Antithrombin Deficiency Is Associated with Prothrombotic Plasma Fibrin Clot Phenotype

Abstract

Background: Deficiency of antithrombin increases risk of venous thromboembolism. We hypothesized that antithrombin deficiency affects fibrin clot structure and function.

Methods: We evaluated 148 patients (age: 38 [32-50] years; 70% women) with genetically confirmed antithrombin deficiency and 50 healthy controls. Fibrin clot permeability (K_s) and clot lysis time (CLT) along with thrombin generation capacity were assessed before and after antithrombin activity normalization in vitro.

Results: Antithrombin-deficient patients had lower antithrombin activity (-39%) and antigen levels (-23%) compared with controls (both p < 0.01). Prothrombin fragment 1 + 2 levels were 26.5% higher in patients with antithrombin deficiency than in controls along with 94% increased endogenous thrombin potential (ETP) and 108% higher peak thrombin (all p < 0.01). Antithrombin deficiency was associated with 18% reduced K_s and 35% prolonged CLT (both p < 0.001). Patients with type I (n = 65; 43.9%) compared with type II antithrombin deficiency (n = 83; 56.1%) had 22.5% lower antithrombin activity (p < 0.001) and despite similar fibrinogen levels, 8.4% reduced K_s, 18% prolonged CLT, and 30% higher ETP (all p < 0.01). Reduced K_s was associated with lower antithrombin antigen level (β = - 6.1, 95% confidence interval [CI]: -1.7 to -10.5), while prolonged CLT was associated with lower antithrombin antigen (β = - 69.6, 95% CI: -9.6 to -129.7), activity (β = - 2.4, 95% CI: -0.3 to -4.5), higher PAI-1 (β = 12.1, 95% CI: 7.7-16.5), and thrombin-activatable fibrinolysis inhibitor levels (β = 3.8, 95% CI: 1.9-5.7). Addition of exogenous antithrombin reduced ETP (-42%) and peak thrombin (-21%), and improved K_s (+8%) and CLT (-12%; all p < 0.01).

Conclusion: Our study suggests that enhanced thrombin generation and prothrombotic plasma fibrin clot phenotype can contribute to increased risk of thrombosis in patients with antithrombin deficiency.

Fig. 1

Fibrin clot permeability (K _s ) ( A ) and clot lysis time (CLT) ( B ) in patients with type I compared with type II antithrombin deficiency, and endogenous thrombin potential (ETP) ( C ) and CLT ( D ) in antithrombin-deficient patients with previous VTE compared with those without VTE history. VTE, venous thromboembolism.

Fig. 2

Antithrombin (AT) activity ( p < 0.0001 for ANOVA) ( A ), AT antigen (p = 0.99 for ANOVA) ( B ), fibrin clot permeability (K _s , p = 0.0039 for ANOVA) ( C ), and clot lysis time (CLT; p = 0.001 for ANOVA) ( D ) in antithrombin-deficient patients with different types of mutation in the SERPINC1 gene.

Fig. 3

Representative scanning electron microscopy micrographs of fibrin clot prepared from citrated plasma obtained from healthy control ( A ) and patients with type I ( B ) or type II ( C ) antithrombin deficiency with similar fibrinogen levels (2.79–2.83). Magnification: 5,000× and 10,000 × ; scale bar: 5 and 2 µm.

Fig. 4

Abnormal fibrin fibers present in clots of a subset of antithrombin-deficient patients. Magnification: 10,000 × , scale bar: 2 µm.

Fig. 5

Fibrin clot permeability (K _s ) ( A ) and clot lysis time (CLT) ( B ) after normalization of antithrombin (AT) activity. Data compared using the Wilcoxon signed-rank test.

Fig. 6

A dose-dependent effect of antithrombin addition on ( A ) endogenous thrombin potential (ETP) and ( B ) peak thrombin (both p for trend <0.001).

Fig. 7

A dose-dependent effect on K _s ( A ) and CLT ( B ) after antithrombin addition to commercial normal citrated human plasma immunodepleted of antithrombin (fibrinogen concentration: 2.82 g/L) (both p for trend <0.001). Data are presented as a mean for three experiments.