Cytochrome P450 2C9 Activity Research Articles

Cytochrome P450 2C9 polymorphism in Puerto Rican Alzheimer’s patients and its role in the pharmacokinetics of THC and Melatonin (IGC‐AD1), an investigational drug

AbstractBackgroundAlzheimer’s disease (AD) is a complex and chronic neurodegenerative illness. The AD patients were on many medications to manage their symptoms. Cytochrome P450 2C9 (CYP2C9) is the main enzyme involved in the metabolism of many drugs, including tetrahydrocannabinol (THC), which converts THC into the active metabolite 11‐hydroxy‐delta‐9‐THC metabolite. Individuals who lack CYP2C9 activity will have an increased risk of side effects from the drugs. CYP2C9 phenotypes are graded into groups, including poor (PM), intermediate (IM), normal (NM), and ultra‐rapid (UM) metabolizing phenotypes. IGC‐AD1 has major active ingredients that contain THC and melatonin.MethodIn our FDA‐regulated Phase‐1 trial, we evaluated a pilot study on the CYP2C9 polymorphism and pharmacokinetics of THC in AD patients (n = 12) from the Puerto Rican (PR) population as a safety measure. Using the Mass ARRAY Analyzer 4 instrument (Invitae Inc., MAA4, Agena, San Diego, CA), we determined the following CYP2C9 alleles: *2,*3,*4,*5,*6,*8,*11,*13,*15. We also investigate how polymorphism affects THC PK in IGC‐AD1 patients.ResultIn a Phase I clinical trial, we found that 62% of participants (n = 8) are carriers of at least one polymorphism. One participant has a rare heterozygous CYP2C9*1/*11 polymorphism. The participants with intermediate metabolizers (*1/*3 and *1/*2 allele) showed an increased half‐life of THC and an increased cMAX of OH‐THC compared to normal metabolizers (*1/*1). Participants who were intermediate metabolizers with *1/*2 variance had a lower AUC for THC levels. Altered CYP2C9 will affect the PK of THC and its metabolites.ConclusionFuture studies should include a larger sample size of AD patients from PR and other regions, that will be allowing access to CYP2C9 genetic polymorphism in AD and understand the drug‐related adverse reactions associated with CYP2C9 genetic polymorphism. Polymorphism plays an important role in drug metabolism and should be considered as a part of dosing.

Effect of Capsaicin on Pharmacokinetics and Pharmacodynamics of Nateglinide in normal and diabetic rats

The Cytochrome P-450 (CYP) enzymes present in the human body are responsible for the metabolism of most antidiabetic drugs. These CYP enzymes may metabolize the drugs either to active metabolites or to inactive metabolites. Some phytoconstituents which are present in vegetables, fruits and ayurvedic products will alter the activity of CYP enzymes. In the present research, the alterations in pharmacokinetics and pharmacodynamics of Nateglinide in the presence of a phytochemical like Capsaicin were studied. The study was conducted both in normal and diabetic rats. Rats were divided into different groups. Drug was administered as alone in one group and administered in combination with Capsaicin to other groups. After 8 days of treatment, the blood samples were collected and analysed. The Pharmacokinetic parameters like Cmax, tmax, AUC, MRT, Vd and ClT were estimated for all groups and compared. The mean blood glucose levels before and after treatments were recorded and compared among the groups. From the results, it could be concluded that the Capsaicin has inhibited the activity of CYP 2C9 and CYP 3A4 enzymes, thereby decreased the metabolism of drug which ultimately resulted in the increase of Cmax and AUC. The Capsaicin could raise the antidiabetic effect of drug.

Potential food-drug interaction risk of thymoquinone with warfarin

Thymoquinone, predominant bioactive compound in Nigella sativa L. (N.sativa) oil, may inhibit the activity of cytochrome P450 2C9 (CYP2C9). However, it is not clear whether thymoquinone can affect the pharmacokinetic behavior of warfarin. Thus, we further to investigate the effect of thymoquinone on warfarin 7-hydroxylation activity and to quantitatively evaluate their food-drug interactions (FDIs) potential. Our data demonstrated that thymoquinone could inhibit warfarin 7-hydroxylase activity with IC50 value of 11.35 ± 0.25 μM. The kinetic analysis indicated that thymoquinone exhibited competitive inhibition on warfarin 7-hydroxylation with Ki value of 3.50 ± 0.44 μM. FDIs risk prediction suggested that coadministration of thymoquinone (>18 mg/day) or dietary supplements containing thymoquinone (N.sativa > 1 g/day or N. sativa oil >1 g/day) might influence pharmacokinetic behavior of warfarin. In conclusion, coadministration of thymoquinone or dietary supplements containing thymoquinone in warfarin-treated patients would likely trigger off unexpected potential drug interactions.

