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Concept: CYP3A4

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We have previously described the development of genetic models to study the in vivo functions of the hepatic cytochrome P450 system, through the hepatic deletion of either cytochrome P450 oxidoreductase (POR; HRN line) or cytochrome b5 (Cyb5; HBN line). However, HRN mice still exhibit low levels of mono-oxygenase activity, in spite of the absence of detectable reductase protein. To investigate whether this is because cytochrome b5 and cytochrome b5 reductase can act as sole electron donors to the P450 system, we have crossed HRN with HBN mice to generate a line lacking hepatic expression of both electron donors (HBRN). HBRN mice exhibited exacerbation of the phenotypic characteristics of the HRN line - liver enlargement, hepatosteatosis and increased expression of certain cytochrome P450s. Also, drug metabolising activities in vitro were further reduced relative to the HRN model, in some cases to undetectable levels. Pharmacokinetic studies in vivo demonstrated that midazolam half-life, Cmax and area under the concentration-time curve (AUC) were increased, and clearance was decreased, to a greater extent in the HBRN line than in either the HBN or HRN model. Microsomal incubations using NADPH concentrations below the apparent Km of cytochrome b5 reductase, but well above that for POR, led to the virtual elimination of 7-benzyloxyquinoline turnover in HRN samples. These data provide strong evidence that cytochrome b5/cytochrome b5 reductase can act as a sole electron donors to the cytochrome P450 system in vitro and in vivo.

Concepts: Cytochrome P450, Paracetamol, CYP3A4, P450-containing systems, Cytochrome P450 reductase

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Substantial evidence has shown that most exogenous substances are metabolized by multiple cytochrome P450 (P450) enzymes instead of by merely one P450 isoform. Thus, multi-P450 inhibition leads to greater drug-drug interaction risk than specific P450 inhibition. Herein, we innovatively established an artificial neural network cascade (NNC) model composed of 23 cascaded networks in a ladder-like framework to identify potential multi-P450 inhibitors among natural compounds by integrating 12 molecular descriptors into a P450 inhibition score (PIS). Experimental data reporting in vitro inhibition of five P450 isoforms (CYP1A2, CYP2C9, CYP2C19, CYP2D6, and CYP3A4) were obtained for 8,148 compounds from the Cytochrome P450 Inhibitors Database (CPID). The results indicate significant positive correlation between the PIS values and the number of inhibited P450 isoforms (Spearman’s ρ = 0.684, p < 0.0001). Thus, a higher PIS indicates a greater possibility for a chemical to inhibit the enzyme activity of at least three P450 isoforms. Ten-fold cross-validation of the NNC model suggested an accuracy of 78.7% for identifying whether a compound is a multi-P450 inhibitor or not. Using our NNC model, 22.2% of the approximately 160,000 natural compounds in TCM Database@Taiwan were identified as potential multi-P450 inhibitors. Furthermore, chemical similarity calculations suggested that the prevailing parent structures of natural multi-P450 inhibitors were alkaloids. Our findings show that dissection of chemical structure contributes to confident identification of natural multi-P450 inhibitors and provides a feasible method for virtually evaluating multi-P450 inhibition risk for a known structure.

Concepts: Enzyme, Cytochrome P450, Enzyme inhibitor, Inhibitor, Chemical compound, Neural network, Identification, CYP3A4

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The cytochrome P450 3A4 (CYP3A4) inhibitor clarithromycin may also inhibit liver-specific organic anion-transporting polypeptides (OATP1B1 and OATP1B3). We studied whether concurrent use of clarithromycin and a statin not metabolized by CYP3A4 was associated with an increased frequency of serious adverse events.

Concepts: Statin, Cytochrome P450, CYP3A4, Erythromycin, Simvastatin, Lovastatin, Atorvastatin

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To test whether high-dose statin treatment would result in a reduction in periodontal inflammation as assessed by fluorodeoxyglucose-positron emission tomography/computed tomography, FDG-PET/CT.

Concepts: Atherosclerosis, Statin, CYP3A4, Statins, Atorvastatin, Caduet

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Tacrolimus is a widely used immunosuppressive drug in organ transplantation. The oral bioavailability of tacrolimus varies greatly between individuals and depends largely on the activity of both the cytochrome P450 3A (CYP3A) subfamily and P-glycoprotein (P-gp). The possible influence of single nucleotide polymorphisms (SNPs) of CYP3A subfamily and P-gp (MDR-1) in liver transplant recipients has recently been indicated as one of the most important variables affecting the pharmacokinetics of tacrolimus and the renal injury induced by tacrolimus.

Concepts: DNA, Single-nucleotide polymorphism, Cytochrome P450, Organ transplant, Pharmacokinetics, CYP3A4, Liver transplantation, Grapefruit juice

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Limonene, considered a green solvent, was successfully used to extract simvastatin, lovastatin, and their hydroxy-acid metabolites from human plasma samples. The extraction process was followed by the direct injection of a large volume aliquot (100 μL) from the limonene layer into a Zorbax SB-C(18) Rapid Resolution chromatographic column (50 mm length × 4.6 mm i.d. × 1.8 µm d.p.), operated under gradient elution reversed-phase separation mechanism. Tandem mass spectrometry operated under the multiple reaction monitoring mode was used for detection, providing low quantitation limits in the 0.25-0.5 ng/mL concentration interval. This method was validated and used for quantitation of simvastatin and its hydroxy acid metabolite in incurred plasma samples obtained from two volunteers participating in a bioequivalence study, using lovastatin and its hydroxy analog as internal standards. The results were statistically compared with those produced by means of an alternative RPLC-tandem MS using protein precipitation with acetonitrile. The quality attributes of the two methods are comparatively discussed. The agreement between the quality characteristics of the two methods and the experimental results obtained on real samples may be considered as a consistent basis for the simultaneous use of limonene as extraction medium and injection diluent for hydrophobic compounds in bioanalytical approaches. Copyright © 2012 John Wiley & Sons, Ltd.

