Contraction of Blood Clots Is Impaired in Acute Ischemic Stroke

Thrombosis and Aging: Fibrin Clot Properties and Oxidative Stress

Significance: Aging is a complex process associated with an increased risk of many diseases, including thrombosis. This review summarizes age-related prothrombotic mechanisms in clinical settings of thromboembolism, focusing on the role of fibrin structure and function modified by oxidative stress. Recent Advances: Aging affects blood coagulation and fibrinolysis via multiple mechanisms, including enhanced oxidative stress, with an imbalance in the oxidant/antioxidant mechanisms, leading to loss of function and accumulation of oxidized proteins, including fibrinogen. Age-related prothrombotic alterations are multifactorial involving enhanced platelet activation, endothelial dysfunction, and changes in coagulation factors and inhibitors. Formation of more compact fibrin clot networks displaying impaired susceptibility to fibrinolysis represents a novel mechanism, which might contribute to atherothrombosis and venous thrombosis. Alterations to fibrin clot structure/function are at least in part modulated by post-translational modifications of fibrinogen and other proteins involved in thrombus formation, with a major impact of carbonylation. Fibrin clot properties are also involved in the efficacy and safety of therapy with oral anticoagulants, statins, and/or aspirin. Critical Issues: Since a prothrombotic state is observed in very elderly individuals free of diseases associated with thromboembolism, the actual role of activated blood coagulation in health remains elusive. It is unclear to what extent oxidative modifications of coagulation and fibrinolytic proteins, in particular fibrinogen, contribute to a prothrombotic state in healthy aging. Future Directions: Ongoing studies will show whether novel therapies that may alter oxidative stress and fibrin characteristics are beneficial to prevent atherosclerosis and thromboembolic events associated with aging.

Contribution of Red Blood Cells and Platelets to Blood Clot Computed Tomography Imaging and Compressive Mechanical Characteristics

Thrombus computed tomography (CT) imaging characteristics may correspond with thrombus mechanical properties and thus predict thrombectomy success. The impact of red blood cell (RBC) content on these properties (imaging and mechanics) has been widely studied. However, the additional effect of platelets has not been considered. The objective of the current study was to examine the individual and combined effects of blood clot RBC and platelet content on resultant CT imaging and mechanical characteristics. Human blood clot analogues were prepared from a combination of preselected RBC volumes and platelet concentrations to decouple their contributions. The resulting clot RBC content (%) and platelet content (%) were determined using Martius Scarlet Blue and CD42b staining, respectively. Non-contrast and contrast-enhanced CT (NCCT and CECT) scans were performed to measure the clot densities. CECT density increase was taken as a proxy for clinical perviousness. Unconfined compressive mechanics were analysed by performing 10 cycles of 80% strain. RBC content is the major determinant of clot NCCT density. However, additional consideration of the platelet content improves the association. CECT density increase is influenced by clot platelet and not RBC content. Platelet content is the dominant component driving clot stiffness, especially at high strains. Both RBC and platelet content contribute to the clot's viscoelastic and plastic compressive properties. The current in vitro results suggest that CT density is reflective of RBC content and subsequent clot viscoelasticity and plasticity, and that perviousness reflects the clot's platelet content and subsequent stiffness. However, these indications should be confirmed in a clinical stroke cohort.

The differences of fibrinogen levels in various types of hemorrhagic transformations

Introduction

Hemorrhagic transformation (HT) is a serious complication that can occur spontaneously after an acute ischemic stroke (AIS) or after a thrombolytic/mechanical thrombectomy. Our study aims to explore the potential correlations between fibrinogen levels and the occurrence of spontaneous HT (sHT) and HT after mechanical thrombectomy (tHT).

Methods

A total of 423 consecutive AIS patients diagnosed HT who did not undergone thrombolysis and 423 age- and sex-matched patients without HT (non-HT) were enrolled. Fibrinogen levels were measured within 24 h of admission after stroke. The cohorts were trisected according to fibrinogen levels. The HT were further categorized into hemorrhagic infarction (HI) or parenchymal hematoma (PH) based on their imaging characteristics.

Results

In sHT cohort, fibrinogen levels were higher in HT patients than non-HT patients (p < 0.001 versus p = 0.002). High fibrinogen levels were associated with the severity of HT. HT patients without atrial fibrillation (AF) had higher levels of fibrinogen compared to non-HT (median 3.805 vs. 3.160, p < 0.001). This relationship did not differ among AF patients. In tHT cohort, fibrinogen levels were lower in HT patients than non-HT patients (p = 0.002). Lower fibrinogen levels were associated with the severity of HT (p = 0.004). The highest trisection of fibrinogen both in two cohorts were associated with HT [sHT cohort: OR = 2.515 (1.339-4.725), p = 0.016; that cohort: OR = 0.238 (0.108-0.523), p = 0.003].

Conclusion

Our study suggests that lower fibrinogen level in sHT without AF and higher fibrinogen level in tHT are associated with more severe HT.

Ischaemic Stroke, Thromboembolism and Clot Structure

Ischaemic stroke is a major cause of morbidity and mortality worldwide. Blood clotting and thromboembolism play a central role in the pathogenesis of ischaemic stroke. An increasing number of recent studies indicate changes in blood clot structure and composition in patients with ischaemic stroke. In this review, we aim to summarise and discuss clot structure, function and composition in ischaemic stroke, including its relationships with clinical diagnosis and treatment options such as thrombolysis and thrombectomy. Studies are summarised in which clot structure and composition is analysed both in vitro from patients' plasma samples and ex vivo in thrombi obtained through interventional catheter-mediated thrombectomy. Mechanisms that drive clot composition and architecture such as neutrophil extracellular traps and clot contraction are also discussed. We find that, while in vitro clot structure in plasma samples from ischaemic stroke patients are consistently altered, showing denser clots that are more resistant to fibrinolysis, current data on the composition and architecture of ex vivo clots obtained by thrombectomy are more variable. With the potential of advances in technologies underpinning both the imaging and retrieving of clots, we expect that future studies in this area will generate new data that is of interest for the diagnosis, optimal treatment strategies and clinical management of patients with ischaemic stroke.

Acute Ischemic Stroke Thrombus Composition

Ischemic stroke is caused by a thrombus blocking one or multiple arteries in the brain, resulting in irreversible damage in the associated brain tissue. The aim of therapy is to restore the blood flow as fast as possible. Two recanalization strategies are currently available: pharmacological thrombolysis using recombinant tissue plasminogen activator (rt-PA) and mechanical removal of the thrombus. Despite recent advancements, achieving efficient recanalization remains a challenge. The precise causes of therapy failure are not fully understood but thrombus composition is likely a key factor in successful recanalization. This review explores acute ischemic stroke thrombus composition, its recently identified components, and how it affects stroke treatment. It also discusses how new insights could enhance current recanalization strategies for ischemic stroke patients.

The effect of ultrasound-assisted thrombolysis studied in blood-on-a-chip

BACKGROUND

Thromboembolism, which leads to pulmonary embolism and ischemic stroke, remains one of the main causes of death. Ultrasound-assisted thrombolysis (UAT) is an effective thrombolytic method. However, further studies are required to elucidate the mechanism of ultrasound on arterial and venous thrombi.

METHODS

We employed the blood-on-a-chip technology to simulate thrombus formation in coronary stenosis and deep vein valves. Subsequently, UAT was conducted on the chip to assess the impact of ultrasound on thrombolysis under varying flow conditions. Real-time fluorescence was used to assess thrombolysis and drug penetration. Finally, scanning electron microscopy and immunofluorescence were used to determine the effect of ultrasound on fibrinolysis.

RESULTS

The study revealed that UAT enhanced the thrombolytic rate by 40% in the coronary stenosis chip and by 10% in the deep venous valves chip. This enhancement is attributed to the disruption of crosslinked fibrin fibers by ultrasound, leading to increased urokinase diffusion within the thrombus and accumulation of plasminogen on the fibrinogen α chain. Moreover, the acceleration of the dissolution rate of thrombi in the venous valve chip by ultrasound was not as significant as that in the coronary stenosis chip.

