P2Y12 gene H2 haplotype is not associated with increased adenosine diphosphate-induced platelet aggregation after initiation of clopidogrel therapy with a high loading dose

The influence of P2Y12 gene polymorphisms on clopidogrel therapy in patients after percutaneous coronary intervention

Aim: We aimed to define the influence of P2Y12 polymorphisms (rs6801273, rs2046934, and rs6809699), diabetes, hypertension, obesity, hypercholesterolemia, statins intake, and smoking habit on clopidogrel therapy in patients undergoing percutaneous coronary intervention.Materials & methods: We used PCR-RFLP and PCR-ASO for P2Y12 genotype analysis. The effectiveness of the therapy was measured with the VerifyNow method and defined in platelet reactivity units.Results: Studied polymorphisms had no statistically significant influence on PRU before (PRU0) and 6 months (PRU6) after the procedure. H1/H1 diabetic carriers had significantly higher PRU6 values than patients without diabetes. Obese H1/H2 subjects had significantly lower PRU6 values than H1/H2 non-obese carriers.Conclusion: We found that obesity and diabetes may influence the long-term outcome of antiplatelet therapy.

Pharmacogenetic considerations in therapy with novel antiplatelet and anticoagulant agents

Antiplatelets and anticoagulants are extensively used in cardiovascular medicine for the prevention and treatment of thrombosis in the venous and arterial circulations. Wide inter-individual variability has been observed in response to antiplatelets and anticoagulants, which triggered researchers to investigate the genetic basis of this variability. Data from extensive pharmacogenetic studies pointed to strong evidence of association between polymorphisms in candidate genes and the pharmacokinetics and pharmacodynamic action and clinical response of the antiplatelets clopidogrel and the anticoagulant warfarin. In this review, we conducted an extensive search on Medline for the time period of 2009-2023. We also searched the PharmGKB website for levels of evidence of variant-drug combinations and for drug labels and clinical guidelines. We focus on the pharmacogenetics of novel antiplatelets and anticoagulants while excluding acetylsalicylic acid, warfarin and heparins, and discuss the current knowledge with emphasis on the level of evidence.

Role of P2Y12 Receptor in Thrombosis

P2Y₁₂ receptor is a 342 amino acid Gi-coupled receptor predominantly expressed on platelets. P2Y₁₂ receptor is physiologically activated by ADP and inhibits adenyl cyclase (AC) to decrease cyclic AMP (cAMP) level, resulting in platelet aggregation. It also activates PI3 kinase (PI3K) pathway leading to fibrinogen receptor activation, and may protect platelets from apoptosis. Abnormalities of P2Y₁₂ receptor include congenital deficiencies or high activity in diseases like diabetes mellitus (DM) and chronic kidney disease (CKD), exposing such patients to a prothrombotic condition. A series of clinical antiplatelet drugs, such as clopidogrel and ticagrelor, are designed as indirect or direct antagonists of P2Y₁₂ receptor to reduce incidence of thrombosis mainly for patients of acute coronary syndrome (ACS) who are at high risk of thrombotic events. Studies on novel dual-/multi-target antiplatelet agents consider P2Y₁₂ receptor as a promising part in combined targets. However, the clinical practical phenomena, such as "clopidogrel resistance" due to gene variations of cytochrome P450 or P2Y₁₂ receptor constitutive activation, call for better antiplatelet agents. Researches also showed inverse agonist of P2Y₁₂ receptor could play a better role over neutral antagonists. Personalized antiplatelet therapy is the most ideal destination for antiplatelet therapy in ACS patients with or without other underlying diseases like DM or CKD, however, there is still a long way to go.

The Personalization of Clopidogrel Antiplatelet Therapy: The Role of Integrative Pharmacogenetics and Pharmacometabolomics

Dual antiplatelet therapy of aspirin and clopidogrel is pivotal for patients undergoing percutaneous coronary intervention. However, the variable platelets reactivity response to clopidogrel may lead to outcome failure and recurrence of cardiovascular events. Although many genetic and nongenetic factors are known, great portion of clopidogrel variable platelets reactivity remain unexplained which challenges the personalization of clopidogrel therapy. Current methods for clopidogrel personalization include CYP2C19 genotyping, pharmacokinetics, and platelets function testing. However, these methods lack precise prediction of clopidogrel outcome, often leading to insufficient prediction. Pharmacometabolomics which is an approach to identify novel biomarkers of drug response or toxicity in biofluids has been investigated to predict drug response. The advantage of pharmacometabolomics is that it does not only predict the response but also provide extensive information on the metabolic pathways implicated with the response. Integrating pharmacogenetics with pharmacometabolomics can give insight on unknown genetic and nongenetic factors associated with the response. This review aimed to review the literature on factors associated with the variable platelets reactivity response to clopidogrel, as well as appraising current methods for the personalization of clopidogrel therapy. We also aimed to review the literature on using pharmacometabolomics approach to predict drug response, as well as discussing the plausibility of using it to predict clopidogrel outcome.

Relationship between clopidogrel-related polymorphisms and variable platelet reactivity at 1 year: A cohort study from Han Chinese

Background:

This study was designed to investigate the effect of clopidogrel-related gene polymorphisms on platelet reactivity and clinical outcome in Chinese Han patients.

