Influence of fibrin network conformation and fibrin fiber diameter on fibrinolysis speed: dynamic and structural approaches by confocal microscopy

Stress Hyperglycemia Ratio Is Associated With High Thrombus Burden in Patients With Acute Coronary Syndrome

The blood glucose level at admission indicates (with some limitations) poor prognosis and thrombus burden in patients with the acute coronary syndrome (ACS). Our study aimed to measure the predictive value of the stress hyperglycemia ratio (SHR), an indicator of stress hyperglycemia, showing increased thrombus burden in patients with ACS. Patients (n = 1222) with ACS were enrolled in this cross-sectional study. Coronary thrombus burden was classified as high and low. SHR was calculated by dividing the admission serum glucose by the estimated average glucose derived from HbA1c. Low thrombus burden was detected in 771 patients, while high thrombus burden (HTB) was detected in 451 patients. SHR was found to be significantly higher in patients with HTB (1.1 ± .3 vs 1.06 ± .4; P = .002). SHR was determined as a predictor of HTB (odds ratio (OR) 1.547 95% CI (1.139-2.100), P < .001) as a result of univariate analysis. According to multivariate analysis, SHR was determined as an independent risk factor for HTB (OR 1.328 CI (1.082-1.752), P = .001). We found that SHR predicted thrombus burden with higher sensitivity than admission glucose level in patients with ACS.

How Clot Composition Influences Fibrinolysis in the Acute Phase of Stroke: A Proteomic Study of Cerebral Thrombi

BACKGROUND

The dramatic clinical improvement offered by mechanical thrombectomy raised questions about the relevance of prior intravenous thrombolysis in large-vessel occlusion strokes. Hence, studying intravenous thrombolysis susceptibility and its dependence on thrombus composition is crucial. We used an observational proteomic study of whole thrombi retrieved by mechanical thrombectomy to identify factors associated with fibrin content and fibrinolytic activity (FA).

METHODS

In 104 stroke patients, the thrombi proteome was established by mass spectrometry coupled to liquid chromatography. FA was estimated in clots both outside (FAout) by measuring D-dimer levels at the blood-thrombus interface and inside (FAin) by evaluating the ratio of fibrinogen α to its plasmin-cleaved forms using proteomics coupled with protein electrophoresis. The factors associated with fibrin content, FAin, and FAout were determined by intravenous thrombolysis-adjusted linear regression.

RESULTS

FAout (P<0.0001) and FAin (P=0.0147) were driven by recombinant tissue-type plasminogen activator (r-tPA) administration (47/104) and thrombus composition. Indeed, FAout was greater with fibrin-rich than erythrocyte-rich thrombi, presumably because of more (r)tPA substrates. Thus, FAout was increased with cardioembolic thrombi (72/104), which are rich in fibrin (P=0.0300). Opposite results were found inside the thrombus, suggesting that (r)tPA penetrability was hampered by the density of the fibrinous cap. Moreover, blood cells had a strong impact on thrombus structure and susceptibility to (r)tPA. Indeed, fibrin content was negatively associated with erythrocyte-specific proteins in the thrombus, admission hematocrit (P=0.0139), and hemoglobin level (P=0.0080), which underlines the key role of erythrocytes in thrombus composition. Also, an increased number of neutrophils impaired FAout (P=0.0225), which suggests that their aggregation around the thrombus prevented the (r)tPA attack. Only FAout was significantly associated with reduced thrombus weight (P=0.0310), increased recanalization rate (P=0.0150), good clinical outcome (P=0.0480), and reduced mortality (P=0.0080).

CONCLUSIONS

Proteomics can offer new insights into the close relationship between thrombus composition and susceptibility to fibrinolysis, paving the way for new adjuvant therapies.

A Perspective on How Fibrinaloid Microclots and Platelet Pathology May be Applied in Clinical Investigations

Microscopy imaging has enabled us to establish the presence of fibrin(ogen) amyloid (fibrinaloid) microclots in a range of chronic, inflammatory diseases. Microclots may also be induced by a variety of purified substances, often at very low concentrations. These molecules include bacterial inflammagens, serum amyloid A, and the S1 spike protein of severe acute respiratory syndrome coronavirus 2. Here, we explore which of the properties of these microclots might be used to contribute to differential clinical diagnoses and prognoses of the various diseases with which they may be associated. Such properties include distributions in their size and number before and after the addition of exogenous thrombin, their spectral properties, the diameter of the fibers of which they are made, their resistance to proteolysis by various proteases, their cross-seeding ability, and the concentration dependence of their ability to bind small molecules including fluorogenic amyloid stains. Measuring these microclot parameters, together with microscopy imaging itself, along with methodologies like proteomics and imaging flow cytometry, as well as more conventional assays such as those for cytokines, might open up the possibility of a much finer use of these microclot properties in generative methods for a future where personalized medicine will be standard procedures in all clotting pathology disease diagnoses.

Overall haemostatic potential assay for prediction of outcomes in venous and arterial thrombosis and thrombo-inflammatory diseases

Thromboembolic diseases including arterial and venous thrombosis are common causes of morbidity and mortality globally. Thrombosis frequently recurs and can also complicate many inflammatory conditions through the process of 'thrombo-inflammation,' as evidenced during the COVID-19 pandemic. Current candidate biomarkers for thrombosis prediction, such as D-dimer, have poor predictive efficacy. This limits our capacity to tailor anticoagulation duration individually and may expose lower risk individuals to undue bleeding risk. Global coagulation assays, such as the Overall Haemostatic Potential (OHP) assay, that investigate fibrin generation and fibrinolysis, may provide a more accurate and functional assessment of hypercoagulability. We present a review of fibrin's critical role as a central modulator of thrombotic risk. The results of our studies demonstrating the OHP assay as a predictive biomarker in venous thromboembolism, chronic renal disease, diabetes mellitus, post-thrombotic syndrome, and COVID-19 are discussed. As a comprehensive and global measurement of fibrin generation and fibrinolytic capacity, the OHP assay may be a valuable addition to future multi-modal predictive tools in thrombosis.

Reprograming Clots for In Vivo Chemical Targeting in Traumatic Brain Injury

Traumatic brain injury (TBI) is a critical public health concern, yet there are no therapeutics available to improve long-term outcomes. Drug delivery to TBI remains a challenge due to the blood-brain barrier and increased intracranial pressure. In this work, a chemical targeting approach to improve delivery of materials to the injured brain, is developed. It is hypothesized that the provisional fibrin matrix can be harnessed as an injury-specific scaffold that can be targeted by materials via click chemistry. To accomplish this, the brain clot is engineered in situ by delivering fibrinogen modified with strained cyclooctyne (SCO) moieties, which incorporated into the injury lesion and is retained there for days. Improved intra-injury capture and retention of diverse, clickable azide-materials including a small molecule azide-dye, 40 kDa azide-PEG nanomaterial, and a therapeutic azide-protein in multiple dosing regimens is subsequently observed. To demonstrate therapeutic translation of this approach, a reduction in reactive oxygen species levels in the injured brain after delivery of the antioxidant catalase, is achieved. Further, colocalization between azide and SCO-fibrinogen is specific to the brain over off-target organs. Taken together, a chemical targeting strategy leveraging endogenous clot formation is established which can be applied to improve therapeutic delivery after TBI.

Fibrinaloid Microclots and Atrial Fibrillation

Atrial fibrillation (AF) is a comorbidity of a variety of other chronic, inflammatory diseases for which fibrinaloid microclots are a known accompaniment (and in some cases, a cause, with a mechanistic basis). Clots are, of course, a well-known consequence of atrial fibrillation. We here ask the question whether the fibrinaloid microclots seen in plasma or serum may in fact also be a cause of (or contributor to) the development of AF. We consider known 'risk factors' for AF, and in particular, exogenous stimuli such as infection and air pollution by particulates, both of which are known to cause AF. The external accompaniments of both bacterial (lipopolysaccharide and lipoteichoic acids) and viral (SARS-CoV-2 spike protein) infections are known to stimulate fibrinaloid microclots when added in vitro, and fibrinaloid microclots, as with other amyloid proteins, can be cytotoxic, both by inducing hypoxia/reperfusion and by other means. Strokes and thromboembolisms are also common consequences of AF. Consequently, taking a systems approach, we review the considerable evidence in detail, which leads us to suggest that it is likely that microclots may well have an aetiological role in the development of AF. This has significant mechanistic and therapeutic implications.

