Human platelets express functional ectonucleotidases that restrict platelet activation signaling

Platelets favor the outgrowth of established metastases

Despite abundant evidence demonstrating that platelets foster metastasis, anti-platelet agents have low therapeutic potential due to the risk of hemorrhages. In addition, whether platelets can regulate metastasis at the late stages of the disease remains unknown. In this study, we subject syngeneic models of metastasis to various thrombocytopenic regimes to show that platelets provide a biphasic contribution to metastasis. While potent intravascular binding of platelets to tumor cells efficiently promotes metastasis, platelets further support the outgrowth of established metastases via immune suppression. Genetic depletion and pharmacological targeting of the glycoprotein VI (GPVI) platelet-specific receptor in humanized mouse models efficiently reduce the growth of established metastases, independently of active platelet binding to tumor cells in the bloodstream. Our study demonstrates therapeutic efficacy when targeting animals bearing growing metastases. It further identifies GPVI as a molecular target whose inhibition can impair metastasis without inducing collateral hemostatic perturbations.

Low ectonucleotidase activity and increased neutrophil-platelet aggregates in patients with antiphospholipid syndrome

ABSTRACT

Many patients with antiphospholipid syndrome had decreased ectonucleotidase activity on neutrophils and platelets, which enabled extracellular nucleotides to trigger neutrophil-platelet aggregates. This phenotype was replicated by treating healthy neutrophils and platelets with patient-derived antiphospholipid antibodies or ectonucleotidase inhibitors.

Ayurvedic preparations of Raudra Rasa inhibit agonist-mediated platelet activation and restrict thrombogenicity without affecting cell viability

Ayurveda is considered to be one of the most ancient forms of medicine still practiced. The Ayurvedic preparation Raudra Rasa and its derivatives have been widely employed against cancer since the 12th century, but the effect of these traditional formulations on platelet function and signaling has not previously been examined. Here we demonstrate that Raudra Rasa and its derivatives significantly reduce thrombin-induced integrin activation and granule secretion in platelets, as observed by reduced PAC-1 binding and P-selectin externalization, respectively. These formulations also inhibited thrombin-stimulated phosphatidylserine exposure, mitochondrial reactive oxygen species generation, and mitochondrial transmembrane potential in platelets. Consistent with the above, Raudra Rasa significantly reduced thrombin-induced tyrosine phosphorylation of the platelet proteins, as well as phosphorylation of the enzymes AKT and GSK-3β. In summary, Raudra Rasa inhibits agonist-mediated platelet activation without affecting cell viability, suggesting it may have therapeutic potential as an anti-platelet/anti-thrombotic agent.

Strategic analysis of body composition indices and resting platelet ATP levels in professional soccer players for better platelet-rich plasma therapy

Background: Autologous platelet-rich plasma (PRP) therapy is ambiguously thought to be more effective in elite athletes than in sedentary patients, although the possible importance of recipient responsiveness remains poorly understood. To address this issue, along with the well-known PRP quality, in this initial study, we evaluated two candidate biomarkers: body composition indices (BCIs), which reflect systemic physical conditions, and resting platelet ATP levels, which reflect platelet energy expenditure and the mass of energy generation units. Methods: In this cross-sectional cohort study, blood samples were collected from male professional soccer players (PSPs) on a local professional team during the off-season and platelet ATP levels were quantified using an ATP luminescence assay kit. BCIs were measured using the body mass impedance method. Age-matched male sedentary participants were used as the controls. Results: Among the BCIs, the body mass index, basal metabolic rate (BMR), and skeletal muscle weight levels were higher in the PSPs than in the controls. The platelet ATP levels in the PSPs group were significantly lower than those in the control group. The correlation between BMR and platelet ATP levels was moderately negative in the control group, but weakly positive in the PSPs group. Conclusion: Owing to regular physical exercise, PSPs had higher BMR levels and lower platelet ATP levels without a significant mutual correlation compared to sedentary controls. This study did not indicate the influence of these biomarkers on the success of PRP therapy but provided evidence for a better understanding of PRP therapy, particularly for elite athletes.

The role of platelets in immune-mediated inflammatory diseases

Immune-mediated inflammatory diseases (IMIDs) are characterized by excessive and uncontrolled inflammation and thrombosis, both of which are responsible for organ damage, morbidity and death. Platelets have long been known for their role in primary haemostasis, but they are now also considered to be components of the immune system and to have a central role in the pathogenesis of IMIDs. In patients with IMIDs, platelets are activated by disease-specific factors, and their activation often reflects disease activity. Here we summarize the evidence showing that activated platelets have an active role in the pathogenesis and the progression of IMIDs. Activated platelets produce soluble factors and directly interact with immune cells, thereby promoting an inflammatory phenotype. Furthermore, platelets participate in tissue injury and promote abnormal tissue healing, leading to fibrosis. Targeting platelet activation and targeting the interaction of platelets with the immune system are novel and promising therapeutic strategies in IMIDs.

