Hypoxia and Ischemia Promote a Maladaptive Platelet Phenotype

Research priorities for peripheral artery disease: A statement from the Society for Vascular Medicine

Lower-extremity peripheral artery disease (PAD) affects approximately 236 million people worldwide and at least eight million people in the United States (US). Despite availability of new therapies that prevent major adverse cardiovascular events (MACE), these and major adverse limb events (MALE) remain common and occur more frequently in people with PAD, either with or without coronary artery disease (CAD), compared to people with CAD who do not have PAD. The most effective therapies to prevent cardiovascular events are not identical in people with PAD and those with CAD. Walking impairment and the risk of lower-extremity amputation are significantly greater in people with PAD compared to those without PAD. This report from the Society for Vascular Medicine (SVM) proposes and summarizes high-priority topics for scientific investigation in PAD, with the goal of improving health outcomes in people with PAD. To develop this report, a multidisciplinary team of scientists and clinicians reviewed literature, proposed high-priority topics for scientific investigation, and voted to rank the highest priority topics for scientific investigation. Priorities for clinical scientific investigation include: determine the current prevalence of PAD in the US by age, sex, race, and ethnicity; improve methods to diagnose PAD; develop new medical therapies to eliminate walking impairment; and improve implementation of established therapies to reduce rates of MACE and MALE in people with PAD. Priorities in basic science and translational science investigation include: developing animal models that closely resemble the vascular, skeletal muscle, and platelet pathology in patients with PAD and defining the genetic and epigenetic contributors to PAD and PAD-associated outcomes. Successful investigation of these research priorities will require more well-trained investigators focused on scientific investigation of PAD, greater and more efficient enrollment of diverse patients with PAD in randomized clinical trials, and increased research funding dedicated to PAD.

Nbeal2 knockout mice are not protected against hypoxia-induced pulmonary vascular remodeling and pulmonary hypertension

ABSTRACT

Inflammation drives the initiation and progression of pulmonary hypertension (PH). Platelets, increasingly recognized as immune cells, are activated and increased in the lungs of patients with PH. Platelet activation leads to the release of α-granule chemokines, many of which are implicated in PH. We hypothesized that hypoxia-induced secretion of platelet α-granule-stored proteins and PH would be prevented in Neurobeachin-like 2 knockout (Nbeal2-/-) α-granule-deficient mice. Wild-type (WT) and Nbeal2-/- mice were maintained in normoxia or exposed to 10% hypobaric hypoxia for 3, 14, 21, or 35 days. We observed macrothrombocytopenia, increased circulating neutrophils and monocytes, and increased lung interstitial macrophages (IMs) in Nbeal2-/- mice at baseline. Hypoxia-induced platelet activation was attenuated, and hypoxia-induced increase in lung platelet factor 4 (PF4) and platelets was delayed in Nbeal2-/- mice compared with in WT mice. Finally, although pulmonary vascular remodeling (PVR) and PH were attenuated at day 21, Nbeal2-/- mice were not protected against hypoxia-induced PVR and PH at day 35. Although this mutation also affected circulating monocytes, neutrophils, and lung IMs, all of which are critical in the development of experimental PH, we gained further support for the role of platelets and α-granule proteins, such as PF4, in PH progression and pathogenesis and made several observations that expand our understanding of α-granule-deficient mice in chronic hypoxia.

Oxygen Concentration Plays a Critical Role in Fibrinogen-Mediated Platelet Activation via Inactivation of αIIbβ3 and Modulation of Fibrinogen

In the vascular system, pathological conditions that cause hypoxia are associated with increased platelet activity and thrombosis. Using a platelet spreading assay, we show that severe hypoxia (i.e., 1%), venous (i.e., 5%), and, surprisingly, arterial (i.e., 12%) oxygen concentrations cause a significant reduction in platelet surface area coverage on fibrinogen in comparison to atmospheric oxygen condition (i.e., 21% oxygen), whilst adhesion and spreading on collagen and CRP were not affected. Importantly, the addition of thrombin or zinc restored full platelet spreading on fibrinogen, indicating that the inhibition of platelet spreading on fibrinogen was due to defective integrin activation. Analysis of integrin activation with FACs via PAC-1 staining supported a significant reduction in integrin activation in hypoxic conditions. Interestingly, a fibrinogen matrix prepared at 1%, 5%, or 12% oxygen failed to induce full platelet spreading, even when the experiments were performed at atmospheric oxygen concentration, indicating that the structure and activity of the fibrinogen coating is affected by oxygen. The effect of oxygen on different matrix proteins is critical to understand, as these data clearly demonstrate that collagen and CRP can support platelet activation at all O2 concentrations, whilst fibrinogen mediated platelet activation and spreading is lost at physiological and pathological O2 concentrations. These data have clear implications for thrombus formation data and highlight the role of oxygen in regulating platelet function.

Platelet Reduction in Rats Exposed to Chronic Hypoxia Is Associated with Interaction of Glycoprotein Ib Alpha von Willebrand Factor

Chronic high-altitude hypoxia is associated with reduced platelet count, but it is unclear whether the decrease in platelet count is due to impaired production or increased clearance. This study examines how hypoxia affects platelet production and apoptosis and elucidates the impact of glycoprotein Ibα-von Willebrand factor interaction on platelets in rats using a hypobaric hypoxia chamber. The results showed that the number of megakaryocytes increased under hypoxia; however, the levels of differentiation and polyploidy decreased, while those of apoptosis increased. Platelet production did not reduce according to the reticulated platelet percentage, while platelet apoptosis enhanced; these results suggest that increased platelet clearance was the main reason behind platelet reduction. Our previous microarray results indicated that glycoprotein Ibα (GPIbα) expression increased under hypoxia, which was a protein involved in platelet clearance; therefore, we examined the interaction of platelet GPIbα with the von Willebrand factor (vWF) both in vivo and in vitro to explore the effect of this process on platelets and whether it is related to platelet apoptosis. Under hypoxia, the stronger interaction between GPIbα and vWF promoted platelet apoptosis; inhibiting this interaction reduced platelet apoptosis and increased platelet counts. Platelet reduction is associated with apoptosis induced by the interaction between GPIbα and vWF.

Cellular and Molecular Mechanisms Leading to Air Travel-Induced Thrombosis

Venous thromboembolism, characterized by deep vein thrombosis and pulmonary embolism, is the third cardiovascular disease in the world. Deep vein thrombosis occurs when a blood clot forms in areas of impaired blood flow, and it is significantly affected by environmental factors. Local hypoxia, caused by venous stasis, plays a critical role in deep vein thrombosis under normal conditions, and this effect is intensified when the Po2 decreases, such as during air travel or high-altitude exposure. The lower oxygen levels and reduced pressure at high altitudes further contribute to deep vein thrombosis development. These conditions increase the pro-coagulant activity of neutrophils, platelets, and red blood cells, which interact on the surface of activated endothelial cells, promoting clot formation. Understanding the mechanisms involved in thrombus formation when Po2 is reduced, with or without pressure reduction, is crucial for preventing the development of venous thromboembolisms in such conditions and identifying innovative therapeutic targets. This literature review explores the mechanisms involved in thrombus formation related to high-altitude conditions and discusses the pro-coagulant consequences induced by environmental disturbances.

