Spontaneous bleeding in thrombocytopenia: Is it really spontaneous?

The role of platelets and megakaryocytes in sepsis and ARDS

Since the global COVID-19 pandemic, there has been a renewed focus on lung injury during infection. Systemic inflammatory responses such as acute respiratory distress syndrome (ARDS) and sepsis are a leading cause of morbidity and mortality for both adults and children. Improvements in clinical care have improved outcomes but mortality remains ∼40% and significant morbidity persists for those patients with severe disease. Mechanistic studies of the underlying biological processes remain essential to identifying therapeutic targets. Furthermore, methods for identifying the underlying drivers of organ failure are key to treating and preventing tissue injury. In this review, we discuss the contribution of megakaryocytes (MKs) and platelets to the pathogenesis of systemic inflammatory syndromes. We explore the role of MKs and the new identification of extramedullary MKs during sepsis. We describe the alterations in the platelet transcriptome during sepsis. Lastly, we explore platelet function as defined by aggregation, activation and the formation of heterotypic aggregates. Much more work is necessary to explore the contribution of platelets to these heterogenous syndromes, but the foundation of platelets as key contributors to inflammation has been laid.

Hemostasis without clot formation: how platelets guard the vasculature in inflammation, infection, and malignancy

Platelets are key vascular effectors in hemostasis, with activation signals leading to fast recruitment, aggregation, and clot formation. The canonical process of hemostasis is well-characterized and shares many similarities with pathological thrombus formation. However, platelets are also crucially involved in the maintenance of vascular integrity under both steady-state and inflammatory conditions by ensuring blood vessel homeostasis and preventing microbleeds. In these settings, platelets use distinct receptors, signaling pathways, and ensuing effector functions to carry out their deeds. Instead of simply forming clots, they mainly act as individual sentinels that swiftly adapt their behavior to the local microenvironment. In this review, we summarize previously recognized and more recent studies that have elucidated how anucleate, small platelets manage to maintain vascular integrity when faced with challenges of infection, sterile inflammation, and even malignancy. We dissect how platelets are recruited to the vascular wall, how they identify sites of injury, and how they prevent hemorrhage as single cells. Furthermore, we discuss mechanisms and consequences of platelets' interaction with leukocytes and endothelial cells, the relevance of adhesion as well as signaling receptors, in particular immunoreceptor tyrosine-based activation motif receptors, and cross talk with the coagulation system. Finally, we outline how recent insights into inflammatory hemostasis and vascular integrity may aid in the development of novel therapeutic strategies to prevent hemorrhagic events and vascular dysfunction in patients who are critically ill.

Spontaneous Bilateral Hyphema in a Patient With Idiopathic Thrombocytopenic Purpura

The aim of this case report is to present an unusual case of idiopathic thrombocytopenic purpura (ITP) with bilateral spontaneous hyphema. It refers to an 82-year-old Caucasian woman who presented with acute unilateral vision loss. The patient's medical history includes arterial hypertension, hypothyroidism, and uneventful bilateral cataract surgery. Bilateral anterior chamber hyphema was noted on gonioscopy, along with unilateral corneal edema. Hematology workup set the diagnosis of ITP. The cause of spontaneous bleeding in ITP patients is explained by the "second hit" hypothesis, suggesting that a secondary factor such as high blood pressure or minor trauma is necessary to cause rupture to a vessel's wall, which is already affected by the low platelet counts. The authors propose that, in this patient, the "second hit" was likely due to basement membrane alterations caused by arterial hypertension. The rarity of bilateral spontaneous hyphema cases and possible etiologies are emphasized.

Thromboinflammatory challenges in stroke pathophysiology

Despite years of encouraging translational research, ischemic stroke still remains as one of the highest unmet medical needs nowadays, causing a tremendous burden to health care systems worldwide. Following an ischemic insult, a complex signaling pathway emerges leading to highly interconnected thrombotic as well as neuroinflammatory signatures, the so-called thromboinflammatory cascade. Here, we thoroughly review the cell-specific and time-dependent role of different immune cell types, i.e., neutrophils, macrophages, T and B cells, as key thromboinflammatory mediators modulating the neuroinflammatory response upon stroke. Similarly, the relevance of platelets and their tight crosstalk with a variety of immune cells highlights the relevance of this cell-cell interaction during microvascular dysfunction, neovascularization, and cellular adhesion. Ultimately, we provide an up-to-date overview of therapeutic approaches mechanistically targeting thromboinflammation currently under clinical translation, especially focusing on phase I to III clinical trials.

