Altered fibrin clot structure/function in patients with idiopathic venous thromboembolism and in their relatives

Intraoperative Thrombophilia-Associated Thrombosis of Both Saphenous Veins during Harvesting for Coronary Artery Bypass Grafting

Introduction  Intraoperative thrombosis of saphenous veins (SV) during open harvesting is very rare. Case Report  We present a case of a 60-year-old male patient with multivessel coronary artery disease and a history of a non-ST elevation acute coronary syndrome, and type-2 diabetes mellitus admitted for coronary artery bypass grafting, in whom bilateral intraoperative SV thrombosis occurred during graft harvesting. Routine thrombophilia screening showed no abnormalities and cancer was excluded. Compared with healthy controls, we observed prolonged fibrin clot lysis time and increased thrombin generation reflected by endogenous thrombin potential. Scanning electron microscopy of the thrombosed material revealed compact and thick fibrin layer on the clot surface with a solid mass of unusually compressed platelets and erythrocytes underneath. The patient was tested for fibrinogen and factor (F) XIII polymorphisms, and was found to be heterozygous for β-fibrinogen HaeIII (-455G > A) and FXIII Val34Leu (100G > T). Conclusion  β-fibrinogen HaeIII and FXIII Val34Leu polymorphisms are reflected in reduced clot permeability and susceptibility to lysis, and might contribute to intraoperative SV thrombosis during vascular grafting procedures. Carriers of those are at risk of primary venous graft failure after bypass procedures.

Plasma fibrin clot proteomics in patients with acute pulmonary embolism: Association with clot properties

It has been reported that 476 proteins can be detected in plasma fibrin clots from patients with venous thromboembolism. Plasma fibrin clots proteomic composition in relation to their properties has not been studied in acute pulmonary embolism (PE). Clots generated from plasma of 20 PE patients and 20 healthy controls were assessed using mass spectrometry, clot permeability (K_s), and clot lysis time (CLT). The proteomic composition of plasma fibrin clots from acute PE patients differed from that of control subjects in regard to 198 clot-bound proteins. In the acute PE group, we observed increased clot-bound fibrinogen, apolipoprotein B-100, platelet glycoprotein Ib, lipopolysaccharide-binding protein, and histones H3 + 4 and reduced fibronectin, α2-antiplasmin, α2-macroglobulin, factor (F)XIII, histidine-rich glycoprotein, antithrombin, von Willebrand Factor, plasminogen, and prothrombin. Among PE patients, low K_s (≤3.83 × 10^-9 cm²) was associated with increased clot-bound C-reactive protein, kininogen-1, protein S, β-2-microglobulin, and thromboxane-A synthase when compared with patients having K_s > 3.83 × 10^-9 cm². K_s correlated inversely with FIX and FV, thrombin-activatable fibrinolysis inhibitor, complement C1s, C7, C8, and apolipoprotein A-I. The specific protein composition in plasma fibrin clots from acute PE patients is associated with denser clot formation. Several proteins unrelated to the coagulation system can modulate fibrin phenotype in acute thrombotic states. SIGNIFICANCE: Our study significantly advances the field of thrombosis and hemostasis. The plasma fibrin clot proteomics findings fill the gap of knowledge about the presence and the role of other proteins to the plasma fibrin clot in the acute phase of pulmonary embolism, aside fibrinogen, which is the main component of fibrin. The reported methodology, which involves the sample preparation using Multienzyme Digestion-Filter Aided Sample Preparation (MED FASP), data acquisition with the Quadrupole-Orbitrap mass spectrometer, and data analysis using the advanced tools such as MaxQuant, Total Protein Approach and Perseus, allows to gain not only the qualitative, but also the quantitative insights into the microworld of proteins entangled among the fibrin network. By comparing the clots formed from plasma of patients with acute pulmonary embolism with the clots from healthy control, we provide the specific protein composition associated with unfavorable clot properties observed in this disease. Moreover, our findings emphasize that several proteins unrelated to the coagulation system, can modulate fibrin phenotype in acute thrombotic states.

Super-Resolution Microscopy Reveals an Altered Fibrin Network in Cirrhosis: The Key Role of Oxidative Stress in Fibrinogen Structural Modifications

Cirrhotic patients show a reduced synthesis of both pro- and anti-coagulant factors. Recent reports indicate that they are characterized by a higher risk of thrombotic rather than hemorrhagic complications, but the mechanisms conferring this risk are not fully elucidated. Oxidative-mediated fibrinogen modifications may explain, at least in part, a prothrombotic profile. The aim of the present pilot study was to investigate the alterations in fibrinogen structure and function in patients with cirrhosis of various severity and to correlate these findings with the mechanisms of thrombus formation. We assessed in plasma specific oxidative stress markers and measured oxidative modifications, functional and structural parameters in purified fibrinogen fractions obtained from cirrhotic patients and control subjects. We enrolled 15 cirrhotic patients (5 patients belonging to each of the three Child-Turcotte-Pugh classes) and 20 age- and sex-matched healthy controls. Plasma redox status, fibrinogen oxidative modifications, thrombin-catalyzed fibrin polymerization and fibrin resistance to plasmin-induced lysis were significantly altered in cirrhotic patients and were associated to disease severity. Importantly, clot structure obtained by stimulated emission depletion (STED) super-resolution microscopy indicated modifications in fiber diameter and in clot porosity in cirrhotic patients. Fibrin fiber diameter significantly decreased in cirrhotic patients when compared to controls, and this difference became more marked with disease progression. In parallel, fibrin pore size progressively decreased along with disease severity. In cirrhotic patients, fibrinogen clot analysis and oxidative-dependent changes reveal novel structural and functional fibrinogen modifications which may favor thrombotic complications in cirrhosis.

Dense and dangerous: The tissue plasminogen activator-resistant fibrinolysis shutdown phenotype is due to abnormal fibrin polymerization

BACKGROUND

Both hyperfibrinolysis and fibrinolysis shutdown can occur after severe trauma. The subgroup of trauma patients with fibrinolysis shutdown resistant to tissue plasminogen activator (t-PA)-mediated fibrinolysis have increased mortality. Fibrin polymerization and structure may influence fibrinolysis subgroups in trauma, but fibrin architecture has not been characterized in acutely injured subjects. We hypothesized that fibrin polymerization measured in situ will correlate with fibrinolysis subgroups.

METHODS

Blood samples were collected from trauma patients and noninjured controls. We selected samples across a range of fibrinolysis phenotypes (shutdown, physiologic, hyperfibrinolysis) and t-PA sensitivities (sensitive, physiologic, resistant) determined by thrombelastography. Plasma clots were created in situ with fluorescent fibrinogen and imaged using confocal microscopy for analysis of clot architecture in three dimensions. For each clot, we quantified the fiber resolvability, a metric of fiber distinctness or clarity, by mapping the variance of fluorescence intensity relative to background fluorescence. We also determined clot porosity by measuring the size and distribution of the gaps between fibrin fibers in three-dimensional space. We compared these measures across fibrinolysis subgroups.

RESULTS

Fiber resolvability was significantly lower in all trauma subgroups compared with controls (n = 35 and 5, respectively; p < 0.05). We observed markedly different patterns of fibrin architecture among trauma patients stratified by fibrinolysis subgroup. Subjects with t-PA-resistant fibrinolysis shutdown exhibited abnormal, densely packed fibrin clots nearly devoid of pores. Individuals with t-PA-hypersensitive fibrinolysis shutdown had highly irregular clots with pores as large as 2500 μm to 20,000 μm, versus 78 μm to 1250 μm in noninjured controls.

CONCLUSION

Fiber resolvability was significantly lower in trauma patients than controls, and subgroups of fibrinolysis differ in the porosity of the fibrin clot structure. The dense fibrin network in the t-PA-resistant group may prevent access to plasmin, suggesting a mechanism for thrombotic morbidity after injury.

Prothrombotic fibrin clot properties associated with NETs formation characterize acute pulmonary embolism patients with higher mortality risk

Venous thromboembolism is associated with formation of denser fibrin clots resistant to lysis. We investigated whether prothrombotic plasma clot properties are associated with the severity of acute pulmonary embolism (PE). We enrolled 126 normotensive acute PE patients (aged 58 ± 14 years) and 25 age- and sex-matched healthy controls. Plasma fibrin clot permeability (K_s), clot lysis time (CLT), endogenous thrombin potential (ETP), plasminogen activator inhibitor-1 (PAI-1), and citrullinated histone H3 (citH3) were evaluated on admission. PE patients compared to controls had 370% higher citH3 levels, 41% higher ETP, 16.5% reduced K_s, and 25.6% prolonged CLT. Patients with intermediate-high (n = 29) and intermediate-low (n = 77) PE mortality risk had reduced K_s and prolonged CLT, increased PAI-1 and ETP as compared to low-risk PE (n = 20) patients. Prolonged CLT was predicted by PAI-1 and citH3, while low K_s by C-reactive protein. During a 12-month follow-up 9 (7.1%) patients who had 24% higher ETP, 45% higher citH3 levels, and 18% prolonged CLT at baseline died. High ETP combined with elevated citH3 levels and prolonged CLT was associated with eightfold increased risk of PE-related death. Prothrombotic fibrin clot properties and enhanced neutrophil extracellular traps formation are associated with higher early mortality risk in acute PE patients, which suggests a prognostic role of these biomarkers.

