Mean platelet volume: Interrelation with platelet aggregation activity and glycoprotein IIb-IIIa and Ib expression levels

Increased mean platelet volume (MPV) is an independent risk factor of thrombotic events in patients with cardiovascular diseases. Interactions of MPV with platelet aggregation activity and contents of glycoprotein (GP) IIb-IIIa (αIIb/β3 integrin, fibrinogen receptor) and GP Ib (von Willebrand factor receptor) have been investigated in this study. The study was performed in a group of healthy volunteers (n = 38) and a group of patients with acute coronary syndrome (ACS, n = 116). Patient’s blood was collected at days 1, 3–5 and 8–12 after ACS development. All patients received acetylsalicylic acid (ASA, inhibitor of thromboxane A2 synthesis) as the antiaggregant therapy and most of them also received clopidogrel (ADP receptor antagonist), except 44 patients who had not taken clopidogrel at day 1 before first blood collection. Aggregation of volunteers’ platelets was stimulated by 1.25, 2.5, 5 and 20 μM ADP, while aggregation of patients’ platelets was stimulated by 5 and 20 μM ADP. GP IIb-IIIa and GP Ib content on the platelet surface was measured using ¹²⁵I-labelled monoclonal antibodies. GP IIb-IIIa and GP Ib genetic polymorphisms were determined in ACS patients. In healthy donors significant correlations between MPV and aggregation levels have been recognized at 1.25 μM and 2.5 μM ADP (correlation coefficient (r) values of 0.396 and 0.373, p < 0.05), while at 5 μM and 20 μM ADP these interactions did not reach the level of statistical significance (r values of 0.279 and 0.205, p > 0.05). Correlations between MPV and aggregation levels were observed at day 1 of ACS in a subgroup of patients receiving ASA but before the beginning of clopidogrel treatment (r values of 0.526, p < 0.001 and 0.368, p < 0.05 for 5 and 20 μM ADP, respectively). Correlations between these parameters were not found during combined treatment of patients with ASA and clopidogrel. Strong direct correlations between MPV and GP IIb-IIIa and GP Ib contents were detected in both healthy donors and ACS patients (at all time points): the r values ranged from 0.439 to 0.647 (p ≤ 0.001 for all correlations). Genetic polymorphisms of GP IIb-IIIa (GP IIIa Leu33Pro) and GP Ib ((?5)T/C (Kozak) and Thr145Met) identified in ACS patients did not affect expression levels of corresponding glycoproteins. The data obtained indicate that increased MPV values correlate with increased platelet aggregation activity and enhanced GP IIb-IIIa and GP Ib expression.     

Cangrelor increases the magnitude of platelet inhibition and reduces interindividual variability in clopidogrel-pretreated subjects

BackgroundInadequate platelet inhibition despite aspirin and clopidogrel therapy during and after a percutaneous coronary intervention is associated with an impaired clinical outcome. Cangrelor, a direct and reversible P2Y₁₂ inhibitor that is currently in development, has the potential to achieve higher levels of inhibition of ADP-induced platelet aggregation than clopidogrel. The aim of the present study was to compare the magnitude of platelet inhibition in clopidogrel-pretreated patients before and after the in vitro addition of a subtherapeutic dose of cangrelor. MethodsBlood samples were drawn from patients pretreated with clopidogrel and aspirin who were undergoing elective percutaneous coronary intervention (n=39). Platelet function analysis with ‘classical’ light transmittance aggregometry (both peak and late aggregation [at 6 min]) was performed before and after the in vitro addition of cangrelor (0.25 μmol/l) to platelet-rich plasma (PRP). After an incubation period of five minutes, platelet aggregation was induced by 5 and 20 μmol/l ADP. ResultsThe in vitro addition of 0.25μmol/l cangrelor to the PRP from clopidogrel-treated subjects resulted in an additional reduction in ADP-induced platelet aggregation. For ADP concentrations of 5 and 20 μmol/l, peak aggregation showed a decrease of 75 and 85%, respectively (p<0.001 for both), while late aggregation was almost completely diminished (p=0.003 and p<0.001, respectively). Furthermore, the interindividual variation in inhibition of ADP-induced platelet aggregation by clopidogrel was greatly reduced after the addition of cangrelor. ConclusionWe demonstrate that the in vitro addition of even a subtherapeutic dose of cangrelor to the PRP of clopidogrel-pretreated patients results in an additional reduction of ADP-induced platelet aggregation. Moreover, cangrelor was able to diminish the interindividual variation observed in clopidogrel-inhibited platelet aggregation. (Neth Heart J 2009;17:195–8.)     

