Potential Association of Circulating MicroRNA-181c and MicroRNA-484 Levels with Cardiorespiratory Fitness after Myocardial Infarction: A Pilot Study

OBJECTIVES: In the field of exercise physiology, there has been great interest in exploring circulating microRNAs (miRs) as potential biomarkers. However, it remains to be determined whether circulating miRs reflect cardiorespiratory fitness. The aim of this study was to investigate the association between circulating levels of specific miRs and cardiorespiratory fitness evaluated by cardiopulmonary exercise testing (CPET) after acute myocardial infarction (MI). METHODS: Twenty patients who had had an acute MI were included. All patients underwent CPET in the convalescent phase. Quantitative real-time polymerase chain reaction analyses for miR-181 members (a/b/c) and miR-484 were performed to determine the expression levels in the peripheral blood of the included patients and healthy control subjects (n=5). RESULTS: Post-MI patients showed impaired exercise tolerance and ventilatory efficiency in CPET analysis. Compared with controls, circulating levels of miR-181a and 181c were gradually and significantly elevated through the 1st to 7th days after acute MI, whereas miR-181b and miR-484 were not. Circulating miR levels did not correlate with clinical or echocardiographic parameters. However, circulating levels of miR-181c and miR-484 on the 7th day showed significant positive correlations with the anaerobic threshold and peak oxygen consumption from CPET analysis. Moreover, miR-181c levels were inversely associated with the ventilatory inefficiency index. Patients with high exercise capacity after MI showed significantly higher expressions of circulating miR-181c and miR-484 than those with low exercise capacity. CONCLUSIONS: The results of this pilot study suggest that circulating levels of miR-181c and miR-484 after acute MI may be predictive biomarkers of post-MI cardiorespiratory fitness.