Clopidogrel inhibits platelet-leukocyte interactions and thrombin receptor agonist peptide-induced platelet activation in patients with an acute coronary syndrome

OBJECTIVES: We sought to characterize the effects of clopidogrel on the activation of circulating platelets, the activation and aggregation of ex vivo platelets, and the interactions with leukocytes in patients with a non-ST-segment elevation in acute coronary syndromes (ACS). BACKGROUND: The significant benefits of clopidogrel in cardiovascular trials suggest that blockage of the P2Y(12) receptor may be associated with important biologic consequences. METHODS: Blood samples obtained from 23 ACS patients before and 24 h after a loading dose of clopidogrel (300 mg) were analyzed by whole-blood flow cytometry, light transmission aggregometry in platelet-rich plasma, and plasma enzyme-linked immunoassays. A thrombin receptor agonist peptide (TRAP) and adenosine diphosphate (ADP) were used as agonists. Normal individuals pretreated with aspirin served as controls. RESULTS: Clopidogrel attenuated platelet aggregation to both ADP (10 micromol/l) and TRAP (10 micromol/l) by 22% and P-selectin expression by 16% and 25%, respectively. The drug decreased the excess platelet-monocyte and platelet-neutrophil conjugates found in the blood of ACS patients (p < 0.01) and prevented their formation ex vivo with agonist stimulation. Plasma levels of soluble CD40L were reduced by 27% (p < 0.001) and of soluble P-selectin by 15% (p < 0.001). CONCLUSIONS: Clopidogrel attenuates the agonist effects of ADP and TRAP on platelet secretion, aggregation, and formation of platelet-monocyte and platelet-neutrophil conjugates in patients with ACS. These effects may all contribute to the clinical benefits of the drug in these syndromes.     

The effect of clopidogrel, aspirin and both antiplatelet drugs on platelet function in patients with peripheral arterial disease

Peripheral arterial disease (PAD) is associated with platelet hyperactivity. Aspirin and clopidogrel, two platelet inhibitors, act by different mechanisms. Aspirin inhibits thromboxane A2 synthesis and clopidogrel acts on the P2Y12 platelet ADP receptor. We evaluated the effect of clopidogrel (75 mg/day), aspirin (75 mg/day) and then both drugs on several platelet function indices in patients with PAD (n = 20). There was a significant (P = 0.0001) decrease in ADP-induced aggregation, after clopidogrel but not after taking aspirin. Clopidogrel plus aspirin significantly decreased spontaneous platelet aggregation (SPA) (P = 0.01 to P = 0.002) but SPA was not significantly altered by either aspirin or clopidogrel monotherapy. Similarly, monotherapy did not inhibit serotonin (5HT)-induced aggregation but there was a sigificant inhibition (P = 0.03 to P < 0.02) after combination therapy. ADP (0.8 microM)-induced platelet shape change (PSC) was significantly inhibited by clopidogrel (P = 0.004) or aspirin (P = 0.01). This was also true for 5HT-induced PSC (clopidogrel, P = 0.01; aspirin, P = 0.03). Soluble P-selectin decreased significantly (from 32 +/- 24 to 25 +/- 17 ng/ml, P = 0.04) with combination therapy. Plasma platelet-derived growth factor and intraplatelet 5HT levels were not altered by combination therapy. In PAD, clopidogrel is a more potent inhibitor of ADP-induced platelet activation than aspirin; combination therapy is more effective than clopidogrel or aspirin monotherapy. These potentially clinically relevant findings should be evaluated in appropriately designed trials.     

Disaggregation Following Agonist-Induced Platelet Activation in Patients on Dual Antiplatelet Therapy

Disaggregation as the difference between maximal and final platelet aggregation by light transmission aggregometry indicates the stability of platelet aggregates. We evaluated the extent of disaggregation after platelet stimulation with adenosine diphosphate (ADP), arachidonic acid (AA), collagen, epinephrine, and thrombin receptor-activating peptide (TRAP)-6 in 323 patients on dual antiplatelet therapy with daily aspirin and clopidogrel (group 1), prasugrel (group 2), or ticagrelor (group 3) therapy. All patients in group 1 underwent elective angioplasty and stenting, whereas all patients included in groups 2 and 3 suffered from acute coronary syndromes (STEMI or NSTEMI) and underwent urgent PCI. Significant differences between maximal and final platelet aggregation were observed with all agonists throughout the groups (all p<0.001). Disaggregation was highest using AA (clopidogrel 36.5%; prasugrel/ticagrelor 100%) and ADP (clopidogrel 21.7%; prasugrel/ticagrelor 100%). In contrast, low disaggregation was observed after platelet stimulation with collagen and TRAP-6 in clopidogrel-treated patients, and after platelet stimulation with collagen and epinephrine in prasugrel- and ticagrelor-treated patients. In conclusion, pathways of platelet activation that are not inhibited by standard antiplatelet therapy allow persisting platelet aggregation and may at least in part be responsible for adverse ischemic events.     