Comparison of Aggregometry with Flow Cytometry for the Assessment of Agonists′-Induced Platelet Reactivity in Patients on Dual Antiplatelet Therapy

Data on the agreement between aggregometry and platelet activation by flow cytometry regarding the measurement of on-treatment platelet reactivity to arachidonic acid (AA) and adenosine diphosphate (ADP) are scarce. We therefore sought to compare three platelet aggregation tests with flow cytometry for the assessment of the response to antiplatelet therapy. Platelet aggregation in response to AA and ADP was determined by light transmission aggregometry (LTA), the VerifyNow assays, and multiple electrode aggregometry (MEA) in 316 patients receiving aspirin and clopidogrel therapy after angioplasty with stent implantation. AA- and ADP-induced P-selectin expression and activated glycoprotein (GP) IIb/IIIa were determined by flow cytometry. LTA, the VerifyNow P2Y₁₂ assay and MEA in response to ADP correlated significantly (all p<0.001), and the best correlation was observed between LTA and the VerifyNow P2Y₁₂ assay (r = 0.63). ADP-induced platelet reactivity by all aggregation tests correlated significantly with ADP-induced P-selectin expression and activated GPIIb/IIIa (all p<0.001). The best correlation was seen between the VerifyNow P2Y₁₂ assay and activated GPIIb/IIIa (r = 0.68). The platelet surface expressions of P-selectin and activated GPIIb/IIIa in response to ADP were significantly higher in patients with high on-treatment residual platelet reactivity (HRPR) to ADP by all test systems (all p<0.001). A rather poor correlation was observed between AA-induced platelet reactivity by LTA and the VerifyNow aspirin assay (r = 0.15, p = 0.007), while both methods did not correlate with MEA. AA-induced platelet reactivity by all aggregation tests correlated significantly, but rather poorly with AA-induced P-selectin expression (all p<0.05), while only AA-induced platelet reactivity by LTA correlated significantly with AA-induced activated GPIIb/IIIa (r = 0.21, p<0.001). The platelet surface expression of P-selectin in response to AA was significantly higher in patients with HRPR by LTA AA and MEA AA (both p<0.02). In contrast, P-selectin expression in response to AA was similar in patients without and with HRPR by the VerifyNow aspirin assay (p = 0.5), and platelet surface activated GPIIb/IIIa in response to AA did not differ significantly between patients without and with HRPR to AA by all test systems (all p>0.1). In conclusion, ADP-induced platelet reactivity by aggregometry translates partly into flow cytometry. In contrast, AA-induced platelet reactivity correlates poorly between different platelet aggregation tests, and between aggregometry and flow cytometry. Overall, both approaches capture different aspects of platelet function and are therefore not interchangeable in the assessment of agonists´-induced platelet reactivity. Clinical outcome data are needed to determine which test systems and settings are associated with different in vivo consequences.     

瑞舒伐他汀和阿托伐他汀在急性冠脉综合症中对氯吡格雷抗血小板活性的对比研究

目的：在急性冠脉综合征（acute coronary syndromes,ACS）的治疗中,抗血小板治疗及调脂治疗是最基础的治疗方案。近来有学者提出,氯吡格雷和他汀类药物都经过细胞色素CYP3A4途径代谢,二者因存在竞争性抑制,有可能降低氯吡格雷抗血小板的活性。本试验将针对阿托伐他汀及瑞舒伐他汀进行研究。方法：选择急性冠脉综合症的患者42例,所有患者均接受氯吡格雷治疗（负荷剂量300mg,维持剂量75mg／d）。随机分配为A、B两组,A组（n=20）服用阿托伐他汀治疗（20mg／d）,B组（n=22服用瑞舒伐他汀治疗（10mg／d）。分别于氯吡格雷服用前、服药治疗后3天、服药治疗后7天后采静脉血送检,测定ADP（10μmol／L）诱导的血小板聚集率。结果：阿托伐他汀组（A组）及瑞舒伐他汀组（B组）相比,服用氯吡格雷前ADP诱导的血小板聚集率基线值无统计学差异。服用氯吡格雷3日及7日后,ADP诱导的血小板聚集率明显降低,（3．85±2．58）vs（3．09±2．27）,（0．65±0．88）vs（1．05±0．95）,P〉0．05,无明显统计学差异。结论：氯吡格雷的确可以降低血小板的活性。同时,短期之内氯吡格雷的抗血小板活性未受到他汀类的影响。包括经过CPY3A4途径的他汀,如阿托伐他汀。     

Does glycoprotein IIB/IIIA resistance exist?

