Platelet receptor P2RY12 haplotypes predict restenosis after percutaneous coronary interventions

The role of platelet P2Y12 receptors in inflammation

Inflammation is a complex pathophysiological process underlying many clinical conditions. Platelets contribute to the thrombo-inflammatory response. Platelet P2Y12 receptors amplify platelet activation, potentiating platelet aggregation, degranulation and shape change. The contents of platelet alpha granules, in particular, act directly on leucocytes, including mediating platelet-leucocyte aggregation and activation via platelet P-selectin. Much evidence for the role of platelet P2Y12 receptors in inflammation comes from studies using antagonists of these receptors, such as the thienopyridines clopidogrel and prasugrel, and the cyclopentyltriazolopyrimidine ticagrelor, in animal and human experimental models. These suggest that antagonism of P2Y12 receptors decreases markers of inflammation with some evidence that this reduces incidence of adverse clinical sequelae during inflammatory conditions. Interpretation is complicated by pleiotropic effects such as those of the thienopyridines on circulating leucocyte numbers and of ticagrelor on adenosine reuptake. The available evidence suggests that P2Y12 receptors are prominent mediators of inflammation and P2Y12 receptor antagonism as a potentially powerful strategy in a broad range of inflammatory conditions. LINKED ARTICLES: This article is part of a themed issue on Platelet purinergic receptor and non-thrombotic disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.4/issuetoc.

Pharmacogenetics of P2Y12 receptor inhibitors

Oral P2Y12 inhibitors are commonly prescribed for cardiovascular disease and include clopidogrel, prasugrel, and ticagrelor. Each of these drugs has its strengths and weaknesses. Prasugrel and ticagrelor are more potent inhibitors of platelet aggregation and were shown to be superior to clopidogrel in preventing major adverse cardiovascular events after an acute coronary syndrome and percutaneous coronary intervention (PCI) in the absence of genotyping. However, both are associated with an increased risk for non-coronary artery bypass-related bleeding. Clopidogrel is a prodrug requiring bioactivation, primarily via the CYP2C19 enzyme. Approximately 30% of individuals have a CYP2C19 no function allele and decreased or no CYP2C19 enzyme activity. Clopidogrel-treated carriers of a CYP2C19 no function allele have decreased exposure to the clopidogrel active metabolite and lesser inhibition of platelet aggregation, which likely contributed to reduced clopidogrel efficacy in clinical trials. The pharmacogenetic data for clopidogrel are most robust in the setting of PCI, but evidence is accumulating for other indications. Guidance is available from expert consensus groups and regulatory agencies to assist with integrating genetic information into P2Y12 inhibitor prescribing decisions, and CYP2C19 genotype-guided antiplatelet therapy after PCI is one of the most common examples of clinical pharmacogenetic implementation. Herein, we review the evidence for pharmacogenetic associations with clopidogrel response and outcomes with genotype-guided P2Y12 inhibitor selection and describe guidance to assist with pharmacogenetic implementation. We also describe processes for applying genotype data for P2Y12 inhibitor therapy selection and remaining gaps in the field. Ultimately, consideration of both clinical and genetic factors may guide selection of P2Y12 inhibitor therapy that optimally balances the atherothrombotic and bleeding risks.

Mechanisms of drug-eluting stent restenosis

Drug-eluting stents (DES) were developed to overcome in-stent restenosis (ISR), which has long been considered the main complication limiting the long-term efficacy of coronary stenting. New-generation DES which composed of advanced stent design with and without specific biocompatible polymer contributes a reduction of the incidence of ISR to rate ranging from 5 to 10%. The precise reasons of DES restenosis are still controversial and not fully understood. Angiographic and coronary images at the index procedure, systemic status of patients, medications, and intracoronary imaging at ISR site are all considered to find the possible mechanisms of DES restenosis. Multiple biological, genetic, mechanical, and technical factors might intricately contribute to DES restenosis. Biological and genetic factors of ISR are not able to be sufficiently modified by the current medical approaches. Tailored treatments avoiding mechanical and technical factors of ISR are required to reduce DES restenosis. Elucidation of DES restenosis leads to further improvement in the current DES system and finds the optimal approach to treat DES restenosis. The possible mechanisms of DES restenosis are discussed in this review.

