P2Y12 regulates platelet adhesion/activation, thrombus growth, and thrombus stability in injured arteries

Modeling platelet P2Y1/12 pathway to integrin activation

Through experimental studies, many details of the pathway of integrin αIIbβ3 activation by ADP during the platelet aggregation process have been mapped out. ADP binds to two separate G protein-coupled receptors on platelet surfaces, leading to alterations in the regulation of the small GTPase RAP1. We seek to 1) gain insights into the relative contributions of both pathways to RAP1-mediated integrin activation and to 2) predict wild-type and mutated cell behavior in response to a continuous range of external agonist concentrations. To this end, we develop a dynamical systems model detailing the action of each protein in the two pathways up to the regulation of RAP1. We perform a parameter estimation using flow-cytometry data to determine a number of unknown rate constants. We then validate with already-published data; in particular, the model confirmed the effect of impaired P2Y1 receptor desensitization or reduced RASA3 expression on RAP1 activation. We then predict the effect of protein expression levels on integrin activation and show that components of the P2Y12 pathway are critical to the regulation of integrin. This model aids in our understanding of interindividual variability in platelet response to ADP and therapeutic P2Y12 inhibition. It also provides a more detailed view of platelet activation in the ongoing mathematical study of platelet aggregation.

Design and Pharmacological Characterization of a Novel Antithrombotic P2Y1 Receptor-Based Vaccine

Platelet activation processes begin when injury to blood vessels exposes the subendothelial matrix, leading platelets to attach to it, where they become activated and exert their hemostatic function. Excessive platelet aggregation is associated with thrombotic disorders such as arterial thrombosis. To manage such diseases, medications that inhibit thrombosis are continuously sought, despite potential drawbacks that include hemorrhage. This study described the development of a novel peptide-based vaccine that targets the purinergic ADP P2Y1 receptor (abbreviated EL2Vac) and its pharmacological characterization. Thus, we designed and developed an EL2Vac that targets the ligand-binding domain of the P2Y1 receptor protein, which is located in its second extracellular loop (EL2). We then evaluated the vaccine's ability to trigger an immune response (antibody production) in immunized mice, modulate platelet function, its antithrombotic activity, and any effects on hemostasis, by employing a thrombosis model and the tail bleeding time assay. Results showed significant levels of antibody production in mice treated with EL2Vac, in comparison with the random peptide vaccine control (EL2rVac), which persisted at least up to six months post vaccination. Moreover, we observed significant inhibition of the ADP-induced aggregation response in platelets from EL2Vac-treated mice, relative to those from EL2rVac controls. This inhibition was selective for ADP, as other agonists, such as the thromboxane A2 receptor (TPR) agonist U46619 or high-dose collagen, had no detectable effect on aggregation. As for its capacity to protect against thrombosis, our data showed a significant delay in the occlusion time of the EL2Vac mice when compared with the random peptide control vaccine, which was also observed (at least) six months post vaccination. Interestingly, EL2Vac did not appear to prolong the tail bleeding time, supporting the notion that it is devoid of a bleeding diathesis. As a conclusion, this study documents the design and evaluation of a novel peptide-based vaccine, EL2Vac, which appears to selectively target the P2Y1 receptor and protect against thrombus formation without impairing hemostasis. Thus, EL2Vac may provide a promising clinical option to treat thromboembolic disorders.

Biological sex, microglial signaling pathways, and radiation exposure shape cortical proteomic profiles and behavior in mice

Patients receiving cranial radiation therapy experience tissue damage and cognitive deficits that severely decrease their quality of life. Experiments in rodent models show that these adverse neurological effects are in part due to functional changes in microglia, the resident immune cells of the central nervous system. Increasing evidence suggests that experimental manipulation of microglial signaling can regulate radiation-induced changes in the brain and behavior. Furthermore, many studies show sex-dependent neurological effects of radiation exposure. Despite this, few studies have used both males and females to explore how sex and microglial function interact to influence radiation effects on the brain. Here, we used a system levels approach to examine how deficiencies in purinergic and fractalkine signaling, two important microglial signaling pathways, impact brain proteomic and behavioral profiles in irradiated and control male and female mice. We performed a comprehensive analysis of the cortical proteomes from irradiated and control C57BL/6J, P2Y12-/-, and CX3CR1-/- mice of both sexes using multiple bioinformatics methods. We identified distinct proteins and biological processes, as well as behavioral profiles, regulated by sex, genotype, radiation exposure, and their interactions. Disrupting microglial signaling, had the greatest impact on proteomic expression, with CX3CR1-/- mice showing the most distinct proteomic profile characterized by upregulation of CX3CL1. Surprisingly, radiation exposure caused relatively smaller proteomic changes in glial and synaptic proteins, including Rgs10, Crybb1, C1qa, and Hexb. While we observed some radiation effects on locomotor behavior, biological sex as well as loss of P2Y12 and CX3CR1 signaling had a stronger influence on locomotor outcomes in our model. Lastly, loss of P2Y12 and CX3CR1 strongly regulated exploratory behaviors. Overall, our findings provide novel insights into the molecular pathways and proteins that are linked to P2Y12 and CX3CR1 signaling, biological sex, radiation exposure, and their interactions.

Platelets isolation and ectonucleotidase assay: Revealing functional aspects of the communication between the vasculature and the immune system

Platelets are enucleated fragments of cells with a diversity of internal granules. They are responsible for functions related to hemostasis, coagulation, and inflammation. The activation of these processes depends on a cascade coordinated by cytokines, chemokines, and components of purinergic signaling, such as ATP, ADP, and adenosine. Platelets express distinct components of the purinergic system: P2X1, P2Y1, PY12, and P2Y14 receptors; and the ectonucleotidases NTPDase, NPP, and 5NTE (ecto-5'-nucleotidase). Except for P2Y14, which has not yet exhibited a known function, all other components relate to the biological processes mentioned before. Platelets are known to display specific responses to microorganisms, being capable of recognizing pathogen-associated molecular patterns (PAMPs), engulfing certain classes of viruses, and participating in NETosis. Platelet function dysregulation implicates various pathophysiological processes, including cardiovascular diseases (CVDs) and infections. In COVID-19 patients, platelets exhibit altered purinergic signaling and increased activation, contributing to inflammation. Excessive platelet activation can lead to complications from thrombosis, which can affect the circulation of vital organs. Therefore, controlling the activation is necessary to end the inflammatory process and restore homeostasis. Ectonucleotidases, capable of hydrolyzing ATP, ADP, and AMP, are of fundamental importance in activating platelets, promising pharmacological targets for clinical use as cardiovascular protective drugs. In this review, we revisit platelet biology, the purinergic receptors and ectonucleotidases on their surface, and their importance in platelet activity. Additionally, we describe methods for isolating platelets in humans and murine, as well as the main techniques for detecting the activity of ectonucleotidases in platelets. Considering the multitude of functions revealed by platelets and their potential use as potent bioreactors able to secrete and present molecules involved in the communication of the vasculature with the immune system, it is crucial to deeply understand platelet biology and purinergic signaling participation to contribute to the developing of therapeutic strategies in diseases of the cardiovascular, inflammatory, and immune systems.

A Systematic Review on Biochemical Perspectives on Natural Products in Wound Healing: Exploring Phytochemicals in Tissue Repair and Scar Prevention

Wound healing is a critical process in tissue repair following injury, and traditional herbal therapies have long been utilized to facilitate this process. This review delves into the mechanistic understanding of the significant contribution of pharmacologically demonstrated natural products in wound healing. Natural products, often perceived as complex yet safely consumed compared to synthetic chemicals, play a crucial role in enhancing the wound-healing process. Drawing upon a comprehensive search strategy utilizing databases such as PubMed, Scopus, Web of Science, and Google Scholar, this review synthesizes evidence on the role of natural products in wound healing. While the exact pharmacological mechanisms of secondary metabolites in wound healing remain to be fully elucidated, compounds from alkaloids, phenols, terpenes, and other sources are explored here to delineate their specific roles in wound repair. Each phytochemical group exerts distinct actions in tissue repair, with some displaying multifaceted roles in various pathways, potentially enhancing their therapeutic value, supported by reported safety profiles. Additionally, these compounds exhibit promise in the prevention of keloids and scars. Their potential alongside economic feasibility may propel them towards pharmaceutical product development. Several isolated compounds, including chlorogenic acid, thymol, and eugenol from natural sources, are undergoing investigation in clinical trials, with many reaching advanced stages. This review provides mechanistic insights into the significant role of pharmacologically demonstrated natural products in wound healing processes.

