Mechanisms of platelet activation by thrombin: A short history

Platelet flux in trauma-associated venous thromboembolism: A secondary analysis of the Consortium of Leaders in the Study of Traumatic Thromboembolism (CLOTT) studies

BACKGROUND

Venous thromboembolism (VTE) after traumatic injury is morbid. Evaluating changes in platelets in injured patients who develop VTE could identify platelet-based strategies for management of thrombotic complications after injury.

METHODS

In a prospectively designed secondary analysis of a multicenter cohort study conducted by the Consortium of Leaders in the Study of Traumatic Thromboembolism (CLOTT1) study group, injured patients aged 18 to 40 years admitted for a minimum of 48 hours with at least one risk factor for VTE were evaluated. A subset of CLOTT1 patients had platelet aggregometry and thromboelastography performed to examine platelet function (CLOTT2). Patients who developed VTE were compared with those who did not.

RESULTS

Of 7,805 patients from CLOTT1 (mean [SD] age, 29.1 [6.4] years; 1,987 [25.5%] female), 425 (5.4%) developed VTE. Platelet count was lower at each time point for patients with VTE (admission: 242 [234-251] vs. 254 [252-256], p < 0.01; hospital day 1: 157 [150-164] vs. 197 [195-198], p < 0.01; all counts ×109/L). An initial 10-point reduction in platelet count was associated with development of VTE (odds ratio, 1.32 [1.13-1.53]; p < 0.01) controlling for shock, injury severity, coagulopathy, sex, and product transfusion. When evaluating 129 CLOTT2 patients, velocity of platelet aggregation was higher on admission in the VTE group (18.5 vs. 12.8 aggregation units/min; p < 0.01) in response to adenosine diphosphate stimulation. In response to thrombin stimulation, velocity of platelet aggregation was higher at 48 hours (34.4 vs. 12.3 aggregation units/min; p < 0.01), and overall aggregation was higher in the VTE group at 72 hours (area under the curve, 173.2 vs. 129.6; p < 0.01). Thromboelastography results were not different between groups.

CONCLUSION

This study identified an association of early reduction in platelet count with the development of VTE in injured patients at risk for VTE. P2Y1/2 and protease-activated receptor 1 receptor stimulation changes in platelet aggregation responses are altered in VTE patients. Interrogating platelet count and functional responses may be beneficial in evaluating thrombotic complications after injury.

LEVEL OF EVIDENCE

Diagnostic Test/Criteria; Level II.

Activation dynamics study of trapped platelets using a lab-built optical tweezers micro-raman spectrometer

It is well documented that platelet disorders can result from various causes and can lead to different disease conditions such as cardiovascular diseases (CVDs), thrombocythemia, thrombocytopenia, Autoimmune diseases, Alzheimer's disease (AD), and even cancer, to name a few. The diagnosis of many of these diseases mainly depends on imaging examinations, clinical analysis and neuropsychological tests, these may be time taking procedures and, have a high chances of false positive/false negative results. The Raman tweezers spectroscopy can provide trust worthy results without much time delay. In the present study the activation dynamics of platelets were studied and observed that the activation leads to biochemical and morphological changes, such as the formation of filopodia on the platelet surface, transformation in the shape from discoid to spherical, and translocation of aminophospholipids from inner leaflet to the outer leaflet of the plasma membrane. The Raman bands corresponding to phospholipids shows remarkable intensity variations during activation. The detailed knowledge regarding the activation dynamics of platelets will be important in monitoring CVDs, ADs, etc. and this paper illustrates a prospective method that can be incorporated into clinical settings in the near future to study and analyze platelet activation. This study will be the first to display the trapping of platelets in its live form to study their activation dynamics using an in-house assembled optical tweezers micro-Raman spectrometer.

Platelet Physiology

Platelets are the smallest blood cells, numbering 150 to 350 × 109/L in healthy individuals. The ability of activated platelets to adhere to an injured vessel wall and form aggregates was first described in the 19th century. Besides their long-established roles in thrombosis and hemostasis, platelets are increasingly recognized as pivotal players in numerous other pathophysiological processes including inflammation and atherogenesis, antimicrobial host defense, and tumor growth and metastasis. Consequently, profound knowledge of platelet structure and function is becoming more important in research and in many fields of modern medicine. This review provides an overview of platelet physiology focusing particularly on the structure, granules, surface glycoproteins, and activation pathways of platelets.

Efficacy of Autologous Platelet-Rich Plasma Injections for Treating Plantar Fasciitis

Introduction Plantar fasciitis, a common cause of heel pain, is often treated conservatively. Platelet-rich plasma (PRP) injections have emerged as a promising treatment option. This study aimed to evaluate the efficacy of autologous PRP injections for plantar fasciitis. The objective of this study was to assess the effectiveness of autologous PRP injections delivered at the plantar fascia origin in reducing pain (measured by the Visual Analog Scale (VAS) pain intensity score) in patients with plantar fasciitis. Materials and methods A prospective cohort study was conducted at the Department of Orthopedics, Hayatabad Medical Complex, Peshawar. Patients with plantar fasciitis, a VAS pain score ≥ 7, and failure of conservative treatment were included. A single injection of autologous PRP was administered to the plantar fascia. Pain reduction was assessed using the VAS score at a 12-week follow-up. Result The study included 163 patients. Success was achieved in 80.3% of cases, showing that autologous PRP injection resulted in significant pain improvement in patients with plantar fasciitis (p≤0.05). An increased likelihood of successful treatment was observed in individuals with symptoms lasting less than 12 months. No other variables (gender, age group, residence, literacy) significantly impacted treatment efficacy. Conclusion Autologous PRP injections may be a promising treatment option for plantar fasciitis, particularly when administered early. Further research is needed to validate these findings and explore optimal patient selection criteria.

O-GlcNAcylation: Crosstalk between Hemostasis, Inflammation, and Cancer

O-linked β-N-acetylglucosamine (O-GlcNAc, O-GlcNAcylation) is a post-translational modification of serine/threonine residues of proteins. Alterations in O-GlcNAcylation have been implicated in several types of cancer, regulation of tumor progression, inflammation, and thrombosis through its interaction with signaling pathways. We aim to explore the relationship between O-GlcNAcylation and hemostasis, inflammation, and cancer, which could serve as potential prognostic tools or clinical predictions for cancer patients' healthcare and as an approach to combat cancer. We found that cancer is characterized by high glucose demand and consumption, a chronic inflammatory state, a state of hypercoagulability, and platelet hyperaggregability that favors thrombosis; the latter is a major cause of death in these patients. Furthermore, we review transcription factors and pathways associated with O-GlcNAcylation, thrombosis, inflammation, and cancer, such as the PI3K/Akt/c-Myc pathway, the nuclear factor kappa B pathway, and the PI3K/AKT/mTOR pathway. We also review infectious agents associated with cancer and chronic inflammation and potential inhibitors of cancer cell development. We conclude that it is necessary to approach both the diagnosis and treatment of cancer as a network in which multiple signaling pathways are integrated, and to search for a combination of potential drugs that regulate this signaling network.

Hutchinson-Gilford progeria syndrome mice display accelerated arterial thrombus formation and increased platelet reactivity

INTRODUCTION

Hutchinson-Gilford Progeria Syndrome (HGPS) is an ultra-rare premature aging genetic disorder caused by a point mutation in the lamin A gene, LMNA. Children with HGPS display short lifespans and typically die due to myocardial infarction or ischemic stroke, both acute cardiovascular events that are tightly linked to arterial thrombosis. Despite this fact, the effect of the classic HGPS LMNA gene mutation on arterial thrombosis remains unknown.

METHODS

Heterozygous LmnaG609G knock-in (LmnaG609G/+) mice, yielding an equivalent classic mutation observed in HGPS patients (c.1824C>T; pG608G mutation in the human LMNA gene) and corresponding wild-type (WT) control littermates underwent photochemically laser-induced carotid injury to trigger thrombosis. Coagulation and fibrinolytic factors were measured. Furthermore, platelet activation and reactivity were investigated.

RESULTS

LmnaG609G/+ mice displayed accelerated arterial thrombus formation, as underlined by shortened time to occlusion compared to WT littermates. Levels of factors involved in the coagulation and fibrinolytic system were comparable between groups, while LmnaG609G/+ animals showed higher plasma levels of thrombin-antithrombin complex and lower levels of antithrombin. Bone marrow analysis showed larger megakaryocytes in progeric mice. Lastly, enhanced platelet activation upon adenosine diphosphate, collagen-related peptide, and thrombin stimulation was observed in LmnaG609G/+ animals compared to the WT group, indicating a higher platelet reactivity in progeric animals.

CONCLUSIONS

LMNA mutation in HGPS mice accelerates arterial thrombus formation, which is mediated, at least in part, by enhanced platelet reactivity, which consequently augments thrombin generation. Given the wide spectrum of antiplatelet agents available clinically, further investigation is warranted to consider the most suitable antiplatelet regimen for children with HGPS to mitigate disease mortality and morbidity.

