The balance of pro- and anticoagulant processes underlying thrombin generation

Mathematical models of coagulation-are we there yet?

BACKGROUND

Mathematical models of coagulation have been developed to mirror thrombin generation in plasma, with the aim of investigating how variation in coagulation factor levels regulates hemostasis. However, current models vary in the reactions they capture and the reaction rates used, and their validation is restricted by a lack of large coherent datasets, resulting in questioning of their utility.

OBJECTIVES

To address this debate, we systematically assessed current models against a large dataset, using plasma coagulation factor levels from 348 individuals with normal hemostasis to identify the causes of these variations.

METHODS

We compared model predictions with measured thrombin generation, quantifying and comparing the ability of each model to predict thrombin generation, the contributions of the individual reactions, and their dependence on reaction rates.

RESULTS

We found that no current model predicted the hemostatic response across the whole cohort and all produced thrombin generation curves that did not resemble those obtained experimentally. Our analysis has identified the key reactions that lead to differential model predictions, where experimental uncertainty leads to variability in predictions, and we determined reactions that have a high influence on measured thrombin generation, such as the contribution of factor XI.

CONCLUSION

This systematic assessment of models of coagulation, using large dataset inputs, points to ways in which these models can be improved. A model that accurately reflects the effects of the multiple subtle variations in an individual's hemostatic profile could be used for assessing antithrombotics or as a tool for precision medicine.

Prothrombin conversion and thrombin decay in patients with cirrhosis-role of prothrombin and antithrombin deficiencies

BACKGROUND

Thrombin generation (TG) in the presence of thrombomodulin (TG-TM) in the plasma of patients with cirrhosis (PWC) is tilted toward a hypercoagulable phenotype. Low protein C and elevated factor VIII levels play a role, but other determinants, such as the prothrombin/antithrombin pair, must also be studied.

OBJECTIVES

The objectives were (i) to quantitatively assess the subprocesses (prothrombin conversion and thrombin decay) and (ii) to understand the underlying mechanism by studying TG dynamics after prothrombin and antithrombin plasma level correction in PWC.

METHODS

We studied TG-TM in plasma samples of 36 healthy controls (HCs) and 41 PWC with prothrombin and antithrombin levels of <70% and after their correction. We initiated coagulation with an intermediate picomolar concentration of tissue factor. We determined the overall thrombin potential, prothrombin conversion, and thrombin decay.

RESULTS

TG-TM was increased in PWC compared with HC due to impaired thrombin inhibition. Indeed, thrombin decay capacity (min-1) decreased from 0.37 (0.35-0.40) in HC to 0.33 (0.30-0.37) in the Child-Turcotte-Pugh A (CTP-A; P = .09), 0.27 (0.26-0.30) in the CTP-B (P < .001), and 0.20 (0.19-0.20) in the CTP-C (P < .001) group. Concomitant correction of prothrombin and antithrombin increased endogenous thrombin potential with prothrombin conversion surpassing thrombin decay. By contrast, when we corrected only antithrombin, TG-TM was normalized and even consistent with a hypocoagulable phenotype in the CTP-C group.

CONCLUSION

Our results highlight that in PWC, hypercoagulability (evidenced in the presence of TM) is due to impaired thrombin decay, whereas low prothrombin levels do not translate into decreased prothrombin conversion, likely due to altered TM-activated protein C negative feedback.

Low thrombin generation in postmenopausal women using estetrol

OBJECTIVE

Estetrol (E4) represents a novel estrogen of interest to relieve vasomotor symptoms. E4 activates the nuclear estrogen receptor α (ERα) but antagonizes the estradiol ERα-dependent membrane-initiated steroid signaling pathway. The distinct pharmacological properties of E4 could explain its low impact on hemostasis. This study aimed to assess the effect of E4 on coagulation in postmenopausal women, using the thrombin generation assay (TGA).

METHODS

Data were collected from a multicenter, randomized, placebo-controlled, dose-finding study in postmenopausal women (NCT02834312). Oral E4 (2.5 mg, n = 42; 5 mg, n = 29; 10 mg, n = 34; or 15 mg, n = 32) or placebo (n = 31) was administered daily for 12 weeks. Thrombograms and TGA parameters were extracted for each subject at baseline and after 12 weeks of treatment.

RESULTS

After 12 weeks of treatment, all treatment groups showed a mean thrombogram (±95% confidence interval [CI] of the mean) within the reference ranges, that is, the 2.5th-97.5th percentile of all baseline thrombograms (n = 168), as well as for TGA parameters.

CONCLUSIONS

The intake of E4 15 mg for 12 weeks led to significant but not clinically relevant changes compared to baseline as the mean values (±95% CI of the mean) remained within reference ranges, demonstrating a neutral profile of this estrogen on hemostasis.

Altered whole blood thrombin generation and hyperresponsive platelets in patients with pancreatic cancer

BACKGROUND

Thromboembolic disease is a major complication in patients with pancreatic ductal adenocarcinoma (PDAC). Patients with PDAC often have altered blood cell counts, which are associated with venous thromboembolism (VTE) development. The high thrombotic risk in patients with PDAC may be partially caused by procoagulant blood cells.

OBJECTIVES

The aim of this study was to compare blood cell-dependent coagulation between patients with PDAC (n = 18) and healthy controls matched for age and sex (n = 18).

METHODS

Thrombin generation (TG) was measured in whole blood (WB) and plasma. The capacity of platelets to release granules (PGRCs) was measured in WB. We explored the occurrence of thromboembolic events in patients with PDAC during a 6-month follow-up.

RESULTS

Patients showed an increased endogenous thrombin potential in WB compared with controls. This difference was not observed in plasma, indicating a procoagulant effect of blood cells. Both in WB and plasma, the lag time was prolonged in patients compared with controls. Patients had hyperresponsive platelets, with a shorter time to peak granule release. Of the 18 patients with PDAC, 4 developed a venous thromboembolism (22%) and 1 developed an arterial thrombosis (6%). A shorter lag time in WB, but not in plasma, and an increased PGRC were associated with thromboembolic events.

CONCLUSION

Patients with PDAC have an increased and delayed WB TG coagulation profile compared with controls. A shorter lag time in WB TG and increased PGRC are associated with the incidence of thromboembolic events. Platelets appear to be key players in thrombosis development. Measuring hemostasis in WB could improve thrombosis risk estimation in patients with PDAC.

A thrombin-driven neural net diagnoses the antiphospholipid syndrome without the need for interruption of anticoagulation

ABSTRACT

Thrombosis is an important manifestation of the antiphospholipid syndrome (APS). The thrombin generation (TG) test is a global hemostasis assay, and increased TG is associated with thrombosis. APS is currently diagnosed based on clinical and laboratory criteria, the latter defined as anti-cardiolipin, anti-β2-glycoprotein I antibodies, or lupus anticoagulant (LA). APS testing is often performed after a thrombotic episode and subsequent administration of anticoagulation, which might hamper the interpretation of clotting assays used for LA testing. We set out to develop an artificial neural network (NN) that can diagnose APS in patients who underwent vitamin K antagonist (VKA) treatment, based on TG test results. Five NNs were trained to diagnose APS in 48 VKA-treated patients with APS and 64 VKA-treated controls, using TG and thrombin dynamics parameters as inputs. The 2 best-performing NNs were selected (accuracy, 96%; sensitivity, 96%-98%; and specificity, 95%-97%) and further validated in an independent cohort of VKA-anticoagulated patients with APS (n = 33) and controls (n = 62). Independent clinical validation favored 1 of the 2 selected NNs, with a sensitivity of 88% and a specificity of 94% for the diagnosis of APS. In conclusion, the combined use of TG and NN methodology allowed for us to develop an NN that diagnoses APS with an accuracy of 92% in individuals with VKA anticoagulation (n = 95). After further clinical validation, the NN could serve as a screening and diagnostic tool for patients with thrombosis, especially because there is no need to interrupt anticoagulant therapy.

High alpha-2-macroglobulin levels are a risk factor for cardiovascular disease events: A Moli-sani cohort study

BACKGROUND

α2-macroglobulin (α2M) is a versatile endopeptidase inhibitor that plays a role in cell growth, inflammation and coagulation. α2M is an inhibitor of key coagulation enzyme thrombin. Hypercoagulability due to an excess of thrombin production can cause thrombotic events. Therefore, we investigated the association of α2M levels and cardiovascular events in a subset of the general Italian population.

