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)

Human first-trimester placentas were screened for the expression of xenobiotic-metabolizing cytochrome P450 (CYP) genes. mRNAs of CYP1A1, CYP1A2, CYP2C, CYP2D6, CYP2E1, CYP2F1, CYP3A4, CYP3A5, CYP3A7, and CYP4B1 were identified by reverse transcriptase-polymearse chain reaction (RT-PCR) in at least some of the six placental samples studied. CYP2A and CYP2B message were absent in all samples. The level of all of these CYP mRNAs was lower compared to the corresponding levels in liver or lung. the catalytic activity marker (7-ethoxyresorufin O-deethylase) was inducible in the placentas by maternal cigarette smoking. Thus, the regulatory system of placental CYP1A1, mediated by the Ah-receptor, appears to be developed as early as the first trimester of pregnancy. Three immunoreactive bands from placental microsomes were detected by an antihuman CYP3A4 antibody, but no functional activity of CYP3A enzymes could be detected. These results show that placental tissue during the first trimester of pregnancy has the potential of expressing several CYP genes, and forms a basis for subsequent analysis of these forms at the protein and functional level.
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PMID:Detection of cytochrome P450 gene expression in human placenta in first trimester of pregnancy. 869 64

The calcium channel blocker verapamil [2,8-bis-(3,4-dimethoxyphenyl)-6-methyl-2-isopropyl-6-azaoctanitrile+ ++] undergoes extensive biotransformation in man. We have previously demonstrated cytochrome P450 (CYP) 3A4 and 1A2 to be the enzymes responsible for verapamil N-dealkylation (formation of D-617 [2-(3,4-dimethoxyphenyl)-5-methylamino-2-isopropylvaleronitrile], and verapamil N-demethylation (formation of norverapamil [2,8-bis-(3,4-dimethoxyphenyl)-2-isopropyl-6-azaoctanitrile]), while there was no involvement of CYP3A4 and CYP1A2 in the third initial metabolic step of verapamil, which is verapamil O-demethylation. This pathway yields formation of D-703 [2-(4-hydroxy-3-methoxyphenyl)-8-(3,4-dimethoxyphenyl)-6-methyl-2-isopro pyl-6-azaoctanitrile] and D-702 [2-(3,4-dimethoxyphenyl)-8-(4-hydroxy-3-methoxyphenyl)-6-methyl-2-isopro pyl-6-azaoctanitrile]. The enzymes catalyzing verapamil O-demethylation have not been characterized so far. We have therefore identified and characterized the enzymes involved in verapamil O-demethylation in humans by using the following in vitro approaches: (I) characterization of O-demethylation kinetics in the presence of the microsomal fraction of human liver, (II) inhibition of verapamil O-demethylation by specific antibodies and selective inhibitors and (III) investigation of metabolite formation in microsomes obtained from yeast strain Saccharomyces cerevisiae W(R), that was genetically engineered for stable expression of human CYP2C8, 2C9 and 2C18. In human liver microsomes (n=4), the intrinsic clearance (CLint), as derived from the ratio of Vmax/Km, was significantly higher for O-demethylation to D-703 compared to formation of D-702 following incubation with racemic verapamil (13.9 +/- 1.0 vs 2.4 +/- 0.6 ml*min-1*g-1, mean+/-SD; p<0.05), S-verapamil (16.8 +/- 3.3 vs 2.2 +/- 1.2 ml* min-1*g-1, p<0.05) and R-verapamil (12.1 +/- 2.9 vs 3.6 +/- 1.3 ml*min-1*g-1; p<0.05), thus indicating regioselectivity of verapamil O-demethylation process. The CLint of D-703 formation in human liver microsomes showed a modest but significant degree of stereoselectivity (p<0.05) with a S/R-ratio of 1.41 +/- 0.17. Anti-LKM2 (anti-liver/kidney microsome) autoantibodies (which inhibit CYP2C9 and 2C19) and sulfaphenazole (a specific CYP2C9 inhibitor) reduced the maximum rate of formation of D-703 by 81.5 +/- 4.5% and 45%, that of D-702 by 52.7 +/- 7.5% and 72.5%, respectively. Both D-703 and D-702 were formed by stably expressed CYP2C9 and CYP2C18, whereas incubation with CYP2C8 selectively yielded D-703. In conclusion, our results show that enzymes of the CYP2C subfamily are mainly involved in verapamil O-demethylation. Verapamil therefore has the potential to interact with other drugs which inhibit or induce these enzymes.
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PMID:Cytochromes of the P450 2C subfamily are the major enzymes involved in the O-demethylation of verapamil in humans. 875 Sep 25

