Mechanism Of Platelet Adhesion Research Articles

Platelet Function and Therapeutic Applications in Dogs: Current Status and Future Prospects.

Simple SummaryPlatelets, small blood cells produced from megakaryocytes mainly in the bone marrow, are implicated not only in hemostasis, but also in different physiological and pathophysiological processes. This paper reviews canine platelet structure and functions, including an accurate description of the numerous surface receptors involved in the mechanisms of platelet adhesion and aggregation. In addition, we describe the most important canine platelet disorders that can affect platelet numbers (thrombocytopenias and thrombocytosis) or platelet function (thrombopathias). Platelet-related tests are vital in the analysis of primary hemostatic disorders and for this reason, we also discuss the efficacy of various tests in the diagnosis of canine platelet disorders. Finally, innovative therapeutic approaches based on the use of platelets and their derivatives for the treatment of various canine diseases such as inflammatory conditions (tendinitis and osteoarthritis) and for wound healing and tissue repair are reported.Significant progress has been made in the functional characterization of canine platelets in the last two decades. The role of canine platelets in hemostasis includes their adhesion to the subendothelium, activation, and aggregation, leading to primary clot formation at the site of injury. Studies on canine platelet function and advancements in laboratory testing have improved the diagnosis and understanding of platelet-related disorders as well as the knowledge of the mechanisms behind these diseases. This review focuses on the most recent discoveries in canine platelet structure, function, and disorders; and discusses the efficacy of various tests in the diagnosis of platelet-related disorders. With the relatively recent discovery of angiogenetic and reparative effects of growth factors found in platelets, this review also summarizes the use of canine platelet-rich plasma (PRP) alone or in association with stem cells in regenerative therapy. The characterization of proteomic and lipidomic profiles and development of platelet gene therapy in veterinary species are areas of future study with potential for major therapeutic benefits.

The use of microfluidics in hemostasis

This article reviews the application of microfluidic technologies in hemostasis. The emphasis is on promising developments in devices for clinical applications and novel approaches to modeling complex hemodynamics. Microfluidics combined with micropatterning of prothrombotic substrates provides devices for measuring platelet function and coagulation with low blood volumes (∼100 μl) over a wide range of shear stresses. This technology has been applied to the diagnosis of bleeding and thrombotic disorders, as well as to dosing and monitoring of anticoagulation and antiplatelet agents. Microfluidic devices that mimic vascular geometries such as bifurcations, stenosis, and complex interconnected networks yield complex flow fields that have revealed new mechanisms of platelet adhesion and aggregation. Applying techniques from tissue engineering by endothelializing these networks is beginning to close the gap between in-vitro and in-vivo models of vascular injury. Microfluidic technology enables researchers to create in-vitro models of vascular disease with unprecedented control of the biochemical and biophysical conditions. Two promising directions are flow-dependent clinical assays and biomimetic vascular networks. These approaches are particularly well suited for modeling the microvasculature. However, caution should be used when extrapolating results from microfluidic channels to the pathophysiology of thrombosis in large arteries and veins.

Studies on the Essential Intramolecular Interaction Between the A1 and A2 Domains of von Willebrand Factor

Haemostasis depends on the balanced participation of von Willebrand factor (vWF), a large multimeric and multidomain glycoprotein with essential role during the initial steps of blood clotting. Mature vWF circulates in plasma with the form of multimers comprised of several domains with diverse functions. More specifically, the A1 domain of vWF plays crucial role in haemostasis, regulating the mechanism of platelet adhesion in sites of vascular injury while A2 domain regulates the normal turnover of vWF. Recent studies have implied that an intramolecular interaction between A1 and A2 domains exists, which prevents platelets adhesion and subsequently inhibits the initial step of the blood coagulation mechanism. In an effort to elucidate the essential nature of the interaction between these two domains, we produced and purified the corresponding recombinant unmodified polypeptides. The secondary structure of the two domains was studied individually and as a mixture using circular dichroism spectroscopy. The observed interaction was verified by ELISA competition assays using antibodies and their ability to form productive interactions was further characterized kinetically. In silico analysis (docking and molecular dynamics simulations) of the A1-A2 binding indicated three possible structural models highlighting the crucial, for this interaction, region.

Die Rolle der Thrombozyten in der Pathophysiologie des akuten Koronarsyndroms

Cardiovascular diseases, especially ischaemic heart disease, are actually the most frequent causes of death in the Western world and represent a central challenge for modern research and medicine. The pathophysiology of ischaemic heart disease is based upon the development and biological remodelling of atherosclerotic plaques. Mainly at late stages, but also in the early phase of atherosclerosis, rupture of the atherosclerotic plaque occurs and may lead to the clinical manifestation of acute coronary syndromes, including unstable angina pectoris, non-transmural or transmural myocardial infarction. Next to inflammation mediating cells like monocytes, platelets play an essential role at early and late stages of atherosclerotic disorders. This review summarizes the basic pathophysiological mechanism of platelet adhesion and secretion, the molecular steps involved in platelet mediated thrombus formation in the atherosclerotic microenvironment and the role of platelet accumulation in reperfused myocardium.

Platelet adhesion mediated by fibrinogen-intercelllular adhesion molecule-1 binding induces tissue injury in the postischemic liver in vivo.