冠状动脉支架术后三联抗血小板药物治疗对血小板功能的影响

目的探讨三联抗血小板药物治疗对冠状动脉(冠脉)支架术后患者血小板活化和聚集功能的影响。方法120例冠心病行冠脉支架植入术患者,随机分为三联组(阿司匹林、氯吡格雷和西洛他唑)和两联组(阿司匹林和氯吡格雷),三联组于术后第1天起加服西洛他唑。两组分别于术后第1天服用西洛他唑前及第5天测定血小板活化复合物(PAC-1)和CD_(62)p,同时测定5μmol/L及20μmol/L ADP诱导的血小板最大聚集率(MPAR)。结果两组临床基线资料及CD_(62)p、PAC-1和MPAR基线值差异均无统计学意义。分别计算各指标第二次测定值与基线值的差值,两组ΔMPAR差异无统计学意义,但三联组和两联组ΔCD_(62)p和ΔPAC-1分别为[(5.12±11.25)%比(1.08±4.97)%,P＜0.05]和[(12.12±12.30)%比(2.22±15.15)%,P＜0.01]。对急性冠脉综合征(ACS)患者亚组分析结果表明三联组ΔMPAR(5μmol/L)[(8.68±10.35)％比(2.92±13.06)%,P=0.018]、ΔMPAR(20μmol/L)[(11.05±11.14)%比(5.16±13.27)%,P=0.019]、ΔCD_(62)p[(5.57±12.08)％比(1.35±4.42)%,P=0.028】和ΔPAC-1[(11.62±12.73)%比(1.29±15.73)%,P= 0.001]均显著高于两联组。3个月临床随访显示三联组与两联组主要不良心、脑血管事件发生率分别为0和3.3%(2/60),出血发生率分别为5%(3/60)和3.3%(2/60),均无统计学意义。结论三联抗血小板药物治疗与常规两联治疗相比能更有效地抑制冠脉支架术后血小板活化和聚集,但其疗效和安全性还需大规模临床试验证实。     

Effectiveness of reloading to overcome clopidogrel nonresponsiveness in patients with acute myocardial infarction

Whether increasing doses of clopidogrel can overcome nonresponsiveness was evaluated. Clopidogrel nonresponsiveness was found in up to 25% of treated patients and was associated with worse prognosis in patients with acute coronary syndrome and patients undergoing coronary intervention. Adenosine diphosphate (ADP)-induced platelet aggregation was prospectively determined on day 4 of acute myocardial infarction in 200 consecutive patients, who received clopidogrel 300 mg as a loading dose and 75 mg/day thereafter. Thirty patients (15%) had ADP-induced platelet aggregation >or=80% using light transmittance aggregometry and were considered clopidogrel nonresponders. Nonresponders were reloaded with clopidogrel 600 mg, followed by 150 mg/day for 4 weeks. A 75-mg/day dose was resumed thereafter. ADP-induced platelet aggregation was reassessed 4 hours after reloading and biweekly for 10 weeks. Flow cytometry was used to determine platelet P-selectin expression and fibrinogen binding before and 4 hours after reloading. ADP-induced platelet aggregation significantly decreased 4 hours after reloading (from 83 +/- 6% to 56 +/- 14%; p <0.01). The decrease in platelet aggregation was maintained throughout the 4-week doubled maintenance dose. After resuming a maintenance dose of 75 mg/day, ADP-induced platelet aggregation returned to 66 +/- 12% (p <0.001), and 5 patients (17%) had ADP-induced platelet aggregation >or=80%. Flow cytometry showed a significant decrease in P-selectin expression (from 37 +/- 16% to 26 +/- 13%; p <0.01) and fibrinogen binding (from 84 +/- 7% to 70 +/- 13%; p <0.01) in ADP-stimulated platelets 4 hours after reloading. In conclusion, clopidogrel reloading and increased maintenance dose may overcome clopidogrel nonresponsiveness in patients with acute myocardial infarction.     

