Effects of hydroxyurea on the membrane of erythrocytes and platelets in sickle cell anemia

Background and Objectives. Adhesion molecules on the surface of erythrocytes, leukocytes and platelets are involved in vascular occlusion in sickle cell anemia. Hydroxyurea treatment of sickle cell anemia patients leads to clinical improvement and reduces the incidence of vaso-occlusive episodes. It has been previously demonstrated that hydroxyurea treatment also reduces the expression of adhesion molecules on the surface of erythrocytes. Phosphatidylserine (PS) exposure on the surface of erythrocytes has been considered to be the main determinant of altered erythrocyte adhesion in sickle cell anemia. In this study we examine the expression of PS on the surface of erythrocytes and platelets of sickle cell anemia patients before and during treatment with hydroxyurea. Design and Methods. Blood samples from 15 sickle cell anemia patients were analyzed before and during treatment with hydroxyurea. The profile of PS expression was examined by flow cytometry. Results. Hydroxyurea was effective, as determined by the patients' clinical improvement and increased hemoglobin (8.3 vs 9.1 g/dL, p < 0.005), F cells (15.9% vs 37.1%, p < 0.005) and mean corpuscular volume ( 82 fL vs 101 fL, p < 0.005). PS expression on the surface of erythrocytes and platelets decreased from 6.27% to 2.96% (p < 0.005) and from 13.5% to 4.7% (p < 0.005), respectively. Interpretation and Conclusions. Hydroxyurea treatment reduces PS expression on the surface of erythrocytes and platelets, thus contributing to the favorable effects of this therapy.