Elevating local concentrations of GPIIb–IIIa antagonists counteracts platelet thrombus stability

Henry E Speich,Geoffrey D Moodie,Lisa K Jennings,Lindsey T Lands,Ronit R Furman

doi:10.1007/s11239-012-0814-7

Abstract

Glycoprotein IIb–IIIa (GPIIb–IIIa) antagonists have the capacity to destabilize coronary thrombi and restore vessel patency. Antagonist concentration and residence time, which can be increased by local intracoronary (LIC) administration, and thrombus age may be key factors that influence thrombus stability. Light transmission aggregometry was used to examine the effects of exposing human platelet aggregates to extremely high local levels of GPIIb–IIIa antagonists versus conventional therapeutic levels in vitro. Freshly-formed or aged platelet aggregates were subjected to GPIIb–IIIa antagonists (abciximab, eptifibatide) or direct thrombin inhibitor bivalirudin at concentrations simulating either conventional intravenous (IV) or LIC administration. The degree of antagonist-induced disaggregation was significantly higher using elevated (LIC) doses versus conventional (IV) doses (60.1 % vs. 7.4 % for abciximab, 41.6 % or 45.3 % vs. 17.6 % for eptifibatide, p < 0.01). Bivalirudin did not promote disaggregation. Microscopy confirmed noticeably smaller, more dispersed aggregates for antagonist LIC treatments. Dosing at LIC levels also induced more disaggregation than IV levels when aggregates were aged for 30 min prior to exposure. An in vitro perfusion model was used to simulate the fluid dynamics of IV or LIC administration of abciximab using a microporous local drug delivery balloon catheter such as the Atrium ClearWay™ RX. The perfusion model resulted in more rapid thrombus clearance with LIC dosing levels compared to IV. In summary, boosting the concentration of GPIIb–IIIa antagonists enhances dispersal of human platelet aggregates in vitro. These data provide a foundation for investigating increased local concentrations of GPIIb–IIIa antagonists in patients, as with LIC administration.

Highlights

Platelets play a vital role in primary hemostasis
The current study examined the capacity for extremely high local concentrations of abciximab and eptifibatide, as may be achieved through local intracoronary (LIC) administration, to disperse preformed platelet aggregates in vitro
Once maximal aggregation was achieved at 3.5 min, the freshlyformed aggregates were exposed to pre-specified concentrations of GPIIb–IIIa antagonists or respective vehicle controls and the extent of disaggregation was measured at 5, 10 and 15 min after addition of the antagonist

Summary

Introduction

Platelets play a vital role in primary hemostasis. While circulating platelets are normally quiescent, they can be rapidly stimulated upon adherence to exposed subendothelial matrix components and by soluble agonists at sites of vascular injury. A complex interplay of adhesive interactions and intracellular signaling pathways, including granule secretion and cytoskeletal reorganization, facilitate platelet activation and aggregation to form a platelet-rich thrombus that arrests bleeding. Ex vivo, and clinical studies clearly outline the capability of these agents to prevent platelet aggregation by inhibiting fibrinogen-mediated crosslinking of activated platelets via the activated GPIIb–IIIa receptor [4,5,6]. Recent studies reveal that these agents may have additional effects on platelets aggregates that have already formed, causing them to disengage and disperse [7,8,9,10,11]. Previous work in our laboratory confirmed that GPIIb–IIIa antagonists abciximab and eptifibatide readily dispersed freshly-formed platelet aggregates [12]. The choice of antagonist, antagonist concentration, and age of the platelet aggregates affected the extent of platelet disaggregation

Methods

Results

Conclusion