M icroRNAs (miRNAs) are small noncoding RNAs with cell-type specific expression patterns that are released by cells into the circulation as part of membranous particles or protein complexes.1 Thus, miRNAs can be readily quantified by real-time polymerase chain reactions (qPCRs) in plasma and serum and have generated increasing interest as potential new biomarkers.2 Our group has previously identified plateletrelated miRNA signatures that are predictive of cardiovascular events. 3 In addition, we measured miRNAs in healthy volunteers and in patients with symptomatic atherosclerosis before and after initiation of dual antiplatelet therapy and demonstrated reduced plasma levels of platelet-related miRNAs on platelet inhibition. Kaudewitz et al Plasma MicroRNAs and Platelet Function 421Dual oral antiplatelet therapy (acetylsalicylic acid [ASA]+a P2Y 12 inhibitor) is commonly used for the management of non-ST-segment-elevation acute coronary syndromes (ACS) and ST-segment-elevation myocardial infarction.5 ASA irreversibly inhibits cyclooxygenase 1 in platelets, thereby repressing thromboxane A 2 (TxA 2 ) synthesis and, consequently, platelet activation. Clopidogrel, prasugrel, and ticagrelor target the P2Y 12 receptor for ADP. However, interindividual variability in the platelet response to clopidogrel has been reported. Prasugrel and ticagrelor exhibit a more consistent antiplatelet effect and have shown benefits over clopidogrel in patients with ACS but also increase the risk of bleeding. 6,7 It is currently unclear whether plasma levels of platelet-related miRNAs correlate with the residual platelet activity in patients with ACS and how different antiplatelet agents alter miRNAs.In this study, we used RNA sequencing to characterize small RNAs in plasma. Then, we compared the effect of different antiplatelet agents and explored the association of small RNAs (miRNAs and YRNAs) with platelet function tests in patients with ACS. Moreover, we correlated their plasma levels to platelet activation markers in the prospective, population-based Bruneck study 3 and investigated whether a single-nucleotide polymorphism (SNP) that facilitates miR-126 processing 8 alters circulating miR-126 levels and platelet reactivity. These epidemiological observations were complemented by preclinical studies, assessing platelet function in mice on treatment with antagomiRs directed against miR-126 and by mechanistic studies measuring miR-126 targets. MethodsAn expanded Methods section is available in the Online Data Supplement. Next-Generation SequencingSmall RNA libraries were generated from non-normalized RNA (ranging from 375 pg to 1 ng) extracted from equal volumes of platelet-poor plasma (PPP) and platelet-rich plasma (PRP) from healthy human volunteers. Before library preparation, RNA was spiked with equal amounts of C. elegans miR-39 star (cel-miR-39*) to assist in normalization. Libraries were prepared using the small RNA library preparation kit version 2.0 (Illumina Cambridge Ltd) according to manufacturer's protocol with limi...

Because metastasis is associated with the majority of cancer-related deaths, its prevention is a clinical aspiration. Prostanoids are a large family of bioactive lipids derived from the activity of cyclooxygenase-1 (COX-1) and COX-2. Aspirin impairs the biosynthesis of all prostanoids through the irreversible inhibition of both COX isoforms. Long-term administration of aspirin leads to reduced distant metastases in murine models and clinical trials, but the COX isoform, downstream prostanoid, and cell compartment responsible for this effect are yet to be determined. Here, we have shown that aspirin dramatically reduced lung metastasis through inhibition of COX-1 while the cancer cells remained intravascular and that inhibition of platelet COX-1 alone was sufficient to impair metastasis. Thromboxane A 2 (TXA 2 ) was the prostanoid product of COX-1 responsible for this antimetastatic effect. Inhibition of the COX-1/TXA 2 pathway in platelets decreased aggregation of platelets on tumor cells, endothelial activation, tumor cell adhesion to the endothelium, and recruitment of metastasis-promoting monocytes/macrophages, and diminished the formation of a premetastatic niche. Thus, platelet-derived TXA 2 orchestrates the generation of a favorable intravascular metastatic niche that promotes tumor cell seeding and identifies COX-1/TXA 2 signaling as a target for the prevention of metastasis.

