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Title:Butyrate-induced upregulation of intestinal glucose transport and signaling pathways represent a possible nutrient therapy for individuals with malabsorptive disorders
Author(s):Mangian, Heather
Director of Research:Tappenden, Kelly A.
Doctoral Committee Chair(s):Fahey, George C.
Doctoral Committee Member(s):Tappenden, Kelly A.; Nakamura, Manabu T.; Dilger, Ryan N.
Department / Program:Nutritional Sciences
Discipline:Nutritional Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:Ph.D.
Genre:Dissertation
Subject(s):butyrate
malabsorption
glucose absorption
proglucagon
glucose transporter-2 (GLUT2)
sodium-dependent glucose cotransporter-1 (SGLT1)
Nutrient transport
glucagon-like peptide-1 (GLP-1)
glucagon-like peptide-2 (GLP-2)
distal intestine
proximal intestine
short chain fatty acid (SCFA)
Free Fatty Acid Receptor 2 (FFAR2)
Free Fatty Acid Receptor 3 (FFAR3)
fermentation
intestine
Abstract:Individuals with significant intestinal malabsorption face challenges digesting and absorbing sufficient nutrients. A number of intestinal diseases, including celiac disease, short bowel syndrome (SBS), necrotizing enterocolitis (NEC), and the inflammatory bowel diseases, Crohn’s disease and ulcerative colitis, contribute to malabsorption. The treatment of severe malabsorption often requires medical nutrition support strategies, including parenteral nutrition (PN), that are costly and associated with complications when administered as a long-term solution. Beyond the financial burden of intestinal diseases, there is an added price of psychological stress, medical complications, and limitations in lifestyle. Interventions aimed at increasing intestinal transport capacity may mitigate the negative consequences of a damaged intestine, and reduce the need or intensity of costly supportive therapies. Attaining nutrients is a careful orchestration of diet, digestion, and absorption. In a typical “Western” diet, approximately half the calories are derived from carbohydrates that are digested to monosaccharides (glucose, fructose, and galactose) in preparation for absorption. D-glucose is the major transport form of fuel for most tissues and, therefore, the focus of these studies. It is transported by the hexose transporters sodium-dependent glucose cotransporter-1 (SGLT1) and glucose transporter 2 (GLUT2). GLUT2 is a high-capacity, facilitative intestinal monosaccharide transporter that is upregulated by the short-chain fatty acids (SCFA) derived from the intestinal microbiota during fermentation. The objective was to identify the impact of the SCFA, butyrate, upon intestinal glucose transport capacity. The hypothesis that ileal butyrate would increase glucose transport capacity and that this would occur through increased GLUT2 abundance, or signaling, was tested. Further, possible mechanisms through stimulation of enteroendocrine L-cells by butyrate were examined. The initial studies used Caco2-BBE monolayers as an in vitro model for the human intestine to test for the upregulation of GLUT2 mRNA abundance by butyrate and other SCFA. Next, the impact of butyrate on glucose transport by the intestine was examined using the Sprague Dawley rat as an in vivo model. Finally, proglucagon mRNA, and the G-protein coupled receptors (GPCR), Free Fatty Acid Receptor FFAR2) and Free Fatty Acid Receptor 3 (FFAR3), were measured. To establish that butyrate increased the glucose transport capacity of the intestine through upregulation of GLUT2, mRNA abundance and promoter activation were measured in differentiated Caco2-BBe monolayers. Caco2-BBe monolayers were treated for 0.5-24 h with 0-20 mM butyrate and GLUT2 mRNA was measured using quantitative reverse transcription–polymerase chain reaction (RT-PCR). GLUT2 mRNA abundance was higher with 1-4 h of exposure to 2.5, 7.5, and 10 mM butyrate (P < .0001). Following transient transfection of the Caco2-BBe monolayers with the pGL3 luciferase reporter vector, butyrate treatment induced promoter activity in a dose-dependent fashion (P < 0.0001). Analysis of the GLUT2 promoter indicated that regions –282/+522, –216/+522, and –145/+522 had a heightened (P <0 .05) response to butyrate compared with 1135/+522 and 564/+522. These results demonstrated that butyrate upregulates GLUT2 mRNA abundance in Caco2-BBe monolayers by activating specific regions within the human GLUT2 promoter. Next, butyrate induced increases in GLUT2 mRNA were tested in vivo. Sprague Dawley rats were surgically modified with an ileal cannula for infusion of either 10 mM butyrate or saline solution (for 96 or 156 min) and a portal cannula for blood sampling. All rats received the tracer (3-O-[methyl-14C] –D-glucose (8 uCi) within a liquid meal, but were randomized to be FED (3 mg/kg BW D-glucose) or FASTED (0 mg/kg BW D-glucose). Glucose absorption by the proximal intestine decreased after extended ileal saline infusion compared to a shorter saline infusion (P< 0.05), but butyrate infusion attenuated this decrease. The mRNA abundance of hexose transporters responsible for glucose absorption also were measured. Butyrate increased jejunal GLUT2 (by 23%; P<0.05) but not SGLT1 mRNA. Within the L-cell, proglucagon mRNA abundance (the transcript coding for GLP-1 and GLP-2) was 2-fold higher in the cecum of butyrate-treated rats (P<0.0014). Butyrate also increased FFAR2 and FFAR3 mRNA abundance in the cecum. Taken together, butyrate increased glucose transport by the proximal intestine supported by an increase of jejunal GLUT2 and stimulation of FFAR2, FFAR3, and proglucagon within the L-cells in the cecum. Unexpectedly, the prolonged infusion of saline into the ileum decreased glucose transport by the proximal intestine. It is likely that saline prevented contact of intestinal contents with the mucosa and dramatically reduced stimulation of the mucosal cells. Treatment of the distal intestine with butyrate attenuated the loss of glucose transport capacity attributed to extended ileal saline. Thus, 10 mM butyrate, a physiologically relevant concentration, effectively maintained glucose absorption. The contact of butyrate with the mucosa of the distal ileum, cecum, and colon stimulated the intestinal L-cell to increase the abundance of proglucagon and the GPCR FFAR2 and FFAR3. These finding focus attention on butyrate, proglucagon, and its derived peptides (GLP-1, GLP-2) along with the taste receptors FFAR2 and FFAR3 for their important roles in intestinal absorption. The upregulation of glucose transport by butyrate is a nutrient therapy for individuals with malabsorptive disorders.
Issue Date:2014-05-30
URI:http://hdl.handle.net/2142/49775
Rights Information:Copyright 2014 Heather Jean Mangian
Date Available in IDEALS:2014-05-30
2016-09-22
Date Deposited:2014-05


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