Investigation into novel gut-microbiome mediated pathways in cardiovascular disease

Dietary metabolism is increasingly implicated in the regulation of cardiovascular disease and there is intense focus on understanding this relationship. The bacterial flora, which shows heterogeneity between individuals with seasonal and dietary influences, generates metabolites from dietary nutrients. One pathway involves carnitine, a large nutritional component of red meat, which is digested by bacteria into the downstream metabolite, trimethylamine N-oxide (TMAO). TMAO has been the primary focus of recent investigations as being both causative and predictive of heart disease which has included studies on the latter in heart failure and in myocardial infarction cohorts. Mechanistic actions of TMAO on heart disease, however, are still not well understood. The aim of the present study is to investigate mechanistic actions of TMAO by conducting metabolic pathway analysis of TMAO through a strategic series of experimental studies. These studies include investigations on the molecular and cellular basis of excitability, conduction and electrical remodelling in heart failure. Initial experiments using calcium fluorescence imaging suggested that the calcium transients of cardiomyocytes were larger in the presence of high levels of TMAO. It was hypothesised that TMAO altered ion channels response by potentiation of calcium currents. These changes in ionic currents would lead to pronounced changes in the cardiac action potential and so have effects on excitation contraction coupling. Furthermore, experiments were completed to demonstrate the molecular and cellular effects of TMAO, and its relationships with energy substrate uptake and utilisation. To investigate this, this work used a combination of evaluation of ATP, evaluation of LDH and a metabolic flux analyser to assess rates of oxygen consumption on rat and human cardiac cells. Once again, this experimental approach showed that high concentrations of TMAO negatively impacted cardiac cells function by altering cells bioenergetics. In summary, this work was able to provide insight on the mechanistic actions of TMAO and to find evidence of alterations of normal cardiac function by high levels of TMAO.