Activity Of Clopidogrel Research Articles

EVALUATION OF PLATELET AGGREGATION IN CLINICAL PRACTICE

Evaluation of platelet function with subsequent modification of antiplatelet therapy regimen is one of the areas of personalized medicine. Analysis of the causes of inadequate antiplatelet action of clopidogrel, the association of residual platelet reactivity with clinical outcomes and a review of the research on the change of antiplatelet therapy in patients with ischemic heart disease after percutaneous interventions based on the results of platelet function testing, were the aim of this review.

CYP2C19 polymorphisms and coronary heart disease risk factors synergistically impact clopidogrel response variety after percutaneous coronary intervention

Platelet inhibition by clopidogrel is highly variable and the elevated platelet activity will increase the risk of major adverse cardiovascular events after percutaneous coronary intervention (PCI). CYP2C19 loss-of-function (LOF) alleles and risk factors of coronary heart disease (CAD) were reported to be associated with the low response of clopidogrel. This study was carried out to analyze the contributions of CYP2C19 polymorphisms and risk factors to the various clopidogrel responses in Chinese patients with stable CAD after PCI. The platelet reactivity index (PRI) was measured in 145 patients who underwent PCI using the vasodilator-stimulated phosphoprotein assay. Gene chip hybrid tests were used to analyze the genetic polymorphisms of CYP2C19. With a cutoff value of 50% in PRI, 20.67% (31/145) of the patients were defined to be clopidogrel resistant. With respect to the normal *1, *2, and *3 LOF CYP2C19 alleles, patients were classified into three metabolism phenotypes: 39.31% were extensive, 47.59% were intermediate, and 13.10% were poor metabolizers (PMs). Of the enrolled patients, 53.82 and 9.66%, respectively, were carriers of *2 and *3 alleles. There was a significant difference in PRI between PM and either extensive or intermediate metabolizers (P<0.05). In all, 36.84% of the patients with the PM phenotype were clopidogrel resistant. Carriers of two CYP2C19 LOF alleles, BMI, and the presence of type 2 diabetes were three independent risk factors for clopidogrel resistance. Genetic CYP2C19 polymorphisms and CAD risk factors - type 2 diabetes mellitus and BMI - synergistically affect the antiplatelet activity of clopidogrel and the occurrence of major adverse cardiovascular events after PCI.

Letter by Chyrchel et al Regarding Article, “Unexpected Effect of Proton Pump Inhibitors: Elevation of the Cardiovascular Risk Factor Asymmetric Dimethylarginine”

Ghebremariam et al1 brilliantly demonstrated that proton pump inhibitors (PPIs) inhibit dimethylarginine dimethylaminohydrolase, a key enzyme metabolizing the endogenous nitric oxide synthase antagonist asymmetrical dimethylarginine. This finding offers a novel mechanism for the putative ability of PPIs to attenuate benefits of antiplatelet agents, an effect initially attributed to the interaction of PPIs with clopidogrel activation by a hepatic enzyme (CYP2C19).2 …

Structure of the human P2Y12 receptor in complex with an antithrombotic drug

P2Y receptors (P2YRs), a family of purinergic G-protein-coupled receptors (GPCRs), are activated by extracellular nucleotides. There are a total of eight distinct functional P2YRs expressed in human, which are subdivided into P2Y1-like receptors and P2Y12-like receptors. Their ligands are generally charged molecules with relatively low bioavailability and stability in vivo, which limits our understanding of this receptor family. P2Y12R regulates platelet activation and thrombus formation, and several antithrombotic drugs targeting P2Y12R--including the prodrugs clopidogrel (Plavix) and prasugrel (Effient) that are metabolized and bind covalently, and the nucleoside analogue ticagrelor (Brilinta) that acts directly on the receptor--have been approved for the prevention of stroke and myocardial infarction. However, limitations of these drugs (for example, a very long half-life of clopidogrel action and a characteristic adverse effect profile of ticagrelor) suggest that there is an unfulfilled medical need for developing a new generation of P2Y12R inhibitors. Here we report the 2.6 Å resolution crystal structure of human P2Y12R in complex with a non-nucleotide reversible antagonist, AZD1283. The structure reveals a distinct straight conformation of helix V, which sets P2Y12R apart from all other known class A GPCR structures. With AZD1283 bound, the highly conserved disulphide bridge in GPCRs between helix III and extracellular loop 2 is not observed and appears to be dynamic. Along with the details of the AZD1283-binding site, analysis of the extracellular interface reveals an adjacent ligand-binding region and suggests that both pockets could be required for dinucleotide binding. The structure provides essential insights for the development of improved P2Y12R ligands and allosteric modulators as drug candidates.