Combining dipyridamole and cilostazol with up-dosing antihistamines improves outcomes in chronic spontaneous urticaria with high D-dimer levels: A randomized controlled trial

In a double-blind, randomized controlled trial, we investigated the effectiveness of adding antiplatelet drugs to up-dosing antihistamines for the treatment of chronic spontaneous urticaria (CSU) in patients with elevated D-dimer levels who had an inadequate response to conventional antihistamine doses. Twenty patients with Urticaria Activity Score over 7 days (UAS7) ≥16 and D-dimer >500 ng/mL were randomized to receive either antiplatelet therapy (cilostazol 150 mg/day + dipyridamole 50 mg/day) with antihistamine (desloratadine 20 mg/day) or antihistamine alone for 4 weeks. The antiplatelet group demonstrated a greater decrease in UAS7 compared to the control group (28.10 to 8.90 vs. 22.90 to 16.40, p < 0.001 vs. p = 0.054). Both groups experienced improved quality of life (DLQI), but the improvement was greater in the antiplatelet group (p = 0.046). D-dimer levels decreased only in the antiplatelet group (1133.67 ng/mL to 581.89 ng/mL, p = 0.013) with no significant change observed in the control group. This suggests that combining dipyridamole and cilostazol with up-dosing antihistamines may be more effective for CSU patients with high D-dimer levels compared to up-dosing antihistamines alone. This could be due to a reduction in platelet activation, as evidenced by the decrease in D-dimer levels observed in the antiplatelet group.

Anti-Platelet Activity of Sea Buckthorn Seeds and Its Relationship with Thermal Processing

Sea buckthorn (Hippophae rhamnoides L.) is a tree or shrub with small, orange berries. Sea buckthorn seeds have shown many properties beneficial to human health, including antioxidant, anti-hypertensive, anti-hyperlipidemic, and retinoprotective activities. Seeds, as a component of food, are often exposed to high temperatures, which can increase or decrease their biological activity. In our previous study, we showed that both raw and roasted sea buckthorn seeds had significant antioxidant activity, which was measured in human plasma in vitro. In this paper, we evaluated the effect of extracts from raw and roasted sea buckthorn seeds on several parameters of hemostasis in vitro, including thrombus formation in full blood (measured by the Total Thrombus formation Analysis System-T-TAS), blood platelet activation (based on the exposition of P-selectin, the active form of GPIIb/IIIa on their surface and platelet-derived microparticles formation), aggregation (measured with impedance aggregometry), adhesion to fibrinogen and collagen, arachidonic acid metabolism in washed platelets stimulated by thrombin, and COX-1 activity. We also measured the levels of free 8-isoprostane in plasma and the total non-enzymatic antioxidant status of plasma. The extract from roasted seeds (50 µg/mL) significantly prolonged the time of occlusion measured by T-TAS-the AUC10 (area under the curve) value was decreased by approximately 18%. Both extracts decreased the exposition of the active form of GPIIb/IIIa on the surface of platelets activated with 10 μM ADP (by 38.4-62.2%) and 20 μM ADP (by 39.7-51.3%). Moreover, the extract from raw seeds decreased the exposition of P-selectin on the surface of platelets stimulated with 20 μM ADP (by 31.2-34.9%). The adhesion of thrombin-stimulated platelets to fibrinogen and collagen was inhibited only by the extract from roasted sea buckthorn seeds (by 20-30%). Moreover, the extract from raw seeds inhibited the level of TBARS (thiobarbituric acid-reactive substances, an indicator of enzymatic peroxidation of arachidonic acid) in washed platelets stimulated with thrombin; the activity of COX-1 was inhibited by both extracts, although the effect of the extract from raw seeds was stronger. These results indicate that sea buckthorn seeds have anti-platelet activity that is not decreased by thermal processing, but more research is needed to determine which exact chemical compounds and mechanisms are responsible for this phenomenon.

The evolving knowledge on primary hemostasis in patients with cirrhosis: A comprehensive review

Patients with cirrhosis develop complex alterations in primary hemostasis that include both hypocoagulable and hypercoagulable features. This includes thrombocytopenia, multiple alterations of platelet function, and increased plasma levels of von Willebrand factor. Contrary to the historical view that platelet dysfunction in cirrhosis might be responsible for an increased bleeding tendency, the current theory posits a rebalanced hemostasis in patients with cirrhosis. Severe thrombocytopenia is not indicative of the bleeding risk in patients undergoing invasive procedures and does not dictate per se the need for pre-procedural prophylaxis. A more comprehensive and individualized risk assessment should combine hemostatic impairment, the severity of decompensation and systemic inflammation, and the presence of additional factors that may impair platelet function, such as acute kidney injury and bacterial infections. Although there are multiple, complex alterations of platelet function in cirrhosis, their net effect is not yet fully understood. More investigations evaluating the association between alterations of platelet function and bleeding/thrombosis may improve risk stratification in patients with decompensated cirrhosis. Besides hemostasis, the assessment of von Willebrand factor Ag and ADP-induced, whole-blood platelet aggregation normalized by platelet count (VITRO score and PLT ratio) are promising biomarkers to predict the risk of hepatic decompensation and survival in both compensated and decompensated patients. Further investigations into the in vivo interplay between platelets, circulating blood elements, and endothelial cells may help advance our understanding of cirrhotic coagulopathy. Here, we review the complex changes in platelets and primary hemostasis in cirrhosis and their potential clinical implications.

Bioactive components and molecular mechanisms of Salvia miltiorrhiza Bunge in promoting blood circulation to remove blood stasis

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia miltiorrhiza Bunge (SM) is an outstanding herbal medicine with various traditional effects, especially promoting blood circulation to remove blood stasis. It has been widely used for centuries to treat blood stasis syndrome (BSS)-related diseases. BSS is one of the basic pathological syndromes of diseases such as cardiovascular and cerebrovascular diseases in traditional East Asian medicine, which is characterized by disturbance of blood circulation. However, the bioactive components and mechanisms of SM in the treatment of BSS have not been systematically reviewed. Therefore, this article outlines the anti-BSS effects of bioactive components of SM, concentrating on the molecular mechanisms.

AIM OF THE REVIEW

To summarize the bioactive components of SM against BSS and highlight its potential targets and signaling pathways, hoping to provide a modern biomedical perspective to understand the efficacy of SM on enhancing blood circulation to remove blood stasis.

MATERIALS AND METHODS

A comprehensive literature search was performed to retrieve articles published in the last two decades on bioactive components of SM used for BSS treatment from the online electronic medical literature database (PubMed).

RESULTS

Phenolic acids and tanshinones in SM are the main bioactive components in the treatment of BSS, including but not limited to salvianolic acid B, tanshinone IIA, salvianolic acid A, cryptotanshinone, Danshensu, dihydrotanshinone, rosmarinic acid, protocatechuic aldehyde, and caffeic acid. They protect vascular endothelial cells by alleviating oxidative stress and inflammatory damage and regulating of NO/ET-1 levels. They also enhance anticoagulant and fibrinolytic capacity, inhibit platelet activation and aggregation, and dilate blood vessels. Moreover, lowering blood lipids and improving blood rheological properties may be the underlying mechanisms of their anti-BSS. More notably, these compounds play an anti-BSS role by mediating multiple signaling pathways such as Nrf2/HO-1, TLR4/MyD88/NF-κB, PI3K/Akt/eNOS, MAPKs (p38, ERK, and JNK), and Ca2+/K+ channels.

CONCLUSIONS

Both phenolic acids and tanshinones in SM may act synergistically to target different signaling pathways to achieve the effect of promoting blood circulation.

Impact of Factor Xa Inhibition on Coagulation, Platelet Reactivity, and Thrombosis in Patients with Peripheral Artery Disease

BACKGROUND

The role of thrombin in vascular pathology is a focus of investigation. The incorporation of direct Factor Xa inhibition into practice patterns is based on its theoretical dual-pathway attenuation of both thrombin generation and platelet aggregation. However, quantification of the effect of direct anti-Xa medications on platelet function is not established. Thromboelastography with platelet mapping (TEG-PM) leverages dual-pathway metrics to provide comprehensive coagulation profiles. We evaluated the effects of direct oral anticoagulants (DOACs) on coagulation and platelet function profiles and correlate these data with postoperative major adverse limb events (MALEs) in patients with PAD.

METHODS

We conducted a prospective study of patients undergoing lower extremity revascularization with serial perioperative TEG-PM analysis. Patients on DOACs were compared to those not on DOACs, and stratified by concurrent mono-antiplatelet or dual-antiplatelet regimens (MAPT/DAPT). Postoperative MALE was recorded and difference in antithrombotic regimens and TEG-PM analysis compared between groups.

RESULTS

Four hundred seventy-one samples from 141 patients were analyzed. Twenty-nine point five percent were reflective of circulating DOAC therapy. Compared to MAPT alone, patients on DOAC + MAPT exhibited longer time to clot formation (R-time) [7.4 (±2.4) vs. 6.7 (±2.7); P < 0.02], but less platelet inhibition. Patients on DAPT exhibited greater platelet inhibition compared to either group [23.7 (±26.9) vs. 31.0 (±28.3) vs. 42.2 (±31.2); P < 0.01]. Patients who experienced MALE were more likely to be on DOAC therapy [43.8% vs. 22.0% P = 0.02]. Thromboelastography with platelet mapping analysis from patients who experienced MALE also demonstrated longer R-time [8.6 (±3.9 vs. 7.3 (±3.0); P = 0.05] and increased maximum clot amplitude (MA) [66.7 (±4.2) vs. 61.8 (±8.2); P = 0.001].

