Antiplatelet drugs: which targets for which treatments?

Phillyrin and its metabolites treat pulmonary embolism by targeting PLCβ3 to inhibit platelet activation

ETHNOPHARMACOLOGICAL RELEVANCE

Lian Qiao (LQ), the dried fruit of Forsythia suspensa (Thunb.) Vahl, is a well-documented traditional Chinese medicine known for its detoxifying and heat-clearing properties. Clinically, compounds containing LQ are widely used to treat thrombotic diseases, indicating that it may have antithrombotic effects. However, its exact mechanism of action remains unknown.

AIM OF THE STUDY

This study aimed to verify the antithrombotic effect of LQ and further explore the material basis and target mechanism of its antithrombotic effect using various biological methods.

MATERIALS AND METHODS

An epinephrine-collagen-thrombin-induced mouse model of acute pulmonary embolism (APE) was established to study the effects of LQ on thrombus development. A UPLC/Q/TOF-MS screening and identification system based on the inhibition of platelet aggregation and Ca2+ antagonism was established to determine the pharmacodynamic components of LQ that inhibit platelet activation. The inhibitory effect of active ingredients on platelet activation, and the determination of the target of their inhibitory effect on platelet activation have been studied using chemical proteomics. Furthermore, based on the structure and function of the target protein, a multidisciplinary approach was adopted to analyze the molecular mechanism of active ingredient binding to target proteins and to evaluate the effects of active ingredients on the downstream signaling pathways of target proteins.

RESULTS

LQ showed significant anticoagulant effects in APE model mice. Phillyrin and phillygenin were the antiplatelet-activating components of LQ. PLCβ3 was identified as a target for inhibiting platelet activation by phillyrin and its metabolites. The mechanism underlying the effect involves phillyrin and its metabolites inhibiting PLCβ3 activity by blocking the binding of PLCβ3 to Gαq through non-covalently targeting the ASN260 of PLCβ3, thus inhibiting the downstream Gαq-PLCβ3-Ca2+ signaling pathway, effectively hindering platelet activation and therefore playing an anticoagulant role.

CONCLUSION

This study not only proposes and validates the antithrombotic effect of LQ for the first time but also finds that phillyrin and phillygenin are the main pharmacological substances through which LQ exerts antithrombotic activity and reveals a novel mechanism by which they exert antiplatelet activity by directly targeting and inhibiting PLCβ3 activity. These findings significantly contribute to our understanding of the therapeutic potential of phillyrin and provide important clues for the discovery and development of new antiplatelet drugs.

Safety and efficacy of desmopressin (DDAVP) in preventing hematoma expansion in intracranial hemorrhage associated with antiplatelet drugs use: A systematic review and metaanalysis

INTRODUCTION

One of the most serious complications associated with antiplatelet agents is antiplatelet-associated intracranial hemorrhage (AA-ICH). Desmopressin is a synthetic antidiuretic hormone (ADH) analog. It has been linked to improving patient outcomes in antiplatelet-induced intracranial hemorrhage. The secondary outcomes included the incidence of thrombotic complications and neurological outcomes.

METHODS

A systematic search was conducted on three databases (PubMed, Cochrane, and ClinicalTrials.gov) to find eligible literature that compares desmopressin (DDAVP) versus controls in patients with AA-ICH. The Mantel-Haenszel statistic was used to determine an overall effect estimate for each outcome by calculating the risk ratios and 95% confidence intervals (CI). Heterogeneity was measured using the I2 test. The risk of bias in studies was calculated using the New Castle Ottowa Scale.

RESULTS

Five studies were included in the analysis with a total of 598 patients. DDAVP was associated with a nonsignificant decrease in the risk of hematoma expansion (RR = .8, 95% CI,.51-1.24; p = .31, I2 = 44%). It was also associated with a non-significant decrease in the risk of thrombotic events (RR,.83; 95% CI,.25-2.76; p = .76, I2 = 30%). However, patients in the DDAVP group demonstrated a significant increase in the risk of poor neurological outcomes (RR, 1.31; 95% CI, 1.07-1.61; p = .01, I2 = 0%). The risk of bias assessment showed a moderate to low level of risk.

CONCLUSION

DDAVP was associated with a nonsignificant decrease in hematoma expansion and thrombotic events. However, it was also associated with a significantly poor neurological outcome in the patients. Thus, until more robust clinical trials are conducted, the use of DDAVP should be considered on a case-to-case basis.

4'-O-MethylbavachalconeB Targeted 14-3-3ζ Blocking the Integrin β3 Early Outside-In Signal to Inhibit Platelet Aggregation and Thrombosis

14-3-3ζ protein, the key target in the regulation and control of integrin β3 outside-in signaling, is an attractive new strategy to inhibit thrombosis without affecting hemostasis. In this study, 4'-O-methylbavachalconeB (4-O-MB) in Psoraleae Fructus was identified as a 14-3-3ζ ligand with antithrombosis activity by target fishing combined with ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UHPLC-Q-TOF-MS) analysis. The competitive inhibition analysis showed that 4-O-MB targeted 14-3-3ζ and blocked the 14-3-3ζ/integrin β3 interaction with inhibition constant (Ki) values of 9.98 ± 0.22 μM. Molecular docking and amino acid mutation experiments confirmed that 4-O-MB specifically bound to 14-3-3ζ through LSY9 and SER28 to regulate the 14-3-3ζ/integrin β3 interaction. Besides, 4-O-MB affected the integrin β3 early outside-in signal by inhibiting AKT and c-Src phosphorylation. Meanwhile, 4-O-MB could inhibit ADP-, collagen-, or thrombin-induced platelet aggregation function but had no effect on platelet adhesion to collagen-coated surfaces in vivo. Administration of 4-O-MB could significantly inhibit thrombosis formation without disturbing hemostasis in mice. These findings provide new prospects for the antithrombotic effects of Psoraleae Fructus and the potential application of 4-O-MB as lead compounds in the therapy of thrombosis by targeting 14-3-3ζ.

