Контракция (ретракция) сгустков крови и тромбов: патогенетическое и клиническое значение

This review is the frst systematic description of spontaneous blood clot shrinkage, aka clot retraction or contraction. The driver of this process is the contraction of the actin-myosin complex inside activated platelets. The platelet contractile force is transmitted via focal contacts to extracellular fbrin fbers, causing compaction of the three-dimensional fbrin network along with the embedded erythrocytes. The main structural consequences of clot contraction include redistribution of the fbrin-platelet meshwork toward the periphery of the clot and compression of erythrocytes in the core of the clot followed by their deformation into polyhedral cells called “polyhedrocytes”. These structural signatures of clot contraction in ex vivo thrombi and thrombotic emboli derived from various locations indicate that thrombi undergo intravital contraction within blood vessels in vivo. Pathogenic consequences of clot contraction may vary. Thus, contraction of a thrombus changes the vessel lumen, thereby modulating local blood flow in the thrombotic occlusion area. Thrombus shrinkage changes its porosity and permeability for fbrinolytic enzymes. The extent of thrombus compression and densifcation can determine the likelihood of its mechanical rupture, i. e. thrombotic embolization. Several clinical studies have revealed that clot contraction is suppressed in the blood of patients with (pro)thrombotic conditions, such as ischemic stroke, venous thrombosis, and systemic lupus erythematosus. This reduction of clot contraction is due to platelet dysfunction caused by their chronic hyperactivation and energetic exhaustion. Clot contraction depends significantly on cellular and protein composition of the blood; in particular, a high hematocrit and hyperfbrinogenemia both reduce clot contraction, while activated monocytes enhance clot contraction by expressing tissue factor and promoting thrombin generation. The degree of clot contraction abnormalities in thrombotic states generally correlates with disease severity, which confrms the pathogenic importance of clot contraction. In patients with pulmonary embolism clot contraction is decreased signifcantly compared to that in isolated venous thrombosis, indirectly suggesting that a less compacted thrombus is more prone to embolization. This observation points to a potential diagnostic and prognostic value of the clot contraction assay as a novel test for ongoing or threatening thromboembolism. Collectively, contraction of blood clots and thrombi is an underappreciated and understudied process that has a major pathogenic and clinical signifcance in (pro)thrombotic conditions of various etiologies.Обзор представляет собой первое систематическое описание самопроизвольного сжатия сгустков крови, известного под названием ретракции, или контракции. Движущая сила этого процесса – сокращение актомиозинового комплекса внутри активированных тромбоцитов. Сократительная сила тромбоцитов передается через фокальные контакты на волокна фибрина, вызывая компактизацию трехмерной фибриновой сети и заключенных в ней эритроцитов. Главными структурными последствиями контракции сгустков крови считаются перераспределение фибрино-тромбоцитарных агрегатов на поверхность сгустка и компрессия эритроцитов в центре сгустка, их деформация с образованием многогранников (полиэдров), названных полиэдроцитами. Наличие морфологических признаков контракции в ex vivo тромбах и тромботических эмболах разной локализации свидетельствует о том, что они претерпевают прижизненную внутрисосудистую контракцию in vivo. Патогенетические последствия контракции тромбов могут быть разными. Так, степень контракции тромба изменяет просвет сосуда и тем самым модулирует локальную гемодинамику в области тромботической окклюзии; сжатие тромба меняет его порозность и проницаемость для фибринолитических ферментов; степень уплотнения может определять риск эмболизации, то есть отрыва тромба. Клинические исследования показали, что в крови больных с (про)тромботическими состояниями, такими как ишемический инсульт, венозный тромбоз, системная красная волчанка, контрактильная способность сгустков существенно угнетена вследствие дисфункции тромбоцитов, обусловленной их хронической гиперактивацией и энергетическим истощением. Контракция сгустков существенно зависит от белкового и клеточного состава крови, в частности, высокий гематокрит и гиперфибриногенемия угнетают контракцию, а активированные моноциты усиливают сокращение тромбоцитов путем экспрессии тканевого фактора и усиления генерации тромбина. Степень нарушения контракции сгустков крови при тромботических состояниях в целом коррелирует с тяжестью заболевания, что указывает на патогенетическое значение контракции. Достоверное снижение степени контракции у пациентов с легочной тромбоэмболией по сравнению с изолированным венозным тромбозом косвенно подтверждает, что менее сжатый тромб более склонен к эмболизации. Это говорит о потенциальном диагностическом и прогностическом значении лабораторного теста на контракцию сгустков крови как признака текущей или угрожающей тромбоэмболии. По совокупности имеющихся данных, контракция сгустков крови и тромбов представляет собой недооцененный и малоизученный процесс, который имеет большое патогенетическое и клиническое значение при тромбозах и предтромботических состояниях различной этиологии

