Short-term venous stasis induces fibrinolytic activation but not thrombin formation

Fibrinolysis biomarker, thrombin, and activated protein C level alterations after coagulation activation depend on type of thrombophilia and clinical phenotype

Background

Recently, we have shown alterations in the anticoagulant response to recombinant activated factor VII (rFVIIa)-induced coagulation activation in patients with thrombophilia.

Objectives

This study aimed to extend this in vivo model to fibrinolysis biomarkers.

Methods

This interventional in vivo study included 56 patients with thrombophilia and previous venous thromboembolism (VTE+), 38 without VTE (VTE-), and 35 healthy controls. Plasma levels of D-dimer, plasmin-α2-antiplasmin (PAP) complex, and plasminogen activator inhibitor-1 (PAI-1) were monitored for over 8 hours after rFVIIa infusion (15 μg/kg) along with thrombin markers and activated protein C (APC).

Results

Throughout cohorts, median PAP increased by 40% to 52% (P < 3.9 × 10-10) and PAI-1 decreased by 59% to 79% (P < 3.5 × 10-8). In contrast to thrombin-antithrombin (TAT) complex, which also increased temporarily (44% to 115%, P < 3.6 × 10-6), changes in PAP and PAI-1 did not reverse during the observation period. The area under the measurement-time curves (AUCs) of PAP and TAT, which are measures of plasmin and thrombin formation, respectively, were each greater in the VTE+ cohort than in healthy controls (median PAP-AUC = 0.48 vs 0.27 ng·h/L [P = .003], TAT-AUC = 0.12 vs 0.03 nmol·h/L [P = 2.5 × 10-4]) and were correlated with one another (r = 0.554). As evidenced by the respective AUCs, asymptomatic factor (F)V Leiden carriers showed less PAP formation (0.22 vs 0.41 ng·h/L, P = 9 × 10-4), more pronounced PAI-1 decline (0.10 vs 0.18 ng·h/L, P = .01), and increased APC formation (28.7 vs 15.4 pmol·h/L, P = .02) than those within the VTE+ group (n = 19 each).

Conclusion

rFVIIa-induced thrombin formation is associated with fibrinolysis parameter changes outlasting the concomitant anticoagulant response. Both correlate with thrombosis history in FV Leiden and might help explain its variable clinical expressivity.

Ex Vivo Modeling of the PC (Protein C) Pathway Using Endothelial Cells and Plasma: A Personalized Approach

BACKGROUND

The endothelial cell-dependent PC (protein C) pathway is critically involved in the regulation of coagulation, anti-inflammatory, and cytoprotective signaling. Its reactivity shows high interindividual variability, and it contributes to prothrombotic disorders, such as the FVL (factor V Leiden) mutation.

METHODS

Endothelial colony-forming cells (ECFCs) were isolated from heparinized peripheral blood from healthy individuals and FVL carriers. Confluent monolayers of ECFCs were overlaid with plasma, and thrombin formation was initiated by addition of tissue factor (1 pmol/L). Subsequently, thrombin and APC (activated PC) formation rates were measured over time using oligonucleotide-based enzyme capture assays. To induce downregulation of TM (thrombomodulin) expression, ECFCs were stimulated with IL-1β (interleukin 1β). In vivo APC response rates were monitored in study participants after infusion of low-dose rFVIIa (recombinant activated factor VII).

RESULTS

The median peak APC concentration was 1.12 nmol/L in experiments with IL-1β stimulated ECFCs and 3.66 nmol/L without IL-1β. Although thrombin formation rates were comparable, APC formation rates were significantly higher in FVL carriers (n=6) compared to noncarriers (n=5) as evidenced by a higher ratio between the area under the curve of APC generation to the area under the curve of thrombin generation (median 0.090 versus 0.031, P=0.017). These ex vivo results were correlated with an increased APC response to rFVIIa-induced thrombin formation in FVL carriers in vivo.

CONCLUSIONS

Patient-specific ex vivo modeling of the PC pathway was achieved using blood-derived ECFCs. The correlation between in and ex vivo APC response rates confirms that the autologous PC model accurately depicts the in vivo situation.

