title: Effect of cytochrome P450 (CYP) inducers on caffeine metabolism in the rat.
abstract: Our previous studies, carried out using rat cDNA-expressed cytochrome P450 (CYP) isoforms, liver microsomes and specific CYP inhibitors, showed that the 1-N- and 3-N-demethylation of caffeine at a therapeutic concentration was predominantly catalyzed by CYP1A2 and CYP2C, its 7-N-demethylation was governed by P450s of the CYP2C subfamily, while its 8-hydroxylation was specifically mediated by CYP1A2. The present study was aimed at corroborating the above-described results using another experimental model, i.e. a study of caffeine metabolism in the liver microsomes and specific CYP inducers. Animals received one of the following inducers: beta-naphthoflavone (100 mg/kg i.p. for 4 days), phenobarbital (10 mg/kg for 6 days or 100 mg/kg i.p. for 4 days), pregnenolone 16alpha-carbonitrile (100 mg/kg i.p. for 4 days) or 15% ethanol ( approximately 11 g/kg in drinking water for 6 days). Sixteen hours after the last dose of an inducer liver microsomes were prepared and the caffeine metabolism and CYP isoform activities (testosterone 2alpha-, 2beta-, 6beta-, 7alpha-, 16beta-hydroxylation and warfarin 7-hydroxylation) were investigated. beta-Naphthoflavone (mainly a CYP1A inducer and CYP2C11 inhibitor) potently accelerated the metabolism of caffeine, the effect on 7-N-demethylation being the weakest. Moreover, the influence of beta-naphthoflavone on caffeine metabolism was more potent at the substrate concentration of 100 microM than 800 microM, in particular in the case of 7-N-demethylation and 8-hydroxylation. Pregnenolone-16alpha-carbonitrile (mainly a CYP3A inducer and CYP2C11 inhibitor) moderately induced 8-hydroxylation only. Phenobarbital (an inducer of CYP2B and other CYPs and a CYP2C11 inhibitor) moderately stimulated the metabolism of caffeine, but practically did not affect 7-N-demethylation. Ethanol (mainly a CYP2E1 inducer) modestly increased the rates of the N-demethylation reactions. The presently obtained data confirm the pivotal role of CYP1A2 in the metabolism of caffeine, as well as the involvement of CYP3A in the 8-hydroxylation of caffeine and that of CYP2C11 in its 7-N-demethylation.
authors.affiliation: Department of Pharmacokinetics and Drug Metabolism, Institute of Pharmacology, Polish Academy of Sciences, Smetna 12, PL 31-343 Kraków, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Kot
authors.forename: Władysława A
authors.initials: WA
authors.lastname: Daniel
mesh_terms: D000818:Animals; D001571:Benzoflavones / Q000494:pharmacology; D002110:Caffeine / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D004790:Enzyme Induction / Q000187:drug effects; D000431:Ethanol / Q000494:pharmacology; D007527:Isoenzymes / Q000502:physiology; D008297:Male; D010634:Phenobarbital / Q000494:pharmacology; D011285:Pregnenolone Carbonitrile / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D001571:Benzoflavones; D007527:Isoenzymes; D011285:Pregnenolone Carbonitrile; D002110:Caffeine; D000431:Ethanol; C011512:alpha-naphthoflavone; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital