Procoagulant effect of phosphatidylserine exposed to extracellular vesicles, blood cells and endothelial cells in patients with aortic stenosis

Background The mechanism of thrombotic complications in patients with aortic stenosis (AS) is unknown. Our aim was to evaluate the levels of phosphodiesterase (PS) in blood cells, endothelial cells (ECs), and extracellular vesicles (EVs) and its procoagulant activity (PCA) in different degrees of AS. Methods Exposed PS in blood cells, ECs and EVs were analyzed by flow cytometry. PCA was evaluated by clotting time (CT), intrinsic factor Xa (FXa), extrinsic FXa, thrombin and fibrin formation assays. We also evaluated the inhibitory effects of lactadherin (Lact) and anti-tissue factor (anti-TF) on PCA in severe AS patients. Results Our results demonstrated that positive phosphatedylserin (PS + ) with total EVs, platelet EVs (PEVs), positive tissue factor EVs (TF + EVs), and endothelial-derived EVs (EEVs) levels were significantly higher in mild to severe AS than controls. Patients with AS had significantly higher percentages of PS + red blood cells (RBCs), white blood cells (WBCs), platelets (PLTs) and ECs compared to controls. In addition, we further confirmed that PS + blood cells, ECs and EVs significantly contributed to shortened CT and dramatically increased FXa, thrombin and final fibrin generation in mild to severe AS compared to controls. Furthermore, in severe AS, lactadherin significantly inhibited PCA of PS exposure in blood cells, ECs and EVs, whereas anti-TF had no effect. Conclusion Our study revealed a previously unrecognized association between exposed PS levels on blood cells, ECs and EVs and PCA in AS. Lactadherin promises to be a new therapy by blocking PS to prevent thrombosis in AS patients.