Platelet adhesion and activation mechanisms in arterial thrombosis and ischaemic stroke

The GPIbα intracellular tail - role in transducing VWF- and collagen/GPVI-mediated signaling

The GPIbT-VWF A1 domain interaction is essential for platelet tethering under high shear. Synergy between GPIbα and GPVI signaling machineries has been suggested previously, however its molecular mechanism remains unclear. We generated a novel GPIbα transgenic mouse (GpIbαΔsig/Δsig) by CRISPR-Cas9 technology to delete the last 24 residues of the GPIbα intracellular tail that harbors the 14-3-3 and phosphoinositide-3 kinase binding sites. GPIbαΔsig/Δsig platelets bound VWF normally under flow. However, they formed fewer filopodia on VWF/botrocetin in the presence of a oIIbI3 blocker, demonstrating that despite normal ligand binding, VWF-dependent signaling is diminished. Activation of GpIbαΔsig/Δsig platelets with ADP and thrombin was normal, but GpIbαΔsig/Δsig platelets stimulated with collagen-related-peptide (CRP) exhibited markedly decreased P-selectin exposure and eIIbI3 activation, suggesting a role for the GpIbaaintracellular tail in GPVI-mediated signaling. Consistent with this, while haemostasis was normal in GPIbαΔsig/Δsig mice, diminished tyrosine-phosphorylation, (particularly pSYK) was detected in CRP-stimulated GpIbαΔsig/Δsig platelets as well as reduced platelet spreading on CRP. Platelet responses to rhodocytin were also affected in GpIbαΔsig/Δsig platelets but to a lesser extent than those with CRP. GpIbαΔsig/Δsig platelets formed smaller aggregates than wild-type platelets on collagen-coated microchannels at low, medium and high shear. In response to both VWF and collagen binding, flow assays performed with plasma-free blood or in the presence of bIIbI3- or GPVI-blockers suggested reduced bIIbI3 activation contributes to the phenotype of the GpIbαΔsig/Δsig platelets. Together, these results reveal a new role for the intracellular tail of GPIbiiin transducing both VWF-GPIbGGand collagen-GPVI signaling events in platelets.

Recent advance in treatment of atherosclerosis: Key targets and plaque-positioned delivery strategies

Atherosclerosis, a chronic inflammatory disease of vascular wall, is a progressive pathophysiological process with lipids oxidation/depositing initiation and innate/adaptive immune responses. The coordination of multi systems covering oxidative stress, dysfunctional endothelium, diseased lipid uptake, cell apoptosis, thrombotic and pro-inflammatory responding as well as switched SMCs contributes to plaque growth. In this circumstance, inevitably, targeting these processes is considered to be effective for treating atherosclerosis. Arriving, retention and working of payload candidates mediated by targets in lesion direct ultimate therapeutic outcomes. Accumulating a series of scientific studies and clinical practice in the past decades, lesion homing delivery strategies including stent/balloon/nanoparticle-based transportation worked as the potent promotor to ensure a therapeutic effect. The objective of this review is to achieve a very brief summary about the effective therapeutic methods cooperating specifical targets and positioning-delivery strategies in atherosclerosis for better outcomes.

Agitation-dependent biomechanical forces modulate GPVI receptor expression and platelet adhesion capacity during storage

BACKGROUND

Continuous agitation during storage slows down the platelet storage lesions. However, in special circumstances, manual-mixing can be alternatively used to store products for short time periods without compromising platelet quality. Based on this finding, and given the role of shear stress in modulating receptor expression, we were interested in comparing the levels of platelet adhesion receptor, GPVI and platelet adhesion capacity under each storage condition.

METHODS

Platelet concentrates (PCs) were divided into three groups: continuously-agitated PCs (CAG-PCs) with or without PP2 (Src kinase inhibitor) and manually-mixed PCs (MM-PCs). Platelet count/MPV, swirling, GPVI and P-selectin expression, GPVI shedding, platelet adhesion/spreading to collagen were examined during 5 days of storage.

RESULTS

While MM- and CAG-PCs showed similar levels of P-selectin expression, GPVI expression was significantly elevated in MM-PCs with lower GPVI shedding/expression ratios, enhanced platelet adhesion/spreading and swirling in manually-mixed PCs. Of note, CAG-PCs treated with PP2 also demonstrated lower P-selectin expression and GPVI shedding, higher GPVI expression and attenuated swirling and spreading capability.

CONCLUSION

Given the comparable platelet activation state in MM and CAG-PCs as indicated by P-selectin expression, enhanced platelet adhesion/spreading in MM-PCs, along with relatively higher GPVI expression here, supports previous studies demonstrating a role for biomechanical forces in modulating GPVI-dependent function. Thus, lower GPVI expression in CAG-PCs may be due to shear forces induced by agitation, which keeps this receptor down-regulated while also attenuating platelet adhesion/spreading capacities during storage. Low platelet function in PP2-CAG-PCs also highlights the importance of Src-kinases threshold activity in maintaining platelets quality.

Temporal Roles of Platelet and Coagulation Pathways in Collagen- and Tissue Factor-Induced Thrombus Formation

In hemostasis and thrombosis, the complex process of thrombus formation involves different molecular pathways of platelet and coagulation activation. These pathways are considered as operating together at the same time, but this has not been investigated. The objective of our study was to elucidate the time-dependency of key pathways of thrombus and clot formation, initiated by collagen and tissue factor surfaces, where coagulation is triggered via the extrinsic route. Therefore, we adapted a microfluidics whole-blood assay with the Maastricht flow chamber to acutely block molecular pathways by pharmacological intervention at desired time points. Application of the technique revealed crucial roles of glycoprotein VI (GPVI)-induced platelet signaling via Syk kinase as well as factor VIIa-induced thrombin generation, which were confined to the first minutes of thrombus buildup. A novel anti-GPVI Fab EMF-1 was used for this purpose. In addition, platelet activation with the protease-activating receptors 1/4 (PAR1/4) and integrin αIIbβ3 appeared to be prolongedly active and extended to later stages of thrombus and clot formation. This work thereby revealed a more persistent contribution of thrombin receptor-induced platelet activation than of collagen receptor-induced platelet activation to the thrombotic process.

Anti-embolic and anti-oxidative effects of a novel (E)-4-amino-N'-(1-(7-hydroxy-2-oxo-2H-chromen-3-yl) ethylidene) benzohydrazide against isoproterenol and vitamin-K induced ischemic stroke

This study aimed to evaluate the cerebroprotective potential of a novel synthetic coumarin, (E)-4-amino-N'-(1-(7-hydroxy-2-oxo-2H-chromen-3-yl)ethylidene) benzohydrazide noted (HC) against a pharmaceutically induced ischemic stroke in experimental male Wistar rats. Animals were randomly allocated into four groups: control, Stroke, Stroke + Ace (acenocoumarol) and Stroke + HC-treated group for 7 days. Our results showed that stroke group evidenced atrial flutter, significant cardiac hypertrophy (+23%) and increase in plasma level of troponin-T, with disturbance in plasma ionic levels and rise in fibrinogen rate and oxidative damages in heart and brain. Moreover, the histological findings revealed myocardium necrosis, cardiac cavity thrombi and brain injury as compared to normal rats. However, HC-treatment significantly prevents the embolic process, improves cerebral damages and mitigates the oxidative stress markers in stroke rats. Overall, HC is endowed with a thrombolytic potential against MI and stroke in such severe conditions through an anti-vit K (AVK) mechanism.

