Variable effect of P2Y12 inhibition on platelet thrombus volume in flowing blood

Abstract

Summary. Background and objectives: Patients treated with percutaneous coronary intervention receive aspirin and P2Y12 ADP receptor inhibitors to reduce thrombotic complications. The choice of methodology for monitoring the effects of treatment and assessing its efficacy is still a topic of debate. We evaluated how decreased P2Y12 function influences platelet aggregate (thrombus) size measured ex vivo. Methods and results: We used confocal videomicroscopy to measure in real time the volume of platelet thrombi forming upon blood perfusion over fibrillar collagen type I at a wall shear rate of 1500 s )1. The average volume was significantly smaller in 31 patients receiving aspirin and clopidogrel (19) or ticlopidine (12) than in 21 controls, but individual values were above the lower limit of the normal distribution, albeit mostly within the lower quartile, in 61.3% of cases. Disaggregation of platelet thrombi at later perfusion times occurred frequently in the patients. Vasodilator-stimulated phosphoprotein phosphorylation, reflecting P2Y12 inhibition, was also decreased in the patient group, and only 22.6% of individual values were above the lower normal limit. We found no correlation between volume of thrombus formed on collagen fibrils and level of P2Y12 inhibition, suggesting that additional and individually variable factors can influence the inhibitory effect of treatment on platelet function. Conclusions: Measurements of platelet thrombus formation in flowing blood reflects the consequences of antiplatelet therapy in a manner that is not proportional to P2Y12 inhibition. Combining the results of the two assays may improve the assessment of thrombotic risk.

Development of a perfusion chamber assay to study in real time the kinetics of thrombosis and the antithrombotic characteristics of antiplatelet drugs

“…Second, it has become clear from clinical conditions such as unstable angina and from experiments in animals such as those using the Folts model that platelet factors exist that mediate or inhibit thrombus stability. Our data obtained in blood from healthy volunteers confirmed the fact the clinical efficacy of the state-of-the art antiplatelet therapy (clopidogrel + aspirin) utilized in the management of post-atherothrombotic events certainly stems from a synergism in destabilization activities of the two drugs [11,12,24]. They also suggested that high levels of inhibition of the P2Y 12 receptor may be sufficient to provide substantial benefits in agreement with others [17,25].…”

Detection of platelet sensitivity to inhibitors of COX-1, P2Y1, and P2Y12 using a whole blood microfluidic flow assay

“…We report findings with some similarities and differences to the prior flow studies of Lucitt et al [17] and Menolicchio et al [18]. Lucitt et al found no effect on the rate of platelet coverage of the collagen surface with in vitro ASA addition at 1500 s −1 .…”

The Role of P2Y₁₂ Receptor and Activated Platelets During Inflammation

“…Similar results were observed in a mouse model of atherothrombosis, where pre-treatment with the P2Y 12 antagonists ticagrelor or cangrelor could not only inhibit thrombus formation, but also decrease its stability [66]. Similar results were observed in ex vivo thrombus formation with human platelets from coronary heart disease patients treated with clopidogrel [67], further confirming the important role of P2Y 12 during thrombus formation and its stability.…”