In the presence of strong P2Y 12 receptor blockade, aspirin provides little additional inhibition of platelet aggregation. J Thromb Haemost 2011; 9: 552-61.Summary. Background: Aspirin and antagonists of platelet ADP P2Y 12 receptors are often coprescribed for protection against thrombotic events. However, blockade of platelet P2Y 12 receptors can inhibit thromboxane A 2 (TXA 2 )-dependent pathways of platelet activation independently of aspirin. Objectives: To assess in vitro whether aspirin adds additional antiaggregatory effects to strong P2Y 12 receptor blockade. Methods: With the use of platelet-rich plasma from healthy volunteers, determinations were made in 96-well plates of platelet aggregation, TXA 2 production and ADP/ATP release caused by ADP, arachidonic acid, collagen, epinephrine, TRAP-6 amide and U46619 (six concentrations of each) in the presence of prasugrel active metabolite (PAM; 0.1-10 lmol L ) and PAM + aspirin, aspirin generally failed to produce more inhibition than PAM or additional inhibition to that caused by PAM. The antiaggregatory effects of PAM were associated with reductions in the platelet release of both TXA 2 and ATP + ADP. Similar effects were found when either citrate or lepirudin were used as anticoagulants, and when traditional light transmission aggregometry was conducted at low stirring speeds. Conclusions: P2Y 12 receptors are critical to the generation of irreversible aggregation through the TXA 2 -dependent pathway. As a result, strong P2Y 12 receptor blockade alone causes inhibition of platelet aggregation that is little enhanced by aspirin. The clinical relevance of these observations remains to be determined.

Objectives-Statins and fibrates are hypolipidemic drugs which decrease cardiac events in individuals without raised levels of cholesterol. These drugs inhibit platelet function, but the mechanisms by which this pleiotropic effect is exerted are not known. Methods and Results-We used a range of approaches to show statins inhibit human platelet activation in vitro while engaging PPAR␣ and PPAR␥. The effects of simvastatin were prevented by the PPAR␥ antagonist GW9662 or the PPAR␣ antagonist GW6471. In a small-scale human study fluvastatin activated PPAR␣ and PPAR␥ in platelets and reduced aggregation in response to arachidonic acid ex vivo. The effects of fenofibrate were prevented by PPAR␣ antagonism with GW6471. Fenofibrate increased bleeding time in wild-type, but not in PPAR␣ Ϫ/Ϫ mice. The inhibitory effect of fenofibrate, but not simvastatin, on aggregation was prevented by deletion of PPAR␣ in murine platelets. PKC␣, which influences platelet activation, associated and immune-precipitated with PPAR␥ in platelets stimulated with statins and with PPAR␣ in platelets stimulated with fenofibrate. Conclusions-This study is the first to provide a unifying explanation of how fibrates and statins reduce thrombotic and cardiovascular risk. Our findings that PPARs associate with PKC␣ in platelets also provide a mechanism by which these effects are mediated. Key Words: platelets Ⅲ statin Ⅲ fibrate Ⅲ PPAR␣, PPAR␥ S tatins are widely prescribed cholesterol-lowering drugs that are first-line treatments for the prevention of coronary artery disease and atherosclerosis, reducing the incidence of thrombotic events such as heart attack and stroke. 1 Statins inhibit the activity of a key enzyme in cholesterol synthesis within the body, 3-hydroxymethyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase, and so reduce cholesterol formation. 2 Statins are classified as natural (eg, pravastatin), synthetic (eg, fluvastatin), or semisynthetic (eg, simvastatin). Like the statins, the fibrates are widely used See accompanying article on page 620lipid-lowering drugs that reduce the incidence of heart attack and stroke. [3][4][5] Fibrates reduce triglycerides and increase high-density lipoprotein cholesterol. Importantly, statins and fibrates are preventative against heart attack and stroke, even in individuals with normal levels of circulating cholesterol. 1,2,6 However, the mechanisms by which statins or fibrates cause these noncholesterol related, or pleiotropic, protective effects are not completely understood.Interestingly both statins and fibrates inhibit platelet function, 3,7 which is, of course, a widely recognized property of drugs such as aspirin and clopidogrel that are used to reduce the incidence of heart attacks and strokes. 6,8 However, the mechanisms by which statins and fibrates inhibit platelets are unclear. It is not known whether they are a consequence of lowering cholesterol or mediated via some other mechanism. 1,3,9 Here we show that statins and fibrates have rapid and direct inhibitory effects on platelet function ...