Haplotype of platelet receptor P2RY12 gene is associated with residual clopidogrel on-treatment platelet reactivity

OBJECTIVE

To investigate a possible association between common variations of the P2RY12 and the residual clopidogrel on-treatment platelet reactivity after adjusting for the influence of CYP2C19 tested by thromboelastography (TEG).

METHODS

One hundred and eighty patients with acute coronary syndrome (ACS) treated with clopidogrel and aspirin were included and platelet function was assessed by TEG. Five selected P2RY12 single nucleotide polymorphisms (SNPs; rs6798347, rs6787801, rs6801273, rs6785930, and rs2046934), which cover the common variations in the P2RY12 gene and its regulatory regions, and three CYP2C19 SNPs (^*2,^*3,^*17) were genotyped and possible haplotypes were analyzed.

RESULTS

The high on-treatment platelet reactivity (HTPR) prevalence defined by a platelet inhibition rate <30% by TEG in adenosine diphosphate (ADP)-channel was 69 (38.33%). Six common haplotypes were inferred from four of the selected P2RY12 SNPs (denoted H₀ to H₅) according to the linkage disequilibrium R square (except for rs2046934). Haplotype H₁ showed a significantly lower incidence of HTPR than the reference haplotype (H₀) in the total study population while haplotypes H₁ and H₂ showed significantly lower incidences of HTPR than H₀ in the nonsmoker subgroup after adjusting for CYP2C19 effects and demographic characteristics. rs2046934 (T744C) did not show any significant association with HTPR.

CONCLUSIONS

The combination of common P2RY12 variations including regulatory regions rather than rs2046934 (T744C) that related to pharmacodynamics of clopidogrel in patients with ACS was independently associated with residual on-clopidogrel platelet reactivity. This is apart from the established association of the CYP2C19. This association seemed more important in the subgroup defined by smoking.

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.

Genetics of coronary artery disease and myocardial infarction

Atherosclerotic coronary artery disease (CAD) comprises a broad spectrum of clinical entities that include asymptomatic subclinical atherosclerosis and its clinical complications, such as angina pectoris, myocardial infarction (MI) and sudden cardiac death. CAD continues to be the leading cause of death in industrialized society. The long-recognized familial clustering of CAD suggests that genetics plays a central role in its development, with the heritability of CAD and MI estimated at approximately 50% to 60%. Understanding the genetic architecture of CAD and MI has proven to be difficult and costly due to the heterogeneity of clinical CAD and the underlying multi-decade complex pathophysiological processes that involve both genetic and environmental interactions. This review describes the clinical heterogeneity of CAD and MI to clarify the disease spectrum in genetic studies, provides a brief overview of the historical understanding and estimation of the heritability of CAD and MI, recounts major gene discoveries of potential causal mutations in familial CAD and MI, summarizes CAD and MI-associated genetic variants identified using candidate gene approaches and genome-wide association studies (GWAS), and summarizes the current status of the construction and validations of genetic risk scores for lifetime risk prediction and guidance for preventive strategies. Potential protective genetic factors against the development of CAD and MI are also discussed. Finally, GWAS have identified multiple genetic factors associated with an increased risk of in-stent restenosis following stent placement for obstructive CAD. This review will also address genetic factors associated with in-stent restenosis, which may ultimately guide clinical decision-making regarding revascularization strategies for patients with CAD and MI.

Clinical pharmacokinetics and pharmacodynamics of clopidogrel

Acute coronary syndromes (ACS) remain life-threatening disorders, which are associated with high morbidity and mortality. Dual antiplatelet therapy with aspirin and clopidogrel has been shown to reduce cardiovascular events in patients with ACS. However, there is substantial inter-individual variability in the response to clopidogrel treatment, in addition to prolonged recovery of platelet reactivity as a result of irreversible binding to P2Y12 receptors. This high inter-individual variability in treatment response has primarily been associated with genetic polymorphisms in the genes encoding for cytochrome (CYP) 2C19, which affect the pharmacokinetics of clopidogrel. While the US Food and Drug Administration has issued a boxed warning for CYP2C19 poor metabolizers because of potentially reduced efficacy in these patients, results from multivariate analyses suggest that additional factors, including age, sex, obesity, concurrent diseases and drug-drug interactions, may all contribute to the overall between-subject variability in treatment response. However, the extent to which each of these factors contributes to the overall variability, and how they are interrelated, is currently unclear. The objective of this review article is to provide a comprehensive update on the different factors that influence the pharmacokinetics and pharmacodynamics of clopidogrel and how they mechanistically contribute to inter-individual differences in the response to clopidogrel treatment.

