Effect of anticoagulants on fibrin clot structure: A comparison between vitamin K antagonists and factor Xa inhibitors

Fibrinogen levels and clot properties identify patients who benefit from catheter-directed thrombolysis after DVT

ABSTRACT

Ultrasound-accelerated catheter-directed thrombolysis (UA-CDT) to improve patency after deep vein thrombosis (DVT) has not conclusively been shown to prevent postthrombotic syndrome (PTS) but might benefit patients who are unlikely to obtain patency with standard treatment. We hypothesized that these patients could be selected based on their fibrin clot properties. To study this, patients with acute iliofemoral DVT from the CAVA (Ultrasound-Accelerated Catheter-Directed Thrombolysis Versus Anticoagulation for the Prevention of Post-thrombotic Syndrome) trial had blood samples taken at inclusion. Fibrin clot properties in plasma were determined by turbidimetric clotting (lag time and maximal turbidity) and lysis assays (time to 50% lysis and lysis rate), permeation assay, and confocal microscopy (fiber density), as well as levels of fibrin clot modifiers fibrinogen and C-reactive protein (CRP). Patency was defined as >90% iliofemoral vein compressibility at 12-month ultrasound. PTS was defined as ≥5 Villalta score at 6 or 12 months. In total, 91 of 152 patients were included, including 43 with additional UA-CDT and 48 with standard treatment. Patients with additional UA-CDT more often obtained patency (55.8 vs 27.1%) Patients who obtained patency had longer lag times and lower maximal turbidity, fibrinogen, and CRP; only maximal turbidity and fibrinogen remained associated when adjusting for treatment, thrombus load, and body mass index. Fibrinogen levels had an optimal cutoff at 4.85 g/L. Low fibrinogen levels best predicted patency. Additional UA-CDT decreased the risk of PTS only in patients with high fibrinogen. Therefore, additional UA-CDT might prevent PTS in selected patients based on routinely measured fibrinogen levels. This study was registered at www.ClinicalTrials.gov as #NCT00970619.

Fibrin Clot Properties in Cancer: Impact on Cancer-Associated Thrombosis

Cancer is associated with a high risk of venous thromboembolism (VTE) and its recurrence. There is evidence that the prothrombotic fibrin clot phenotype, involving the formation of denser and stiffer clots relatively resistant to lysis, occurs in cancer patients, which is in part related to enhanced inflammation, oxidative stress, and coagulation activation, along with the release of neutrophil extracellular traps, indicating that fibrin-related mechanisms might contribute to cancer-associated thrombosis (CAT). Multiple myeloma and its therapy have been most widely explored in terms of altered fibrin characteristics, but prothrombotic fibrin clot features have also been reported in patients with active solid cancer, including lung cancer and gastrointestinal cancer. Patient-related factors such as advanced age, smoking, and comorbidities might also affect fibrin clot characteristics and the risk of CAT. Prothrombotic fibrin clot features have been shown to predict the detection of cancer in patients following VTE during follow-up. Cancer-specific therapies and anticoagulation can favorably modify the phenotype of a fibrin clot, which may alter the course of CAT. It is unclear whether the fibrin clot phenotype might help identify patients with CAT who are more likely to experience recurrent events. This narrative review summarizes the current knowledge on the role of fibrin clot structure and function in cancer patients in the context of CAT.

A comparative in vitro study of the anticoagulant effect of branded versus generic rivaroxaban

BACKGROUND

Several generic formulations of rivaroxaban were recently marketed to be used interchangeably with their branded equivalent. However, there have been no previously published studies that directly compared the in vitro anticoagulant effect of branded vs. generic rivaroxaban. The aim of this in vitro study was to compare the effects of three raw rivaroxaban materials, obtained from the branded (Xarelto®) and two generic (Rivarolto® and Rivaroxaban Sandoz®) rivaroxaban formulations on an array of coagulation assays.

METHODS

A pool of normal plasma was spiked with several concentrations of the three rivaroxaban (range 50-750 ng/ml). The concentrations were assessed with a rivaroxaban calibrated anti-Xa assay and confirmed by ultra-high-performance liquid chromatography-mass spectrometry coupled with tandem mass spectrometry (UHPLC-MS/MS). The following assays were performed: Prothrombin time (PT), activated Partial Thromboplastin time (aPTT), Diluted Russell's Viper Venom Test (dRVVT), Thrombin time (TT), Clauss Fibrinogen, Factor VII, VIII and IX assays, and thromboelastography.

