A New Workflow for Drug Metabolite Profiling by Utilizing Advanced Tribrid Mass Spectrometry and Data-Processing Techniques

Drug metabolite profiling utilizes liquid chromatography with tandem mass spectrometry (LC/MS/MS) to acquire ample information for metabolite identification and structural elucidation. However, there are still challenges in detecting and characterizing all potential metabolites that can be masked by a high biological background, especially the unknown and uncommon ones. In this work, a novel metabolite profiling workflow was established on a platform using a state-of-the-art tribrid high-resolution mass spectrometry (HRMS) system. Primarily, an instrumental method was developed based on the novel design of the tribrid system that facilitates in-depth MSⁿ scans with two fragmentation devices. Additionally, different advanced data acquisition techniques were assessed and compared, and automatic background exclusion and deep-scan approaches were adopted to promote assay efficiency and metabolite coverage. Finally, different data-analysis techniques were explored to fully extract metabolite data from the information-rich MS/MS data sets. Overall, a workflow combining tribrid mass spectrometry and advanced acquisition methodology has been developed for metabolite characterization in drug discovery and development. It maximizes the tribrid HRMS platform's utility and enhances the coverage, efficiency, quality, and speed of metabolite profiling assays.

The FDA-approved drugs ticlopidine, sertaconazole, and dexlansoprazole can cause morphological changes in C. elegans

Urgent need for treatments limit studies of therapeutic drugs before approval by regulatory agencies. Analyses of drugs after approval can therefore improve our understanding of their mechanism of action and enable better therapies. We screened a library of 1443 Food and Drug Administration (FDA)-approved drugs using a simple assay in the nematode C. elegans and found three compounds that caused morphological changes. While the anticoagulant ticlopidine and the antifungal sertaconazole caused both accumulations that resulted in distinct distortions of pharyngeal anatomy and lethality upon acute exposure, the proton-pump inhibitor dexlansoprazole caused molting defects and required exposure during larval development. Such easily detectable defects in a powerful genetic model system advocate the continued exploration of current medicines using a variety of model organisms to better understand drugs already prescribed to millions of patients.

Influence of genetic co-factors on the population pharmacokinetic model for clopidogrel and its active thiol metabolite

PURPOSE

A high interindividual variability is observed in the pharmacokinetics of clopidogrel, a widely used antiplatelet drug. In the present study, a joint parent-metabolite population pharmacokinetic model was developed to adequately describe observed concentrations of clopidogrel and its active thiol metabolite (H4).

METHODS

The study included 63 patients undergoing elective coronarography or percutaneous coronary intervention. The population pharmacokinetic model was developed in the NONMEM 7.3 software, and first-order conditional estimation method with interaction was applied. Also, the influence of covariates was evaluated (age, weight, body mass index (BMI), obesity defined as BMI ≥ 30 kg/m2, sex, diabetes mellitus, co-administration of PPI or statins, presence of CYP2C19*2, CYP2C19*17, CYP3A4*1G alleles, and ABCB1 3435 TT genotype).

RESULTS

It was found that the only significant covariate was the presence of CYP2C19*2 allele, which had an impact on lower conversion of clopidogrel to H4. As a result, predicted area under the time-concentration curve values was lower in carriers of this allele, with median 5.94 ng h/ml (interquartile range 3.92-12.51 [ng∙h/ml]) vs. 12.70 ng h/ml in non-carriers (interquartile range, 7.00-19.39 [ng∙h/ml]), respectively (p = 0.004).

CONCLUSIONS

Developed model predicts that the only significant covariate influencing the observed concentrations and therefore the exposure to the active H4 metabolite is the presence of CYP2C19*2 allele.

Molecular spectroscopic and thermodynamic studies on the interaction of anti-platelet drug ticlopidine with calf thymus DNA

Ticlopidine is an anti-platelet drug which belongs to the thienopyridine structural family and exerts its effect by functioning as an ADP receptor inhibitor. Ticlopidine inhibits the expression of TarO gene in S. aureus and may provide protection against MRSA. Groove binding agents are known to disrupt the transcription factor DNA complex and consequently inhibit gene expression. Understanding the mechanism of interaction of ticlopidine with DNA can prove useful in the development of a rational drug designing system. At present, there is no such study on the interaction of anti-platelet drugs with nucleic acids. A series of biophysical experiments were performed to ascertain the binding mode between ticlopidine and calf thymus DNA. UV-visible and fluorescence spectroscopic experiments confirmed the formation of a complex between ticlopidine and calf thymus DNA. Moreover, the values of binding constant were found to be in the range of 10³M^-1, which is indicative of groove binding between ticlopidine and calf thymus DNA. These results were further confirmed by studying the effect of denaturation on double stranded DNA, iodide quenching, viscometric studies, thermal melting profile as well as CD spectral analysis. The thermodynamic profile of the interaction was also determined using isothermal titration calorimetric studies. The reaction was found to be endothermic and the parameters obtained were found to be consistent with those of known groove binders. In silico molecular docking studies further corroborated well with the experimental results.

Comparison of Two Point-of-Care CYP2C19 Genotyping Assays for Genotype-Guided Antiplatelet Therapy

BACKGROUND

CYP2C19 polymorphisms contribute about 12% of the variability in the antiplatelet effect of clopidogrel, which is commonly prescribed for patients undergoing percutaneous coronary intervention. For these patients, rapid turnaround time of CYP2C19 genotyping may be critical. We validated and compared the performance of two point-of-care CYP2C19 genotype tests, Nanosphere Verigene CYP2C19 Nucleic Acid Test and Spartan RX CYP2C19 System.

