Remote platelet function testing using P-selectin expression in patients with recent cerebral ischaemia on clopidogrel.

Background: Antiplatelet agents reduce recurrence after cerebral ischaemia but are not effective in all patients, in part because of treatment resistance. The primary aim was to assess the proportion of patients who are insensitive to clopidogrel. The secondary aim was to assess the association between insensitivity to clopidogrel and recurrent cerebrovascular events.

Circulating Microparticles in Patients with Symptomatic Carotid Disease Are Related to Embolic Plaque Activity and Recent Cerebral Ischaemia.

Background And Purpose: In order to assess the association of microparticles derived from activated platelets (PMP) or endothelial cells (EMP) with risk markers for recurrent embolic events in patients with symptomatic carotid artery disease, we studied the associations between PMP/EMP and three risk markers: plaque haemorrhage (PH), micro-embolic signals and cerebral diffusion abnormalities.

Methods: Patients with recently symptomatic high-grade carotid artery stenosis (60-99%, 42 patients, 31 men; mean age 75 ± 8 years) and 30 healthy volunteers (HV, 11 men; mean age 56 ± 12 years) were prospectively recruited. Patients were characterised by carotid magnetic resonance imaging (presence of PH [MRI PH]), brain diffusion MRI (cerebral ischaemia [DWI+]) and transcranial Doppler ultrasound (micro-embolic signals [MES+]).

Triple versus guideline antiplatelet therapy to prevent recurrence after acute ischaemic stroke or transient ischaemic attack: the TARDIS RCT.

Background: Two antiplatelet agents are better than one for preventing recurrent stroke after acute ischaemic stroke or transient ischaemic attack (TIA). Therefore, intensive treatment with three agents might be better still, providing it does not cause undue bleeding.

Objective: To compare the safety and efficacy of intensive therapy with guideline antiplatelet therapy for acute ischaemic stroke and TIA.

Platelet aggregation measured by single-platelet counting and using PFA-100 devices.

Platelets play a crucial role in haemostasis and thrombosis and evaluation of platelet function in vitro, in particular platelet aggregation responses, has been one of the most common and useful ways of evaluating the risk of bleeding and thrombotic events and assessing the effects of various compounds and conditions on platelets. Traditional approaches to assessing platelet aggregation require specialised equipment and trained laboratory personnel and have other limitations. Studying platelet aggregation in whole blood offers a more physiologically relevant measurement.

Clinical utility of remote platelet function measurement using P-selectin: assessment of aspirin, clopidogrel, and prasugrel and bleeding disorders.

Vascular diseases such as myocardial infarction and ischemic stroke are associated with increased platelet function whilst the risk of recurrence is reduced by antiplatelet agents such as aspirin, clopidogrel, and prasugrel. However, some patients exhibit high platelet reactivity, especially with clopidogrel. Existing platelet function tests may not be ideal in that they can be expensive, are often time consuming, and measurements must be made near to the patient and within a few hours of blood collection.

How does measurement of platelet P-selectin compare with other methods of measuring platelet function as a means of determining the effectiveness of antiplatelet therapy?

Measurement of P-selectin on activated platelets as a means of measuring platelet function utilizing the technology described here has the advantage of not requiring immediate access to specialist equipment and expertise. Blood samples are activated, fixed, stored, and transported to a central laboratory for flow cytometric analysis. Here we have compared P-selectin with other more traditional approaches to measuring platelet function in blood and/or platelet-rich plasma (PRP) from patients with acute coronary syndromes on treatment for at least 1 month with either aspirin and clopidogrel or aspirin with prasugrel.

Antiplatelet therapy with aspirin, clopidogrel, and dipyridamole versus clopidogrel alone or aspirin and dipyridamole in patients with acute cerebral ischaemia (TARDIS): a randomised, open-label, phase 3 superiority trial.