RESULTS

The results obtained by the three rivaroxaban at similar concentrations were comparable. Increasing concentrations of the three rivaroxaban showed a strong positive correlation with the PT, aPTT and dRVVT assays (r > 0.95, p < 0.01 for all), and a strong negative correlation with the Factors assays (r < -0.95, p < 0.01 for all). TT and Clauss Fibrinogen were not affected by rivaroxaban. No significant difference was identified in the mean assays' results obtained by the three rivaroxaban.

CONCLUSION

This study showed that the branded and generic rivaroxaban exert an identical in vitro anticoagulant effect across a wide range of concentrations.

Magnetic coagulometry: towards a new nanotechnological tool for ex vivo monitoring coagulation in human whole blood

Blood clotting disorders consisting of unwanted blood clot formation or excessive bleeding are some of the main causes of death worldwide. However, there are significant limitations in the current methods used to clinically monitor the dynamics of clot formation in human whole blood ex vivo. Here a new magnetic coagulometry platform for testing ex vivo coagulation is described. This platform exploits the sensitivity of the out-of-phase component of alternating current (AC) magnetic susceptibility (χ'') to variations in mobility and agglomeration of magnetic nanoparticles when trapped during blood clot formation. By labelling human whole blood with magnetic nanoparticles, the out-of-phase component of AC magnetic susceptibility shows that the dynamics of blood clot formation correlates with a decrease in the out-of-phase component χ'' over time activation of coagulation. This is caused by a rapid immobilisation of nanoparticles upon blood coagulation and compaction. In contrast, this rapid fall in the out-of-phase component χ'' is significantly slowed down when blood is pre-treated with three different anticoagulant drugs. Remarkably, the system showed sensitivity towards the effect of clinically used direct oral anticoagulation (DOAC) drugs in whole blood coagulation, in contrast to the inability of clinical routine tests prothrombin time (PT) and partial thromboplastin time (PTT) to efficiently monitor this effect. Translation of this nanomagnetic approach into clinic can provide a superior method for monitoring blood coagulation and improve the efficiency of the current diagnostic techniques.

Initiation of warfarin is associated with decreased mortality in patients with infective endocarditis: A population-based cohort study

IMPORTANCE

The use of warfarin to prevent thromboembolism in patients with infective endocarditis (IE) remains controversial due to potentially increased bleeding risks.

DESIGN

Population-based retrospective cohort study.

PARTICIPANTS

Patients aged 18 or older and diagnosed with IE in Hong Kong between January 1st, 1997 and August 31st, 2020 were included. Patients with use of any anticoagulant 30 days before IE diagnosis were excluded. Patients initiated on warfarin within 14 days of IE diagnosis and patients without warfarin use were matched for baseline characteristics using 1:1 propensity score matching.

EXPOSURE

Warfarin use within 14 days of IE diagnosis.

MAIN OUTCOMES AND MEASURES

Patients were followed up to 90 days for the outcomes of ischemic stroke, all-cause mortality, intracranial hemorrhage, and gastrointestinal bleeding. Cox regression was used to determine hazard ratios (HRs) [95 % confidence intervals (CIs)] between treatment groups. Fine-Gray competing risk regression with all-cause mortality as the competing event was performed as a sensitivity analysis. In addition to 90-day analyses, landmark analyses were performed at 30 days of follow-up.

RESULTS

The matched cohort consisted of 675 warfarin users (57.0 % male, age 59 ± 16 years) and 675 warfarin non-users (53.5 % male, age 61 ± 19 years). Warfarin users had a 50 % decreased 90-day risk in all-cause mortality (HR:0.50 [0.39-0.65]), without significantly different 90-day risks of ischemic stroke (HR:1.04 [0.70-1.53]), intracranial hemorrhage (HR:1.25 [0.77-2.04]), and gastrointestinal bleeding (HR:1.04 [0.60-1.78]). Thirty-day landmark analysis showed similar results. Competing risk regression showed significantly higher 30-day cumulative incidence of intracranial hemorrhage in warfarin users (sub-HR:3.34 [1.34-8.31]), but not at 90-day (sub-HR:1.63 [0.95-2.81]). Results from Fine-Gray regression were otherwise congruent with those from Cox regression.

CONCLUSIONS AND RELEVANCE

Warfarin initiated within 14 days of IE diagnosis was associated with significantly decreased risks of mortality but higher risks of intracranial hemorrhage, with similar risks of ischemic stroke and gastrointestinal bleeding, compared with non-use of warfarin with 14 days of IE diagnosis.