CONCLUSION

These findings highlight the differential impact of ultrasound on thrombolysis under various flow conditions and emphasize the valuable role of the blood-on-a-chip technology in exploring thrombolysis mechanisms.

A novel technique to quantify the kinetics of blood clot contraction based on the expulsion of fluorescently labeled albumin into serum

BACKGROUND

The platelet-driven contraction or retraction of blood clots has been utilized to obtain blood serum for laboratory studies, but now, in vitro clot contraction assays are used in research laboratories and clinics to assess platelet functionality. The static final extent of clot contraction measured using a clot size or expelled serum volume can be supplemented substantially with a dynamic analysis.

OBJECTIVES

To provide a step-by-step protocol for a relatively simple and affordable new automated methodology to follow the kinetics of blood clot contraction, which allows for simultaneous measurements of various samples at a time and requires only a fluorescence plate reader.

METHODS

The kinetics of clot contraction in whole blood was assessed by continuously detecting the fluorescence intensity of fluorescein isothiocyanate-albumin added to a blood sample before clotting and expelled into the serum during clot shrinkage.

RESULTS

The clots are formed and fluorescence is measured in the wells of a black multiwell plate using a standard plate fluorescent reader. The specificity of this technique for clot contraction has been demonstrated by the strong inhibitory effects of blebbistatin, latrunculin A, and abciximab. To validate the new technique, increased fluorescence intensity in the contracting clots was measured in parallel with a visual decrease in clot size performed with the same blood samples.

CONCLUSION

The resulting clot contraction dynamics based on the expulsion of fluorescein isothiocyanate-albumin can be quantified using a number of kinetic parameters as well as a phase kinetics analysis. The advantages and drawbacks of the new technique are discussed.

Mechanics and microstructure of blood plasma clots in shear driven rupture

Intravascular blood clots are subject to hydrodynamic shear and other forces that cause clot deformation and rupture (embolization). A portion of the ruptured clot can block blood flow in downstream vessels. The mechanical stability of blood clots is determined primarily by the 3D polymeric fibrin network that forms a gel. Previous studies have primarily focused on the rupture of blood plasma clots under tensile loading (Mode I), our current study investigates the rupture of fibrin induced by shear loading (Mode II), dominating under physiological conditions induced by blood flow. Using experimental and theoretical approaches, we show that fracture toughness, i.e. the critical energy release rate, is relatively independent of the type of loading and is therefore a fundamental property of the gel. Ultrastructural studies and finite element simulations demonstrate that cracks propagate perpendicular to the direction of maximum stretch at the crack tip. These observations indicate that locally, the mechanism of rupture is predominantly tensile. Knowledge gained from this study will aid in the development of methods for prediction/prevention of thrombotic embolization.

Exploring Predictive Factors for Heart Failure Progression in Hypertensive Patients Based on Medical Diagnosis Data from the MIMIC-IV Database

Heart failure is associated with a significant mortality rate, and an elevated prevalence of this condition has been noted among hypertensive patients. The identification of predictive factors for heart failure progression in hypertensive individuals is crucial for early intervention and improved patient outcomes. In this study, we aimed to identify these predictive factors by utilizing medical diagnosis records for hypertension patients from the MIMIC-IV database. In particular, we employed only diagnostic history prior to hypertension to enable patients to anticipate the onset of heart failure at the moment of hypertension diagnosis. In the methodology, chi-square tests and XGBoost modeling were applied to examine age-specific predictive factors across four groups: AL (all ages), G1 (0 to 65 years), G2 (65 to 80 years), and G3 (over 80 years). As a result, the chi-square tests identified 34, 28, 20, and 10 predictive factors for the AL, G1, G2, and G3 groups, respectively. Meanwhile, the XGBoost modeling uncovered 19, 21, 27, and 33 predictive factors for these respective groups. Ultimately, our findings reveal 21 overall predictive factors, encompassing conditions such as atrial fibrillation, the use of anticoagulants, kidney failure, obstructive pulmonary disease, and anemia. These factors were assessed through a comprehensive review of the existing literature. We anticipate that the results will offer valuable insights for the risk assessment of heart failure in hypertensive patients.

Megakaryocyte-induced contraction of plasma clots: cellular mechanisms and structural mechanobiology

ABSTRACT

Nonmuscle cell contractility is an essential feature underlying diverse cellular processes such as motility, morphogenesis, division and genome replication, intracellular transport, and secretion. Blood clot contraction is a well-studied process driven by contracting platelets. Megakaryocytes (MKs), which are the precursors to platelets, can be found in bone marrow and lungs. Although they express many of the same proteins and structures found in platelets, little is known about their ability to engage with extracellular proteins such as fibrin and contract. Here, we have measured the ability of MKs to compress plasma clots. Megakaryocytes derived from human induced pluripotent stem cells (iPSCs) were suspended in human platelet-free blood plasma and stimulated with thrombin. Using real-time macroscale optical tracking, confocal microscopy, and biomechanical measurements, we found that activated iPSC-derived MKs (iMKs) caused macroscopic volumetric clot shrinkage, as well as densification and stiffening of the fibrin network via fibrin-attached plasma membrane protrusions undergoing extension-retraction cycles that cause shortening and bending of fibrin fibers. Contraction induced by iMKs involved 2 kinetic phases with distinct rates and durations. It was suppressed by inhibitors of nonmuscle myosin IIA, actin polymerization, and integrin αIIbβ3-fibrin interactions, indicating that the molecular mechanisms of iMK contractility were similar or identical to those in activated platelets. Our findings provide new insights into MK biomechanics and suggest that iMKs can be used as a model system to study platelet contractility. Physiologically, the ability of MKs to contract plasma clots may play a role in the mechanical remodeling of intravascular blood clots and thrombi.

Platelet mechanosensing as key to understanding platelet function

PURPOSE OF REVIEW

This review highlights how the perception of platelet function is evolving based on recent insights into platelet mechanobiology.

RECENT FINDINGS

The mechanosensitive ion channel Piezo1 mediates activation of free-flowing platelets under conditions of flow acceleration through mechanisms independent of adhesion receptors and classical activation pathways. Interference with the initiation of platelet migration or with the phenotypic switch of migrating platelets to a procoagulant state aggravates inflammatory bleeding. Mechanosensing of biochemical and biophysical microenvironmental cues during thrombus formation feed into platelet contractile force generation. Measurements of single platelet contraction and bulk clot retraction show promise to identify individuals at risk for hemorrhage.

SUMMARY

New findings unravel novel mechanotransduction pathways and effector functions in platelets, establishing mechanobiology as a pivotal component of platelet function. These insights highlight limitations of existing treatments and offer new potential therapeutic approaches and diagnostic avenues based on mechanobiological principles. Further extensive research is required to distinguish between core hemostatic and pathological mechanisms influenced by platelet mechanosensing.

A microfluidic hemostatic diagnostics platform: Harnessing coagulation-induced adaptive-bubble behavioral perception

Clinical viscoelastic hemostatic assays, which have been used for decades, rely on measuring biomechanical responses to physical stimuli but face challenges related to high device and test cost, limited portability, and limited scalability.. Here, we report a differential pattern using self-induced adaptive-bubble behavioral perception to refresh it. The adaptive behaviors of bubble deformation during coagulation precisely describe the transformation of viscoelastic hemostatic properties, being free of the precise and complex physical devices. And the integrated bubble array chip allows microassays and enables multi-bubble tests with good reproducibility. Recognition of the developed bubble behaviors empowers automated and user-friendly diagnosis. In a prospective clinical study (clinical model development [n = 273]; clinical assay [n = 44]), we show that the diagnostic accuracies were 99.1% for key viscoelastic hemostatic assay indicators (reaction time [R], kinetics time [K], alpha angle [Angle], maximum amplitude [MA], lysis at 30 min [LY30]; n = 220) and 100% (n = 44) for hypercoagulation, healthy, and hypocoagulation diagnoses. This should provide fresh insight into existing paradigms and help more clinical needs.