Platelet function testing is not embedded into routine clinical practice, because no optimal, easy, reproducible and multipathway platelet aggregation test can be accomplished in vitro. Only recently, the relationship between the level of platelet aggregation inhibition by platelet inhibitors and clinical outcome in acute myocardial infarction became more clear.1-5 High platelet reactivity was found in patients who experienced stent thrombosis, and patients with clopidogrel resistance were at increased risk of recurrent atherothrombotic events.1,2 Furthermore, in ST-elevation myocardial infarction (STEMI) increased levels of platelet aggregation were found compared with unstable angina or control patients.4 In a thrombolysis study, higher platelet receptor occupancy was coupled with better angiographic and electrocardiographic outcome.     

Is platelet inhibition due to thienopyridines increased in elderly patients, in patients with previous stroke and patients with low body weight as a possible explanation of an increased bleeding risk?

Background

The TRITON-TIMI 38 study has identified three subgroups of patients with a higher risk of bleeding during treatment with the thienopyridine prasugrel: patients with a history of stroke or transient ischaemic attack (TIA), patients ≥75 years and patients with a body weight <60 kg. However, the underlying pathobiology leading to this increased bleeding risk remains to be elucidated. The higher bleeding rate may be due to a stronger prasugrel-induced inhibition of platelet aggregation in these subgroups. The aim of the present study was to determine whether on-treatment platelet reactivity is lower in these risk subgroups as compared with other patients in a large cohort on the thienopyridine clopidogrel undergoing elective coronary stenting.

Methods

A total of 1069 consecutive patients were enrolled. On-clopidogrel platelet reactivity was measured in parallel by light transmittance aggregometry, the VerifyNow® P2Y12 assay and the PFA-100 collagen/ADP cartridge.

Results

Fourteen patients (1.5%) had a prior history of stroke or TIA, 138 patients (14.5%) were older than 75 years and 30 patients (3.2%) had a body weight <60 kg. Age ≥?75 years and a history of stroke were independent predictors of a higher on-treatment platelet reactivity. In contrast, a body weight <60 kg was significantly associated with a lower on-treatment platelet reactivity.

Conclusion

In two high-risk subgroups for bleeding, patients ≥?75 years and patients with previous stroke, on-clopidogrel platelet reactivity is increased. In contrast, in patients with a low body weight, on-clopidogrel platelet reactivity is decreased, suggesting that a stronger response to a thienopyridine might only lead to more bleeds in patients with low body weight     

瑞舒伐他汀和阿托伐他汀在急性冠脉综合症中对氯吡格雷抗血 小板活性的对比研究

目的：在急性冠脉综合征( acute coronary syndromes, ACS )的治疗中,抗血小板治疗及调脂治疗是最基础的治疗方案。近来 有学者提出,氯吡格雷和他汀类药物都经过细胞色素CYP 3A4 途径代谢,二者因存在竞争性抑制,有可能降低氯吡格雷抗血小板 的活性。本试验将针对阿托伐他汀及瑞舒伐他汀进行研究。方法：选择急性冠脉综合症的患者42 例,所有患者均接受氯吡格雷治 疗（负荷剂量300 mg,维持剂量75 mg/d）。随机分配为A、B 两组,A 组（n=20）服用阿托伐他汀治疗（20 mg/d）,B 组（n=22 服用瑞 舒伐他汀治疗（10 mg/d）。分别于氯吡格雷服用前、服药治疗后3 天、服药治疗后7 天后采静脉血送检,测定ADP（10 滋mol/L）诱导 的血小板聚集率。结果：阿托伐他汀组（A 组）及瑞舒伐他汀组（B 组）相比,服用氯吡格雷前ADP 诱导的血小板聚集率基线值无 统计学差异。服用氯吡格雷3 日及7 日后,ADP诱导的血小板聚集率明显降低,(3.85± 2.58)vs(3.09± 2.27),(0.65± 0.88)vs(1.05± 0.95),P>0.05,无明显统计学差异。结论：氯吡格雷的确可以降低血小板的活性。同时,短期之内氯吡格雷的抗血小板活性未受到 他汀类的影响,包括经过CPY3A4途径的他汀,如阿托伐他汀。     