Response to aspirin and clopidogrel monitored with different platelet function methods

Laboratory non-response to aspirin or clopidogrel is defined as an inability to cause in vitro detectable platelet function inhibition. It would be beneficial to monitor response to aspirin or clopidogrel with widely available and routinely used platelet function methods, like the platelet function analyzer (PFA-100) or the fully automated coagulation analyzer BCT. The aim of this study was to assess the potential of the coagulation analyzer BCT and the platelet function analyzer PFA-100 in monitoring the response of aspirin and clopidogrel. A group of 125 consecutive patients with arterial occlusive disease treated either with aspirin 100 mg/day (82 patients) or clopidogrel 75 mg/day (43 patients) as only antiplatelet drug were investigated. For the first time platelet-enriched plasma (PRP), not adjusted to a fixed predetermined concentration of platelets, was used for aggregation studies and the effect of clopidogrel alone without combination of aspirin treatment on platelet function was investigated. Response to aspirin was observed in 85% (70/82) of patients using PFA-100, while performing the arachidonic acid-induced aggregation on the BCT showed an inhibitory effect to aspirin in 91% (75/82) of patients. Non-response to aspirin was assessed with both platelet function methods in 7% (6/82) of patients. Clopidogrel response was observed in 58% (25/43) of patients when performing ADP-induced aggregation on the BCT. On the PFA-100 the antiplatelet effect of clopidogrel could not be detected. In conclusion, measurement of platelet aggregation on the BCT using native platelet-enriched plasma allows the quantification of individual inhibitory effects to aspirin as well as to clopidogrel, while the PFA-100 seems only suitable to investigate the degree of platelet inhibition induced by aspirin but not by clopidogrel.     

Effects of clopidogrel on “aspirin specific” pathways of platelet inhibition

The most widely accepted methods of assessing response to clopidogrel involve isolated ADP-induced platelet aggregation. Whilst poor response determined by these assays correlates with adverse clinical events, the number of “poor responders” is far higher than the number of events attributed to treatment failure. Clopidogrel may have effects that cannot be assessed using isolated ADP-induced aggregation. We have investigated the effect of clopidogrel on Arachidonic Acid (AA) induced platelet activation–an “aspirin specific” pathway using a novel near patient assay. Thirty four volunteers on no medication and 36 patients, on maintenance therapy with aspirin 75 mg daily, were recruited. Blood tests for Thrombelastogram PlateletMapping were taken immediately prior to and 6 hours after administration of a 600 mg clopidogrel loading dose. Changes in the area under the response curve at 15 minutes (AUC15) with both ADP- and AA-stimulation were calculated as were the corresponding percentage platelet and percentage clotting inhibition (%PIn and %CIn). There were predictable and significant changes in the AUC15 of the ADP channel in response to clopidogrel and the corresponding %PIn and %CIn in both volunteers and patients. There were also significant reductions in the AUC15 of the AA channel (presented as Mean +/? 95%CI), by 27.2 +/? 11.8%, p = 0.005 in volunteers and 35.0 +/? 8.2%, p < 0.001 in patients) and increases in the %PIn and %CIn calculated using the AA channel in volunteers (by 20.0 +/? 11.4%, p + 0.02 and 32.3 +/? 12.8%, p < 0.001 respectively) and patients (by 24.2 +/? 8.6%, p < 0.001 and by 18.0 +/? 8.6, p < 0.001 respectively). Clopidogrel has both independent and aspirin-synergistic effects on AA-induced platelet activation suggesting potentiation of the antiplatelet activity of aspirin. This effect may be clinically important and is not detected by current “gold standard” methods of assessing response to clopidogrel.     

Specific impairment of human platelet P2Y(AC) ADP receptor-mediated signaling by the antiplatelet drug clopidogrel.