Impaired contraction of blood clots precedes and predicts postoperative venous thromboembolism

© 2020, The Author(s). Deep vein thrombosis (DVT) is a common but unpredictable complication of surgical interventions. To reveal an association between the blood clot contraction (retraction) and the incidence of postoperative venous thrombosis, 78 patients with brain tumors that were operated on were studied, of which 23 (29%) were diagnosed with postoperative DVT. A clot contraction assay, along with other hemostatic and hematologic tests, was performed 1–3 days before the surgery and on the 1st day and 5–7th days after the surgery. On the 1st postoperative day, clot contraction was significantly suppressed in patients who subsequently developed DVT, compared to the patients without DVT. Importantly, this difference was observed at least 5 days before DVT had developed. The weakening of contraction on the 1st postoperative day was more pronounced in the DVT patients with malignant versus benign brain tumors, atherosclerosis, hypertension, as well as in patients receiving steroids before and during the operation. These results indicate that impaired clot contraction in the postoperative period is associated with imminent DVT, suggesting that it is a prothrombotic risk factor and promotional mechanism. The clot contraction assay has a predictive value in assessing the threat of postoperative thrombosis in patients with benign and malignant brain tumors

Changes in the parameters of thrombodynamics and blood clot contraction in patients with rheumatoid arthritis

© 2020 Ima-Press Publishing House. All rights reserved. Autoimmune diseases, including rheumatoid arthritis (RA), are risk factors for thrombotic events. Understanding the pathogenetic role of hemostatic changes in RA can assist in developing measures for prevention, prognosis, early diagnosis, and treatment of immune thromboses. Objective: to investigate the state of platelet and plasma hemostasis in patients with RA, as compared to other laboratory parameters and clinical manifestations of the disease. Subjects and methods. Hemostasis was investigated using two relatively new laboratory tests: thrombodynamics and kinetics of blood clot contraction (BCC). Examinations were made in 60 patients with RA and in 50 apparently healthy individuals of the control group. Results and discussion. In patients with RA, the parameters of thrombodynamics and BCC were found to be significantly different from the normal values. According to thrombodynamics, there was an increase in plasma clot growth rate, size, and density, which indicates chronic hypercoagulation. The rate and completeness of BCC were substantially reduced due to platelet dysfunction in patients with RA compared to healthy individuals. The changes in the parameters of thrombodynamics and BCC correlated with the laboratory signs of systemic inflammation and depended on the radiographic stage of the disease. Conclusion. The results of this investigation confirm that hemostatic disorders are present in RA and indicate the informative value of thrombodynamics and BCC tests as indicators of a pre-thrombotic state, including autoimmune pathology

Accelerated spatial fibrin growth and impaired contraction of blood clots in patients with rheumatoid arthritis

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. Rheumatoid arthritis (RA) is an autoimmune disease associated with thrombotic complications. To elucidate pathogenic mechanisms, hemostatic disorders in RA were correlated with other laboratory and clinical manifestations. Hemostasis was assessed using relatively new complementary tests, the spatial growth of a plasma clot (Thrombodynamics assay), and contraction of whole blood clots. Platelet functionality was assessed with flow cytometry that quantified the expression of P-selectin and the fibrinogen-binding capacity of platelets before and after activation with a thrombin receptor-activating peptide. Parameters of fibrin clot growth and the kinetics of contraction of blood clots were significantly altered in patients with RA compared to the control group. In Thrombodynamics measurements, an increase in the clot growth rate, size, and optical density of plasma clots altogether indicated chronic hypercoagulability. The rate and extent of blood clot contraction in patients with RA was significantly reduced and associated with platelet dysfunction revealed by an impaired response to activation. Changes in the parameters of clot growth and contraction correlated with the laboratory signs of systemic inflammation, including hyperfibrinogenemia. These results confirm the pathogenic role of hemostatic disorders in RA and support the validity of fibrin clot growth and the blood clot contraction assay as indicators of a (pro)thrombotic state

Effects of hyperhomocysteinemia on the platelet-driven contraction of blood clots

Hyperhomocysteinemia (HHcy) is associated with thrombosis, but the mechanistic links between them are not understood. We studied effects of homocysteine (Hcy) on clot contraction in vitro and in a rat model of HHcy. Incubation of blood with exogenous Hcy for 1 min enhanced clot contraction, while 15-min incubation led to a dose-dependent suppression of contraction. These effects were likely due to direct Hcy-induced platelet activation followed by exhaustion, as revealed by an increase in fibrinogen-binding capacity and P-selectin expression determined by flow cytometry. In the blood of rats with HHcy, clot contraction was enhanced at moderately elevated Hcy levels (10-50 µM), while at higher Hcy levels (>50 µM), the onset of clot contraction was delayed. HHcy was associated with thrombocytosis combined with a reduced erythrocyte count and hypofibrinogenemia. These data suggest that in HHcy, platelets get activated directly and indirectly, leading to enhanced clot contraction that is facilitated by the reduced content and resilience of fibrin and erythrocytes in the clot. The excessive platelet activation can lead to exhaustion and impaired contractility, which makes clots larger and more obstructive. In conclusion, HHcy modulates blood clot contraction, which may comprise an underappreciated pro- or antithrombotic mechanism