Weisheng-tang protects against ischemic brain injury by modulating microglia activation through the P2Y12 receptor

Background: Stroke, a leading cause of death and disability, lacks effective treatments. Post-stroke secondary damage worsens the brain microenvironment, further exacerbating brain injury. Microglia's role in responding to stroke-induced damage in peri-infarct regions is crucial. In this study, we explored Weisheng-tang's potential to enhance ischemic outcomes by targeting microglia. Methods: We induced middle cerebral artery occlusion and reperfusion in mice, followed by behavioral assessments and infarct volume analyses after 48 h, and examined the changes in microglial morphology through skeleton analysis. Results: Weisheng-tang (300 mg/kg) significantly reduced infarction volume and alleviated neurological and motor deficits. The number of activated microglia was markedly increased within the peri-infarct territory, which was significantly reversed by Weisheng-tang. Microglial morphology analysis revealed that microglial processes were retracted owing to ischemic damage but were restored in Weisheng-tang-treated mice. This restoration was accompanied by the expression of the purinergic P2Y12 receptor (P2Y12R), a key regulator of microglial process extension. Weisheng-tang increased neuronal Kv2.1 clusters while suppressing juxtaneuronal microglial activation. The P2Y12R inhibitor-ticagrelor-eliminated the tissue and functional recovery that had been observed with Weisheng-tang after ischemic damage. Discussion: Weisheng-tang improved experimental stroke outcomes by modulating microglial morphology through P2Y12R, shedding light on its neuroprotective potential in ischemic stroke.

G-protein coupled receptors regulates Tauopathy in neurodegeneration

In Alzheimer's disease, the microtubule-associated protein, Tau misfolds to form aggregates and filaments in the intra- and extracellular region of neuronal cells. Microglial cells are the resident brain macrophage cells involved in constant surveillance and activated by the extracellular deposits. Purinergic receptors are involved in the chemotactic migration of microglial cells towards the site of inflammation. From our recent study, we have observed that the microglial P2Y12 receptor is involved in phagocytosis of full-length Tau species such as monomers, oligomers and aggregates by actin-driven chemotaxis. This study shows the interaction of repeat-domain of Tau (TauRD) with the microglial P2Y12 receptor and the corresponding residues for interaction have been analyzed by various in-silico approaches. In the cellular studies, TauRD was found to interact with microglial P2Y12R and induces its cellular expression confirmed by co-immunoprecipitation and western blot analysis. Furthermore, the P2Y12R-mediated TauRD internalization has demonstrated activation of microglia with an increase in the Iba1 level, and TauRD becomes accumulated at the peri-nuclear region for the degradation.

Current Strategies to Guide the Antiplatelet Therapy in Acute Coronary Syndromes

The role of antiplatelet therapy in patients with acute coronary syndromes is a moving target with considerable novelty in the last few years. The pathophysiological basis of the treatment depends on platelet biology and physiology, and the interplay between these aspects and clinical practice must guide the physician in determining the best therapeutic options for patients with acute coronary syndromes. In the present narrative review, we discuss the latest novelties in the antiplatelet therapy of patients with acute coronary syndromes. We start with a description of platelet biology and the role of the main platelet signal pathways involved in platelet aggregation during an acute coronary syndrome. Then, we present the latest evidence on the evaluation of platelet function, focusing on the strengths and weaknesses of each platelet's function test. We continue our review by describing the role of aspirin and P2Y12 inhibitors in the treatment of acute coronary syndromes, critically appraising the available evidence from clinical trials, and providing current international guidelines and recommendations. Finally, we describe alternative therapeutic regimens to standard dual antiplatelet therapy, in particular for patients at high bleeding risk. The aim of our review is to give a comprehensive representation of current data on antiplatelet therapy in patients with acute coronary syndromes that could be useful both for clinicians and basic science researchers to be up-to-date on this complex topic.

Flow cytometry for comprehensive assessment of platelet functional activity in response to ADP stimulation

OBJECTIVES

Flow cytometry with adenosine diphosphate (ADP) allows to characterize molecular changes of platelet function caused by this physiologically important activation, but the methodology has not been thoroughly investigated, standardized and characterized yet. We analyzed the influence of several major variables and chose optimal conditions for platelet function assessment.

METHODS

For activation, 2.5 μM CaCl2 , 5 μM ADP and antibodies were added to diluted blood and incubated for 15 min. We analyzed kinetics of antibody binding and effects of their addition sequence, agonist concentration, blood dilution, exogenous calcium addition and platelet fixation.

RESULTS

We tested our protocol on 11 healthy children, 22 healthy adult volunteers, 9 patients after a month on dual antiplatelet therapy after percutaneous coronary intervention (PCI), 7 adult patients and 14 children with immune thrombocytopenia (ITP). We found that our protocol is highly sensitive to ADP stimulation with low percentage of aggregates formation. The assay is also sensitive to platelet function inhibition in post-PCI patients. Finally, platelet preactivation with ITP plasma was stronger and caused increase in activation response to ADP stimulation compared to preactivation with low dose of ADP.

CONCLUSIONS

Our assay is sensitive to antiplatelet therapy and platelet preactivation in ITP patients under physiological conditions with minimal percentage of aggregates formation.

Blood oxygen regulation via P2Y12R expressed in the carotid body

BACKGROUND

Peripheral blood oxygen monitoring via chemoreceptors in the carotid body (CB) is an integral function of the autonomic cardiorespiratory regulation. The presence of the purinergic P2Y12 receptor (P2Y12R) has been implicated in CB; however, the exact role of the receptor in O2 sensing and signal transduction is unknown.

METHODS

The presence of P2Y12R was established by immunoblotting, RT qPCR and immunohistochemistry. Primary glomus cells were used to assess P2Y12R function during hypoxia and hypercapnia, where monoamines were measured by HPLC; calcium signal was recorded utilizing OGB-1 and N-STORM Super-Resolution System. Ingravescent hypoxia model was tested in anaesthetized mice of mixed gender and cardiorespiratory parameters were recorded in control and receptor-deficient or drug-treated experimental animals.

RESULTS

Initially, the expression of P2Y12R in adult murine CB was confirmed. Hypoxia induced a P2Y12R-dependent release of monoamine transmitters from isolated CB cells. Receptor activation with the endogenous ligand ADP promoted release of neurotransmitters under normoxic conditions, while blockade disrupted the amplitude and duration of the intracellular calcium concentration. In anaesthetised mice, blockade of P2Y12R expressed in the CB abrogated the initiation of compensatory cardiorespiratory changes in hypoxic environment, while centrally inhibited receptors (i.e. microglial receptors) or receptor-deficiency induced by platelet depletion had limited influence on the physiological adjustment to hypoxia.

CONCLUSIONS

Peripheral P2Y12R inhibition interfere with the complex mechanisms of acute oxygen sensing by influencing the calcium signalling and the release of neurotransmitter molecules to evoke compensatory response to hypoxia. Prospectively, the irreversible blockade of glomic receptors by anti-platelet drugs targeting P2Y12Rs, propose a potential, formerly unrecognized side-effect to anti-platelet medications in patients with pulmonary morbidities.

Interaction of Tau with G-Protein-Coupled Purinergic P2Y12 Receptor by Molecular Docking and Molecular Dynamic Simulation

Alzheimer's disease, a progressive neurological disorder, is characterized by the accumulation of neurofibrillary tangles and senile plaques by Tau and amyloid-β, respectively, in the brain microenvironment. The misfolded protein aggregates interact with several components of neuronal and glial cells such as membrane lipids, receptors, transporters, enzymes, cytoskeletal proteins, etc. Under pathological conditions, Tau interacts with several G-protein-coupled receptors (GPCRs), which undergoes either receptor signaling or desensitization followed by internalization of the protein complex. The purinergic GPCR, P2Y12 which is expressed in microglial cells, plays a key role in its activation and migration. Microglial cells sense and migrate to the site of injury aided by P2Y12 receptor that interacts with ADP released from damaged cells. P2Y12 receptor also interacts with misfolded Tau accumulated at the extracellular space and promotes receptor-mediated internalization. Immunocolocalization and co-immunoprecipitation studies demonstrated the interaction of Tau species with the P2Y12 receptor. Later, in-silico analyses were carried out with the repeat domain of Tau (TauRD), which has been identified as the interacting partner of P2Y12 receptor by in-vitro studies. Molecular docking and molecular dynamics simulation studies show the stability and the type of interaction in TauRD-receptor complex. Tau interaction with P2Y12 receptor plays a significant role in maintaining the active state of microglia which could lead to neuroinflammation and neuronal damage in AD brain. Hence, blocking P2Y12-Tau interaction and P2Y12-mediated Tau internalization in microglial cells could be possible therapeutic strategies in downregulating the severity of neuroinflammation in AD.

Microglia are involved in regulating histamine-dependent and non-dependent itch transmissions with distinguished signal pathways

Although itch and pain have many similarities, they are completely different in perceptual experience and behavioral response. In recent years, we have a deep understanding of the neural pathways of itch sensation transmission. However, there are few reports on the role of non-neuronal cells in itch. Microglia are known to play a key role in chronic neuropathic pain and acute inflammatory pain. It is still unknown whether microglia are also involved in regulating the transmission of itch sensation. In the present study, we used several kinds of transgenic mice to specifically deplete CX3CR1+ microglia and peripheral macrophages together (whole depletion), or selectively deplete microglia alone (central depletion). We observed that the acute itch responses to histamine, compound 48/80 and chloroquine were all significantly reduced in mice with either whole or central depletion. Spinal c-fos mRNA assay and further studies revealed that histamine and compound 48/80, but not chloroquine elicited primary itch signal transmission from DRG to spinal Npr1- and somatostatin-positive neurons relied on microglial CX3CL1-CX3CR1 pathway. Our results suggested that microglia were involved in multiple types of acute chemical itch transmission, while the underlying mechanisms for histamine-dependent and non-dependent itch transmission were different that the former required the CX3CL1-CX3CR1 signal pathway.

Protease-activated receptors and glycoprotein VI cooperatively drive the platelet component in thromboelastography

BACKGROUND

Thromboelastography (TEG) is used for real-time determination of hemostatic status in patients with acute risk of bleeding. Thrombin is thought to drive clotting in TEG through generation of polymerized fibrin and activation of platelets through protease-activated receptors (PARs). However, the specific role of platelet agonist receptors and signaling in TEG has not been reported.

OBJECTIVES

Here, we investigated the specific receptors and signaling pathways required for platelet function in TEG using genetic and pharmacologic inhibition of platelet proteins in mouse and human blood samples.

METHODS

Clotting parameters (R time, α-angle [α], and maximum amplitude [MA]), were determined in recalcified, kaolin-triggered citrated blood samples using a TEG 5000 analyzer.

RESULTS

We confirmed the requirement of platelets, platelet contraction, and αIIbβ3 integrin function for normal α and MA. Loss of the integrin adaptor Talin1 in megakaryocytes/platelets (Talin1mKO) also reduced α and MA, but only minimal defects were observed in samples from mice lacking Rap1 GTPase signaling. PAR4mKO samples showed impaired α but normal MA. However, impaired TEG traces similar to those in platelet-depleted samples were observed with samples from PAR4mKO mice depleted of glycoprotein VI on platelets or with addition of a Syk inhibitor. We reproduced these results in human blood with combined inhibition of PAR1, PAR4, and Syk.

CONCLUSION

Our results demonstrate that standard TEG is not sensitive to platelet signaling pathways critical for integrin inside-out activation and platelet hemostatic function. Furthermore, we provide the first evidence that PARs and glycoprotein VI play redundant roles in platelet-mediated clot contraction in TEG.

Purinergic receptor P2Y12 boosts autoimmune hepatitis through hexokinase 2-dependent glycolysis in T cells

Increasing evidence suggests that immunometabolism has started to unveil the role of metabolism in shaping immune function and autoimmune diseases. In this study, our data show that purinergic receptor P2Y12 (P2RY12) is highly expressed in concanavalin A (ConA)-induced immune hepatitis mouse model and serves as a potential metabolic regulator in promoting metabolic reprogramming from oxidative phosphorylation to glycolysis in T cells. P2RY12 deficiency or inhibition of P2RY12 with P2RY12 inhibitors (clopidogrel and ticagrelor) are proved to reduce the expression of inflammatory mediators, cause CD4⁺ and CD8⁺ effector T cells hypofunction and protect the ConA-induced immune hepatitis. A combined proteomics and metabolomics analysis revealed that P2RY12 deficiency causes redox imbalance and leads to reduced aerobic glycolysis by downregulating the expression of hexokinase 2 (HK2), a rate-limiting enzyme of the glycolytic pathway, indicating that HK2 might be a promising candidate for the treatment of diseases associated with T cell activation. Further analysis showed that P2RY12 prevents HK2 degradation by activating the PI3K/Akt pathway and inhibiting lysosomal degradation. Our findings highlight the importance of the function of P2RY12 for HK2 stability and metabolism in the regulation of T cell activation and suggest that P2RY12 might be a pivotal regulator of T cell metabolism in ConA-induced immune hepatitis.

miR-6076 rs1463411 polymorphisms are associated with bleeding during clopidogrel treatment in patients with acute coronary syndrome

Bleeding is a major adverse event during clopidogrel treatment in patients with acute coronary syndrome (ACS). However, the potential mechanism affecting bleeding among individuals is unclear. Herein, we investigated the involvement of CYP2C19*2 and CYP2C19*3, as well as 10 miRNA polymorphisms, in bleeding in Chinese patients with ACS during the first year of clopidogrel treatment. The miR-6076 rs1463411 G polymorphism was significantly associated with the risk of bleeding (P < 0.001), and the rs1463411 GT + GG genotype significantly increased the risk of bleeding (adjusted odds ratio, 6.09; 95% confidence interval, 1.09-34.0; P < 0.001). Dual luciferase assay showed that miR-6076 significantly decreased the mRNA expression of P2RY12 (P < 0.05). P2RY12 mRNA and protein levels were significantly lower in cells transfected with miR-6076-G than in cells transfected with miR-6076-T (P < 0.05). The findings indicate that miR-6076 targets P2RY12 mRNA and that miR-6076 rs1463411 T/G polymorphisms differentially regulate P2RY12 mRNA and protein levels in cells. rs1463411 G polymorphism may increase the risk of bleeding during clopidogrel treatment in patients with ACS.

An Optically Controlled Virtual Microsensor for Biomarker Detection In Vivo

Current technologies for the real-time analysis of biomarkers in vivo, such as needle-type microelectrodes and molecular imaging methods based on exogenous contrast agents, are still facing great challenges in either invasive detection or lack of active control of the imaging probes. In this study, by combining the design concepts of needle-type microelectrodes and the fluorescence imaging method, a new technique is developed for detecting biomarkers in vivo, named as "optically controlled virtual microsensor" (OCViM). OCViM is established by the organic integration of a specially shaped laser beam and fluorescent nanoprobe, which serve as the virtual handle and sensor tip, respectively. The laser beam can trap and manipulate the nanoprobe in a programmable manner, and meanwhile excite it to generate fluorescence emission for biosensing. On this basis, fully active control of the nanoprobe is achieved noninvasively in vivo, and multipoint detection can be realized at sub-micrometer resolution by shifting a nanoprobe among multiple positions. By using OCViM, the overexpression and heterogenous distribution of biomarkers in the thrombus is studied in living zebrafish, which is further utilized for the evaluation of antithrombotic drugs. OCViM may provide a powerful tool for the mechanism study of thrombus progression and the evaluation of antithrombotic drugs.

Construction of enzyme-laden vascular scaffolds based on hyaluronic acid oligosaccharides-modified collagen nanofibers for antithrombosis and in-situ endothelialization of tissue-engineered blood vessels

The current use of synthetic grafts often yields low patency in the reconstruction of small-diameter blood vessels owing to the deposition of thrombi and imperfect coverage of the endothelium on the graft lumen. Therefore, the design of vascular scaffolds with antithrombotic performance and endothelialization is greatly required. Herein, we developed an enzyme-laden scaffold based on hyaluronic acid oligosaccharides-modified collagen nanofibers (labeled HA-COL) to improve the anti-platelet capacity and endothelialization of vascular grafts. In this study, HA-COL nanofibers not only encouraged the endothelialization of vascular scaffolds, but acted as an antiplatelet enzyme-laden platform. Apyrase (Apy) and 5'-nucleotidase (5'-NT) were covalently grafted onto the nanofibers, which in turn converted the platelet-sensitive substance: adenosine diphosphate (ADP) into adenosine monophosphate (AMP) and adenosine, thereby, improving the antithrombotic performance of the scaffolds. Notably, the catalytic end-product: adenosine would work in coordination with HA-COL to synergistically enhance the endothelialization of the vascular scaffolds. The results demonstrated that the enzyme-laden scaffolds maintained catalytic performance, reduced platelet adhesion and aggregation, and guaranteed higher patency after 1-month in situ transplantation. Moreover, these scaffolds showed optimal cytocompatibility, tissue compatibility, scaffold biodegradability and tissue regenerative capability during in vivo implantation. Overall, these engineered vascular scaffolds demonstrated their capacity for endothelialization and antithrombotic performance, suggesting their potential for small-diameter vascular tissue engineering applications. STATEMENT OF SIGNIFICANCE: Considering the critical problems in small-diameter vascular reconstruction, the enzyme-laden vascular scaffolds were prepared for improving in-situ endothelialization and antithrombotic performances of artificial blood vessels. The electrospun HA-COL nanofibers were used as the main matrix materials, which provided favorable structural templates for the regeneration of vasculature and functioned as a platform for the loading of enzymes. The enzyme-laden scaffolds with the biomimetic cascading reaction would convert ADP into adenosine, thereby, decreasing the sensitivity of platelets and improving the antithrombotic performance of tissue-engineered blood vessels (TEBVs). The nanofibrous scaffolds exhibited optimal cytocompatibility, tissue compatibility and regenerative capability, working together with catalytic products of dual-enzyme reaction that would synergistically contribute to TEBVs endothelialization. This study provides a new method for the improvement of in-situ endothelialization of small-diameter TEBVs while qualified with antithrombotic performance.