Effect of prothrombin Belgrade mutation, causing antithrombin resistance, on fibrin clot properties

INTRODUCTION

Prothrombin Belgrade mutation is the result of the c.1787G>A substitution in the prothrombin gene. It is located in the antithrombin and sodium binding site and leads to impaired inactivation of thrombin by antithrombin, resulting in antithrombin resistance and thrombotic disorders. However, it negatively affects sodium binding and may have hypocoagulant effects. Considering that prothrombin Belgrade mutation mechanism is still not fully elucidated and that sodium binding is important for thrombin affinity towards fibrinogen, our aim was to determine whether this mutation affects fibrin clot formation and lysis.

METHODS

Using HEK293T cell line, recombinant wild type and mutated prothrombin were generated by transient transfection. Samples that correspond to plasma of a non-carrier, heterozygous and homozygous carriers were reconstituted using prothrombin deficient plasma and recombinant proteins. Reconstituted samples were used in OHP assay (Overall Hemostasis Potential) to determine kinetic profiles of coagulation and fibrinolysis. Clot turbidity assay was performed to observe kinetics of clot formation and lysis more closely. Fibrin clots formed in reconstituted plasma samples were analyzed by confocal microscopy to determine density of fibrin network. Fibrin clots were additionally observed using electron microscopy to determine thickness of individual fibrin fibers.

RESULTS

No significant difference found in OHP, OCP, OFP, and fibrin network density between wild type, heterozygous, and homozygous carrier reconstituted plasma samples. There were significant differences between samples for slope and slope time parameters in kinetic profiles and fibrin fiber thickness.

CONCLUSIONS

Results indicate that prothrombin Belgrade mutation has no significant impact on fibrinolysis, however it may affect kinetics of clot formation and its architecture.

The effect of plasmin-mediated degradation on fibrinolysis and tissue plasminogen activator diffusion

We modify a three-dimensional multiscale model of fibrinolysis to study the effect of plasmin-mediated degradation of fibrin on tissue plasminogen activator (tPA) diffusion and fibrinolysis. We propose that tPA is released from a fibrin fiber by simple kinetic unbinding, as well as by "forced unbinding," which occurs when plasmin degrades fibrin to which tPA is bound. We show that, if tPA is bound to a small-enough piece of fibrin that it can diffuse into the clot, then plasmin can increase the effective diffusion of tPA. If tPA is bound to larger fibrin degradation products (FDPs) that can only diffuse along the clot, then plasmin can decrease the effective diffusion of tPA. We find that lysis rates are fastest when tPA is bound to fibrin that can diffuse into the clot, and slowest when tPA is bound to FDPs that can only diffuse along the clot. Laboratory experiments confirm that FDPs can diffuse into a clot, and they support the model hypothesis that forced unbinding of tPA results in a mix of FDPs, such that tPA bound to FDPs can diffuse both into and along the clot. Regardless of how tPA is released from a fiber, a tPA mutant with a smaller dissociation constant results in slower lysis (because tPA binds strongly to fibrin), and a tPA mutant with a larger dissociation constant results in faster lysis.

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.

Clot or Not? Reviewing the Reciprocal Regulation Between Lipids and Blood Clotting

Both hyperlipidemia and thrombosis contribute to the risks of atherosclerotic cardiovascular diseases, which are the leading cause of death and reduced quality of life in survivors worldwide. The accumulation of lipid-rich plaques on arterial walls eventually leads to the rupture or erosion of vulnerable lesions, triggering excessive blood clotting and leading to adverse thrombotic events. Lipoproteins are highly dynamic particles that circulate in blood, carry insoluble lipids, and are associated with proteins, many of which are involved in blood clotting. A growing body of evidence suggests a reciprocal regulatory relationship between blood clotting and lipid metabolism. In this review article, we summarize the observations that lipoproteins and lipids impact the hemostatic system, and the clotting-related proteins influence lipid metabolism. We also highlight the gaps that need to be filled in this area of research.

Internal fibrinolysis of fibrin clots is driven by pore expansion

Blood clots, which are composed of blood cells and a stabilizing mesh of fibrin fibers, are critical in cessation of bleeding following injury. However, their action is transient and after performing their physiological function they must be resolved through a process known as fibrinolysis. Internal fibrinolysis is the degradation of fibrin by the endogenous or innate presence of lytic enzymes in the bloodstream; under healthy conditions, this process regulates hemostasis and prevents bleeding or clotting. Fibrin-bound tissue plasminogen activator (tPA) converts nearby plasminogen into active plasmin, which is bound to the fibrin network, breaking it down into fibrin degradation products and releasing the entrapped blood cells. It is poorly understood how changes in the fibrin structure and lytic protein ratios influence the biochemical regulation and behavior of internal fibrinolysis. We used turbidity kinetic tracking and microscopy paired with mathematical modeling to study fibrin structure and lytic protein ratios that restrict internal fibrinolysis. Analysis of simulations and experiments indicate that fibrinolysis is driven by pore expansion of the fibrin network. We show that this effect is strongly influenced by the ratio of fibrin:tPAwhen compared to absolute tPA concentration. Thus, it is essential to consider relative protein concentrations when studying internal fibrinolysis both experimentally and in the clinic. An improved understanding of effective internal lysis can aid in development of better therapeutics for the treatment of bleeding and thrombosis.

Preparation and Mechano-Functional Characterization of PEGylated Fibrin Hydrogels: Impact of Thrombin Concentration

Three-dimensional (3D) neuronal cultures grown in hydrogels are promising platforms to design brain-like neuronal networks in vitro. However, the optimal properties of such cultures must be tuned to ensure a hydrogel matrix sufficiently porous to promote healthy development but also sufficiently rigid for structural support. Such an optimization is difficult since it implies the exploration of different hydrogel compositions and, at the same time, a functional analysis to validate neuronal culture viability. To advance in this quest, here we present a combination of a rheological protocol and a network-based functional analysis to investigate PEGylated fibrin hydrogel networks with gradually higher stiffness, achieved by increasing the concentration of thrombin. We observed that moderate thrombin concentrations of 10% and 25% in volume shaped healthy networks, although the functional traits depended on the hydrogel stiffness, which was much higher for the latter concentration. Thrombin concentrations of 65% or higher led to networks that did not survive. Our results illustrate the difficulties and limitations in preparing 3D neuronal networks, and stress the importance of combining a mechano-structural characterization of a biomaterial with a functional one.

In vitro effect of hydroxyethyl starch on COVID-19 patients-associated hypofibrinolytic state

Background

Despite systematic thromboprophylaxis, 30% of the COVID-19 patients in intensive care units develop thrombosis. This occurrence is associated with a hypofibrinolytic state measured by thromboelastometry when adding tissue plasminogen activator (tPA) to citrated whole blood for a further run for EXTEM (ROTEM).

Objectives

Because hydroxyethyl starches (HESs) affect fibrin polymerization, we have assessed its potential effect on in vitro tPA-induced fibrinolysis.

Methods

Fifteen successive COVID-19 patients from the local intensive care units were selected for tPA resistance occurrence. HES was added to whole blood samples with proportion similar to the pharmacologic recommendations. Samples were run for EXTEM on a ROTEM delta device after further addition of tPA. Paired controls were whole blood samples with the same volume of saline added. To assess the impact of HES on coagulation, thrombin generation was measured in 10 COVID-19 patients in the presence of either HES or saline; then, the clots obtained were used to generate electron microscope images.

Results

Clot firmness at 5 minutes and the lysis index at 30 minutes were decreased in presence of HES compared with saline (Wilcoxon test, P < .01 for HES vs saline and HES vs untreated). However, no statistically significant difference was observed for all thrombin generation assay parameters studied (endogenous thrombin potential, peak thrombin, and time to peak). With HES, fibrin fibers of either COVID-19 patients or control subjects were thicker than those of saline-treated samples.

Conclusion

These results highlight that HES increased apparent in vitro tPA-induced fibrinolysis in case of severe COVID-19 disease. Use of this plasma volume expander may translate as a potential help against COVID-19-induced thrombosis occurrence.