KEY POINTS

Question: Is warfarin, initiated within 14 days of a diagnosis of infective endocarditis (IE), efficacious and safe?

FINDINGS

In this propensity score-matched, population-based, prospective cohort study from Hong Kong, warfarin use within 14 days of IE diagnosis was associated with a 50 % decrease in the risk of all-cause mortality, albeit with higher risk of intracranial hemorrhage, and without significant differences in the risk of ischaemic stroke and gastrointestinal bleeding. Meaning: In patients with IE, warfarin use within 14 days of diagnosis may have mortality benefits, despite increased risks of intracranial hemorrhage.

Antithrombotic and prohemorrhagic actions of different concentrations of apixaban in patients exposed to single and dual antiplatelet regimens

We evaluated modifications in the hemostatic balance of different concentrations of apixaban (APIX) in 25 healthy donors and 53 patients treated with aspirin (ASA, n = 21), ASA and clopidogrel (ASA + CLOPI, n = 11), or ASA and ticagrelor (ASA + TICA, n = 21). Blood samples from participants were spiked ex vivo with apixaban 0 (APIX0), 40 (APIX40), and 160 ng/mL (APIX160). We assessed the effects of APIX on (1) clot formation, by ROTEM thromboelastometry; (2) thrombin generation primed by platelets; and (3) platelet and fibrin interactions with a thrombogenic surface, in a microfluidic model with circulating blood. APIX caused dose-related prolongations of clotting time with minimal impact on other ROTEM parameters. Thrombin generation was significantly inhibited by APIX160, with ASA + TICA actions showing the strongest inhibition (p < 0.01 vs APIX0). Microfluidic studies showed that APIX160 was more potent at suppressing platelet and fibrin interactions (p < 0.001 vs. APIX0). APIX40 demonstrated a consistent antithrombotic action but with a favorable protective effect on the structural quality of fibrin. APIX potentiated the antithrombotic effects of current antiplatelet regimens. APIX at 40 ng/mL, enhanced the antithrombotic action of single or dual antiplatelet regimens but was more conservative for hemostasis than the 160 ng/mL concentration.

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.

Mechanisms for Reduced Fibrin Clot Formation on Liquid-Infused Surfaces

Biomedical devices are prone to blood clot formation (thrombosis), and liquid-infused surfaces (LIS) are effective in reducing the thrombotic response. However, the mechanisms that underpin this performance, and in particular the role of the lubricant, are not well understood. In this work, it is investigated whether the mechanism of LIS action is related to i) inhibition of factor XII (FXII) activation and the contact pathway; ii) reduced fibrin density of clots formed on surfaces; iii) increased mobility of proteins or cells on the surface due to the interfacial flow of the lubricant. The chosen LIS is covalently tethered, nanostructured layers of perfluorocarbons, infused with thin films of medical-grade perfluorodecalin (tethered-liquid perfluorocarbon), prepared with chemical vapor deposition previously optimized to retain lubricant under flow. Results show that in the absence of external flow, interfacial mobility is inherently higher at the liquid-blood interface, making it a key contributor to the low thrombogenicity of LIS, as FXII activity and fibrin density are equivalent at the interface. The findings of this study advance the understanding of the anti-thrombotic behavior of LIS-coated biomedical devices for future coating design. More broadly, enhanced interfacial mobility may be an important, underexplored mechanism for the anti-fouling behavior of surface coatings.

Ischemic Stroke of Suspected Cardioembolic Origin Despite Anticoagulation: Does Thrombus Analysis Help to Clarify Etiology?

Introduction

Despite sufficient oral anticoagulation (OAC) to prevent cardioembolism, some patients suffer from cerebral ischemic strokes of suspected cardioembolic origin. Reasons for that are not clarified yet. In certain cases, the suspected cardioembolic origin of stroke is questioned. This study aimed to understand the thrombi origin and pathophysiology in patients suffering from stroke despite OAC by the analysis of histologic thrombus composition and imaging characteristics.

Materials and Methods

On two distinct cohorts, we retrospectively analyzed histologic (n = 92) and imaging features (n = 64), i.e., thrombus perviousness in admission CT imaging, of cerebral thrombi retrieved by the endovascular treatment for a large vessel occlusion of the anterior circulation. In each group, patients with non-cardioembolic strokes and suspected cardioembolic strokes with or without anticoagulation were compared.

