Related Experiment Video
Updated: Aug 27, 2025

Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures
Published on: March 28, 2017
Estimation of fraction of drug metabolism by a single UDP-glucuronosyl transferase enzyme using relative expression
Tomoyo Honda1, Wataru Obuchi1, Yumi Nishiya1
1Drug Metabolism & Pharmacokinetics Research Laboratory, R&D Division, Daiichi Sankyo Company, Ltd, Shinagawa-ku, Japan.
Abstract:
The estimation of the contributions of UDP-glucuronosyl transferase (UGT) isoforms to the overall metabolism still suffers from technical difficulties due to limited information on enzyme levels in recombinant systems and specific inhibitors, unlike the case for cytochrome P450s (CYPs). The protein expression levels of UGT in both recombinant system microsomes (RM) and human liver microsomes (HLM) were quantified using liquid chromatography-tandem mass spectrometry, and the relative expression factor (REF) value of HLM to recombinant microsomes was estimated to evaluate the fractions of drug metabolism by a single UGT enzyme (fmUGT) of UGT substrates. The REF values of UGT1A1, UGT1A3, UGT1A9, UGT2B4, UGT2B7, and UGT2B17 were 0.228, 0.0714, 0.0665, 0.420, 0.118, and 0.0442, respectively. fmUGTs in HLM were estimated for several typical UGT substrates utilizing these values and metabolic clearances in RM. These values were comparable to the reported values estimated by various methods. This study provided useful information on REF values, which promote a robust estimation of fmUGT values for UGT substrates when evaluating the contribution of UGT isoforms to total metabolic clearance.
Related Concept Videos
Phase II Reactions: Glucuronidation
Drug Metabolism: Phase II Reactions
One-Compartment Open Model: Urinary Excretion Data and Determination of k
One-Compartment Open Model: Wagner-Nelson and Loo Riegelman Method for ka Estimation
On...
Renal Drug Excretion: Tubular Secretion
Factors Affecting Drug Biotransformation: Biological
Species differences: Variations in enzyme systems across species can cause disparities in drug metabolism. For instance, humans may metabolize certain drugs faster than rodents, altering therapeutic effects.
Strain differences: Genetic variations within a species can result in differing enzyme activity, impacting drug response and toxicity. For example, some mouse strains may...

