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Background The contact factor XII (FXII) activates upon contact with a variety of charged surfaces. Activated FXII (FXIIa) activates factor XI, which activates factor IX, resulting in thrombin generation, platelet activation, and fibrin formation. In both in vitro and in vivo rabbit models, components of medical devices, including extracorporeal oxygenators, are known to incite fibrin formation in a FXII‐dependent manner. Since FXII has no known role in hemostasis and its inhibition is therefore likely a safe antithrombotic approach, we investigated whether FXII inhibition also reduces accumulation of platelets in extracorporeal oxygenators. Objectives We aimed to determine the effect of FXII inhibition on platelet deposition in perfused extracorporeal membrane oxygenators in nonhuman primates. Methods A potent FXII neutralizing monoclonal antibody, 5C12, was administered intravenously to block contact activation in baboons. Extracorporeal membrane oxygenators were temporarily deployed into chronic arteriovenous access shunts. Radiolabeled platelet deposition in oxygenators was quantified in real time using gamma camera imaging. Biochemical assays were performed to characterize the method of action of 5C12. Results The anti‐FXII monoclonal antibody 5C12 recognized both the alpha and beta forms of human and baboon FXII by binding to the protease‐containing domain, and inhibited FXIIa activity. Administration of 5C12 to baboons reduced platelet deposition and fibrin formation in the extracorporeal membrane oxygenators, in both the presence and absence of systemic low‐dose unfractionated heparin. The antiplatelet dose of 5C12 did not cause measurable increases in template bleeding times in baboons. Conclusions FXII represents a possible therapeutic and safe target for reducing platelet deposition and fibrin formation during medical interventions including extracorporeal membrane oxygenation.

The effect of dandelion root and its various ingredients on the biological functions of blood platelets has not been well investigated. Thus, the objective of our in vitro study was to examine the five root fractions (A–E), differing in chemical composition, for changes induced in the human platelets’ model using selected hemostatic parameters. As a result, the best anti-platelet potential was shown by preparation enriched with hydroxyphenylacaetate inositol esters – PIEs (fraction C). On the other hand, the best overall protective effect against oxidation of lipids and proteins of platelets, and the best inhibitory effect on the generation of O2− were observed in the presence of fraction A (SL-amino acid adducts enriched fraction). Thus, PIEs and SLs rich plant organs, such as dandelion root, may be considered as potentially suitable additives for functional food products used in prophylaxis and treatment of cardiovascular diseases associated with hyperactivation of blood platelets.

In severe COVID-19, which is characterized by blood clots and neutrophil-platelet aggregates in the circulating blood and different tissues, an increased incidence of cardiovascular complications and venous thrombotic events has been reported. The inflammatory storm that characterizes severe infections may act as a driver capable of profoundly disrupting the complex interplay between platelets, endothelium, and leukocytes, thus contributing to the definition of COVID-19-associated coagulopathy. In this frame, P-selectin represents a key molecule expressed on endothelial cells and on activated platelets, and contributes to endothelial activation, leucocyte recruitment, rolling, and tissue migration. Briefly, we describe the current state of knowledge about P-selectin involvement in COVID-19 pathogenesis, its possible use as a severity marker and as a target for host-directed therapeutic intervention.

Chronic oxidative stress (OS) can be an important factor of acute myeloid leukemia (AML) progression, however, there are no data on the extent/consequence of OS after transfusion of packed red blood cells (pRBCs) and platelet concentrates (PCs), which are commonly used in the treatment of leukemia-associated anemia and thrombocytopenia. We aimed to investigate the effects of pRBC/PC transfusion on the OS markers, i.e., thiol and carbonyl (CO) groups, 3-nitrotyrosine (3-NT), thiobarbituric acid reactive substances (TBARS), advanced glycation end products (AGE), total antioxidant capacity (TAC), SOD, GST, and LDH, in the blood plasma of AML patients, before and 24 h post-transfusion. In this exploratory study, 52 patients were examined, of which 27 were transfused with pRBCs and 25 with PCs. Age-matched healthy subjects were also enrolled as controls. Our results showed the oxidation of thiols, increased 3-NT, AGE levels, and decreased TAC in AML groups versus controls. After pRBC transfusion, CO groups, AGE, and 3-NT significantly increased (by approximately 30, 23, and 35%, p &lt, 0.05, p &lt, 0.05, and p &lt, 0.01, respectively) while thiols reduced (by 18%, 0.05). The PC transfusion resulted in the raise of TBARS and AGE (by 45%, 0.01 and 31%, 0.001), respectively). Other variables showed no significant post-transfusion changes. In conclusion, transfusion of both pRBCs and PCs was associated with an increased OS, however, transfusing the former may have more severe consequences, since it is associated with the irreversible oxidative/nitrative modifications of plasma proteins.

Platelet concentrates (PCs), mostly represented by platelet-rich plasma (PRP) and platelet-rich fibrin (PRF) are autologous biological blood-derived products that may combine plasma/platelet-derived bioactive components, together with fibrin-forming protein able to create a natural three-dimensional scaffold. These types of products are safely used in clinical applications due to the autologous-derived source and the minimally invasive application procedure. In this narrative review, we focus on three main topics concerning the use of platelet concentrate for treating musculoskeletal conditions: (a) the different procedures to prepare PCs, (b) the composition of PCs that is related to the type of methodological procedure adopted and (c) the clinical application in musculoskeletal medicine, efficacy and main limits of the different studies.

Diagnostic value of blood platelet (PLT) and serum total bilirubin (TBIL) for central serous chorioretinopathy (CSC) was investigated. A total of 537 patients with CSC and 182 people with normal physical conditions were selected from June 2012 to August 2016. The 537 patients included 294 males and 243 females with an average age of 45.5±17.8 years, and all patients were treated in the Department of Ophthalmology of Yantai Hospital of Traditional Chinese Medicine and the Department of Ophthalmology of Yantai Liuhuangding Hospital. Clinical data of the patients were retrospectively analyzed. The 182 people with normal physical conditions included 103 males and 79 females with an average age of 43.6±15.2 years, and they were set as the control group. PLT and TBIL tests at admission and after treatment were collected and compared between CSC and the control group to analyze the diagnostic values of PLT and TBIL for CSC. PLT level in the CSC group was significantly higher than that in the control group, but TBIL level in the CSC group was significantly lower than that in the control group (p