Abnormal clot microstructure formed in blood containing HIT-like antibodies

INTRODUCTION

Thrombosis is a severe and frequent complication of heparin-induced thrombocytopenia (HIT). However, there is currently no knowledge of the effects of HIT-like antibodies on the resulting microstructure of the formed clot, despite such information being linked to thrombotic events. We evaluate the effect of the addition of pathogenic HIT-like antibodies to blood on the resulting microstructure of the formed clot.

MATERIALS AND METHODS

Pathogenic HIT-like antibodies (KKO) and control antibodies (RTO) were added to samples of whole blood containing Unfractionated Heparin and Platelet Factor 4. The formed clot microstructure was investigated by rheological measurements (fractal dimension; d_f) and scanning electron microscopy (SEM), and platelet activation was measured by flow cytometry.

RESULTS AND CONCLUSIONS

Our results revealed striking effects of KKO on clot microstructure. A significant difference in d_f was found between samples containing KKO (d_f = 1.80) versus RTO (d_f = 1.74; p < 0.0001). This increase in d_f was often associated with an increase in activated platelets. SEM images of the clots formed with KKO showed a network consisting of a highly branched and compact arrangement of thin fibrin fibres, typically found in thrombotic disease. This is the first study to identify significant changes in clot microstructure formed in blood containing HIT-like antibodies. These observed alterations in clot microstructure can be potentially exploited as a much-needed biomarker for the detection, management and monitoring of HIT-associated thrombosis.

Fibrinogen, factor XIII and α2-antiplasmin genotypes are associated with inflammatory activity and anti-citrullinated protein antibodies

BACKGROUND

Fibrin(ogen) derivatives, crosslinked fibrin and fibrinolysis play important roles in inflammation and are involved in pathogenesis of rheumatoid arthritis (RA). About 2/3 of RA patients exhibit anti-citrullinated protein antibodies (ACPA) that target deiminated fibrinogen. Genetic variants of β-fibrinogen (FGB) (rs1800790G>A) and factor XIII A-subunit (F13A) Val34Leu (rs5985) are known to influence interactively inflammatory processes. It is hypothesized that predisposition for dense fibrin clots is related to better inflammation control.

METHODS

To test this hypothetical model a cohort of 924 patients (288 RA and 636 non-RA patients) (3545 observations) was genotyped for FGB (rs1800790G>A, rs1800788C>T), α-fibrinogen (FGA) (rs6050A>G, rs2070006G>A, rs2070016T>C), γ-fibrinogen (FGG) (rs1049636T>C), F13A Val34Leu (rs5985) and α₂-antiplasmin (A2AP) Arg6Trp (rs2070863). Genotype constellations potentially predisposing for dense fibrin clots were defined and their relation to inflammatory activity as measured by C-reactive protein (CRP) and disease activity score of 28 joints (DAS28) was assessed in univariate and multivariate analyses. The relation of these genotype constellations with presence of ACPA was tested.

RESULTS

Genotype constellations involving FGB rs1800790G>A and FGA rs2070016T>C were inversely associated with CRP levels (≥10 mg/L) (OR: 0.49, P < 10^-8/7_adj = 0.0001; OR: 0.52, P < 0.0005/P_adj = 0.01). In RA, both genotype constellations were observed with higher frequencies of low disease activity (DAS28 ≤ 3.2) (OR: 2.66, P = .009; OR 2.78, P = .01) and lower frequencies of high disease activity (DAS28>5.1) (OR: 0.52, P < .03, OR: 0.42, P = .01). Associations with CRP depended on A2AP 6Arg/Arg genotype known to be necessary for optimal anti-fibrinolytic capacity (P = .001). Finally, Genotype constellations involving FGB rs1800790G>A and FGA rs2070016T>C were found to be associated with ACPA-positivity in RA (OR: 2.18, P < .03; OR: 1.95, P = .09).

CONCLUSIONS

These results support the hypothesis that genotypes, which increase fibrin clot density and anti-fibrinolytic capacity, reduce inflammatory activity and are related to humoral autoimmunity in RA.

A prothrombotic state and denser clot formation in patients following acute limb ischemia of unknown cause

INTRODUCTION

Fibrin clot structure differs between healthy individuals and those following thromboembolic events. Dense and poorly lysable fibrin clots have also been reported in peripheral artery disease. We studied fibrin clot properties and its determinants in individuals with a history of acute lower limb ischemia (ALI) of unknown cause.

MATERIALS AND METHODS

In this case-control study, we enrolled 43 patients who experienced ALI of unknown cause, and two age-and sex-matched reference groups: (1) patients with cryptogenic non-lacunar stroke (n = 43) and (2) individuals without any history of thromboembolism (n = 43, control group). Plasma fibrin clot properties, along with thrombin generation and fibrinolysis markers were assessed following ≥3 months of anticoagulation.

RESULTS

Compared with the control group, the ALI group exhibited more compact plasma fibrin clots (13.4% lower permeability [K_s], p = .001), decreased formed clot lysis (12.5% lower D-D_rate, p = .001) and unaltered clot lysis potential, along with enhanced thrombin generation potential (49% higher peak thrombin concentration, p < .0001). There were no differences in these variables between ALI and stroke patients. Patients with ALI had slightly higher α₂-antiplasmin and lower plasminogen activator inhibitor 1 levels compared with the stroke and control groups (all p < .01).

CONCLUSIONS

Patients who experienced ALI of unknown cause display a prothrombotic fibrin clot phenotype, including increased clot density and hypofibrinolysis associated with higher thrombin generation, which might suggest potential benefits from prolonged anticoagulation in this disease.

Ex vivo properties of plasma clot formation and lysis in patients with cancer at risk for venous thromboembolism, arterial thrombosis, and death

A prothrombotic state is frequently observed in patients with cancer and contributes to the risks of venous thromboembolism (VTE), arterial thromboembolism (ATE), tumor progression, and death. Altered ex vivo properties of plasma clot formation and lysis have been observed in patients with cancer. The aim of this prospective study was to comprehensively characterize the relationship between plasma clot properties, inflammation, hypercoagulability, thrombotic complications, and mortality in patients with cancer using a tissue-factor-based turbidimetric assay of clot formation and lysis. Turbidity parameters were determined in 815 patients with newly-diagnosed or recurrent cancer and 97 healthy controls. Patients were followed-up for 2 years and rates of VTE (n = 72 events), ATE (n = 21 events), and death (n = 304 events) were assessed. Compared to controls, cancer patients' turbidity profiles showed an increased clot formation potential and higher resistance toward fibrinolysis. Elevated biomarkers of inflammation and hemostasis, such as C-reactive protein, FVIII, and thrombin generation explained substantial amounts of variation in turbidity parameters. In a prospective analysis, altered parameters of clot formation identified cancer patients at high risk of ATE (Hazard ratio [HR] per doubling of peak absorbance: 4.43, 95% CI: 1.50-13.07, P = 0.007) and death (HR per doubling of peak absorbance: 2.73, 2.00-3.72, P< 0.0001); these findings were independent of other prognostic covariates. Contrarily, turbidity parameters were not associated with risk of VTE (HR per doubling of peak absorbance: 1.15, 0.66-2.01, P = 0.62). We conclude that patients with cancer have altered ex vivo properties of clot formation which predict risks of ATE and mortality but not VTE.

Pulmonary embolism location is associated with the co-existence of the deep venous thrombosis

: Multiple studies have shown that in approximately half of individuals with pulmonary embolism (PE), the deep venous thrombosis (DVT) is not evident at the moment of PE diagnosis. The underlying factors and the origin of PE in these patients are not completely understood: missed DVT, embolization of DVT in its entirety, or de-novo PE being possible explanations. The aim of this study was to evaluate the differences in PE patient with or without co-existing DVT. Sixty-three consecutive PE patients were included. Whole leg bilateral Doppler compression ultrasound was performed to all patients. The PE location and extension, C-reactive protein, platelet count, hemostatic markers FV, FVIII, FXIIIa, Fibrinogen, von Willebrand factor antigen, thrombomodulin were assessed. Thorough clinical assessment including echocardiography and pulmonary function tests were performed upon arrival and seven months later. The mean age of the patients was 57 years (SD 17.3) and 33 (52%) were women. Thirty-one patients (49.2%) had co-existing DVT. The presence of DVT was associated with the proximal location of the PE (100%), whereas none of the patients (n = 10) with exclusively peripheral PE had co-existing DVT. The PE extension, the measured hemostatic and inflammatory markers or the patient characteristics did not statistically differ between patients with isolated PE and PE with co-existing DVT. In roughly half of the PE patients no DVT could be detected. The location of the PE was associated with the presence of co-existing DVT. There were no differences in the PE extension, hemostatic markers or in the patient characteristic between patients with isolated PE or PE with co-existing DVT.