Mice expressing nonpolymerizable fibrinogen have reduced arterial and venous thrombosis with preserved hemostasis

ABSTRACT

Elevated circulating fibrinogen levels correlate with increased risk for both cardiovascular and venous thromboembolic diseases. In vitro studies show that formation of a highly dense fibrin matrix is a major determinant of clot structure and stability. Here, we analyzed the impact of nonpolymerizable fibrinogen on arterial and venous thrombosis as well as hemostasis in vivo using FgaEK mice that express normal levels of a fibrinogen that cannot be cleaved by thrombin. In a model of carotid artery thrombosis, FgaWT/EK and FgaEK/EK mice were protected from occlusion with 4% ferric chloride (FeCl3) challenges compared with wild-type (FgaWT/WT) mice, but this protection was lost, with injuries driven by higher concentrations of FeCl3. In contrast, fibrinogen-deficient (Fga-/-) mice showed no evidence of occlusion, even with high-concentration FeCl3 challenge. Fibrinogen-dependent platelet aggregation and intraplatelet fibrinogen content were similar in FgaWT/WT, FgaWT/EK, and FgaEK/EK mice, consistent with preserved fibrinogen-platelet interactions that support arterial thrombosis with severe challenge. In an inferior vena cava stasis model of venous thrombosis, FgaEK/EK mice had near complete protection from thrombus formation. FgaWT/EK mice also displayed reduced thrombus incidence and a significant reduction in thrombus mass relative to FgaWT/WT mice after inferior vena cava stasis, suggesting that partial expression of nonpolymerizable fibrinogen was sufficient for conferring protection. Notably, FgaWT/EK and FgaEK/EK mice had preserved hemostasis in multiple models as well as normal wound healing times after skin incision, unlike Fga-/- mice that displayed significant bleeding and delayed healing. These findings indicate that a nonpolymerizable fibrinogen variant can significantly suppress occlusive thrombosis while preserving hemostatic potential in vivo.

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.

Tissue-type plasminogen activator (tPA) homozygous Tyr471His mutation associates with thromboembolic disease

Tissue-type plasminogen activator (tPA) encoded by PLAT is a major mediator that promotes fibrinolysis and prevents thrombosis. Pathogenetic mutations in PLAT associated with venous thromboembolism have rarely been reported. Here, we report the first case of a homozygous point mutation c.1411T>C (p.Y471H) in PLAT leading to thromboembolic events and conduct related functional studies. The corresponding tPA mutant protein (tPA-Y471H) and wild-type tPA (tPA-WT) were synthesized in vitro, and mutant mice (PLATH/H mice) were constructed. The molecular docking and surface plasmon resonance results indicated that the mutation impeded the hydrogen-bonding interactions between the protease domain of tPA and the kringle 4 domain of plasminogen, and the binding affinity of tPA and plasminogen was significantly reduced with a difference of one order of magnitude. mRNA half-life assay showed that the half-life of tPA-Y471H was shortened. The inferior vena cava thrombosis model showed that the rate of venous thrombosis in PLATH/H mice was 80% compared with 53% in wild-type mice. Our data suggested a novel role for the protease domain of tPA in efficient plasminogen activation, and demonstrated that this tPA mutation could reduce the fibrinolysis function of the body and lead to an increased propensity for thrombosis.

Fibrin clots from patients with acute-on-chronic liver failure are weaker than those from healthy individuals and patients with sepsis without underlying liver disease

BACKGROUND

Previous studies identified decreased clot permeability, without differences in fibrin fiber density in clots, from patients with cirrhosis compared with those from healthy controls (HCs). Fibrinogen hypersialylation could be the reason for this discrepancy.

OBJECTIVES

The aim of this work was to study mechanical properties of clots and reassess clot permeability in relation to hypersialylation in patients with stable cirrhosis, acute decompensation, and acute-on-chronic liver failure (ACLF). Sepsis patients without liver disease were included to distinguish between liver-specific and inflammation-driven phenotypes.

METHODS

Pooled plasma was used for rheology and permeability experiments. Permeability was assessed with compression using a rheometer and by liquid permeation. Purified fibrinogen treated with neuraminidase was used to study the effects of fibrinogen hypersialylation on liquid permeation.

RESULTS

Mechanical properties of clots from patients with stable cirrhosis and acute decompensation were similar to those of clots from HCs, but clots from patients with ACLF were softer and ruptured at lower shear stress. Clots from sepsis patients without liver disease were stiffer than those from the other groups, but this effect disappeared after adjusting for increased plasma fibrinogen concentrations. Permeability was similar between clots under compression from HCs and clots under compression from patients but decreased with increasing disease severity in liquid permeation. Removal of fibrinogen sialic acid residues increased permeability more in patients than in controls.

CONCLUSION

Clots from patients with ACLF have weak mechanical properties despite unaltered fibrin fiber density. Previous liquid permeation experiments may have erroneously concluded that clots from patients with ACLF are prothrombotic as fibrinogen hypersialylation leads to underestimation of clot permeability in this setting, presumably due to enhanced water retention.

The Fibrinolytic System and Its Measurement: History, Current Uses and Future Directions for Diagnosis and Treatment

The fibrinolytic system is a key player in keeping the haemostatic balance, and changes in fibrinolytic capacity can lead to both bleeding-related and thrombosis-related disorders. Our knowledge of the fibrinolytic system has expanded immensely during the last 75 years. From the first successful use of thrombolysis in myocardial infarction in the 1960s, thrombolytic therapy is now widely implemented and has reformed treatment in vascular medicine, especially ischemic stroke, while antifibrinolytic agents are used routinely in the prevention and treatment of major bleeding worldwide. Despite this, this research field still holds unanswered questions. Accurate and timely laboratory diagnosis of disturbed fibrinolysis in the clinical setting remains a challenge. Furthermore, despite growing evidence that hypofibrinolysis plays a central role in, e.g., sepsis-related coagulopathy, coronary artery disease, and venous thromboembolism, there is currently no approved treatment of hypofibrinolysis in these settings. The present review provides an overview of the fibrinolytic system and history of its discovery; measurement methods; clinical relevance of the fibrinolytic system in diagnosis and treatment; and points to future directions for research.

Association of Fibrinolytic Potential and Risk of Mortality in Cancer Patients

Cancer is a leading cause of death, and the fibrinolytic system shows cooperative effects that facilitate the growth of tumors and the appearance of metastases. This prospective study aimed to evaluate the fibrinolytic potential in cancer patients and its association with mortality outcomes using the fluorometric method of simultaneous thrombin and plasmin generation. The study included 323 cancer patients and 148 healthy individuals. During the 12-month follow-up, 68 patients died. Compared to the control group, cancer patients showed alterations in thrombin production consistent with a hypercoagulability profile, and an increase in plasmin generation. Mortality risk was associated with two parameters of thrombin in both univariate and multivariable analysis: maximum amplitude (Wald 11.78, p < 0.001) and area under the curve (Wald 8.0, p < 0.005), while such associations were not observed for plasmin. In conclusion, this was the first study able to demonstrate the simultaneous evaluation of thrombin and plasmin generation in newly diagnosed untreated cancer patients. Patients with cancer have been observed to exhibit a hypercoagulable profile. During the study, two parameters linked to thrombin generation, MA and AUC, were identified and found to have a potential association with mortality risk. However, no associations were found with parameters related to plasmin generation.

Computational modeling of blood clot lysis considering the effect of vessel wall and pulsatile blood flow

Stroke is one of the major causes of global death, which can occur due to blockage in a blood vessel by a clot. The immediate dissolving of the clot is essential to restore the blood flow and prevent tissue necrosis. Clot dissolution can be achieved via thrombolytic therapy using plasminogen activators. In this study, a clot dissolution model is developed for a three-dimensional patient-specific carotid artery that investigates the effect of different vessel wall models on clot dissolution. The lysis pattern of the clot and hemodynamics of blood flow are evaluated using three different models of the vessel wall, namely, rigid, linear elastic, and Mooney-Rivlin hyperelastic. The effect of flow condition is considered by solving the Navier-Stokes equations for the free flow domain and the Brinkman equation for the clot domain with the same pressure and velocity fields. This will result in continuous pressure and velocity over the interfaces of the free flow and clot domains. The blood inflow is assumed to be pulsatile. In addition, the species transport driven by diffusion and convection is considered to be different in the porous medium and plasma. The obtained results show that in all models, the starting time of clot volume decrease is almost the same and the clot starts dissolving from the inner curvature of the artery. However, in the hyperelastic model, dissolving the clot takes longer compared to the other two models. By monitoring the vessel wall deformation, the exact time of vessel recanalization is determined.

