Procoagulant Activity of Blood and Endothelial Cells via Phosphatidylserine Exposure and Microparticle Delivery in Patients with Diabetic Retinopathy

Background/Aims: The mechanisms for thrombosis in diabetic retinopathy (DR) are complex and need to be further elucidated. The purpose of this study was to test phosphatidylserine (PS) exposure on microparticles (MPs) and MP-origin cells from the circulation and to analyze cell-/MP-associated procoagulant activity (PCA) in DR patients. Methods: PS-positive MPs and cells from healthy controls (n = 20) and diabetic patients (n = 60) were analyzed by flow cytometry and confocal microscopy. Clotting time and purified coagulation complex assays were used to measure PCA. Results: PS exposure on platelets and monocytes was higher in proliferative DR (PDR) patients than in non-PDR patients or controls. The highest levels of MPs (derived from platelets [30%], erythrocytes [13%], leukocytes [28%], and endothelial cells [10%]) were found in patients with PDR. In addition, PS exposure on blood cells and shed MPs in DR patients led to significantly increased FXa and FIIa generation, fibrin formation, and markedly shortened coagulation time. Moreover, lactadherin reduced 70% of PCA by blocking PS, while an anti-tissue factor antibody had a smaller effect. Conclusion: Our results confirmed that PCA in DR patients may be partly ascribed to PS exposure and MP release from blood and endothelial cells. Lactadherin may act as an efficient anticoagulant factor in this process.