Patient care services: What pharmacists do

Patient care services: What pharmacists do

APhA honors outstanding achievements at Annual Meeting

Each year, APhA recognizes exceptional contributors to the profession at the Annual Meeting. The following award winners will be honored at APhA2014 in Orlando.

Abstract T P341: Impact Of Cytochrome P450 2C19 Polymorphism On High On-treatment Platelet Reactivity In Stroke Patients Treated With Clopidogrel

BACKGROUND: Clopidogrel is one of the most commonly used anti-platelet drugs. Recent reports suggested the association of allelic variants of the genes modulating metabolic activation (CYP2C19 and paraoxonase-1) and bioavailability (ABCB1) of clopidogrel with high on-treatment platelet reactivity (HTPR), possibly resulting in the recurrence of thrombotic events. However, these studies mostly examined patients with coronary heart disease and the impact of these polymorphisms in stroke patients is largely unknown. METHODS: We conducted a multicenter, prospective cohort study of 518 Japanese patients from 14 hospitals who were administrated clopidogrel. Residual platelet reactivity was determined by a change in light transmission induced by platelet aggregation in platelet-rich plasma after adding ADP. The vasodilator-stimulated phosphoprotein (VASP) index was also measured using flow cytometry. We investigated the association of polymorphisms of aforementioned enzymes with HTPR. RESULTS: In terms of CYP2C19 loss-of-function polymorphisms (*2 and *3), the prevalence of intermediate (IM: *1*2 or *1*3) or poor (PM: *2*2, *2*3, or *3*3) metabolizer was much higher (IM: 47% or PM: 15%) in Japanese than in Caucasian populations. Residual platelet reactivity was significantly higher in PM and IM groups than that in the wild-type extensive metabolizer (EM: *1*1) group assessed by 5 μM ADP-induced platelet aggregation (PM: 69.4% ± 17.1%, IM: 59.7% ± 16.2%, EM: 51.5% ± 17.5%, p &lt; 0.0001) and VASP index (PM: 66.6% ± 14.1%, IM: 52.4% ± 16.0%, EM: 42.9% ± 15.0%, p &lt; 0.0001). Furthermore, HTPR determined by both assays was associated with the ABCB1 polymorphism (rs1045642) but not with the paraoxonase-1 Q192R mutation. CONCLUSIONS: Our results indicate that both CYP2C19 and ABCB1 polymorphisms significantly contribute to HTPR in stroke patients treated with clopidogrel. At present, we are monitoring these patients for a two-year period to determine whether these genetic variants and HTPR affect the recurrence of thrombotic events.

Antiplatelet Effect of Clopidogrel Can Be Reduced by Calcium-Channel Blockers

PurposeClopidogrel is metabolized by the hepatic cytochrome P450 (CYP) system into its active thiol metabolite. CYP3A4 is involved in the metabolism of both clopidogrel and dihydropyridine calcium channel blockers (CCBs). A few reports have suggested an inhibitory interaction between CCBs and clopidogrel. Accordingly, the aim of this study was to determine the effect of CCBs on the antiplatelet activity of clopidogrel by serial P2Y12 reaction unit (PRU) measurements.Materials and MethodsWe assessed changes in antiplatelet activity in patients receiving both clopidogrel and CCBs for at least 2 months prior to enrollment in the study. The antiplatelet activity of clopidogrel was measured by VerifyNow P2Y12 assay in the same patient while medicated with CCBs and at 8 weeks after discontinuation of CCBs. After discontinuation of the CCBs, angiotensin receptor blockers were newly administered to the patients or dosed up for control of blood pressure.ResultsThirty patients finished this study. PRU significantly decreased after discontinuation of CCBs (238.1±74.1 vs. 215.0±69.3; p=0.001). Of the 11 patients with high post-treatment platelet reactivity to clopidogrel (PRU≥275), PRU decreased in nine patients, decreasing below the cut-off value in seven of these nine patients after 8 weeks. Decrease in PRU was not related to CYP2C19 genotype.ConclusionCCBs inhibit the antiplatelet activity of clopidogrel.