Development of a super-hydrophilic anaerobic tube for the optimization of platelet-rich fibrin

Horizontal platelet-rich fibrin (H-PRF) contains a variety of bioactive growth factors and cytokines that play a key role in the process of tissue healing and regeneration. The blood collection tubes used to produce Solid-PRF (plasmatrix (PM) tubes) have previously been shown to have a great impact on the morphology, strength and composition of the final H-PRF clot. Therefore, modification to PM tubes is an important step toward the future optimization of PRF. To this end, we innovatively modified the inner wall surface of the PM tubes with plasma and adjusted the gas environment inside the PM tubes to prepare super-hydrophilic anaerobic plasmatrix tubes (SHAP tubes). It was made anaerobic for the preparation of H-PRF with the aim of improving mechanical strength and bioactivity. The findings demonstrated that an anaerobic environment stimulated platelet activation within the PRF tubes. After compression, the prepared H-PRF membrane formed a fibrous cross-linked network with high fracture strength, ideal degradation characteristics, in addition to a significant increase in size. Thereafter, the H-PRF membranes prepared by the SHAP tubes significantly promoted collagen synthesis of gingival fibroblast and the mineralization of osteoblasts while maintaining excellent biocompatibility, and advantageous antibacterial properties. In conclusion, the newly modified PRF tubes had better platelet activation properties leading to better mechanical strength, a longer degradation period, and better regenerative properties in oral cell types including gingival fibroblast and alveolar osteoblasts. It also improves the success rate of H-PRF preparation in patients with coagulation dysfunction and expands the clinical application scenario.

Clinical Characteristics, Current Treatment Options, Potential Mechanisms, Biomarkers, and Therapeutic Targets in Avascular Necrosis of Femoral Head

Avascular necrosis of femoral head (AVNFH) is a debilitating disease of the young, affecting the quality of life significantly and eventually leading to total hip replacement surgery. The disease is diagnosed clinico-radiologically and MRI is the investigation of choice to diagnose the early stages of the disease. There is neither an early biomarker for detection nor is there a permanent cure for the disease and most of the patients are managed with various combinations of surgical and medical management protocols. In this review, we comprehensively address the etiopathogenesis, clinical characteristics, therapeutic procedures, bone characteristics, histopathology, multi-omic studies, finite element modeling, and systems analysis that has been performed in AVNFH. The etiology includes various factors that compromise the blood supply to the femoral head which also includes contributions by environmental and genetic factors. Multi-omic analysis has shown an association of deregulated pathways with the disease. The cell types involved include mesenchymal stem cells, osteoblasts, osteoclasts, endothelial and immune cells. Biochemical, hematological, histopathology, IHC, and other bone remodeling and degradation marker studies have been performed. A systems analysis using multi-omic data sets from published literature was carried out, the relevance of which is discussed to delineate potential mechanisms in etiopathogenesis, diagnosis, and effective management of this debilitating disease.

A Divergent Platelet Transcriptome in Patients with Lipedema and Lymphedema

Lipedema and lymphedema are physically similar yet distinct diseases that are commonly misdiagnosed. We previously reported that lipedema and lymphedema are associated with increased risk for venous thromboembolism (VTE). The underlying etiology of the prothrombotic profile observed in lipedema and lymphedema is unclear, but may be related to alterations in platelets. Our objective was to analyze the platelet transcriptome to identify biological pathways that may provide insight into platelet activation and thrombosis. The platelet transcriptome was evaluated in patients with lymphedema and lipedema, then compared to control subjects with obesity. Patients with lipedema were found to have a divergent transcriptome from patients with lymphedema. The platelet transcriptome and impacted biological pathways in lipedema were surprisingly similar to weight-matched comparators, yet different when compared to overweight individuals with a lower body mass index (BMI). Differences in the platelet transcriptome for patients with lipedema and lymphedema were found in biological pathways required for protein synthesis and degradation, as well as metabolism. Key differences in the platelet transcriptome for patients with lipedema compared to BMI-matched subjects involved metabolism and glycosaminoglycan processing. These inherent differences in the platelet transcriptome warrant further investigation, and may contribute to the increased risk of thrombosis in patients with lipedema and lymphedema.

Under the dual effect of inflammation and pulmonary fibrosis, CTD-ILD patients possess a greater susceptibility to VTE

As an autoimmune disease, the persistent systemic inflammatory response associated with connective tissue disease (CTD) is involved in the development of venous thromboembolism (VTE). However, clinical data showed that the risk of VTE in patients differed between subtypes of CTD, suggesting that different subtypes may have independent mechanisms to promote the development of VTE, but the specific mechanism lacks sufficient research at present. The development of pulmonary fibrosis also contributes to the development of VTE, and therefore, patients with CTD-associated interstitial lung disease (CTD-ILD) may be at higher risk of VTE than patients with CTD alone or patients with ILD alone. In addition, the activation of the coagulation cascade response will drive further progression of the patient's pre-existing pulmonary fibrosis, which will continue to increase the patient's risk of VTE and adversely affect prognosis. Currently, the treatment for CTD-ILD is mainly immunosuppressive and antirheumatic therapy, such as the use of glucocorticoids and janus kinase-inhibitors (JAKis), but, paradoxically, these drugs are also involved in the formation of patients' coagulation tendency, making the clinical treatment of CTD-ILD patients with a higher risk of developing VTE challenging. In this article, we review the potential risk factors and related mechanisms for the development of VTE in CTD-ILD patients to provide a reference for clinical treatment and prevention.

Dysregulated platelet function in patients with postacute sequelae of COVID-19

BACKGROUND

Postacute sequelae of COVID-19 (PASC), also referred to as "Long COVID", sometimes follows COVID-19, a disease caused by SARS-CoV-2. Although SARS-CoV-2 is well known to promote a prothrombotic state, less is known about the thrombosis risk in PASC. Our objective was to evaluate platelet function and thrombotic potential in patients following recovery from SARS-CoV-2, but with clear symptoms of patients with PASC.

METHODS

patients with PASC and matched healthy controls were enrolled in the study on average 15 months after documented SARS-CoV-2 infection. Platelet activation was evaluated by light transmission aggregometry (LTA) and flow cytometry in response to platelet surface receptor agonists. Thrombosis in platelet-deplete plasma was evaluated by Factor Xa activity. A microfluidics system assessed thrombosis in whole blood under shear stress conditions.

RESULTS

A mild increase in platelet aggregation in patients with PASC through the thromboxane receptor was observed, and platelet activation through the glycoprotein VI (GPVI) receptor was decreased in patients with PASC compared to age- and sex-matched healthy controls. Thrombosis under shear conditions as well as Factor Xa activity were reduced in patients with PASC. Plasma from patients with PASC was an extremely potent activator of washed, healthy platelets - a phenomenon not observed when stimulating healthy platelets after incubation with plasma from healthy individuals.