MATERIALS AND METHODS

Our CLIA certified Molecular Diagnostic Laboratory performed 99 Verigene tests and 108 Spartan RX CYP2C19 assays. We compared performance and genotype results between the two platforms, across runs, and among technologists. Based on our validation results, we started offering CYP2C19 genotyping using the Spartan RX CYP2C19 assay for post-percutaneous coronary intervention patients.

RESULTS

Laboratory validation genotype results were consistent between both assays when the assays produced results (100% accuracy); however, the Verigene CYP2C19 had a 33% no call rate. In contrast, Spartan consistently showed accurate results. Using a newly established clinical workflow, we assayed 342 post-percutaneous coronary intervention patients with the Spartan test. Within one hour of submitting patient samples, ordering physicians were notified of any clinically significant results and provided clinical decision support.

CONCLUSIONS

Every approach has its limitations, but our practice of using the Spartan RX CYP2C19 test in our acute cardiac workflow provides accurate and rapid results to guide clinical decision-making at the point-of-care. Prospective follow-up is ongoing to evaluate outcomes and effectiveness of CYP2C19 testing.

CHARACTERIZATION OF BINDING SITES OF CLOPIDOGREL AND INTERFERENCE OF LINOLEIC ACID AT THE BINDING SITE ON BOVINE SERUM ALBUMIN

Binding of clopidogrel to serum albumin has been characterized in the presence and absence of linoleic acid by equilibrium dialysis method where ranitidine and diazepam were used as specific probes. Our findings suggested two binding sites for clopidogrel: a high affinity site (k₁ = 11.5 x 10⁵ M⁻¹) with low capaci- ty (n₁ = 1.2) and low affinity site (k₂ = 2.1 x 10⁵ M⁻¹) with high capacity (n. = 9.3). Interaction of linoleic acid with clopidogrel in the presence of ranitidine shows an increment of clopidogrel from 71 to 85.5% at concen- tration of (1 x 10⁵ M) to (6 x 10⁵ M). However, interaction of linoleic acid with clopidogrel in the presence of diazepam exhibits significant rise in free fraction of clopidogrel from 93 to 116% at concentration of (0 x 10' M) to (4 x 10⁵ M). At higher concentrations, linoleic acid displaced clopidogrel from its binding sites on serum albumin. This may cause escalation of free drug in the blood, which alters pharmacokinetic properties of clopi- dogrel taken with high fat diet.

Impact of the CYP2C19 Gene Polymorphism on Clopidogrel Personalized Drug Regimen and the Clinical Outcomes

BACKGROUND

Although the relationship between CYP2C19 genotype and clopidogrel metabolism has been studied clearly, we have not seen the report that clopidogrel was administered at a dose adjusted based on genotyping. The two main polymorphism loci of CYP2C19 gene were detected by the CYP2C19 genetic testing. ADP platelet aggregation technology was used to investigate the correlation between clinical effect and the clopidogrel dose, genetic metabolic type, physiological, pathological and other factors, to provide new ideas for clopidogrel therapy for percutaneous coronary intervention postoperation patients.

METHODS

A total of 48 patients were enrolled. All patients were given clopidogrel routine maintenance dose treatment and underwent CYP2C19 genotyping and platelet function testing. Patients were divided into extensive metabolizers, intermediate metabolizers, and poor metabolizers based on the different CYP2C19 genotypes. The clopidogrel dosage was adjusted to double the maintenance dose for the ineffective patients.

RESULTS

The study showed that all patients had no toxic side effects. The low responsiveness to clopidogrel in patients with diabetes is closely related to insulin resistance. Patients with hypertension and hyperlipidemia may increase the risk of clopidogrel resistance. The occurrence of clopidogrel resistance is associated with the CYP2C19 polymorphism in the < 65-year-old female patients.

CONCLUSIONS

For percutaneous coronary intervention in postoperative patients, research data is still lacking regarding clopidogrel dosage on the basis of different CYP2C19 genotypes. Looking forward, more rigorous research programs need to be designed to bring more guidance for clinical application.

Significant Improvement of Metabolic Characteristics and Bioactivities of Clopidogrel and Analogs by Selective Deuteration

In the search for prodrug analogs of clopidogrel with improved metabolic characteristics and antiplatelet bioactivity, a group of clopidogrel and vicagrel analogs selectively deuterated at the benzylic methyl ester group were synthesized, characterized, and evaluated. The compounds included clopidogrel-d₃ (8), 2-oxoclopidogrel-d₃ (9), vicagrel-d₃ (10a), and 12 vicagrel-d₃ analogs (10b–10m) with different alkyl groups in the thiophene ester moiety. The D₃C-O bond length in 10a was shown by X-ray single crystal diffraction to be shorter than the H₃C-O bond length in clopidogrel, consistent with the slower rate of hydrolysis of 8 than of clopidogrel in rat whole blood in vitro. A study of the ability of the compounds to inhibit ADP-induced platelet aggregation in fresh rat whole blood collected 2 h after oral dosing of rats with the compounds (7.8 μmol/kg) showed that deuteration increased the activity of clopidogrel and that increasing the size of the alkyl group in the thiophene ester moiety reduced activity. A preliminary pharmacokinetic study comparing 10a with vicagrel administered simultaneously as single oral doses (72 μmol/kg of each drug) to male Wistar rats showed 10a generated more of its active metabolite than vicagrel. These results suggest that 10a is a potentially superior antiplatelet agent with improved metabolic characteristics and bioactivity, and less dose-related toxicity.

[Computational Pharmacological Study on Clopidogrel Metabolism Enzymes Influenced by Fufang Danshen Dripping Pill]

OBJECTIVE

To investigate the effect of Fufang Danshen Dripping Pill on Clopidogrel metabolism enzymes target such as human liver carboxylesterasel (CES1), cytochrome P450 3A4, CYP450 2C19, CYP450 1A2, and CYP450 2B6, and to interpret the interaction effects.