A simplified mesoscale 3D model for characterizing fibrinolysis under flow conditions

One of the routine clinical treatments to eliminate ischemic stroke thrombi is injecting a biochemical product into the patient's bloodstream, which breaks down the thrombi's fibrin fibers: intravenous or intravascular thrombolysis. However, this procedure is not without risk for the patient; the worst circumstances can cause a brain hemorrhage or embolism that can be fatal. Improvement in patient management drastically reduced these risks, and patients who benefited from thrombolysis soon after the onset of the stroke have a significantly better 3-month prognosis, but treatment success is highly variable. The causes of this variability remain unclear, and it is likely that some fundamental aspects still require thorough investigations. For that reason, we conducted in vitro flow-driven fibrinolysis experiments to study pure fibrin thrombi breakdown in controlled conditions and observed that the lysis front evolved non-linearly in time. To understand these results, we developed an analytical 1D lysis model in which the thrombus is considered a porous medium. The lytic cascade is reduced to a second-order reaction involving fibrin and a surrogate pro-fibrinolytic agent. The model was able to reproduce the observed lysis evolution under the assumptions of constant fluid velocity and lysis occurring only at the front. For adding complexity, such as clot heterogeneity or complex flow conditions, we propose a 3-dimensional mesoscopic numerical model of blood flow and fibrinolysis, which validates the analytical model's results. Such a numerical model could help us better understand the spatial evolution of the thrombi breakdown, extract the most relevant physiological parameters to lysis efficiency, and possibly explain the failure of the clinical treatment. These findings suggest that even though real-world fibrinolysis is a complex biological process, a simplified model can recover the main features of lysis evolution.

Tranexamic acid for the prevention of postpartum bleeding in women with anaemia: Statistical analysis plan for the WOMAN-2 trial: an international, randomised, placebo-controlled trial

Background: Postpartum haemorrhage (PPH) is responsible for over 50,000 maternal deaths every year. Most of these deaths are in low- and middle-income countries. Tranexamic acid (TXA) reduces bleeding by inhibiting the enzymatic breakdown of fibrin blood clots. TXA decreases surgical bleeding and reduces deaths from bleeding after traumatic injury. When given within three hours of birth, TXA reduces deaths from bleeding in women with PPH. However, for many women, treatment of PPH is too late to prevent death. World-wide, over one-third of pregnant women are anaemic and many are severely anaemic. These women have an increased risk of PPH and are more likely to die if PPH occurs. There is an urgent need to identify ways to prevent severe postpartum bleeding in anaemic women. The WOMAN-2 trial will quantify the effects of TXA on postpartum bleeding in women with anaemia. Results: This statistical analysis plan (version 1.0; dated 22 February 2023) has been written based on information in the WOMAN-2 Trial protocol version 2.0, dated 30 June 2022. The primary outcome of the WOMAN-2 trial is the proportion of women with a clinical diagnosis of primary PPH. Secondary outcomes are maternal blood loss and its consequences (estimated blood loss, haemoglobin, haemodynamic instability, blood transfusion, signs of shock, use of interventions to control bleeding); maternal health and wellbeing (fatigue, headache, dizziness, palpitations, breathlessness, exercise tolerance, ability to care for her baby, health related quality of life, breastfeeding); and other health outcomes (deaths, vascular occlusive events, organ dysfunction, sepsis, side effects, time spent in higher level facility, length of hospital stay, and status of the baby). Conclusions: WOMAN-2 will provide reliable evidence about the effects of TXA in women with anaemia. Registration: WOMAN-2 was prospectively registered at the International Standard Randomised Controlled Trials registry ( ISRCTN62396133) on 07/12/2017 and ClinicalTrials.gov on 23/03/2018 ( NCT03475342).

Profibrinolytic effects of rivaroxaban are mediated by thrombin-activatable fibrinolysis inhibitor and are attenuated by a naturally occurring stabilizing mutation in enzyme

Rivaroxaban is a direct factor Xa inhibitor, recently implemented as a favorable alternative to warfarin in anticoagulation therapy. Rivaroxaban effectively reduces thrombin generation, which plays a major role in the activation of thrombin activatable fibrinolysis inhibitor (TAFI) to TAFIa. Based on the antifibrinolytic role of TAFIa, we hypothesized that rivaroxaban would consequently induce more rapid clot lysis. In vitro clot lysis assays were used to explore this hypothesis and additionally determine the effects of varying TAFI levels and a stabilizing Thr325Ile polymorphism (rs1926447) in the TAFI protein on the effects of rivaroxaban. Rivaroxaban was shown to decrease thrombin generation, resulting in less TAFI activation, thus enhancing lysis. These effects were also shown to be less substantial in the presence of greater TAFI levels or the more stable Ile325 enzyme. These findings suggest a role for TAFI levels and the Thr325Ile polymorphism in the pharmacodynamics and pharmacogenomics of rivaroxaban.

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.

Fibrin-glycoprotein VI interaction increases platelet procoagulant activity and impacts clot structure

BACKGROUND

The glycoprotein VI (GPVI) signaling pathway was previously reported to direct procoagulant platelet activity through collagen binding. However, the impact of GPVI-fibrin interaction on procoagulant platelet development and how it modulates the clot structure are unknown.

OBJECTIVES

To determine the effect of GPVI-fibrin interaction on the platelet phenotype and its impact on the clot structure.

METHODS

Procoagulant platelets in platelet-rich plasma clots were determined by scanning electron microscopy (wild-type and GPVI-deficient murine samples) and confocal microscopy. Procoagulant platelet number, clot density, clot porosity, and clot retraction were determined in platelet-rich plasma or whole blood clots of healthy volunteers in the presence of tyrosine kinase inhibitors (PRT-060318, ibrutinib, and dasatinib) and eptifibatide.

RESULTS

GPVI-deficient clots showed a higher nonprocoagulant vs procoagulant platelet ratio than wild-type clots. The fiber density and the procoagulant platelet number decreased in the presence of Affimer proteins, inhibiting GPVI-fibrin(ogen) interaction and the tyrosine kinase inhibitors. The effect of GPVI signaling inhibitors on the procoagulant platelet number was exacerbated by eptifibatide. The tyrosine kinase inhibitors led to an increase in clot porosity; however, no differences were observed in the final clot weight, following clot retraction with the tyrosine kinase inhibitors, except for ibrutinib. In the presence of eptifibatide, clot retraction was impaired.

CONCLUSION

Our findings showed that GPVI-fibrin interaction significantly contributes to the development of procoagulant platelets and that inhibition of GPVI signaling increases clot porosity. Clot contractibility was impaired by the integrin αIIbβ3 and Btk pathway inhibition. Thus, inhibition of GPVI-fibrin interactions can alleviate structural characteristics that contribute to a prothrombotic clot phenotype, having potential important implications for novel antithrombotic interventions.

Development of a new plasma rich in growth factors membrane with improved optical properties

PURPOSE

The aim of the present work was to develop a fibrin membrane using plasma rich in growth factors (PRGF) technology with improved optical properties to be used for the treatment of ocular surface diseases.

BASIC PROCEDURES

Blood was drawn from three healthy donors, and the volume of PRGF obtained from each donor was divided into two main groups: i) PRGF or ii) platelet-poor plasma (PPP). Each membrane was then used pure or diluted to 90 %, 80 %, 70 %, 60 % and 50 %. The transparency of each of the different membranes was evaluated. The degradation and morphological characterization of each membrane was also performed. Finally, a stability study of the different fibrin membranes was performed.

MAIN FINDINGS

The transmittance test showed that the fibrin membrane with the best optical characteristics was obtained after removal of platelets and dilution of fibrin to 50 % (50 % PPP). No significant differences (p > 0.05) were observed between the different membranes in the fibrin degradation test. The stability test showed that the membrane at 50 % PPP retains its optical and physical characteristics after storage at - 20 °C for 1 month compared to storage at 4 °C.

PRINCIPAL CONCLUSIONS

The present study describes the development and characterization of a new fibrin membrane with improved optical characteristics while maintaining mechanical and biological characteristics. The physical and mechanical properties of the newly developed membrane are preserved after storage for at least 1 month at - 20 °C.