METHODS

We determined α2M levels in the baseline samples of a prospective cohort (n = 19,688; age: 55 ± 12 years; 47.8 % men) of the Moli-sani study and investigated the association with the cardiovascular events (n = 432, 2.2 %) in the median follow-up period of 4.3 years. Hazard ratios (HR) with 95 % confidence intervals (CI) were calculated by multivariable Cox regression and adjusted for a large panel of confounding factors.

RESULTS

α2M levels above the 90th percentile were significantly associated with cardiovascular disease (CVD) events after full adjustment for age, sex, current smoking, BMI, oral contraceptive use, cardiovascular diseases, hypertension, hypercholesterolemia, diabetes and history of cancer (HR: 1.36; CI: 1.06-1.74). Moreover, high α2M was associated with coronary heart disease (CHD; HR: 1.47; CI: 1.12-1.91), but not stroke. Stratification for CVD at baseline showed that high α2M levels are associated with CHD events in subjects without CVD at baseline (HR: 1.40; CI: 1.00-1.95) and subjects with CVD at baseline (HR: 1.58; CI: 1.02-2.44).

CONCLUSION

We show in a prospective cohort that high levels of α2M could be a risk factor for cardiovascular events, especially coronary heart disease events.

Exercise and hypoxia-induced hypercoagulability is counterbalanced in women in part by decreased platelet reactivity

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation.

Crucial roles of red blood cells and platelets in whole blood thrombin generation

Red blood cells (RBCs) and platelets contribute to the coagulation capacity in bleeding and thrombotic disorders. The thrombin generation (TG) process is considered to reflect the interactions between plasma coagulation and the various blood cells. Using a new high-throughput method capturing the complete TG curve, we were able to compare TG in whole blood and autologous platelet-rich and platelet-poor plasma to redefine the blood cell contributions to the clotting process. We report a faster and initially higher generation of thrombin and shorter coagulation time in whole blood than in platelet-rich plasma upon low concentrations of coagulant triggers, including tissue factor, Russell viper venom factor X, factor Xa, factor XIa, and thrombin. The TG was accelerated with increased hematocrit and delayed after prior treatment of RBC with phosphatidylserine-blocking annexin A5. RBC treatment with ionomycin increased phosphatidylserine exposure, confirmed by flow cytometry, and increased the TG process. In reconstituted blood samples, the prior selective blockage of phosphatidylserine on RBC with annexin A5 enhanced glycoprotein VI-induced platelet procoagulant activity. For patients with anemia or erythrocytosis, cluster analysis revealed high or low whole-blood TG profiles in specific cases of anemia. The TG profiles lowered upon annexin A5 addition in the presence of RBCs and thus were determined by the extent of phosphatidylserine exposure of blood cells. Profiles for patients with polycythemia vera undergoing treatment were similar to that of control subjects. We concluded that RBC and platelets, in a phosphatidylserine-dependent way, contribute to the TG process. Determination of the whole-blood hypo- or hyper-coagulant activity may help to characterize a bleeding or thrombosis risk.

Long Non-Coding RNAs in Venous Thromboembolism: Where Do We Stand?

Venous thromboembolism (VTE), a common condition in Western countries, is a cardiovascular disorder that arises due to haemostatic irregularities, which lead to thrombus generation inside veins. Even with successful treatment, the resulting disease spectrum of complications considerably affects the patient's quality of life, potentially leading to death. Cumulative data indicate that long non-coding RNAs (lncRNAs) may have a role in VTE pathogenesis. However, the clinical usefulness of these RNAs as biomarkers and potential therapeutic targets for VTE management is yet unclear. Thus, this article reviewed the emerging evidence on lncRNAs associated with VTE and with the activity of the coagulation system, which has a central role in disease pathogenesis. Until now, ten lncRNAs have been implicated in VTE pathogenesis, among which MALAT1 is the one with more evidence. Meanwhile, five lncRNAs have been reported to affect the expression of TFPI2, an important anticoagulant protein, but none with a described role in VTE development. More investigation in this field is needed as lncRNAs may help dissect VTE pathways, aiding in disease prediction, prevention and treatment.

A Review of Quantitative Systems Pharmacology Models of the Coagulation Cascade: Opportunities for Improved Usability

Despite the numerous therapeutic options to treat bleeding or thrombosis, a comprehensive quantitative mechanistic understanding of the effects of these and potential novel therapies is lacking. Recently, the quality of quantitative systems pharmacology (QSP) models of the coagulation cascade has improved, simulating the interactions between proteases, cofactors, regulators, fibrin, and therapeutic responses under different clinical scenarios. We aim to review the literature on QSP models to assess the unique capabilities and reusability of these models. We systematically searched the literature and BioModels database reviewing systems biology (SB) and QSP models. The purpose and scope of most of these models are redundant with only two SB models serving as the basis for QSP models. Primarily three QSP models have a comprehensive scope and are systematically linked between SB and more recent QSP models. The biological scope of recent QSP models has expanded to enable simulations of previously unexplainable clotting events and the drug effects for treating bleeding or thrombosis. Overall, the field of coagulation appears to suffer from unclear connections between models and irreproducible code as previously reported. The reusability of future QSP models can improve by adopting model equations from validated QSP models, clearly documenting the purpose and modifications, and sharing reproducible code. The capabilities of future QSP models can improve from more rigorous validation by capturing a broader range of responses to therapies from individual patient measurements and integrating blood flow and platelet dynamics to closely represent in vivo bleeding or thrombosis risk.

Expression of B-cell activating factor in pediatric patients with immune thrombocytopenia: a single institutional series and review of literature

B-cell-activating factor (BAFF) is a crucial cytokine supporting survival and differentiation of B cells. Dysregulation of BAFF is involved in the pathogenesis of B-cell related autoimmune diseases including immune thrombocytopenia (ITP). The aim of this study was to evaluate the significance of BAFF expression in pediatric ITP patients. Eighty pediatric patients with ITP are subdivided in three groups. Group I included (32 patients) diagnosed with acute ITP less than 3 months, group II (48 patients) diagnosed with persistent ITP (from 3 to 12 months) and chronic ITP (more than 12 months) and group III 20 healthy controls. Complete blood picture, autoimmune profile, antiplatelet antibodies, coagulation profile, bone marrow examination, and RT-PCR were performed to detect the expression for BAF for all participants in this study. BAFF expression levels significantly increased in cases rather than in controls. BAFF Expression Value significantly increased in groups I & II (3.10 ± 1.99&3.29 ± 2.58) compared to controls (0.83 ± 0.45) as p < .001 for both. On the other hand, groups I & II were comparable in BAFF Expression Value (p = .470). BAFF expression increased in ITP patients, implying a function in the disease's pathogenesis.

Abacavir use is associated with increased prothrombin conversion

There is ongoing debate as to whether abacavir (ABC) increases the risk for cardiovascular disease(CVD) in people living with HIV (PLHIV) and the mechanisms underlying this possible association. We recently showed that the use of an ABC-containing regimen was independently associated with increased thrombin generation (TG). In the present study, we aim to explore these findings further, by studying the mechanistical processes that underly the global thrombin generation test via thrombin dynamics analysis. Thrombin dynamics analysis can pinpoint the cause of increased thrombin generation associated with ABC-use either to the procoagulant prothrombin conversion pathway or the anticoagulant thrombin inactivation pathway. In this cross-sectional study, 208 virally suppressed PLHIV were included, of whom 94 were on a ABC-containing regimen, 92 on a tenofovir disoproxil fumarate (TDF)-containing regimen, and the remainder on other regimens. We used Calibrated Automated Thrombinography to measure thrombin generation and perform thrombin dynamics analysis. The total amount of prothrombin conversion, as well as the maximum rate of prothrombin conversion were significantly increased in PLHIV on an ABC containing regimen compared to other treatment regimens. The levels of pro- and anticoagulant factors were comparable, indicating that the ABC-induced changes affect the kinetics of prothrombin conversion rather than procoagulant factor levels. Moreover, Von Willebrand Factor (VWF), active VWF and VWF pro-peptide levels were significantly higher in PLHIV than controls without HIV. However, they did not differ between ABC and non-ABC treated participants.