Pathophysiology and targeted treatment of cholesterol crystal embolism and the related thrombotic angiopathy

Cholesterol crystal (CC) embolism is a complication of advanced atherosclerotic plaques located in the major arteries. This pathological condition is primarily induced by interventional and surgical procedures or occurs spontaneously. CC can induce a wide range of tissue injuries including CC embolism syndrome, a spontaneous or intervention-induced complication of advanced atherosclerosis, while treatment of CC embolism has remained empiric. Vascular occlusions caused by CC embolism may exceed the ischemia tolerance of many tissues, particularly when small arteries are affected. The main approach to CC embolism is primary prophylaxis in patients at risk by stabilizing atherosclerotic plaques and avoiding unnecessary catheter interventions. During CC embolism, the use of platelet inhibitors to avoid abnormal activation and aggregation and anticoagulants may reduce the risk of vascular occlusions and tissue ischemia. This probably explains the relatively low prevalence of clinical manifestations of CC embolism, which are frequently found in autopsy studies. In this review, we summarized the current knowledge on the pathophysiology of CC embolism syndrome deriving from clinical observations and experimental mouse models. Furthermore, we described the risk factors of CC embolism in humans as well as the experimental studies based on empiric treatments. We also discuss potential therapeutic interventions based on recent experimental data and emerging drug options evolving from other research domains. Given the substantial unmet medical need to improve the outcomes of CC embolism, the identification of effective treatment strategies is urgently needed.

Synthesis and Biological Evaluation of Novel Thiadiazole Derivatives as Antiplatelet Agents

A novel series of thiadiazole compounds was synthesized through the reaction of thiosemicarbazone intermediates with 2, 3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The antiplatelet activity of the synthesized compounds was evaluated using an aggregation test with adenosine diphosphate (ADP) and arachidonic acid (AA) as platelet aggregation inducers. Among the synthesized analogs, compound 3b exhibited the most potent inhibition of platelet aggregation induced by ADP (half maximal inhibitory concentration [IC50] = 39 ± 11 µM). Molecular docking studies of 3b revealed hydrogen bonds between the nitrogen of the thiadiazole ring and Lys280. The tolyl ring exhibited hydrophobic interactions with Tyr105, similar to the antagonist co-crystallized with P2Y12 (PDB ID: 4NTJ). These compounds have the potential to serve as lead molecules for designing P2Y12 inhibitors.

Ultra-high-throughput Ca2+ assay in platelets to distinguish ITAM-linked and G-protein-coupled receptor activation

Antiplatelet drugs targeting G-protein-coupled receptors (GPCRs), used for the secondary prevention of arterial thrombosis, coincide with an increased bleeding risk. Targeting ITAM-linked receptors, such as the collagen receptor glycoprotein VI (GPVI), is expected to provide a better antithrombotic-hemostatic profile. Here, we developed and characterized an ultra-high-throughput (UHT) method based on intracellular [Ca2+]i increases to differentiate GPVI and GPCR effects on platelets. In 96-, 384-, or 1,536-well formats, Calcium-6-loaded human platelets displayed a slow-prolonged or fast-transient [Ca2+]i increase when stimulated with the GPVI agonist collagen-related peptide or with thrombin and other GPCR agonists, respectively. Semi-automated curve fitting revealed five parameters describing the Ca2+ responses. Verification of the UHT assay was done with a robustness compound library and clinically relevant platelet inhibitors. Taken together, these results present proof of principle of distinct receptor-type-dependent Ca2+ signaling curves in platelets, which allow identification of new inhibitors in a UHT way.

Preparations from selected cucurbit vegetables as antiplatelet agents

Increased blood platelet activation plays an important role in cardiovascular diseases (CVDs). Recent experiments indicate that certain fruits and vegetables, including onion, garlic, and beetroot, have anti-platelet potential and therefore may reduce the likelihood of CVDs. While vegetables from the Cucuritaceae family are known to exerting beneficial antioxidant and anti-inflammatory effects, their effects on blood platelet activation are poorly understood. Therefore, the aim of the present study was to determine the effect on platelet adhesion of preparations from selected cucurbits: pumpkin (Cucurbita pepo; fruit without seeds), zucchini (Cucurbita pepo convar. giromontina; fruit with seeds), cucumber (Cucumis sativus; fruit with seeds), white pattypan squash (Cucurbita pepo var. patisoniana; fruit without seeds) and yellow pattypan squash (Cucurbita pepo var. patisoniana, fruit without seeds). It also evaluates the activity of these preparations on enzymatic lipid peroxidation in thrombin-activated washed blood platelets by TBARS assay. The study also determines the anti-platelet properties of these five cucurbit preparations in whole blood by flow cytometry and with the total thrombus-formation analysis system (T-TAS) and evaluates the cytotoxicity of the tested preparations against platelets based on LDH activity. The results indicate that the yellow Cucurbita pepo var. patisoniana preparation demonstrated stronger anti-platelet properties than the other tested preparations, reducing the adhesion of thrombin-activated platelets to collagen/fibrinogen, and inhibiting arachidonic acid metabolism and GPIIb/IIIa expression on 10 µM ADP-activated platelets. None of the preparations was found to cause platelet lysis. Our findings provide new information on the anti-platelet activity of the tested cucurbit preparations and their potential for treating CVDs associated with platelet hyperactivity.

Platelet-Cancer Interplay: Molecular Mechanisms and New Therapeutic Avenues

Although platelets are critically involved in thrombosis and hemostasis, experimental and clinical evidence indicate that platelets promote tumor progression and metastasis through a wide range of physical and functional interactions between platelets and cancer cells. Thrombotic and thromboembolic events are frequent complications in patients with solid tumors. Hence, cancer modulates platelet function by directly inducing platelet-tumor aggregates and triggering platelet granule release and altering platelet turnover. Also, platelets enhance tumor cell dissemination by activating endothelial cell function and recruiting immune cells to primary and metastatic tumor sites. In this review, we summarize current knowledge on the complex interactions between platelets and tumor cells and the host microenvironment. We also critically discuss the potential of anti-platelet agents for cancer prevention and treatment.