Results

Fibrin/platelet content of suspected cardioembolic thrombi (mean/SD 57.2% ± 13) is higher than in non-cardioembolic thrombi (48.9% ± 17; p = 0.01). In suspected cardioembolic thrombi, the fibrin/platelet content does not differ in the subgroups of patients with (57.3% ± 13) and without prior OAC treatment (56.6% ±13; p = 0.8), both with higher values than non-cardioembolic thrombi. Thrombus perviousness (ε) of suspected cardioembolic OAC thrombi (mean/SD: 0.09 ± 0.06) differs significantly from non-cardioembolic thrombi (0.02 ± 0.02; p < 0.001). Further, ε is higher in suspected cardioembolic thrombi with OAC than in cardioembolic thrombi without OAC (0.06 ± 0.03; p = 0.04) and with insufficient OAC (0.04 ± 0.02; p = 0.07).

Conclusion

Thrombi of the suspected cardioembolic origin of patients with prior OAC do not differ in their histologic composition from those without prior OAC, but both differ from non-cardioembolic thrombi. These histologic results make a non-cardioembolic etiology for strokes despite prior OAC rather unlikely but favor other reasons for these ischemic events. Perviousness assessment reinforces the histologic findings, with additional information about the OAC thrombi, which present with higher perviousness. This suggests that OAC would not affect the relative histologic thrombus composition but may alter the microstructure, as reflected by perviousness.

Plasminogen-Loaded Fibrin Scaffold as Drug Delivery System for Wound Healing Applications

Plasminogen is a protein involved in intravascular and extravascular fibrinolysis, as well as in wound healing, cell migration, tissue formation and angiogenesis. In recent years its role in healing of tympanic perforations has been demonstrated in plasminogen deficient mice. The aim of this work was to fabricate a fibrin-based drug delivery system able to provide a local and sustained release of plasminogen at the wound site. Initially, the biological activity of plasminogen was evaluated by in vitro experiments on cell cultures. A metabolic assay (MTT) was carried out on L929 mouse fibroblast to determine the concentration that does not affect cell viability, which turned out to be 64 nM. The effect of plasminogen on cell migration was evaluated through a scratch test on human keratinocytes: cells treated with 64 nM plasminogen showed faster scratch closure than in complete medium. Fibrin scaffold loaded with plasminogen was fabricated by a spray process. SEM analysis showed the typical nano-fibrillar structure of a fibrin scaffold. Tensile tests highlighted significantly higher value of the ultimate stress and strain of fibrin scaffold with respect to fibrin clot. The in-vitro release kinetic showed an initial plasminogen burst, after that the release slowed, reaching a plateau at 7 days. Plasminogen-loaded fibrin scaffold applied in full-thickness diabetic mouse lesions showed a significantly higher closure rate at 14 days than scaffold used as a reference material. Histological analysis demonstrated an improved reepithelization and collagen deposition in granulation tissue in mouse treated with plasminogen-loaded fibrin scaffold in comparison to unloaded fibrin scaffold. The obtained results demonstrated the suitability of the fibrin scaffold loaded with plasminogen as drug delivery system and suggest its use in wound healing applications, such as for the treatment of chronic diabeticulcers.

Fibrin Clot Properties in Atherosclerotic Vascular Disease: From Pathophysiology to Clinical Outcomes

Fibrin is a major component of thrombi formed on the surface of atherosclerotic plaques. Fibrin accumulation as a consequence of local blood coagulation activation takes place inside atherosclerotic lesions and contributes to their growth. The imbalance between thrombin-mediated fibrin formation and fibrin degradation might enhance atherosclerosis in relation to inflammatory states reflected by increased fibrinogen concentrations, the key determinant of fibrin characteristics. There are large interindividual differences in fibrin clot structure and function measured in plasma-based assays and in purified fibrinogen-based systems. Several observational studies have demonstrated that subjects who tend to generate denser fibrin networks displaying impaired clot lysis are at an increased risk of developing advanced atherosclerosis and arterial thromboembolic events. Moreover, the majority of cardiovascular risk factors are also associated with unfavorably altered fibrin clot properties, with their improvement following effective therapy, in particular with aspirin, statins, and anticoagulant agents. The prothrombotic fibrin clot phenotype has been reported to have a predictive value in terms of myocardial infarction, ischemic stroke, and acute limb ischemia. This review article summarizes available data on the association of fibrin clot characteristics with atherosclerotic vascular disease and its potential practical implications.