The reversible P2Y antagonist cangrelor influences the ability of the active metabolites of clopidogrel and prasugrel to produce irreversible inhibition of platelet function.

BACKGROUND: Agents that act as antagonists at P2Y(12) ADP receptors on platelets are in use (clopidogrel), and in development for use (cangrelor and prasugrel), in patients with cardiovascular disease. Cangrelor is a direct-acting reversible antagonist being developed for short-term infusion; clopidogrel and prasugrel are oral prodrugs that provide irreversible inhibition via transient formation of active metabolites. At the cessation of cangrelor infusion, patients are likely to receive clopidogrel or prasugrel as a means of maintaining antiplatelet therapy. OBJECTIVES: To apply an experimental in vitro approach to investigate the possibility that cangrelor influences the ability of the active metabolites of clopidogrel and prasugrel to inhibit ADP-mediated platelet function. METHODS: The effects of cangrelor and the active metabolites of clopidogrel (C-AM) and prasugrel (P-AM) on platelet function were assessed by ADP-induced platelet P-selectin expression in whole blood. The method involved rapid removal of the antagonists by dilution, and measurement of residual platelet inhibition. RESULTS: Cangrelor, C-AM and P-AM markedly inhibited P-selectin expression. The effect of cangrelor, but not of C-AM and P-AM, was reversible following antagonist removal. Preincubation of blood with cangrelor prior to addition of C-AM or P-AM reduced the ability of metabolites to irreversibly antagonize P2Y(12). Irreversible inhibition was maintained when blood was preincubated with metabolites prior to cangrelor. CONCLUSIONS: Cangrelor influences the ability of the active metabolites of clopidogrel or prasugrel to inhibit platelet function irreversibly. Careful consideration should be given to the timing of administration of an oral P2Y(12) antagonist following cangrelor infusion.

Acyl derivatives of coenzyme A inhibit platelet function via antagonism at P2Y1 and P2Y12 receptors: a new finding that may influence the design of anti-thrombotic agents.

We have performed a detailed investigation of the effects on platelet function of coenzyme A (CoA) and several acyl-CoAs. Platelet aggregation was measured by turbidimetry and by platelet counting; platelet shape change was measured using light scattering; P-selectin, Ca2+ mobilization and vasodilator-stimulated phosphoprotein (VASP) phosphorylation were measured by flow cytometry. The compounds investigated inhibited ADP-induced platelet aggregation; those with saturated acyl groups containing 16-18 carbons were most effective. The effects of palmitoyl-CoA (16:0) were studied in depth. It inhibited platelet shape change and Ca2+ mobilization brought about by ADP (but not other agonists) indicating antagonism at P2Y(1) receptors, and also inhibited ADP-induced P-selectin expression. Effects of palmitoyl-CoA on the platelet aggregation and Ca2+ mobilization induced by several different agonists and agonist combinations were compared with those of MRS 2179 (a P2Y(1) antagonist) and AR-C69931 (a P2Y(12) antagonist), and were consistent with palmitoyl-CoA acting mainly at P2Y(1) but also with partial antagonism at P2Y(12) receptors. Antagonism at P2Y(12) receptors was confirmed in studies of VASP-phosphorylation. Palmitoyl-CoA did not act as an antagonist at P2X(1) receptors. The results are discussed in relation to the possibility that acyl-CoAs may contribute as endogenous modulators of platelet function and might serve as lead compounds for the design of novel antithrombotics.

[Platelet activation and inflammation markers in patients with coronary heart disease and depression].

AIM: To study morphological features and functional activity of platelets, their relations with the level of inflammation markers in coronary heart disease (CHD) patients with depression. MATERIAL AND METHODS: The study group consisted of 33 CHD patients with stable effort angina (NY-HA FC I-III), 14 had depression, 19 were free of depression. Sixteen healthy volunteers comprised the control group. Platelet aggregation was registered by a mean size of aggregates and turbidometrically. Platelets shape, leukocytic-thrombocytic and erythrocytic-thrombocytic aggregates (LTA, ETA) in the whole blood were studied electron-microscopically. The levels of IL-2, IL-6, TNF-alpha, sVCAM, hsCRP were measured in the blood, serotonin--in platelets. RESULTS: Spontaneous aggregation enhanced in 52.6% CHD patients (p < 0.05). The blood contained reticular platelets, high number of prothrombocytes (p < 0.05), mean volume of thrombocytes was greater (p < 0.05). This reflected changes in megakaryocytopoiesis. Some of the patients had LTA and ETA. Out of inflammation markers, only IL-6 and sVCAM were elevated (p < 0.01), hsCRP concentration rose, but not above normal range. Serotonin in platelets was the same in the patients and controls. Depression aggravated the disorders and elevated other indices. Spontaneous aggregation was high in 71.4% of depressive CHD patients. The count of reticular platelets, prothrombocytes, mean volume platelets were also elevated. LTA and ETA were high in all the depressive patients. Elevated were also concentrations of IL-6, sVCAM, IL-2, hsCRP. Serotonin in platelets was low (p < 0.05). CONCLUSION: Depression stimulates functional activity of platelets, is a factor of risk of intravascular inflammation and contributes to development of thrombotic complications in CHD patients.