Inhibitory Effects of Glycoprotein IIb/IIIa Antagonists and Aspirin on the Release of Soluble CD40 Ligand During Platelet Stimulation

Abstract

Background-Glycoprotein (GP) IIb/IIIa antagonists inhibit platelet aggregation, an activity attributed to the clinical benefits of these drugs in settings that involve acute coronary thrombosis. However, platelet activation and subsequent aggregation are now known to cause the release of a soluble form of CD40 ligand (sCD40L), a prothrombotic and proinflammatory protein with GP IIb/IIIa binding activity and an established role in atherosclerotic lesion progression. The present study was designed to determine what effect GP IIb/IIIa antagonists have on the release of sCD40L. Methods and Results-Doses of eptifibatide, abciximab, and tirofiban that inhibited platelet aggregation by at least 80% also inhibited sCD40L release in vitro (by 85%, 57%, and 80%, respectively). When platelets were stimulated with a thrombin receptor agonist, inhibition by GP IIb/IIIa antagonists occurred without affecting the release of ␤TG, an ␣-granule protein. Unexpectedly, concentrations of the 3 antagonists that blocked aggregation by only 20% to 50% potentiated the release of sCD40L (by 19% to 26%). Platelets from aspirin-treated individuals were partially protected from sCD40L release, but only when the agonist was collagen, an affect augmented by the addition of GP IIb/IIIa antagonists. Conclusions-These studies suggest that the mechanisms responsible for the clinical benefits of GP IIb/IIIa antagonists (at doses that optimally inhibit aggregation) and of aspirin may not be limited to the inhibition of thrombosis through their blockade of platelet aggregation but may also involve the inhibition of inflammation and thrombosis through their blockade of sCD40L release. These studies also provide a mechanism by which suboptimal doses of GP IIb/IIIa antagonists may be proinflammatory. . Arterial thrombosis in these settings is dependent on platelet aggregation, a process mediated by the binding of soluble fibrinogen to GP IIb/IIIa on the surface of stimulated platelets. GP IIb/IIIa antagonists are effective in these indications because they block the binding of soluble fibrinogen to GP IIb/IIIa and therefore inhibit platelet aggregation. Interestingly, some trials suggest less accrual of events such as myocardial infarction and death in the treatment arm than are observed in the placebo arm during the year after an event. Thus, the clinical benefit extends well past the time of acute administration of GP IIb/IIIa antagonists, which is often less than 20 hours. 2,3 Although it has been considered that thrombosis-mediated ischemia is a culprit for long-term negative consequences, including atherosclerotic lesion progression after acute arterial coronary thrombosis, it is also possible that thrombosis itself could generate such factors, which could be blocked by GP IIb/IIIa antagonists.Platelet stimulation and subsequent aggregation are known to cause the expression or release of several factors that could affect vascular pathology. These include TXA2, a costimulator of platelets that has vasoconstrictive activity; P-selectin, an ␣-granule...

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