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Pharmacognosy Research Oct 2013To date, many findings reveal that most of the modern drugs have the ability to interact with herbal drugs.
CONTEXT
To date, many findings reveal that most of the modern drugs have the ability to interact with herbal drugs.
AIMS
This study was conducted to determine the inhibitory effects of mitragynine on cytochrome P450 2C9, 2D6 and 3A4 activities.
METHODS AND MATERIAL
The in vitro study was conducted using a high-throughput luminescence assay.
STATISTICAL ANALYSIS
Statistical analysis was conducted using one-way ANOVA and Dunnett's test with P < 0.05 vs. control. The IC50 values were calculated using the GraphPad Prism(®) 5 (Version 5.01, GraphPad Software, Inc., USA).
RESULTS
Assessment using recombinant enzymes showed that mitragynine gave the strongest inhibitory effect on CYP2D6 with an IC50 value of 0.45±0.33 mM, followed by CYP2C9 and CYP3A4 with IC50 values of 9.70±4.80 and 41.32±6.74 μM respectively. Positive inhibitors appropriate for CYP2C9, CYP2D6, and CYP3A4 which are sulfaphenazole, quinidine and ketoconazole were used respectively. Vmax values of CYP2C9, CYP2D6 and CYP3A4 were 0.0005, 0.01155 and 0.0137 μM luciferin formed/pmol/min respectively. Km values of CYP2C9, CYP2D6, and CYP3A4 were 32.65, 56.01, and 103.30 μM respectively. Mitragynine noncompetitively inhibits CYP2C9 and CYP2D6 activities with the Ki values of 61.48 and 12.86 μM respectively. On the other hand, mitragynine inhibits CYP3A4 competitively with a Ki value of 379.18 μM.
CONCLUSIONS
The findings of this study reveal that mitragynine might inhibit cytochrome P450 enzyme activities, specifically CYP2D6. Therefore, administration of mitragynine together with herbal or modern drugs which follow the same metabolic pathway may contribute to herb-drug interactions.
PubMed: 24174816
DOI: 10.4103/0974-8490.118806 -
The Journal of Physiology Aug 2012While it is accepted that NO is responsible for ∼60% of the plateau in cutaneous thermal hyperaemia, a large portion of the response remains unknown. We sought to...
While it is accepted that NO is responsible for ∼60% of the plateau in cutaneous thermal hyperaemia, a large portion of the response remains unknown. We sought to determine whether the remaining ∼40% could be attributed to EDHF-mediated activation of KCa channels, and whether the epoxyeicosatrienoic acids (EETs), derived via cytochrome P450, were the predominant EDHF active in the response. Four microdialysis fibres were placed in the forearm skin of 20 subjects. In Protocol 1 (n = 10): (1) Control, (2) N(G)-nitro-l-arginine methyl ester (l-NAME), (3) a KCa channel inhibitor, tetraethylammonium (TEA), and (4) TEA + l-NAME. In Protocol 2 (n = 10): (1) Control, (2) l-NAME, (3) a cytochrome P450 inhibitor, sulfaphenazole, and (4) sulfaphenazole + l-NAME. Local heating to 42°C was performed and skin blood flow was measured with laser Doppler flowmetry. Data are presented as the percentage of maximal cutaneous vascular conductance (CVC). All drug sites attenuated plateau CVC from the control site (86 ± 1%) to 79 ± 3% with sulfaphenazole (P = 0.02 from control), 71 ± 3% with TEA (P = 0.01 from control), and further to 38 ± 2% with l-NAME (P < 0.001 from control, P < 0.001 from TEA). Plateau was largely attenuated with sulfaphenazole + l-NAME (24 ± 2%; P = 0.002 from l-NAME), and nearly abolished with l-NAME + TEA (13 ± 2%; P = 0.001 from sulfaphenazole + l-NAME), which was not different from baseline (P = 0.14). Furthermore, the initial peak was just 17 ± 2% with TEA + l-NAME (P < 0.001 from l-NAME). These data suggest EDHFs are responsible for a large portion of initial peak and the remaining 40% of the plateau phase, as administration of TEA in combination with l-NAME abolished the majority of hyperaemia. These data also suggest EETs contribute to about half of the EDHF response.