Clopidogrel is an effective new antiplatelet agent useful for the treatment of ischemic cerebrovascular, cardiac, and peripheral arterial disease. However, the mechanism of clopidogrel action is not well understood, although it is known to inhibit ADP-evoked platelet aggregation. In the current study, the effect of clopidogrel on recently identified human platelet ADP receptors and their signaling pathways was investigated by using platelets from clopidogrel-treated subjects, 6 healthy volunteers (2 females and 4 males) who received 75 mg of clopidogrel daily for 7 days. Blood was taken and various platelet receptor signaling pathways were analyzed before treatment, after 7 days of medication, and 4 weeks after treatment had ceased. Platelet tests included the analysis of aggregation, rapid calcium influx, calcium mobilization from intracellular stores, adenylyl cyclase, and phosphorylation of vasodilator-stimulated phosphoprotein (VASP). The data indicate that clopidogrel does not affect those platelet ADP receptors coupled to cation influx (P2X1 ADP receptors) or calcium mobilization (P2Y1 ADP receptors). In contrast, clopidogrel treatment specifically impairs the ADP receptor coupled to G(i)/adenylyl cyclase (P2Y(AC) ADP receptors). Clopidogrel abolishes the inhibitory P2Y(AC) receptor-mediated ADP effects on prostaglandin E(1)-stimulated, cAMP-dependent phosphorylation of VASP without affecting epinephrine, thrombin, and thromboxane signaling. VASP phosphorylation is known to be closely correlated with the inhibition of platelet and fibrinogen receptor (glycoprotein IIb/IIIa) activation. Therefore, inhibition of the platelet P2Y(AC) ADP receptor and its intracellular signaling, including decreased VASP phosphorylation, is suggested as a molecular mechanism of clopidogrel action.     

Platelet aggregation and P-selectin levels during exercise treadmill test in patients with ischaemic heart disease

INTRODUCTION: Coronary artery disease (CAD) is associated with higher platelet activation sometimes despite aspirin use. There are conflicting data concerning platelet activation course during physical exercise in patients on aspirin with CAD. AIM: To assess platelet activation pattern during physical exercise in patients with CAD. METHODS: The study included 35 patients (20 men, 15 women) aged 64.7+/-10 years with CAD (CCS II) on aspirin treatment (75 mg daily) and a control group of 10 healthy subjects adjusted for age and gender. Treadmill testing was performed using the Bruce protocol. Platelet aggregation was measured with optical aggregation with the agonists ADP (10 microM), collagen (2 microg/ml) and arachidonic acid (0.5 mg/ml) before and at peak exercise; P-selectin platelet and soluble expression (basal and after stimulation with thrombin) was assessed with cytofluorometry before, at peak exercise and 1 hour after. RESULTS: There were no differences in collagen and ADP aggregation between patients and the control group. There was a significant increase of ADP aggregation at peak exercise in the control group (p <0.05). There was a positive correlation between platelet aggregation before exercise and at peak exercise with ADP (r=+0.86) and with collagen (r=+0.61). There was no difference in soluble P-selectin concentration between patients and the control group. Platelet P-selectin expression without stimulation with thrombin 1 hour after exercise was significantly higher in patients than in the control group (p <0.05). CONCLUSIONS: 1. Physical exercise does not intensify platelet aggregation in patients with CAD on 75 mg aspirin daily. 2. Despite taking aspirin, platelet activation measured with the expression of platelet P-selectin increases and there is further intensification during exercise testing. 3. The concentration of soluble P-selectin in patients with CAD does not reflect the expression of platelet P-selectin.     

Effects of clopidogrel on platelet activation and coagulation of non-anticoagulated rat blood under high shear stress

Clopidogrel is a new thienopyridine derivative similar to ticlopidine, which inhibits adenosine diphosphate-induced platelet aggregation. The in vitro effects of clopidogrel on shear-induced platelet activation and coagulation were assessed after oral administration to rats, by subjecting non-anticoagulated blood to haemostatometry. Clopidogrel significantly inhibited shear-induced platelet activation and coagulation 2 h after administration at doses of 7.5 and 15 mg/kg. Both ticlopidine (200 mg/kg) and aspirin (200 mg/kg) inhibited shear-induced platelet activation, but not coagulation. The peak inhibition of plaetelet activation by clopidogrel occurred 2 h after oral administration, but significant inhibition persisted even after 24 h. These results suggest that clopidogrel could be a more potent antithrombotic agent than ticlopidine or aspirin, and also that ADP plays an important role in shear-induced platelet activation.     

