Induction of cytochrome P450s by rutaecarpine and metabolism of rutaecarpine by cytochrome P450s

Rutaecarpine is an alkaloid originally isolated from the unripe fruit of Evodia rutaecarpa. Recently, rutaecarpine has been characterized to have an anti-inflammatory activity through cyclooxygenase-2 inhibition. In the present studies, the effects of rutaecarpine on liver cytochrome P450 s (P450s) and P450 s involved in the metabolism of rutaecarpine were studied in vivo and in vitro, respectively, because the data are crucial in the early development of rutaecarpine as a new drug candidate. Oral administration to male ICR mice of rutaecarpine for 3 consecutive days induced liver P450 1A-, 2B- and 2E1-selective monooxygenase activities. The induction of P450 1A and 2B by rutaecarpine was confirmed by Western immunoblotting. When rutaecarpine was incubated with rat liver microsomes in the presence of an NADPH-generating system, five metabolites were detected by UV and mass spectral analyses. The 3-methylcholanthrene- and phenobarbital-induced microsomes greatly increased the formation of metabolites. Our present results suggest that rutaecarpine might induce P450 1A and 2B in mice, and that P450 1A and 2B might predominantly metabolize rutaecarpine in rat liver microsomes.     

Studying cytochrome P450 kinetics in drug metabolism

BACKGROUND: Determination of cytochrome P450 enzyme-mediated kinetics in vitro can be useful for predicting drug dosing and clearance in humans. Expressed P450s, human liver microsomes, human hepatocytes (both fresh and cryopreserved), and human liver slices are used to estimate K(m) and V(max) values for determination of intrinsic clearance of the drug for scale-up to predict in vivo clearance. OBJECTIVE: To describe the advantages and disadvantages of the various in vitro systems used to estimate kinetic parameters for disposition of drugs and the various kinetic profiles that can be observed. METHODS: A review of the literature was conducted to evaluate the utility of the various in vitro preparations, the methods for determining kinetic parameters and the types of kinetic profiles that may be observed. RESULTS/CONCLUSIONS: The choice of in vitro system for determining kinetic parameters will depend on the objective of the studies, as each system has advantages and disadvantages. Kinetic parameter determinations must be carefully assessed to assure that the correct kinetic model is applied and the most accurate kinetic parameters are determined.     

The oxidative metabolism of dimemorfan by human cytochrome P450 enzymes

To characterize the human cytochrome P450 (P450) forms involved in dimemorfan oxidation (DFO), human liver microsomes, and recombinant P450s were investigated. Liquid chromatography-mass spectral analysis suggested that metabolite (M)1 ([M + H]⁺ m/z at 272.200) and M2 ([M + H]⁺ m/z at 242.190) were d-3-hydroxymethyl-N-methylmorphinan and d-3-methylmorphinan, respectively. Kinetic analyses of microsomal DFO showed that the substrate concentration showing a half-maximal velocity (S₅₀) of M1 formation was less than that of M2. Microsomal M1 and M2 formation activities correlated significantly with the CYP2D6 marker, dextromethorphan O-demethylation activity. The M2 formation activity was also correlated with the CYP3A4 marker, nifedipine oxidation activity. Microsomal M1 and M2 formation was most sensitive to the inhibition by a CYP2D6 inhibitor, paroxetine and a CYP3A4 inhibitor, ketoconazole, respectively. The immunoinhibition-defined P450 contributions indicated the participation of CYP2C9, CYP2C19, and CYP2D6 in the M1 formation and CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 in the M2 formation. Among recombinant P450s, CYP2D6 had the highest intrinsic clearance with a K_m value of 0.02 mM in forming M1. CYP2B6, CYP2C9, and CYP2C19 had the K_m or S₅₀ values smaller than those (1 mM) of CYP2D6 and CYP3A4 in forming M2. These results indicated the participation of multiple P450 forms in DFO. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:1063–1077, 2010     

细胞色素P450的基因多态性与药物代谢

细胞色素P450（cytochrome P450，CYP）是重要的药物代谢酶，参与催化多种内源和外源化合物，特别是多种临床药物的生物转化。CYP存在广泛的基因多态性和表型多态性，使其对于各种化合物的代谢存在统计学个体差异。核受体是配体依赖性转录因子超家族，与药物代谢过程中的基因表达调控密切相关，被外源物质活化后诱导或抑制CYP基因的表达。现综述CYP与药物代谢、CYP的基因多态性、CYP表达的诱导机制、核受体及其配体诱导CYP表达及近年研究CYP450的各种实验方法。     

