Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.14.13.97 (CYP3A4)
 6,365 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Stereoselective metabolism of cibenzoline succinate, an oral antiarrhythmic drug, was investigated on hepatic microsomes from humans and rats and microsomes from cells expressing human cytochrome P450s (CYPs). Four main metabolites, M1 (p-hydroxycibenzoline), M2 (4,5-dehydrocibenzoline), and unknown metabolites M3 and M4, were formed by human and rat liver microsomes. The intrinsic clearance (CL(int)) of the M1 formation from R(+)-cibenzoline was 23-fold greater than that of S(-)-cibenzoline in human liver microsomes, whereas the R(+)/S(-)-enantiomer ratio of CL(int) for M2, M3, and M4 formation was 0.39 to 0.83. The total CL(int) for the formation of the four main metabolites from S(-)- and R(+)-cibenzoline was 1.47 and 1.64 microl/min/mg, respectively, suggesting that the total CL(int) in R(+)-enantiomer was slightly greater than that in S(-)-enantiomer in human liver microsomes. The M1 formation from R(+)-cibenzoline was highly correlated with bufuralol 1'-hydroxylation and CYP2D6 content and was inhibited by quinidine, a potent inhibitor of CYP2D6. Additionally, only microsomes containing recombinant CYP2D6 were capable of M1 formation. These results suggest that the M1 formation from R(+)-cibenzoline was catalyzed by CYP2D6. The formation of M2, M3, and M4 from S(-)- and R(+)-cibenzoline was highly correlated with testosterone 6beta-hydroxylation and CYP3A4 content. Ketoconazole, which is a potent inhibitor of CYP3A4/5, had a strong inhibitory effect on their formation, and the M4 formation from R(+)-cibenzoline was inhibited by quinidine by 45%. The formation of M2 was also inhibited by quinidine by 46 to 52% at lower cibenzoline enantiomers (5 microM), whereas the inhibition by quinidine was not observed at a higher substrate concentration (100 microM). In male rat liver microsomes, ketoconazole and quinidine inhibited the formation of the main metabolites, M1 and M3, >74% and 44 to 59%, respectively. These results provide evidence that CYP3A and CYP2D play a major role in the stereoselective metabolism of cibenzoline in humans and male rats.
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PMID:Stereoselective metabolism of cibenzoline, an antiarrhythmic drug, by human and rat liver microsomes: possible involvement of CYP2D and CYP3A. 1095 Aug 60

The purpose of the study was to elucidate human intestinal cytochrome P450 isoform(s) involved in the metabolism of an antihistamine, ebastine, having two major pathways of hydroxylation and N-dealkylation. The ebastine dealkylase in human intestinal microsomes was CYP3A4, based on the inhibition studies with antibodies against CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, and CYP3A isoforms and their selective inhibitors. However, ebastine hydroxylase could not be identified. We then examined the inhibitory effects of anti-CYP4F antibody and 17-octadecynoic acid, an inhibitor of the CYP4 family, on ebastine hydroxylation in intestinal microsomes, since CYP4F was recently found to be the predominant ebastine hydroxylase in monkey intestine; and a novel CYP4F isoform (CYP4F12), also capable of hydroxylating ebastine, was found to exist in human intestine. However, the inhibitory effects were only partial (about 20%) and thus it was thought that, although human CYP4F was involved in ebastine hydroxylation, another predominant enzyme exists. Further screening showed that the hydroxylation was inhibited by arachidonic acid. CYP2J2 was selected as a candidate expressed in the intestine and closely related to arachidonic acid metabolism. The catalytic activity of recombinant CYP2J2 was much higher than that of CYP4F12. Anti-CYP2J antibody inhibited the hydroxylation to about 70% in human intestinal microsomes. These results demonstrate that CYP2J2 is the predominant ebastine hydroxylase in human intestinal microsomes. Thus, the present paper for the first time indicates that, in human intestinal microsomes, both CYP2J and CYP4F subfamilies not only metabolize endogenous substrates but also are involved in the drug metabolism.
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PMID:Involvement of CYP2J2 and CYP4F12 in the metabolism of ebastine in human intestinal microsomes. 1175 29