Comparison of platelet P2Y(12) ADP receptor-mediated pathway inhibition in triple versus dual antiplatelet therapy as assessed by VASP-phosphorylation in Japanese patients undergoing coronary stenting

Despite wide interindividual variability in response to clopidogrel, platelet P2Y(12) ADP receptor inhibition in Japanese patients has not been fully studied using specific methodology. This study compared platelet P2Y(12) ADP receptor inhibition during treatment with clopidogrel versus clopidogrel plus cilostazol in patients undergoing coronary stenting. Forty-two patients in whom platelet function was measured within 2 months after coronary stenting were enrolled. All patients were treated with aspirin 100 or 200 mg/day, and were divided into a dual therapy group (aspirin plus clopidogrel 75 mg/day; n = 34) and a triple therapy group (aspirin plus clopidogrel 75 mg/day plus cilostazol 200 mg/day; n = 8). Vasodilator-stimulated phosphoprotein (VASP) phosphorylation analysis and 5 and 20 μmol/L-induced maximal platelet aggregation were assessed. No differences were found in baseline characteristics except for a higher incidence of diabetes mellitus (DM) in the triple therapy group. Although there were no differences in platelet aggregation between the 2 groups, VASP index was significantly lower in the triple therapy group than in the dual therapy group (23.1 ± 15.3% versus 51.2 ± 19.9%; P = 0.001). The rate of low responsiveness to clopidogrel, defined by VASP index > 50%, was lower in the triple therapy group than in the dual therapy group (12.5% versus 55.9%; P = 0.047). Similarly, in DM patients the triple therapy group had a lower VASP index compared with the dual therapy group (23.1 ± 15.3% versus 47.0 ± 23.5%; P = 0.015).Clopidogrel plus cilostazol is more effective in inhibiting the platelet P2Y(12) ADP receptor pathway than clopidogrel alone. This may be useful for reducing clopidogrel resistance in Japanese patients.     

Cilostazol could ameliorate platelet responsiveness to clopidogrel in patients undergoing primary percutaneous coronary intervention.

BACKGROUND: Cilostazol increases the cyclic adenosine monophosphate levels in platelets and might ameliorate the antiplatelet activity of clopidogrel. This study investigated the additional effect of cilostazol on platelet aggregation measured by a VerifyNow analyzer and soluble CD40 ligand (sCD40L) as a marker of activated platelet in patients undergoing primary percutaneous coronary intervention (PCI). METHODS AND RESULTS: Sixty cases of primary PCI were randomly assigned to dual (aspirin and clopidogrel) or triple (dual plus cilostazol) therapy. The antiplatelet effects of aspirin and clopidogrel were evaluated by VerifyNow tests. The plasma sCD40L levels at admission, 24 h and 21 days were measured by the ELISA method. The arachidonic acid induced platelet aggregation was similar in both groups. However, the triple group had a significantly lower P2Y12 reaction unit (dual 208.8+/-69.0 vs triple 168.2+/-79.2, p=0.041) and higher % inhibition of adenosine diphosphate (ADP)-induced platelet aggregation (dual 23.8+/-21.4% vs triple 40.5+/-21.0%, p=0.004). In the multivariate analysis, cilostazol was a negative predictor for low responders to clopidogrel (95% confidence interval 0.067-0.711). The plasma sCD40L levels were not significantly different between the 2 groups at the same point of time. CONCLUSIONS: The addition of cilostazol to the combination of aspirin plus clopidogrel significantly increases the inhibition of ADP-induced platelet aggregation. However, there was no additive effect on aspirin-induced antiplatelet activity or lowering of sCD40L.     

Aspirin and clopidogrel in acute coronary syndromes: therapeutic insights from the CURE study

Platelet adhesion, activation, and aggregation are central to thrombus formation, which follows atherosclerotic plaque disruption and causes acute coronary syndromes. Aspirin and clopidogrel exert their antiplatelet effects by inhibiting thromboxane A2 production and adenosine diphosphate-induced platelet aggregation pathways, respectively. Aspirin has proven benefits in primary and secondary prevention of coronary artery disease. Clopidogrel, an alternative antiplatelet agent used in patients with aspirin intolerance, is especially useful in combination with aspirin after coronary stent procedures. The CURE (Clopidogrel in Unstable Angina to Prevent Recurrent Events) study demonstrates for the first time the benefit of adding clopidogrel to aspirin rather than using aspirin alone in patients having acute coronary syndromes without ST-segment elevation myocardial infarction. Patients who are resistant to aspirin (up to 10%) have higher rates of cardiovascular events and may derive special benefit from the combination therapy. Aspirin resistance can be assessed through platelet aggregometry testing, measurement of urinary thromboxane metabolites, and, possibly, genomic testing in the future.     

How to test the effect of aspirin and clopidogrel in patients on dual antiplatelet therapy?