CONCLUSIONS

patients with PASC show dysregulated responses in platelets and coagulation in plasma, likely caused by a circulating molecule that promotes thrombosis. A hitherto undescribed protective response appears to exist in patients with PASC to counterbalance ongoing thrombosis that is common to SARS-CoV-2 infection.

Perfluorocarbon Nanoparticles Incorporating Ginkgolide B: Artificial O2 Carriers with Antioxidant Activity and Antithrombotic Effect

Ischemic stroke primarily leads to insufficient oxygen delivery in ischemic area. Prompt reperfusion treatment for restoration of oxygen is clinically suggested but mediates more surging reactive oxygen species (ROS) generation and oxidative damage, known as ischemia-reperfusion injury (IRI). Therefore, the regulation of oxygen content is a critical point to prevent cerebral ischemia induced pathological responses and simultaneously alleviate IRI triggered by the sudden oxygen restoration. In this work, we constructed a perfluorocarbon (PFC)-based artificial oxygen nanocarrier (PFTBA-L@GB), using an ultrasound-assisted emulsification method, alleviates the intracerebral hypoxic state in ischemia stage and IRI after reperfusion. The high oxygen solubility of PFC allows high oxygen efficacy. Furthermore, PFC has the adhesion affinity to platelets and prevents the overactivation of platelet. The encapsulated payload, ginkgolide B (GB) exerts its anti-thrombosis by antagonism on platelet activating factor and antioxidant effect by upregulation of antioxidant molecular pathway. The versatility of the present strategy provides a practical approach to build a simple, safe, and relatively effective oxygen delivery agent to alleviate hypoxia, promote intracerebral oxygenation, anti-inflammatory, reduce intracerebral oxidative stress damage and thrombosis and caused by stroke.

Dysregulated Platelet Function in Patients with Post-Acute Sequelae of COVID-19

Background

Post-acute sequelae of COVID-19 (PASC), also referred as Long-COVID, sometimes follows COVID-19, a disease caused by SARS-CoV-2. While SARS-CoV-2 is well-known to promote a prothrombotic state, less is known about the thrombosis risk in PASC.

Aim

Our objective was to evaluate the platelet function and thrombotic potential in patients following recovery from SARS-CoV-2 with clear symptoms of PASC.

Methods

PASC patients and matched healthy controls were enrolled in the study on average 15 months after documented SARS-CoV-2 infection. Platelet activation was evaluated by Light Transmission Aggregometry (LTA) and flow cytometry in response to platelet surface receptor agonists. Thrombosis in platelet-deplete plasma was evaluated by Factor Xa activity. A microfluidics system assessed thrombosis in whole blood under shear stress conditions.

Results

A mild increase in platelet aggregation in PASC patients through the thromboxane receptor was observed and platelet activation through the glycoprotein VI (GPVI) receptor was decreased in PASC patients compared to age- and sex-matched healthy controls. Thrombosis under shear conditions as well as Factor Xa activity were reduced in PASC patients. Plasma from PASC patients was an extremely potent activator of washed, healthy platelets - a phenomenon not observed when stimulating healthy platelets after incubation with plasma from healthy individuals.

Conclusions

PASC patients show dysregulated responses in platelets and coagulation in plasma, likely caused by a circulating molecule that promotes thrombosis. A hitherto undescribed protective response appears to exists in PASC patients to counterbalance ongoing thrombosis that is common to SARS-CoV-2 infection.

Saint Paraskeva Medical Center, Lviv, Ukraine, Chooklin S, Chuklin S, Saint Paraskeva Medical Center, Lviv, Ukraine. PATHOPHYSIOLOGICAL MECHANISMS OF DEEP VEIN THROMBOSIS

Deep venous thrombosis is a frequent multifactorial disease and most of the time is triggered by the interaction between acquired risk factors, particularly immobility, and hereditary risk factors such as thrombophilias. The mechanisms underlying deep venous thrombosis are not fully elucidated; however, in recent years the role of venous flow, endothelium, platelets, leukocytes, and the interaction between inflammation and hemostasis has been determined. Alteration of venous blood flow produces endothelial activation, favoring the adhesion of platelets and leukocytes, which, through tissue factor expression and neutrophil extracellular traps formation, contribute to the activation of coagulation, trapping more cells, such as red blood cells, monocytes, eosinophils, lymphocytes. The coagulation factor XI-driven propagation phase of blood coagulation plays a major role in venous thrombus growth, but a minor role in hemostasis. In this work, the main mechanisms involved in the pathophysiology of deep vein thrombosis are described.

Thrombotic Alterations under Perinatal Hypoxic Conditions: HIF and Other Hypoxic Markers

Hypoxia is considered to be a stressful physiological condition, which may occur during labor and the later stages of pregnancy as a result of, among other reasons, an aged placenta. Therefore, when gestation or labor is prolonged, low oxygen supply to the tissues may last for minutes, and newborns may present breathing problems and may require resuscitation maneuvers. As a result, poor oxygen supply to tissues and to circulating cells may last for longer periods of time, leading to life-threatening conditions. In contrast to the well-known platelet activation that occurs after reperfusion of the tissues due to an ischemia/reperfusion episode, platelet alterations in response to reduced oxygen exposition following labor have been less frequently investigated. Newborns overcome temporal hypoxic conditions by changing their organ functions or by adaptation of the intracellular molecular pathways. In the present review, we aim to analyze the main platelet modifications that appear at the protein level during hypoxia in order to highlight new platelet markers linked to complications arising from temporal hypoxic conditions during labor. Thus, we demonstrate that hypoxia modifies the expression and activity of hypoxic-response proteins (HRPs), including hypoxia-induced factor (HIF-1), endoplasmic reticulum oxidase 1 (Ero1), and carbonic anhydrase (CIX). Finally, we provide updates on research related to the regulation of platelet function due to HRP activation, as well as the role of HRPs in intracellular Ca2+ homeostasis.

Protection of β2GPI Deficient Mice from Thrombosis Reflects a Defect in PAR3-facilitated Platelet Activation

Background

Antibodies to β2-glycoprotein I (β2GPI) cause thrombosis in antiphospholipid syndrome, however the role of β2GPI itself in regulation of coagulation pathways in vivo is not well understood.

Methods

We developed β2GPI-deficient mice (Apoh -/- ) by deleting exon 2 and 3 of Apoh using CRISPR/Cas9 and compared the propensity of wild-type (WT) and Apoh -/- mice to develop thrombosis using rose bengal and FeCl 3 -induced carotid thrombosis, laser-induced cremaster arteriolar injury, and inferior vena cava (IVC) stasis models. We also compared tail bleeding times and assessed platelet activation in WT and Apoh -/- mice in the absence and presence of exogenous β2GPI.

