Prediction of Drug Clearance by Glucuronidation from in Vitro Data: Use of Combined Cytochrome P450 and UDP-Glucuronosyltransferase Cofactors in Alamethicin-Activated Human Liver Microsomes

• Published in: Drug metabolism and disposition Vol. 37; no. 1; pp. 82 - 89
• Main Authors: KILFORD, Peter J, STRINGER, Rowan, SOHAL, Bindi, HOUSTON, J. Brian, GALETIN, Aleksandra
• Format: Journal Article
• Language: English
• Published: Bethesda, MD American Society for Pharmacology and Experimental Therapeutics 01-01-2009
• Subjects: Alamethicin - pharmacology; Biological and medical sciences; Chromatography, Liquid; Cytochrome P-450 Enzyme System - metabolism; Glucuronides - metabolism; Glucuronosyltransferase - metabolism; Humans; In Vitro Techniques; Medical sciences; Microsomes, Liver - drug effects; Microsomes, Liver - enzymology; Microsomes, Liver - metabolism; Pharmacology. Drug treatments; Tandem Mass Spectrometry; Human; Drug; UDP-glucuronosyltransferase; Digestive system; Enzyme; Transferases; Cytochrome P450; Liver; Glycosyltransferases; Prediction; Glucuronic acid conjugation; Clearance; Metabolism; Microsome; Macrolide; Cofactor; In vitro; Antibiotic; Hexosyltransferases; Protein synthesis inhibitor; Pharmacokinetics; Antibacterial agent; Predictive factor
• ISSN: 0090-9556; 1521-009X
• DOI: 10.1124/dmd.108.023853

Glucuronidation via UDP-glucuronosyltransferase (UGT) is an increasingly important clearance pathway. In this study intrinsic
clearance (CL int ) values for buprenorphine, carvedilol, codeine, diclofenac, gemfibrozil, ketoprofen, midazolam, naloxone, raloxifene, and
zidovudine were determined in pooled human liver microsomes using the substrate depletion approach. The in vitro clearance
data indicated a varying contribution of glucuronidation to the clearance of the compounds studied, ranging from 6 to 79%
for midazolam and gemfibrozil, respectively. The CL int was ob tained using either individual or combined cofactors for cytochrome P450 (P450) and UGT enzymes with alamethicin activation
and in the presence and absence of 2% bovine serum albumin (BSA). In the presence of combined P450 and UGT cofactors, CL int ranged from 2.8 to 688 μl/min/mg for zidovudine and buprenorphine, respectively; the clearance was approximately equal to
the sum of the CL int values obtained in the presence of individual cofactors. The unbound intrinsic clearance (CL int, u ) was scaled to provide an in vivo predicted CL int ; the data obtained in the presence of combined cofactors resulted in 5-fold underprediction on average. Addition of 2% BSA
to the incubation with both P450 and UGT cofactors reduced the bias in the clearance prediction, with 8 of 10 compounds predicted
within 2-fold of in vivo values with the exception of raloxifene and gemfibrozil. The current study indicates the applicability
of combined cofactor conditions in the assessment of clearance for compounds with a differential contribution of P450 and
UGT enzymes to their elimination. In addition, improved predictability of microsomal data is observed in the presence of BSA,
in particular for UGT2B7 substrates.