CYP2C19 Enzyme Research Articles

Phenotyping of Human CYP450 Enzymes by Endobiotics: Current Knowledge and Methodological Approaches.

Drug response is subject to an important within- and between-individual variability owing, mainly, to pharmacokinetic and pharmacodynamic factors. Pharmacokinetics includes metabolism by cytochrome P450 (CYP450), major enzymes of phase I reactions that are responsible for the biotransformation of around 60% of the currently approved drugs. CYP450 activity and/or expression are influenced by multiple intrinsic and extrinsic factors, such as drug-drug interactions or genetic polymorphisms. Present phenotyping strategies with xenobiotics used to assess CYP450 activity could be replaced by less invasive procedures using endogenous CYP450 biomarkers. In this work, we review existing knowledge on endobiotics and their ability to characterise variability of the CYP1A2, CYP2C19, CYP2D6 and CYP3A enzymes in humans. To date, it appears that there is a lack of clinical data for the majority of the endogenous compounds described in the literature or some important limitations to allow their use in clinical practice. Additional studies are needed to fill the gap or to identify new candidates, in particular through the use of metabolomics. The use of multivariate models is also a very promising approach to enhance prediction by combining several endogenous phenotyping metrics and other covariates.

Variability in human drug metabolizing cytochrome P450 CYP2C9, CYP2C19 and CYP3A5 activities caused by genetic variations in cytochrome P450 oxidoreductase

A broad spectrum of human diseases are caused by mutations in the NADPH cytochrome P450 oxidoreductase (POR). Cytochrome P450 proteins perform several reactions, including the metabolism of steroids, drugs, and other xenobiotics. In 2004 the first human patients with defects in POR were reported, and over 250 variations in POR are known. Information about the effects of POR variants on drug metabolizing enzymes is limited and has not received much attention. By analyzing the POR sequences from genomics databases, we identified potentially disease-causing variations and characterized these by in vitro functional studies using recombinant proteins. Proteins were expressed in bacteria and purified for activity assays. Activities of cytochrome P450 enzymes were tested in vitro using liposomes prepared with lipids into which P450 and P450 reductase proteins were embedded. Here we are reporting the effect of POR variants on drug metabolizing enzymes CYP2C9, CYP2C19, and CYP3A5 which are responsible for the metabolism of many drugs. POR Variants A115V, T142A, A281T, P284L, A287P, and Y607C inhibited activities of all P450 proteins tested. Interestingly, the POR variant Q153R showed a reduction of 20–50% activities with CYP2C9 and CYP2C19 but had a 400% increased activity with CYP3A5. The A287P is most common POR mutation found in patients of European origin, and significantly inhibited drug metabolism activities which has important consequences for monitoring and treatment of patients. In vitro, functional assays using recombinant proteins provide a useful model for establishing the metabolic effect of genetic mutations. Our results indicate that detailed knowledge about POR variants is necessary for correct diagnosis and treatment options for persons with POR deficiency and the role of changes in drug metabolism and toxicology due to variations in POR needs to be addressed.

Method for Determining CYP2C9 Activity in Earthworms and its Responses to Benzo[a]pyrene or Pyrene in Soil

In this study, high‐performance liquid chromatography–tandem mass spectrometry (LC‐MS/MS) for determining CYP2C9 activity in the earthworm Eisenia fetida using diclofenac as the substrate is developed and validated for the first time. The high sensitivity, selectivity, and excellent accuracy and precision of this approach permit the use of very low incubation concentrations of microsome protein (10–100 μg mL−1). Using this method, CYP2C9 activity in earthworms in response to increasing doses of benzo[a]pyrene (B[a]P) or pyrene (0.12, 0.24, 0.48, and 0.96 mg kg−1) in soil is determined. The results suggest that the enzyme CYP2C9 did exist in earthworms and show that CYP2C9 activity responded to B[a]P or pyrene highly different. A significant enhancement of CYP2C9 activity is observed at low doses (0.12–0.24 mg kg−1) of B[a]P at days 3 and 14, while a clear inhibition is observed at high doses (0.48–0.96 mg kg−1) of B[a]P at day 14. The responses of CYP2C9 activity to pyrene are bell shaped, independent of exposure duration, and not inhibited during the entire experiment. In contrast, at the highest dose of pyrene, CYP2C9 activity reaches its minimal value, which is insignificantly different from the control. It is thus concluded that the CYP2C9 activity of earthworms can be used as a biomarker for monitoring B[a]P‐ or pyrene‐contaminated soil.