The aim of the study was to determine the morphological changes in the cellular elements of blood in rats of different ages under conditions of prolonged hypokinesia. Research into the structural and functional properties of platelets and erythrocytes was carried out by electron microscope and by biochemical methods in 90 mature male rats aged 2, 12 and 24 months. We found that in young (2 month animals) there was a significant increase in the relative content of activated platelets while the normal content of aggregated and degranulated forms with the appearance of single platelets was maintained with an imbalance of alpha and delta granules. In 12-month-old animals, platelet hemostasis disorders were manifested by a significant increase in the relative content of activated platelets (by 125.8–134.7%) with an increase in aggregated and degranulated forms, the appearance of numerous platelets with an imbalance of alpha- and delta-granules, and reduction of mitochondria (by 24.9–27.8%). In 24 month old animals there was a sharp violation of platelet hemostasis due to a significant increase in the content of activated, degranulated and aggregated platelets, the release of the majority of granules, the development of intravascular platelet hyperactivation, an increase in the number of reversible and irreversibly transformed erythrocytes, an increase in the level of aggregation, in particular the appearance of complex cellular aggregates and bizarre forms of red blood cells. The greatest degree of manifestation of morpho-functional changes was revealed in animals aged 24 months, with relative stability of the hemostasis system in 2 and 12 month old animals. Our results showed that irrespective of age, the degree of disturbance of platelet-erythrocyte hemostasis rose as the period of hypokinesia increased and also depended on the increase in the level of serum creatinine. Taken together, intravascular platelet hyperactivation, an imbalance in the content of all types of granules, the transformation of surface cytoarchitectonics of erythrocytes, and the formation of platelet aggregates may play the role of an early predictor of the development of hypokinetic disease

Background: This study aimed to define the sex-divided reference intervals for platelet indices (mean platelet volume (MPV), platelet distribution width (PDW), platelet large cell ratio (P-LCR) and plateletcrit (PCT)) on the Sysmex XN-10. Methods: A total of 2376 samples were assayed for full blood count on the Sysmex XN-10 haematology analyzer. After removing the outliers, reference intervals were calculated using the mean ± 2SD. The P value 0.05 was adopted to denote statistical significance. Results: There was a statistical significance (α = 0.05) between sex-divided reference intervals for MPV (p = 0.007), P-LCR (p = 0.015) and PCT (p

Continuous flow ventricular assist devices (cfVADs) while effective in advanced heart failure, remain plagued by thrombosis related to abnormal flows and elevated shear stress. To limit cfVAD thrombosis, patients utilize complex anti-thrombotic regimens built upon a foundation of aspirin (ASA). While much data exists on ASA as a modulator of biochemically-mediated platelet activation, limited data exists as to the efficacy of ASA as a means of limiting shear-mediated platelet activation, particularly under elevated shear stress common within cfVADs. We investigated the ability of ASA (20, 25 and 125 μM) to limit shear-mediated platelet activation under conditions of: 1) constant shear stress (30 dynes/cm2and 70 dynes/cm2); 2) dynamic shear stress, and 3) initial high shear exposure (70 dynes/cm2) followed by low shear exposure-i.e. a platelet sensitization protocol, utilizing a hemodynamic shearing device providing uniform shear stress in vitro. The efficacy of ASA to limit platelet activation mediated via passage through a clinical cfVAD system (DeBakey Micromed) in vitro was also studied. ASA reduced platelet activation only under conditions of low shear stress (38% reduction compared to control, n = 10, p < 0.004), with minimal protection at higher shear stress and under dynamic conditions (n = 10, p > 0.5) with no limitation of platelet sensitization. ASA had limited ability (25.6% reduction in platelet activation rate) to modulate shear-mediated platelet activation induced via cfVAD passage. These findings, while performed under "deconstructed" non-clinical conditions by utilizing purified platelets alone in vitro, provide a potential contributory mechanistic explanation for the persistent thrombosis rates experienced clinically in cfVAD patients despite ASA therapy. An opportunity exists to develop enhanced pharmacologic strategies to limit shear-mediated platelet activation at elevated shear levels associated with mechanical circulatory support devices.

Spent hop extract (SHE) is hypothesized to possess multifaceted anticoagulant effect and to reduce platelet reactivity in a direct manner and to improve the antiplatelet action of endothelium. The results demonstrated that SHE, rich in flavanols (50% of total phenolic compounds), hydroxycinnamic acids, proanthocyanidin oligomers, flavan-3-ol monomers, and flavonol glycosides, inhibited ADP-induced platelet aggregation up to 11% for 7.5 µg/ml or up to 23% for 15 µg/ml, P 0.05. Additionally, SHE ameliorated anticoagulant activity of human endothelial cells to significantly reduce platelet reactivity. This effect could be related to the increased expression/activity of the ecto-ADPase (CD39). ADP-induced platelet reactivity was reduced in the case of platelets incubated with the extract-treated endothelial cells compared to the untreated cells. Diabetic rats fed with SHE demonstrated longer survival time than the group treated with placebo. In conclusion, our study provided evidence for a potential beneficial role of SHE in the regulation of platelet and endothelial function.

Inflammatory bowel disease (IBD) includes ulcerative colitis and Crohn's disease. It is a group of chronic disorders characterized by inflammation of the gastrointestinal track with unknown etiology. Currently applied biomarkers include CRP, ESR, pANCA, ASCA, and fecal calprotectin. The etiopathogenesis of IBD is multifactorial. In patients with IBD in inflamed alimentary tract mucosa the number of recruited monocytes and activated macrophages which are source of cytokines. In IBD, the exacerbation is accompanied by thrombocytosis. Platelets play a crucial role in the hemostasis and inflammatory response. Selectins, which regulates the hemostasis and inflammatory response, stimulates the secretion of many inflammatory mediators such as β-thromboglobuline, CD40L, fibrinogen, IL-1β, platelet factor-4. In the course of IBD the following changes are observed: an increase in the number of platelets (reactive thrombocytosis), PDW and PCT, reduction in MPV, increased production and excretion of granular content products (P-selectin, GP53, β-TG, PF-4, vWF, fibrinolytic inhibitors).

SummaryBackground Histone deacetylases (HDACs) play a key role in signaling in many cell types. However, little is known about the participation of HDACs, particularly sirtuins (SIRTs), in platelet reactivity. Objective To investigate the role of HDACs in platelets, we examined the effects of SIRT inhibition on platelet function and protein acetylation in human platelets. Methods We used washed platelets obtained from healthy subjects. Cambinol (SIRT1 and SIRT2 inhibitor), AGK2 (specific SIRT2 inhibitor) and EX527 (specific SIRT1 inhibitor) were used as SIRT inhibitors. Platelets were stimulated with collagen, thrombin, or U46619, and platelet responses were determined according to optical aggregometry findings, dense granule release, and cytosolic calcium levels (Fura-2AM fluorescence). Protein acetylation and phosphorylation were assessed by immunoblotting. Results SIRT inhibition remarkably reduced platelet responses (aggregation, granule release, and cytosolic calcium level; P

Introduction Platelets activation/aggregation with subsequent thrombus formation is the main event in the pathophysiology of acute coronary syndrome. Once activated, platelets show an extensive cytoskeleton rearrangement that leads to recruitment of additional platelets to finally cause haemostatic plug formation. Thus, the cytoskeleton plays a pivotal role in this phenomenon. Colchicine (COLC) is an anti-inflammatory drug proven to reduce major cardiovascular events in patients with coronary artery disease. The molecular mechanisms by which COLC exerts these protective effects remain partially still unknown. Since COLC causes disruption of tubulin, a component of cell cytoskeleton, we investigated whether this drug might interfere with platelet aggregation by acting on cytoskeleton rearrangement. Methods and results Platelets isolated from healthy volunteers were activated with Adenosine Diphosphate (ADP, 20 μM) Collagen (COLL, 60 μg/ml) and Thrombin Activating Receptor Peptide (TRAP 25 μM) with/without COLC 10 μM pretreatment. After stimulus, aggregation was measured by light aggregometry overtime. Microtubules structure was assessed by immunohistochemistry and key proteins involved in regulation of actin-filament assembly and contractility such as Myosin Phosphatase Targeting subunit (MYPT), LIM domain kinase 1(LIMK1) and cofilin were evaluated by Western Blot analysis. Colchicine pretreatment significantly blunted ADP/COLL/TRAP-induced platelet aggregation (up to 40%). COLC effects appeared mediated by microtubules depolymerization and cytoskeleton disarrangement associated to inactivation of MYPT and LIMK1 that finally interfered with cofilin activity. Conclusions Our data indicate that colchicine exerts anti-platelet effects in vitro via inhibition of key proteins involved in cytoskeleton rearrangement, suggesting that its beneficial cardiovascular properties may be due, at least in part, to an inhibitory effect of platelet activity.

