Effect of glycoprotein IIb/IIIa antagonists on the HIT serum induced activation of platelets.

Heparin-induced thrombocytopenia is an increasingly common side effect associated with heparin usage. In the more severe manifestation of the syndrome, patients can develop thrombosis; a 10% mortality is associated with heparin induced thrombocytopenia. To date, the therapeutic options for patients with heparin-induced thrombocytopenia are limited. Glycoprotein IIb/IIIa inhibitors have been shown to block platelet aggregation induced by a wide variety of agonists. The ability of antibody and synthetic small molecule inhibitors of glycoprotein IIb/IIIa to block in vitro activation and aggregation of platelets in response to heparin-induced thrombocytopenia positive serum/heparin was examined using flow cytometry, platelet aggregometry, and luminescence aggregometry. Abciximab, YM 337, and SR 121566A were each found to inhibit platelet microparticle formation and P-selectin expression in whole blood, in response to heparin-induced thrombocytopenia positive serum/heparin. In a platelet rich plasma system, the platelet aggregation response was inhibited by all three agents. The IC50 for inhibition of heparin-induced thrombocytopenia positive serum/heparin induced platelet aggregation by SR 121566A was 18 nM, a concentration which was 4 to 8 fold lower than that observed for collagen and arachidonic acid induced aggregation. Adenosine triphosphate release from activated platelets, as measured by luminescence aggregometry, was concentration-dependently inhibited by SR 121566A. These results suggest that glycoprotein Ilb/IIIa inhibitors may be beneficial in the management of heparin-induced thrombocytopenia and warrant further investigation.