Materials and Methods:

Three hundred and thirty-six percutaneous coronary intervention - treated patients were recruited and followed for 1 year. Blood samples were collected from all patients for DNA genotyping. The platelet reactivity unit was measured by the VerifyNow technique. The CYP2C19*2, CYP2C19*3, CYP2C19*17, ATP-binding cassette subfamily B member 1, ITGB3, CYP2C9*3, CYP2B6*9, and P2Y12 alleles were assessed.

Results:

The clinical endpoints were related to previous heart disease history (11.90% vs. 28.57%, P = 0.017), stroke (12.24% vs. 16.67%, P = 0.039), and diabetes (27.55% vs. 52.38%, P = 0.047). High on-treatment platelet reactivity (HTPR) was frequent in advanced age (P = 0.019), male gender (P = 0.016), hypertension (P = 0.033), and chronic renal failure (P = 0.040). There were more endpoints in the CYP2C19*2 and P2Y12 mutant carriers (76.19% vs. 43.20%, P < 0.001; 50.00% vs. 35.71%, P = 0.001, respectively), whereas fewer in the CYP2C19*17 mutant carriers (11.90% vs. 56.46%, P = 0.001). CYP2C19*2 and P2Y12 polymorphism manifested HTPR (194.25 ± 45.91 vs. 151.38 ± 58.14, P < 0.001; 180.33 ± 67.25 vs. 161.89 ± 56.49, P = 0.008, respectively), whereas CYP2C19*17 mutant improved platelet reactivity (97.17 ± 45.38 vs. 169.08 ± 57.15, P = 0.003). However, there were no further cardiovascular deaths in endpoint patients.

Conclusion:

In Han Chinese people of mainland China, clopidogrel-related gene polymorphisms are related to variable platelet reactivity after clopidogrel maintenance dosing, which influences major adverse cardiovascular events, without an effect on cardiac death.

Does i-T744C P2Y12 Polymorphism Modulate Clopidogrel Response among Moroccan Acute Coronary Syndromes Patients?

Background. An interindividual variability in response to Clopidogrel has been widely described in patients with acute coronary syndromes (ACS). The contribution of genetics on modulating this response was widely discussed. The objective of our study was to investigate the potential effect of i-T744C P2Y12 polymorphism on Clopidogrel response in a sample of Moroccan ACS patients. We tried also to determine the frequency of this polymorphism among Moroccan ACS compared to healthy subjects. Methods and Results. 77 ACS patients versus 101 healthy controls were recruited. DNA samples were genotyped by PCR-RFLP method. The VerifyNow assay was used to evaluate platelet function among ACS patients. Our results show that the mutant allele C was more frequent among ACS ST (+) than ST (−) patients (39% versus 19.8%, resp.), when the wild-type allele was more represented in the ACS ST (−) group (80.2%). The C allele frequency was higher among resistant than nonresistant patients (30% versus 20.8%, resp.). Comparison of ACS patients and healthy controls shows higher frequency of mutant C allele among cases compared to controls (22.73% versus 19.31%, resp.); there was a statistically significant association of the recessive and additive transmission models with the ACS development risk (OR [95% CI] = 1.78 [1.58–5.05], P = 0.01 and OR [95% CI] = 1.23 [0.74–2.03], P < 0.001, resp.), increasing thus the association of this polymorphism with the pathology. Conclusion. Our results suggest that this polymorphism may have a potential effect on Clopidogrel response among our Moroccan ACS patients and also on ACS development.

Influence of P2Y12 polymorphisms on platelet activity but not ex-vivo antiplatelet effect of ticagrelor in healthy Chinese male subjects

Activation of platelet implicated a series of signal conduction including outside-in and inside-out related receptor-mediated signaling pathways. Ticagrelor is the first reversible P2Y12 receptor antagonist that exhibits rapid antiplatelet effect. Given that platelet aggregation varies among individuals, genetic polymorphisms in P2Y12 and subsequent signal molecular such as the G-protein beta 3 subunit (GNB3) are supposed to influence the antiplatelet effect of ticagrelor. The aim of this study was to determine whether genetic polymorphisms in P2Y12 and GNB3 genes influence ex-vivo antiplatelet activity of ticagrelor in healthy Chinese subjects. A total of 196 healthy Chinese male individuals were recruited. ADP-induced platelet aggregation was determined by using light transmittance aggregometry at baseline and after incubation of the platelet-rich plasma with 15 and 50 μmol/l ticagrelor, respectively. Nine single-nucleotide polymorphisms (SNPs) in P2Y12 and the GNB3 rs5443 polymorphism were genotyped by PCR-direct sequencing. P2Y12 haplotypes were inferred. Baseline platelet aggregation was increased in carriers of the common alleles of P2Y12 SNPs (rs1907637, rs2046934, and rs6809699) and rs6787801 TC heterozygotes (P < 0.05 for all). Results of the haplotype analyses were consistent with those of the single SNPs. Ticagrelor at both concentrations of 15 and 50 μmol/l decreased ADP-induced platelet aggregation significantly (P < 0.05, respectively). Neither single SNPs nor haplotypes of P2Y12 affected ticagrelor-induced ex-vivo inhibition of platelet aggregation. P2Y12 and GNB3 polymorphisms have no effect on the ex-vivo antiplatelet activity of ticagrelor in healthy Chinese male subjects.