The Impact of CYP2C9*11 Allelic Variant on the Pharmacokinetics of Phenytoin and (S)-Warfarin.

Cytochrome P450 2C9 (CYP2C9) is responsible for the oxidative metabolism of about 15% of commonly used drugs, some of which are characterized by a narrow therapeutic window. CYP2C9 is highly polymorphic, and over 60 alleles have been described. CYP2C9*2 and CYP2C9*3 are the most common polymorphisms among White patients and both are associated with decreased activity. The evidence concerning the functional importance of less frequent variant alleles is scarce. The objective of the current study was to characterize the in vivo activity of CYP2C9 among carriers of CYP2C9*11, one of the "African" alleles and the fourth most common CYP2C9 variant allele among White patients by using two prototype substrates, phenytoin and (S)‐warfarin. Single 300‐mg phenytoin and 20‐mg warfarin doses were given to 150 healthy Ethiopian Jewish participants who were nonsmokers, at least one week apart. (S)‐warfarin oral clearance and phenytoin metabolic ratio (PMR) derived from the ratio of 5‐(4‐hydroxyphenyl)‐5‐phenylhydantoin in 24‐hour urine collection to plasma phenytoin 12 hours (PMR 24/12) or 24 hours (PMR 24/24) post dosing, were used as markers of CYP2C9 activity. PMR 24/12 and PMR 24/24 were reduced by 50% and 62.2%, respectively, among carriers of CYP2C9*1/*11 (n = 13) as compared with carriers of CYP2C9*1/*1 (n = 127) (false discovery rate (FDR) q < 0.001). The respective decrease in (S)‐warfarin oral clearance was 52.6% (FDR q < 0.001). In conclusion, the enzyme encoded by CYP2C9*11 is characterized by a more than 50% decrease in the enzymatic activity, resembling the extent of decrease associated with CYP2C9*3 ("no‐function allele"). Among patients of African ancestry, CYP2C9*11 genetic analysis should be considered prior to prescribing of narrow therapeutic window drugs such as phenytoin, warfarin, nonsteroidal anti‐inflammatory drugs, or siponimod.

Potential herb-drug interaction risk of thymoquinone and phenytoin

Thymoquinone is a main bioactive compound of Nigella sativa L. (N.sativa), which has been used for clinical studies in the treatment of seizures due to its beneficial neuroprotective activity and antiepileptic effects. It has been evidenced that thymoquinone may inhibit the activity of cytochrome P450 2C9 (CYP2C9). However, little is known about the effect of thymoquinone or N.sativa on the pharmacokinetic behavior of phenytoin, a second-line drug widely used in the management of status epilepticus. In this study, we systematically investigated the risk of the potential pharmacokinetic drug interaction between thymoquinone and phenytoin. The inhibitory effect of thymoquinone on phenytoin hydroxylation activity by CYP2C9 was determined using UPLC-MS/MS by measuring the formation rates for p-hydroxyphenytoin (p-HPPH). The potential for drug-interaction between thymoquinone and phenytoin was quantitatively predicted by using in vitro-in vivo extrapolation (IVIVE). Our data demonstrated that thymoquinone displayed effective inhibition against phenytoin hydroxylation activity. Enzyme kinetic studies showed that thymoquinone exerted a competitive inhibition against phenytoin hydroxylation with a Ki value of 4.45 ± 0.51 μM. The quantitative prediction from IVIVE suggested that the co-administration of thymoquinone (>18 mg/day) or thymoquinone-containing herbs (N.sativa > 1 g/day or N.sativa oil >1 g/day) might result in a clinically significant herb-drug interactions. Additional caution should be taken when thymoquinone or thymoquinone-containing herbs are co-administered with phenytoin, which may induce unexpected potential herb-drug interactions via the inhibition of CYP2C9.