Oxidative metabolism of carbamazepine results in covalent binding of its reactive metabolite to liver microsomal proteins, which has been proposed as an important event in pathogenesis of the hypersensitivity reactions to this drug. Although the proposed reactive metabolites are produced by cytochrome P450 enzymes (P450 or CYP), the impact of the formation of unstable metabolites on the enzyme itself has not been elucidated. The present study examines the alteration of P450 enzyme activities during the metabolism of carbamazepine. Liver microsomes from rats and humans were preincubated with carbamazepine in the presence of NADPH, and subsequently assayed for monooxygenase activities representing several P450s. No evidence was obtained for inactivation of CYP2C11, CYP3A, CYP1A1/2 or CYP2B1/2 in rat liver microsomes during the carbamazepine metabolism, whereas the CYP2D enzyme was inactivated in a manner related to the preincubation time. Interestingly, under the same protocol human liver microsomes did not exhibit inactivation of CYP2D6, as well as there being no CYP2C8, CYP2C9 or CYP3A4 inactivation, whereas CYP1A2 was inactivated. Reduced glutathione could not protect against the observed inactivation of the P450s. These results suggest that CYP2D enzyme(s) in rats and CYP1A2 in humans biotransform carbamazepine into reactive metabolites, resulting in inactivation of the enzyme themselves, and raise the possibility that the P450 isoforms participate in toxicity induced by the drug in both animal species.
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PMID:Differential selectivity in carbamazepine-induced inactivation of cytochrome P450 enzymes in rat and human liver. 1176 Aug 14

1-(3-Trifluoromethylphenyl)piperazine (TFMPP) is a designer drug with serotonergic properties. Previous studies with male Wistar rats (WI) had shown, that TFMPP was metabolized mainly by aromatic hydroxylation. In the current study, it was examined whether this reaction may be catalyzed by cytochrome P450 (CYP)2D6 by comparing TFMPP vs. hydroxy TFMPP ratios in urine from female Dark Agouti rats, a model of the human CYP2D6 poor metabolizer phenotype (PM), male Dark Agouti rats, an intermediate model, and WI, a model of the human CYP2D6 extensive metabolizer phenotype. Furthermore, the human hepatic CYPs involved in TFMPP hydroxylation were identified using cDNA-expressed CYPs and human liver microsomes. Finally, TFMPP plasma levels in the above mentioned rats were compared. The urine studies suggested that TFMPP hydroxylation might be catalyzed by CYP2D6 in humans. Studies using human CYPs showed that CYP1A2, CYP2D6 and CYP3A4 catalyzed TFMPP hydroxylation, with CYP2D6 being the most important enzyme accounting for about 81% of the net intrinsic clearance, calculated using the relative activity factor approach. The hydroxylation was significantly inhibited by quinidine (77%) and metabolite formation in poor metabolizer genotype human liver microsomes was significantly lower (63%) compared to pooled human liver microsomes. Analysis of the plasma samples showed that female Dark Agouti rats exhibited significantly higher TFMPP plasma levels compared to those of male Dark Agouti rats and WI. Furthermore, pretreatment of WI with the CYP2D inhibitor quinine resulted in significantly higher TFMPP plasma levels. In conclusion, the presented data give hints for possible differences in pharmacokinetics in human PM and human CYP2D6 extensive metabolizer phenotype subjects relevant for risk assessment.
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PMID:Cytochrome P450 dependent metabolism of the new designer drug 1-(3-trifluoromethylphenyl)piperazine (TFMPP). In vivo studies in Wistar and Dark Agouti rats as well as in vitro studies in human liver microsomes. 1469 36

Fenproporex (FP) is known to be N-dealkylated to R(-)-amphetamine (AM) and S(+)-amphetamine. Involvement of the polymorphic cytochrome P450 (CYP) isoform CYP2D6 in metabolism of such amphetamine precursors is discussed controversially in literature. In this study, the human hepatic CYPs involved in FP dealkylation were identified using recombinant CYPs and human liver microsomes (HLM). These studies revealed that not only CYP2D6 but also CYP1A2, CYP2B6 and CYP3A4 catalyzed this metabolic reaction for both enantiomers with slight preference for the S(+)-enantiomer. Formation of amphetamine was not significantly changed by quinidine and was not different in poor metabolizer HLM compared to pooled HLM. As in vivo experiments, blood levels of R(-)-amphetamine and S(+)-amphetamine formed after administration of FP were determined in female Dark Agouti rats (fDA), a model of the human CYP2D6 poor metabolizer phenotype (PM), male Dark Agouti rats (mDA), an intermediate model, and in male Wistar rats (WI), a model of the human CYP2D6 extensive metabolizer phenotype. Analysis of the plasma samples showed that fDA exhibited significantly higher plasma levels of both amphetamine enantiomers compared to those of WI. Corresponding plasma levels in mDA were between those in fDA and WI. Furthermore, pretreatment of WI with the CYP2D inhibitor quinine resulted in significantly higher amphetamine plasma levels, which did not significantly differ from those in fDA. The in vivo studies suggested that CYP2D6 is not crucial to the N-dealkylation but to another metabolic step, most probably to the ring hydroxylation. Further studies are necessary for elucidating the role of CYP2D6 in FP hydroxylation.
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PMID:Fenproporex N-dealkylation to amphetamine--enantioselective in vitro studies in human liver microsomes as well as enantioselective in vivo studies in Wistar and Dark Agouti rats. 1529 57

