Optical coherence tomography (OCT) has been considered as the ideal tool for the evaluation of atherosclerotic plaques. Circulating trimethylamine-N-oxide (TMAO), which is a metabolite of the dietary lipid phosphatidylcholine, has recently been linked to elevated coronary artery disease (CAD) risk. The objective of the study was to investigate the relation between circulating TMAO level and coronary plaque vulnerability assessed by OCT in patients with CAD. A total of 26 patients with CAD were recruited to assess coronary plaque using OCT and measure plasma TMAO level. According to plaque rupture status, patients were divided into plaque rupture group (n = 12) and nonplaque rupture group (n = 14). Plasma TMAO level was significantly higher in patients with plaque rupture than in those with nonplaque rupture (8.6 +/- 4.8 mu mol/L vs 4.2 +/- 2.4 mu mol/L, p = 0.011). Moreover, positive correlations between plasma TMAO level and lipid arc (r = 0.43, p = 0.031), lipid volume index (r = 0.39, p = 0.048) were also observed. In conclusion, circulating TMAO level may reflect coronary plaque vulnerability and progression. (C) 2016 Elsevier Inc. All rights reserved.