Concepts: Mass spectrometry, Statin, Chromatography, Analytical chemistry, CYP3A4, Tandem mass spectrometry, Statins, Liquid-liquid extraction

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The H97-I trial (1997-2004) for Hodgkin lymphoma at intermediate stage (HL-I) included 269 patients who were randomized to receive three or four cycles of doxorubicin, bleomycin, vinblastine and dacarbazine (ABVD). The 197 patients who reached complete remission (CR) (73.2%, p = 0.41 between arms) received radiotherapy (RT); their 10-year progression-free survival (PFS) rate was 87.7 ± 3.0%, similar to that of the 180 patients of a historical control group (HCG) in CR after three ABVD cycles before RT. The 59 patients who reached post-ABVD partial remission (PR) received one course of intensive chemotherapy (i.v., mg/m(2), vindesine 5, adriamycin 90, BCNU 140, etoposide 600, methylprednisolone 600) before RT. In spite of this additional intensive chemotherapy, their PFS rate (78.4 ± 6.3%) remained significantly lower (p = 0.03) than that of the 197 patients who reached post-ABVD CR, and was similar to that of the 60 patients of the HCG in PR after three ABVD cycles who did not receive additional chemotherapy before RT.

Concepts: Chemotherapy, Lymphoma, Hodgkin's lymphoma, Doxorubicin, CYP3A4, ABVD, Antineoplastic drugs, Vinblastine

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Extracts, subfractions, isolated anthocyanins and procyanidins, and two phenolic acids from aronia [Aronia melanocarpa] were investigated for their CYP3A4 inhibitory effects, using midazolam as the probe substrate and recombinant insect cell microsomes expressing CYP3A4 as the enzyme source. Procyanidin B5 was a considerably stronger CYP3A4 inhibitor in vitro than the isomeric procyanidin B2 and comparable to bergamottin, a known CYP3A4 inhibitor from grapefruit juice. The inhibitory activity of proanthocyanidin-containing fractions was correlated to the degree of polymerization. Among the anthocyanins, cyanidin 3-arabinoside showed stronger CYP3A4 inhibition than cyanidin 3-galactoside and cyanidin 3-glucoside. Thus, the ability to inhibit CYP3A4 in vitro seems to be influenced by the sugar unit linked to the anthocyanidin.

Concepts: Cytochrome P450, Enzyme inhibitor, CYP3A4, Grapefruit, Grapefruit juice, Proanthocyanidins, B type proanthocyanidin, Bergamottin

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1. A fast, straightforward and cost-effective assay was validated for the assessment of CYP induction in cryopreserved human hepatocytes cultured in 48-well plates. The cocktail strategy (in situ incubation) was used to assess the induction of CYP1A2, CYP2B6, CYP2C9 and CYP3A4 by using the recommended probe substrate, i.e. phenacetin, bupropion, diclofenac and midazolam, respectively. 2. Cryopreserved human hepatocytes were treated for 72 h with prototypical reference inducers, β-naphthoflavone (25 µM), phenobarbital (500 µM) and rifampicin (10 µM) as positive controls for CYP induction. The use of a cocktail strategy has been validated and compared to the classical approach (single incubation). The need of using phase II inhibitor (salicylamide) in CYP induction assay was also investigated. 3. By using three different batches of cryopreserved human hepatocytes and our conditions of incubations, we showed that there was no relevant drug-drug interaction using the cocktail strategy. The same conclusions were observed when a broad range of enzyme activity has to be assessed (wide range of reference inducers, i.e. EC(50)-E(max) experiment). In addition, the interassay reproducibility assessment showed that the day-to-day variability was minimal. 4. In summary, the study showed that the conditions used (probe substrates, concentration of probe substrate and time of incubation) for the cocktail approach were appropriate for investigations of CYP induction potential of new chemical entities. In addition, it was also clear that the use of salicylamide in the incubation media was not mandatory and could generate drug-drug interactions. For this reason, we recommend to not use salicylamide in CYP induction assay.

Concepts: Enzyme, Assessment, Cytochrome P450, CYP1A2, CYP3A4, CYP2C9, CYP2B6, New chemical entity

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Activation of the pregnane X receptor (PXR) and subsequently its target genes, including those encoding drug transporters and metabolizing enzymes, while playing substantial roles in xenobiotics detoxification, might cause undesired drug-drug interactions. Recently, an increased awareness has been given to dietary components for potential induction of diet-drug interactions through activation of PXR. Here, we studied, whether piperine (PIP), a major component extracted from the widely-used daily spice black pepper, could induce PXR-mediated expression of cytochrome P450 3A4 (CYP3A4) and multidrug resistance protein 1 (MDR1). Our results showed that PIP activated human PXR (hPXR)-mediated CYP3A4 and MDR1 expression in human hepatocytes, intestine cells, and a mouse model; PIP activated hPXR by recruiting its coactivator SRC-1 in both cellular and cell-free systems; PIP bound to the hPXR ligand binding domain in a competitive ligand binding assay in vitro. The dichotomous effects of PIP on induction of CYP3A4 and MDR1 expression observed here and inhibition of their activity reported elsewhere challenges the potential use of PIP as a bioavailability enhancer and suggests that cautions should be taken for PIP consumption during drug treatment in patients, particularly those who favor daily pepper spice or rely on certain pepper remedies.

Concepts: DNA, Protein, Gene, Metabolism, Cytochrome P450, Steroid, CYP3A4, Black pepper