Platelets (PLTs) deteriorate over time when stored within blood banks through a biological process known as PLT storage lesion (PSL). Here, we describe the refinement of the biochemical model of PLT metabolism, iAT-PLT-636, and its application to describe and investigate changes in metabolism during PLT storage. Changes in extracellular acetate and citrate were measured in buffy coat and apheresis PLT units over 10 days of storage in the PLT additive solution T-Sol. Metabolic network analysis of these data was performed alongside our prior metabolomics data to describe the metabolism of fresh (days 1–3), intermediate (days 4–6), and expired (days 7–10) PLTs. Changes in metabolism were studied by comparing metabolic model flux predictions of iAT-PLT-636 between stages and between collection methods. Extracellular acetate and glucose contribute most to central carbon metabolism in PLTs. The anticoagulant citrate is metabolized in apheresis-stored PLTs and is converted into aconitate and, to a lesser degree, malate. The consumption of nutrients changes during storage and reflects altered PLT activation profiles following their collection. Irrespective of the collection method, a slowdown in oxidative phosphorylation takes place, consistent with mitochondrial dysfunction during PSL. Finally, the main contributors to intracellular ammonium and NADPH are highlighted. Future optimization of flux through these pathways provides opportunities to address intracellular pH changes and reactive oxygen species, which are both of importance to PSL. The metabolic models provide descriptions of PLT metabolism at steady state and represent a platform for future PLT metabolic research.

Background Arachidonic acid metabolism by cyclooxygenase (COX) is a major pathway for blood platelets’ activation, which is associated with pro-thrombotic platelet activity and the production of pro-inflammatory mediators. Inhibition of COX activity is one of the major means of anti-platelet pharmacotherapy preventing arterial thrombosis and reducing the incidence of cardiovascular events. Recent studies have presented that a silymarin (standardized extract of Milk thistle (Silybum marianum)) can inhibit the COX pathway. Accordingly, the aim of our study was to determine the effects of three major flavonolignans (silybin, silychristin and silydianin) on COX pathway activity in blood platelets. Methods We determined the effect of flavonolignans on arachidonic acid induced blood platelet aggregation, COX pathway metabolites formation, as well as COX activity in platelets. Additionally, we analysed the potential mechanism of this interaction using the bioinformatic ligand docking method. Results We observed that tested compounds decrease the platelet aggregation level, both thromboxane A2 and malondialdehyde formation, as well as inhibit the COX activity. The strongest effect was observed for silychristin and silybin. In our in silico study we showed that silychristin and silybin have conformations which interact with the active COX site as competitive inhibitors, blocking the possibility of substrate binding. Conclusions The results obtained from this study clearly present the potential of flavonolignans as novel antiplatelet and anti-inflammatory agents.

Background: Several studies have demonstrated that platelet counts in Helicobacter pylori-positive patients with chronic idiopathic thrombocytopenic purpura improved significantly after successful eradication of the infection. However, depending of the geographical region of the study the results have been highly divergent. Objective: The purpose of this study was to evaluate the effect of H. pylori eradication therapy on platelet count in a cohort of chronic idiopathic thrombocytopenic purpura patients from northeastern Brazil. Method: H. pylori status was determined in 28 chronic idiopathic thrombocytopenic purpura patients using the rapid urease test and histology. H. pylori-positive patients received standard triple therapy for one week. The effect of the eradication therapy was evaluated using the 13C-urea breath test two to three months after treatment. Results: The prevalence of H. pylori infection was similar to that found in the general population. Twenty-two patients (78.5%) were H. pylori-positive. Fifteen were treated, 13 (86%) of whom successfully. At six months, 4/13 (30%) displayed increased platelet counts, which remained throughout follow-up (12 months). Platelet response was not associated to mean baseline platelet count, duration of chronic idiopathic thrombocytopenic purpura, gender, age, previous use of medication, or splenectomy. Conclusions: H. pylori eradication therapy showed relatively low platelet recovery rates, comparable with previous studies from southeastern Brazil. The effect of H. pylori eradication on platelet counts remained after one year of follow-up suggesting that treating H. pylori infection might be worthwhile in a subset of chronic idiopathic thrombocytopenic purpura patients. Keywords: Helicobacter pylori eradication, Blood platelet, Idiopathic thrombocytopenic purpura

Background Hepatocellular carcinoma (HCC) is a heterogeneous disease with both tumor and liver factors being involved. Aims To investigate HCC clinical phenotypes and factors related to HCC size. Methods Prospectively-collected HCC patients' data from a large Italian database were arranged according to the maximum tumor diameter (MTD) and divided into tumor size terciles, which were then compared in terms of several common clinical parameters and patients' survival. Results An higer MTD tercile was significantly associated with increased blood alpha-fetoprotein (AFP), gamma-glutamyl transpeptidase (GGTP), and platelet levels. Patients with higher platelet levels had larger tumors and higher GGTP levels, with lower bilirubin levels. However, patients with the highest AFP levels had larger tumors and higher bilirubin levels, reflecting an aggressive biology. AFP correlation analysis revealed the existence of 2 different groups of patients: those with higher and with lower AFP levels, each with different patient and tumor characteristics. The Cox proportional-hazard model showed that a higher risk of death was correlated with GGTP and bilirubin levels, tumor size and number, and portal vein thrombosis (PVT), but not with AFP or platelet levels. Conclusions An increased tumor size was associated with increased blood platelet counts, AFP and GGTP levels. Platelet and AFP levels were important indicators of tumor size, but not of survival.