CYP 450 2C19 polymorphisms in Indian patients with coronary artery disease

BackgroundDual antiplatelet therapy is the cornerstone in the management of acute coronary syndromes (ACS) and prevention of stent thrombosis (ST). Genetic polymorphisms in CYP2C19 gene involved in hepatic activation of clopidogrel leads to clopidogrel non-responsiveness and may influence clinical outcomes. These polymorphisms in CYP2C19 gene and their impact on clinical outcome in coronary artery disease (CAD) have not been studied in Indian population.MethodsWe studied 110 consecutive patients (mean age 55.7 ± 10.7 years; 90% male) taking clopidogrel with angiographically proven CAD for various genetic polymorphisms in CYP2C19 gene. Relationship between loss of function mutation and clinical presentation with recurrent ACS including ST was analyzed.ResultsOut of 110 patients, 26 (23.64%) had normal genotype, 52 (47.23%) had loss of function mutation *2 and 39 (35.45%) had a gain of function mutation *17, 7 (6.36%) patients were undefined metabolizers (*2/*17) which were excluded from analyses. Final analyses included 103 patients, with 45 (40.90%) having loss of function. Overall 51 patients had ACS, with 27 developing recurrence while on clopidogrel. The prevalence of loss of function mutation was no different between the group with recurrences and those without recurrences (55.6% vs. 50%, p = 0.7). Two patients developed ST while on clopidogrel; both had loss of function mutation.ConclusionCYP2C19 gene polymorphisms are common in Indian population. Loss of function mutation status did not affect the clinical outcomes. A larger study also considering P2Y12 receptor polymorphisms together with platelet activity testing, may be required to establish the role of CYP2C19 gene polymorphisms in clinical practice.

Treatment Options for Patients With Poor Clopidogrel Response

A significant percentage of patients demonstrate a poor antiplatelet response to clopidogrel. With the emergence of testing for genetic variations in drug-metabolizing enzyme function and testing for platelet function, it is becoming more common to identify patients as poor responders to clopidogrel. This leaves the clinician in a difficult situation when confronted with a patient deemed to be a poor clopidogrel responder as there is no clear therapeutic strategy for treating these patients. In this situation, a number of alternatives to conventional dosing of clopidogrel have been investigated, including increasing the dosage of clopidogrel, switching from clopidogrel to either prasugrel or ticagrelor, or adding cilostazol to clopidogrel therapy. All of these options have demonstrated pharmacologic benefit in terms of greater antiplatelet effects compared with standard clopidogrel dosing in patients with high on-treatment platelet reactivity or a genetic loss-of-function variant of CYP2C19, the main enzyme responsible for clopidogrel activation. However, the impact of each of these alternative therapies on clinical outcomes is poorly understood. Early studies have not shown a clinical benefit by increasing the clopidogrel dosage or switching to prasugrel although there is still much to be discovered in this area. Of the alternatives to standard dosing of clopidogrel, switching to either prasugrel or ticagrelor has the most potential benefit, but again, there is limited evidence to support this practice in patients who demonstrate high on-treatment platelet reactivity while on clopidogrel although the evidence is somewhat more supportive in patients who have a CYP2C19 loss-of-function variant allele. The evidence for increasing the dosage of clopidogrel or adding cilostazol is the least supportive, making these alternatives difficult to justify. Given the limited evidence to support switching treatments, some providers may simply opt to continue standard dosing of clopidogrel pending the results of ongoing trials. Much research is needed and is currently underway in this area, which will be helpful in establishing future treatment protocols for patients with poor clopidogrel response.