CONCLUSIONS

Direct oral anticoagulant therapy resulted in a prolonged R-time but had no impact on platelet inhibition. Patients who experienced MALE were more often on DOACs and demonstrated an increased R-time, but also showed greater platelet reactivity evident by increased MA, suggesting DOACs may not be effective at protecting against MALE. Further research comparing DOAC therapy to a DAPT approach may add clarity to emerging multimodal antithrombotic recommendations.

Antiplatelet drugs: Potential therapeutic options for the management of neurodegenerative diseases

The blood platelet plays an important role but often remains under-recognized in several vascular complications and associated diseases. Surprisingly, platelet hyperactivity and hyperaggregability have often been considered the critical risk factors for developing vascular dysfunctions in several neurodegenerative diseases (NDDs) like Alzheimer's disease, Parkinson's disease, Huntington's disease, and multiple sclerosis. In addition, platelet structural and functional impairments promote prothrombotic and proinflammatory environment that can aggravate the progression of several NDDs. These findings provide the rationale for using antiplatelet agents not only to prevent morbidity but also to reduce mortality caused by NDDs. Therefore, we thoroughly review the evidence supporting the potential pleiotropic effects of several novel classes of synthetic antiplatelet drugs, that is, cyclooxygenase inhibitors, adenosine diphosphate receptor antagonists, protease-activated receptor blockers, and glycoprotein IIb/IIIa receptor inhibitors in NDDs. Apart from this, the review also emphasizes the recent developments of selected natural antiplatelet phytochemicals belonging to key classes of plant-based bioactive compounds, including polyphenols, alkaloids, terpenoids, and flavonoids as potential therapeutic candidates in NDDs. We believe that the broad analysis of contemporary strategies and specific approaches for plausible therapeutic treatment for NDDs presented in this review could be helpful for further successful research in this area.

The medicinal panorama of benzimidazoles and their scaffolds as anticancer and antithrombotic agents: A review

Nitrogen-containing heterocyclic scaffolds have become a prospective pharmacophore with therapeutic importance due to their biological similarities with natural and synthetic drugs. Among all nitrogen heterocyclic compounds, benzimidazoles and their derivatives are privileged molecules structurally akin to naturally available nucleotides, enabling them to intercommunicate with numerous biopolymers in biological systems. This reason enlightens modern researchers worldwide to assess their potential significance in the context of synthetic and biological chemistry. Therefore, it is crucial to merge the latest data with the prior documentation to apprehend the ongoing situation of the benzimidazole moiety in various therapeutic zones of research. The current work displays that the benzimidazole center is a versatile nucleus that offers the necessary data of synthetic alterations for pre-existing compounds to provide new scaffolds to resist numerous therapeutic sectors, including those associated with anticancer and antithrombosis. Due to the potential significance of benzimidazoles, this review aims to emphasize the latest innovations in synthesizing several other notable benzimidazole substrates and their significant pharmacological prospects for the future, including anticancer and antithrombosis.

Aged-Signal-Eliciting Nanoparticles Stimulated Macrophage-Mediated Programmed Removal of Inflammatory Neutrophils

Excessive infiltration of activated neutrophils is regarded as a predominant cause of tissue injury in neutrophilic inflammation. Although programmed cell death like apoptosis maintains the homeostasis of activated neutrophils, this process is disrupted by an abnormal inflammatory response. Unlike endogenous calreticulin exposed during apoptosis, exogenous calreticulin acts as an "aged" signal and initiates premature macrophage-mediated programmed cell removal (PrCR), which is independent of apoptosis. Here, we report a nano-mediated strategy to stimulate the precise clearance of activated neutrophils initiated with artificial aged signal and alleviated inflammation. Polymeric nanoparticles PC@PLGA were fabricated by cloaking poly(lactic-co-glycolic acid) (PLGA) with a hybrid membrane derived from platelet-derived extracellular vesicles (PEVs, denoted by P) and the calreticulin-expressed membrane obtained from doxorubicin-treated cells (denoted by C). P-selectin in PEVs favors PC@PLGA to anchor activated neutrophils, while calreticulin mimics exogenous "aged" signal secreted by macrophages to trigger PrCR. We showed that PC@PLGA specifically targeted activated neutrophils and misled macrophages to recognize them as "aged" neutrophils and then initiated premature PrCR and prevented proinflammatory response and tissue damage in a mouse model of acute lung injury and severe acute pancreatitis. The collective findings indicate the efficiency of specific elimination of activated neutrophils with exogenous aged signal in improving inflammation therapy.

Crosstalk of Immune Cells and Platelets in an Ovarian Cancer Microenvironment and Their Prognostic Significance

Ovarian cancer (OC) is one of the deadliest gynecological cancers, largely due to the fast development of metastasis and drug resistance. The immune system is a critical component of the OC tumor microenvironment (TME) and immune cells such as T cells, NK cells, and dendritic cells (DC) play a key role in anti-tumor immunity. However, OC tumor cells are well known for evading immune surveillance by modulating the immune response through various mechanisms. Recruiting immune-suppressive cells such as regulatory T cells (Treg cells), macrophages, or myeloid-derived suppressor cells (MDSC) inhibit the anti-tumor immune response and promote the development and progression of OC. Platelets are also involved in immune evasion by interaction with tumor cells or through the secretion of a variety of growth factors and cytokines to promote tumor growth and angiogenesis. In this review, we discuss the role and contribution of immune cells and platelets in TME. Furthermore, we discuss their potential prognostic significance to help in the early detection of OC and to predict disease outcome.

The Tissue Factor Pathway in Cancer: Overview and Role of Heparan Sulfate Proteoglycans

Historically, the only focus on tissue factor (TF) in clinical pathophysiology has been on its function as the initiation of the extrinsic coagulation cascade. This obsolete vessel-wall TF dogma is now being challenged by the findings that TF circulates throughout the body as a soluble form, a cell-associated protein, and a binding microparticle. Furthermore, it has been observed that TF is expressed by various cell types, including T-lymphocytes and platelets, and that certain pathological situations, such as chronic and acute inflammatory states, and cancer, may increase its expression and activity. Transmembrane G protein-coupled protease-activated receptors can be proteolytically cleaved by the TF:FVIIa complex that develops when TF binds to Factor VII (PARs). The TF:FVIIa complex can activate integrins, receptor tyrosine kinases (RTKs), and PARs in addition to PARs. Cancer cells use these signaling pathways to promote cell division, angiogenesis, metastasis, and the maintenance of cancer stem-like cells. Proteoglycans play a crucial role in the biochemical and mechanical properties of the cellular extracellular matrix, where they control cellular behavior via interacting with transmembrane receptors. For TFPI.fXa complexes, heparan sulfate proteoglycans (HSPGs) may serve as the primary receptor for uptake and degradation. The regulation of TF expression, TF signaling mechanisms, their pathogenic effects, and their therapeutic targeting in cancer are all covered in detail here.

The protective effect of rivaroxaban with or without aspirin on inflammation, oxidative stress, and platelet reactivity in isoproterenol-induced cardiac injury in rats

Coronary artery diseases are principal sources of mortality and disability in global human population. Progressively, rivaroxaban is being evaluated for the prevention of atherosclerotic thrombi, particularly with anti-platelet agents. Hence, the current report aimed to investigate the cardioprotective effect of rivaroxaban on isoproterenol (ISO)-induced cardiac injury model in rats and the possible synergistic effect when combined with aspirin. Male Wistar rats were randomly assigned into five different groups. Cardiac injury was induced by subcutaneous injection of ISO (85 mg/kg) for 2 consecutive days. Rat tail bleeding time was performed prior to sacrifice. Cardiac enzymes, platelet activity, inflammatory, and oxidative stress biomarkers levels were measured using enzyme-linked immunoassay (ELISA). Pre-administration of rivaroxaban alone and on combination with aspirin prevented ISO-induced increase in cardiac thiobarbituric acid reactive substances (TBARS), interleukin 6 (IL-6), and thromboxane B2 (TXB2) levels. Moreover, a significant prolongation of bleeding time was demonstrated among aspirin, rivaroxaban, and aspirin plus rivaroxaban treated groups. On the other hand, the combination treatment of aspirin plus rivaroxaban showed no marked difference in these biomarkers and bleeding time relative to either drug administered separately. However, a prominent decrease of cardiac 6-keto prostaglandin F1α (6-Keto-PGF1α) level was displayed in the combination treatment when compared with ISO and rivaroxaban-treated groups, whereas no significant improvement was seen in cardiac glycoprotein V (GPV) levels except in aspirin-treated group. The study results demonstrated that rivaroxaban decreases cardiac oxidative stress, inflammation, and platelets reactivity. However, the addition of rivaroxaban to aspirin did not seem to show synergistic antioxidant, anti-inflammatory, or antiplatelet effect.