Glanzmann's thrombasthenia (GT) is a rare congenital bleeding disorder associated with decreased platelet aggregation due to qualitative/quantitative deficiencies of the fibrinogen receptor. Severe bleeding episodes and perioperative bleeding are typically managed with platelet transfusions, although patients can develop anti-platelet antibodies or experience clinical refractoriness. The GT Registry (GTR) was established to collect efficacy/safety data on hemostatic treatments for GT, including recombinant factor VIIa (rFVIIa). At the request of the United States Food and Drug Administration, three hematology experts evaluated platelet refractoriness, antibody status, and rFVIIa efficacy data on a case-by-case basis to support a potential indication for rFVIIa in GT. Adjudication included 195 patients with 810 events (619 severe bleeding episodes, 192 surgeries), and a consensus algorithm was developed to describe adjudicators' coding of refractoriness and antibody status based on treatment patterns over time. Most rFVIIa-treated events were in patients without refractoriness or antibodies. Adjudicators rated most rFVIIa-treated bleeding episodes as successful (251/266, 94.4%; rFVIIa only, 101/109, 92.7%; rFVIIa ± platelets ± other agents, 150/157, 95.5%); efficacy was consistent in patients with platelet refractoriness ± antibodies (75/79, 94.9%), antibodies only (10/10, 100.0%), and neither/unknown (166/177, 93.8%). Adjudicators also rated most rFVIIa-treated surgeries as successful (159/160, 99.4%; rFVIIa only, 65/66, 98.5%; rFVIIa ± platelets ± other agents, 94/94, 100.0%); efficacy was consistent in patients with platelet refractoriness ± antibodies (69/70, 98.6%), antibodies only (24/24, 100.0%), and neither/unknown (66/66, 100.0%). Unblinding the adjudicators to investigator efficacy ratings changed few assessments. Doses of rFVIIa were narrowly distributed, regardless of other hemostatic agents used. This article is protected by copyright. All rights reserved.

Purpose of Review: This review aims to summarize and discuss safety and effectiveness of the long-term use of ticagrelor in patients with coronary artery disease (CAD). Recent Findings: Ticagrelor is an orally administered, direct, and reversible inhibitor of the P2Y12-platelet receptor. Long-term use of ticagrelor in patients with previous myocardial infarction (MI) has been investigated in the PEGASUS-TIMI-54 trial. Overall, 21,162 patients with a spontaneous MI 1 to 3 years before randomization were randomly assigned to ticagrelor 90 mg bid, ticagrelor 60 mg bid, or placebo. Compared with placebo, both doses of ticagrelor showed that they were capable of significantly reducing the primary efficacy endpoint, although with a significant increase in TIMI major bleeding. Intracranial hemorrhage or fatal bleeding did not differ across groups. Summary: These findings establish clear benefit of DAPT extension with ticagrelor beyond 1 year of treatment, which comes with a tradeoff of clinically meaningful bleeding. Altogether, current evidence suggests that the duration of DAPT remains a patient-by-patient decision based on thrombotic and bleeding risk profiles.

Objective— Platelet- and fibrin-dependent thrombus formation is regulated by blood flow and exposure of collagen and tissue factor. However, interactions between these blood-borne and vascular components are not well understood. Approach and Results— Here, we developed a method to assess whole-blood thrombus formation on microspots with defined amounts of collagen and tissue factor, allowing determination of the mechanical properties and intrathrombus composition. Confining the collagen content resulted in diminished platelet deposition and fibrin formation at high shear flow conditions, but this effect was compensated by a larger thrombus size and increased accumulation of fibrin in the luminal regions of the thrombi at the expense of the base regions. These thrombi were more dependent on tissue factor–triggered thrombin generation. Microforce nanoindentation analysis revealed a significantly increased microelasticity of thrombi with luminal-oriented fibrin. At a low shear rate, fibrin fibers tended to luminally cover the thrombi, again resulting in a higher microelasticity. Studies with blood from patients with distinct hemostatic insufficiencies indicated an impairment in the formation of a platelet–fibrin thrombus in the cases of dilutional coagulopathy, thrombocytopenia, Scott syndrome, and hemophilia B. Conclusions— Taken together, our data indicate that (1) thrombin increases the platelet thrombus volume; (2) tissue factor drives the formation of fibrin outside of the platelet thrombus; (3) limitation of platelet adhesion redirects fibrin from bottom to top of the thrombus; (4) a lower shear rate promotes thrombus coverage with fibrin; (5) the fibrin distribution pattern determines thrombus microelasticity; and (6) the thrombus-forming process is reduced in patients with diverse hemostatic defects.

Platelet concentrates for surgical use are tools of regenerative medicine designed for the local release of platelet growth factors into a surgical or wounded site, in order to stimulate tissue healing or regeneration. Leukocyte content and fibrin architecture are 2 key characteristics of all platelet concentrates and allow to classify these technologies in 4 families, but very little is known about the impact of these 2 parameters on the intrinsic biology of these products. In this demonstration, we highlight some outstanding differences in the growth factor and matrix protein release between 2 families of platelet concentrate: Pure Platelet-Rich Plasma (P-PRP, here the Anitua's PRGF - Preparation Rich in Growth Factors - technique) and Leukocyte- and Platelet-Rich Fibrin (L-PRF, here the Choukroun's method). These 2 families are the extreme opposites in terms of fibrin architecture and leukocyte content. The slow release of 3 key growth factors (Transforming Growth Factor β1 (TGFβ1), Platelet-Derived Growth Factor AB (PDGF-AB) and Vascular Endothelial Growth Factor (VEGF)) and matrix proteins (fibronectin, vitronectin and thrombospondin-1) from the L-PRF and P-PRP gel membranes in culture medium is described and discussed. During 7 days, the L-PRF membranes slowly release significantly larger amounts of all these molecules than the P-PRP gel membranes, and the 2 products display different release patterns. In both platelet concentrates, vitronectin is the sole molecule to be released almost completely after only 4 hours, suggesting that this molecule is not trapped in the fibrin matrix and not produced by the leukocytes. Moreover the P-PRP gel membranes completely dissolve in the culture medium after less than 5 days only, while the L-PRF membranes are still intact after 7 days. This simple demonstration shows that the polymerization and final architecture of the fibrin matrix considerably influence the strength and the growth factor trapping/release potential of the membrane. It also suggests that the leukocyte populations have a strong influence on the release of some growth factors, particularly TGFβ1. Finally, the various platelet concentrates present very different biological characteristics, and an accurate definition and characterization of the different families of product is a key issue for a better understanding and comparison of the reported clinical effects of these surgical adjuvants.

OBJECTIVE: A novel mechanism of platelet destruction involving the CD47/ signal regulatory protein-α (SIRPα) system has recently been suggested in a mouse model of immune thrombocytopenia (ITP). The CD47 molecule serves as ligand for SIRPα receptor and as receptor for thrombospondin acting as antagonistic to phagocyte activity and a regulator of apoptosis, respectively. In this study, we evaluated if the CD47/SIRPα axis may be involved in the apoptosis and clearance of platelets in human ITP. MATERIALS AND METHODS: Using flow cytometry, we characterized whether expression of CD47 on fresh and in vitro-aged platelets- and of SIRPα receptor on CD14-derived dendritic cells (DCs), macrophages, circulating DCs, and monocytes is reduced is ITP; whether the in vitro platelet phagocytic capacity of CD14-derived DCs and macrophages is differentially modulated in the presence or absence of antibodies against CD47 and SIRPα in ITP; and whether platelets are more susceptible to the CD47-induced death signal in ITP. RESULTS: We demonstrated that low platelet count in ITP is not due to increased phagocytosis associated with decreased expression of CD47 on the platelet surface and, despite reduced SIRPα expression, blockage of SIRPα on immature CD14-derived DCs or CD47 on platelets by specific antibodies failed to modify platelet uptake/phagocytosis of DCs. In contrast, targeting platelet CD47 with specific antibody significantly increases platelet phagocytosis of CD14-derived macrophages, and platelets are not healthy because they show increased apoptosis and are resistant to CD47-induced death signal. CONCLUSIONS: Our results demonstrate that the CD47 pathway in ITP patients abnormally modulates platelet homeostasis.

