Skip Navigation

This Article
Right arrow Full Text Freely available
Right arrow FREE Full Text (PDF) Freely available
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrow Search for citing articles in:
ISI Web of Science (18)
Right arrowRequest Permissions
Right arrow Disclaimer
Google Scholar
Right arrow Articles by Born, S. L.
Right arrow Articles by Lehman-McKeeman, L. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Born, S. L.
Right arrow Articles by Lehman-McKeeman, L. D.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

Toxicological Sciences 58, 23-31 (2000)
Copyright © 2000 by the Society of Toxicology

Biotransformation and Toxicokinetics

In Vitro Kinetics of Coumarin 3,4-Epoxidation: Application to Species Differences in Toxicity and Carcinogenicity

Stephanie L. Born*,1, Douglas Caudill*, Bill J. Smith{dagger} and Lois D. Lehman-McKeeman*

* The Procter & Gamble Company, Human and Environmental Safety Division, Miami Valley Laboratories, P.O. Box 538707, Cincinnati, Ohio 45253-8707; and {dagger} CNS Discovery/Drug Metabolism, Central Research Division, Pfizer, Inc., Groton, Connecticut 06340

Coumarin, a natural product and fragrance ingredient, is a well recognized rat liver toxicant, and dietary administration at toxic dosages increased the incidence of rat cholangiocarcinomas and parenchymal liver-cell tumors in a chronic bioassay. Hepatotoxicity in rats is site- and species-specific, and is thought to result from the formation of coumarin 3,4-epoxide and its rearrangement product, o-hydroxyphenylacetaldehyde (o-HPA). The goals of the current study were to describe the in vitro kinetics of the metabolic activation of coumarin, and determine whether species differences in susceptibility to liver injury correlate with coumarin bioactivation determined in vitro. Coumarin 3,4-epoxidation was quantified via the formation of o-HPA in pooled hepatic microsomes from female B6C3F1 mice, male F344 rats, and individual humans (n = 12 subjects), and the apparent kinetic constants for o-HPA production were calculated using nonlinear regression and fitting to either a one-enzyme or two-enzyme model. Eadie-Hofstee analyses indicated that o-HPA formation was biphasic in both rat and mouse liver. Although the apparent high affinity Km in rat and mouse liver microsomes was 38.9 and 47.2 µM, respectively, the overall rate of o-HPA formation was far greater in mouse than in rat liver microsomes. Furthermore, the total clearance (CLint) of coumarin via o-HPA formation in mouse liver microsomes was 4-fold greater than in rat liver microsomes. Since mice are relatively resistant to hepatotoxicity, the data indicated that rates of o-HPA formation in rat and mouse liver microsomes were not directly predictive of liver toxicity in vivo, and further suggested that o-HPA detoxification played a role in modulating coumarin-mediated toxicity. The current studies also indicated that coumarin 3,4-epoxidation in human hepatic microsomes was minimal. In human liver microsomes (n = 12), the kinetics of o-HPA formation were best described by a single enzyme model, with the Km for o-HPA formation ranging from 1320–7420 µM. In the most active human sample, the intrinsic clearance of coumarin via the 3,4-epoxidation pathway was 1/9 and 1/38 that of the rat and mouse, respectively. The in vitro kinetics of o-HPA formation, and in particular, the large quantities of coumarin required for o-HPA production in human liver microsomes, strongly suggest that humans are unlikely to produce toxicologically relevant concentrations of this metabolite following low level coumarin exposures.

Key Words: coumarin; epoxidation; liver; kinetics; toxicity; in vitro; rat; mouse; human.


Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?


This article has been cited by other articles:


Home page
 Hum Exp ToxicolHome page
T Uehara, N Kiyosawa, T Shimizu, K Omura, M Hirode, T Imazawa, Y Mizukawa, A Ono, T Miyagishima, T Nagao, et al.
Species-specific differences in coumarin-induced hepatotoxicity as an example toxicogenomics-based approach to assessing risk of toxicity to humans
Human and Experimental Toxicology, January 1, 2008; 27(1): 23 - 35.
[Abstract] [PDF]

Home page
 Drug Metab. Dispos.Home page
A. S. Kienhuis, H. M. Wortelboer, J.-C. Hoflack, E. J. Moonen, J. C.S. Kleinjans, B. van Ommen, J. H. M. van Delft, and R. H. Stierum
Comparison of Coumarin-Induced Toxicity between Sandwich-Cultured Primary Rat Hepatocytes and Rats in Vivo: A Toxicogenomics Approach
Drug Metab. Dispos., December 1, 2006; 34(12): 2083 - 2090.
[Abstract] [Full Text] [PDF]

Home page
 Toxicol SciHome page
J. D. Vassallo, S. M. Hicks, G. P. Daston, and L. D. Lehman-McKeeman
Metabolic Detoxification Determines Species Differences in Coumarin-Induced Hepatotoxicity
Toxicol. Sci., August 1, 2004; 80(2): 249 - 257.
[Abstract] [Full Text] [PDF]

Home page
 Drug Metab. Dispos.Home page
S. L. Born, D. Caudill, K. L. Fliter, and M. P. Purdon
Identification of the Cytochromes P450 That Catalyze Coumarin 3,4-Epoxidation and 3-Hydroxylation
Drug Metab. Dispos., May 1, 2002; 30(5): 483 - 487.
[Abstract] [Full Text] [PDF]


Disclaimer:
Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.