Interpretation and Validation of Maximum Absorbance Data Obtained from Turbidimetry Analysis of Plasma Clots

Turbidimetry is used to characterize fibrin clot properties. In purified systems, maximum absorbance (MA) directly relates to fibrin fiber cross-sectional area. However, in plasma samples there are discrepancies in the relationships between MA and fibrinogen concentration, fiber diameter, other clot properties, and cardiovascular disease outcomes, which complicate data interpretation. This study aims to advance understanding of MA of plasma clots through testing how well it relates to fundamental dependence on fibrinogen concentration and fiber diameter as predicted by light scattering theory, other clot properties and lifestyle, and biochemical variables. Plasma samples from 30 apparently healthy individuals with a fibrinogen concentration from 2.4 to 6.4 g/L were included. We performed turbidimetry, permeability, scanning electron microscopy, and rheometry on in vitro formed plasma clots. MA correlated more strongly with fibrinogen concentration (r = 0.65; p < 0.001) than with fiber diameter (r = 0.47; p = 0.01), which combined explained only 46% of the MA variance. Of additional variables measured, only low-density lipoprotein cholesterol correlated with MA (r = 0.46; p = 0.01) and clot lysis (r = 0.62; p < 0.0001) but not with fiber diameter or fibrinogen concentration. MA correlated with clot lysis time (r = 0.59; p = 0.001), storage modulus (r = 0.61; p = 0.001), and loss modulus (r = 0.59; p = 0.001), and negatively with clot permeability (r = -0.60; p = 0.001) also after adjustment for fibrinogen concentration and fiber diameter. Increased MA is indicative of a prothrombotic clot phenotype irrespective of fibrinogen concentration. MA is more indicative of overall clot density than of fiber diameter. Other plasma components can alter internal fiber density without altering fiber diameter and should be considered when interpreting MA of plasma samples.

Plasma Fibrin Clot Properties Are Unfavorably Altered in Women following Venous Thromboembolism Associated with Combined Hormonal Contraception

The use of hormonal contraception is associated with an increased risk of venous thromboembolism (VTE). Unfavorably altered fibrin clot phenotype has been reported in patients following unprovoked VTE who are at risk of recurrences. It remains unknown whether fibrin clot characteristics in women with contraception-related VTE differ from those in unprovoked VTE. We studied three age-matched groups of women: (1) after contraception-related VTE, (n = 48) (2) after unprovoked VTE (n = 48), and (3) controls (n = 48). Plasma fibrin clot permeability (K _s), turbidity of clot formation, efficiency of fibrinolysis using clot lysis time (CLT), and rate of increase in D-dimer during lytic clot degradation (D-D_rate), along with thrombin generation and fibrinolysis proteins were determined. Compared with the controls, patients following contraception-related and unprovoked VTE formed faster (lag phase, -8.8% and -20.4%, respectively) fibrin clots of increased density (K _{s ,} -8.6% and -13.4%, respectively) displaying impaired fibrinolysis as evidenced by prolonged CLT (+11.5% and +14.5%, respectively) and lower D-D_rate (-7.1% and -5.6%, respectively), accompanied with higher plasminogen activator inhibitor-1 (PAI-1, +14.9% and +17.8%, respectively) and elevated peak thrombin generation (+63.8% and +36.7%, respectively). The only differences between women with unprovoked and contraception-related VTE were lower fibrin mass in plasma clots (D-D_max, -8.6%), along with higher peak thrombin generation (+19.8%) and shorter lag phase (-6.8%) in the latter group. This study suggests that women after contraception-related VTE, similar to those following unprovoked VTE, have denser fibrin clot formation and impaired clot lysis. These findings might imply higher risk of VTE recurrence in women with the prothrombotic clot phenotype.

Prothrombotic clot properties can predict venous ulcers in patients following deep vein thrombosis: a cohort study

Venous ulcers are the most severe manifestation of post-thrombotic syndrome (PTS). We have previously demonstrated that formation of compact fibrin clots resistant to lysis is observed in patients following deep-vein thrombosis (DVT) who developed PTS. The current study investigated whether unfavourable fibrin clot properties can predict post-thrombotic venous ulcers. In a cohort study on 186 consecutive patients following DVT, we determined plasma fibrin clot characteristics, including clot permeability and lysability, inflammatory markers, thrombin generation, fibrinolysis proteins at 3 months since the index event. Occurrence of PTS and venous ulcers was recorded during follow-up (median, 53; range 24 to 76 months). Fifty-seven DVT patients (30.6%) developed PTS, including 12 subjects (6.45%) with a venous ulcer (4 individuals with recurrent ulcers). Patients who developed ulcers compared with the remainder had at enrolment 13.0% lower clot permeability (Ks), 17.4% longer clot lysis time (CLT), 13.1% longer lag phase of clot formation, and 5.0% higher maximum absorbance, with no difference in fibrinogen, C-reactive protein, and thrombin generation. The baseline prothrombotic fibrin clot phenotype (Ks ≤ 6.5 × 10-9 cm2 and CLT > 100 min) was associated with a higher risk of ulcers [hazard ratio (HR), 5.37; 95% confidence interval (CI), 1.3-21.5]. A multivariate model adjusted for age, sex, and fibrinogen showed that independent predictors of the ulcer occurrence were body mass index (HR 1.53; 95% CI 1.30-1.86), CLT (HR 1.43; 95% CI 1.04-2.05), and α2-antiplasmin (HR 0.95; 95% CI 0.90-0.99). This study suggests that formation of denser fibrin clots with impaired fibrinolysis predisposes to post-thrombotic venous ulcers.

Prothrombotic fibrin clot properties associated with increased endogenous thrombin potential and soluble P-selectin predict occult cancer after unprovoked venous thromboembolism

BACKGROUND

Compact fibrin clots relatively resistant to lysis are observed in patients at increased risk of venous thromboembolism (VTE) including malignancy. The citrullinated histone H3 (H3Cit) predicts VTE in cancer patients.

OBJECTIVES

We performed a cohort study to investigate whether abnormal clot properties predict cancer diagnosis following unprovoked VTE.

METHODS

In 369 consecutive patients aged <70 years without malignancy detected during routine screening, we determined plasma clot permeability (Ks ) and clot lysis time (CLT), along with several prothrombotic markers and H3Cit after 2 to 8 months since VTE.

RESULTS

During follow-up (median, 37; interquartile range, 33-39 months), malignancy was diagnosed in 22 patients (6%), who were older. This group had denser fibrin networks (-13% Ks ), impaired fibrinolysis (+25.5% CLT), increased endogenous thrombin potential (ETP,+7%), soluble P-selectin (+40.3%), and H3Cit (+169.2%) measured off anticoagulation after median 4 months since VTE. The Ks and CLT correlated with H3Cit (r = -.58 and r = .31, P < .05, respectively). The Kaplan-Meier survival analysis showed that reduced Ks (the first quartile, ≤6.2 × 10-9  cm2 ), prolonged CLT (the top quartile, >106 min), and higher ETP (the top quartile, >1657 nM × min) were predictors of cancer diagnosed during follow-up. The multivariable Cox proportional hazards model showed that patients with the prothrombotic clot phenotype (low Ks and long CLT) had the highest risk of cancer diagnosis [hazard ratio(HR), 23.4; 95% confidence interval (CI), 6.67-82.15].

CONCLUSIONS

Prothrombotic clot properties following unprovoked VTE might help identify patients at risk of a diagnosis of cancer within the first 3 years of follow-up.

Clot Structure and Implications for Bleeding and Thrombosis

The formation of a fibrin clot matrix plays a critical role in promoting hemostasis and wound healing. Fibrin dynamics can become disadvantageous in the formation of aberrant thrombus development. Structural characteristics of clots, such as fiber diameter, clot density, stiffness, or permeability, can determine overall clot integrity and functional characteristics that have implications on coagulation and fibrinolysis. This review examines known factors that contribute to changes in clot structure and the presence of structural clot changes in various disease states. These insights provide valuable information in forming therapeutic strategies for disease states where alterations in clot structure are observed. Additionally, the implications of structural changes in clot networks on bleeding and thrombus development in terms of disease states and clinical outcomes are also examined in this review.

Thrombin-generating potential, plasma clot formation, and clot lysis are impaired in patients with bleeding of unknown cause

BACKGROUND

In a large proportion of patients with a mild to moderate bleeding tendency no diagnosis can be established (bleeding of unknown cause, BUC).

OBJECTIVES

To investigate possible dysfunctions in thrombin generation and plasma clot formation and lysis in patients with BUC from the Vienna Bleeding Biobank (VIBB).

PATIENTS AND METHODS

Thrombin generation and plasma clot properties of 382 BUC patients were compared to those of 100 healthy controls and 16 patients with factor VIII (FVIII) activity ≤50%.

RESULTS

Thrombin generation was significantly impaired in BUC patients compared to healthy controls, exhibiting a prolonged lag time and time to peak and decreased maximum thrombin generation, velocity index, and area under the curve (AUC). The assessment of clot formation and lysis in BUC patients revealed a lower clot formation rate (Vmax), resulting in a longer TTP, increased absorbance (ΔAbs), and a shorter clot lysis time (CLT) than in healthy controls. Comparing patients with FVIII activity ≤ 50% to those with BUC, parameters of thrombin generation and clot formation and lysis were either stronger or comparably impaired. Bleeding severity did not correlate with parameters of thrombin generation, clot formation, or clot lysis.

