Role of the gut microbiota in the control of cardio-metabolic risk

An altered blood lipid profile and a suboptimal diet are among the main modifiable risk factors of cardiovascular diseases (CVDs), which remain the number one cause of death worldwide. Type 2 diabetes and non-alcoholic fatty liver disease (NAFLD) promote endothelial dysfunction, an early key biomarker of CVD and atherosclerosis-related clinical events, that lead to microcirculation damage. Increasing evidence shows that gut microbes regulate host physiological and metabolic pathways, namely by producing bioactive metabolites (e.g. bile acids [BAs]). This PhD thesis is a proof-of-concept of the involvement of the gut microbiota in the nutritional and pharmacological control of cardio-metabolic risk in mice. Our first experimental data reveal that widely prescribed hypolipidemic drugs (i.e. simvastatin and ezetimibe) are able to modulate microbial composition in murine model by changing the relative abundance of the Lactobacillus genus. Furthermore, these changes are associated with modified expression of genes coding for cholesterol-homeostasis in the liver and jejunum. During the second phase of the thesis, we develop a model of endothelial dysfunction in small resistance arteries (mesenteric arteries) associated with the NAFLD phenotype. Deficiency in n-3 polyunsaturated fatty acids (PUFAs) is a nutritional characteristic of the Western diet. We knew that wild-type mice fed an n-3 PUFA-depleted diet develop the “hepatic phenotype” of NAFLD in mice. The same n-3 PUFA-depleted diet given to Apolipoprotein E knock-out (Apoe-/-) mice for 12 weeks accelerates the process of endothelial dysfunction, decreases nitrosylated-hemoglobin (Hb-NO) levels and induces hepatic steatosis, independently of obesity, fat intake or inflammation. In the last part of the thesis, we describe, in this model, the impact of gut microbiota modulation by inulin-type fructans (ITFs), considered to be prebiotics. We highlight that ITF supplementation for two weeks is able to improve endothelial function in small resistance arteries (i.e. mesenteric arteries) and plaque-prone vessels (i.e. carotid arteries) isolated from n-3 PUFA-depleted Apoe-/- mice by activating the NOS/NO pathway and restoring Hb-NO levels. ITFs profoundly modulate microbial composition in favor of NO-producing bacteria (e.g. those from the Enterobacteriaceae family or the Bifidobacterium genus) and in disfavor of bacteria involved in secondary BA synthesis (e.g. those from the Lachnospiraceae or Ruminococcaceae families). Modifying the composition of the gut microbiota changes its ability to produce bacterial metabolites, as indicated by increased primary and free BA concentration and higher GLP-1 production, both of which can directly or indirectly activate the NOS/NO pathway by enhancing eNOS phosphorylation. This PhD thesis is the starting point for future clinical trials studying the role of gut microbes in the control of cardio-metabolic risk through prebiotic-based intervention.