Several Non-salt and Solid Thienopyridine Derivatives as Oral P2Y12 Receptor Inhibitors with Good Stability

A series of novel thienopyridine derivatives were designed and synthesized as P2Y₁₂ receptor inhibitors. Several solid compounds were assessed for inhibitory effect where they exhibited stronger potency than clopidogrel. Compound 6b and 6g were evaluated for metabolism to verify that they could overcome clopidogrel resistance and for toxicity where they showed lower toxicity than prasugrel. Compound 6b exhibited lower risk of bleeding than prasugrel and showed good stability under stress testing. Overall, as a promising antiplatelet agent, representative compound 6b showed the following advantages: (1) no drug resistance for CYP2C19 poor metabolizers; (2) higher potency than clopidogrel; (3) lower toxicity than prasugrel; (4) lower risk of bleeding than prasugrel; (5) good stability as a non-salt solid.

Immune-vascular mural cell interactions: consequences for immune cell trafficking, cerebral blood flow, and the blood-brain barrier

Brain barriers are crucial sites for cerebral energy supply, waste removal, immune cell migration, and solute exchange, all of which maintain an appropriate environment for neuronal activity. At the capillary level, where the largest area of brain-vascular interface occurs, pericytes adjust cerebral blood flow (CBF) by regulating capillary diameter and maintain the blood-brain barrier (BBB) by suppressing endothelial cell (EC) transcytosis and inducing tight junction expression between ECs. Pericytes also limit the infiltration of circulating leukocytes into the brain where resident microglia confine brain injury and provide the first line of defence against invading pathogens. Brain "waste" is cleared across the BBB into the blood, phagocytosed by microglia and astrocytes, or removed by the flow of cerebrospinal fluid (CSF) through perivascular routes-a process driven by respiratory motion and the pulsation of the heart, arteriolar smooth muscle, and possibly pericytes. "Dirty" CSF exits the brain and is probably drained around olfactory nerve rootlets and via the dural meningeal lymphatic vessels and possibly the skull bone marrow. The brain is widely regarded as an immune-privileged organ because it is accessible to few antigen-primed leukocytes. Leukocytes enter the brain via the meninges, the BBB, and the blood-CSF barrier. Advances in genetic and imaging tools have revealed that neurological diseases significantly alter immune-brain barrier interactions in at least three ways: (1) the brain's immune-privileged status is compromised when pericytes are lost or lymphatic vessels are dysregulated; (2) immune cells release vasoactive molecules to regulate CBF, modulate arteriole stiffness, and can plug and eliminate capillaries which impairs CBF and possibly waste clearance; and (3) immune-vascular interactions can make the BBB leaky via multiple mechanisms, thus aggravating the influx of undesirable substances and cells. Here, we review developments in these three areas and briefly discuss potential therapeutic avenues for restoring brain barrier functions.

A Rare Case of Clopidogrel-Induced Migratory Polyarthritis in a Patient With Recent Myocardial Infarction

Clopidogrel is an antiplatelet drug used for secondary prevention of myocardial infarction, and it is also used in patients with cerebrovascular ischemia. Patients with acute myocardial infarction tend to be on dual antiplatelet therapy for 12 months followed by aspirin lifelong to prevent the risk of stent thrombosis. The most common side effects of clopidogrel are bleeding, neutropenia, and rash; however, arthritis is also one of the rare side effects. We present a case of a 53-year-old patient who had a recent myocardial infarction and was commenced on dual antiplatelet therapy in the form of aspirin and clopidogrel. He started to have severe joint pain, particularly in his knees and shoulders, and was not able to mobilize anymore only three weeks after starting the medications. His clopidogrel was stopped and the patient showed dramatic improvement within three to four days after discontinuation with complete resolution one week later.

Capillary-associated microglia regulate vascular structure and function through PANX1-P2RY12 coupling in mice

Microglia are brain-resident immune cells with a repertoire of functions in the brain. However, the extent of their interactions with the vasculature and potential regulation of vascular physiology has been insufficiently explored. Here, we document interactions between ramified CX3CR1 + myeloid cell somata and brain capillaries. We confirm that these cells are bona fide microglia by molecular, morphological and ultrastructural approaches. Then, we give a detailed spatio-temporal characterization of these capillary-associated microglia (CAMs) comparing them with parenchymal microglia (PCMs) in their morphological activities including during microglial depletion and repopulation. Molecularly, we identify P2RY12 receptors as a regulator of CAM interactions under the control of released purines from pannexin 1 (PANX1) channels. Furthermore, microglial elimination triggered capillary dilation, blood flow increase, and impaired vasodilation that were recapitulated in P2RY12-/- and PANX1-/- mice suggesting purines released through PANX1 channels play important roles in activating microglial P2RY12 receptors to regulate neurovascular structure and function.

Synthesis and biological evaluation of N 6 derivatives of 8-azapurine as novel antiplatelet agents

Two series of novel N 6 derivatives of 8-azapurine I and II were designed as antiplatelet agents. Series I and II were N 6 amino derivatives and N 6 hydrazone derivatives of 8-azapurine, respectively. The compounds were synthesized in acceptable yields via conventional procedures, including nucleophilic substitution, diazotization, and amination or hydrazonation with amino alcohol and 4,6-dichloropyrimidine as starting materials. To assess the ability of the synthesized compounds as antiplatelet agents, the ADP-induced platelet aggregation assay of Born was performed both in vitro and in vivo using ticagrelor as a reference control substance. The analysis of the structure-activity relationship and molecular docking were also discussed in detail. The results demonstrated that series I and II compounds exhibited antiplatelet activity in vitro and IIh was the most active compound (IC50 = 0.20 μM) among the target compounds, being almost 4-fold better than ticagrelor (IC50 = 0.74 μM). For a preliminary assessment of the safety profile, a bleeding test (mouse tail) and a single-dose toxicity test were conducted. The use of compound IIh resulted in a shorter bleeding time, less blood loss and lower acute toxicity compared to ticagrelor. In addition, a molecular docking study was performed to investigate the binding capacity and binding mode between IIh and P2Y12.

Synthesis and biological evaluation of N4 -hydrazone derivatives of 5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one as novel anticancer agents with antimetastatic adjunct efficacy

To obtain new anticancer agents with antimetastatic adjunct efficacy, a series of novel N⁴ -hydrazone derivatives of 5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one were designed and synthesized by an eight-step reaction, with appropriate yields. All the synthesized compounds were evaluated for their antiproliferative activity against A549 and MCF-7 cells and for antiplatelet aggregation activity in vitro. The results showed that compounds 25 and 35 not only showed potent antiproliferative activity against the A549 (IC₅₀  = 15.3 and 21.4 μM) and MCF-7 (IC₅₀  = 15.6 and 10.9 μM) cell lines but also showed certain antiplatelet aggregation activity (inhibition rates: 47.0% and 45.8%). These results indicated that the structural modification on the N⁴ -hydrazone moiety of 5,7-dihydro-6H-pyrrolo[2,3-d]pyrimidin-6-one is promising to obtain novel anticancer compounds with antimetastatic adjunct efficacy. In addition, a molecular docking study was performed to investigate the possible targets, and these results indicated that compounds 25 and 35 have the potential to target EGFR, HER2, and P2Y₁₂ .

The Molecular Aspects of Disturbed Platelet Activation through ADP/P2Y12 Pathway in Multiple Sclerosis

Epidemiological studies confirm a high risk of ischemic events in secondary-progressive multiple sclerosis (SP MS) patients, directly associated with an increased level of pro-thrombotic activity of platelets. Our work aimed to verify potential molecular abnormalities of the platelet P2Y₁₂ receptor expression and functionality as a cause of an increased risk of thromboembolism observed in the course of MS. We have demonstrated an enhanced platelet reactivity in response to adenosine diphosphate (ADP) in SP MS relative to controls. We have also shown an increased mRNA expression for the P2RY12 gene in both platelets and megakaryocytes, as well as enhanced density of these receptors on the platelet surface. We postulate that one of the reasons for the elevated risk of ischemic events observed in MS may be a genetically or phenotypically reinforced expression of the platelet P2Y₁₂ receptor. In order to analyze the effect of the PAR1 (protease activated receptor type 1) signaling pathway on the expression level of P2Y₁₂, we also analyzed the correlation parameters between P2Y₁₂ expression and the markers of platelet activation in MS induced by selective PAR1 agonist (thrombin receptor activating peptide-6, TRAP-6). Identifying the molecular base responsible for the enlarged pro-thrombotic activity of platelets in SP MS could contribute to the implementation of prevention and targeted treatment, reducing the development of cardiovascular disorders in the course of the disease.

Platelet transfusion for patients with platelet dysfunction: effectiveness, mechanisms, and unanswered questions

PURPOSE OF REVIEW

In this review, we discuss current clinical guidelines and potential underlying mechanisms regarding platelet transfusion therapy in patients at risk of bleeding, comparing management of patients with thrombocytopenia versus those with qualitative platelet disorders.