Metabolism of the prototype human CYP2D6 substrates debrisoquine and bufuralol proceeds at a much slower rate in mice; therefore, the mouse has been proposed as an animal model for the human CYP2D6 genetic deficiency. To interpret the molecular mechanism of this deficiency, a cDNA belonging to the CYP2D gene subfamily (Cyp2d22) has been cloned and sequenced from a mouse mammary tumor-derived cell line. In the current study, Cyp2d22 enzyme was overexpressed and purified from insect cells using a baculovirus-mediated system. The activity of this purified enzyme was directly compared with purified human CYP2D6 toward codeine, dextromethorphan, and methadone as substrates. Purified Cyp2d22 was found to catalyze the O-demethylation of dextromethorphan with significantly higher K(m) values (250 microM) than that (4.2 microM) exhibited by purified human CYP2D6. The K(m) for dextromethorphan N-demethylation by Cyp2d22 was found to be 418 microM, much lower than that observed with human CYP2D6 and near the K(m) for dextromethorphan N-demethylation catalyzed by CYP3A4. CYP2D6 catalyzed codeine O-demethylation, whereas Cyp2d22 and CYP3A4 mediated codeine N-demethylation. Furthermore, methadone, a known CYP3A4 substrate and CYP2D6 inhibitor, was N-demethylated by Cyp2d22 with a K(m) of 517 microM and V(max) of 4.9 pmol/pmol/min. Quinidine and ketoconazole, potent inhibitors to CYP2D6 and CYP3A4, respectively, did not show strong inhibition toward Cyp2d22-mediated dextromethorphan O- or N-demethylation. These results suggest that mouse Cyp2d22 has its own substrate specificity beyond CYP2D6-like-deficient activity.
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PMID:Expression, purification, and characterization of mouse CYP2d22. 1659 12

The increasing number of transgenic or gene knockout mouse models generated for use in drug metabolism studies has meant that a greater understanding of the function and substrate specificities of murine cytochromes P450 (P450s) has become essential, particularly with the recent advances in "humanized" mouse models. In this study, we have heterologously expressed nine murine P450s--Cyp1a1, Cyp1a2, Cyp1b1, Cyp2a4, Cyp2b20, Cyp2c29, Cyp2d22, Cyp2e1, and Cyp3a11--individually with human P450 oxidoreductase to generate functional monooxygenase systems in Escherichia coli. We have identified a suitable fluorogenic probe for each P450 and determined the apparent kinetic parameters. These probes have enabled the screening of a panel of 31 test compounds classified as "drugs," "natural compounds," "endogenous compounds," and "pesticides" by measurement of IC(50), thus allowing the comparison of binding affinities. Human P450s CYP2C9, CYP2D6, and CYP3A4 were also included in the study to enable direct comparisons to be made with the mouse enzymes. Although there were general similarities between human and mouse P450s, perhaps the most significant finding in this study was the observation that, despite 77% amino acid identity, Cyp2d22 and CYP2D6 were remarkably dissimilar in a range of enzymatic properties, with potentially serious implications for pharmacokinetic studies using CYP2D substrates. The data presented in this study provide a solid foundation with which to assess the degree of similarity (or difference) between mouse and human P450s involved in xenobiotic metabolism and can be used as a basis for further studies.
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PMID:Functional expression and comparative characterization of nine murine cytochromes P450 by fluorescent inhibition screening. 1842 Jul 80