Results

Compared to WT littermates, Apoh -/- mice demonstrated a prolonged time to occlusion of the carotid artery after exposure to rose bengal or FeCl 3 , and reduced platelet and fibrin accumulation in cremasteric arterioles after laser injury. Similarly, significantly smaller thrombi were retrieved from the IVC of Apoh -/- mice 48 hours after IVC occlusion. The activated partial thromboplastin time (aPTT) and prothrombin time, as well as aPTT reagent- and tissue factor-induced thrombin generation times using plasma from Apoh -/- and WT mice revealed no differences. However, we observed significant prolongation of tail bleeding in Apoh -/- mice, and reduced P-selectin expression and binding of fibrinogen to the activated α2bβ3 integrin on platelets from these mice after stimulation with low thrombin concentrations; these changes were reversed by exogenous β2GPI. An antibody to PAR3 blocked thrombin-induced activation of WT, but not Apoh -/- platelets, as well as the ability of β2GPI to restore the activation response of Apoh -/- platelets to thrombin. β2GPI deficiency did not affect platelet activation by a PAR4-activator peptide, or ADP.

Conclusions

In mice, β2GPI may mediate procoagulant activity by enhancing the ability of PAR3 to present thrombin to PAR4, promoting platelet activation at low thrombin concentrations.

Key Points

β2GPI deficient mice are protected from experimental arterial, venous, and microvascular thrombosis.β2GPI deficient mice display prolonged tail bleeding times and reduced PAR3-facilitated platelet activation by low concentrations of thrombin.

Platelets at the Vessel Wall in Non-Thrombotic Disease

Platelets are small, anucleate entities that bud from megakaryocytes in the bone marrow. Among circulating cells, platelets are the most abundant cell, traditionally involved in regulating the balance between thrombosis (the terminal event of platelet activation) and hemostasis (a protective response to tissue injury). Although platelets lack the precise cellular control offered by nucleate cells, they are in fact very dynamic cells, enriched in preformed RNA that allows them the capability of de novo protein synthesis which alters the platelet phenotype and responses in physiological and pathological events. Antiplatelet medications have significantly reduced the morbidity and mortality for patients afflicted with thrombotic diseases, including stroke and myocardial infarction. However, it has become apparent in the last few years that platelets play a critical role beyond thrombosis and hemostasis. For example, platelet-derived proteins by constitutive and regulated exocytosis can be found in the plasma and may educate distant tissue including blood vessels. First, platelets are enriched in inflammatory and anti-inflammatory molecules that may regulate vascular remodeling. Second, platelet-derived microparticles released into the circulation can be acquired by vascular endothelial cells through the process of endocytosis. Third, platelets are highly enriched in mitochondria that may contribute to the local reactive oxygen species pool and remodel phospholipids in the plasma membrane of blood vessels. Lastly, platelets are enriched in proteins and phosphoproteins which can be secreted independent of stimulation by surface receptor agonists in conditions of disturbed blood flow. This so-called biomechanical platelet activation occurs in regions of pathologically narrowed (atherosclerotic) or dilated (aneurysmal) vessels. Emerging evidence suggests platelets may regulate the process of angiogenesis and blood flow to tumors as well as education of distant organs for the purposes of allograft health following transplantation. This review will illustrate the potential of platelets to remodel blood vessels in various diseases with a focus on the aforementioned mechanisms.

Association between PaO2/FiO2 ratio and thrombotic events in COVID-19 patients

PaO₂/FiO₂ (P/F ratio) is considered a marker of hypoxia/hypoxemia and mortality. Several prothrombotic changes are associated with the decrease of P/F ratio. The role of P/F ratio in patients with arterial and venous thrombosis remains unclear. The aim of this study was to assess in patients with coronavirus disease 2019 (COVID-19), the association between P/F ratio and arterial/venous thrombosis. One thousand and four hundred and six COVID-19 patients were recruited; 289 (21%) patients had P/F ratio < 200 and 1117 (79%) ≥ 200. Compared to the patients with P/F ratio ≥ 200, those with P/F ratio < 200 were older and with higher levels of glycemia, D-dimer and lower levels of albumin. Multiple linear regression analysis showed that albumin (standardized coefficient β:  0.156; SE: 0.001; p = 0.0001) and D-dimer (standardized coefficient β: -0.135; SE: 0.0001; p = 0.0001) were associated with P/F ratio. During the hospitalization 159 patients were transferred in intensive care unit (ICU), 253 patients died, 156 patients had arterial or venous thrombotic events. A bivariate logistic analysis was performed to analyze the predictors of thrombosis in COVID-19 patients; P/F ratio < 200 (Odds Ratio: [OR] 1.718, 95% Confidence Interval [CI] 1.085-2.718, p = 0.021), albumin (OR 1.693, 95% CI 1.055-2.716, p = 0.029), D-dimer (OR 3.469, 95% CI 2.110-5.703, p < 0.0001), coronary artery disease (CAD) (OR 1.800, 95% CI 1.086-2.984, p = 0.023) and heart failure (OR 2.410 95% CI 1.385-4.193, p = 0.002) independently predicted thrombotic events in this population. This study suggests that the P/F ratio is associated with thrombotic events by promoting a hypercoagulation state in patients hospitalized for COVID-19.

Platelets in Myocardial Ischemia/Reperfusion Injury

Coronary artery disease, including myocardial infarction (MI), remains a leading cause of global mortality. Rapid reperfusion therapy is key to the improvement of patient outcome but contributes substantially to the final cardiac damage. This phenomenon is called "ischemia/reperfusion injury (IRI)." The underlying mechanisms of IRI are complex and not fully understood. Contributing cellular and molecular mechanisms involve the formation of microthrombi, alterations in ion concentrations, pH shifts, dysregulation of osmolality, and, importantly, inflammation. Beyond their known action as drivers of the development of coronary plaques leading to MI, platelets have been identified as important mediators in myocardial IRI. Circulating platelets are activated by the IRI-provoked damages in the vascular endothelium. This leads to platelet adherence to the reperfused endothelium, aggregation, and the formation of microthrombi. Furthermore, activated platelets release vasoconstrictive substances, act via surface molecules, and enhance leukocyte infiltration into post-IR tissue, that is, via platelet-leukocyte complexes. A better understanding of platelet contributions to myocardial IRI, including their interaction with other lesion-associated cells, is necessary to develop effective treatment strategies to prevent IRI and further improve the condition of the reperfused myocardium. In this review, we briefly summarize platelet properties that modulate IRI. We also describe the beneficial impacts of antiplatelet agents as well as their mechanisms of action in IRI beyond classic effects.

Platelet olfactory receptor activation limits platelet reactivity and growth of aortic aneurysms

As blood transitions from steady laminar flow (S-flow) in healthy arteries to disturbed flow (D-flow) in aneurysmal arteries, platelets are subjected to external forces. Biomechanical platelet activation is incompletely understood and is a potential mechanism behind antiplatelet medication resistance. Although it has been demonstrated that antiplatelet drugs suppress the growth of abdominal aortic aneurysms (AAA) in patients, we found that a certain degree of platelet reactivity persisted in spite of aspirin therapy, urging us to consider additional antiplatelet therapeutic targets. Transcriptomic profiling of platelets from patients with AAA revealed upregulation of a signal transduction pathway common to olfactory receptors, and this was explored as a mediator of AAA progression. Healthy platelets subjected to D-flow ex vivo, platelets from patients with AAA, and platelets in murine models of AAA demonstrated increased membrane olfactory receptor 2L13 (OR2L13) expression. A drug screen identified a molecule activating platelet OR2L13, which limited both biochemical and biomechanical platelet activation as well as AAA growth. This observation was further supported by selective deletion of the OR2L13 ortholog in a murine model of AAA that accelerated aortic aneurysm growth and rupture. These studies revealed that olfactory receptors regulate platelet activation in AAA and aneurysmal progression through platelet-derived mediators of aortic remodeling.