Search for Venous Endothelial Biomarkers Heralding Venous Thromboembolism in Space: A Qualitative Systematic Review of Terrestrial Studies

Background: The recent discovery of a venous thrombosis in the internal jugular vein of an astronaut has highlighted the need to predict the risk of venous thromboembolism in otherwise healthy individuals (VTE) in space. Virchow’s triad defines the three classic risk factors for VTE: blood stasis, hypercoagulability, and endothelial disruption/dysfunction. Among these risk factors, venous endothelial disruption/dysfunction remains incompletely understood, making it difficult to accurately predict risk, set up relevant prophylactic measures and initiate timely treatment of VTE, especially in an extreme environment.

Methods: A qualitative systematic review focused on endothelial disruption/dysfunction was conducted following the guidelines produced by the Space Biomedicine Systematic Review Group, which are based on Cochrane review guidelines. We aimed to assess the venous endothelial biochemical and imaging markers that may predict increased risk of VTE during spaceflight by surveying the existing knowledge base surrounding these markers in analogous populations to astronauts on the ground.

Results: Limited imaging markers related to endothelial dysfunction that were outside the bounds of routine clinical practice were identified. While multiple potential biomarkers were identified that may provide insight into the etiology of endothelial dysfunction and its link to future VTE, insufficient prospective evidence is available to formally recommend screening potential astronauts or healthy patients with any currently available novel biomarker.

Conclusion: Our review highlights a critical knowledge gap regarding the role biomarkers of venous endothelial disruption have in predicting and identifying VTE. Future population-based prospective studies are required to link potential risk factors and biomarkers for venous endothelial dysfunction to occurrence of VTE.

Thrombophilia screening revisited: an issue of personalized medicine

Clinical thrombophilia is the consequence of multiple gene and/or environment interactions. Thrombophilia screening requires a targeted patient with specific indication, in which a finding would have implications. Carrying out a thrombophilia examination in the physician's practice is often a cause of uncertainty and concern. The concerns begin in choosing the right patient to be examined, are associated with the time of investigation, with the choice of analysis, the test-material and with the correct interpretation of the results. Difficulties, which can influence the results, can occur with both organization and blood sampling. As common for any analysis, pre-analytical, analytical and post-analytical factors should be considered, as well as the possibility of false positive or false negative results. Finally, recommendation of correct therapeutic and prophylactic measures for the patient and his relatives is an additional focus. In this article we want to provide-on the basis of the evidence and personal experience-the theory of thrombophilia-investigation, the indications for testing, as well as practical recommendations for treatment options.

Simulated Hypergravity Activates Hemostasis in Healthy Volunteers

Background

Hypergravity may promote human hemostasis thereby increasing thrombotic risk. Future touristic suborbital spaceflight will expose older individuals with chronic medical conditions, who are at much higher thromboembolic risk compared with professional astronauts, to hypergravity. Therefore, we tested the impact of hypergravity on hemostasis in healthy volunteers undergoing centrifugation.

Methods and Results

We studied 20 healthy seated men before and after 15 minutes under 3 Gz hypergravity on a long‐arm centrifuge. We obtained blood samples for hemostasis testing before, immediately after, and 30 minutes after centrifugation. Tests included viscoelastic thromboelastometry, platelet impedance aggregometry, endothelial activation markers, blood rheology testing, microparticle analyses, and clotting factor analysis. Exposure to hypergravity reduced plasma volume by 12.5% (P=0.002) and increased the red blood cell aggregation index (P<0.05). With hypergravity, thrombelastographic clotting time of native blood shortened from 719±117 seconds to 628±89 seconds (P=0.038) and platetet reactivity increased (P=0.045). Hypergravity shortened partial thromboplastin time from 28 (26–29) seconds to 25 (24–28) seconds (P<0.001) and increased the activity of coagulation factors (eg, factor VIII 117 [93–134] versus 151 [133–175] %, P<0.001). Tissue factor concentration was 188±95 pg/mL before and 298±136 pg/mL after hypergravity exposure (P=0.023). Antithrombin (P=0.005), thrombin‐antithrombin complex (P<0.001), plasmin‐alpha2‐antiplasmin complex (0.002), tissue‐plasminogen activatior (P<0.001), and plasminogen activator inhibitor‐1 (P=0.002) increased with centrifugation. Statistical adjustment for plasma volume attenuated changes in coagulation.