Topics: Adolescent; Aryl Hydrocarbon Hydroxylases; Biological Factors; Cytochrome P-450 CYP2C9; Eicosanoids; Enzyme Inhibitors; Female; Hot Temperature; Humans; Hyperemia; Male; NG-Nitroarginine Methyl Ester; Nitric Oxide Synthase; Potassium Channel Blockers; Potassium Channels, Calcium-Activated; Skin Temperature; Sulfaphenazole; Tetraethylammonium; Vasodilation; Young Adult
PubMed: 22674719
DOI: 10.1113/jphysiol.2012.236398 -
Drug Metabolism and Disposition: the... Jul 2022The utility of chemical inhibitors in cytochrome P450 (CYP) reaction phenotyping is highly dependent on their selectivity and potency for their target CYP isoforms. In...
Defining the Selectivity of Chemical Inhibitors Used for Cytochrome P450 Reaction Phenotyping: Overcoming Selectivity Limitations with a Six-Parameter Inhibition Curve-Fitting Approach.
The utility of chemical inhibitors in cytochrome P450 (CYP) reaction phenotyping is highly dependent on their selectivity and potency for their target CYP isoforms. In the present study, seventeen inhibitors of CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4/5 commonly used in reaction phenotyping were evaluated for their cross-enzyme selectivity in pooled human liver microsomes. The data were evaluated using a statistical desirability analysis to identify (1) inhibitors of superior selectivity for reaction phenotyping and (2) optimal concentrations for each. Among the inhibitors evaluated, α-naphthoflavone, furafylline, sulfaphenazole, tienilic acid, -benzylnirvanol, and quinidine were most selective, such that their respective target enzymes were inhibited by ~95% without inhibiting any other CYP enzyme by more than 10%. Other commonly employed inhibitors, such as ketoconazole and montelukast, among others, were of insufficient selectivity to yield a concentration that could adequately inhibit their target enzymes without affecting other CYP enzymes. To overcome these shortcomings, an experimental design was developed wherein dose response data from a densely sampled multi-concentration inhibition curve are analyzed by a six-parameter inhibition curve function, allowing accounting of the inhibition of off-target CYP isoforms inhibition and more reliable determination of maximum targeted enzyme inhibition. The approach was exemplified using rosiglitazone -demethylation, catalyzed by both CYP2C8 and 3A4, and was able to discern the off-target inhibition by ketoconazole and montelukast from the inhibition of the targeted enzyme. This methodology yields more accurate estimates of CYP contributions in reaction phenotyping. Isoform-selective chemical inhibitors are important tools for identifying and quantifying enzyme contributions as part of a CYP reaction phenotyping assessment for projecting drug-drug interactions. However, currently employed practices fail to adequately compensate for shortcomings in inhibitor selectivity and the resulting confounding impact on estimates of the CYP enzyme contribution to drug clearance. In this report, we describe a detailed IC study design with 6-parameter modeling approach that yields more accurate estimates of enzyme contribution.
PubMed: 35777846
DOI: 10.1124/dmd.122.000884 -
Journal of Pharmacological Sciences Sep 2008Epoxyeicosatrienoic acids (EETs), including 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET, are produced by cytochrome P450 (P450) such as CYP2C8 and 2C9; and they are...