Prothrombotic state, endothelial injury, and echocardiographic changes in non-active sarcoidosis patients

Sarcoidosis is a multisystem inflammatory granulomatous disease of unknown cause that most commonly affects lungs and lymph nodes, with frequent yet asymptomatic cardiac involvement. The epidemiologically associated cardiovascular risk suggests an underlying prothrombotic state and endothelial dysfunction, currently understudied in the available literature. Therefore, we aimed to investigate prothrombotic plasma properties together with selected echocardiographic and laboratory biomarkers of cardiovascular injury in that disease. N = 53 patients with pulmonary sarcoidosis in clinical remission and N = 66 matched controls were assessed for inflammatory and endothelial injury biomarkers, plasma thrombin generation profile, and echocardiographic and lung function parameters. Sarcoidosis cases had impaired systolic and diastolic left ventricular function, higher concentrations of inflammatory markers, D-dimer and factor VIII activity compared to the controls. The coexistence of extrapulmonary disease was associated with elevated circulating vascular cell adhesion molecule 1, while cases with hypercalcemia had higher thrombomodulin concentration. Sarcoidosis was characterized by the unfavorably altered thrombin generation profile, reflected by the 16% higher endogenous thrombin potential (ETP), 24% increased peak thrombin concentration, and 12% shorter time to thrombin peak in comparison to the control group. ETP was higher in cases with proxies of pulmonary restriction, extrapulmonary-extracutaneous manifestation, and need for corticosteroids use. Despite the clinical remission, sarcoidosis is related to prothrombotic plasma properties and signs of endothelial injury, likely contributing to the higher risk of cardiovascular events. In addition, subclinical cardiac involvement may play an additional role, although further clinical and experimental studies are needed to verify these findings.

External validation of the MidiCAT variant of thrombography: Comparison with calibrated automated thrombography and study of the centrifugation scheme

Introduction

To perform Calibrated Automated Thrombography (CAT), the use of reduced plasma volumes (referred to as “MidiCAT”) makes it possible to more efficiently use limited volumes of valuable biobanked plasma samples and decreases expenses for reagents. It is, however, unclear whether the MidiCAT procedure is suitable when thrombin generation (TG) is studied in the presence of added thrombomodulin (TG-TM). Moreover, a simplified centrifugation scheme would facilitate biobanking, if appropriate, for more sensitive coagulation studies. We aimed to compare the results of “MidiCAT” (halved plasma and reagent volumes) with those from regular CAT, in the absence or presence of TM, as well as to study the impact of a single-centrifugation scheme for plasma preparation before freezing.

Materials and methods

Plasma samples were prepared from the citrated blood from 20 Geneva hospital diverse patients without gross coagulation abnormalities with a single- or double-centrifugation scheme. Samples were kept frozen at −80°C and thawed just before the TG assay in duplicate under two conditions: 1 pM tissue factor (TF) or 5 pM TF + TM.

Results and discussion

(1) We externally validated “MidiCAT” and also extended the validation to TG-TM. Whatever the method (CAT or MidiCAT), intra-assay (assessed with duplicates) CV was below 6% (1 pM TF) or below 10% (5 pM TF + TM) for ETP. Agreement between the MidiCAT and CAT results was satisfactory; the p coefficients were above 0.95 for ETP and above 0.90 for most other parameters; biases for ETP were +10.0% (1 pM FT) and +13.5% (5 pM + TM). (2) The centrifugation scheme markedly affected the results obtained in the presence of TM, whereas the bias and limit of agreement (difference plots) were low for the no TM condition. The bias in the presence of TM was obvious, more marked with plasma samples sensitive to TM when double centrifuged: the lower the ETP-TM, the greater the relative difference between the ETP-TM of plasma samples prepared with just single centrifugation and the reference plasma samples. Thus, a single-centrifugation procedure, as is often used for plasma biobanking, is suitable for TG study only if it is not performed in the presence of TM.

Coagulation parameters predict COVID-19-related thrombosis in a neural network with a positive predictive value of 98%

Thrombosis is a major clinical complication of COVID-19 infection. COVID-19 patients show changes in coagulation factors that indicate an important role for the coagulation system in the pathogenesis of COVID-19. However, the multifactorial nature of thrombosis complicates the prediction of thrombotic events based on a single hemostatic variable. We developed and validated a neural net for the prediction of COVID-19-related thrombosis. The neural net was developed based on the hemostatic and general (laboratory) variables of 149 confirmed COVID-19 patients from two cohorts: at the time of hospital admission (cohort 1 including 133 patients) and at ICU admission (cohort 2 including 16 patients). Twenty-six patients suffered from thrombosis during their hospital stay: 19 patients in cohort 1 and 7 patients in cohort 2. The neural net predicts COVID-19 related thrombosis based on C-reactive protein (relative importance 14%), sex (10%), thrombin generation (TG) time-to-tail (10%), α₂-Macroglobulin (9%), TG curve width (9%), thrombin-α₂-Macroglobulin complexes (9%), plasmin generation lag time (8%), serum IgM (8%), TG lag time (7%), TG time-to-peak (7%), thrombin-antithrombin complexes (5%), and age (5%). This neural net can predict COVID-19-thrombosis at the time of hospital admission with a positive predictive value of 98%-100%.

Low antithrombin levels are associated with low risk of cardiovascular death but are a risk factor for cancer mortality

Background

Thrombosis is common in subjects suffering from cardiovascular diseases (CVD) and cancer. Hypercoagulation plays a pivotal role in the pathophysiology of thrombosis. Therefore, the inactivation of thrombin, the key enzyme in coagulation, is tightly regulated via antithrombin (AT). AT deficiency is related to thrombosis and cardiovascular death. In this study we investigated the association between AT levels and mortality, in particularly cardiovascular-related and cancer-related death in the general population.

Methods

We studied the association of AT levels and mortality in a prospective cohort sampled from the general Italian population (n = 19,676). AT levels were measured in the baseline samples, and mortality was recorded during a median follow-up period of 8.2 years. Cox regression was performed to investigate the association of all-cause, CVD-related and cancer-related mortality with variations in AT levels.

Results

In total, 989 subjects died during follow-up, of which 373 subjects of CVD and 353 of cancer-related causes. Cox analysis revealed that, after adjustment for age, sex, current smoking, BMI, diabetes, hypertension, hypercholesterolemia, history of cardiovascular disease, history of cancer, vitamin K antagonists, antiplatelet medication, heparin and oral contraceptives AT levels were not associated with all-cause mortality (HRQ1vsQ5: 0.92, 95% CI:0.74–1.15). Interestingly, the risk of CVD-related mortality was reduced in subjects with low AT levels compared to subjects with higher AT levels, after adjustment for age and sex and other confounders did not change the association (HRQ1vsQ5: 0.64, 95% CI:0.44–0.91). Moreover, low AT levels were associated with increased cancer mortality in a fully adjusted model (HRQ1vsQ2-5: 1.26, 95% CI:0.88–1.81).

Conclusions

Low AT levels are associated to a lower risk of fatal cardiovascular events in the general population, regardless of age, sex and medication use. In contrast, low AT levels are associated with lower cancer survival. For the first time we show that AT levels lower than the normal range in the general population, even before the development or diagnosis of cancer, are associated with an elevated risk of cancer death.

Thrombin generation potential is increased in patients with autoimmune inflammatory myopathies

PURPOSE

Dermatomyositis and polymyositis (DM/PM) are rare autoimmune inflammatory myopathies, characterized by an increased risk of cardiovascular and thromboembolic events, likely related to the prothrombotic plasma properties. The aim of this study was to assess the in vitro thrombin generation profile as a biomarker of plasma procoagulant properties in DM/PM patients.

METHODS

In 58 clinically stable DM/PM patients and 67 controls matched for sex, age, body mass index, we measured plasma thrombin generation potential using the Calibrated Automated Thrombinography (CAT) and analyzed its relationship with clinical disease characteristics, including autoantibodies profile.

RESULTS

Patients with DM/PM had a 21% increase in endogenous thrombin potential (ETP), 36% higher peak thrombin concentration, and 11% faster thrombin generation, compared to controls (p ​< ​0.001, all, also after adjustment for potential confounders). Interestingly, although both diseases did not differ in thrombin generation potential, heterogenous variables predicted elevated ETPs in both of them. In DM, that was higher fibrinogen, C-reactive protein, and total cholesterol, whereas in PM, presence of arthritis and increased blood platelet count. Surprisingly, thrombin formation capacity remained in a robust inverse relationship with serum troponin (r ​= ​-0.67, p ​< ​0.001) in the patient group.

CONCLUSIONS

DM/PM patients are characterized by an increased thrombin generation potential, suggesting prothrombotic plasma properties in both diseases. However, more studies are needed to verify its rationale and role in DM/PM clinical course and unfavorable clinical outcomes.

Semi-automated thrombin dynamics applying the ST Genesia thrombin generation assay

Background

The haemostatic balance is an equilibrium of pro- and anticoagulant factors that work synergistically to prevent bleeding and thrombosis. As thrombin is the central enzyme in the coagulation pathway, it is desirable to measure thrombin generation (TG) in order to detect possible bleeding or thrombotic phenotypes, as well as to investigate the capacity of drugs affecting the formation of thrombin. By investigating the underlying processes of TG (i.e., prothrombin conversion and inactivation), additional information is collected about the dynamics of thrombin formation.