Codeine is metabolized by glucuronidation, by O-demethylation to morphine, and by N-demethylation to norcodeine. The enzyme responsible for the O-demethylation to morphine has been identified as cytochrome P4502D6 (CYP2D6). The purpose of the present study was to identify the specific P450 enzyme responsible for codeine N-demethylation. Microsomal preparations (250 pmol of P450) obtained from 12 human liver donors were incubated with 20 microM codeine and analyzed for norcodeine formation. Codeine N-demethylation activity was linearly correlated with nifedipine oxidation activity (r = 0.90, p < 0.001), a marker of CYP3A4, but not with codeine O-demethylation, a marker of CYP2D6. Preincubation with troleandomycin (50 microM), or gestodene (50 microM) inhibitors of CYP3A4, decreased the rate of production of norcodeine by 60 and 45% compared to control values, respectively. Similarly, ketoconazole (10 microM) and erythromycin (10 microM) inhibited codeine N-demethylation by 75 and 35%, respectively. In contrast, the presence of quinidine, sulfaphenazole, or diethyldithiocarbamate in the incubation mixture had no effect on norcodeine formation. Preincubation with antibodies raised to CYP3A4 (5 mg lgG/nmol P450) caused 96% inhibition of norcodeine production, whereas preimmune IgG or antibodies raised to CYP2A6 and CYP2C had no effect. Additionally, significant norcodeine production was observed with purified CYP3A4 derived from human liver microsomes. In conclusion, codeine N-demethylation activity cosegregates with CYP3A4 activity. Coadministration of codeine with selective inhibitors of CYP3A4 may result in increased morphine production and enhanced pharmacodynamic effects due to shunting down the CYP2D6 pathway.
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PMID:Microsomal codeine N-demethylation: cosegregation with cytochrome P4503A4 activity. 881 73

The metabolic dealkylation of nine nitrosodialkylamines, including five symmetrical (nitrosodimethylamine, nitrosodiethylamine, nitrosodipropylamine, nitrosodibutylamine and nitrosodiamylamine) and four asymmetrical nitrosodialkylamines (nitrosomethylethylamine, nitrosomethylpropylamine, nitrosomethylbutylamine and nitrosomethylamylamine), was investigated in 14 samples of human liver microsomes. All these nitrosodialkylamines were dealkytated to aldehydes that were separated by reversed phase HPLC and UV detected as dinitrophenylhydrazones. As the length of the alkyl chain increased from methyl to pentyl, dealkylation of symmetrical nitrosodialkylamines became less efficiently catalyzed by cytochrome P450. Conversely, oxidation of the methyl moiety of asymmetrical nitrosomethylalkylamines increased with the size of the alkyl moiety, while dealkylation of the longer alkyl group decreased. N-Dealkylase activities were significantly correlated with P450 activities measured in human liver microsomes. These catalytic activities involve CYP2A6 (coumarin 7-hydroxylation), CYP2C (mephenytoin 4-hydroxylation and tolbutamide hydroxylation), CYP2D6 (dextromethorphan O-demethylation), CYP2E1 (chlorzoxazone and p-nitrophenol hydroxylation) and CYP3A4 (nifedipine oxidation). By using 10 heterologously expressed P450s, it was shown that nitrosodimethylamine was mainly demethylated by CYP2E1. However, such enzyme specificity was lost with increasing size of the alkyl group. Therefore, the chain length of the alkyl group of nitrosodialkylamines determined the P450 involved in its oxidation. All these results emphasize that the catalytic site of P450 2EI has a geometric configuration such that only small molecules like nitrosodimethylamine fit favorably within the putative active site of the enzyme. Furthermore, there is good evidence that P450s other than P450 2E1, such as P450 2A6, 2C8/2C9/2C19 and 3A4, are involved in the metabolism of nitrosodialkylamines bearing bulky alkyl chains.
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PMID:Cytochrome P450 metabolic dealkylation of nine N-nitrosodialkylamines by human liver microsomes. 882 31

