Syk Inhibition Induces Platelet Dependent Peri-islet Hemorrhage in the Rat Pancreas.

Spleen tyrosine kinase (Syk) is a nonreceptor tyrosine kinase that is an important signaling enzyme downstream of immunoreceptors containing an intracellular immunoreceptor tyrosine activating motif (ITAM). These receptors encompass a wide variety of biological functions involved in autoimmune disease pathogenesis. There has been considerable interest in the development of inhibitors of the Syk pathway for the treatment of rheumatoid arthritis and systemic lupus erythematosus.

Platelet activation in a population of critically ill dogs as measured with whole blood flow cytometry and thromboelastography.

Objective: To determine whether critically ill dogs had increased platelet activation and whether the proportion of activated platelets correlated with severity of illness.

Animals: 82 dogs in the intensive care unit of a veterinary teaching hospital and 24 healthy control dogs.

Procedures: Flow cytometry with monoclonal mouse anti-human CD61 and CD62 antibodies in resting and ADP-treated samples and kaolin-activated thromboelastography were used to compare platelet activation in blood samples of critically ill and control dogs.

Antiplatelet activity, P2Y₁ and P2Y₁₂ inhibition, and metabolism in plasma of stereoisomers of diadenosine 5',5'″-P¹ ,P⁴-dithio-P²,P³-chloromethylenetetraphosphate.

Background: Diadenosine tetraphosphate (Ap4A), a constituent of platelet dense granules, and its P1,P4-dithio and/or P2,P3-chloromethylene analogs, inhibit adenosine diphosphate (ADP)-induced platelet aggregation. We recently reported that these compounds antagonize both platelet ADP receptors, P2Y1 and P2Y12. The most active of those analogs, diadenosine 5',5″″-P1,P4-dithio-P2,P3-chloromethylenetetraphosphate, (compound 1), exists as a mixture of 4 stereoisomers.

P2Y12 receptor blockade augments glycoprotein IIb-IIIa antagonist inhibition of platelet activation, aggregation, and procoagulant activity.

Background: New antiplatelet agents that provide greater, more consistent inhibition of the platelet ADP receptor P2Y12 may be used in combination with glycoprotein (GP) IIb-IIIa antagonists, but their combined effect on platelet function and procoagulant activity is not well studied. Therefore, the objective of this study was to evaluate the independent and complementary effects of P2Y12 and GPIIb-IIIa inhibition on platelet function and procoagulant activity.

Methods And Results: Healthy donor blood was treated with the active metabolite of prasugrel (R-138727 5 μmol/L), GPIIb-IIIa antagonists (abciximab 3 μg/mL or eptifibatide 0.

Platelet activation and inhibition in sickle cell disease (pains) study.

Platelet activation/aggregation in sickle cell disease (SCD) may promote tissue ischemia, suggesting that antiplatelet therapy may be useful. However, the assessment of platelet function and the effect of antiplatelet therapy in blood from SCD patients may be confounded by hemolysis with the release of adenosine 5'-diphosphate (ADP). Here we evaluate the levels of platelet activation markers in SCD adolescents vs.

Clopidogrel pharmacokinetics and pharmacodynamics vary widely despite exclusion or control of polymorphisms (CYP2C19, ABCB1, PON1), noncompliance, diet, smoking, co-medications (including proton pump inhibitors), and pre-existent variability in platelet function.

Objectives: This study sought to determine whether known genetic, drug, dietary, compliance, and lifestyle factors affecting clopidogrel absorption and metabolism fully account for the variability in clopidogrel pharmacokinetics and pharmacodynamics.

Background: Platelet inhibition by clopidogrel is highly variable. Patients with reduced inhibition have increased risk for major adverse cardiovascular events.

Concurrent acute myeloid leukemia and T lymphoblastic lymphoma in a patient with rearranged PDGFRB genes.

Concurrent hematologic malignancies are relatively rare. We encountered a case of concurrent acute myeloid leukemia (AML) and T lymphoblastic lymphoma. The bone marrow chromosome analysis showed the karyotype 46, XY, t(5;12)(q33;p13), which indicated presence of PDGFRB gene translocations.