Epoxyeicosatrienoic acids (EETs), including 5,6-EET, 8,9-EET, 11,12-EET, and 14,15-EET, are produced by cytochrome P450 (P450) such as CYP2C8 and 2C9; and they are hydrolyzed to dihydroxyeicosatrienoic acids (DHETs) by epoxide hydrolase. Particular interest in the epoxygenase reaction has developed because of the potent biological activities (modulation of vascular tone and anti-inflammatory activity, etc.) attributed to EETs. We focused on a new biological function of EETs and DHETs, which induce vascular endothelial growth factor (VEGF) and erythropoietin (EPO) under hypoxia. Human hepatoma cells, Hep3B, and human umbilical artery endothelial cells (HUAEC) were used in this study. An inhibitor of phospholipase A(2), methyl arachidonyl fluorophosphonate (MAFP), and inhibitors of P450s inhibited the VEGF and EPO induction of HUAEC and Hep3B, respectively, under hypoxia. Overexpression of CYP2C8 in Hep3B induced EPO and VEGF under hypoxia. Sulfaphenazole, an inhibitor of CYP2C8/2C9 suppressed luciferase promoter activity with the hypoxia response element (HRE) of VEGF in HUAEC. Exogenous 11,12-EET and 14,15-DHET induced reporter activity in HUAEC and Hep3B cells concomitant with increased levels of hypoxia-inducible factor-1alpha (HIF-1alpha), which is a key factor in the hypoxia response, but 11,12-DHET and 14,15-EET did not. These results suggested that EETs and DHETs play an important role in the hypoxia response of cells.
Topics: Arachidonic Acid; Aryl Hydrocarbon Hydroxylases; Blotting, Western; Cell Hypoxia; Cell Line, Tumor; Cytochrome P-450 CYP2C8; Eicosanoids; Erythropoietin; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Luciferases; Myocytes, Smooth Muscle; Reverse Transcriptase Polymerase Chain Reaction; Vascular Endothelial Growth Factor A
PubMed: 18776712
DOI: 10.1254/jphs.08122fp -
British Journal of Clinical Pharmacology Aug 1999To compare the oxidative metabolism of (S)-mephenytoin and proguanil in vitro and to determine the involvement of various cytochrome P450 isoforms. (Comparative Study)
Comparative Study
AIMS
To compare the oxidative metabolism of (S)-mephenytoin and proguanil in vitro and to determine the involvement of various cytochrome P450 isoforms.
METHODS
The kinetics of the formation of 4'-hydroxymephenytoin and cycloguanil in human liver microsomes from 10 liver samples were determined, and inhibition of formation was studied using specific chemical inhibitors and monoclonal antibodies directed towards specific CYP450 isoforms. Expressed CYP450 enzymes were used to characterize further CYP isoform contribution in vitro. Livers were genotyped for CYP2C19 using PCR amplification of genomic DNA followed by restriction endonuclease digestion.
RESULTS
All livers were wildtype with respect to CYP2C19, except HLS#5 whose genotype was CYP2C19*1/CYP2C19*2. The Km, Vmax and CLint values for the formation of 4'-hydroxymephenytoin from (S)-mephenytoin and the formation of cycloguanil from proguanil ranged from 50.8 to 51.6 and 43-380 microm, 1.0-13.9 and 0.5-2.5 nmol mg-1 h-1, and 20.2-273.8 and 2.7-38.9 microl h-1 mg-1, respectively. There was a significant association between the Vmax values of cycloguanil and 4'-hydroxymephenytoin formation (rs=0.95, P=0.0004). Cycloguanil formation was inhibited significantly by omeprazole (CYP2C19/3A), troleandomycin (CYP3A), diethyldithiocarbamate (CYP2E1/3A), furafylline (CYP1A2), and (S)-mephenytoin. 4'-Hydroxymephenytoin formation was inhibited significantly by omeprazole, diethyldithiocarbamate, proguanil, furafylline, diazepam, troleandomycin, and sulphaphenazole (CYP2C9). Human CYP2E1 and CYP3A4 monoclonal antibodies did not inhibit the formation of cycloguanil or 4'-hydroxymephenytoin, and cycloguanil was formed by expressed CYP3A4 and CYP2C19 supersomes. However, only expressed CYP2C19 and CYP2C19 supersomes formed 4'-hydroxymephenytoin.