Probing interactions of red blood cells and contracting fibrin platelet clots

Contraction of blood clots plays an important role in blood clotting, a natural process that restores hemostasis and regulates thrombosis in the body. Upon injury, a chain of events culminate in the formation of a soft plug of cells and fibrin fibers attaching to wound edges. Platelets become activated and apply contractile forces to shrink the overall clot size, modify clot structure, and mechanically stabilize the clot. Impaired blood clot contraction results in unhealthy volumetric, mechanical, and structural properties of blood clots associated with a range of severe medical conditions for patients with bleeding and thrombotic disorders. Due to the inherent mechanical complexity of blood clots and a confluence of multiple interdependent factors governing clot contraction, the mechanics and dynamics of clot contraction and the interactions with red blood cells (RBCs) remain elusive. Using an experimentally informed, physics-based mesoscale computational model, we probe the dynamic interactions among platelets, fibrin polymers, and RBCs, and examine the properties of contracted blood clots. Our simulations confirm that RBCs strongly affect clot contraction. We find that RBC retention and compaction in thrombi can be solely a result of mechanistic contraction of fibrin mesh due to platelet activity. Retention of RBCs hinders clot contraction and reduces clot contractility. Expulsion of RBCs located closer to clot outer surface results in the development of a dense fibrin shell in thrombus clots commonly observed in experiments. Our simulations identify the essential parameters and interactions that control blood clot contraction process, highlighting its dependence on platelet concentration and the initial clot size. Furthermore, our computational model can serve as a useful tool in clinically relevant studies of hemostasis and thrombosis disorders, and post thrombotic clot lysis, deformation, and breaking.

Molecular basis of clot retraction and its role in wound healing

Clot retraction is important for the prevention of bleeding, in the manifestations of thrombosis and for tissue repair. The molecular mechanisms behind clot formation are complex. Platelet involvement begins with adhesion at sites of vessel injury followed by platelet aggregation, thrombin generation and fibrin production. Other blood cells incorporate into a fibrin mesh that is consolidated by FXIIIa-mediated crosslinking and platelet contractile activity. The latter results in the asymmetric redistribution of erythrocytes into a tighter central mass providing the clot with stability and resistance to fibrinolysis. Integrin αIIbβ3 on platelets is the key player in these events, bridging fibrin and the platelet cytoskeleton. Glycoprotein VI participates in thrombus formation but not in the retraction. Rheological and environmental factors influence clot construction with retraction driven by the platelet cytoskeleton with actomyosin acting as the motor. Activated platelets provide procoagulant activity stimulating thrombin generation together with the release of a plethora of biologically active proteins and substances from storage pools; many form chemotactic gradients within the fibrin or the underlying matrix. Also released are newly synthesized metabolites and lipid-rich vesicles that circulate within the vasculature and mimic platelet functions. Platelets and their released elements play key roles in wound healing. This includes promoting stem cell and mesenchymal stromal cell recruitment, fibroblast and endothelial cell migration, angiogenesis and matrix formation. These properties have led to the use of autologous clots in therapies designed to accelerate tissue repair while offering the potential for genetic manipulation in both inherited and acquired diseases.

Association of clot ultrastructure with clot perviousness in stroke patients

Clot perviousness on computerized tomography (CT) is predictive of response to reperfusion therapy. This study aimed to determine the association of clot perviousness with ultrastructural features of clot in stroke patients undergoing endovascular thrombectomy. We quantitatively analyzed the ultrastructural components identified using scanning electron microscopy. The clot components were determined in the inner portions of the clots. Clot perviousness was assessed as thrombus attenuation increase (TAI) using noncontrast CT and CT angiography. We compared the association between the identified ultrastructural components and clot perviousness. The proportion of pores consisted of 3.5% on scanning electron microscopy images. The proportion of porosity in the inner portion was 2.5%. Among the ultrastructural components, polyhedrocytes were most commonly observed. The mean TAI was 9.3 ± 10.0 (median 5.6, interquartile range 1.1-14.3) Hounsfield units. TAI correlated positively with inner porosity (r = 0.422, p = 0.020). Among the ultrastructural clot components, TAI was independently associated with polyhedrocytes (B = - 0.134, SE = 0.051, p = 0.008). Clot perviousness is associated with porosity and the proportion of polyhdrocytes of clots.

Activation of Piezo1 channels in compressed red blood cells augments platelet-driven contraction of blood clots

BACKGROUND

Piezo1 is a mechanosensitive cationic channel that boosts intracellular [Ca2+]i. Compression of red blood cells (RBCs) during platelet-driven contraction of blood clots may cause the activation of Piezo1.

OBJECTIVES

To establish relationships between Piezo1 activity and blood clot contraction.

METHODS

Effects of a Piezo1 agonist, Yoda1, and antagonist, GsMTx-4, on clot contraction in vitro were studied in human blood containing physiological [Ca2+]. Clot contraction was induced by exogenous thrombin. Activation of Piezo1 was assessed by Ca2+ influx in RBCs and with other functional and morphologic features.

RESULTS

Piezo1 channels in compressed RBCs are activated naturally during blood clot contraction and induce an upsurge in the intracellular [Ca2+]i, followed by phosphatidylserine exposure. Adding the Piezo1 agonist Yoda1 to whole blood increased the extent of clot contraction due to Ca2+-dependent volumetric shrinkage of RBCs and increased platelet contractility due to their hyperactivation by the enhanced generation of endogenous thrombin on activated RBCs. Addition of rivaroxaban, the inhibitor of thrombin formation, or elimination of Ca2+ from the extracellular space abrogated the stimulating effect of Yoda1 on clot contraction. The Piezo1 antagonist, GsMTx-4, caused a decrease in the extent of clot contraction relative to the control both in whole blood and in platelet-rich plasma. Activated Piezo1 in compressed and deformed RBCs amplified the platelet contractility as a positive feedback mechanism during clot contraction.

CONCLUSION

The results obtained demonstrate that the Piezo1 channel expressed on RBCs comprises a mechanochemical modulator of blood clotting that may be considered a potential therapeutic target to correct hemostatic disorders.

Why platelet mechanotransduction matters for hemostasis and thrombosis

Mechanotransduction is the ability of cells to "feel" or sense their mechanical microenvironment and integrate and convert these physical stimuli into adaptive biochemical cellular responses. This phenomenon is vital for the physiology of numerous nucleated cell types to affect their various cellular processes. As the main drivers of hemostasis and clot retraction, platelets also possess this ability to sense the dynamic mechanical microenvironments of circulation and convert those signals into biological responses integral to clot formation. Like other cell types, platelets leverage their "hands" or receptors/integrins to mechanotransduce important signals in responding to vascular injury to achieve hemostasis. The clinical relevance of cellular mechanics and mechanotransduction is imperative as pathologic alterations or aberrant mechanotransduction in platelets has been shown to lead to bleeding and thrombosis. As such, the aim of this review is to provide an overview of the most recent research related to platelet mechanotransduction, from platelet generation to platelet activation, within the hemodynamic environment and clot contraction at the site of vascular injury, thereby covering the entire "life cycle" of platelets. Additionally, we describe the key mechanoreceptors in platelets and discuss the new biophysical techniques that have enabled the field to understand how platelets sense and respond to their mechanical microenvironment via those receptors. Finally, the clinical significance and importance of continued exploration of platelet mechanotransduction have been discussed as the key to better understanding of both thrombotic and bleeding disorders lies in a more complete mechanistic understanding of platelet function by way of mechanotransduction.

Combined computational modeling and experimental study of the biomechanical mechanisms of platelet-driven contraction of fibrin clots

While blood clot formation has been relatively well studied, little is known about the mechanisms underlying the subsequent structural and mechanical clot remodeling called contraction or retraction. Impairment of the clot contraction process is associated with both life-threatening bleeding and thrombotic conditions, such as ischemic stroke, venous thromboembolism, and others. Recently, blood clot contraction was observed to be hindered in patients with COVID-19. A three-dimensional multiscale computational model is developed and used to quantify biomechanical mechanisms of the kinetics of clot contraction driven by platelet-fibrin pulling interactions. These results provide important biological insights into contraction of platelet filopodia, the mechanically active thin protrusions of the plasma membrane, described previously as performing mostly a sensory function. The biomechanical mechanisms and modeling approach described can potentially apply to studying other systems in which cells are embedded in a filamentous network and exert forces on the extracellular matrix modulated by the substrate stiffness.