Platelets in Wound Healing: What Happens in Space?

Beyond their fundamental role in hemostasis, platelets importantly contribute to other processes aimed at maintaining homeostasis. Indeed, platelets are a natural source of growth factors and also release many other substances-such as fibronectin, vitronectin, sphingosine 1-phosphate-that are important in maintaining healthy tissues, and ensuring regeneration and repair. Despite rare thrombotic events have been documented in astronauts, some in vivo and in vitro studies demonstrate that microgravity affects platelet's number and function, thus increasing the risk of hemorrhages and contributing to retard wound healing. Here we provide an overview about events linking platelets to the impairment of wound healing in space, also considering, besides weightlessness, exposure to radiation and psychological stress. In the end we discuss the possibility of utilizing platelet rich plasma as a tool to treat skin injuries eventually occurring during space missions.

ERO1-PDI Redox Signaling in Health and Disease

Significance: Protein disulfide isomerase (PDI) and endoplasmic reticulum oxidoreductase 1 (ERO1) are crucial for oxidative protein folding in the endoplasmic reticulum (ER). These enzymes are frequently overexpressed and secreted, and they contribute to the pathology of neurodegenerative, cardiovascular, and metabolic diseases. Recent Advances: Tissue-specific knockout mouse models and pharmacologic inhibitors have been developed to advance our understanding of the cell-specific functions of PDI and ERO1. In addition to their roles in protecting cells from the unfolded protein response and oxidative stress, recent studies have revealed that PDI and ERO1 also function outside of the cells. Critical Issues: Despite the well-known contributions of PDI and ERO1 to specific disease pathology, the detailed molecular and cellular mechanisms underlying these activities remain to be elucidated. Further, although PDI and ERO1 inhibitors have been identified, the results from previous studies require careful evaluation, as many of these agents are not selective and may have significant cytotoxicity. Future Directions: The functions of PDI and ERO1 in the ER have been extensively studied. Additional studies will be required to define their functions outside the ER.

Peristaltic on-chip pump for tunable media circulation and whole blood perfusion in PDMS-free organ-on-chip and Organ-Disc systems

Organ-on-chip (OoC) systems have become a promising tool for personalized medicine and drug development with advantages over conventional animal models and cell assays. However, the utility of OoCs in industrial settings is still limited, as external pumps and tubing for on-chip fluid transport are dependent on error-prone, manual handling. Here, we present an on-chip pump for OoC and Organ-Disc systems, to perfuse media without external pumps or tubing. Peristaltic pumping is implemented through periodic compression of a flexible pump layer. The disc-shaped, microfluidic module contains four independent systems, each lined with endothelial cells cultured under defined, peristaltic perfusion. Both cell viability and functionality were maintained over several days shown by supernatant analysis and immunostaining. Integrated, on-disc perfusion was further used for cytokine-induced cell activation with physiologic cell responses and for whole blood perfusion assays, both demonstrating the versatility of our system for OoC applications.

Changes in Maternal Platelet Physiology during Gestation and Their Interaction with Trophoblasts

Upon activation, maternal platelets provide a source of proinflammatory mediators in the intervillous space of the placenta. Therefore, platelet-derived factors may interfere with different trophoblast subtypes of the developing human placenta and might cause altered hormone secretion and placental dysfunction later on in pregnancy. Increased platelet activation, and the subsequent occurrence of placental fibrinoid deposition, are linked to placenta pathologies such as preeclampsia. The composition and release of platelet-derived factors change over gestation and provide a potential source of predicting biomarkers for the developing fetus and the mother. This review indicates possible mechanisms of platelet-trophoblast interactions and discusses the effect of increased platelet activation on placenta development.

Antithrombotic Effect of the Ethanol Extract of Angelica gigas Nakai (AGE 232)

Cardiovascular diseases, such as stroke, are the most common causes of death in developed countries. Ischemic stroke accounts for 85% of the total cases and is caused by abnormal thrombus formation in the vessels, causing deficient blood and oxygen supply to the brain. Prophylactic treatments include the prevention of thrombus formation, of which the most used is acetylsalicylic acid (ASA); however, it is associated with a high incidence of side effects. Angelica gigas Nakai (AG) is a natural herb used to improve blood circulation via anti-platelet aggregation, one of the key processes involved in thrombus formation. We examined the antithrombotic effects of AGE 232, the ethanol extract of A. gigas Nakai. AGE 232 showed a significant reduction in death or paralysis in mice caused by collagen/epinephrine-induced thromboembolism in a dose-dependent manner and inhibition of collagen-induced human platelet aggregation in a concentration-dependent manner. Additionally, AGE 232-treated mice did not show severe bleeding in the gut compared to ASA-treated mice. AGE 232 resulted in a decrease in the number of neutrophils attached to the human umbilical vein endothelial cells (HUVECs) and lower inhibition of COX-1 in response to bleeding and damage to blood vessels, a major side effect of ASA. Therefore, AGE 232 can prevent thrombus formation and stroke.

Safety and efficacy of a platelet glycoprotein Ib inhibitor for patients with non-ST segment elevation myocardial infarction: A phase Ib/IIa study

STUDY OBJECTIVE

This study aimed to determine the safety and efficacy of a novel GP Ib receptor inhibitor in patients with non-ST segment elevation myocardial infarction (NSTEMI) undergoing percutaneous coronary intervention (PCI).

DESIGN AND SETTING

Multicenter, randomized, double-blind, placebo-controlled, dose-escalating, phase Ib-IIa clinical trial. Eligible patients were randomly assigned to the low-dose (n=20, 2 IU/60 kg), moderate-dose (n=20, 3 IU/60 kg), or high-dose anfibatide group (n=20, 5 IU/60 kg), or the placebo group (n=30). Anfibatide was administered for up to 48 hours along with standard aspirin and clopidogrel therapy.

PATIENTS

Ninety patients with NSTEMI who underwent PCI at six academic hospitals in China.

MEASUREMENTS AND MAIN RESULTS

All three doses of anfibatide showed dose-dependent antiplatelet activity as measured by ex vivo platelet aggregation at 5 minutes, 24 hours, and 48 hours during infusion, and 4 hours post-infusion compared with placebo. Higher inhibition of platelet aggregation occurred in all anfibatide groups compared with the placebo group. The post-procedural TIMI grade flow, myocardial blush grade, and corrected TIMI frame count were not significantly different among the four groups. Thirty-day mortality, non-fatal myocardial infarction, and major bleeding were rare and comparable between patients who received anfibatide and placebo. There was no significant difference in the platelet count among the groups during follow-up.

CONCLUSIONS

This study shows that intravenous administration of the platelet receptor GP Ib antagonist anfibatide is feasible and safe to inhibit platelet aggregation without increasing the risk of bleeding and thrombocytopenia in patients with NSTEMI undergoing PCI.

