Purpose: Dual antiplatelet therapy (DAT) with aspirin and P2Y12 receptor inhibitors is the treatment of choice in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI). Platelets and platelet-derived microvesicles (PMVs) play a crucial role in the arterial thrombotic process. Measuring platelet function is methodologically demanding and measurement of PMVs could therefore offer an additional method to assess platelet function in previously frozen and stored samples from large biobanks. In the present study we investigated how platelet function measured with multiplate and PMVs measured by flow cytometry were affected by clopidogrel treatment in patients with ACS and PCI.
Methods: 200 patients with ACS who underwent PCI were included in the study and venous blood samples were obtained at discharge. All patients were loaded with 600 mg clopidogrel before PCI. Platelets were activated with ADP (6.4 mM) and analysed by whole blood impedance aggregometry (WBA; MultiplateTM). Aggregation ≥47 U (WBA) defined low responders to DAT.
PMVs were measured by flow cytometry (Beckman Gallios) in samples prepared from stored platelet poor plasma (2000g, 20 min in room temperature). Twenty μl of sample were incubated with lactadherin-FITC and CD42a-PE (platelet antigen GPIX) and CD62P-APC (P-selectin).
Results: Platelet function measured with WBA revealed that 35 of 180 patients (19%) were low responders and 148 (81%) patients were normal responders with clopidogrel treatment. Levels of PMVs were almost two fold higher in the low responder group compared to patient that responded well to treatment (for both CD42a and CD62P, positive PMVs, p<0.005 and p<0.004 respectively).
Conclusions: Patients with high on clopidogrel treatment platelet reactivity have elevated levels of circulating PMVs, indicating ongoing platelet activation despite DAT. PMVs can be used as biomarkers to assess platelet function in plasma samples from large prospective clinical studies.