细胞色素P450与药物代谢的研究现状

细胞色素P450(CYP)在众多中西药物代谢中起着非常重要的作用。本文综述了与药物代谢相关的CYP亚型、CYP与药物相互作用的关系及中药对CYP的影响，旨在合理解释和预测临床上药物间相互作用和药物不良反应等。同时选择适当的药物作为探针来评价CYP的活性，为实现临床个体化给药提供科学依据。     

Endotoxin depresses hepatic cytochrome P450-mediated drug metabolism in women

Aims In men, the inflammatory response to intravenous endotoxin depresses apparent oral clearances of antipyrine, hexobarbitone, and theophylline. The aim of this study was to investigate whether there might be gender differences in the regulation of hepatic cytochromes P450.
Methods Experiments were carried out in seven healthy women volunteers (ages 19–51, median 22 years). Each woman received a cocktail of the three drugs on two occassions, once after a saline injection and again after endotoxin.
Results Endotoxin injections, but not saline, caused the expected physiologic responses of inflammation including fever and increases in circulating tumor necrosis factor-α, interleukin-6, and C-reactive protein. When compared with the saline control studies, endotoxin significantly decreased clearances of all probes: antipyrine, 31% (95%CI 21%–41%); hexobarbitone, 20% (95%CI 10–31%); and theophylline, 20% (95%CI 10%–30%). The decreases were comparable with those found in the men previously studied (35%, 27%, and 22%, respectively).
Conclusions These data show that endotoxin-induced inflammation decreases hepatic cytochrome P450-mediated metabolism of selected probe drugs in women as it does in men.     

Inhibition of cytochrome P450 2C8-mediated drug metabolism by the flavonoid diosmetin

The aim of this study was to assess the effects of diosmetin and hesperetin, two flavonoids present in various medicinal products, on CYP2C8 activity of human liver microsomes using paclitaxel oxidation to 6α-hydroxy-paclitaxel as a probe reaction. Diosmetin and hesperetin inhibited 6α-hydroxy-paclitaxel production in a concentration-dependent manner, diosmetin being about 16-fold more potent than hesperetin (mean IC(50) values 4.25 ± 0.02 and 68.5 ± 3.3 μM for diosmetin and hesperetin, respectively). Due to the low inhibitory potency of hesperetin, we characterized the mechanism of diosmetin-induced inhibition only. This flavonoid proved to be a reversible, dead-end, full inhibitor of CYP2C8, its mean inhibition constant (K(i)) being 3.13 ± 0.11 μM. Kinetic analysis showed that diosmetin caused mixed-type inhibition, since it significantly decreased the V(max) (maximum velocity) and increased the K(m) value (substrate concentration yielding 50% of V(max)) of the reaction. The results of kinetic analyses were consistent with those of molecular docking simulation, which showed that the putative binding site of diosmetin coincided with the CYP2C8 substrate binding site. The demonstration that diosmetin inhibits CYP2C8 at concentrations similar to those observed after in vivo administration (in the low micromolar range) is of potential clinical relevance, since it may cause pharmacokinetic interactions with co-administered drugs metabolized by this CYP.     

Porcine cytochrome P450 and metabolism

The pig and especially the minipig are becoming increasingly used as a test animal both in pharmacological and toxicological testing of new compounds. The minipig is used because of its size, it is easy to handle and less test substrate is required. When using an animal species for testing it is of importance to know if the test animal's posses the same abilities to metabolize drugs as humans. Some of the P450 enzymes have been characterized in the pig regarding substrate specificity, inhibition and regulation. The porcine enzymes CYP1A, CYP2A and CYP3A all metabolize the same test substrates as the human enzymes, whereas the enzymes CYP2B, CYP2D, and CYP2E in pig on the other hand seem to be different from the human enzymes concerning metabolism of the well know test substrates. Some of the porcine enzymes have been sequenced i.e. CYP1A, CYP2A, CYP2B, CYP2D, CYP2E and CYP3A and not surprisingly the porcine CYPs that metabolize the human test substrates are about 75% identical in cDNA sequences. What is needed is inhibitory antibodies against each of the porcine enzymes, in order to test whether a test compound is metabolized by one or the other enzyme. Until now chemical inhibitors have been used, but they are rarely 100% specific. Anti-human inhibitory antibodies have also been used, but they may not recognize the porcine enzyme and therefore will not inhibit the reaction. Antibodies for immunoblotting would also make it possible to estimate how much of the total P450 the individual enzymes comprise. From what is known about the porcine P450, it can be concluded that the pig seems to be a good test species if CYP1A, CYP2A or CYP3A are involved in the metabolism of the test compound, depending on the contribution of other enzymes in competing pathways.     

