Emicizumab Augments Thrombus Formation in Whole Blood from Patients with Hemophilia A under High Shear Flow Conditions

The Evaluation of Clot Waveform Analyses for Assessing Hypercoagulability in Patients Treated with Factor VIII Concentrate

BACKGROUND

Regular prophylactic therapy has become an increasingly common treatment for severe hemophilia. Therefore, hypercoagulability-a potential risk factor of thrombosis-is a cause for concern in hemophilic patients treated with a high dose of FVIII concentrate. In clot waveform analysis (CWA)-thrombin time (TT), a small amount of thrombin activates clotting factor VIII (FVIII) instead of fibrinogen, resulting in FVIII measurements using CWA-TT with a small amount of thrombin.

METHODS

The coagulation ability of patients treated with FVIII concentrate or emicizumab was evaluated using activated partial thromboplastin time (APTT), TT and a small amount of tissue factor-induced FIX activation assay (sTF/FIXa) using CWA.

RESULTS

The FVIII activity based on CWA-TT was significantly greater than that based on the CWA-APTT or chromogenic assay. FVIII or FVIII-like activities based on the three assays in plasma without emicizumab were closely correlated; those in plasma with emicizumab based on CWA-TT and chromogenic assays were also closely correlated. CWA-APTT and CWA-TT showed different patterns in patients treated with FVIII concentrates compared to those treated with emicizumab. In particular, CWA-TT in patients treated with FVIII concentrate showed markedly higher peaks in platelet-rich plasma than in platelet-poor plasma. CWA-APTT showed lower coagulability in hemophilic patients treated with FVIII concentrate than in healthy volunteers, whereas CWA-sTF/FIXa did not. In contrast, CWA-TT showed hypercoagulability in hemophilic patients treated with FVIII concentrate.

CONCLUSIONS

CWA-TT can be used to evaluate the thrombin bursts that cause hypercoagulability in patients treated with emicizumab. Although routine APTT evaluations demonstrated low coagulation ability in patients treated with FVIII concentrate, CWA-TT showed hypercoagulability in these patients, suggesting that the evaluation of coagulation ability may be useful when using multiple assays.

Emicizumab enhances thrombus formation in vitro under high shear flow conditions in whole blood from patients with type 1 and type 3 von Willebrand disease

INTRODUCTION

Type 1 and type 3 von Willebrand disease (VWD) are caused by partial and complete, quantitative deficiency of von Willebrand factor (VWF), respectively, and factor (F)VIII/VWF complex concentrates are used for haemostatic treatment. Emicizumab, mimics activated FVIII, reduces bleeding in haemophilia A patients. The effects of emicizumab on haemostasis in both types of VWD remain to be fully established, however.

AIM

To examine the effects of emicizumab on thrombogenesis in type 1 and type 3 VWD.

PATIENTS/METHODS

Perfusion chamber experiments under high shear conditions (2500 s^-1 ) combined with immunostaining were performed using whole blood samples from patients with type 1 (VWF:Ag 25 U/dl) and type 3 VWD (<1.0 U/dl).

RESULTS

The addition of FVIII (1 U/ml) to type 1 blood did not affect thrombus formation, whilst supplementation with VWF (1.6 U/ml) or FVIII/VWF (1 U/ml/1.6 U/ml) enhanced thrombogenesis to a similar extent. FVIII/VWF promoted thrombus formation significantly more than VWF alone, however, in type 3 blood. Emicizumab (100 μg/ml) augmented thrombus formation in type 3 blood compared to FVIII, and this potency seemed to be somewhat greater than that of VWF. Surface coverage of formed thrombus in type 3 VWD was less than that in type 1 VWD, but thrombus height was comparable in both. The addition of emicizumab to type 3 blood enhanced thrombin generation and fibrin formation compared to control IgG.

CONCLUSION

Emicizumab promoted mechanisms of thrombus formation in vitro in type 3 and type 1 VWD, suggesting the possibility of alternative therapeutic protocols in these patients.