Grant Abstract: Intestinal Biotin Absorption: Physiological and Pathophysiological Aspects

Grant Number: 5R01DK058057-18
PI Name: Said
Project Title: Intestinal Biotin Absorption: Physiological and Pathophysiological Aspects

Abstract: The long-term objectives of this renewal application continue to focus on investigating the molecular physiology of the intestinal absorption process of the water- soluble vitamin biotin, the transport system involved, i.e., the Sodium-dependent Multi- Vitamin Transporter (SMVT), and how the absorption process is affected by external/environmental factors and pathophysiological conditions. Biotin is indispensable for normal cellular metabolism, proliferation and survival. The vitamin acts as a co-factor for multiple carboxylases that play critical roles in fatty acid, glucose and amino acid metabolism. Emerging evidence also highlight an important roles for biotin in immune function and in gene expression. Humans and other mammals cannot synthesize biotin, and thus, must obtain the vitamin from exogenous sources via intestinal absorption. Intestinal absorption of biotin occurs via a Na+-dependent and regulated carrier-mediated process. In studies performed during the current funding period, we have generated a conditional (intestine-specific) SMVT- knockout (KO) mouse model to establish the relative contribution of SMVT toward intestinal carrier-mediated biotin absorption and obtained evidence that this system is the only biotin uptake system that operates in the gut. Unexpectedly, however, we came across a very interesting phenomenon in that all the SMVT KO mice developed spontaneous chronic intestinal inflammation, especially in the cecum. In other studies, we found that chronic alcohol exposure significantly inhibit intestinal biotin uptake and that the inhibition is mediated at the level of transcription of the SLC5A6 gene (the gene that encodes SMVT); our new preliminary findings suggest that the latter is, at least in part, mediated via epigenetic mechanism(s). In other new preliminary studies, we found that infecting mice with S. Typhimurium, and exposure to pro-inflammatory cytokines or to bacterial LPS to lead to a significant inhibition in intestinal biotin uptake. Based on our recently published observations and our new preliminary findings, our working hypotheses in this proposal are that the SMVT system is important for the maintenance of normal intestinal immunity and integrity, and that Salmonella infection, as well as exposure of the gut to pro-inflammatory cytokines or to bacterial LPS lead to a significant inhibition in intestinal biotin uptake. We also hypothesize that the inhibition in SLC5A6 transcription by chronic alcohol exposure is mediated, at least in part, via epigenetic mechanism(s). Three specific aims are proposed to test these hypotheses and will utilize state-of-the-art in vitro and n vivo physiological, cellular and molecular approaches. Results of these investigations should provide novel and valuable information regarding the role of SMVT in the maintenance of normal intestinal homeostasis and health, and on how infection with enteric pathogens (Salmonella), as well as exposure to pro-inflammatory cytokines (as in IBD), and to bacterial LPS (as in infection with gram negative bacteria) affect the absorption of the indispensable micronutrient biotin. The results should also shed further light onto how chronic exposure to alcohol (the most common and costly drug abuse, and a significant contributor to many disease categories) affect the normal physiology of intestinal biotin absorption.

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