Comparison of a New P2Y12 Receptor Specific Platelet Aggregation Test with Other Laboratory Methods in Stroke Patients on Clopidogrel Monotherapy

Background

Clinical studies suggest that 10-50% of patients are resistant to clopidogrel therapy. ADP induced platelet aggregation, a widely used test to monitor clopidogrel therapy, is affected by aspirin and is not specific for the P2Y12 receptor inhibited by clopidogrel.

Objectives

To develop a P2Y12-specific platelet aggregation test and to compare it with other methods used for monitoring clopidogrel therapy.

Patients/Methods

Study population included 111 patients with the history of ischemic stroke being on clopidogrel monotherapy and 140 controls. The effect of clopidogrel was tested by a newly developed ADP(PGE1) aggregation test in which prostaglandin E1 treated platelets are used. Results of conventional ADP induced platelet aggregation, VerifyNow P2Y12 assay and ADP(PGE1) aggregation were compared to those obtained by flow cytometric analysis of vasodilator stimulated phosphoprotein (VASP) phosphorylation. Reference intervals for all assays were determined according to the guidelines of Clinical Laboratory Standards Institute.

Results

The P2Y12-specificity of ADP(PGE1) test was proven by comparing it with ADP aggregation in the presence of P2Y1 antagonist, adenosine 3’, 5’-diphosphate. The method was not influenced by aspirin treatment. Approximately 50% of patients were clopidogrel resistant by conventional ADP aggregation and VerifyNow tests. The ADP(PGE1) method and the VASP phosphorylation assay identified 25.9% and 11.7% of patients as non-responders, respectively. ADP(PGE1) aggregation showed good correlation with VASP phosphorylation and had high diagnostic efficiency.

Conclusion

The new ADP(PGE1) method is a reliable test for monitoring P2Y12 receptor inhibition by platelet aggregation. As a subset of patients are non-responders, monitoring clopidogrel therapy by adequate methods is essential.     

ABCB1 基因单核苷酸多态性rs2235048 与氯吡格雷抵抗的相关关系

目的:探讨ABCB1基因单核苷酸多态位点rs2235048在中国汉族人群中的分布及其与氯吡格雷抵抗(Clopidogrelresistance,CR)发生的相关关系。方法:采用光学比浊法测定20μmol/L ADP诱导的残余血小板聚集率(Residual plateletagglutination,RPA)。当RPA≥70%时,即为CR。所有入选患者分为CR组和氯吡格雷非抵抗组(Non-clopidogrel resistance,NCR)。采用焦磷酸测序法测定ABCB1基因rs2235048单核苷酸多态位点在CR组和NCR组的基因型及等位基因分布频率。结果:ABCB1基因rs2235048多态在CR组和NCR组基因型分布频率符合Hardy-Weinberg平衡。在CR组和NCR组中,ABCB1基因rs2235048多态的基因型频率分布无统计学差异(P=0.527,X2=1.281);T、C等位基因频率在两组间分布频率也没有统计学差异(P=0.740,OR=0.958,95%CI=0.742～1.236)。结论:对PCI术后服用氯吡格雷的冠心病患者进行分析发现,ABCB1基因单核苷酸多态位点rs2235048与冠心病患者CR的发生无相关关系。     

High Platelet Reactivity in Patients with Acute Coronary Syndromes Undergoing Percutaneous Coronary Intervention: Randomised Controlled Trial Comparing Prasugrel and Clopidogrel

Background

Prasugrel is more effective than clopidogrel in reducing platelet aggregation in acute coronary syndromes. Data available on prasugrel reloading in clopidogrel treated patients with high residual platelet reactivity (HRPR) i.e. poor responders, is limited.

Objectives

To determine the effects of prasugrel loading on platelet function in patients on clopidogrel and high platelet reactivity undergoing percutaneous coronary intervention for acute coronary syndrome (ACS).