METHODS

The CES1, cytochrome P450 3A4, CYP450 2C19, CYP450 1A2 and CYP450 2B6 which involved in Clopidogrel metabolism were selected at first, the chemical ligand database were created then, and finally the interaction effects between the ligand database and Clopidogrel metabolism target were explored.

RESULT

1 MX1 (CES1), 3NXU (CYP450 3A4), 4GQS (CYP450 2C19), 2HI4 (CYP450 1A2) and 3IBD(CYP450 2B6) as well as THA, RIT, OXU, Chlorzoxazone and CPZ were used as receptors and cutoff for each target respectively. The number of hits with potentially positive activities with metabolism enzymes target from the bioactive compounds in the preparation was 29, 8, 31, 51 and 44, respectively. These computational pharmacological docking studies were in accordance with the referenced cocktail experiment results.

CONCLUSION

It is suggested that Fufang Danshen Dripping Pill has inhibitory effects on Clopidogrel metabolism enzymes target such as CES1, Cytochrome P450 3A4, CYP450 2C19, CYP450 1A2 and CYP450 2B6.

The pharmacogenetics of carboxylesterases: CES1 and CES2 genetic variants and their clinical effect

Human carboxylesterase 1 (CES1) and carboxylesterase 2 (CES2) are serine esterases responsible for the hydrolysis of ester and amide bonds present in a number of pharmaceutical products. Several common genetic variants of the CES1 and CES2 genes have been shown to influence drug metabolism and clinical outcomes. Polymorphisms of the CES1 gene have been reported to affect the metabolism of dabigatran etexilate, methylphenidate, oseltamivir, imidapril, and clopidogrel, whereas variants of the CES2 gene have been found to affect aspirin and irinotecan. Although the findings of these studies may be preliminary, they demonstrate the potential clinical utility of CES polymorphisms; however, more research is required, especially with respect to CES2. In this review, we outline the functional, molecular, and genetic properties of CES1 and CES2, and highlight recent studies that have shown relations between CES1 and CES2 variants and contemporary pharmacotherapy.

Implementation of a pharmacogenomics service in a community pharmacy

OBJECTIVE To determine the feasibility of implementing a pharmacogenomics service in a community pharmacy. SETTING A single community pharmacy that is part of a regional chain known for offering innovative pharmacy services. PRACTICE DESCRIPTION Community pharmacists at the project site routinely provide clinical pharmacy services, including medication therapy management, immunizations, point-of-care testing, blood pressure monitoring, and diabetes education. PRACTICE INNOVATION The implementation of a pharmacogenomic testing and interpretation service for the liver isoenzyme cytochrome P450 2C19. PARTICIPANTS 18 patients taking clopidogrel, a drug metabolized by CYP2C19. MAIN OUTCOME MEASURES Rate of patient participation, rate of prescriber acceptance of pharmacist recommendation, time to perform genetic testing service, and number of claims submitted to and paid by insurance. RESULTS Of 41 patients taking clopidogrel and meeting project criteria, 18 (43.9%) enrolled and completed testing and interpretation of pharmacogenomic results. The mean time pharmacists spent completing all stages of the project with each participant was 76.6 minutes. The mean time to complete participation in the project (time between person's first and second visit) was 30.1 days. Nine patients had wild-type alleles, and pharmacists recommended continuation of therapy as ordered. Genetic variants were found in the other nine patients, and all pharmacist recommendations for modifications in therapy were ultimately accepted by prescribers. Overall, 17 patients consented to filing of reimbursement claims with their insurers. Five were not able to be billed due to submission difficulties. Of the remaining 12, none was paid. CONCLUSION A pharmacogenomics service can be an extension of medication therapy management services in a community pharmacy. Prescribers are receptive to having community pharmacists conduct pharmacogenomics testing, but reimbursement is a challenge.

Glutathione trapping of reactive drug metabolites produced by biomimetic metalloporphyrin catalysts

RATIONALE

Metalloporphyrins can be useful in the production of drug metabolites, as they enable easier production of oxidative metabolites usually produced by the cytochrome P450 enzymes. Our aim was to test metalloporphyrin-based biomimetic oxidation (BMO) methods for production and S-glutathione trapping of reactive drug metabolites in addition to phase I metabolites.

METHODS

Clozapine, ticlopidine and citalopram were selected as model compounds. These were incubated with the BMO assay and the incubations were analyzed with high-resolution liquid chromatography/mass spectrometry (LC/MS) and tandem mass spectrometry (LC/MS/MS). Additionally, incubations with human liver S9 fraction were performed to compare the results with the BMO assay.

RESULTS

Six glutathione conjugates were identified for clozapine from the S9 incubation, while the BMO assay produced four of these. Four out of the five phase I metabolites produced by S9 were detected using the BMO assay. For ticlopidine, four glutathione conjugates were detected from the S9 incubation, but none of these were observed using the BMO assay. Eight of the nine phase I metabolites produced by S9 incubation were detected in the BMO assay. As expected, no glutathione conjugates were detected for citalopram, and the same three phase I metabolites were detected in both S9 and BMO incubations.

CONLUSIONS

Differences in formation of GSH-trapped reactive metabolites by BMO assay between clozapine and ticlopidine are probably due to different reactive intermediates and reaction mechanisms. The reactive intermediate of clozapine, the nitrenium ion was generated, but the reactive intermediates of ticlopidine, S-oxide and epoxide, were not detected from the incubations. However, the results show that for selected cases the use of biomimetic assays can be used to produce high amounts of S-glutathione conjugates identical to those from liver subfraction incubations, on a scale that is relevant for purification and subsequent identification by NMR spectroscopy; which is often difficult using incubations with liver subfractions.

