Tissue Factor-Independent Coagulation Correlates with Clinical Phenotype in Factor XI Deficiency and Replacement Therapy

Abstract

Background In factor XI (FXI) deficiency, bleeding cannot be predicted by routine analyses. Since FXI is involved in tissue factor (TF)-independent propagation loop of coagulation, we hypothesized that investigating the spatiotemporal separated phases of coagulation (TF-dependent and -independent) could improve diagnostics. Objectives This article investigates the correlation of parameters describing TF-dependent and -independent coagulation with the clinical phenotype of FXI deficiency and their ability to assess hemostasis after FXI replacement. Methods We analyzed: (1) plasma from healthy controls (n = 53); (2) normal plasma (n = 4) spiked with increasing concentrations of a specific FXI inhibitor (C7P); (3) plasma from FXI-deficient patients (n = 24) with different clinical phenotypes (13 bleeders, 8 non-bleeders, 3 prothrombotics); (4) FXI-deficient plasma spiked with FXI concentrate (n = 6); and (5) plasma from FXI-deficient patients after FXI replacement (n = 7). Thrombin generation was measured with the reference method calibrated automated thrombogram and with Thrombodynamics (TD), a novel global assay differentiating TF-dependent and -independent coagulation. Results C7P dose-dependently decreased FXI activity, prolonged activated partial thromboplastin time, and hampered TF-independent coagulation. In FXI-deficient bleeders, TD parameters describing TF-independent propagation of coagulation and fibrin clot formation were reduced compared with controls and FXI-deficient nonbleeders and increased in FXI-deficient patients with prothrombotic phenotype. Receiver operating characteristic analysis indicated that TF-independent parameters were useful for discriminating FXI-deficient bleeders from non-bleeders. In FXI-deficient plasma spiked with FXI concentrate and in patients receiving FXI replacement, TD parameters were shifted toward hypercoagulation already at plasma FXI levels around 20%. Conclusion TF-independent coagulation parameters assessed by TD have the potential to identify the clinical phenotype in FXI-deficient patients and to monitor FXI replacement therapy.

How to Capture the Bleeding Phenotype in FXI-Deficient Patients

“…Global TG assays have been used to assess hemostatic potential after FXI replacement with FXI concentrates. 44,57,58 In general, these studies showed that after in vitro spiking of FXI-deficient plasma or after infusion of FXI concentrate in patients, TG was improved. Of note, after the infusion of FXI concentrate, TF-independent parameters measured ex vivo by TD assay shifted toward hypercoagulation at levels of FXI of about 30%.…”

“…TF þ , presence of tissue factor; TF À , absence of tissue factor. cohort of 24 FXI-deficient individuals, Bertaggia Calderara et al 44 could observed that FXI-deficient bleeders were characterized by a significant lower TG and clot formation rate in the TF-independent phase of coagulation. An algorithm based on combinatorial ROC analysis of TG and fibrin clot formation parameters could identify all of the FXI-deficient patients with bleeding phenotype and 82% of FXI patients without bleeding symptoms.…”

“…The studies from Zucker et al, 39 Guéguen et al, 40 and Bertaggia Calderara et al 44 found that TG measured by CAT assay in PPP using TF at 1 pM could not discriminate between FXI-deficient bleeder and non-bleeder individuals. Of note, Zucker et al 39 used CTI in collecting tubes to prevent contact activation, while Guéguen et al 40 and Bertaggia Calderara et al 44 did not.…”

“…Identification of FXI clinical phenotype by CAT assay has produced conflictual results (summarized in ►Table 1). [39][40][41][42][43][44][45] This may be explained by the different criteria used to classify patients in bleeders or non-bleeders and by the various experimental conditions used to measure TG. Standard bleeding scores are inadequate for predicting bleeding risk in FXIdeficient patients.…”

“…Of note, Pike et al 49 found that if the assay was performed in PRP þ CTI, FXI-deficient bleeders had a longer clot formation time with decreased velocity of fibrin generation, which is in agreement with studies using other assays. 39,41,44 Turbidimetric assay is a quite accessible technique and is performed in citrated CTI-treated PPP, in the presence of low TF concentration and recalcification. The assay can be done in the presence of tissue plasminogen activator (tPA) to monitor fibrinolysis; readings are done in a plate reader with absorbance at 405 nm and monitoring of turbidity allows building a clot formation/fibrinolysis curve, characterized by several parameters (onset of clot formation, clot formation rate, time to peak, peak turbidity change, and area under the curve).…”