Fetal hemoglobin and hydroxycarbamide moduate both plasma concentration and cellular origin of circulating microparticles in sickle cell anemia children.

Microparticles are cell membrane-derived microvesicles released during cell apoptosis and activation processes. They have been described as bio-markers in various vascular diseases, including sickle cell anemia, and associated with an increased risk of thrombosis. We investigated the effects of fetal hemoglobin level, a factor known to modulate the clinical expression of sickle cell anemia, and that of hydroxycarbamide treatment which reduces the frequency of vasoocclusive crises, the canonical clinical manifestation of the disease, on both the plasma concentration and the cellular origin of circulating microparticles. Flow cytometry was used to characterize microparticles in 62 sickle cell anemia children at steady state aged 2 months-16 years; 13 of them were treated with hydroxycarbamide. In untreated children, we observed negative correlations between fetal hemoglobin levels and the absolute plasma concentration of microparticles as well as that of microparticles specifically derived from platelets, erythrocytes, and monocytes. Compared to untreated children, those treated with hydroxyurea showed lower concentrations of total microparticles as a consequence of decreased microparticles shed by platelets and erythrocytes. In conclusion, in our sickle cell patients, neonatal decline of fetal hemoglobin coincided with an increase in circulating microparticles derived from erythrocytes, platelets, and monocytes. Hydroxyurea treatment was associated with a decrease in microparticles derived from erythrocytes and platelets.