Platelet Factor XIIIa Release During Platelet Aggregation and Plasma Clot Strength Measured by Thrombelastography in Patients with Coronary Artery Disease Treated with Clopidogrel.

Abstract

It has been estimated that up to half of circulating Factor XIIIa (FXIIIa) is stored in platelets. The release of FXIIIa from platelets upon stimulation with ADP in patients with coronary artery disease treated with dual antiplatelet therapy has not been previously examined. Samples from 96 patients with established coronary artery disease treated with aspirin and clopidogrel were examined. Platelet aggregation was performed by light transmittance aggregometry (LTA) in platelet rich plasma (PRP) with platelet poor plasma (PPP) as reference and ADP 5μM as agonist. Kaolin activated TEG was performed in citrate PPP. PRP after aggregation was centrifuged and plasma supernatant (PSN) collected. FXIIIa was measured in PPP and PSN.Platelet aggregation after stimulation with ADP 5μM resulted in 24% additional FXIIIa release in PSN as compared to PPP (99.3 ± 27 vs. 80.3 ± 24 %, p<0.0001). FXIIIa concentration in PSN correlated with maximal plasma clot strength (TEG-G) (r=0.48, p<0.0001), but not in PPP (r=0.15, p=0.14). Increasing quartiles of platelet derived FXIIIa were associated with incrementally higher TEG-G (p=0.012). FXIIIa release was similar between clopidogrel responders and non-responders (p=0.18). In summary, platelets treated with aspirin and clopidogrel release a significant amount of FXIIIa upon aggregation by ADP. Platelet derived FXIIIa may contribute to differences in plasma TEG-G, and thus in part provide a mechanistic explanation for high clot strength observed as a consequence of platelet activation. Variability in clopidogrel response does not significantly influence FXIIIa release from platelets.