CONCLUSION

Patients with BUC have an impaired hemostatic capacity reflected by a lower thrombin-generation potential, a lower clot formation rate, increased clot turbidity, and shorter clot lysis time, which might contribute to their increased bleeding tendency. Assays monitoring these parameters can alert physicians of hemostatic impairment and should be considered in situations where traditional hemostatic lab tests fail to reveal the clinical bleeding tendency.

Elevated activated partial thromboplastin time-based clot waveform analysis markers have strong positive association with acute venous thromboembolism

Introduction

A hypercoagulable state is a predisposition for venous thromboembolism (VTE). The activated partial thromboplastin time (aPTT)-based clot waveform analysis (CWA) is a global haemostatic measure but its role in assessment of hypercoagulability and thrombotic disorders is uncertain. We aimed to study the changes of CWA parameters in acute VTE. We hypothesized that patients with acute VTE would demonstrate higher CWA values than control patients without VTE and having elevated CWA parameters is associated with acute VTE.

Materials and methods

Clot waveform analysis data from patients (N = 45) with objectively proven acute VTE who had an aPTT performed prior to initiation of anticoagulation were compared with controls (N = 111). The CWA parameters measured were min1, min2, max2 and delta change.

Results

While the mean aPTT between VTE patients and controls did not differ (P = 0.830), the mean CWA parameters were significantly higher among VTE patients than controls (min1, P < 0.001; min2, P = 0.001; max2, P = 0.002; delta change, P < 0.001). There were significantly more cases within the VTE group exhibiting CWA values above their reference intervals than the control group (all P < 0.001), with the odds ratios for VTE of 8.0, 5.2, 4.8 and 18.6 for min1, min2, max2 and delta change, respectively (all P < 0.001).

Conclusions

Patients with acute VTE had elevated aPTT-based CWA parameters than controls. Higher CWA parameters were significantly associated with acute VTE.

Prothrombotic fibrin clot properties are associated with post-discharge venous thromboembolism in acutely ill medical patients

INTRODUCTION

Reduced clot permeability and lysability have been reported in patients who experienced venous thromboembolism (VTE) following lower limb injury despite pharmacological thromboprophylaxis. We hypothesized that similarly altered fibrin clot properties characterize patients with post-discharge VTE despite thromboprophylaxis during prior hospitalization due to acute medical illnesses.

METHODS

In a case-control study, we assessed 48 patients who developed VTE within 4 weeks post-discharge despite pharmacological thromboprophylaxis during hospitalization (the thromboprophylaxis group) and three age- and sex-matched control groups (n = 48 each): (1) patients who developed VTE following hospitalization without pharmacological thromboprophylaxis (the no-thromboprophylaxis group), (2) patients with unprovoked VTE and (3) individuals without history of VTE (the no-VTE group). Blood samples were obtained following ≥3 months of anticoagulation in VTE patients. Fibrin clot properties, thrombin generation and fibrinolysis activators and inhibitors were assessed.

RESULTS

Compared with the no-VTE group, the thromboprophylaxis group formed denser fibrin networks reflected by lower clot permeability (K_s, -13%) and impaired fibrinolysis, as evidenced by prolonged clot lysis time (CLT, +14%) and lower rate of D-dimer release from clots (D-D_rate, -9%) accompanied by elevated high-sensitivity C-reactive protein (hsCRP, +79%), peak thrombin generation (+55%) and α₂-antiplasmin (+10%, all p < 0.05). Similar fibrin clot features were observed following unprovoked VTE. The thromboprophylaxis group had also lower K_s (-13%), elevated α₂-antiplasmin (+18%) and higher peak thrombin generation (+25%, all p < 0.05) as compared with the no-thromboprophylaxis group.

CONCLUSIONS

Unfavorably altered plasma clot properties and increased thrombin generation characterize medical patients with post-discharge VTE despite receiving pharmacological thromboprophylaxis during hospitalization for acute conditions.

Plasma fibrin clot proteomics in healthy subjects: Relation to clot permeability and lysis time

BACKGROUND

Little is known about fibrin clot composition in relation to its structure and lysability. We investigated plasma clots protein composition and its associations with clot properties.

METHODS

We studied 20 healthy subjects aged 31-49 years in whom plasma fibrin clot permeability (K_s) and clot lysis time (CLT) were determined. A proteomic analysis of plasma fibrin clots was based on quantitative liquid chromatography-mass spectrometry.

RESULTS

Among 494 clot-bound proteins identified in all clots, the highest concentrations were for fibrinogen chains (about 64% of the clot mass) and fibronectin (13%). α₂-antiplasmin (2.7%), factor XIIIA (1.2%), complement component C3 (1.2%), and histidine-rich glycoprotein (HRG, 0.61%) were present at relatively high concentrations. Proteins present in concentrations <0.5% included (pro)thrombin, plasminogen, apolipoproteins, or platelet factor 4 (PF4). Fibrinogen-α and -γ chains were associated with age, while body-mass index with clot-bound apolipoproteins (all p < .05). K_s correlated with fibrinogen-γ and PF4 amounts within plasma clots. CLT was associated with fibrinogen-α and -γ, PF4, and HRG (all p < .05).

CONCLUSIONS

This study is the first to show associations of two key measures of clot properties with protein content within plasma clots, suggesting that looser fibrin clots with enhanced lysability contain less fibrinogen-γ chain, platelet-derived PF4, and HRG.

SIGNIFICANCE

Our study for the first time suggests that more permeable fibrin clots with enhanced lysability contain less fibrinogen-γ chain, platelet-derived factor 4, and histidine-rich glycoprotein, which is related to accelerated clot lysis. The current findings might have functional consequences regarding clot structure, stability, and propagation of thrombin generation, and detailed proteomic analysis of clots in various disorders opens new perspective for coagulation and fibrin research.

Improving fibrinolysis in venous thromboembolism: impact of fibrin structure

Introduction. Fibrinolysis is of key importance in maintaining vessel patency. Impaired fibrinolysis associated with more compact fibrin structure has been shown in patients with venous thromboembolism (VTE), including deep-vein thrombosis and pulmonary embolism (PE). Currently, recombinant or modified plasminogen activators are the only commonly available thrombolytic agents. However, they are fraught with side effects and suboptimal effectiveness. Areas covered. Based on the available literature, the current evidence linking fibrinolysis with VTE and potential therapeutic targets among fibrinolysis proteins are presented. Expert opinion. Prolonged clot lysis time has been reported as a new predictor of first-time and recurrent VTE, including PE. Anticoagulant therapy, including non-vitamin K antagonist oral anticoagulants, has a favorable impact on fibrinolysis in VTE patients. Several VTE risk factors are also related to lower efficiency of fibrinolysis and their treatment improve fibrinolysis, in part by alterations to fibrin properties. There is an increasing number of studies aiming at developing novel profibrinolytic therapeutic agents for treatment of VTE patients, mostly targeting the antifibrinolytic proteins, i.e. antiplasmin, plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor.

Unfavourably altered plasma clot properties in patients with primary Raynaud's phenomenon: association with venous thromboembolism

Associations of Raynaud’s phenomenon (RP) with venous thromboembolism (VTE) are unclear. We investigated the occurrence of RP together with prothrombotic state markers and fibrin clot properties in VTE patients. In this prospective cohort study we enrolled 360 patients free of known autoimmune disease. D-dimer, von Willebrand factor (vWF), plasma clot permeability (K_s), clot lysis time (CLT) along with fibrinolysis activators and inhibitors were determined at least 3 months since the VTE event. The presence/absence of RP was diagnosed at least 6 months before VTE. Primary RP occurred in 57 subjects (17%) with a 3.6-fold higher prevalence among women. Patients with RP had 11% higher fibrinogen, 16% higher vWF, 5% lower K_s, and 10% longer CLT (all p < 0.05). Females with RP (21%) had 6.6% lower K_s, 11.2% longer CLT, and 18.5% higher vWF (all p < 0.05) compared with men. CLT was predicted by PAI-1 and vWF levels. Regression analysis showed that RP was a predictor of prolonged CLT in the whole patient group (OR 3.46, 95% CI 1.92–6.24) and in women following VTE (OR 2.75, 95% CI 1.31–5.78). Primary RP patients tend to form denser plasma fibrin clots displaying impaired lysability and increased endothelial damage. RP might be a novel risk factor for VTE, especially in women.

Fibrinolysis and Inflammation in Venous Thrombus Resolution

Clinical observations and accumulating laboratory evidence support a complex interplay between coagulation, inflammation, innate immunity and fibrinolysis in venous thromboembolism (VTE). VTE, which includes deep vein thrombosis (DVT) and pulmonary embolism (PE), and the subsequent complications of post-thrombotic syndrome (PTS), are significant causes of morbidity and mortality in patients. Clinical risk factors for VTE include cancer, major trauma, surgery, sepsis, inflammatory bowel disease, paralysis, prolonged periods of immobility, and aging. Abnormalities in venous blood flow or stasis initiates the activation of endothelial cells, and in concert with platelets, neutrophils and monocytes, propagates VTE in an intact vein. In addition, inflammatory cells play crucial roles in thrombus recanalization and restoration of blood flow via fibrinolysis and vascular remodeling. Faster resolution of the thrombus is key for improved disease prognosis. While in the clinical setting, anticoagulation therapy is successful in preventing propagation of venous thrombi, current therapies are not designed to inhibit inflammation, which can lead to the development of PTS. Animal models of DVT have provided many insights into the molecular and cellular mechanisms involved in the formation, propagation, and resolution of venous thrombi as well as the roles of key components of the fibrinolytic system in these processes. Here, we review the recent advances in our understanding of fibrinolysis and inflammation in the resolution of VTE.