Cytochrome P450 (CYP) activity in human liver microsomes was measured after the O-demethylation of [O-methyl 14C]naproxen (NAPase). The formation of [14C]formaldehyde in the presence of microsomes was described by an apparent KM(1) and Vmax(1) of 0.16 +/- 0.09 mM and 4.1 +/- 2.8 nmol HCHO/min/mg protein (mean +/- SD; N = 5 different livers), respectively, over a relatively wide naproxen concentration (5-1600 microM) range. With two sets of microsomes, a high KM NAPase component was also detected (mean KM2 = 2.7 mM; mean Vmax2 = 23 nmol HCHO/min/mg). As expected, the O-demethylation of naproxen (0.4 mM) was found to be highly correlated with tolbutamide hydroxylase (TOLase) activity in a panel of human liver microsomes (r = 0.82, p < 0.01, N = 10) and was inhibited (32-54%) by a number of purported CYP2C (CYP2C9/10) inhibitors/substrates (e.g. phenytoin, sulfaphenazole, tienilic acid, tolbutamide, and ibuprofen). Only marginal decreases in activity (< or = 14%) were observed with inhibitors of other CYP proteins. However, NAPase activity was also found to correlate significantly with CYP1A2 [ethoxyresorufin O-deethylase (ERODase)] activity (r = 0.68, p < 0.05, n = 11). In addition, the reaction was inhibited (36-75%, N = 11 different livers) by furafylline (FURA), a CYP1A2-selective mechanism-based inhibitor. The effect of FURA and tienilic acid was additive, leading to 90 +/- 4.2% inhibition of NAPase activity. FURA-inhibited activity also significantly correlated with ERODase activity (r = 0.78, p < 0.01, N = 11), whereas tienilic acid-inhibited activity correlated with TOLase activity (r = 0.63, p < 0.05, N = 10). In human B-lymphoblast microsomes, cDNA-expressed CYP1A2 exhibited relatively high activity (KM = 0.25 mM; Vmax = 24 nmol/min/nmol CYP), when compared with CYP2A6, CYP2D6, CYP2E1, CYP2B6, and CYP3A4. The kinetic parameters for reconstituted purified human liver microsomal CYP2C9 (KM = 0.43 mM; Vmax = 11 nmol/min/nmol CYP) were comparable with those of CYP1A2. It is concluded that the O-demethylation of naproxen (< or = 0.4 mM) is catalyzed by CYP2C subfamily members (CYP2C9/10) and CYP1A2 in human liver microsomes.
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PMID:[O-methyl 14C]naproxen O-demethylase activity in human liver microsomes: evidence for the involvement of cytochrome P4501A2 and P4502C9/10. 882

Cytochrome P-450 (CYP) catalyzes phase I metabolic reactions of psychotropic drugs. The main isoenzymes responsible for their biotransformation are CYP1A2, CYP2D6, CYP3A4 and these of the subfamily CYP2C. The majority of metabolites of psychotropic drugs are biologically active. Some of them retain pharmacological properties of parent compounds (eg. selective serotonin reuptake inhibitors, risperidone, carbamazepine, benzodiazepines), but others display quite different (eg. amitriptyline, buspirone) or even opposite (trazodone) profiles. They are present in vivo in concentrations high enough to contribute to pharmacological and clinical effects of the administrated drugs. Active metabolites of psychotropics are also characterized by pharmacokinetic properties different from their parent compounds, e.g. half-life time, plasma protein binding, blood-brain-barrier penetration, the cerebrospinal fluid (CSF) protein binding and tissue binding. These properties lead, in turn, to differences in the brain/plasma and the CSF/plasma concentration ratios between a drug and its metabolites. Therefore studies relating a pharmacological or therapeutic response of psychotropic drug to its plasma concentrations should not disregard the presence of its active metabolites, considering their distinct pharmacological and pharmacokinetic properties. With regard to a low therapeutic index of psychotropics, interindividual differences in the rate of their metabolism, genetic polymorphism of their main metabolic pathways and metabolic interactions in clinical drug combinations, the phenotyping of patients at the beginning of therapy and a control of drug concentrations (and its active metabolites) at a steady state and during coadministration of another drug, may increase the efficiency and safety of the pharmacotherapy of psychiatric disorders.
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PMID:Metabolism of psychotropic drugs: pharmacological and clinical relevance. 886 27