Adequate platelet inhibition is mandatory in patients undergoing percutaneous coronary intervention in order to prevent recurrent thrombotic events. Dual antiplatelet therapy with aspirin and thienopyridine (e.g., clopidogrel) is the treatment of choice in this setting, providing clear clinical benefit in most of the patients. However, a wide interindividual variability exists in the response to antiplatelet drugs and several factors may contribute to determine fluctuation in platelet reactivity, even within the individual patient. Several methodologies and devices have been developed to monitor individual response to antiplatelet treatment, assessing different pathways of platelet activation and aggregation. Studies performed with the use of these methodologies have clearly demonstrated that patients with high post-treatment residual platelet reactivity present a higher risk of ischemic events both at short (during or soon after percutaneous coronary intervention) and long term. In these patients, more aggressive antithrombotic strategies, based on the results of platelet function tests, may be beneficial in order to reduce ischemic complications after percutaneous coronary intervention. © 2010 Future Medicine Ltd.

Platelet reactivity is greater in patients with stable angina and with more extensive peripheral vascular atherosclerosis. We sought to evaluate whether impaired peripheral microcirculatory endothelial function might correlate with platelet reactivity after clopidogrel and therefore predispose to an unfavorable outcome after percutaneous coronary intervention (PCI). In 52 consecutive patients with stable angina undergoing elective PCI, endothelial function was assessed by (1) endothelial peripheral arterial tonometry (measuring the "Endoscore"); (2) the von Willebrandt factor antigen level and ristocetin co-factor activity. Basal platelet reactivity was assessed by soluble P-selectin. Patients then received a 600-mg clopidogrel loading dose ≥12 hours before PCI. A blood sample was withdrawn 12 hours later, but before PCI, to assess platelet reactivity using the P2Y12 reaction unit and percentage of P2Y12 inhibition with the point-of-care VerifyNow P2Y12 assay. Troponin T was assessed 24 hours after PCI. The Endoscore inversely correlated with von Willebrandt factor antigen activity (r = -0.52, p = 0.0001) and soluble P-selectin concentration (r = -0.36, p = 0.021), suggesting greater platelet reactivity with increased impaired endothelial function. After clopidogrel, the Endoscore correlated directly with the percentage of P2Y12 inhibition (r = 0.36, p = 0.009) and inversely with the P2Y12 reaction unit (r = -0.41, p = 0.002), suggesting greater residual platelet reactivity with more impaired endothelial function. The average Endoscore was significantly lower in patients with troponin T elevation (troponin positive group 0.267 ± 0.091) than in patients without troponin T elevation (troponin negative group 0.508 ± 0.041, p = 0.015 vs troponin positive). In conclusion, an impaired endothelial response before clopidogrel was associated with greater platelet reactivity after clopidogrel. This link might explain the unfavorable PCI outcomes in patients with more severe endothelial impairment. © 2010 Elsevier Inc. All rights reserved.

A recent article published in this journal, entitled “The influence of herbal medicine on platelet function and coagulation: a narrative review,” byMcEwen,1 nicely reviewed how herbal medicines can play a role in modifying cardiovascular diseases (CVDs), and also highlighted the interaction of herbal medicines with standard anticoagulant medicinal therapy. Here, we wish to further reflect on the effects of Danshen on the cardiovascular system, and also to report the novel underlying mechanism of its main constituents on platelets function and hemostasis. To our knowledge, these aspects have not been previously fully described. CVDs are the main causes of morbidity and mortality worldwide.2 They include myocardial infarction, stroke, rheumatic heart disease, and also peripheral artery disease and venous thrombosis.3 The underlying mechanisms diverge depending on the disease in question.4 Scientists working on CVDsagree that inmost cases hyper-platelet aggregation seems to be a crucial step in cardiovascular hemostasis and in the development and progression of CVDs. For these reasons, pharmacological therapies with agents that modulate platelet reactivity have proven to be effective in the treatment and/or in the prevention of CVDs.5 Moreover, advancements in technology and better knowledge of both platelet biology and biological functions of natural products have facilitated this process and pushed researchers to search for new and more reliable targets. Finally, but not less important, research into natural compounds founded on their ethnopharmacological information, has provided significant contributions to drug improvement and has paved the way for new pharmacological tools.6 Danshen has beenwidely used in traditional folk medicine in China and, to a lesser extent,within theUnited States and several European countries to treat CVDs and cerebrovascular diseases.7 Its cardiovascular beneficial actions are attributable to “thinning” the blood and reducing blood clotting, as well as to “invigorate” theblood or improve circulation. AlthoughDanshen is officially listed in the Chinese Pharmacopeia, the cardiovascular pharmacology of its active constituents has not yet been fully described. To date, more than 40 lipophilic tanshinones and 50 hydrophilic phenolics-like compounds have been isolated from Danshen root and extensively investigated for their cardiovascular activities.8 If we had to promote an “ideal candidate” from one of these lipophilic/phenolics-like compounds in the context of CVDs, this would be without any doubt tanshinone IIA (TIIA) and cryptotanshinone (CRY). Indeed, the discovery of these derivatives of phenanthrene-quinone isolated from Danshen have completely changed the way we look at many Danshen-mediated pharmacological properties.9 Recently, the pharmacological properties of TIIA andCRY in the cardiovascular systemhave attractedgreat interest. Emerging experimental studies and clinical trials have demonstrated that both the compounds prevent atherosclerosis and atherogenesis, as well as cardiac injury due the pleiotropic inhibition of low-density lipoprotein oxidation, monocyte adhesion to endothelium, smooth muscle cell migration and proliferation, macrophage cholesterol accumulation, and proinflammatory cytokine production.10,11 Moreover, few but representative studies have reported the effects of Danshen and TIIA on human blood platelets, human cardiomyocytes and vascular endothelial cells.12–14 However, no preclinical studies and clinical evidences have as yet underlined the key role of TIIA and CRY on platelet biology. A recent article15 has changed this scenario showing that TIIA in vitro selectively inhibited rat platelet aggregation induced by reversible adenosine diphosphate (ADP) stimuli (3 μM) in a concentration-dependent manner (0.5–50 μM). Nevertheless, TIIA was less active against the irreversible stimuli induced by ADP (10 μM) and collagen (10 μg/mL). Moreover, experiments performed on platelet lysates collected at different time-point after the addition of the stimuli shown that TIIA modulated tubulin acetylation and inhibited Erk-2 phosphorylation. Concomitantly, TIIA administrated intraperitoneally at 10 mg/kg significantly prolonged the Letter to the Editor