Effect of platelet receptor gene polymorphisms on outcomes in ST-elevation myocardial infarction patients after percutaneous coronary intervention

Polymorphisms in platelet receptor genes may influence platelet function. This study aimed to assess the impact of five polymorphisms of genes encoding platelet receptors on the risk of ischemic and bleeding events in ST-elevation myocardial infarction (STEMI) patients after percutaneous coronary intervention (PCI). 503 consecutive Chinese patients with STEMI after an uneventful PCI and exposed to standard dual antiplatelet therapy for 12 months were enrolled. Polymorphisms of platelet receptors, GPIa (ITGA2, 807C > T, rs1126643), GPVI (GP6, 13254T > C, rs1613662), PAR-1 (F2R, IVS-14A > T, rs168753) and P2Y12 (P2RY12, 34C > T, rs6785930 and H1/H2 haplotype, 52G > T, rs6809699) were detected by the ligase detection reaction. The follow-up period was 12 months. Overall, 34 (6.8%) ischemic events occurred and 46 (9.1%) major bleedings occurred. Multivariate Cox regression analysis showed the carriage of F2R rs168753 minor allele was an independent predictor of the composite ischemic events (HR 0.387, 95% CI 0.193-0.778, p = 0.008) after adjusted for established risk factors. Multivariate logistic regression model identified that carriage of P2RY12 rs6809699 minor allele (OR 2.71, 95% CI 1.298-5.659, p = 0.008) was an independent predictor of major bleedings. The associations were then validated in a second cohort of 483 STEMI patients. In STEMI patients after PCI, F2R rs168753 minor allele could significantly contribute to the risk of ischemic events, and P2RY12 rs6809699 minor allele could predict bleedings. The genetic testing of platelet receptors can be valuable in predicting adverse events in STEMI patients after PCI.

Genetic polymorphisms of platelet receptors in patients with acute myocardial infarction and resistance to antiplatelet therapy

METHODS

The studied group comprises 124 patients with acute myocardial infarction on dual antiplatelet therapy with acetylsalicylic acid (ASA) and thienopyridines. Antiplatelet therapy was monitored by platelet-rich plasma light transmittance aggregometry (LTA) using the APACT 4004 analyzer (Helena Laboratories) and by whole blood impedance aggregometry (multiple electrode aggregometry [MEA]) using the Multiplate analyzer (Dynabyte). Platelet aggregation was detected after stimulation with arachidonic acid for detection of aspirin resistance and with adenosine diphosphate (ADP) and prostaglandin E1 for detection of thienopyridine resistance. To determine the frequencies of P2Y12 (i-744T>C; rs2046934), P2Y12 (34C>T; rs6785930), COX-1 (-842A>G; rs10306114), GPVI (13254T>C; rs1613662), and GPIbA (5T>C; rs2243093) polymorphisms, DNA of patients with AIM was tested by real-time-polymerase chain reaction and melting curve analysis using the LightCycler 480 analyzer (Roche Diagnostics).

RESULTS

The cut-off points used for patients with effective ASA therapy are 25% of aggregated platelets and 220 area under the curve (AUC)/min if LTA or MEA, respectively. The cut-off points used for effective thienopyridine therapy are 45% of aggregated platelets or 298 AUC/min, respectively. Both LTA and MEA found that aspirin and thienopyridine therapies failed in 14.51% and 25.8%, respectively. The data were statistically processed using the SPSS version 15 software (SPSS, Inc.). Associations between receptor mutation status and response to therapy were assessed with Fisher's exact test. The significance level was set at 0.05.