Blood cells: an historical account of the roles of purinergic signalling

The involvement of purinergic signalling in the physiology of erythrocytes, platelets and leukocytes was recognised early. The release of ATP and the expression of purinoceptors and ectonucleotidases on erythrocytes in health and disease are reviewed. The release of ATP and ADP from platelets and the expression and roles of P1, P2Y(1), P2Y(12) and P2X1 receptors on platelets are described. P2Y(1) and P2X(1) receptors mediate changes in platelet shape, while P2Y(12) receptors mediate platelet aggregation. The changes in the role of purinergic signalling in a variety of disease conditions are considered. The successful use of P2Y(12) receptor antagonists, such as clopidogrel and ticagrelor, for the treatment of thrombosis, myocardial infarction and stroke is discussed.

The pharmacogenetic control of antiplatelet response: candidate genes and CYP2C19

INTRODUCTION

Aspirin, clopidogrel, prasugrel and ticagrelor are antiplatelet agents for the prevention of ischemic events in patients with acute coronary syndromes (ACS), percutaneous coronary intervention (PCI) and other indications. Variability in response is observed to different degrees with these agents, which can translate to increased risks for adverse cardiovascular events. As such, potential pharmacogenetic determinants of antiplatelet pharmacokinetics, pharmacodynamics and clinical outcomes have been actively studied.

AREAS COVERED

This article provides an overview of the available antiplatelet pharmacogenetics literature. Evidence supporting the significance of candidate genes and their potential influence on antiplatelet response and clinical outcomes are summarized and evaluated. Additional focus is directed at CYP2C19 and clopidogrel response, including the availability of clinical testing and genotype-directed antiplatelet therapy.

EXPERT OPINION

The reported aspirin response candidate genes have not been adequately replicated and few candidate genes have thus far been implicated in prasugrel or ticagrelor response. However, abundant data support the clinical validity of CYP2C19 and clopidogrel response variability among ACS/PCI patients. Although limited prospective trial data are available to support the utility of routine CYP2C19 testing, the increased risks for reduced clopidogrel efficacy among ACS/PCI patients that carry CYP2C19 loss-of-function alleles should be considered when genotype results are available.

Effect of genetic variation in P2Y12 on TRAP-stimulated platelet response in healthy subjects

In platelets, thrombin receptor signaling depends upon the release of adenosine diphosphate and subsequent activation at purinergic subtype Y (P2Y) receptors. The purpose of this study is to evaluate the influence of specific P2Y12 polymorphisms on platelet reactivity in healthy subjects mediated by thrombin receptor activating peptide (TRAP). We recruited a total of 29 healthy volunteers who had been previously genotyped for two polymorphisms of the P2Y12 receptor: the H2 haplotype (rs2046934) and 34C>T (rs6785930). Flow cytometry and the VerifyNow assay were used to assess platelet activation and aggregation stimulated by TRAP in the presence and absence of specific receptor antagonists for the P2Y1, P2Y12, and thromboxane A2 receptors. We identified a significant recessive effect of the P2Y12-receptor H2 haplotype on TRAP-induced flow cytometry. Specifically, H2/H2 carriers (n = 5) demonstrated a significant reduction in both glycoprotein IIb/IIIa receptor activation (p < 0.001) and CD62P expression (p = 0.035). While the VerifyNow assay did not reveal any effect of haplotype on TRAP-mediated platelet aggregation (p = 0.72), the H2/H2 subjects demonstrated greater platelet inhibition in the presence of cangrelor, a specific receptor antagonist for the P2Y12 receptor (p = 0.023). No consistent effects of the separate 34C>T genotype (rs6785930) were demonstrated under the conditions evaluated. The findings of this study suggest a potential association between P2Y12-receptor H2/H2 carriers and reduced platelet function mediated by TRAP in healthy volunteers.

Single nucleotide polymorphism network: a combinatorial paradigm for risk prediction

Risk prediction for a particular disease in a population through SNP genotyping exploits tests whose primary goal is to rank the SNPs on the basis of their disease association. This manuscript reveals a different approach of predicting the risk through network representation by using combined genotypic data (instead of a single allele/haplotype). The aim of this study is to classify diseased group and prediction of disease risk by identifying the responsible genotype. Genotypic combination is chosen from five independent loci present on platelet receptor genes P2RY1 and P2RY12. Genotype-sets constructed from combinations of genotypes served as a network input, the network architecture constituting super-nodes (e.g., case and control) and nodes representing individuals, each individual is described by a set of genotypes containing M markers (M = number of SNP). The analysis becomes further enriched when we consider a set of networks derived from the parent network. By maintaining the super-nodes identical, each network is carrying an independent combination of M-1 markers taken from M markers. For each of the network, the ratio of case specific and control specific connections vary and the ratio of super-node specific connection shows variability. This method of network has also been applied in another case-control study which includes oral cancer, precancer and control individuals to check whether it improves presentation and interpretation of data. The analyses reveal a perfect segregation between super-nodes, only a fraction of mixed state being connected to both the super-nodes (i.e. common genotype set). This kind of approach is favorable for a population to classify whether an individual with a particular genotypic combination can be in a risk group to develop disease. In addition with that we can identify the most important polymorphism whose presence or absence in a population can make a large difference in the number of case and control individuals.