Circulation: Cardiovascular Interventions Editors’ Picks

<i>Circulation: Cardiovascular Interventions</i> Editors’ Picks

Statin and clopidogrel pharmacological interaction

Antiplatelet therapy with clopidogrel should be administered to patients with acute coronary syndromes and those submitted to percutaneous coronary intervention (PCI) (secondary prevention). Clopidogrel is a pro-drug which requires hepatic cytochrome P450 (CYP) metabolic activation to produce the active metabolite that inhibits platelet aggregation. CYP2C19 and CYP3A4/5 are the principal contributors in the two-step hepatic oxidation of clopidgrel. However, the response to clopidogrel is not uniform; it varies from patients platelet reactivity on standard-dose clopidogrel are at increased risk of recurrence of adverse cardiovascular events. Also drug-drug interactions that influence the function of CYP isoenzymes may affect the response to clopidogrel. Lipophilic statins, such as atorvastatin, are predominantly metabolized by CYP3A4 and may interfere with CYP activation of clopidogrel, contrary to what happens with hydrophilic statins, such as rosuvastin or pravastatin. Recently, it has been shown that in patients who presented post-PCI high on-treatment platelet reactivity on standard-dose clopidogrel during chronic treatment with clopidogrel and low-dose atorvastatin (10 mg), switching to a non-CYP3A4-metabolized statin, such as rosuvastatin or pravastatin, resulted in a significant decrease in platelet reactivity. The clinical benefit of statins is attributed to mulitple mechanisms which go beyond their lipid-lowering effects and include also antithrombotic properties. In particular, atorvastatin inhibits adenosine diphospate and thrombin-induced platelet aggregation. Moreover, pharmacodynamic studies appear to show some synergy between clopidogrel and atorvastatin: the enhancement of clopidogrel effects due to atorvastatin seems to be dose-related and independent of LDL cholesterol reduction. A recent study shows that the addition of high-dose atorvastatin (80mg) for 30 days significantly improves the pharmacodynamic effects of double-dose clopidogrel, reducing platelet reactivity and improving optimal clopidogrel response in statin naïve patients with high-on treatment platelet reactivity on standard-dose clopidogrel. These pharmacodynamic studies suggest that switching to a no CYP3A4-metabolized statin in patients with high on-treatment platelet reactivity on standard-dose clopidogre on chronic treatment with low-dose atorvastatin or administration of high-dose atorvastatin maybe two alternative strategies to avoid possible negative drug-drug interactions and to improve individual patient response to clopidogrel.

Pharmacodynamic effects of atorvastatin vs. rosuvastatin in coronary artery disease patients with normal platelet reactivity while on dual antiplatelet therapy

Background: Levels of platelet reactivity in patients on Dual Antiplatelet Therapy (DAPT) can potentially be influenced by concomitant treatment with statins that inhibit the CYP3A4 system involved in the activation of clopidogrel. Recent studies have shown that a high platelet reactivity during co-administration of clopidogrel and a CYP3A4-metabolized statin (i.e atorvastatin) can be lowered by switching to a non-CYP3A4-metabolized statin (i.e rosuvastatin). Aim of this study was to verify if atorvastatin and rosuvastatin have different pharmacodynamic effects also when they are given to patients with Coronary Artery Disease (CAD) with baseline normal platelet reactivity while on DAPT. Methods: A total of 100 stable CAD patients receiving DPAT (clopidogrel 75 mg plus aspirin 100 mg) who had evidence of normal platelet reactivity after a 1-week statin wash-out period entered the PEARL trial. Patients were randomly assigned to atorvastatin (20 mg day, N=50) or rosuvastatin (10 mg day, N=50) for 30 days. After another 1-week wash-out period to avoid any carryover effect, cross-over was performed, and patients were switched to the other drug which was continued for 30 days. Platelet reactivity (expressed as P2Y (12) reaction units (PRU) by the point-of-care VerifyNow assay [Accumetrics, San Diego, California]) was measured before and at the end of each 30-day treatment period. High platelet reactivity after clopidogrel was defined as a PRU value>208. Results: After the 30-day treatment with atorvastatin, platelet reactivity did not significantly change as compared with baseline, pre-treament evaluation (119±66 vs 136±59 PRU, NS), with 2 patients only showing a PRU>208. Similarly, after 30-day treatment with rosuvastatin, platelet reactivity was unchanged as compared with baseline (135±46 vs 128±62 PRU, NS), with PRU>208 occurring in 3 patients. Conclusion: Atorvastatin does not negatively affect DAPT as compared with rosuvastatin when is given to stable CAD patients with baseline normal platelet reactivity while on DAPT. ClinicalTrials.gov Identifier: [NCT01567774][1]. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01567774&atom=%2Fehj%2F34%2Fsuppl_1%2FP4849.atom