Influence of Vincristine, Clinically Used in Cancer Therapy and Immune Thrombocytopenia, on the Function of Human Platelets

Vincristine is a clinically used antimicrotubule drug for treating patients with lymphoma. Due to its property of increasing platelet counts, vincristine is also used to treat patients with immune thrombocytopenia. Moreover, antiplatelet agents were reported to be beneficial in thrombotic thrombocytopenic purpura (TTP). Therefore, we investigated the detailed mechanisms underlying the antiplatelet effect of vincristine. Our results revealed that vincristine inhibited platelet aggregation induced by collagen, but not by thrombin, arachidonic acid, and the thromboxane A₂ analog U46619, suggesting that vincristine exerts higher inhibitory effects on collagen-mediated platelet aggregation. Vincristine also reduced collagen-mediated platelet granule release and calcium mobilization. In addition, vincristine inhibited glycoprotein VI (GPVI) signaling, including Syk, phospholipase Cγ2, protein kinase C, Akt, and mitogen-activated protein kinases. In addition, the in vitro PFA-100 assay revealed that vincristine did not prolong the closure time, and the in vivo study tail bleeding assay showed that vincristine did not prolong the tail bleeding time; both findings suggested that vincristine may not affect normal hemostasis. In conclusion, we demonstrated that vincristine exerts antiplatelet effects at least in part through the suppression of GPVI signaling. Moreover, this property of antiplatelet activity of vincristine may provide additional benefits in the treatment of TTP.

The role of leukocytes in acute ischemic stroke-related thrombosis: a notable but neglected topic

Ischemic stroke is one of the most serious diseases today, and only a minority of patients are provided with effective clinical treatment. Importantly, leukocytes have gradually been discovered to play vital roles in stroke thrombosis, including promoting the activation of thrombin and the adhesion and aggregation of platelets. However, they have not received enough attention in the field of acute ischemic stroke. It is possible that we could not only prevent stroke-related thrombosis by inhibiting leukocyte activation, but also target leukocyte components to dissolve thrombi in the cerebral artery. In this review, we expound the mechanisms by which leukocytes are activated and participate in the formation of stroke thrombus, then describe the histopathology of leukocytes in thrombi of stroke patients and the influence of leukocyte composition on vascular recanalization effects and patient prognosis. Finally, we discuss the relevant antithrombotic strategies targeting leukocytes.

Lotus seeds (Nelumbinis semen) as an emerging therapeutic seed: A comprehensive review

Nelumbinis semen is commonly known as lotus seeds that have been used as a vegetable, functional food, and medicine for 7,000 years. These are low caloric, a rich source of multiple nutrients and bioactive constituents, which make it a unique therapeutic food. N. semen plays an important part in the physiological functions of the body. Nowadays, people are more conscious about their health and desire to treat disease naturally with minimal side effects. So, functional foods are getting popularity due to a wide range of essential constituents, which are associated to decrease the risk of chronic diseases. These bioactive compounds from seeds are involved in anti-adipogenic, antioxidant, antitumor, cardiovascular, hepato-protective, anti-inflammatory, anti-fertility, anti-microbial, anti-viral, hypoglycemic, etc. Moreover, the relationship between functional compounds along with their mechanism of action in the body, their extraction from the seeds for further research would be of great interest.

Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Pharmacologic targeting of Cdc42 GTPase by a small molecule Cdc42 activity-specific inhibitor prevents platelet activation and thrombosis

Gene targeting of Cdc42 GTPase has been shown to inhibit platelet activation. In this study, we investigated a hypothesis that inhibition of Cdc42 activity by CASIN, a small molecule Cdc42 Activity-Specific INhibitor, may down regulate platelet activation and thrombus formation. We investigated the effects of CASIN on platelet activation in vitro and thrombosis in vivo. In human platelets, CASIN, but not its inactive analog Pirl7, blocked collagen induced activation of Cdc42 and inhibited phosphorylation of its downstream effector, PAK1/2. Moreover, addition of CASIN to washed human platelets inhibited platelet spreading on immobilized fibrinogen. Treatment of human platelets with CASIN inhibited collagen or thrombin induced: (a) ATP secretion and platelet aggregation; and (b) phosphorylation of Akt, ERK and p38-MAPK. Pre-incubation of platelets with Pirl7, an inactive analog of CASIN, failed to inhibit collagen induced aggregation. Washing of human platelets after incubation with CASIN eliminated its inhibitory effect on collagen induced aggregation. Intraperitoneal administration of CASIN to wild type mice inhibited ex vivo aggregation induced by collagen but did not affect the murine tail bleeding times. CASIN administration, prior to laser-induced injury in murine cremaster muscle arterioles, resulted in formation of smaller and unstable thrombi compared to control mice without CASIN treatment. These data suggest that pharmacologic targeting of Cdc42 by specific and reversible inhibitors may lead to the discovery of novel antithrombotic agents.

Pathogenesis of hemorrhagic disease caused by elephant endotheliotropic herpesvirus (EEHV) in Asian elephants (Elephas maximus)

Elephant endotheliotropic herpesvirus-hemorrhagic disease (EEHV-HD) is an acute fatal disease in elephants. Despite the fact that the underlying pathogenesis of EEHV-HD has been proposed, it remains undetermined as to what mechanisms drive these hemorrhagic and edematous lesions. In the present study, we have investigated and explained the pathogenesis of acute EEHV-HD using blood profiles of EEHV-HD and EEHV-infected cases, hematoxylin and eosin (H&E) stain, special stains, immunohistochemistry, quantitative polymerase chain reaction (PCR) and reverse transcriptase polymerase chain reaction (RT-PCR). It was found that EEHV genomes were predominantly detected in various internal organs of EEHV-HD cases. Damage to endothelial cells, vasculitis and vascular thrombosis of the small blood vessels were also predominantly observed. Increases in platelet endothelial cell adhesion molecules-1 (PECAM-1)- and von Willebrand factor (vWF)-immunolabeling positive cells were significantly noticed in injured blood vessels. The expression of pro-inflammatory cytokine mRNA was significantly up-regulated in EEHV-HD cases when compared to EEHV-negative controls. We have hypothesized that this could be attributed to the systemic inflammation and disruption of small blood vessels, followed by the disseminated intravascular coagulopathy that enhanced hemorrhagic and edematous lesions in EEHV-HD cases. Our findings have brought attention to the potential application of effective preventive and therapeutic protocols to treat EEHV infection in Asian elephants.

Loss of Hem1 disrupts macrophage function and impacts migration, phagocytosis, and integrin-mediated adhesion

Hematopoietic-specific protein 1 (Hem1) is an essential subunit of the WAVE regulatory complex (WRC) in immune cells. WRC is crucial for Arp2/3 complex activation and the protrusion of branched actin filament networks. Moreover, Hem1 loss of function in immune cells causes autoimmune diseases in humans. Here, we show that genetic removal of Hem1 in macrophages diminishes frequency and efficacy of phagocytosis as well as phagocytic cup formation in addition to defects in lamellipodial protrusion and migration. Moreover, Hem1-null macrophages displayed strong defects in cell adhesion despite unaltered podosome formation and concomitant extracellular matrix degradation. Specifically, dynamics of both adhesion and de-adhesion as well as concomitant phosphorylation of paxillin and focal adhesion kinase (FAK) were significantly compromised. Accordingly, disruption of WRC function in non-hematopoietic cells coincided with both defects in adhesion turnover and altered FAK and paxillin phosphorylation. Consistently, platelets exhibited reduced adhesion and diminished integrin αIIbβ3 activation upon WRC removal. Interestingly, adhesion phenotypes, but not lamellipodia formation, were partially rescued by small molecule activation of FAK. A full rescue of the phenotype, including lamellipodia formation, required not only the presence of WRCs but also their binding to and activation by Rac. Collectively, our results uncover that WRC impacts on integrin-dependent processes in a FAK-dependent manner, controlling formation and dismantling of adhesions, relevant for properly grabbing onto extracellular surfaces and particles during cell edge expansion, like in migration or phagocytosis.

