Phosphatidylserine-exposing blood cells and microparticles induce procoagulant activity in non-valvular atrial fibrillation.

Background: The definitive role of phosphatidylserine (PS) in the prothrombotic state of non-valvular atrial fibrillation (NVAF) remains unclear. Our objectives were to study the PS exposure on blood cells and microparticles (MPs) in NVAF, and evaluate their procoagulant activity (PCA).

Methods: NVAF patients without (n = 60) and with left atrial thrombi (n = 18) and controls (n = 36) were included in our study. Exposed PS was analyzed with flow cytometry and confocal microscopy. PCA was evaluated using clotting time, factor Xa (FXa), thrombin and fibrin formation.

Results: PS blood cells and MPs were significantly higher in NVAF patients without and with left atrial thrombi (both P < 0.01) than in controls. Patients with left atrial thrombi showed increased PS platelets, neutrophils, erythrocytes and MPs compared with patients without thrombi (all P < 0.05). Moreover, in patients with left atrial thrombi, MPs primarily originated from platelets (56.1%) followed by leukocytes (21.9%, including MPs from neutrophils, monocytes and lymphocytes), erythrocytes (12.2%) and endothelial cells (8.9%). Additionally, PS blood cells and MPs contributed to markedly shortened coagulation time and dramatically increased FXa/thrombin/fibrin (all P < 0.001) generation in both NVAF groups. Furthermore, blockade of exposed PS on blood cells and MPs with lactadherin inhibited PCA by approximately 80%. Lastly, we found that the amount of PS platelets and MPs was positively correlated with thrombus diameter (all p < 0.005).

Conclusions: Our results suggest that exposed PS on blood cells and MPs play a procoagulant role in NVAF patients. Blockade of PS prior to thrombus formation might be a novel therapeutic approach in these patients.