuronosyltransferase UGT1A4, UGT1A8, and UGT1A10.
MedLine Citation:
PMID:  18838507     Owner:  NLM     Status:  MEDLINE    
Valproic acid (VPA) is a widely used anticonvulsant that is also approved for mood disorders, bipolar depression, and migraine. In vivo, valproate is metabolized oxidatively by cytochromes P450 and beta-oxidation, as well as conjugatively via glucuronidation. The acyl glucuronide conjugate (valproate-glucuronide or VPAG) is the major urinary metabolite (30-50% of the dose). It has been hypothesized that glucuronidation of antiepileptic drugs is spared over age, despite a known decrease in liver mass. The formation rates of VPAG in a bank of elderly (65 years onward) human liver microsomes (HLMs) were measured by liquid chromatography/tandem mass spectrometry and compared with those in a younger (2-56 years) HLM bank. In vitro kinetic studies with recombinant UDP-glucuronosyltransferases (UGTs) were completed. A 5- to 8-fold variation for the formation of VPAG was observed within the microsomal bank obtained from elderly and younger donors. VPAG formation ranged from 6.0 to 53.4 nmol/min/mg protein at 1 mM substrate concentration (n=36). The average velocities at 0.25, 0.5, and 1 mM VPA were 7.0, 13.4, and 25.4 nmol/min/mg protein, respectively, in the elderly HLM bank. Rates of VPAG formation were not significantly different in the HLM bank obtained from younger subjects. Intrinsic clearances (V(max)/K(m)) for several cloned, expressed UGTs were determined. UGT1A4, UGT1A8, and UGT1A10 also were found to catalyze the formation of VPAG in vitro. This is the first reported activity of these UGTs toward VPA glucuronidation. UGT2B7 had the highest intrinsic clearance, whereas UGT1A1 demonstrated no activity. In conclusion, our investigation revealed no differences in VPAG formation in younger versus elderly HMLs and revealed three other UGTs that form VPAG in vitro.
Upendra A Argikar; Rory P Remmel
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural     Date:  2008-10-06
Journal Detail:
Title:  Drug metabolism and disposition: the biological fate of chemicals     Volume:  37     ISSN:  1521-009X     ISO Abbreviation:  Drug Metab. Dispos.     Publication Date:  2009 Jan 
Date Detail:
Created Date:  2008-12-24     Completed Date:  2009-03-02     Revised Date:  2010-09-21    
Medline Journal Info:
Nlm Unique ID:  9421550     Medline TA:  Drug Metab Dispos     Country:  United States    
Other Details:
Languages:  eng     Pagination:  229-36     Citation Subset:  IM    
Department of Medicinal Chemistry, College of Pharmacy, 8-101 WDH, 308 Harvard St. SE, University of Minnesota, Minneapolis, Minnesota 55414, USA.
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MeSH Terms
Aged, 80 and over
Aging / metabolism*
Child, Preschool
Chromatography, High Pressure Liquid
Glucuronides / metabolism*
Glucuronosyltransferase / metabolism*
Isoenzymes / metabolism*
Microsomes, Liver / metabolism*
Middle Aged
Reference Standards
Tandem Mass Spectrometry
Valproic Acid / metabolism*
Grant Support
Reg. No./Substance:
0/Glucuronides; 0/Isoenzymes; 99-66-1/Valproic Acid; EC

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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