Insights into Nanoarchitectual Structures to Enhance the Catalysis Properties of Human Liver Microsomes

Building a nanoarchitectual structure using 1-Pyrenylbutylamine and functionalized multiwalled carbon nanotubes (MWNT) will create an abundance of aminated sites on an electrode for electrostatic interactions binding Human Liver Microsomes (HLM). This increase in secondary interactions will allow for a higher concentration of HLM to bind to the electrode creating a higher catalytic current and increased stability of the bioprocesses involved. Using inexpensive HLM on this nanostructure with applied potential, without NADPH as an electron source, could prove to be a viable bioreactor for swift drug metabolism and inhibition assays. Using cyclic voltammetry the research confirms that High Purity Graphite (HPG) electrodes structured with aminated MWNTs in conjunction with pi-pi stacking of 1-Pyrenylbutylamine with adsorbed HLM increases the catalytic current over 4x that of HLM directly adsorbed on HPG. This nanostructural design demonstrates an almost 2x higher catalytic current using HLM over costly recombinant created CYP enzymes. The formal potential of -0.46 indicates that the CYP reductase is functioning in the HLM and the first to receive the electron transfer as published previously in this lab with recombinant enzymes. Long term impedances stability tests demonstrate that the carbon electrode with this nanostructure is more stable than a costly gold electrode. Using HPLC to measure the hydroxylation of diclofenac to 4’-hydroxydiclofenac HLM outperforms the recombinant enzymes also. Inhibition of the CYP2C9 enzyme in HLM by the competitive inhibitor sulphenazole shown by HPLC indicates that CYP2C9 is responsible for the reduction of diclofenac. This nanostructure design makes improvements over the plain electrode, and could prove to be a feasible method upon to build an inexpensive platform to examine newly developing drugs.

Non‐Additive Effects of Changing the Composition of the Cytochrome P450 Ensemble in Human Liver Microsomes: the Focus on CYP2E1 and Alcohol‐Drug Interactions

Recent studies on a large selection of human liver microsomes (HLM) demonstrated the lack of a straight correlation between the composition of human cytochrome P450 ensemble and the profile of drug metabolism. At the same time, there is an emerging recognition of the functional importance of physical interactions between multiple P450 species co‐localized in the microsomal membrane. Due to complex effects of these interactions any change in the content of a particular P450 enzyme may affect drug metabolism in a complex, hard‐to‐predict manner. Of particular practical importance are the functional effects of the changes in the composition of P450 ensemble induced by alcohol consumption. Although the multi‐fold increase in the content of cytochrome P450 2E1 (CYP2E1) in liver observed in both alcoholics and moderate alcohol consumers is well documented, the role of CYP2E1 in the instances of alcohol‐drug interactions is commonly considered insignificant due to a minor role of this enzyme in drug metabolism. However, the involvement of CYP2E1 in alcohol‐drug interactions may stretch far beyond its immediate effects on the metabolism of its substrates.The aim of this study is to probe the effect of increasing concentrations of CYP2E1 in HLM on the metabolism of drug substrates of other P450 species. In a search for a model system suitable for these studies we introduced a method based on incorporation of purified cytochromes P450 into HLM that allows creating the microsomal preparations with altered composition of the P450 ensemble. Incorporation of CYP2E1 into HLM results in an increase in the rate of CYP2E1‐dependent metabolism of chlorzoxazone, which is proportional to the amount of the incorporated enzyme up to its content of 0.3 nmol per mg protein (or ~50% of CYP2E1 in the total P450 content). Studies with a series of substrates of drug‐metabolizing P450 species showed that CYP2E1 incorporation also results in pronounced alterations in the metabolism of substrates of several other P450 enzymes. The most important effect is observed on CYP2C19. The changes in the effective KM and Vmax values with such probe substrates as 7‐etoxy‐4‐cyanocoumarin (CEC, the substrate of CYP2C19 and CYP1A2), 7‐dimethylamino‐4‐trifluoromethylcoumarin (coumarin‐152, the substrate of CYP2B6, CYP2C19 and CYP2C9) and N‐butyl 7‐methoxy‐4‐(aminomethyl)‐coumarin (BMAMC, the substrate of CYP1A2, CYP2C19 and CYP2D6) reveal a substantial decrease in the involvement of CYP2C19 in their metabolism. Furthermore, increase in CYP2E1 content causes an important changes in the function of CYP3A enzymes, which is revealed in a compromised homotropic cooperativity, decreased affinity and increased Vmax observed with 7‐benzyloxyquinoline, a selective substrate of CYP3A4 and CYP3A5. These observations suggest that ethanol‐dependent induction CYP2E1 may be involved in pronounced pharmacokinetic interactions of alcohol with such drug substrates of CYP2C19 and CYP3A enzymes as benzodiazepines (diazepam), tricyclic antidepressants (amitriptylline, imipramine) and anticonvulsants (phenytoin, carbamazepine).Support or Funding InformationThis research was supported by grant R21‐AA024548 from NIH.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pharmacokinetics, tissue distribution, plasma protein binding, and metabolism study of mefunidone, a novel pirfenidone derivative.