Clot Retraction and Its Correlation with the Function of Platelet Integrin αIIbβ3

Clot retraction results from retractions of platelet filopodia and fibrin fibers and requires the functional platelet αIIbβ3 integrin. This assay is widely used to test the functions of platelets and fibrinogen as well as the efficacy of fibrinolysis. Changes in clot retraction have been found in a variety of hemostatic abnormalities and, more recently, in arterial thrombosis. Despite its broad clinical use and low cost, many aspects of clot retraction are poorly understood. In the present study, we performed two clinical standard clot retraction assays using whole-blood and platelet-rich plasma (PRP) samples to determine how clot retraction correlates with platelet counts and mean volume, the density of αIIbβ3 integrin and PLA genotypes, and plasma fibrinogen levels. We found that clot retraction was affected by platelet counts, but not mean platelet volume. It correlated with the surface density of the integrin αIibβ3, but not PLA genotypes. These results indicate that clot retraction measures a unique aspect of platelet function and can serve as an additional means to detect functional changes in platelets.

Acute reperfusion treatment and secondary prevention of cancer-related stroke: comprehensive overview and proposal of clinical algorithm

Cancer-related stroke (CRS), referring to ischemic stroke occurring in cancer patients without other clear etiology, represents a clinical challenge, as it is associated with unfavorable clinical outcomes including high rates of recurrence and mortality. There are scarce international recommendations and limited consensus statements on CRS management. For this comprehensive overview, the available studies/reviews/meta-analyses on the use of acute reperfusion and secondary prevention treatments for cancer patients with ischemic stroke, focusing on antithrombotic agents, were collected and summarized. A practical management algorithm was designed per the available data. In short, acute reperfusion in the form of intravenous thrombolysis and mechanical thrombectomy appears to be safe in CRS and can be considered for eligible patients, though the functional outcomes are often poor, and mostly defined by the preexisting condition. Many patients carry indications for anticoagulation, in which case vitamin K antagonists are not preferred, while low-molecular weight heparins remain the treatment of choice; direct oral anticoagulants can be alternatively considered but are contraindicated for gastrointestinal malignancies. For patients without clear anticoagulation indications, no net benefit for anticoagulation compared to aspirin has been shown. Other targeted treatment options should be evaluated in an individualized approach, alongside the appropriate management of conventional cerebrovascular risk factors. Oncological treatment should be swiftly initiated/continued. In conclusion, acute CRS remains a clinical challenge, with many patients suffering recurrent stroke, despite preventive measures. More randomized-controlled clinical trials are urgently needed to pinpoint the most effective management options for this subset of stroke patients.

Tensile and Compressive Mechanical Behaviour of Human Blood Clot Analogues

Endovascular thrombectomy procedures are significantly influenced by the mechanical response of thrombi to the multi-axial loading imposed during retrieval. Compression tests are commonly used to determine compressive ex vivo thrombus and clot analogue stiffness. However, there is a shortage of data in tension. This study compares the tensile and compressive response of clot analogues made from the blood of healthy human donors in a range of compositions. Citrated whole blood was collected from six healthy human donors. Contracted and non-contracted fibrin clots, whole blood clots and clots reconstructed with a range of red blood cell (RBC) volumetric concentrations (5-80%) were prepared under static conditions. Both uniaxial tension and unconfined compression tests were performed using custom-built setups. Approximately linear nominal stress-strain profiles were found under tension, while strong strain-stiffening profiles were observed under compression. Low- and high-strain stiffness values were acquired by applying a linear fit to the initial and final 10% of the nominal stress-strain curves. Tensile stiffness values were approximately 15 times higher than low-strain compressive stiffness and 40 times lower than high-strain compressive stiffness values. Tensile stiffness decreased with an increasing RBC volume in the blood mixture. In contrast, high-strain compressive stiffness values increased from 0 to 10%, followed by a decrease from 20 to 80% RBC volumes. Furthermore, inter-donor differences were observed with up to 50% variation in the stiffness of whole blood clot analogues prepared in the same manner between healthy human donors.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Role of tRNA-Derived Fragments in Neurological Disorders: a Review

tRFs are small tRNA derived fragments that are emerging as novel therapeutic targets and regulatory molecules in the pathophysiology of various neurological disorders. These are derived from precursor or mature tRNA, forming different subtypes that have been reported to be involved in neurological disorders like stroke, Alzheimer's, epilepsy, Parkinson's, MELAS, autism, and Huntington's disorder. tRFs were earlier believed to be random degradation debris of tRNAs. The significant variation in the expression level of tRFs in disease conditions indicates their salient role as key players in regulation of these disorders. Various animal studies are being carried out to decipher their exact role; however, more inputs are required to transform this research knowledge into clinical application. Future investigations also call for high-throughput technologies that could help to bring out the other hidden aspects of these entities. However, studies on tRFs require further research efforts to overcome the challenges posed in quantifying tRFs, their interactions with other molecules, and the exact mechanism of function. In this review, we are abridging the current understanding of tRFs, including their biogenesis, function, relevance in clinical therapies, and potential as diagnostic and prognostic biomarkers of these neurological disorders.

Spatial heterogeneity of occlusive thrombus in acute ischemic stroke: A systematic review

Following the advent of mechanical thrombectomy, occlusive clots in ischemic stroke have been amply characterized using conventional histopathology. Many studies have investigated the compositional variability of thrombi and the consequences of thrombus composition on treatment response. More recent evidence has emerged about the spatial heterogeneity of the clot or the preferential distribution of its components and compact nature. Here we review this emerging body of evidence, discuss its potential clinical implications, and propose the development of adequate characterization techniques.

Blood clot contraction: Mechanisms, pathophysiology, and disease

A State of the Art lecture titled "Blood Clot Contraction: Mechanisms, Pathophysiology, and Disease" was presented at the International Society on Thrombosis and Haemostasis (ISTH) Congress in 2022. This was a systematic description of blood clot contraction or retraction, driven by activated platelets and causing compaction of the fibrin network along with compression of the embedded erythrocytes. The consequences of clot contraction include redistribution of the fibrin-platelet meshwork toward the periphery of the clot and condensation of erythrocytes in the core, followed by their deformation from the biconcave shape into polyhedral cells (polyhedrocytes). These structural signatures of contraction have been found in ex vivo thrombi derived from various locations, which indicated that clots undergo intravital contraction within the blood vessels. In hemostatic clots, tightly packed polyhedrocytes make a nearly impermeable seal that stems bleeding and is impaired in hemorrhagic disorders. In thrombosis, contraction facilitates the local blood flow by decreasing thrombus obstructiveness, reducing permeability, and changing susceptibility to fibrinolytic enzymes. However, in (pro)thrombotic conditions, continuous background platelet activation is followed by platelet exhaustion, refractoriness, and impaired intravital clot contraction, which is associated with weaker thrombi predisposed to embolization. Therefore, assays that detect imperfect in vitro clot contraction have potential diagnostic and prognostic values for imminent or ongoing thrombosis and thrombotic embolism. Collectively, the contraction of blood clots and thrombi is an underappreciated and understudied process that has a pathogenic and clinical significance in bleeding and thrombosis of various etiologies. Finally, we have summarized relevant new data on this topic presented during the 2022 ISTH Congress.

