Abstract 12848: Increased Fractalkine Levels Are Associated With Impaired Clopidogrel Responsiveness in Patients With Coronary Artery Disease by Activating a Signal Transduction Pathway Similar to P2y12
Background: Fractalkine contributes to platelet activation and plays a pivotal role in atherogenesis. Fractalkine activates an intraplatelet signaling pathway similar to the one activated by ADP via P2Y12, which is the drug target of clopidogrel. However, the exact downstream pathway for fractalkine has not been described yet.
Methods and results: Blood samples were obtained from healthy volunteers and from 40 patients under chronic clopidogrel treatment (more than 5 days following a 600 mg loading dose). Serum fractalkine levels were determined by ELISA. Clopidogrel responsiveness was determined by the platelet-reactivity index (PRI) based on adenylyl cyclase-dependent stimulation of vasodilator-stimulated phosphoprotein (VASP) phosphorylation. Western blot analyses were performed with washed platelets which were stimulated with fractalkine (1–2μg/ml) and / or ADP (5μM) respectively. When analyzing coronary artery disease patients based on their serum fractalkine levels, patients within the highest quartile of fractalkine (2042±25pg/ml) had the weakest response to clopidogrel (PRI 68±4%) and patients within the lowest quartile (479±50 pg/ml) of fractalkine had the strongest response (PRI 48±7%, p=0.0106). In vitro, fractalkine further increased the PRI in clopidogrel-treated patients indicating a potential signaling mechanism, which could lead to activation of targets downstream of P2Y12. Fractalkine by itself induced PI3-kinase (PI3K) activation leading to Akt- phosphorylation at Ser 473 compared to non-stimulated samples (p<0.01 vs. basal for 1 and 2 μg/ml fractalkine). Moreover, fractalkine even potentiated PI3K activation when added to ADP compared to ADP stimulation alone (p<0.05 2μg/ml fractalkine + 5μM ADP vs 5μM ADP).
Conclusion: In addition to desensitizing platelets to PGE1 via Giα, fractalkine induces PI3K-dependent Akt-phosphorylation via a Gβγ-protein similar to ADP signaling through P2Y12. Consequently, fractalkine increases the platelet ADP response in clopidogrel-treated patients. Once released from an atherosclerotic lesion, this mechanism could contribute locally to impaired clopidogrel responsiveness at the vulnerable plaque.
- © 2010 by American Heart Association, Inc.