Background and Aims: Vascular negative remodeling characterized by excessive neointimal hyperplasia is the main cause for restenosis after reascularization of arterial ischemic diseases. The application effects of current methods for inhibiting neointimal hyperplasia are not sufficient enough. Previous studies demonstrated that the intestinal microbial metabolite trimethylamine N-oxide (TMAO) is associated with the risks of cardiovascular disease, but the relationship between TMAO level and the arterial remodeling process after injury is not reported so far. Therefore, this study was conducted to investigate the role of TMAO in specific neointimal hyperplasia and the mechanism, so as to provide a referential framework for studying the problem of restenosis after arterial injury.  
Methods: A total of 50 SD rats were used. Ten rats were served as normal control group, and the remaining 40 rats were equally randomized into 4 groups after creation of abdominal aortic balloon-injury model, and then were fed with the regular diet (model group), 1.5%TMAO solution (TMAO enhancing group), 1.0%DMB (inhibitory agent of TMAO production) solution (TMAO inhibition group), and suspending solution of fecal microbiota from normal rats through suspending (fecal microbiota transplantation group), respectively. Four weeks after model creation, the arterial blood samples were extracted to measure the plasm TMAO concentration by LC/MS, and injured segments of the abdominal aorta were harvested to observe the pathological changes by HE and EVG staining as well as the CD31 positive endothelial cells by immunohistochemical staining, and determine the expressions of eNOS and phosphorylation of eNOS at Ser1177 (p-eNOS Ser1177) by Western blot, as well as the ROS expression by immunofluorescence.
Results: Compared with the normal control group, in the other 4 groups, the plasma TMAO concentrations were all increased to different extents, with varied degrees of neointimal thickening and fragmentation or loss of the elastic fibers in the injured vascular segment, and all these changes were most marked in TMAO enhancing group followed by model group, with all differences significant (all P<0.05), while some differences were not significant between TMAO inhibition group or fecal microbiota transplantation group versus normal control group (all P>0.05). There was no significant difference in CD31 positive cells among the groups (P>0.05). There was no significant difference in the total eNOS expression levels among the groups (P>0.05), but the p-eNOS Ser1177 expression levels and numbers of ROS positive cells were reduced in all the modeling groups compared with normal control group, and these changes were also most evident in TMAO enhancing group followed by model group with all differences significant (all P<0.05), while the p-eNOS Ser1177 expression levels in TMAO inhibition group and fecal microbiota transplantation group showed no significant difference with normal control group, and the number of ROS positive cells showed no significant difference in fecal microbiota transplantation group and normal control group (all P>0.05).
Conclusion: TMAO level is increased after artery injury, and TMAO can promote the negative remodeling of the artery after injury. The mechanism may be associated with its facilitating the pathological migration and proliferation of the endothelial cells via eNOS-ROS pathway and thereby accelerating the neointimal hyperplasia.