Novel Antithrombotic Agents in Ischemic Cardiovascular Disease: Progress in the Search for the Optimal Treatment

Ischemic cardiovascular diseases have a high incidence and high mortality worldwide. Therapeutic advances in the last decades have reduced cardiovascular mortality, with antithrombotic therapy being the cornerstone of medical treatment. Yet, currently used antithrombotic agents carry an inherent risk of bleeding associated with adverse cardiovascular outcomes and mortality. Advances in understanding the pathophysiology of thrombus formation have led to the discovery of new targets and the development of new anticoagulants and antiplatelet agents aimed at preventing thrombus stabilization and growth while preserving hemostasis. In the following review, we will comment on the key limitation of the currently used antithrombotic regimes in ischemic heart disease and ischemic stroke and provide an in-depth and state-of-the-art overview of the emerging anticoagulant and antiplatelet agents in the pipeline with the potential to improve clinical outcomes.

Carbamylation of Integrin IIb 3: The Mechanistic Link to Platelet Dysfunction in ESKD

BACKGROUND

Bleeding diatheses, common among patients with ESKD, can lead to serious complications, particularly during invasive procedures. Chronic urea overload significantly increases cyanate concentrations in patients with ESKD, leading to carbamylation, an irreversible modification of proteins and peptides.

METHODS

To investigate carbamylation as a potential mechanistic link between uremia and platelet dysfunction in ESKD, we used liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) to quantify total homocitrulline, and biotin-conjugated phenylglyoxal labeling and Western blot to detect carbamylated integrin α IIb β 3 (a receptor required for platelet aggregation). Flow cytometry was used to study activation of isolated platelets and platelet-rich plasma. In a transient transfection system, we tested activity and fibrinogen binding of different mutated forms of the receptor. We assessed platelet adhesion and aggregation in microplate assays.

RESULTS

Carbamylation inhibited platelet activation, adhesion, and aggregation. Patients on hemodialysis exhibited significantly reduced activation of α IIb β 3 compared with healthy controls. We found significant carbamylation of both subunits of α IIb β 3 on platelets from patients receiving hemodialysis versus only minor modification in controls. In the transient transfection system, modification of lysine 185 in the β 3 subunit was associated with loss of receptor activity and fibrinogen binding. Supplementation of free amino acids, which was shown to protect plasma proteins from carbamylation-induced damage in patients on hemodialysis, prevented loss of α IIb β 3 activity in vitro.

CONCLUSIONS

Carbamylation of α IIb β 3-specifically modification of the K185 residue-might represent a mechanistic link between uremia and dysfunctional primary hemostasis in patients on hemodialysis. The observation that free amino acids prevented the carbamylation-induced loss of α IIb β 3 activity suggests amino acid administration during dialysis may help to normalize platelet function.

Platelet activation by SARS-CoV-2 implicates the release of active tissue factor by infected cells

Platelets are hyperactivated in coronavirus disease 2019 (COVID-19). However, the mechanisms promoting platelet activation by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are not well understood. This may be due to inherent challenges in discriminating the contribution of viral vs host components produced by infected cells. This is particularly true for enveloped viruses and extracellular vesicles (EVs), as they are concomitantly released during infection and share biophysical properties. To study this, we evaluated whether SARS-CoV-2 itself or components derived from SARS-CoV-2-infected human lung epithelial cells could activate isolated platelets from healthy donors. Activation was measured by the surface expression of P-selectin and the activated conformation of integrin αIIbβ3, degranulation, aggregation under flow conditions, and the release of EVs. We find that neither SARS-CoV-2 nor purified spike activates platelets. In contrast, tissue factor (TF) produced by infected cells was highly potent at activating platelets. This required trace amounts of plasma containing the coagulation factors FX, FII, and FVII. Robust platelet activation involved thrombin and the activation of protease-activated receptor (PAR)-1 and -4 expressed by platelets. Virions and EVs were identified by electron microscopy. Through size-exclusion chromatography, TF activity was found to be associated with a virus or EVs, which were indistinguishable. Increased TF messenger RNA (mRNA) expression and activity were also found in lungs in a murine model of COVID-19 and plasma of severe COVID-19 patients, respectively. In summary, TF activity from SARS-CoV-2–infected cells activates thrombin, which signals to PARs on platelets. Blockade of molecules in this pathway may interfere with platelet activation and the coagulation characteristic of COVID-19.

The GPIb-IX complex on platelets: insight into its novel physiological functions affecting immune surveillance, hepatic thrombopoietin generation, platelet clearance and its relevance for cancer development and metastasis

The glycoprotein (GP) Ib-IX complex is a platelet receptor that mediates the initial interaction with subendothelial von Willebrand factor (VWF) causing platelet arrest at sites of vascular injury even under conditions of high shear. GPIb-IX dysfunction or deficiency is the reason for the rare but severe Bernard-Soulier syndrome (BSS), a congenital bleeding disorder. Although knowledge on GPIb-IX structure, its basic functions, ligands, and intracellular signaling cascades have been well established, several advances in GPIb-IX biology have been made in the recent years. Thus, two mechanosensitive domains and a trigger sequence in GPIb were characterized and its role as a thrombin receptor was deciphered. Furthermore, it became clear that GPIb-IX is involved in the regulation of platelet production, clearance and thrombopoietin secretion. GPIb is deemed to contribute to liver cancer development and metastasis. This review recapitulates these novel findings highlighting GPIb-IX in its multiple functions as a key for immune regulation, host defense, and liver cancer development.

[The role of thrombin in the pathogenesis of atherosclerosis and its complications]

Thrombin is a key regulator of the homeostasis system. Also, it actively participates in progression of various systemic diseases, including atherosclerosis. There is a large amount of experimental and clinical data on the involvement of thrombin in the pathogenesis of ischemic heart disease (IHD). Thus, studying thrombin activity regulation is promising. Also, the question whether it is possible to use biomarkers of thrombin activity as predictors of cardiovascular complications in IHD patients is relevant. The present review focuses on major mechanisms of thrombin functioning, its role in development and progression of atherosclerosis, and available tests for evaluation of thrombin functional activity. Major clinical studies are discussed that evaluated the efficacy of thrombin inhibitors and protease-activated receptor antagonists.

Immunomodulatory role of thrombin in cancer progression

Coagulation proteases and the generation of thrombin are increased in tumors. In addition, chemotherapeutic agents commonly used to treat malignant cancers can exacerbate cancer-associated thromboses. Thrombin can modify tumor cell behavior directly through the activation of protease-activated receptors (PAR) or indirectly by generating fibrin matrices. In addition to its role in generating fibrin to promote hemostasis, thrombin acts directly on multiple effector cells of the immune system impacting both acute and chronic inflammatory processes. Thrombin-mediated release of interleukin-6, tumor necrosis factor-α, and monocyte chemoattractant protein-1 leads to the accumulation of multiple tumor-infiltrating immunosuppressive cell populations including myeloid derived suppresser cells, M2-like macrophages, and T regulatory cells. Ablation of PAR-1 from the tumor microenvironment, but not the tumor, has been shown to dramatically reduce tumor growth and metastasis in multiple tumor models. Thrombin-activated platelets release immunosuppressive cytokines including transforming growth factor-β that can inhibit natural killer cell activity, helping tumor cells to evade host immunosurveillance. Taken together, there is strong evidence that thrombin influences cancer progression via multiple mechanisms, including the tumor immune response, with thrombin emerging as a target for novel therapeutic strategies for cancer.

A Prospective Observational Study on Multiplate®-, ROTEM®- and Thrombin Generation Examinations Before and Early After Implantation of a Left Ventricular Assist Device (LVAD)

Background

Heart failure patients are frequently on coagulation-active medications before LVAD implantation and perioperative bleeding is a frequent complication after left ventricular assist device (LVAD) implantation. The role of point-of-care coagulation tests in assessing bleeding risk for LVAD implantation and the early postoperative time course of these tests is not well established.

Methods

We prospectively enrolled 25 patients with terminal heart failure undergoing LVAD implantation. Study related TRAP-, ASPI- and ADP- tests of Multiplate^® platelet aggregometry, ROTEM^® rotational thromboelastometry (INTEM, EXTEM, FIBTEM), thrombin generation assay and conventional laboratory studies were measured at 11 predefined time-points during the first 21 postoperative days. We examined if preoperative TRAP-, ASPI-, ADP- and ROTEM values are correlated with estimated total blood loss (primary outcome parameter) during the first 21 days after LVAD implantation and compared the baseline values of these measurements between patients with a bleeding event to those without. We performed Spearman's correlation and non-parametric tests for paired and non-paired comparisons.