Characterization of cytochrome P450s mediating ipriflavone metabolism in human liver microsomes

Ipriflavone, a synthetic flavonoid for the prevention and treatment of osteoporosis, has been reported to be extensively metabolized in man to seven metabolites (M1-M7). This study was performed to characterize the human liver cytochrome P450s (CYP) responsible for the metabolism of ipriflavone. Hydroxylation at the beta-ring to M3, O-dealkylation to M1 and oxidation at isopropyl group to M4 and M5 are major pathways for ipriflavone metabolism in three different human liver microsome preparations. The specific CYPs responsible for ipriflavone oxidation to the active metabolites, M1, M3, M4 and M5 were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by expressed recombinant CYP enzymes. The inhibitory potencies of ipriflavone and its five metabolites, M1-M5 on seven clinically important CYPs were investigated in human liver microsomes. Our results demonstrate that CYP3A4 plays the major role in O-dealkylation of ipriflavone to M1 and CYP1A2 plays a dominant role in the formation of M3, M4 and M5. Ipriflavone and/or its five metabolites were found to inhibit potently the metabolism of CYPs 1A2, 2C8, 2C9 and 2C19 substrates.     

Determination of the human cytochrome P450s involved in the metabolism of 2n-propylquinoline

1 2n-Propylquinoline (2nPQ) is a newly developed drug for visceral antileishmaniasis and its activity has been previously evaluated in mice following oral administration. The study was carried out to investigate the kinetic formation of 2nPQ metabolites and to characterize the human liver CYP forms involved in its oxidative metabolism. 2. The inhibition of 2nPQ metabolite formation by specific substrates or inhibitors of CYP forms and correlation studies were performed in human liver microsomes. 2nPQ biotransformation was then studied in human lymphoblasts expressing specific CYPs and microsomal epoxide hydrolase. 3. Three major metabolites were produced by human liver microsomes and their structures were identified by ESI-LC/MS: dihydroxy-2n-propylquinoline, 3'-hydroxy-2n-propylquinoline and 1'-hydroxy-2n-propylquinoline. An intermediary metabolite, epoxy-2n-propylquinoline, formed by CYP was also biotransformed by microsomal epoxide hydrolase into dihydroxy-2n-propylquinoline. 4. 2nPQ oxidation follows Michaelis-Menten kinetics. In human liver microsomes, its metabolism was extremely inhibited by pilocarpine, coumarin and diethyldithiocarbamate. From a panel of 12 human liver microsome samples, the rate of 2nPQ oxidation was highly correlated with the activities of CYP2A6 and CYP2E1. Human lymphoblasts expressing specific CYPs showed the involvement of CYP2A6, CYP2E1 and CYP2C19. 5. The results indicate that 2nPQ metabolites are 3'- and 1'-hydroxylated by human liver microsomes and an epoxy-2n-propylquinoline is biotransformed into a dihydroxy-2n-propylquinoline by microsomal epoxide hydrolase.     

Automated definition of the enzymology of drug oxidation by the major human drug metabolizing cytochrome P450s.

A fully automated assay to determine the enzymology of drug oxidation by the major human hepatic cytochrome P450s (CYPs; CYP1A2, -2C9, -2C19, -2D6, and -3A4) coexpressed functionally in Escherichia coli with human NADPH-P450 reductase has been developed and validated. Ten prototypic substrates were chosen for which clearance was primarily CYP-dependent, and the activities of these five major CYPs were represented. A range of intrinsic clearance (CL(int)) values were obtained for substrates in both pooled human liver microsomes (HLM; 1-380 microl. min(-1)mg(-1)) and recombinant CYPs (0.03-7 microl. min(-1)pmol(-1)) and thus the percentage contribution of individual CYPs toward their oxidative metabolism could be estimated. All the assignments were consistent with the available literature data. Tolbutamide was metabolized by CYP2C9 (70%) and CYP2C19 (30%), diazepam by CYP2C19 (100%), ibuprofen by CYP2C9 (90%) and CYP2C19 (10%), and omeprazole by CYP2C19 (68%) and CYP3A4 (32%). Metoprolol and dextromethorphan were primarily CYP2D6 substrates and propranolol was metabolized by CYP2D6 (59%), CYP1A2 (26%), and CYP2C19 (15%). Diltiazem, testosterone, and verapamil were metabolized predominantly by CYP3A4. In addition, the metabolite profile for the CYP-dependent clearance of several markers determined by mass spectroscopy was as predicted from the literature. There was a good correlation between the sum of individual CYP CL(int) and HLM CL(int) (r(2) = 0.8, P <.001) for the substrates indicating that recombinant CYPs may be used to predict HLM CL(int) data. This report demonstrates that recombinant human CYPs may be useful as an approach for the prediction of the enzymology of human CYP metabolism early in the drug discovery process.     