Admission maximum amplitude-reaction time ratio: Association between thromboelastography values predicts poor outcome in injured children

INTRODUCTION

Thromboelastography (TEG)-derived maximum amplitude-reaction time (MA-R) ratio that accounts for both hypocoagulable and hypercoagulable changes in coagulation is associated with poor outcomes in adults. The relationship between these TEG values and outcomes has not been studied in children.

METHODS

In a retrospective cohort study, a level I pediatric trauma center database was queried for children younger than 18 years who had a TEG assay on admission between 2016 and 2020. Demographics, injury characteristics, and admission TEG values were recorded. The MA-R ratio was calculated and divided into quartiles. Main outcomes included mortality, transfusion within 24 hours of admission, and thromboembolism. A logistic regression model was generated adjusting for age, Injury Severity Score, injury mechanism, admission shock, and Glasgow Coma Scale.

RESULTS

In total, 657 children were included, of which 70% were male and 75% had blunt mechanism injury. The median (interquartile range) age was 11 (4-14) years, the median (interquartile range) Injury Severity Score was10 (5-22), and in-hospital mortality was 7% (n = 45). Of these patients, 17% (n = 112) required transfusion. Most R and MA values were within normal limits. On unadjusted analysis, the lowest MA-R ratio quartile was associated with increased mortality (15% vs. 4%, 5%, and 4%, respectively; p < 0.001) and increased transfusion need (26% vs. 12%, 16%, and 13%, respectively; p = 0.002) compared with higher quartiles. In the logistic regression models, a low MA-R ratio was independently associated with increased in-hospital mortality (odds ratio [95% confidence interval], 4.4 [1.9-10.2]) and increased need for transfusion within 24 hours of admission (odds ratio [95% confidence interval], 2.0 [1.2-3.4]) compared with higher MA-R ratio. There was no association between MA-R ratio and venous thromboembolic events (venous thromboembolic event rate by quartile: 4%, 2%, 1%, and 3%).

CONCLUSION

Although individual admission TEG values are not commonly substantially deranged in injured children, the MA-R ratio is an independent predictor of poor outcome. Maximum amplitude-reaction time ratio may be a useful prognostic tool in pediatric trauma; validation is necessary.

LEVEL OF EVIDENCE

Therapeutic/Care Management; Level III.

A systematic review and comparison of automated tools for quantification of fibrous networks

Fibrous networks are essential structural components of biological and engineered materials. Accordingly, many approaches have been developed to quantify their structural properties, which define their material properties. However, a comprehensive overview and comparison of methods is lacking. Therefore, we systematically searched for automated tools quantifying network characteristics in confocal, stimulated emission depletion (STED) or scanning electron microscopy (SEM) images and compared these tools by applying them to fibrin, a prototypical fibrous network in thrombi. Structural properties of fibrin such as fiber diameter and alignment are clinically relevant, since they influence the risk of thrombosis. Based on a systematic comparison of the automated tools with each other, manual measurements, and simulated networks, we provide guidance to choose appropriate tools for fibrous network quantification depending on imaging modality and structural parameter. These tools are often able to reliably measure relative changes in network characteristics, but absolute numbers should be interpreted with care. STATEMENT OF SIGNIFICANCE: Structural properties of fibrous networks define material properties of many biological and engineered materials. Many methods exist to automatically quantify structural properties, but an overview and comparison is lacking. In this work, we systematically searched for all publicly available automated analysis tools that can quantify structural properties of fibrous networks. Next, we compared them by applying them to microscopy images of fibrin networks. We also benchmarked the automated tools against manual measurements or synthetic images. As a result, we give advice on which automated analysis tools to use for specific structural properties. We anticipate that researchers from a large variety of fields, ranging from thrombosis and hemostasis to cancer research, and materials science, can benefit from our work.

Fibrinolysis: an illustrated review

In response to vessel injury (or other pathological conditions), the hemostatic process is activated, resulting in a fibrous, cellular-rich structure commonly referred to as a blood clot. Succeeding the clot's function in wound healing, it must be resolved. This illustrated review focuses on fibrinolysis-the degradation of blood clots or thrombi. Fibrin is the main mechanical and structural component of a blood clot, which encases the cellular components of the clot, including platelets and red blood cells. Fibrinolysis is the proteolytic degradation of the fibrin network that results in the release of the cellular components into the bloodstream. In the case of thrombosis, fibrinolysis is required for restoration of blood flow, which is accomplished clinically through exogenously delivered lytic factors in a process called external lysis. Fibrinolysis is regulated by plasminogen activators (tissue-type and urokinase-type) that convert plasminogen into plasmin to initiate fiber lysis and lytic inhibitors that impede this lysis (plasminogen activator inhibitors, alpha 2-antiplasmin, and thrombin activatable fibrinolysis inhibitor). Furthermore, the network structure has been shown to regulate lysis: thinner fibers and coarser clots lyse faster than thicker fibers and finer clots. Clot contraction, a result of platelets pulling on fibers, results in densely packed red blood cells (polyhedrocytes), reduced permeability to fibrinolytic factors, and increased fiber tension. Extensive research in the field has allowed for critical advancements leading to improved thrombolytic agents. In this review, we summarize the state of the field, highlight gaps in knowledge, and propose future research questions.

Location, location, location: Fibrin, cells, and fibrinolytic factors in thrombi

Thrombi are heterogenous in nature with composition and structure being dictated by the site of formation, initiating stimuli, shear stress, and cellular influences. Arterial thrombi are historically associated with high platelet content and more tightly packed fibrin, reflecting the shear stress in these vessels. In contrast, venous thrombi are generally erythrocyte and fibrin-rich with reduced platelet contribution. However, these conventional views on the composition of thrombi in divergent vascular beds have shifted in recent years, largely due to recent advances in thromboectomy and high-resolution imaging. Interestingly, the distribution of fibrinolytic proteins within thrombi is directly influenced by the cellular composition and vascular bed. This in turn influences the susceptibility of thrombi to proteolytic degradation. Our current knowledge of thrombus composition and its impact on resistance to thrombolytic therapy and success of thrombectomy is advancing, but nonetheless in its infancy. We require a deeper understanding of thrombus architecture and the downstream influence on fibrinolytic susceptibility. Ultimately, this will aid in a stratified and targeted approach to tailored antithrombotic strategies in patients with various thromboembolic diseases.

Physiological fibrin hydrogel modulates immune cells and molecules and accelerates mouse skin wound healing

Introduction

Wound healing is a complex process to restore homeostasis after injury and insufficient skin wound healing is a considerable problem in medicine. Whereas many attempts of regenerative medicine have been made for wound healing with growth factors and cell therapies, simple pharmacological and immunological studies are lagging behind. We investigated how fibrin hydrogels modulate immune cells and molecules in skin wound healing in mice.

Methods

Physiological fibrin hydrogels (3.5 mg/mL fibrinogen) were generated, biophysically analyzed for stiffness and protein contents and were structurally studied by scanning electron microscopy. Physiological fibrin hydrogels were applied to full thickness skin wounds and, after 3 days, cells and molecules in wound tissues were analyzed. Leukocytes, endothelial cells, fibroblasts and keratinocytes were explored with the use of Flow Cytometry, whereas cytokines and matrix metalloproteinases were analyzed with the use of qPCR, ELISAs and zymography. Skin wound healing was analyzed microscopically at day 3, macroscopically followed daily during repair in mice and compared with commercially available fibrin sealant Tisseel.

Results

Exogenous fibrin at physiological concentrations decreased neutrophil and increased non-classical Ly6Clow monocyte and resolutive macrophage (CD206⁺ and CX3CR1⁺) populations, at day 3 after injury. Fibrin hydrogel reduced the expression of pro-inflammatory cytokines and increased IL-10 levels. In line with these findings, gelatinase B/MMP-9 was decreased, whereas gelatinase A/MMP-2 levels remained unaltered. Frequencies of dermal endothelial cells, fibroblasts and keratinocytes were increased and keratinocyte migration was enhanced by fibrin hydrogel. Importantly, physiological fibrin accelerated the healing of skin wounds in contrast to the highly concentrated fibrin sealant Tisseel, which delayed wound repair and possessed a higher fiber density.

Conclusion

Collectively, we show that adding a tailored fibrin hydrogel scaffold to a wound bed positively influences the healing process, modulating leukocyte populations and inflammatory responses towards a faster wound repair.