To the editor: Immune thrombocytopenia (ITP) is an autoimmune disorder whose primary pathogenesis is mediated by Fc receptor (FcR) clearance of antibody-opsonized platelets by spleen macrophages.[1][1] Recently, however, an Fc-independent mechanism of platelet clearance mediated by antibodies

The effects of resveratrol (trans-3,4′,5-trihydroxystilbene) on activation responses and the polyphosphoinositide metabolism in human blood platelets have been studied. Resveratrol partially inhibited secretory responses (liberation of dense granule nucleotides and lysosomal acid hydrolases), microparticle formation and protein phosphorylations induced by thrombin. The effects of resveratrol on phosphoinositide metabolites, phosphatidate (PtdOH), phosphatidylinositol (PtdIns), phosphatidylinositol-4-phosphate (PtdIns-4(5)-P), phosphatidylinositol 4,5-bisphosphate (PtdIns-4,5-P2), phosphatidylinositol-3,4-bisphosphate (PtdIns-3,4-P2) and phosphatidylinositol-3,4,5-trisphosphate (PtdIns-3,4,5-P3) were monitored in blood platelets prelabelled with [32P]Pi. Resveratrol not only inhibited the marked increase in levels of PtdOH in platelets activated by thrombin (0.1 U/ml) but it decreased the steady state levels of the other polyphosphoinositide metabolites. The distribution of 32P in phosphoinositides in activated platelets was consistent with inhibition of CDP-DAG inositol transferase and a weak inhibition of PtdIns-4(5)-P kinase. These observations show that resveratrol has a profound effect on phospholipids, particularly on polyphosphoinositide metabolism, and may decrease the amount of PtdIns-4,5-P2 available for signalling in these cells.

Many drugs are nowadays available to inhibit platelet activation and aggregation, especially in patients with acute coronary syndromes and undergoing percutaneous coronary intervention with stent implantation. Primary targets are represented by enzymes or receptors involved in platelet activation. Genetic mutations in these targets contribute to the inter-individual variability in platelet responses therefore weakening the efficacy of antiplatelet agents. High on treatment platelet reactivity is a condition characterized by low levels of platelet inhibition despite the use of antiplatelet drugs. This could be responsible for re-infarction, stent-thrombosis and strokes, affecting short and long-term prognosis after coronary revascularization. So far, to test antiplatelet resistance either the assessment of platelet function or the identification of genetic carriers of poly morphisms have been pursued. Although several methods are now available to test platelet reactivity, it is still debated whether its routine assessment gives real benefits in clinical practice. The present review aims at examining current evidences on genetic polymorphisms affecting optimal platelet inhibition.

The contribution of vessel wall-derived tissue factor (TF) to atherothrombosis is well established, whereas the pathophysiological relevance of the blood-borne TF is still a matter of debate, and controversies on the presence of platelet-associated TF still exist. In the past 15 years, several studies have documented the presence of TF in human platelets, the capacity of human platelets to use TF mRNA to make de novo protein synthesis, and the increase in the percentage of TF positive platelets in pathological conditions such as coronary artery disease (CAD). The exposure of vessel wall-derived TF at the site of vascular injury would play its main role in the initiation phase, whereas the blood-borne TF carried by platelets would be involved in the propagation phase of thrombus formation. More recent data indicate that megakaryocytes are committed to release into the bloodstream a well-defined number of TF-carrying platelets, which represents only a fraction of the whole platelet population. These findings are in line with the evidence that platelets are heterogeneous in their functions and only a subset of them is involved in the hemostatic process. In this review we summarize the existing knowledge on platelet associated TF and speculate on its relevance to physiology and to atherothrombosis and CAD.

Patients with Klinefelter syndrome (KS) exhibit an increased cardiovascular risk, but underlying mechanisms are largely unknown. The present cross-sectional study has been conducted to evaluate platelet reactivity and the expression of platelet activation markers (8-iso-prostaglandin F2α[8-iso-PGF2α] and 11-dehydro-thromboxane-B₂[11-dehydro-TXB2]) in KS patients and healthy controls. Twenty-three consecutive KS patients under testosterone replacement therapy have been included as case group and 46 age-matched healthy males recruited among hospital staff served as controls. Light transmission aggregometry was performed in both cases and controls and maximal platelet aggregation (max-A%) was defined as maximal light transmittance reached within 5min after the addition of 0.2 or 0.4mm arachidonic acid (AA). A≥50% irreversible light transmittance (LT-50%) following platelet stimulation defined an adequate platelet aggregation and AC-50% was defined as the minimal agonist concentration needed to achieve LT-50%. The AC-50% was 0.26mm AA for KS and 0.36mm for controls (p&nbsp

Introduction The Leukocyte-PRF (Leukocyte-Platelet Rich Fibrin) belongs to a second generation of platelet concentrates which doesn’t need a biochemical blood manipulation. It is used for tissue healing and regeneration in periodontal and oral-maxillofacial surgery. We report two cases of hyperplastic gingival lesions treated by exeresis and application of PRF membranes in order to improve and accelerate tissue healing. Case Presentation Two patients (one Caucasian female, 78-year-old, and one Caucasian male, 30-year-old) were treated for hyperplastic gingival lesions. They underwent to exeresis of lesions and application of PRF membranes. Tissue healing was clinically evaluated after one, three, seven, fourteen and thirty post-operative days. No recurrences were observed after two years of semiannual follow up. Conclusion We obtained rapid and good healing of soft tissues probably due to the elevated content of leukocytes, platelets and growth factors in the leukocyte-platelet rich fibrin. According to our results we suggest L-PRF employment for wounds covering after exeresis of oral neoformations such as hyperplastic gingival lesions.

SummaryPlatelets carry megakaryocyte-derived mRNAs whose translation efficiency before and during activation is not known, although this can greatly affect platelet functions, both under basal conditions and in response to physiological and pathological stimuli, such as those involved in acute coronary syndromes. Aim of the present study was to determine whether changes in microRNA (miRNA) expression occur in response to activating stimuli and whether this affects activity and composition of platelet transcriptome and proteome. Purified platelet-rich plasmas from healthy volunteers were collected and activated with ADP, collagen, or thrombin receptor activating peptide. Transcriptome analysis by RNA-Seq revealed that platelet transcriptome remained largely unaffected within the first 2 hours of stimulation. In contrast, quantitative proteomics showed that almost half of > 700 proteins quantified were modulated under the same conditions. Global miRNA analysis indicated that reorganisation of platelet proteome occurring during activation reflected changes in mature miRNA expression, which therefore, appears to be the main driver of the observed discrepancy between transcriptome and proteome changes. Platelet functions significantly affected by modulated miRNAs include, among others, the integrin/cytoskeletal, coagulation and inflammatory-immune response pathways. These results demonstrate a significant reprogramming of the platelet miRNome during activation, with consequent significant changes in platelet proteome and provide for the first time substantial evidence that fine-tuning of resident mRNA translation by miRNAs is a key event in platelet pathophysiology.