RECENT FINDINGS

Platelet transfusion therapy is highly effective in managing bleeding in patients with hypoproliferative thrombocytopenia. Clinical trials have demonstrated that platelet transfusion can be used at a lower trigger threshold and reduced platelet doses, and may be used therapeutically rather than prophylactically in some situations, although additional data are needed. In patients with inherited platelet disorders such as Glanzmann's Thrombasthenia or those with RASGRP2 mutations, platelet transfusion may be ineffective because of competition between transfused and endogenous platelets at the site of vascular injury. Successful management of these patients may require transfusion of additional platelet units, or mechanism-driven combination therapy with other pro-hemostatic agents. In patients on antiplatelet therapy, timing of transfusion and inhibitor mechanism-of-action are key in determining therapeutic success.

SUMMARY

Expanding our understanding of the mechanisms by which transfused platelets exert their pro-hemostatic function in various bleeding disorders will improve the appropriate use of platelet transfusion.

The role of P2Y receptors in regulating immunity and metabolism

P2Y receptors are G protein-coupled receptors whose physiological agonists are the nucleotides ATP, ADP, UTP, UDP and UDP-glucose. Eight P2Y receptors have been cloned in humans: P2Y1R, P2Y2R, P2Y4R, P2Y6R, P2Y11R, P2Y12R, P2Y13R and P2Y14R. P2Y receptors are expressed in lymphoid tissues such as thymus, spleen and bone marrow where they are expressed on lymphocytes, macrophages, dendritic cells, neutrophils, eosinophils, mast cells, and platelets. P2Y receptors regulate many aspects of immune cell function, including phagocytosis and killing of pathogens, antigen presentation, chemotaxis, degranulation, cytokine production, and lymphocyte activation. Consequently, P2Y receptors shape the course of a wide range of infectious, autoimmune, and inflammatory diseases. P2Y12R ligands have already found their way into the therapeutic arena, and we envision additional ligands as future drugs for the treatment of diseases caused by or associated with immune dysregulation.

Whole Blood miR-210, miR-122, miR-223 Expression Levels and Their Relationship With Iron Status Parameters and Hypercoagulability Indices in Children With Iron Deficiency Anemia

MicroRNAs have the potential to regulate systemic and cellular iron homeostasis at multiple points. In iron deficiency anemia (IDA), hypoxia, platelet reactivity, and potentially microRNAs play a role in the development of hypercoagulability. A total of 57 children diagnosed with IDA between October 2016 and October 2017 and 48 healthy children were included in this cross-sectional study. Blood count parameters, serum iron, transferrin saturation, ferritin level, maximum clot firmness (MCF), and clot formation time index, which are indicators of hypercoagulability in rotational thromboelastometry test, of the IDA and control groups obtained in our previous study were recorded. miR-210, miR-122, and miR-223 levels were analyzed. There was no difference in the miR-210, miR-122, and miR-223 levels between the IDA and control groups. Patients with hemoglobin (Hb) <8 g/dL had higher miR-210 levels than patients with Hb>8 g/dL (P<0.05). There was a negative correlation between miR-210 and Hb and ferritin levels, a positive correlation between miR-122 and ferritin levels, and a negative correlation between miR-223 and MCF index. In IDA, there is a close relationship between the severity of anemia and miR-210, and miR-210 expression is slightly increased in those with severe anemia. miR-210 and miR-122 collectively play a role in maintaining the iron balance. The correlation between miR-223, a platelet function regulator, and the MCF index, suggested that miR-223 has a role in the development of hypercoagulability in IDA.

ADP receptor P2y12 prevents excessive primitive hematopoiesis in zebrafish by inhibiting Gata1

In the past two decades, purinergic signaling has emerged as a key regulator of hematopoiesis in physiological and pathological conditions. ADP receptor P2y12 is a crucial component of this signaling, but whether it is involved in primitive hematopoiesis remains unknown. To elucidate the function of P2y12 and provide new insights for drug development, we established a zebrafish P2y12 mutant by CRISPR/Cas 9-based genetic modification system, and investigated whether P2y12 acted as an important regulator for primitive hematopoiesis. By using mass spectrometry (MS) combined with RNA sequencing, we showed that absence of P2y12 induced excessive erythropoiesis, evidenced by significantly increased expression of mature erythrocytes marker α-globin (Hbae1 and Hbae3), β-globin (Hbbe1 and Hbbe3). Expression pattern analysis showed that P2y12 was mainly expressed in red blood cells and endothelial cells of early zebrafish embryos. Further studies revealed that primitive erythroid progenitor marker Gata1 was markedly up-regulated. Remarkably, inhibition of Gata1 by injection of Gata1 morpholino could rescue the erythroid abnormality in P2y12 mutants. The present study demonstrates the essential role of purinergic signaling in differentiation of proerythrocytes during primitive hematopoiesis, and provides potential targets for treatment of blood-related disease and drug development.

Loss of P2Y12 Has Behavioral Effects in the Adult Mouse

While microglia have been established as critical mediators of synaptic plasticity, the molecular signals underlying this process are still being uncovered. Increasing evidence suggests that microglia utilize these signals in a temporally and regionally heterogeneous manner. Subsequently, it is necessary to understand the conditions under which different molecular signals are employed by microglia to mediate the physiological process of synaptic remodeling in development and adulthood. While the microglial purinergic receptor P2Y12 is required for ocular dominance plasticity, an adolescent form of experience-dependent plasticity, it remains unknown whether P2Y12 functions in other forms of plasticity at different developmental time points or in different brain regions. Using a combination of ex vivo characterization and behavioral testing, we examined how the loss of P2Y12 affects developmental processes and behavioral performance in adulthood in mice. We found P2Y12 was not required for an early form of plasticity in the developing visual thalamus and did not affect microglial migration into barrels in the developing somatosensory cortex. In adult mice, however, the loss of P2Y12 resulted in alterations in recognition and social memory, as well as anxiety-like behaviors, suggesting that while P2Y12 is not a universal regulator of synaptic plasticity, the loss of P2Y12 is sufficient to cause functional defects.

Selatogrel, a reversible P2Y12 receptor antagonist, has reduced off-target interference with haemostatic factors in a mouse thrombosis model

INTRODUCTION

Selatogrel is a reversible antagonist of the P2Y12 receptor. In rat thrombosis/haemostasis models, selatogrel was associated with lower blood loss than clopidogrel or ticagrelor at equivalent anti-thrombotic effect.

MATERIAL AND METHODS

We sought to elucidate the mechanism underlying the observed differences in blood loss, using real-time intravital microscopy in mouse.

RESULTS

Selatogrel, ticagrelor and clopidogrel dose-dependently inhibited laser-induced platelet thrombus formation. At maximal antithrombotic effect, only small mural platelets aggregates, corresponding to hemostatic seals, were present. The phenotype of these hemostatic seals was dependent on the type of P2Y12 receptor antagonist. In the presence of clopidogrel and ticagrelor, detachment of platelets from the hemostatic seals was increased, indicative of reduced stability. In contrast, in the presence of selatogrel, platelet detachment was not increased. Moreover, equivalent antithrombotic dosing regimens of ticagrelor and clopidogrel reduced laser-induced calcium mobilization in the endothelium, restricted neutrophil adhesion and subsequent fibrin formation and thus reduced fibrin-mediated stabilization of the hemostatic seals. The effects of ticagrelor were also observed in P2Y12 receptor deficient mice, indicating that the effects are off-target and independent of the P2Y12 receptor. In contrast, selatogrel did not interfere with these elements of haemostasis in wild-type or in P2Y12 receptor deficient mice.

CONCLUSION

In the presence of selatogrel the stability of hemostatic seals was unperturbed, translating to an improved blood loss profile. Our data suggest that the mechanism underlying the differences in blood loss profiles of P2Y12 receptor antagonists is by off-target interference with endothelial activation, neutrophil function and thus, fibrin-mediated stabilization of haemostatic seals.

How microglia sense and regulate neuronal activity

Microglia are innate immune cells of the central nervous system that sense extracellular cues. Brain injuries, inflammation, and pathology evoke dynamic structural responses in microglia, altering their morphology and motility. The dynamic motility of microglia is hypothesized to be a critical first step in sensing local alterations and engaging in pattern-specific responses. Alongside their pathological responses, microglia also sense and regulate neuronal activity. In this review, we consider the extracellular molecules, receptors, and mechanisms that allow microglia to sense neuronal activity changes under both hypoactivity and hyperactivity. We also highlight emerging in vivo evidence that microglia regulate neuronal activity, ranging from physiological to pathophysiological conditions. In addition, we discuss the emerging role of calcium signaling in microglial responses to the extracellular environment. The dynamic function of microglia in monitoring and influencing neuronal activity may be critical for brain homeostasis and circuit modification in health and disease.