Objectives

To obtain reference values for thrombin dynamics (TD) analysis in 112 healthy donors using an automated system for TG.

Methods

TG was measured on the ST Genesia, fibrinogen on the Start, anti-thrombin (AT) on the STA R Max and α₂Macroglobulin (α₂M) with an in-house chromogenic assay.

Results

TG was measured using STG-BleedScreen, STG-ThromboScreen and STG-DrugScreen. The TG data was used as an input for TD analysis, in combination with plasma levels of AT, α₂M and fibrinogen that were 113% (108-118%), 2.6 μM (2.2 μM-3.1 μM) and 2.9 g/L (2.6-3.2 g/L), respectively. The maximum rate of the prothrombinase complex (PCmax) and the total amount of prothrombin converted (PCtot) increased with increasing tissue factor (TF) concentration. PC_tot increased from 902 to 988 nM, whereas PC_max increased from 172 to 508 nM/min. Thrombin (T)-AT and T-α₂M complexes also increased with increasing TF concentration (i.e., from 860 to 955 nM and from 28 to 33 nm, respectively). PC_tot, T-AT and T-α₂M complex formation were strongly inhibited by addition of thrombomodulin (-44%, -43%, and -48%, respectively), whereas PC_max was affected less (-24%). PC_tot, PC_max, T-AT, and T-α₂M were higher in women using oral contraceptives (OC) compared to men/women without OC, and inhibition by thrombomodulin was also significantly less in women on OC (p < 0.05).

Conclusions

TG measured on the ST Genesia can be used as an input for TD analysis. The data obtained can be used as reference values for future clinical studies as the balance between prothrombin conversion and thrombin inactivation has shown to be useful in several clinical settings.

Population-wide persistent hemostatic changes after vaccination with ChAdOx1-S

Various vaccines were developed to reduce the spread of the Severe Acute Respiratory Syndrome Cov-2 (SARS-CoV-2) virus. Quickly after the start of vaccination, reports emerged that anti-SARS-CoV-2 vaccines, including ChAdOx1-S, could be associated with an increased risk of thrombosis. We investigated the hemostatic changes after ChAdOx1-S vaccination in 631 health care workers. Blood samples were collected 32 days on average after the second ChAdOx1-S vaccination, to evaluate hemostatic markers such as D-dimer, fibrinogen, α2-macroglobulin, FVIII and thrombin generation. Endothelial function was assessed by measuring Von Willebrand Factor (VWF) and active VWF. IL-6 and IL-10 were measured to study the activation of the immune system. Additionally, SARS-CoV-2 anti-nucleoside and anti-spike protein antibody titers were determined. Prothrombin and fibrinogen levels were significantly reduced after vaccination (−7.5% and −16.9%, p < 0.0001). Significantly more vaccinated subjects were outside the normal range compared to controls for prothrombin (42.1% vs. 26.4%, p = 0.026) and antithrombin (23.9% vs. 3.6%, p = 0.0010). Thrombin generation indicated a more procoagulant profile, characterized by a significantly shortened lag time (−11.3%, p < 0.0001) and time-to-peak (−13.0% and p < 0.0001) and an increased peak height (32.6%, p = 0.0015) in vaccinated subjects compared to unvaccinated controls. Increased VWF (+39.5%, p < 0.0001) and active VWF levels (+24.1 %, p < 0.0001) pointed toward endothelial activation, and IL-10 levels were significantly increased (9.29 pg/mL vs. 2.43 pg/mL, p = 0.032). The persistent increase of IL-10 indicates that the immune system remains active after ChAdOx1-S vaccination. This could trigger a pathophysiological mechanism causing an increased thrombin generation profile and vascular endothelial activation, which could subsequently result in and increased risk of thrombotic events.

Functional changes in hemostasis during asexual and sexual parasitemia in a controlled human malaria infection

Decreased platelet count is an early phenomenon in asexual Plasmodium falciparum parasitemia, but its association with acute or long-term functional changes in platelets and coagulation is unknown. Moreover, the impact of gametocytemia on platelets and coagulation remains unclear. We investigated the changes in platelet number and function during early asexual parasitemia, gametocytemia and convalescence in 16 individuals participating in a controlled human malaria infection study, and studied its relationship with changes in total and active von Willebrand factor levels (VWF) and the coagulation system. Platelet activation and reactivity were determined by flow cytometry, and the coagulation system was assessed using different representative assays including antigen assays, activity assays and global functional assays. Platelet count was decreased during asexual blood stage infection but normalized during gametocytemia. Platelet P-selectin expression was slightly increased during asexual parasitemia, gametocytemia and at day 64. In contrast, platelet reactivity to different agonists remained unchanged, except a marked decrease in reactivity to low dose collagen-related peptide-XL. Thrombin generation and antigen assays did not show a clear activation of the coagulation during asexual parasitemia, whereas total and active VWF levels were markedly increased. During gametocytemia and on day 64, the endogenous thrombin potential, thrombin peak and velocity index were increased and prothrombin conversion and plasma prothrombin levels were decreased. We conclude that the decreased platelet count during asexual parasitemia is associated with increased active VWF levels (i.e. endothelial activation), but not platelet hyperreactivity or hypercoagulability, and that the increased platelet clearance in asexual parasitemia could cause spontaneous VWF-platelet complexes formation.

Haemostatic differences between SARS-CoV-2 PCR-positive and negative patients at the time of hospital admission

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is associated with thrombosis. We conducted a cohort study of consecutive patients, suspected of SARS-CoV-2 infection presented to the emergency department. We investigated haemostatic differences between SARS-CoV-2 PCR positive and negative patients, with dedicated coagulation analysis. The 519 included patients had a median age of 66 years, and 52.5% of the patients were male. Twenty-six percent of the patients were PCR-positive for SARS-CoV-2.PCR positive patients had increased levels of fibrinogen and (active) von Willebrand Factor (VWF) and decreased levels of protein C and α2-macroglobulin compared to the PCR negative patients. In addition, we found acquired activated protein C resistance in PCR positive patients. Furthermore, we found that elevated levels of factor VIII and VWF and decreased levels of ADAMTS-13 were associated with an increased incidence of thrombosis in PCR positive patients. In conclusion, we found that PCR positive patients had a pronounced prothrombotic phenotype, mainly due to an increase of endothelial activation upon admission to the hospital. These findings show that coagulation tests may be considered useful to discriminate severe cases of COVID-19 at risk for thrombosis.

Tailoring the effect of antithrombin-targeting therapy in haemophilia A using in silico thrombin generation

Factor (F) VIII deficiency causes bleeding in haemophilia A patients because of the reduced formation of procoagulant enzyme thrombin, which is needed to make the blood clot. We measured the dynamics of coagulation in haemophilia A patients by measuring thrombin generation (TG). Additionally, we quantified the procoagulant process of prothrombin conversion and anticoagulant process of thrombin inhibitor complex formation. In haemophilia A, prothrombin conversion is severely reduced, causing TG to be low. Nevertheless, the thrombin inactivation capacity of these patients is comparable to that in healthy subjects, leading to a severe imbalance between procoagulant and anticoagulant processes and a subsequent increased bleeding risk. A novel therapy in haemophilia A is the targeting of anticoagulant pathway, e.g. thrombin inhibitor antithrombin (AT), to restore the haemostatic balance. We simulated the effect of AT reduction on TG in silico. Lowering AT levels restored TG dose-dependently and an AT reduction of 90-95% led to almost normal TG in most patients . However, the variation in response to AT reduction was large between patients, indicating that this approach should be tailored to each individual patients. Ideally, TG and thrombin dynamics simulation could in the future contribute to the management of patients undergoing AT targeting therapy.

Altered fibrin clot properties and fibrinolysis in patients with atrial fibrillation: practical implications

Compelling evidence indicates that a hypercoagulable state occurs in patients with atrial fibrillation (AF) including those in sinus rhythm following paroxysmal and persistent AF. Activation of blood coagulation in AF reflects heightened thrombin generation with the subsequent increased formation of fibrin as evidenced by elevated soluble fibrin monomers and D-dimer. Formation of denser fibrin meshworks, relatively resistant to plasmin-mediated lysis has been demonstrated in patients with AF. The presence of stroke risk factors in AF, such as diabetes, heart failure, hypertension, previous myocardial infarction, or stroke, advanced age have been shown to be linked to the prothrombotic clot characteristics, including reduced clot permeability and lysability. Importantly, biomarkers, including cardiac troponins and N-terminal pro-brain natriuretic peptide, are associated with thrombin generation and fibrin-related markers in AF patients. Recently, increased fibrin clot density (low clot permeability measured in plasma-based assays) and impaired fibrinolysis measured off anticoagulation have been demonstrated to predict ischaemic cerebrovascular events in patients with AF receiving vitamin K antagonists and those on rivaroxaban. The current review summarizes evidence for a role of altered fibrin clot properties and hypofibrinolysis in AF and their prognostic value in terms of adverse events.