Effect of P2Y1 and P2Y12 genetic polymorphisms on the ADP-induced platelet aggregation in a Korean population

BACKGROUND

P2Y1 and P2Y12 receptors are expressed in platelet membranes and are involved in ADP-induced platelet aggregation. Genetic polymorphisms of P2Y1 and P2Y12 play a major role in the variation of ADP-induced platelet aggregation and in response in antiplatelet therapy.

OBJECTIVE

To evaluate the allele frequencies of P2Y1 and P2Y12 genetic polymorphisms in a Korean population and to assess their role in ADP (5 μmol/L)-induced maximal platelet aggregation.

METHODS

P2Y1 (c.1622A>G) and P2Y12 (i-139C>T, i-744T>C, i-ins801, c.52G>T, c.34C>T) polymorphisms were analyzed in 158 Korean healthy participants using pyrosequencing methods. Their ADP-induced maximal platelet aggregation was assessed by the turbidometric method.

RESULTS

The observed allele frequencies of P2Y1 and P2Y12 were as follows: 0.3101 for P2Y1 c.1622A>G; 0.1804 for P2Y12 i-139C>T, 0.1804 for i-744T>C, 0.1804 for i-801insA, 0.1266 for P2Y12 c.52G>T, and 0.2658 for P2Y12 c.34C>T. ADP-induced maximal platelet aggregation was not influenced by the P2Y1 c.1622A>G polymorphism and was also not affected by three intronic P2Y12 polymorphisms and the P2Y12 c.34C>T polymorphism. However, the P2Y12 c.52G>T polymorphism caused a substantial difference in ADP-induced maximal platelet aggregation (62.75% for c.52GG, 66.27% for c.52GT, and 80.60% for c.52TT; P=0.0092).

CONCLUSIONS

The P2Y1 and P2Y12 genes were very polymorphic in a Korean population. Three intronic P2Y12 polymorphisms (i-139C>T, i-744T>C, i-801insA) were in complete linkage disequilibrium but not with the c.52C>T polymorphism in this population. Maximal platelet aggregation in response to ADP is associated with the c.52C>T polymorphism but not with the three intronic polymorphisms or the P2Y1 c.1622A>T polymorphism.

Genetic variation of platelet function and pharmacology: an update of current knowledge

Platelets are critically involved in atherosclerosis and acute thrombosis. The platelet phenotype shows a wide variability documented by the inherited difference of platelet reactivity, platelet volume and count and function of platelet surface receptors. Several candidate genes have been put into focus and investigated for their functional and prognostic role in healthy individuals and patients with cardiovascular (CV) disease treated with antiplatelet agents. In addition to genetic variation, other clinical, disease-related and demographic factors are important so-called non-genetic factors. Due to the small effect sizes of single nucleotide polymorphisms (SNP) in candidate genes and due to the low allele frequencies of functional relevant candidate SNPs, the identification of genetic risk factors with high predictive values generally depends on the sample size of study cohorts. In the post-genome era new array and bioinformatic technologies facilitate high throughput genome-wide association studies (GWAS) for the identification of novel candidate genes in large cardiovascular cohorts. One of the crucial aspects of platelet genomic studies is the precise definition of a specific clinical phenotype (e.g. stent thrombosis) as this will impact importantly the findings of genomic studies like GWAS. Here, we provide an update on genetic variation of platelet receptors and drug metabolising enzymes under specific consideration of data derived by GWAS. The potential impact of this information and the role in personalised therapeutic concepts will be discussed.

Historical lessons in translational medicine: cyclooxygenase inhibition and P2Y12 antagonism

The development of drugs that inhibit platelets has been driven by a combination of clinical insights, fundamental science, and sheer luck. The process has evolved as the days of stumbling on therapeutic gems, such as aspirin, have long passed and have been replaced by an arduous process in which a drug is designed to target a specific protein implicated in a well-characterized pathophysiological process, or so we would like to believe. The development of antiplatelet therapy illustrates the importance of understanding the mechanisms of disease and the pharmacology of the compounds we develop, coupled with careful clinical experimentation and observation and, yes, still, a fair bit of luck.

Genetic determinants of response to cardiovascular drugs

PURPOSE OF REVIEW

To survey genetic variation contributing to variable responsiveness and toxicity to important cardiovascular drugs and highlight recent developments in the field of cardiovascular pharmacogenomics and personalized medicine.

RECENT FINDINGS

Previously recognized pharmacogenomic associations with drug efficacy have been further validated (e.g. with clopidogrel and warfarin) and shown to influence clinically important outcomes. The clinical significance of variants modulating toxicity (e.g. SLCO1B1 with simvastatin) has also been confirmed. The genetic contribution to variable efficacy and toxicity of other important classes of cardiovascular drugs, such as beta-blockers, is becoming increasingly recognized. Prospective trials testing whether the use of genomic information improves clinical care are underway. Guidance based on the most well-established pharmacogenomic findings has appeared in prescribing labeling and is in the early stages of being implemented into routine clinical care.