Mefunidone (MFD), a novel derivation of pirfenidone (PFD), exhibits promising anti-renal fibrosis activity. To avoid early development failures and attrition in clinical phase 1, an evaluation of the preclinical pharmacokinetic (PK) properties of MFD was conducted in this study. The absolute bioavailability was evaluated in Sprague Dawley rats and cynomolgus monkeys, who received an intragastric or intravenous administration at the dose of 31.25mg/kg and 10mg/kg, respectively. Tissue distribution and plasma protein binding studies were performed to evaluate the distribution characteristics of MFD. The enzymes involved in the metabolism of MFD were assayed by calculating the inhibition rate using the in vitro incubation system of human liver microsomes. The metabolic pathway of MFD was also examined in the in vitro incubation system as well as in rats in vivo. The results revealed satisfactory absorption of MFD in vivo, with an absolute bioavailability of MFD in rats and monkeys of approximately 77.2% and 70.0%, respectively. MFD was rapidly distributed to all tissues and was highly concentrated in the kidney, which was the target organ of MFD. The plasma protein binding rates in rat, monkey, and human plasma were 36.40%-41.68%, 30.88%-63.92%, and 37.75%-57.77%, respectively. MFD was primarily metabolized by the enzymes CYP3A4, CYP2C9, and CYP2C8. The metabolic pathway of MFD is nitrogen demethylation of the pyridine ring of the MFD nucleus, hydroxylation of the aromatic ring, and demethylation of the piperazine ring. In conclusion, MFD exhibited good PK properties in the initial preclinical PK study. The results strongly support further research to investigate the potential of MFD as a clinical anti-renal fibrosis drug.

Crystal Structure of CYP2C9*2 Genetic Variant in Complex with an Angiotensin II Receptor Blocker Drug Losartan

Cytochrome P450 (CYP)‐dependent monooxygenases are a superfamily of heme‐containing enzymes involved in the metabolism of various xenobiotics. The drug metabolizing CYP2C9 enzyme metabolizes up to 20% of the clinical drugs that include losartan, warfarin, ibuprofen, tolbutamide, and glimepiride. The CYP2C9*2 and *3 are the two prevalent genetic variants that demonstrate significant reduction of the catalytic activity compared to the wild‐type (WT) enzyme for many important CYP2C9 substrates. Despite the abundant structural information available regarding various CYPs, the structural information about the effect of genetic polymorphisms on drug binding has remained scant. The CYP2C9*2 variant represents an amino acid change from arginine to cysteine at position 144, also referred to as R144C. To understand how genetic variation in CYP2C9 affects drug binding and oxidation, we solved the crystal structure of CYP2C9*2 in complex with the antihypertensive drug losartan using X‐ray crystallography. The prodrug losartan is an angiotensin II receptor antagonist that is predominantly metabolized by CYP2C9 and CYP3A4. The overall structure of the CYP2C9*2‐losartan complex illustrate remarkable differences compared to the WT complex. These include altered conformation of important secondary structural elements and residue side chains previously shown to be responsible for binding interactions with different substrates. Furthermore, the new structure revealed significant changes in binding of losartan compared to the previously solved losartan complexes of the CYP2C9 WT, *3 and *30. The structure highlights how single nucleotide polymorphism affects drug binding and yield insights into altered metabolism. Overall, the structural complex provides a useful framework to study, computationally as well as biophysically, the binding of different substrates to genetic variants of CYP2C9 and understand the effect of amino acid substitution in decreased hydroxylation activity of the enzyme.Support or Funding InformationThe authors are grateful to Albany College of Pharmacy and Health Sciences for funding.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Evaluation of lentinan effects on cytochrome P450 activity in rats by a cocktail method.