A familial case of MYH9 gene mutation associated with multiple functional and structural platelet abnormalities

Mutations in the MYH9 gene result in macrothrombocytopenia often associated with hemorrhages. Here, we studied the function and structure of platelets in three family members with a heterozygous mutation R1933X in the MYH9 gene, characteristic of closely related disorders known as the May-Hegglin anomaly and Sebastian syndrome. The examination included complete blood count, blood smear microscopy, platelet flow cytometry (expression of P-selectin and active integrin αIIbβ3 before and after activation), the kinetics of platelet-driven contraction (retraction) of blood clots, as well as scanning/transmission electron microscopy of platelets. Despite severe thrombocytopenia ranging (36-86) × 10⁹/l, none of the patients had hemorrhages at the time of examination, although they had a history of heavy menstruation, spontaneous ecchymosis, and postpartum hemorrhage. Flow cytometry showed background platelet activation, revealed by overexpression of P-selectin and active αIIbβ3 integrin above normal levels. After TRAP-induced stimulation, the fractions of platelets expressing P-selectin in the proband and her sister were below normal response, indicating partial platelet refractoriness. The initiation of clot contraction was delayed. Electron microscopy revealed giant platelets with multiple filopodia and fusion of α-granules with dilated open canalicular system, containing filamentous and vesicular inclusions. The novel concept implies that the R1933X mutation in the MYH9 gene is associated not only with thrombocytopenia, but also with qualitative structural and functional defects in platelets. Platelet dysfunction includes impaired contractility, which can disrupt the compaction of hemostatic clots, making the clots weak and permeable, therefore predisposing patients with MYH9 gene mutations to the hemorrhagic phenotype.

Contribution of septins to human platelet structure and function

Although septins have been well-studied in nucleated cells, their role in anucleate blood platelets remains obscure. Here, we elucidate the contribution of septins to human platelet structure and functionality. We show that Septin-2 and Septin-9 are predominantly distributed at the periphery of resting platelets and co-localize strongly with microtubules. Activation of platelets by thrombin causes clustering of septins and impairs their association with microtubules. Inhibition of septin dynamics with forchlorfenuron (FCF) reduces thrombin-induced densification of septins and lessens their colocalization with microtubules in resting and activated platelets. Exposure to FCF alters platelet shape, suggesting that septins stabilize platelet cytoskeleton. FCF suppresses platelet integrin αIIbβ3 activation, promotes phosphatidylserine exposure on activated platelets, and induces P-selectin expression on resting platelets, suggesting septin involvement in these processes. Inhibition of septin dynamics substantially reduces platelet contractility and abrogates their spreading on fibrinogen-coated surfaces. Overall, septins strongly contribute to platelet structure, activation and biomechanics.

A sensitive and adaptable method to measure platelet-fibrin clot contraction kinetics

Background

Platelet-fibrin clot contraction is critical for wound closure and maintenance of vessel patency, yet a molecular understanding of the process has lagged because of a lack of flexible quantitative assay systems capable of assaying multiple samples simultaneously.

Objectives

We devised a sensitive and inexpensive method to assess clot contraction kinetics under multiple conditions.

Methods

Clot contraction was measured using time-lapse digital photography, automated image processing with customized software, and detailed kinetic analysis using available commercial programs.

Results

Our system was responsive to alterations in platelet counts and calcium, fibrinogen, and thrombin concentrations, and our analysis detected and defined three phases of platelet-fibrin clot formation: initiation, contraction, and stabilization. Lag time, average contraction velocity, contraction extent, and area under the curve were readily calculated from the data. Using pharmacological agents (blebbistatin and eptifibatide), we confirmed the importance of myosin IIA and the interactions of integrin αIIbβ3-fibrinogen/fibrin in clot contraction. As further proof of our system's utility, we showed how 2-deoxyglucose affects contraction, demonstrating the importance of platelet bioenergetics, specifically glycolysis.

Conclusions

Our system is an adaptable platform for assessing the effects of multiple conditions and interventions on clot contraction kinetics in a regular laboratory setting, using readily available materials. The automated image processing software we developed will be made freely available for noncommercial uses. This assay system can be used to directly compare and define the effects of different treatments or genetic manipulations on platelet function and should provide a robust tool for future hemostasis/thrombosis research and therapeutic development.

Chronic Immune Platelet Activation Is Followed by Platelet Refractoriness and Impaired Contractility

Autoimmune diseases, including systemic lupus erythematosus (SLE), have a high risk of thrombotic and hemorrhagic complications associated with altered platelet functionality. We studied platelets from the blood of SLE patients and their reactivity. The surface expression of phosphatidylserine, P-selectin, and active integrin αIIbβ3 were measured using flow cytometry before and after platelet stimulation. Soluble P-selectin was measured in plasma. The kinetics of platelet-driven clot contraction was studied, as well as scanning and transmission electron microscopy of unstimulated platelets. Elevated levels of membrane-associated phosphatidylserine and platelet-attached and soluble P-selectin correlated directly with the titers of IgG, anti-dsDNA-antibodies, and circulating immune complexes. Morphologically, platelets in SLE lost their resting discoid shape, formed membrane protrusions and aggregates, and had a rough plasma membrane. The signs of platelet activation were associated paradoxically with reduced reactivity to a physiological stimulus and impaired contractility that revealed platelet exhaustion and refractoriness. Platelet activation has multiple pro-coagulant effects, and the inability to fully contract (retract) blood clots can be either a hemorrhagic or pro-thrombotic mechanism related to altered clot permeability, sensitivity of clots to fibrinolysis, obstructiveness, and embologenicity. Therefore, chronic immune platelet activation followed by secondary platelet dysfunction comprise an understudied pathogenic mechanism that supports hemostatic disorders in autoimmune diseases, such as SLE.

Hemostasis Disturbances in Continuous-Flow Left Ventricular Assist Device (CF-LVAD) Patients—Rationale and Study Design

Left ventricular assist devices are a treatment option for end-stage heart failure patients. Despite advancing technologies, bleeding and thromboembolic events strongly decrease the survival and the quality of life of these patients. Little is known about prognostic factors determining these adverse events in this group of patients. Therefore, we plan to investigate 90 consecutive left ventricular assist device (LVAD) patients and study in vitro fibrin clot properties (clot lysis time, clot permeability, fibrin ultrastructure using a scanning electron microscope) and the calibrated automated thrombogram in addition to the von Willebrand factor antigen, fibrinogen, D-dimer, prothrombin time/international normalized ratio (PT/INR), and activated partial thromboplastin time (APTT) to identify prognostic factors of adverse outcomes during the course of therapy. We plan to assess the hemostasis system at four different time points, i.e., before LVAD implantation, 3–4 months after LVAD implantation, 6–12 months after LVAD implantation, and at the end of the study (at 5 years or at the time of the adverse event). Adverse outcomes were defined as bleeding events (bleeding in general or in the following subtypes: severe bleeding, fatal bleeding, gastrointestinal bleeding, intracranial bleeding), thromboembolic events (stroke or transient ischemic attack, pump thrombosis, including thrombosis within the pump or its inflow or outflow conduits, arterial peripheral thromboembolism), and death.

ADP and thromboxane inhibitors both reduce global contraction of clot length, while thromboxane inhibition attenuates internal aggregate contraction

Platelet contractility drives clot contraction to enhance clot density and stability. Clot contraction is typically studied under static conditions, with fewer studies of wall-adherent platelet clots formed under flow. We tested the effect of inhibitors of ADP and/or thromboxane A2 (TXA2) signaling on clot contraction. Using an eight-channel microfluidic device, we perfused PPACK-treated whole blood (WB) ± acetylsalicylic acid (ASA), 2-methylthioAMP (2-MeSAMP), and/or MRS-2179 over collagen (100/s) for 7.5 min, then stopped flow to observe contraction for 7.5 minutes. Two automated imaging methods scored fluorescent platelet percent contraction over the no-flow observation period: (1) “global” measurement of clot length and (2) “local” changes in surface area coverage of the numerous platelet aggregates within the clot. Total platelet fluorescence intensity (FI) decreased with concomitant decrease in global aggregate contraction when ASA, 2-MeSAMP, and/or MRS-2179 were present. Total platelet FI and global aggregate contraction were highly correlated ( R²  = 0.87). In contrast, local aggregate contraction was more pronounced than global aggregate contraction across all inhibition conditions. However, ASA significantly reduced local aggregate contraction relative to conditions without TXA2 inhibition. P-selectin display was significantly reduced by ADP and TXA2 inhibition, but there was limited detection of global or local aggregate contraction in P-selectin-positive platelets across all conditions, as expected for densely packed “core” platelets. Our results demonstrate that global aggregate contraction is inhibited by ASA, 2-MeSAMP, and MRS-2179, while ASA more potently inhibited local aggregate contraction. These results help resolve how different platelet antagonists affect global and local clot structure and function.

