Platelets in hemostasis and thrombosis: role of integrins and their ligands

Novel GPIb-independent platelet aggregation induced by botrocetin: implications for diagnosis and antithrombotic therapy

BACKGROUND

Snake venom botrocetin facilitates von Willebrand factor (VWF) binding to platelet GPIbα and has been widely used for the diagnosis of von Willebrand disease and GPIb-related disorders. Botrocetin is also commonly employed for the development/characterization of antithrombotics targeting the GPIb-VWF axis.

OBJECTIVES

To explore the alternative receptor(s)/mechanisms that participate in botrocetin-induced platelet aggregation.

METHODS

The effects of botrocetin on platelet aggregation were examined using platelets from wild-type, VWF- and fibrinogen-deficient, GPIbα-deficient, IL4Rα/GPIbα-transgenic, ITGA2B and ITGB3-deficient mice, and Bernard-Soulier syndrome and healthy human samples. Platelet-fibrinogen and platelet-VWF interaction were measured using flow cytometry. GPIbα-VWF binding was evaluated utilizing enzyme-linked immunosorbent assay. Botrocetin-αIIbβ3 and botrocetin-GPIbα interactions were measured using enzyme-linked immunosorbent assay and fluorescence anisotropy assays. Heparinized whole blood from healthy donors was examined for thrombus formation and growth in a perfusion chamber.

RESULTS

Botrocetin could induce aggregation of platelets from a Bernard-Soulier syndrome patient and GPIbα-deficient mice as well as platelets lacking the N-terminal extracellular domain of GPIbα. Botrocetin could interact with αIIbβ3 and facilitated αIIbβ3-VWF interaction independent of GPIb. Botrocetin competitively bound to the ligand-binding domain of activated rather than resting αIIbβ3. Although botrocetin-induced platelet aggregation requires VWF, strikingly, in the absence of VWF, botrocetin blocked fibrinogen and other ligand binding to αIIbβ3 and inhibited platelet aggregation and thrombus formation. Consistently, recombinant botrocetin defective in VWF binding inhibited αIIbβ3- and GPIb-mediated platelet aggregation, spreading, and thrombus formation.

CONCLUSION

Our study provides insights into avoiding the misdiagnosis of GPIb-related disorders and developing botrocetin mutants as potential new antithrombotics that may simultaneously target both αIIbβ3 and GPIbα.

Redox regulation of platelet function and thrombosis

Platelets are well-known players in several cardiovascular diseases such as atherosclerosis and venous thrombosis. There is increasing evidence demonstrating that reactive oxygen species (ROS) are generated within activated platelets. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is a major source of ROS generation in platelets. Ligand binding to platelet receptor glycoprotein (GP) VI stimulates intracellular ROS generation consisting of a spleen tyrosine kinase-independent production involving NOX activation and a following spleen tyrosine kinase-dependent generation. In addition to GPVI, stimulation of platelet thrombin receptors (protease-activated receptors [PARs]) can also trigger NOX-derived ROS production. Our recent study found that mitochondria-derived ROS production can be induced by engagement of thrombin receptors but not by GPVI, indicating that mitochondria are another source of PAR-dependent ROS generation apart from NOX. However, mitochondria are not involved in GPVI-dependent ROS generation. Once generated, the intracellular ROS are also involved in modulating platelet function and thrombus formation; therefore, the site-specific targeting of ROS production or clearance of excess ROS within platelets is a potential intervention and treatment option for thrombotic events. In this review, we will summarize the signaling pathways involving regulation of platelet ROS production and their role in platelet function and thrombosis, with a focus on GPVI- and PAR-dependent platelet responses.

Antiplatelet mechanism of a subtilisin-like serine protease from Solanum tuberosum (StSBTc-3)

The aims of this study are to characterize the antiplatelet activity of StSBTc-3, a potato serine protease with fibrino (geno) lytic activity, and to provide information on its mechanism of action. The results obtained show that StSBTc-3 inhibits clot retraction and prevents platelet aggregation induced by thrombin, convulxin, and A23187. Platelet aggregation inhibition occurs in a dose-dependent manner and is not affected by inactivation of StSBTc-3 with the inhibitor of serine proteases phenylmethylsulfonyl fluoride (PMSF). In addition, StSBTc-3 reduces fibrinogen binding onto platelets. In-silico calculations show a high binding affinity between StSBTc-3 and human α2bβ3 integrin suggesting that the antiplatelet activity of StSBTc-3 could be associated with the fibronectin type III domain present in its amino acid sequence. Binding experiments show that StSBTc-3 binds to α2bβ3 preventing the interaction between α2bβ3 and fibrinogen and, consequently, inhibiting platelet aggregation. StSBTc-3 represents a promising compound to be considered as an alternative to commercially available drugs used in cardiovascular therapies.

Celastrol inhibits platelet function and thrombus formation

INTRODUCTION

Celastrol is an active pentacyclic triterpenoid extracted from Tripterygium wilfordii and has anti-inflammatory and anti-tumor properties. Whether Celastrol modulates platelet function remains unknown. Our study investigated its role in platelet function and thrombosis.

METHODS

Human platelets were isolated and incubated with Celastrol (0, 1, 3 and 5 μM) at 37 °C for 1 h to measure platelet aggregation, granules release, spreading, thrombin-induced clot retraction and intracellular calcium mobilization. Additionally, Celastrol (2 mg/kg) was intraperitoneally administrated into mice to evaluate hemostasis and thrombosis in vivo.

RESULTS

Celastrol treatment significantly decreased platelet aggregation and secretion of dense or alpha granules induced by collagen-related peptide (CRP) or thrombin in a dose-dependent manner. Additionally, Celastrol-treated platelets showed a dramatically reduced spreading activity and decreased clot retraction. Moreover, Celastrol administration prolonged tail bleeding time and inhibited formation of arterial/venous thrombosis. Furthermore, Celastrol significantly reduced calcium mobilization.

CONCLUSION

Celastrol inhibits platelet function and venous/arterial thrombosis, implying that it might be utilized for treating thrombotic diseases.

Platelet-targeted gene therapy induces immune tolerance in hemophilia and beyond

Blood platelets have unique storage and delivery capabilities. Platelets play fundamental roles in hemostasis, inflammatory reactions, and immune responses. Beyond their functions, platelets have been used as a target for gene therapy. Platelet-targeted gene therapy aims to deliver a sustained expression of neo-protein in vivo by genetically modifying the target cells, resulting in a cure for the disease. Even though there has been substantial progress in the field of gene therapy, the potential development of immune responses to transgene products or vectors remains a significant concern. Of note, multiple preclinical studies using platelet-specific lentiviral gene delivery to hematopoietic stem cells in hemophilia have demonstrated promising results with therapeutic levels of neo-protein that rescue the hemorrhagic bleeding phenotype and induce antigen-specific immune tolerance. Further studies using ovalbumin as a surrogate protein for platelet gene therapy have shown robust antigen-specific immune tolerance induced via peripheral clonal deletions of antigen-specific CD4- and CD8-T effector cells and induction of antigen-specific regulatory T (Treg) cells. This review discusses platelet-targeted gene therapy, focusing on immune tolerance induction.

Image-based flow simulation of platelet aggregates under different shear rates

Hemodynamics is crucial for the activation and aggregation of platelets in response to flow-induced shear. In this paper, a novel image-based computational model simulating blood flow through and around platelet aggregates is presented. The microstructure of aggregates was captured by two different modalities of microscopy images of in vitro whole blood perfusion experiments in microfluidic chambers coated with collagen. One set of images captured the geometry of the aggregate outline, while the other employed platelet labelling to infer the internal density. The platelet aggregates were modelled as a porous medium, the permeability of which was calculated with the Kozeny-Carman equation. The computational model was subsequently applied to study hemodynamics inside and around the platelet aggregates. The blood flow velocity, shear stress and kinetic force exerted on the aggregates were investigated and compared under 800 s-1, 1600 s-1 and 4000 s-1 wall shear rates. The advection-diffusion balance of agonist transport inside the platelet aggregates was also evaluated by local Péclet number. The findings show that the transport of agonists is not only affected by the shear rate but also significantly influenced by the microstructure of the aggregates. Moreover, large kinetic forces were found at the transition zone from shell to core of the aggregates, which could contribute to identifying the boundary between the shell and the core. The shear rate and the rate of elongation flow were investigated as well. The results imply that the emerging shapes of aggregates are highly correlated to the shear rate and the rate of elongation. The framework provides a way to incorporate the internal microstructure of the aggregates into the computational model and yields a better understanding of the hemodynamics and physiology of platelet aggregates, hence laying the foundation for predicting aggregation and deformation under different flow conditions.

