Glycoprotein Ibα inhibition and ADP receptor antagonists, but not aspirin, reduce platelet thrombus formation in flowing blood exposed to atherosclerotic plaques

Abstract

Anti-platelet drugs are used to prevent intra-arterial thrombus formation after rupture of atherosclerotic plaques. Until now, the inhibitory effect of present and future anti-platelet drugs such as aspirin, ADP receptor P2Y(1)/P2Y(12) antagonists and glycoprotein (GP) Ibalpha inhibitors on the interaction of platelets with human plaques is not known. To study those effects we obtained human atherosclerotic plaques by surgical endarterectomy. Plaques induced maximal platelet aggregation in hirudinized platelet-rich plasma (PRP) and blood that was effectively inhibited by aspirin, the P2Y(1) antagonist MRS2179 and the P2Y(12) antagonist AR-C69931MX, but not by GPIbalpha blockade with the mAB 6B4. Inhibition of platelet aggregation by MRS2179 was 74 +/- 37% and 68 +/- 20%, by AR-C69931MX 94 +/- 7% and 80 +/- 6%, and by aspirin 88 +/- 19% and 64 +/- 28%, in PRP and blood, respectively (mean +/- SD; n = 6-12 with plaques from 6 patients). The combination of both ADP receptor antagonists completely inhibited plaque-induced platelet aggregation in hirudinized PRP and blood. Under arterial flow conditions (1,500s(-1)), blockade of platelet GPIbalpha resulted in a strong decrease of plaque-stimulated platelet adhesion/aggregate formation of 77 +/- 5% (mean +/- SD; n = 4). Furthermore, MRS2179, AR-C69931MX and their combination reduced plaque-dependent platelet aggregate formation by 35 +/- 14%, 32 +/- 13% and 58 +/- 12% (mean +/- SD; n = 5), respectively. Aspirin was without significant effect. In conclusion, a GPIbalpha-blocking antibody, as well as P2Y(1) and P2Y(12) receptor antagonists, alone or in combination, reduce in contrast to aspirin human plaque-induced platelet thrombus formation under arterial flow. Although these new anti-platelet agents inhibit platelet thrombus formation after plaque rupture, more efficient platelet blockers are required.

Calcium-Channel Blockers Reduce the Antiplatelet Effect of Clopidogrel

“…Whole blood aggregation was determined using an impedance aggregometer (Multiple Platelet Function Analyzer/Multiplate Analyzer, Dynabyte Medical, Munich, Germany). The system detects the electrical impedance change due to the adhesion and aggregation of platelets on 2 independent electrode-set surfaces in the test cuvette (24,25). A 1:2 mixture of 0.9% NaCl and whole blood anticoagulated with hirudin (200 U/ml, Dynabyte, Munich, Germany) were stirred at 37°C for 3 min in the test cuvettes; adenosine diphosphate (ADP [6.4 M, Dynabyte Medical, Munich, Germany]) was added, and the increase in electrical impedance was recorded continuously for 5 min.…”

The role of PGE2 in human atherosclerotic plaque on platelet EP3 and EP4 receptor activation and platelet function in whole blood

“…The role of PGE 2 in human atherosclerotic plaque 163 to glycoprotein Ib [27,28], it could not be excluded by these measurements that PGE 2 influences platelet adhesion and thrombus formation under flow conditions. To address this possibility, we performed flow experiments, simulating flow conditions in moderately stenosed coronary arteries.…”

Acute and persistent platelet and coagulant activities in atherothrombosis

“…This has been demonstrated for the GPIb-V-IX complex, interacting with collagen-bound VWF, which was mediated initial platelet adhesion to plaque material at high, but not at low wall-shear rates [22]. Another contributor is the platelet ADP receptor P2Y 12 , which was found to act by stabilizing thrombi formed on disrupted plaques of Apoe À/À mice in vivo as well as in flow devices in vitro [23] (Fig.…”

“…1). In contrast, the other platelet ADP receptor, P2Y 1 , does not seem to have a major role in thrombus formation [18,22]. Finally, atherothrombus formation in vivo was inhibited by blocking phosphoinositide 3-kinase b or integrin a IIb b 3 [9,10], which are implicated in platelet aggregation.…”