CONCLUSION

The aim of our work was to use the two functional laboratory methods described earlier to assess both aspirin and thienopyridine resistance and to determine the contribution of genetic polymorphisms of platelet receptors to resistance to antiplatelet therapy in AIM. Fisher's exact test showed a significant statistical correlation between platelet function tests suitable for monitoring ASA resistance, that is, LTA and MEA, and mutation status of COX1_A1 (-A842G). Fisher's exact test showed no statistically significant correlations between platelet function tests suitable for monitoring ASA resistance, that is, LTA and MEA, and mutation status of GP1bA (-5T>C) and GP6 (T13254C). Fisher's exact test showed no statistically significant correlation between mutational statuses of the receptors P2RY12 (i-T744C), P2RY12 (C34T), GP1bA (-5T>C), or GP6 (T13254C) and response to antiplatelet therapy with 75 mg of clopidogrel.

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.

Increased platelet activation and thrombosis in transgenic mice expressing constitutively active P2Y12

BACKGROUND

In our previous in vitro study, we reported a constitutively active chimeric P2Y(12) (cP2Y(12)) and found that AR-C78511 is a potent inverse agonist at this receptor. The role of cP2Y(12) in platelet activation and thrombosis is not clear.

OBJECTIVES

To investigate the physiologic implications of cP2Y(12) for platelet activation and thrombus formation, and to evaluate the antiplatelet activity of AR-C78511 as an inverse agonist.

METHODS AND RESULTS

We generated transgenic mice conditionally and platelet-specifically expressing cP2Y(12). High-level expression of cP2Y(12) in platelets increased platelet reactivity, as shown by increased platelet aggregation in response to multiple platelet agonists. Moreover, transgenic mice showed a shortened bleeding time, and more rapid and stable thrombus formation in mesenteric artery injured with FeCl(3). The constitutive activity of cP2Y(12) in platelets was confirmed by decreased platelet cAMP levels and constitutive Akt phosphorylation in the absence of agonists. AR-C78511 reversed the cAMP decrease in transgenic mouse platelets, and exhibited a superior antiplatelet effect to that of AR-C69931MX in transgenic mice.

CONCLUSIONS

These findings further emphasize the importance of P2Y(12) in platelet activation, hemostasis, and thrombosis, as well as the prothrombotic role of the constitutive activity of P2Y(12). Our data also validate the in vivo inverse agonist activity of AR-C78511, and confirm its superior antiplatelet activity over neutral antagonists.

Systematic testing of literature reported genetic variation associated with coronary restenosis: results of the GENDER Study

Background

Coronary restenosis after percutaneous coronary intervention still remains a significant problem, despite all medical advances. Unraveling the mechanisms leading to restenosis development remains challenging. Many studies have identified genetic markers associated with restenosis, but consistent replication of the reported markers is scarce. The aim of the current study was to analyze the joined effect of previously in literature reported candidate genes for restenosis in the GENetic DEterminants of Restenosis (GENDER) databank.

Methodology/Principal Findings

Candidate genes were selected using a MEDLINE search including the terms ‘genetic polymorphism’ and ‘coronary restenosis’. The final set included 36 genes. Subsequently, all single nucleotide polymorphisms (SNPs) in the genomic region of these genes were analyzed in GENDER using set-based analysis in PLINK. The GENDER databank contains genotypic data of 2,571,586 SNPs of 295 cases with restenosis and 571 matched controls. The set, including all 36 literature reported genes, was, indeed, significantly associated with restenosis, p = 0.024 in the GENDER study. Subsequent analyses of the individual genes demonstrated that the observed association of the complete set was determined by 6 of the 36 genes.

Conclusion

Despite overt inconsistencies in literature, with regard to individual candidate gene studies, this is the first study demonstrating that the joint effect of all these genes together, indeed, is associated with restenosis.