Identification of alcohol-dependent clopidogrel metabolites using conventional liquid chromatography/triple quadrupole mass spectrometry

RATIONALE

Clopidogrel (CLO) is a prodrug used to prevent ischemic events in patients undergoing percutaneous coronary intervention or with myocardial infarction. A previous study found ethyl clopidogrel (ECLO) is formed by transesterification of CLO when incubated with alcohol in human liver microsomes. We hypothesize that ECLO will be subject to further metabolism and developed an assay to identify its metabolites.

METHODS

A liquid chromatography/triple quadrupole mass spectrometry (LC/MS/MS) method was developed to identify metabolites of ECLO. According to the predicted metabolic pathway of ECLO, precursor-product ion pairs were used to screen the possible metabolites of ECLO in human liver S9 fractions. Subsequently, the detected metabolites were characterized by the results of product ion scan.

RESULTS

In the presence of alcohol, CLO was tranesterified to ECLO, which was further oxidized to form ethylated 2-oxo-clopidogrel and several ethylated thiol metabolites including the ethylated form of the H4 active metabolite.

CONCLUSIONS

The ECLO formed by transesterification with alcohol is subject to metabolism by CYP450 enzymes producing ethylated forms of 2-oxo-clopidogrel and the active H4 thiol metabolite.

Identification of CYP2C19 inhibitors from phytochemicals using the recombinant human enzyme model

The aim of the present study was to develop the recombinant insect cell-expressed protein as an in vitro model for inhibitors screening for human cytochrome P450 2C19 (CYP2C19), and to use the model to investigate the inhibition effect of three phytochemicals on CYP2C19 in vitro. Omeprazole was applied as the probe substrate. The estimated inhibitory constant (K(i)) of ticlopidine and fluvoxamine were 0.64 +/- 0.025 microM and 0.29 +/- 0.090 microM, respectively. After co-incubation with ticlopidine or fluvoxamine, the mean omeprazole Michaelis-Menten constant (K(m)) increased from 4.99 +/- 0.22 microM to 16.25 +/- 1.22 microM or 19.20 +/- 1.73 microM, respectively, while omeprazole's mean V(max) did not vary much. Both ticlopidine and fluvoxamine were competitive inhibitors of CYP2C19. The IC50 of three phytochemicals, isoalantolactone, curcumol and schisandrin A was determined as 38.91 microM, 121.0 microM and 86.41 microM, and the K(i) as 5.02 +/- 1.04 microM, 35.84 +/- 8.95 microM, and 4.46 +/- 0.017 microM, respectively. The in vitro model for inhibitor screening established using recombinant CYP2C19 could be used to assess the inhibition potential of drug candidates. Isoalantolactone and schisandrin A are potent inhibitors of CYP2C19, while curcumol is a moderate potent inhibitor of CYP2C19.

Proton pump inhibitors and clopidogrel: an association to avoid?

Dual antiplatelet therapy with aspirin and clopidogrel reduces cardiovascular events following an acute coronary syndrome or stent implantation, but the associated increased risk of gastro-intestinal bleeding often leads to the co-administration of proton pump inhibitors (PPIs). PPIs have been shown to decrease antiplatelet effects of clopidogrel ex vivo, raising concerns about the cardiovascular safety of this drug combination. Clinical trials investigating PPI-clopidogrel interactions have provided conflicting results and are all subject to methodological critiques. The much desired and much needed prospective, double-bind, randomized, placebo-controlled trials with adequate follow-up and sample size have not yet been performed. Indeed, the Clopidogrel and the Optimization of GI Events Trial, which would have had such characteristics, was stopped prematurely. As a consequence, the question of the PPI-clopidogrel interaction is still unresolved, and clinical consequences cannot be excluded. At this time such combination therapy should, therefore, be provisionally advocated only for patients at high risk of bleeding (prior upper gastro-intestinal bleeding, advanced age, concomitant use of warfarin, steroidal or non-steroidal anti-inflammatory drugs and Helicobacter pylori infection) and avoiding PPIs with strong affinity for cytochrome CYP2C19, such as omeprazole and esomeprazole.

Hepatocellular toxicity of clopidogrel: mechanisms and risk factors

Clopidogrel is a prodrug used widely as a platelet aggregation inhibitor. After intestinal absorption, approximately 90% is converted to inactive clopidogrel carboxylate and 10% via a two-step procedure to the active metabolite containing a mercapto group. Hepatotoxicity is a rare but potentially serious adverse reaction associated with clopidogrel. The aim of this study was to find out the mechanisms and susceptibility factors for clopidogrel-associated hepatotoxicity. In primary human hepatocytes, clopidogrel (10 and 100 μM) was cytotoxic only after cytochrome P450 (CYP) induction by rifampicin. Clopidogrel (10 and 100 μM) was also toxic for HepG2 cells expressing human CYP3A4 (HepG2/CYP3A4) and HepG2 cells co-incubated with CYP3A4 supersomes (HepG2/CYP3A4 supersome), but not for wild-type HepG2 cells (HepG2/wt). Clopidogrel (100 μM) decreased the cellular glutathione content in HepG2/CYP3A4 supersome and triggered an oxidative stress reaction (10 and 100 µM) in HepG2/CYP3A4, but not in HepG2/wt. Glutathione depletion significantly increased the cytotoxicity of clopidogrel (10 and 100 µM) in HepG2/CYP3A4 supersome. Co-incubation with 1 μM ketoconazole or 10mM glutathione almost completely prevented the cytotoxic effect of clopidogrel in HepG2/CYP3A4 and HepG2/CYP3A4 supersome. HepG2/CYP3A4 incubated with 100 μM clopidogrel showed mitochondrial damage and cytochrome c release, eventually promoting apoptosis and/or necrosis. In contrast to clopidogrel, clopidogrel carboxylate was not toxic for HepG2/wt or HepG2/CYP3A4 up to 100 µM. In conclusion, clopidogrel incubated with CYP3A4 is associated with the formation of metabolites that are toxic for hepatocytes and can be trapped by glutathione. High CYP3A4 activity and low cellular glutathione stores may be risk factors for clopidogrel-associated hepatocellular toxicity.