Results

7 out of 25 (28%) patients experienced a bleeding event of which 4 required surgical revision. Of the preoperatively performed measurements the TRAP test [Spearman's Rho (ρ) = −0.5, p = 0.01], INTEM CFT (ρ = 0.72, p < 0.001), INTEM alpha (−0.7, p < 0.001), EXTEM MCF (ρ = −0.63; p < 0.001), EXTEM alpha (ρ = −0.67; p < 0.001), FIBTEM MCF (ρ = −0.41; p = 0.042), Fibrinogen (Clauss) (ρ = −0.5; p = 0.011), Anti-thrombin activity (ρ = −0.49; p = 0.013) and platelet count (ρ = −0.42; p = 0.034) were significantly correlated to total blood loss. Patients undergoing a surgical bleeding revision had significantly reduced values in TRAP—[31.5 IQR (17.25–43.5U) vs. 69 IQR (52.5–87U); p = 0.004], ASPI—[16.5 IQR (5.5–35.7U) vs. 39 IQR (24.5–62.5U); p = 0.038], ADP—[30 IQR (22–69U) vs. 12.5 IQR (8.7–21.5U); p = 0.01], EXTEM MCF—[63 IQR (57.7–63.7) vs. 67 IQR (65–75.5); p = 0.019] and EXTEM alpha [74 IQR (68.75–74) vs. 79 IQR (78–80.5); p = 0.002] values before LVAD implantation.

Conclusion

Multiplate^® and ROTEM^® measurements before LVAD implantation may identify LVAD candidates with platelet dysfunction and alterations of the primary hemostasis and could guide anesthetists and intensive care practitioners in bleeding risk stratification and in the perioperative clinical management.

Mechanisms Underlying Dichotomous Procoagulant COAT Platelet Generation-A Conceptual Review Summarizing Current Knowledge

Procoagulant platelets are a subtype of activated platelets that sustains thrombin generation in order to consolidate the clot and stop bleeding. This aspect of platelet activation is gaining more and more recognition and interest. In fact, next to aggregating platelets, procoagulant platelets are key regulators of thrombus formation. Imbalance of both subpopulations can lead to undesired thrombotic or bleeding events. COAT platelets derive from a common pro-aggregatory phenotype in cells capable of accumulating enough cytosolic calcium to trigger specific pathways that mediate the loss of their aggregating properties and the development of new adhesive and procoagulant characteristics. Complex cascades of signaling events are involved and this may explain why an inter-individual variability exists in procoagulant potential. Nowadays, we know the key agonists and mediators underlying the generation of a procoagulant platelet response. However, we still lack insight into the actual mechanisms controlling this dichotomous pattern (i.e., procoagulant versus aggregating phenotype). In this review, we describe the phenotypic characteristics of procoagulant COAT platelets, we detail the current knowledge on the mechanisms of the procoagulant response, and discuss possible drivers of this dichotomous diversification, in particular addressing the impact of the platelet environment during in vivo thrombus formation.

Dual-target synergistic antithrombotic mechanism of a Dabigatran etexilate analogue (HY023016)

Thrombin has long been considered a desirable antithrombotic target, but anti-thrombin therapy without anti-platelet therapy has never achieved the ideal effect. HY023016, derived from dabigatran etexilate, exhibited a potent antithrombotic efficacy. In the present study, mechanisms underlying this effect were explored. HY023016 strongly decreased the binding of thrombin to recombinant GPIbα N-terminal sequence which was confirmed by surface plasmon resonance. Flow cytometry revealed that HY023016 selectively decreased the binding of antibody to GPIbα and inhibited the washed human platelet aggregation induced by thrombin. Fluorescence experiment showed that HY023016 remarkably inhibited exosite II by a loss of affinity for the γ'-peptide of fibrinogen. Using intravital microscopy, we observed and recorded the dynamic process of thrombus formation and found that HY023016 effectively prevented thrombus formation in rat arteriovenous shunt thrombosis model. On the basis of these findings, we propose that HY023016 provides a novel insight into the antithrombotic mechanism, which exerts synergistic anticoagulant and antiplatelet effects through thrombin and GPIbα.

Platelet and Cancer-Cell Interactions Modulate Cancer-Associated Thrombosis Risk in Different Cancer Types

The first cause of death in cancer patients, after tumoral progression itself, is thrombo-embolic disease. This cancer-associated hypercoagulability state is known as Trousseau's syndrome, and the risk for developing thrombotic events differs according to cancer type and stage, as well as within patients. Massive platelet activation by tumor cells is the key mediator of thrombus formation in Trousseau's syndrome. In this literature review, we aimed to compare the interactions between cancer cells and platelets in three different cancer types, with low, medium and high thrombotic risk. We chose oral squamous cell carcinoma for the low-thrombotic-risk, colorectal adenocarcinoma for the medium-thrombotic-risk, and pancreatic carcinoma for the high-thrombotic-risk cancer type. We showcase that understanding these interactions is of the highest importance to find new biomarkers and therapeutic targets for cancer-associated thrombosis.

Impacts of Commonly Used Edible Plants on the Modulation of Platelet Function

Cardiovascular diseases (CVDs) are a primary cause of deaths worldwide. Thrombotic diseases, specifically stroke and coronary heart diseases, account for around 85% of CVDs-induced deaths. Platelets (small circulating blood cells) are responsible for the prevention of excessive bleeding upon vascular injury, through blood clotting (haemostasis). However, unnecessary activation of platelets under pathological conditions, such as upon the rupture of atherosclerotic plaques, results in thrombus formation (thrombosis), which can cause life threatening conditions such as stroke or heart attack. Therefore, antiplatelet medications are usually prescribed for people who are at a high risk of thrombotic diseases. The currently used antiplatelet drugs are associated with major side effects such as excessive bleeding, and some patients are resistant to these drugs. Therefore, numerous studies have been conducted to develop new antiplatelet agents and notably, to establish the relationship between edible plants, specifically fruits, vegetables and spices, and cardiovascular health. Indeed, healthy and balanced diets have proven to be effective for the prevention of CVDs in diverse settings. A high intake of fruits and vegetables in regular diet is associated with lower risks for stroke and coronary heart diseases because of their plethora of phytochemical constituents. In this review, we discuss the impacts of commonly used selected edible plants (specifically vegetables, fruits and spices) and/or their isolated compounds on the modulation of platelet function, haemostasis and thrombosis.

A longitudinal sampling study of transcriptomic and epigenetic profiles in patients with thrombocytopenia syndrome

Severe fever with thrombocytopenia syndrome (SFTS) is a novel tick-borne infectious disease caused by a new type of SFTS virus (SFTSV). Here, a longitudinal sampling study is conducted to explore the differences in transcript levels after SFTSV infection, and to characterize the transcriptomic and epigenetic profiles of hospitalized patients. The results reveal significant changes in the mRNA expression of certain genes from onset to recovery. Moreover, m⁶A-seq reveals that certain genes related with immune regulation may be regulated by m⁶A. Besides the routine tests such as platelet counts, serum ALT and AST levels testing, distinct changes in myocardial enzymes, coagulation function, and inflammation are well correlated with the clinical data and sequencing data, suggesting that clinical practitioners should monitor the above indicators to track disease progression and guide personalized treatment. In this study, the transcript changes and RNA modification may lend a fresh perspective to our understanding of the SFTSV and play a significant role in the discovery of drugs for effective treatment of this disease.

Rapid screening and identification of anticoagulation component from carthami flos by two-dimensional thrombin affinity chromatography combined with HPLC-MS/MS

Carthami flos, commonly known as Honghua in China, is the dried floret of safflower and widely acknowledged as a blood stasis promoting herb. The study aimed at investigating the relationship between thrombin and carthami flos through a high-performance thrombin affinity chromatography combined with a high-performance liquid chromatography-tandem mass spectrometry system. First, thrombin was immobilized on the glutaraldehyde-modified amino silica gel to prepare the thrombin affinity stationary phase, which was packed into a small column (1.0 × 2.0 mm, id) for recognizing the anticoagulant active components of carthami flos. The target component was enriched and analyzed by the high-performance liquid chromatography-tandem mass spectrometry system. Finally, hydroxysafflor yellow A was screened out and identified as the active component. The anticoagulant effects of hydroxysafflor yellow A were analyzed by anticoagulant experiments in vitro, and the interaction of hydroxysafflor yellow A with thrombin was investigated by the molecular docking method. The results proved that hydroxysafflor yellow A (30 μg/mL, 0.05 mM) and carthami flos extract (30 μg/mL) could prolong activated partial thrombin time and thrombin time by 50 and 11%, respectively. Moreover, hydroxysafflor yellow A exhibits a good hydrogen bond field and stereo field matching with thrombin. Overall, it was concluded that hydroxysafflor yellow A might exert an anticoagulation effect by interacting with thrombin and thus could be potential anticoagulant drugs for the prevention and treatment of venous thrombosis.

Thrombin: A Pivotal Player in Hemostasis and Beyond

The serine protease thrombin, a naturally derived enzyme, plays a key role in hemostasis by converting fibrinogen to fibrin and activating coagulation factor XIII whereby the fibrin clot is stabilized. Furthermore, thrombin activates platelets through protease-activated receptors on the platelet surface. Conversely, thrombin also exerts anticoagulant effects, enhancing the protein C activity while complexed with thrombomodulin. During recent years, it has become evident that thrombin has significant effects beyond hemostasis, as it contributes also to modulation of the endothelium, promotes inflammation and angiogenesis, and plays a role in tumor progression. Yet, due to the very short half-life and almost immediate inhibition in fluid phase by antithrombin, thrombin itself remains elusive, and only indirect measurement of thrombin generation is possible. This review provides a description of structure and mechanisms of action of thrombin both in physiological and pathological processes. Furthermore, it summarizes laboratory tests that measure in vivo or ex vivo thrombin generation, and presents knowledge on the value of these biomarkers in bleeding disorders, cardiopulmonary bypass surgery, and thromboembolic risk assessment in different patient populations. Finally, this review outlines further perspectives on using thrombin generation biomarkers for research purposes and in clinical practice.