Effects of testosterone and 17β-oestradiol on expression of the G protein-coupled receptor P2Y12 in megakaryocytic DAMI cells

P2Y12 is an important G protein-coupled receptor that is involved in ADP-induced platelet aggregation, which is essential for normal haemostasis. Gender differences in the incidence of cardiovascular disease have been proposed to be linked to the effects of sex hormones on cardiovascular-related genes. We examined the influences of testosterone and 17β-oestradiol on P2Y12 gene expression in megakaryocytic DAMI cell line. Altered levels of P2Y12 mRNA, protein and the cAMP-dependent vasodilator-stimulated phosphoprotein-Ser157 (VASP-Ser157) phosphorylation were investigated after treatment with 17β-oestradioal or testosterone as compared to the control groups. Quantitative real-time PCR revealed that the P2Y12 mRNA levels were increased by testosterone in a dose-dependent manner, whereas 17β-oestrodiol had no effect on P2Y12 gene expression. Induction of the P2Y12 protein by testosterone was found in Western blots of the proteins isolated from testosterone-treated cells. Testosterone-mediated P2Y12 expression was repressed at both the transcriptional and translational levels by the anti-androgen receptor bicalutamide. Treatment with testosterone also resulted in a decrease in the level of VASP-Ser157 phosphorylation, as compared to the control group. The decrease in the level of VASP-Ser157 phosphorylation was reversed by bicalutamide. These findings suggest a novel pathway for testosterone regulation of P2Y12 expression in a megakaryocytic DAMI cell line. Further studies using primary human megakaryocytes and platelets could be necessary to know the effect of hormones on the P2Y12 expression in circulating platelets.

Gene-by-environment effect of house dust mite on purinergic receptor P2Y12 (P2RY12) and lung function in children with asthma

BACKGROUND

Distinct receptors likely exist for leukotriene (LT)E(4), a potent mediator of airway inflammation. Purinergic receptor P2Y12 is needed for LTE(4)-induced airways inflammation, and P2Y12 antagonism attenuates house dust mite-induced pulmonary eosinophilia in mice. Although experimental data support a role for P2Y12 in airway inflammation, its role in human asthma has never been studied.

OBJECTIVE

To test for association between variants in the P2Y12 gene (P2RY12) and lung function in human subjects with asthma, and to examine for gene-by-environment interaction with house dust mite exposure.

METHODS

Nineteen single nucleotide polymorphisms (SNPs) in P2RY12 were genotyped in 422 children with asthma and their parents (n = 1266). Using family based methods, we tested for associations between these SNPs and five lung function measures. We performed haplotype association analyses and tested for gene-by-environment interactions using house dust mite exposure. We used the false discovery rate to account for multiple comparisons.

RESULTS

Five SNPs in P2RY12 were associated with multiple lung function measures (P-values 0.006–0.025). Haplotypes in P2RY12 were also associated with lung function (P-values 0.0055–0.046). House dust mite exposure modulated associations between P2RY12 and lung function, with minor allele homozygotes exposed to house dust mite demonstrating worse lung function than those unexposed (significant interaction P-values 0.0028–0.040).

CONCLUSIONS AND CLINICAL RELEVANCE

The P2RY12 variants were associated with lung function in a large family-based asthma cohort. House dust mite exposure caused significant gene-by-environment effects. Our findings add the first human evidence to experimental data supporting a role for P2Y12 in lung function. P2Y12 could represent a novel target for asthma treatment.

P2RY1 and P2RY12 polymorphisms and on-aspirin platelet reactivity in patients with coronary artery disease

INTRODUCTION

Association of P2RY1 and P2RY12 polymorphisms with on-aspirin platelet reactivity was investigated.

MATERIALS AND METHODS

Platelet reactivity was assessed by the light transmission aggregometry and TxB(2) assay in 423 patients with coronary artery disease (CAD) on aspirin. High residual platelet reactivity (RPR) was defined by ≥20% and ≥70% maximal aggregation stimulated with 0.5 mg/mL arachidonic acid (AA) and 10 μm ADP, respectively. Moderate RPR was considered aggregation ≥20% with AA, ≥70% with ADP, or ≥1 ng/mL stimulated TxB(2) . Fourteen P2RY1 and 35 P2RY12 single nucleotide polymorphisms (SNPs) were genotyped.

