Plasma fibrin clots of pulmonary embolism patients present increased amounts of factor XIII and alpha2-antiplasmin at 3 months' anticoagulation since the acute phase.

Fibrin cross-linking by coagulation factor (F)XIII leads to clot stabilization. Reduced plasma FXIII levels have been reported in acute pulmonary embolism (PE) patients. We investigated the impact of anticoagulant therapy on clot-bound amounts of FXIII and α2-antiplasmin and their associations with fibrin clot properties in patients with PE. Clots generated from plasma of 18 acute symptomatic patients on admission and after a 3-month treatment with rivaroxaban were assessed off anticoagulation using mass spectrometry. Plasma FXIII and α2-antiplasmin activity were determined at the 2 time points along with thrombin generation markers, plasma fibrin clot permeability (Ks), and clot lysis time (CLT). Following anticoagulant therapy, clot-bound FXIII increased from 2.97 (interquartile range, 1.98 - 4.08) to 4.66 (3.5 - 6.9) mg/g protein and α2-antiplasmin from 9.4 (7.2 - 10.6) to 11 (9.5 - 14) mg/g protein (both p < 0.0001). The two parameters showed positive correlation at baseline only (r = 0.63, p = 0.0056). Similarly to clot-bound amounts, plasma FXIII (+25.8%) and α2-antiplasmin activity (+12%) increased at 3 months. Plasma FXIII activity on admission, but not after 3 months since the index PE, was associated with amounts of clot-bound FXIII (r = 0.35, p = 0.043) and α2-antiplasmin (r = 0.47, p = 0.048). At baseline, clot-bound FXIII correlated with plasma F1+2 prothrombin fragments levels (r = 0.51, p = 0.03), while clot-bound α2-antiplasmin correlated with CLT (r = 0.43, p = 0.036). At 3 months associations of clot-bound FXIII and α2-antiplasmin were abolished. This study assessed for the first time changes in the fibrin clot composition following acute PE, suggesting an increase of clot-bound and plasma FXIII and α2-antiplasmin levels after 3 months.

Effects of direct oral anticoagulants on thromboelastographic parameters and fibrin clot properties in patients with venous thromboembolism.

Data concerning the impact of direct oral anticoagulants (DOACs) on the thromboelastography (TEG) indices in venousthromboembolism (VTE) patients are limited. The goal of this study was to compare the impact of DOACs on clot properties measured in whole blood using TEG kaolin test and in plasma obtained from real-life VTE patients. We assessed 53 patients, including 20 on rivaroxaban, 20 on apixaban, and 13 on dabigatran. Using the TEG® 5000, coagulation status was evaluated in whole blood samples, while plasma fibrin clot permeability (Ks) and its susceptibility to lysis (CLT) were assessed in citrated plasma. Plasma concentrations of rivaroxaban (99 [48 - 311] ng/ml) and apixaban (85 [40 - 105] ng/ml) were positively associated with Ks and inversely with CLT, while dabigatran concentrations (71 [39 - 98] ng/ml) correlated positively with Ks. Moreover, Ks was associated with clot formation times (R and K), time to maximum clot strength (TMA), coagulation index (CI) reflecting the overall coagulation status, and whole blood clot lysis time (TEG-CLT). Blood clot lysis index (CL30) was associated with plasma CLT in all patients on DOACs, while TMA correlated with CLT only in patients on apixaban. Higher DOAC concentrations were associated with longer retardation of whole blood clot formation and longer time needed to reach maximum level of its strength as well as with more permeable clots. We concluded that plasma fibrin clot properties correlate with corresponding TEG indices suggesting that TEG might be helpful in providing prognostic information about DOAC influence in VTE patients.

Viscoelastic properties of plasma fibrin clots are similar in patients on rivaroxaban and vitamin K antagonists.

Unfavorable fibrin clot features have been observed in patients with venous thromboembolism (VTE). We investigated whether rivaroxaban, a direct factor Xa inhibitor, and vitamin K antagonists (VKAs) can improve plasma clot viscoelastic properties. We studied four age- and sex-matched groups: 25 healthy controls, 15 VTE patients taking rivaroxaban 20 mg/day (blood concentration, 145 (67 - 217) ng/ml), 15 VTE patients taking VKA (INR: 2 - 3), and 15 VTE patients who stopped oral anticoagulant therapy (OAT). Using a hybrid rheometier the storage (G') and loss (G") moduli were evaluated in citrated plasma after addition of 5 pmol/l tissue factor. Fiber thickness within clots was assessed using scanning electron microscopy. Higher G' but not G" was observed for VTE patients taking rivaroxaban (+34%; post hoc, P = 0.029) compared to controls. As reflected by lower G' and G", patients taking rivaroxaban (-19% and -30%; post hoc, P = 0.0013 and P < 0.0001, respectively) formed less stiff and viscous clots compared to VTE patients after OAT withdrawal, also after adjustment for fibrinogen. VTE patients treated with rivaroxaban and VKA had similar clot viscoelastic properties (post hoc, P = 0.85 for G' and P = 0.29 for G"). G' and G" correlated with plasma rivaroxaban concentrations (r = -0.67, P = 0.005 and r = -0.59, P = 0.021, respectively), and the time from the last dose of rivaroxaban intake (r = 0.59, P = 0.02 and r = 0.58, P = 0.022, respectively). G' and G" showed no association with INR in patients on VKAs. G' or G" were not associated with fibrin diameter on scanning electron microscopy images in either group. Our preliminary study shows that both rivaroxaban and VKA improve clot viscoelastic properties in VTE patients, which might contribute to their antithrombotic effects. G' and G" may reflect specific clot physical features, beyond key plasma clot characteristics, which highlights benefits from comprehensive plasma clot analysis in patients with thrombotic diseases.