Cancer-Associated Thrombosis: Risk Factors, Molecular Mechanisms, Future Management

Venous thromboembolism (VTE) is a major health problem in patients with cancer. Cancer augments thrombosis and causes cancer-associated thrombosis (CAT) and vice versa thrombosis amplifies cancer progression, termed thrombosis-associated cancer (TAC). Risk factors that lead to CAT and TAC include cancer type, chemotherapy, radiotherapy, hormonal therapy, anti-angiogenesis therapy, surgery, or supportive therapy with hematopoietic growth factors. There are some other factors that have an effect on CAT and TAC such as tissue factor, neutrophil extracellular traps (NETs) released in response to cancer, cancer procoagulant, and cytokines. Oncogenes, estrogen hormone, and thyroid hormone with its integrin αvβ3 receptor promote angiogenesis. Lastly, patient-related factors can play a role in development of thrombosis in cancer. Low-molecular-weight heparin and direct oral anticoagulants (DOACs) are used in VTE prophylaxis and treatment rather than vitamin K antagonist. Now, there are new directions for potential management of VTE in patients with cancer such as euthyroid, blockade of thyroid hormone receptor on integrin αvβ3, sulfated non-anticoagulant heparin, inhibition of NETs and stratifying low and high-risk patients with significant bleeding problems with DOACs.

Thrombin- and plasmin-like and platelet-aggregation-inducing activities of Plumeria alba L. latex: Action of cysteine protease

ETHNOPHARMACOLOGICAL RELEVANCE

In folk medicine, parts of Plumeria alba L. are used for the treatment of many diseases, with its latex being used for curing skin diseases and promoting wound healing.

AIM OF THE STUDY

This study aimed to study the role of P. alba L. latex in hemostasis and platelet aggregation.

MATERIALS AND METHODS

The latex of P. alba L. was processed to remove waxes and enrich protein content, and the final extract was named Plumeria alba L. natant latex (PaNL). PaNL was analyzed for protease activity against casein. The type of protease in PaNL was identified by using protease inhibitors such as E-64, phenylmethylsulfonyl fluoride, ethylenediaminetetraacetic acid, and pepstatin A. Human fibrinogen, fibrin, and collagen types I and IV were subjected to hydrolysis with different concentrations of PaNL. The thrombin-like activity of PaNL was determined by analyzing its fibrinogen-clotting and procoagulant activities. The role of PaNL in platelet aggregation was also investigated. Its hemorrhagic and edema-inducing activities were evaluated in a mouse model. Phytochemical compounds were identified by gas chromatography-mass spectroscopy.

RESULTS

The findings of casein/gelatin zymography confirmed that PaNL possesses protease activity. The results of the protease inhibition study indicated the presence of a cysteine-type protease(s) in PaNL. PaNL hydrolyzed the subunits of fibrinogen, fibrin, and collagen types I and IV. Its fibrin-degradation activity indicated that PaNL possesses plasmin-like activity. PaNL induced clotting of citrated human plasma within 3 min of incubation in the absence of CaCl_2, indicating the presence of thrombin-like activity, which was further confirmed by the results of the fibrinogen-clotting assay. PaNL induced platelet aggregation in the absence of agonists. There was no hemolytic activity. Mice injected with PaNL did not show edema/ hemorrhagic activity.

CONCLUSION

PaNL possesses procoagulant, fibrino(geno)lytic, thrombin- and plasmin-like activities and induces platelet aggregation, which could explain its usage for wound treatment in folk medicine.

Effects of argatroban therapy for stroke patients: A meta-analysis

BACKGROUND

The therapeutic efficacy and safety of argatroban for stroke patients remain controversial. The purpose of this study was to collect all evidence and perform a meta-analysis to comprehensively evaluate the effects of argatroban for stroke patients compared with no-argatroban regimens.

METHODS

The databases of PubMed, EMBASE and the Cochrane library were searched from their inception up to December 2020. Categorical outcomes were summarized as odds ratio (OR) and 95% confidence interval (CI); while continuous data were pooled as standardized mean difference (SMD) and 95%CI.

RESULTS

A total of 11 studies were enrolled. Overall meta-analysis showed infusion of argatroban significantly improved neurological functions of stroke patients compared with control treatment, showing increased National Institutes of Health Stroke Scale (NIHSS) score change (SMD = 1.02; 95% CI, 0.58-1.46, p < 0.001), modified Barthel Index (SMD = 3.81; 95% CI, 2.72-4.89, p < 0.001) as well as a decreased incidence of early neurological deterioration (OR = 0.48; 95% CI: 0.28-0.84, p = 0.01). Argatroban treatment did not increase the risk of symptomatic intracerebral hemorrhage (p = 0.733), asymptomatic intracranial hemorrhage (p = 0.608), gastrointestinal bleeding (p = 0.601), major systemic hemorrhage (p = 0.582) and mortality (p = 0.797), except minor systemic hemorrhage (OR = 2.40; 95% CI: 1.15-5.02, p = 0.020). Subgroup analyses for NIHSS score change and complications obtained the similar conclusions.

CONCLUSION

Argatroban infusion may be an effective and safe therapeutic option to improve functional outcomes of stroke patients.

Brazilian propolis (AF-08) inhibits collagen-induced platelet aggregation without affecting blood coagulation

Brazilian propolis (AF-08) is a dietary supplement containing a variety of flavonoids. It is used worldwide as a folk medicine. Flavonoids and a diet of fruits and vegetables containing them have been shown to reduce the risk of cardiovascular diseases (CVDs). Most of CVDs are caused by arterial thrombus formation. A thrombus is formed by the interaction between adhesion and aggregation of platelets to damaged blood vessels and blood coagulation consisting of extrisic and intrinsic pathways. Platelet aggregation and blood coagulation are closely linked to thrombosis. Therefore, we evaluated the effectiveness of AF-08 or its component flavonoids against thrombosis by examining their inhibition of platelet aggregation and blood coagulation. Human platelet-rich plasma was incubated with serial dilutions of AF-08 for 10 min to assess its inhibitory effect on platelet aggregation caused by collagen. The inhibitory effect of AF-08 on blood coagulation was evaluated by the prothrombin time (PT) and activated partial thromboplastin time (APTT), which reflect the coagulation function of extrinsic and intrinsic pathways, respectively. AF-08 significantly inhibited collagen-induced platelet aggregation but not PT and APTT, indicating that AF-08 inhibited platelet aggregation but not blood coagulation. Among three flavonoids contained in AF-08, apigenin and chrysin obviously inhibited platelet aggregation but the inhibitory effect of kaempferol was less effective. The three flavonoids did not affect PT and APTT. The inhibitory activity of AF-08 on human platelet aggregation without affecting blood coagulation was suggested to be partially due to apigenin and chrysin. AF-08 may be effective in suppressing platelet-based arterial thrombus formation and reducing the risk of CVDs.

Cancer-Associated Thrombosis: A New Light on an Old Story

Cancer-associated thrombosis (CAT) is a rising and significant phenomenon, becoming the second leading cause of death in cancer patients. Pathophysiology of CAT differs from thrombosis in the non-cancer population. There are additional risk factors for thrombosis specific to cancer including cancer type, histology, and treatment, such as chemotherapy. Recently developed scoring systems use these risk factors to stratify the degree of risk and encourage thromboprophylaxis in intermediate- to high-risk patients. Anticoagulation is safely used for prophylaxis and treatment of CAT. Both of these have largely been with low-molecular-weight heparin (LMWH), rather than the vitamin K antagonist (VKA); however, there has been increasing evidence for direct oral anticoagulant (DOAC) use. Consequently, international guidelines have also adapted to recommend the role of DOACs in CAT. Using DOACs is a turning point for CAT, but further research is warranted for their long-term risk profile. This review will discuss mechanisms, risk factors, prophylaxis and management of CAT, including both LMWH and DOACs. There will also be a comparison of current international guidelines and how they reflect the growing evidence base.