Proteomics: A Tool to Study Platelet Function

Platelets are components of the blood that are highly reactive, and they quickly respond to multiple physiological and pathophysiological processes. In the last decade, it became clear that platelets are the key components of circulation, linking hemostasis, innate, and acquired immunity. Protein composition, localization, and activity are crucial for platelet function and regulation. The current state of mass spectrometry-based proteomics has tremendous potential to identify and quantify thousands of proteins from a minimal amount of material, unravel multiple post-translational modifications, and monitor platelet activity during drug treatments. This review focuses on the role of proteomics in understanding the molecular basics of the classical and newly emerging functions of platelets. including the recently described role of platelets in immunology and the development of COVID-19.The state-of-the-art proteomic technologies and their application in studying platelet biogenesis, signaling, and storage are described, and the potential of newly appeared trapped ion mobility spectrometry (TIMS) is highlighted. Additionally, implementing proteomic methods in platelet transfusion medicine, and as a diagnostic and prognostic tool, is discussed.

Mechanisms of thrombosis and research progress on targeted antithrombotic drugs

Globally, the incidence of thromboembolic diseases has increased in recent years, accompanied by an increase in patient mortality. Currently, several targeting delivery strategies have been developed to treat thromboembolic diseases. In this review, we discuss the mechanisms of thrombolysis and current anticoagulant drugs, particularly those with targeting capability, highlighting advances in the accurate treatment of thrombolysis with fewer adverse effects. Such approaches include magnetic drug-loading systems combined with molecular imaging to recanalize blood vessels and systems based on chimeric Arg-Gly-Asp (RGD) sequences that can target platelet glycoprotein receptor. With such progress in targeted antithrombotic drugs, targeted thrombolysis treatment shows significant potential benefit for patients.

Phosphoinositide 3-kinases in platelets, thrombosis and therapeutics

Our knowledge on the expression, regulation and roles of the different phosphoinositide 3-kinases (PI3Ks) in platelet signaling and functions has greatly expanded these last twenty years. Much progress has been made in understanding the roles and regulations of class I PI3Ks which produce the lipid second messenger phosphatidylinositol 3,4,5 trisphosphate (PtdIns(3,4,5)P3). Selective pharmacological inhibitors and genetic approaches have allowed researchers to generate an impressive amount of data on the role of class I PI3Kα, β, δ and γ in platelet activation and in thrombosis. Furthermore, platelets do also express two class II PI3Ks (PI3KC2α and PI3KC2β), thought to generate PtdIns(3,4)P2 and PtdIns3P, and the sole class III PI3K (Vps34), known to synthesize PtdIns3P. Recent studies have started to reveal the importance of PI3KC2α and Vps34 in megakaryocytes and platelets, opening new perspective in our comprehension of platelet biology and thrombosis. In this review, we will summarize previous and recent advances on platelet PI3Ks isoforms. The implication of these kinases and their lipid products in fundamental platelet biological processes and thrombosis will be discussed. Finally, the relevance of developing potential antithrombotic strategies by targeting PI3Ks will be examined.

Mediterranean Diet Decreases the Initiation of Use of Vitamin K Epoxide Reductase Inhibitors and Their Associated Cardiovascular Risk: A Randomized Controlled Trial

Our aim is to assess whether following a Mediterranean Diet (MedDiet) decreases the risk of initiating antithrombotic therapies and the cardiovascular risk associated with its use in older individuals at high cardiovascular risk. We evaluate whether participants of the PREvención con DIeta MEDiterránea (PREDIMED) study allocated to a MedDiet enriched in extra-virgin olive oil or nuts (versus a low-fat control intervention) disclose differences in the risk of initiation of: (1) vitamin K epoxide reductase inhibitors (acenocumarol/warfarin; n = 6772); (2) acetylsalicylic acid as antiplatelet agent (n = 5662); and (3) other antiplatelet drugs (cilostazol/clopidogrel/dipyridamole/ditazol/ticlopidine/triflusal; n = 6768). We also assess whether MedDiet modifies the association between the antithrombotic drug baseline use and incident cardiovascular events. The MedDiet intervention enriched with extra-virgin olive oil decreased the risk of initiating the use of vitamin K epoxide reductase inhibitors relative to control diet (HR: 0.68 [0.46-0.998]). Their use was also more strongly associated with an increased risk of cardiovascular disease in participants not allocated to MedDiet interventions (HRcontrol diet: 4.22 [1.92-9.30], HRMedDiets: 1.71 [0.83-3.52], p-interaction = 0.052). In conclusion, in an older population at high cardiovascular risk, following a MedDiet decreases the initiation of antithrombotic therapies and the risk of suffering major cardiovascular events among users of vitamin K epoxide reductase inhibitors.

Platelets in Healthy and Disease States: From Biomarkers Discovery to Drug Targets Identification by Proteomics

Platelets are a heterogeneous small anucleate blood cell population with a central role both in physiological haemostasis and in pathological states, spanning from thrombosis to inflammation, and cancer. Recent advances in proteomic studies provided additional important information concerning the platelet biology and the response of platelets to several pathophysiological pathways. Platelets circulate systemically and can be easily isolated from human samples, making proteomic application very interesting for characterizing the complexity of platelet functions in health and disease as well as for identifying and quantifying potential platelet proteins as biomarkers and novel antiplatelet therapeutic targets. To date, the highly dynamic protein content of platelets has been studied in resting and activated platelets, and several subproteomes have been characterized including platelet-derived microparticles, platelet granules, platelet releasates, platelet membrane proteins, and specific platelet post-translational modifications. In this review, a critical overview is provided on principal platelet proteomic studies focused on platelet biology from signaling to granules content, platelet proteome changes in several diseases, and the impact of drugs on platelet functions. Moreover, recent advances in quantitative platelet proteomics are discussed, emphasizing the importance of targeted quantification methods for more precise, robust and accurate quantification of selected proteins, which might be used as biomarkers for disease diagnosis, prognosis and therapy, and their strong clinical impact in the near future.