RESULTS

High RPR was detected in 24% of the patients. Moderate RPR was observed in 31% with AA, 57% with 5 μm ADP, and 82% with 10 μm ADP. Stimulated TxB(2) was ≥1 ng/mL in 23% of patients. P2RY12 SNP rs9859538 was associated with high RPR (OR = 2.16, 95% CI = 1.24-3.75, P-value = 0.004). Four P2RY12 SNPs, rs1491974, rs10513398, rs3732765, and rs10935841, showed association with moderate RPR (OR = 1.79-2.94, P-value = 0.04-0.028), while five, rs7615865, rs1388623, rs1388622, rs7634096, and rs7637803, were associated with low RPR (OR = 0.50-0.55, P-value = 0.008-0.026), following ADP stimulation. TxB(2) level <1 ng/mL was linked to five P2RY1 SNPs, rs1439010, rs1371097, rs701265, rs12497578, and rs2312265 (OR = 0.36-0.54, P-value = 0.003-0.039).

CONCLUSIONS

Polymorphisms in P2RY1 and P2RY12 are associated with on-aspirin platelet reactivity in patients with CAD.

Restenosis after PCI. Part 1: pathophysiology and risk factors

Restenosis is a complex disease for which the pathophysiological mechanisms have not yet been fully elucidated, but are thought to include inflammation, proliferation, and matrix remodeling. Over the years, many predictive clinical, biological, (epi)genetic, lesion-related, and procedural risk factors for restenosis have been identified. These factors are not only useful in risk stratification of patients, they also contribute to our understanding of this condition. Furthermore, these factors provide evidence on which to base treatment tailored to the individual and aid in the development of novel therapeutic modalities. In this Review, we will evaluate the available evidence on the pathophysiological mechanisms of restenosis and provide an overview of the various risk factors, together with the possible clinical application of this knowledge.

Connexin 37 limits thrombus propensity by downregulating platelet reactivity

BACKGROUND

Formation of platelet plug initiates hemostasis after vascular injury and triggers thrombosis in ischemic disease. However, the mechanisms leading to the formation of a stable thrombus are poorly understood. Connexins comprise a family of proteins that form gap junctions enabling intercellular coordination of tissue activity, a process termed gap junctional intercellular communication.

METHODS AND RESULTS

In the present study, we show that megakaryocytes and platelets express connexin 37 (Cx37). Deletion of the Cx37 gene in mice shortens bleeding time and increases thrombus propensity. Aggregation is increased in murine Cx37(-/-) platelets or in murine Cx37(+/+) and human platelets treated with gap junction blockers. Intracellular microinjection of neurobiotin, a Cx37-permeant tracer, revealed gap junctional intercellular communication in platelet aggregates, which was impaired in Cx37(-/-) platelets and in human platelets exposed to gap junction blockers. Finally, healthy subjects homozygous for Cx37-1019C, a prognostic marker for atherosclerosis, display increased platelet responses compared with subjects carrying the Cx37-1019T allele. Expression of these polymorphic channels in communication-deficient cells revealed a decreased permeability of Cx37-1019C channels for neurobiotin.

CONCLUSIONS

We propose that the establishment of gap junctional communication between Cx37-expressing platelets provides a mechanism to limit thrombus propensity. To our knowledge, these data provide the first evidence incriminating gap junctions in the pathogenesis of thrombosis.

Single nucleotide polymorphisms of the purinergic 1 receptor are not associated with myocardial infarction in a Latvian population

The purinergic 1 receptor (P2RY1) has been implicated in development of heart disease and in individual pharmacodynamic response to anticoagulant therapies. However, the association of polymorphisms in the P2RY1 gene with myocardial infarction (MI), and its associated conditions, has yet to be reported in the literature. We evaluated seven known SNPs in P2RY1 for association with MI in a Latvian population. Seven independent parameters that are related to MI [body mass index (BMI), type 2 diabetes (T2D), angina pectoris, hypertension, hyperlipidemia, atrial fibrillation and heart failure] were investigated. No significant association with MI was observed for any of the polymorphisms. Those SNPs for which the P value was close to significance were located in coding or promoter regions. Intriguingly, carriers of the minor allele in the P2RY1 gene locus showed a tendency towards higher onset age for MI, suggesting a possible protective effect of these SNPs against MI or their contribution in progression as opposed to onset. Finally, a linkage disequilibrium (LD) plot was generated for these polymorphisms in the Latvian population. The results of this study suggest that the role of P2RY1 in individuals from Latvian population is likely to be principally involved in platelet aggregation and thromboembolic diseases, and not as a significant contributing factor to the global metabolic syndrome.

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.

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.