Patients

Patients with ACS on clopidogrel who were scheduled for PCI found to have a platelet reactivity ≥40 AUC with the Multiplate Analyzer, i.e. “poor responders” were randomised to prasugrel (60 mg loading and 10 mg maintenance dose) or clopidogrel (600 mg reloading and 150 mg maintenance dose). The primary outcome measure was proportion of patients with platelet reactivity <40 AUC 4 hours after loading with study medication, and also at one hour (secondary outcome). 44 patients were enrolled and the study was terminated early as clopidogrel use decreased sharply due to introduction of newer P2Y12 inhibitors.

Results

At 4 hours after study medication 100% of patients treated with prasugrel compared to 91% of those treated with clopidogrel had platelet reactivity <40 AUC (p = 0.49), while at 1 hour the proportions were 95% and 64% respectively (p = 0.02). Mean platelet reactivity at 4 and 1 hours after study medication in prasugrel and clopidogrel groups respectively were 12 versus 22 (p = 0.005) and 19 versus 34 (p = 0.01) respectively.

Conclusions

Routine platelet function testing identifies patients with high residual platelet reactivity (“poor responders”) on clopidogrel. A strategy of prasugrel rather than clopidogrel reloading results in earlier and more sustained suppression of platelet reactivity. Future trials need to identify if this translates into clinical benefit.

Trial Registration

ClinicalTrials.gov NCT01339026     

The Ratio of ADP- to TRAP-Induced Platelet Aggregation Quantifies P2Y12-Dependent Platelet Inhibition Independently of the Platelet Count

Objective

This study aimed to assess the association of clinical factors with P2Y₁₂-dependent platelet inhibition as monitored by the ratio of ADP- to TRAP-induced platelet aggregation and conventional ADP-induced aggregation, respectively.

Background

Controversial findings to identify and overcome high platelet reactivity (HPR) after coronary stent-implantation and to improve clinical outcome by tailored anti-platelet therapy exist. Monitoring anti-platelet therapy ex vivo underlies several confounding parameters causing that ex vivo platelet aggregation might not reflect in vivo platelet inhibition.

Methods

In a single centre observational study, multiple electrode aggregometry was performed in whole blood of patients after recent coronary stent-implantation. Relative ADP-induced aggregation (r-ADP-agg) was defined as the ratio of ADP- to TRAP- induced aggregation reflecting the individual degree of P2Y₁₂-mediated platelet reactivity.

Results

Platelet aggregation was assessed in 359 patients. Means (± SD) of TRAP-, ADP-induced aggregation and r-ADP-agg were 794 ± 239 AU*min, 297 ± 153 AU*min and 37 ± 14%, respectively. While ADP- and TRAP-induced platelet aggregation correlated significantly with platelet count (ADP: r = 0.302; p<0.001; TRAP: r = 0.509 p<0.001), r-ADP-agg values did not (r = -0.003; p = 0.960). These findings were unaltered in multivariate analyses adjusting for a range of factors potentially influencing platelet aggregation. The presence of an acute coronary syndrome and body weight were found to correlate with both ADP-induced platelet aggregation and r-ADP-agg.

Conclusion

The ratio of ADP- to TRAP-induced platelet aggregation quantifies P2Y₁₂-dependent platelet inhibition independently of the platelet count in contrast to conventional ADP-induced aggregation. Furthermore, r-ADP-agg was associated with the presence of an acute coronary syndrome and body weight as well as ADP-induced aggregation. Thus, the r-ADP-agg is a more valid reflecting platelet aggregation and potentially prognosis after coronary stent-implantation in P2Y₁₂-mediated HPR than conventional ADP-induced platelet aggregation.     

Effect of gender difference on platelet reactivity

Background

Previous studies have suggested that women do not accrue equal therapeutic benefit from antiplatelet medication as compared with men. The physiological mechanism and clinical implications behind this gender disparity have yet to be established.

Methods

On-treatment platelet reactivity was determined in 717 men and 234 women on dual antiplatelet therapy, undergoing elective coronary stent implantation. Platelet function testing was performed using arachidonic acid and adenosine diphosphate-induced light transmittance aggregometry (LTA) and the VerifyNow P2Y12 and Aspirin assays. Also the incidence of all-cause death, non-fatal acute myocardial infarction, stent thrombosis and ischaemic stroke was evaluated.