Electrochemical determination of (S)-7-hydroxywarfarin for analysis of CYP2C9 catalytic activity

An electrochemical method for the quantitative determination of (S)-7-hydroxywarfarin as a metabolite of the vitamin K antagonist warfarin has been developed to analyze the catalytic activity of cytochrome P450 2C9 (CYP2C9). The electrochemical properties of (S)-7-hydroxywarfarin were investigated using screen-printed carbon electrodes. We have shown by cyclic voltammetry that irreversible (S)-7-hydroxywarfarin electrochemical oxidation, in contrast to (S)-warfarin, can be registered by an oxidation peak at approximately 0.6 V (vs. Ag pseudo-reference electrode). A linear dependence of the oxidation peak amplitude in the range of 0.57–0.61 V on (S)-7-hydroxywarfarin concentration (in the range of 0.1–1 μM) was shown by the square-wave voltammetry method. The limit of (S)-7-hydroxywarfarin detection and the sensitivity were calculated as 0.091 μM and 0.0075 A/M, respectively. Using an electrochemical system based on recombinant human CYP2C9 immobilized on screen-printed carbon electrodes modified by didodecyldimethylammonium bromide, we have shown the possibility of (S)-7-hydroxywarfarin electrochemical quantification without separation of the enzymatic system component. The (S)-7-hydroxywarfarin quantitative electrochemical determination was used to calculate the kinetic parameters of CYP2C9 immobilized on electrode toward (S)-warfarin: the values of the maximal reaction rate (Vmax) and the Michaelis constant (KM) were calculated as 0.1 ± 0.002 min−1 and 3.03 ± 0.38 μM, respectively. The usage of an enzymatic CYP2C9-containing electrode as a catalyst and an indicator electrode as a sensor for the formation of metabolite allows to effectively register the kinetic parameters of the process. Such a two-electrode system can be applied to assess drug-drug interactions.

The interactions of abiraterone and its pharmacologically active metabolite D4A with cytochrome P450 2C9 (CYP2C9)

Interactions of cytochrome P450 2C9 (CYP2C9) were studied with the antitumor drug abiraterone and its pharmacologically active metabolite D4A, promising as an agent for prostate cancer treatment. It was shown by absorption spectroscopy, that both investigated compounds induced spectral changes of CYP2C9, indicating interactions of the pyridine nitrogen atom with the heme iron ion of the active site of the enzyme, but interactions of the ligands with the enzyme could be mediated by a water molecule bound to the heme iron ion. Based on the spectral changes, the values of dissociation constants (KS) for complexes of abiraterone and D4A with CYP2C9 were calculated as 1.73±0.14 μM and 3.95±0.16 μM. Both compounds inhibited O-demethylase activity of CYP2C9 towards its substrate. At 100 μM concentration of naproxen the concentrations of abiraterone, D4A and sulfaphenazole inhibiting CYP2C9 activity by 50% (IC50) were determined as 13.9 μM, 40 μM and 41 μM, respectively. The obtained results can be used for prognosis of drug-drug interactions at CYP2C9 level during administration of abiraterone or D4A as an antitumor agent for prostate cancer treatment in complex pharmacotherapy.

In vitro cytochrome P450- and transporter-mediated drug interaction potential of 6β-hydroxy-21-desacetyl deflazacort-A major human metabolite of deflazacort.