Pharmacodynamic comparison of pitavastatin versus atorvastatin on platelet reactivity in patients with coronary artery disease treated with dual antiplatelet therapy

Background: Levels of platelet reactivity in patients on Dual Antiplatelet Therapy (DAPT) can be influenced by concomitant treatment with medications (i.e. statins) that inhibit the CYP3A4 system involved in the activation of clopidogrel. Atorvastatin and simvastatin are metabolized by CYP3A4, while pitavastatin is mostly excreted unchanged in bile and undergoes minimal biotransformation through the cytochrome P450 system. The primary objective of this study was to compare the pharmacodynamic effects of a CYP3A4-metabolized statin (atorvastatin) versus a non-CYP3A4-metabolized statin (pitavastatin) in patients with coronary artery disease (CAD) treated with DAPT. Methods: A total of 102 CAD patients receiving DPAT (clopidogrel 75 mg plus aspirin 100 mg) after percutaneous coronary intervention entered the PORTO trial. After a 1-week statin wash-out period, patients were randomly assigned to atorvastatin (20 mg day, N=51) or pitavastatin (4 mg day, N=51) for 30 days. After another 1-week wash-out period to avoid any carryover effect, cross-over was performed, and patients were switched to the other drug which was continued for 30 days. Platelet reactivity (expressed as P2Y (12) reaction units (PRU) by the point-of-care VerifyNow assay) was measured before and at the end of each 30-day treatment period. High platelet reactivity after clopidogrel was defined as a PRU value >208. Results: After the 30-day treatment period with atorvastatin, platelet reactivity was significantly higher as compared with pre-treatment values (212±96 vs 166±79 PRU, p=0.010), with a more common occurrence of patients showing a PRU>208 (57% vs. 35%, p=0.047). Conversely, after the 30-day treatment period with pitavastatin, platelet reactivity was unchanged as compared with pre-treatment values (178±81 vs 189±73 PRU, NS), with no difference in the frequency of patients showing a PRU>208 before and after treatment (41% vs. 37%, NS). Conclusion: Pitavastatin, a non-CYP3A4-metabolized statin, does not negatively affect levels of platelet reactivity as compared with atorvastatin in CAD patients on DAPT. ClinicalTrials.gov Identifier: [NCT01648829][1]. [1]: /lookup/external-ref?link_type=CLINTRIALGOV&access_num=NCT01648829&atom=%2Fehj%2F34%2Fsuppl_1%2FP4915.atom

CYP2C19 Genetic Polymorphism, Rabeprazole and Esomeprazole Have no Effect on the Antiplatelet Action of Clopidogrel

The aim of this study is to investigate the effect of CYP2C19 polymorphism and cotherapy with rabeprazole or esomeprazole on the antiplatelet effect of clopidogrel. Patients receiving clopidogrel 75 mg ± rabeprazole or esomeprazole underwent genotyping for CYP2C19*2 and CYP2C19*3, and vasodilator-stimulated phosphoprotein testing to measure platelet reactivity index (PRI). Two hundred thirty-nine consecutive patients were enrolled as follows: 92 clopidogrel (C group), 94 clopidogrel + rabeprazole (CR), and 53 clopidogrel + esomeprazole (CE). Forty-five patients had loss of function (LOF) polymorphism (43 heterozygous; 2 homozygous mutant for CYP2C19*2). The mean PRI was 20.7% ± 21.9% in the C group, 19.1% ± 20.9% in the CR group, and 24.5% ± 22.9% in the CE group (P = NS). High on-treatment platelet reactivity (HPR), defined as PRI >50%, was observed in 12 (13.0%), 13 (13.8%), and 10 (18.9%) patients on C, CR, and CE, respectively (P = NS). HPR was similar in rapid metabolizers between groups. On multivariate logistic regression, neither CYP2C19 LOF alleles nor proton pump inhibitor cotherapy were associated with HPR. The use of proton pump inhibitors was indicated in 30.6% of recipients. As a conclusion, CYP2C19*2 LOF allele and the use of esomeprazole or rabeprazole have no effect on the action of clopidogrel.