Deciphered coagulation profile to diagnose the antiphospholipid syndrome using artificial intelligence

The antiphospholipid syndrome (APS) is diagnosed by the presence of lupus anticoagulant and/or antibodies against cardiolipin or β₂-glycoprotein-1 and the occurrence of thrombosis or pregnancy morbidity. The assessment of overall coagulation is known to differ in APS patients compared to normal subjects. The accelerated production of key factor thrombin causes a prothrombotic state in APS patients, and the reduced efficacy of the activated protein C pathway promotes this effect. Even though significant differences exist in the coagulation profile between normal controls and APS patients, it is not possible to rely on a single test result to diagnose APS. A neural network is a computing system inspired by the human brain that can be trained to distinguish between healthy subjects and patients based on subject specific data. In a first cohort of patients, we developed a neural networking that diagnoses APS. We clinically validated this neural network in a separate cohort consisting of APS patients, normal controls, controls visiting the hospital for other indications and two diseased control groups (thrombosis patients and auto-immune disease patients). The positive predictive value ranged from 62% in the hospital controls to 91% in normal controls and the negative predictive value of the neural network ranged from 86% in the thrombosis control group to 95% in the hospital controls. The sensitivity of the neural network was higher than 90% in all control groups. In conclusion, we developed a neural network that accurately diagnoses APS in the validation cohort. After further clinical validation in newly diagnosed patients, this neural network could possibly be clinically implemented to diagnose APS based on thrombin generation data.

Cross-sectional assessment of haemostatic profile and hepatic dysfunction in Fontan patients

Background

Fontan-associated liver disease is accompanied by a hypercoagulable state. While hepatic dysfunction in Fontan patients is common, its relationship with haemostatic changes and clinical outcomes in this patient population remains unclear.

Objective

To correlate liver dysfunction and haemostatic profiles with clinical outcomes in the Fontan population.

Patients/methods

Patients were enrolled in a multicentre, cross-sectional study in Australia and New Zealand. Hepatic structure and function were assessed using serum-based calculations (Fibrotest and model for end-stage liver disease excluding international normalised ratio scores). Haemostatic profiles were assessed by Thrombin Generation. Platelet function was assessed via Platelet Factor 4 (PF4) and P-selectin (P-SEL). Clinical outcomes were obtained from the Australian and New Zealand Fontan Registry.

Results

Seventy-three patients participated in the study (mean age 18.9±8.5 years with a mean of 13.5±6.9 years post-Fontan). The Endogenous Thrombin Potential (ETP) for patients who suffered thrombotic events (TE) (1366.4±66.2 nM/min) was higher compared with patients with major bleeding events (1011.1±138.4 nM/min) (p=0.03). Except for a negative correlation between Fibrotest-score and PF4 (p=0.045), PF4 and P-SEL concentrations did not correlate with markers of hepatic dysfunction or structural abnormality.

Conclusions

Increased ETP is associated with TE during clinical follow-up after Fontan. This study reinforces that hepatic dysfunction may contribute to the derangement of coagulation factors, impacting the individual risk of haemostatic complications for the Fontan population.

Increased tissue factor activity promotes thrombin generation at type 1 diabetes onset in children

OBJECTIVE

In type 1 diabetes (T1D), a prothrombotic status due to elevated coagulation factors coincides with metabolic derailment. In a previous study, we discovered altered thrombin generation profiles in children with T1D. These alterations are potentially most pronounced at T1D onset and ameliorated after insulin treatment. We tested this hypothesis in a longitudinal study, measuring thrombin generation together with coagulation parameters in children at T1D onset and during follow-up.

MATERIALS AND METHODS

Twenty-three children (12 female, age: 9.4 [2.7-17.3] years; median [range]) were tested at T1D onset and after long-term insulin treatment. Thrombin generation was measured using calibrated automated thrombography. Tissue factor (TF) activity and tissue factor pathway inhibitor (TFPI) activity were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

A procoagulant shift was observed in thrombin generation traces at T1D onset compared to follow-up (time to peak: 5.67 [4.11-7.67] min vs 6.39 [4.89-10.44] min, P < .001). These alterations at T1D onset coincided with increased TF activity (5.18 [0.01-12.97] pmol/L vs 2.67 [0.04-10.41] pmol/L, P < .05) and increased TFPI activity (0.051 [0.038-0.074] U/mL vs 0.035 [0.026-0.056] U/mL, P < .05).

CONCLUSION

The procoagulant shift in thrombin generation at T1D onset is a result of increased TF activity, but this effect is partially counterbalanced by increased TFPI levels. Elevated TF and TFPI levels hint to a fragile hemostatic balance at the endothelial lining of blood vessels. Additional prothrombotic stimuli may tip over this balance explaining the increased thrombotic risk of children with T1D.

Deciphering the coagulation profile through the dynamics of thrombin activity

Thrombosis has proven to be extremely difficult to predict. Measuring the generation of thrombin is a very sensitive method to detect changes in the hemostatic system. We developed a method based on the generation of thrombin to further fingerprint hemostasis, which we have named thrombin dynamics. Via this method we are able to exactly measure the prothrombin conversion and thrombin inactivation, and any change in the coagulation cascade will be reflected in these two processes. In the current study we analyzed the importance of the members of the prothrombin complex on the dynamics of thrombin activation and inactivation. We show that prothrombin conversion is predominantly influenced by factor X and antithrombin, which will provide essential insights in complex thrombosis-related diseases, such as liver cirrhosis and kidney failure.

Delayed Thrombin Generation Is Associated with Minor Bleedings in Venous Thromboembolism Patients on Rivaroxaban: Usefulness of Calibrated Automated Thrombography

Bleeding is the most feared and difficult to predict adverse event of anticoagulation. We sought to investigate whether calibrated automated thrombography (CAT) parameters are associated with minor bleeding (MB) in anticoagulated patients following venous thromboembolism (VTE). Enrolled were 132 patients on rivaroxaban, 145 on vitamin K antagonists (VKA) and 31 controls who stopped anticoagulation. Prior to the next dose of the anticoagulant, we measured CAT parameters, along with rivaroxaban concentration and INR. During a median follow-up of 10 months, we recorded minor and major bleedings. On rivaroxaban, 27 (20.5%) patients with MB had longer time to start thrombin generation, lower peak thrombin generation and lower endogenous thrombin potential compared with subjects without MB (all p < 0.001). All CAT parameters, except for peak thrombin generation (p = 0.049), were similar in VKA patients with (n = 25, 17.2%) vs. without MBs. By logistic regression, time to start thrombin generation (p = 0.007) and unprovoked VTE (p = 0.041) independently predicted MBs on rivaroxaban. Major bleedings were more frequent in patients with MBs (17.3% vs. 1.8%, p < 0.001). Abnormal CAT parameters characterize VTE patients prone to MBs on rivaroxaban, but not on VKA. Time to start thrombin generation measured about 24 h since the last rivaroxaban dose might help predict MBs.

Reference values for thrombin dynamics in platelet rich plasma

Thrombin generation (TG) is a better determinant of the overall function of the hemostatic system than routinely used clotting time-based assays and can be studied more in detail by thrombin dynamics analysis. Platelet poor plasma is often used to measure TG, however, measuring the contribution of the platelets is also important as patients with a low platelet count or with dysfunctional platelets have an increased risk of developing bleeding. In this study, platelet rich plasma (PRP) was collected from 117 healthy individuals. PRP was measured undiluted and diluted to a varying platelet concentration of 10*10⁹/L to 400*10⁹/L. Prothrombin conversion and thrombin inactivation were calculated from the data obtained by the TG parameters and coagulation factor levels (antithrombin, α₂Macroglobulin (α₂M) and fibrinogen). Reference ranges of TG and thrombin dynamics in PRP of 117 healthy individuals were established. Peak, velocity index and the maximum rate of prothrombin conversion increased linearly with platelet count, but endogenous thrombin potential reached a maximum at 150*10⁹/L as seen in a subset population (n = 20). More extensive analysis revealed that a platelet count below 50*10⁹/L did not affect TG parameters (except for the ETP). Correlation analysis indicated that the platelet count mainly affected the rate of prothrombin conversion. Inhibition of thrombin by antithrombin and α₂M increased with increasing TG, but the ratio of inhibition by antithrombin or α₂M remained the same independently of the total thrombin formed. In conclusion, TG and thrombin dynamics were assessed in PRP of healthy donors to provide reference values for future TG studies in PRP. Increasing the platelet count mainly affected the rate of prothrombin conversion and TG, rather than the total amount of thrombin formed.