6β‐Hydroxy‐21‐desacetyl deflazacort (6β‐OH‐21‐desDFZ) is a major circulating but not biologically active metabolite of deflazacort (DFZ). In vitro studies were performed to evaluate cytochrome P450 (CYP)‐ and transporter‐mediated drug interaction potentials of 6β‐OH‐21‐desDFZ. Up to 50 µM, the highest soluble concentration in the test system, 6β‐OH‐21‐desDFZ weakly inhibited (IC50 > 50 µM) the enzyme activity of CYPs 1A2, 2B6, 2C8, 2C9, and 2D6, while moderately inhibiting CYP2C19 and CYP3A4 with IC50 values of approximately 50 and 35 μM, respectively. The inhibition was neither time‐dependent nor metabolism‐based. Incubation of up to 50 µM 6β‐OH‐21‐desDFZ with plated cryopreserved human hepatocytes for 48 h resulted in no meaningful concentration‐dependent induction of either mRNA levels or enzyme activity of CYP1A2, CYP2B6, or CYP3A4. In transporter inhibition assays, 6β‐OH‐21‐desDFZ, up to 50 µM, did not show interaction with human OAT1, OAT3, and OCT2 transporters. It weakly inhibited (IC50 > 50 µM) human MATE1, MATE2‐K, and OCT1 transporter activity, and moderately inhibited human MDR1, OATP1B1, and OATP1B3 transporter activity with IC50 values of 19.81 μM, 37.62 μM, and 42.22 μM, respectively. 14C‐6β‐OH‐21‐desDFZ was biosynthesized using bacterial biotransformation and the subsequent study showed that 6β‐OH‐21‐desDFZ was not a substrate for human BCRP, MDR1, MATE1, MATE2‐K, OAT1, OATP1B1, OATP1B3, and OCT2 transporters, but appeared to be an in vitro substrate for the human OAT3 uptake transporter. At plasma concentrations of 6β‐OH‐21‐desDFZ seen in the clinic, CYP‐ and transporter‐mediated drug–drug interactions are not expected following administration of a therapeutic dose of DFZ in Duchenne muscular dystrophy (DMD) patients.

Identification and Enzymatic Activity Evaluation of a Novel CYP2C9 Allelic Variant Discovered in a Patient.

Warfarin is a widely prescribed anticoagulant but the doses required to attain the optimum therapeutic effect exhibit dramatic inter-individual variability. Pharmacogenomics-guided warfarin dosing has been recommended to improve safety and effectiveness. We analyzed the cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) genes among 120 patients taking warfarin. A new coding variant was identified by sequencing CYP2C9. The novel A > G mutation at nucleotide position 14,277 led to an amino acid substitution of isoleucine with valine at position 213 (I213V). The functional consequence of the variant was subsequently evaluated in vitro. cDNA of the novel variant was constructed by site-directed mutagenesis and the recombinant protein was expressed in vitro using a baculovirus–insect cell expression system. The recombinant protein expression was quantified at apoprotein and holoprotein levels. Its enzymatic activities toward tolbutamide, warfarin and losartan were then assessed. It exhibited changed apparent Km values and increases of 148%, 84% and 67% in the intrinsic clearance of tolbutamide, warfarin and losartan, respectively, compared to wild-type CYP2C9*1, indicating dramatically enhanced in vitro enzymatic activity. Our study suggests that the amino acid at position 213 in wild-type CYP2C9*1 may be important for the enzymatic activity of CYP2C9 toward tolbutamide, warfarin and losartan. In summary, a patient taking high-dose warfarin (6.0 mg/day) in order to achieve the target international normalized ratio was found to have a mutation in the CYP2C9 gene.

Human Cytochrome P450 2C9 and its Polymorphic Modifications: Electroanalysis, Catalytic Properties and Approaches to the Regulation of Enzymatic Activity

The electrochemical properties of cytochrome P450 2C9 (CYP2C9) and polymorphic modifications P450 2C9*2 (CYP2C9*2) and P450 2C9*3 (CYP2C9*3) were studied. To analyze the comparative catalytic activity, the enzymes were immobilized on electrodes modified with a membrane-like synthetic surfactant (didodecyldimethylammonium bromide (SPE/DDAB). Peaks of reduction and oxidation of the heme iron, which confirms the adequate choice of the type of modified electrode, characterize cyclic voltammograms of cytochromes P450 under anaerobic conditions. The midpoint potential, Emid, of cytochrome P450 2C9 was -0.318 ± 0.01 V, and Emid =-0.324 ± 0.01 V, and Emid = -0.318 ± 0.03 V for allelic variant 2C9*2 and allelic variant 2C9*3, respectively. In the presence of substrate diclofenac under aerobic conditions, cytochrome P450 2C9 and its polymorphic modifications P450 2C9*2 and P450 2C9*3 exhibit catalytic properties registered by increasing the catalytic current. The amplitude ratio of diclofenac/oxygen currents ((IDF/IO2, catalytic index) is 1.80 for cytochrome P450 2C9, 1.33 and 2.18 for isoforms 2C9 *2 and 2C9*3, respectively. Antioxidant medications mexidol and taurine (at a concentration of 98 μM and 100 μM, respectively) stimulated aerobic reduction of cytochromes P450 heme iron. In the presence of mexidol, an increase in the catalytic activity of cytochrome P450 2C9 in relation to diclofenac by 1.7 times is registered. Taurine, vitamin-like compound with antioxidant properties also stimulates the metabolism of diclofenac by 1.5 times.