Contribution of exome sequencing to the identification of genes involved in the response to clopidogrel in cardiovascular patients

BACKGROUND

On-clopidogrel platelet reactivity (PR) is associated with the risk of thrombotic or bleeding event in selected populations of high-risk patients. PR is a highly heritable phenotype and a few variants of cytochrome genes, essentially CYP2C19, are associated with PR but only explain 5% to 12% of the variability.

OBJECTIVE

The aim of this study is to delineate genetic determinants of on-clopidogrel PR using high-throughput sequencing.

METHODS

We performed a whole exome sequencing of 96 low- and matched high-PR patients in a discovery cohort. Exomes from genes with variants significantly associated with PR were sequenced in 96 low- and matched high-PR patients from an independent replication cohort.

RESULTS

We identified 585 variants in 417 genes with an adjusted P value < .05. In the replication cohort, all top variants including CYP2C8, CYP2C18, and CYP2C19 from the discovery population were found again. An original network analysis identified several candidate genes of potential interest such as a regulator of PI3K, a key actor in the downstream signaling pathway of the P2Y12 receptor.

CONCLUSION

This study emphasizes the role of CYP-related genes as major regulators of clopidogrel response, including the poorly investigated CYP2C8 and CYP2C18.

Platelet decoys inhibit thrombosis and prevent metastatic tumor formation in preclinical models

Platelets are crucial for normal hemostasis; however, their hyperactivation also contributes to many potentially lethal pathologies including myocardial infarction, stroke, and cancer. We hypothesized that modified platelets lacking their aggregation and activation capacity could act as reversible inhibitors of platelet activation cascades. Here, we describe the development of detergent-extracted human modified platelets (platelet decoys) that retained platelet binding functions but were incapable of functional activation and aggregation. Platelet decoys inhibited aggregation and adhesion of platelets on thrombogenic surfaces in vitro, which could be immediately reversed by the addition of normal platelets; in vivo in a rabbit model, pretreatment with platelet decoys inhibited arterial injury-induced thromboembolism. Decoys also interfered with platelet-mediated human breast cancer cell aggregation, and their presence decreased cancer cell arrest and extravasation in a microfluidic human microvasculature on a chip. In a mouse model of metastasis, simultaneous injection of the platelet decoys with tumor cells inhibited metastatic tumor growth. Thus, our results suggest that platelet decoys might represent an effective strategy for obtaining antithrombotic and antimetastatic effects.

Role of aspirin in primary prevention of cardiovascular disease

The benefits of aspirin therapy for the secondary prevention of cardiovascular disease clearly outweigh the risks of bleeding, and low-dose aspirin is uniformly recommended in this setting. However, no clear consensus exists about whether, and if so in whom, aspirin therapy is appropriate for the primary prevention of cardiovascular disease. Three trials of low-dose aspirin versus placebo in three populations at increased risk of myocardial infarction or ischaemic stroke in the absence of established cardiovascular disease were reported in 2018. The ASPREE trial in elderly people was terminated early for futility because aspirin had no effect on disability-free survival but significantly increased the risk of major haemorrhage and, unexpectedly, all-cause mortality. In the ASCEND trial in patients with diabetes mellitus and no evidence of vascular disease, aspirin significantly reduced serious vascular events but increased major bleeding. In the ARRIVE trial in people with multiple risk factors for cardiovascular disease, aspirin had no effect on major cardiovascular events but increased gastrointestinal bleeding. The aim of this Review is to place these new results in the context of previous evidence on aspirin for the primary prevention of cardiovascular disease and to appraise whether the new evidence is likely to enable the more targeted use of aspirin in particular individuals for whom the net benefit is both clinically worthwhile and statistically definite.

The gut microbiome and cardiovascular disease: current knowledge and clinical potential

Cardiovascular disease (CVD) is the leading cause of death worldwide. The human body is populated by a diverse community of microbes, dominated by bacteria, but also including viruses and fungi. The largest and most complex of these communities is located in the gastrointestinal system and, with its associated genome, is known as the gut microbiome. Gut microbiome perturbations and related dysbiosis have been implicated in the progression and pathogenesis of CVD, including atherosclerosis, hypertension, and heart failure. Although there have been advances in the characterization and analysis of the gut microbiota and associated bacterial metabolites, the exact mechanisms through which they exert their action are not well understood. This review will focus on the role of the gut microbiome and associated functional components in the development and progression of atherosclerosis. Potential treatments to alter the gut microbiome to prevent or treat atherosclerosis and CVD are also discussed.

Is the endothelial cell responsible for the thrombus core and shell architecture?

Ischemia leading to heart attacks and strokes is the major cause of deaths in the world. This report explores the possibility that intracellular material from ruptured endothelial cells is partially responsible for the heterogeneous core-and-shell blood clot architecture, typically observed using intravital microscopy. As evidence, we present a fluid dynamic argument that platelet agonists emanating from the injury cannot activate platelets in the thrombus core, given that they would have to travel against flow of blood escaping into the extravascular. Furthermore, we demonstrate visual evidence that the core material appears to be continuous and originating from the damaged endothelium. Finally, we present a mechanism, illustrating the steps of platelet recruitment into the thrombus and sealing of the injury. If correct, the model presented herein will be beneficial to the understanding and treatment of heart attacks, strokes and hemophilia.

Novel compounds of hybrid structure pyridazinone–coumarin as potent inhibitors of platelet aggregation

Aim: The current limitations of antiplatelet therapy promote the search for new antithrombotic agents. Here we describe novel platelet aggregation inhibitors that combine pyridazinone and coumarin scaffolds in their structure. Results: The target compounds were synthesized in good yield from maleic anhydride, following a multistep strategy. The in vitro studies demonstrated significant antiplatelet activity in many of these compounds, with IC50 values in the low micromolar range, revealing that the activity was affected by the substitution pattern of the two selected cores. Additional studies point out their effect as inhibitors of glycoprotein (Gp) IIb/IIIa activation. Conclusion: This novel hybrid structure can be considered a good prototype for the development of potent platelet aggregation inhibitors.