ADP/P2Y1 aggravates inflammatory bowel disease through ERK5-mediated NLRP3 inflammasome activation

Inflammasomes are essential for inflammation and pathogen elimination in response to microbial infection and endogenous danger signals. However, the mechanism of inflammasome activation by endogenous danger signals mediated posttranslational modification and the connection between inflammasomes and inflammatory diseases remains elusive. In this study, we found that ADP was highly released from injured colonic tissue as a danger signal during inflammatory bowel disease. Consequently, extracellular ADP activated the NLRP3 inflammasome through P2Y₁ receptor-mediated calcium signaling, which led to the maturation and secretion of IL-1β and further aggravation of experimental colitis. Genetic ablation or pharmacological blockade of the P2Y₁ receptor significantly ameliorated DSS-induced colitis and endotoxic shock through reducing NLRP3 inflammasome activation. Moreover, ERK5-mediated tyrosine phosphorylation of ASC was essential for activation of the NLRP3 inflammasome. Thus, our study provides a novel theoretical basis for posttranslational modification of ASC in NLRP3 inflammasome activation and revealed that ADP/P2Y₁ is a potential drug target for inflammatory bowel disease.

Core and shell platelets of a thrombus: A new microfluidic assay to study mechanics and biochemistry

BACKGROUND

Hemostatic clots have a P-selectin positive platelet core covered with a shell of P-selectin negative platelets.

OBJECTIVE

To develop a new human blood microfluidic assay to interrogate core/shell mechanics.

METHODS

A 2-stage assay perfused whole blood over collagen/± tissue factor (TF) for 180 seconds at 100 s-1 wall shear rate, followed by buffer perfusion at either 100 s-1 (venous) or 1000 s-1 (arterial). This microfluidic assay used an extended channel height (120 µm), allowing buffer perfusion well before occlusion.

RESULTS

Clot growth on collagen stopped immediately with buffer exchange, revealing ~10% reduction in platelet fluorescence intensity (at 100 s-1) and ~30% (at 1000 s-1) by 1200 seconds. Thrombin generation (on collagen/TF) reduced erosion at either buffer flow rate. P-selectin-positive platelets were stable (no erosion) against 1000 s-1, in contrast to P-selectin negative platelets. Thrombin inhibition (with D-Phe-Pro-Arg-CMK) reduced the number of P-selectin-positive platelets and lowered thrombus stability through the reduction of P-selectin-positive platelets. Interestingly, fibrin inhibition (with H-Gly-Pro-Arg-Pro-OH acetate salt) increased the number of P-selectin-positive platelets but did not lower stability, suggesting that fibrin was only in the core region. Thromboxane inhibition reduced P-selectin-positive platelets and caused a nearly 60% reduction of the clot at arterial buffer flow. P2Y1 antagonism reduced clot size and the number of P-selectin-positive platelets and reduced the stability of P-selectin-negative platelets.

CONCLUSION

The 2-stage assay (extended channel height plus buffer exchange) interrogated platelet stability using human blood. Under all conditions, P-selectin-positive platelets never left the clot.

Negative feedback control of neuronal activity by microglia

Microglia, the brain’s resident macrophages, help to regulate brain function by removing dying neurons, pruning non-functional synapses, and producing ligands that support neuronal survival¹. Here we show that microglia are also critical modulators of neuronal activity and associated behavioural responses in mice. Microglia respond to neuronal activation by suppressing neuronal activity, and ablation of microglia amplifies and synchronizes the activity of neurons, leading to seizures. Suppression of neuronal activation by microglia occurs in a highly region-specific fashion and depends on the ability of microglia to sense and catabolize extracellular ATP, which is released upon neuronal activation by neurons and astrocytes. ATP triggers the recruitment of microglial protrusions and is converted by the microglial ATP/ADP hydrolysing ectoenzyme CD39 into AMP; AMP is then converted into adenosine by CD73, which is expressed on microglia as well as other brain cells. Microglial sensing of ATP, the ensuing microglia-dependent production of adenosine, and the adenosine-mediated suppression of neuronal responses via the adenosine receptor A₁R are essential for the regulation of neuronal activity and animal behaviour. Our findings suggest that this microglia-driven negative feedback mechanism operates similarly to inhibitory neurons and is essential for protecting the brain from excessive activation in health and disease.

Microglia-Centered Combinatorial Strategies Against Glioblastoma

Tumor-associated microglia (MG) and macrophages (MΦ) are important components of the glioblastoma (GBM) immune tumor microenvironment (iTME). From the recent advances in understanding how MG and GBM cells evolve and interact during tumorigenesis, we emphasize the cooperation of MG with other immune cell types of the GBM-iTME, mainly MΦ and T cells. We provide a comprehensive overview of current immunotherapeutic clinical trials and approaches for the treatment of GBM, which in general, underestimate the counteracting contribution of immunosuppressive MG as a main factor for treatment failure. Furthermore, we summarize new developments and strategies in MG reprogramming/re-education in the GBM context, with a focus on ways to boost MG-mediated tumor cell phagocytosis and associated experimental models and methods. This ultimately converges in our proposal of novel combinatorial regimens that locally modulate MG as a central paradigm, and therefore may lead to additional, long-lasting, and effective tumoricidal responses.

Ticagrelor With or Without Aspirin After PCI: The TWILIGHT Platelet Substudy

BACKGROUND

An evolving strategy in the setting of percutaneous coronary intervention (PCI) involves withdrawal of acetylsalicylic acid (ASA), or aspirin, while maintaining P2Y₁₂ inhibition. However, the pharmacodynamic effects of this approach on blood thrombogenicity and platelet reactivity remain unknown.

OBJECTIVES

This study sought to compare the antithrombotic potency of ticagrelor alone versus ticagrelor plus ASA among high-risk patients undergoing PCI with drug-eluting stents.

METHODS

This was a mechanistic substudy within the TWILIGHT (Ticagrelor With Aspirin or Alone in High-Risk Patients After Coronary Intervention) trial, which randomized patients undergoing PCI to ticagrelor plus placebo versus ticagrelor plus ASA following 3 months of dual antiplatelet therapy. Substudy participants were enrolled after randomization, at which time ex vivo assays to quantify thrombus size under dynamic flow conditions and platelet reactivity were performed. Pharmacodynamic assessments were repeated 1 to 6 months thereafter. The primary endpoint was thrombus size at the post-randomization visit with platelet reactivity following stimuli to arachidonic acid, collagen, adenosine diphosphate, and thrombin as secondary endpoints. Results were analyzed using analysis of covariance.

RESULTS

A total of 51 patients were enrolled, among whom 42 underwent perfusion assays at baseline and follow-up with a median time between studies of 1.5 months. The adjusted mean difference in post-randomization thrombus area was similar between groups: -218.2 μm² (95% confidence interval [CI]: -575.9 to 139.9 μm²; p = 0.22). Markers sensitive to cyclo-oxygenase-1 blockade, including platelet reactivity in response to arachidonic acid (mean difference: 10.9 U; 95% CI: 1.9 to 19.9 U) and collagen (mean difference: 9.8 U; 95% CI: 0.8 to 18.8 U) stimuli were higher among patients receiving placebo, whereas levels of platelet reactivity were similar with adenosine diphosphate and thrombin.

CONCLUSIONS

Among high-risk patients receiving drug-eluting stents, the antithrombotic potency of ticagrelor monotherapy is similar to that of ticagrelor plus ASA with respect to ex vivo blood thrombogenicity, whereas markers sensitive to cyclo-oxygenase-1 blockade are increased in the absence of ASA. (Platelet Substudy of the TWILIGHT Trial; NCT04001374).

Platelets and Defective N-Glycosylation

N-glycans are covalently linked to an asparagine residue in a simple acceptor sequence of proteins, called a sequon. This modification is important for protein folding, enhancing thermodynamic stability, and decreasing abnormal protein aggregation within the endoplasmic reticulum (ER), for the lifetime and for the subcellular localization of proteins besides other functions. Hypoglycosylation is the hallmark of a group of rare genetic diseases called congenital disorders of glycosylation (CDG). These diseases are due to defects in glycan synthesis, processing, and attachment to proteins and lipids, thereby modifying signaling functions and metabolic pathways. Defects in N-glycosylation and O-glycosylation constitute the largest CDG groups. Clotting and anticlotting factor defects as well as a tendency to thrombosis or bleeding have been described in CDG patients. However, N-glycosylation of platelet proteins has been poorly investigated in CDG. In this review, we highlight normal and deficient N-glycosylation of platelet-derived molecules and discuss the involvement of platelets in the congenital disorders of N-glycosylation.

Impaired Spontaneous/Endogenous Fibrinolytic Status as New Cardiovascular Risk Factor?: JACC Review Topic of the Week

Endogenous fibrinolysis is a powerful natural defense mechanism against lasting arterial thrombotic occlusion. Recent prospective studies have shown that impaired endogenous fibrinolysis (or hypofibrinolysis) can be detected in a significant number of patients with acute coronary syndrome (ACS) using global assays and is a strong marker of future cardiovascular risk. This novel risk biomarker is independent of traditional cardiovascular risk factors and unaffected by antiplatelet therapy. Most prospective prognostic data have been obtained using a global assay using native whole blood at high shear or plasma turbidimetric assays, which are described herein. Tests of endogenous fibrinolysis could be used to identify patients with ACS who, despite antiplatelet therapy, remain at high cardiovascular risk. This review discusses the impact of currently available medications and those in development that favorably modulate fibrinolytic status and may offer a potential new avenue to improve outcomes in ACS.