Direct Thrombin Inhibitor Dabigatran Compromises Pulmonary Endothelial Integrity in a Murine Model of Breast Cancer Metastasis to the Lungs; the Role of Platelets and Inflammation-Associated Haemostasis

Activation of the coagulation cascade favours metastatic spread, but antithrombotic therapy might also have detrimental effects on cancer progression. In this study, we characterized the effects of dabigatran, a direct reversible thrombin inhibitor, on the pulmonary endothelial barrier and metastatic spread in a murine model of breast cancer metastasis. Dabigatran etexilate (100 mg kg−1) was administered to mice twice daily by oral gavage. Pulmonary metastasis, pulmonary endothelium permeability in vivo, and platelet reactivity were evaluated after intravenous injection of 4T1 breast cancer cells into BALB/c mice. The effect of dabigatran on platelet-dependent protection of pulmonary endothelial barrier in the presence of an inflammatory stimulus was also verified in vitro using human lung microvascular endothelial cell (HLMVEC) cultures. Dabigatran-treated mice harbored more metastases in their lungs and displayed increased pulmonary endothelium permeability after cancer cell injection. It was not associated with altered lung fibrin deposition, changes in INFγ, or complement activation. In the in vitro model of the pulmonary endothelial barrier, dabigatran inhibited platelet-mediated protection of pulmonary endothelium. In a murine model of breast cancer metastasis, dabigatran treatment promoted pulmonary metastasis by the inhibition of platelet-dependent protection of pulmonary endothelial barrier integrity.

[Epidemiology of spontaneous nasal, ear and throat bleedings]

Bleeding is a life-threatening condition, requiring an urgent care. The first line of treatment this kind of patients is ambulance doctors (emergency medical team). Spontaneous bleeding (SB), in this case, don't have a traumatic agent (including surgical trauma).

STUDY OBJECTIVE

The purpose of this study was to evaluate spontaneous bleeding epidemiological profile of Moscow city emergency service.

METHODS

Study included statistical reports of Moscow city emergency services medical teams (EMT) were servicing adults. We analyzed total number of calls and number of EMT calls to pa-tients with SB during the period between 2015 and 2019. The excluding criteria was EMT re-calls to patents with SB.

RESULTS

In a study, it was found that over five-year period of observation, EMT made 15 709 862 calls, included 215 840 calls (1.37%) to patients with SB. It was found that the most frequency sources of SB were: the gastrointestinal tract (33.18%), the nasal cavity (28.14%) and the vagina with the uterus (23.91%). There is the proportion of patients suffering of SB from ENT organs is 28.52% in structure of Moscow city Emergency Medical Service. There are the proportion of epistaxis 98.65%, ear bleeding - 0.89%, throat bleeding - 0.46% in structure of SB from ENT organs. We analyzed, that spontaneous epistaxis most frequent between October and April. This period characterized with 70.6% EMT calls from the total EMT calls to patients with SE.

Meropenem-induced thrombocytopenia: a paediatric case

Meropenem is a broad-spectrum carbapenem widely used to treat both Gram-positive and negative bacterial infections, including extended-spectrum beta-lactamase-producing microbes. We describe the occurrence of thrombocytopenia and hypersensitivity in a boy receiving intravenous meropenem for intra-abdominal sepsis secondary to perforated appendicitis. The patient developed a pruritic maculopapular rash with occasional petechiae, associated with severe thrombocytopenia, after 7 days of meropenem administration. Investigations for other causes of thrombocytopenia, including possible line sepsis, were unfruitful, and the thrombocytopenia did not resolve until cessation of meropenem. Drug-induced reactions should be considered in children receiving meropenem who present with a rash and thrombocytopenia.

Bleeding frequency during physiotherapy in thrombocytopenic patients undergoing hematopoietic stem cell transplantation

BACKGROUND

During hematopoietic stem cell transplantation (HSCT) the patients perform activities of low and moderate intensity because have reduced hematological lineages, leaving them susceptible to hemorrhagic events. The objective of this study was to describe the frequency of bleeding events, severity, and possible association with physical exercise in thrombocytopenic patients.

METHODS

A retrospective study with seventy-seven HSCT patients hospitalised, that had a platelet count ≤ 50,000 /μL and received physical exercise during physiotherapy intervention.

