PB0266 - Procoagulant platelets - unrecognized potential for bleeding prevention in hemophilia A?

Background: In patients with hemophilia A (PWH), bleeding severity generally correlates with the residual FVIII levels. However, different bleeding phenotypes can be observed in patients with equal FVIII levels, suggestion that other parameters may contribute to the variable bleeding phenotype. In this study, we investigate the role of procoagulant platelets (PLTs) in patients with hemophilia.

Aims: Determination of the procoagulant potential to prevent bleeding in patients with hemophilia

Methods: The potential to form procoagulant PLTs was investigated in PWH and healthy controls (HC) by testing CD62p and Annexin-V (PS) double staining and analysis by flow cytometry (FC) in presence of buffer and after stimulation with TRAP/CVX. We also measured thrombin generation (TG) in a calibrated automated thrombinoscope in platelet rich plasma (PRP) and platelet poor plasma (PPP) samples from PWH and controls.

Results: The procoagulant potential of platelets after stimulation with TRAP/CVX (Increase in procoagulant platelets compared to the buffer reaction) in PWH (meanSEM: 55.327.29) are significantly higher compared to healthy controls (HC) (31.974.04, p=0.0076). In TG we demonstrate the influence of this procoagulant potential on thrombin generation by first showing the dependence with the inhibition of lactadherin. In low FVIII environment (<=10%) the lag time (Buffer vs. Lactadherin meanSEM: 5.80.15 vs. 7.290.3, p=0.0037) and time to peak (ttpeak) (23.961.4 vs. 38.93.9, p=0.0148) are significantly prolonged and the thrombin peak is significantly lower (p=0.0095) compared to normal factor levels. In HC lag time and ttpeak are were not affected by PS inhibition (data p=0.3, and p=0.07, respectively) indicating that the PS dependency is stronger in low FVIII environments. Activation of PRP samples with TRAP-6+CVX heightened the TG of HC, as well as in PWH.

Conclusion(s): A high proportion of procoagulant platelet formation improves TG in hemophilia patients. This indicates a crucial role of procoagulant PLTs in allowing hemophilia patients to compensate their FVIII deficiency.