Development of Shiny app tools to simplify and standardize the analysis of hemostasis assay data: communication from the SSC of the ISTH

Low factor XIII levels and altered fibrinolysis in patients with multiple myeloma

BACKGROUND

Acquired factor FXIII (FXIII) deficiency can be immune- or non-immune mediated and may cause severe bleeding symptoms. The incidence of acquired FXIII deficiency and its etiology in patients with multiple myeloma (MM) are poorly understood.

OBJECTIVES

To assess FXIII levels and the balance of fibrinolysis in newly diagnosed, untreated MM and monoclonal gammopathy of undetermined significance (MGUS) patients.

METHODS

FXIII activity, mixing studies, FXIII-A2B2 antigen, total FXIII-B antigen were measured in platelet-poor plasma from 17 untreated MM patients, 33 untreated MGUS patients, and 30 age and sex-matched healthy controls. Besides routine laboratory measurements, the balance of coagulation and fibrinolysis was evaluated using quantitative fibrin monomer (FM) test, thrombin-antithrombin assay, α2-antiplasmin activity, plasmin-α2-antiplasmin (PAP) complex, D-dimer, plasmin generation assay, clot lysis assay, and ClotPro-TPA test.

RESULTS

FXIII-A2B2 levels were significantly lower in MM patients compared to controls [median (IQR):14.6 (11.2-19.4) vs. 21.8 (17.1-26.4) mg/L, p = 0.0015], whereas total FXIII-B did not differ between groups. Decrease in FXIII activity was parallel to the decrease in FXIII-A2B2. An immune-mediated inhibitory mechanism was ruled out. Free/total FXIII-B was significantly higher in MM patients compared to MGUS and healthy controls, suggesting an etiology of FXIII-A consumption. In MM and MGUS patients, FM, D-dimer, and PAP complex were significantly elevated compared to controls, indicating hypercoagulability and ongoing fibrinolysis.

CONCLUSIONS

Low FXIII levels due to consumption were observed in MM patients at diagnosis. Hypercoagulability and ongoing fibrinolysis were detected in MM and MGUS, indicating that a disturbed hemostasis balance is already present in the latter benign condition.

Sources of bias and limitations of thrombinography: inner filter effect and substrate depletion at the edge of failure algorithm

BACKGROUND

Fluorogenic thrombin generation (TG) is a global hemostasis assay that provides an overall representation of hemostasis potential. However, the accurate detection of thrombin activity in plasma may be affected by artifacts inherent to the assay-associated fluorogenic substrate. The significance of the fluorogenic artifacts or their corrections has not been studied in hemophilia treatment applications.

METHODS

We sought to investigate TG in hemophilia plasma samples under typical and worst-case fluorogenic artifact conditions and assess the performance of artifact correction algorithms. Severe hemophilic plasma with or without added Factor VIII (FVIII) was evaluated using commercially available and in-house TG reagents, instruments, and software packages. The inner filter effect (IFE) was induced by spiking elevated amounts of fluorophore 7-amino-4-methylcoumarin (AMC) into plasma prior to the TG experiment. Substrate consumption was modeled by adding decreasing amounts of Z-Gly-Gly-Arg-AMC (ZGGR-AMC) to plasma or performing TG in antithrombin deficient plasma.

RESULTS

All algorithms corrected the AMC-induced IFE and antithrombin-deficiency induced substrate consumption up to a certain level of either artifact (edge of failure) upon which TG results were not returned or overestimated. TG values in FVIII deficient (FVIII-DP) or supplemented plasma were affected similarly. Normalization of FVIII-DP resulted in a more accurate correction of substrate artifacts than algorithmic methods.

CONCLUSIONS

Correction algorithms may be effective in situations of moderate fluorogenic substrate artifacts inherent to highly procoagulant samples, but correction may not be required under typical conditions for hemophilia treatment studies if TG parameters can be normalized to a reference plasma sample.

Pharmacodynamics Monitoring of Emicizumab in Patients with Hemophilia A

BACKGROUND

 Emicizumab is a bispecific antibody mimicking coagulation factor VIII (FVIII) employed to treat patients with hemophilia A (PwHA) regardless of FVIII inhibitor status. The identification of biological markers reflecting the hemostatic competence of patients under emicizumab therapy would have a great clinical value. Unfortunately, emicizumab over-corrects standard coagulation assays, precluding their use for evaluating the hemostatic correction achieved in vivo. Here, we investigated whether global coagulation assays (GCA) would allow monitoring the biological response to non-factor replacement therapy with emicizumab.

MATERIALS AND METHODS

 Six adults PwHA received a weekly dose of emicizumab of 3 mg/kg during weeks (W) 1 4 and 1.5 mg/kg from W5 onwards. Response to treatment was monitored weekly by emicizumab plasma concentration, thrombin generation (TG), and fibrin clot formation (FCF) and structure. TG and FCF results were compared to patient baseline, FVIII replacement, and healthy donors.

RESULTS

 TG and FCF significantly increased in PwHA after the loading period, reaching a plateau that lasted until the end of monitoring. Similarly, fibrin clot network became denser with thinner fibrin fibers. However, TG contrary to FCF remained at the lower limits of reference values. Remarkably, despite having similar plateau concentrations of emicizumab some patients showed markedly different degrees of TG and FCF improvement.

CONCLUSION

 Our study enriches the knowledge on the use of GCA to monitor non-factor replacement therapy, indicating that TG and FCF could act as direct markers of emicizumab biological activity. GCA allow to capture and visualize the individually variable response to emicizumab, leading a step forward to the personalization of patient treatment.

Physiological correction of hereditary mild hypofibrinogenemia during pregnancy

INTRODUCTION

Hereditary hypofibrinogenemia is a rare fibrinogen disorder characterised by decreased levels of fibrinogen. Pregnant women with hypofibrinogenemia are at risk of adverse obstetrical outcomes, depending on the fibrinogen level.

AIM

We investigated how the physiological changes of hemostasis throughout the pregnancy impact the hemostatic balance in a woman with hereditary mild hypofibrinogenemia.

METHODS

Fibrin clot properties were analyzed by turbidimetry and scanning electron microscopy, clot weight and red blood cells retention were measured by whole clot contraction, and in vitro thrombin generation was assessed by calibrated automated thrombogram and ex vivo by TAT.

RESULTS

Throughout the pregnancy, the fibrinogen levels increased reaching normal values in the third trimester (activity 3.1 g/L, antigen 3.2 g/L). In parallel, the fibrin polymerisation increased, the fibrinolysis decreased, the fibrin clot network became denser with thicker fibrin fibers, and the fibrin clot weight and red blood cells retention increased, reaching control's value at the third trimester. Similarly, in vitro and ex vitro thrombin generation increased, reaching maximum values at the delivery.