New insights into neonatal coagulation: normal clot formation despite lower intra-clot thrombin levels

BACKGROUND

Healthy neonates exhibit no bleeding tendencies, but exhibit longer partial thromboplastin times than adults. Lower clotting factor levels may be balanced by lower inhibitor levels, which is not reflected in routine coagulation assays, but could result in normal clot formation in vivo. The novel thrombodynamics assay simulates a damaged vessel with tissue factor immobilized to a surface. We hypothesized that intra-clot thrombin levels and spatial fibrin clot formation with this assay are comparable in neonates and adults.

METHODS

Coagulation was tested in plasma from venous neonatal blood (N = 12), cord blood (N = 30), and adult blood (N = 20) using thrombodynamics and calibrated automated thrombography.

RESULTS

Neonates exhibited a higher initial rate of clot formation than adults (adult: 60.7 ± 3.9 µm/min; neonatal: 66.8 ± 3.9 µm/min; cord: 68.1 ± 3.3 µm/min; P < 0.001) and a comparable stationary rate of clot formation (adult: 35.8 ± 8.5 µm/min; neonatal: 37.0 ± 4.6 µm/min; cord: 36.0 ± 5.2 µm/min; P = 0.834). Intra-clot thrombin levels were lower in neonates (adult: 41.9 ± 11.2 AU/l; neonatal: 22.6 ± 10.2 AU/l; cord: 23.6 ± 9.7 AU/l; P < 0.001), but the longitudinal rate of thrombin propagation was comparable (adult: 27.2 ± 4.2 µm/min neonatal; 27.9 ± 2.9 µm/min; cord: 27.6 ± 3.4 µm/min; P = 0.862).

CONCLUSIONS

Despite lower intra-clot thrombin levels, neonates exhibit normal spatial fibrin clot growth, which concurs with clinically well-functioning hemostasis in healthy neonates.

Rivaroxaban pharmacodynamics in healthy volunteers evaluated with thrombin generation and the active protein C system: Modeling and assessing interindividual variability

BACKGROUND

Rivaroxaban is a direct factor Xa inhibitor with substantial inter-individual pharmacokinetic (PK) variability. Pharmacodynamic (PD) variability, especially assessed with thrombin generation (TG), has been less documented.

OBJECTIVES

(i) To assess TG parameter time profiles in healthy volunteers, with TG being studied under different conditions and (ii) to model the relationship between rivaroxaban concentrations and TG parameters and subsequently estimate interindividual variability.

METHODS

Sixty healthy male volunteers (DRIVING-NCT01627665) received a single 40-mg rivaroxaban dose. Blood sampling was performed at baseline and 10 predefined time points over 24 h. The TG was investigated with the fully automated ST-Genesia system (Stago), using two tissue-factor (TF) concentrations, in the absence (-), or presence (+) of thrombomodulin (TM) for the lowest one. The PD models were built to characterize the relationships between plasma rivaroxaban concentrations and endogenous thrombin potential (ETP) or peak height induced by the lowest TF concentration.

RESULTS

Thrombin generation parameter time profiles with the lowest TF concentration showed a good sensitivity to rivaroxaban, especially +TM (active protein C negative feedback). The relationship between rivaroxaban concentrations and TG parameters was modeled with a sigmoidal relation. Mean rivaroxaban concentrations halving the baseline value of ETP and peak height (-TM) (C50 ) were of 284 and 33.2 ng/mL, respectively: +TM, C50 declined to 19.4 and 13.8 ng/mL, reflecting a powerful inhibitory effect. The estimated C50 population coefficients of variation were of 12.2% (-TM) and 31.3% (+TM) with the peak height models, 34.8% (+TM) with the ETP model.

CONCLUSIONS

This low-rivaroxaban to moderate-rivaroxaban PD variability in healthy volunteers contrasts with the substantial PK variability and deserves to be studied in different patient settings.

Increased activity of lipoprotein-associated phospholipase A2 in non-severe asthma

BACKGROUND

Given increased risk of cardiovascular events in asthma we hypothesized that lipoprotein-associated phospholipase A₂ (Lp-PLA₂), an enzyme involved in atherosclerosis, is associated with proinflammatory and prothrombotic blood alterations in this disease.

METHODS

In 164 adult asthmatics (63 with severe asthma) we measured plasma Lp-PLA₂ activity using the PLAC test. We determined its relations to inflammation and prothrombotic blood alterations.

RESULTS

In asthma, Lp-PLA₂ was inversely related to the age (β = -0.1 [-0.18 to -0.02]) and was lower in women (n = 122 [74%], 205 [182-242] vs. 243 [203-262] nmol/min/ml, p = 0.001). Interestingly, Lp-PLA₂ correlated negatively with the asthma severity score (β = -0.15 [-0.23 to -0.07]), being 10.3% higher in those with non-severe (mild or moderate) asthma (n = 101, 62%) as compared to the severe disease subtype (224 [191-261] vs. 203 [181-229], p = 0.006 after adjustment for potential confounders). Lp-PLA₂ activity was positively related to the levels of low-density lipoprotein (β = 0.1 [0.02-0.18]), triglycerides (β = 0.11 [0.03-0.19]) and glucose (β = 0.1 [0.02-0.18]) and inversely to the tumor necrosis factor α (β = -0.27 [-0.35 to -0.2]), high sensitivity C-reactive protein (β = -0.1 [-0.19 to -0.02]) and fibrinogen (β = -0.12 [-0.21 to -0.03]), as well as prothrombin (β = -0.16 [-0.24 to -0.08]), and parameters describing thrombin generation potential, such as endogenous thrombin potential (β = -0.14 [-0.21 to -0.06]) and peak thrombin generated (β = -0.2 [-0.28 to -0.12]).

CONCLUSIONS

Elevated Lp-PLA₂ activity in non-severe asthmatics suggests increased atherosclerotic risk in this group. Lower Lp-PLA₂ activity accompanied by its inverse relationship to inflammatory or prothrombotic blood biomarkers observed in turn in severe asthmatics might be related to the pathogenesis of more severe asthma phenotype.

Ozbek O. Thrombin lag time is increased in children with mild asthma

BACKGROUND

Inflammation and coagulation are closely linked events. Thrombin is the key enzyme in coagulation system and also has roles in inflammation.

OBJECTIVE

The aim of our study was to evaluate thrombin generation in children with mild asthma.

METHODS

Forty-two children with mild asthma and 49 healthy children were included in the study. All patients performed spirometry. Thrombin generation tests (TGT) were performed with a calibrated automated thrombogram (CAT) in children without asthma exacerbation during the last six months. During CAT assay thrombogram curves were obtained. The area under the curve showed endogenous thrombin potentials and indicated the total amount of endogenous thrombin generated; the peak height showed the highest thrombin value, thrombin lag time and time to thrombin peak were measured.

RESULTS

Thrombin lag time was significantly longer in children with asthma (3.98±1.2min) compared to those in the control group (3.29±0.6min) (p<0.01). Children with asthma also had longer thrombin tail time compared to the control group (19.5±8.9min vs. 16.7±2.9min, p=0.02). Thrombin peak was inversely correlated with FEF 25-75 (r=-0.41, p<0.01). Thrombin lag time was inversely correlated with FEF 25-75 (r=-0.39, p<0.01).

CONCLUSION

Inflammation in mild asthma seems to disturb coagulation but this disturbance may not be so strong as to increase thrombin levels and may only affect the initiation phase of thrombin generation.