Characterization of cytochrome P450s mediating ipriflavone metabolism in human liver microsomes

Ipriflavone, a synthetic flavonoid for the prevention and treatment of osteoporosis, has been reported to be extensively metabolized in man to seven metabolites (M1–M7). This study was performed to characterize the human liver cytochrome P450s (CYP) responsible for the metabolism of ipriflavone. Hydroxylation at the β-ring to M3, O-dealkylation to M1 and oxidation at isopropyl group to M4 and M5 are major pathways for ipriflavone metabolism in three different human liver microsome preparations. The specific CYPs responsible for ipriflavone oxidation to the active metabolites, M1, M3, M4 and M5 were identified using a combination of correlation analysis, immuno-inhibition, chemical inhibition in human liver microsomes and metabolism by expressed recombinant CYP enzymes. The inhibitory potencies of ipriflavone and its five metabolites, M1–M5 on seven clinically important CYPs were investigated in human liver microsomes. Our results demonstrate that CYP3A4 plays the major role in O-dealkylation of ipriflavone to M1 and CYP1A2 plays a dominant role in the formation of M3, M4 and M5. Ipriflavone and/or its five metabolites were found to inhibit potently the metabolism of CYPs 1A2, 2C8, 2C9 and 2C19 substrates.     

Multiple oxidants in cytochrome P450 catalyzed reactions: implications for drug metabolism

The activation of molecular oxygen by Cytochromes P450 to the ultimate mono-oxygen oxidant species involves three distinct dioxygen species coordinated to the heme iron. These intermediates have different chemical properties, and have recently been proposed to participate in some Cytochrome P450-catalyzed oxidation reactions. This article reviews the extent of our current knowledge on the roles proposed for the heme- peroxo, hydroperoxo, and superoxo complexes in various reactions. The extent to which such species contribute to the breadth of reactions catalyzed by Cytochrome P450 has yet to be defined, and more definitive experiments are needed to establish such species in the reactions they are proposed to effect.     

Monoclonal antibodies and multifunctional cytochrome P450: drug metabolism as paradigm

Monoclonal antibodies are reagents par excellence for analyzing the role of individual cytochrome P450 isoforms in multifunctional biological activities catalyzed by cytochrome P450 enzymes. The precision and utility of the monoclonal antibodies have heretofore been applied primarily to studies of human drug metabolism. The unique and precise specificity and high inhibitory activity toward individual cytochrome P450s make the monoclonal antibodies extraordinary tools for identifying and quantifying the role of each P450 isoform in the metabolism of a drug or nondrug xenobiotic. The monoclonal antibodies identify drugs metabolized by individual, several, or polymorphic P450s. A comprehensive collection of monoclonal antibodies has been isolated to human P450s: 1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C family, 2C19, 2D6, 2E1, 3A4/5, and 2J2. The monoclonal antibodies can also be used for identifying drugs and/or metabolites useful as markers for in vivo phenotyping. Clinical identification of a patient's phenotype, coupled with precise knowledge of a drug's metabolism, should lead to a reduction of adverse drug reactions and improved drug therapeutics, thereby promoting advances in drug discovery.     

Prediction of drug metabolism: the case of cytochrome P450 2D6

Cytochromes P450 (Cyt P450s) constitute the most important biotransformation enzymes involved in the biotransformation of drugs and other xenobiotics. Because drug metabolism by Cyt P450s plays such an important role in the disposition and in the pharmacological and toxicological effects of drugs, early consideration of ADME-properties is increasingly seen as essential for the discovery and the development of new drugs and drug candidates. The primary aim of this paper is to present various computational approaches used to rationalize and predict the activity and substrate selectivity of Cyt P450s, as well as the possibilities and limitations of these approaches, now and in the future. Attention is also paid to the experimental validation of these approaches by using high-throughput screening (HTS) of affinities to drug-drug interactions at the level of Cyt P450-isoenzymes. Since human Cyt P450 2D6 is one of the most important drug metabolizing enzymes and since in this regard much pioneering work has been done with this Cyt P450, Cyt P450 2D6 is chosen as a model for this discussion. Apart from early mechanism-based ab initio calculations on substrates of Cyt P450 2D6, pharmacophore modeling of ligands (i.e. both substrates and inhibitors) of Cyt P450 2D6 and protein homology modeling have been used successfully for the rationalisation and prediction of metabolite formation by this Cyt P450 isoenzyme. Significant protein structure-related species differences have been reported recently. It is concluded that not one computational approach is capable of rationalizing and reliably predicting metabolite formation by Cyt P450 2D6, but that it is rather the combination of the various complimentary approaches. It is moreover concluded, that experimental validation of the computational models and predictions is often still lacking. With the advent of novel, easily and well applicable in vitro based high throughput assays for ligand binding and turnover this limitation could be overcome soon, however. When effective links with other new and recent developments, such as bioinformatics, neural network computing, genomics and proteomics can be created, in silico rationalisation and prediction of drug metabolism by Cyt P450s is likely to become one of the key technologies in early drug discovery and development processes.     

