Gut microbiota is a unique microbiological community consisting of different microorganisms (mostly bacteria) that reside in the human intestine. Host immune and inflammatory homeostasis can be directly affected by these microorganisms. Indeed, gut microbiota imbalance, called dysbiosis, has been correlated with the occurrence of numerous disorders. Therefore, gut microbiota modulation has emerged as a promising strategy to prevent and manage the development of different metabolic diseases, including type 2 diabetes mellitus (T2DM), insulin resistance (IR) and obesity. In turn, probiotics have emerged as an alternative therapy, as microbiota-modulating agents, to ameliorate T2DM and T2DM-related disturbances, including IR, obesity, metabolic syndrome (MS), hepatic steatosis and inflammation. In this regard, the present thesis aims to study in-depth the normoglycemic and antiobesogenic activities of the probiotic Pediococcus acidilactici CECT9879 (pA1c®) in different in vivo models, to elucidate its mechanism of action, and the impact that exerts on gut microbiota. In the first Chapter, the normoglycemic and lipid-lowering activities of the probiotic pA1c®, and the determination of its mechanism of action were demonstrated in the Caenorhabditis elegans (C. elegans) in vivo model. In Chapter 2, through a screening conducted in C. elegans, the most normoglycemic synbiotics (between pA1c® and other bioactive compounds) were selected (being pA1c®+chromium picolinate (PC)+ Oatàß-glucans (BGC) the most active), and their mechanisms of action were described. Moreover, the normoglycemic efficacy of the selected synbiotics, as well as their microbiota-modulating effect by 16s metagenomics were evaluated in male mice. In Chapter 3, the activity of pA1c® against T2DM-related comorbidities independent of glucose metabolism, including inflammation, hypercholesterolemia, obesity and dyslipidemia, as well as its gut microbiota-shaping potential by 16s metagenomics were reported in rats. In chapter 4, the role of pA1c® and heat-inactivated pA1c® (pA1c® HI) in the regulation of glucose metabolism and in the modulation of the gut microbiota by shot-gun sequencing was shown in diet-induced gestational diabetes mellitus (GDM)-mice and in T2DM-female-mice. It was demonstrated that supplementation with pA1c®, alone and in combination with PC and BGC, together with the pA1c® HI significantly enhance the carbohydrate and lipid metabolism of C. elegans, mice and rats, based on hyperglycemia reduction, blood glucose regulation, adiposity and hepatic steatosis attenuation and IR alleviation. The different mechanistic studies carried out in this work demonstrate that these effects are mainly mediated by regulating the insulin signaling pathway, and by activating the peroxisomal- and mitochondrial-fatty acid (FA) Oatàß-glucans oxidation process and reducing lipogenesis in all in vivo models. The anti-diabetic properties of pA1c® have been accompanied by the reduction of the visceral adiposity by the inhibition of the hepatic lipogenesis, the decrease of the intrahepatic triglycerides (TGs), the enhancement of the cholesterol metabolism and the reduction of pro-inflammatory cytokines. Lastly, metagenomic analyses demonstrated that the probiotic was able to colonize the colon in all pA1c®-treated animals, settle in the intestine and revert the HFS diet-induced dysbiosis, through the increase in T2DM beneficial bacteria, the decrease in T2DM negative bacteria, the increase in the microbial Oatàß-glucans-diversity, the promotion of SCFA producing-bacteria and the competition of Pediococcus acidilactici with obesity and dyslipidemia-associated bacteria, such as species of the genus Streptococcus.
Thus, pA1c® could be considered as a potential probiotic strain for the prevention and management of T2DM and GDM and its related complications such as MS, obesity, IR, chronic inflammation, hypercholesterolemia, hepatic steatosis and gut microbiota dysbiosis.