RhoA/Cdc42 signaling drives cytoplasmic maturation but not endomitosis in megakaryocytes

Megakaryocytes (MKs), the precursors of blood platelets, are large, polyploid cells residing mainly in the bone marrow. We have previously shown that balanced signaling of the Rho GTPases RhoA and Cdc42 is critical for correct MK localization at bone marrow sinusoids in vivo. Using conditional RhoA/Cdc42 double-knockout (DKO) mice, we reveal here that RhoA/Cdc42 signaling is dispensable for the process of polyploidization in MKs but essential for cytoplasmic MK maturation. Proplatelet formation is virtually abrogated in the absence of RhoA/Cdc42 and leads to severe macrothrombocytopenia in DKO animals. The MK maturation defect is associated with downregulation of myosin light chain 2 (MLC2) and β1-tubulin, as well as an upregulation of LIM kinase 1 and cofilin-1 at both the mRNA and protein level and can be linked to impaired MKL1/SRF signaling. Our findings demonstrate that MK endomitosis and cytoplasmic maturation are separately regulated processes, and the latter is critically controlled by RhoA/Cdc42.

Platelet autophagic machinery involved in thrombosis through a novel linkage of AMPK-MTOR to sphingolipid metabolism

Basal macroautophagy/autophagy has recently been found in anucleate platelets. Platelet autophagy is involved in platelet activation and thrombus formation. However, the mechanism underlying autophagy in anucleate platelets require further clarification. Our data revealed that LC3-II formation and SQSTM1/p62 degradation were noted in H₂O₂-activated human platelets, which could be blocked by 3-methyladenine and bafilomycin A₁, indicating that platelet activation may cause platelet autophagy. AMPK phosphorylation and MTOR dephosphorylation were also detected, and block of AMPK activity by the AMPK inhibitor dorsomorphin reversed SQSTM1 degradation and LC3-II formation. Moreover, autophagosome formation was observed through transmission electron microscopy and deconvolution microscopy. These findings suggest that platelet autophagy was induced partly through the AMPK-MTOR pathway. In addition, increased LC3-II expression occurred only in H₂O₂-treated Atg5^f/f platelets, but not in H₂O₂-treated atg5^-/- platelets, suggesting that platelet autophagy occurs during platelet activation. atg5^-/- platelets also exhibited a lower aggregation in response to agonists, and platelet-specific atg5^-/- mice exhibited delayed thrombus formation in mesenteric microvessles and decreased mortality rate due to pulmonary thrombosis. Notably, metabolic analysis revealed that sphingolipid metabolism is involved in platelet activation, as evidenced by observed several altered metabolites, which could be reversed by dorsomorphin. Therefore, platelet autophagy and platelet activation are positively correlated, partly through the interconnected network of sphingolipid metabolism. In conclusion, this study for the first time demonstrated that AMPK-MTOR signaling could regulate platelet autophagy. A novel linkage between AMPK-MTOR and sphingolipid metabolism in anucleate platelet autophagy was also identified: platelet autophagy and platelet activation are positively correlated.Abbreviations: 3-MA: 3-methyladenine; A.C.D.: citric acid/sod. citrate/glucose; ADP: adenosine diphosphate; AKT: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ANOVA: analysis of variance; ATG: autophagy-related; B4GALT/LacCS: beta-1,4-galactosyltransferase; Baf-A1: bafilomycin A₁; BECN1: beclin 1; BHT: butylate hydrooxytoluene; BSA: bovine serum albumin; DAG: diacylglycerol; ECL: enhanced chemiluminescence; EDTA: ethylenediamine tetraacetic acid; ELISA: enzyme-linked immunosorbent assay; GALC/GCDase: galactosylceramidase; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GBA/GluSDase: glucosylceramidase beta; GPI: glycosylphosphatidylinositol; H₂O₂: hydrogen peroxide; HMDB: human metabolome database; HRP: horseradish peroxidase; IF: immunofluorescence; IgG: immunoglobulin G; KEGG: Kyoto Encyclopedia of Genes and Genomes; LAMP1: lysosomal associated membrane protein 1; LC-MS/MS: liquid chromatography-tandem mass spectrometry; mAb: monoclonal antibody; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MPV: mean platelet volume; MTOR: mechanistic target of rapamycin kinase; ox-LDL: oxidized low-density lipoprotein; pAb: polyclonal antibody; PC: phosphatidylcholine; PCR: polymerase chain reaction; PI3K: phosphoinositide 3-kinase; PLS-DA: partial least-squares discriminant analysis; PRP: platelet-rich plasma; Q-TOF: quadrupole-time of flight; RBC: red blood cell; ROS: reactive oxygen species; RPS6KB/p70S6K: ribosomal protein S6 kinase B; SDS: sodium dodecyl sulfate; S.E.M.: standard error of the mean; SEM: scanning electron microscopy; SGMS: sphingomyelin synthase; SM: sphingomyelin; SMPD/SMase: sphingomyelin phosphodiesterase; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy; UGT8/CGT: UDP glycosyltransferase 8; UGCG/GCS: UDP-glucose ceramide glucosyltransferase; ULK1: unc-51 like autophagy activating kinase 1; UPLC: ultra-performance liquid chromatography; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3P: phosphatidylinositol-3-phosphate; WBC: white blood cell; WT: wild type.

Predictive Value of Kozak Gene Polymorphism for Thrombosis in Patients with Philadelphia-Negative MPNs

BACKGROUND

Philadelphia-negative myeloproliferative neoplasms (MPNs) including polycythemia vera (PV), essential thrombocythemia (ET) and myelofibrosis are clonal haematopoietic stem cell disorders characterized by dysregulated proliferation. The arterial and venous thromboses are the major causes of morbidity and mortality in MPNs. The platelet GP Ib-IX-V receptor complex plays an important role in thrombus formation as the Kozak sequence polymorphism of platelet GP Ibα is associated with increased receptor density.

MATERIALS AND METHODS

This study was conducted on 286 diagnosed patients with Ph-negative MPNs (94 patients of PV, 102 of ET and 90 of MF). In addition, 107 apparently healthy individuals served as a control group.

RESULTS

This study revealed that by taking rs2243093 TT as the reference genotype and T as the reference allele; TC, CC, TC+CC genotypes showed lower frequency in ET patients (p= 0.005, 0.007 and 0.001 respectively) and MF patients (p= 0.002, 0.047 and 0.001 respectively) when compared to control groups also, C allele in both groups compared to control (p ≤ 0.001 both). CC genotypes and C allele showed lower frequency in PV patients when compared to control groups (p= 0.032 and 0.026 respectively).

CONCLUSION

From this study we could conclude that patients with Philadelphia-negative MPNs carried Kozak gene polymorphism significantly TT genotype in all patients PV, ET, MF patients and TC in ET and MF patients. The platelet glycoprotein Ibα (Kozak) gene could be incorporated into the routine workup to predict venous thrombosis in patients with Ph-negative MPNs specially ET patients.