Therapeutic Drug Monitoring, CYP2C9 Genotyping and Phenotyping in the Treatment of Diabetes with Glibenclamide Products

Rational use of glybenclamide products in the treatment of patients with type 2 diabetes remains a high-priority task. The paper offers a summary of the main groups of glibenclamide drugs and describes pharmacogenetics of glybenclamide. Glibenclamide is metabolized by the enzyme cytochrome P450 2C9 (CYP2C9). Individuals with genetically determined low CYP2C9 activity are at an increased risk of hypoglycaemia. Carriers of CYP2C9*3 and CYP2C9*2 alleles tend to have higher concentrations of glybenclamide in blood and increased insulin secretion. Pharmacogenetic testing of patients and drug concentration monitoring using HPLC-MS can help reduce the risk of hypoglycemia during glibenclamide treatment. Based on literature review the authors selected the method characterised by a simple sample preparation procedure, short analysis time, and a wide analytical range for the substances being determined. This method can be useful both for bioequivalence studies and evaluation of glibenclamide products interchangeability. Glibenclamide pharmacokinetics is characterised by high interindividual variability. This may lead to both an increased risk of hypoglycemia and drug inefficacy, therefore, when prescribing glibenclamide, a physician should carefully control the efficacy and safety of drug therapy.

Evaluation of changes in cytochrome P450 2C19 activity in type 2 diabetic rats before and after treatment, by using isolated perfused liver model.

Objective(s):Alteration in drug metabolism is very likely in diabetes mellitus. This study assessed changes in CYP2C19 enzymatic activity in the liver using omeprazole as a probe in the animal model of type II diabetes (T2DM) before and after treatment with metformin and cinnamon.Materials and Methods:Twenty-eight male Wistar rats were randomly divided into seven groups. Fourteen days after induction of type 2 diabetic mellitus (T2DM), rats in the test group received metformin, cinnamon, and metformin plus cinnamon daily for 14 days. On day 28, rats were subjected to liver perfusion by Krebs-Henseleit buffer containing omeprazole as a CYP2C19 probe. Perfusate samples were analyzed by HPLC-UV to evaluate the activity of CYP2C19.Results:Mean metabolic ratio of omeprazole was changed from 0.091±0.005 in the control group to 0.054±0.005 in the untreated-diabetic rats. This average was increased inordinately to 0.218±0.036 in the treated rats with metformin. Interestingly, the administration of cinnamon in combination with metformin in diabetic rats caused the enzyme activity to return to (0.085±0.002) approximately the observed levels in the control group (0.091±0.005).Conclusion:Results showed that despite the suppression of the CYP2C19 enzyme activity in T2DM rats, metformin treatment could increase the enzyme activity. Simultaneous application of cinnamon and metformin can modulate the function of CYP2C19 to the observed level in the control group and make it more predictable to treat diabetes mellitus and fate of drugs that are metabolized by this enzyme.

Physiologically Based Pharmacokinetic (PBPK) Modeling and Simulation of Lornoxicam to Develop Personalized Drug Optimization regarding to CYP2C9 Genetic Polymorphism

