Maltooligosaccharide Chemosensation by Intestinal Enteroendocrine L-Cells Regulates the Endogenous Release of Gut Hormones and Contributes to Weight Management in Vivo
Abstract
As obesity has become one of the most prevalent metabolic diseases, and diabetes mellitus has become the seventh leading causes of death in the United States, alternative food/nutrition-based approaches to tackle obesity that are both efficacious and cost effective are in high demand. Since starch and its derived products are the principal dietary supply of glucose, strategies of using slowly digestible starch to achieve moderated glycemic response and prolonged glucose delivery, as well as to locationally digest starch into the ileum, have shown successful results such as moderation of insulinemia and reducing food intake in obese animals. An important regulator of appetite suppression is the neuroendocrine system of the gut-brain axis. Glucagon-like peptide-1 (GLP-1), oxyntomodulin (OXM), and peptide YY (PYY) are the main anorexigenic peptide products of the intestinal enterendocrine L-cells that regulate postprandial insulin levels as well as satiety signals. The stimulation of the enteroendocrine L-cells throughout the gastrointestinal tract through glucose, fatty acids and proteins has been extensively studied and confirmed. However, the stimulatory effect of complex dietary carbohydrates on L-cells is not described. In this dissertation, we investigated the in vitro intestinal cell chemosensation of L-cells to α-amylase starch digestion products, named maltooligosaccharides (MOS), and in the possible application of using slowly digestible starch delivery of MOS in vivo. In Chapter II of this dissertation, we reported a significantly higher stimulatory effect of MOS on GLP-1 and OXM secretion compared to glucose in mouse and human L-cells, respectively. Additionally, maltotriose enhanced the relative expression of the gastrointestinal peptide, cholecystokinin. Moreover, MOS exhibited protective effects on barrier function and monolayer integrity of intestinal epithelial cells. In Chapters III and IV, we performed a multiomics approach where transcriptomic analysis and global protein profiling of mouse L-cells treated with different types of MOS showed that the carbohydrates exhibit their effects through the induction of exocytosis of GLP-1- or OXMcontaining vesicles and not through a positive regulation of the proglucagon gene expression. It is suggested that MOS induce higher secretion, but not higher synthesis, of the proglucagon gene products. In addition, maltotriose treatment downregulated the relative expression of the glucotoxicity marker, thioredoxin-interacting protein, and upregulated the relative expression of tight junction proteins supporting a role of MOS in barrier function integrity. Translating the in vitro findings into an in vivoapplication that is beneficial for human health required the use of controllable tool for the delivery of MOS throughout the small intestine for sensing by a higher number of L-cells. Slowly digestible starch (SDS), compared to rapidly digestible starch, provided such a tool. For this purpose, we used alginate-entrapped SDS microspheres that digest distally into the ileum to examine the role of SDS in the intervention and prevention of obesity in C57BL/6J diet-induced obese (DIO) and lean mice models. Results showed that 20% SDS in low-fat diets significantly improved weight loss and food intake reduction in DIO mice converted to low-fat diet for 12 weeks. Similarly, 15% SDS in high-fat diets showed significant reduction in body fat percent and significant increase in lean body mass as well as considerable reduction in weight gain rate and food intake in lean mice fed on 45% of calories high-fat diet. Immunohistochemistry of small intestine of mice in both the intervention and prevention studies revealed an even and thorough distribution of GLP-1 positive L-cells.
Degree
Ph.D.
Advisors
Hamaker, Purdue University.
Subject Area
Endocrinology|Neurosciences|Pharmaceutical sciences|Public health
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.