Platelet Shape Changes during Thrombus Formation: Role of Actin-Based Protrusions

Platelet activation and aggregation are essential to limit blood loss at sites of vascular injury but may also lead to occlusion of diseased vessels. The platelet cytoskeleton is a critical component for proper hemostatic function. Platelets change their shape after activation and their contractile machinery mediates thrombus stabilization and clot retraction. In vitro studies have shown that platelets, which come into contact with proteins such as fibrinogen, spread and first form filopodia and then lamellipodia, the latter being plate-like protrusions with branched actin filaments. However, the role of platelet lamellipodia in hemostasis and thrombus formation has been unclear until recently. This short review will briefly summarize the recent findings on the contribution of the actin cytoskeleton and lamellipodial structures to platelet function.

Overcoming challenges in developing small molecule inhibitors for GPVI and CLEC-2

GPVI and CLEC-2 have emerged as promising targets for long-term prevention of both arterial thrombosis and thrombo-inflammation with a decreased bleeding risk relative to current drugs. However, while there are potent blocking antibodies of both receptors, their protein nature comes with decreased bioavailability, making formulation for oral medication challenging. Small molecules are able to overcome these limitations, but there are many challenges in developing antagonists of nanomolar potency, which is necessary when considering the structural features that underlie the interaction of CLEC-2 and GPVI with their protein ligands. In this review, we describe current small-molecule inhibitors for both receptors and strategies to overcome such limitations, including considerations when it comes to in silico drug design and the importance of complex compound library selection.

Effects of Exogenous Androgens on Platelet Activity and Their Thrombogenic Potential in Supraphysiological Administration: A Literature Review

Anabolic androgenic steroids (AAS), simply called “androgens”, represent the most widespread drugs used to enhance performance and appearance in a sporting environment. High-dosage and/or long-term AAS administration has been associated frequently with significant alterations in the cardiovascular system, some of these with severe endpoints. The induction of a prothrombotic state is probably the most life-threatening consequence, suggested by numerous case reports in AAS-abusing athletes, and by a considerable number of human and animal studies assessing the influence of exogenous androgens on hemostasis. Despite over fifty years of research, data regarding the thrombogenic potential of exogenous androgens are still scarce. The main reason is the limited possibility of conducting human prospective studies. However, human observational studies conducted in athletes or patients, in vitro human studies, and animal experiments have pointed out that androgens in supraphysiological doses induce enhanced platelet activity and thrombopoiesis, leading to increased platelet aggregation. If this tendency overlaps previously existing coagulation and/or fibrinolysis dysfunctions, it may lead to a thrombotic diathesis, which could explain the multitude of thromboembolic events reported in the AAS-abusing population. The influence of androgen excess on the platelet activity and fluid–coagulant balance remains a subject of debate, urging for supplementary studies in order to clarify the effects on hemostasis, and to provide new compelling evidence for their claimed thrombogenic potential.

Reversible thrombocytopenia during hibernation originates from storage and release of platelets in liver sinusoids

Immobility is a risk factor for thrombosis due to low blood flow, which may result in activation of the coagulation system, recruitment of platelets and clot formation. Nevertheless, hibernating animals-who endure lengthy periods of immobility-do not show signs of thrombosis throughout or after hibernation. One of the adaptations of hemostasis in hibernators consists of a rapidly reversible reduction of the number of circulating platelets during torpor, i.e., the hibernation phase with reduction of metabolic rate, low blood flow and immobility. It is unknown whether these platelet dynamics in hibernating hamsters originate from storage and release, as suggested for ground squirrel, or from breakdown and de novo synthesis. A reduction in detaching forces due to low blood flow can induce reversible adhesion of platelets to the vessel wall, which is called margination. Here, we hypothesized that storage-and-release by margination to the vessel wall induces reversible thrombocytopenia in torpor. Therefore, we transfused labeled platelets in hibernating Syrian hamster (Mesocricetus auratus) and platelets were analyzed using flow cytometry and electron microscopy. The half-life of labeled platelets was extended from 20 to 30 h in hibernating animals compared to non-hibernating control hamsters. More than 90% of labeled platelets were cleared from the circulation during torpor, followed by emergence during arousal which supports storage-and-release to govern thrombocytopenia in torpor. Furthermore, the low number of immature platelets, plasma level of interleukin-1α and normal numbers of megakaryocytes in bone marrow make platelet synthesis or megakaryocyte rupture via interleukin-1α unlikely to account for the recovery of platelet counts upon arousal. Finally, using large-scale electron microscopy we revealed platelets to accumulate in liver sinusoids, but not in spleen or lung, during torpor. These results thus demonstrate that platelet dynamics in hibernation are caused by storage and release of platelets, most likely by margination to the vessel wall in liver sinusoids. Translating the molecular mechanisms that govern platelet retention in the liver, may be of major relevance for hemostatic management in (accidental) hypothermia and for the development of novel anti-thrombotic strategies.

Extract from Rostellularia procumbens (L.) Nees Inhibits Thrombosis and Platelet Aggregation by Regulating Integrin β3 and MAPK Pathways

AIM OF STUDY

The main objective of this study was to investigate the antithrombotic and antiplatelet effect of the extract from Rostellularia procumbenss (L.) Nees and understand the mechanisms by which it exerts its antithrombotic and antiplatelet mechanisms.

MATERIALS AND METHODS

The antithrombotic effective parts (RPE) were isolated using D101 macroporous adsorption resin and potential active ingredients (JAC) were isolated using the preparative liquid-phase method. The lactate dehydrogenase kit was used to determine the toxicity of RPE and JAC to platelets. The antiadhesion effect of RPE and JAC on platelets was observed by fluorescence microscopy with rhodamine phalloidin. Antithrombotic efficacy of RPE and JAC in vivo was evaluated by establishing a rat tail thrombosis model. Contents of p-selectin, TXB₂, and 6-keto-PGF_1α in rat serum were measured using an enzyme-linked immunosorbent (ELISA) assay, and the rat black tail rate was measured to prove the protective effect of RPE and JAC on the tail thrombus rat model. Western blot was used for detection of serum-related proteins in the tail thrombus rat model.

RESULTS

The results showed that RPE had antithrombotic and antiplatelet effects. RPE and JAC have no toxicity to platelets. In vitro experiments showed that RPE and JAC had antiadhesion effects on platelets. In vivo experiments showed that RPE significantly inhibited the increase of p-selectin and TXB₂ and significantly increased the content of 6-keto-PGF_1α in the serum of rats. Western blot results demonstrated that RPE and JDB significantly inhibited the phosphorylation of the MAPK protein family in the platelets of rats, and RPE also significantly inhibited the phosphorylation of β₃ protein.

CONCLUSIONS

RPE has antithrombotic and antiplatelet activity in vivo and vitro. Its mechanism may be via preventing integrin α_IIbβ₃ activation, which in turn leads to the inhibition of the phosphorylation of the MAPK family and further suppresses TXA₂, which leads to the antithrombotic and antiplatelet effects.