Dimethyl fumarate possesses antiplatelet and antithrombotic properties

BACKGROUND

Dimethyl fumarate (DMF) is a methyl ester of fumaric acid and has been approved for treating multiple sclerosis (MS) and psoriasis due to anti-inflammatory effect. There is a close association between platelets and the pathogenesis of MS. Whether DMF affects platelet function remains unclear. Our study intends to evaluate DMF's effect on platelet function.

METHODS

Washed human platelets were treated with different concentrations of DMF (0, 50, 100 and 200 μM) at 37 °C for 1 h followed by analysis of platelet aggregation, granules release, receptors expression, spreading and clot retraction. In addition, mice received intraperitoneal injection of DMF (15 mg/kg) to assess tail bleeding time, arterial and venous thrombosis.

RESULTS

DMF significantly inhibited platelet aggregation and the release of dense/alpha granules in response to collagen-related peptide (CRP) or thrombin stimulation dose-dependently without altering the expression of platelet receptors α_IIbβ3, GPIbα, and GPVI. In addition, DMF-treated platelets presented significantly reduced spreading on collagen or fibrinogen and thrombin-mediated clot retraction along with the decreased phosphorylation of c-Src and PLCγ2. Moreover, administration of DMF into mice significantly prolonged the tail bleeding time and impaired arterial and venous thrombus formation. Furthermore, DMF reduced the generation of intracellular reactive oxygen species and calcium mobilization, and inhibited NF-κB activation and the phosphorylation of ERK1/2, p38 and AKT.

CONCLUSION

DMF inhibits platelet function and arterial/venous thrombus formation. Considering the presence of thrombotic events in MS, our study indicates that DMF treatment for patients with MS might obtain both anti-inflammatory and anti-thrombotic benefits.

SARS-CoV-2 RBD and Its Variants Can Induce Platelet Activation and Clearance: Implications for Antibody Therapy and Vaccinations against COVID-19

The COVID-19 pandemic caused by SARS-CoV-2 virus is an ongoing global health burden. Severe cases of COVID-19 and the rare cases of COVID-19 vaccine-induced-thrombotic-thrombocytopenia (VITT) are both associated with thrombosis and thrombocytopenia; however, the underlying mechanisms remain inadequately understood. Both infection and vaccination utilize the spike protein receptor-binding domain (RBD) of SARS-CoV-2. We found that intravenous injection of recombinant RBD caused significant platelet clearance in mice. Further investigation revealed the RBD could bind platelets, cause platelet activation, and potentiate platelet aggregation, which was exacerbated in the Delta and Kappa variants. The RBD-platelet interaction was partially dependent on the β3 integrin as binding was significantly reduced in β3-/- mice. Furthermore, RBD binding to human and mouse platelets was significantly reduced with related αIIbβ3 antagonists and mutation of the RGD (arginine-glycine-aspartate) integrin binding motif to RGE (arginine-glycine-glutamate). We developed anti-RBD polyclonal and several monoclonal antibodies (mAbs) and identified 4F2 and 4H12 for their potent dual inhibition of RBD-induced platelet activation, aggregation, and clearance in vivo, and SARS-CoV-2 infection and replication in Vero E6 cells. Our data show that the RBD can bind platelets partially though αIIbβ3 and induce platelet activation and clearance, which may contribute to thrombosis and thrombocytopenia observed in COVID-19 and VITT. Our newly developed mAbs 4F2 and 4H12 have potential not only for diagnosis of SARS-CoV-2 virus antigen but also importantly for therapy against COVID-19.

Doxorubicin-Induced Platelet Activation and Clearance Relieved by Salvianolic Acid Compound: Novel Mechanism and Potential Therapy for Chemotherapy-Associated Thrombosis and Thrombocytopenia

Doxorubicin (Dox) is a widely utilized chemotherapeutic; however, it carries side effects, including drug-induced immune thrombocytopenia (DITP) and increased risk of venous thromboembolism (VTE). Currently, the mechanisms for Dox-associated DITP and VTE are poorly understood, and an effective inhibitor to relieve these complications remains to be developed. In this study, we found that Dox significantly induced platelet activation and enhanced platelet phagocytosis by macrophages and accelerated platelet clearance. Importantly, we determined that salvianolic acid C (SAC), a water-soluble compound derived from Danshen root traditionally used to treat cardiovascular diseases, inhibited Dox-induced platelet activation more effectively than current standard-of-care anti-platelet drugs aspirin and ticagrelor. Mechanism studies with tyrosine kinase inhibitors indicate contributions of phospholipase C, spleen tyrosine kinase, and protein kinase C signaling pathways in Dox-induced platelet activation. We further demonstrated that Dox enhanced platelet-cancer cell interaction, which was ameliorated by SAC. Taken together, these findings suggest SAC may be a promising therapy to reduce the risk of Dox-induced DITP, VTE, and the repercussions of amplified platelet-cancer interaction in the tumor microenvironment.

Platelet Desialylation Is a Novel Mechanism and Therapeutic Target in Daboia siamensis and Agkistrodon halys Envenomation-Induced Thrombocytopenia

Venom-induced thrombocytopenia (VIT) is one of the most important hemotoxic effects of a snakebite, which is often associated with venom-induced consumptive coagulopathy (VICC). Refractory thrombocytopenia without significant coagulation abnormalities has also been reported after envenomation by some viperid snakes; however, the mechanisms are not well understood and therapeutic strategies are lacking. Here, we found that patients injured by Daboia siamensis or Agkistrodon halys snakes, who were resistant to standard antivenom treatment, had developed coagulopathy-independent thrombocytopenia. Venoms from these viperid snakes, rather than from the elapid snake (Bungarus multicinctus), induced platelet surface expression of neuraminidase-1 (NEU-1), and significantly increased the desialylation of the glycoproteins on human platelets. The desialylated platelets caused by viperid snake venoms were further internalized by macrophages, which resulted in reduced platelet numbers in peripheral blood. Importantly, neuraminidase inhibitor significantly decreased viper venom-induced platelet desialylation, therefore inhibiting platelet phagocytosis by macrophages, and alleviating venom-induced thrombocytopenia. Collectively, these findings support an important role for desialylated platelet clearance in the progression of viper envenomation-induced, coagulopathy-independent thrombocytopenia. Our study demonstrates that the neuraminidase inhibitor may be a potential therapy or adjuvant therapy to treat snakebite-induced thrombocytopenia.

Hypoxia and low temperature upregulate transferrin to induce hypercoagulability at high altitude

Studies have shown significantly increased thromboembolic events at high altitude. We recently reported that transferrin could potentiate blood coagulation, but the underlying mechanism for high altitude-related thromboembolism is still poorly understood. Here, we examined the activity and concentration of plasma coagulation factors and transferrin in plasma collected from long-term human residents and short-stay mice exposed to varying altitudes. We found that the activities of thrombin and factor XIIa (FXIIa) along with the concentrations of transferrin were significantly increased in the plasma of humans and mice at high altitudes. Furthermore, both hypoxia (6% O2) and low temperature (0°C), 2 critical high-altitude factors, enhanced hypoxia-inducible factor 1α (HIF-1α) levels to promote the expression of the transferrin gene, whose enhancer region contains HIF-1α binding site, and consequently, to induce hypercoagulability by potentiating thrombin and FXIIa. Importantly, thromboembolic disorders and pathological insults in mouse models induced by both hypoxia and low temperature were ameliorated by transferrin interferences, including transferrin antibody treatment, transferrin downregulation, and the administration of our designed peptides that inhibit the potentiation of transferrin on thrombin and FXIIa. Thus, low temperature and hypoxia upregulated transferrin expression-promoted hypercoagulability. Our data suggest that targeting the transferrin-coagulation pathway is a novel and potentially powerful strategy against thromboembolic events caused by harmful environmental factors under high-altitude conditions.