Detection and characterization of ticlopidine conjugates in rat bile using high-resolution mass spectrometry: applications of various data acquisition and processing tools

Ticlopidine, an antiplatelet drug, undergoes extensive oxidative metabolism to form S-oxide, N-oxide, hydroxylated and dealkylated metabolites. However, metabolism of ticlopidine via conjugation has not been thoroughly investigated. In this study, multiple data acquisition and processing tools were applied to the detection and characterization of ticlopidine conjugates in rat bile. Accurate full-scan mass spectrometry (MS) and collision-induced dissociation (CID) MS/MS data sets were recorded using isotope pattern-dependent acquisition on an LTQ/Orbitrap system. In addition, mass spectral data from online H/D exchanging and high collision energy dissociation (HCD) were recorded. Data processes were carried out using extracted ion chromatography (EIC), mass defect filter (MDF) and isotope pattern filter (IPF). The total ion chromatogram displayed a few major conjugated metabolites and many endogenous components. Profiles from EIC and IPF processes exhibited multiple conjugates with no or minimal false positives. However, ticlopidine conjugates that were not predictable or lost a chorine atom were not found by EIC or IPF, respectively. MDF was able to detect almost all of ticlopidine conjugates although it led to a few more false positives. In addition to CID spectra, data from HCD, H/D exchanging experiments and isotope pattern simulation facilitated structural characterization of unknown conjugates. Consequently, 20 significant ticlopidine conjugates, including glucuronide, glutathione, cysteinylglycine, cysteine and N-acetylcysteine conjugates, were identified in rat bile, a majority of which are associated with bioactivation and not previously reported. This study demonstrates the utility and limitation of various high-resolution MS-based data acquisition and processing techniques in detection and characterization of conjugated metabolites.

[Informativeness of genetic factors for optimization of personalized therapy with clopidogrel]

We studied occurrence of allele variants *1, *2, *3, and *17 of CYP2C19 gene and polymorphic variants of ABCB1 gene in clopidogrel treated patients from West Siberian and Far Eastern regions and determined contribution of these polymorphisms to laboratory efficacy of clopidogrel. In dependence on magnitude of change of platelet aggregation we distinguished groups of patients with different sensitivity to clopidogrel. We found association between polymorphic variant CYP2C19*2 with changes of platelet aggregation after administration of clopidogrel. An additional group of patients with augmented platelet aggregation after administration of clopidogrel was detected. There was no correlation between the latter effect and any of studied polymorphisms.

Genetic testing in patients with acute coronary syndrome undergoing percutaneous coronary intervention: a cost-effectiveness analysis

BACKGROUND

The CYP2C19 genotype is a predictor of adverse cardiovascular events in acute coronary syndrome (ACS) patients undergoing percutaneous coronary intervention (PCI) treated with clopidogrel.

OBJECTIVES

We aimed to evaluate the cost-effectiveness of a CYP2C19*2 genotype-guided strategy of antiplatelet therapy in ACS patients undergoing PCI, compared with two 'no testing' strategies (empiric clopidogrel or prasugrel).

METHODS

We developed a Markov model to compare three strategies. The model captured adverse cardiovascular events and antiplatelet-related complications. Costs were expressed in 2010 US dollars and estimated using diagnosis-related group codes and Medicare reimbursement rates. The net wholesale price for prasugrel was estimated as $5.45 per day. A generic estimate for clopidogrel of $1.00 per day was used and genetic testing was assumed to cost $500.

RESULTS

Base case analyses demonstrated little difference between treatment strategies. The genetic testing-guided strategy yielded the most QALYs and was the least costly. Over 15 months, total costs were $18 lower with a gain of 0.004 QALY in the genotype-guided strategy compared with empiric clopidogrel, and $899 lower with a gain of 0.0005 QALY compared with empiric prasugrel. The strongest predictor of the preferred strategy was the relative risk of thrombotic events in carriers compared with wild-type individuals treated with clopidogrel. Above a 47% increased risk, a genotype-guided strategy was the dominant strategy. Above a clopidogrel cost of $3.96 per day, genetic testing was no longer dominant but remained cost-effective.

CONCLUSIONS

Among ACS patients undergoing PCI, a genotype-guided strategy yields similar outcomes to empiric approaches to treatment, but is marginally less costly and more effective.

[Clopidogrel metabolism related gene polymorphisms in Chinese patients with acute coronary syndrome]

OBJECTIVE

To detect the single nucleotide polymorphisms of clopidogrel metabolism related genes (CYP2C19, ABCB1 and PON1) in Chinese patients with acute coronary syndrome (ACS) by genotype analysis.

METHODS

Genetic analysis was performed in patients admitted to Fuwai Hospital from 2005 to 2008 with ACS within 4 weeks. The detection of polymorphisms was performed by TaqMan real-time PCR method. The alleles genotyped were CYP2C19 *2-*8, *17, ABCB1 C3435T, PON1 Q192R and PON1 L55M. Minor allele frequency (MAF) was calculated. Patients were classified as one of the 5 categories by clopidogrel metabolizer phenotypes as extensive [without any "loss-of-function" (LOF) allele *2-*8 or "gain-of-function" (GOF) allele *17], intermediate (with only one LOF allele), Poor (with two or more LOF alleles), ultra (with one or two GOF alleles) or unknown (with one LOF allele and one GOF allele).