Soluble P-Selectin and von Willebrand Factor Rise in Healthy Volunteers Following Non-exertional Ascent to High Altitude

Reduced oxygen tensions experienced at high altitudes are thought to predispose to thrombosis, yet there are few studies linking hypoxia, platelet activation, and thrombosis. Reports of platelet phenotypes in hypoxia are inconsistent, perhaps due to differing degrees of hypoxia experienced and the duration of exposure. This study aimed to investigate the relationship between soluble P-selectin, a marker of platelet activation, and von Willebrand factor (vWF) on exposure to hypoxia. We measured plasma concentrations of P-selectin and vWF in sixteen healthy volunteers before, during and after the APEX 2 expedition. APEX 2 consisted of a non-exertional ascent to 5,200 m, followed by 7 consecutive days at high altitude. We showed that high altitude significantly increased mean plasma P-selectin and vWF compared to pre-expedition levels. Both plasma marker levels returned to baseline post-expedition. We found a strong positive correlation between vWF and P-selectin, but no association between P-selectin and platelet count. Our results are consistent with previous work showing evidence of platelet activation at high altitude and demonstrate that the rise in P-selectin is not simply due to an increase in platelet count. As vWF and P-selectin could be derived from either platelets or endothelial cells, further work assessing more specific markers of endothelial activation is proposed to provide insight into the source of these potential pro-thrombotic biomarkers at altitude.

The Burden of Hypercoagulability in COVID-19

The novel coronavirus disease 2019 (COVID-19) infection has widespread impact on multiple organ systems, including damage to endothelial cells. Various studies have found evidence for direct mechanisms by which interaction between severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) and endothelial cells lead to extensive damage to the latter, and indirect mechanisms, such as excessively elevated cytokines, can also result in the same outcome. Damage to the endothelium results in release of thrombotic factors and inhibition of fibrinolysis. This confers a significant hypercoagulability burden on patients infected or recovering from COVID-19 infection. In this case report, the authors report the case of a gentleman presenting with extensive deep vein thrombosis and pulmonary embolism, in the context of recent COVID-19 infection. The postulated mechanisms and management are discussed.

The Effects of Mild Intermittent Hypoxia Exposure on the Abdominal Subcutaneous Adipose Tissue Proteome in Overweight and Obese Men: A First-in-Human Randomized, Single-Blind, and Cross-Over Study

Adipose tissue (AT) oxygen tension (pO₂) has been implicated in AT dysfunction and metabolic perturbations in both rodents and humans. Compelling evidence suggests that hypoxia exposure alters metabolism, at least partly through effects on AT. However, it remains to be elucidated whether mild intermittent hypoxia (MIH) exposure impacts the AT proteome. We performed a randomized, single-blind, and cross-over study to investigate the effects of seven consecutive days of MIH (FiO₂ 15%, 3x2h/d) compared to normoxia (FiO₂ 21%) exposure on the AT proteome in overweight/obese men. In vivo AT insulin sensitivity was determined by the gold standard hyperinsulinemic-euglycemic clamp, and abdominal subcutaneous AT biopsies were collected under normoxic fasting conditions following both exposure regimens (day 8). AT proteins were isolated and quantified using liquid chromatography-mass spectrometry. After correction for blood contamination, 1,022 AT protein IDs were identified, of which 123 were differentially expressed following MIH (p < 0.05). We demonstrate for the first time that MIH exposure, which markedly reduces in vivo AT oxygen tension, impacts the human AT proteome. Although we cannot exclude that a single differentially expressed protein might be a false positive finding, several functional pathways were altered by MIH exposure, also after adjustment for multiple testing. Specifically, differentially expressed proteins were involved in redox systems, cell-adhesion, actin cytoskeleton organization, extracellular matrix composition, and energy metabolism. The MIH-induced change in AT TMOD3 expression was strongly related to altered in vivo AT insulin sensitivity, thus linking MIH-induced effects on the AT proteome to metabolic changes in overweight/obese humans.

Diagnostic Potential of Exosomal HypoxamiRs in the Context of Hypoxia-Sumoylation-HypoxamiRs in Early Onset Preeclampsia at the Preclinical Stage

As the search for non-invasive preclinical markers of preeclampsia (PE) expands, the number of studies on the diagnostic potential of exosomes is growing. Changes in the partial pressure of oxygen caused by impaired uteroplacental perfusion in PE are a powerful inducer of increased production and release of exosomes from cells, which also determine their cargo. At the same time, the expression pattern of oxygen-dependent microRNAs (miRNAs), called "hypoxamiRs", is modulated, and their packing into exosomes is strictly regulated by sumoylation. In connection therewith, we emphasize the evaluation of exosomal hypoxamiR expression (miR-27b-3p, miR-92b-3p, miR-181a-5p, and miR-186-5p) using quantitative RT-PCR, as well as SUMO 1-4 and UBC9 (by Western blotting), in pregnant women with early-onset PE. The findings show that miR-27b-3p and miR-92b-3p expression was significantly changed at 11-14 and 24-26 weeks of gestation in the blood plasma of pregnant women with early-onset PE, which subsequently manifested. High sensitivity and specificity (AUC = 1) were demonstrated for these miRNAs in the first trimester, and significant correlations with a decrease in hemoglobin (r = 0.71, p = 0.002; r = -0.71, p = 0.002) were established. In mid-pregnancy, the miR-27b-3p expression was found to correlate with an increase in platelets (r = -0.95, p = 0.003), and miR-92b-3p was associated with a decrease in the prothrombin index (r = 0.95, p = 0.003). Specific exomotifs of studied miRNAs were also identified, to which the sumoylated ribonucleoprotein hnRNPA2/B1 binds, carrying out their packaging into exosomes. The expression of conjugated SUMO 1 (p = 0.05), SUMO 2/3/4 (p = 0.03), and UBC9 (p = 0.1) was increased in exosomes at early-onset PE, and the expression of free SUMO 1 (p = 0.03) and SUMO 2/3/4 (p = 0.01) was significantly increased in the placenta, as an adaptive response to hypoxia. Moreover, SUMO 2/3/4 was negatively correlated with miR-27b-3p expression in the placenta. In conclusion, the diagnostic potential of exosomal hypoxamiRs mediated by sumoylation may form the basis for the development of combined specific targets for the treatment of early-onset PE, as hnRNPA2/B1 is a target of miR-27b-3p, and its sumoylation creates miR-27b-3p-hnRNPA2/B1-SUMO 1-4 cross-talk.

Sex-Dependent Effect of Platelet Nitric Oxide: Production and Platelet Reactivity in Healthy Individuals

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Platelet reactivity is greater in healthy women compared with men.

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Following an oral nitrate load, platelet nitric oxide production increased disproportionately more in healthy women than healthy men with attenuated platelet reactivity in women and enhanced platelet reactivity in men.