CONCLUSION

In this case of hereditary mild hypofibrinogenemia we observed a physiological increase of fibrinogen and thrombin generation. Future studies should focus on moderate and severe hypofibrinogenemia, to assess fibrinogen variation and the overall impact of increased TG on the hemostasis balance.

Congruent identification of imbalanced fibrinolysis by 2 distinct clot lysis time assays

Background

A plasma-based clot lysis time (CLT) assay is an established research test to assess plasma fibrinolytic potential, with application in hyperfibrinolytic or hypofibrinolytic conditions. Interprotocol variations make comparisons between laboratories challenging. The aim of this study was to compare the results of 2 different CLT assays performed by 2 distinct research laboratories by using their own protocol.

Methods

We evaluated fibrinolysis in the plasma of 60 patients undergoing hepatobiliary surgery and in plasma from a healthy donor that was spiked with commonly used anticoagulant drugs (enoxaparin, dabigatran, and rivaroxaban) in 2 distinct laboratories (Aarhus and Groningen) by using 2 different assays that differ, among others, in tissue plasminogen activator (tPA) concentration.

Results

Overall conclusions on fibrinolytic potential in patients undergoing hepatobiliary surgery were similar between the 2 CLT assays, with hyperfibrinolytic and hypofibrinolytic profiles identified at the same time points during and after surgery. Severe hypofibrinolysis was less commonly reported in the Aarhus assay (36/319 samples; 11%) than in the Groningen assay (55/319 samples; 17%). No clot formation was observed in 31 of 319 samples in the Aarhus assay vs 0 of 319 samples in the Groningen assay. Clotting times increased much more profoundly on the addition of all 3 anticoagulants in the Aarhus assay.

Conclusions

Despite the differences in laboratory, protocol, reagents, operator, data processing, and analysis, overall conclusions on fibrinolytic capacity are similar between the 2 laboratories. With a higher concentration of tPA in the Aarhus assay, the test becomes less sensitive for the detection of hypofibrinolysis and is more sensitive to the addition of anticoagulants.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Altered fibrin network structure and fibrinolysis in intensive care unit patients with COVID-19, not entirely explaining the increased risk of thrombosis

BACKGROUND

Severe acute respiratory syndrome coronavirus 2 infection is associated with an increased incidence of thrombosis.

OBJECTIVES

By studying the fibrin network structure of coronavirus disease 2019 (COVID-19) patients, we aimed to unravel pathophysiological mechanisms that contribute to this increased risk of thrombosis. This may contribute to optimal prevention and treatment of COVID-19 related thrombosis.

PATIENTS/METHODS

In this case-control study, we collected plasma samples from intensive care unit (ICU) patients with COVID-19, with and without confirmed thrombosis, between April and December 2020. Additionally, we collected plasma from COVID-19 patients admitted to general wards without thrombosis, from ICU patients with pneumococcal infection, and from healthy controls. Fibrin fiber diameters and fibrin network density were quantified in plasma clots imaged with stimulated emission depletion microscopy and confocal microscopy. Finally, we determined the sensitivity to fibrinolysis.

RESULTS

COVID-19 ICU patients (n = 37) and ICU patients with pneumococcal disease (n = 7) showed significantly higher fibrin densities and longer plasma clot lysis times than healthy controls (n = 7). No differences were observed between COVID-19 ICU patients with and without thrombosis, or ICU patients with pneumococcal infection. At a second time point, after diagnosis of thrombosis or at a similar time point in patients without thrombosis, we observed thicker fibers and longer lysis times in COVID-19 ICU patients with thrombosis (n = 19) than in COVID-19 ICU patients without thrombosis (n = 18).

CONCLUSIONS

Our results suggest that severe COVID-19 is associated with a changed fibrin network structure and decreased susceptibility to fibrinolysis. Because these changes were not exclusive to COVID-19 patients, they may not explain the increased thrombosis risk.

Differential impact of tamoxifen and aromatase inhibitors on thrombin generation: the prospective HEMOBREAST cohort

Tamoxifen and aromatase inhibitors (AIs) are potent antitumoral agents against breast cancer. Tamoxifen increases the risk of venous thromboembolism (VTE), but the influence of AIs on the risk of VTE remains unclear. To inform clinical decisions, we evaluated associations of tamoxifen or AIs with changes of surrogate hemostatic biomarkers. This prospective cohort included 107 women with localized breast cancer starting tamoxifen (n = 42) or an AI (n = 65). Thrombin generation (CAT) its sensitivity to thrombomodulin (TM) or activated protein C (APC), and specific coagulation parameters, were measured before and 10-16 weeks after initiation of treatmen Compared with baseline, endogenous thrombin potential and thrombin peak increased in tamoxifen users (+86 nM × min; 95% confidence interval [CI], 30-142; and +33 nM; 95% CI, 21-45) but not in AI users (n = 65; +44 nM × min; 95% CI, -4 to 93; and +7 nM; 95% CI, -3 to 17). Normalized TM sensitivity ratios increased with tamoxifen (+0.26; 95% CI, 0.19-0.33y) but not with AI (+0.02; 95% CI, -0.03 to 0.07). Plasma levels of fibrinogen, antithrombin, protein C, and Tissue Factor Pathway Inhibitor decreased, and free protein S increased with tamoxifen but not with AIs. The observed shift toward increased coagulability associated with tamoxifen is in line with its known increased risk of VTE. In contrast, AIs do not appear to impact hemostasis, suggesting a lack of associated VTE risk. The trial was registered at www.clinicaltrials.gov as #NCT03381963.

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

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

Tranexamic acid rapidly inhibits fibrinolysis, yet transiently enhances plasmin generation in vivo

Tranexamic acid (TXA) is a lysine analogue that inhibits plasmin generation and has been used for decades as an antifibrinolytic agent to reduce bleeding. Recent reports have indicated that TXA can paradoxically promote plasmin generation. Blood was obtained from 41 cardiac surgical patients randomly assigned to TXA or placebo before start of surgery (preOP), at the end of surgery (EOS), then again on postoperative day 1 (POD-1) as well as POD-3. Plasma levels of tissue-type plasminogen activator (t-PA), urokinase (u-PA), the plasmin-antiplasmin (PAP) complex, as well as t-PA and u-PA-induced clot lysis assays were then determined. Clot lysis and PAP complex levels were also assessed in healthy volunteers before and at various time points after taking 1 g TXA orally. Surgery induced an increase in circulating t-PA, yet not u-PA at EOS. t-PA levels were unaffected by TXA; however, u-PA levels were significantly reduced in patients on POD-3. t-PA and u-PA-induced clot lysis were both inhibited in plasma from TXA-treated patients. In contrast, PAP complex formation, representing plasmin generation, was unexpectedly enhanced in the plasma of patients administered TXA at the EOS time point. In healthy volunteers, oral TXA effectively blocked fibrinolysis within 30 min and blockade was sustained for 8 h. However, TXA also increased PAP levels in volunteers 4 h after administration. Our findings demonstrate that TXA can actually augment PAP complex formation, consistent with an increase in plasmin generation in vivo despite the fact that it blocks fibrinolysis within 30 min. This may have unanticipated consequences in vivo.