Dual antiplatelet therapy with clopidogrel and aspirin is frequently used for the prevention of recurrent ischemic events. Various laboratory methods are used to detect the effect of these drugs administered in monotherapy, however their value in dual therapy has not been explored. Here, we determined which methods used for testing the effect of clopidogrel or aspirin are influenced by the other antiplatelet agent. One arm of the study included 53 ischemic stroke patients being on clopidogrel monotherapy showing effective inhibition of the P2Y₁₂ ADP receptor. Laboratory tests routinely used for the detection of aspirin resistance (arachidonic acid (AA)-induced platelet aggregation/secretion, AA-induced thromboxane B₂ (TXB₂) production in platelet-rich plasma and VerifyNow Aspirin assay) were carried out on samples obtained from these patients. The other arm of the study involved 52 patients with coronary artery disease being on aspirin monotherapy. Methods used for testing the effect of clopidogrel (ADP-induced platelet aggregation and secretion, flow cytometric analysis of vasodilator-stimulated phosphoprotein (VASP) phosphorylation and a newly developed P2Y₁₂-specific platelet aggregation (ADP[PGE₁] test)) were performed on samples obtained from these patients. Clopidogrel monotherapy significantly inhibited AA-induced platelet aggregation and secretion, moreover, AA-induced TXB₂ production was also significantly decreased. VASP phosphorylation and AA-induced platelet aggregation showed fair correlation in patients taking clopidogrel only. Clopidogrel did not inhibit the VerifyNow Aspirin test significantly. Aspirin monotherapy influenced ADP-induced platelet aggregation and secretion, but did not have an effect on VASP phosphorylation and on the ADP[PGE₁] platelet aggregation test.     

Antiplatelet effects of angiotensin-converting enzyme inhibitors compared with aspirin and clopidogrel: a pilot study with whole-blood aggregometry

Background Although specific antiplatelet drugs are well-established and effective in atherosclerosis prevention, recent clinical trials have also shown that use of angiotensin-converting enzyme (ACE) inhibitors results in a decrease in cardiovascular events. Therefore, in this study, we sought to assess the coagulative activity of patients with cardiovascular disease grouped for treatment with either ACE inhibitors, aspirin, clopidogrel/aspirin, or none of these medications. Methods Blood samples from 303 patients with cardiovascular disease were analyzed with whole-blood aggregometry. Platelet aggregation was determined by the increase in impedance across paired electrodes in response to the aggregatory agents adenosine diphosphate (ADP) or collagen. Results As the central finding, platelet aggregation was attenuated by ACE inhibitors and by aspirin or clopidogrel/aspirin, which was indicated by a lower impedance increase compared with no medication. With ACE inhibition, platelet aggregation decreased by 33% (P = .042) after ADP induction. No significant antithrombotic effect was seen with aspirin alone (17%, P = 1.0), whereas a decrease in ADP-induced platelet aggregation was extensive with clopidogrel/aspirin (85%, P = .001). After collagen induction, platelet aggregation was reduced by 16% (P = .028) in the presence of ACE inhibitor therapy, whereas inhibition with aspirin and clopidogrel/aspirin was 23% (P = .004) and 35% (P = .026), respectively, compared with participants who were not treated. Conclusions These ex vivo data on whole-blood aggregometry provide direct evidence that ACE inhibitors decrease platelet aggregation, whereas aspirin and clopidogrel are confirmed as established antithrombotics. Pleiotropic effects of ACE inhibition on platelet function may contribute to the clinical benefit observed with this drug class on major cardiovascular end points. (Am Heart J 2003;145:343-8.)     

Aspirin and clopidogrel drug response in patients undergoing percutaneous coronary intervention: the role of dual drug resistance.