RESULTS

A total of 2800 ACS patients were enrolled [mean age (59.0 ± 12.3) years and 2236 males (79.9%)]. There were 74% patients with ST-segment elevation myocardial infarction (STEMI, n = 2072), 22.0% patients with non-ST-segment elevation myocardial infarction (NSTEMI, n = 617) and 4.0% patients with unstable angina (UA, n = 111). The minor allele frequency (MAF) for each genotype of CYP2C19 *2, *3, *4, *17 was 28.7%, 4.6%, 0.1% and 1.2%, respectively. There was no LOF allele *5-*8 in the study population. The MAF for ABCB1 C3435T, PON1 Q192R and PON1 L55M was 39.4%, 37.8% and 4.4%, respectively. Clopidogrel metabolizer groups were defined as extensive in 41.7%, intermediate in 45.6%, poor in 10.3%, ultra in 1.9% and unknown in 0.6% patients, respectively. There were no significant differences for all genotypes between males and females. Total LOF carriers of CYP2C19 were 56.4% and GOF carriers were 2.5%.

CONCLUSIONS

Our study demonstrated a high distribution of the LOF allele of CYP2C19 in China ACS population.

Genetic considerations

Dual antiplatelet therapy with aspirin and a P2Y(12) receptor antagonist improves outcomes in patients with acute coronary syndrome and in those treated with percutaneous coronary intervention (PCI) and a coronary stent. Candidate gene and genome-wide association studies have found that common genetic polymorphisms of the cytochrome P450 (CYP) 2C19 isoenzyme that result in a loss of functional activity are associated with less exposure of clopidogrel active metabolite and a diminished antiplatelet effect. Meta-analyses of registries and genetic substudies of randomized clinical trials demonstrate that carriers of these polymorphisms who are treated with clopidogrel are at an increased risk of cardiovascular events, particularly stent thrombosis, compared with noncarriers. This deleterious effect appears to be attenuated in patients not treated with PCI. The influence of polymorphisms of other genes, such as ABCB1, is inconsistent across clinical studies. The clinical efficacy of the newer P2Y(12) antagonists prasugrel and ticagrelor do not appear to be affected by the CYP2C19 genotype, but these agents increase major bleeding not related to coronary artery bypass surgery. Although data from randomized clinical trials are currently lacking, these observations suggest that a pharmacogenomic-guided approach to antiplatelet therapy in acute coronary syndrome could potentially maximize ischemic benefit while minimizing bleeding risk.

CYP2C19 genotype, clopidogrel metabolism, platelet function, and cardiovascular events: a systematic review and meta-analysis

CONTEXT

The US Food and Drug Administration recently recommended that CYP2C19 genotyping be considered prior to prescribing clopidogrel, but the American Heart Association and American College of Cardiologists have argued evidence is insufficient to support CYP2C19 genotype testing.

OBJECTIVE

To appraise evidence on the association of CYP2C19 genotype and clopidogrel response through systematic review and meta-analysis.

DATA SOURCES

PubMed and EMBASE from their inception to October 2011.

STUDY SELECTION

Studies that reported clopidogrel metabolism, platelet reactivity or clinically relevant outcomes (cardiovascular disease [CVD] events and bleeding), and information on CYP2C19 genotype were included.

DATA EXTRACTION

We extracted information on study design, genotyping, and disease outcomes and investigated sources of bias.

RESULTS

We retrieved 32 studies of 42,016 patients reporting 3545 CVD events, 579 stent thromboses, and 1413 bleeding events. Six studies were randomized trials ("effect-modification" design) and the remaining 26 reported individuals exposed to clopidogrel ("treatment-only" design). In treatment-only analysis, individuals with 1 or more CYP2C19 alleles associated with lower enzyme activity had lower levels of active clopidogrel metabolites, less platelet inhibition, lower risk of bleeding (relative risk [RR], 0.84; 95% CI, 0.75-0.94; absolute risk reduction of 5-8 events per 1000 individuals), and higher risk of CVD events (RR, 1.18; 95% CI, 1.09-1.28; absolute risk increase of 8-12 events per 1000 individuals). However, there was evidence of small-study bias (Harbord test P = .001). When analyses were restricted to studies with 200 or more events, the point estimate was attenuated (RR, 0.97; 95% CI, 0.86-1.09). In effect-modification studies, CYP2C19 genotype was not associated with modification of the effect of clopidogrel on CVD end points or bleeding (P > .05 for interaction for both). Other limitations included selective outcome reporting and potential for genotype misclassification due to problems with the * allele nomenclature for cytochrome enzymes.

CONCLUSION

Although there was an association between the CYP2C19 genotype and clopidogrel responsiveness, overall there was no significant association of genotype with cardiovascular events.

[Interaction between clopidogrel and proton pump inhibitors]

The drug interaction between proton pump inhibitors and clopidogrel has been the subject of much study in recent years. Contradictory results regarding the effect of proton pump inhibitors on platelet reactivity and on clinical outcome in clopidogrel-treated patients have been reported in literature. Concomitant use of omeprazole and clopidogrel was found to decrease the exposure (AUC) to clopidogrel's active metabolite by 50% and to sharply increase platelet reactivity, as a result of inhibition by omeprazole of CYP2C19, a cytochrome P450 (CYP) enzyme. Pantoprazole has a much weaker effect on clopidogrel's pharmacokinetics and on platelet reactivity during concomitant use. The influence of the other proton pump inhibitors when used simultaneously with clopidogrel has not yet been investigated in adequately randomized studies. Regulatory agencies state that the combination of clopidogrel and the CYP2C19 inhibitors omeprazole and esomeprazole should be avoided. To date, there is no conclusive evidence of a clinically-relevant interaction between any of the proton pump inhibitors and clopidogrel.