MicroCT Can Characterize Clots Retrieved With Mechanical Thrombectomy From Acute Ischemic Stroke Patients–A Preliminary Report

Background

Characterization of the clot occluding the arteries in acute ischemic stroke received ample attention, in terms of elucidating the relationship between the clot composition, its etiology and its amenability for pharmacological treatment and mechanical thrombectomy approaches. Traditional analytical techniques such as conventional 2D histopathology or electron microscopy sample only small parts of the clot. Visualization and analysis in 3D are necessary to depict and comprehend the overall organization of the clot. The aim of this study is to investigate the potential of microCT for characterizing the clot composition, structure, and organization.

Methods

In a pilot study, we analyzed with microCT clots retrieved from 14 patients with acute ischemic stroke. The following parameters were analyzed: overall clot density, clot segmentation with various density thresholds, clot volume.

Results

Our findings show that human clots are heterogeneous in terms of CT intra-clot density distribution. After fixation in formalin, the clots display a shift toward negative values. On average, we found the mean HU values of red clots retrieved from patients to be −153 HU, with SD = 23.8 HU, for the intermediate clots retrieved from patients −193 HU, SD = 23.7 HU, and for the white clots retrieved from patients −229 HU, SD = 64.8 HU.

Conclusion

Our study shows that volumetric and density analysis of the clot opens new perspectives for clot characterization and for a better understanding of thrombus structure and composition.

No Histological Difference between Large Atherosclerotic and Cardiogenic Embolic Thrombus

Background

The continuous development of endovascular treatment technology provides more opportunities for the histological study of thrombus. According to Trial of Org 10 172 in Acute Stroke Treatment (TOAST), clinicians take different strategies in anticoagulant or antiplatelet therapy. There are some patients still suffering from recurrent stroke while they took anticoagulant or antiplatelet drugs regularly for secondary prevention. In view of that, we found that histological analysis of thrombus can provide guidance for secondary prevention.

Aim

Exploring the histological characteristics differences between large atherosclerotic and cardiogenic embolic thrombosis in order to guide clinical secondary prevention of the two stroke subtypes.

Methods

A total of 54 patients with acute ischemic stroke were collected from December 2019 to April 2021. Identify stroke subtypes according to TOAST classification. Stain thrombus specimens with hematoxylin-eosin staining, and perform statistical analysis on the components (red blood cells and fibrin/platelets) of thrombus.

Results

In cardiogenic thrombi, the composition of RBCs was dominant (51.38 ± 18.463%) compared to that of fibrin/platelets (48.62 ± 18.463%). Similarly, among the thrombi of large artery atherosclerotic, RBCs (50.40 ± 20.100%) compared to fibrin/platelets (49.60 ± 20.100%). There was no statistical difference in RBCs or fibrin/platelet composition of both cardiogenic and atherosclerotic thrombi (P = 0.89).

Conclusions

The histologic composition of thrombi in cardiogenic and atherosclerotic had no statistical difference. These thrombi are all mixed thrombus, which are rich in RBCs, fibrinogen, and platelets. Anticoagulation combined with antiplatelet may be a more effective secondary prevention strategy.

Extent of intravital contraction of arterial and venous thrombi and pulmonary emboli

Ratio of compressed polyhedral to native biconcave RBCs in blood clots and thrombi is a “ruler” to measure extent of clot contraction.

The extent of intravital contraction of ex vivo arterial and venous thrombi is associated with their origins, age, and embologenicity.

Blood clots and thrombi undergo platelet-driven contraction/retraction followed by structural rearrangements. We have established quantitative relationships between the composition of blood clots and extent of contraction to determine intravital contraction of thrombi and emboli based on their content. The composition of human blood clots and thrombi was quantified using histology and scanning electron microscopy. Contracting blood clots were segregated into the gradually shrinking outer layer that contains a fibrin-platelet mesh and the expanding inner portion with compacted red blood cells (RBCs). At 10% contraction, biconcave RBCs were partially compressed into polyhedral RBCs, which became dominant at 20% contraction and higher. The polyhedral/biconcave RBC ratio and the extent of contraction displayed an exponential relationship, which was used to determine the extent of intravital contraction of ex vivo thrombi, ranging from 30% to 50%. In venous thrombi, the extent of contraction decreased gradually from the older (head) to the younger (body, tail) parts. In pulmonary emboli, the extent of contraction was significantly lower than in the venous head but was similar to the body and tail, suggesting that the emboli originate from the younger portion(s) of venous thrombi. The extent of contraction in arterial cerebral thrombi was significantly higher than in the younger parts of venous thrombi (body, tail) and pulmonary emboli but was indistinguishable from the older part (head). A novel tool, named the “contraction ruler,” has been developed to use the composition of ex vivo thrombi to assess the extent of their intravital contraction, which contributes to the pathophysiology of thromboembolism.

Cleavage of talin by calpain promotes platelet-mediated fibrin clot contraction

Calpain-catalyzed talin cleavage in platelets promotes fibrin clot contraction.

Calpain cleaves talin in proximity to vinculin binding sites, likely initiating vinculin binding to talin to promote clot contraction.

Blood clot contraction is driven by traction forces generated by the platelet cytoskeleton that are transmitted to fibrin fibers via the integrin αIIbβ3. Here we show that clot contraction is impaired by inhibitors of the platelet cytosolic protease calpain. We used subtiligase-mediated labeling of amino termini and mass spectrometry to identify proteolytically cleaved platelet proteins involved in clot contraction. Of 32 calpain-cleaved proteins after TRAP stimulation, 14 were cytoskeletal, most prominently talin and vinculin. A complex of talin and vinculin constitutes a mechanosensitive clutch connecting integrins bound to the extracellular matrix with the actin cytoskeleton. Accordingly, we focused on talin and vinculin. Talin is composed of an N-terminal head domain and a C-terminal rod domain organized into a series of 4- and 5-helix bundles. The bundles contain 11 vinculin binding sites (VBSs), each of which is an α-helix packed into a bundle interior and requiring structural rearrangement to initiate vinculin binding. We detected 8 calpain-mediated cleavages in talin, 2 previously identified in unstructured regions and 6 in α-helical regions in proximity to a VBS. There is evidence in vitro that applying mechanical force across talin enables vinculin binding to the talin rod. However, we found that inhibiting platelet cytoskeletal contraction had no effect on talin cleavage, indicating that talin cleavage by calpain in platelets does not require cytoskeleton-generated tensile force. Therefore, it is likely that calpain acts in the later stages of clot retraction through focal adhesion disassembly.

A review on the association of thrombus composition with mechanical and radiological imaging characteristics in acute ischemic stroke

Thrombus composition and mechanical properties significantly impact the ease and outcomes of thrombectomy procedures in patients with acute ischemic stroke. A wide variation exists in the composition of thrombi between patients. If a relationship can be determined between the composition of a thrombus and its mechanical behaviour, as well as between the composition of a thrombus and its radiological imaging characteristics, then there is the potential to personalise thrombectomy treatment based on each individual thrombus. This review aims to give an overview of the current literature addressing this issue. Here, we present a scoping review detailing associations between thrombus composition, mechanical behaviour and radiological imaging characteristics. We conducted two searches 1) on the association between thrombus composition and the mechanical behaviour of the tissue and 2) on the association between radiological imaging characteristics and thrombus composition in the acute stroke setting. The review suggests that higher fibrin and lower red blood cell (RBC) content contribute to stiffer thrombi independent of the loading mode. Further, platelet-contracted thrombi are stiffer than non-contracted compositional counterparts. Fibrin content contributes to the elastic portion of viscoelastic behaviour while RBC content contributes to the viscous portion. It is possible to identify fibrin-rich or RBC-rich thrombi with computed tomography and magnetic resonance imaging vessel signs. Standardisation is required to quantify the association between thrombus density on non-contrast computed tomography and the RBC content. The characterisation of the thrombus fibrin network has not been addressed so far in radiological imaging but may be essential for the prediction of device-tissue interactions and distal thrombus embolization. The association between platelet-driven clot contraction and radiological imaging characteristics has not been explicitly investigated. However, evidence suggests that perviousness may be a marker of clot contraction.

