Fractalkine promotes platelet activation and vascular dysfunction in congestive heart failure.

UNLABELLED: Endothelial dysfunction and enhanced platelet reactivity in congestive heart failure (CHF) contribute to poor prognosis. CHF patients display an impaired responsiveness to clopidogrel. Fractalkine activates platelets and elevated plasma levels of this chemokine are a feature of CHF. We here addressed the interrelation of fractalkine, platelet reactivity and clopidogrel efficacy in humans and rats with CHF. Fractalkine serum levels determined by ELISA were increased in CHF patients (CHF: 1548 ± 650 pg/ml; CONTROL: 968 ± 575 pg/ml, p<0.01) and following CHF induction in rats (CHF: 1509 ± 753 pg/ml; Sham: 1181 ± 275 pg/ml, p<0.05). Expression of fractalkine and its receptor CX3CR1 was enhanced in aortas of CHF rats as determined by immunofluorescence microscopy and molecular analysis. Fractalkine significantly aggravated endothelial dysfunction and augmented P-selectin expression on platelets from CHF rats. Platelet surface expression of CX3CR1 was increased in CHF rats, who displayed an impaired response to clopidogrel (platelet reactivity to ADP: CHF 30 ± 22%; Sham: 8 ± 5%, p<0.05). Similarly in humans with CHF, elevated fractalkine levels were accompanied by reduced clopidogrel responsiveness. Patients with high on-clopidogrel treatment platelet P2Y12 reactivity displayed higher fractalkine levels (1525 ± 487 pg/ml) than those with sufficient clopidogrel response (684 ± 315 pg/ml, p<0.01). In conclusion, in CHF fractalkine was increased on the endothelium and in blood serum, and platelet surface-expression of CX3CR1 was enhanced. Fractalkine diminished endothelial function beyond the impairment already observed in CHF and was associated with a reduced responsiveness to the platelet inhibitor clopidogrel. These findings may indicate a novel pathophysiological mechanism contributing to impaired clopidogrel responsiveness in CHF.

The novel P2Y 12 antagonist AZD6140 rapidly and reversibly reduces platelet activation in diabetic rats.

INTRODUCTION: Excessive platelet activation fundamentally contributes to cardiovascular events and mortality in patients with diabetes mellitus. Functional resistance has been described for current antiplatelet therapies in broad populations that include patients with diabetes. We investigated acute and chronic effects of AZD6140, a reversible oral rapid-onset P2Y(12) antagonist, on platelet reactivity in diabetic rats. MATERIALS AND METHODS: Diabetes was induced by streptozotocin injection in male Wistar rats. After 4 weeks, AZD6140 was administered (5mg/kg by gavage) and achieved sufficient plasma levels within 30 minutes. Platelet reactivity was determined by ADP-induced P-selectin expression, aggregation and adhesion on fibrinogen coated membranes under arterial flow conditions. RESULTS: At 0.5 hour, AZD6140 strongly reduced ADP-induced P-selectin surface expression, inhibited ADP-induced platelet aggregation, and significantly reduced platelet adhesion to fibrinogen under arterial flow conditions. Chronic treatment with AZD6140 (10mg/kg bid for 2 weeks, based on data obtained in the acute study) starting at day 14 reduced P-selectin surface expression on circulating platelets, indicating lower in vivo platelet activation. Platelet reactivity was improved 12 hours after the last dose, while basal platelet activity remained reduced. AZD6140 was rapidly absorbed in diabetic rats and inhibited platelet reactivity. Chronic treatment lowered in vivo platelet activation of circulating platelets. CONCLUSION: AZD6140 inhibits platelet reactivity in diabetic rats rapidly and reversibly. Markers of tonic platelet activation, which were increased in diabetic rats, were lowered to levels comparable to non-diabetic rats following chronic treatment with AZD6140.