Microparticles from splenectomized β-thalassemia/HbE patients play roles on procoagulant activities with thrombotic potential

Abstract

Thromboembolic events including cerebral thrombosis, deep vein thrombosis, and pulmonary embolism are major complications in β-thalassemia. Damaged red blood cells and chronic platelet activation in splenectomized β-thalassemia/HbE patients were associated with increased microparticles (MPs) releases into blood circulation. MPs are small membrane vesicles, which play important roles on coagulation. However, the role of MP in thalassemia is poorly understood. In this study, the effects of splenectomized-MPs on platelet activation and aggregation were investigated. The results showed that isolated MPs from fresh platelet-free plasma of patients and normal subjects directly induce platelet activation, platelet aggregation, and platelet-neutrophil aggregation in a dose-dependent manner. Interestingly, MPs obtained from splenectomized patients are more efficient in induction of platelet activation (P-selectin) when compared to MPs from normal subjects (P < 0.05), tenfold lower than pathophysiological level, at 1:0.1 platelet MP ratio. Co-incubation of splenectomized-MPs with either normal-, non-splenectomized- or splenectomized-platelets at 1:10 platelet MP ratio increased platelet activation up to 5.1 ± 2.2, 5.6 ± 3.7, and 9.5 ± 3.0%, respectively, when normalized with individual baseline. These findings suggest that splenectomized patients were proned to be activated by MPs, and splenectomized-MPs could play an important role on chronic platelet activation and aggregation, leading to thrombus formation in β-thalassemia/HbE patients.

Microparticles from β-thalassaemia/HbE patients induce endothelial cell dysfunction

“…Haematological analysis revealed that β-thalassaemia/HbE patients had an anaemia phenotype with increased numbers of platelets and MPs (annexin V+ MPs) as described in previous studies 13 – 15 . The number of MPs originating from platelets and RBCs of β-thalassaemia/HbE was higher than normal-MPs.…”

“…In this study, the amount of MPs (5 × 10 6 particles/mL) used was about three fold lower than the physiological number of MPs in circulation in normal subjects (1.6 × 10 7 particles/mL). However, the percentages of platelet activation in platelets from splenectomised patients treated with splenectomised-MPs at 10-fold lower to 100-fold higher than physiological levels were significantly increased when compared to platelets treated with normal-MPs, and in dose dependent manner 15 . HUVECs incubated with MPs obtained from sickle cell disease (SCD) patients at about 5-fold lower than physiological levels resulted in increased reactive oxygen species production and apoptosis when compared with that of normal controls.…”

“…We have previously shown that MPs obtained from β-thalassaemia/HbE patients induced platelet activation, platelet aggregation and platelet-neutrophil aggregation, which partly contributes to the hypercoagulable state in β-thalassaemia/HbE patients 15 . The studies presented above represent the effects of the MPs on endothelial cell activation that leads to the increased adhesion of leukocytes to endothelial cells.…”

“…Interestingly, the level of MPs was correlated with platelet factor 3-like activity and prothrombinase complex activity 14 . We have previously shown that MPs obtained from β-thalassaemia/HbE patients induced platelet activation, platelet aggregation and platelet-neutrophil aggregation 15 . MPs are capable of interacting with other cells in the circulatory system that participate in various physiologic and pathologic processes, including the endothelial cells that line the inner surface of the vasculature.…”

Extracellular Vesicle Characteristics in β-thalassemia as Potential Biomarkers for Spleen Functional Status and Ineffective Erythropoiesis

“…After splenectomy, blood cell counts and circulating MPs increase. This has been observed in patients with immune thrombocytopenia (Fontana et al, 2008; Sewify et al, 2013), β-thalassemia intermedia (β-TI) patients (Pattanapanyasat et al, 2007; Habib et al, 2008; Westerman et al, 2008; Klaihmon et al, 2017) and TDT patients; in the latter group, splenectomy has been associated with higher levels of MPs (Tantawy et al, 2013; Elsayh et al, 2014; Agouti et al, 2015) and increased procoagulant activity of platelet MPs (Agouti et al, 2015). However, there have been no studies characterizing EVs in thalassemic patients with hypersplenism.…”