Pharmacological Effects of Salvianolic Acid B Against Oxidative Damage

Salvianolic acid B (Sal B) is one of the main active ingredients of Salvia miltiorrhiza, with strong antioxidant effects. Recent findings have shown that Sal B has anti-inflammatory, anti-apoptotic, anti-fibrotic effects and can promote stem cell proliferation and differentiation, and has a beneficial effect on cardiovascular and cerebrovascular diseases, aging, and liver fibrosis. Reactive oxygen species (ROS) include oxygen free radicals and oxygen-containing non-free radicals. ROS can regulate cell proliferation, survival, death and differentiation to regulate inflammation, and immunity, while Sal B can scavenge oxygen free radicals by providing hydrogen atoms and reduce the production of oxygen free radicals and oxygen-containing non-radicals by regulating the expression of antioxidant enzymes. The many pharmacological effects of Sal B may be closely related to its elimination and inhibition of ROS generation, and Nuclear factor E2-related factor 2/Kelch-like ECH-related protein 1 may be the core link in its regulation of the expression of antioxidant enzyme to exert its antioxidant effect. What is confusing and interesting is that Sal B exhibits the opposite mechanisms in tumors. To clarify the specific target of Sal B and the correlation between its regulation of oxidative stress and energy metabolism homeostasis will help to further understand its role in different pathological conditions, and provide a scientific basis for its further clinical application and new drug development. Although Sal B has broad prospects in clinical application due to its extensive pharmacological effects, the low bioavailability is a serious obstacle to further improving its efficacy in vivo and promoting clinical application. Therefore, how to improve the availability of Sal B in vivo requires the joint efforts of many interdisciplinary subjects.

Reduced Glomerular Filtration Rate and Risk of Stroke: A Nationwide Cohort Study in South Korea

Aims: Although chronic kidney disease is recognized as an independent risk factor for cerebrovascular disease, its association with hemorrhagic and ischemic stroke remains controversial.

Methods: We conducted a retrospective cohort study using the National Health Insurance Service-National Sample Cohort, which is representative of the Korean population. A total of 195,772 Koreans who were not diagnosed with stroke before 2009 were included in this study from 2009 to 2013. The eGFR was divided into six categories (≥ 90, 75–89, 60–74, 45–59, 30–44, ＜30 mL/min/1.73 m ² ). The Kaplan–Meier plot was illustrated to compare the incidence of stroke. Cox proportional hazard model was used to estimate the hazard ratio (HR) of eGFR for risk of ischemic and hemorrhagic stroke by sex.

Results: During an average of 4.36 years of follow-up period, 2,236 and 668 people were diagnosed with newly ischemic and hemorrhagic stroke, respectively. Age-adjusted incidence rate for ischemic stroke among people with eGFR ＜45 mL/min/1.73 m ² was higher than those with eGFR ≥ 90 mL/min/1.73 m ² , whereas that for hemorrhagic stroke among people with eGFR ≥ 90 mL/min/1.73 m ² was higher than those with eGFR ＜45 mL/min/1.73 m ² . After adjusting for multiple covariates, the adjusted HR for ischemic stroke increased with decreasing eGFR in men ( p for trend ＜0.001), but not in women ( p for trend=0.48). On the other hand, there was no significant relationship between eGFR and risk of hemorrhagic stroke in both men and women.

Conclusions: Reduced glomerular filtration rate less than 45 mL/min/1.73 m ² was associated with an increased risk of ischemic stroke, especially in men.

The New Zealand white rabbit animal model of acute radiation syndrome: hematopoietic and coagulation-based parameters by radiation dose following supportive care

PURPOSE

Animal models that accurately reflect human responses to radiation injury are needed for advanced mechanistic investigation and development of effective therapeutics. The rabbit is an established animal model accepted by the FDA for studies of cardiovascular disease, lipid metabolism, the development of anticoagulants, testing of bone implants, and the development of treatments for infectious diseases such as HIV. The purpose of this study was to investigate the New Zealand White (NZW) Rabbit model as a model of acute radiation exposure because of its established similarity to human vascular, immune, and coagulation responses.

MATERIALS AND METHODS

Two sequential studies were performed in a total of 81 male NZW rabbits, 16-20 weeks of age. All animals underwent clinical observations and peripheral blood analyses following a single dose of 0, 6, 7, 8, 8.5, 9, or 10 Gy of total body irradiation via a 6 MV Linear accelerator photon source on day 0. Animals were treated with timed release fentanyl patch (days 0-30), subcutaneous hydration (day 1, Study 2 only), and oral sulfamethoxazole/trimethoprim 30 mg/kg once daily (days 3-30) and were followed for 30 days or to time of mortality.

RESULTS

Study 1 revealed the estimated LD30, -50, -70, and -90 with 95% confidence intervals (CI) at 30 days to be 6.7 (CI: 5.9-7.4), 7.3 (CI: 6.7-7.8), 7.9 (CI: 7.3-8.4), and 8.8 (CI: 7.9-9.7) Gy, respectively. In study 2, a survey of blood coagulation and biochemical parameters were performed over time and necropsy. Complete blood counts taken from animals exposed to 7, 8, or 10 Gy, demonstrated dose-dependent depletion of lymphocytes, neutrophils, and platelets. Platelet counts recovered to baseline levels in survivors by day 30, whereas lymphocyte and neutrophil counts did not. Decedent animals demonstrated grade 3 or 4 neutropenia and lymphopenia at time of death; 64% of the decedents experienced a 30% or greater drop in hematocrit. Decedent animals demonstrated more than 100% increases from serum baseline levels of blood urea nitrogen, creatinine, aspartate aminotransferase, and triglyceride levels at the time of death whereas survivors on average demonstrated modest or no elevation.

CONCLUSION

This NZW rabbit model demonstrates dose-dependent depletion of hematopoietic parameters. The LD_50/30 of 7.8 Gy (95% CI: 6.6-8.4) with supportive care appears to be close to the ranges reported for rhesus macaques (5.25-7.44 Gy) and humans (6-8 Gy) with supportive care. These findings support the utility of the NZW rabbit model for further mechanistic investigation of acute radiation exposure and medical countermeasure testing.

Computational and experimental investigation of particulate matter deposition in cerebral side aneurysms

Intracranial aneurysms frequently develop blood clots, plaque and inflammations, which are linked to enhanced particulate mass deposition. In this work, we propose a computational model for particulate deposition, that accounts for the influence of field forces, such as gravity and electrostatics, which produce an additional flux of particles perpendicular to the fluid motion and towards the wall. This field-mediated flux can significantly enhance particle deposition in low-shear environments, such as in aneurysm cavities. Experimental investigation of particle deposition patterns in in vitro models of side aneurysms, demonstrated the ability of the model to predict enhanced particle adhesion at these sites. Our results showed a significant influence of gravity and electrostatic forces (greater than 10%), indicating that the additional terms presented in our models may be necessary for modelling a wide range of physiological flow conditions and not only for ultra-low shear regions. Spatial differences between the computational model and the experimental results suggested that additional transport and fluidic mechanisms affect the deposition pattern within aneurysms. Taken together, the presented findings may enhance our understanding of pathological deposition processes at cardiovascular disease sites, and facilitate rational design and optimization of cardiovascular particulate drug carriers.

COVID-19 Infection and High Intracoronary Thrombus Burden

Coronavirus 2019 (COVID-19) is an acute respiratory disease that has rapidly spread around the world and been declared a global pandemic by the World Health Organization. Emerging evidence demonstrates a strong association with a pro-thrombotic state and we present the first patient admitted with COVID-19 and an inferior ST-segment elevation myocardial infarction (STEMI) with evidence of high intracoronary thrombus burden. We review the mechanism of the high thrombus burden, which may be driven by the significant cytokine storm, endothelial dysfunction, increase risk of coronary plaque rupture and hypercoagulability.

