EVALUATION OF 3′-AZIDO-3′-DEOXYTHYMIDINE, MORPHINE, AND CODEINE AS PROBE SUBSTRATES FOR UDP-GLUCURONOSYLTRANSFERASE 2B7 (UGT2B7) IN HUMAN LIVER MICROSOMES: SPECIFICITY AND INFLUENCE OF THE UGT2B7*2 POLYMORPHISM

1 September 2003

journal article
research article
Published by Elsevier in Drug Metabolism and Disposition

Vol. 31 (9) , 1125-1133
https://doi.org/10.1124/dmd.31.9.1125

Abstract

UDP-glucuronosyltransferase 2B7 (UGT2B7) is involved in the glucuronidation of a wide array of clinically important drugs and endogenous compounds in humans. The aim of this study was to identify an isoform-selective probe substrate that could be used to investigate genetic and environmental influences on glucuronidation mediated by UGT2B7. Three potential probe substrates [3′-azido-3′-deoxythymidine (AZT), morphine, and codeine], were evaluated using recombinant UGTs and human liver microsomes (HLMs; n = 54). Of 11 different UGTs screened, UGT2B7 was the principal isoform mediating AZT glucuronidation, morphine-3-glucuronidation, and morphine-6-glucuronidation. Codeine was glucuronidated equally well by UGT2B4 and UGT2B7. Enzyme kinetic analysis of these activities typically showed higher apparent K_m values for HLMs (pooled and individual) compared with UGT2B7. This difference was least (less than 2-fold higher K_m) for AZT glucuronidation and greatest (3- to 6-fold higher K_m) for codeine glucuronidation. Microsomal UGT2B7 protein content correlated well with AZT glucuronidation (r_s = 0.77), to a lesser extent with morphine-3-glucuronidation (r_s = 0.50) and morphine-6-glucuronidation (r_s = 0.51), but very weakly with codeine glucuronidation (r_s = 0.33). Livers were also genotyped for the UGT2B7^*2 (H268Y) polymorphism. No effect of genotype on microsomal glucuronidation or UGT2B7 protein content was observed. In conclusion, although both AZT and morphine can serve as in vitro probe substrates for UGT2B7, AZT appears to be more selective than morphine. Codeine is not a useful UGT2B7 probe substrate because of significant glucuronidation by UGT2B4. The UGT2B7^*2 polymorphism is not a determinant of glucuronidation of AZT, morphine, or codeine in HLMs.

Keywords

POLYMORPHISM

This publication has 23 references indexed in Scilit:

Validation of Serotonin (5-Hydroxtryptamine) as an in Vitro Substrate Probe for Human UDP-Glucuronosyltransferase (UGT) 1A6
Drug Metabolism and Disposition, 2003
Serotonin (5-hydroxytryptamine) glucuronidation in vitro : assay development, human liver microsome activities and species differences
Xenobiotica, 2003
In vitro–in vivo correlations for drugs eliminated by glucuronidation: Investigations with the model substrate zidovudine
British Journal of Clinical Pharmacology, 2002
Human Drug Metabolism and the Cytochromes P450: Application and Relevance of In Vitro Models
The Journal of Clinical Pharmacology, 2001
Relative Enzymatic Activity, Protein Stability, and Tissue Distribution of Human Steroid-Metabolizing UGT2B Subfamily Members
Endocrinology, 2001
Molecular basis for deficient acetaminophen glucuronidation in cats
Biochemical Pharmacology, 1997
Glucuronidation of 3′-azido-3′-deoxythymidine catalyzed by human liver UDP-glucuronosyltransferase: Significance of nucleoside hydrophobicity and inhibition by xenobiotics
Biochemical Pharmacology, 1991
Phenobarbital inducible UDP-glucuronosyltransferase is responsible for glucuronidation of 3′-azido-3′-deoxythymidine: Characterization of the enzyme in human and rat liver microsomes
Archives of Biochemistry and Biophysics, 1990
Glucuronidation of Codeine and Morphine in Human Liver and Kidney Microsomes: Effect of Inhibitors
Basic & Clinical Pharmacology & Toxicology, 1990
In vitro evidence for the involvement of at least two forms of human liver UDP-glucuronosyltransferase in morphine 3-glucuronidation
Biochemical Pharmacology, 1988