In vivo thrombin generation and subsequent APC formation are increased in factor V Leiden carriers

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.

Characterization of circulating thrombin in patients with septic shock: a prospective observational study

Septic shock is characterized by a dysregulated response to infection, hypotension and activation of the coagulation system. Markers of coagulation activation are commonly used to diagnose and monitor ensuing coagulopathies. In this study, we sought to determine levels of circulating thrombin in patients with septic shock. To characterize levels of circulating, active thrombin in patients with septic shock. 48 patients with septic shock were included in this prospective, observational study. Blood samples were obtained on admission, day 1, day 3 and day 6. Levels of active thrombin were measured using a standardized, clinically applicable oligonucleotide (aptamer)-based enzyme-capture assay (OECA). Thrombin levels were correlated with established indirect thrombin parameters, conventional coagulation tests, laboratory parameters, patient characteristics and outcome. Elevated levels of thrombin were detected in 27 patients (56.3%) during the course of the study. Thrombin levels were positively correlated with thrombin-antithrombin complexes (r = 0.30, p < 0.05) and negatively associated with FVII levels (r = - 0.28, p < 0.05). Thrombin levels on admission did not predict 30-day mortality (OR 0.82, 95% CI 0.23-2.92, p = 0.77). Circulating levels of active thrombin can be measured in a subset of patients with septic shock. Although thrombin levels are correlated with established markers of coagulation, they do not provide additional prognostic information.

Activated Factor XI is Increased in Plasma in Response to Surgical Trauma but not to Recombinant Activated FVII-Induced Thrombin Formation

Aim: Feedback activation of factor XI (FXI) by thrombin is believed to play a critical role in the amplification phase of thrombin generation and to contribute to thrombosis development and hemostasis. However, the activation of FXI by thrombin has been shown in vitro to require a cofactor. In this study, the role of thrombin in activated FXI (FXIa) formation in vivo is investigated.

Methods: The study population comprised probands in whom coagulation activation was triggered by low-dose (15 µg/kg) recombinant activated factor VII (rFVIIa, n =89), of whom 34 with (VTE+) and 45 without a history of venous thromboembolism (VTE−), and patients undergoing major orthopedic surgeries ( n =45). FXIa was quantified via an enzyme capture assay using a monoclonal FXI-specific antibody. Thrombin formation was monitored using an oligonucleotide-based enzyme capture assay and the thrombin activation markers prothrombin fragment 1＋2 (F1＋2) and thrombin–antithrombin complex (TAT).

Results: In the rFVIIa cohort, FXIa and thrombin remained below their lower limit of quantification of 3.48 and 1.06 pmol/L, respectively. By contrast, during the surgeries, median FXIa levels increased from 3.69 pmol/L pre-operatively to 9.41 pmol/L mid-operatively ( P =4·10 ⁻⁴ ) and remained significantly elevated 24 h thereafter, with 9.38 pmol/L ( P =0.001). Peak levels of F1+2 were comparable in the VTE+, VTE−, and surgery cohort (235, 268, and 253 pmol/L), whereas peak TAT levels were higher in the surgery cohort (53.1, 33.9, and 147.6 pmol/L).

Conclusions: Under in vivo conditions, the activation of FXI requires specific local features that are present at the wounded site including potential cofactors of thrombin.

Thrombin generation measurement using the ST Genesia Thrombin Generation System in a cohort of healthy adults: Normal values and variability

BACKGROUND

Thrombin generation (TG) assays evaluate the balance between pro- and anticoagulant forces, to better assess bleeding and thrombotic risks. Although TG readouts obtained with the calibrated automated TG have been investigated in multiple clinical conditions, TG still needs standardization and clinical validation. The automated TG instrument ST Genesia® (STG, Stago, Asnières-sur-Seine, France) provides a normalization of TG parameters based on a reference plasma aiming to reduce the interlaboratory variability and the variability between different measurement runs.

OBJECTIVES

To evaluate STG in a group of healthy adults.

METHODS

Reference intervals in healthy adults and variability of the new standardized reagents for bleeding (BleedScreen) and thrombophilic (ThromboScreen) conditions were determined using STG.

RESULTS

TG was measured in platelet-free plasma (PFP) samples of 123 healthy adults. Reference intervals were determined for TG parameters. Intra- and interassay coefficients of variation were calculated on quality controls and PFP samples from healthy adults. Oral contraception (OC) possibly influenced TG parameters, resulting in a higher median and a broader reference interval for peak height and endogenous thrombin potential (ETP) in women aged 20 to 49 years than in all other sex and age categories. Therefore, we propose the following reference interval categories: men, women aged <50 years not using OC, women aged <50 years using OC, and women aged ≥50 years. Normalization was effective to reduce the interassay variability of quality controls for ETP (BleedScreen assay), and peak height and ETP (ThromboScreen assay without thrombomodulin), but had little impact on PFP sample variability.

CONCLUSION

STG appears suitable for accurate measurement of TG in healthy adults.

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.