Reduced nicotinamide adenine dinucleotide phosphate inhibits rat platelet aggregation and p38 phosphorylation

Previous studies found that reduced nicotinamide adenine dinucleotide phosphate (NADPH) protected neurons against ischemia/reperfusion-induced injury. In addition to ROS reduction and ATP increment, preliminary data suggested that NADPH inhibited ADP and thrombin-induced platelet aggregation. As the effect of NADPH on platelet function was not reported by other investigators, the actions of NADPH on platelet function and mechanisms of actions were investigated in the present study. In vitro studies, the effects of different concentrations of NADPH on platelet aggregation induced by ADP (10 μM), thrombin (0.05 U/mL) or AA (50 μM) were determined. The results showed that NADPH could inhibit platelet aggregation induced by ADP, thrombin or AA in a concentration dependent manner. When the inhibitory effects of NAD⁺, NADH, NADP⁺ and NADPH on platelet aggregation were compared, NADPH demonstrated the relatively best effect on platelet aggregation. In vivo studies, the effects of NADPH on platelet aggregation, tail bleeding time, coagulation response and ferric chloride-induced thrombosis were determined in mice or rats. The maximum aggregation rate of platelets of rats injected with NADPH (5 mg/kg) was lower than platelets from control rats. NADPH transiently prolonged tail bleeding time in mice at 30 min after the injection of NADPH (7.5 mg/kg), while aspirin (15 mg/kg) significantly prolonged the tail bleeding time in mice at all time points examined. NADPH (5 mg/kg), as well as aspirin (10 mg/kg), had no effect on coagulation response in rats. Using a FeCl₃-induced abdominal aorta injury thrombosis model, administration of NADPH (5 mg/kg) significantly delayed the onset of vessel occlusion, while aspirin (10 mg/kg) almost completely prevented the vessel occlusion. With microscopic examination the thrombi in injured vessel sections of rats received NADPH were much smaller and less dense than that of rats received vehicle treatment. ADP induced an increase in phosphorylation of p38 and the effect was markedly inhibited by the p38 inhibitor SB203580. Similarly, NADPH also inhibited ADP-induced phosphorylation of p38. Similar to NADPH, SB203580 robustly inhibited ADP- and thrombin-induced platelet aggregation. In addition, NADPH also reduced ADP-induced increases in ROS in platelets. The current results demonstrated that NADPH inhibited platelet aggregation, oxidative stress and p38 phosphorylation, suggesting that NADPH might be a novel compound for management of high risk of cardiovascular disease.

Development of a gut microbe-targeted nonlethal therapeutic to inhibit thrombosis potential

Trimethylamine N-oxide (TMAO) is a gut microbiota-derived metabolite that enhances both platelet responsiveness and in vivo thrombosis potential in animal models, and TMAO plasma levels predict incident atherothrombotic event risks in human clinical studies. TMAO is formed by gut microbe-dependent metabolism of trimethylamine (TMA) moiety-containing nutrients, which are abundant in a Western diet. Here, using a mechanism-based inhibitor approach targeting a major microbial TMA-generating enzyme pair, CutC and CutD (CutC/D), we developed inhibitors that are potent, time-dependent, and irreversible and that do not affect commensal viability. In animal models, a single oral dose of a CutC/D inhibitor significantly reduced plasma TMAO levels for up to 3 d and rescued diet-induced enhanced platelet responsiveness and thrombus formation, without observable toxicity or increased bleeding risk. The inhibitor selectively accumulated within intestinal microbes to millimolar levels, a concentration over 1-million-fold higher than needed for a therapeutic effect. These studies reveal that mechanism-based inhibition of gut microbial TMA and TMAO production reduces thrombosis potential, a critical adverse complication in heart disease. They also offer a generalizable approach for the selective nonlethal targeting of gut microbial enzymes linked to host disease limiting systemic exposure of the inhibitor in the host.

Inhibitory effects of luteolin‑4'‑O‑β‑D‑glucopyranoside on P2Y12 and thromboxane A2 receptor‑mediated amplification of platelet activation in vitro

Platelet activation and subsequent accumulation at sites of vascular injury are central to thrombus formation, which is considered to be a trigger of several cardiovascular diseases. Callicarpa nudiflora (C. nudiflora) Hook is a traditional Chinese medicinal herb for promoting blood circulation by removing blood stasis. In our previous study, several compounds extracted from this herb, including luteolin‑4'‑O‑β‑D‑glucopyranoside (LGP), were revealed to exert inhibitory effects on adenosine diphosphate (ADP)‑induced platelet aggregation. The aim of present study was to confirm these antiplatelet effects and elucidate the potential mechanisms. Using a platelet‑aggregation assay, it was revealed that LGP significantly inhibited platelet aggregation induced by ADP, U46619 and arachidonic acid. It was also found that LGP exhibited marked inhibitory effects on the activation of αIIbβ3 integrin, the secretion of serotonin from granules, and the synthesis of thromboxane A2. In addition, the results showed that LGP suppressed Ras homolog family member A and phosphoinositide 3‑kinase/Akt/glycogen synthase kinase 3β signal transduction. Data from a radiolabeled ligand‑binding assay indicated that LGP exhibited apparent competing effects on thromboxane receptor (TP) and P2Y12 receptors. In conclusion, the data presented here demonstrated that LGP, a natural compound from C. nudiflora Hook, inhibited the development of platelet aggregation and amplification of platelet activation. These inhibitory effects may be associated with its dual‑receptor inhibition on P2Y12 and TP receptors.

1, 6-di-O-caffeoyl-β-D-glucopyranoside, a natural compound from Callicarpa nudiflora Hook impairs P2Y12 and thromboxane A2 receptor-mediated amplification of platelet activation and aggregation

BACKGROUND

Platelet activation and subsequent accumulation at sites of vascular injury perform a central role in thrombus formation, which is believed to be the trigger of several cardiovascular diseases, such as atherosclerosis, myocardial infarction and strokes. In this sense, the search for agents that are capable of blocking platelets aggregation has important implications for these diseases. Callicarpa nudiflora (C. nudiflora) Hook is a traditional Chinese medicine herb for eliminating stasis to subdue swelling and hemostasis. Our previous study found several compounds extracted from this herb, including 1, 6-di-O-caffeoyl-β-D-glucopyranoside (CGP), showed inhibitory effects on adenosine diphosphate (ADP) induced platelet aggregation.