Restenosis is associated with prothrombotic plasma fibrin clot characteristics in endovascularly treated patients with critical limb ischemia

INTRODUCTION

Hypolysible fibrin clots composed of tightly packed fibers characterize patients with peripheral artery disease (PAD) especially those with critical limb ischemia (CLI). Little is known about the impact of a prothrombotic clot phenotype on restenosis following endovascular revascularization in CLI. The goal of this study was to compare fibrin clot properties and their determinants in CLI patients with restenosis after endovascular treatment (ET) and those free of this complication.

METHODS

85 patients with CLI and restenosis within 1 year after ET on optimal pharmacotherapy and 47 PAD control patients without restenosis were included into the study. Plasma fibrin clot permeability (Ks, a measure of the average pore size in the fibrin network) and clot lysis time (CLT) with its potential determinants were determined. During follow-up, the composite endpoint including re-intervention, amputation and death was assessed.

RESULTS

Compared with the control group, patients with restenosis had reduced Ks (- 9.5%, p < 0.001), prolonged CLT (+ 12.4%, p = 0.003), higher thrombin generation (+ 7.9%, p < 0.001) and elevated von Willebrand factor (vWF) antigen (+ 14.2%, p < 0.001). During a 24 months follow-up the composite endpoint occurred in 54 CLI patients with restenosis (63.5%) and nine control patients (19.1%, p < 0.001) with no association with baseline Ks and CLT.

CONCLUSION

The increased thrombin formation and unfavorable fibrin clot properties occur in patients with CLI who experienced restenosis despite optimal endovascular and pharmacological therapy.

Predictors of neutrophil extracellular traps markers in type 2 diabetes mellitus: associations with a prothrombotic state and hypofibrinolysis

BACKGROUND

Type 2 diabetes mellitus (T2DM) is associated with a hypercoagulable state and increased neutrophil extracellular traps formation (NETosis). We investigated predictors of NETosis and cell death markers in circulating blood and their association with a prothrombotic state in T2DM.

METHODS

In a cross-sectional study involving 113 T2DM patients aged 63.7 ± 8.2 years, we investigated citrullinated histone H3 (H3Cit), cell-free deoxyribonucleic acid (cfDNA), myeloperoxidase, neutrophil elastase, and inflammation markers, along with thrombin generation (TG), plasma clot lysis time (CLT), clot permeability (Ks) and fibrinolysis inhibitors.

RESULTS

On multivariate logistic regression analysis adjusted for age and gender, predictors of high H3Cit (≥ 7.36 ng/mL, upper quartile) were: glycated hemoglobin (HbA1c) ≥ 7.0% and interleukin-6. Interleukin-6 was also found to be a predictor of high cfDNA (≥ 2.84 µg/mL, upper quartile) along with glucose. Citrullinated histone H3 and cfDNA correlated positively with CLT and inversely with Ks, while TG associated solely with cfDNA. These associations were not seen with myeloperoxidase and neutrophil elastase. Patients with previous myocardial infarction (n = 21, 18.6%) had higher H3Cit (+108%, p < 0.001) and cfDNA (+45%, p = 0.022). On multivariable analysis adjusted for potential confounders, H3Cit and cfDNA, along with plasminogen activator inhibitor-1 and concomitant cardiovascular disease, were predictors of CLT. Citrullinated histone H3 alone was a predictor of Ks and only cfDNA was a predictor of peak thrombin generated.

CONCLUSIONS

In T2DM, NETosis detectable in circulating blood is associated with inflammatory state and a prothrombotic state, especially hypofibrinolysis.

A Prothrombotic State in Patients With a History of Left Ventricular Thrombus

Left ventricular thrombus (LVT) is associated with a hypercoagulable state and occurs most frequently after myocardial infarction (MI). Blood prothrombotic alterations might predispose to LVT formation, its recurrence, and subsequent cerebrovascular events. We investigated 58 patients with a history of LVT unrelated to recent MI or LV ejection fraction <25% and 58 well-matched control subjects. We determined plasma clot permeability, fibrinolytic efficiency, thrombin generation, and endothelial markers after 3 to 6 months of anticoagulant treatment. During follow-up we recorded LVT and thromboembolic events. Patients with LVT more often had LV akinesia, congestive heart failure, and prothrombotic state as evidenced by increased endogenous thrombin potential, lower antithrombin, lower clot permeability, and longer clot lysis time associated with lower antiplasmin, higher plasminogen activator inhibitor-1, thrombin activatable fibrinolysis inhibitor, and von Willebrand factor. During follow-up (57.5 ± 8.1 months for LVT patients and 59.6 ± 5.3 months for controls) strokes, transient ischemic attacks, or LVT occurred in 18 (31%) LVT patients and in 6 (10.3%) control subjects (4.1 vs 1.4% per year, p = 0.006). LVT recurred in 10 (2.3%/year) patients, who had higher risk of stroke/transient ischemic attacks (relative risk = 4.73, 95% confidence interval 1.8 to 40.4). The most compact clot formation at baseline, defined as the lowest quartile of clot permeability (≤5.4 × 10^-9 cm²) was a predictor of recurrent LVT (relative risk = 4.67, 95% confidence interval 1.32 to 18.37). This study shows that a persistent prothrombotic state involving enhanced thrombin generation, hypofibrinolysis, and formation of more compact fibrin clots characterizes patients who develop LVT not related to MI and those prone to its recurrence.

Recurrent venous thromboembolism patients form clots with lower elastic modulus than those formed by patients with non-recurrent disease

Essentials Venous thromboembolism (VTE) recurrence leads to decreased clot elastic modulus in plasma. Recurrent VTE is not linked to changes in clot structure, fiber radius, or factor XIII activity. Other plasma components may play a role in VTE recurrence. Prospective studies should resolve if clot stiffness can be used as predictor for recurrent VTE. SUMMARY: Background Venous thromboembolism (VTE) is associated with a high risk of recurrent events after withdrawal of anticoagulation. Objectives To determine the difference in plasma clot mechanical properties between patients with recurrent VTE (rVTE) and those with non-recurrent VTE (nrVTE). Methods We previously developed a system for determining clot mechanical properties by use of an in-house magnetic tweezers system. This system was used to determine the mechanical properties of clots made from plasma of 11 patients with rVTE and 33 with nrVTE. Plasma was mixed with micrometer-sized beads, and thrombin and calcium were added to induce clotting; the mixture was then placed in small capillary tubes, and clotting was allowed to proceed overnight. Bead displacements upon manipulation with magnetic forces were analyzed to determine clot elastic and viscous moduli. Fibrin clot structure was analyzed with turbidimetry and confocal microscopy. Factor XIII was measured by pentylamine incorporation into fibrin. Results Clots from rVTE patients showed nearly two-fold less elastic and less viscous moduli than clots from nrVTE patients, regardless of male sex, unprovoked events, family history of VTE, fibrinogen concentration, or body mass index. No differences were observed in clot structure, fibrinolysis rates, or FXIII levels. Conclusion Using magnetic tweezers for the first time in patient samples, we found that plasma clots from rVTE patients showed a reduced elastic modulus and a reduced viscous modulus as compared with clots from nrVTE patients. These data indicate a possible role for fibrin clot viscoelastic properties in determining VTE recurrence.

Altered fibrin clot properties in advanced lung cancer: strong impact of cigarette smoking

BACKGROUND

Dense fibrin networks resistant to lysis have been reported in patients at high risk of thromboembolism. Little is known about fibrin clot properties in cancer. We investigated fibrin clot properties and their determinants in patients with inoperable lung cancer.

METHODS

We enrolled 150 patients with advanced lung cancer prior to therapy and 90 control subjects matched by age, sex, cardiovascular disease, and diabetes. Plasma clot permeability (K_s), turbidimetric analysis of clot formation, clot lysis time (CLT), microparticle-associated tissue factor (MP-TF) activity, thrombin generation, and serum cotinine levels were determined.

RESULTS

Lung cancer patients, compared with controls, formed at a faster rate (- 8.1% lag phase) denser plasma fibrin networks (- 27.2% K_s) that displayed impaired lysis (+ 26.5% CLT), along with 19.5% higher MP-TF activity and 100% higher peak thrombin generated, also after adjustment for potential confounders. Cotinine levels were associated with fibrin maximum absorbance (r = 0.20, p = 0.016) and K_s (r = - 0.50, p < 0.0001) in cancer patients. On multivariate regression analysis, an increase in cotinine levels was a predictor of low K_s (the lower quartile, < 5.8 × 10^-9 cm²; odds ratio = 1.21 per 10 ng/ml, 95% confidence interval 1.02-1.46), but not CLT.