Imaging Platelet Processes and Function-Current and Emerging Approaches for Imaging in vitro and in vivo

Platelets are small anucleate cells that are essential for many biological processes including hemostasis, thrombosis, inflammation, innate immunity, tumor metastasis, and wound healing. Platelets circulate in the blood and in order to perform all of their biological roles, platelets must be able to arrest their movement at an appropriate site and time. Our knowledge of how platelets achieve this has expanded as our ability to visualize and quantify discreet platelet events has improved. Platelets are exquisitely sensitive to changes in blood flow parameters and so the visualization of rapid intricate platelet processes under conditions found in flowing blood provides a substantial challenge to the platelet imaging field. The platelet's size (~2 μm), rapid activation (milliseconds), and unsuitability for genetic manipulation, means that appropriate imaging tools are limited. However, with the application of modern imaging systems to study platelet function, our understanding of molecular events mediating platelet adhesion from a single-cell perspective, to platelet recruitment and activation, leading to thrombus (clot) formation has expanded dramatically. This review will discuss current platelet imaging techniques in vitro and in vivo, describing how the advancements in imaging have helped answer/expand on platelet biology with a particular focus on hemostasis. We will focus on platelet aggregation and thrombus formation, and how platelet imaging has enhanced our understanding of key events, highlighting the knowledge gained through the application of imaging modalities to experimental models in vitro and in vivo. Furthermore, we will review the limitations of current imaging techniques, and questions in thrombosis research that remain to be addressed. Finally, we will speculate how the same imaging advancements might be applied to the imaging of other vascular cell biological functions and visualization of dynamic cell-cell interactions.

Knockout and Knock-in Mouse Models to Study Purinergic Signaling

Purinergic signaling involves extracellular purines and pyrimidines acting upon specific cell surface purinoceptors classified into the P1, P2X, and P2Y families for nucleosides and nucleotides. This widespread signaling mechanism is active in all major tissues and influences a range of functions in health and disease. Orthologs to all but one of the human purinoceptors have been found in mouse, making this laboratory animal a useful model to study their function. Indeed, analyses of purinoceptors via knock-in or knockout approaches to produce gain or loss of function phenotypes have revealed several important therapeutic targets. None of the homozygous purinoceptor knockouts proved to be developmentally lethal, which suggest that either these receptors are not involved in key developmental processes or that the large number of receptors in each family allowed for functional compensation. Different models for the same purinoceptor often show compatible phenotypes but there have been examples of significant discrepancies. These revealed unexpected differences in the structure of human and mouse genes and emphasized the importance of the genetic background of different mouse strains. In this chapter, we provide an overview of the current knowledge and new trends in the modifications of purinoceptor genes in vivo. We discuss the resulting phenotypes, their applications and relative merits and limitations of mouse models available to study purinoceptor subtypes.

Rivaroxaban Reduces Arterial Thrombosis by Inhibition of FXa-Driven Platelet Activation via Protease Activated Receptor-1

RATIONALE

A reduced rate of myocardial infarction has been reported in patients with atrial fibrillation treated with FXa (factor Xa) inhibitors including rivaroxaban compared with vitamin K antagonists. At the same time, low-dose rivaroxaban has been shown to reduce mortality and atherothrombotic events in patients with coronary artery disease. Yet, the mechanisms underlying this reduction remain unknown.

OBJECTIVE

In this study, we hypothesized that rivaroxaban's antithrombotic potential is linked to a hitherto unknown rivaroxaban effect that impacts on platelet reactivity and arterial thrombosis.

METHODS AND RESULTS

In this study, we identified FXa as potent, direct agonist of the PAR-1 (protease-activated receptor 1), leading to platelet activation and thrombus formation, which can be inhibited by rivaroxaban. We found that rivaroxaban reduced arterial thrombus stability in a mouse model of arterial thrombosis using intravital microscopy. For in vitro studies, atrial fibrillation patients on permanent rivaroxaban treatment for stroke prevention, respective controls, and patients with new-onset atrial fibrillation before and after first intake of rivaroxaban (time series analysis) were recruited. Platelet aggregation responses, as well as thrombus formation under arterial flow conditions on collagen and atherosclerotic plaque material, were attenuated by rivaroxaban. We show that rivaroxaban's antiplatelet effect is plasma dependent but independent of thrombin and rivaroxaban's anticoagulatory capacity.

CONCLUSIONS

Here, we identified FXa as potent platelet agonist that acts through PAR-1. Therefore, rivaroxaban exerts an antiplatelet effect that together with its well-known potent anticoagulatory capacity might lead to reduced frequency of atherothrombotic events and improved outcome in patients.

Impaired hemostatic activity of healthy transfused platelets in inherited and acquired platelet disorders: Mechanisms and implications

Platelet transfusions can fail to prevent bleeding in patients with inherited platelet function disorders (IPDs), such as Glanzmann's thrombasthenia (GT; integrin αIIbβ3 dysfunction), Bernard-Soulier syndrome [BSS; glycoprotein (GP) Ib/V/IX dysfunction], and the more recently identified nonsyndromic RASGRP2 variants. Here, we used IPD mouse models and real-time imaging of hemostatic plug formation to investigate whether dysfunctional platelets impair the hemostatic function of healthy donor [wild-type (WT)] platelets. In Rasgrp2-/- mice or mice with platelet-specific deficiency in the integrin adaptor protein TALIN1 ("GT-like"), WT platelet transfusion was ineffective unless the ratio between mutant and WT platelets was ~2:1. In contrast, thrombocytopenic mice or mice lacking the extracellular domain of GPIbα ("BSS-like") required very few transfused WT platelets to normalize hemostasis. Both Rasgrp2-/- and GT-like, but not BSS-like, platelets effectively localized to the injury site. Mechanistic studies identified at least two mechanisms of interference by dysfunctional platelets in IPDs: (i) delayed adhesion of WT donor platelets due to reduced access to GPIbα ligands exposed at sites of vascular injury and (ii) impaired consolidation of the hemostatic plug. We also investigated the hemostatic activity of transfused platelets in the setting of dual antiplatelet therapy (DAPT), an acquired platelet function disorder (APD). "DAPT" platelets did not prolong the time to initial hemostasis, but plugs were unstable and frequent rebleeding was observed. Thus, we propose that the endogenous platelet count and the ratio of transfused versus endogenous platelets should be considered when treating select IPD and APD patients with platelet transfusions.

In vitro and in silico evaluation of stereoselective effect of ginsenoside isomers on platelet P2Y12 receptor

BACKGROUND

P2Y₁₂ receptor (P2Y₁₂R) is a newly discovered Gi-coupled ADP receptor that plays critical role in platelet function. Ginsenosides are the main constituents responsible for most of pharmacological actions of ginseng, especially cardio-cerebrovascular protective efficacy that is closely related to the influence on platelet function.

HYPOTHESIS/PURPOSE

To explore stereoselective effect of naturally abundant ginsenoside isomers, including the C-20 epimers of protopanaxadiol (PPD), protopanaxatriol (PPT), and their glycosides Rg2, Rg3, Rh1, Rh2 on P2Y₁₂R in platelets.

STUDY DESIGN/METHODS

Both in vitro assay and in silico molecular docking study were performed to investigate the stereoselective effects.

RESULTS

In vitro assay using washed rat platelets revealed differential effects of ginsenoside isomers on ADP-induced platelet aggregation with the direction and degree of action varying with chemical structures. More to the point, the ginsenoside 20S-Rh2 but not its 20R-epimer was found to be the only one that could significantly promote in vitro platelets aggregation induced by ADP. The correlation analysis demonstrated that ginsenosides may have impact on P2Y₁₂R related platelet functions through a cAMP-dependent pathway. Molecular docking stimulation further indicated that ginsenoside isomers could be potent substrate of P2Y₁₂R with differential protein-ligand interaction that would be responsible for the stereoselective efficacy of C-20 ginsenoside epimers. Hydrogen bonding with Asp266 via the C-20 hydroxyl may provide ginsenosides with promoting effect on ADP-induced platelets aggregation, whereas interactions with Tyr105 could contribute to the promotion of inhibitory efficacy.

CONCLUSION

Ginsenosides are potent P2Y₁₂R substrate with stereoselective effects on P2Y₁₂R-related platelet function, which result from their chemical diversity and are closely related to the different interaction ways as P2Y₁₂R ligand.