Associations of thrombus perviousness derived from entire thrombus segmentation with functional outcome in patients with acute ischemic stroke

Thrombus perviousness is strongly associated with functional outcome and intravenous alteplase treatment success in patients with acute ischemic stroke. Accuracy of thrombus attenuation increase (TAI) assessment may be compromised by a heterogeneous thrombus composition and interobserver variations of currently used manual measurements. We hypothesized that TAI is more strongly associated with clinical outcomes when evaluated on the entire thrombus. In 195 patients, five TAI measures were performed: one manual by placing three regions of interest (TAI_manual) and four automated ones assessing densities from the entire thrombus. The automated TAI measures were calculated by comparing quartiles; Q1, Q2, and Q3 of the non-contrast and contrast enhanced thrombus density distribution and using the lag of the maximum of the cross correlations (MCC). Associations with functional outcome (mRS at 90 days) were assessed with univariate and multivariable analyses. All entire TAI measures were significantly associated with functional outcome with odd ratios (OR) of 1.63(95 %CI:1.19-2.25, p = 0.003) for Q1, 1.56(95 %CI:1.16-2.10, p = 0.003) for Q2, 1.24(95 %CI:1.00-1.54, p = 0.045) for Q3, and 1.70(95 %CI:1.24-2.34, p = 0.001) for MCC per 10 HU increase in univariate models. TAI_manual was not significantly associated with functional outcome (p = 0.055). In the multivariable logistic regression models including age, NIHSS, and recanalization, only TAI measures derived from the entire thrombus were independently associated with favorable outcome; OR of 1.64(95 %CI:1.01-2.66, p = 0.048) for Q2 and 1.82(1.13-2.95, p = 0.014) for MCC per 10 HU increase of thrombus attenuation. The novel perviousness measures of the entire thrombus are more strongly associated with functional outcome than the traditional manual perviousness assessments.

Quantification and optimization of clot retraction in washed human platelets by Sonoclot coagulation analysis

INTRODUCTION

Clot retraction is a pivotal process for haemostasis, where platelets develop a contractile force in fibrin meshwork and lead to the increased rigidity of clot. The pathophysiological alteration in contractile forces generated by the platelet-fibrin meshwork can lead to haemostatic disorders. Regardless of its utter significance, clot retraction remains a limited understood process owing to lack of quantification methodology. Sonoclot analysis is a point-of-care technique used in clinical laboratories for whole blood analysis that provides in vitro qualitative as well as quantitative assessment of coagulation process from initial fibrin formation to clot retraction.

METHODS

Human washed platelets were isolated by differential centrifugation method and analysed via optical imaging, microscopy and Sonoclot analysis using 1-2 × 10⁸ /mL of washed platelets, 1 U/mL of thrombin, 1 mg/mL of fibrinogen and 1 mM of calcium chloride.

RESULTS

In this study, we demonstrate the novelty of this instrument in the quantitative evaluation of clot retraction in washed platelets and attempted to optimize the reference range of Sonoclot parameters including ACT - 87.3 ± 20.997, CR - 16.23 ± 3.538 and PF - 3.57 ± 0.629, (n = 10).

DISCUSSION

Sonoclot analysis provides a simple and quantitative method to better understand in vitro clot retraction and its modulation by retraction components including platelet count, fibrinogen and platelet-fibrin interaction compared with existing conventional methods. Sonoclot may prove to be a valuable tool in thrombus biology research to understand fundamental basis of blood clot retraction.

Clot Retraction: Cellular Mechanisms and Inhibitors, Measuring Methods, and Clinical Implications

Platelets have important functions in hemostasis. Best investigated is the aggregation of platelets for primary hemostasis and their role as the surface for coagulation leading to fibrin- and clot-formation. Importantly, the function of platelets does not end with clot formation. Instead, platelets are responsible for clot retraction through the concerted action of the activated αIIbβ3 receptors on the surface of filopodia and the platelet's contractile apparatus binding and pulling at the fibrin strands. Meanwhile, the signal transduction events leading to clot retraction have been investigated thoroughly, and several targets to inhibit clot retraction have been demonstrated. Clot retraction is a physiologically important mechanism allowing: (1) the close contact of platelets in primary hemostasis, easing platelet aggregation and intercellular communication, (2) the reduction of wound size, (3) the compaction of red blood cells to a polyhedrocyte infection-barrier, and (4) reperfusion in case of thrombosis. Several methods have been developed to measure clot retraction that have been based on either the measurement of clot volume or platelet forces. Concerning the importance of clot retraction in inborn diseases, the failure of clot retraction in Glanzmann thrombasthenia is characterized by a bleeding phenotype. Concerning acquired diseases, altered clot retraction has been demonstrated in patients with coronary heart disease, stroke, bronchial asthma, uremia, lupus erythematodes, and other diseases. However, more studies on the diagnostic and prognostic value of clot retraction with methods that have to be standardized are necessary.

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.

Pathologically stiff erythrocytes impede contraction of blood clots

BACKGROUND

Blood clot contraction, volume shrinkage of the clot, is driven by platelet contraction and accompanied by compaction of the erythrocytes and their gradual shape change from biconcave to polyhedral, with the resulting cells named polyhedrocytes.

OBJECTIVES

Here, we examined the role of erythrocyte rigidity on clot contraction and erythrocyte shape transformation.

METHODS

We used an optical tracking methodology that allowed us to quantify changes in contracting clot size over time.

RESULTS AND CONCLUSIONS

Erythrocyte rigidity has been shown to be increased in sickle cell disease (SCD), and in our experiments erythrocytes from SCD patients were 4-fold stiffer than those from healthy subjects. On average, the final extent of clot contraction was reduced by 53% in the clots from the blood of patients with SCD compared to healthy individuals, and there was significantly less polyhedrocyte formation. To test if this reduction in clot contraction was due to the increase in erythrocyte rigidity, we used stiffening of erythrocytes via chemical cross-linking (glutaraldehyde), rigidifying Wrightb antibodies (Wrb ), and naturally more rigid llama ovalocytes. Results revealed that stiffening erythrocytes result in impaired clot contraction and fewer polyhedrocytes. These results demonstrate the role of erythrocyte rigidity in the contraction of blood clots and suggest that the impaired clot contraction/shrinkage in SCD is due to the reduced erythrocyte deformability, which may be an underappreciated mechanism that aggravates obstructiveness of erythrocyte-rich (micro)thrombi in SCD.

Mechanisms of fibrinolysis resistance and potential targets for thrombolysis in acute ischaemic stroke: lessons from retrieved stroke emboli

There has been growing interest and insight into the histological composition of retrieved stroke emboli. One of the main focuses of the stroke clot analysis literature has been the implications of clot composition on mechanical thrombectomy procedures. However, the holy grail of clot analysis may not be in the field of clot–device interaction, but rather, in understanding mechanisms of fibrinolysis resistance. The mechanisms underlying the low response to fibrinolytic therapy, even with the newer, more powerful agents, remain poorly understood. While factors such as embolus size, location and collateral status influence alteplase delivery and recanalisation rates; compositional analyses focused on histological and ultrastructural characteristics offer unique insights into mechanisms of alteplase resistance. In this review, we strive to provide comprehensive review of current knowledge on clot composition and ultrastructural analyses that help explain resistance to fibrinolysis.