Platelet-rich plasma: a comparative and economical therapy for wound healing and tissue regeneration

Rise in the incidences of chronic degenerative diseases with aging makes wound care a socio-economic burden and unceasingly necessitates a novel, economical, and efficient wound healing treatment. Platelets have a crucial role in hemostasis and thrombosis by modulating distinct mechanistic phases of wound healing, such as promoting and stabilizing the clot. Platelet-rich plasma (PRP) contains a high concentration of platelets than naïve plasma and has an autologous origin with no immunogenic adverse reactions. As a consequence, PRP has gained significant attention as a therapeutic to augment the healing process. Since the past few decades, a robust volume of research and clinical trials have been performed to exploit extensive role of PRP in wound healing/tissue regeneration. Despite these rigorous studies and their application in diversified medical fields, efficacy of PRP-based therapies is continuously questioned owing to the paucity of large samplesizes, controlled clinical trials, and standard protocols. This review systematically delineates the process of wound healing and involvement of platelets in tissue repair mechanisms. Additionally, emphasis is laid on PRP, its preparation methods, handling, classification,application in wound healing, and PRP as regenerative therapeutics combined with biomaterials and mesenchymal stem cells (MSCs).

Characterization of CD41+ cells in the lymph node

Lymph nodes (LNs) are the critical sites of immunity, and the stromal cells of LNs are crucial to their function. Our understanding of the stromal compartment of the LN has deepened recently with the characterization of nontraditional stromal cells. CD41 (integrin αIIb) is known to be expressed by platelets and hematolymphoid cells. We identified two distinct populations of CD41⁺Lyve1⁺ and CD41⁺Lyve1^- cells in the LNs. CD41⁺Lyve1^- cells appear in the LN mostly at the later stages of the lives of mice. We identified CD41⁺ cells in human LNs as well. We demonstrated that murine CD41⁺ cells express mesodermal markers, such as Sca-1, CD105 and CD29, but lack platelet markers. We did not observe the presence of platelets around the HEVs or within proximity to fibroblastic reticular cells of the LN. Examination of thoracic duct lymph fluid showed the presence of CD41⁺Lyve1^- cells, suggesting that these cells recirculate throughout the body. FTY720 reduced their trafficking to lymph fluid, suggesting that their egress is controlled by the S1P1 pathway. CD41⁺Lyve1^- cells of the LNs were sensitive to radiation, suggestive of their replicative nature. Single cell RNA sequencing data showed that the CD41⁺ cell population in naïve mouse LNs expressed largely stromal cell markers. Further studies are required to examine more deeply the role of CD41⁺ cells in the function of LNs.

Cucurbitacins Elicit Anti-Platelet Activity via Perturbation of the Cytoskeleton and Integrin Function

Cucurbitacins are dietary compounds that have been shown to elicit a range of anti-tumour, anti-inflammatory and anti-atherosclerotic activities. Originally identified as signal transducer and activator of transcription, STAT, inhibitors, a variety of mechanisms of action have since been described, including dysregulation of the actin cytoskeleton and disruption of integrin function. Integrin outside-in signalling and cytoskeletal rearrangements are critical for the propagation of stable thrombus formation and clot retraction following platelet adhesion at the site of vessel damage. The effects of cucurbitacins on platelet function and thrombus formation are unknown. We report for the first time anti-platelet and anti-thrombotic effects of cucurbitacins B, E and I in human platelets. Treatment of platelets with cucurbitacins resulted in attenuation of platelet aggregation, secretion and fibrinogen binding following stimulation by platelet agonists. Cucurbitacins were also found to potently inhibit other integrin- and cytoskeleton-mediated events, including adhesion, spreading and clot retraction. Further investigation of cytoskeletal dynamics found treatment with cucurbitacins altered cofilin phosphorylation, enhanced activation and increased F actin polymerisation and microtubule assembly. Disruption to cytoskeletal dynamics has been previously shown to impair integrin activation, platelet spreading and clot retraction. Anti-platelet properties of cucurbitacins were found to extend to a disruption of stable thrombus formation, with an increase in thrombi instability and de-aggregation under flow. Our research identifies novel, anti-platelet and anti-thrombotic actions of cucurbitacins that appear to be linked to dysregulation of cytoskeletal dynamics and integrin function.

Viper venoms drive the macrophages and hepatocytes to sequester and clear platelets: novel mechanism and therapeutic strategy for venom-induced thrombocytopenia

Venomous snakebites cause clinical manifestations that range from local to systemic and are considered a significant global health challenge. Persistent or refractory thrombocytopenia has been frequently reported in snakebite patients, especially in cases caused by viperidae snakes. Viper envenomation-induced thrombocytopenia may persist in the absence of significant consumption coagulopathy even after the antivenom treatment, yet the mechanism remains largely unknown. Our study aims to investigate the mechanism and discover novel therapeutic targets for coagulopathy-independent thrombocytopenia caused by viper envenomation. Here we found that patients bitten by Protobothrops mucrosquamatus and Trimeresurus stejnegeri, rather than Naja. atra may develop antivenom-resistant and coagulopathy-independent thrombocytopenia. Crude venoms and the derived C-type lectin-like proteins from these vipers significantly increased platelet surface expression of neuraminidase and platelet desialylation, therefore led to platelet ingestion by both macrophages and hepatocytes in vitro, and drastically decreased peripheral platelet counts in vivo. Our study is the first to demonstrate that desialylation-mediated platelet clearance is a novel mechanism of viper envenomation-induced refractory thrombocytopenia and C-type lectin-like proteins derived from the viper venoms contribute to snake venom-induced thrombocytopenia. The results of this study suggest the inhibition of platelet desialylation as a novel therapeutic strategy against viper venom-induced refractory thrombocytopenia.

Soy Isoflavones Inhibit Both GPIb-IX Signaling and αIIbβ3 Outside-In Signaling via 14-3-3ζ in Platelet

Soy diet is thought to help prevent cardiovascular diseases in humans. Isoflavone, which is abundant in soybean and other legumes, has been reported to possess antiplatelet activity and potential antithrombotic effect. Our study aims to elucidate the potential target of soy isoflavone in platelet. The anti-thrombosis formation effect of genistein and daidzein was evaluated in ex vivo perfusion chamber model under low (300 s-1) and high (1800 s-1) shear forces. The effect of genistein and daidzein on platelet aggregation and spreading was evaluated with platelets from both wildtype and GPIbα deficient mice. The interaction of these soy isoflavone with 14-3-3ζ was detected by surface plasmon resonance (SPR) and co-immunoprecipitation, and the effect of αIIbβ3-mediated outside-in signaling transduction was evaluated by western blot. We found both genistein and daidzein showed inhibitory effect on thrombosis formation in perfusion chamber, especially under high shear force (1800 s-1). These soy isoflavone interact with 14-3-3ζ and inhibited both GPIb-IX and αIIbβ3-mediated platelet aggregation, integrin-mediated platelet spreading and outside-in signaling transduction. Our findings indicate that 14-3-3ζ is a novel target of genistein and daidzein. 14-3-3ζ, an adaptor protein that regulates both GPIb-IX and αIIbβ3-mediated platelet activation is involved in soy isoflavone mediated platelet inhibition.