A modified in vitro clot lysis assay predicts outcomes and safety in acute ischemic stroke patients undergoing intravenous thrombolysis

The outcome of intravenous thrombolysis using recombinant tissue plasminogen activator (rt-PA) is only favorable in ≈ 40% of acute ischemic stroke (AIS) patients. Moreover, in ≈ 6-8% of cases, intracerebral hemorrhage (ICH) develops. We tested whether a modification of clot lysis assay (CLA), might predict therapy outcomes and safety. In this prospective observational study, blood samples of 231 AIS patients, all receiving intravenous rt-PA, were taken before thrombolysis. Cell-free DNA (cfDNA), CLA and CLA supplemented with cfDNA and histones (mCLA) were determined from the blood samples. Stroke severity was determined by NIHSS on admission. ICH was classified according to ECASSII. Short- and long-term outcomes were defined at 7 and 90 days post-event according to ΔNIHSS and by the modified Rankin Scale, respectively. Stroke severity demonstrated a step-wise positive association with cfDNA levels, while a negative association was found with the time to reach 50% lysis (50%CLT) parameter of CLA and mCLA. ROC analysis showed improved diagnostic performance of the mCLA. Logistic regression analysis proved that 50%CLT is a predictor of short-term therapy failure, while the AUC parameter predicts ICH occurrence. A modified CLA, supplemented with cfDNA and histones, might be a promising tool to predict short-term AIS outcomes and post-lysis ICH.

Euglobulin clot lysis time reveals a high frequency of fibrinolytic activation in trauma

Activation of the fibrinolytic system plays a central role in the host response to trauma. There is significant heterogeneity in the degree of fibrinolysis activation at baseline that is usually assessed by whole blood thromboelastography (TEG). Few studies have focused on plasma markers of fibrinolysis that could add novel insights into the frequency and mechanisms of fibrinolytic activation in trauma. Global fibrinolysis in plasma was assessed using a modified euglobulin clot lysis time (ECLT) assay in 171 major trauma patients and compared to commonly assessed analytes of fibrinolysis. The median ECLT in trauma patients was significantly shorter at 8.5 h (IQR, 1.3-19.5) compared to 19.9 h (9.8-22.6) in healthy controls (p < 0.0001). ECLT values ≤2.5th percentile of the reference range were present in 83 (48.5%) of trauma patients, suggesting increased fibrinolytic activation. Shortened ECLT values were associated with elevated plasmin-antiplasmin (PAP) complexes and free tissue plasminogen activator (tPA) levels in plasma. Sixteen (9.2%) individuals met the primary outcome for massive transfusion, here defined as the critical administration threshold (CAT) of 3 units of packed red cells in any 60-minute period within the first 24 h. In a univariate screen, plasma biomarkers associated with CAT included D-dimer (p < 0.001), PAP (p < 0.05), free tPA (p < 0.05) and ECLT (p < 0.05). We conclude that fibrinolytic activation, measured by ECLT, is present in a high proportion of trauma patients at presentation. The shortened ECLT is partially driven by high tPA levels and is associated with high levels of circulating PAP complexes. Further studies are needed to determine whether ECLT is an independent predictor of trauma outcomes.

Kallikrein directly interacts with and activates Factor IX, resulting in thrombin generation and fibrin formation independent of Factor XI

Prekallikrein (PK) is a zymogen that is converted to kallikrein (PKa) by factor (F)XIIa. PK and FXII reciprocally activate each other; the resulting FXIIa initiates activation of the coagulation system via the cleavage of FXI to FXIa, which then activates FIX. This manuscript describes a novel high-affinity binding interaction between FIX(a) and PK(a) and reports that PKa can dose- and time-dependently activate FIX to generate FIXa, resulting in thrombin generation and clot formation independent of FXIa. Characterization of the kinetics of FIX activation reveal that PKa is a more significant activator of FIX than previously considered. This work highlights a new amendment to the coagulation cascade where PKa can directly activate FIX.

Kallikrein (PKa), generated by activation of its precursor prekallikrein (PK), plays a role in the contact activation phase of coagulation and functions in the kallikrein-kinin system to generate bradykinin. The general dogma has been that the contribution of PKa to the coagulation cascade is dependent on its action on FXII. Recently this dogma has been challenged by studies in human plasma showing thrombin generation due to PKa activity on FIX and also by murine studies showing formation of FIXa-antithrombin complexes in FXI deficient mice. In this study, we demonstrate high-affinity binding interactions between PK(a) and FIX(a) using surface plasmon resonance and show that these interactions are likely to occur under physiological conditions. Furthermore, we directly demonstrate dose- and time-dependent cleavage of FIX by PKa in a purified system by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and chromogenic assays. By using normal pooled plasma and a range of coagulation factor-deficient plasmas, we show that this action of PKa on FIX not only results in thrombin generation, but also promotes fibrin formation in the absence of FXII or FXI. Comparison of the kinetics of either FXIa- or PKa-induced activation of FIX suggest that PKa could be a significant physiological activator of FIX. Our data indicate that the coagulation cascade needs to be redefined to indicate that PKa can directly activate FIX. The circumstances that drive PKa substrate specificity remain to be determined.

Characterisation and application of recombinant FVIII-neutralising antibodies from haemophilia A inhibitor patients

The development of anti-drug antibodies (ADAs) is a serious outcome of treatment strategies involving biological medicines. Coagulation factor VIII (FVIII) is used to treat haemophilia A patients, but its immunogenicity precludes a third of severe haemophiliac patients from receiving this treatment. The availability of patient-derived anti-drug antibodies can help us better understand drug immunogenicity and identify ways to overcome it. Thus, there were two aims to this work: (i) to develop and characterise a panel of recombinant, patient-derived, monoclonal antibodies covering a range of FVIII epitopes with varying potencies, kinetics and mechanism of action, and (ii) to demonstrate their applicability to assay development, evaluation of FVIII molecules and basic research. For the first objective we used recombinant antibodies to develop a rapid, sensitive, flexible and reproducible ex vivo assay that recapitulates inhibitor patient blood using blood from healthy volunteers. We also demonstrate how the panel can provide important information about the efficacy of FVIII products and reagents without the need for patient or animal material. These materials can be used as experimental exemplars or controls, as well as tools for rational, hypothesis-driven research and assay development in relation to FVIII immunogenicity and FVIII-related products.

