Microparticles in sickle cell disease.

Several pathophysiological pathways in sickle cell disease (SCD), the most prevalent hemoglobinopathy worldwide, result in activation of circulating blood cells and the release of submicron vesicles, so-called microparticles (MPs). MPs are candidate biomarkers in vascular disease that exhibit functional biological properties. Compared to healthy individuals, higher level of plasma MPs, mostly derived from platelets and red blood cells (RBC), has been repeatedly observed in SCD patients in their steady-state condition. In contrast, conflicting results have been obtained on the impact of SCD complications and hydroxyurea treatment on circulating MP concentrations, largely due to non-standardized pre- and analytical procedures. Several factors responsible for the increased release of MPs by RBC have been identified in SCD such as sickling/unsickling, oxidative stress and abnormal activity of RBC acid sphingomyelinase. Besides their well-known pro-coagulant effect, sickle RBC-derived MPs produced ex vivo can induce ROS production by endothelial cells and promote a pro-inflammatory and pro-adhesive phenotype that may lead to renal occlusion in SCD mice. However, the functional properties of circulating MPs in human sickle cell disease remain to be studied and fully characterized.