Lornoxicam is a non‐steroidal anti‐inflammatory drug (NSAID) of oxicam class that has analgesic and anti‐inflammatory effects. Lornoxicam decreases various prostaglandin synthesis via inhibition of cyclo‐oxygenase (COX). Lornoxicam is primarily metabolized to 5’‐hydroxy lornoxicam through cytochrome P450 2C9 (CYP2C9) enzyme. Polymorphism of the CYP2C9 enzyme, e.g., CYP2C9*3 and CYP2C9*13, are associated with decreased activity of CYP2C9. Consequently, the difference of CYP2C9 activity by polymorphism triggers diverse drug concentration and response despite equal dose administration. For individual drug optimization, we develop a predictable pharmacokinetic model based on physiological characteristics related to CYP2C9 activity. In our research, 13 healthy Korean male subjects were included in the pharmacokinetic study of lornoxicam. All subjects were divided into three different CYP2C9*1/*1, CYP2C9*1/*3, and CYP2C9*1/*13 groups. 8mg dose of lornoxicam was administered to individual subjects. After administration, venous blood samples were collected and analyzed by HPLC‐UV method. Pharmacokinetic parameter values were predicted using PBPK software, PK‐Sim® 8. Vmax and Km parameter values were adjusted to reflect a difference in CYP2C9 activity based on in vitro CYP2C9 kinetic studies of lornoxicam. Simulated pharmacokinetic data were compared to our clinical data for the development and verification of the lornoxicam model and assessed for validity using a 99.998% confidence interval and two‐fold error criteria. In our clinical trial, pharmacokinetic parameters, e.g., AUCinf, Cmax, Tmax, and half‐life, were considerably changed in CYP2C9*1/*3 and CYP2C9*1/*13 groups compared to CYP2C9*1/*1 group. Firstly, AUCinf, Cmax, Tmax, and half‐life values are 2730.2, 655.7, 2.2, 2.74 in CYP2C9*1/*1 group, secondly 5464, 815.3, 1.6, 4.99 in CYP2C9*1/*3, finally 5315, 935.1, 2.3, 5.19 in CYP2C9*1/*13 respectively. For predicted data for this is as follows: 3099.2, 640.9, 1.5, 2.9 in CYP2C9*1/*1, 5312.5, 748.3, 1.6, 5.2 in CYP2C9*1/*3, 5551, 782.7, 1.6, 4.17 in CYP2C9*1/*13. Based on these result, simulated values were within suitable assessment for model development. Values for verification conducted simulation in Chinese ethnic also were fit in the assessment. Therefore, the PBPK model of lornoxicam was confirmed development successfully. Unfortunately, we could not find pharmacokinetic profiles in the ethnic group except the Chinese. So, we verified the PBPK model by conducting simulation only in Chinese ethnic. Because of this limitation, we expect to be able to develop a more validated model through the verification of various ethnic in further studies.PBPK model of lornoxicam in CYP2C9*1/*1 genotypes.Figure 1PBPK model of lornoxicam in CYP2C9*1/*3 genotypes. Km and Vmax values were scaledFigure 2

Study Protocol for a Pilot, Open-Label, Prospective, and Observational Study to Evaluate the Pharmacokinetics of Drugs Administered to Patients during Extracorporeal Circulation; Potential of In Vivo Cytochrome P450 Phenotyping to Optimise Pharmacotherapy.

Pharmacokinetic alterations of medications administered during surgeries involving cardiopulmonary bypass (CPB) and extracorporeal membrane oxygenation (ECMO) have been reported. The impact of CPB on the cytochrome P450 (CYP) enzymes’ activity is the key factor. The metabolic rates of caffeine, dextromethorphan, midazolam, omeprazole, and Losartan to the CYP-specific metabolites are validated measures of in vivo CYP 1A2, 2D6, 3A4, 2C19, and 2C9 activities, respectively. The study aim is to assess the activities of major CYPs in patients on extracorporeal circulation (EC). This is a pilot, prospective, open-label, observational study in patients undergoing surgery using EC and patients undergoing laparoscopic cholecystectomy as a control group. CYP activities will be measured on the day, and 1–2 days pre-surgery/3–4 days post-surgery (cardiac surgery and Laparoscopic cholecystectomy) and 1–2 days after starting ECMO, 1–2 weeks after starting ECMO, and 1–2 days after discontinuation from ECMO. Aforementioned CYP substrates will be administered to the patient and blood samples will be collected at 0, 1, 2, 4, and 6 h post-dose. Major CYP enzymes’ activities will be compared in each participant on the day, and before/after surgery. The CYP activities will be compared in three study groups to investigate the impact of CYPs on EC.

Evaluation of Omeprazole Limited Sampling Strategies to Estimate Constitutive Cytochrome P450 2C19 Activity in Healthy Adults: Erratum.