Objective(s):In this study, a cocktail of probe drugs was used to assess whether lentinan could influence the activities of rat enzymes CYP3A4, CYP2D6, CYP1A2, CYP2C19, and CYP2C9 in vivo. Materials and Methods:Fourteen days after intraperitoneal injection of lentinan, rats were given an oral dose of a cocktail solution containing phenacetin, tolbutamide, omeprazole, metoprolol, and midazolam. Then, we obtained blood in specific durations for the determination of plasma concentration of the probe drugs using UPLC-MS/MS. We also evaluated the pharmacokinetic parameters using the DAS 2.0 software. Results:We found that various concentrations of lentinan increased the activity of rat CYP1A2, CYP3A4, CYP2D6, and CYP2C19 but not CYP2C9. Conclusion:These findings suggest that clinical application of lentinan combination with CYP3A4, CYP1A2, CYP2C19, or CYP2D6 should be given careful consideration as this may lead to herb-drug interactions and hence treatment failure.

Clopidogrel Resistance in Lower Extremity Arterial Endovascular Interventions.

Antiplatelet pharmacotherapy for endovascular interventions has been widely adopted, with clopidogrel being one of the most common agents prescribed. A fraction of patients is resistant to clopidogrel resulting in decreased platelet inhibition despite adequate use. This finding is often termed high on-treatment platelet reactivity (HPR) and may lead to decreased patency in lower extremity arterial endovascular interventions. Current literature on HPR with lower extremity arterial endovascular interventions is limited to only a few studies. Resistance to clopidogrel is largely a result of CYP2C19 enzyme loss of function alleles. Several tests are available to measure clopidogrel resistance but light transmittance aggregometry remains the gold standard, yet direct genetic testing may be more reliable. One-year patency rates following lower extremity arterial endovascular interventions in patients with clopidogrel resistance (HPR) range between 35%-83% whereas those with the proper response to clopidogrel range between 73%-100%. Patients with decreased CYP2C19 activity show a significant decrease in one-year patency of endovascular femoropopliteal interventions (35% vs. 73%; p=0.006). Among patients tested for platelet function after in-stent thrombosis, up to 53% are resistant to clopidogrel. Lack of robust data limits our ability to predict patency in lower extremity arterial interventions for patients with HPR, but there is little doubt that longer patency seems to favor non-HPR patients. Large population, prospective trials are needed to guide our practice.

In Vitro Metabolism of 25B-NBF, 2-(4-Bromo-2,5-Dimethoxyphenyl)-N-(2-Fluorobenzyl)ethanamine, in Human Hepatocytes Using Liquid Chromatography⁻Mass Spectrometry.

25B-NBF, 2-(4-bromo-2,5-dimethoxyphenyl)-N-(2-fluorobenzyl)ethanamine, is a new psychoactive substance classified as a phenethylamine. It is a potent agonist of the 5-hydroxytryptamine receptor, but little is known about its metabolism and elimination properties since it was discovered. To aid 25B-NBF abuse screening, the metabolic characteristics of 25B-NBF were investigated in human hepatocytes and human cDNA-expressed cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes using liquid chromatography–high resolution mass spectrometry. At a hepatic extraction ratio of 0.80, 25B-NBF was extensively metabolized into 33 metabolites via hydroxylation, O-demethylation, bis-O-demethylation, N-debenzylation, glucuronidation, sulfation, and acetylation after incubation with pooled human hepatocytes. The metabolism of 25B-NBF was catalyzed by CYP1A1, CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2J2, CYP3A4, and UGT2B7 enzymes. Based on these results, it is necessary to develop a bioanalytical method for the determination of not only 25B-NBF but also its metabolites in biological samples for the screening of 25B-NBF abuse.