[Clopidogrel and proton pump inhibitors: insufficient evidence of interaction]

As both proton pump inhibitors (PPIs) and clopidogrel are metabolized by CYP2C19, an enzyme of the cytochrome P450 system, this could lead to drug competition. Recent studies have raised concerns that interaction of PPIs and clopidogrel could reduce the efficacy of clopidogrel and thus increase events such as myocardial infarction. This has resulted in opposing opinions and controversial recommendations. Optimal protection of patients at high risk for cardiovascular events is warranted. On the other hand, optimal gastroprotection for patients at risk for gastrointestinal bleeding is of clinical relevance. Despite the large number of studies, current evidence does not support the existence of an interaction between PPIs and clopidogrel. In agreement with international guidelines the approach of providing this combination therapy to those patients with an accepted indication for gastroprotection and secondary cardiovascular prevention is justified.

Reduced-function CYP2C19 genotype and risk of adverse clinical outcomes among patients treated with clopidogrel predominantly for PCI: a meta-analysis

CONTENT

Clopidogrel, one of the most commonly prescribed medications, is a prodrug requiring CYP450 biotransformation. Data suggest its pharmacologic effect varies based on CYP2C19 genotype, but there is uncertainty regarding the clinical risk imparted by specific genotypes.

OBJECTIVE

To define the risk of major adverse cardiovascular outcomes among carriers of 1 (≈ 26% prevalence in whites) and carriers of 2 (≈ 2% prevalence in whites) reduced-function CYP2C19 genetic variants in patients treated with clopidogrel.

DATA SOURCES AND STUDY SELECTION

A literature search was conducted (January 2000-August 2010) in MEDLINE, Cochrane Database of Systematic Reviews, and EMBASE. Genetic studies were included in which clopidogrel was initiated in predominantly invasively managed patients in a manner consistent with the current guideline recommendations and in which clinical outcomes were ascertained.

DATA EXTRACTION

Investigators from 9 studies evaluating CYP2C19 genotype and clinical outcomes in patients treated with clopidogrel contributed the relevant hazard ratios (HRs) and 95% confidence intervals (CIs) for specific cardiovascular outcomes by genotype.

RESULTS

Among 9685 patients (91.3% who underwent percutaneous coronary intervention and 54.5% who had an acute coronary syndrome), 863 experienced the composite end point of cardiovascular death, myocardial infarction, or stroke; and 84 patients had stent thrombosis among the 5894 evaluated for such. Overall, 71.5% were noncarriers, 26.3% had 1 reduced-function CYP2C19 allele, and 2.2% had 2 reduced-function CYP2C19 alleles. A significantly increased risk of the composite end point was evident in both carriers of 1 (HR, 1.55; 95% CI, 1.11-2.17; P = .01) and 2 (HR, 1.76; 95% CI, 1.24-2.50; P = .002) reduced-function CYP2C19 alleles, as compared with noncarriers. Similarly, there was a significantly increased risk of stent thrombosis in both carriers of 1 (HR, 2.67; 95% CI, 1.69-4.22; P < .0001) and 2 (HR, 3.97; 95% CI, 1.75-9.02; P = .001) CYP2C19 reduced-function alleles, as compared with noncarriers.

CONCLUSION

Among patients treated with clopidogrel for percutaneous coronary intervention, carriage of even 1 reduced-function CYP2C19 allele appears to be associated with a significantly increased risk of major adverse cardiovascular events, particularly stent thrombosis.

[Clopidogrel--proton pump inhibitors drug interaction: implications to clinical practice]

Recent studies have raised the concern that proton pump inhibitors (PPIs) could potentially interfere with clopidogrel antiplatelet effect. This association is frequent in clinical practice and is recommended by recent consensus guidelines in patients taking dual antiplatelet therapy to prevent gastrointestinal (GI) bleeding. Clopidogrel is a pro-drug which needs to be metabolized into its active metabolite, by cytochrome P450, especially by CYP2C19 isoenzyme. Various PPIs can inhibit CYP2C19, which could possibly decrease clopidogrel bioactivation process and, therefore, its antiplatelet effect. Various platelet function studies have shown that omeprazol can significantly decrease clopidogrel inhibitory effect on platelet P2Y12 receptor, leading to an increase in the number of patients who are "nonresponders" to clopidogrel. These pharmacokinetic studies also shown that this is not probably a class effect of PPIs, because they are metabolized to varying degrees by CYP2C19. The clinical impact of these observations remains uncertain, because various observational studies have shown conflicting results, and remains to demonstrate if PPIs can really increase the risk of cardiovascular events in patients taking clopidogrel. In this review we will discuss the pharmacokinetic basis underlying this drug interaction, the effect of different PPIs on platelet function tests and we will analyze in detail the potential clinical implications of using this association, both on cardiovascular and gastrointestinal events. Until further data is available, some clinical strategies can be recommended: (1) individual gastrointestinal risk assessment, with PPIs administration only to patients on dual anti-platelet therapy with additional GI risk factors; (2) preferential use of PPIs that have shown less interference with clopidogrel efficacy; (3) wide separation of PPI and clopidogrel dosing to minimize the risk of interaction (PPI may be given before breakfast and clopidogrel at bedtime); (4) or alternative use of histamine-2-receptor antagonist therapy, in patients at low GI risk.