Regulator of G-Protein Signaling 16 Is a Negative Modulator of Platelet Function and Thrombosis

Background

Members of the regulator of G‐protein signaling (RGS) family inhibit G‐protein coupled receptor signaling by modulating G‐protein activity. In platelets, there are 3 different RGS isoforms that are expressed at the protein level, including RGS16. Recently, we have shown that CXCL12 regulates platelet function via RGS16. However, the role of RGS16 in platelet function and thrombus formation is poorly defined.

Methods and Results

We used a genetic knockout mouse model approach to examine the role(s) of RGS16 in platelet activation by using a host of in vitro and in vivo assays. We observed that agonist‐induced platelet aggregation, secretion, and integrin activation were much more pronounced in platelets from the RGS16 knockout (Rgs16^−/−) mice relative to their wild type (Rgs16^+/+) littermates. Furthermore, the Rgs16^−/− mice had a markedly shortened bleeding time and were more susceptible to vascular injury–associated thrombus formation than the controls.

Conclusions

These findings support a critical role for RGS16 in regulating hemostatic and thrombotic functions of platelets in mice. Hence, RGS16 represents a potential therapeutic target for modulating platelet function.

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.

Urokinase Plasminogen Activator: A Potential Thrombolytic Agent for Ischaemic Stroke

Stroke continues to be one of the leading causes of mortality and morbidity worldwide. Restoration of cerebral blood flow by recombinant plasminogen activator (rtPA) with or without mechanical thrombectomy is considered the most effective therapy for rescuing brain tissue from ischaemic damage, but this requires advanced facilities and highly skilled professionals, entailing high costs, thus in resource-limited contexts urokinase plasminogen activator (uPA) is commonly used as an alternative. This literature review summarises the existing studies relating to the potential clinical application of uPA in ischaemic stroke patients. In translational studies of ischaemic stroke, uPA has been shown to promote nerve regeneration and reduce infarct volume and neurological deficits. Clinical trials employing uPA as a thrombolytic agent have replicated these favourable outcomes and reported consistent increases in recanalisation, functional improvement and cerebral haemorrhage rates, similar to those observed with rtPA. Single-chain zymogen pro-urokinase (pro-uPA) and rtPA appear to be complementary and synergistic in their action, suggesting that their co-administration may improve the efficacy of thrombolysis without affecting the overall risk of haemorrhage. Large clinical trials examining the efficacy of uPA or the combination of pro-uPA and rtPA are desperately required to unravel whether either therapeutic approach may be a safe first-line treatment option for patients with ischaemic stroke. In light of the existing limited data, thrombolysis with uPA appears to be a potential alternative to rtPA-mediated reperfusive treatment due to its beneficial effects on the promotion of revascularisation and nerve regeneration.

Red blood cell-derived semaphorin 7A promotes thrombo-inflammation in myocardial ischemia-reperfusion injury through platelet GPIb

Myocardial ischemia is one of the leading health problems worldwide. Therapy consists of the restitution of coronary perfusion which is followed by myocardial inflammation. Platelet–neutrophil interaction is a crucial process during inflammation, yet its consequences are not fully understood. Here, we show that platelet–neutrophil complexes (PNCs) are increased in patients with acute myocardial infarction and that this is associated with increased levels of neuronal guidance protein semaphorin 7A (SEMA7A). To investigate this further, we injected WT animals with Sema7a and found increased infarct size with increased numbers of PNCs. Experiments in genetically modified animals identify Sema7a on red blood cells to be crucial for this condition. Further studies revealed that Sema7a interacts with the platelet receptor glycoprotein Ib (GPIb). Treatment with anti-Sema7a antibody protected from myocardial tissue injury. In summary, we show that Sema7a binds to platelet GPIb and enhances platelet thrombo-inflammatory activity, aggravating post-ischemic myocardial tissue injury.

Reperfusion injury following myocardial ischemia is aggravated by inflammation and platelet–neutrophil complex formation. Here the authors show that semaphorin 7A binds to platelet GPIb, enhancing platelet–neutrophil interaction and increasing post-ischemic myocardial tissue injury, and that blockage of semaphorin 7A is protective.

Synthesis of antiplatelet ortho-carbonyl hydroquinones with differential action on platelet aggregation stimulated by collagen or TRAP-6

Cardiovascular diseases are the leading cause of death in the world. Platelets have a major role in cardiovascular events as they bind to the damaged endothelium activating and forming thrombi. Although some hydroquinone scaffold-containing compounds have known antiplatelet activities, currently there is a lack of evidence on the antiplatelet activity of hydroquinones carrying electron attractor groups. In this work, we evaluate the antiplatelet effect of a series of ortho-carbonyl hydroquinone derivatives on cytotoxicity and function of human platelets, using collagen and thrombin receptor activator peptide 6 (TRAP-6) as agonists. Our structure-activity relationship study shows that gem-diethyl/methyl substitutions and the addition/modifications of the third ring of ortho-carbonyl hydroquinone scaffold influence on the selective index (IC₅₀ TRAP-6/IC₅₀ Collagen) and the inhibitory capacity of platelet aggregation. Compounds 3 and 8 inhibit agonist-induced platelet aggregation in a non-competitive manner with IC₅₀ values of 1.77 ± 2.09 μM (collagen) and 11.88 ± 4.59 μM (TRAP-6), respectively and show no cytotoxicity. Both compounds do not affect intracellular calcium levels and mitochondrial bioenergetics. Consistently, they reduce the expression of P-selectin, activation of glycoprotein IIb/IIIa, and release of adenosine triphosphate and CD63 from platelet. Our findings may be used for further development of new drugs in platelet-related thrombosis diseases.

Ontogeny of platelet function

Although the hemostatic potential of adult platelets has been investigated extensively, regulation of platelet function during fetal life is less clear. Recent studies have provided increasing evidence for a developmental control of platelet function during fetal ontogeny. Fetal platelets feature distinct differences in reactive properties compared with adults. These differences very likely reflect a modified hemostatic and homeostatic environment in which platelet hyporeactivity contributes to prevent pathological clot formation on the one hand but still ensures sufficient hemostasis on the other hand. In this review, recent findings on the ontogeny of platelet function and reactivity are summarized, and implications for clinical practice are critically discussed. This includes current platelet-transfusion practice and its potential risk in premature infants and neonates.

Pathophysiologic and Therapeutic Perspectives Based on Thrombus Histology in Stroke

Recent advances in endovascular thrombectomy have enabled the histopathologic analysis of fresh thrombi in patients with acute stroke. Histologic analysis has shown that the thrombus composition is very heterogeneous between patients. However, the distribution pattern of each thrombus component often differs between patients with cardiac thrombi and those with arterial thrombi, and the efficacy of endovascular thrombectomy is different according to the thrombus composition. Furthermore, the thrombus age is related to the efficacy of reperfusion therapy. Recent studies have shown that neutrophils and neutrophil extracellular traps contribute to thrombus formation and resistance to reperfusion therapy. Histologic features of thrombi in patients with stroke may provide some clues to stroke etiology, which is helpful for determining the strategy of stroke prevention. Research on thrombus may also be helpful for improving reperfusion therapy, including the development of new thrombolytic agents.