Conclusions

Hypergravity triggers low‐level hemostasis activation through endothelial cell activation, increased viscoelasticity, and augmented platelet reactivity, albeit partly counteracted through endogenous coagulation inhibitors release. Hemoconcentration may contribute to the response.

Venous stasis-induced fibrinolysis prevents thrombosis in mice: role of α2-antiplasmin

Stasis of venous blood triggers deep vein thrombosis by activating coagulation, yet its effects on the fibrinolytic system are not fully understood. We examined the relationship between stasis, fibrinolysis, and the development of experimental venous thrombosis. Effects of stasis-induced deep vein thrombosis and fibrinolysis on thrombosis were examined by inferior vena cava ligation in congenic mice with and without α2-antiplasmin (α2AP), the primary inhibitor of plasmin. Venous thrombus weights were measured and thrombus composition was determined by Martius scarlet blue and immunofluorescence staining. Venous thrombi from α2AP^+/+ mice contained plasminogen activators, plasminogen activator inhibitor-1, plasminogen, and α2AP, which changed with thrombus age. Normal, α2AP^+/+ mice developed large, occlusive thrombi within 5 hours after ligation; thrombi were even larger in plasminogen-deficient mice (P < .001). No significant thrombus formation was seen in α2AP^-/- mice (P < .0001) or in α2AP^+/+ mice treated with an α2AP-inactivating antibody (P < .001). Venous stasis activated fibrinolysis, measured by D-dimer levels, in α2AP^-/- mice vs α2AP^+/+ mice (P < .05). Inhibition of fibrinolysis by the indirect plasmin inhibitor ε-aminocaproic acid or by α2AP restored thrombosis in α2AP^-/- mice. In addition to its effects on acute thrombosis, thrombus formation was also markedly suppressed in α2AP^-/- mice vs α2AP^+/+ mice (P < .0001) 1, 7, and 14 days after ligation. We conclude that experimental venous stasis activates the fibrinolytic system to block the development of venous thrombosis. Suppression of fibrinolysis by α2AP appears essential for stasis-induced thrombus development, which suggests that targeting α2AP may prove useful for preventing venous thrombosis.

Increased Activated Protein C Response Rates Reduce the Thrombotic Risk of Factor V Leiden Carriers But Not of Prothrombin 20210G>A Carriers

RATIONALE

Carriers of the most common prothrombotic mutations FVL (factor V Leiden) and FII (prothrombin) 20210G>A show a highly variable clinical phenotype. Using standardized in vivo coagulation activation followed by activity pattern analysis we have recently shown, that the FVL mutation accelerates thrombin and APC (activated protein C) formation in carriers without a history of venous thromboembolism (VTE).

OBJECTIVE

The aim of this prospective cohort study was to investigate, if the FII 20210G>A mutation induces a similar reaction pattern, and if the response rates differ in FVL and FII 20210G>A mutation carriers with prior VTE (VTE+).

METHODS AND RESULTS

We comparatively analyzed 30 FVL carriers, 28 FII 20210G>A carriers (thereof 13 VTE+ each) and 15 healthy controls. Changes in plasma levels of thrombin, prothrombin activation fragment 1+2 (F1+2), TAT (thrombin-antithrombin complex), APC, and D-dimer were monitored over 8 hours after infusion of recombinant factor VIIa (15 µg/kg). An increase of F1+2 and TAT levels was observed, that did neither differ between FVL and FII 20210G>A carriers nor between asymptomatic and VTE+ carriers of these mutations. Median plasma levels of APC increased more (P=0.008) in FVL carriers (from 1.39 to 7.79 pmol/L) than in FII 20210G>A carriers (from 1.03 to 5.79 pmol/L), and more in FII 20210G>A carriers (P=2×10^-4) than in healthy controls (from 0.86 to 3.00 pmol/L). Most importantly, however, the APC response was greater (P=0.015) in asymptomatic (n=13) than in VTE+ (n=12) heterozygous FVL carriers, with an increase of APC levels from 1.44 to 8.11 pmol/L versus 1.27 to 5.62 pmol/L.

CONCLUSIONS

These in vivo data demonstrate that the FII 20210G>A and FVL mutations share an intermediate phenotype that is characterized by increased thrombin formation after coagulation activation. Furthermore, our data support the conclusion that the APC activating capacity of FVL carriers modifies the thrombotic risk of this common prothrombotic mutation.