PURPOSE

The aim of current study is confirmation of the anti-platelet effects and elucidation of the probable mechanisms.

METHODS

The experiments were performed on platelet rich plasma freshly isolated from SD rat. ADP, U46619 or arachidonic acid (AA) induced platelet aggregation assay were performed to evaluate the anti-platelet properties of CGP. Activated α_IIbβ₃ integrin abundance, serotonin (5-HT) secretion, thromboxane A₂ (TXA₂) synthesis was determined to assess the effects of CGP on platelet activation. Furthermore, RhoA and PI3K/Akt/GSK3β signal transduction were analyzed by Western Blotting assay. In addition, radiolabelled ligand binding assay was involved to evaluate the ability of CGP binding to thromboxane prostanoid (TP) and P2Y₁₂ receptors.

RESULTS

CGP inhibited platelet aggregation induced by ADP, U46619 and arachidonic acid (AA), significantly. Furthermore, it is also found that LGP exhibited obvious inhibitory effects on α_IIbβ₃ integrin activation, serotonin (5-HT) secretion from granule and thromboxane A₂ (TXA₂) synthesis. Next, we found that CGP suppressed RhoA and PI3K/Akt/GSK3β signal transduction. Data from radiolabelled ligand binding assay showed that CGP displayed apparent competing effects on TP and P2Y₁₂ receptors.

CONCLUSION

Collectively, the data presented here demonstrated that CGP, a natural compound from Callicarpa nudiflora Hook, inhibited the development of platelet aggregation and amplification of platelet activation. These inhibitory effects may be associated with its dual-receptor inhibition on P2Y₁₂ and TP receptors.

Platelets: an outlook from biology through evidence-based achievements in critical care

Since the original observations by Bizzozero and Osler, we have seen tremendous advances in the understanding of platelets far beyond haemostasis and the restoration of injured endothelium. In this mini-review on platelets, we will briefly outline their historical description and the importance of their evolution, focusing on a 450 million years old living fossil of Limulus polyphemus, a marine chelicerate arthropod, which helped researchers explain the basis for the immunity role of platelets and make correlations with platelet ultrastructure and function. In addition, the impact of the Limulus Amoebocyte Lysate (LAL) test for modern medicine is highlighted. The role of platelets in cardiovascular diseases, their relevance in arterial and venous thrombosis, and the utilization of antithrombotic drugs as therapeutic agents are also reported. Furthermore, platelet receptors are crucial in aggravating or mitigating other diseases, such as cancer and infections, which can recruit cells and have numerous interactions in a process recently coined "NETosis formation", which is also briefly depicted.

The effect of anthocyanin supplementation in modulating platelet function in sedentary population: a randomised, double-blind, placebo-controlled, cross-over trial

The anti-thrombotic properties of anthocyanin (ACN) supplementation was evaluated in this randomised, double-blind, placebo (PBO) controlled, cross-over design, dietary intervention trial in sedentary population. In all, sixteen participants (three males and thirteen females) consumed ACN (320 mg/d) or PBO capsules for 28 d followed by a 2-week wash-out period. Biomarkers of thrombogenesis and platelet activation induced by ADP; platelet aggregation induced by ADP, collagen and arachidonic acid; biochemical, lipid, inflammatory and coagulation profile were evaluated before and after supplementation. ACN supplementation reduced monocyte-platelet aggregate formation by 39 %; inhibited platelet endothelial cell adhesion molecule-1 expression by 14 %; reduced platelet activation-dependant conformational change and degranulation by reducing procaspase activating compound-1 (PAC-1) (↓10 %) and P-selectin expression (↓14 %), respectively; and reduced ADP-induced whole blood platelet aggregation by 29 %. Arachidonic acid and collagen-induced platelet aggregation; biochemical, lipid, inflammatory and coagulation parameters did not change post-ACN supplementation. PBO treatment did not have an effect on the parameters tested. The findings suggest that dietary ACN supplementation has the potential to alleviate biomarkers of thrombogenesis, platelet hyperactivation and hyper-aggregation in sedentary population.

Design, development and characterization of ACT017, a humanized Fab that blocks platelet's glycoprotein VI function without causing bleeding risks

Glycoprotein VI is a platelet-specific collagen receptor critical for in vivo formation of arterial thrombosis. It is also considered as an attractive target for the development of anti-thrombotic drugs because blocking glycoprotein (GP)VI inhibits platelet aggregation without inducing detrimental effects on physiologic hemostasis.

Here, we present data on the identification, in vitro and ex vivo pharmacology of a humanized Fab fragment designated as ACT017. ACT017 was selected out of 15 humanized variants based upon structural and functional properties. It was produced under GMP-like conditions followed by detailed physico-chemical analysis and functional characterization indicating high antigen-binding specificity and affinity. In addition, we demonstrate, in a dose-escalation study, that ACT017 has a high capacity to specifically inhibit collagen-induced platelet aggregation ex vivo after injection to the macaque without inducing thrombocytopenia, GPVI depletion or bleeding side effects as is the case for conventional anti-platelets. Therefore, ACT017 is a promising therapeutic candidate for the development of a new generation of safe and efficient anti-thrombotic drugs.

Anti-GPVI Fab SAR264565 effectively blocks GPVI function in ex vivo human platelets under arterial shear in a perfusion chamber

INTRODUCTION

Glycoprotein VI (GPVI) is the major platelet receptor for collagen-mediated platelet adhesion and activation. SAR264565 is an anti-GPVI-Fab, binds to GPVI with high affinity, and blocks GPVI function in human platelets in vitro.