Pharmacogenetics of non-steroidal anti-inflammatory drugs: existing problems for clinical practice

NSAIDs are the most commonly used drugs in clinical practice for pain relief in various diseases. To date, considerable scientific material has been accumulated on the pharmacogenetics of NSAIDs and the role of genetic factors that can influence the pharmacokinetics and pharmacodynamics of drugs, changing the efficacy and toxicity profile. The most clinically significant changes in pharmacokinetics in carriers of slow alleles of CYP2C9*3 have been identified for celecoxib and flurbiprofen, which determines the need for testing and lowering of drug doses. Studies were carried out to study the role of polymorphism of the metabolizing enzymes CYP2C9, CYP2C8, UGT in the development of gastrotoxicity and gastrointestinal bleeding during application NSAIDs, as well as diclofenac’s hepatotoxicity. The association of «slow» alleles CYP2C8*3 and CYP2C9*2,*3 with the risk of gastrointestinal bleeding associated with NSAID use, which are substrates of CYP2C9 and CYP2C8, is shown. The effect of variants of alleles PTGS1 (gene COX-1) and PTGS2 (gene COX-2) on pharmacodynamics, efficacy and toxicity of NSAIDs, in particular, the severity of the analgesic effect and cardiotoxicity of the drugs, was studied. In this way, pharmacogenetic predictors of adverse effects that patients can experience, and the need for dose adjustment based on the patient’s genotype, or individualizing the choice of alternative NSAIDs to increase the effectiveness of analgesia, have been determined.

Cannabidiol: A New Hope for Patients With Dravet or Lennox-Gastaut Syndromes.

To review the efficacy, safety, pharmacology and pharmacokinetics of pure, plant-derived cannabidiol (CBD; Epidiolex) in the treatment of Dravet syndrome (DS) and Lennox-Gastaut syndrome (LGS). Relevant information was identified through EMBASE and Ovid MEDLINE (1946 to October 2018). Product labeling and https://www.clinicaltrials.gov were also reviewed. English language articles evaluating efficacy and safety in humans with treatment-resistant epilepsies were reviewed; additional pharmacology and pharmacokinetic studies in humans, animals, and in vitro were also included. Pure, plant-based CBD is a pharmaceutical grade extract that exhibits clinically significant antiseizure properties, with a hypothesized multimodal mechanism of action. In the GWPCARE trial series, CBD displayed superior efficacy in reducing key seizure frequencies (convulsive seizures in DS; drop seizures in LGS) by 17% to 23% compared with placebo as adjunctive therapy to standard antiepileptic drugs in patients 2 years of age and older. Common adverse effects were somnolence, diarrhea, and elevated hepatic transaminases. Noteworthy drug-drug interactions included clobazam, valproates, and significant inducers/inhibitors of CYP2C19 and 3A4 enzymes. Relevance to Patient Care and Clinical Practice: A discussion regarding CBD dosing, administration, adverse effects, monitoring parameters, and interactions is provided to guide clinicians. CBD offers patients with DS and LGS a new treatment option for refractory seizures. This is the first cannabis-derived medication with approval from the US Food and Drug Administration. This CBD formulation significantly reduces seizures as an adjunct to standard antiepileptic therapies in patients ≥2 years old with DS and LGS and is well tolerated.

