Sickle cell disease as a vascular disorder

In sickle cell disease (SCD), hemoglobin S (HbS) red blood cells (RBCs) are characteristically deformed and inflexible. Often breaking down in the circulation, they exhibit increased adhesive properties with the endothelium and activated neutrophils and platelets, increasing the risk of occlusion of the microcirculation. SCD is categorized into two sub-phenotypes: hyperhemolytic, associated with priapism, leg ulcers, pulmonary hypertension, and stroke, and high hemoglobin/viscosity, which may promote vaso-occlusion-associated pain, acute chest syndrome, and osteonecrosis.

The sub-phenotypes are not completely distinct. Hemolysis may trigger vaso-occlusion, contributing to vascular complications. Targeting P-selectin, a key mediator of cross-talk between hyperhemolysis and vaso-occlusion, may be beneficial for vascular and vaso-occlusion-associated complications. English-language articles from PubMed on the topic of SCD and vaso-occlusive crises (VOCs) were reviewed from 1 January 2000 to 1 January 2019 using the search terms 'sickle cell disease,' 'vaso-occlusive crises,' and 'selectin.'

Besides targeting P-selectin, other strategies to counter VOCs and RBC sickling are being pursued. These include platelet inhibition to counter aggregation, intercellular adhesion, and thrombosis during VOCs; gene therapy to correct the homozygous missense mutation in the β-globin gene, causing polymerization of HbS; L-glutamine, possibly reducing oxidative stress in sickled RBCs; and fetal hemoglobin inducers.