Visualization of Platelet Integrins via Two-Photon Microscopy Using Anti-transmembrane Domain Peptides Containing a Blue Fluorescent Amino Acid

The fluorescent reporters commonly used to visualize proteins can perturb both protein structure and function. Recently, we found that 4-cyanotryptophan (4CN-Trp), a blue fluorescent amino acid, is suitable for one-photon imaging applications. Here, we demonstrate its utility in two-photon fluorescence microscopy by using it to image integrins on cell surfaces. Specifically, we used solid-phase peptide synthesis to generate CHAMP peptides labeled with 4-cyanoindole (4CNI) at their N-termini to image integrins on cell surfaces. CHAMP (computed helical anti-membrane protein) peptides spontaneously insert into membrane bilayers to target integrin transmembrane domains and cause integrin activation. We found that 4CNI labeling did not perturb the ability of CHAMP peptides to insert into membranes, bind to integrins, or cause integrin activation. We then used two-photon fluorescence microscopy to image 4CNI-containing integrins on the surface of platelets. Compared to a 4CNI-labeled scrambled peptide that uniformly decorated cell surfaces, 4CNI-labeled CHAMP peptides were present in discrete blue foci. To confirm that these foci represented CN peptide-containing integrins, we co-stained platelets with integrin-specific fluorescent monoclonal antibodies and found that CN peptide and antibody fluorescence coincided. Because 4CNI can readily be biosynthetically incorporated into proteins with little if any effect on protein structure and function, it provides a facile way to directly monitor protein behavior and protein-protein interactions in cellular environments. In addition, these results clearly demonstrate that the two-photon excitation cross section of 4CN-Trp is sufficiently large to make it a useful two-photon fluorescence reporter for biological applications.

Slounase, a Batroxobin Containing Activated Factor X Effectively Enhances Hemostatic Clot Formation and Reducing Bleeding in Hypocoagulant Conditions in Mice

Uncontrolled bleeding associated with trauma and surgery is the leading cause of preventable death. Batroxobin, a snake venom-derived thrombin-like serine protease, has been shown to clot fibrinogen by cleaving fibrinopeptide A in a manner distinctly different from thrombin, even in the presence of heparin. The biochemical properties of batroxobin and its effect on coagulation have been well characterized in vitro. However, the efficacy of batroxobin on hemostatic clot formation in vivo is not well studied due to the lack of reliable in vivo hemostasis models. Here, we studied the efficacy of batroxobin and slounase, a batroxobin containing activated factor X, on hemostatic clot composition and bleeding using intravital microcopy laser ablation hemostasis models in micro and macro vessels and liver puncture hemostasis models in normal and heparin-induced hypocoagulant mice. We found that prophylactic treatment in wild-type mice with batroxobin, slounase and activated factor X significantly enhanced platelet-rich fibrin clot formation following vascular injury. In heparin-treated mice, batroxobin treatment resulted in detectable fibrin formation and a modest increase in hemostatic clot size, while activated factor X had no effect. In contrast, slounase treatment significantly enhanced both platelet recruitment and fibrin formation, forming a stable clot and shortening bleeding time and blood loss in wild-type and heparin-treated hypocoagulant mice. Our data demonstrate that, while batroxobin enhances fibrin formation, slounase was able to enhance hemostasis in normal mice and restore hemostasis in hypocoagulant conditions via the enhancement of fibrin formation and platelet activation, indicating that slounase is more effective in controlling hemorrhage.

GPIbα is the driving force of hepatic thrombopoietin generation

Thrombopoietin (TPO), a glycoprotein hormone produced predominantly in the liver, plays important roles in the hematopoietic stem cell (HSC) niche, and is essential for megakaryopoiesis and platelet generation. Long-standing understanding proposes that TPO is constitutively produced by hepatocytes, and levels are fine-tuned through platelet and megakaryocyte internalization/degradation via the c-Mpl receptor. However, in immune thrombocytopenia (ITP) and several other diseases, TPO levels are inconsistent with this theory. Recent studies showed that platelets, besides their TPO clearance, can induce TPO production in the liver. Our group also accidentally discovered that platelet glycoprotein (GP) Ibα is required for platelet-mediated TPO generation, which is underscored in both GPIbα-/- mice and patients with Bernard-Soulier syndrome. This review will introduce platelet versatilities and several new findings in hemostasis and platelet consumption but focus on its roles in TPO regulation. The implications of these new discoveries in hematopoiesis and the HSC niche, particularly in ITP, will be discussed.

The 14-3-3ζ-c-Src-integrin-β3 complex is vital for platelet activation

Several adaptor molecules bind to cytoplasmic tails of β-integrins and facilitate bidirectional signaling, which is critical in thrombosis and hemostasis. Interfering with integrin-adaptor interactions spatially or temporally to inhibit thrombosis without affecting hemostasis is an attractive strategy for the development of safe antithrombotic drugs. We show for the first time that the 14-3-3ζ-c-Src-integrin-β3 complex is formed during platelet activation. 14-3-3ζ-c-Src interaction is mediated by the -PIRLGLALNFSVFYYE- fragment (PE16) on the 14-3-3ζ and SH2-domain on c-Src, whereas the 14-3-3ζ-integrin-β3 interaction is mediated by the -ESKVFYLKMKGDYYRYL- fragment (EL17) on the 14-3-3ζ and -KEATSTF- fragment (KF7) on the β3-integrin cytoplasmic tail. The EL17-motif inhibitor, or KF7 peptide, interferes with the formation of the 14-3-3ζ-c-Src-integrin-β3 complex and selectively inhibits β3 outside-in signaling without affecting the integrin-fibrinogen interaction, which suppresses thrombosis without causing significant bleeding. This study characterized a previously unidentified 14-3-3ζ-c-Src-integrin-β3 complex in platelets and provided a novel strategy for the development of safe and effective antithrombotic treatments.

Role of platelets and breast cancer stem cells in metastasis

The high mortality rate of breast cancer is mainly caused by the metastatic ability of cancer cells, resistance to chemotherapy and radiotherapy, and tumor regression capacity. In recent years, it has been shown that the presence of breast cancer stem cells is closely associated with the migration and metastatic ability of cancer cells, as well as with their resistance to chemotherapy and radiotherapy. The tumor microenvironment is one of the main molecular factors involved in cancer and metastatic processes development, in this sense it is interesting to study the role of platelets, one of the main communicator cells in the human body which are activated by the signals they receive from the microenvironment and can generate more than one response. Platelets can ingest and release RNA, proteins, cytokines and growth factors. After the platelets interact with the tumor microenvironment, they are called "tumor-educated platelets." Tumor-educated platelets transport material from the tumor microenvironment to sites adjacent to the tumor, thus helping to create microenvironments conducive for the development of primary and metastatic tumors. It has been observed that the clone capable of carrying out the metastatic process is a cancer cell with stem cell characteristics. Cancer stem cells go through a series of processes, including epithelial-mesenchymal transition, intravasation into blood vessels, movement through blood vessels, extravasation at the site of the establishment of a metastatic focus, and site colonization. Tumor-educated platelets support all these processes. 

Enhanced Endothelial Cell Delivery for Repairing Injured Endothelium via Pretargeting Approach and Bioorthogonal Chemistry

Arterial wall injury often leads to endothelium cell activation, endothelial detachment, and atherosclerosis plaque formation. While abundant research efforts have been placed on treating the end stages of the disease, no cure has been developed to repair injured and denude endothelium often occurred at an early stage of atherosclerosis. Here, a pretargeting cell delivery strategy using combined injured endothelial targeting nanoparticles and bioorthogonal click chemistry approach was developed to deliver endothelial cells to replenish the injured endothelium via a two-step process. First, nanoparticles bearing glycoprotein 1b α (Gp1bα) proteins and tetrazine (Tz) were fabricated to provide a homogeneous nanoparticle coating on an injured arterial wall via the interactions between Gp1bα and von Willebrand factor (vWF), a ligand that is present on denuded endothelium. Second, transplanted endothelium cells bearing transcyclooctene (TCO) would be quickly immobilized on the surfaces of nanoparticles via TCO:Tz reactions. In vitro binding studies under both static and flow conditions confirmed that our novel Tz-labeled Gp1bα-conjugated poly(lactic-co-glycolic acid) (PLGA) nanoparticles can successfully pretargeted toward the injured site and support rapid adhesion of endothelial cells from the circulation. Ex vivo results also confirm that such an approach is highly efficient in mediating the local delivery of endothelial cells at the sites of arterial injury. The results support that this pretargeting cell delivery approach may be used for repairing injured endothelium in situ at its early stage.