Results

Women had higher baseline platelet counts than men. Women exhibited a higher magnitude of on-aspirin platelet reactivity using LTA, but not using the VerifyNow Aspirin assay. The magnitude of on-clopidogrel platelet reactivity was significantly higher in women as compared with men with both tests used. The cut-off value to identify patients at risk as well as the incidence of clinical endpoints was similar between women and men (16/234[6.8%] vs. 62/717[8.6%], p = 0.38).

Conclusion

Although the magnitude of platelet reactivity was higher in women, the absolute difference between genders was small and both the cut-off value to identify patients at risk and the incidence of the composite endpoint were similar between genders. Thus, it is unlikely that the difference in platelet reactivity accounts for a worse prognosis in women.     

替格瑞洛与氯吡格雷对急性冠脉综合征患者经皮冠脉动脉介入术后血小板抑制效果的比较

目的:比较替格瑞洛与氯吡格雷对急性冠脉综合征(ACS)患者经皮冠脉动脉介入术(PCI)后血小板的抑制效果。方法:选择2014年3月至8月在我院经替格瑞洛联合阿司匹林治疗的ACS患者85例(替格瑞洛组),按性别、年龄2:1匹配原则随机抽取同一时间服用氯吡格雷联合阿司匹林治疗患者170例(氯吡格雷组)为研究对象,两组患者均行PCI治疗,并于服用抗血小板药物负荷剂量2天(PCI术后)进行血栓弹力图(TEG)检测,观察和比较两组患者经ADP途径及经AA途径的血小板抑制率。结果:氯吡格雷组和替格瑞洛组经ADP途径的血小板抑制率分别为(66.60±25.57)%、(82.10±18.87)%,两组比较差异有统计学意义(P0.05)。氯吡格雷组ADP抑制率50%患者占总人数的29.4%,替格瑞洛组ADP抑制率50%的患者占总人数的10.6%,两组差异有统计学意义(P0.05),氯吡格雷组ADP抑制率75%者占总人数的41.8%;而替格瑞洛组ADP抑制率75%的患者占总人数的69.4%,两组抑制率差异也存在统计学意义(P0.05)。氯吡格雷组和替格瑞洛组经AA途径的血小板抑制率分别为(88.70±23.89)%、(90.32±18.09)%,两组比较差异无统计学意义(P0.05)。结论:替格瑞洛对ACS患者PCI术后血小板的抑制作用优于氯吡格雷。     

Pannexin1 Single Nucleotide Polymorphism and Platelet Reactivity in a Cohort of Cardiovascular Patients

Pannexin1 (Panx1), a membrane channel-forming protein permitting the passage of small-sized molecules, such as ATP, is expressed in human platelets. Recently, we showed that inhibiting Panx1 affects collagen-induced platelet aggregation but not aggregation triggered by other agonists. We also found that a single nucleotide polymorphism (SNP; rs1138800) in the Panx1 gene encoded for a gain-of-function channel (Panx1-400C) and was associated with enhanced collagen-induced platelet reactivity. Here, we assessed the association of this SNP with platelet reactivity in a cohort of 758 stable cardiovascular patients from the ADRIE study treated with aspirin and/or clopidogrel. We found that presence of the Panx1-400C allele was not associated with platelet reactivity in stable cardiovascular patients, irrespective of the platelet aggregation agonist used (collagen, ADP or arachidonic acid) or the anti-platelet drug regimen. Moreover, the Panx1-400A?>?C SNP did also not affect the re-occurrence of cardiac ischemic events in the same stable cardiovascular patient cohort.     

The Relationship between Fractional Flow Reserve,Platelet Reactivity and Platelet Leukocyte Complexes in Stable Coronary Artery Disease

Background

The presence of stenoses that significantly impair blood flow and cause myocardial ischemia negatively affects prognosis of patients with stable coronary artery disease. Altered platelet reactivity has been associated with impaired prognosis of stable coronary artery disease. Platelets are activated and form complexes with leukocytes in response to microshear gradients caused by friction forces on the arterial wall or flow separation. We hypothesized that the presence of significantly flow-limiting stenoses is associated with altered platelet reactivity and formation of platelet-leukocyte complexes.