In vitro metabolism of genistein and tangeretin by human and murine cytochrome P450s

Recombinant cytochrome P450 (CYP) 1A2, 3A4, 2C9 or 2D6 enzymes obtained from Escherichia coli and human liver microsomes samples were used to investigate the ability of human CYP enzymes to metabolize the two dietary flavonoids, genistein and tangeretin. Analysis of the metabolic profile from incubations with genistein and human liver microsomes revealed the production of five different metabolites, of which three were obtained in sufficient amounts to allow a more detailed elucidation of the structure. One of these metabolites was identified as orobol, the 3'-hydroxylated metabolite of genistein. The remaining two metabolites were also hydroxylated metabolites as evidenced by LC/MS. Orobol was the only metabolite formed after incubation with CYP1A2. The two major product peaks after incubation of tangeretin with human microsomes were identical with 4'-hydroxy-5,6,7,8-tetramethoxyflavone and 5,6-dihydroxy-4',7,8-trimethoxyflavone, previously identified in rat urine in our laboratory. By comparison with UV spectra and LC/MS fragmentation patterns of previously obtained standards, the remaining metabolites eluting after 14, 17 and 20 min. were found to be demethylated at the 4',7-, 4',6-positions or hydroxylated at the 3'- and demethylated at the 4'-positions, respectively. Metabolism of tangeretin by recombinant CYP1A2, 3A4, 2D6 and 2C9 resulted in metabolic profiles that qualitatively were identical to those observed in the human microsomes. Inclusion of the CYP1A2 inhibitor fluvoxamine in the incubation mixture with human liver microsomes resulted in potent inhibition of tangeretin and genistein metabolism. Other isozymes-selective CYP inhibitors had only minor effects on tangeretin or genistein metabolism. Overall the presented observations suggest major involvement of CYP1A2 in the hepatic metabolism of these two flavonoids.     

Roles of human cytochrome P450 enzymes involved in drug metabolism and toxicological studies

Multiple forms of cytochrome P450 (P450 or CYP) enzymes play important roles in the oxidation of structurally diverse xenobiotics and endobiotics. Interindividual variations in the level and activity of P450 enzymes were investigated in the human liver microsomes. Although the total P450 content was higher in Caucasian samples than in Japanese ones, the relative levels (percentage of total P450) of individual forms of P450 determined immunochemically were not very different. CYP3A (about 30% of total P450) and CYP2C (about 20%) enzymes were major forms. Different P450 enzymes in the human liver play major roles in a variety of drug oxidations and the hepatic contents of these P450 forms could be affective to determine which P450 enzymes play major roles in drug metabolism in individual humans. Recently recombinant P450 enzymes from different sources, e.g., microsomes of human lymphoblastoid cells, of yeast, and insect cells infected with baculovirus systems, and Escherichia coli membranes containing coexpressed P450 and reductase, have been widely used for drug metabolism research. However, the marker activities or kinetic parameters of human P450 enzymes reported are not always similar. Cytochrome b5 can enhance the activities of recombinant P450 systems in some cases using different mechanisms. These differences in activities may be a critical factor for understanding the roles of human P450 enzymes involved in drug metabolism. This review provides useful information for the study of drug biotransformation in humans and for the basis of drug toxicities and carcinogenesis.     

Cytochrome P450s and other enzymes in drug metabolism and toxicity

The cytochrome P450 (P450) enzymes are the major catalysts involved in the metabolism of drugs. Bioavailability and toxicity are 2 of the most common barriers in drug development today, and P450 and the conjugation enzymes can influence these effects. The toxicity of drugs can be considered in 5 contexts: on-target toxicity, hypersensitivity and immunological reactions, off-target pharmacology, bioactivation to reactive intermediates, and idiosyncratic drug reactions. The chemistry of bioactivation is reasonably well understood, but the mechanisms underlying biological responses are not. In the article we consider what fraction of drug toxicity actually involves metabolism, and we examine how species and human interindividual variations affect pharmacokinetics and toxicity.