Risk Factors for Thrombus Formation on the Amplatzer Cardiac Plug After Left Atrial Appendage Occlusion

This study sought to identify risk factors for thrombus formation on the Amplatzer Cardiac Plug (ACP) (St. Jude Medical, St. Paul, Minnesota) after left atrial appendage occlusion. Left atrial appendage occlusion with the ACP aims to reduce the risk of embolic stroke and bleeding complications associated with vitamin K antagonists in patients with atrial fibrillation. We performed transesophageal echocardiography before discharge and after 3, 6, and 12months in 34 patients with atrial fibrillation undergoing ACP implantation and receiving dual antiplatelet therapy. Clinical, echocardiographic, and hemostaseological parameters were retrospectively analyzed to identify risk factors for thrombus formation. Three patients had thrombi before discharge, 3 more at the 3-month follow-up. Nodifferences were found in left atrial volume, left atrial appendage velocity, spontaneous echo contrast, transmitral gradient, or mitral regurgitation between patients without or with thrombi. CHADS2 (Congestion, Hypertension, Age, Diabetes, and Stroke) score (2.0 ± 1.1 vs. 4.3 ± 1.0), CHA2DS2-VASc (CHADS2 plus Vascular Disease and Sex Category) score (5.2 ± 1.3 vs. 6.8 ± 0.8), and pre-interventional platelet count (215.9 ± 63.9/nl vs. 282.5 ± 84.4/nl) were higher and ejection fraction (50.6 ± 11.4% vs. 39.7 ± 10.6%) lower in those with thrombi. Factor 2, factor 5, or methylenetetrahydrofolate reductase mutations and genetic variants associated with reduced clopidogrel activity were not more frequent in patients with thrombi. Transesophageal echocardiography identified 17.6% of patients with thrombus formation on the ACP despite dual antiplatelet therapy. CHADS2 and CHA2DS2-VASc scores, platelet count, and ejection fraction are risk factors for such thrombus formation.

Investigation of drug–drug interactions between clopidogrel and fluoxetine

Drug-drug interactions may contribute to the variability of the response of clopidogrel. Several hypotheses have been proposed concerning the potential modification of clopidogrel pharmacokinetics and pharmacodynamics by fluoxetine. This open-label crossover study assessed the effect of fluoxetine on the pharmacological activity of clopidogrel in healthy volunteers. Eight healthy male volunteers received a single 600-mg loading dose of clopidogrel followed by 20 mg of fluoxetine on 4 days and then 20 mg of fluoxetine plus 600 mg of clopidogrel on the fifth day. Eleven blood samples were withdrawn after clopidogrel administration to determine plasma concentrations of clopidogrel active metabolite (CAM) and platelet function. Platelet aggregation was measured by light transmittance aggregometry (LTA) and platelet reactivity index by flow cytometric vasodilator-stimulated phosphoprotein (VASP) analysis. The areas under the curve and maximum plasma concentrations of CAM were, respectively, 20.6 and 25.3% lower after co-administration of fluoxetine compared with administration of clopidogrel alone. The percentage maximum platelet aggregation values in the presence of 5 μM and 10 μM adenosine diphosphate, measured by LTA, were, respectively, 13.9 and 22.4% lower after fluoxetine co-administration. The platelet reactivity index measured by the flow cytometric VASP method was 36.8% lower when clopidogrel was administered in conjunction with fluoxetine.

