DMD Simcyp

Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Tang, C.
Right arrow Articles by Lin, J. H.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Tang, C.
Right arrow Articles by Lin, J. H.

Vol. 30, Issue 6, 648-654, June 2002

Effect of Albumin on Phenytoin and Tolbutamide Metabolism in Human Liver Microsomes: An Impact More Than Protein Binding

Cuyue Tang, Yuh Lin, A. David Rodrigues, and Jiunn H. Lin

Department of Drug Metabolism, Merck Research Laboratories, West Point, PA

The cytochrome P450 (P450)-dependent conversion of phenytoin (PHT) to p-hydroxy phenytoin (pHPPH), and tolbutamide (TLB) to 4-hydroxy tolbutamide (hydroxy-TLB), in human liver microsomes was studied in the presence of increasing concentrations (0-4%) of bovine serum albumin (BSA). Therefore, the free fraction (fu) of PHT and TLB varied. Whereas the fu of PHT (5 µM) decreased, an increase (3-fold), rather than a decrease in the pHPPH formation rate was observed when BSA (<1%) was present. The stimulation was attributed to a significant decrease in apparent Km. The change, however, was diminished as the BSA concentration reached 4% (PHT fu = 0.2), in which the reaction velocity remained the same as that measured in the absence of BSA. Therefore, unchanged Km (16.2 ± 0.7 µM) and Vmax (9.4 ± 0.2 pmol/min/mg of protein) values were determined based on total PHT concentrations, whereas correction for fu led to an unbound Km (Kmu) of ~3.2 µM. Similarly, the metabolism of TLB (50 µM) was enhanced (~2-fold) in the presence of 0.25% BSA but remained only 35% of the control activity (no BSA) at 1% BSA. However, the remaining activity was higher (3-fold) than that determined with an equivalent free concentration of TLB (4 µM) calculated according to its fu (0.08). The difference became less significant when BSA concentration was 4% (fu < 0.02). Collectively, the results suggest a 2-fold effect of BSA on PHT and TLB hydroxylation: first, facilitation of the reactions via a decrease in Km; second, a decrease in fu leading to a drop in reaction rate. For a given P450 reaction, therefore, the effect of BSA may depend upon enzyme affinity, catalytic capacity, and the extent of protein binding.

Copyright © 2002 by The American Society for Pharmacology and Experimental Therapeutics


This article has been cited by other articles:


Home page
 Drug Metab. Dispos.Home page
X. Wei, G. Dai, Z. Liu, H. Cheng, Z. Xie, R. Klisovic, G. Marcucci, and K. K. Chan
Enzyme Kinetics of GTI-2040, a Phosphorothioate Oligonucleotide Targeting Ribonucleotide Reductase
Drug Metab. Dispos., November 1, 2008; 36(11): 2227 - 2233.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
A. Rowland, D. J. Elliot, K. M. Knights, P. I. Mackenzie, and J. O. Miners
The "Albumin Effect" and in Vitro-in Vivo Extrapolation: Sequestration of Long-Chain Unsaturated Fatty Acids Enhances Phenytoin Hydroxylation by Human Liver Microsomal and Recombinant Cytochrome P450 2C9
Drug Metab. Dispos., May 1, 2008; 36(5): 870 - 877.
[Abstract] [Full Text] [PDF]

Home page
 J. Pharmacol. Exp. Ther.Home page
A. Rowland, P. Gaganis, D. J. Elliot, P. I. Mackenzie, K. M. Knights, and J. O. Miners
Binding of Inhibitory Fatty Acids Is Responsible for the Enhancement of UDP-Glucuronosyltransferase 2B7 Activity by Albumin: Implications for in Vitro-in Vivo Extrapolation
J. Pharmacol. Exp. Ther., April 1, 2007; 321(1): 137 - 147.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
C. Chang, P. M. Bahadduri, J. E. Polli, P. W. Swaan, and S. Ekins
Rapid Identification of P-glycoprotein Substrates and Inhibitors
Drug Metab. Dispos., December 1, 2006; 34(12): 1976 - 1984.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
A. Rowland, D. J. Elliot, J. A. Williams, P. I. Mackenzie, R. G. Dickinson, and J. O. Miners
IN VITRO CHARACTERIZATION OF LAMOTRIGINE N2-GLUCURONIDATION AND THE LAMOTRIGINE-VALPROIC ACID INTERACTION
Drug Metab. Dispos., June 1, 2006; 34(6): 1055 - 1062.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
N. Raghavan, D. Zhang, M. Zhu, J. Zeng, and L. Christopher
CYP2D6 CATALYZES 5-HYDROXYLATION OF 1-(2-PYRIMIDINYL)-PIPERAZINE, AN ACTIVE METABOLITE OF SEVERAL PSYCHOACTIVE DRUGS, IN HUMAN LIVER MICROSOMES
Drug Metab. Dispos., February 1, 2005; 33(2): 203 - 208.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
R. L. Walsky and R. S. Obach
VALIDATED ASSAYS FOR HUMAN CYTOCHROME P450 ACTIVITIES
Drug Metab. Dispos., June 1, 2004; 32(6): 647 - 660.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
H. M. Jones, D. Hallifax, and J. B. Houston
QUANTITATIVE PREDICTION OF THE IN VIVO INHIBITION OF DIAZEPAM METABOLISM BY OMEPRAZOLE USING RAT LIVER MICROSOMES AND HEPATOCYTES
Drug Metab. Dispos., May 1, 2004; 32(5): 572 - 580.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
B. Rochat, E. M. J. Gillam, and M. S. Lennard
Evaluation of Recombinant Cytochromes P450 Activity in Metabolic Pathways
Drug Metab. Dispos., January 1, 2003; 31(1): 145 - 146.
[Full Text] [PDF]


Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
All ASPET Journals Molecular Pharmacology Pharmacological Reviews
Molecular Interventions Drug Metabolism and Disposition

Copyright © 2002 by the American Society for Pharmacology and Experimental Therapeutics.