Characterization of CYP2C Induction in Cryopreserved human hepatocytes and ITS Application in the prediction of the clinical consequences of the induction

Abstract CYP2C enzymes play key roles in drug metabolism, and clinical drug-drug interactions caused by CYP2C induction have been reported. The aim of this study was to establish a method to predict the potency of CYP2C inductions considering the mechanism. We first investigated the relations of CYP2C induction with CYP3A4 or CYP2B6 induction in human hepatocytes after 48-h exposure with 19 inducers. The fold-induction values of CYP2C8 and CYP2C9 were well correlated with those of CYP3A4, whereas the inducers were separated into 2 groups showing different correlations with CYP2B6 induction for CYP2C8 and CYP2C9 induction. In the regression models established, the fold-induction values of CYP2C8 and CYP2C9 were well expressed as the functions of those of CYP3A4 and CYP2B6, while no such obvious correlation was observed for CYP2C19 induction. These results suggest that CYP2Cs are not simply coinduced with CYP3A4 and that CYP2C8 and CYP2C9 inductions are regulated by both pregnane X receptor and constitutive androstane receptor with different contributions. Finally, simple correlations were proposed using the experimental Emax values obtained and plasma concentrations of CYP2C9 substrates from the literature, and positive correlations were observed. These data provide methods to estimate the clinical impact of CYP2C9 induction from in vitro data.

Expression of Cyp2c8 Enzyme in Non-Small Cell Lung Cancer with 6α-Hydroxy Paclitaxel Drug by Flow Cytometric Technique

Expression of Cyp2c8 Enzyme in Non-Small Cell Lung Cancer with 6α-Hydroxy Paclitaxel Drug by Flow Cytometric Technique

CYP2C9 polymorphism is not associated with elevated carcinoembryonic antigen levels

Background: Carcinoembryonic antigen (CEA) is a glycoprotein that can be elevated in a number of benign and malignant conditions. In colorectal cancer, it is used as a prognostic marker and to detect recurrence. However, it lacks specificity and may become elevated in individuals without a history of cancer or other identifiable cause leading to costly and invasive investigation. Objective: The aim of this study was to assess whether genetic polymorphisms in the liver enzyme CYP2C9 could explain high CEA levels in otherwise normal individuals. Design: This is a case-control study. Setting: Individuals were genotyped for the poor metabolizer (PM) alleles CYP2C9*2 and CYP2C9*3 using predesigned TaqMan single nucleotide polymorphisms assays. Patients and Methods: Nineteen individuals with previously clinically unexplained elevated CEA and 567 healthy Caucasian controls were included. Main Outcome Measures: Chi-square analysis was used to test for association of CYP2C9 genotype with plasma CEA concentration. Sample Size: Nineteen individuals with previously clinically unexplained elevated CEA and 567 healthy Caucasian controls were included. Results: Fifteen of the 19 individuals with previously high CEA had elevated plasma CEA (>3.0μg/L) on re-testing. The frequency of CYP2C9 PM alleles in these 15 patients was not significantly higher than the frequency in controls. Conclusion: CEA concentrations do not appear to be influenced by CYP2C9 genotype, so this cannot be used to explain elevated CEA in the absence of an obvious clinical cause. Limitation: Small sample size.

Relevance of CYP2C9 Function in Valproate Therapy.

Background: Genetic polymorphisms of drug metabolizing enzymes can substantially modify the pharmacokinet-ics of a drug and eventually its efficacy or toxicity; however, inferring a patient’s drug metabolizing capacity merely from his or her genotype can lead to false prediction. Non-genetic host factors (age, sex, disease states) and environmental factors (nutrition, co-medication) can transiently alter the enzyme expression and activities resulting in genotype-phenotype mis-match. Although valproic acid is a well-tolerated anticonvulsant, pediatric patients are particularly vulnerable to valproate in-jury that can be partly attributed to the age-related differences in metabolic pathways.Methods: CYP2C9 mediated oxidation of valproate, which is the minor metabolic pathway in adults, appears to become the principal route in children. Genetic and non-genetic variations in CYP2C9 activity can result in significant inter- and intra-individual differences in valproate pharmacokinetics and valproate induced adverse reactions.Results: The loss-of-function alleles, CYP2C9*2 or CYP2C9*3, display significant reduction in valproate metabolism in children; furthermore, low CYP2C9 expression in patients with CYP2C9*1/*1 genotype also leads to a decrease in valproate metabolizing capacity. Due to phenoconversion, the homozygous wild genotype, expected to be translated to CYP2C9 en-zyme with normal activity, is transiently switched into poor (or extensive) metabolizer phenotype.Conclusion: Novel strategy for valproate therapy adjusted to CYP2C9-status (CYP2C9 genotype and CYP2C9 expression) is strongly recommended in childhood. The early knowledge of pediatric patients’ CYP2C9-status facilitates the optimization of valproate dosing which contributes to the avoidance of misdosing induced adverse reactions, such as abnormal blood lev-els of ammonia and alkaline phosphatase, and improves the safety of children’s anticonvulsant therapy.