Microglial P2Y12 Receptor Regulates Seizure-Induced Neurogenesis and Immature Neuronal Projections

Seizures are common in humans with various etiologies ranging from congenital aberrations to acute injuries that alter the normal balance of brain excitation and inhibition. A notable consequence of seizures is the induction of aberrant neurogenesis and increased immature neuronal projections. However, regulatory mechanisms governing these features during epilepsy development are not fully understood. Recent studies show that microglia, the brain's resident immune cell, contribute to normal neurogenesis and regulate seizure phenotypes. However, the role of microglia in aberrant neurogenic seizure contexts has not been adequately investigated. To address this question, we coupled the intracerebroventricular kainic acid model with current pharmacogenetic approaches to eliminate microglia in male mice. We show that microglia promote seizure-induced neurogenesis and subsequent seizure-induced immature neuronal projections above and below the pyramidal neurons between the DG and the CA3 regions. Furthermore, we identify microglial P2Y12 receptors (P2Y12R) as a participant in this neurogenic process. Together, our results implicate microglial P2Y12R signaling in epileptogenesis and provide further evidence for targeting microglia in general and microglial P2Y12R in specific to ameliorate proepileptogenic processes.SIGNIFICANCE STATEMENT Epileptogenesis is a process by which the brain develops epilepsy. Several processes have been identified that confer the brain with such epileptic characteristics, including aberrant neurogenesis and increased immature neuronal projections. Understanding the mechanisms that promote such changes is critical in developing therapies to adequately restrain epileptogenesis. We investigated the role of purinergic P2Y12 receptors selectively expressed by microglia, the resident brain immune cells. We report, for the first time, that microglia in general and microglial P2Y12 receptors in specific promote both aberrant neurogenesis and increased immature neuronal projections. These results indicate that microglia enhance epileptogenesis by promoting these processes and suggest that targeting this immune axis could be a novel therapeutic strategy in the clinic.

Pharmacology of P2Y receptors

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes divided into two subgroups (P2Y₁, P2Y₂, P2Y₄, P2Y₆, and P2Y₁₁) and (P2Y₁₂, P2Y₁₃, and P2Y₁₄). The P2Y receptors are expressed in various cell types and play important roles in physiology and pathophysiology including inflammatory responses and neuropathic pain. The antagonism of P2Y₁₂ receptors is used in pharmacotherapy for the prevention and therapy of cardiovascular events. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel inhibit platelet P2Y₁₂ receptors and reduce thereby platelet aggregation. The P2Y₂ receptor agonist diquafosol is used for the treatment of the dry eye syndrome. The P2Y receptor subtypes differ in their amino acid sequences, their pharmacological profiles and their signaling transduction pathways. Recently, selective receptor ligands have been developed for all subtypes. The published crystal structures of the human P2Y₁ and P2Y₁₂ receptors as well as receptor models will facilitate the development of novel drugs for pharmacotherapy.

P2RY12:rs7637803 TT variant genotype increases coronary artery aneurysm risk in Kawasaki disease in a southern Chinese population

BACKGROUND

Activated-platelet increases the risk of thrombosis in Kawasaki disease (KD) patients with a coronary artery aneurysm (CAA). The ADP pathway is one of the platelet activation and aggregation pathways. The P2RY12 gene encodes the ADP receptor that is highly concentrated on platelets. However, few studies have reported on P2RY12 in relation to KD susceptibility with or without CAA.

METHODS

We recruited 1335 healthy controls and 776 KD patients, including 103 with CAA, and selected five P2RY12 polymorphisms: rs9859538, rs1491974, rs7637803, rs6809699 and rs2046934. The present study focused on the relationship between the P2RY12 polymorphisms and KD with or without CAA.

RESULTS

Among all of the selected polymorphisms, single-locus analysis showed no significant association between the P2RY12 polymorphism and KD susceptibility. However, we found a significant relationship between rs7637803 and CAA risk in KD patients [CT versus CC: odds ratio (OR) = 0.41, 95% confidence interval (CI) = 0.22-0.75; p = 0.0041; TT versus CC: OR = 2.90, 95% CI = 1.12-7.46; p = 0.0276]. Stratification analysis by age in KD patients indicated that the rs7637803 TT genotype increased CAA formation risk among children aged (OR = 3.90, 95% CI = 1.42-10.69; p = 0.0081) and increased the onset risk of CAA in males (OR = 6.28, 95% CI = 2.01-19.65; p = 0.0016). The combined effect of the five selected P2RY12 risk genotypes with the KD patients compared to non-mutated P2RY12 genotypes (score: 0) showed that patients with P2RY12 genotype polymorphisms (score: 1-5) had a significantly increased CAA risk (p = 0.0086). Stratification analysis for the severity of CAA found that the rs7637803 TT genotype reduced giant CAA (GCAA) risk (OR = 4.60, 95% CI = 1.70-12.41; p = 0.0026).

CONCLUSIONS

The results of the present study indicate that the P2RY12 rs7637803 genotype might be used as a biomarker to predict the occurrence of GCAA.

Effect of P2Y12 inhibitors on thrombus stability and endogenous fibrinolysis

Although used routinely to reduce thrombotic events in patients with coronary disease, the effects of P2Y₁₂ inhibitors on thrombus stability and endogenous fibrinolysis are largely unknown. Blood taken from patients pre- and post-aspirin (n = 20) and on aspirin alone and on dual antiplatelet therapy comprising aspirin plus clopidogrel (n = 20), ticagrelor (n = 20) or cangrelor (n = 20), was tested using the Global Thrombosis Test. The number of "rebleeds" or drops (D) after early platelet-rich thrombus formation (occlusion time, OT), and before final lasting occlusion, was used as an inverse measure of thrombus stability. Whilst clopidogrel had no effect, ticagrelor and cangrelor both increased D significantly, reflecting increased thrombus instability [D pre- and post-clopidogrel 4.3 ± 1.6 vs. 4.5 ± 1.4, p = 0.833; pre- and post-ticagrelor 4.1 ± 2.4 vs. 6.8 ± 5.1, p = 0.048; pre- and post-cangrelor 3.6 ± 2.0 vs. 7.9 ± 8.9, p = 0.046]. Platelet reactivity was reduced by all P2Y₁₂ inhibitors, demonstrated by OT prolongation (clopidogrel 378 ± 87 s vs. 491 ± 93 s, p < 0.001; ticagrelor 416 ± 122 s vs. 549 ± 121 s, p < 0.001; cangrelor 381 ± 146 s vs. 613 ± 210 s, p < 0.001). The magnitude of OT prolongation compared to baseline (ΔOT) was significantly greater for cangrelor compared to clopidogrel and ticagrelor. Cangrelor was the only agent to enhance fibrinolysis (lysis time pre- and post-cangrelor 1622[1240-2048]s vs. 1388[960-1634]s, p = 0.005). We demonstrate the ability to assess the effect of pharmacotherapy on thrombus stability in vitro and show that P2Y₁₂ inhibitors potentiate thrombus instability at high shear. Cangrelor, and to a lesser extent ticagrelor, de-stabilised thrombus formation and cangrelor also enhanced fibrinolysis. Potentiation of thrombus instability could become a new pharmacological target, that may be particularly important in acute coronary syndromes.

Reduction in Subtypes and Sizes of Myocardial Infarction With Ticagrelor in PEGASUS-TIMI 54

Background Ticagrelor reduced cardiovascular death, myocardial infarction (MI), or stroke in patients with prior MI in PEGASUS-TIMI 54 (Prevention of Cardiovascular Events [eg, Death From Heart or Vascular Disease, Heart Attack, or Stroke] in Patients With Prior Heart Attack Using Ticagrelor Compared to Placebo on a Background of Aspirin). MI can occur in diverse settings and with varying severity; therefore, understanding the types and sizes of MI events prevented is of clinical importance. Methods and Results MIs were adjudicated by a blinded clinical events committee and categorized by subtype and fold elevation of peak cardiac troponin over the upper limit of normal. A total of 1042 MIs occurred in 898 of the 21 162 randomized patients over a median follow-up of 33 months. The majority of the MIs (76%) were spontaneous (Type 1), with demand MI (Type 2) and stent thrombosis (Type 4b) accounting for 13% and 9%, respectively; sudden death (Type 3), percutaneous coronary intervention-related (Type 4a) and coronary artery bypass graft-related (Type 5) each accounted for <1%. Half of MIs (520, 50%) had a peak troponin ≥10x upper limit of normal and 21% of MIs (220) had a peak troponin ≥100× upper limit of normal. A total of 21% (224) were ST-segment-elevation MI STEMI. Overall ticagrelor reduced MI (4.47% versus 5.25%, hazard ratio 0.83, 95% confidence interval 0.72-0.95, P=0.0055). The benefit was consistent among the subtypes, including a 31% reduction in MIs with a peak troponin ≥100× upper limit of normal (hazard ratio 0.69, 95% confidence interval 0.53-0.92, P=0.0096) and a 40% reduction in ST-segment elevation MI (hazard ratio 0.60, 95% confidence interval 0.46-0.78, P=0.0002). Conclusions In stable outpatients with prior MI, the majority of recurrent MIs are spontaneous and associated with a high biomarker elevation. Ticagrelor reduces the MI consistently among subtypes and sizes including large MIs and ST-segment elevation MI. Clinical Trial Registration URL: https://www.clinicaltrials.gov . Unique identifier: NCT01225562.