Development of MALDI MS peptide array for thrombin inhibitor screening

The development of in situ methods for the analysis and visualization of enzyme activity is of paramount importance in drug discovery, research, and development. In this work, the functionalized and array patterned indium tin oxide (ITO) glass slides were fabricated by non-covalent immobilization of amphipathic phospholipid-tagged peptides encompassing the thrombin cleavage site on steric acid-modified ITO slides. The fabricated peptide arrays provide 60 spots per slide, and are compatible with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) measurement, free matrix peak interference, and tolerance to repeated aqueous washing. The peptide arrays were used for the investigation of thrombin activity and screening for its potential inhibitors. The thrombin activity and its Michaelis-Menten constant (K_m) for immobilized peptide substrate was determined using developed MALDI MS peptide array. To investigate the applicability and effectiveness of peptide arrays, the anti-thrombin activity of grape seed proanthocyanidins with different degrees of polymerization (DP) was monitored and visualized. MALDI MS imaging results showed that the fractions of proanthocyanidins with the mean DP of 4.61-6.82 had good thrombin inhibitory activity and their half-maximal inhibitory concentration (IC₅₀) were below 10 μg/mL. Therefore, the developed peptide array is a reliable platform for the discovery of natural thrombin inhibitors.

Imbalance in Coagulation/Fibrinolysis Inhibitors Resulting in Extravascular Thrombin Generation in Gliomas of Varying Levels of Malignancy

Neoplastic processes are integrally related to disturbances in the mechanisms regulating hemostatic processes. Brain tumors, including gliomas, are neoplasms associated with a significantly increased risk of thromboembolic complications, affecting 20-30% of patients. As gliomas proliferate, they cause damage to the brain tissue and vascular structures, which leads to the release of procoagulant factors into the systemic circulation, and hence systemic activation of the blood coagulation system. Hypercoagulability in cancer patients may be, at least in part, a result of the inadequate activity of coagulation inhibitors. The aim of the study was to evaluate the expression of the inhibitors of the coagulation and fibrinolysis systems (tissue factor pathway inhibitor, TFPI; tissue factor pathway inhibitor-2 TFPI-2; protein C, PC; protein S, PS, thrombomodulin, TM; plasminogen activators inhibitor, PAI-1) in gliomas of varying degrees of malignancy. Immunohistochemical studies were performed on 40 gliomas, namely on 13 lower-grade (G2) gliomas (8 astrocytomas, 5 oligodendrogliomas) and 27 high-grade gliomas (G3-12 anaplastic astrocytomas, 4 anaplastic oligodendrogliomas; G4-11 glioblastomas). A strong expression of TFPI-2, PS, TM, PAI-1 was observed in lower-grade gliomas, while an intensive color immunohistochemical (IHC) reaction for the presence of TFPI antigens was detected in higher-grade gliomas. The presence of PC antigens was found in all gliomas. Prothrombin fragment 1+2 was observed in lower- and higher-grade gliomas reflecting local activation of blood coagulation. Differences in the expression of coagulation/fibrinolysis inhibitors in the tissues of gliomas with varying degrees of malignancy may be indicative of their altered role in gliomas, going beyond that of their functions in the hemostatic system.

Influence of PAR-1 in patients with non-valvular atrial fibrillation: The antiplatelet effect of dabigatran

INTRODUCTION

Dabigatran, a direct thrombin inhibitor, has been widely used in patients with non-valvular atrial fibrillation (NVAF) and is considered to have an antiplatelet effect. However, the mechanisms remain unclear. We evaluated protease-activated receptor-1 (PAR-1) expression and activation by thrombin on platelets from NVAF patients, before and after dabigatran treatment, in addition to the expression of platelet activation marker CD62P.

MATERIALS AND METHODS

The study included 18 NVAF patients. We used flow cytometry to measure the binding of PAR-1 monoclonal antibodies (SPAN12 and WEDE15) and the expression of CD62P with and without thrombin stimulation, before, 14 days after, and 28 days after treatment with dabigatran. Coagulation fibrinolysis markers were also measured.

RESULTS

PAR-1 expression was significantly lower in NVAF patients than in healthy controls (HC); it was further reduced by thrombin stimulation. CD62P expression was almost absent on the platelets in NVAF patients, but was significantly increased by thrombin stimulation. PAR-1 expression was not significantly different before and after treatment; CD62P expression was inhibited by dabigatran. The levels of coagulation markers were significantly higher in NVAF patients than in HC, and decreased after treatment.

CONCLUSIONS

Lower expression of PAR-1 in NVAF patients resulted from the cleavage of PAR-1 on some platelets, by exposure to small amounts of thrombin in vivo. The therapeutic effect of dabigatran in NVAF patients was demonstrated by inhibition of CD62P expression on the platelet upon thrombin stimulation in vitro. Our results indicate that dabigatran may reveal antithrombotic activity with antiplatelet and anticoagulant effects.

Platelet Membrane Receptor Proteolysis: Implications for Platelet Function

The activities of adhesion and signaling receptors in platelets are controlled by several mechanisms. An important way of regulation is provided by proteolytic cleavage of several of these receptors, leading to either a gain or a loss of platelet function. The proteases involved are of different origins and types: (i) present as precursor in plasma, (ii) secreted into the plasma by activated platelets or other blood cells, or (iii) intracellularly activated and cleaving cytosolic receptor domains. We provide a comprehensive overview of the proteases acting on the platelet membrane. We describe how these are activated, which are their target proteins, and how their proteolytic activity modulates platelet functions. The review focuses on coagulation-related proteases, plasmin, matrix metalloproteinases, ADAM(TS) isoforms, cathepsins, caspases, and calpains. We also describe how the proteolytic activities are determined by different platelet populations in a thrombus and conversely how proteolysis contributes to the formation of such populations.

Vorapaxar-modified polysulfone membrane with high hemocompatibility inhibits thrombosis

Hemodialysis therapy is intended for patients suffering from renal insufficiency, pancreatitis, and other serious diseases. Platelets are an important active ingredient in the thrombosis induced by hemodialysis membranes. So far, there are few studies of hemodialysis membranes focusing on the effects of protease-activated receptor 1 (PAR1) activation on the platelet membrane. Among various antithrombotic agents, vorapaxar is a novel PAR1 inhibitor with high efficacy. In this study, we constructed a vorapaxar-modified polysulfone (VMPSf) membrane using immersion-precipitation phase transformation methods and characterized the microstructure in terms of hydrophilicity and mechanical properties. The water contact angle of the VMPSf membrane was 22.45% lower than that of the PSf membrane. A focused determination of platelet morphology was obtained using scanning electron microscopy. Meanwhile, we evaluated the effects of a VMPSf membrane on platelet adhesion. We observed that the VMPSf membrane could reduce the number of adhered platelets without altering their spherical or elliptical shape. The PAR1 levels in VMPSf membranes were 7.4 MFI lower than those in PSf membranes, suggesting that this modified membrane can effectively inhibit platelet activation. Activated partial thromboplastin time (APTT, 5.3 s extension) and thrombin time (TT, 2.1 s extension) reflect good anticoagulant properties. Recalcification time (80.6 s extension) and fibrinogen adsorption (9.9 μg/cm² reduction) were related to antithrombotic properties. To determine the biosafety of VMPSf membranes, we investigated antianaphylactic and anti-inflammatory properties in vitro and acute toxicity in vivo, it was obvious that C3a and C5a had decreased to 9.6 and 0.8 ng/mL, respectively. The results indicated that the VMPSf membrane has potential for clinical application.

Ticagrelor Inhibits Toll-Like and Protease-Activated Receptor Mediated Platelet Activation in Acute Coronary Syndromes

Purpose

Since ticagrelor inhibits the cellular uptake of adenosine, thereby increasing extracellular adenosine concentration and biological activity, we hypothesized that ticagrelor has adenosine-dependent antiplatelet properties. In the current study, we compared the effects of ticagrelor and prasugrel on platelet activation in acute coronary syndrome (ACS).

Methods

Platelet surface expression of P-selectin and activated glycoprotein (GP) IIb/IIIa in response to adenosine diphosphate (ADP), the toll-like receptor (TLR)-1/2 agonist Pam3CSK4, the TLR-4 agonist lipopolysaccharide (LPS), the protease-activated receptor (PAR)-1 agonist SFLLRN, and the PAR-4 agonist AYPGKF were measured by flow cytometry in blood from 80 ticagrelor- and 80 prasugrel-treated ACS patients on day 3 after percutaneous coronary intervention. Residual platelet aggregation to arachidonic acid (AA) and ADP were assessed by multiple electrode aggregometry and light transmission aggregometry.

Results

ADP-induced platelet activation and aggregation, and AA-induced platelet aggregation were similar in patients on ticagrelor and prasugrel, respectively (all p ≥ 0.3). Further, LPS-induced platelet surface expression of P-selectin and activated GPIIb/IIIa did not differ significantly between ticagrelor- and prasugrel-treated patients (both p > 0.4). In contrast, Pam3CSK4-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly lower in ticagrelor-treated patients (both p ≤ 0.005). Moreover, SFLLRN-induced platelet surface expression of P-selectin and activated GPIIb/IIIa were significantly less pronounced in patients on ticagrelor therapy compared to prasugrel-treated patients (both p < 0.03). Finally, PAR-4 mediated platelet activation as assessed by platelet surface expression of activated GPIIb/IIIa following stimulation with AYPGKF was significantly lower in patients receiving ticagrelor (p = 0.02).

Conclusion

Ticagrelor inhibits TLR-1/2 and PAR mediated platelet activation in ACS patients more strongly than prasugrel.