Psoriatic disease is associated with systemic inflammation, endothelial activation, and altered haemostatic function

Psoriasis is a chronic, immune-mediated inflammatory skin disease, affecting approximately 2% of the general population, which can be accompanied by psoriatic arthritis (PsA). The condition has been associated with an increased cardiovascular burden. Hypercoagulability is a potential underlying mechanism that may contribute to the increased risk of major cardiovascular events in psoriatic individuals. Whole blood samples were collected from 20 PsA patients and 20 healthy individuals. The concentrations of inflammatory molecules (C-reactive protein, serum amyloid A, soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and soluble P-selectin) were determined by enzyme-linked immunosorbent assays. In addition, clotting efficiency was evaluated by thromboelastography. The fibrin network architecture was also assessed by scanning electron microscopy. Elevated levels of circulating inflammatory molecules were significantly associated with the presence of psoriatic disease. Furthermore, an increased tendency towards thrombus formation was significantly predictive of disease presence. Scanning electron microscopy revealed that fibrin clots were denser in psoriatic individuals, compared to healthy controls, with an increased fibrin fibre diameter associated with psoriatic disease. Our results add to the accumulating evidence of the systemic nature of psoriasis and the subsequent risk of cardiovascular comorbidities, potentially due to an acquired hypercoagulability. We suggest that haemostatic function should be monitored carefully in psoriatic patients that present with severe disease, due to the pre-eminent risk of developing thrombotic complications.

Influence of Onset to Imaging Time on Radiological Thrombus Characteristics in Acute Ischemic Stroke

Introduction: Radiological thrombus characteristics are associated with patient outcomes and treatment success after acute ischemic stroke. These characteristics could be expected to undergo time-dependent changes due to factors influencing thrombus architecture like blood stasis, clot contraction, and natural thrombolysis. We investigated whether stroke onset-to-imaging time was associated with thrombus length, perviousness, and density in the MR CLEAN Registry population.

Methods: We included 245 patients with M1-segment occlusions and thin-slice baseline CT imaging from the MR CLEAN Registry, a nation-wide multicenter registry of patients who underwent endovascular treatment for acute ischemic stroke within 6.5 h of onset in the Netherlands. We used multivariable linear regression to investigate the effect of stroke onset-to-imaging time (per 5 min) on thrombus length (in mm), perviousness and density (both in Hounsfield Units). In the first model, we adjusted for age, sex, intravenous thrombolysis, antiplatelet use, and history of atrial fibrillation. In a second model, we additionally adjusted for observed vs. non-observed stroke onset, CT-angiography collateral score, direct presentation at a thrombectomy-capable center vs. transfer, and stroke etiology. We performed exploratory subgroup analyses for intravenous thrombolysis administration, observed vs. non-observed stroke onset, direct presentation vs. transfer, and stroke etiology.

Results: Median stroke onset-to-imaging time was 83 (interquartile range 53–141) min. Onset to imaging time was not associated with thrombus length nor perviousness (β 0.002; 95% CI −0.004 to 0.007 and β −0.002; 95% CI −0.015 to 0.011 per 5 min, respectively) and was weakly associated with thrombus density in the fully adjusted model (adjusted β 0.100; 95% CI 0.005–0.196 HU per 5 min). The subgroup analyses showed no heterogeneity of these findings in any of the subgroups, except for a significantly positive relation between onset-to-imaging time and thrombus density in patients transferred from a primary stroke center (adjusted β 0.18; 95% CI 0.022–0.35).

Conclusion: In our population of acute ischemic stroke patients, we found no clear association between onset-to-imaging time and radiological thrombus characteristics. This suggests that elapsed time from stroke onset plays a limited role in the interpretation of radiological thrombus characteristics and their effect on treatment results, at least in the early time window.

Microelectromechanical System Measurement of Platelet Contraction: Direct Interrogation of Myosin Light Chain Phosphorylation

Myosin Light Chain (MLC) regulates platelet contraction through its phosphorylation by Myosin Light Chain Kinase (MLCK) or dephosphorylation by Myosin Light Chain Phosphatase (MLCP). The correlation between platelet contraction force and levels of MLC phosphorylation is unknown. We investigate the relationship between platelet contraction force and MLC phosphorylation using a novel microelectromechanical (MEMS) based clot contraction sensor (CCS). The MLCK and MLCP pair were interrogated by inhibitors and activators of platelet function. The CCS was fabricated from silicon using photolithography techniques and force was validated over a range of deflection for different chip spring constants. The force of platelet contraction measured by the clot contraction sensor (CCS) was compared to the degree of MLC phosphorylation by Western Blotting (WB) and ELISA. Stimulators of MLC phosphorylation produced higher contraction force, higher phosphorylated MLC signal in ELISA and higher intensity bands in WB. Inhibitors of MLC phosphorylation produced the opposite. Contraction force is linearly related to levels of phosphorylated MLC. Direct measurements of clot contractile force are possible using a MEMS sensor platform and correlate linearly with the degree of MLC phosphorylation during coagulation. Measured force represents the mechanical output of the actin/myosin motor in platelets regulated by myosin light chain phosphorylation.

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.

In Vitro Clot Trapping Efficiency of the FDA Generic Inferior Vena Cava Filter in an Anatomical Model: An Experimental Fluid-Structure Interaction Benchmark

PURPOSE

Robust experimental data for performing validation of fluid-structure interaction (FSI) simulations of the transport of deformable solid bodies in internal flow are currently lacking. This in vitro experimental study characterizes the clot trapping efficiency of a new generic conical-type inferior vena cava (IVC) filter in a rigid anatomical model of the IVC with carefully characterized test conditions, fluid rheological properties, and clot mechanical properties.

METHODS

Various sizes of spherical and cylindrical clots made of synthetic materials (nylon and polyacrylamide gel) and bovine blood are serially injected into the anatomical IVC model under worst-case exercise flow conditions. Clot trapping efficiencies and their uncertainties are then quantified for each combination of clot shape, size, and material.

RESULTS

Experiments reveal the clot trapping efficiency increases with increasing clot diameter and length, with trapping efficiencies ranging from as low as approximately 42% for small 3.2 mm diameter spherical clots up to 100% for larger clot sizes. Because of the asymmetry of the anatomical IVC model, the data also reveal the iliac vein of clot origin influences the clot trapping efficiency, with the trapping efficiency for clots injected into the left iliac vein up to a factor of 7.5 times greater than that for clots injected into the right iliac (trapping efficiencies of approximately 10% versus 75%, respectively).

CONCLUSION

Overall, this data set provides a benchmark for validating simulations predicting IVC filter clot trapping efficiency and, more generally, low-Reynolds number FSI modeling.

Visualizing thrombosis to improve thrombus resolution

The severity, course, and outcomes of thrombosis are determined mainly by the size and location of the thrombus, but studying thrombus structure and composition has been an important but challenging task. The substantial progress in determination of thrombus morphology has become possible due to new intravital imaging methodologies in combination with mechanical thrombectomy, which allows extraction of a fresh thrombus from a patient followed by microscopy. Thrombi have been found to contain various structural forms of fibrin along with platelet aggregates, leukocytes, and red blood cells, many of which acquire a polyhedral shape (polyhedrocytes) as a result of intravital platelet-driven contraction. The relative volume fractions of thrombus components and their structural forms vary substantially, depending on the clinical and pathogenic characteristics. This review summarizes recent research that describes quantitative and qualitative morphologic characteristics of arterial and venous thrombi that are relevant for the pathogenesis, prophylaxis, diagnosis, and treatment of thrombosis.

Microengineered Flexural Post Rings for Effective Blood Sample Fencing and High-Throughput Measurement of Clot Retraction Force

During blood clotting, clot retraction alters its mechanical properties and critically affects hemostasis. Despite that, existing clot retraction assays hold limitations such as large footprint and low throughput. In this work, we report the design of flexural post rings for a miniaturized assay of clot retraction force (CRF) with high throughput. Leveraging surface tensions, the post rings hold blood samples in a highly reproducible fashion while simultaneously serving as cantilever beams to measure the CRF. We investigated the effect on the device performance of major parameters, namely, surface hydrophobicity, post number, and post stiffness. We then tested the devices using 14 patient samples and revealed the correlation between CRF and fibrinogen levels. We further implemented an automated liquid handler and developed a high-throughput platform for clot retraction assay. The device's small sample consumption, simple operation, and good compatibility with existing automation facilities make it a promising high-throughput clot retraction assay.