Phenytoin metabolism by human cytochrome P450: Involvement of P450 3A and 2C Fprms in secondary metabolism and drug-protein adduct formation1

Cuttle, L., Munns, A., Hogg, N., Scott, J. R., Hooper, W. D., Dickinson, R. G. and Gillam, E. M. J. (2000) Phenytoin metabolism by human cytochrome P450: Involvement of P450 3A and 2C Fprms in secondary metabolism and drug-protein adduct formation1. Drug Metabolism and Disposition, 28 8: 945-950.

Author Cuttle, L.
Munns, A.
Hogg, N.
Scott, J. R.
Hooper, W. D.
Dickinson, R. G.
Gillam, E. M. J.
Title Phenytoin metabolism by human cytochrome P450: Involvement of P450 3A and 2C Fprms in secondary metabolism and drug-protein adduct formation1
Journal name Drug Metabolism and Disposition   Check publisher's open access policy
ISSN 0090-9556
Publication date 2000-08-01
Year available 2000
Sub-type Article (original research)
Open Access Status Not yet assessed
Volume 28
Issue 8
Start page 945
End page 950
Total pages 6
Editor J.R. Halpert
Place of publication Bethesda, USA
Publisher The American
Language eng
Subject C1
320504 Toxicology (incl. Clinical Toxicology)
730102 Immune system and allergy
Abstract 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., 2C9*1, 2C9*2, and 2C9*3. 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, 2C9*1, 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.
Keyword Pharmacology & Pharmacy
Pharmacology & Pharmacy
PHARMACOLOGY & PHARMACY
Q-Index Code C1
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Medicine Publications
 
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Created: Tue, 10 Jun 2008, 22:31:09 EST