A comprehensive appraisal of dabigatran etexilate clinical evidence and applications: a 10-year-long story

During the last decade, non-vitamin K antagonist oral anticoagulants (NOACs) revolutionized the thromboprophylaxis management of several medical conditions, including atrial fibrillation and venous thromboembolism. Dabigatran etexilate was the first NOAC widely available worldwide, and it is currently the only one that directly inhibits thrombin. More recently, the availability of idarucizumab, a specific reversal agent, has increased the safety of dabigatran use in clinical practice, especially for those patients with severe and life-threatening bleeding. This review aims to summarize current evidence on dabigatran, starting from its pharmacological characteristics, and providing an updated overview of pivotal randomized controlled trials and real-world data on its efficacy and safety.

Whole blood flow cytometry protocol for the assessment of platelet phenotype, function, and cellular interactions

Platelets are a key component of the hemostatic system and their roles in inflammation via interactions with leukocytes have also gained attention in recent years. Changes in platelet phenotype and function can cause bleeding and/or thrombosis and, as such, monitoring platelet-specific changes is crucial to assessing hemostasis in the clinical setting. Currently, available platelet function tests such as platelet aggregometry and thromboelastography require a large volume of blood, which is a major limitation for the pediatric population. Whole blood flow cytometric analysis of platelets is increasingly utilized in recent years, primarily due to the sensitivity of this method, but also because it only requires a small amount of blood with minimal sample manipulation. We have developed a whole blood flow cytometry methodological approach that enables the assessment of platelet phenotype, function, and their interactions with monocytes and neutrophils.

Arctigenin attenuates platelet activation and clot retraction by regulation of thromboxane A2 synthesis and cAMP pathway

Pathophysiological reaction of platelets in the blood vessel is an indispensable part of thrombosis and cardiovascular disease, which is the most common cause of death in the world. In this study, we performed in vitro assays to evaluate antiplatelet activity of arctigenin in human platelets and attempted to identify the mechanism responsible for thromboxane A₂ (TXA₂) generation, integrin α_IIbβ₃ activation and cAMP pathway. Arctigenin exhibited obvious inhibitory effects on collagen-, thrombin-, and ADP-induced human platelet aggregation, granule secretion, TXA₂ generation, integrin α_IIbβ₃ activation, and clot retraction. Additionally, we found that arctigenin attenuated PI3K/Akt/mTOR/GSK-3β and MAPK signaling pathways, and increased cAMP level. Accordingly, the findings support that arctigenin attenuates thrombotic events through the inhibition of platelet activation and platelet plug formation. Therefore, we suggest that arctigenin may have therapeutic potential as an antiplatelet and antithrombotic agent.

Pulmonary Artery Thrombosis: A Diagnosis That Strives for Its Independence

According to a widespread theory, thrombotic masses are not formed in the pulmonary artery (PA) but result from migration of blood clots from the venous system. This concept has prevailed in clinical practice for more than a century. However, a new technologic era has brought forth more diagnostic possibilities, and it has been shown that thrombotic masses in the PA could, in many cases, be found without any obvious source of emboli. Chronic obstructive pulmonary disease, asthma, sickle cell anemia, emergency and elective surgery, viral pneumonia, and other conditions could be complicated by PA thrombosis development without concomitant deep vein thrombosis (DVT). Different pathologies have different causes for local PA thrombotic process. As evidenced by experimental results and clinical observations, endothelial and platelet activation are the crucial mechanisms of this process. Endothelial dysfunction can impair antithrombotic function of the arterial wall through downregulation of endothelial nitric oxide synthase (eNOS) or via stimulation of adhesion receptor expression. Hypoxia, proinflammatory cytokines, or genetic mutations may underlie the procoagulant phenotype of the PA endothelium. Both endotheliocytes and platelets could be activated by protease mediated receptor (PAR)- and receptors for advanced glycation end (RAGE)-dependent mechanisms. Hypoxia, in particular induced by high altitudes, could play a role in thrombotic complications as a trigger of platelet activity. In this review, we discuss potential mechanisms of PA thrombosis in situ.

Mouse models of hemostasis

Hemostasis is the normal process that produces a blood clot at a site of vascular injury. Mice are widely used to study hemostasis and abnormalities of blood coagulation because their hemostatic system is similar in most respects to that of humans, and their genomes can be easily manipulated to create models of inherited human coagulation disorders. Two of the most widely used techniques for assessing hemostasis in mice are the tail bleeding time (TBT) and saphenous vein bleeding (SVB) models. Here we discuss the use of these methods in the evaluation of hemostasis, and the advantages and limits of using mice as surrogates for studying hemostasis in humans.

Mimicking the Endothelium: Dual Action Heparinized Nitric Oxide Releasing Surface

The management of thrombosis and bacterial infection is critical to ensure the functionality of medical devices. While administration of anticoagulants is the current antithrombotic clinical practice, a variety of complications, such as uncontrolled hemorrhages or heparin-induced thrombocytopenia, can occur. Additionally, infection rates remain a costly and deadly complication associated with use of these medical devices. It has been hypothesized that if a synthetic surface could mimic the biochemical mechanisms of the endothelium of blood vessels, thrombosis could be reduced, anticoagulant use could be avoided, and infection could be prevented. Herein, the interfacial biochemical effects of the endothelium were mimicked by altering the surface of medical grade silicone rubber (SR). Surface modification was accomplished via heparin surface immobilization (Hep) and the inclusion of a nitric oxide (NO) donor into the SR polymeric matrix to achieve synergistic effects (Hep-NO-SR). An in vitro bacteria adhesion study revealed that Hep-NO-SR exhibited a 99.46 ± 0.17% reduction in viable bacteria adhesion compared to SR. An in vitro platelet study revealed Hep-NO-SR reduced platelet adhesion by 84.12 ± 6.19% compared to SR, while not generating a cytotoxic response against fibroblast cells. In a 4 h extracorporeal circuit model without systemic anticoagulation, all Hep-NO-SR samples were able to maintain baseline platelet count and device patency; whereas 66% of SR samples clotted within the first 2 h of study. Results indicate that Hep-NO-SR creates a more hemocompatible and antibacterial surface by mimicking two key biochemical functions of the native endothelium.

Effects of Antiplatelet and Nonsteroidal Anti-inflammatory Medications on Platelet-Rich Plasma: A Systematic Review

Background:

Platelet-rich plasma (PRP) has wide applications in orthopaedic care. Its beneficial effects are attributed to the growth factor profile from the platelet secretome. In theory, these effects would be diminished by medications that inhibit platelet activation and/or the subsequent release of growth factors.

Purpose:

To determine whether commonly used antiplatelets, nonsteroidal anti-inflammatory drugs (NSAIDs), or anticoagulant medications affect platelet growth factor release in PRP.

Study Design:

Systematic review; Level of evidence, 2.

Method:

A systematic review of the literature related to antiplatelet, anti-inflammatory, and anticoagulant drugs was performed following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. We used the Downs and Black objective quality scoring system. The literature search consisted of PubMed and Cochrane Library databases. Search terms consisted of 1 item selected from “platelet-rich plasma,” “platelet-derived growth factor,” and “platelet-rich plasma AND growth factor” combined with 1 item from “antiplatelet,” “aspirin,” “anticoagulant,” and “NSAID.” Only studies published within the past 25 years were included.

Results:

A total of 15 studies met the inclusion criteria: 7 studies detected no significant decrease in growth factors or mitogenesis, whereas 6 detected a decrease with antiplatelet agents, 1 detected mixed results with an antiplatelet agent, and 1 had mixed results with an antiplatelet agent/vasodilator. In terms of PRP activation, all 3 studies assessing collagen, the 2 studies analyzing adenosine diphosphate alone, and the 1 study investigating arachidonic acid found a decrease in growth factor concentration.

Conclusion:

Antiplatelet medications may decrease the growth factor release profile in a cyclooxygenase 1– and cyclooxygenase 2–dependent manner. Eight of 15 studies found a decrease in growth factors or mitogenesis. However, more studies are needed to comprehensively understand antiplatelet effects on the PRP secretome.

Platelet activation and prothrombotic mediators at the nexus of inflammation and atherosclerosis: Potential role of antiplatelet agents

Platelets are central to inflammation-related manifestations of cardiovascular diseases (CVD) such as atherosclerosis. Platelet-activating factor (PAF), thrombin, thromboxane A₂ (TxA₂), and adenosine diphosphate (ADP) are some of the key agonists of platelet activation that are at the intersection between a plethora of inflammatory pathways that modulate pro-inflammatory and coagulation processes. The aim of this article is to review the role of platelets and the relationship between their structure, function, and the interactions of their constituents in systemic inflammation and atherosclerosis. Antiplatelet therapies are discussed with a view to primary prevention of CVD by the clinical reduction of platelet reactivity and inflammation. Current antiplatelet therapies are effective in reducing cardiovascular risk but increase bleeding risk. Novel therapeutic antiplatelet approaches beyond current pharmacological modalities that do not increase the risk of bleeding require further investigation. There is potential for specifically designed nutraceuticals that may become safer alternatives to pharmacological antiplatelet agents for the primary prevention of CVD but there is serious concern over their efficacy and regulation, which requires considerably more research.