A nitrate-rich diet has many cardiovascular benefits, but the mechanism behind this is unclear. We hypothesized that the ingestion of nitrate augments nitrate to nitrite reduction, leading to nitric oxide (NO) production, which may suppress platelet reactivity. In a randomized, double-blinded, placebo-controlled study involving healthy individuals, ingestion of nitrate augmented saliva and plasma nitrite/nitrate concentration and enhanced platelet NO production disproportionately in women compared with men. The response of elevated platelet NO in men was increased platelet reactivity and the response of markedly elevated platelet NO in women slightly inhibited platelet reactivity.

Practical Considerations of Dissolved Oxygen Levels for Platelet Function under Hypoxia

Investigating human platelet function in low-oxygen environments is important in multiple settings, including hypobaric hypoxia (e.g., high altitude), sea level hypoxia-related disease, and thrombus stability. These studies often involve drawing blood from which platelets are isolated and analysed at atmospheric conditions or re-exposed to low oxygen levels in hypoxia chambers before testing. However, it remains unknown how the in vitro handling of the samples itself changes their dissolved oxygen concentration, which might affect platelet function and experimental results. Here, we prepared healthy donor platelet-rich plasma and washed platelet (WP) suspensions and exposed them to 2% oxygen. We found that the use of hypoxia pre-equilibrated tubes, higher platelet concentrations (>2 × 10⁸/mL versus 2 × 10⁷/mL), smaller volumes (600 µL versus 3 mL), and presence of plasma reduced the time for samples to reach 2% oxygen. Notably, oxygen levels decreased below 2% in most suspensions, but also in WP maintained at atmospheric 21% oxygen. Additionally, platelet spreading on fibrinogen was decreased when using hypoxic fibrinogen-coated culture plates regardless of the oxygen percentage (2% or 21%) in which platelet incubation took place. Thus, sample handling and experimental conditions should be carefully monitored in platelet-hypoxia studies as they might compromise results interpretation and comparison across studies.

Vaso-occlusive crisis in sickle cell disease: a vicious cycle of secondary events

Painful vaso-occlusive crisis (VOC) remains the most common reason for presenting to the Emergency Department and hospitalization in patients with sickle cell disease (SCD). Although two new agents have been approved by the Food and Drug Administration for treating SCD, they both target to reduce the frequency of VOC. Results from studies investigating various approaches to treat and shorten VOC have so far been generally disappointing. In this paper, we will summarize the complex pathophysiology and downstream events of VOC and discuss the likely reasons for the disappointing results using monotherapy. We will put forward the rationale for exploring some of the currently available agents to either protect erythrocytes un-involved in the hemoglobin polymerization process from sickling induced by the secondary events, or a multipronged combination approach that targets the complex downstream pathways of VOC.

Mortality rate and biomarker expression within COVID-19 patients who develop acute ischemic stroke: a systematic review and meta-analysis

Objective:

To describe the mortality difference between acute ischemic stroke (AIS) and non-AIS groups within COVID-19 patients.

Materials & methods:

We included observational studies through September 2020 that categorized COVID-19 patients into two groups (with and without AIS).

Results:

Eight studies with a total sample size of 19,399 COVID-19 patients were included. The pooled risk difference showed that patients with COVID-19 who developed AIS had significantly higher mortality than those without AIS by a risk difference of 24% (95% CI: 0.10–0.39; p = 0.001). In two studies, the COVID-19+AIS group had significantly higher lymphocytes, procalcitonin and creatinine levels.

Conclusion:

Developing AIS significantly adds to the mortality of COVID-19. Timely interventions to manage those patients are strongly recommended.

We systematically searched for COVID-19 studies that categorized patients into two groups: with and without acute ischemic stroke (AIS). Of 5100 unique records, eight studies with a total of 19,399 COVID-19 patients were included. The overall mortality rate of COVID-19 patients who developed AIS was 29.6% compared with 2.6% in those without AIS. We therefore conclude that development of AIS increases the mortality rate of COVID-19, and recommend timely intervention for such patients.

COVID-19 and Cardiovascular Disease: From Bench to Bedside

A pandemic of historic impact, coronavirus disease 2019 (COVID-19) has potential consequences on the cardiovascular health of millions of people who survive infection worldwide. Severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), the etiologic agent of COVID-19, can infect the heart, vascular tissues, and circulating cells through ACE2 (angiotensin-converting enzyme 2), the host cell receptor for the viral spike protein. Acute cardiac injury is a common extrapulmonary manifestation of COVID-19 with potential chronic consequences. This update provides a review of the clinical manifestations of cardiovascular involvement, potential direct SARS-CoV-2 and indirect immune response mechanisms impacting the cardiovascular system, and implications for the management of patients after recovery from acute COVID-19 infection.

"Silent Hypoxemia" Leads to Vicious Cycle of Infection, Coagulopathy and Cytokine Storm in COVID-19: Can Prophylactic Oxygen Therapy Prevent It?

Humankind is facing its worst pandemic of the twenty-first century, due to infection of a novel coronavirus named as SARS-CoV2, started from Wuhan in China. Till now, 15 million people are infected, causing more than 600,000 deaths. The disease, commonly known as, COVID-19, was initially thought to be associated with ARDS only, but later on revealed to have many unexplained and atypical clinical features like coagulopathy and cytokinemia, leading to multi-organ involvements. The patients also suffer from 'Silent Hypoxemia', where there is no immediate respiratory signs and symptoms even though alarmingly low SpO₂ level. We hypothesize that this covert hypoxemia may lead to molecular changes exacerbating coagulopathy and cytokine storm in COVID19 patients, which again, in turn, causes a vicious cycle of more hypoxemia/hypoxia and progression of the infection to more severe stages through HIF-1α dependent pathway. Although molecular mechanisms are yet to be substantiated by scientific evidence, hypoxemia remains an independent worsening factor in serious COVID 19 patients. Keeping all in mind, we propose that even in the early and asymptomatic cases, prophylactic oxygen therapy to be initiated to break the vicious cycle and to reduce the mortality in COVID 19 to save precious human lives.

Could cilostazol be beneficial in COVID-19 treatment? Thinking about phosphodiesterase-3 as a therapeutic target

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes coronavirus disease 2019 (COVID-19) that has emerged and rapidly spread across the world. The COVID-19 severity is associated to viral pneumonia with additional extrapulmonary complications. Hyperinflammation, dysfunctional immune response and hypercoagulability state are associated to poor prognosis. Therefore, the repositioning of multi-target drugs to control the hyperinflammation represents an important challenge for the scientific community. Cilostazol, a selective phosphodiesterase type-3 inhibitor (PDE-3), is an antiplatelet and vasodilator drug, that presents a range of pleiotropic effects, such as antiapoptotic, anti-inflammatory, antioxidant, and cardioprotective activities. Cilostazol also can inhibit the adenosine uptake, which enhances intracellular cAMP levels. In the lungs, elevated cAMP promotes anti-fibrotic, vasodilator, antiproliferative effects, as well as mitigating inflammatory events. Interestingly, a recent study evaluated antiplatelet FDA-approved drugs through molecular docking-based virtual screening on viral target proteins. This study revealed that cilostazol is a promising drug against COVID-19 by inhibiting both main protease (Mpro) and Spike glycoprotein, reinforcing its use as a promising therapeutic approach for COVID-19. Considering the complexity associated to COVID-19 pathophysiology and observing its main mechanisms, this article raises the hypothesis that cilostazol may act on important targets in development of the disease. This review highlights the importance of drug repurposing to address such an urgent clinical demand safely, effectively and at low cost, reinforcing the main pharmacological actions, to support the hypothesis that a multi-target drug such as cilostazol could play an important role in the treatment of COVID-19.