In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation.

The effects of eltrombopag, a thrombopoietin-receptor agonist, on platelet function in immune thrombocytopenia (ITP) are not fully characterized. This study used whole blood flow cytometry to examine platelet function in 20 patients receiving eltrombopag treatment at days 0, 7, and 28. Platelet surface expression of activated GPIIb/IIIa, P-selectin, and GPIb was measured with and without low and high adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP) concentrations.

The human endogenous circadian system causes greatest platelet activation during the biological morning independent of behaviors.

Background: Platelets are involved in the thromboses that are central to myocardial infarctions and ischemic strokes. Such adverse cardiovascular events have day/night patterns with peaks in the morning (~9 AM), potentially related to endogenous circadian clock control of platelet activation. The objective was to test if the human endogenous circadian system influences (1) platelet function and (2) platelet response to standardized behavioral stressors.

The influence of intermittent hypoxemia on platelet activation in obese patients with obstructive sleep apnea.

Objectives: Literature regarding platelet function in obstructive sleep apnea (OSA) has considerable limitations. Given the central role of platelets in atherothrombosis and the known cardiovascular risk of OSA, we hypothesized that OSA severity is predictive of platelet function, independent of known comorbidities.

Design: Obese subjects, without comorbidities, underwent overnight, in-lab polysomnography.

The Platelet Activity After Clopidogrel Termination (PACT) study.

Background: "Rebound" platelet hyperreactivity after discontinuation of clopidogrel has been proposed to lead to increased thrombotic risk, including late stent thrombosis. However the hypothesis that discontinuation of clopidogrel results in platelet hyperreactivity has never been rigorously tested. We therefore performed a randomized, double-blind, placebo-controlled, crossover study: the Platelet Activity after Clopidogrel Termination (PACT) study.

Association of cyclooxygenase-1-dependent and -independent platelet function assays with adverse clinical outcomes in aspirin-treated patients presenting for cardiac catheterization.

Background: Poor clinical outcome in aspirin-treated patients has been termed aspirin resistance and may result from inadequate inhibition of platelet cyclooxygenase-1 (COX-1) by aspirin. The objectives of this study were to determine prospectively whether COX-1-dependent and other platelet function assays correlate with clinical outcomes in aspirin-treated patients.

Methods And Results: Blood was collected before percutaneous coronary intervention from 700 consecutive aspirin-treated (81 or 325 mg for > or =3 days) patients.

Nephropathy in type 1 diabetes is associated with increased circulating activated platelets and platelet hyperreactivity.

Patients with diabetes mellitus (DM) have increased platelet activation compared to non-diabetic controls. Platelet hyperreactivity has been associated with adverse cardiovascular outcomes in Type 2 DM, and with diabetic nephropathy. We investigated the relationship between platelet activation and nephropathy in Type 1 DM.

The platelet hyporeactivity of extremely low birth weight neonates is age-dependent.

Introduction: We have previously demonstrated that, as compared to adults, the platelets of extremely low birth weight (ELBW) neonates are markedly hyporeactive on day 0-1 of life. The purpose of this study was to examine the age dependency of this hyporeactivity.

Materials And Methods: On days 0-1, 3-4, and 10-14, peripheral blood was collected from 14 stable ELBW neonates and compared to peripheral blood from normal adults run in parallel.

Whole blood analysis of leukocyte-platelet aggregates.

In inflammatory and thrombotic syndromes, platelets aggregate with circulating leukocytes, especially monocytes and neutrophils. The platelet binding is initiated primarily through platelet surface expression of P-selectin (CD62P) following activation-dependent degranulation. The levels of P-selectin involved can be low enough to make direct measurement difficult, but detection of leukocyte-platelet aggregates is relatively simply by whole-blood flow cytometry.

Immunophenotypic analysis of platelets.

Platelets are the smallest cellular component in the peripheral circulation. Their primary role is maintenance of hemostasis. The evaluation of platelets by flow cytometry has proven beneficial in the investigation of many disease states, including inherited defects, cardiovascular disease, stroke, and many other inflammatory processes.

Effects of physiologic agonists on canine whole blood flow cytometry assays of leukocyte-platelet aggregation and platelet activation.