CONCLUSION

Advanced lung cancer is associated with the prothrombotic plasma clot phenotype largely driven by smoking.

Decreased Levels of Histidine-Rich Glycoprotein in Advanced Lung Cancer: Association with Prothrombotic Alterations

Background

Histidine-rich glycoprotein (HRG) displays anticoagulant and antifibrinolytic properties in animal models, but its effects in humans are unclear. We investigated serum HRG levels and their associations with the disease stage and prothrombotic alterations in lung cancer (LC) patients.

Methods

In 148 patients with advanced LC prior to anticancer therapy (87 non-small-cell LC and 61 small-cell LC) versus 100 well-matched controls, we measured HRG levels in association with clot permeability (K_s), clot turbidimetry (lag phase and maximum absorbance), and clot lysis time (CLT).

Results

Compared to controls, LC patients had 45.9% lower HRG levels with no associations with demographics and comorbidities. Decreased HRG, defined as the 90^th percentile of control values (<52.7 μg/ml), was 16 times more common in subjects with than without LC (OR = 16.4, 95% CI 9.2-23.5, p < 0.01). HRG < 38 μg/ml discriminated stage IIIAB/limited disease from IV/extensive disease (ED) LC. In LC patients, HRG correlated inversely with CLT (r = −0.41, p < 0.001), but not with other fibrin variables. Among stage IV/ED LC, HRG correlated significantly with K_s and lag phase (r = 0.28 and r = 0.33, respectively, both p < 0.001). LC patients with low K_s (10^th percentile of control values) combined with prolonged CLT (90^th percentile of control values) had reduced HRG levels compared to the remainder (p = 0.003). No such observations were noted in controls.

Conclusions

Our study is the first to show that decreased HRG levels occur in advanced LC and are associated with the disease stage and hypofibrinolysis.

Elevated lipoprotein(a) as a new risk factor of cerebral venous sinus thrombosis: association with fibrin clot properties

Elevated lipoprotein(a) [Lp(a)] has been reported to be associated with prothrombotic clot phenotype. We hypothesized that increased Lp(a) contributes to cerebral venous sinus thrombosis (CVST) and its recurrence in relation to clot features. In 80 consecutive patients (aged 39.36 ± 10.18 years, 61 women) following the first CVST after anticoagulation withdrawal, we assessed Lp(a) levels and plasma clot properties. Recurrence of CVST was recorded during follow-up (median 53, interquartile range 40-59 months). Lp(a) levels were inversely associated with clot permeability (K_s, r = - 0.58, P < 0.001) and the rate of D-dimer release from clots in the presence of tissue plasminogen activator (r = - 0.27, P = 0.017) along with increased maximum absorbance of fibrin gels (r = 0.42, P < 0.001) and maximum D-dimer levels achieved during lysis (D-D_max, r = 0.29, P = 0.01). Recurrence of CVST was observed in 12 patients (15%) after median follow-up of 26 months. Lp(a) concentrations were higher in patients with recurrence of CVST compared to the remainder (14.15 [8.85-25.25] vs. 28.3 [18.9-35.6] mg/dL; P = 0.001). The risk of recurrent CVST was fourfold higher among 17 (21.25%) patients with Lp(a) > 30 mg/dL compared to the remainder (adjusted hazard ratio, 3.9; 95% confidence interval [CI] 1.23-12.4). Recurrence of CVST was associated with 14% lower K_s (P = 0.001) and 10% higher D-D_max (P = 0.008), with no differences in other clot features. Multiple logistic regression model showed that CVST recurrence was independently associated with Lp(a) (odds ratio 1.09, 95% CI 1.02-1.16). Increased Lp(a) characterizes subjects at elevated risk of recurrent CVST after anticoagulation withdrawal, which could be partly explained by formation of denser fibrin clots.

Faster fibrin clot degradation characterizes patients with central pulmonary embolism at a low risk of recurrent peripheral embolism

It is unclear whether thrombus location in pulmonary arteries is associated with particular clot characteristics. We assessed 156 patients following either central or peripheral pulmonary embolism (PE). Plasma clot lysis time, the rate of D-dimer release from plasma clots (D-D_rate) with the maximum D-dimer concentration achieved (D-D_max), as well as fibrin formation on turbidimetry, plasma clot permeation, thrombin generation, and fibrinolytic parameters were measured 3–6 months after PE. Patients following central PE (n = 108, 69.3%) were more likely smokers (38.9% vs 18.8%; p = 0.01), less likely carriers of factor XIII Val34Leu allele (40.7% vs 62.5%, p = 0.01), exhibited 16.7% higher D-D_rate and 12.7% higher tissue plasminogen activator antigen (tPA:Ag) compared with peripheral PE (p = 0.02 and p < 0.0001, respectively). Saddle PE patients (n = 31, 19.9%) had 11.1% higher D-D_rate and 7.3% higher D-D_max compared with central PE (both p < 0.05). Twenty-three recurrent PE episodes, including 15 central episodes, during a median follow-up of 52.5 months were recorded. Plasma D-dimer and tPA:Ag were independent predictors for central recurrent PE, whereas D-D_rate and peak thrombin predicted peripheral recurrent PE. Plasma clots degradation is faster in patients following central PE compared with peripheral PE and fibrinolysis markers might help to predict a type of recurrent PE.

Altered fibrin clot properties in advanced lung cancer: impact of chemotherapy

Background

Faster formation of dense and poorly lyzable fibrin networks have been reported in patients at risk of thromboembolism, including cancer patients. We sought to investigate whether chemotherapy affects plasma fibrin clot properties and their determinants in lung cancer patients.

Methods

In this observational study we enrolled 83 consecutive patients with advanced inoperable lung cancer. Plasma fibrin clot permeability (K_s), turbidimetric analysis of clot formation, clot lysis time (CLT), microparticle-associated tissue factor (MP-TF) activity, and thrombin generation parameters were investigated at enrolment and 3-4 months after standard chemotherapy.

Results

Lung cancer patients after 4 (range, 4-5) cycles of chemotherapy had 35.6% higher D-dimer, 22.1% lower MP-TF activity, and unaltered fibrinogen compared with baseline. Chemotherapy resulted also in 7.5% increased K_s, 8.6% prolonged lag phase, and 5.4% shortened CLT, while thrombin generation was unchanged. Chemotherapy-related differences in clot structure were confirmed by scanning electron microscopy images. Fibrin clot properties after chemotherapy did not differ among histological types of lung cancer, cancer stages or chemotherapy regimens. Interestingly, never smoking (n=13, 16%) was associated with looser post-treatment fibrin structure as reflected by 12.3% higher K_s. Multiple linear regression showed that more advanced cancer stage, higher peak thrombin generation, and higher white blood cell count determined post-treatment change in K_s, while active smoking was associated with change in CLT.

Conclusions

Three-month chemotherapy in lung cancer patients improves clot properties despite unaffected thrombin generation, suggesting that anticancer treatment might quickly produce antithrombotic actions.

Differences in plasma fibrin clot composition in patients with thrombotic antiphospholipid syndrome compared with venous thromboembolism

The prothrombotic fibrin clot phenotype has been reported in patients with thrombotic antiphospholipid syndrome (APS) and venous thromboembolism (VTE). Protein composition of plasma fibrin clots in APS has not been studied. We evaluated 23 patients with thrombotic APS, 19 with VTE alone, and 20 well-matched controls. A proteomic analysis of fibrin clots generated from citrated plasma was based on liquid chromatography-mass spectrometry. Plasma levels of thrombospondin-1 (TSP1), apolipoprotein(a), A-I, and B-100, complement components (C)3a, C5b-C9, histidine-rich glycoprotein (HRG), and prothrombin were evaluated using immunoenzymatic tests. In plasma fibrin clots of APS patients, compared with VTE subjects and controls, we identified decreased amounts of (pro)thrombin, antithrombin-III, apolipoprotein A-I, and HRG with no differences in plasma levels of antithrombin, prothrombin, along with lower plasma HRG and apolipoprotein A-I. In APS patients, plasma HRG positively correlated with amounts of clot-bound HRG, while apolipoprotein A-I was inversely associated with clot-bound levels of this protein. The most predominant proteins within the clots of APS patients were bone marrow proteoglycan, C5-C9, immunoglobulins, apolipoprotein B-100, platelet-derived proteins, and TSP1. Our study is the first to demonstrate differences in the protein composition of fibrin clots generated from plasma of thrombotic APS patients versus those with VTE alone.

Risk assessment and management of preoperative venous thromboembolism following femoral neck fracture

BACKGROUND

Limited studies are available to investigate the prevalence of preoperative venous thromboembolism (VTE) in elderly patients with femoral neck fractures. Our primary aim was to determine the incidences of VTE and its risk or protective factors in such patient population. The secondary objective was to evaluate the need of therapeutic anticoagulation for isolated calf muscular venous thrombosis (ICMVT) prior to femoral neck fracture surgery.