Assessment of Shear-Dependent Kinetics of Primary Haemostasis With a Microfluidic Acoustic Biosensor

Primary haemostasis is a complex dynamic process, which involves in-flow interactions between platelets and sub-endothelial matrix at the area of the damaged vessel wall. It results in a first haemostatic plug, which stops bleeding, before coagulation ensues and consolidates it. The diagnosis of primary haemostasis defect would benefit from evaluation of the whole sequence of mechanisms involved in platelet plug formation in flow. This work proposes a new approach that is based on characterization of the shear-dependent kinetics that enables the evaluation of the early stages of primary haemostasis. We used a label-free method with a quartz crystal microbalance (QCM) biosensor to measure the platelet deposits over time onto covalently immobilized type I fibrillar collagen. We defined three metrics: total frequency shift, lag time, and growth rate. The measurement was completed at four predefined shear rates prevailing in small vessels (500, 770, 1000 and 1500 s^-1) during five minutes of perfusion with anticoagulated normal whole blood. The rate of the frequency shift over the first five minutes was strongly influenced by shear rate conditions, presenting a maximum around 770 s^-1, and varying by a factor larger than three in the studied shear rate range. To validate the biosensor signal, the total frequency shift was compared to results obtained by atomic force microscopy (AFM) on final platelet deposits. The results show that shear-dependent kinetic assays are promising as an advanced method for screening of primary haemostasis.

Tantalum-containing mesoporous bioactive glass powder for hemostasis

This study evaluates the hemostatic properties of tantalum-containing mesoporous bioactive glasses (Ta-MBGs) through a suite of in-vitro methods: hemolysis percentage, zeta potential, blood coagulation assays (Activated Partial Thromboplastin Time - APTT and Prothrombin Time - PT) and cytotoxicity tests. Five compositions of Ta-MBG, with x mol% Ta₂O₅ added to the glass series (80-x)SiO₂-15CaO-5P₂O₅-xTa₂O₅ where x=0 (0Ta), x=0.5 (0.5Ta), x=1 (1Ta), x=5 (5Ta), and x=10 (10Ta) mol%, were synthesised. The hemostatic potential of all the Ta-MBGs was confirmed by their negative zeta potential (-23 to -31 mV), which enhances the intrinsic pathway of blood coagulation. The hemolysis percentages of all Ta-MBGs except 10Ta showed statistically significant reductions compared to the same experiments carried out both in the absence of a sample ('no treatment' group) and in the presence of 10Ta. These observations validate the consideration of Ta-MBGs as hemostatic agents as they do not cause significant lysis of red blood cells. Cytotoxicity analysis revealed that Ta-MBGs had no effect on bovine fibroblast viability. Furthermore, a reduction in both APTT (a test to evaluate the intrinsic pathway of coagulation) and PT (a test to evaluate the extrinsic pathway) signified enhancement of hemostasis: 5Ta caused a significant reduction in APTT compared to 'no treatment', 1Ta and 10Ta and a significant reduction in PT compared to 0Ta. Therefore, we conclude that 5mol% of Ta optimised the hemostatic properties of these mesoporous bioactive glasses.

Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

Integrins are a family of cell surface receptors crucial to fundamental cellular functions such as adhesion, signaling, and viability, deeply involved in a variety of diseases, including the initiation and progression of cancer, of coronary, inflammatory, or autoimmune diseases. The natural ligands of integrins are glycoproteins expressed on the cell surface or proteins of the extracellular matrix. For this reason, short peptides or peptidomimetic sequences that reproduce the integrin-binding motives have attracted much attention as potential drugs. When challenged in clinical trials, these peptides/peptidomimetics let to contrasting and disappointing results. In the search for alternative utilizations, the integrin peptide ligands have been conjugated onto nanoparticles, materials, or drugs and drug carrier systems, for specific recognition or delivery of drugs to cells overexpressing the targeted integrins. Recent research in peptidic integrin ligands is exploring new opportunities, in particular for the design of nanostructured, micro-fabricated, cell-responsive, stimuli-responsive, smart materials.

Crosstalk Between Platelets and Microbial Pathogens

Platelets, small anucleate cells circulating in the blood, are critical mediators in haemostasis and thrombosis. Interestingly, recent studies demonstrated that platelets contain both pro-inflammatory and anti-inflammatory molecules, equipping platelets with immunoregulatory function in both innate and adaptive immunity. In the context of infectious diseases, platelets are involved in early detection of invading microorganisms and are actively recruited to sites of infection. Platelets exert their effects on microbial pathogens either by direct binding to eliminate or restrict dissemination, or by shaping the subsequent host immune response. Reciprocally, many invading microbial pathogens can directly or indirectly target host platelets, altering platelet count or/and function. In addition, microbial pathogens can impact the host auto- and alloimmune responses to platelet antigens in several immune-mediated diseases, such as immune thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia. In this review, we discuss the mechanisms that contribute to the bidirectional interactions between platelets and various microbial pathogens, and how these interactions hold relevant implications in the pathogenesis of many infectious diseases. The knowledge obtained from "well-studied" microbes may also help us understand the pathogenesis of emerging microbes, such as SARS-CoV-2 coronavirus.

Iron-Deficiency and Estrogen Are Associated With Ischemic Stroke by Up-Regulating Transferrin to Induce Hypercoagulability

RATIONALE

Epidemiological studies have identified an associate between iron deficiency (ID) and the use of oral contraceptives (CC) and ischemic stroke (IS). To date, however, the underlying mechanism remains poorly understood. Both ID and CC have been demonstrated to upregulate the level and iron-binding ability of Tf (transferrin), with our recent study showing that this upregulation can induce hypercoagulability by potentiating FXIIa/thrombin and blocking antithrombin-coagulation proteases interactions.

OBJECTIVE

To investigate whether Tf mediates IS associated with ID or CC and the underlying mechanisms.

METHODS AND RESULTS

Tf levels were assayed in the plasma of IS patients with a history of ID anemia, ID anemia patients, venous thromboembolism patients using CC, and ID mice, and in the cerebrospinal fluid of some IS patients. Effects of ID and estrogen administration on Tf expression and coagulability and the underlying mechanisms were studied in vivo and in vitro. High levels of Tf and Tf-thrombin/FXIIa complexes were found in patients and ID mice. Both ID and estrogen upregulated Tf through hypoxia and estrogen response elements located in the Tf gene enhancer and promoter regions, respectively. In addition, ID, administration of exogenous Tf or estrogen, and Tf overexpression promoted platelet-based thrombin generation and hypercoagulability and thus aggravated IS. In contrast, anti-Tf antibodies, Tf knockdown, and peptide inhibitors of Tf-thrombin/FXIIa interaction exerted anti-IS effects in vivo.

CONCLUSIONS

Our findings revealed that certain factors (ie, ID and CC) upregulating Tf are risk factors of thromboembolic diseases decipher a previously unrecognized mechanistic association among ID, CC, and IS and provide a novel strategy for the development of anti-IS medicine by interfering with Tf-thrombin/FXIIa interactions.

Model Combining Tumor Molecular and Clinicopathologic Risk Factors Predicts Sentinel Lymph Node Metastasis in Primary Cutaneous Melanoma

PURPOSE

More than 80% of patients who undergo sentinel lymph node (SLN) biopsy have no nodal metastasis. Here we describe a model that combines clinicopathologic and molecular variables to identify patients with thin and intermediate thickness melanomas who may forgo the SLN biopsy procedure due to their low risk of nodal metastasis.

PATIENTS AND METHODS

Genes with functional roles in melanoma metastasis were discovered by analysis of next generation sequencing data and case control studies. We then used PCR to quantify gene expression in diagnostic biopsy tissue across a prospectively designed archival cohort of 754 consecutive thin and intermediate thickness primary cutaneous melanomas. Outcome of interest was SLN biopsy metastasis within 90 days of melanoma diagnosis. A penalized maximum likelihood estimation algorithm was used to train logistic regression models in a repeated cross validation scheme to predict the presence of SLN metastasis from molecular, clinical and histologic variables.