Prothrombin conversion is accelerated in the antiphospholipid syndrome and insensitive to thrombomodulin

Antiphospholipid syndrome (APS) is a condition in which the presence of antibodies against phospholipid-binding proteins is associated with thrombophilia and/or pregnancy morbidity. Although antiphospholipid antibodies have anticoagulant characteristics in vitro, they are associated with thromboembolic complications. Thrombin generation (TG) is a sensitive global test of coagulation, and elevated TG is associated with thrombosis. Increased TG can be caused by increased prothrombin conversion, decreased thrombin inactivation, or a combination of both. In this study, we measured TG in APS patients and healthy controls with and without vitamin K antagonist (VKA) treatment at 1 and 5 pM tissue factor and with thrombomodulin. Prothrombin conversion and thrombin inactivation were determined by thrombin dynamics analysis. The TG peak was increased in nontreated APS patients at 1 pM TF compared with nontreated controls. Prothrombin conversion was significantly increased in nontreated APS patients. In contrast, prothrombin conversion did not differ in controls and patients that were on VKA therapy. Thrombin inactivation was comparable between controls and APS patients in the presence and absence of VKAs. Both TG (peak and ETP) and prothrombin conversion were significantly higher in APS patients with prior thrombosis compared with patients without a history of thrombosis. In this study, we demonstrate that in APS, the hemostatic balance shifts toward a more prothrombotic phenotype due to elevated prothrombin conversion but unchanged thrombin inactivation rates. Within the group of APS patients, increased TG and prothrombin conversion are associated with a history of thrombosis.

Polyhedrocytes in blood clots of type 2 diabetic patients with high cardiovascular risk: association with glycemia, oxidative stress and platelet activation

Background

Little is known about factors that affect the composition of contracted blood clots in specific diseases. We investigated the content of polyhedral erythrocytes (polyhedrocytes) formed in blood clots and its determinants in type 2 diabetes (T2D) patients.

Methods

In 97 patients with long-standing T2D [median HbA_1c, 6.4% (interquartile range 5.9–7.8)], we measured in vitro the composition of blood clots, including a clot area covered by polyhedrocytes using scanning electron microscopy and the erythrocyte compression index (ECI), defined as a ratio of the mean polyhedrocyte area to the mean native erythrocyte area. Moreover, plasma fibrin clot permeability (K_s), clot lysis time (CLT), thrombin generation, oxidative stress [total protein carbonyl (total PC), total antioxidant capacity and thiobarbituric acid reactive substances (TBARS)], and platelet activation markers were determined. The impact of glucose concentration on polyhedrocytes formation was assessed in vitro.

Results

Polyhedrocytes content in contracted clots was positively correlated with glucose (r = 0.24, p = 0.028), glycated hemoglobin (r = 0.40, p = 0.024), total cholesterol (r = 0.22, p = 0.044), TBARS (r = 0.60, p = 0.0027), P-selectin (r = 0.54, p = 0.0078) and platelet factor-4, PF4 (r = 0.59, p = 0.0032), but not with thrombin generation, platelet count, K_s or CLT. Patients who formed more polyhedrocytes (≥ 10th percentile) (n = 83, 85.6%) had higher glucose (+ 15.7%, p = 0.018), fibrinogen (+ 16.6%, p = 0.004), lower red blood cell distribution width (RDW, − 8.8%, p = 0.034), reduced plasma clot density (− 21.8% K_s, p = 0.011) and impaired fibrinolysis (+ 6.5% CLT, p = 0.037) when compared to patients with lesser amount of polyhedrocytes (< 10th percentile). ECI and the content of polyhedrocytes were strongly associated with total PC (r = 0.79, p = 0.036 and r = 0.67, p = 0.0004, respectively). In vitro an increase of glucose concentration by 10 mmol/L was associated with 94% higher polyhedrocytes content (p = 0.033) when compared to the baseline (7.1 mM). After adjustment for age, sex and fibrinogen, multiple regression analysis showed that RDW was the only independent predictor of polyhedrocytes content in T2D (OR = 0.61, 95% CI 0.39–0.92).

Conclusions

Poor glycemic control, together with enhanced platelet activation and oxidative stress, increase the content of polyhedrocytes in blood clots generated in T2D patients.

Electronic supplementary material

The online version of this article (10.1186/s12933-018-0789-6) contains supplementary material, which is available to authorized users.

Increased blood levels of cellular fibronectin in asthma: Relation to the asthma severity, inflammation, and prothrombotic blood alterations

BACKGROUND

Recently, we have reported that asthma is characterized by prothrombotic blood alterations, which were related to the low-grade inflammatory state. Inflammation, however, may also lead to vascular dysfunction. The aim of this study was to evaluate plasma levels of cellular fibronectin (cFN), a marker of vascular injury in asthmatics, and to analyze their impact on described previously prothrombotic blood alterations.

METHODS

In a cross-sectional study, we investigated 164 adult stable asthmatics and 72 matched controls. Plasma cFN was measured using an ELISA. Its relations to inflammation, thrombin generation, fibrinolytic capacity, expressed as clot lysis time (CLT), and platelet markers were evaluated.

RESULTS

Asthma was associated with 50.1% higher plasma cFN levels as compared with controls (p < 0.001, after adjustment for potential confounders). There was a positive association of cFN with asthma severity and inverse with the FEV₁/VC index (β = 0.2 [95%CI:0.13-0.28] and β = -0.15 [95%CI: -0.23 to -0.07], respectively). In asthmatics cFN positively correlated with high-sensitivity C-reactive protein (β = 0.24 [95%CI:0.16-0.32]), fibrinogen (β = 0.13 [95%CI:0.04-0.21]), interleukin-6 (β = 0.23 [95%CI:0.15-0.3]), platelet factor 4 (β = 0.14 [95%CI:0.06-0.21]), plasminogen (β = 0.11 [95%CI:0.04-0.19]) and CLT (β = 0.35 [95%CI:0.28-0.42]). In both groups cFN was related to the endogenous thrombin potential (ETP) (β = 0.51 [95%CI:0.44-0.57], and β = 0.17 [95%CI:0.07-0.27], respectively). Multiple regression models showed that cFN was the most potent independent predictor of both ETP and CLT in asthmatics.

CONCLUSION

Presented study is the first to show increased plasma cellular fibronectin in asthma, which is associated with disease severity, inflammation, and prothrombotic blood alterations. This novel observation suggests a previously unknown modulator of prothrombotic plasma properties in asthmatics.

A reduction of prothrombin conversion by cardiac surgery with cardiopulmonary bypass shifts the haemostatic balance towards bleeding

Cardiac surgery with cardiopulmonary bypass (CPB) is associated with blood loss and post-surgery thrombotic complications. The process of thrombin generation is disturbed during surgery with CPB because of haemodilution, coagulation factor consumption and heparin administration. We aimed to investigate the changes in thrombin generation during cardiac surgery and its underlying pro- and anticoagulant processes, and to explore the clinical consequences of these changes using in silico experimentation. Plasma was obtained from 29 patients undergoing surgery with CPB before heparinisation, after heparinisation, after haemodilution, and after protamine administration. Thrombin generation was measured and prothrombin conversion and thrombin inactivation were quantified. In silico experimentation was used to investigate the reaction of patients to the administration of procoagulant factors and/or anticoagulant factors. Surgery with CPB causes significant coagulation factor consumption and a reduction of thrombin generation. The total amount of prothrombin converted and the rate of prothrombin conversion decreased during surgery. As the surgery progressed, the relative contribution of α2-macroglobulin-dependent thrombin inhibition increased, at the expense of antithrombin-dependent inhibition. In silico restoration of post-surgical prothrombin conversion to pre-surgical levels increased thrombin generation excessively, whereas co-administration of antithrombin resulted in the normalisation of post-surgical thrombin generation. Thrombin generation is reduced during surgery with cardiopulmonary bypass because of a balance shift between prothrombin conversion and thrombin inactivation. According to in silico predictions of thrombin generation, this new balance increases the risk of thrombotic complications with prothrombin complex concentrate administration, but not if antithrombin is co-administered.

Low paediatric thrombin generation is caused by an attenuation of prothrombin conversion

Thrombin generation (TG) is decreased in children. TG is determined by two underlying processes: the conversion of prothrombin to thrombin and the inactivation of thrombin. Therefore, lower TG capacity in children can either be caused by a reduction of prothrombin conversion, an increase of thrombin inactivation, or both. In 36 children and 8 adults, TG and the factors that determine thrombin inactivation (antithrombin, α2 Macroglobulin (α2M) and fibrinogen) were measured. Prothrombin conversion, thrombin inhibitor complex formation, and the overall thrombin decay capacity were determined. In silico modelling was performed to determine the contribution prothrombin conversion and thrombin inactivation to deviant paediatric TG. Both the amount of prothrombin converted and the maximal prothrombin conversion rate are significantly reduced in children as compared to adults. This is partly due to the prothrombin levels being lower and partly to a lower prothrombin conversion rate. The overall thrombin decay capacity is not significantly different in children, but α2Macroglobulin plays a more important role than it does in adults. In silico experiments demonstrate that reduced prothrombin conversion and to a lesser extent elevated α2M levels provide an explanation for low TG in children. Young age has a dual effect on prothrombin conversion. Lower plasma prothrombin levels result in decreased prothrombin conversion but the rate of prothrombin conversion is also decreased, i. e. the development of prothrombinase is lower than in adults.