CONCLUSIONS
The oxidative metabolism of (S)-mephenytoin and proguanil in vitro is catalysed by CYPs 2C19 and 1A2, with the significant association between Vmax values suggesting that the predominant enzymes involved in both reactions are similar. However the degree of selectively of both drugs for CYP isoforms needs further investigation, particularly the involvement of CYP3A4 in the metabolism of proguanil. We assert that proguanil may not be a suitable alternative to (S)-mephenytoin as a probe drug for the CYP2C19 genetic polymorphism.
Topics: Adult; Aged; Antibodies, Monoclonal; Anticonvulsants; Antimetabolites; Cytochrome P-450 Enzyme System; Enzyme Inhibitors; Female; Folic Acid Antagonists; Genotype; Humans; In Vitro Techniques; Isoenzymes; Male; Mephenytoin; Microsomes, Liver; Middle Aged; Oxidation-Reduction; Proguanil; Triazines
PubMed: 10417492
DOI: 10.1046/j.1365-2125.1999.00005.x -
The Journal of Pharmacology and... Dec 2009Epoxyeicosatrienoic acids (EETs) are endothelium-derived metabolites of arachidonic acid. They relax vascular smooth muscle by membrane hyperpolarization. These actions...
Epoxyeicosatrienoic acids (EETs) are endothelium-derived metabolites of arachidonic acid. They relax vascular smooth muscle by membrane hyperpolarization. These actions are inhibited by the EET antagonist, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EE5ZE). We synthesized 20-(125)iodo-14,15-EE5ZE (20-(125)I-14,15-EE5ZE), a radiolabeled EET antagonist, and characterized its binding to cell membranes. 14,15-EET (10(-9)-10(-5)M) caused a concentration-related relaxation of the preconstricted bovine coronary artery and phosphorylation of p38 in U937 cells that were inhibited by 20-(125)I-14,15-EE5ZE. Specific 20-(125)I-14,15-EE5ZE binding to U937 cell membranes reached equilibrium within 5 min and remained unchanged for 30 min. The binding was saturable and reversible, and it exhibited K(D) and B(max) values of 1.11 +/- 0.13 nM and 1.13 +/- 0.04 pmol/mg protein, respectively. Guanosine 5'-O-(3-thio)triphosphate (10 muM) did not change the binding, indicating antagonist binding of the ligand. Various EETs and EET analogs (10(-10)-10(-5)M) competed for 20-(125)I-14,15-EE5ZE binding with an order of potency of 11,12-EET = 14,15-EET > 8,9-EET = 14,15-EE5ZE > 15-hydroxyeicosatetraenoic acid = 14,15-dihydroxyeicosatrienoic acid. 8,9-Dihydroxyeicosatrienoic acid and 11-hydroxyeicosatetraenoic acid did not compete for binding. The soluble and microsomal epoxide hydrolase inhibitors (1-cyclohexyl-3-dodecyl-urea, elaidamide, and 12-hydroxyl-elaidamide) and cytochrome P450 inhibitors (sulfaphenazole and proadifen) did not compete for the binding. However, two cytochrome P450 inhibitors, N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) and miconazole competed for binding with K(i) of 1558 and 315 nM, respectively. Miconazole and MS-PPOH, but not proadifen, inhibited 14,15-EET-induced relaxations. These findings define an EET antagonist's binding site and support the presence of an EET receptor. The inhibition of binding by some cytochrome P450 inhibitors suggests an alternative mechanism of action for these drugs and could lead to new drug candidates that target the EET binding sites.
Topics: 8,11,14-Eicosatrienoic Acid; Animals; Binding Sites; Blotting, Western; Cattle; Cell Membrane; Coronary Vessels; Cytochrome P-450 Enzyme Inhibitors; Dose-Response Relationship, Drug; Epoxide Hydrolases; Epoxy Compounds; Humans; Iodine Radioisotopes; Ligands; Phosphorylation; U937 Cells; Vasodilation; p38 Mitogen-Activated Protein Kinases
PubMed: 19762546
DOI: 10.1124/jpet.109.157818 -
Zhongguo Yao Li Xue Bao = Acta... Sep 1998To study the effect of cytochrome P-450 (CYP450) inhibitors on clomipramine (Clo) N-demethylation in vitro.