Background: Intensive antiplatelet therapy with three agents might be more effective than guideline treatment for preventing recurrent events in patients with acute cerebral ischaemia. We aimed to compare the safety and efficacy of intensive antiplatelet therapy (combined aspirin, clopidogrel, and dipyridamole) with that of guideline-based antiplatelet therapy.

Methods: We did an international, prospective, randomised, open-label, blinded-endpoint trial in adult participants with ischaemic stroke or transient ischaemic attack (TIA) within 48 h of onset.

UDP-sugars activate P2Y receptors to mediate vasoconstriction of the porcine coronary artery.

Aims: UDP-sugars can act as extracellular signalling molecules, but relatively little is known about their cardiovascular actions. The P2Y receptor is a G-coupled receptor which is activated by UDP-glucose and related sugar nucleotides. In this study we sought to investigate whether P2Y receptors are functionally expressed in the porcine coronary artery using a selective P2Y receptor agonist, MRS2690, and a novel selective P2Y receptor antagonist, PPTN (4,7-disubstituted naphthoic acid derivative).

Remote Assessment of Platelet Function in Patients with Acute Stroke or Transient Ischaemic Attack.

Background: The TARDIS trial assessed the safety and efficacy of intensive versus guideline antiplatelet agents given for one month in patients with acute stroke or TIA. The aim of this substudy was to assess the effect of antiplatelet agents taken at baseline on platelet function reactivity and activation.

Methods: Platelet function, assessed by remotely measured surface expression of P-selectin, was assessed in patients at their time of randomisation.

Novel strategies for assessing platelet reactivity.

There are many approaches to assessing platelet reactivity and many uses for such measurements. Initially, measurements were based on the ability of platelets separated from other blood cells to aggregate together following activation with an appropriate 'aggregating agent'. Later, measurements of platelet aggregation in blood itself were performed, and this led to a point-of-care approach to platelet function testing.

Baseline characteristics of the 3096 patients recruited into the 'Triple Antiplatelets for Reducing Dependency after Ischemic Stroke' trial.

Background The risk of recurrence following ischemic stroke or transient ischemic attack is highest immediately after the event. Antiplatelet agents are effective in reducing the risk of recurrence and two agents are superior to one in the early phase after ictus. Design The triple antiplatelets for reducing dependency after ischemic stroke trial was an international multicenter prospective randomized open-label blinded-endpoint trial that assessed the safety and efficacy of short-term intensive antiplatelet therapy with three agents (combined aspirin, clopidogrel and dipyridamole) as compared with guideline treatment in acute ischemic stroke or transient ischemic attack.

Safety and efficacy of intensive vs. guideline antiplatelet therapy in high-risk patients with recent ischemic stroke or transient ischemic attack: rationale and design of the Triple Antiplatelets for Reducing Dependency after Ischaemic Stroke (TARDIS) trial (ISRCTN47823388).

Rationale: The risk of recurrence following a stroke or transient ischemic attack is high, especially immediately after the event.

Hypothesis: Because two antiplatelet agents are superior to one in patients with non-cardioembolic events, more intensive treatment might be even more effective.

Sample Size Estimates: The sample size of 4100 patients will allow a shift to less recurrence, and less severe recurrence, to be detected (odds ratio 0·68) with 90% power at 5% significance.

A platelet P-selectin test predicts adverse cardiovascular events in patients with acute coronary syndromes treated with aspirin and clopidogrel.

There is wide variation in response to antiplatelet therapy and high on-treatment platelet reactivity is associated with adverse cardiovascular events. The objective here was to determine whether the results of a novel strategy for assessing platelet reactivity (based on P-selectin measurement) are associated with clinical outcomes in patients with acute coronary syndromes (ACS). This was a prospective cohort study of 100 ACS patients taking aspirin and clopidogrel.

Ticagrelor: a P2Y12 antagonist for use in acute coronary syndromes.

Agents that inhibit platelet function are used routinely in the treatment and prevention of acute coronary syndromes. The main antiplatelet treatments used combine aspirin with one of the thienopyridine P2Y(12) antagonists, either clopidogrel or prasugrel. By blocking the synthesis of thromboxane A(2) in platelets and by blocking the effects of ADP, respectively, these agents reduce platelet activity, platelet aggregation and thrombus formation.