METHODS

The effect of SAR26456 on platelet responsiveness in the blood of 21 healthy male subjects was investigated using Sakariassen's ex vivo thrombogenesis perfusion chamber model on a collagen-coated surface under conditions mimicking arterial flow. Ex vivo effects of SAR264565 (10 and 100 μg/mL) were investigated before administration of aspirin or clopidogrel to study subjects (baseline), after aspirin (2× 300 mg) administration alone, and after combined aspirin (2× 300 mg)/clopidogrel (600 mg) administration. Additional ex vivo and in vitro platelet tests were also performed.

RESULTS

Addition of SAR264565 to the perfusion chamber dose-dependently reduced platelet and fibrin deposition, reaching statistical significance at 100 μg/mL (415 ± 67 compared to 137 ± 36 platelets/cm², [p < 0.01] and fibrin 0.095 ± 0.014 compared to 0.032 ± 0.008 μg/cm², [p < 0.001]). Aspirin administration caused an additive and dose-dependent reduction of SAR264565-induced platelet and fibrin deposition. Combined aspirin/clopidogrel administration did not lead to additional SAR264565-induced inhibition of platelet or fibrin deposition.

CONCLUSION

GPVI antagonism by the anti-GPVI-Fab fragment SAR264565 dose-dependently inhibits platelet adhesion and fibrin formation on a collagen surface under arterial shear. Additive inhibition is observed after prior aspirin administration with no further amplification on top of a combination of aspirin with clopidogrel. Ex vivo antiplatelet tests confirmed a selective inhibiting effect of SAR264565 on collagen-induced platelet activation.

Adenosine A2A receptor agonists with potent antiplatelet activity

Selected adenosine A_2A receptor agonists (PSB-15826, PSB-12404, and PSB-16301) have been evaluated as new antiplatelet agents. In addition, radioligand-binding studies and receptor-docking experiments were performed in order to explain their differential biological effects on a molecular level. Among the tested adenosine derivatives, PSB-15826 was the most potent compound to inhibit platelet aggregation (EC₅₀ 0.32 ± 0.05 µmol/L) and platelet P-selectin cell-surface localization (EC₅₀ 0.062 ± 0.2 µmol/L), and to increase intraplatelets cAMP levels (EC₅₀ 0.24 ± 0.01 µmol/L). The compound was more active than CGS21680 (EC₅₀ 0.97±0.07 µmol/L) and equipotent to NECA (EC₅₀ 0.31 ± 0.05 µmol/L) in platelet aggregation induced by ADP. In contrast to the results from cAMP assays, K_i values determined in radioligand-binding studies were not predictive of the A_2A agonists' antiplatelet activity. Docking studies revealed the key molecular determinants of this new family of adenosine A_2A receptor agonists: differences in activities are related to π-stacking interactions between the ligands and the residue His264 in the extracellular loop of the adenosine A_2A receptor which may result in increased residence times. In conclusion, these results provide an improved understanding of the requirements of antiplatelet adenosine A_2A receptor agonists.

Mutant botrocetin-2 inhibits von Willebrand factor-induced platelet agglutination

Essentials Botrocetin-2 (Bot2) binds to von Willebrand factor (VWF) and induces platelet agglutination. We identified Bot2 residues that are required for binding to VWF and glycoprotein (GP) Ib. We produced a mutant Bot2 that binds to VWF but inhibits platelet agglutination. Mutant Bot2 could be used as a potential anti-thrombotic reagent to block VWF-GPIb interaction.

SUMMARY

Background Botrocetin-2 (Bot2) is a botrocetin-like protein composed of α and β subunits that have been cloned from the snake Bothrops jararaca. Bot2 binds specifically to von Willebrand factor (VWF), and the complex induces glycoprotein (GP) Ib-dependent platelet agglutination. Objectives To exploit Bot2's VWF-binding capacity in order to attempt to create a mutant Bot2 that binds to VWF but inhibits platelet agglutination. Methods and Results Several point mutations were introduced into Bot2 cDNA, and the recombinant protein (recombinant Bot2 [rBot2]) was purified on an anti-botrocetin column. The mutant rBot2 with either Ala at Asp70 in the β subunit (Aspβ70Ala), or Argβ115Ala and Lysβ117Ala, showed reduced platelet agglutination-inducing activity. rBot2 with Aspβ70Ala showed little binding activity towards immobilized VWF on an ELISA plate, whereas rBot2 with Argβ115Ala/Lysβ117Ala showed reduced binding activity towards GPIb (glycocalicin) after forming a complex with VWF. rBot2 point-mutated to oppositely charged Glu at both Argβ115 and Lysβ117 showed normal binding activity towards VWF but no platelet-agglutinating activity. Furthermore, this doubly mutated protein inhibited ristocetin-induced or high shear stress-induced platelet aggregation, and restrained thrombus formation under flow conditions. Conclusions Asp70 in the β subunit of botrocetin is important for VWF binding, and Arg115 and Lys117 in the β subunit are essential for interaction with GPIb. Doubly mutated rBot2, with Argβ115Glu and Lysβ117Glu, repels GPIb and might have potential as an antithrombotic reagent that specifically blocks VWF function. This is the first report on an artificial botrocetin that can inhibit the VWF-GPIb interaction.

The P2Y1 receptor antagonist MRS2500 prevents carotid artery thrombosis in cynomolgus monkeys