RESULTS

Expression of genes with roles in epithelial-to-mesenchymal transition (glia derived nexin, growth differentiation factor 15, integrin β3, interleukin 8, lysyl oxidase homolog 4, TGFβ receptor type 1 and tissue-type plasminogen activator) and melanosome function (melanoma antigen recognized by T cells 1) were associated with SLN metastasis. The predictive ability of a model that only considered clinicopathologic or gene expression variables was outperformed by a model which included molecular variables in combination with the clinicopathologic predictors Breslow thickness and patient age; AUC, 0.82; 95% CI, 0.78-0.86; SLN biopsy reduction rate of 42% at a negative predictive value of 96%.

CONCLUSION

A combined model including clinicopathologic and gene expression variables improved the identification of melanoma patients who may forgo the SLN biopsy procedure due to their low risk of nodal metastasis.

Coenzyme Q10 attenuates platelet integrin αIIbβ3 signaling and platelet hyper-reactivity in ApoE-deficient mice

CoQ10 supplementation in ApoE^−/− mice attenuates high-fat diet-induced platelet hyper-reactivity via down-regulating platelet αIIbβ3 signaling, and thus protecting against atherothrombosis.

Coenzyme Q10 Upregulates Platelet cAMP/PKA Pathway and Attenuates Integrin αIIbβ3 Signaling and Thrombus Growth

SCOPE

Platelet integrin αIIbβ3 is the key mediator of atherothrombosis. Supplementation of coenzyme Q10 (CoQ10), a fat-soluble molecule that exists in various foods, exerts protective cardiovascular effects. This study aims to investigate whether and how CoQ10 acts on αIIbβ3 signaling and thrombosis, the major cause of cardiovascular diseases.

METHODS AND RESULTS

Using a series of platelet functional assays in vitro, it is demonstrated that CoQ10 reduces human platelet aggregation, granule secretion, platelet spreading, and clot retraction. It is further demonstrated that CoQ10 inhibits platelet integrin αIIbβ3 outside-in signaling. These inhibitory effects are mainly mediated by upregulating cAMP/PKA pathway, where CoQ10 stimulates the A_2A adenosine receptor and decreases phosphodiesterase 3A phosphorylation. Moreover, CoQ10 attenuates murine thrombus growth and vessel occlusion in a ferric chloride (FeCl₃ )-induced thrombosis model in vivo. Importantly, the randomized, double-blind, placebo-controlled clinical trial in dyslipidemic patients demonstrates that 24 weeks of CoQ10 supplementation increases platelet CoQ10 concentrations, enhances the cAMP/PKA pathway, and attenuates αIIbβ3 outside-in signaling, leading to decreased platelet aggregation and granule release.

CONCLUSION

Through upregulating the platelet cAMP/PKA pathway, and attenuating αIIbβ3 signaling and thrombus growth, CoQ10 supplementation may play an important protective role in patients with risks of cardiovascular diseases.

Quantitative Characterization of Shear-Induced Platelet Receptor Shedding: Glycoprotein Ibα, Glycoprotein VI, and Glycoprotein IIb/IIIa

The structural integrity of platelet receptors is essential for platelets to play the normal hemostatic function. The high non-physiologic shear stress (NPSS) commonly exists in blood-contacting medical devices and has been shown to cause platelet receptor shedding. The loss of platelet receptors may impair the normal hemostatic function of platelets. The aim of this study was to quantify NPSS-induced shedding of three key receptors on the platelet surface. Human blood was subjected to the matrix of well-defined shear stresses and exposure times, generated by using a custom-designed blood-shearing device. The expression of three key platelet receptors, glycoprotein (GP) Ibα, GPVI, and GPIIb/IIIa, in sheared blood was quantified using flow cytometry. The quantitative relationship between the loss of each of the three receptors on the platelet surface and shear condition (shear stress level and exposure time) was explored. It was found that these relationships followed well the power law functional form. The coefficients of the power law models for the shear-induced shedding of these platelet receptors were derived with coefficients of determination (R) of 0.77, 0.73, and 0.78, respectively. The power law models with these coefficients may be potentially used to predict the shear-induced platelet receptor shedding of human blood.

Inflammation Induced by Platelet-Activating Viperid Snake Venoms: Perspectives on Thromboinflammation

Envenomation by viperid snakes is characterized by systemic thrombotic syndrome and prominent local inflammation. To date, the mechanisms underlying inflammation and blood coagulation induced by Viperidae venoms have been viewed as distinct processes. However, studies on the mechanisms involved in these processes have revealed several factors and signaling molecules that simultaneously act in both the innate immune and hemostatic systems, suggesting an overlap between both systems during viper envenomation. Moreover, distinct classes of venom toxins involved in these effects have also been identified. However, the interplay between inflammation and hemostatic alterations, referred as to thromboinflammation, has never been addressed in the investigation of viper envenomation. Considering that platelets are important targets of viper snake venoms and are critical for the process of thromboinflammation, in this review, we summarize the inflammatory effects and mechanisms induced by viper snake venoms, particularly from the Bothrops genus, which strongly activate platelet functions and highlight selected venom components (metalloproteases and C-type lectins) that both stimulate platelet functions and exhibit pro-inflammatory activities, thus providing insights into the possible role(s) of thromboinflammation in viper envenomation.

Antimicrobial effects of various platelet rich concentrates-vibes from in-vitro studies-a systematic review

Aim

The aim of the current review was to outline the existing information related to antimicrobial properties of various platelet concentrates, as experimented in various in-vitro studies.

Background

One of the most interesting recent landmarks in the field of biological therapy has been the discovery that platelets, in addition to being capable of releasing hundreds of proteins and growth factors, can also release immunomodulatory agents with antimicrobial activity. Several international research groups have reported antimicrobial activities in both human platelets and other types of platelet rich plasma preparations.

Review Result

This review was carried-out pursuing a systematic approach. An electronic search was conducted on MEDLINE and GOOGLE SCHOLAR databases using suitable search terminologies. It included preclinical studies which assessed the antimicrobial activity of Autologous Platelet Concentrates(APC).Ten in-vitro studies and one animal study, which investigated APC effects on various microorganisms, were included. Almost in all the included in-vitro studies, it was found that complete breakdown of microbial load could not be achieved by any of the APC preparations but there occurred a reduction in the growth of microorganisms. Thus APCs displayed a bacteriostatic rather than bacteriocidal activity.The only animal study included in this review which had both in-vitro and in-vivo evaluation, also showed reduction of infection caused by different microorganisms.

Conclusion

Although the precise mechanism of synergy with microbial pathogens needs further validation, platelet concentrates proved to have antimicrobial properties.

Blood platelet surface receptor genetic variation and risk of thrombotic episodes

Haemostasis is a set of processes whose main task is to prevent blood loss by creating barriers in damaged vessels. Because of the large number of platelet surface receptors and their many agonists, platelets can be activated in normal and pathologic states leading to thromboembolic complications. Although age, blood pressure, LDL and HDL, diabetes, lack of physical activity, obesity and stress are well established risk factors, recent work has shown that platelet receptor polymorphisms also impact platelet function. The most common polymorphisms include 14A/T (PAR-1), 139C/T, 744T/C, 52G/T, i-ins801A (P2Y12), 1622A/G, -5T/C (GPIbα) 1565C/T (GPIIb/IIIa) and 807C/T (GPIa/IIa). This review examines the influence of these polymorphisms on cardiovascular disease including myocardial infarction, deep venous thromboembolism and acute coronary syndromes. Elucidation of these genetic variations will facilitate our understanding of the complex molecular mechanisms involved with physiologic and pathophysiologic platelet activation and clot formation.

Monitoring of platelet function parameters and microRNA expression levels in patients with prostate cancer treated with volumetric modulated arc radiotherapy

Radiotherapy (RT) may result in platelet activation and thrombosis development. To the best of our knowledge, the potential effect of volumetric-modulated arc therapy (VMAT), a novel radiotherapy technique, on platelet function and microRNA (miRNA/miR) expression has not been previously investigated. The present study aimed to determine the effect of VMAT on the alterations in platelet function parameters and miRNA expression levels. A total of 25 patients with prostate cancer and 25 healthy subjects were included in the present study. Blood samples were collected from the patient group on the day prior to RT (pre-RT), the day RT was completed (post-RT day 0), and 40 days following the end of therapy (post-RT day 40). Platelet count, mean platelet volume (MPV) value, platelet aggregation, plasma P-selectin, thrombospondin-1, platelet factor 4, plasma miR-223 and miR-126 expression levels were measured. A significant decrease in platelet count in the post-RT day 0 group was measured in comparison with the pre-RT and the post-RT day 40 groups. Pre-RT MPV values were higher than those of the post-RT day 0 and the post-RT day 40 groups. No significant differences were observed in the levels of platelet activation markers or miR-223 and miR-126 expression levels between the RT groups. Although RT may result in a reduction in platelet and MPV counts, the results of the present study indicate that platelet activation markers are not affected by VMAT. Therefore, it is possible that no platelet activation occurs during VMAT, owing to the conformal dose distributions, improved target volume coverage and the sparing of normal tissues from undesired radiation.

