The role of Trymethylamine N-oxide (TMAO) in the modulation of the endothelial function: an 'in vitro' study.

Trimethylamine N-oxide (TMAO) is a diet-derived compound, that could be introduced directly through fish products or indirectly from its dietary precursors, L-carnitine, choline and betaine. These precursors are metabolized by the gut microbiota to trimethylamine (TMA), that is absorbed by the enterocytes in the colon and transported via the portal circulation to the liver; here Flavin-containing monooxygenase 3 (FMO3) oxidizes TMA to TMAO. Several studies suggest a proatherogenic role of TMAO, as high plasma concentration of this molecule seems to be correlated with platelet hyperreactivity and endothelial dysfunction. However, the molecular mechanisms involved in these detrimental effects of TMAO are still unclear. Thus, the aim of this study is to investigate the effects of TMAO on endothelial cells, in both basal condition and in presence of known vascular stressors; moreover, the role of TMAO in the modulation of the endothelial purinergic response sustaining vasodilation was investigated. The experiments were performed on bovine aortic endothelial cells (BAE-1), by assessing cell viability and several functional parameters with specific fluorescent probes. The study showed no direct effects of TMAO on viability, ROS production and mitochondrial membrane potential in BAEC, in both basal and stressed conditions. Nevertheless, we observed that TMAO lead an alteration of the purinergic response in both calcium signal and nitric oxide (NO) release. Results obtained in this study suggest a possible role of TMAO in reducing the purinergic response of endothelial cells on the calcium/NO pathway, and thus interfering with the physiological vasodilatory mechanisms.