A Modified in vitro Clot Lysis Assay Predicts Outcomes in Non-traumatic Intracerebral Hemorrhage Stroke Patients-The IRONHEART Study

Background: Non-traumatic intracerebral hemorrhage (ICH) accounts for 10–15% of all strokes and results in a higher rate of mortality as compared to ischemic strokes. In the IRONHEART study, we aimed to find out whether a modified in vitro clot lysis assay method, that includes the effect of neutrophil extracellular traps (NETs) might predict ICH outcomes.

Patients and Methods: In this prospective, observational study, 89 consecutive non-traumatic ICH patients were enrolled. Exclusion criteria included aneurysm rupture, cancer, liver- or kidney failure or hemorrhagic diathesis. On admission, detailed clinical and laboratory investigations were performed. ICH volume was estimated based on CT performed on admission, day 14 and 90. A conventional in vitro clot lysis assay (CLA) and a modified CLA (mCLA) including cell-free-DNA and histones were performed from stored platelet-free plasma taken on admission. Clot formation and lysis in case of both assays were defined using the following variables calculated from the turbidimetric curves: maximum absorbance, time to maximum absorbance, clot lysis times (CLT) and area under the curve (CLA AUC). Long-term ICH outcomes were defined 90 days post-event by the modified Rankin Scale (mRS). All patients or relatives provided written informed consent.

Results: Patients with more severe stroke (NIHSS>10) presented significantly shorter clot lysis times of the mCLA in the presence of DNA and histone as compared to patients with milder stroke [10%CLT: NIHSS 0–10: median 31.5 (IQR: 21.0–40.0) min vs. NIHSS>10: 24 (18–31.0) min, p = 0.032]. Shorter clot lysis times of the mCLA showed significant association with non-survival by day 14 and with unfavorable long-term outcomes [mRS 0–1: 36.0 (22.5.0–51.0) min; mRS 2–5: 23.5 (18.0–36.0) min and mRS 6: 22.5 (18.0–30.5) min, p = 0.027]. Estimated ICH volume showed significant negative correlation with mCLA parameters, including 10%CLT (r = −0.3050, p = 0.009). ROC analysis proved good diagnostic performance of mCLA for predicting poor long-term outcomes [AUC: 0.73 (0.57–0.89)]. In a Kaplan-Meier survival analysis, those patients who presented with an mCLA 10%CLT result of >38.5 min on admission showed significantly better survival as compared to those with shorter clot lysis results (p=0.010).

Conclusion: Parameters of mCLA correlate with ICH bleeding volume and might be useful to predict ICH outcomes.

An international collaborative study to establish the WHO 3rd International Standard for Thrombin: Communication from the ISTH SSC subcommittee on factor XIII and fibrinogen

The calibration of thrombin products relies on the World Health Organization (WHO) 2nd International Standard (IS) for Thrombin (01/580) which defines the international unit (IU) for thrombin potency. With stocks of the 2nd IS (01/580) running low, an international collaborative study was organized to calibrate a replacement. Twenty laboratories from 13 countries took part in the study and measured the potency of two candidate replacement standards (coded 01/578 and 19/188) relative to the 2nd IS. In total, 111 valid assays were returned, which were a combination of plasma/fibrinogen clotting assays and chromogenic assays. Variation between and within laboratories was low, with inter- and intra-laboratory geometric coefficient of variation (GCV) generally <5% for all assay methods and substrates. For 01/578, potency estimates by clotting assays (101.1 IU/ampoule) were significantly lower than estimates by chromogenic assays (111.5 IU/ampoule). Mean potency estimates for 19/188 were 90.4 IU/ampoule by clotting assay and 88.1 IU/ampoule by chromogenic assay, which was not a statistically significant difference. The close ratio between clotting and chromogenic assay potency estimates for 19/188 suggests it has a higher α-thrombin content than 01/578 and is equivalent to the current IS (01/580). Accelerated degradation studies predicted excellent long-term stability profiles for preparations 01/580, 01/578, and 19/188. Based on the results of this study, the WHO Expert Committee on Biological Standardization established 19/188 as the 3rd IS for Thrombin with a potency of 90 IU/ampoule in August 2020.

Comparison of different activators of coagulation by turbidity analysis of hereditary dysfibrinogenemia and controls

Turbidity analysis is widely used as a quantitative technique in hereditary dysfibrinogenemia. We aimed to compare several coagulation triggers in hereditary dysfibrinogenemia and control plasmas. We included 20 patients with hereditary dysfibrinogenemia, 19 with hotspot mutations Aα Arg35His (n = 9), Aα Arg35Cys (n = 2), γ Arg301His (n = 6), γ Arg301Cys (n = 2), and one with Aα Phe27Tyr, and a commercial pooled normal plasma. Fibrin polymerization was activated by bovine or human thrombin or tissue factor (TF), in the presence or absence of tissue type plasminogen activator. The lag time (min), slope (mOD/s), maximum absorbance (MaxAbs, mOD), and area under the curve (AUCp, OD s) were calculated from the fibrin polymerization curves and the time for 50% clot degradation (T50, min), AUCf (OD s) and the overall fibrinolytic potential from fibrinolysis curves. The lag time was significantly shorter and AUC increased in Aα Arg35His patients with bovine thrombin as compared with human thrombin. The MaxAbs and AUCp were significantly higher in γArg301His patients with bovine thrombin compared with human thrombin. Fibrin polymerization parameters of patients' samples were closer to those of control when assessed with TF compared with both human and bovine thrombin. T50 and overall fibrinolytic potential were similar in all samples regardless of the coagulation trigger used, however, with TF the AUCf of Aα Arg35His and γ Arg301His groups were significantly decreased compared with control. Bovine and human thrombin cannot be used equally for studying fibrin polymerization in hotspot hereditary dysfibrinogenemia or control plasmas.

Incorporation of α2-Plasmin Inhibitor into Fibrin Clots and Its Association with the Clinical Outcome of Acute Ischemic Stroke Patients

Cross-linking of α2-plasmin inhibitor (α2-PI) to fibrin by activated factor XIII (FXIIIa) is essential for the inhibition of fibrinolysis. Little is known about the factors modifying α2-PI incorporation into the fibrin clot and whether the extent of incorporation has clinical consequences. Herein we calculated the extent of α2-PI incorporation by measuring α2-PI antigen levels from plasma and serum obtained after clotting the plasma by thrombin and Ca²⁺. The modifying effect of FXIII was studied by spiking of FXIII-A-deficient plasma with purified plasma FXIII. Fibrinogen, FXIII, α2-PI incorporation, in vitro clot-lysis, soluble fibroblast activation protein and α2-PI p.Arg6Trp polymorphism were measured from samples of 57 acute ischemic stroke patients obtained before thrombolysis and of 26 healthy controls. Increasing FXIII levels even at levels above the upper limit of normal increased α2-PI incorporation into the fibrin clot. α2-PI incorporation of controls and patients with good outcomes did not differ significantly (49.4 ± 4.6% vs. 47.4 ± 6.7%, p = 1.000), however it was significantly lower in patients suffering post-lysis intracranial hemorrhage (37.3 ± 14.0%, p = 0.004). In conclusion, increased FXIII levels resulted in elevated incorporation of α2-PI into fibrin clots. In stroke patients undergoing intravenous thrombolysis treatment, α2-PI incorporation shows an association with the outcome of therapy, particularly with thrombolysis-associated intracranial hemorrhage.