Adenosine diphosphate directly induces platelet aggregation via the G-protein coupled P2Y1 and P2Y12 receptors. P2Y12, but not P2Y1, receptor antagonists are available in the clinic. The relevance of the P2Y1 receptor as an antiplatelet target has been studied in rodents, but not in higher species. We therefore examined effects of the pharmacological blockade of the P2Y1 receptor with its selective antagonist MRS2500 in monkey models of electrolytic-mediated arterial thrombosis (ECAT) and kidney bleeding time (KBT). Abciximab, a GPIIb-IIIa antagonist, and cangrelor, a P2Y12 antagonist, were utilized to validate these monkey models. Compounds were given IV at 15-60 min before thrombosis initiation in anesthetized monkeys. Scanning electron microscopy showed the luminal surface of thrombotic artery covered with platelet aggregates and fibrin network. Administration of abciximab at 0.25 and 0.7 mg/kg IV significantly reduced thrombus weight by 71 ± 1 and 100 ± 0 %, and increased KBT by 10.0 ± 0.1- and 10.1 ± 0-fold, respectively (n = 3/dose). Likewise, cangrelor at 0.6 and 2 mg/kg/h IV significantly reduced thrombus weight significantly by 72 ± 9 % and 100 ± 0 % and increased KBT by 2.1 ± 0.1- and 9.8 ± 0.2-fold, respectively (n = 3/dose). MRS2500 [mg/kg + mg/kg/h IV] at 0.09 + 0.14 and 0.45 + 0.68 significantly reduced thrombus weight by 57 ± 1 % and 88 ± 1 % and increased KBT by 2.1 ± 0.3- and 4.9 ± 0.6-fold, respectively (n = 4/dose). In summary, MRS2500 prevented occlusive arterial thrombosis at a dose that moderately prolonged KBT, indicating a role of P2Y1 receptors in arterial thrombosis and hemostasis in monkeys. Thus P2Y1 receptor antagonism provides a suitable target for drug discovery.

Platelets and platelet adhesion molecules: novel mechanisms of thrombosis and anti-thrombotic therapies

Platelets are central mediators of thrombosis and hemostasis. At the site of vascular injury, platelet accumulation (i.e. adhesion and aggregation) constitutes the first wave of hemostasis. Blood coagulation, initiated by the coagulation cascades, is the second wave of thrombin generation and enhance phosphatidylserine exposure, can markedly potentiate cell-based thrombin generation and enhance blood coagulation. Recently, deposition of plasma fibronectin and other proteins onto the injured vessel wall has been identified as a new "protein wave of hemostasis" that occurs prior to platelet accumulation (i.e. the classical first wave of hemostasis). These three waves of hemostasis, in the event of atherosclerotic plaque rupture, may turn pathogenic, and cause uncontrolled vessel occlusion and thrombotic disorders (e.g. heart attack and stroke). Current anti-platelet therapies have significantly reduced cardiovascular mortality, however, on-treatment thrombotic events, thrombocytopenia, and bleeding complications are still major concerns that continue to motivate innovation and drive therapeutic advances. Emerging evidence has brought platelet adhesion molecules back into the spotlight as targets for the development of novel anti-thrombotic agents. These potential antiplatelet targets mainly include the platelet receptors glycoprotein (GP) Ib-IX-V complex, β3 integrins (αIIb subunit and PSI domain of β3 subunit) and GPVI. Numerous efforts have been made aiming to balance the efficacy of inhibiting thrombosis without compromising hemostasis. This mini-review will update the mechanisms of thrombosis and the current state of antiplatelet therapies, and will focus on platelet adhesion molecules and the novel anti-thrombotic therapies that target them.

[Anti-platelets without a bleeding risk: novel targets and strategies]

Anti-platelet agents such as aspirin, clopidogrel and antagonists of integrin αIIbβ3 allowed to efficiently reduce morbidity and mortality associated with arterial thrombosis. A major limit of these drugs is that they increase the risk of bleeding. During the last few years, several innovative anti-thrombotic strategies with a potentially low bleeding risk were proposed. These approaches target the collagen receptor glycoprotein (GP) VI, the GPIb/von Willebrand factor axis, the thrombin receptor PAR-1, the activated form of integrin αIIbβ3 or the ADP receptor P2Y1. While an antagonist of PAR-1 was recently marketed, the clinical proofs of the efficiency and safety of the other agents remain to be established. This review evaluates these new anti-platelet approaches toward safer anti-thrombotic therapies.

Anthocyanins in obesity-associated thrombogenesis: a review of the potential mechanism of action

Platelet dysfunction, oxidative stress and dyslipidemia are important contributors to pro-thrombotic progression particularly in obese and hyper-cholesterolemic populations.

Platelets in hemostasis and thrombosis: Novel mechanisms of fibrinogen-independent platelet aggregation and fibronectin-mediated protein wave of hemostasis

Platelets are small anucleate cells generated from megakaryocytes in the bone marrow. Although platelet generation, maturation, and clearance are still not fully understood, significant progress has been made in the last 1-2 decades. In blood circulation, platelets can quickly adhere and aggregate at sites of vascular injury, forming the platelet plug (i.e. the first wave of hemostasis). Activated platelets can also provide negatively charged phosphatidylserinerich membrane surface that enhances cell-based thrombin generation, which facilitates blood coagulation (i.e. the second wave of hemostasis). Platelets therefore play central roles in hemostasis. However, the same process of hemostasis may also cause thrombosis and vessel occlusion, which are the most common mechanisms leading to heart attack and stroke following ruptured atherosclerotic lesions. In this review, we will introduce the classical mechanisms and newly discovered pathways of platelets in hemostasis and thrombosis, including fibrinogen-independent platelet aggregation and thrombosis, and the plasma fibronectin-mediated "protein wave" of hemostasis that precedes the classical first wave of hemostasis. Furthermore, we briefly discuss the roles of platelets in inflammation and atherosclerosis and the potential strategies to control atherothrombosis.

Purinergic Receptors in Thrombosis and Inflammation

Under various pathological conditions, including thrombosis and inflammation, extracellular nucleotide levels may increase because of both active release and passive leakage from damaged or dying cells. Once in the extracellular compartment, nucleotides interact with plasma membrane receptors belonging to the P2 purinergic family, which are expressed by virtually all circulating blood cells and in most blood vessels. In this review, we focus on the specific role of the 3 platelet P2 receptors P2Y1, P2Y12, and P2X1 in hemostasis and arterial thrombosis. Beyond platelets, these 3 receptors, along with the P2Y2, P2Y6, and P2X7 receptors, constitute the main P2 receptors mediating the proinflammatory effects of nucleotides, which play important roles in various functions of circulating blood cells and cells of the vessel wall. Each of these P2 receptor subtypes specifically contributes to chronic or acute vascular inflammation and related diseases, such as atherosclerosis, restenosis, endotoxemia, and sepsis. The potential for therapeutic targeting of these P2 receptor subtypes is also discussed.