Regulation of platelet function and thrombosis by omega-3 and omega-6 polyunsaturated fatty acids

Thrombosis is the most common underlying pathology responsible for morbidity and mortality in cardiovascular disease (CVD). Platelet adhesion, activation, and aggregation play central roles in hemostasis; however, the same process may also cause thrombosis and vessel occlusion at the site of ruptured atherosclerotic lesions leading to heart attack and stroke. ω-3 and ω-6 polyunsaturated fatty acids (PUFAs) are an essential component of the platelet phospholipid membrane and play a major role in many aspects of platelet function. Dietary supplementation of ω-3 and ω-6 PUFAs has long been used to slow the progression of CVD and to prevent acute cardiovascular events. Despite this, the role of ω-3 and ω-6 PUFAs and their oxylipin metabolites in platelet function remains controversial due to the lack in our understanding of the mechanistic regulation controlling platelet reactivity in vitro and substantial evidence for PUFA regulation of thrombotic events in vivo. In this review, we will outline the role of platelet physiology in hemostasis and the effect of ω-3 and ω-6 PUFAs on platelet function, with special emphasis on in vivo effects on hemostasis and thrombosis due to the role of PUFAs and their bioactive lipids in circulation. Further, recent mechanistic insights and evidence for cardio-protective effects of PUFAs and their bioactive lipids will be discussed.

Platelet transfusions improve hemostasis and survival in a substudy of the prospective, randomized PROPPR trial

Transfusing platelets during massive hemorrhage is debated because of a lack of high-quality evidence concerning outcomes in trauma patients. The objective of this study was to examine the effect of platelet transfusions on mortality in severely injured trauma patients. This work analyzed PROPPR (Pragmatic, Randomized Optimal Platelet and Plasma Ratios) trial patients who received only the first cooler of blood products, which either did or did not contain platelets. Primary outcomes were all-cause mortality at 24 hours and 30 days and hemostasis. Secondary outcomes included cause of death, complications, and hospital-, intensive care unit (ICU)-, and ventilator-free days. Continuous variables were compared using Wilcoxon rank sum tests. Categorical variables were compared using Fisher's exact tests. There were 261 PROPPR patients who achieved hemostasis or died before receiving a second cooler of blood products (137 received platelets and 124 did not). Patients who received platelets also received more total plasma (median, 3 vs 2 U; P < .05) by PROPPR intervention design. There were no differences in total red blood cell transfusions between groups. After controlling for plasma volume, patients who received platelets had significantly decreased 24-hour (5.8% vs 16.9%; P < .05) and 30-day mortality (9.5% vs 20.2%; P < .05). More patients in the platelet group achieved hemostasis (94.9% vs 73.4%; P < .01), and fewer died as a result of exsanguination (1.5% vs 12.9%; P < .01). Patients who received platelets had a shorter time on mechanical ventilation (P < .05); however, no differences in hospital- or ICU-free days were observed. In conclusion, early platelet administration is associated with improved hemostasis and reduced mortality in severely injured, bleeding patients. This trial was registered at www.clinicaltrials.gov as # NCT01545232.

Ultraviolet-Based Pathogen Inactivation Systems: Untangling the Molecular Targets Activated in Platelets

Transfusions of platelets are an important cornerstone of medicine; however, recipients may be subject to risk of adverse events associated with the potential transmission of pathogens, especially bacteria. Pathogen inactivation (PI) technologies based on ultraviolet illumination have been developed in the last decades to mitigate this risk. This review discusses studies of platelet concentrates treated with the current generation of PI technologies to assess their impact on quality, PI capacity, safety, and clinical efficacy. Improved safety seems to come with the cost of reduced platelet functionality, and hence transfusion efficacy. In order to understand these negative impacts in more detail, several molecular analyses have identified signaling pathways linked to platelet function that are altered by PI. Because some of these biochemical alterations are similar to those seen arising in the context of routine platelet storage lesion development occurring during blood bank storage, we lack a complete picture of the contribution of PI treatment to impaired platelet functionality. A model generated using data from currently available publications places the signaling protein kinase p38 as a central player regulating a variety of mechanisms triggered in platelets by PI systems.

Cancer and platelet crosstalk: opportunities and challenges for aspirin and other antiplatelet agents

Platelets have long been recognized as key players in hemostasis and thrombosis; however, growing evidence suggests that they are also significantly involved in cancer, the second leading cause of mortality worldwide. Preclinical and clinical studies showed that tumorigenesis and metastasis can be promoted by platelets through a wide variety of crosstalk between platelets and cancer cells. For example, cancer changes platelet behavior by directly inducing tumor-platelet aggregates, triggering platelet granule and extracellular vesicle release, altering platelet phenotype and platelet RNA profiles, and enhancing thrombopoiesis. Reciprocally, platelets reinforce tumor growth with proliferation signals, antiapoptotic effect, and angiogenic factors. Platelets also activate tumor invasion and sustain metastasis via inducing an invasive epithelial-mesenchymal transition phenotype of tumor cells, promoting tumor survival in circulation, tumor arrest at the endothelium, and extravasation. Furthermore, platelets assist tumors in evading immune destruction. Hence, cancer cells and platelets maintain a complex, bidirectional communication. Recently, aspirin (acetylsalicylic acid) has been recognized as a promising cancer-preventive agent. It is recommended at daily low dose by the US Preventive Services Task Force for primary prevention of colorectal cancer. The exact mechanisms of action of aspirin in chemoprevention are not very clear, but evidence has emerged that suggests a platelet-mediated effect. In this article, we will introduce how cancer changes platelets to be more cancer-friendly and highlight advances in the modes of action for aspirin in cancer prevention. We also discuss the opportunities, challenges, and opposing viewpoints on applying aspirin and other antiplatelet agents for cancer prevention and treatment.

Bio-inspired nanomedicine strategies for artificial blood components

Blood is a fluid connective tissue where living cells are suspended in noncellular liquid matrix. The cellular components of blood render gas exchange (RBCs), immune surveillance (WBCs) and hemostatic responses (platelets), and the noncellular components (salts, proteins, etc.) provide nutrition to various tissues in the body. Dysfunction and deficiencies in these blood components can lead to significant tissue morbidity and mortality. Consequently, transfusion of whole blood or its components is a clinical mainstay in the management of trauma, surgery, myelosuppression, and congenital blood disorders. However, donor-derived blood products suffer from issues of shortage in supply, need for type matching, high risks of pathogenic contamination, limited portability and shelf-life, and a variety of side-effects. While robust research is being directed to resolve these issues, a parallel clinical interest has developed toward bioengineering of synthetic blood substitutes that can provide blood's functions while circumventing the above problems. Nanotechnology has provided exciting approaches to achieve this, using materials engineering strategies to create synthetic and semi-synthetic RBC substitutes for enabling oxygen transport, platelet substitutes for enabling hemostasis, and WBC substitutes for enabling cell-specific immune response. Some of these approaches have further extended the application of blood cell-inspired synthetic and semi-synthetic constructs for targeted drug delivery and nanomedicine. The current study provides a comprehensive review of the various nanotechnology approaches to design synthetic blood cells, along with a critical discussion of successes and challenges of the current state-of-art in this field. WIREs Nanomed Nanobiotechnol 2017, 9:e1464. doi: 10.1002/wnan.1464 For further resources related to this article, please visit the WIREs website.