In an effort to determine which members of the cytochrome P450 (CYP) superfamily are expressed in human breast tissue and tumors, RNA-polymerase chain reaction studies have been undertaken. Detection of expressed CYP mRNAs identifies those forms of the enzyme that are capable of expression in breast tissue, and provides insight into the potential for in situ xenobiotic and therapeutic drug metabolism. CYP1A1 mRNA was present in (5/11) breast tissues and (6/13) tumors. When normal and tumor tissues were from the same individuals, higher amplification occurred in normal tissues. CYP1B1 mRNA was present in all but one tissue, and CYP2C mRNA forms were present in all of the tissues. CYP3A4 mRNA was present in (8/11) normal breast tissues and (2/13) tumor tissues, and CYP3A5 mRNA was present in (9/11) normal tissues and (2/13) tumor tissues. The expression of the CYP3A mRNA forms was not coincident, suggesting differential regulation. CYP2D6 mRNA was present in (10/11) normal breast tissue and (10/13) tumors. Two splice variants of CYP2D6 mRNA were also detected; one with a 207 bp intron spliced in was detected in all of the normal tissue samples and (11/13) tumors, whereas another (which lacks a 3'-portion of exon 6) was detected in (9/11) normal breast tissues and (7/13) tumors. Thus, examples of each of the xenobiotic-metabolizing CYP1, CYP2, and CYP3 subfamilies were detected in low levels in human normal breast tissue and tumors. The machinery for possible in situ bioactivation of xenobiotics and modification of therapeutic drugs is thus present in human breast tissue.
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PMID:Expression of cytochromes P450 in human breast tissue and tumors. 886 26

Ropivacaine is a new amide-type local anesthetic agent. Unlike bupivacaine and mepivacaine, two structurally similar local anesthetic compounds, ropivacaine is exclusively the S-(-)-enantiomer. Ropivacaine is predominantly eliminated by extensive metabolism in the liver, with only 1% of the dose being excreted unchanged in the urine of humans. Four of the metabolites formed in human liver microsomes were identified as 3-OH-ropivacaine, 4-OH-ropivacaine, 2-OH-methyl-ropivacaine, and 2',6'-pipecoloxylidide (PPX). The enzymes involved in the human metabolism of ropivacaine have not been identified. To ascertain which forms of cytochrome P450 are involved, ropivacaine was incubated with human microsomes from 10 different livers having different cytochrome P450 activities. A strong correlation was found between the formation of 3-OH-ropivacaine and CYP1A (r = 0.87-0.89) and between the formation of 4-OH-ropivacaine, 2-OH-ropivacaine, and PPX and CYP3A (r = 0.97-1). Incubation of ropivacaine and human liver microsomes in the presence of alpha-naphthoflavone or furafylline, inhibitors of CYP1A, decreased the formation of 3-OH-ropivacaine by about 85%, without affecting the formation of the other metabolites. The formation of 4-OH-ropivacaine, 2-OH-methyl-ropivacaine, and PPX was markedly inhibited in the presence of troleandomycin, an inhibitor of CYP3A. Microsomes from cells expressing CYP1A2 formed 3-OH-ropivacaine, whereas 4-OH-ropivacaine, 2-OH-methyl-ropivacaine, and PPX were formed in microsomes from cells expressing CYP3A4. Inhibitors of CYP2C (sulfaphenazole), CYP2D6 (quinidine), and 2E1 (diethyldithiocarbamate) did not inhibit the formation of any metabolite from ropivacaine. In conclusion, CYP1A catalyzes the formation of 3-OH-ropivacaine, the main metabolite formed in vivo, whereas the formation of 4-OH-ropivacaine, 2-OH-methyl-ropivacaine, and PPX was catalyzed by CYP3A.
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PMID:Ropivacaine, a new amide-type local anesthetic agent, is metabolized by cytochromes P450 1A and 3A in human liver microsomes. 888 4

