The relationship between trimethylamine N-oxide and cardiovascular disease: effects on vascular cell function and association with atherosclerotic plaque characteristics.

The animal source foods-derived metabolite trimethylamine N-oxide (TMAO) has been associated with cardiovascular disease (CVD) and risk of major adverse cardiovascular events (MACE). Studies have shown that TMAO affects the development of atherosclerosis in vivo, and that it can induce a dysfunctional phenotype in human vascular endothelial cells in vitro, a key cell type in the pathogenesis of atherosclerosis. Less is known about the effect of TMAO on other major cell types in the vascular wall, including vascular smooth muscle cells (VSMC), which play a critical and complex role in atherogenesis and atherosclerotic plaque progression. In vivo and ex vivo studies of TMAO in atherosclerosis have been largely limited to identifying associations between markers of plaque development and TMAO levels in the blood.

In this project, two parallel studies were carried out to investigate whether TMAO affects the function of human VSMCs in a pathological manner, and whether TMAO can be detected and quantified in atherosclerotic plaque. The aims were to bring more insight into how TMAO promotes the development of atherosclerosis, and to explore the relationship between intra-plaque levels of TMAO and plaque characteristics. Using fluorescence imaging techniques, TMAO stimulation was found to disrupt the organisation of DNA in human smooth muscle cell lines isolated from donor umbilical cord arteries. Using a novel tissue homogenisation, metabolite extraction, and liquid chromatography-mass spectrometry based method, TMAO was detected and quantified in human carotid artery plaques, acquired from patients who underwent carotid endarterectomy. Plaque TMAO levels ranged between 0.002μM/mg and 0.03μM/mg. An association was found between intra-plaque TMAO concentrations and matrix metalloproteinase-8 levels.

These findings provide new information on the effect of TMAO on VSMCs and verify the occurrence of TMAO in atherosclerotic plaque, as well as establish the capacity to measure intra-plaque concentrations of TMAO-related metabolites. This project thereby introduces a novel approach to the study of TMAO in atherosclerosis.