Abstract: Objective　To investigate the relationship between the expression level of plasma microRNA-223 (miR-223) and platelet reactivity as well as clinical prognosis in patients with acute coronary syndrome (ACS) after clopidogrel administration. Methods　A total of 208 ACS patients received percutaneous coronary intervention (PCI) were enrolled consecutively. All patients were treated with loading doses of clopidogrel combined with aspirin (DAPT) before intervention. Real-time PCR was used to quantify the expression level of plasma miR-223, and the platelet reactive index (PRI) was quantified through flow cytometry. Patients were divided into two groups according to the PRI median, low PRI group (PRI≤56.3%) and high PRI group (PRI>56.3%), with 104 cases in each group. Plasma miR-223 expression levels, basic clinical data and biochemical index were compared between two groups of patients. After 2-year follow-up, Cox proportional risk regression analysis was used to estimate the influencing factors of plasma miR-223 level, PRI, troponin I (TnI), B-type natriuretic peptide (BNP) and other parameters for major adverse cardiovascular events (MACE). The receiver operating characteristic (ROC) curve was plotted to evaluate the predictive ability of plasma miR-223 and PRI levels for MACE. Results　The level of circulating miR-223 was negatively correlated with PRI (rs=-0.420, P＜0.05), and miR-223 expression level was significantly higher in low PRI group compared with that of high PRI group [1.15 (0.58，1.80) vs.0.64 (0.26，1.08), Z=0.471, P＜0.05]. MACE occurred in 30 patients (14.4%), and the incidence of MACE was lower in low PRI group than that in high PRI group (P < 0.05). Cox proportional risk regression analysis showed that the plasma miR-223 level and PRI were independent risk factors for predicting MACE in ACS patients. The AUC of plasma miR-223 and PRI for predicting the occurrence of MACE in ACS patients was 0.700 (95%CI: 0.609-0.791, P＜0.05) and 0.710 (95%CI: 0.606-0.815, P＜0.05), respectively. Conclusion　The circulating miR-223 level is negatively correlated with PRI in ACS patients after taking clopidogrel. The circulating miR-223 level and PRI are independent factors for predicting MACE in ACS patients after PCI.

Key words: acute coronary syndrome, platelet aggregation inhibitors, microRNAs, miR-223, clopidogrel, platelet reactive index, dual antiplatelet therapy