Platelets play a role in both the innate and adaptive immune systems. Methods for detecting activated platelets and leukocyte-platelet aggregates (LPAs) are useful for basic and applied research concerning the role of platelets in inflammation and immune disorders. The aim of the study was to develop flow cytometric assays for detection of platelets binding to monocytes and neutrophils and for activated platelets in canine whole blood and to investigate the effect of physiologic agonists.

Effect of adenosine A2 receptor stimulation on platelet activation-aggregation: differences between canine and human models.

Introduction: Adenosine A(2) agonists improve arterial patency in experimental models of recurrent thrombosis, an effect purportedly triggered by stimulation of platelet A(2) receptors and subsequent down-regulation of platelet function. However: (i) there is no direct evidence to substantiate this premise; and (ii) given the recognized differences among species in platelet signaling, it is possible that the mechanisms of A(2) receptor stimulation may be model-dependent. Accordingly, we applied an integrated in vivo and in vitro approach, using both canine and human models, to test the hypothesis that the anti-thrombotic effects of A(2) agonist treatment are due in part to inhibition of platelet activation.

The active metabolite of prasugrel inhibits ADP-stimulated thrombo-inflammatory markers of platelet activation: Influence of other blood cells, calcium, and aspirin.

The novel thienopyridine prodrug prasugrel, a platelet P2Y(12) ADP receptor antagonist, requires in vivo metabolism for activity. Although pharmacological data have been collected on the effects of prasugrel on platelet aggregation, there are few data on the direct effects of the prasugrel's active metabolite, R-138727, on other aspects of platelet function. Here we examined the effects of R-138727 on thrombo-inflammatory markers of platelet activation, and the possible modulatory effects of other blood cells, calcium, and aspirin.

Cystic fibrosis heterozygotes do not have increased platelet activation.

Introduction: We have previously demonstrated platelet hyperreactivity in cystic fibrosis (CF) patients. Carriers of one CF mutation (heterozygotes) have been shown to have abnormalities related to the presence of only one-half the normal amount of CF transmembrane conductance regulator protein. Platelet hyperreactivity in CF heterozygotes would be an important cardiovascular risk factor, since approximately 1 in 25 Caucasians is a CF carrier.

Residual arachidonic acid-induced platelet activation via an adenosine diphosphate-dependent but cyclooxygenase-1- and cyclooxygenase-2-independent pathway: a 700-patient study of aspirin resistance.

Background: Thrombotic events still occur in aspirin-treated patients with coronary artery disease.

Methods And Results: To better understand aspirin "resistance," serum thromboxane B2 (TXB2) and flow cytometric measures of arachidonic acid-induced platelet activation (before and after the ex vivo addition of aspirin and indomethacin) were analyzed in 700 consecutive aspirin-treated patients undergoing cardiac catheterization. In 680 of 682 evaluable patients, serum TXB2 concentrations were reduced compared with nonaspirinated healthy donors.

Platelet activation in cystic fibrosis.

Cystic fibrosis (CF) is caused by a mutation of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). We examined platelet function in CF patients because lung inflammation is part of this disease and platelets contribute to inflammation. CF patients had increased circulating leukocyte-platelet aggregates and increased platelet responsiveness to agonists compared with healthy controls.

Application of flow cytometry to platelet disorders.

Flow cytometry is a powerful and versatile tool that can be used to yield definitive information regarding the phenotypic status of platelets. The method provides a quantitative assessment of the physical and antigenic properties of platelets (e.g.

Release of soluble CD40L from platelets is regulated by glycoprotein IIb/IIIa and actin polymerization.

Objectives: The purpose of this study was to examine the effects of glycoprotein (GP) IIb/IIIa antagonists (abciximab, eptifibatide, and tirofiban) and other inhibitors on translocation of CD40L from intraplatelet stores to the platelet surface and on the release of soluble CD40L (sCD40L) from platelets.

Background: CD40L is a proinflammatory and prothrombotic ligand in the tumor necrosis factor family.

Methods: Platelet surface CD40L was measured by flow cytometry, and sCD40L was measured by enzyme-linked immunosorbent assay.