INHIBITION OF PLASMA-MEDIATED ADHERENCE OF SICKLE ERYTHROCYTES TO MICROVASCULAR ENDOTHELIUM BY CONFORMATIONALLY CONSTRAINED RGD-CONTAINING PEPTIDES

Adherence of sickle erythrocytes to vascular endothelium likely initia tes or participates in microvascular occlusion, leading to ischemic ti ssue and organ damage characteristic of sickle-cell pain episodes. In vitro, sickle-cell adherence to endothelium involves adhesive plasma p roteins and integrin and nonintegrin receptors on sickle cells and end othelial cells, The involvement of arginine-glycine-aspartic acid (RGD ) sequences in adhesive plasma proteins and integrin receptors suggest s that RGD-containing peptides may inhibit sickle-cell/endothelial-cel l adherence. In the present study, inhibition of plasma-mediated sick[ e-erythrocyte adherence to endothelium using conformationally constrai ned RGD-containing peptides was quantified in vitro under continuous f low at a shear stress of 1.0 dyn/cm(2), Two conformationally constrain ed RGD peptides were investigated: 6Z (which has high affinity for alp ha(5) beta 1, alpha(v) beta(3), alpha(IIIb)beta(3) integrin receptors) , and TP9201 (which preferentially binds to alpha(IIb)beta(3)). Peptid e 6Z at 50 mu M inhibited plasma-mediated sickle-cell adherence to mic rovascular endothelium 70% when incubated with sickle red cells, and 6 3% when incubated with endothelium. Under similar conditions, peptide TP9201 inhibited plasma-mediated sickle-cell adherence up to 85% at co ncentrations from 250 to 500 mu M TP9201. The inhibition of plasma-med iated adherence by conformationally constrained RGD peptides, but not by linear or circular constructs, suggests that the tertiary structure of the peptide containing the binding sequence is important. Inhibiti on of plasma-mediated sickle-cell adhesion with these peptides in vitr o suggests that such conformationally constrained RGD peptides could p rovide therapeutic interventions in the course of the disease by inhib iting receptor-ligand interactions. (C) 1996 Wiley-Liss, Inc.