Aspirin induces platelet receptor shedding via ADAM17 (TACE).

Aspirin is effective in the therapy of cardiovascular diseases, because it causes acetylation of cyclooxygenase 1 (COX-1) leading to irreversible inhibition of platelets. Additional mechanisms can be suspected, because patients treated with other platelet COX inhibitors such as indomethacin do not display an increased bleeding tendency as observed for aspirin-treated patients. Recently, aspirin and other anti-inflammatory drugs were shown to induce shedding of L-selectin in neutrophils in a metalloproteinase-dependent manner.

Platelet NAD(P)H-oxidase-generated ROS production regulates alphaIIbbeta3-integrin activation independent of the NO/cGMP pathway.

Platelets play a crucial role in the physiology of primary hemostasis and pathophysiologic processes such as arterial thrombosis. Accumulating evidence suggests a role of reactive oxygen species (ROSs) in platelet activation. Here we show that platelets activated with different agonists produced intracellular ROSs, which were reduced by reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidase inhibitors and superoxide scavengers.

Monitoring of clopidogrel action: comparison of methods.

Background: Clopidogrel is a potent drug for prevention of adverse effects during and after coronary intervention. Increasing experience indicates that a significant proportion of patients do not respond adequately to clopidogrel. Because failure of antiplatelet therapy can have severe consequences, there is need for a reliable assay to quantify the effectiveness of clopidogrel treatment.

Anti-glycoprotein VI treatment severely compromises hemostasis in mice with reduced alpha2beta1 levels or concomitant aspirin therapy.

Background: Platelet inhibition is a major strategy to prevent arterial thrombosis, but it is frequently associated with increased bleeding because of impaired primary hemostasis. The activating platelet collagen receptor, glycoprotein VI (GP VI), may serve as a powerful antithrombotic target because its inhibition or absence results in profound protection against arterial thrombosis but no major bleeding in mice.

Methods And Results: Mice lacking (-/-) or expressing half-levels (+/-) of the other major platelet collagen receptor, integrin alpha2beta1, were injected with the anti-GP VI antibody JAQ1 and analyzed on day 5.

G13 is an essential mediator of platelet activation in hemostasis and thrombosis.

Platelet activation at sites of vascular injury is essential for primary hemostasis, but also underlies arterial thrombosis leading to myocardial infarction or stroke. Platelet activators such as adenosine diphosphate, thrombin or thromboxane A(2) (TXA(2)) activate receptors that are coupled to heterotrimeric G proteins. Activation of platelets through these receptors involves signaling through G(q), G(i) and G(z) (refs.

The C-terminal peptide of thrombospondin-1 stimulates distinct signaling pathways but induces an activation-independent agglutination of platelets and other cells.

A peptide from the C-terminal domain of thrombospondin-1 (4N1-1) has been proposed to stimulate platelet aggregation by a novel mechanism involving both an activation-independent agglutination and an activation-dependent, glycoprotein (GP) IIb/IIIa-mediated aggregation which involves GPVI signaling but does not involve CD47. The present study demonstrates that 4N1-1 stimulated a different pattern of signal transduction pathways than the GPVI agonist convulxin. Furthermore, 4N1-1-induced platelet aggregation was activation-independent and not dependent on GPVI or GPIIb/IIIa.

Dipyridamole enhances NO/cGMP-mediated vasodilator-stimulated phosphoprotein phosphorylation and signaling in human platelets: in vitro and in vivo/ex vivo studies.

Background And Purpose: Dipyridamole and in particular dipyridamole in combination with low-dose aspirin are very effective in preventing recurrent stroke. However, the mechanism(s) underlying this dipyridamole effect have not been elucidated. Since dipyridamole inhibits the cGMP-specific phosphodiesterase type V in vitro, we hypothesized and tested whether therapeutically relevant dipyridamole concentrations enhance NO/cGMP-mediated effects in intact human platelets studied ex vivo.

Targeting of the collagen-binding site on glycoprotein VI is not essential for in vivo depletion of the receptor.

Glycoprotein (GP) VI is an essential collagen receptor on platelets and may serve as an attractive target for antithrombotic therapy. We have previously shown that a monoclonal antibody (mAb) against the major collagen-binding site on mouse GPVI (JAQ1) induces irreversible down-regulation of the receptor and, consequently, long-term antithrombotic protection in vivo. To determine whether this unique in vivo effect of JAQ1 is based on its interaction with the ligand-binding site on GPVI, we generated new mAbs against different epitopes on GPVI (JAQ2, JAQ3) and tested their in vitro and in vivo activity.

Inhibition of platelet P2Y12 and alpha2A receptor signaling by cGMP-dependent protein kinase.

The important role of cGMP and cGMP-dependent protein kinase (cGPK) for the inhibition of platelet activation and aggregation is well established and due to the inhibition of fundamental platelet responses such as agonist-stimulated calcium increase, exposure of adhesion receptors and actin polymerization. The diversity of cGMP binding proteins and their synergistic interaction with cAMP signaling in inhibiting platelets indicates that a variety of cGMP targets contribute to its antiplatelet action. Since stimulation of G(i)-proteins was recently shown to be essential for complete platelet activation/aggregation, the possibility that G(i)-signaling events are cGMP/cGPK targets was investigated.