Platelet integrin αIIbβ3 plays a key role in venous thrombogenesis in a mouse model
AbstractVenous thrombosis (VT) is a common vascular disease associated with reduced survival and a high recurrence rate. Previous studies have shown that the accumulation of platelets and neutrophils at sites of endothelial cell activation is a primary event in VT, but a role for platelet IIb{beta}3 in the initiation of venous thrombosis has not been established. This task has been complicated by the increased bleeding linked to partial agonism of current IIb{beta}3 inhibitory drugs such as tirofiban (Aggrastat(R)). Here, we show that m-tirofiban, an engineered version of tirofiban, is not a partial agonist of IIb{beta}3. This is based on its cryo-EM structure in complex with human full-length IIb{beta}3 and its inability to increase expression of an activation-sensitive epitope on platelet IIb{beta}3. m-tirofiban abolished agonist-induced platelet aggregation ex vivo at concentrations that preserved clot retraction and markedly suppressed the accumulation of platelets, neutrophils, and fibrin on thrombin-activated endothelium in real-time using intravital microscopy in a mouse model of venous thrombogenesis. Unlike tirofiban, however, m-tirofiban did not increase bleeding at the thrombosis-inhibitory dose. These findings establish a key role for IIb{beta}3 in the initiation of VT, provide a guiding principle for designing potentially safer inhibitors for other integrins, and suggest that pure antagonists of IIb{beta}3 like m-tirofiban merit further consideration as potential thromboprophylaxis agents in patients at high-risk for VT and hemorrhage.