Fibrinogen Replacement Therapy for Traumatic Coagulopathy: Does the Fibrinogen Source Matter?

Fibrinogen is the first coagulation protein to reach critically low levels during traumatic haemorrhage. There have been no differential effects on clinical outcomes between the two main sources of fibrinogen replacement: cryoprecipitate and fibrinogen concentrate (Fg-C). However, the constituents of these sources are very different. The aim of this study was to determine whether these give rise to any differences in clot stability that may occur during trauma haemorrhage. Fibrinogen deficient plasma (FDP) was spiked with fibrinogen from cryoprecipitate or Fg-C. A panel of coagulation factors, rotational thromboelastography (ROTEM), thrombin generation (TG), clot lysis and confocal microscopy were performed to measure clot strength and stability. Increasing concentrations of fibrinogen from Fg-C or cryoprecipitate added to FDP strongly correlated with Clauss fibrinogen, demonstrating good recovery of fibrinogen (r² = 0.99). A marked increase in Factor VIII, XIII and α₂-antiplasmin was observed in cryoprecipitate (p < 0.05). Increasing concentrations of fibrinogen from both sources were strongly correlated with ROTEM parameters (r² = 0.78-0.98). Cryoprecipitate therapy improved TG potential, increased fibrinolytic resistance and formed more homogeneous fibrin clots, compared to Fg-C. In summary, our data indicate that cryoprecipitate may be a superior source of fibrinogen to successfully control bleeding in trauma coagulopathy. However, these different products require evaluation in a clinical setting.

Measuring Fibrinolysis

Physiological fibrinolysis under normal conditions progresses slowly, in contrast to coagulation which is triggered rapidly to stop bleeding and defend against microbial invasion. Methods to detect fibrinolysis abnormalities are less simple and poorly standardized compared with common coagulation tests. Fibrinolysis can be accelerated by preparing euglobulin from plasma to reduce endogenous inhibitors, or by adding plasminogen activators to normal plasma. However, these manipulations complicate interpretation of results and diagnosis of a "fibrinolysis deficit." Many observational studies on antigen levels of fibrinolysis inhibitors, plasminogen activator inhibitor 1 or thrombin-activatable fibrinolysis inhibitor, zymogen or active enzyme have been published. However, conclusions are mixed and there are clear problems with harmonization of results. Viscoelastic methods have the advantage of being rapid and are used as point-of-care tests. They also work with whole blood, allowing the contribution of platelets to be explored. However, there are no agreed protocols for applying viscoelastic methods in acute care for the diagnosis of hyperfibrinolysis or to direct therapy. The emergence of SARS-CoV-2 and the dangers of associated coagulopathy provide new challenges. A common finding in hospitalized patients is high levels of D-dimer fibrin breakdown products, indicative of ongoing fibrinolysis. Well-established problems with D-dimer testing standardization signal that we should be cautious in using results from such tests as prognostic indicators or to target therapies.

Characterisation of a novel thrombomodulin c.1487delC,p.(Pro496Argfs*10) variant and evaluation of therapeutic strategies to manage the rare bleeding phenotype

INTRODUCTION

A novel variant in the thrombomodulin (TM) gene, c.1487delC,p.(Pro496Argfs*10), referred to as Pro496Argfs*10, was identified in a family with an unexplained bleeding disorder. The Pro496Argfs*10 variant results in loss of the transmembrane and intracellular segments of TM and is associated with an increase in soluble TM (sTM) in the plasma. The aim of this study was to characterise the effect of elevated sTM on thrombin generation (TG) and fibrinolysis, and to evaluate therapeutic strategies to manage the patients.

METHODS

Plasma samples were obtained from two patients carrying the variant. TG was triggered using 5 pM tissue factor and measured using the Calibrated Automated Thrombogram. A turbidity clot lysis assay was used to monitor fibrinolysis. TM antigen was quantified by ELISA.

RESULTS

Patients with the Pro496Argfs*10 variant had significantly elevated plasma sTM compared to controls (372.6 vs. 6.0 ng/ml). TG potential was significantly lower in patients but was restored by inhibition of activated protein C (APC) or addition of activated Factor VII (FVIIa) or platelet concentrates. In vitro experiments suggested that activated prothrombin complex concentrates (APCC) posed a risk of thrombosis. The time to 50% lysis was significantly prolonged in patients compared to controls, 69.7 vs. 42.3 min. Clot lysis time was shortened by inhibition of activated thrombin activatable fibrinolysis inhibitor (TAFIa).

CONCLUSIONS

Our data demonstrate that increased sTM enhances APC generation and reduces TG. Simultaneously, the rate of fibrinolysis is delayed due to increased TAFI activation by sTM. Treatment with platelet or FVIIa concentrates may be beneficial to manage this rare bleeding disorder.

Fibrin clot properties to assess the bleeding phenotype in unrelated patients with hypodysfibrinogenemia due to novel fibrinogen mutations

Congenital hypodysfibrinogenemia is a rare fibrinogen disorder, defined by decreased levels of a dysfunctional fibrinogen. We present the functional and structural characterization of two new fibrinogen variants. A duplication of 32 bases in FGA exon 5, p.Ser382GlyfsTer50 was identified in a patient (P1) with history of hemoptysis and traumatic cerebral bleeding. A missense mutation in FGG exon 8, p.Ala353Ser was identified in two siblings (P2 and P3) with tendency to bruising and menorrhagia. Fibrin polymerization was studied in plasma and in purified fibrinogen by turbidimetry. Fibrin structure was studied by a permeability assay, laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). In both plasma and purified fibrinogen samples, all patients had an abnormal polymerization characterized by a decreased maximal absorption compared to controls. The permeation constant (Ks) was markedly increased in all patients: 31 ± 9 × 10^-9 cm² in P1, and 20 ± 0.1 × 10^-9 cm² in P2 and P3, compared to 6 ± 2 × 10^-9 cm² in the control (p < 0.05). The presence of very large pores that accounts for the increased Ks was confirmed by LSCM and SEM patients' clots images. By SEM, the patients' fibrin fibers diameters were thicker: 90 ± 25 nm in P1, 162 ± 64 nm in P2 and 132 ± 46 nm in P3 compared to 74 ± 25 nm in control (p < 0.0001). In conclusion, both new causative fibrinogen mutations altered clot structure by forming thick fibers, diminishing fiber branching, and increasing pore filling space. These structural changes to clots explain the patients' bleeding phenotypes.