RESULTS

Regarding bleeding events, only six were related to physical exercise, and bleeding events occurred more frequently at platelet levels ≤ 10,000 /μL. The most frequent bleeding event was epistaxis, considered of low severity, and with the moderate possibility of being related to physical exercise; followed by extremity hematoma, considered of medium severity and highly related to physical exercise. In this study, there was no occurrence of bleeding events considered of high severity.

CONCLUSION

Bleeding frequency in supervised physical exercise during physiotherapy in adults with thrombocytopenia undergoing HSCT is minor and relatively rare but occurs more frequently in patients with platelet count ≤10,000 /μL. These results encourage the maintenance of physical activity in this population who is at high risk of developing immobility-related complications.

Investigating the Multi-Faceted Nature of Radiation-Induced Coagulopathies in a Göttingen Minipig Model of Hematopoietic Acute Radiation Syndrome

Coagulopathies are well documented after acute radiation exposure at hematopoietic doses, and radiation-induced bleeding is notably one of the two main causes of mortality in the hematopoietic acute radiation syndrome. Despite this, understanding of the mechanisms by which radiation alters hemostasis and induces bleeding is still lacking. Here, male Göttingen minipigs received hematopoietic doses of 60Co gamma irradiation (total body) and coagulopathies were characterized by assessing bleeding, blood cytopenia, fibrin deposition, changes in hemostatic properties, coagulant/anticoagulant enzyme levels, and markers of inflammation, endothelial dysfunction, and barrier integrity to understand if a relationship exists between bleeding, hemostatic defects, bone marrow aplasia, inflammation, endothelial dysfunction and loss of barrier integrity. Acute radiation exposure induced coagulopathies in the Göttingen minipig model of hematopoietic acute radiation syndrome; instances of bleeding were not dependent upon thrombocytopenia. Neutropenia, alterations in hemostatic parameters and damage to the glycocalyx occurred in all animals irrespective of occurrence of bleeding. Radiation-induced bleeding was concurrent with simultaneous thrombocytopenia, anemia, neutropenia, inflammation, increased heart rate, decreased nitric oxide bioavailability and endothelial dysfunction; bleeding was not observed with the sole occurrence of a single aforementioned parameter in the absence of the others. Alteration of barrier function or clotting proteins was not observed in all cases of bleeding. Additionally, fibrin deposition was observed in the heart and lungs of decedent animals but no evidence of DIC was noted, suggesting a unique pathophysiology of radiation-induced coagulopathies. These findings suggest radiation-induced coagulopathies are the result of simultaneous damage to several key organs and biological functions, including the immune system, the inflammatory response, the bone marrow and the cardiovasculature.

The endothelial barrier and cancer metastasis: Does the protective facet of platelet function matter?

Overwhelming evidence suggests that platelets have a detrimental role in promoting cancer spread via platelet-cancer cell interactions linked to thrombotic mechanisms. On the other hand, a beneficial role of platelets in the preservation of the endothelial barrier in inflammatory conditions has been recently described, a phenomenon that could also operate in cancer-related inflammation. It is tempting to speculate that some antiplatelet strategies to combat cancer metastasis may impair the endogenous platelet-dependent mechanisms preserving endothelial barrier function. If the protective function of platelets is impaired, it may lead to increased endothelial permeability and more efficient cancer cell intravasation in the primary tumor and cancer cell extravasation at metastatic sites. In this commentary, we discuss current evidence that could support this hypothesis.

Acquired Glanzmann thrombasthenia: From antibodies to anti-platelet drugs

In contrast to the inherited platelet disorder given by mutations in the ITGA2B and ITGB3 genes, mucocutaneous bleeding from a spontaneous inhibition of normally expressed αIIbβ3 characterizes acquired Glanzmann thrombasthenia (GT). Classically, it is associated with autoantibodies or paraproteins that block platelet aggregation without causing a fall in platelet count. However, inhibitory antibodies to αIIbβ3 are widely associated with primary immune thrombocytopenia (ITP), occur in secondary ITP associated with leukemia and related disorders, solid cancers and myeloma, other autoimmune diseases, following organ transplantation while cytoplasmic dysregulation of αIIbβ3 function features in myeloproliferative and myelodysplastic syndromes. Antibodies to αIIbβ3 occur during viral and bacterial infections, while drug-dependent antibodies reacting with αIIbβ3 are a special case. Direct induction of acquired GT is a feature of therapies that block platelets in coronary artery disease. This review looks at these conditions, emphasizing molecular mechanisms, therapy, patient management and future directions for research.