ABSTRACT
A host of gastrointestinal (GI) peptides influence the regulation of vital functions, such as growth, appetite, stress, gut motility, energy expenditure, digestion and inflammation, as well as glucose and lipid homeostasis. Hence, impairments in the synthesis/secretion of glucagon-like peptide-1 (GLP-1), leptin, nesfatin-1, glucose-dependent insulinotropic peptide (GIP), ghrelin (acylated and unacylated forms), oxyntomodulin, vasoactive intestinal peptide, somatostatin, cholecystokinin, peptide tyrosineâtyrosine, GLP-2 and pancreatic polypeptide were previously associated with the development of obesity-related disorders. It is currently emphasized that the beneficial metabolic outcomes associated with the normalization of the gut microbiota (GM) is influenced by increases in GLP-1 and peptide YY secretion as well as by decreases in acylated ghrelin production. These effects are associated with reductions in body weight and adiposity in combination with the normalization of glucose and lipid metabolism. However, important questions remain unanswered regarding how GLP-1, peptide tyrosineâtyrosine, acylated ghrelin and other metabolically relevant GI peptides interact with the GM to modulate the host's metabolic functions. In addition, it is likely that the GM and other biologically active GI peptides influence metabolic functions, such as glucose control, although the mechanisms remain ill-defined. In this review, we investigate how GM and GI peptides influence glucose metabolism in experimental models, such as germ-free animals and dietary interventions. Emphasis is placed on pathways through which GM and GI peptides could modulate intestinal permeability, nutrient absorption, short-chain fatty acid production, metabolic endotoxemia, oxidative stress and low-grade inflammation.
