SwitzerlandTo cite this article: Fontana P, Nolli S, Reber G, de Moerloose P. Biological effects of aspirin and clopidogrel in a randomized cross-over study in 96 healthy volunteers. J Thromb Haemost 2006; 4: 813-9.Summary. Background: Some data suggest that biological ÔresistanceÕ to aspirin or clopidogrel may influence clinical outcome. Objective: The aim of this study was to evaluate the relationship between aspirin and clopidogrel responsiveness in healthy subjects. Methods: Ninety-six healthy subjects were randomly assigned to receive a 1-week course of aspirin 100 mg day )1 followed by a 1-week course of clopidogrel (300 mg on day 1, then 75 mg day), or the reverse sequence, separated by a 2-week wash-out period. The drug effects were assessed by means of serum TxB 2 assay, platelet aggregation tests, and the PFA-100 Ò and Ultegra RPFA-Verify Now Ò methods. Results: Only one subject had true aspirin resistance, defined as a serum TxB 2 level > 80 pg lL )1 at the end of aspirin administration and confirmed by platelet incubation with aspirin. PFA-100 Ò values were normal in 29% of the subjects after aspirin intake, despite a drastic reduction in TxB 2 production; these subjects were considered to have aspirin pseudo-resistance. Clopidogrel responsiveness was not related to aspirin pseudo-resistance. Selected polymorphisms of platelet receptor genes were not associated with either aspirin or clopidogrel responsiveness. Conclusions: In healthy subjects, true aspirin resistance is rare and aspirin pseudo-resistance is not related to clopidogrel responsiveness.

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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.

Background Platelets are an abundant source of micro-ribonucleic acids (miRNAs) that may play a role in the regulation of platelet function. Some miRNAs, such as miR-126-3p, have been noted as potential biomarkers of platelet reactivity and the recurrence of cardiovascular events. However, the biological relevance of these associations remains uncertain, and the functional validation of candidate miRNAs on human-derived cells is lacking. Objective This article functionally validates miR-126-3p as a regulator of platelet reactivity in platelet-like structures (PLS) derived from human haematopoietic stem cells. Materials and Methods CD34+-derived megakaryocytes were transfected with miR-126-3p and differentiated in PLS. PLS reactivity was assessed using perfusion in a fibrinogen-coated flow chamber. miR-126-3p's selected gene targets were validated using quantitative polymerase chain reaction, protein quantification and a reporter gene assay. Results CD34+-derived megakaryocytes transfected with miR-126-3p generated PLS exhibiting 156% more reactivity than the control. These functional data were in line with those obtained analysing CD62P expression. Moreover, miR-126-3p transfection was associated with the down-regulation of a disintegrin and metalloproteinase-9 (ADAM9) messenger RNA (mRNA), a validated target of miR-126-3p, and of Plexin B2 (PLXNB2) mRNA and protein, an actin dynamics regulator. Silencing PLXNB2 led to similar functional results to miR-126-3p transfection. Finally, using a reporter gene assay, we validated PLXNB2 as a direct target of miR-126-3p. Conclusion We functionally validated miR-126-3p as a regulator of platelet reactivity in PLS derived from human haematopoietic stem cells. Moreover, PLXNB2 was validated as a new gene target of miR-126-3p in human cells, suggesting that miR-126-3p mediates its effect on platelets, at least in part, through actin dynamics regulation.

Summary. Background: Poor response to both aspirin and clopidogrel (dual poor responsiveness [DPR]) is a major risk factor for recurrent ischemic events. Objectives: The aim of this study was to identify factors associated with DPR, defined with specific tests, and derive a predictive clinical score. Methods: We studied 771 consecutive stable cardiovascular patients treated with aspirin (n = 223), clopidogrel (n = 111), or both drugs (n = 437). Aspirin responsiveness was evaluated by serum thromboxane (Tx)B 2 assay, and clopidogrel responsiveness by calculating the platelet reactivity index (PRI) on the basis of the phosphorylation status of the vasodilator phosphoprotein. The analysis was focused on patients treated with both drugs, and on independent predictors of DPR. Results: Among patients on dual therapy, there was no relevant correlation between TxB 2 levels and PRI values (r = 0.11). Sixty-seven patients (15.4%) had DPR. Diabetes [odds ratio (OR) 1.89, 95% confidence interval (CI) 1.06-3.39], high body weight (> 86 kg vs. < 77 kg, OR 4.74, 95% CI 2.49-9.73), low aspirin dose (75-81 mg vs. ‡ 160 mg, OR 0.12, 95% CI 0.09-0.93) and high Creactive protein (CRP) level (> 1.6 mg L )1 vs. < 0.6 mg L )1 , OR 3.66, 95% CI 1.74-8.72) were independently associated with DPR, via increased TxB 2 levels, increased PRI, or both.These associations with TxB 2 and PRI were reproduced across the whole population. With use of a factor-weighed score (c-index = 0.74), the predicted prevalence of DPR was 57% in the highest strata of the score as compared with < 4% for the lowest strata. Conclusions: Diabetes, body weight, the aspirin dose and CRP levels are readily available independent predictors of DPR, and some are potential targets for reducing its prevalence.