Metabolic activity testing can underestimate acute drug cytotoxicity as revealed by HepG2 cell clones overexpressing cytochrome P450 2C19 and 3A4

Preclinical drug safety assessment includes in vitro studies with physiologically relevant cell cultures. As an in vitro system for hepatic toxicology testing, we have been generating cell clones of human hepatoblastoma cell line HepG2 by lentiviral transduction of phase I cytochrome P450 (CYP) enzymes. Here, we present a stable CYP2C19-overexpressing HepG2 cell clone (HepG2-2C19 C1) showing an enzyme activity of approximately 82 pmol x min−1 x mg−1 total cellular protein. The phenotypic stability over several passages of HepG2-2C19 C1 renders them to be a suitable reference cell clone for benchmarking CYP2C19 enzyme activity. In addition, we were interested to analyze acute cytotoxicity of the model drug cyclophosphamide (CPA) metabolized by HepG2-2C19 C1 and by a previously generated CYP3A4-overexpressing HepG2 cell clone. Upon 10 mM CPA exposure, we were able to detect its metabolites 4-hydroxy-cyclophosphamide and acrolein in CYP3A4- and CYP2C19-expressing cell clones, but not in parental HepG2 cell line. XTT and ATP assays showed a modest reduction of cell viability of not more than 50% with high dose (10 mM) CPA treatment. By contrast, dramatic acute cytotoxic effects of CPA were evident by the formation of nuclear γH2AX foci and by increased cell death events. These effects were paralleled by substantial decreases of cell membrane integrity as measured by the trypan blue exclusion test. Our data on CYP enzyme overexpressing HepG2 cell clones clearly show that cytotoxicity of CPA is dramatically underestimated by standard metabolic activity tests. Thus, additional tests to quantitate DNA damage formation and cell death induction might be required to realistically assess cytotoxicity of such compounds.

Quantitative Modeling Analysis Demonstrates the Impact of CYP2C19 and CYP2D6 Genetic Polymorphisms on the Pharmacokinetics of Amitriptyline and Its Metabolite, Nortriptyline.

Amitriptyline is a tricyclic antidepressant that is metabolized mainly by CYP2C19 and CYP2D6 enzymes. Higher plasma levels of amitriptyline and its active metabolite, nortriptyline, are associated with an increased risk of adverse events including anticholinergic effects. The aim of this study was to evaluate the effects of CYP2C19 and CYP2D6 genetic polymorphisms on amitriptyline and nortriptyline pharmacokinetics. Twenty-four Korean healthy adult male volunteers were enrolled in the study after stratification by their CYP2C19 and CYP2D6 genotypes. Serial blood draws for pharmacokinetic analysis were made after a single oral 25-mg dose of amitriptyline was administered. Plasma amitriptyline and nortriptyline concentrations were measured by a validated liquid chromatography with tandem mass spectrometry. Population pharmacokinetic modeling analysis was conducted using NONMEM, which evaluated the effects of CYP2C19 and CYP2D6 genotypes on amitriptyline and nortriptyline pharmacokinetics. The biotransformation of amitriptyline into nortriptyline was significantly different between subjects with the CYP2C19*2/*2, *2/*3, and *3/*3 genotypes and those with the other genotypes, with an estimated metabolic clearance of 17 and 61.5 L/h, respectively. Clearance of amitriptyline through pathways other than biotransformation into nortriptyline was estimated as 18.8 and 30.6 L/h for subjects with the CYP2D6*10/*10 and *10/*5 genotypes and those with the other genotypes, respectively. This study demonstrated a quantitative effect of the CYP2C19 and CYP2D6 genotypes on amitriptyline and nortriptyline pharmacokinetics. Production of nortriptyline from amitriptyline was associated with CYP2C19 genotypes, and clearance of amitriptyline through pathways other than biotransformation into nortriptyline was associated with CYP2D6 genotypes. These observations may be useful in developing individualized, optimal therapy with amitriptyline.