Antithrombotic medications and their impact on fibrin clot structure and function.

Fibrin constitutes a major protein component of intravascular thrombi in all locations. Fibrin formation and its functions are essential for physiological hemostasis and the pathologic thrombosis. Formation of dense fibrin networks which are relatively resistant to lysis is observed in patients with venous or arterial thromboembolism, including myocardial infarction, ischemic stroke and venous thromboembolism. Measures of clot characteristics, in particular clot permeability and clot lysis time, may predict arterial and venous recurrent thromboembolic events. Medications, including vitamin K antagonists (VKA), direct oral anticoagulants (DOAC), and parenteral direct or indirect thrombin or activated factor X inhibitors increase clot permeability, reflecting fibrin network density, in association with enhanced efficiency of fibrinolysis. These effects are only in part related to decreased thrombin generation. There is evidence that aspirin can also favorably alter fibrin clot properties probably through acetylation of fibrinogen. No such effects were observed for P2Y12 inhibitors. Of note, plasma fibrin clot permeability has been shown to predict adverse clinical outcomes in patients receiving oral anticoagulants, which might have practical implications. The current review summarizes data on effects of antithrombotic agents on fibrin clot phenotype in cardiovascular disease.

Asthma is associated with enhanced thrombin formation and impaired fibrinolysis.

BACKGROUND: There is evidence that altered blood coagulation and fibrinolysis are involved in the pathogenesis of asthma. Increased thromboembolic risk has been reported in asthmatics. OBJECTIVE: To investigate whether enhanced thrombin generation and impaired fibrinolysis occur in asthmatics. METHODS: Plasma thrombin generation profile together with a computational assessment of thrombin dynamics and fibrinolytic capacity expressed as clot lysis time (CLT) were determined in 164 consecutive patients with stable asthma and 72 controls matched for age, gender, weight and smoking. RESULTS: Asthma patients had 20.2% increased endogenous thrombin potential (ETP), 41.4% higher peak thrombin concentration, 61% higher maximal prothrombin conversion rate, 15.5% faster rate of thrombin formation (all, P < 0.0001) and 10% lower thrombin decay capacity (P = 0.0004) compared with controls. Asthmatics had also 14.4% longer CLT (P = 0.001) associated with 21.3% higher plasminogen activator inhibitor-1 (PAI-1) (P < 0.0001), and 13% higher plasma α2 -macroglobulin (P = 0.0002). Using ETP and CLT above 75th percentile of the control values as the cut-off levels, we found increased risks of enhanced thrombin generation and hypofibrinolysis in asthmatics, also after correction for potential confounders. ETP and CLT were associated inversely with forced expiratory volume in 1 s/vital capacity (FEV1 /VC) index, after adjustment for age and body mass index. Non-allergic asthma (n = 70, 42.6%) was characterized by 17.5% longer CLT (P = 0.02), which positively associated with PAI-1. Thrombin generation profile was not affected by allergy. CONCLUSION AND CLINICAL RELEVANCE: Asthma is associated with enhanced thrombin generation and impaired fibrinolysis, which might contribute to thromboembolic events in this disease.

Fibrinogen depletion after plasma-dilution: impairment of proteolytic resistance and reversal via clotting factor concentrates.

In trauma patients, resuscitation treatment of intravascular volume may cause haemodilution including blood cell- and plasma-dilution. After plasma-dilution, fibrinogen is the first factor that decreases to critically low concentrations. Fibrin formed in lowered levels is susceptible to fibrinolysis, a natural forerunner for bleeding. To assess whether a fibrinogen concentrate or a factor XIII (FXIII) concentrate can reverse the impairment of fibrin properties after plasma dilution, different laboratory methods were used to determine thrombin generation and fibrin quantity/quality in a normal plasma sample diluted in vitro. Coagulation and clot lysis by plasmin were triggered with tissue factor and rt-PA, respectively.We found that while the endogenous thrombin potential (ETP) was unaffected after plasma-dilution due to postponement of thrombin decay, levels of fibrinogen and hence fibrin were decreased in dilution degree-dependency. The imbalance between influence of the dilution on thrombin activity and fibrin formation brought unexpected outcomes of fibrin properties: the formed clots favoured the degradation by plasminbut the fibrin networks remained tighter/less permeable. This proteolytic tendency was partly overturned by the fibrinogen concentrate added (total fibrinogen ≥ 2 g/l), and much more affected if used in combination with tranexamic acid (a fibrinolysis inhibitor) at small doses. No reversal effect resulted from the FXIII concentrate added. We conclude that plasma-dilution did reduce the proteolytic resistance of formed clots. The fibrinogen concentrate, better together with small doses of tranexamic acid, may reverse the impairment of fibrin property.The FXIII concentrate is not effective in this regard in our in vitro model using platelet-poor plasma.