Potential interaction between proton pump inhibitor and clopidogrel

Clopidogrel is an anti-platelet agent commonly used in patients with atherosclerotic cardiovascular (CV) disease. Although formerly considered safe, several studies reported that the use of clopidogrel may cause a significant increase in the rate of gastrointestinal (GI) bleeding. This adverse effect could be minimized by coadministration of proton pump inhibitor (PPI). However, since PPI and clopidogrel share the same metabolic pathway, it has been hypothesized that the administration of PPI following clopidogrel therapy may cause a reduction in its anti-platelet effect, thereby increasing the risk of CV events. Recent studies found no significant inhibition in the activation of clopidogrel by CYP2C19 with administration of PPI in vitro. Pharmacokinetic and pharmacodynamic studies, as well as clinical studies, reported conflicting results regarding the potential interaction between PPI and clopidogrel. Until now, the available study investigated the PPI-clopidogrel interaction are primarily observational. The COGENT study is the only prospective, placebo-controlled trial examined the PPI-clopidogrel interaction. This study revealed no significant increase in CV events in patients receiving PPI following clopidogrel therapy, compared to the control group. Though remains controversial, current expert consensus recommended the administration of PPI in patients receiving clopidogrel, particularly in high-risk patients. (Med J Indones. 2013;22:57-62) Keywords: Cardiovascular, clopidogrel, gastrointestinal, proton pump inhibitor

Regulatory polymorphisms in CYP2C19 affecting hepatic expression

Cytochrome P450 2C19 is responsible for the metabolism of many drugs, including the activation of clopidogrel. The allele CYP2C19*17 is associated with ultra-rapid metabolizer phenotypes by increasing gene transcription. This study tests to what extent CYP2C19*17 enhances CYP2C19 expression in human liver and whether additional regulatory variants contribute to variation in CYP2C19 expression. CYP2C19 mRNA was measured with quantitative real-time PCR (qRT-PCR), enzyme activity as metabolic velocity with S-mephenytoin as the substrate and allelic mRNA expression ratio with SNaPshot in human livers. CYP2C19 transcribed exons and a 4kb promoter region were sequenced using IonTorrent PGM or Sanger sequencing and screened for polymorphisms associated with total hepatic CYP2C19 mRNA, enzyme activity and allelic mRNA ratios. Livers heterozygote and homozygous for CYP2C19*17 had mRNA levels 1.8-fold (p=0.028) and 2.9-fold (p=0.006), respectively, above homozygous reference allele livers. CYP2C19*17 heterozygotes were also associated with increased allelic mRNA expression (allelic ratio ~1.8-fold, SD±0.6, p<0.005), whereas CYP2C19 enzyme activity was elevated 2.3-fold, with borderline significance (p=0.06) in CYP2C19*17 carriers. One liver sample of African ancestry displayed a 2-fold allelic expression ratio, and another sample, a ~12-fold increase in metabolic velocity. Neither case was accounted for by *17, which indicates the presence of additional regulatory variants. Our findings confirm *17 as a regulatory polymorphism enhancing hepatic CYP2C19 expression 2-fold with potential to compensate for the loss of function allele CYP2C19*2. Additional regulatory factors may also enhance CYP2C19 expression in African American populations.

Establishment of a CYP2C19 Genotyping Assay for Clinical Use

Conversion of clopidogrel (Plavix) to its active metabolite is catalyzed largely by the P450 enzyme 2C19 (CYP2C19). Numerous allelic variants of CYP2C19 exist. The *1 allele is considered wild type, whereas the *2 and *3 alleles have no in vivo enzymatic activity. Conversely, the *17 allele has increased expression, resulting in increased clopidogrel activation. Poor metabolizers (*2/*2 and *2/*3 genotypes) experience higher rates of therapeutic failure. For this reason, we have validated a CYP2C19 genotyping assay for the *1, *2, *3, and *17 alleles. Genomic DNA extracted from 30 deidentified EDTA whole-blood samples from patients was analyzed at 2 independent facilities using specific TaqMan realtime polymerase chain reaction primers and probes. Concordant genotypes were generated on all samples tested. Of the 30 samples, 15 were CYP2C19*1/*1, 8 were CYP2C19*1/*17, 5 were CYP2C19*1/*2, and 2 were CYP2C19*2/*17. There were no CYP2C19*3 alleles or *2/*2 homozygous genotypes detected. This CYP2C19 genotyping assay is appropriate for clinical testing, demonstrating excellent interlaboratory concordance, enabling the selection of the most effective clopidogrel treatment regimen for patients undergoing percutaneous coronary intervention.