Methods

One hundred patients with stable angina were studied. Hemodynamic significance of all coronary stenoses was assessed with Fractional Flow Reserve (FFR). Patients were classified FFR-positive (at least one lesion with FFR≤0.75) or FFR-negative (all lesions FFR>0.80). Whole blood samples were stimulated with increasing concentrations of ADP, TRAP, CRP and Iloprost with substimulatory ADP. Expression of P-selectin as platelet activation marker and platelet–leukocyte complexes were measured by flowcytometry. Patients were stratified on clopidogrel use. FFR positive and negative patient groups were compared on platelet reactivity and platelet-leukocyte complexes.

Results

Platelet reactivity between FFR-positive patients and FFR-negative patients did not differ. A significantly lower percentage of circulating platelet-neutrophil complexes in FFR-positive patients and a similar non-significant decrease in percentage of circulating platelet-monocyte complexes in FFR-positive patients was observed.

Conclusion

The presence of hemodynamically significant coronary stenoses does not alter platelet reactivity but is associated with reduced platelet-neutrophil complexes in peripheral blood of patients with stable coronary artery disease.     

Recent advances in the pharmacogenetics of clopidogrel

Clopidogrel has been used to prevent recurrent ischemic events after acute coronary syndrome and/or coronary stent implantation. An impaired platelet response to this drug (residual high platelet reactivity) has been identified as a risk factor for recurrent ischemic events. The platelet response to clopidogrel is highly heritable (73%) suggesting a substantial genetic component. Two sequential cytochrome P450-dependent oxidative steps are required to convert clopidogrel to its active metabolite. The first step leads to the formation of 2-oxo-clopidogrel, which is then metabolized to the active metabolite. Cytochrome P450s are large highly polymorphic family of mono-oxygenases. Many alleles have been reported, and some of these are able to modify the activity of proteins, reducing or increasing the concentration of active metabolites and the drug effect. Loss-of-function variants in the hepatic cytochrome 2C19 (mainly *2 allele) system have been found to be the predominant genetic mediators of clopidogrel response. Variant carriers have higher treatment platelet reactivity and higher risk of adverse cardiac events including stent thrombosis, myocardial infarction, and death. Although value of CYP2C19 genotyping has been demonstrated in ACS population treated with PCI, there is still a wide interindividual variability within each genotype to systematically advocate this genetic testing in clinical practice. The CYP2C19*2 variant only explained 12% of the platelet response to clopidogrel. In the near future, it is highly probable that additional gene variants or epigenetic phenomenon will emerge as significant contributors to clopidogrel response that will allow recommending genetic testing for routine use. The purpose of this review is to discuss the contribution of individual genetic differences responsible for variations of action and clopidogrel efficacy.     

Leptin Does Not Play a Major Role in Platelet Aggregation in Obesity and Leptin Deficiency

Objective: A recent study suggested that high concentrations of leptin enhance platelet aggregations. Therefore, the aim of this study was to investigate whether platelet aggregation is altered in patients with leptin gene mutations compared with obese subjects or controls. Research Methods and Procedures: Four men (one homozygous man and his three heterozygous brothers) carrying a leptin gene mutation; 20 age‐matched, healthy, unrelated men; and 18 age‐matched obese men were enrolled in the study. Adenosine diphosphate (ADP)‐, collagen‐, and epinephrine‐induced platelet aggregation were evaluated in all individuals. Results: Our results show that patients with the leptin gene mutation (both the homozygous and heterozygous patients) had significantly higher ADP‐induced (78.3 ± 3.4% vs. 57.9 ± 9.3%, p = 0.001), collagen‐induced (78.1 ± 2.9% vs. 56.7 ± 9.3%, p = 0.007), and epinephrine‐induced (76.5 ± 9.2% vs. 59.5 ± 7.70%, p = 0.003) platelet aggregation compared with controls. However, ADP‐, collagen‐, or epinephrine‐induced platelet aggregations were similar to those in obese patients. Platelet aggregation responses to a combination of pretreatment with leptin at concentrations of 20, 50, 100, or 500 ng/mL for 5 minutes and ADP at concentrations of 2 μmol/liter also were evaluated. However, we did not find significant increases in platelet aggregation even at high concentrations of leptin (100 or 500 ng/mL) in leptin‐deficient patients, obese subjects, or controls. Discussion: Our data show that similar to findings in obese humans, homozygous or heterozygous leptin deficiency is associated with increased platelet aggregation compared with controls, and that higher concentrations of leptin do not increase platelet aggregation.     

