Publication Date:
2009-11-20
Description:
Abstract 2998 Poster Board II-976 Introduction: The platelet surface receptor glycoprotein (GP) IIbIIIa (integrin αaIIbβ3) mediates platelet aggregation and plays a key role in hemostasis and thrombosis. Numerous GPIIbIIIa antagonists have been designed and tested as inhibitors of platelet aggregation. Two of these antagonists, eptifibatide (Integrilin) and tirofiban (Aggrastat) have been approved by the U.S. Food and Drug Administration (FDA) and widely used for preventing and treating thrombotic complications in patients undergoing percutaneous coronary intervention and in patients with acute coronary syndromes. It has been reported, however, that some GPIIbIIIa antagonists, such as orbofiban and xemilofiban, promote apoptosis in cardiomyocytes by activation of the apoptosis executioner caspase-3, raising the possibility that platelets also may be susceptible to pro-apoptotic effects of eptifibatide and tirofiban. Over the past decade it has been well-documented that apoptosis occurs not only in nucleated cells but also in anucleated platelets stimulated with thrombin, calcium ionophores, very high shear stresses and platelet storage (Leytin et al, J Thromb Haemost 4: 2656, 2006; Mason et al, Cell 128: 1173, 2007). It has been further reported that platelet activation and apoptosis may be induced by different mechanisms and/or require different levels of triggering stumuli (Leytin et al, Br J Haematol 136: 762, 2007; Br J Haematol 142: 494, 2008). Recently, we have shown that injection of anti-GPIIb antibody induced caspase-3 activation in mouse platelets in vivo (Leytin et al, Br J Haematol 133: 78, 2006), suggesting that direct GPIIbIIIa-mediated pro-apoptotic signaling is able to trigger caspase-3 activation within platelets. Study Design and Methods: The current study aimed to examine, for the first time, the effect of eptifibatide and tirofiban on caspase-3 activation in human platelets. We studied the effects of eptifibatide and tirofiban on caspase-3 activation in resting platelets, which express GPIIbIIIa receptors in their non-active (“closed”) conformation, and in platelets stimulated with thrombin or calcium ionophore A23187, which induce transition of GPIIbIIIa receptors into active (“open”) conformation. Resting platelets were treated with control buffer, 0.48 μM eptifibatide or 0.48 μM tirofiban, and stimulated platelets were treated with 1 U/mL thrombin or 10 μM A23187, or preincubated with eptifibatide or tirofiban before treatment with thrombin or A23187. Caspase-3 activation was determined by flow cytometry using the cell-penetrating FAM-DEVD-FMK probe, which covalently binds to active caspase-3. Results and Discussion: We found that treatment of resting platelets with eptifibatide and tirofiban did not affect caspase-3 activation (P〉0.05, n=7). In contrast, a 2.3-2.7-fold increase of caspase-3 activation was observed in platelets after thrombin or A23187 stimulation (P
Print ISSN:
0006-4971
Electronic ISSN:
1528-0020
Topics:
Biology
,
Medicine
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