Isoform-Dependent Changes in Cytochrome P450-Mediated Drug Metabolism after Portal Vein Ligation in the Rat

Background: Surgical removal of complicated liver tumors may be realized in two stages via selective portal vein ligation, inducing the atrophy of portally ligated lobes and the compensatory hypertrophy of nonligated liver lobes. Unlike morphological changes, functional aspects such as hepatic cytochrome P450 (CYP)-mediated drug metabolism remain vaguely understood, despite its critical role in both drug biotransformation and hepatic functional analysis. Our goal was the multilevel characterization of hepatic CYP-mediated drug metabolism after portal vein ligation in the rat. Methods: Male Wistar rats (n = 24, 210–230 g) were analyzed either untreated (controls; n = 4) or 24/48/72/168/336 h (n = 4 each) following portal vein ligation affecting approximately 80% of the liver parenchyma. Besides the weights of ligated and nonligated lobes, pentobarbital (30 mg/kg)-induced sleeping time, CYP1A(2), CYP 2B(1/2), CYP2C(6/11/13), CYP3A(1) enzyme activities, and corresponding isoform mRNA expressions, as well as CYP3A1 protein expression were determined by in vivo sleeping test, CYP isoform-selective assays, polymerase chain reaction, and immunohistochemistry, respectively. Results: Portal vein ligation triggered atrophy in ligated lobes and hypertrophy nonligated lobes. Sleeping time was transiently elevated (p = 0.0451). After an initial rise, CYP1A, CYP2B, and CYP3A enzyme activities dropped until 72 h, followed by a potent increase only in the nonligated lobes, paralleled by an early (24–48 h) transcriptional activation only in nonligated lobes. CYP2C enzyme activities and mRNA levels were bilaterally rapidly decreased, showing a late reconvergence only in nonligated lobes. CYP3A1 immunohistochemistry indicated substantial differences in positivity in the early period. Conclusions: Beyond the atrophy-hypertrophy complex, portal vein ligation generated a transient suppression of global and regional drug metabolism, re-established by an adaptive, CYP isoform-dependent transcriptional response of the nonligated lobes.

CYP2C19 polymorphism in relation to the pharmacotherapy optimization of commonly used drugs.

Purpose: The CYP2C19 isoenzyme plays an important role in the efficacy and safe use of many drugs. The aim of this review is to demonstrate how CYP2C19 mutations influence everyday patient treatment, leading to adverse drug reactions or therapy failure in many common diseases. Methods: A PubMed literature search was performed on clinical publications evaluating the impact of CYP2C19 on pharmacotherapy outcome. Main fields of medicine with strong outcome dependency on the CYP2C19 genotype were selected. We also focused on clinical recommendations for the use of drugs referring to CYP2C19 polymorphism. Results: The fields of medicine where clinical outcome particularly depends on CYP2C19 polymorphism are gastroenterology, cardiology, psychiatry, mycology and oncology. CYP2C19 is involved in proton pump inhibitors metabolism, thus it can influence reflux therapy, ulcer prevention and Helicobacter pylori eradication treatment. The CYP2C19 enzyme plays also a vital role in the two bioactivation steps of clopidogrel leading to lower (CYP2C19*17 carriers) or higher (CYP2C19*2 carriers) risk of major adverse cardiovascular events. It affects the antidepressant treatment and methadone replacement therapy as well as voriconazole prophylaxis. The presence of a *2 allele is associated with longer relapse-free time or better survival, and the *17 allele with more favorable outcomes in breast cancer patients treated with tamoxifen. Conclusions: Knowledge of the CYP2C19 polymorphism could positively affect individual treatment and lead to better patient outcomes in many cases. The introduction of pharmacogenetic testing into medical practice would be a good way to minimize negative outcomes of therapy, and to reduce unnecessary medical costs.