Platelets are thought to be involved in the induction of hepatic ischemia-reperfusion (I/R) injury. The mechanisms of platelet adhesion in the hepatic microvasculature and the role of platelets in the pathogenesis of I/R-induced liver damage in vivo remain unclear. In C57BL/6 mice, platelet- and leukocyte-endothelial cell interactions were quantitatively analyzed using intravital fluorescence microscopy in sham-operated animals, after warm lobar hepatic I/R (90/20 min) in wild-type and intercellular adhesion molecule (ICAM)-1-deficient mice, and after I/R in wild-type mice treated with an antifibrinogen antibody. Fibrinogen deposition on the endothelium was detected by intravital microscopy and by immunostaining. Reperfusion injury was assessed by measurement of liver enzyme and caspase-3 activities and of lipid peroxidation. Hepatic I/R induced fibrinogen deposition on hepatic endothelium, followed by a dramatic increase in the number of firmly adherent platelets in the liver microvasculature. Simultaneously, the number of adherent leukocytes in postsinusoidal venules and the aspartate aminotransferase/alanine aminotransferase and caspase-3 activities were elevated. Although ICAM-1 deficiency attenuated postischemic adherence of both platelets and leukocytes, the application of an antifibrinogen antibody selectively reduced the number of adherent platelets but did not influence leukocyte adhesion. The selective blockade of platelet adherence significantly prevented the postischemic increase in liver enzyme and caspase-3 activities. Furthermore, sinusoidal perfusion failure and lipid peroxidation were attenuated in the treated group. These in vivo data show that platelet adhesion mediated through fibrinogen deposition on ICAM-1 expressed on the endothelium of postischemic hepatic microvessels induces microvascular injury and hepatocellular apoptosis after I/R of the liver during early reperfusion.

A New Method For Continuous Measurement of Platelet Adhesion Under Flow Conditions

Platelet adhesion to the subendothelial tissue or biomaterial surface is an initial step in the formation of the hemostatic plug or thrombus. To clarify the mechanism of platelet adhesion in vivo, a simple and reproducible method for quantitation of platelet adhesion under flow conditions is required. In this study, a mechanical device for continuous recording of platelet adhesion under flow conditions using a quartz crystal microbalance was developed, an extremely sensitive sensor capable of measuring mass changes in the nanogram range. The relationship between surface mass change (delta W) and resonant frequency change (delta f) for pie-zoelectric crystals is given by the Sauerbrey equation: delta f = -fo2 delta W/NA pi (fo; fundamental frequency (5MHz) A; the area of quartz plate undergoing oscillation N; frequency constant for AT-cut quartz crystal pi; density of quartz crystal). Although the perfusion of buffer solution alone or addition of washed red cell suspension (Ht 30%) and formaldehyde-fixed platelets have no effect on delta f, addition of washed platelets in the presence of red cells caused an increase in delta f. To confirm that the increase in delta f results from platelet adhesion to the material surface, adherent and subsequently aggregated platelets were visualized by fluorescence microscopy using fluorescein-isothiocyanate labeled antiplatelet membrane glycoprotein Ib monoclonal antibody. There was a good correlation between the increase in delta f and the extent of platelet adhesion and subsequent aggregation.(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulation factor VIII. Localization in the aqueous outflow pathways.

Antihemophilic factor A-von Willebrand factor (AHF-vWF) is a protein involved in the first phase of blood coagulation and in the mechanism of platelet adhesion. The localization of this protein has been studied in the anterior segment of fetal and adult human eye by a direct immunofluorescence method. It was found that AHF-vWF is present in the wall of aqueous outflow pathways but not in that of Schlemm canal. As it has fibrinolytic activity in the endothelium of Schlemm canal, this structure can be expected to be especially well protected against fibrin deposition and occlusion by platelets and thrombi. The ciliary processes of the adult eye had no AHF-vWF activity. Instead, fluorescein isothiocyanate-fluorescence could be seen in the vessel wall of the ciliary processes of the fetal eye. This difference may be connected with the function of aqueous secretion.

Increased von Willebrand-antihaemophilic factor a in diabetic retinopathy.

The von Willebrand factor‐Factor VIII (vW‐AHF) related protein and the AHF (antihaemophilic factor A) activity have been measured in the blood of 63 diabetic patients with and without diabetic retinopathy. Compared to normals, diabetic patients showed a clear increase in both vW‐AHF related protein and AHF activity. Patients with retinopathy had a level of vW‐AHF related protein significantly higher than patients without retinopathy. Since the von Willebrand factor is involved in the mechanism of platelet adhesion and aggregation these findings may contribute to an explanation of the increased platelet stickiness known to occur in diabetics and especially in those with retinal changes.

Apparent Similarity of Mechanisms of Platelet Adhesion and Aggregation

SummaryA correlation between effects of a series of compounds on platelet adhesion, aggregation, and retraction of the clot, and their effects on platelet electrophoretic mobility, ecto-ATPase activities, and AChE activity has been sought. Compounds which inhibited aggregation induced by ADP or epinephrine also inhibited platelet adhesion to glass. Six compounds which inhibited adhesion and aggregation did not inhibit clot retraction. The data suggest that the effect of thrombin on platelet electrophoretic mobility and ecto-ATPase activities may have less influence on platelet function than was formerly believed. However, the effects of test compounds on platelet AChE activity suggest that this enzyme may play a role in aggregation and adhesion. Platelet adhesion and aggregation may operate by similar mechanisms.