Extracellular Histones Inhibit Fibrinolysis through Noncovalent and Covalent Interactions with Fibrin

Histones released into circulation as neutrophil extracellular traps are causally implicated in the pathogenesis of arterial, venous, and microvascular thrombosis by promoting coagulation and enhancing clot stability. Histones induce structural changes in fibrin rendering it stronger and resistant to fibrinolysis. The current study extends these observations by defining the antifibrinolytic mechanisms of histones in purified, plasma, and whole blood systems. Although histones stimulated plasminogen activation in solution, they inhibited plasmin as competitive substrates. Protection of fibrin from plasmin digestion is enhanced by covalent incorporation of histones into fibrin, catalyzed by activated transglutaminase, coagulation factor FXIII (FXIIIa). All histone subtypes (H1, H2A, H2B, H3, and H4) were crosslinked to fibrin. A distinct, noncovalent mechanism explains histone-accelerated lateral aggregation of fibrin protofibrils, resulting in thicker fibers with higher mass-to-length ratios and in turn hampered fibrinolysis. However, histones were less effective at delaying fibrinolysis in the absence of FXIIIa activity. Therapeutic doses of low-molecular-weight heparin (LMWH) prevented covalent but not noncovalent histone-fibrin interactions and neutralized the effects of histones on fibrinolysis. This suggests an additional antithrombotic mechanism for LMWH beyond anticoagulation. In conclusion, for the first time we report that histones are crosslinked to fibrin by FXIIIa and promote fibrinolytic resistance which can be overcome by FXIIIa inhibitors and histone-binding heparinoids. These findings provide a rationale for targeting the FXIII-histone-fibrin axis to destabilize fibrin and prevent potentially thrombotic fibrin networks.

Development of an updated assay for prekallikrein activator in albumin and immunoglobulin therapeutics

Background

Prekallikrein activator (PKA) is a contaminating enzyme found in therapeutic albumin and immunoglobulin products. The level is commonly measured using methods such as that defined by the European Pharmacopoeia (Ph Eur) with traceability to the WHO International Standard for PKA. This method generally works well, but problems are sometimes observed.

Materials and methods

A simplified one‐step method has been developed to replace the existing Ph Eur two‐step method which consists of kallikrein generation followed by kallikrein measurement using a chromogenic substrate. Analysis of data from the one‐stage method is simplified by the use of a dedicated online app.

Results

The one‐stage method was validated against the current Ph Eur method using batches of albumin and immunoglobulins. Problem batches of immunoglobulins were investigated using the one‐stage method. Improved methodology using true initial rate determinations and use of acid‐treated prekallikrein substrate (PKS) helped understand and reduce artefactual results.

Conclusions

The one‐stage method and associated app streamline real‐time determination of PKA and promote good principles of enzyme assays to limit substrate depletion, while also conserving expensive PKS. Blanking steps and reproducibility are simplified.

Fibrin Clot Formation and Lysis in Plasma

Disturbance in the balance between fibrin formation and fibrinolysis can lead to either bleeding or thrombosis; however, our current routine coagulation assays are not sensitive to altered fibrinolysis. The clot formation and lysis assay is a dynamic plasma-based analysis that assesses the patient’s capacity for fibrin formation and fibrinolysis by adding an activator of coagulation as well as fibrinolysis to plasma and measuring ex vivo fibrin clot formation and breakdown over time. This assay provides detailed information on the fibrinolytic activity but is currently used for research only, as the assay is prone to inter-laboratory variation and as it demands experienced laboratory technicians as well as specialized personnel to validate and interpret the results. Here, we describe a protocol for the clot formation and lysis assay used at our research laboratory.

A new pedigree with thrombomodulin-associated coagulopathy in which delayed fibrinolysis is partially attenuated by co-inherited TAFI deficiency

BACKGROUND

Thrombomodulin-associated coagulopathy (TM-AC) is a rare bleeding disorder in which a single reported p.Cys537* variant in the thrombomodulin gene THBD causes high plasma thrombomodulin (TM) levels. High TM levels attenuate thrombin generation and delay fibrinolysis.

OBJECTIVES

To report the characteristics of pedigree with a novel THBD variant causing TM-AC, and co-inherited deficiency of thrombin-activatable fibrinolysis inhibitor (TAFI).

PATIENTS/METHODS

Identification of pathogenic variants in hemostasis genes by next-generation sequencing and case recall for deep phenotyping.

RESULTS

Pedigree members with a previously reported THBD variant predicting p.Pro496Argfs*10 and chain truncation in TM transmembrane domain had abnormal bleeding and greatly increased plasma TM levels. Affected cases had attenuated thrombin generation and delayed fibrinolysis similar to previous reported TM_AC cases with THBD p.Cys537*. Coincidentally, some pedigree members also harbored a stop-gain variant in CPB2 encoding TAFI. This reduced plasma TAFI levels but was asymptomatic. Pedigree members with TM-AC caused by the p.Pro496Argfs*10 THBD variant and also TAFI deficiency had a partially attenuated delay in fibrinolysis, but no change in the defective thrombin generation.

CONCLUSIONS

These data extend the reported genetic repertoire of TM-AC and establish a common molecular pathogenesis arising from high plasma levels of TM extra-cellular domain. The data further confirm that the delay in fibrinolysis associated with TM-AC is directly linked to increased TAFI activation. The combination of the rare variants in the pedigree members provides a unique genetic model to develop understanding of the thrombin-TM system and its regulation of TAFI.

3K3A-Activated Protein C Variant Does Not Interfere With the Plasma Clot Lysis Activity of Tenecteplase

BACKGROUND AND PURPOSE

A recombinant engineered variant of APC (activated protein C), 3K3A-APC, lacks anticoagulant properties (<10%) while preserving APCs anti-inflammatory, anti-apoptotic, and neuroprotective functions and is very promising in clinical trials for ischemic stroke. Therapeutic intervention with single bolus administration of the third-generation tPA (tissue-type plasminogen activator), tenecteplase, is anticipated to be widely adopted for treatment of acute ischemic stroke. 3K3A-APC is well-tolerated in stroke patients dosed with alteplase, and in vitro studies show 3K3A-APC does not interfere with alteplase-induced clot lysis. The purpose of this in vitro study was to assess the influence of 3K3A-APC on tenecteplase-induced clot lysis.

METHODS

Tenecteplase-mediated lysis of thrombin generated plasma clots of human normal pooled plasma was monitored in the presence of varying doses of 3K3A-APC. The effects on fibrinolysis by tenecteplase and alteplase were compared.

RESULTS

The presence of 3K3A-APC shortened the time for clot lysis induced by tenecteplase at very low levels but not at higher therapeutic concentrations of tenecteplase. Comparisons of alteplase-mediated clot lysis to tenecteplase clot lysis showed that both thrombolytic agents behaved similarly in the presence of 3K3A-APC.