We evaluated the response to clopidogrel among aspirin-resistant versus aspirin-sensitive patients undergoing elective coronary stenting. Patients (n = 150) treated with aspirin but not clopidogrel had blood samples drawn at baseline and 24 h after clopidogrel loading. Depending on the definition used, 9% to 15% were resistant to aspirin and 24% to clopidogrel. About half of the aspirin-resistant patients were also resistant to clopidogrel. As a group, aspirin-resistant patients had lower response to clopidogrel (assessed by platelet aggregation and activation markers) than aspirin-sensitive patients. Both aspirin- and clopidogrel-resistant patients had higher incidence of creatine kinase-MB elevation than the respective sensitive patients. OBJECTIVES: We sought to evaluate the response to clopidogrel among aspirin-resistant versus aspirin-sensitive patients undergoing percutaneous coronary intervention (PCI). BACKGROUND: Wide variability has been reported in response to aspirin and clopidogrel. There are limited data on the simultaneous responses to both drugs. METHODS: Elective PCI patients (n = 150) who received aspirin for > or = 1 week but not clopidogrel were included. All patients received bivalirudin during PCI. Blood samples were drawn at baseline and 20 to 24 h after a 300-mg clopidogrel dose. Aspirin resistance was defined by > or = 2 of 3 criteria: rapid platelet function analyzer-ASA score > or = 550, 5 micromol/l adenosine diphosphate (ADP)-induced aggregation > or = 70%, and 0.5 mg/ml arachidonic acid-induced aggregation > or = 20%. Clopidogrel resistance was defined as baseline minus post-treatment aggregation < or = 10% in response to 5 and 20 micromol/l ADP. RESULTS: Nineteen (12.7%) patients were resistant to aspirin and 36 (24%) to clopidogrel. Nine (47.4%) of the aspirin-resistant patients were also clopidogrel resistant. Aspirin-resistant patients were more likely to be women and have diabetes than were aspirin-sensitive patients. They also had lower response to clopidogrel, assessed by platelet aggregation and activation markers (flow cytometry-determined PAC-1 binding and P-selectin expression). Elevation of creatine kinase-myocardial band after stenting occurred more frequently in aspirin-resistant versus aspirin-sensitive patients (38.9% vs. 18.3%; p = 0.04) and in clopidogrel-resistant versus clopidogrel-sensitive patients (32.4% vs. 17.3%; p = 0.06). CONCLUSIONS: Aspirin-resistant patients as a group have reduced response to clopidogrel. Furthermore, we have identified a unique group of dual drug-resistant patients who may be at increased risk for thrombotic complications after PCI.     

The Retention Index Test Homburg (RTH-II): Response to clopidogrel and comparison with aggregometry and CD62P-expression

The Retention Index Test Homburg (RTH-II) is quoted to detect effects of shear stress on platelets, which involve ADP receptor signaling. RTH-II might be a tool for monitoring antiplatelet therapy for compounds that interfere with ADP induced platelet activation and secretion. In a series of investigations, we used an ADP (2 microM) triggered RTH-II in parallel with light-transmittance aggregometry and flow cytometry in subjects before and after clopidogrel. A loading dose of 225 mg clopidogrel leads to a significant reduction (p < 0.01) in the ADP-stimulated retention index (RI) from 69 +/- 15 to 48 +/- 21%, in the aggregation response to 5 microM ADP (from 50 +/- 20 to 29 +/- 21%) and the expression of CD62P (from 64 +/- 11 to 41 +/- 17%). Correlation analysis showed that the RI corresponds significantly to CD62P-expression (p < 0.01) but not to aggregation. We also found a strong correlation (p < 0.01) between the ADP-stimulated RI and the expression of CD62P after stimulation with 2 microM ADP, whereas no correlation was seen for RI vs. binding of PAC-1 or aggregation. Platelets not retained in the filter had lower CD62P expression than measured in the sample before the filter passage (54 vs. 35%). A direct interaction of CD62P with platelet ligands might lead to enhanced retention in RTH and explain the correlation of RI with CD62P expression. The RTH-II might be a simple and easy to handle platelet function assay for monitoring effects on P2Y(12)-inhibitors on platelet degranulation, perhaps in addition to aggregometry.     

Cyclooxygenase-2 inhibitors enhance shear stress-induced platelet aggregation.