METHODS

This is a retrospective case-control study, including 301 femoral neck fracture patients who were admitted to our institution between January 2014 and March 2017. Bilateral Doppler ultrasonography was performed in each of the patients as a preoperative VTE screening. The event rate of VTE was calculated, and significant risk or protective factors were determined by using a multivariate logistic regression model. Patients with ICMVT were divided into anticoagulation and no anticoagulation groups to assess the efficacy and safety of preoperative therapeutic anticoagulation. Intraoperative blood loss, drainage volume, blood transfusion, perioperative hemoglobin change, and rate of thrombosis extension were compared between the two groups.

RESULTS

The overall preoperative incidence of VTE in patients with femoral neck fracture was 18.9% (57/301), in which deep vein thrombosis (DVT) was 18.9% and pulmonary embolism (PE) was 1%. Among the DVT cases, 77.2% (44/57) were ICMVTs. Multiple fractures (odds ratio [OR] = 9.418; 95% confidence interval [CI] = 2.537 to 34.96), coexisting movement disorder (OR = 3.862; 95% CI = 1.658 to 8.993), bed rest for more than 7 days (OR = 2.082; 95% CI = 1.011 to 4.284) as well as elevated levels of D-dimer (OR = 1.019; 95% CI = 1.002 to 1.037) and fibrinogen (OR = 1.345; 95% CI = 1.008 to 1.796) led to an increase in the risk of VTE, while the recent use of antiplatelet drug (OR = 0.424; 95% CI = 0.181 to 0.995) and prophylactic anticoagulation (OR = 0.503; 95% CI = 0.263 to 0.959) decreased the risk of VTE. For the 39 patients with ICMVT undergoing femoral neck fracture surgery, there were no significant differences in the rate of thrombosis extension between anticoagulation and no anticoagulation groups, but significantly decreased postoperative hemoglobin was observed in the anticoagulation group.

CONCLUSION

Our findings showed a high prevalence of preoperative VTE in elderly patients with femoral neck fracture, with risk factors identified. We found that the most detected VTE were ICMVTs. Our study suggested that a direct surgery without preoperative use of therapeutic anticoagulation for ICMVT would not reduce the risk of thrombus extension, and the therapeutic use of anticoagulation may worsen postoperative anemia.

Erythrocyte compression index is impaired in patients with residual vein obstruction

Defective clot contraction has been postulated to contribute to thrombosis. We aimed to evaluate the association of residual vein obstruction (RVO) with erythrocyte compression within the whole-blood clot. We studied 32 patients with venous thromboembolism (VTE) taking vitamin K antagonists (VKAs) for at least 3 months (median time in therapeutic range 60%), including 12 (37.5%) with RVO, and 32 age- and sex-matched controls. In all study participants we evaluated whole blood clot retraction, expressed as the erythrocyte compression index (ECI), defined as a ratio of mean polyhedrocyte area to mean native erythrocyte area, along with clot area covered by polyhedrocytes, plasma clot permeability (Ks), clot lysis time (CLT), and thrombin generation. In both groups higher ECI, indicating impaired clot contraction, increased with older age, higher body mass index, red blood cell distribution width, and lower platelet count (all p < 0.05), but not with red blood cell count. In VTE patients ECI was 15.8% higher than in controls (median 63.6 vs. 54.9%, p = 0.021). Subjects with RVO had 20% higher ECI and 155% lower clot area covered by polyhedrocytes. RVO patients had also prolonged CLT by 41%, but not Ks, and elevated peak thrombin generation by 33%, as compared to those without RVO (all p < 0.05). This study is the first to show impaired compression of erythrocytes in RVO patients despite VKA anticoagulation. Altered ECI coexisted with hypolysability and increased thrombin generation. ECI might be useful in the diagnostic process of RVO or post-thrombotic syndrome and can help optimize the anticoagulant therapy.

Comparison of antithrombin-dependent and direct inhibitors of factor Xa or thrombin on the kinetics and qualitative characteristics of blood clots

BACKGROUND

Venous thromboembolism (VTE) is associated with significant morbidity and mortality.

OBJECTIVES

We investigated the impact of direct and AT-dependent FXa or thrombin inhibitors on thrombus formation.

METHODS

Whole blood thromboelastometry and thrombin generation were assessed after triggering the TF pathway. Clinically relevant concentrations of rivaroxaban, fondaparinux, dabigatran or tinzaparin and an association of rivaroxaban and dabigatran were examined.

RESULTS

All agents delayed thrombus formation in a concentration-dependent manner, as documented by the prolongation of the clotting time (CT) and clot formation time (CFT). Rivaroxaban did not significantly alter the α-angle or maximum clot firmness (MCF). In contrast, dabigatran and fondaparinux altered the process of clot structure by decreasing the α-angle, but did not modify clot firmness. The later property was significantly affected only by tinzaparin that also reduced the MCF. The association of rivaroxaban and dabigatran did not affect the MCF, although it amplified the effect on CFT and α-angle.

CONCLUSIONS

All agents delayed thrombus formation. However, the compounds differed substantially with respect to fibrin polymerization rate and clot firmness. Comparison of the data obtained by thrombin generation assessment with those obtained by the thromboelastometric study shows that the delay in clot formation is principally associated with prolongation of the initiation phase of thrombin formation as well as a reduction of the propagation phase. Tinzaparin was much more potent than the other agents both with regard to suppression of thrombin generation and by delay in clot formation.

Impact of γ'γ' fibrinogen interaction with red blood cells on fibrin clots

AIM

γ' fibrinogen has been associated with thrombosis. Here the interactions between γ'γ' or γAγA fibrinogen and red blood cells (RBCs), and their role on fibrin clot properties were studied.

MATERIALS & METHODS

Atomic Force microscopy (AFM)-based force spectroscopy, rheological, electron and confocal microscopy, and computational approaches were conducted for both fibrinogen variants.

RESULTS & CONCLUSION

AFM shows that the recombinant human (rh)γ'γ' fibrinogen increases the binding force and the frequency of the binding to RBCs compared with rhγAγA, promoting cell aggregation. Structural changes in rhγ'γ' fibrin clots, displaying a nonuniform fibrin network were shown by microscopy approaches. The presence of RBCs decreases the fibrinolysis rate and increases viscosity of rhγ'γ' fibrin clots. The full length of the γ' chain structure, revealed by computational analysis, occupies a much wider surface and is more flexible, allowing an increase of the binding between γ' fibers, and eventually with RBCs.

Fibrinogen and factor XIII: newly recognized roles in venous thrombus formation and composition

PURPOSE OF REVIEW

In spite of significant morbidity and mortality associated with venous thromboembolism, the underlying pathogenesis remains poorly understood.

RECENT FINDINGS

Clues to operant pathogenic mechanisms are found in the unique morphology and composition of these thrombi, which have substantial red blood cell and fibrin content. Recent studies have revealed biochemical and biophysical mechanisms that dictate fibrin structure in venous thrombi and promote retention of red blood cells within the contracted clots. These mechanisms include newly recognized contributions of fibrin network structure and factor XIII(a)-mediated fibrin crosslinking to venous thrombus composition, size, and stability.

SUMMARY

Continued work to elucidate mechanisms by which fibrin(ogen), factor XIII, and red blood cells contribute to venous thrombus formation, structure, and stability may expose novel molecular targets and strategies for reducing thrombosis and thrombotic complications in certain at-risk patients.

Altered structure and function of fibrinogen after cleavage by Factor VII Activating Protease (FSAP)

Factor VII Activating Protease (FSAP) is a plasma protease affecting both coagulation and fibrinolysis. Although a role in hemostasis is still unclear, the identification of additional physiologic substrates will help to elucidate its role in this context. FSAP has been reported to cleave fibrinogen, but the functional consequences of this are not known. We have therefore undertaken this study to determine the implications of this cleavage for fibrin-clot formation and its lysis. Treatment of human fibrinogen with FSAP released an N-terminal peptide from the Bβ chain (Bβ1-53) and subsequently the fibrinopeptide B; within the Aα chain a partial truncation of the αC-region by multiple cleavages was seen. The truncated fibrinogen showed a delayed thrombin-catalyzed polymerization and formed fibrin clots of reduced turbidity, indicative of thinner fibrin fibers. Confocal laser scanning and scanning electron microscopy of these clots revealed a less coarse fibrin network with thinner fibers and a smaller pore size. A lower pore size was also seen in permeability studies. Unexpectedly, FSAP-treated fibrinogen or plasma exhibited a significantly faster tPA-driven lysis, which correlated exclusively with cleavage of fibrinogen and not with activation of plasminogen activators. Similar observations were also made in plasma after activation of endogenous zymogen FSAP, but not in plasma of carrier of the rare Marburg I single nucleotide polymorphism. In conclusion, altering fibrin clot properties by fibrinogenolysis is a novel function of FSAP in the vasculature, which facilitates clot lysis and may in vivo contribute to reduced fibrin deposition during thrombosis.

The effect of tyramine infusion and exercise on blood flow, coagulation and clot microstructure in healthy individuals

BACKGROUND

The long term benefits of exercise on the cardiovascular status of a patient have been proven, however, their benefit/risk relationship with exercise intensity is unclear. Furthermore, many thromboembolic diseases such as myocardial infarction and ischaemic stroke are associated with profound catecholamine release. In this study we explore the relationship between catecholamine release and hemodynamic changes and their effect on coagulation.