CONCLUSIONS

These results indicate that 3K3A-APC does not interfere with tenecteplase's clot lysis function.

An international collaborative study to establish the WHO 4th International Standard for Streptokinase: Communication from the SSC of the ISTH

Streptokinase is used worldwide as a cost-effective treatment for acute myocardial infarction. Manufacturers use the World Health Organization (WHO) International Standard (IS) for Streptokinase to potency label their products, ensuring consistent, safe, and effective dosing. Stocks of the third IS for streptokinase (coded 00/464) are running low, and an international collaborative study was organized to calibrate a replacement. A total of 15 laboratories from nine countries took part, using chromogenic and/or fibrin clot lysis methods to determine the potency of two candidate preparations, coded 16/356 (sample B) and 16/358 (sample C), relative to the third IS (00/464). A third sample (88/824, sample A), which was used in the collaborative studies to establish the second and third IS, was also included. There was good agreement in potency estimates from different assay methods and low variability both within and between laboratories. Long-term stability modeling indicated the candidates are very stable. Comparison of potency estimates for 88/824 (sample A) with potencies calculated in previous studies revealed a variability of only 1.9% over the course of three collaborative studies spanning 30 years and more than 50 years of streptokinase standardization. This indicates excellent continuity of the International Unit (IU) and assay methods. Following agreement by study participants and Scientific and Standardization Committee experts of the International Society on Thrombosis and Haemostasis, the WHO Expert Committee on Biological Standardization established 16/358 (sample C) as the fourth IS for Streptokinase with a potency of 1013 IU per ampoule in October 2019.

Rosuvastatin use increases plasma fibrinolytic potential: a randomised clinical trial

We conducted a study to assess the effect of rosuvastatin use on fibrinolysis in patients with previous venous thromboembolism (VTE). This was a post hoc analysis within the STAtins Reduce Thrombophilia (START) study (NCT01613794). Plasma fibrinolytic potential, fibrinogen, plasmin inhibitor, plasminogen activator inhibitor‐1 (PAI‐1) and thrombin‐activatable fibrinolysis inhibitor (TAFI) were measured before and after four weeks of rosuvastatin or no treatment in participants with prior confirmed VTE, after ending anticoagulant therapy. In the non‐rosuvastatin group (n = 121), plasma fibrinolytic potential and individual fibrinolysis parameters did not change at the end of the study versus the baseline, whereas in the rosuvastatin group (n = 126), plasma fibrinolytic potential increased: the mean clot lysis time decreased by 8·75 min (95% CI −13·8 to −3·72), and plasmin inhibitor levels and TAFI activity were lower at the end of the study (−0·05 U/ml; 95% CI −0·07 to −0·02 and −4·77%; 95% CI −6·81 to −2·73, respectively). PAI‐1 levels did not change and fibrinogen levels were 0·17 g/l (95% CI 0·04–0·29) higher. In participants with prior VTE, rosuvastatin use led to an increased fibrinolytic potential compared with non‐statin use. Our findings support the need for further studies on the possible role for statins in the secondary prevention of VTE.

Tranexamic acid is an active site inhibitor of urokinase plasminogen activator

TXA is an active-site inhibitor of uPA. TXA attenuates MDA-MB-231 BAG cell migration and inhibits endogenous uPA activity.

Structure, Mechanical, and Lytic Stability of Fibrin and Plasma Coagulum Generated by Staphylocoagulase From Staphylococcus aureus

Staphylococcus aureus causes localized infections or invasive diseases (abscesses or endocarditis). One of its virulence factors is staphylocoagulase (SCG), which binds prothrombin to form a complex with thrombin-like proteolytic activity and leads to uncontrolled fibrin generation at sites of bacterial inoculation. The aim of this study was to characterize the formation, structure, mechanical properties and lysis of SCG-generated clots. Recombinant SCG was expressed in Escherichia coli, purified and the amidolytic activity of its complexes with human prothrombin (SCG-PT) and thrombin (SCG-T) was determined using human thrombin as a reference. Fibrin clots were prepared from purified fibrinogen and human plasma using thrombin, SCG-PT or SCG-T as a coagulase. The kinetics of clot formation and lysis by tissue-type plasminogen activator (tPA) were monitored with turbidimetric assays. Fibrin ultrastructure was examined with scanning electron microscopy and small-angle X-ray scattering (SAXS). Fibrin clot porosity was characterized with fluid permeation assays, whereas the viscoelastic properties and mechanical stability were evaluated with oscillation rheometry. Compared to thrombin, the amidolytic and clotting activity of SCG-PT was 1.6- to 2.5-fold lower on a molar basis. SCG-T had equivalent amidolytic, but reduced clotting activity both on pure fibrinogen (1.6-fold), and in plasma (1.3-fold). The SCG-PT and SCG-T generated fibrin with thicker fibers (10-60% increase in median diameter) than thrombin due to increased number of fibrin protofibrils per fiber cross-section. According to the fluid permeability of the clots SCG-PT and SCG-T promoted the formation of more porous structures. The shear stress resistance in the pure fibrin and plasma clots generated by SCG-PT was significantly lower than in the thrombin clots (243.8 ± 22.0 Pa shear stress was sufficient for disassembly of SCG-PT fibrin vs. 937.3 ± 65.6 Pa in thrombin clots). The tPA-mediated lysis of both pure fibrin and plasma clots produced by SCG-PT or SCG-T was accelerated compared to thrombin, resulting in up to a 2.1-fold increase in tPA potency. Our results indicate that SCG generates a thrombus scaffold with a structure characterized by impaired mechanical stability and increased lytic susceptibility. This proneness to clot disintegration could have implications in the septic embolism from endocardial bacterial vegetation.

Thrombin generation and fibrin clot structure after vitamin D supplementation

OBJECTIVE

Vitamin D deficiency is associated with increased risks of arterial and venous cardiovascular events. Hypothetically, supplementation with vitamin D may lead to a less prothrombotic phenotype, as measured by global coagulation assays and fibrin clot structure.

METHODS

In this prospective cohort study, we enrolled adult outpatients attending the Primary Care Division of the Geneva University Hospitals with a severe vitamin D deficiency (25-hydroxyvitamin-D3 (25-OHD) <25 nmol/L), excluding obese patients or with a recent acute medical event. We evaluated changes in coagulation times, thrombin generation assay, clot formation and clot lysis time, 25-OHD and parathormone before and 1-3 months after cholecalciferol oral supplementation with one-time 300,000 IU then 800 IU daily. Paired t-tests with a two-sided alpha of 0.05 compared absolute mean differences.