SUMMARY

Clinically validated gene variants that modulate responsiveness to cardiovascular drugs continue to be discovered and validated. Early steps are underway to translate these discoveries into clinical care.

Aspirin and platelet adenosine diphosphate receptor antagonists in acute coronary syndromes and percutaneous coronary intervention: role in therapy and strategies to overcome resistance

Platelet activation and aggregation are key components in the cascade of events causing thrombosis following plaque rupture. Antiplatelet therapy is essential in the treatment of patients with acute coronary syndromes (ACS) and for those requiring percutaneous coronary intervention (PCI). Aspirin (acetylsalicylic acid) is a well established antiplatelet therapy and is mandated for secondary prevention of cardiovascular events following ACS. In patients with ACS, the addition of clopidogrel to aspirin is more effective than aspirin alone. For patients undergoing PCI, dual antiplatelet therapy with aspirin and clopidogrel is warranted. Aspirin should be continued indefinitely after PCI. Pretreatment of patients with clopidogrel prior to PCI lowers the incidence of cardiovascular events, yet the optimum timing of drug administration and dose are still being investigated, as is the duration of therapy following PCI. Late-stent thrombosis with drug-eluting stents has pushed the recommendation for duration of clopidogrel therapy up to 1 year and perhaps beyond, in patients without risks for bleeding. The concepts of aspirin and clopidogrel resistance are important clinical questions. No uniform definition exists for aspirin or clopidogrel resistance. Measurements of resistance are often highly variable and do not necessarily correlate with clinical resistance. Noncompliance remains the most prominent mode of resistance. Screening of selected patient populations for resistance or pharmacologic intervention of those patients termed 'resistant' warrants further study.

Polymorphisms of platelet ADP receptor P2RY12 in the risk of venous thromboembolism in the Korean population

Although it was thought that platelets did not play a significant role in the pathogenesis of venous thromboembolism (VTE), several studies demonstrated that a marked activation of platelets occurs in patients with VTE. We carried out a case-control study to investigate the effect of the T744C P2RY12 polymorphism on the risk of VTE in the Korean population. We enrolled 154 consecutive patients with VTE and 415 healthy controls. Genotype frequencies for patients with TT, TC, and CC were 71.4%, 24.7%, and 3.9% and in the controls, 68.2%, 30.1%, and 1.7%, respectively. T744C P2RY12 polymorphism did not significantly affect the risk of VTE. Our study shows that T744C P2RY12 polymorphism did not significantly affect the risk of VTE in the Korean population.

High on treatment platelet reactivity

The addition of clopidogrel to aspirin for patients undergoing percutaneous coronary intervention (PCI) had significantly reduced cardiovascular events. However, despite dual antiplatelet therapy ischaemic events still occur, especially stent thrombosis, which is associated with a high mortality rate. Inter-individual response to clopidogrel is highly variable. It was shown that 4-46% could be considered as high on treatment platelet reactivity (HTPR). Recent studies had demonstrated a relationship between HTPR and ischaemic events in the setting of PCI. Actually the assessment of platelet reactivity in routine practice and its interpretation to make a decision is a debatable issue.

Variability of clopidogrel response in patients with type 2 diabetes mellitus

The global prevalence of diabetes mellitus (DM) continues to climb, and is accompanied by an increase in DM associated complications, most often manifesting as coronary heart disease. Platelet dysfunction has been implicated as a central contributor to the increased risk of coronary artery disease in patients with DM, and it is not surprising that the anti-platelet agent, clopidogrel, has been shown to have efficacy in both short and long term outcomes in patients with acute coronary syndrome and those undergoing percutaneous coronary intervention. However, accumulating data suggest a clinically relevant sub-optimal clopidogrel response in some patients with DM. The exact mechanism of these observations is not yet fully understood, but appears to be related to reduced concentrations of circulating clopidogrel active metabolite, with less variability in pharmacodynamic and clinical response suggested by the evaluation of newer P2Y(12) antagonists, such as prasugrel and ticagrelor. More research is needed to better understand both the pharmacology and clinical consequences of these observations.

Molecular defects of the platelet P2 receptors

Human platelets express three types of P2 receptors, which play important roles in platelet function: P2X(1), P2Y(1) and P2Y(12). Only patients with either quantitative or qualitative abnormalities of the platelet P2Y(12) receptor have been well-characterized so far. Deficiencies of P2Y(12) are associated with nucleotide deletions in the open-reading frame, frameshifts, and early truncation of the protein, or with a nucleotide substitution in the transduction initiation codon. Congenital dysfunctions of P2Y(12) are associated with molecular defects involving the sixth trans-membrane domain or the adjacent third extracellular loop of the receptor, which identify a region of the protein whose integrity is necessary for normal receptor function. A mutation, predicting a lysine to glutamate (Lys174Glu) substitution was associated with decreased ligand binding to the receptor, suggesting that it is responsible for disruption of the adenosine diphosphate (ADP)-binding site of the receptor. Patients with P2Y(12) defects display a mild-to-moderate bleeding diathesis, characterized by mucocutaneous bleedings and excessive post-surgical and post-traumatic blood loss. Defects of P2Y(12) should be suspected when ADP, even at high concentrations (≥10 μM), is unable to induce full, irreversible platelet aggregation. Tests that evaluate the degree of inhibition of adenylyl cyclase by ADP should be used to confirm the diagnosis.