Anna Dietrich-Muszalska, Anna KwiatkowskaDepartment of Biological Psychiatry of the Chair of Experimental and Clinical Physiology, Medical University of Lodz, Lodz, PolandAbstract: Blood platelets are considered to be a peripheral marker in schizophrenia and other psychiatric disorders. Oxidative stress in schizophrenia may be responsible for changes in platelet metabolism and function; therefore, the aim of this study was to examine and compare the generation of superoxide anions and activity of an antioxidant enzyme (glutathione peroxidase [GPx]) in blood platelets in patients with schizophrenia and healthy subjects. The level of superoxide anions generated in platelets after thrombin and platelet-activating factor stimulation and activity of GPx in patients with schizophrenia and healthy volunteers was estimated. The results obtained from the study indicate that the generation of superoxide anions in platelets as a response of platelets in patients with schizophrenia to such activating factors as thrombin or platelet-activating factor is higher than in the response of platelets of healthy subjects. In platelets from schizophrenic patients, suppressed GPx activity of about 67% was observed.Keywords: schizophrenia, blood platelet, superoxide anion, activating factors, glutathione peroxidase

Background and objectivesAlthough several studies demonstrated that platelet count is higher in women, decreases with age, and is influenced by genetic background, most clinical laboratories still use the reference interval 150-400×10(9) platelets/L for all subjects. The present study was to identify age- and sex-specific reference intervals for platelet count.MethodsWe analysed electronic records of subjects enrolled in three population-based studies that investigated inhabitants of seven Italian areas including six geographic isolates. After exclusion of patients with malignancies, liver diseases, or inherited thrombocytopenias, which could affect platelet count, reference intervals were estimated from 40,987 subjects with the non parametric method computing the 2.5° and 97.5° percentiles.ResultsPlatelet count was similar in men and women until the age of 14, but subsequently women had steadily more platelets than men. The number of platelets decreases quickly in childhood, stabilizes in adulthood, and further decreases in oldness. The final result of this phenomenon is that platelet count in old age was reduced by 35% in men and by 25% in women compared with early infancy. Based on these findings, we estimated reference intervals for platelet count ×10(9)/L in children (176-452), adult men (141-362), adult women (156-405), old men (122-350) and, old women (140-379). Moreover, we calculated an "extended" reference interval that takes into account the differences in platelet count observed in different geographic areas.ConclusionsThe age-, sex-, and origin-related variability of platelet count is very wide, and the patient-adapted reference intervals we propose change the thresholds for diagnosing both thrombocytopenia and thrombocytosis in Italy.

In the last ten years the contribution of both vessel wall-derived tissue factor (TF) and platelets to atherosclerosis has been revisited. At the beginning of the 2000 a circulating blood-borne TF has been proposed to sustain coagulation activation and propagation on the edge of a growing thrombus. Concomitantly with the observation that platelets not only contribute to thrombus formation, but also take part to the onset of the atherosclerotic lesion, evidences have been provided that they express functionally active TF, making them able to trigger the coagulation cascade.

Despite advances in neuroimaging, the diagnosis of idiopathic Parkinson's disease (PD) remains clinical. The identification of biological markers for an early diagnosis is of great interest to start a neuroprotective therapy aimed at slowing, blocking or reversing the disease progression. Vesicular monoamine transporter 2 (VMAT2) sequesters cytoplasmic dopamine into synaptic vesicles for storage and release. Thus, VMAT2 impairment can regulate intra- and extracellular dopamine levels, influencing oxidative stress and neuronal death. Because in vivo imaging studies have demonstrated a VMAT2 reduction in PD patients greater than would be explained by neuronal loss alone, as an exploratory study we assessed VMAT2 mRNA and protein levels in platelets from 39 PD patients, 39 healthy subjects and 10 patients with vascular parkinsonism (VP) to identify a possible peripheral biomarker for PD. A significant reduction (p < 0.05) of VMAT2 mRNA levels was demonstrated in PD patients versus healthy controls. Patients with VP showed VMAT2 mRNA levels similar to controls. No difference in VMAT2 mRNA levels was found in untreated versus treated patients. No correlation was observed between mRNA levels and demographic or clinical characteristics. Furthermore, eight SNPs tagging the VMAT2 gene did not show effects on VMAT2 mRNA levels. Western blot analysis did not allow the quantification of VMAT2 protein expression in blood platelets. Although further studies in a greater number of cases are needed to confirm our data, the reduction in VMAT2 mRNA in platelets from PD patients suggests the existence of a systemic impairment of this transporter possibly contributing to PD pathology.

Blood platelets are emerging as important immunomodulatory cells, but complement interaction with platelets is not well understood. Several platelet structures have been described as complement protein 1q (C1q) binding receptors, such as C1qRp/CD93 and gC1qR. However, there are conflicting results whether these receptors are C1q binding structures, or even at all expressed on the cell surface. Recently, the collagen-binding integrin alphaIIbetaI was reported to bind C1q on mast cells, and this receptor is also present on platelets. The aim of this study was to further characterize the effects of C1q on platelets, by quantifying the platelet surface expression of P-selectin (CD62P) and monitoring the formation of platelet-neutrophil aggregates. Using flow cytometry, we found that C1q dose-dependently triggered a rapid but moderate and transient up-regulation of P-selectin already within 5s of C1q exposure. Pre-incubation with an antibody directed against gC1qR significantly inhibited (with 57% compared to control) the up-regulation, whereas an antibody towards the alphaIIbetaI-integrin showed no effect. Stimulation with C1q did not change the cytosolic calcium-levels, as measured with the fluorescent ratiometric probe Fura-2, however, a protein kinase C inhibitor (GF109203x) blocked the C1q-induced P-selectin expression. Furthermore, pre-incubation of platelets with C1q diminished both the collagen as well as the collagen-related peptide-induced up-regulation of P-selectin, most evident after 90s of stimulation. This indicates that C1q may regulate platelet activation via the GPVI receptor, which is a novel finding. Moreover, C1q antagonized the collagen-induced formation of platelet-neutrophil aggregates, indicating a reduced interaction between platelet P-selectin and neutrophil P-selectin glycoprotein ligand-1(PSGL-1/CD162). In summary, C1q induces a moderate rapid platelet P-selectin expression, modulates subsequent collagen and collagen-related peptide stimulation of platelets, and inhibits the formation of platelet-neutrophil aggregates. These immuno-regulatory effects of C1q may have a crucial role in innate immunity and inflammation. Original Publication:Caroline Skoglund, Jonas Wetterö, Pentti Tengvall and Torbjörn Bengtsson, C1q induces a rapid up-regulation of P-selectin and modulates collagen- and collagen-related peptide-triggered activation in human platelets, 2010, Immunobiology, (215), 12, 987-995.http://dx.doi.org/10.1016/j.imbio.2009.11.004Copyright: Elsevier Science B. V., Amsterdamhttp://www.elsevier.com/

Autologous platelet gel, which is usually prepared by adding thrombin and calcium to a platelet concentrate, is used to accelerate bone repair as a possible alternative to recombinant growth factors (GF), through the osteogenic GF released from a-granules. The advantages of platelet gel lie in its mimicking the GF effects of the physiological bone healing and regenerative processes, in addition to a relatively simple and low cost technique. Moreover, if autologous platelet gel is used, immunological reactions are avoided. In in vitro systems, platelet gel stimulated osteogenic differentiation of bone marrow stromal cells, while it inhibited complete osteoclast differentiation and activation. Moreover, platelet gel favoured endothelial cell proliferation and expression of pro-osteogenic functions. In experimental animals and in clinical application, the efficacy of platelet gel was increased by the combination with bone allografts, acting as scaffolds, and with bone marrow stromal cells. © Springer-Verlag 2009.