Platelet lamellipodium formation is not required for thrombus formation and stability

During platelet spreading, the actin cytoskeleton undergoes rapid rearrangement, forming filopodia and lamellipodia. Controversial data have been published on the role of lamellipodia in thrombus formation and stability. The Wiskott-Aldrich syndrome protein-family verprolin-homologous protein (WAVE)-regulatory complex, which has been shown in other cells to drive lamellipodium formation by enhancing actin nucleation via the actin-related protein 2/3 (Arp2/3) complex, is activated by Ras-related C3 botulinum toxin substrate 1 (Rac1) interaction with the WAVE complex subunit cytoplasmic fragile X mental retardation 1-interacting protein 1 (Cyfip1). We analyzed Cyfip1flox/floxPf4-Cre mice to investigate the role of Cyfip1 in platelet function. These mice displayed normal platelet counts and a slight reduction in platelet volume. Activation of mutant platelets was only moderately reduced to all tested agonists as measured by αIIbβ3 integrin activation and P-selectin surface exposure. However, lamellipodium formation of mutant platelets was completely abolished on different matrices. Nevertheless, Cyfip1-deficient platelets formed stable thrombi on collagen fibers ex vivo and in 2 models of occlusive arterial thrombosis in vivo. Similarly, the hemostatic function and maintenance of vascular integrity during inflammation of the skin and lung were unaltered in the mutant mice. Investigation of platelet morphology in an induced thrombus under flow revealed that platelets rather form filopodia in the thrombus shell, and are flattened with filopodium-like structures when in direct contact to collagen fibers at the bottom of the thrombus. We provide for the first time direct evidence that platelet lamellipodium formation is not required for stable thrombus formation, and that morphological changes of platelets differ between a static spreading assay and thrombus formation under flow.

Hypoxia Modulates Platelet Purinergic Signalling Pathways

BACKGROUND

 Hypoxia resulting from ascent to high-altitude or pathological states at sea level is known to increase platelet reactivity. Previous work from our group has suggested that this may be adenosine diphosphate (ADP)-specific. Given the clinical importance of drugs targeting ADP pathways, research into the impact of hypoxia on platelet ADP pathways is highly important.

METHODS

 Optimul aggregometry was performed on plasma from 29 lowland residents ascending to 4,700 m, allowing systematic assessment of platelet reactivity in response to several platelet agonists. Aggregometry was also performed in response to ADP in the presence of inhibitors of the two main ADP receptors, P2Y₁ and P2Y₁₂ (MRS2500 and cangrelor, respectively). Phosphorylation of vasodilator-stimulated phosphoprotein (VASP), a key determinant of platelet aggregation, was analysed using the VASPFix assay.

RESULTS

 Hypobaric hypoxia significantly reduced the ability of a fixed concentration of cangrelor to inhibit ADP-induced aggregation and increased basal VASP phosphorylation. However, in the absence of P2Y receptor inhibitors, we did not find evidence of increased platelet sensitivity to any of the agonists tested and found reduced sensitivity to thrombin receptor-activating peptide-6 amide.

CONCLUSION

 Our results provide evidence of increased P2Y₁ receptor activity at high altitude and suggest down-regulation of the P2Y₁₂ pathway through increased VASP phosphorylation. These changes in ADP pathway activity are of potential therapeutic significance to high-altitude sojourners and hypoxic sea level patients prescribed platelet inhibitors and warrant further investigation.

VAS2870 and VAS3947 attenuate platelet activation and thrombus formation via a NOX-independent pathway downstream of PKC

NADPH oxidase (NOX) enzymes are involved in a various physiological and pathological processes such as platelet activation and inflammation. Interestingly, we found that the pan-NOX inhibitors VAS compounds (VAS2870 and its analog VAS3947) exerted a highly potent antiplatelet effect. Unlike VAS compounds, concurrent inhibition of NOX1, 2, and 4 by treatment with ML171, GSK2795039, and GKT136901/GKT137831 did not affect thrombin and U46619-induced platelet aggregation. These findings suggest that VAS compounds may inhibit platelet aggregation via a NOX-independent manner. Thus, we aimed to investigate the detailed antiplatelet mechanisms of VAS compounds. The data revealed that VAS compounds blocked various agonist-induced platelet aggregation, possibly via blocking PKC downstream signaling, including IKKβ and p38 MAPK, eventually reducing platelet granule release, calcium mobilization, and GPIIbIIIa activation. In addition, VAS compounds inhibited mouse platelet aggregation-induced by collagen and thrombin. The in vivo study also showed that VAS compounds delayed thrombus formation without affecting normal hemostasis. This study is the first to demonstrate that, in addition to inhibiting NOX activity, VAS compounds reduced platelet activation and thrombus formation through a NOX-independent pathway downstream of PKC. These findings also indicate that VAS compounds may be safe and potentially therapeutic agents for treating patients with cardiovascular diseases.

Platelets as Modulators of Cerebral Ischemia/Reperfusion Injury

Ischemic stroke is among the leading causes of disability and death worldwide. In acute ischemic stroke, the rapid recanalization of occluded cranial vessels is the primary therapeutic aim. However, experimental data (obtained using mostly the transient middle cerebral artery occlusion model) indicates that progressive stroke can still develop despite successful recanalization, a process termed "reperfusion injury." Mounting experimental evidence suggests that platelets and T cells contribute to cerebral ischemia/reperfusion injury, and ischemic stroke is increasingly considered a thrombo-inflammatory disease. The interaction of von Willebrand factor and its receptor on the platelet surface, glycoprotein Ib, as well as many activatory platelet receptors and platelet degranulation contribute to secondary infarct growth in this setting. In contrast, interference with GPIIb/IIIa-dependent platelet aggregation and thrombus formation does not improve the outcome of acute brain ischemia but dramatically increases the susceptibility to intracranial hemorrhage. Here, we summarize the current understanding of the mechanisms and the potential translational impact of platelet contributions to cerebral ischemia/reperfusion injury.

Antithrombotic effect of SP-8008, a benzoic acid derivative, through the selective inhibition of shear stress-induced platelet aggregation

Background and Purpose

Bleeding is one of the most critical adverse effects of antithrombotic drugs, and many efforts have been made to discover novel antiplatelet agents without bleeding complications. Shear stress‐induced platelet aggregation (SIPA), where the interaction of von Willebrand factor (vWF) and platelet glycoprotein (GP) Ib constitutes the initial step, is a promising target to overcome bleeding problems, as SIPA occurs only in pathological conditions. Here, we describe SP‐8008, a novel modulator of vWF–GP Ib interactions and evaluated its antiplatelet/antithrombotic effects.

Experimental Approach

Newly synthesized compounds were screened for antiplatelet effects in vitro, using human platelets exposed to high shear stress. Aggregation, intracellular calcium level, granule secretion, and integrin activation were assessed. Molecular modelling using virtual docking and flow cytometry were used to evaluate effects on vWF–GP Ib interactions. Antithrombotic effects in vivo were determined in rats, using arterial thrombosis and shear stress‐specific thrombosis. Transection tail bleeding time was used to evaluate adverse effects.

Key Results

SP‐8008 was a potent inhibitor of SIPA, with IC₅₀ of 1.44 ± 0.09 μM. SP‐8008 effectively and broadly blocked shear stress‐induced platelet activation events, without any significant toxicity. Importantly, SP‐8008 was highly selective against SIPA, effectively interfering with vWF–GP Ib engagement. Most importantly, SP‐8008 exerted significant antithrombotic effects in vivo in both shear stress‐specific and arterial thrombosis, without prolonging bleeding time.

Conclusions and Implications

Our results demonstrated that SP‐8008 can be a novel selective antiplatelet agent with improved safety profile.