Peptides based on αV-binding domains of erythrocyte ICAM-4 inhibit sickle red cell-endothelial interactions and vaso-occlusion in the microcirculation

Growing evidence shows that adhesion molecules on sickle erythrocytes interact with vascular endothelium leading to vaso-occlusion. Erythrocyte intercellular adhesion molecule-4 (ICAM-4) binds alpha V-integrins, including alpha V beta 3 on endothelial cells. To explore the contribution of ICAM-4 to vascular pathology of sickle cell disease, we tested the effects of synthetic peptides, V(16) PFWVRMS (FWV) and T(91) RWATSRI (ATSR), based on alpha V-binding domains of ICAM-4 and capable of inhibiting ICAM-4 and alpha V-binding in vitro. For these studies, we utilized an established ex vivo microvascular model system that enables intravital microscopy and quantitation of adhesion under shear flow. In this model, the use of platelet-activating factor, which causes endothelial oxidant generation and endothelial activation, mimicked physiological states known to occur in sickle cell disease. Infusion of sickle erythrocytes into platelet-activating factor-treated ex vivo rat mesocecum vasculature produced pronounced adhesion of erythrocytes; small-diameter venules were sites of maximal adhesion and frequent blockage. Both FWV and ATSR peptides markedly decreased adhesion, and no vessel blockage was observed with either of the peptides, resulting in improved hemodynamics. ATSR also inhibited adhesion in unactivated microvasculature. Although infused fluoresceinated ATSR colocalized with vascular endothelium, pretreatment with function-blocking antibody to alpha V beta 3-integrin markedly inhibited this interaction. Our data strengthen the thesis that ICAM-4 on sickle erythrocytes binds endothelium via alpha V beta 3 and that this interaction contributes to vaso-occlusion. Thus peptides or small molecule mimetics of ICAM-4 may have therapeutic potential.