“Going with the flow” in modeling fibrinolysis

The formation of thrombi is shaped by intravascular shear stress, influencing both fibrin architecture and the cellular composition which has downstream implications in terms of stability against mechanical and fibrinolytic forces. There have been many advancements in the development of models that incorporate flow rates akin to those found in vivo. Both thrombus formation and breakdown are simultaneous processes, the balance of which dictates the size, persistence and resolution of thrombi. Therefore, there is a requirement to have models which mimic the physiological shear experienced within the vasculature which in turn influences the fibrinolytic degradation of the thrombus. Here, we discuss various assays for fibrinolysis and importantly the development of novel models that incorporate physiological shear rates. These models are essential tools to untangle the molecular and cellular processes which govern fibrinolysis and can recreate the conditions within normal and diseased vessels to determine how these processes become perturbed in a pathophysiological setting. They also have utility to assess novel drug targets and antithrombotic drugs that influence thrombus stability.

Fibrinolysis Regulation: A Promising Approach to Promote Osteogenesis

Soon after bone fracture, the initiation of the coagulation cascade results in the formation of a blood clot, which acts as a natural material to facilitate cell migration and osteogenic differentiation at the fracture site. The existence of hematoma is important in early stage of bone healing, but the persistence of hematoma is considered harmful for bone regeneration. Fibrinolysis is recently regarded as a period of critical transition in angiogenic-osteogenic coupling, it thereby is vital for the complete healing of the bone. Moreover, the enhanced fibrinolysis is proposed to boost bone regeneration through promoting the formation of blood vessels, and fibrinolysis system as well as the products of fibrinolysis also play crucial roles in the bone healing process. Therefore, the purpose of this review is to elucidate the fibrinolysis-derived effects on osteogenesis and summarize the potential approaches-improving bone healing by regulating fibrinolysis, with the purpose to further understand the integral roles of fibrinolysis in bone regeneration and to provide theoretical knowledge for potential fibrinolysis-related osteogenesis strategies. Impact statement Fibrinolysis emerging as a new and viable therapeutic intervention to be contained within osteogenesis strategies, however to now, there have been no review articles which collates the information between fibrinolysis and osteogenesis. This review, therefore, focusses on the effects that fibrinolysis exerts on bone healing, with a purpose to provide theoretical reference to develop new strategies to modulate fibrinolysis to accelerate fibrinolysis thus enhancing bone healing.

Correlation of Insulin Resistance With Short-Term Outcome in Nondiabetic Patients With ST-Segment Elevation Myocardial Infarction

BACKGROUND

 Obviously, hyperglycemia and insulin resistance (IR) are common in patients with acute ST-segment elevation myocardial infarction (STEMI). Additionally, IR is a substantial risk factor for cardiovascular diseases. The study aims to evaluate the association between IR and short-term outcomes of acute STEMI patients without diabetes mellitus in the form of reperfusion success, the occurrence of heart failure, the development of arrhythmias, and mortality.

METHOD

 A cross-sectional study was done from August 2021 to December 2021 in two cardiology centers in Al-Sadr Teaching hospital and Basrah Oil hospital in Basrah, Southern Iraq. Sixty-one nondiabetic hospitalized patients with acute STEMI were included in the study. Twenty-five (41%) of them received thrombolytics and 36 (59%) were managed with percutaneous transluminal coronary angioplasty. From each patient, a fasting blood sample was taken for calculation of the Homeostasis Model Assessment for IR (HOMA-IR) and triglyceride glucose index (TyG) index. The patients were evaluated within 1-week for (reperfusion success, echocardiography for calculation of the ejection fraction (EF), arrhythmias, and mortality), and within 4-weeks for mortality.

RESULTS

 Within the tertile 3 of the HOMA-IR and TyG index, significant higher 4-week mortality (35% and 30%, respectively). Pearson correlation also showed significant and negative correlations between both HOMA-IR and TyG index values and EF. While reperfusion success, arrhythmias, and 1-week mortality did not correlate significantly with both HOMA-IR and TyG index.

CONCLUSION

 IR as defined by HOMA-IR and TyG index was significantly associated with poor outcomes in patients with acute STEMI in the form of EF<55 and 4-week mortality.

Optimization of a Plasma Rich in Growth Factors Membrane for the Treatment of Inflammatory Ocular Diseases

The main purpose of the present study is to develop an immunosafe fibrin membrane obtained by plasma rich in growth factors technology (is-mPRGF) with improved mechanical properties that could be applied in patients with inflammatory ocular diseases. Blood was drawn from three healthy donors and centrifuged, and the collected PRGF was activated and distributed into two groups: (i) mPRGF: a PRGF membrane maintained at 37 °C for 30 min; (ii) IS5+30: mPRGF incubated at 37 °C for 5 min and then incubated at 56 °C for 30 min. The content of both membranes was analyzed for several growth factors such as IgE and the complement activation, as well as biological activity on different ocular surface cells. Furthermore, the physical and mechanical characterizations were also evaluated. IS5+30 completely reduced the complement activity and decreased the IgE while preserving the concentration of the main growth factors. IS5+30 induced similar biological activity regarding mPRGF on the different ocular surface cells analyzed. Furthermore, no significant differences in release kinetics or fibrin degradation were observed between both membranes. Summarizing, IS5+30 totally reduces complement activity while preserving the concentration of most growth factors and their biological activity. Furthermore, the physical and mechanical properties of the fibrin membrane are preserved after heat inactivation.

Cryoprecipitate transfusion in trauma patients attenuates hyperfibrinolysis and restores normal clot structure and stability: Results from a laboratory sub-study of the FEISTY trial

BACKGROUND

Fibrinogen is the first coagulation protein to reach critical levels during traumatic haemorrhage. This laboratory study compares paired plasma samples pre- and post-fibrinogen replacement from the Fibrinogen Early In Severe Trauma studY (FEISTY; NCT02745041). FEISTY is the first randomised controlled trial to compare the time to administration of cryoprecipitate (cryo) and fibrinogen concentrate (Fg-C; Riastap) in trauma patients. This study will determine differences in clot strength and fibrinolytic stability within individuals and between treatment arms.

METHODS

Clot lysis, plasmin generation, atomic force microscopy and confocal microscopy were utilised to investigate clot strength and structure in FEISTY patient plasma.

RESULTS

Fibrinogen concentration was significantly increased post-transfusion in both groups. The rate of plasmin generation was reduced 1.5-fold post-transfusion of cryo but remained unchanged with Fg-C transfusion. Plasminogen activator inhibitor 1 activity and antigen levels and Factor XIII antigen were increased post-treatment with cryo, but not Fg-C. Confocal microscopy analysis of fibrin clots revealed that cryo transfusion restored fibrin structure similar to those observed in control clots. In contrast, clots remained porous with stunted fibres after infusion with Fg-C. Cryo but not Fg-C treatment increased individual fibre toughness and stiffness.

CONCLUSIONS

In summary, our data indicate that cryo transfusion restores key fibrinolytic regulators and limits plasmin generation to form stronger clots in an ex vivo laboratory study. This is the first study to investigate differences in clot stability and structure between cryo and Fg-C and demonstrates that the additional factors in cryo allow formation of a stronger and more stable clot.

Effects of clot contraction on clot degradation: A mathematical and experimental approach

Thrombosis, resulting in occlusive blood clots, blocks blood flow to downstream organs and causes life-threatening conditions such as heart attacks and strokes. The administration of tissue plasminogen activator (t-PA), which drives the enzymatic degradation (fibrinolysis) of these blood clots, is a treatment for thrombotic conditions, but the use of these therapeutics is often limited due to the time-dependent nature of treatment and their limited success. We have shown that clot contraction, which is altered in prothrombotic conditions, influences the efficacy of fibrinolysis. Clot contraction results in the volume shrinkage of blood clots, with the redistribution and densification of fibrin and platelets on the exterior of the clot and red blood cells in the interior. Understanding how these key structural changes influence fibrinolysis can lead to improved diagnostics and patient care. We used a combination of mathematical modeling and experimental methodologies to characterize the process of exogenous delivery of t-PA (external fibrinolysis). A three-dimensional (3D) stochastic, multiscale model of external fibrinolysis was used to determine how the structural changes that occur during the process of clot contraction influence the mechanism(s) of fibrinolysis. Experiments were performed based on modeling predictions using pooled human plasma and the external delivery of t-PA to initiate lysis. Analysis of fibrinolysis simulations and experiments indicate that fibrin densification makes the most significant contribution to the rate of fibrinolysis compared with the distribution of components and degree of compaction (p < 0.0001). This result suggests the possibility of a certain fibrin density threshold above which t-PA effective diffusion is limited. From a clinical perspective, this information can be used to improve on current therapeutics by optimizing timing and delivery of lysis agents.