Evaluation of Omeprazole Limited Sampling Strategies to Estimate Constitutive Cytochrome P450 2C19 Activity in Healthy Adults: Erratum.

Inhibitory kinetics of fruit components on CYP2C19 activity

It has been suggested that the fruit components resveratrol (RSV), 6′, 7′-dihydroxybergamottin (DHB), and bergamottin (BG) might inhibit cytochrome P450 2C19 (CYP2C19) activity, but the mode and potency of such inhibition are yet to be investigated. This study aimed to investigate the mode and kinetics of the inhibition of CYP2C19-based omeprazole metabolism by RSV or grapefruit juice components (DHB or BG). RSV and DHB reduced CYP2C19 activity in a preincubation time-dependent manner, suggesting that they inactivated CYP2C19 via mechanism-based inhibition (MBI). Although BG inactivated CYP2C19 in a preincubation time- and concentration-dependent manner, suggesting that both MBI and reversible inhibition contributed to these effects, the concentration required to achieve 50% inhibition was 26-fold higher for reversible inhibition than for MBI (0.859 and 0.0331 μM, respectively), indicating that the inhibition of CYP2C19 by BG is primarily attributable to MBI. Based on the estimated intestinal concentrations of these components, it is considered that >90% of CYP2C19 would be inactivated after the consumption of normal amounts of grapefruit juice or RSV-containing substances. In conclusion, these findings suggest that food containing these components has the potential to evoke drug-food interactions caused by the MBI of intestinal CYP2C19 activity in the clinical setting.

CYP2C19-Guided Escitalopram and Sertraline Dosing in Pediatric Patients: A Pharmacokinetic Modeling Study.

Objective: Cytochrome P4502C19 (CYP2C19) is a highly polymorphic gene that encodes an enzyme that metabolizes escitalopram and sertraline, two selective serotonin reuptake inhibitors (SSRIs) that are FDA approved for pediatric use and commonly used to treat anxiety and depressive disorders in youth. Using pharmacokinetic (PK) models in adolescents, we sought to (1) model SSRI dosing across CYP2C19 phenotypes to compare SSRI exposure (area under curve, AUC) and maximum concentration (Cmax), (2) evaluate the impact of b.i.d. dosing (in rapid metabolizers [RM] and ultrarapid metabolizers [UM]) on SSRI exposure and Cmax, and (3) determine pharmacogenomically-informed dosing strategies to provide similar exposure across CYP2C19 phenotypes in adolescents. Methods: Using PK parameters in CYP2C19 phenotype groups and previously reported pediatric PK data for escitalopram and sertraline, we modeled exposure (AUC0-24) and Cmax and determined CYP2C19-guided dosing strategies. Results: Compared with normal CYP2C19 metabolizers treated with either escitalopram or sertraline, Cmax and AUC0-24 were higher in slower metabolizers and lower in patients with increased CYP2C19 activity, although the magnitude of these differences was more pronounced for escitalopram than for sertraline. For escitalopram, poor metabolizers (PMs) require 10 mg/day and UMs require 30 mg/day to achieve an exposure that is equivalent to 20 mg/day in a normal metabolizer (NM). For sertraline, to achieve AUC0-24 and Cmax similar to NMs receiving 150 mg/day, PMs require 100 mg/day, whereas a dose of 200 mg/day was required in rapid and UMs. For UMs, b.i.d. escitalopram dosing was necessary to achieve comparable trough levels and exposure to NMs. Conclusions: This simulation study raises the possibility that achieving similar escitalopram and sertraline plasma concentrations could require dose adjustments in CYP2C19 poor metabolizers and UMs, although the magnitude of these differences were more pronounced for escitalopram than for sertraline. However, prospective trials of pharmacogenomically guided dosing in the pediatric population are needed to extend the findings of these modeling studies.

Evaluation of Omeprazole Limited Sampling Strategies to Estimate Constitutive Cytochrome P450 2C19 Activity in Healthy Adults.