Identification of P2Y12 single-nucleotide polymorphisms and their influences on the variation in ADP-induced platelet aggregation

INTRODUCTION

Although P2Y12 has a significant role in normal hemostasis and thrombosis, no genetic study has been described about the association between P2Y12 variants and the extent of ADP-induced platelet activation in the Korean population.

MATERIALS AND METHODS

The expression levels of two reference sequences of P2Y12 mRNA transcripts (variants 1 and 2) were examined in the whole blood before direct DNA sequencing. The subjects were screened for single-nucleotide polymorphisms (SNPs) in P2Y12 by direct DNA sequencing (n=50). Frequencies of P2Y12 single nucleotide polymorphisms (SNPs), linkage disequilibrium blocks, haplotype structures, and haplotype-tagging SNPs were determined. The effects of genetic variation in the P2Y12 gene on the extent of ADP-induced platelet aggregation were studied in healthy Korean men (n=40).

RESULTS

Variant 2 (NM 176876.1) was the predominantly expressed form in all subjects, but variant 1 was also weakly expressed in all cases (n=10). A total of 20 SNPs were identified: 2 in exons, 5 in introns, and 8 and 5 in the 5'-untranslated regions of the known P2Y12 RNA variants 1 and 2, respectively. Genetic analysis of the P2Y12 SNPs and haplotypes revealed a statistically significant association between P2Y12 haplotype, denoted H3, and an increase in the ADP-induced platelet aggregation response relative to that for the reference haplotype H1 (P=0.01).

CONCLUSIONS

Application of these findings to the development of a multivariate model might be useful in explaining the variable outcome of antiplatelet drug therapy in Asian populations.

Antiplatelet and anticoagulant therapies in acute coronary syndromes

The combination of aspirin and clopidogrel is the mainstay antiplatelet therapy for acute coronary syndromes (ACS). However, the dosing of aspirin, the dosing of clopidogrel, the timing of clopidogrel initiation as well as the duration of clopidogrel therapy remain controversial matters. Clopidogrel resistance is an emerging concept with potential clinical implications. In the era of clopidogrel and bivalirudin, the role of glycoprotein IIb/IIIa antagonists is being challenged, yet they are still indicated in a select high-risk population. Concerning anticoagulant use in ACS, newer agents, bivalirudin and fondaparinux, have improved outcomes in comparison to heparin in patients managed with an invasive or conservative strategy, respectively. Combining multiple antiplatelet agents and an anticoagulant is the standard of care for ACS.

Platelet pharmacogenomics

Platelet responsiveness to conventional antiplatelet therapy underlies a high interindividual variability influenced by various factors. For instance, antiplatelet therapy does not curtail the expected effects in a relevant number of patients as demonstrated by the occurrence of repeated cardiovascular events including stent thrombosis and/or by inadequate platelet inhibition measured by in vitro platelet function assays. Besides non-genetic factors such as age, gender, liver and renal function and co-medication, considerable variation of antiplatelet drug responsiveness can be attributed to genetic factors including polymorphisms and genetic variants of platelet surface proteins and drug metabolizing enzymes. Nowadays, platelet pharmacogenomics has started a new field with the goal to link genetic information of various drug targets to interindividual variability of drug response. Evolving data from large cohort studies suggest a promising role for pharmacogenomics in the context of antiplatelet therapy. Additionally, with the revolution of low cost and high-throughput genotyping techniques, genetic testing has become affordable for clinical application and individualization of therapy. However, a key issue to define the future role of pharmacogenomics will rely on the benefit and the timeliness of implementing the genetic information into therapeutic decision. Hence, it warrants further investigations to document the prognostic effects of therapeutic alterations in distinct genotypes. Concerning the safety profile of emerging antiplatelet and antithrombotic drugs in certain risk groups it would be fatal to individualize treatment barely on behalf of an atherothrombotic genotype. In contrast, individual risk assessment combining non-genetic information and pharmacogenetic analysis represents a reasonable concept. Here, we provide a review on current data describing the role of pharmacogenomics in the field of antiplatelet drug treatment in cardiovascular patients with future directions.

Ticagrelor yields consistent dose-dependent inhibition of ADP-induced platelet aggregation in patients with atherosclerotic disease regardless of genotypic variations in P2RY12, P2RY1, and ITGB3

The platelet P2Y(12) receptor is the target of clopidogrel therapy, which has been shown to reduce thromboembolic complications of atherosclerotic disease but has limitations in terms of variability of response and irreversibility of effect. This receptor is also a target for ticagrelor (AZD6140), the first reversibly binding oral P2Y(12) receptor antagonist that does not require metabolic activation and yields more consistent inhibition of platelet aggregation than clopidogrel therapy. Single nucleotide polymorphisms (SNPs) have been described in the gene for this receptor (P2RY12), some of which have been associated with variability in platelet reactivity. SNPs in P2RY1 and ITGB3 have also been reported by some groups to affect platelet reactivity to adenosine diphosphate (ADP). We assessed whether SNPs in these genes influenced the pharmacodynamic response to ticagrelor in patients enrolled in both the DISPERSE study (stable atherosclerotic disease) and the DISPERSE2 study (non-ST-segment elevation acute coronary syndromes). Platelet aggregation data (at baseline and 4 weeks) and DNA samples from clopidogrel-naive Caucasian patients treated with ticagrelor were available for 151 patients. Seventy four SNPs within three genes were genotyped. After adjustment for multiple comparisons, none of these SNPs were found to significantly influence inhibition of ADP-induced platelet aggregation by ticagrelor.