Composition and Organization of Acute Ischemic Stroke Thrombus: A Wealth of Information for Future Thrombolytic Strategies

During the last decade, significant progress has been made in understanding thrombus composition and organization in the setting of acute ischemic stroke (AIS). In particular, thrombus organization is now described as highly heterogeneous but with 2 preserved characteristics: the presence of (1) two distinct main types of areas in the core—red blood cell (RBC)-rich and platelet-rich areas in variable proportions in each thrombus—and (2) an external shell surrounding the core composed exclusively of platelet-rich areas. In contrast to RBC-rich areas, platelet-rich areas are highly complex and are mainly responsible for the thrombolysis resistance of these thrombi for the following reasons: the presence of platelet-derived fibrinolysis inhibitors in large amounts, modifications of the fibrin network structure resistant to the tissue plasminogen activator (tPA)-induced fibrinolysis, and the presence of non-fibrin extracellular components, such as von Willebrand factor (vWF) multimers and neutrophil extracellular traps. From these studies, new therapeutic avenues are in development to increase the fibrinolytic efficacy of intravenous (IV) tPA-based therapy or to target non-fibrin thrombus components, such as platelet aggregates, vWF multimers, or the extracellular DNA network.

Labeling fibrin fibers with beads alter single fibrin fiber lysis, external clot lysis, and produce large fibrin aggregates upon lysis

Fluorescent beads are often used as a tool for visualizing fibrin fibers in single fiber mechanics studies and studies of single fiber lysis. Here we investigate the effect of beads on fibrin fiber lysis and extensibility to enhance understanding of this common research technique. We selected beads of the same diameter as those used in previous studies, as well as, beads of similar size to microparticles in the bloodstream. We used fluorescence microscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) to quantify changes in fiber lysis, fiber extensibility, and clot structure in the presence and absence of beads. Fibrin clot structure and lysis were altered in the presence of beads. Fibrin clots formed with beads had a higher fiber density, smaller diameter fibers, and smaller pores. The rate of lysis for clots was reduced when beads were present. Lysis studies of bead-labeled individual fibers showed that beads, at concentrations similar to those reported for microparticles in the blood, cause a subset of fibers to resist lysis. In the absence of beads, all fibers lyse. These results demonstrate that beads alter fiber lysis through both a change in fibrin clot structure as well as changes to individual fiber lysis behavior. Additionally, the lysis of clots with beads produced large fibrin aggregates. This data encourages researchers to use careful consideration when labeling fibrin fibers with fluorescent beads and suggests that particles binding fibrin(ogen) in the bloodstream may be an underappreciated mechanism increasing the risk of thrombosis.

Thrombosis-associated hypofibrinogenemia: novel abnormal fibrinogen variant FGG c.8G>A with oxidative posttranslational modifications

Here, we present the first case of fibrinogen variant FGG c.8G>A. We investigated the behaviour of this mutated fibrinogen in blood coagulation using fibrin polymerization, fibrinolysis, fibrinopeptides release measurement, mass spectrometry (MS), and scanning electron microscopy (SEM). The case was identified by routine coagulation testing of a 34-year-old man diagnosed with thrombosis. Initial genetic analysis revealed a heterozygous mutation in exon 1 of the FGG gene encoding gamma chain signal peptide. Fibrin polymerization by thrombin and reptilase showed the normal formation of the fibrin clot. However, maximal absorbance within polymerization was lower and fibrinolysis had a longer degradation phase than healthy control. SEM revealed a significant difference in clot structure of the patient, and interestingly, MS detected several posttranslational oxidations of fibrinogen. The data suggest that the mutation FGG c.8G>A with the combination of the effect of posttranslational modifications causes a novel case of hypofibrinogenemia associated with thrombosis.

Aberrant Fibrin Clot Structure Visualized Ex Vivo in Critically Ill Patients With Severe Acute Respiratory Syndrome Coronavirus 2 Infection

OBJECTIVES

Disseminated fibrin-rich microthrombi have been reported in patients who died from COVID-19. Our objective is to determine whether the fibrin clot structure and function differ between critically ill patients with or without COVID-19 and to correlate the structure with clinical coagulation biomarkers.

DESIGN

A cross-sectional observational study. Platelet poor plasma was used to analyze fibrin clot structure; the functional implications were determined by quantifying clot turbidity and porosity.

SETTING

ICU at an academic medical center and an academic laboratory.

PATIENTS

Patients admitted from July 1 to August 1, 2020, to the ICU with severe acute respiratory syndrome coronavirus 2 infection confirmed by reverse transcription-polymerase chain reaction or patients admitted to the ICU with sepsis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Blood was collected from 36 patients including 26 ICU patients with COVID-19 and 10 ICU patients with sepsis but without COVID-19 at a median of 11 days after ICU admission (interquartile range, 3-16). The cohorts were similar in age, gender, body mass index, comorbidities, Sequential Organ Failure Assessment (SOFA) score, and mortality. More patients with COVID-19 (100% vs 70%; p = 0.003) required anticoagulation. Ex vivo fibrin clots formed from patients with COVID-19 appeared to be denser and to have smaller pores than those from patients with sepsis but without COVID-19 (percent area of fluorescent fibrin 48.1% [SD, 16%] vs 24.9% [SD, 18.8%]; p = 0.049). The turbidity and flow-through assays corroborated these data; fibrin clots had a higher maximum turbidity in patients with COVID-19 compared with patients without COVID-19 (0.168 vs 0.089 OD units; p = 0.003), and it took longer for buffer to flow through these clots (216 vs 103 min; p = 0.003). In patients with COVID-19, d-dimer levels were positively correlated with percent area of fluorescent fibrin (ρ = 0.714, p = 0.047). Denser clots (assessed by turbidity and thromboelastography) and higher SOFA scores were independently associated with delayed clot lysis.

CONCLUSIONS

We found aberrant fibrin clot structure and function in critically ill patients with COVID-19. These findings may contribute to the poor outcomes observed in COVID-19 patients with widespread fibrin deposition.

Polyphosphate nanoparticles enhance the fibrin stabilization by histones more efficiently than linear polyphosphates

Introduction

Beyond the three-dimensional fibrin network, the mechanical and lytic stability of thrombi is supported by the matrix of neutrophil extracellular traps (NETs) composed of polyanionic DNA meshwork with attached proteins including polycationic histones. Polyphosphates represent another type of polyanions, which in their linear form are known to enhance the fibrin stabilizing effects of DNA and histones. However, in vivo polyphosphates are also present in the form of nanoparticles (PolyP-NP), the interference of which with the fibrin/NET matrix is poorly characterized.

Aims

To compare the effects of linear and nanoparticulate polyphosphates, and their combinations with relevant NET components (DNA, histone H3) on fibrin formation, structure, and lysis in in vitro assays focusing on histone-polyphosphate interactions.

Methods

Transmission electron microscopy and dynamic light scattering for stability of the PolyP-NP preparations. Turbidimetry for kinetics of fibrinogen clotting by thrombin and fibrin dissolution by tissue-type plasminogen activator/plasminogen. Scanning electron microscopy for fibrin structure. Surface plasmon resonance for strength of histone-PolyP interactions.

Results

Both linear PolyP and PolyP-NP accelerated the fibrin formation and slowed down its dissolution and these effects were strongly dependent on the number of individual PolyP particles and not on their size. Addition of DNA did not modify significantly the PolyP-NP effects on fibrin formation and lysis. Both linear and nanoparticulate PolyP counteracted the effect of histone in the acceleration of fibrinogen clotting by thrombin. PolyP-NP, but not linear PolyP enhanced the prolongation of lysis time in fibrin containing histone and caused more pronounced thickening of the fibrin fibers than the linear form. Finally, PolyP-NP bound weaker to histone than the linear form.

Conclusions

The interaction of PolyP with histone was a stronger modulator of fibrin formation and lysis than its interaction with DNA. In addition, the PolyP nanoparticles enhanced the thrombus stabilizing effects of histone more effectively than linear PolyP.