Omeprazole (OP) is a potent antiulcer drug that is metabolized by liver cytochrome P450 (P450) enzymes. However, the identities of the P450 isoforms responsible for its metabolism have been controversial. 5-Hydroxyomeprazole (5OH-OP) formation cosegregates with the polymorphism of (S)-mephenytoin 4'-hydroxylation in humans, which is now known to be mediated by CYP2C19. Previous in vitro studies have indicated that liver microsomal 50H-OP formation correlates with both (S)-mephenytoin 4'-hydroxylase and CYP3A content. Inhibitor and CYP2C antibody studies also suggested that both enzymes may be involved in the 5-hydroxylation of OP, whereas CYP3A appears to be the predominant enzyme involved in OP sulfone (OP-S) formation. The present studies assessed the contribution of various CYP2C and CYP3A4 enzymes to OP metabolism by using recombinant human enzymes. CYP2C19, CYP2C8, CYP2C18, and CYP2C9 formed a single metabolite with an HPLC retention time identical to that of 5OH-OP. The turnover number for CYP2C19 was 13.4 +/- 1.4 nmol/min/nmol of P450, whereas those for CYP2C8, CYP2C18, and CYP2C9 were 2.2 +/- 0.1, 1.5 +/- 0.1, and approximately equal to 0.5 nmol/min/nmol of P450, respectively. Recombinant human CYP3A4 formed 5OH-OP and OP-S with turnover numbers of 5.7 +/- 1.1 and 7.4 +/- 0.9 nmol/min/nmol of P450, respectively, and formed a minor unidentified metabolite. CYP2C19 had a substantially lower KM for 5OH-OP formation than did CYP3A4, CYP2C8, or CYP2C18. Antibody to CYP2C proteins inhibited approximately equal to 70% of OP 5-hydroxylation at low substrate concentrations, comparable to those that may be encountered at therapeutically relevant doses, whereas antibody to CYP3A4 inhibited approximately equal to 30% of the activity. At high substrate concentrations, the contributions of the two enzymes to OP hydroxylation were roughly comparable (40-50%). In contrast, OP-S formation was completely inhibited by antibody to CYP3A4 proteins. The present study provides the first direct confirmation, using human recombinant P450 enzymes and selective antibody inhibition, that CYP2C19 is a major high affinity OP 5-hydroxylase and CYP3A4 is a low affinity OP-hydroxylating enzyme. The current work also shows, for the first time, that other CYP2C enzymes (CYP2C8, CYP2C9, and CYP2C18) may contribute to OP hydroxylation at high substrate concentrations. In contrast, OP-S was formed principally by CYP3A4.
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PMID:Human CYP2C19 is a major omeprazole 5-hydroxylase, as demonstrated with recombinant cytochrome P450 enzymes. 889 8

Studies using human liver microsomes and nine recombinant human cytochrome P450 (CYP) isoforms (CYP1A1, 1A2, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1 and 3A4) were performed to identify the CYP isoform(s) involved in the major metabolic pathway (3-hydroxylation) of quinine in humans. Eadie-Hofstee plots for the formation of 3-hydroxyquinine exhibited apparently monophasic behavior for all of the 10 different microsomal samples studies. There was interindividual variability in the kinetic parameters, as follows: 1.8-, 3.2- and 3.5-fold for K(m) Vmax and Vmax/K(m), respectively. The mean +/- S.D. values for K(m), Vmax and Vmax/K(m) were 106.1 +/- 19.3 microM, 1.33 +/- 0.48 nmol/mg protein/min and 12.8 +/- 5.1 microliters/mg protein/min, respectively. With 10 different human liver microsomes, the relationships between the 3-hydroxylation of quinine and the metabolic activities for substrates of the respective CYP isoforms were evaluated. The 3-hydroxylation of quinine showed an excellent correlation (r = 0.986, P < .001) with 6 beta-hydroxylation of testosterone, a marker substrate for CYP3A4. A significant correlation (r = 0.768, P < .01) between the quinine 3-hydroxylase and S-mephenytoin 4'-hydroxylase activities was also observed. However, no significant correlation existed between the 3-hydroxylation of quinine and the oxidative activities for substrates for CYP1A2 (phenacetin), 2C9 (diclofenac), 2D6 (desipramine) and 2E1 (chlorzoxazone). Ketoconazole and troleandomycin (inhibitors of CYP3A4) inhibited the 3-hydroxylation of quinine by human liver microsomes with respective mean IC50 values of 0.026 microM and 28.9 microM. Anti-CYP3A antibodies strongly inhibited quinine 3-hydroxylation, whereas weak inhibition was observed in the presence of S-mephenytoin or anti-CYP2C antibodies. Among the nine recombinant human CYP isoforms, CYP3A4 exhibited the highest catalytic activity with respect to the 3-hydroxylation of quinine, compared with the minor activity of CYP2C19 and little discernible or no effect of other CYP isoforms. Collectively, these data suggest that the 3-hydroxylation of quinine is mediated mainly by CYP3A4 and to a minor extent by CYP2C19. Other CYP isoforms used herein appear to be of negligible importance in this major pathway of quinine in humans.
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PMID:Identification of human cytochrome P450 isoforms involved in the 3-hydroxylation of quinine by human live microsomes and nine recombinant human cytochromes P450. 896 57


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