Testing Platelet Activation With a Shear-Dependent Platelet Function Test Versus Aggregation-Based Tests

Abstract

Background-Tests developed to monitor glycoprotein (GP) IIb/IIIa blockade do not properly reflect platelet function in vivo and need a baseline (pretreatment) value. Because GP IIb/IIIa is essential in platelet aggregation and thrombosis under shear conditions, a flow-dependent approach to monitor its inhibition can be used. Methods and Results-We compared a test based on flow-dependent platelet deposition, the Cone and Platelet Analyzer (CPA), with in vitro platelet aggregometry and the Rapid Platelet Function Assay (RPFA) on platelet function after GP IIb/IIIa inhibition. In vitro, increasing concentrations of abciximab (0% to 100% receptor occupancy) were tested. Ex vivo, platelet function was monitored with the CPA and with aggregometry for up to 1 week after abciximab administration. The CPA was better correlated with the percentage of free GP IIb/IIIa receptors than was aggregometry or the RPFA. Only the RPFA, when expressed as a ratio over baseline (pretreatment), was comparable to the CPA. Ex vivo, the CPA, but not aggregometry, showed prolonged platelet inhibition with gradual recovery from GP IIb/IIIa receptor blockade in the first week after abciximab administration. Conclusions-Platelet function assessment by shear-induced deposition is a reliable test to monitor a wide range of GP IIb/IIIa inhibition. Its accuracy does not require a baseline reference. The effects of GP IIb/IIIa blockade on platelet function should be examined under high shear conditions.

Comparative Analysis of Various Platelet Glycoprotein IIb/IIIa Antagonists on Shear-Induced Platelet Activation and Adhesion

“…CPA. The procedure of the CPA operation was recently described (Osende et al, 2001). Briefly, after incubating blood samples with fibans or vehicle for 15 min at room temperature, 200 l was transferred into each of four-well polystyrene plates.…”

“…Concentration-Dependent Effect of Roxifiban and Orbofiban on Shear-Induced Platelet adhesion in Citrated Blood at Room Temperature. Because previous studies were carried out using citrated blood at room temperature (Varon et al, 1997;Shenkman et al, 2000;Osende et al, 2001), the same condition was applied for our initial study to validate our CPA system and its capacity to study the efficacy of small-molecule glycoprotein IIb/IIIa inhibitors. Quantitative data (n ϭ 6) confirmed the dose-dependent inhibition of roxifiban, along with orbofiban, on shear-induced platelet adhesion (Fig.…”

“…The administration of a specific monoclonal antibody against glycoprotein IIb/IIIa (c7E3 or abciximab) to patients in association with coronary angioplasty results in almost complete inhibition of shear-induced aggregation subsequent to vWF-mediated adhesion onto type collagen I (Turner et al, 1995). In this context, the Cone and Plate(let) Analyzer (CPA), but not aggregometry, has been recently shown to monitor prolonged platelet inhibition following gradual recovery of abciximab therapy (Osende et al, 2001).…”

“…To further investigate the role of glycoprotein IIb/IIIa re-ceptors on platelet adhesion under shear conditions in vitro, we characterized various experimental conditions using the CPA system (Varon et al, 1997) to monitor platelet activation and adhesion onto an artificial (polystyrene) surface under a high shear rate (Shenkman et al, 2000;Osende et al, 2001). In the present study, we have investigated the pharmacological property of small molecule glycoprotein IIb/ IIIa antagonists in various experimental conditions including aspirin, various anticoagulants, temperature, and Ca 2ϩ concentration.…”

“…) for 2 min with a rotating Teflon cone, as described in detail previously (Osende et al, 2001). Wells were washed with phosphate-buffered saline for 2 to 3 times and stained with May-Grunwald dye (Sigma Catalog no.…”