Variability of Activated Clotting Time by Site of Sample Draw During Percutaneous Coronary Intervention: A Prospective Single-Center Study

The activated clotting time (ACT) assay is used to monitor and titrate anticoagulation therapy with unfractionated heparin during percutaneous coronary intervention (PCI). Observations at our institution suggested a considerable difference between ACT values drawn from varying arterial sites, prompting the current study. Patients undergoing PCI with unfractionated heparin therapy were prospectively enrolled. Simultaneous arterial blood samples were drawn from the access sheath and the coronary guide catheter. Differences between Hemochron ACT values were determined, and potential interactions with clinical variables were analyzed. Immediately postprocedure, the simultaneous mean guide and sheath ACTs were 327 ± 62 seconds and 257 ± 44 seconds, respectively, with a mean difference of 70 ± 60 seconds (P < .001). Nearly all (90%) ACT values obtained via the guide catheter were higher than the concurrent ACT drawn from the sheath. Logistic regression analysis demonstrated that lower weight-adjusted heparin doses and absence of diabetes were associated with a greater difference between the ACT values. We conclude that the ACT value is substantially greater when assessed via the guide catheter versus the access sheath. Although the biological mechanisms require further study, this difference should be considered when managing anticoagulation during PCI and when reporting ACT as part of research protocols.

COVID‑19 and ischemic stroke: Mechanisms of hypercoagulability (Review)

During the coronavirus disease 2019 (COVID-19) pandemic, some patients with severe COVID-19 exhibited complications such as acute ischemic stroke (AIS), which was closely associated with a poor prognosis. These patients often had an abnormal coagulation, namely, elevated levels of D-dimer and fibrinogen, and a low platelet count. Certain studies have suggested that COVID-19 induces AIS by promoting hypercoagulability. Nevertheless, the exact mechanisms through which COVID-19 leads to a hypercoagulable state in infected patients remain unclear. Understanding the underlying mechanisms of hypercoagulability is of utmost importance for the effective treatment of these patients. The present review aims to summarize the current status of research on COVID-19, hypercoagulability and ischemic stroke. The present review also aimed to shed light into the underlying mechanisms through which COVID-19 induces hypercoagulability, and to provide therapies for different mechanisms for the more effective treatment of patients with COVID-19 with ischemic stroke and prevent AIS during the COVID-19 pandemic.

Sex-Specific Platelet Activation Through Protease-Activated Receptors Reverses in Myocardial Infarction

OBJECTIVE

The platelet phenotype in certain patients and clinical contexts may differ from healthy conditions. We evaluated platelet activation through specific receptors in healthy men and women, comparing this to patients presenting with ST-segment-elevation myocardial infarction and non-ST-segment-elevation myocardial infarction. Approach and Results: We identified independent predictors of platelet activation through certain receptors and a murine MI model further explored these findings. Platelets from healthy women and female mice are more reactive through PARs (protease-activated receptors) compared with platelets from men and male mice. Multivariate regression analyses revealed male sex and non-ST-segment-elevation myocardial infarction as independent predictors of enhanced PAR1 activation in human platelets. Platelet PAR1 signaling decreased in women and increased in men during MI which was the opposite of what was observed during healthy conditions. Similarly, in mice, thrombin-mediated platelet activation was greater in healthy females compared with males, and lesser in females compared with males at the time of MI.

CONCLUSIONS

Sex-specific signaling in platelets seems to be a cross-species phenomenon. The divergent platelet phenotype in males and females at the time of MI suggests a sex-specific antiplatelet drug regimen should be prospectively evaluated.

Systemic Inflammatory Response Syndrome After Surgery: Mechanisms and Protection

The immune system is an evolutionary hallmark of higher organisms that defends the host against invading pathogens and exogenous infections. This defense includes the recruitment of immune cells to the site of infection and the initiation of an inflammatory response to contain and eliminate pathogens. However, an inflammatory response may also be triggered by noninfectious stimuli such as major surgery, and, in case of an overshooting, still not comprehensively understood reaction, lead to tissue destruction and organ dysfunction. Unfortunately, in some cases, the immune system may not effectively distinguish between stimuli elicited by major surgery, which ideally should only require a modest inflammatory response, and those elicited by trauma or pathogenic infection. Surgical procedures thus represent a potential trigger for systemic inflammation that causes the secretion of proinflammatory cytokines, endothelial dysfunction, glycocalyx damage, activation of neutrophils, and ultimately tissue and multisystem organ destruction. In this review, we discuss and summarize currently available mechanistic knowledge on surgery-associated systemic inflammation, demarcation toward other inflammatory complications, and possible therapeutic options. These options depend on uncovering the underlying mechanisms and could include pharmacologic agents, remote ischemic preconditioning protocols, cytokine blockade or clearance, and optimization of surgical procedures, anesthetic regimens, and perioperative inflammatory diagnostic assessment. Currently, a large gap between basic science and clinically confirmed data exists due to a limited evidence base of translational studies. We thus summarize important steps toward the understanding of the precise time- and space-regulated processes in systemic perioperative inflammation.

Immunothrombosis and thromboinflammation in host defense and disease

Platelets are increasingly being recognized for playing roles beyond thrombosis and hemostasis. Today we know that they mediate inflammation by direct interactions with innate immune cells or secretion of cytokines/chemokines. Here we review their interactions with neutrophils and monocytes/macrophages in infection and sepsis, stroke, myocardial infarction and venous thromboembolism. We discuss new roles for platelet surface receptors like GPVI or GPIb and also look at platelet contributions to the formation of neutrophil extracellular traps (NETs) as well as to deep vein thrombosis during infection, e.g. in COVID-19 patients.

Platelet MAPKs-a 20+ year history: What do we really know?

The existence of mitogen activated protein kinases (MAPKs) in platelets has been known for more than 20 years. Since that time hundreds of reports have been published describing the conditions that cause MAPK activation in platelets and their role in regulating diverse platelet functions from the molecular to physiological level. However, this cacophony of reports, with inconsistent and sometimes contradictory findings, has muddied the waters leading to great confusion. Since the last review of platelet MAPKs was published more than a decade ago, there have been more than 50 reports, including the description of novel knockout mouse models, that have furthered our knowledge. Therefore, we undertook an extensive literature review to delineate what is known about platelet MAPKs. We specifically discuss what is currently known about how MAPKs are activated and what signaling cascades they regulate in platelets incorporating recent findings from knockout mouse models. In addition, we will discuss the role each MAPK plays in regulating distinct platelet functions. In doing so, we hope to clarify the role for MAPKs and identify knowledge gaps in this field that await future researchers. In addition, we discuss the limitations of current studies with a particular focus on the off-target effects of commonly used MAPK inhibitors. We conclude with a look at the clinical utility of MAPK inhibitors as potential antithrombotic therapies with an analysis of current clinical trial data.