Background-Molecular imaging is a fast emerging technology allowing noninvasive detection of vascular pathologies.However, imaging modalities offering high resolution currently do not allow real-time imaging. We hypothesized that contrast-enhanced ultrasound with microbubbles (MBs) selectively targeted to activated platelets would offer high-resolution, real-time molecular imaging of evolving and dissolving arterial thrombi. Methods and Results-Lipid-shell based gas-filled MBs were conjugated to either a single-chain antibody specific for activated glycoprotein IIb/IIIa via binding to a Ligand-Induced Binding Site (LIBS-MBs) or a nonspecific single-chain antibody (control MBs). Successful conjugation was assessed in flow cytometry and immunofluorescence double staining. LIBS-MBs but not control MBs strongly adhered to both immobilized activated platelets and microthrombi under flow. Thrombi induced in carotid arteries of C57Bl6 mice in vivo by ferric chloride injury were then assessed with ultrasound before and 20 minutes after MB injection through the use of gray-scale area intensity measurement. Gray-scale units converted to decibels demonstrated a significant increase after LIBS-MB but not after control MB injection (9.55Ϯ1.7 versus 1.46Ϯ1.3 dB; PϽ0.01). Furthermore, after thrombolysis with urokinase, LIBS-MB ultrasound imaging allows monitoring of the reduction of thrombus size (PϽ0.001). Conclusion-We

Trauma hemorrhage is a leading cause of death and disability worldwide. Platelets are fundamental to primary hemostasis, but become profoundly dysfunctional in critically injured patients by an unknown mechanism, contributing to an acute coagulopathy which exacerbates bleeding and increases mortality. The objective of this study was to elucidate the mechanism of platelet dysfunction in critically injured patients. We found that circulating platelets are transformed into procoagulant balloons within minutes of injury, accompanied by the release of large numbers of activated microparticles which coat leukocytes. Ballooning platelets were decorated with histone H4, a damage-associated molecular pattern released in massive quantities after severe injury, and exposure of healthy platelets to histone H4 recapitulated the changes in platelet structure and function observed in trauma patients. This is a report of platelet ballooning in human disease and of a previously unrecognized mechanism by which platelets contribute to the innate response to tissue damage.

SummaryFrom the discovery of the platelet glycoprotein (GP) IIb/IIIa and identification of its central role in haemostasis, the integrin GPIIb/IIIa (αIIbβ3, CD41/CD61) was destined to be an anti-thrombotic target. The subsequent successful development of intravenous ligand-mimetic inhibitors occurred during a time of limited understanding of integrin physiology. Although efficient inhibitors of ligand binding, they also mimic ligand function. In the case of GPIIb/IIIa inhibitors, despite strongly inhibiting platelet aggregation, paradoxical fibrinogen binding and platelet activation can occur. The quick progression to development of small-molecule orally available inhibitors meant that this approach inherited many potential flaws, which together with a short half-life resulted in an increase in mortality and a halt to the numerous pharmaceutical development programs. Limited clinical benefits, together with the success of other anti-thrombotic drugs, in particular P2Y12 ADP receptor blockers, have also led to a restrictive use of intravenous GPIIb/ IIIa inhibitors. However, with a greater understanding of this key platelet-specific integrin, GPIIb/IIIa remains a potentially attractive target and future drug developments will be better informed by the lessons learnt from taking the current inhibitors back to the bench. This overview will review the physiology behind the inherent problems of a ligand-based integrin inhibitor design and discuss novel promising approaches for GPIIb/IIIa inhibition.

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