Effects of Cytochrome P450 2C19 and Paraoxonase 1 Polymorphisms on Antiplatelet Response to Clopidogrel Therapy in Patients with Coronary Artery Disease

Clopidogrel is an antiplatelet prodrug that is recommended to reduce the risk of recurrent thrombosis in coronary artery disease (CAD) patients. Paraoxonase 1 (PON1) is suggested to be a rate-limiting enzyme in the conversion of 2-oxo-clopidogrel to active thiol metabolite with inconsistent results. Here, we sought to determine the associations of CYP2C19 and PON1 gene polymorphisms with clopidogrel response and their role in ADP-induced platelet aggregation. Clopidogrel response and platelet aggregation were determined using Multiplate aggregometer in 211 patients with established CAD who received 75 mg clopidogrel and 75–325 mg aspirin daily for at least 14 days. Polymorphisms in CYP2C19 and PON1 were genotyped and tested for association with clopidogrel resistance. Linkage disequilibrium (LD) and their epistatic interaction effects on ADP-induced platelet aggregation were analysed. The prevalence of clopidogrel resistance in this population was approximately 33.2% (n = 70). The frequencies of CYP2C19*2 and *3 were significantly higher in non-responder than those in responders. After adjusting for established risk factors, CYP2C19*2 and *3 alleles independently increased the risk of clopidogrel resistance with adjusted ORs 2.94 (95%CI, 1.65–5.26; p<0.001) and 11.26 (95%CI, 2.47–51.41; p = 0.002, respectively). Patients with *2 or *3 allele and combined with smoking, diabetes and increased platelet count had markedly increased risk of clopidogrel resistance. No association was observed between PON1 Q192R and clopidogrel resistance (adjusted OR = 1.13, 95%CI, 0.70–1.82; p = 0.622). Significantly higher platelet aggregation values were found in CYP2C19*2 and *3 patients when compared with *1/*1 allele carriers (p = 1.98×10⁻⁶). For PON1 Q192R genotypes, aggregation values were similar across all genotype groups (p = 0.359). There was no evidence of gene-gene interaction or LD between CYP2C19 and PON1 polymorphisms on ADP-induced platelet aggregation. Our findings indicated that only CYP2C19*2 and *3 alleles had an influence on clopidogrel resistance. The risk of clopidogrel resistance increased further with smoking, diabetes, and increased platelet count.     

Results of the Ticlid or Plavix Post-Stents (TOPPS) trial: do they justify the switch from ticlopidine to clopidogrel after coronary stent placement?

In the Ticlid or Plavix Post-Stents (TOPPS) trial, 1016 patients undergoing successful coronary stent placement were randomized to receive aspirin and either ticlopidine or clopidogrel. In this trial, the dosages and regimens of ticlopidine and clopidogrel resembled more closely those used in most catheterization laboratories than did the two previous randomized trials comparing ticlopidine and clopidogrel. The results of the TOPPS trial support the current practice of substituting ticlopidine for clopidogrel in stent patients.     

Nicotinic-type unitary currents in Helix neurons

1. The platelet aggregation response to several known platelet agonists was evaluated in four Asian elephants. The platelets were highly responsive to stimulation with platelet-activating factor (PAF) and collagen, less responsive to adenosine diphosphate (ADP) and non-responsive to arachidonic acid, serotonin and epinephrine. 2. Arachidonic acid (1 x 10(-4) M), while inducing no aggregation, caused the release of 1248 +/- 1147 pg/ul (mean +/- SD) of thromboxane B2 (TXB2), the stable metabolite of thromboxane A2 from stimulated platelet. The addition of 1 x 10(-4) M ADP to platelets caused suboptimal aggregation and the release of only 25 +/- 10 pg TXB2/microliters. 3. The calcium channel blocker, verapamil, produced a dose-dependent inhibition of PAF-induced but not collagen-induced aggregation. The cyclooxygenase inhibitor, acetylsalicylic acid, produced no inhibition of either collagen- or PAF-induced aggregation.