Tripeptide Hyp-Asp-Gly from collagen peptides inhibited platelet activation via regulation of PI3K/Akt-MAPK/ERK1/2 signaling pathway

Platelet activation is involved in cardiovascular thrombosis. Our previous study demonstrated that oral administration of collagen peptides (CPs) inhibited platelet activation, but the mechanism of action of CPs remained to be elucidated. As a continued effort, the objective of this study was to identify the active ingredient of CPs and clarify its molecular mechanism. Simulated absorbate of CPs was prepared by simulated gastrointestinal digestion and intestinal absorption system, and then separated by C18 column. The fraction with the highest antiplatelet activity was subjected to NanoUPLC-ESI-MS/MS for peptide sequencing. Novel tripeptide Hyp-Asp-Gly (ODG) was identified. It had a broad-spectrum inhibition of platelet activation induced by collagen, thrombin, and adenosine diphosphate (ADP). ODG could survive simulated gastrointestinal digestion and be absorbed intact. Furthermore, it showed good stability in plasma. ODG had no significant effect on the PLC-PKC-Ca²⁺ pathway, but it inhibited the PI3K/Akt-MAPK/ERK1/2 signaling. At a dosage of 200 µmol/kg body weight, ODG had an in vivo anti-thrombosis activity without bleeding risk. The present study provides one of the mechanisms of action of CPs and highlights its potential use as a functional component to combat cardiovascular thrombosis. PRACTICAL APPLICATION: This study has suggested that tripeptide Hyp-Asp-Gly(ODG) derived from collagen have potent activities. This novel collagen peptide had a greatpotential to be applied to combat cardiovascular thrombosis in the foodindustry. Meanwhile, this work is expected to provide a theoretical basis forthe development of safe and effective anti-platelet and anti-thrombosis peptides.

Thrombo-Inflammation: A Focus on NTPDase1/CD39

There is increasing evidence for a link between inflammation and thrombosis. Following tissue injury, vascular endothelium becomes activated, losing its antithrombotic properties whereas inflammatory mediators build up a prothrombotic environment. Platelets are the first elements to be activated following endothelial damage; they participate in physiological haemostasis, but also in inflammatory and thrombotic events occurring in an injured tissue. While physiological haemostasis develops rapidly to prevent excessive blood loss in the endothelium activated by inflammation, hypoxia or by altered blood flow, thrombosis develops slowly. Activated platelets release the content of their granules, including ATP and ADP released from their dense granules. Ectonucleoside triphosphate diphosphohydrolase-1 (NTPDase1)/CD39 dephosphorylates ATP to ADP and to AMP, which in turn, is hydrolysed to adenosine by ecto-5'-nucleotidase (CD73). NTPDase1/CD39 has emerged has an important molecule in the vasculature and on platelet surfaces; it limits thrombotic events and contributes to maintain the antithrombotic properties of endothelium. The aim of the present review is to provide an overview of platelets as cellular elements interfacing haemostasis and inflammation, with a particular focus on the emerging role of NTPDase1/CD39 in controlling both processes.

Cyclin Y is expressed in Platelets and Modulates Integrin Outside-in Signaling

Diabetes is associated with platelet hyper-reactivity and enhanced risk of thrombosis development. Here we compared protein expression in platelets from healthy donors and diabetic patients to identify differentially expressed proteins and their possible function in platelet activation. Mass spectrometry analyses identified cyclin Y (CCNY) in platelets and its reduced expression in platelets from diabetic patients, a phenomenon that could be attributed to the increased activity of calpains. To determine the role of CCNY in platelets, mice globally lacking the protein were studied. CCNY^-/- mice demonstrated lower numbers of circulating platelets but platelet responsiveness to thrombin and a thromboxane A₂ analogue were comparable with that of wild-type mice, as was agonist-induced α and dense granule secretion. CCNY-deficient platelets demonstrated enhanced adhesion to fibronectin and collagen as well as an attenuated spreading and clot retraction, indicating an alteration in "outside in" integrin signalling. This phenotype was accompanied by a significant reduction in the agonist-induced tyrosine phosphorylation of β3 integrin. Taken together we have shown that CCNY is present in anucleated platelets where it is involved in the regulation of integrin-mediated outside in signalling associated with thrombin stimulation.

Implications of CD39 in immune-related diseases

Extracellular adenosine triphosphate (eATP) mediates pro-inflammatory responses by recruiting and activating inflammatory cells. CD39 can hydrolyze eATP into adenosine monophosphate (AMP), while CD73 can convert AMP into the immunosuppressive nucleoside adenosine (ADO). CD39 is a rate-limiting enzyme in this cascade, which is regarded as an immunological switch shifting the ATP-mediated pro-inflammatory environment to the ADO- mediated anti-inflammatory status. The CD39 expression can be detected in a wide spectrum of immunocytes, which is under the influence of environmental and genetic factors. It is increasingly suggested that, CD39 participates in some pathophysiological processes, like inflammatory bowel disease (IBD), sepsis, multiple sclerosis (MS), allergic diseases, ischemia-reperfusion (I/R) injury, systemic lupus erythematosus (SLE), diabetes and cancer. Here, we focus on the current understanding of CD39 in immunity, and comprehensively illustrate the diverse CD39 functions within a variety of disorders.