Cytochrome P450s (P450 or CYPs) comprise a superfamily of enzymes that catalyze the oxidation of a wide variety of xenobiotic chemicals including drugs and environmental carcinogens. Recent studies have demonstrated that endogenous chemicals are also oxidized by human P450s which mainly metabolize xenobiotics. In this review, we summarize the expected physiological significance of the biotransfornation as well as Michaelis-Menten constants (Km), maximal velocities (Vmax), Vmax/Km (intrinsic clearance) values, and/or metabolic activities for 33 endogenous substrates, including (1) arachidonic acid and fatty acids, (2) steroid hormones, such as testosterone, progesterone, and allopregnanolone, (3) amines, such as tyramine, and (4) lipid-soluble vitamins, such as retinol and vitamin D3 analogues, mediated human P450 isoforms consisting of so-called drug-metabolizing enzymes for the purpose of predicting the key enzyme(s) in vivo. Arachidonic acid is metabolized via the epoxidation and omega-hydroxylation to many biologically active eicosanoids such as epoxyeicosatrienoic acids and hydroxyeicosatetraenoic acids by multiple P450 isoforms including CYP2C, CYP2E1 and CYP4A11. CYP2D in the brain may be involved in the metabolism of neuronal amines and steroids and in the regulation of the central nervous system. CYP1A2 and CYP3A4 appear to be the major P450 enzymes catalyzing the oxidation of all-trans-retinol to all-trans-retinoic acid in human liver, and CYP3A4 is one of the vitamin D3 25-hydroxylases. Although the significance of the contribution is still unknown in detail, the collective findings provide fundamental and useful information for the biological contribution of the metabolism of endogenous substances by drug-metabolizing enzymes, P450s. In addition, genetic polymorphism of these drug-metabolizing P450s may affect the metabolism of the endobiotics. Forthermore, these findings imply that xenobiotic oxidations by P450 enzymes are affected by endobiotic molecules and that the endobiotic-xenobiotic interactions as well as drug-drug interactions or drug-food/beverage interactions may be of great importance when understanding the basis for pharmacological and toxicological actions of a number of xenobiotic chemicals.
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PMID:Oxidation of endobiotics mediated by xenobiotic-metabolizing forms of human cytochrome. 1959 5

Characteristics of twelve cytochromes P450 (CYPs) from cynomolgus monkeys were compared with those of human CYPs that play an important role in drug metabolism. Eleven members of CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, and CYP3A subfamilies from cynomolgus monkeys exhibited a high degree of homologies (more than 90%) in cDNA and amino acid sequences with corresponding human CYPs, and catalysed typical reactions of corresponding human CYPs. One member of the cynomolgus monkey CYP2C subfamily, CYP2C76, exhibited a lower homology (around 70%) in amino acid sequences with other cynomolgus monkey and human CYP2C subfamilies. CYP2C76 catalysed typical CYP2C substrates with low activities, and has not been found in humans. CYPs identified in cynomolgus monkeys were similar to CYP1A1, CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4, and CYP3A5 in humans. These results indicate that cynomolgus monkeys express CYPs similar to human CYPs that are important in drug metabolism.
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PMID:Cynomolgus monkey CYPs: a comparison with human CYPs. 1962

The cytochrome P450 (P450) family of enzymes is a major player in the metabolism of therapeutic drugs available on the market, and the development of novel drugs has to take into account these enzymes in the fate of new drugs. Testing the pharmacokinetic behavior of new drugs in animals is a common part of the drug development process. Pigs are increasingly used for this purpose because of their similarity of enzymatic pattern to humans. In this study, adult Suffolk White pig liver microsomal samples were analyzed using mass-spectrometry-based techniques to identify and relatively quantify the porcine hepatic P450 enzymes. The total corrected microsomal protein content (milligrams of protein per gram of liver tissue) was estimated at 32.6 and 36.2 mg/g liver tissue in two samples, and the main identified liver P450 subfamilies were CYP1A, CYP2A, CYP2C, CYP2D, CYP2E, and CYP3A. Label-free quantification was performed using the exponentially modified protein abundance index, and the highest abundance enzymes were CYP2A19 at 34% and CYP2D25 at 26% of the total identified drug-metabolizing P450 enzymes. The highest abundance subfamilies were CYP2A (34%), CYP2C (16%), CYP2D (26%), and CYP3A (14%). Moreover, primary sequence alignment was used to identify human homologs of the identified porcine P450s. Porcine CYP1A2 and CYP2E1 were shown to be equivalent to human CYP1A2 and CYP2E1, respectively. Porcine CYP2A19 has the highest sequence homology to human CYP2A6 and CYP2A13, and pig CYP2C33v4 and CYP2C49 are the porcine equivalent of human CYP2C9 and CYP2C18, respectively. Both identified pig CYP3A enzymes (CYP3A29 and CYP39) were highly homologous to CYP3A4/5.
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PMID:Cytochrome P450 Pig liver pie: determination of individual cytochrome P450 isoform contents in microsomes from two pig livers using liquid chromatography in conjunction with mass spectrometry [corrected]. 2179 67


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