OBJECTIVES: We aimed to investigate the effect of parecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor, on in vivo shear stress-induced platelet aggregation in a rat model of arterial bypass with focal narrowing. BACKGROUND: Long-term use of COX-2 inhibitors is associated with increased incidence of adverse cardiovascular events, especially in patients with a history of cardiovascular disease. These patients are at risk for thrombotic occlusion of arterial stenoses initiated by shear stress-induced platelet aggregation. METHODS: To mimic the combination of a tight arterial stenosis and high shear stress in rats, an extracorporeal shunt from carotid to femoral artery was compressed by the rollers of a pump. Platelet aggregation was continuously measured by a photometric detector in the shunt. RESULTS: Pretreatment with parecoxib (20 mg/kg) almost doubled shear stress-induced platelet aggregation (188% vs. 100% in control subjects, p = 0.0003). This was accompanied by a fall in plasma 6-keto-prostaglandin F(1alpha) from 100 +/- 25 pg/ml to 36 +/- 11 pg/ml (p < 0.0001). Enhanced platelet aggregation was also observed with high-dose aspirin (150 mg/kg) (146%; p = 0.02) but not with low-dose aspirin (25 mg/kg), which reduced aggregation (68%; p = 0.01). The effect of parecoxib was neutralized by low-dose (1 mg/kg) clopidogrel (from 188% to 92%; p = 0.0001), but not by low-dose aspirin (from 188% to 177%; p = NS). CONCLUSIONS: In the presence of an arterial stenosis, COX-2 inhibitors enhance shear stress-induced platelet aggregation. This enhancement was prevented by low-dose clopidogrel but not by low-dose aspirin. Clopidogrel might therefore allow COX-2 inhibitors to be used without raising risk of thrombotic occlusion.     

Impact of body mass index on platelet aggregation after administration of a high loading dose of 600 mg of clopidogrel before percutaneous coronary intervention

This study assessed the effect of body mass index (BMI) on platelet aggregation after administration of a high loading dose of clopidogrel 600 mg. Blood samples of 402 patients before percutaneous coronary intervention were collected >or=2 hours after administration of clopidogrel 600 mg. Platelet aggregation was measured in response to adenosine diphosphate (ADP; 5 and 20 microM). Patients were categorized as normal weight (BMI <25 kg/m(2)) or overweight (BMI >or=25 kg/m(2)). ADP-induced platelet aggregation was significantly higher in overweight patients than in normal-weight patients (46.0 +/- 21.8% vs 38.2 +/- 19.3% for ADP 5 microM, p = 0.0007; 55.1 +/- 22.7% vs 45.2 +/- 21.7% for ADP 20 microM, p <0.0001). Multivariate analyses demonstrated high BMI as the only independent predictor for increased ADP-induced platelet aggregation (p 相似文献   

Effect of dipyridamole alone and in combination with aspirin on whole blood platelet aggregation, PGI2 generation, and red cell deformability ex vivo in man

STUDY OBJECTIVE--The aim was to investigate the effects of dipyridamole, aspirin, and a combination of dipyridamole plus aspirin on platelet aggregation in whole blood, PGI2 generation, and red cell deformability ex vivo. SUBJECTS--were 16 male volunteers, aged 22-39 years, mean age, 26.6 years. DESIGN--This was a randomised, double blind, placebo controlled trial. The volunteer received each of the following treatments 10 days apart: dipyridamole 200 mg; aspirin 300 mg; dipyridamole 200 mg plus aspirin 300 mg; matched placebos. MEASUREMENTS AND MAIN RESULTS--Blood was taken for platelet function tests, PGI2 metabolite assay, and red cell deformability before and 2 h after the trial dose was taken. Platelet aggregation was quantified by measuring the fall in single platelet count after stimulation with 2 micrograms.ml-1 collagen or 50 nM platelet activating factor (PAF), or by rollermixing aliquots of blood to initiate spontaneous aggregation. The platelet function tests were completed at 37 degrees C within 10 min of venepuncture. The stable metabolite of PGI2, 6-keto PGF1 alpha, was measured in serum. There was inhibition of spontaneous platelet aggregation by dipyridamole (p less than 0.004), aspirin (p less than 0.005), and the combination of dipyridamole plus aspirin (p less than 0.0001) as compared with placebo. PAF induced platelet aggregation was inhibited by dipyridamole (p less than 0.002) and the combination of dipyridamole plus aspirin (p less than 0.0001) but aspirin alone had no inhibitory effect. Collagen induced platelet aggregation was inhibited by all three treatments: dipyridamole (p less than 0.06), aspirin (p less than 0.0001), and the combination of dipyridamole plus aspirin (p less than 0.0001). PGI2 generation was markedly inhibited by aspirin (p less than 0.0001) and the combination doses (p less than 0.0001) but was unaffected by dipyridamole alone. Of the three active treatments, only dipyridamole alone significantly (p less than 0.001) increased red cell deformability; there was a modest decrease in red cell deformability with aspirin. CONCLUSIONS--The results with PAF support the view that dipyridamole inhibits platelet activation by more than one mechanism; the effect on collagen induced and spontaneous platelet aggregation suggests that the effect of the combination doses is additive and that on red cell deformability the synergy is negative.