PGE(2) reverses G(s)-mediated inhibition of platelet aggregation by interaction with EP3 receptors, but adds to non-G(s)-mediated inhibition of platelet aggregation by interaction with EP4 receptors.

Prostaglandin E(2) (PGE(2)) has intriguing effects on platelet function in the presence of agents that raise cyclic adenosine 3'5'-monophosphate (cAMP). PGE(2) reverses inhibition of platelet aggregation by agents that stimulate cAMP production via a G(s)-linked receptor, but adds to the inhibition of platelet function brought about by agents that raise cAMP through other mechanisms. Here, we used the EP receptor antagonists DG-041 (which acts at the EP3 receptor) and ONO-AE3-208 (which acts at the EP4 receptor) to investigate the role of these receptors in mediating these effects of PGE(2).

P2Y₁₂ and EP3 antagonists promote the inhibitory effects of natural modulators of platelet aggregation that act via cAMP.

Several antiplatelet drugs that are used or in development as antithrombotic agents, such as antagonists of P2Y₁₂ and EP3 receptors, act as antagonists at G(i)-coupled receptors, thus preventing a reduction in intracellular cyclic adenosine monophosphate (cAMP) in platelets. Other antiplatelet agents, including vascular prostaglandins, inhibit platelet function by raising intracellular cAMP. Agents that act as antagonists at G(i)-coupled receptors might be expected to promote the inhibitory effects of agents that raise cAMP.

Anti-platelet therapy: ADP receptor antagonists.

The P2Y(12) receptor on platelets with which ADP interacts has an important role in promoting platelet function and thereby platelet involvement in both haemostasis and thrombosis. Agents that act as antagonists at this receptor are thus likely to provide effective antithrombotic therapy, provided that there are no adverse effects on haemostasis. Here we describe the ADP receptor antagonists that are available and in development.

Adenosine derived from ADP can contribute to inhibition of platelet aggregation in the presence of a P2Y12 antagonist.

Objective: To investigate whether adenosine diphosphate (ADP)-derived adenosine might inhibit platelet aggregation, especially in the presence of a P2Y₁₂ antagonist, where the effects of ADP at the P2Y₁₂ receptor would be prevented.

Methods And Results: Platelet aggregation was measured in response to thrombin receptor activator peptide by platelet counting in platelet-rich plasma (PRP) and whole blood in the presence of ADP and the P2Y₁₂ antagonists cangrelor, prasugrel active metabolite, and ticagrelor. In the presence of a P2Y₁₂ antagonist, preincubation of PRP with ADP inhibited aggregation; this effect was abolished by adenosine deaminase.

PGE1 and PGE2 modify platelet function through different prostanoid receptors.

There is evidence that the overall effects of prostaglandin E(2) (PGE(2)) on human platelet function are the consequence of a balance between promotory effects of PGE(2) acting at the EP3 receptor and inhibitory effects acting at the EP4 receptor, with no role for the IP receptor. Another prostaglandin that has been reported to affect platelet function is prostaglandin E(1) (PGE(1)), however the receptors that mediate its actions on platelet function have not been fully defined. Here we have used measurements of platelet aggregation and P-selectin expression induced by the thromboxane A(2) mimetic U46619 to compare the effects of PGE(1) and PGE(2) on platelet function.

Mode of action of P2Y(12 ) antagonists as inhibitors of platelet function.

P2Y(12) receptor antagonists are antithrombotic agents that inhibit platelet function by blocking the effects of adenosine diphosphate (ADP) at P2Y (12)receptors. However, some P2Y(12) receptor antagonists may affect platelet function through additional mechanisms. It was the objective of this study to investigate the possibility that P2Y(12) antagonists inhibit platelet function through interaction with G-protein-coupled receptors other than P2Y(12) receptors.