AIM
To study the effect of cytochrome P-450 (CYP450) inhibitors on clomipramine (Clo) N-demethylation in vitro.
METHODS
The kinetic parameters of Clo N-demethylation in human liver microsomes were obtained by the Michaelis-Menten equation. The parameters after pretreatment with putative inhibitors of various CYP450 isoforms were compared with controls.
RESULTS
K(m1), K(m2), Vmax1, Vmax2, Vmax1/K(m1), and Vmax2/K(m2) were (0.11 +/- 0.06), (24 +/- 14) mumol.L-1, (114 +/- 47), (428 +/- 188) nmol.g-1.min-1, (1.8 +/- 1.6), and (0.019 +/- 0.005) L.g-1.min-1, respectively. The interindividual variations for the last 4 parameters reached up to 2.5-, 7.3-, 3.4-, and 1.8-fold. At 5 mumol.L-1 of Clo, troleandomycin (Tro), furafylline (Fur), ditiocarb sodium (Dit), and S-mephenytoin (Mep) produced a marked inhibition on Clo N-demethylation while sulfaphenazole (Sul) and quinidine (Qui) had only slight effects. The inhibitory rates by Dit 30, Mep 500, Fur 10, Tro 10, Fur 80, Tro 200 and Fur 80 + Tro 200 mumol.L-1 were 27.0%, 32.9%, 42.8%, 40.5%, 63.9%, 66.4%, and 78.3%, respectively. The IC50 (95% confidence limits) for Fur and Tro were 27.7 (19.1-36.3) and 42.1 (20.9-63.3) mumol.L-1, respectively.
CONCLUSIONS
The N-demethylation of Clo exhibited a biphasic behavior. This reaction was mediated mainly by both CYP1A2 and CYP3A4, to a minor extent by CYP2C19 at the low concentration of Clo in vitro.
Topics: Adult; Clomipramine; Cytochrome P-450 CYP1A2 Inhibitors; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Humans; In Vitro Techniques; Mephenytoin; Methylation; Microsomes, Liver; Middle Aged; Mixed Function Oxygenases; Theophylline; Troleandomycin
PubMed: 10375803
DOI: No ID Found -
British Journal of Pharmacology Apr 20031. The aim of the present study was to identify human cytochrome p-450 isoforms (CYPs) involved in 5-sulphoxidation and N-demethylation of the simplest phenothiazine...
1. The aim of the present study was to identify human cytochrome p-450 isoforms (CYPs) involved in 5-sulphoxidation and N-demethylation of the simplest phenothiazine neuroleptic promazine in human liver. 2. The experiments were performed in the following in vitro models: (A). a study of promazine metabolism in liver microsomes-(a). correlations between the rate of promazine metabolism and the level and activity of CYPs; (b). the effect of specific inhibitors on the rate of promazine metabolism (inhibitors: CYP1A2-furafylline, CYP2D6-quinidine, CYP2A6+CYP2E1-diethyldithiocarbamic acid, CYP2C9-sulfaphenazole, CYP2C19-ticlopidine, CYP3A4-ketoconazole); (B). promazine biotransformation by cDNA-expressed human CYPs (Supersomes 1A1, 1A2, 2A6, 2B6, 2C9, 2C19, 2E1, 3A4); (C). promazine metabolism in a primary culture of human hepatocytes treated with specific inducers (rifampicin-CYP3A4, CYP2B6 and CYP2C inducer, 2,3,7,8-tetrachlordibenzeno-p-dioxin (TCDD)-CYP1A1/1A2 inducer). 3. In human liver microsomes, the formation of promazine 5-sulphoxide and N-desmethylpromazine was significantly correlated with the level of CYP1A2 and ethoxyresorufin O-deethylase and acetanilide 4-hydroxylase activities, as well as with the level of CYP3A4 and cyclosporin A oxidase activity. Moreover, the formation of N-desmethylpromazine was correlated well with S-mephenytoin 4'-hydroxylation. 4. Furafylline (a CYP1A2 inhibitor) and ketoconazole (a CYP3A4 inhibitor) significantly decreased the rate of promazine 5-sulphoxidation, while furafylline and ticlopidine (a CYP2C19 inhibitor) significantly decreased the rate of promazine N-demethylation in human liver microsomes. 