High-dose, but not low-dose, aspirin impairs anticontractile effect of ticagrelor following ADP stimulation in rat tail artery smooth muscle cells.

OBJECTIVE: To compare effects of low- versus high-dose aspirin coadministered with ticagrelor on the reactivity of vascular smooth muscle cells (VSMCs). METHODS: Wistar rats were orally administered ticagrelor (10 mg/kg) and/or aspirin (2 or 10 mg/kg) (n = 7 per each of 4 groups) or placebo (n = 9) 12 and 2 hours before experiments. Anticontractile effects of ticagrelor were assessed in perfusion solution containing ticagrelor (1 µM/L). Changes in perfusion pressure proportional to the degree of adenosine diphosphate analogue- (2-MeS-ADP-) and phenylephrine-induced constriction of rat tail arteries were evaluated. RESULTS: Pretreatment with high- but not low-dose aspirin enhanced the reactivity of VSMCs only in endothelium-lined vessels. Suppression of 2-MeS-ADP-induced VSMC contraction by ticagrelor observed in arteries with and without endothelium was maintained in endothelialized arteries pretreated only with low-dose aspirin. For endothelium-denuded vessels and low-dose aspirin we observed a significant reduction of the maximal effect of ticagrelor with no rightward shift of the concentration-response curve for phenylephrine. With high-dose aspirin pretreatment ticagrelor exerted no anticontractile effect. CONCLUSION: High-dose, but not low-dose, aspirin impairs the anticontractile effect of ticagrelor on ADP-induced VSMC contraction in the rat model. Both the clinical significance and detailed underlying mechanism of our findings require further investigation.

Cytochrome 2C19 polymorphism and response to adjunctive cilostazol versus high maintenance-dose clopidogrel in patients undergoing percutaneous coronary intervention.

BACKGROUND: Among patients treated with clopidogrel, carriers of the cytochrome P450 (CYP) 2C19 loss-of-function allele have shown increased platelet reactivity and higher rates of ischemic events. Although adjunctive cilostazol to dual antiplatelet therapy (or "triple antiplatelet therapy") intensifies platelet inhibition, it remains unknown whether triple antiplatelet therapy after percutaneous coronary intervention can achieve adequate platelet inhibition in patients with the CYP2C19 mutant allele. METHODS AND RESULTS: CYP2C19 genotyping for *1, *2, and *3 was performed in 134 high-risk patients undergoing elective percutaneous coronary intervention. After measurement of preprocedural platelet reactivity, patients were randomly assigned to receive either adjunctive cilostazol 100 mg twice daily (triple group; n=69) or high maintenance-dose (MD) clopidogrel of 150 mg daily (high-MD group; n=65). Using light transmittance aggregometry and the VerifyNow P2Y(12) assay, platelet reactivity was assessed before the index procedure and at 30-day follow-up. The primary end point was absolute change in maximal platelet aggregation (ΔAgg(max)) according to CYP2C19 genotyping. High posttreatment platelet reactivity was defined as 5 µmol/L ADP-induced maximal platelet aggregation >50%. In noncarriers of the CYP2C19*2/*3 mutant allele, ΔAgg(max) values after 5 and 20 µmol/L ADP stimuli did not differ significantly between the triple (n=22) versus the high-MD group (n=22) (23.6±21.6% versus 16.6±15.4%, P=0.224 and 26.4±22.2% versus 18.6±14.9%, P=0.174, respectively). Absolute changes in late platelet aggregation and P2Y(12) reaction unit were not different between the groups. The rate of high posttreatment platelet reactivity at 30-day follow-up also was comparable between the triple versus the high-MD group (4.5% versus 13.6%, P=0.607). In carriers of at least 1 CYP2C19*2/*3 mutant allele, the triple group (n=47) showed greater values of ΔAgg(max) after addition of 5 µmol/L (25.8±16.8% versus 11.1±19.8%, P<0.001) and 20 µmol/L ADP (26.3±16.0% versus 11.5±16.3%, P<0.001) compared with the high-MD group (n=43). Likewise, absolute changes in late platelet aggregation and P2Y(12) reaction unit were consistently greater in the triple versus the high-MD group. Fewer patients in the triple group met the criteria of high posttreatment platelet reactivity at 30-day follow-up compared with the high-MD group (6.4% versus 37.2%, P<0.001). CONCLUSIONS: Among high-risk patients undergoing elective percutaneous coronary intervention, adjunctive cilostazol can achieve consistently intensified platelet inhibition and reduce the risk of high posttreatment platelet reactivity irrespective of CYP2C19 genotyping. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT01012193.

Adding cilostazol to dual antiplatelet therapy achieves greater platelet inhibition than high maintenance dose clopidogrel in patients with acute myocardial infarction: Results of the adjunctive cilostazol versus high maintenance dose clopidogrel in patients with AMI (ACCEL-AMI) study.

BACKGROUND: Optimal platelet inhibition is an important therapeutic adjunct in patients acute myocardial infarction (AMI) undergoing coronary stenting. Whether adjunctive cilostazol to dual antiplatelet therapy (triple antiplatelet therapy) can inhibit enhanced platelet reactivity in patients with AMI yet has not been determined. The aim of this study was to assess the degree of platelet inhibition by triple antiplatelet therapy in patients with AMI. METHODS AND RESULTS: Immediately after emergency room arrival, patients with AMI received clopidogrel (600-mg loading dose, followed by 75 mg daily) and aspirin (300-mg loading dose and 200 mg daily throughout the study period). After patients underwent coronary stenting (n=90), they were randomly assigned to 1 of 3 groups before discharge: standard group, clopidogrel of 75 mg daily (n=30); high maintenance dose (MD) group, clopidogrel of 150 mg daily (n=30); and triple group, adjunctive cilostazol of 100 mg twice daily to clopidogrel of 75 mg daily (n=30). Platelet reactivity was assessed at predischarge and 30-day follow-up by conventional aggregometry and the VerifyNow P2Y12 assay. Predischarge platelet reactivities were similar in the 3 groups. At 30-day follow-up, inhibition of maximal aggregation with 20 microM ADP stimuli was 6.0% in the standard group, 19.1% in the high-MD group, and 42.4% in the triple group (P<0.001), whereas inhibition of late aggregation with 20microM ADP stimuli was 10.8%, 38.1%, and 66.4%, respectively (P<0.001). Similar results were demonstrated when 5 microM ADP was used. Furthermore, percent changes of P2Y12 reaction unit were significantly different among regimens (10.6% in the standard group, 30.7% in the high-MD group, and 43.0% in the triple group; P<0.001). With respect to high-postclopidogrel platelet reactivity (prespecified as 20 microM ADP-induced maximal aggregation >50% of light transmission), fewer patients in the triple group (13.3%) met the criteria as compared with those in the standard (76.7%) and high-MD groups (56.7%) at 30-day follow-up (P<0.001). In the triple group, there were more potent and consistent platelet inhibitions by all parameters as compared with the high-MD group except for percent changes of P2Y12 reaction unit (P=0.071). CONCLUSIONS: Among patients with AMI undergoing coronary stenting, triple antiplatelet therapy results in a greater antiplatelet effect at 30 days as compared with a high-MD clopidogrel or standard dual antiplatelet therapy.