Platelet reactivity (PR) is variable between individuals and modulates clinical outcome in cardiovascular (CV) patients treated with antiplatelet drugs. Although several data point to a genetic control of platelet reactivity, the genes contributing to the modulation of this phenotype are not clearly identified. Integration of data derived from high-throughput technologies may yield novel insights into the molecular mechanisms that govern platelet reactivity. The aim of this study is to identify candidate genes modulating platelet reactivity in aspirin-treated CV patients using an integrative network-based approach. Patients with extreme high (n = 6) or low PR (n = 6) were selected and data derived from quantitative proteomic of platelets and platelet sub-cellular fractions, as well as from transcriptomic analysis were integrated with a network biology approach. Two modules within the network containing 123 and 182 genes were identified. We then specifically assessed the level of miRNAs in these two groups of patients. Among the 12 miRNAs differentially expressed, 2 (miR-135a-5p and miR-204-5p) correlated with PR. The predicted targets of these miRNAs were mapped onto the network, allowing the identification of seven overlapping genes (THBS1, CDC42, CORO1C, SPTBN1, TPM3, GTPBP2, and MAPRE2), suggesting a synergistic effect of these two miRNAs on these predicted targets. Integration of several omics data sets allowed the identification of 2 candidate miRNAs and 7 candidate genes regulating platelet reactivity in aspirin-treated CV patients.

for the Antiplatelet Drug Resistances and Ischemic Events (ADRIE) Study GroupBackground-The biological response to antiplatelet drugs has repeatedly been shown to predict the recurrence of major adverse cardiovascular events (MACEs). However, most studies involved coronary artery disease patients with recent vessel injury shortly after the initiation of antiplatelet therapy. Data on stable cardiovascular patients are scarce, and the added predictive value of specific assays (the vasodilator phosphoprotein assay for the clopidogrel response and serum thromboxane B2 for the aspirin response) and aggregation-based assays relative to common predictors has rarely been addressed. Methods and Results-Stable cardiovascular outpatients participating in the Antiplatelet Drug Resistances and IschemicEvents (ADRIE) study (nϭ771) were tested twice, at 2 separate visits, with specific and aggregation-based assays. Follow-up lasted 3 years, and Ͻ1% of patients were lost to follow-up. MACEs were adjudicated by an independent committee. Multivariate survival analyses included relevant variables identified in univariate analysis and platelet function test results. The C-index was used to express the prognostic value of various multivariate models. MACEs, the primary end point, occurred in 16% of patients. Hypertension, smoking, older age, and elevated low-density lipoprotein cholesterol were predictive of MACE recurrence, with a C-index of 0.63 (PϽ0.001). Neither the specific nor the aggregation-based assays added significant predictive value for the primary end point. Conclusions-Biological

Platelets are small cell fragments, produced by megakaryocytes, in the bone marrow. They play an important role in hemostasis and diverse thrombotic disorders. They are therefore primary targets of antithrombotic therapies. They are implicated in several pathophysiological pathways, such as inflammation or wound repair. In blood circulation, platelets are activated by several pathways including subendothelial matrix and thrombin, triggering the formation of the platelet plug. Studying their proteome is a powerful approach to understand their biology and function. However, particular attention must be paid to different experimental parameters, such as platelet quality and purity. Several technologies are involved during the platelet proteome processing, yielding information on protein identification, characterization, localization, and quantification. Recent technical improvements in proteomics combined with inter-disciplinary strategies, such as metabolomic, transcriptomics, and bioinformatics, will help to understand platelets biological mechanisms. Therefore, a comprehensive analysis of the platelet proteome under different environmental conditions may contribute to elucidate complex processes relevant to platelet function regarding bleeding disorders or platelet hyperreactivity and identify new targets for antiplatelet therapy.