Sickle hemoglobin promotes venous thrombosis through procoagulant activity and is targetable by hemoglobinase therapy

Sickle cell disease (SCD) is characterized by chronic hemolytic anemia and recurrent vaso-occlusive events. Polymerization of deoxygenated sickle hemoglobin (HbS) increases erythrocyte rigidity, promoting microvascular occlusion, tissue hypoxia, and hemolysis. SCD is associated with a heightened risk of deep venous thrombosis, but the mechanisms remain unclear.

To determine the causal role of SCD in venous thrombosis and to evaluate the therapeutic potential of hemoglobin degradation by Plasmodium falciparum plasmepsin I (PMI).

Venous thrombosis was induced by femoral vein ligation in SCD and wild-type (WT) mice. Thrombus morphology was analyzed by scanning electron microscopy. Plasma-free hemoglobin levels were measured during coagulation, and the effects of recombinant PMI on free hemoglobin and thrombus formation were assessed. In addition, in vitro assays evaluated the impact of HbS on clotting time compared with normal hemoglobin.

Thrombi developed in all SCD mice and most WT controls following ligation. Scanning electron microscopy demonstrated distinct thrombus architecture in SCD, featuring rigid, elongated erythrocytes interconnected by fibrin-like strands and frequent membrane disruption, compared with polyhedrocyte-rich WT thrombi. Plasma-free hemoglobin increased during static incubation of SCD blood and was consumed during coagulation, implicating it in clot formation. In vitro, HbS addition shortened the clotting time compared with normal hemoglobin. Treatment with PMI reduced free plasma hemoglobin and significantly decreased thrombus size in SCD mice.

Sickle hemoglobin contributes to venous thrombogenesis through procoagulant activity and thrombus stabilization. Targeting free HbS with hemoglobinase therapy may represent a novel therapeutic strategy for thrombotic complications in SCD.