Limited sampling strategy (LSS) is a validated method to estimate pharmacokinetic (PK) parameters from a reduced number of samples. Omeprazole is used to phenotype in vivo cytochrome P450 (CYP) 2C19 activity. This study examined an LSS using 2 estimation methods to determine apparent oral clearance (CL/F) and thus CYP2C19 activity. Data from 7 previously published studies included healthy subjects receiving a single, oral dose of omeprazole with intensive PK sampling. CL/F was estimated using noncompartmental analysis (NCA) and population PK modeling. LSS was simulated by selecting the 1, 2, 4, and/or 6-hour postdose time points. Linear regression was performed to assess whether CL/F estimated from limited sampling could accurately predict CL/F from the full PK profile. Median CL/F was 23.7 L/h by NCA and 19.3 L/h by population PK modeling. In comparing the LSS NCA estimated versus observed CL/F, all evaluated linear regression models had unacceptable coefficients of determination (r, range: 0.14-0.81). With the population PK approach, 737 plasma concentrations (n = 71) and CYP2C19 genotype data were described with a 1-compartment structural model with mixed zero and first-order absorption and lag time. In comparing the population PK LSS estimated versus observed CL/F, all evaluated linear regression models had unacceptable r (range: 0.02-0.74). Post hoc comparison of CYP2C19 poor metabolizers versus CYP2C19 extensive metabolizers resulted in significantly lower CL/F in poor metabolizers versus extensive metabolizers. Omeprazole LSS performed poorly in estimating CL/F using 2 separate estimation approaches and does not seem to be a suitable method for determining CYP2C19 activity.

Effect of proton pump inhibitors on cytochrome P450 2c19 activity in&#x0D; patients with gastroesophageal reflux disease.

Patients with gastroesophageal reflux disease (GERD) are routinely prescribed one of the six proton pump inhibitors (PPI). All of these PPI are inhibitors of CYP2C19 enzyme to varying degrees. The phenotype 13C-pantoprazole breath test (Ptz-BT) was used to identify patients who are poor metabolizers (PM) and the extent of phenoconversion of CYP2C19 enzyme activity caused by four PPI (omeprazole, esomprazole pantoprazole and rabeprazole) in 54 newly diagnosed GERD patients prior to initiating randomly selected PPI therapy and 30 days after PPI therapy. The phenoconversion after 30 days of PPI therapy in GERD patients was statistically significant (p = 0.001) with omeprazole/esomeprazole (n = 27) strong CYP2C19 inhibitors, while there was no change in CYP2C19 enzyme activity (p = 0.8) with pantoprazole/rabeprazole (n = 27), weak CYP2C19 inhibitors. The rapid, in vivo, and non-invasive phenotype Ptz-BT can evaluate CYP2C19 enzyme activity. More importantly, it can identify GERD patients with low CYP2C19 enzyme activity (PM), caused by PPI or other concomitant medications, who would benefit from dose adjustments to maintain efficacy and avoid toxicity. The existing CYP2C19 genotype tests cannot predict the phenotype nor can it detect phenoconversion due to nongenetic factors.

7-Hydroxylation of warfarin is strongly inhibited by sesamin, but not by episesamin, caffeic and ferulic acids in human hepatic microsomes

Warfarin is a commonly used anticoagulant drug and is a derivate of coumarin. Cytochrome P450 2C9 (CYP2C9) plays the key role in transformation of coumarin and thus, influences determination of warfarin dosage. A number of factors including dietary compounds such as sesamin, caffeic acid and ferulic acids can regulate the activity of CYP2C9. The present study tested the hypothesis that sesamin, episesamin, caffeic acid and ferulic acid decreases the rate of warfarin 7-hydroxylation via inhibition of hepatic CYP2C9. The experiments were conducted on hepatic microsomes from human donors. It was demonstrated that the rate of 7-hydroxylation of warfarin was significantly decreased in the presence of sesamin in the range of concentrations from 5 to 500 nM, and was not affected by episesamin, caffeic acid and ferulic acid in the same range of concentrations. The kinetic analysis indicated non-competitive type of inhibition by sesamin with Ki = 202 ± 18 nM. In conclusion, the results of our in vitro study revealed that sesamin was able to inhibit formation of a major metabolite of warfarin, 7-hydroxywarfarin. The potentially negative consequences of the consumption of high amounts of sesamin-containing food or dietary supplements in warfarin-treated patients need to be further studied.