Phenytoin metabolism by human cytochrome P450 : involvement of P450 3A and 2C forms in secondary metabolism and drug-protein adduct formation

Cuttle, Leila, Munns, A. J., Hogg, N. A., Scott, J. R., Hooper, W. D., Dickinson, R. G., & Gillam, E. M. (2000) Phenytoin metabolism by human cytochrome P450 : involvement of P450 3A and 2C forms in secondary metabolism and drug-protein adduct formation. Drug Metabolism and Disposition: the biological fate of chemicals, 28(8), pp. 945-50.

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The anticonvulsant phenytoin (5,5-diphenylhydantoin) provokes a skin rash in 5 to 10% of patients, which heralds the start of an idiosyncratic reaction that may result from covalent modification of normal self proteins by reactive drug metabolites. Phenytoin is metabolized by cytochrome P450 (P450) enzymes primarily to 5-(p-hydroxyphenyl-),5-phenylhydantoin (HPPH), which may be further metabolized to a catechol that spontaneously oxidizes to semiquinone and quinone species that covalently modify proteins. The aim of this study was to determine which P450s catalyze HPPH metabolism to the catechol, proposed to be the final enzymatic step in phenytoin bioactivation. Recombinant human P450s were coexpressed with NADPH-cytochrome P450 reductase in Escherichia coli. Novel bicistronic expression vectors were constructed for P450 2C19 and the three major variants of P450 2C9, i.e., 2C91, 2C92, and 2C93. HPPH metabolism and covalent adduct formation were assessed in parallel. P450 2C19 was the most effective catalyst of HPPH oxidation to the catechol metabolite and was also associated with the highest levels of covalent adduct formation. P450 3A4, 3A5, 3A7, 2C91, and 2C9*2 also catalyzed bioactivation of HPPH, but to a lesser extent. Fluorographic analysis showed that the major targets of adduct formation in bacterial membranes were the catalytic P450 forms, as suggested from experiments with human liver microsomes. These results suggest that P450 2C19 and other forms from the 2C and 3A subfamilies may be targets as well as catalysts of drug-protein adduct formation from phenytoin.

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ID Code: 67199
Item Type: Journal Article
Refereed: Yes
Additional Information: Articles free to read on journal website after 12 months back to 1st Jan 1997 Cuttle, L Munns, A J Hogg, N A Scott, J R Hooper, W D Dickinson, R G Gillam, E M eng 2000/07/20 11:00 Drug Metab Dispos. 2000 Aug;28(8):945-50.
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Keywords: Anticonvulsants/*metabolism, *Aryl Hydrocarbon Hydroxylases, Autoimmunity, Catechols/analysis, Cytochrome P-450 CYP3A, Cytochrome P-450 Enzyme System/immunology/*metabolism, Epitopes/immunology, Humans, Oxidoreductases, N-Demethylating/immunology/*metabolism, Phenytoin/*metabolism, Recombinant Proteins/metabolism
ISSN: 0090-9556 (print) 1521-009x (online)
Divisions: Current > Schools > School of Biomedical Sciences
Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 2000 The American Society for Pharmacology and Experimental Therapeutics.
Deposited On: 27 Feb 2014 01:09
Last Modified: 03 Feb 2015 05:46

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