Quantitative and qualitative changes in blood cells associated with COVID-19

Aim. To establish the relationship of hematological disorders with the pathogenesis, course and outcomes of COVID-19. Methods. We examined 235 hospitalized patients with moderate and severe forms of acute COVID-19 receiving anticoagulants and immunosuppressive drugs. We studied the full blood cell counts and morphology along with the platelet function by flow cytometry in comparison with the clinical features and synthesis of inflammatory markers. To assess platelet contractility, blood clot contraction (retraction) kinetics was used in combination with scanning electron microscopy of platelets and blood clots. Results. Hemolytic anemia, neutrophilia and lymphopenia were associated with immature erythrocytes and leukocytes, indicating activation of hematopoiesis. Contraction of blood clots in COVID-19 was impaired, especially in severe and lethal cases, as well as in the presence of comorbidities, including myeloproliferative and coronary heart diseases and acute cerebrovascular disease. In male patients, the changes in clot contraction were more pronounced. Suppression of clot contraction correlated directly with anemia and coagulopathy, including a high D-dimer level, which confirms the pathogenetic significance of blood clot contraction in COVID-19. A decrease in platelet contractility was due to moderate thrombocytopenia in combination with chronic platelet activation and secondary platelet dysfunction. The structure and cellular composition of blood clots depended on the extent of contraction; clots with impaired contraction were porous, had a low content of deformed polyhedral erythrocytes (polyhedrocytes) and an even distribution of fibrin. Conclusion. Blood cells undergoing both quantitative and qualitative changes are involved in the pathogenesis of COVID-19; the suppressed platelet-driven contraction of intravital blood clots may be a part of the prothrombotic mechanisms

The distinctive structure and composition of arterial and venous thrombi and pulmonary emboli

© 2020, The Author(s). Although arterial and venous thromboembolic disorders are among the most frequent causes of mortality and morbidity, there has been little description of how the composition of thrombi and emboli depends on their vascular origin and age. We quantified the structure and composition of arterial and venous thrombi and pulmonary emboli using high-resolution scanning electron microscopy. Arterial thrombi contained a surprisingly large amount of fibrin, in addition to platelets. The composition of pulmonary emboli mirrored the most distal part of venous thrombi from which they originated, which differed from the structure of the body and head of the same thrombi. All thrombi and emboli contained few biconcave red blood cells but many polyhedrocytes or related forms of compressed red blood cells, demonstrating that these structures are a signature of clot contraction in vivo. Polyhedrocytes and intermediate forms comprised the major constituents of venous thrombi and pulmonary emboli. The structures within all of the thrombi and emboli were very tightly packed, in contrast to clots formed in vitro. There are distinctive, reproducible differences among arterial and venous thrombi and emboli related to their origin, destination and duration, which may have clinical implications for the understanding and treatment of thrombotic disorders

Altered platelet and coagulation function in moderate-to-severe COVID-19

To reveal if coagulopathies relate to the course of COVID-19, we examined 255 patients with moderate and severe COVID-19, receiving anticoagulants and immunosuppressive drugs. Coagulopathy manifested predominantly as hypercoagulability that correlated directly with systemic inflammation, disease severity, comorbidities, and mortality risk. The prolonged clotting tests in about ¼ of cases were associated with high levels of C-reactive protein and antiphospholipid antibodies, which impeded coagulation in vitro. Contraction of blood clots was hindered in about ½ of patients, especially in severe and fatal cases, and correlated directly with prothrombotic parameters. A decrease in platelet contractility was due to moderate thrombocytopenia in combination with platelet dysfunction. Clots with impaired contraction were porous, had a low content of compressed polyhedral erythrocytes (polyhedrocytes) and an even distribution of fibrin, suggesting that the uncompacted intravital clots are more obstructive but patients could also be prone to bleeding. The absence of consumption coagulopathy suggests the predominance of local and/or regional microthrombosis rather than disseminated intravascular coagulation. The results obtained (i) confirm the importance of hemostatic disorders in COVID-19 and their relation to systemic inflammation; (ii) justify monitoring of hemostasis, including the kinetics of blood clot contraction; (iii) substantiate the active prophylaxis of thrombotic complications in COVID-19