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Profiling Metabolic Transport Along the Segmentally Stratified Rat Colon


The colon has long been considered as a waste-packing organ, but has been gaining importance with the discovery of the complex gut microbiome which is located primarily in the colon. The gut microbiome is comprised of more than 800 species of bacteria that help harvest energy, synthesize vitamins, and shape the immune system. Disturbances in the gut microbiome have been implicated in many diseases including allergies, autism, colorectal cancer, Crohn’s disease, diabetes, and obesity, making it critically important for human health. While the focus of most researchers has been solely on the bacterial component of the gut, little is understood about the mechanism of metabolic communication between the gut microbiome and its human host.

In this work, nuclear magnetic resonance, ion chromatography, and gas chromatography-mass spectrometry are used to identify and quantify major metabolites in extracts of fecal material isolated from the rat ileum, cecum, proximal, mid, and distal colon. These metabolites include short chain fatty acids that are the preferred energy source for colonocyte, amino acids, polyamines, bile acids, choline metabolites, phenolic compounds, and inorganic ions. This study provides information on the luminal metabolome, its stratification along the colon, and the assortment of metabolites available for absorptive transporters within each segment.

Metabolic profiling of along different segments of the colon provides knowledge about the metabolites available in the stool for transport across the epithelial tissue into the bloodstream or for further transformation by the gut microbiome. In this work, use of the Ussing chamber provides evidence of the transport behavior of metabolites including short-chain fatty acids, amino acids, vitamins, and choline derivatives across excised colonic epithelial tissue. These in vitro experiments utilize two chambers separated by epithelial tissue representing both the lumen and serosal sides of the colon. 1H-NMR analysis of these chambers has shown that over a dozen metabolites including SCFAs, amino acids, and choline derivatives are involved in transport.

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