RESULTS

The 48 participants had a mean age of 43.8 ± 13.8 years. After supplementation, 25-OHD levels increased from 17.9 ± 4.6 nmol/L to 62.5 ± 20.7 nmol/L 6.4 ± 3.0 weeks after inclusion. Endogenous thrombin potential and thrombin generation peak values both decreased significantly (-95.4 nM × min (95%CI -127.9 to -62.8), P < 0.001; -15.1 nM (-23.3 to -6.8), P < 0.001). The maximum absorbance by turbidimetry decreased significantly (P = 0.001) after supplementation. There was no change in clot lysis time, coagulation times or plasminogen activator inhibitor-1 and homocysteine levels.

CONCLUSIONS

In severe vitamin D deficiency, a high-dose cholecalciferol supplementation was associated with a reduction in thrombin generation and an average decreased number of fibrin protofibrils per fibers and fibrin fiber size measured by turbidimetry. This suggests that severe vitamin D deficiency may be associated with a potentially reversible prothrombotic profile.

MASP-1 of the complement system alters fibrinolytic behaviour of blood clots

BACKGROUND

The lectin pathway serine protease mannan-binding lectin-associated serine protease 1 (MASP-1) has been demonstrated to be a major link between complement and coagulation, yet little is known about its interactions with the fibrinolytic system. The aim of this work was to assess the effects of MASP-1 on fibrin clot lysis in different experimental settings.

METHODS

Rotational thrombelastometry was used to evaluate the effect of MASP-1 on the lysis of clots formed in whole blood under static conditions. Whole blood clots were also formed in the presence and absence of MASP-1 under flow conditions in the Chandler loop and their lysis was analysed separately by fluorescence release of incorporated labelled fibrin. Real-time observation by laser scanning confocal microscopy was used to investigate the lysis of plasma clots where MASP-1 was present either during clot formation or lysis. Cleavage of tPA or plasminogen by MASP-1 was analysed by gel electrophoresis. We performed a turbidimetric clot lysis assay in the presence and absence of the MASP-1 inhibitor SGMI-1 (Schistocerca gregaria protease inhibitor (SGPI)-based MASP inhibitor-1) to evaluate the effect of endogenous MASP-1 in normal plasma and plasma samples from sepsis patients.

RESULTS

In the thrombelastometric experiments, where MASP-1 was present during the entire clotting and lysis process, MASP-1 had a significant profibrinolytic effect and accelerated clot lysis. When clots were formed in the presence of MASP-1 under flow in the Chandler loop, the effects on fibrinolysis were heterogenous with impaired fibrinolysis in some individuals (n = 5) and no (n = 3) or even the opposite effect (n = 2) in others. In plasma clot lysis observed by confocal microscopy, lysis was prolonged when MASP-1 was added to the lysis solution, yet there was no difference in lysis time when MASP-1 was present during clot formation. When MASP-1 was incubated with tPA or plasminogen, respectively, cleavage of single-chain tPA into two-chain tPA and a slight reduction of plasminogen were observed. SGMI-1 significantly prolonged clot lysis in the turbidimetric clot lysis assay suggesting that MASP-1 accelerated lysis in plasma samples.

CONCLUSION

MASP-1 is able to alter the susceptibility of blood clots to the fibrinolytic system. MASP-1 has complex, mostly promoting effects on fibrinolysis with high inter-individual variation. Interactions of MASP-1 with the fibrinolytic system may be relevant in the development and therapy of cardiovascular and thrombotic diseases.

Increased urokinase and consumption of α2 -antiplasmin as an explanation for the loss of benefit of tranexamic acid after treatment delay

Essentials Delayed treatment with tranexamic acid results in loss of efficacy and poor outcomes. Increasing urokinase activity may account for adverse effects of late tranexamic acid treatment. Urokinase + tranexamic acid produces plasmin in plasma or blood and disrupts clotting. α2 -Antiplasmin consumption with ongoing fibrinolysis increases plasmin-induced coagulopathy. SUMMARY: Background Tranexamic acid (TXA) is an effective antifibrinolytic agent with a proven safety record. However, large clinical trials show TXA becomes ineffective or harmful if treatment is delayed beyond 3 h. The mechanism is unknown but urokinase plasminogen activator (uPA) has been implicated. Methods Inhibitory mechanisms of TXA were explored in a variety of clot lysis systems using plasma and whole blood. Lysis by tissue plasminogen activator (tPA), uPA and plasmin were investigated. Coagulopathy was investigated using ROTEM and activated partial thromboplastin time (APTT). Results IC50 values for antifibrinolytic activity of TXA varied from < 10 to > 1000 μmol L-1 depending on the system, but good fibrin protection was observed in the presence of tPA, uPA and plasmin. However, in plasma or blood, active plasmin was generated by TXA + uPA (but not tPA) and coagulopathy developed leading to no or poor clot formation. The extent of coagulopathy was sensitive to available α2 -antiplasmin. No clot formed with plasma containing 40% normal α2 -antiplasmin after short incubation with TXA + uPA. Adding purified α2 -antiplasmin progressively restored clotting. Plasmin could be inhibited by aprotinin, IC50 = 530 nmol L-1 , in plasma. Conclusions Tranexamic acid protects fibrin but stimulates uPA activity and slows inhibition of plasmin by α2 -antiplasmin. Plasmin proteolytic activity digests fibrinogen and disrupts coagulation, exacerbated when α2 -antiplasmin is consumed by ongoing fibrinolysis. Additional direct inhibition of plasmin by aprotinin may prevent development of coagulopathy and extend the useful time window of TXA treatment.

Measuring fibrinolysis: from research to routine diagnostic assays

Development and standardization of fibrinolysis methods have progressed more slowly than coagulation testing and routine high-throughput screening tests for fibrinolysis are still lacking. In laboratory research, a variety of approaches are available and are applied to understand the regulation of fibrinolysis and its contribution to the hemostatic balance. Fibrinolysis in normal blood is slow to develop. For practical purposes plasminogen activators can be added to clotting plasma, or euglobulin prepared to reduce endogenous inhibitors, but results are complicated by these manipulations. Observational studies to identify a 'fibrinolysis deficit' have concluded that excess fibrinolysis inhibitors, plasminogen activator inhibitor 1 (PAI-1) or thrombin-activatable fibrinolysis inhibitor (TAFI), zymogen or active enzyme, may be associated with an increased risk of thrombosis. However, results are not always consistent and problems of adequate standardization are evident with these inhibitors and also for measurement of fibrin degradation products (D-dimer). Few methods are available to investigate fibrinolysis under flow, or in whole blood, but viscoelastic methods (VMs) such as ROTEM and TEG do permit the contribution of cells, and importantly platelets, to be explored. VMs are used to diagnose clinical hyperfibrinolysis, which is associated with high mortality. There is a debate on the usefulness of VMs as a point-of-care test method, particularly in trauma. Despite the difficulties of many fibrinolysis methods, research on the fibrinolysis system, taking in wider interactions with hemostasis proteins, is progressing so that in future we may have more complete models and better diagnostic methods and therapeutics.