5. The cDNA-expressed human CYPs generated different amounts of promazine metabolites, but the rates of CYP isoforms to catalyse promazine metabolism at therapeutic concentration (10 microM) was as follows: 1A1>2B6>1A2>2C9>3A4>2E1>2A6>2D6>2C19 for 5-sulphoxidation and 2C19>2B6>1A1>1A2>2D6>3A4>2C9>2E1>2A6 for N-demethylation. The highest intrinsic clearance (V(max)/K(m)) was found for CYP1A subfamily, CYP3A4 and CYP2B6 in the case of 5- sulphoxidation, and for CYP2C19, CYP1A subfamily and CYP2B6 in the case of N-demethylation. 6. In a primary culture of human hepatocytes, TCDD (a CYP1A subfamily inducer), as well as rifampicin (mainly a CYP3A4 inducer) induced the formation of promazine 5-sulphoxide and N-desmethylpromazine. 7. Regarding the relative expression of various CYPs in human liver, the obtained results indicate that CYP1A2 and CYP3A4 are the main isoforms responsible for 5-sulphoxidation, while CYP1A2 and CYP2C19 are the basic isoforms that catalyse N-demethylation of promazine in human liver. Of the other isoforms studied, CYP2C9 and CYP3A4 contribute to a lesser degree to promazine 5-sulphoxidation and N-demethylation, respectively. The role of CYP2A6, CYP2B6, CYP2D6 and CYP2E1 in the investigated metabolic pathways of promazine seems negligible.
Topics: Adult; Aged; Antipsychotic Agents; Cytochrome P-450 Enzyme System; Female; Hepatocytes; Humans; Isoenzymes; Male; Microsomes, Liver; Middle Aged; Phenothiazines; Promazine
PubMed: 12721102
DOI: 10.1038/sj.bjp.0705195 -
The Journal of Biological Chemistry Mar 2014Degenerative loss of photoreceptors occurs in inherited and age-related retinal degenerative diseases. A chemical screen facilitates development of new testing routes...
Degenerative loss of photoreceptors occurs in inherited and age-related retinal degenerative diseases. A chemical screen facilitates development of new testing routes for neuroprotection and mechanistic investigation. Herein, we conducted a mouse-derived photoreceptor (661W cell)-based high throughput screen of the Food and Drug Administration-approved Prestwick drug library to identify putative cytoprotective compounds against light-induced, synthetic visual chromophore-precipitated cell death. Different classes of hit compounds were identified, some of which target known genes or pathways pathologically associated with retinitis pigmentosa. Sulfaphenazole (SFZ), a selective inhibitor of human cytochrome P450 (CYP) 2C9 isozyme, was identified as a novel and leading cytoprotective compound. Expression of CYP2C proteins was induced by light. Gene-targeted knockdown of CYP2C55, the homologous gene of CYP2C9, demonstrated viability rescue to light-induced cell death, whereas stable expression of functional CYP2C9-GFP fusion protein further exacerbated light-induced cell death. Mechanistically, SFZ inhibited light-induced necrosis and mitochondrial stress-initiated apoptosis. Light elicited calcium influx, which was mitigated by SFZ. Light provoked the release of arachidonic acid from membrane phospholipids and production of non-epoxyeicosatrienoic acid metabolites. Administration of SFZ further stimulated the production of non-epoxyeicosatrienoic acid metabolites, suggesting a metabolic shift of arachidonic acid under inhibition of the CYP2C pathway. Together, our findings indicate that CYP2C genes play a direct causative role in photochemical stress-induced death of photoreceptors and suggest that the CYP monooxygenase system is a risk factor for retinal photodamage, especially in individuals with Stargardt disease and age-related macular degeneration that deposit condensation products of retinoids.