Plant-based Food Cyanidin-3-Glucoside Modulates Human Platelet Glycoprotein VI Signaling and Inhibits Platelet Activation and Thrombus Formation

Background: Platelets play an important role in hemostasis, thrombosis, and atherosclerosis. Glycoprotein VI (GPVI) is a major platelet receptor that interacts with exposed collagen on injured vessel walls. Our previous studies have shown that anthocyanins (a type of natural plant pigment) attenuate platelet function; however, whether anthocyanins affect collagen-induced GPVI signaling remains unknown.Objective: The objective of this study was to explore the effects of cyanidin-3-glucoside (Cy-3-g, one of the major bioactive compounds in anthocyanins) on platelet activation and thrombosis and the GPVI signaling pathway.Methods: Platelets from healthy men and women were isolated and incubated with different concentrations (0, 0.5, 5, and 50 μM) of Cy-3-g. The expression of activated integrin αIIbβ3, P-selectin, CD63, and CD40L, fibrinogen binding to platelets, and platelet aggregation were evaluated in vitro. Platelet adhesion and aggregation in whole blood under flow conditions were assessed in collagen-coated perfusion chambers. Thrombosis and hemostasis were assessed in 3-4-wk-old male C57BL/6J mice through FeCl₃-induced intravital microscopy and tail bleeding time. The effect of Cy-3-g on collagen-induced human platelet GPVI signaling was explored with Western blot.Results: Cy-3-g attenuated platelet function in a dose-dependent manner. The 0.5-μM dose of Cy-3-g inhibited (P < 0.05) human platelet adhesion and aggregation to collagen at both venous (-54.02%) and arterial (-22.90%) shear stresses. The 5-μM dose inhibited (P < 0.05) collagen-induced human platelet activation (PAC-1: -48.21%, P-selectin: -50.63%), secretion (CD63: -73.89%, CD40L: -43.70%), fibrinogen binding (-56.79%), and aggregation (-17.81%). The 5-μM dose attenuated (P < 0.01) thrombus growth (-66.67%) without prolonging bleeding time in mice. The 50-μM dose downregulated (P < 0.05) collagen-induced GPVI signaling in human platelets and significantly decreased phosphorylation of Syk-linker for activation of T cells (LAT)-SLP76 (Syk: -39.08%, LAT: -32.25%, SLP76: -40.00%) and the expression of Lyn (-31.89%), Fyn (-36.27%), and phospholipase C-γ2 (-39.08%).Conclusions: Cy-3-g inhibits human platelet activation, aggregation, secretion, and thrombus formation, and downregulates the collagen-GPVI signaling pathway. Supplementation of Cy-3-g may have protective effects against atherothrombosis.

Effects of membrane deformability and bond formation/dissociation rates on adhesion dynamics of a spherical capsule in shear flow

Cellular adhesion plays a critical role in biological systems and biomedical applications. Cell deformation and biophysical properties of adhesion molecules are of significance for the adhesion behavior. In the present work, dynamic adhesion of a deformable capsule to a planar substrate, in a linear shear flow, is numerically simulated to investigate the combined influence of membrane deformability (quantified by the capillary number) and bond formation/dissociation rates on the adhesion behavior. The computational model is based on the immersed boundary-lattice Boltzmann method for the capsule-fluid interaction and a probabilistic adhesion model for the capsule-substrate interaction. Three distinct adhesion states, detachment, rolling adhesion and firm adhesion, are identified and presented in a state diagram as a function of capillary number and bond dissociation rate. The impact of bond formation rate on the state diagram is further investigated. Results show that the critical bond dissociation rate for the transition of rolling or firm adhesion to detachment is strongly related to the capsule deformability. At the rolling-adhesion state, smaller off rates are needed for larger capillary number to increase the rolling velocity and detach the capsule. In contrast, the critical off rate for firm-to-detach transition slightly increases with the capillary number. With smaller on rate, the effect of capsule deformability on the critical off rates is more pronounced and capsules with moderate deformability are prone to detach by the shear flow. Further increasing of on rate leads to large expansion of both rolling-adhesion and firm-adhesion regions. Even capsules with relatively large deformability can maintain stable rolling adhesion at certain off rate.

In vitro characterization of SynthoPlate™ (synthetic platelet) technology and its in vivo evaluation in severely thrombocytopenic mice

Essentials Platelet transfusion suffers from availability, portability, contamination, and short shelf-life. SynthoPlate™ (synthetic platelet technology) can resolve platelet transfusion limitations. SynthoPlate™ does not activate resting platelets or stimulate coagulation systemically. SynthoPlate™ significantly improves hemostasis in thrombocytopenic mice dose-dependently.

SUMMARY

Background Platelet transfusion applications face severe challenges, owing to the limited availability and portability, high risk of contamination and short shelf-life of platelets. Therefore, there is significant interest in synthetic platelet substitutes that can provide hemostasis while avoiding these issues. Platelets promote hemostasis by injury site-selective adhesion and aggregation, and propagation of coagulation reactions on their membranes. On the basis of these mechanisms, we have developed a synthetic platelet technology (SynthoPlate™) that integrates platelet-mimetic site-selective 'adhesion' and 'aggregation' functionalities via heteromultivalent surface decoration of lipid vesicles with von Willebrand factor-binding, collagen-binding and active platelet integrin glycoprotein (GP) IIb-IIIa-binding peptides. Objective To evaluate SynthoPlate for its effects on platelets and plasma in vitro, and for systemic safety and hemostatic efficacy in severely thrombocytopenic mice in vivo. Methods In vitro, SynthoPlate was evaluated with aggregometry, fluorescence microscopy, microfluidics, and thrombin and fibrin generation assays. In vivo, SynthoPlate was evaluated for systemic safety with prothrombin and fibrin assays on plasma, and for hemostatic effects on tail-transection bleeding time in severely thrombocytopenic (TCP) mice. Results SynthoPlate did not aggregate resting platelets or spontaneously promote coagulation in plasma, but could amplify the recruitment and aggregation of active platelets at the bleeding site, and thereby site-selectively enhance fibrin generation. SynthoPlate dose-dependently reduced bleeding time in TCP mice, to levels comparable to those in normal mice. SynthoPlate has a reasonable circulation residence time, and is cleared mostly by the liver and spleen. Conclusion The results demonstrate the promise of SynthoPlate as a synthetic platelet substitute in transfusion treatment of platelet-related bleeding complications.

The integrin PSI domain has an endogenous thiol isomerase function and is a novel target for antiplatelet therapy

Integrins are a large family of heterodimeric transmembrane receptors differentially expressed on almost all metazoan cells. Integrin β subunits contain a highly conserved plexin-semaphorin-integrin (PSI) domain. The CXXC motif, the active site of the protein-disulfide-isomerase (PDI) family, is expressed twice in this domain of all integrins across species. However, the role of the PSI domain in integrins and whether it contains thiol-isomerase activity have not been explored. Here, recombinant PSI domains of murine β3, and human β1 and β2 integrins were generated and their PDI-like activity was demonstrated by refolding of reduced/denatured RNase. We identified that both CXXC motifs of β3 integrin PSI domain are required to maintain its optimal PDI-like activity. Cysteine substitutions (C13A and C26A) of the CXXC motifs also significantly decreased the PDI-like activity of full-length human recombinant β3 subunit. We further developed mouse anti-mouse β3 PSI domain monoclonal antibodies (mAbs) that cross-react with human and other species. These mAbs inhibited αIIbβ3 PDI-like activity and its fibrinogen binding. Using single-molecular Biomembrane-Force-Probe assays, we demonstrated that inhibition of αIIbβ3 endogenous PDI-like activity reduced αIIbβ3-fibrinogen interaction, and these anti-PSI mAbs inhibited fibrinogen binding via different levels of both PDI-like activity-dependent and -independent mechanisms. Importantly, these mAbs inhibited murine/human platelet aggregation in vitro and ex vivo, and murine thrombus formation in vivo, without significantly affecting bleeding time or platelet count. Thus, the PSI domain is a potential regulator of integrin activation and a novel target for antithrombotic therapies. These findings may have broad implications for all integrin functions, and cell-cell and cell-matrix interactions.