DMET microarray technology for pharmacogenomics-based personalized medicine

Human genome sequence variation in the form of single nucleotide polymorphisms (SNPs) as well as more complex structural variation such as insertions, duplications, and deletions underlies each individual's response to drugs and thus the likelihood of experiencing an adverse drug reaction. The ongoing challenge of the field of pharmacogenetics is to further understand the relationship between genetic variation and differential drug responses, with the overarching goal being that this will lead to improvements in both the safety and efficacy of drugs. The Affymetrix DMET Plus Premier Pack (DMET stands for Drug Metabolizing Enzymes and Transporters) enables highly multiplexed genotyping of known polymorphisms in Absorption, Distribution, Metabolism, and Elimination (ADME)-related genes on a single array. The DMET Plus Panel interrogates markers in 225 genes that have documented functional significance in phase I and phase II drug metabolism enzymes as well as drug transporters. The power of the DMET Assay has previously been demonstrated with regard to several different drugs including warfarin and clopidogrel. In a research study using an earlier four-color version of the assay, it was demonstrated that warfarin dosing can be influenced by a cytochrome P450 (CYP) 4F2 variant. Additionally, the assay has been used to demonstrate that CYP2C19 variants with decreased enzyme activity led to lower levels of the active clopidogrel metabolite, resulting in a decreased inhibition of platelets and a higher rate of cardiovascular events when compared to noncarriers of the DNA variant. Thus, highly multiplexed SNP genotyping focused on ADME-related polymorphisms should enable research into development of safer drugs with greater efficacy.

Association of platelet responsiveness with clopidogrel metabolism: role of compliance in the assessment of "resistance"

BACKGROUND

Noncompliance is probably the major cause of clopidogrel "resistance." However, noncompliance is difficult to prove without confirming that the drug has been administered. Therefore, detection of plasma clopidogrel and/or metabolite(s) as the reliable objective method to confirm compliance is important.

METHODS

We sought to correlate the inhibition of platelet aggregation (IPA) with plasma levels of unchanged clopidogrel (UC), active thiol metabolite (ATM), and inactive carboxyl metabolite (ICM) in a large cohort of patients with coronary artery disease and ischemic stroke treated with clopidogrel. We conducted secondary post-hoc analyses of IPA and plasma UC, ATM, and ICM in a dataset consisting of presumably compliant patients with coronary disease (n = 422) and post-stroke (n = 209).

RESULTS

Overall noncompliance rate was 22% (n = 138), while such risks were significantly higher in stroke survivors (n = 79, or 38%) when compared to patients with coronary disease (14%; n = 59; P = .001). Only ICM (19,154 +/- 7,228 ng/ml) was suitable for detecting compliance, while UC (15.2 +/- 9.4 ng/ml), and ATM (8.1 +/- 3.7 ng/ml) in most cases are barely detectable, and diminish over time in the stored samples. The best correlation with IPA (r2 = 0.847) was observed for active metabolite, followed by unchanged clopidogrel (r2 = 0.602), and finally inactive metabolite (r2 = 0.529). The predictive value for noncompliance was also high for inactive metabolite (c-statistic = 0.911).

CONCLUSIONS

Therapy with clopidogrel is associated with double-digit underestimated risks for noncompliance, especially in stroke survivors, supporting the hypothesis that lack of IPA, and clopidogrel "resistance" are attributed to hidden noncompliance. Plasma ICM, but not UC, or ATM is a useful marker to monitor compliance to clopidogrel in registries and clinical trials.

Interaction between clopidogrel and proton pump inhibitors: hypothesis to explain multifactorial CYP2C19 inhibition

Clopidogrel is an antiplatelet drug that requires bioactivation to its active metabolite to demonstrate its antiplatelet effect. Formation of the active metabolite involves multiple cytochrome P450 enzymes, with CYP2C19 playing an important role. Clopidogrel is often co-administered with proton pump inhibitors (PPIs) to decrease GI-tract bleeding, and decreased antiplatelet effect has been observed in these patients. This observation cannot be explained by the weak inhibitory effect of PPIs on CYP2C19. A hypothesis is proposed to interpret the phenomenon of PPI inhibition based in part on the finding that clopidogrel is itself an inhibitor of CYP2C19.

Cytochrome p-450 polymorphisms and response to clopidogrel

BACKGROUND

Clopidogrel requires transformation into an active metabolite by cytochrome P-450 (CYP) enzymes for its antiplatelet effect. The genes encoding CYP enzymes are polymorphic, with common alleles conferring reduced function.

METHODS

We tested the association between functional genetic variants in CYP genes, plasma concentrations of active drug metabolite, and platelet inhibition in response to clopidogrel in 162 healthy subjects. We then examined the association between these genetic variants and cardiovascular outcomes in a separate cohort of 1477 subjects with acute coronary syndromes who were treated with clopidogrel in the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel-Thrombolysis in Myocardial Infarction (TRITON-TIMI) 38.

RESULTS

In healthy subjects who were treated with clopidogrel, carriers of at least one CYP2C19 reduced-function allele (approximately 30% of the study population) had a relative reduction of 32.4% in plasma exposure to the active metabolite of clopidogrel, as compared with noncarriers (P<0.001). Carriers also had an absolute reduction in maximal platelet aggregation in response to clopidogrel that was 9 percentage points less than that seen in noncarriers (P<0.001). Among clopidogrel-treated subjects in TRITON-TIMI 38, carriers had a relative increase of 53% in the composite primary efficacy outcome of the risk of death from cardiovascular causes, myocardial infarction, or stroke, as compared with noncarriers (12.1% vs. 8.0%; hazard ratio for carriers, 1.53; 95% confidence interval [CI], 1.07 to 2.19; P=0.01) and an increase by a factor of 3 in the risk of stent thrombosis (2.6% vs. 0.8%; hazard ratio, 3.09; 95% CI, 1.19 to 8.00; P=0.02).

CONCLUSIONS

Among persons treated with clopidogrel, carriers of a reduced-function CYP2C19 allele had significantly lower levels of the active metabolite of clopidogrel, diminished platelet inhibition, and a higher rate of major adverse cardiovascular events, including stent thrombosis, than did noncarriers.