Topics: Amino Acid Sequence; Animals; Aryl Hydrocarbon Hydroxylases; Cell Death; Cell Line; Cytochrome P-450 CYP2C9; Cytochrome P-450 Enzyme System; Cytochrome P450 Family 2; Cytoprotection; Drug Evaluation, Preclinical; Gene Expression; Gene Silencing; Humans; Light; Mice; Molecular Sequence Data; Photoreceptor Cells, Vertebrate; Sequence Alignment; Sulfaphenazole
PubMed: 24519941
DOI: 10.1074/jbc.M113.507152 -
British Journal of Clinical Pharmacology Apr 19951. Studies using human liver microsomes and six recombinant human CYP isoforms (i.e. CYP1A2, 2A6, 2B6, 2D6, 2E1 and 3A4) were performed to identify the cytochrome P450...
1. Studies using human liver microsomes and six recombinant human CYP isoforms (i.e. CYP1A2, 2A6, 2B6, 2D6, 2E1 and 3A4) were performed to identify the cytochrome P450 (CYP) isoform(s) involved in the ring 4-hydroxylation and side-chain N-desisopropylation of propranolol enantiomers in humans. 2. alpha-Naphthoflavone and 7-ethoxyresorufin (selective inhibitors of CYP1A1/2) inhibited the N-desisopropylation of R- and S-propranolol by human liver microsomes by 20 and 40%, respectively, while quinidine (a selective inhibitor of CYP2D6) abolished the 4-hydroxylation of both propranolol enantiomers almost completely. In contrast, sulphaphenazole (CYP2C8/9 inhibitor), S-mephenytoin (CYP2C19 inhibitor), troleandomycin (CYP3A3/4 inhibitor) and diethyldithiocarbamate (CYP2E1 inhibitor) elicited only weak inhibitory effects on propranolol metabolism via the two measured metabolic pathways. 3. Significant (P < 0.01) correlations were observed between the microsomal N-desisopropylation of both propranolol enantiomers and that for the O-deethylation of phenacetin among the 11 different human liver microsome samples (r = 0.98 and 0.77 for R- and S-propranolol, respectively). A marginally significant (r = 0.60, P congruent to 0.05) correlation was also observed between N-desisopropylation of S-, but not of R-propranolol and the 4'-hydroxylation of S-mephenytoin. No significant correlations were observed between the N-desisopropylation of propranolol enantiomers and the 2-hydroxylation of desipramine, the hydroxylation of tolbutamide or the 6 beta-hydroxylation of testosterone. 4. Significant (P < 0.01) correlations were observed between the microsomal 4-hydroxylation of R- and S-propranolol and the 2-hydroxylation of desipramine (r = 0.85 and 0.98, respectively). A weak (r = 0.66), albeit significant (P < 0.05) correlation was observed between the 4-hydroxylation of R-, but not of S-propranolol and the hydroxylation of tolbutamide. No significant correlations were observed between the 4-hydroxylation of propranolol enantiomers and the oxidation of other substrates for CYP1A2, 2C19, and 3A3/4. 5. Recombinant human CYP1A2 and CYP2D6 exhibited comparable catalytic activity with respect to the N-desisopropylation of both propranolol enantiomers; only expressed CYP2D6 exhibited a marked catalytic activity with respect to the 4-hydroxylation of both propranolol enantiomers.(ABSTRACT TRUNCATED AT 400 WORDS)
Topics: Aged; Benzoflavones; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Desipramine; Ditiocarb; Female; Humans; Hydroxylation; In Vitro Techniques; Isoenzymes; Male; Mephenytoin; Microsomes, Liver; Middle Aged; Oxazines; Phenacetin; Propranolol; Quinidine; Recombinant Proteins; Stereoisomerism; Substrate Specificity; Sulfaphenazole; Tolbutamide; Troleandomycin
PubMed: 7640150
DOI: 10.1111/j.1365-2125.1995.tb04472.x