A Cardiovascular Disease-Linked Gut Microbial Metabolite Acts via Adrenergic Receptors

Using untargeted metabolomics (n = 1,162 subjects), the plasma metabolite (m/z = 265.1188) phenylacetylglutamine (PAGln) was discovered and then shown in an independent cohort (n = 4,000 subjects) to be associated with cardiovascular disease (CVD) and incident major adverse cardiovascular events (myocardial infarction, stroke, or death). A gut microbiota-derived metabolite, PAGln, was shown to enhance platelet activation-related phenotypes and thrombosis potential in whole blood, isolated platelets, and animal models of arterial injury. Functional and genetic engineering studies with human commensals, coupled with microbial colonization of germ-free mice, showed the microbial porA gene facilitates dietary phenylalanine conversion into phenylacetic acid, with subsequent host generation of PAGln and phenylacetylglycine (PAGly) fostering platelet responsiveness and thrombosis potential. Both gain- and loss-of-function studies employing genetic and pharmacological tools reveal PAGln mediates cellular events through G-protein coupled receptors, including α2A, α2B, and β2-adrenergic receptors. PAGln thus represents a new CVD-promoting gut microbiota-dependent metabolite that signals via adrenergic receptors.

Fibroblast-specific ERK5 deficiency changes tumor vasculature and exacerbates tumor progression in a mouse model

The roles of cancer-associated fibroblasts (CAFs) have been studied in the tumor progression, and CAFs are expected to become the new targets for cancer pharmacotherapies. CAFs contribute to tumor cell survival and proliferation, tumor angiogenesis, immune suppression, tumor inflammation, tumor cell invasion and metastasis, and extracellular matrix remodeling. However, detailed mechanisms of how CAFs function in the living system remain unclear. CAFs include α-smooth muscle actin, expressing activated fibroblasts similar to myofibroblasts, and are highly capable of producing collagen. Several reports have demonstrated the contributions of extracellular-signal-regulated kinase 5 (ERK5) in fibroblasts to the fibrotic processes; however, the roles of CAF-derived ERK5 remain unclear. To investigate the roles of CAF-derived ERK5 in the tumor progression, we created mice lacking the ERK5 gene specifically in fibroblasts. Colon-26 mouse colon cancer cells were implanted into the mice subcutaneously, and the histological analyses of the tumor tissue were performed after 2 weeks. Immunofluorescence analyses showed that recipient-derived fibroblasts existed within the tumor tissue. The present study demonstrated that fibroblast-specific ERK5 deficiency exacerbated tumor progression and it was accompanied with thicker tumor vessel formation and the increase in the number of activated fibroblasts. We combined the results of The Cancer Genome Atlas (TCGA) database analysis with our animal studies, and indicated that regulating ERK5 activity in CAFs or CAF invasion into the tumor tissue can be important strategies for the development of new targets in cancer pharmacotherapies.

CD154 Induces Interleukin-6 Secretion by Kidney Tubular Epithelial Cells under Hypoxic Conditions: Inhibition by Chloroquine

Inflammation is a major contributor to tubular epithelium injury in kidney disorders, and the involvement of blood platelets in driving inflammation is increasingly stressed. CD154, the ligand of CD40, is one of the mediators supporting platelet proinflammatory properties. Although hypoxia is an essential constituent of the inflammatory reaction, if and how platelets and CD154 regulate inflammation in hypoxic conditions remain unclear. Here, we studied the control by CD154 of the proinflammatory cytokine interleukin- (IL-) 6 secretion in short-term oxygen (O₂) deprivation conditions, using the HK-2 cell line as a kidney tubular epithelial cell (TEC) model. IL-6 secretion was markedly stimulated by CD154 after 1 to 3 hours of hypoxic stress. Both intracellular IL-6 expression and secretion were stimulated by CD154 and associated with a strong upregulation of IL-6 mRNA and increased transcription. Searching for inhibitors of CD154-mediated IL-6 production by HK-2 cells in hypoxic conditions, we observed that chloroquine, a drug that has been repurposed as an anti-inflammatory agent, alleviated this induction. Therefore, CD154 is a potent early stimulus for IL-6 secretion by TECs in O₂ deprivation conditions, a mechanism likely to take part in the deleterious inflammatory consequences of platelet activation in kidney tubular injury. The inhibition of CD154-induced IL-6 production by chloroquine suggests the potential usefulness of this drug as a therapeutic adjunct in conditions associated with acute kidney injury.

The human platelet transcriptome and proteome is altered and pro-thrombotic functional responses are increased during prolonged hypoxia exposure at high altitude

Exposure to hypoxia, through ascension to high altitudes (HAs), air travel, or human disease, is associated with an increased incidence of thrombosis in some settings. Mechanisms underpinning this increased thrombosis risk remain incompletely understood, and the effects of more sustained hypoxia on the human platelet molecular signature and associated functional responses have never been examined. We examined the effects of prolonged (≥2 months continuously) hypobaric hypoxia on platelets isolated from subjects residing at HA (3,700 meters) and, for comparison, matched subjects residing under normoxia conditions at sea level (50 meters). Using complementary transcriptomic, proteomic, and functional methods, we identified that the human platelet transcriptome is markedly altered under prolonged exposure to hypobaric hypoxia at HA. Among the significantly, differentially expressed genes (mRNA and protein), were those having canonical roles in platelet activation and thrombosis, including membrane glycoproteins (e.g. GP4, GP6, GP9), integrin subunits (e.g. ITGA2B), and alpha-granule chemokines (e.g. SELP, PF4V1). Platelets from subjects residing at HA were hyperactive, as demonstrated by increased engagement and adhesion to fibrinogen, fewer alpha granules by transmission electron microscopy, increased circulating PF4 and ADP, and significantly enhanced clot retraction. In conclusion, we identify that prolonged hypobaric hypoxia exposure due to HA alters the platelet transcriptome and proteome, triggering increased functional activation responses that may contribute to thrombosis. Our findings may also have relevance across a range of human diseases where chronic hypoxia, platelet activation, and thrombosis are increased.

The Platelet Napoleon Complex-Small Cells, but Big Immune Regulatory Functions

Platelets have dual physiologic roles as both cellular mediators of thrombosis and immune modulatory cells. Historically, the thrombotic function of platelets has received significant research and clinical attention, but emerging research indicates that the immune regulatory roles of platelets may be just as important. We now know that in addition to their role in the acute thrombotic event at the time of myocardial infarction, platelets initiate and accelerate inflammatory processes that are part of the pathogenesis of atherosclerosis and myocardial infarction expansion. Furthermore, it is increasingly apparent from recent studies that platelets impact the pathogenesis of many vascular inflammatory processes such as autoimmune diseases, sepsis, viral infections, and growth and metastasis of many types of tumors. Therefore, we must consider platelets as immune cells that affect all phases of immune responses.