Impaired fibrinolysis and lower levels of plasma α2-macroglobulin are associated with an increased risk of severe asthma exacerbations

Recently we have reported that asthma is associated with enhanced plasma thrombin formation, impaired fibrinolysis and platelet activation. In the present study we investigated whether described prothrombotic blood alterations might predispose to thromboembolic events or asthma exacerbations. In 164 adult asthmatics we assessed clinical events during 3-year follow-up and analyzed their associations with measured at baseline prothrombotic blood parameters. Data were obtained from 157 (95.7%) of the asthma patients. We documented 198 severe asthma exacerbations (64/year), which occurred in 53 subjects (34%). These patients were older (p = 0.004), had worse asthma control (p = 0.02) and lower spirometry values (p = 0.01), at baseline. Interestingly, this subgroup had longer clot lysis time (CLT), as well as lower α₂-macroglobulin (p = 0.038 and p = 0.04, respectively, after adjustment for potential confounders). Increased CLT and lower α₂-macroglobulin were demonstrated as independent predictors of asthma exacerbation in multiple regression model. Moreover, we documented two episodes of deep vein thrombosis (1.3%), and eight acute coronary syndromes (5.1%). Patients who experienced thromboembolic events (n = 10, 6.4%, 2.1%/year) had lower α₂-macroglobulin (p = 0.04), without differences in efficiency of fibrinolysis and thrombin generation. Impaired fibrinolysis and lower levels of α₂-macroglobulin might predispose to a higher rate of asthma exacerbations, suggesting new links between disturbed hemostasis and asthma.

Decreased prothrombin conversion and reduced thrombin inactivation explain rebalanced thrombin generation in liver cirrhosis

Impaired coagulation factor synthesis in cirrhosis causes a reduction of most pro- and anticoagulant factors. Cirrhosis patients show no clear bleeding or thrombotic phenotype, although they are at risk for both types of hemostatic event. Thrombin generation (TG) is a global coagulation test and its outcome depends on underlying pro- and anticoagulant processes (prothrombin conversion and thrombin inactivation). We quantified the prothrombin conversion and thrombin inactivation during TG in 30 healthy subjects and 52 Child-Pugh (CP-) A, 15 CP-B and 6 CP-C cirrhosis patients to test the hypothesis that coagulation is rebalanced in liver cirrhosis patients. Both prothrombin conversion and thrombin inactivation are reduced in cirrhosis patients. The effect on pro- and anticoagulant processes partially cancel each other out and as a result TG is comparable at 5 pM tissue factor between healthy subjects and patients. This supports the hypothesis of rebalanced hemostasis, as TG in cirrhosis patients remains within the normal range, despite large changes in prothrombin conversion and thrombin inactivation. Nevertheless, in silico analysis shows that normalization of either prothrombin conversion or thrombin inactivation to physiological levels, by for example the administration of prothrombin complex concentrates would cause an elevation of TG, whereas the normalization of both simultaneously maintains a balanced TG. Therefore, cirrhosis patients might require adapted hemostatic treatment.

Factor XIII deficiency enhances thrombin generation due to impaired fibrin polymerization - An effect corrected by Factor XIII replacement

INTRODUCTION

Factor XIII (FXIII) cross-links fibrin, completing blood coagulation. Congenital FXIII deficiency is managed with plasma-derived FXIII (pdFXIII) or recombinant FXIII (rFXIII) concentrates.

AIM

As the mechanisms protecting patients with low FXIII levels (<5IU/dL) from spontaneous bleeds remain unknown we assessed the interplay between thrombin generation (TG), fibrin formation and clot kinetics before and after FXIII administration in three patients with FXIII deficiency.

METHODS

Patients received initially rFXIII (35IU/kg, A-subunit) following with pdFXIII at 1250IU or 2500IU (12-30IU/kg) monthly. TG (CAT), thromboelastometry (ROTEM), prothrombin fragments F1+2, fibrinogen and FXIII activity (FXIII:C) were measured at baseline and one-hour recovery.

RESULTS

FXIII was at the target level of 20±6IU/dL at the 4-week trough. rFXIII corrected FXIII to 98±15 and high-dose pdFXIII to a level of 90±6, whereas low-dose/half dose pdFXIII reached 45±4IU/dL. Although fibrinogen (Clauss Method) was normal, coagulation in FIBTEM was impaired, which FXIII administration tended to correct. CAT implied 1.6- to 1.9-fold enhanced TG, which FXIII administration normalized. Inhibition of fibrin polymerization by Gly-Pro-Arg-Pro peptide mimicked FXIII deficiency in CAT by enhancing TG both in control and FXIII recovery plasma. Antithrombin, α2-macroblobulin-thrombin complex and prothrombin were normal, whereas F1+2 were elevated compatible with in vivo TG.

DISCUSSION

FXIII deficiency impairs fibrinogen function and fibrin formation simultaneously enhancing TG on the poorly polymerizing fibrin strands, when fibrin's antithrombin I -like function is absent. Our study suggests an inverse link between low FXIII levels and enhanced TG modifying structure-function relationship of fibrin to support hemostasis.

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.

Strenuous exercise induces a hyperreactive rebalanced haemostatic state that is more pronounced in men

Physical exercise is recommended for a healthy lifestyle. Strenuous exercise, however, may trigger the haemostatic system, increasing the risk of vascular thrombotic events and the incidence of primary cardiac arrest. Our goal was to study the effects of strenuous exercise on risk factors of cardiovascular disease. Blood was collected from 92 healthy volunteers who participated in the amateur version of the pro-tour Amstel Gold cycling race, before and directly after the race. Thrombin generation showed a shortening of the lag time and time to peak and an increase of the velocity index. Interestingly, the endogenous thrombin potential measured in plasma decreased due to reduced prothrombin conversion. Platelet reactivity increased and this effect was stronger in men than in women. Lower fibrinogen and higher D-dimer levels after exercise indicated higher fibrin formation. On the other hand, fibrinolysis was also elevated as indicated by a shortening of the clot lysis time. Exercise activated the endothelium (von Willebrand factor (VWF) and active VWF levels were elevated) and the immune system (concentrations IL-6, IL-8, MCP-1, RANTES and PDGF increased). Additionally, an increased cardiac troponin T level was measured post-exercise. Strenuous exercise induces a temporary hyperreactive state in the body with enhanced pro- and anticoagulant responses. As strenuous exercise has a more pronounced effect on platelet function in male subjects, this gives a possible explanation for the higher incidence of sudden cardiac death during exercise compared to women. This trial is registered at www.clinicaltrials.gov as NCT02048462.

Comparison of platelet-derived and plasma factor VIII efficacy using a novel native whole blood thrombin generation assay

BACKGROUND

We have recently developed a successful gene therapy approach for hemophilia A in which factor VIII (FVIII) expression is targeted to platelets by the αIIb promoter. Levels of platelet-expressed FVIII (2bF8) achieved by gene therapy may vary between individuals due to differences in ex vivo transduction and gene expression efficiency. Accurate assays to evaluate 2bF8 efficacy are desirable.

OBJECTIVE

To compare the hemostatic efficacy of 2bF8 with replacement therapy over a wide therapeutic dose range.

METHODS

Efficacy of 2bF8 was assessed using a new transgenic mouse model expressing high 2bF8 levels (LV18(tg) ). Blood from LV18(tg) mice or FVIII(null) mice infused with recombinant FVIII was mixed with FVIII(null) blood at different ratios ex vivo to achieve several concentrations of 2bF8 or plasma FVIII. Samples were evaluated with a novel native whole blood thrombin generation assay that uses recalcified whole blood without the addition of tissue factor to initiate coagulation.

RESULTS

FVIII dose dependency was observed in all five thrombin generation parameters. While the total amount of thrombin generated was similar, 2bF8 significantly accelerated thrombin generation compared with plasma FVIII. Remarkably, a 10-fold lower dose of 2bF8 than plasma FVIII (0.2% vs. 2%) significantly shortened the onset and peak of thrombin generation compared with FVIII(null) blood.

CONCLUSION

Using a new transgenic mouse model, we showed that the novel native whole blood thrombin generation assay established here can be used to monitor platelet targeted FVIII gene therapy. The higher therapeutic efficacy of 2bF8 compared with factor replacement therapy seemed to be due to acceleration of thrombin generation.