MATERIALS AND METHODS

Twelve healthy recreationally active males were recruited. Local anesthesia was given and catheters were placed under aseptic conditions, in the femoral artery and vein of the experimental leg. The first experiment involved tyramine infusion into the femoral artery at a dose of 1.0 μmol·min^-1·L leg volume^-1. The second experiment involved single leg knee-extensor exercise performed at 30 W for 15 min. Venous blood was collected at each time point to assess clot microstructure using the d_f biomarker.

RESULTS AND CONCLUSIONS

Tyramine infusion causes a local noradrenaline release in the leg. The increase in noradrenaline was associated with a significant increase in clot microstructure formation (d_f increased from 1.692 ± 0.029 to 1.722 ± 0.047, p = 0.016). Additionally moderate intensity single leg knee extensor exercise, which minimally alters sympathetic activity, also induced an increases in d_f (from 1.688 ± 0.025 to 1.723 ± 0.023, p = 0.001). This suggests that exercise can alter clot microstructure formation both via an increase in catecholeamine levels and by factors related to muscle activity per se, such as increased blood flow and consequent shear. These findings have implications for recommendations of exercise in patients at risk of cardiovascular events.

Blood coagulation dissected

Hemostasis is the physiological control of bleeding and is initiated by subendothelial exposure. Platelets form the primary vascular seal in three stages (localization, stimulation and aggregation), which are triggered by specific interactions between platelet surface receptors and constituents of the subendothelial matrix. As a secondary hemostatic plug, fibrin clot formation is initiated and feedback-amplified to advance the seal and stabilize platelet aggregates comprising the primary plug. Once blood leakage has been halted, the fibrinolytic pathway is initiated to dissolve the clot and restore normal blood flow. Constitutive and induced anticoagulant and antifibrinolytic pathways create a physiological balance between too much and too little clot production. Hemostatic imbalance is a major burden to global healthcare, resulting in thrombosis or hemorrhage.

Elevated leptin and decreased adiponectin independently predict the post-thrombotic syndrome in obese and non-obese patients

Post-thrombotic syndrome (PTS) is a common complication of deep vein thrombosis (DVT). Little is known about the involvement of adipokines in the pathogenesis of DVT. We evaluated whether adipokines can predict PTS. In a prospective cohort study, 320 DVT patients aged 70 years or less were enrolled. Serum adiponectin, leptin and resistin levels were measured three months since the index first-ever DVT. After 2 years’ follow-up PTS was diagnosed in 83 of 309 available patients (26.9%) who had 13.9% lower adiponectin and 16% higher leptin levels compared with the remainder (both p < 0.0001). No PTS-associated differences in C-reactive protein, fibrinogen, D-dimer, plasminogen activator inhibitor-1 and resistin were observed. The multivariable logistic regression adjusted for age, sex, obesity and tissue plasminogen activator (tPa) showed that lower adiponectin (odds ratio [OR], 0.42; 95% confidence interval [CI], 0.31–0.56) and higher leptin levels (OR, 1.49; 95% CI, 1.31–1.69) are independent predictors for PTS. Obesity-stratified logistic regression analysis confirmed that lower adiponectin (OR, 0.49; 95% CI, 0.38–0.64) and higher leptin (OR, 1.41; 95% Cl, 1.25–1.58) levels predicted PTS. Our findings showed that lower adiponectin and higher leptin measured 3 months after DVT, regardless of obesity, can independently predict PTS, which suggests novel links between adipokines and thrombosis.

Prothrombotic State in Asthma Is Related to Increased Levels of Inflammatory Cytokines, IL-6 and TNFα, in Peripheral Blood

Recently, we have reported that asthma is associated with enhanced plasma thrombin formation and impaired fibrinolysis. The mechanisms underlying the prothrombotic state in this disease are unknown. Our aim was to investigate whether prothrombotic alterations in asthmatics are associated with inflammation. We studied 164 adult, white, stable asthmatics and 72 controls matched for age, sex, body mass index (BMI), and smoking. Plasma tumor necrosis factor α (TNFα), interleukin (IL)-6, and serum periostin were evaluated using ELISAs, and their associations with thrombin generation, fibrinolytic capacity, expressed as clot lysis time (CLT), and platelet markers were later analyzed. Asthma was characterized by 62% higher plasma IL-6 and 35% higher TNFα (both, p < 0.0001). Inflammatory cytokines were higher in sporadic and persistent asthmatics compared to controls, also after adjustment for potential confounders. IL-6 was inversely related to the forced expiratory volume in 1 s/vital capacity (FEV₁/VC) spirometry index after correction for age, sex, and BMI. IL-6 and TNFα were associated with C-reactive protein in asthmatics (β = 0.6 [95% CI, 0.54–0.67] and β = 0.33 [95% CI, 0.25–0.41], respectively) and controls (β = 0.43 [95% CI, 0.29–0.57] and β = 0.33 [95% CI, 0.18–0.48], respectively). In asthma, IL-6 and TNFα positively correlated with the endogenous thrombin potential (β = 0.35 [95% CI, 0.28–0.42] and β = 0.15 [95% CI, 0.07–0.23], respectively) but not with CLT or platelet markers. However, TNFα predicted CLT in a multiple linear regression model. Periostin was not associated with any hemostatic parameters. Enhanced thrombin generation is driven in asthma by a systemic inflammatory state mediated by IL-6 and to a lesser extent TNFα, however, not periostin. TNFα might contribute to impaired fibrinolysis.

Impaired plasminogen binding in patients with venous thromboembolism: Association with protein carbonylation

INTRODUCTION

Venous thromboembolism (VTE) is associated with hypofibrinolysis. Its mechanisms are poorly understood. We investigated plasminogen-fibrin interaction and its association with fibrinolytic capacity and protein oxidation/carbonylation in VTE patients.

MATERIALS AND METHODS

Plasma-purified plasminogen conversion to plasmin and surface plasmon resonance employed for plasminogen-fibrin interactions were individually evaluated in all healthy controls and non-anticoagulated patients following VTE, 10-23months since the event. We also assessed plasma fibrin clot permeability (K_s), clot lysis time (LT), activators and inhibitors of fibrinolysis together with oxidation/carbonylation markers.

RESULTS

VTE patients had impaired plasminogen binding to fibrin (apparent Kd, +290%, p=0.002), reduced rate of plasmin generation (-4.7%, p=0.001), and longer LT (+18.6%, p<0.001) compared with controls. Fibrinogen and K_s were similar in both groups. Apparent Kd correlated with LT (r=0.43, p=0.037), tissue plasminogen activator-plasminogen activator inhibitor 1 (tPA-PAI-1) complexes (r=0.63, p=0.012), and active PAI-1 (r=0.49, p=0.03). Compared with controls, VTE patients had higher thiobarbituric acid reactive substances (TBARS), total protein carbonyl content (PC), and lower total antioxidant capacity (all p<0.001), that all were associated with LT (r=0.61, r=0.56, and r=-0.47, respectively, all p<0.05). Impaired plasminogen binding to fibrin reflected by apparent Kd positively correlated with TBARS (r=0.48, p=0.032) and PC (r=0.54, p=0.013) in the whole group.

CONCLUSIONS

Plasminogen-fibrin interactions are altered in young and middle-aged VTE patients, without known thrombophilias, except increased factor VIII. The mechanisms underlying these phenomena remain to be established.

Altered plasma clot properties increase the risk of recurrent deep vein thrombosis: a cohort study

It has been demonstrated that fibrin clots generated from plasma samples obtained from patients with prior thromboembolic events are denser and less susceptible to lysis. Such a prothrombotic fibrin clot phenotype has been suggested as a new risk factor for venous thromboembolism, but its prognostic value is unclear. To assess whether abnormal clot properties can predict recurrent deep vein thrombosis (DVT), we studied 320 consecutive patients aged 18 to 70 years following the first-ever DVT. Plasma clot properties were evaluated after 3 months of anticoagulant treatment since the index event. A mean duration of anticoagulation was 10 months (range, 4-20). Recurrent DVT was observed in 77 patients (25%; 6.6%/year) during a median follow-up of 44 months. Recurrences of DVT were associated with faster formation (-9% lag phase) of denser fibrin networks (-12% fibrin clot permeability [K_s]) and 4% higher maximum absorbance of plasma clots that displayed impaired fibrinolytic degradation (+25% prolonged clot lysis time [CLT]) and a 5% slower rate of increase in D-dimer levels during clot degradation (D-D_rate; all P < .05). Proximal DVT alone, higher C-reactive protein, D-dimer, peak thrombin, lower K_s, shorter lag phase, decreased D-D_rate, and prolonged CLT were independent predictors of recurrences (all P < .05). Individuals characterized by low K_s (≤7.3 × 10^-9 cm²) and prolonged CLT (>96 min) were at the highest risk of recurrent DVT (odds ratio, 15.8; 95% confidence interval, 7.5-33.5). Kaplan-Meier curves showed that reduced K_s and prolonged CLT predicted recurrent DVT. We demonstrate that unfavorably altered clot properties may predict recurrent DVT after anticoagulation withdrawal.