In this brief paper we would like to hypothesize that platelets might represent a "peripheral" contributory source for the elevation of plasma glutamate levels in the setting of acute ischemic stroke: available evidence and possible mechanisms will be discussed, especially drawing attention to the possible relevance for the pathophysiology of early neurological deterioration.

Novel synthetic collagen fibers, poly(PHG) made by polycondensation of Pro-Hyp-Gly, spontaneously assume polymeric structure with molecular weights greater than 10(5). Its application for biomaterials has been explored, but that for a platelet agonist has not been investigated. Poly(PHG)-induced platelet aggregation independently of thromboxane A(2) and integrin alpha2beta1. Poly(PHG)-induced tyrosine phosphorylation of glycoprotein VI (GPVI)-related molecules and failed to activate GPVI/FcRgamma-deficient platelets. Binding of GPVI to poly(PHG) was confirmed by a surface plasmon resonance spectroscopy, suggesting that poly(PHG) activates platelets through GPVI. Poly(PHG) is an useful research tool to investigate GPVI-mediated signals and a substitute for collagen in platelet functional assays.

The density of the serotonin transporter in the plasma membranes of blood platelets was evaluated by labelled paroxetine binding in three different groups. These groups were: normal controls, epileptic patients having undergone a recent seizure (less than 4 days before) and patients who equally recently presented psychogenic non-epileptic seizures (pseudoseizures). Real seizures resulted in a significant decrease of membrane serotonin transporter density. In the instances of pseudoseizures, its membrane density was undistinguishable from that of normal controls. These data lend further support to the idea that down regulation of serotonin transporter may play a homeostatic role in the cessation of epileptic seizures.

Overexpression of APP and SOD induces beta-amyloid deposition and oxidative stress in Down syndrome (DS) patients. Both phenomena may impair glutamate transport and decreased glutamate uptake sites have been demonstrated in patient brains at autopsy. Since alterations of APP metabolism and oxidative damage are systemic, we investigated glutamate uptake in platelets and fibroblasts from DS patients to explore whether abnormalities in this process are inherent properties of DS cells and not secondary to neurodegeneration. Glutamate uptake was significantly decreased in platelets (P

Decreased glutamate uptake and a loss of the astrocytic glutamate transporter EAAT2 (GLT-1) have been shown in spinal cord and motor cortex of patients with ALS. Because platelets express the three major glutamate transporter subtypes, including GLT-1, and possess a high-affinity glutamate uptake, the authors investigated glutamate uptake in platelets from patients with ALS and controls. A 43% reduction of high-affinity glutamate uptake rate (p < 0.0001) was observed in patients with ALS compared with normal controls and chronic neurologic disorder patients, suggesting a systemic impairment of glutamate uptake in ALS

Defects in mitochondrial enzymes have been found not only in substantia nigra, but also in platelets from Parkinson's Disease (PD) patients, suggesting a systemic impairment of energy metabolism. Since platelets present an energy-dependent glutamate uptake similar to that described in central nervous system, glutamate uptake was determined in platelets from 34PD patients and 21 age-related normal controls, as Na+-dependent [3H]glutamate influx; glutamate level was also analyzed by reverse-phase HPLC. A 50% reduction of glutamate uptake (p < 0.001) was observed in idiopathic PD patients, respect to controls and secondary parkinsonian syndromes. The decrease correlated with the severity of PD, measured by the UPDRS (r = -0.54; P < 0.05). Glutamate level was increased in platelets of PD patients, but was not correlated to the uptake decrease. Both phoenomena may be explained by the modifications of mitochondrial enzymes described in platelets, which could be used as a peripheral model of glutamatergic function in PD

A 90-kDa protein-actin stable complex was purified from blood platelets by a short and efficient procedure giving at the same time actin used in polymerization assays. 90-kDa protein free of actin was prepared from the complex by 8 M ureau treatment and renaturation. By its molecular mass, immunological cross-reactivity with macrophage gelsolin and its effect on G- and F-actin the 90-kDa protein appears as the platelet gelsolin.

SUMMARY:Pyruvate dehydrogenase (PDH), α -keto gluturate dehydrogenase (α -KGDH) and lipoamide dehydrogenase (LAD) were measured in platelets of II patients with typical Friedreich's ataxia and 10 normal control subjects. Serum LAD was also evaluated in the same patients. No statistically significant changes were found in platelets for the group as a whole, although some patients had low values (more than one standard deviation below control mean). Serum LAD was significantly reduced in the patients with Friedreich's ataxia. This was not due to associated diabetes.

Capping of the barbed-ends of actin filaments is an important mechanism for control of the cytoskeleton. In platelets, a valuable model system, it has been thought that gelsolin was the major capping protein. We now report that platelets contain approximately 2 microM Cap Z, a calcium insensitive heterodimeric capping protein; two major and additional minor isoforms of both alpha and beta subunits are present. In lysates from resting platelets 75-80% of the Cap Z sediments with the high speed pellet, but if the platelets are activated with thrombin for 10 s, about 15% of the Cap Z leaves the pellet fraction and is found in the high speed supernatant where it is not bound to actin. This translocation of Cap Z to the supernatant is also observed when resting platelets are lysed into buffer containing 50-100 microM GTP gamma S and 10 mM EGTA. Our results suggest that release of Cap Z from some actin filaments could generate free filament barbed-ends. An increase in free barbed-ends has been reported in platelet lysates prepared shortly after thrombin activation.

SUMMARY:Pyruvate dehydrogenase (PDH) activity was measured in platelets from 10 patients with Friedreich's ataxia, and 10 age-matched healthy control subjects. Both total PDH and active PDH activity were measured. There were no significant differences between the two groups.

The formation of the major metabolic products of endogenous arachidonic acid (AA) via cyclooxygenase and lipoxygenase pathways in platelets from normal and type IIA hypercholesterolemic subjects was evaluated. 12-Hydroxyeicosatetraenoic acid (12-HETE) and thromboxane B2(TXB2) were determined by selected ion monitoring (SIM) after extraction and purification of collagen stimulated platelet-rich plasma (PRP). The levels of both arachidonic acid metabolites in the non-stimulated PRP of control and type IIA subjects were below the detection limit of the method, rising significantly after collagen stimulation. Both 12-HETE and TXB2 levels in collagen-stimulated PRP samples from the patients were significantly higher than levels in controls (P less than 0.001). In view of the key role of 12-HETE in mediating smooth muscle cell migration and proliferation and in stimulating macrophage activity, these data may provide information for the understanding of the elevated incidence of thrombosis and atheromatous lesion in patients with type IIA hypercholesterolemia.