Engineered Molecular Therapeutics Targeting Fibrin and the Coagulation System: a Biophysical Perspective

The coagulation cascade represents a sophisticated and highly choreographed series of molecular events taking place in the blood with important clinical implications. One key player in coagulation is fibrinogen, a highly abundant soluble blood protein that is processed by thrombin proteases at wound sites, triggering self-assembly of an insoluble protein hydrogel known as a fibrin clot. By forming the key protein component of blood clots, fibrin acts as a structural biomaterial with biophysical properties well suited to its role inhibiting fluid flow and maintaining hemostasis. Based on its clinical importance, fibrin is being investigated as a potentially valuable molecular target in the development of coagulation therapies. In this topical review, we summarize our current understanding of the coagulation cascade from a molecular, structural and biophysical perspective. We highlight single-molecule studies on proteins involved in blood coagulation and report on the current state of the art in directed evolution and molecular engineering of fibrin-targeted proteins and polymers for modulating coagulation. This biophysical overview will help acclimatize newcomers to the field and catalyze interdisciplinary work in biomolecular engineering toward the development of new therapies targeting fibrin and the coagulation system.

Advantages of Fibrin Polymerization Method without the Use of Exogenous Thrombin for Vascular Tissue Engineering Applications

Fibrin is widely used in vascular tissue engineering. Typically, fibrin polymerization is initiated by adding exogenous thrombin. In this study, we proposed a protocol for the preparation of completely autologous fibrin without the use of endogenous thrombin and compared the properties of the prepared fibrin matrix with that obtained by the traditional method. Fibrinogen was obtained by ethanol precipitation followed by fibrin polymerization by adding either exogenous thrombin and calcium chloride (ExThr), or only calcium chloride (EnThr). We examined the structure, mechanical properties, thrombogenicity, degradation rate and cytocompatibility of fibrin matrices. Factor XIII (FXIII) quantitative assay was performed by ELISA, and FXIII activity was assessed by SDS-PAGE detection of γ-γ cross-links. The results show that network structure of EnThr fibrin was characterized by thinner fibers. The EnThr fibrin matrices had higher strength, stiffness and resistance to proteolytic degradation compared to ExThr fibrin. EnThr fibrin matrices exhibited less thrombogenicity in vitro than ExThr, and retained high cytocompatibility. Thus, the proposed approach has several advantages over the traditional method, namely the fabrication of a completely autologous coating material that has better mechanical properties, higher resistance to proteolysis and lower thrombogenicity.

The Efficacy of Fibrinogen Concentrates in Relation to Cryoprecipitate in Restoring Clot Integrity and Stability against Lysis

Loss of fibrinogen is a feature of trauma-induced coagulopathy (TIC), and restoring this clotting factor is protective against hemorrhages. We compared the efficacy of cryoprecipitate, and of the fibrinogen concentrates RiaSTAP^® and FibCLOT^® in restoring the clot integrity in models of TIC. Cryoprecipitate and FibCLOT^® produced clots with higher maximal absorbance and enhanced resistance to lysis relative to RiaSTAP^®. The fibrin structure of clots, comprising cryoprecipitate and FibCLOT^®, mirrored those of normal plasma, whereas those with RiaSTAP^® showed stunted fibers and reduced porosity. The hemodilution of whole blood reduced the maximum clot firmness (MCF) as assessed by thromboelastography. MCF could be restored with the inclusion of 1 mg/mL of fibrinogen, but only FibCLOT^® was effective at stabilizing against lysis. The overall clot strength, measured using the Quantra^® hemostasis analyzer, was restored with both fibrinogen concentrates but not cryoprecipitate. α₂antiplasmin and plasminogen activator inhibitor-1 (PAI-1) were constituents of cryoprecipitate but were negligible in RiaSTAP^® and FibCLOT^®. Interestingly, cryoprecipitate and FibCLOT^® contained significantly higher factor XIII (FXIII) levels, approximately three-fold higher than RiaSTAP^®. Our data show that 1 mg/mL fibrinogen, a clinically achievable concentration, can restore adequate clot integrity. However, FibCLOT^®, which contained more FXIII, was superior in normalizing the clot structure and in stabilizing hemodiluted clots against mechanical and fibrinolytic degradation.

DEVELOPMENT OF FIBRIN BRANCH STRUCTURE BEFORE AND AFTER GELATION

In [Fogelson and Keener, Phys. Rev. E, 81 (2010), 051922], we introduced a kinetic model of fibrin polymerization during blood clotting that captured salient experimental observations about how the gel branching structure depends on the conditions under which the polymerization occurs. Our analysis there used a moment-based approach that is valid only before the finite time blow-up that indicates formation of a gel. Here, we extend our analyses of the model to include both pre-gel and post-gel dynamics using the PDE-based framework we introduced in [Fogelson and Keener, SIAM J. Appl. Math., 75 (2015), pp. 1346-1368]. We also extend the model to include spatial heterogeneity and spatial transport processes. Studies of the behavior of the model reveal different spatial-temporal dynamics as the time scales of the key processes of branch formation, monomer introduction, and diffusion are varied.

Lipoprotein(a)—The Crossroads of Atherosclerosis, Atherothrombosis and Inflammation

Increased lipoprotein(a) (Lp(a)) levels are an independent predictor of coronary artery disease (CAD), degenerative aortic stenosis (DAS), and heart failure independent of CAD and DAS. Lp(a) levels are genetically determinated in an autosomal dominant mode, with great intra- and inter-ethnic diversity. Most variations in Lp(a) levels arise from genetic variations of the gene that encodes the apolipoprotein(a) component of Lp(a), the LPA gene. LPA is located on the long arm of chromosome 6, within region 6q2.6–2.7. Lp(a) levels increase cardiovascular risk through several unrelated mechanisms. Lp(a) quantitatively carries all of the atherogenic risk of low-density lipoprotein cholesterol, although it is even more prone to oxidation and penetration through endothelia to promote the production of foam cells. The thrombogenic properties of Lp(a) result from the homology between apolipoprotein(a) and plasminogen, which compete for the same binding sites on endothelial cells to inhibit fibrinolysis and promote intravascular thrombosis. LPA has up to 70% homology with the human plasminogen gene. Oxidized phospholipids promote differentiation of pro-inflammatory macrophages that secrete pro-inflammatory cytokines (e. g., interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor-α). The aim of this review is to define which of these mechanisms of Lp(a) is predominant in different groups of patients.

Rotational Thromboelastometry in High-Risk Patients on Dual Antithrombotic Therapy After Percutaneous Coronary Intervention

Aims: Patients using antithrombotic drugs after percutaneous coronary intervention (PCI) are at risk for bleeding and recurrent ischemia. We aimed to explore routine and tissue plasminogen activated (tPA) ROTEM results in a post-PCI population on dual antithrombotic treatment.

Methods and Results: In this prospective cohort, 440 patients treated with double antithrombotic therapy after recent PCI and with ≥3 risk factors for either ischemic or bleeding complications were included and compared with a control group (n = 95) consisting of perioperative patients not using antithrombotic medication. Laboratory assessment, including (tPA) ROTEM, was performed one month post-PCI and bleeding/ischemic complications were collected over a five-month follow-up. Patients were stratified by antithrombotic regimen consisting of a P2Y12 inhibitor with either aspirin (dual antiplatelet therapy; DAPT, n = 323), a vitamin K antagonist (VKA, n = 69) or a direct oral anticoagulant (DOAC, n = 48). All post-PCI patients had elevated ROTEM clot stiffness values, but only the DAPT group additionally presented with a decreased fibrinolytic potential as measured with tPA ROTEM. Patients receiving anticoagulants had prolonged clotting times (CT) when compared to the control and DAPT group; EXTEM and FIBTEM CT could best discriminate between patients (not) using anticoagulants (AUC > 0.97). Furthermore, EXTEM CT was significantly prolonged in DAPT patients with bleeding complications during follow-up (68 [62–70] vs. 62 [57–68], p = 0.030).

Conclusion: ROTEM CT has high potential for identifying anticoagulants and tPA ROTEM could detect a diminished fibrinolytic potential in patients using DAPT. Furthermore, the ability of EXTEM CT to identify patients at risk for bleeding may be promising and warrants further research.