Circulating platelet and erythrocyte microparticles in young children and adolescents with sickle cell disease: Relation to cardiovascular complications.

Sickle cell disease (SCD) is characterized by a complex vasculopathy, consisting of endothelial dysfunction and increased arterial stiffness, with a global effect on cardiovascular function. The hypercoagulable state may result from chronic hemolysis and circulating cell-derived microparticles (MPs) originating mainly from activated platelets and erythrocytes. We measured the levels of platelet and erythrocyte-derived MPs (PMPs and ErMPs) in 50 young SCD patients compared with 40 age- and sex-matched healthy controls and assessed their relation to clinicopathological characteristics and aortic elastic properties. Patients were studied stressing on the occurrence of sickling crisis, transfusion history, hydroxyurea therapy, hematological, and coagulation profile as well as flow cytometric expression of PMPs (CD41b(+)) and ErMPs (glycophorin A(+)). Echocardiography was performed to assess aortic stiffness and distensibility, left ventricular function and pulmonary artery pressure. Both PMPs and ErMPs were significantly elevated in SCD patients compared with control group (p < 0.001). SCD patients had significantly elevated d-dimer and von Willebrand factor antigen (vWF Ag) levels with lower antithrombin III compared with controls (p < 0.001). Aortic stiffness index and pulmonary artery pressure were significantly higher in SCD (p < 0.001), whereas aortic strain and aortic distensibility were significantly lower (p < 0.001) compared with controls. MPs levels were significantly increased in SCD patients with pulmonary hypertension, acute chest syndrome, and stroke as well as those who had history of thrombosis or splenectomy (p < 0.001). Also, patients in sickling crisis during the study had higher PMPs and ErMPs levels than those in steady state (p < 0.001). Patients on hydroxyurea therapy had lower MPs levels than untreated patients (p < 0.001). PMPs and ErMPs were positively correlated with disease duration, transfusion index, white blood cell count, HbS, markers of hemolysis, serum ferritin, D-dimer, and vWF Ag, whereas negatively correlated with hemoglobin and HbF levels (p < 0.05). Both PMPs and ErMPs levels were positively correlated with aortic stiffness, pulmonary artery pressure, and tricuspid regurgitant velocity (p < 0.05) while negatively correlated with aortic distensibility. We suggest that PMPs and ErMPs overproduction may be considered a potential biological marker for vascular dysfunction and disease severity in SCD and may be implicated in the pathogenesis of coagulation abnormalities encountered in those patients. Their levels are closely related to sickling crisis, pulmonary hypertension, markers of hemolysis, fibrinolysis, and iron overload. Therefore, quantification of MPs in SCD may provide utility for identifying patients who are at increased risk of thrombotic events or cardiovascular abnormalities and would help to monitor response to hydroxyurea therapy.