Common Variation in the Platelet Receptor P2RY12 Gene Is Associated With Residual On-Clopidogrel Platelet Reactivity in Patients Undergoing Elective Percutaneous Coronary Interventions

Background— The clinical efficacy of clopidogrel is hampered by a large interindividual variability in platelet inhibition. Polymorphisms in the P2RY12 receptor gene have been suggested to contribute to this variability, but previous studies included a relatively small number of patients and incompletely covered the common variation in the P2RY12 gene. The aim of this study was to comprehensively investigate the possible association between common variation in the entire P2RY12 locus and the magnitude of residual on-clopidogrel platelet reactivity measured by 2 commonly used platelet function assays in a large cohort of patients.

Methods and Results— A total of 1031 consecutive patients with coronary artery disease who were scheduled for elective percutaneous coronary interventions were enrolled. Platelet function was assessed by means of ADP-induced light-transmittance aggregometry and the VerifyNow P2Y12 assay. Six haplotype-tagging single nucleotide polymorphisms were carefully selected to comprehensively cover the total common variation in the P2RY12 gene and its flanking regulatory regions. Six common haplotypes were inferred from these haplotype-tagging single nucleotide polymorphisms (denoted A to F). Haplotype F was associated with significantly lower residual on-clopidogrel platelet reactivity compared with the reference haplotype A. The size of this effect per haplotype allele was approximately 5% aggregation in the ADP-induced light-transmittance aggregometry ( P <0.05) and 11 P2Y12 reaction units in the VerifyNow P2Y12 assay ( P <0.05).

Conclusions— Common variation in the P2RY12 gene is a significant determinant of the interindividual variability in residual on-clopidogrel platelet reactivity in patients with coronary artery disease.

Pharmacogenetics in cardiovascular antithrombotic therapy

Thrombosis is the most important underlying mechanism of coronary artery disease and embolic stroke. Hence, antithrombotic therapy is widely used in these scenarios. However, not all patients achieve the same degree of benefit from antithrombotic agents, and a considerable number of treated patients will continue to experience a new thrombotic event. Such lack of clinical benefit may be related to a wide variability of responses to antithrombotic treatment among individuals (i.e., interindividual heterogeneity). Several factors have been identified in this interindividual heterogeneity in response to antithrombotic treatment. Pharmacogenetics has emerged as a field that identifies specific gene variants able to explain the variability in patient response to a given drug. Polymorphisms affecting the disposition, metabolism, transporters, or targets of a drug all can be implicated in the modification of an individual's antithrombotic drug response and therefore the safety and efficacy of the aforementioned drug. The present paper reviews the modulating role of different polymorphisms on individuals' responses to antithrombotic drugs commonly used in clinical practice.

High loading dose of clopidogrel is unable to satisfactorily inhibit platelet reactivity in patients with glycoprotein IIIA gene polymorphism: a genetic substudy of PRAGUE-8 trial

The study aimed to assess the impact of nine polymorphisms of genes encoding platelet receptors, enzymes, and hemostatic factors on clopidogrel efficacy to inhibit platelet reactivity in patients with stable coronary artery disease undergoing elective coronary angiography either with or without ad hoc percutaneous coronary intervention. The study was performed as a genetic substudy of the PRAGUE-8 trial. Ninety-five patients pretreated with 600 mg clopidogrel at least 6 h prior to coronary angiography were tested. Baseline platelet reactivity to ADP was assessed before the drug was administered. Clopidogrel efficacy was tested again at 12 and 28 h after administration. Polymorphisms of platelet receptors, glycoprotein (GP) Ia (807C/T), GPVI (13254C/T), GPIIIa (PlA1/PlA2), PAR-1 (IVSn-14A/T), P2Y12 (32C/T), P2Y12 (H1/H2) haplotype, gene variations of cyclooxygenase-1, Leiden, and factor II mutations were studied. Flow cytometric tests of vasodilator-stimulated phosphoprotein phosphorylation states were used as a measure of drug efficacy. None of the gene polymorphisms influenced baseline ADP-induced platelet reactivity significantly. Twenty-eight hours after drug administration, differences in suppression of ADP-induced platelet reactivity were observed between polymorphism-positive and polymorphism-negative patients. Inhibition of platelet reactivity, after 600 mg of clopidogrel, was significantly less in carriers of PlA2 (P=0.009) for mean decrease in platelet reactivity index. The proportion of clopidogrel nonresponders (platelet reactivity index >50%) was apparently higher in PlA2 carriers in comparison with PlA1/PlA1 patients (54 vs. 24%, P=0.082). A 600 mg loading dose of clopidogrel failed to acceptably inhibit platelet reactivity in patients who were positive for the PlA2 polymorphism.

Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy

The efficacy of the platelet P2Y12 receptor antagonist clopidogrel, which undergoes cytochrome-mediated metabolism to its active form, shows marked inter-individual variability. We investigated whether polymorphic variations in the P2Y12 gene, which have been linked to platelet aggregation phenotypes, or the cytochrome P450 3A5 gene 6986G > A polymorphism, which largely determines CYP3A5 expression, influence the response to clopidogrel therapy. Fifty-four patients listed for elective percutaneous coronary intervention were studied using ADP-induced optical aggregometry, whole-blood single platelet counting (WBSPC) aggregometry, and flow-cytometric analysis of platelet P-selectin expression and platelet-monocyte conjugate formation. Platelet reactivity was measured at baseline, 4 h post clopidogrel 300 mg, and 10 and 28 days following clopidogrel 75 mg daily. A further 55 patients were studied using ADP-induced WBSPC at baseline and 4 h post clopidogrel 600 mg. Patients were genotyped for P2Y12 haplotype and the CYP3A5 6986G > A single nucleotide polymorphism. Neither genotype was found to significantly influence the inhibition of platelet responses by either clopidogrel regimen. In conclusion, common sequence variations within the P2Y12 and CYP3A5 genes do not contribute any major effect to the inter-patient variability in clopidogrel efficacy.

Genetic variation of CYP2C19 affects both pharmacokinetic and pharmacodynamic responses to clopidogrel but not prasugrel in aspirin-treated patients with coronary artery disease

AIMS

The metabolic pathways leading to the formation of prasugrel and clopidogrel active metabolites differ. We hypothesized that decreased CYP2C19 activity affects the pharmacokinetic and pharmacodynamic response to clopidogrel but not prasugrel.

METHODS AND RESULTS

Ninety-eight patients with coronary artery disease (CAD) taking either clopidogrel 600 mg loading dose (LD)/75 mg maintenance dose (MD) or prasugrel 60 mg LD/10 mg MD were genotyped for variation in six CYP genes. Based on CYP genotype, patients were segregated into two groups: normal function (extensive) metabolizers (EM) and reduced function metabolizers (RM). Plasma active metabolite concentrations were measured at 30 min, 1, 2, 4, and 6 h post-LD and during the MD period on Day 2, Day 14, and Day 29 at 30 min, 1, 2, and 4 h. Vasodilator-stimulated phosphoprotein (VASP) and VerifyNow P2Y12 were measured predose, 2, and 24 +/- 4 h post-LD and predose during the MD period on Day 14 +/- 3 and Day 29 +/- 3. For clopidogrel, active metabolite exposure was significantly lower (P = 0.0015) and VASP platelet reactivity index (PRI, %) and VerifyNow P2Y(12) reaction unit (PRU) values were significantly higher (P < 0.05) in the CYP2C19 RM compared with the EM group. For prasugrel, there was no statistically significant difference in active metabolite exposure or pharmacodynamic response between CYP2C19 EM and RM. Variation in the other five genes demonstrated no statistically significant differences in pharmacokinetic or pharmacodynamic responses.

CONCLUSION

Variation in the gene encoding CYP2C19 in patients with stable CAD contributes to reduced exposure to clopidogrel's active metabolite and a corresponding reduction in P2Y(12) inhibition, but has no significant influence on the response to prasugrel.

Patients with poor responsiveness to thienopyridine treatment or with diabetes have lower levels of circulating active metabolite, but their platelets respond normally to active metabolite added ex vivo

OBJECTIVES

We evaluated the prevalence and mechanism of poor responsiveness to clopidogrel and prasugrel in coronary artery disease patients with and without diabetes.

BACKGROUND

Low platelet inhibition by clopidogrel is associated with ischemic clinical events. A higher 600-mg loading dose (LD) has been advocated to increase responsiveness to clopidogrel.

METHODS

In this study, 110 aspirin-treated patients were randomized to double-blind treatment with clopidogrel 600 mg LD/75 mg maintenance dose (MD) for 28 days or prasugrel 60 mg LD/10 mg MD for 28 days. Pharmacodynamic (PD) response was evaluated by light transmission aggregometry and vasodilator-stimulated phosphoprotein phosphorylation. The PD poor responsiveness was defined with 4 definitions previously associated with worse clinical outcomes. Active metabolites (AM) of clopidogrel and prasugrel were measured. Clopidogrel AM was added ex vivo.

RESULTS

The proportion of patients with poor responsiveness was greater in the clopidogrel group for all definitions at all time points from 1 h to 29 days. Poor responders had significantly lower plasma AM levels compared with responders. Patients with diabetes were over-represented in the poor-responder groups and had significantly lower levels of AM. Platelets of both poor responders and diabetic patients responded fully to AM added ex vivo.

CONCLUSIONS

Prasugrel treatment results in significantly fewer PD poor responders compared with clopidogrel after a 600-mg clopidogrel LD and during MD. The mechanism of incomplete platelet inhibition in clopidogrel poor-responder groups and in diabetic patients is lower plasma levels of its AM and not differences in platelet P2Y(12) receptor function.