Articles in PresS. Am J Physiol Gastrointest Liver Physiol (August 29, 2013). doi:10.1152/ajpgi.00231.2013
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Recent advances in transport of water-soluble vitamins in organs of the digestive system: a
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focus on the colon and the pancreas
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Hamid M. Said
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Departments of Medicine, Physiology/Biophysics, University of California, Irvine, CA 92697 and
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the Department of Veterans Affairs Medical Center, Long Beach, CA 90822
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Running title: Vitamin transport in the large intestine and the pancreas
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- Address for reprint requests and other correspondence: H. M. Said, VA Medical Center-
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151, and Long Beach, CA 90822. Tel: (562) 826-5811. Fax: (562) 826-5675. Email:
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[email protected]
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- The study was supported by grants from the Dept. of Veterans Affairs, and the NIH [DK-
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58057, DK-56061, and AA 018071].
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Copyright © 2013 by the American Physiological Society.
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Summary
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This review focuses on recent advances in our understanding of the mechanisms and
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regulation of water-soluble vitamins (WSV) transport in the large intestine and the pancreas, two
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important organs of the digestive system that have not gotten their fair share of progress until
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recently. WSV, a group of structurally unrelated compounds, are essential for normal cellular
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functions and development, and thus, for overall health and survival of the organism. Humans
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cannot synthesize WSV endogenoursly, rather they obtain them from exogenous sources via
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intestinal absorption. The intestine is exposed to two sources of WSV: a dietary source, and a
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bacterial source (i. e., the WSV that are generated by the large intestinal microbiota).
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Contribution of the latter source toward human nutrition/health has been a subject of debate, and
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doubt, mostly on the basis that the large intestine does not have specialized systems for efficient
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uptake of WSV. However, recent studies utilizing a variety of human and animal colonic
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preparations have clearly demonstrated that such systems do exist in the large intestine. This has
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provided strong support that the microbiota-generated WSV are of nutritonal value to the host,
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and especially to the nutritional needs of the local colonocytes and their helath.
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With regards to the pancreas, WSV are essential for normal metabolic activities of all its
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cell types, and for its exocrine and endocrine functions. Again significant progress has also been
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made regarding the mechanisms involved in the uptake of WSV, and the effect of chronic
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alcohol exposure on the uptake processes.
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Keywords: Colon, pancreas, transport, thiamine, riboflavin, niacin, pyridoxine, biotin, folate.
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Introduction
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The WSV are essential for normal human health and well-being due to their involvement
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in critical metabolic reactions that affect all aspects of cell functions and survival. Deficiency of
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these micronutrients (which could be either systemic or localized, i. e., tissue specific) leads to a
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variety of clinical abnormalities (and ultimately to death), while optimizing their body
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homeostasis improves health and prevents certain diseases. Humans cannot synthesize these
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micronutrients (except for some endogenous synthesis of niacin) and must obtain them from
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exogenous sources via intestinal absorption. The human intestine is exposed to two sources of
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WSV: a dietary source (which is mainly absorbed in the small intestine), and a bacterial source
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(in reference to the vitamins generated by the large intestinal microbiota). It is the intention of
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the first part of this review to focus on recent advances in our understanding of the mechanisms
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involved in the uptake of the microbiota-generated WSV, how these processes are regulated, and
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how they are affected by external factors.
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In the second part of the review, the focus will be on recent advances in the
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understanding of the mechanisms involved in the uptake of WSV by pancreatic exocrine (acinar)
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and endocrine (beta) cells, their regulation, and the effect of chronic exposure to alcohol.
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I) Production of WSV by intestinal microbiota and their absorption in the large intestine:
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A) Production of WSV by large intestinal microbiota: One of the most obvious advantages of
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the symbiosis that exists between a host and its intestinal microorganisms is the supply of
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indispensable nutrients, like vitamins, that are generated by the bacteria. Such a relationship
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between hosts and intestinal microbiota has been recognized for some time. The pioneering work
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of Cooper (22) in 1914 showing that pigeons with polyneuritis due to vitamin B1 (thiamine)
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deficiency could be cured by feeding the animals an extract of fecal material, was among the first
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to suggest that bacterial microflora synthesize WSV. Subsequent studies have confirmed this
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suggestion by actual chemical identification of the vitamin in human and animal fecal material
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(1). The amount of WSV generated by intestinal microbiota vary depending on the type of the
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diet consumed, being larger following consumption of a diet that is rich in complex
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carbohydrates (fiber), than a diet that is rich in simple carbohydrate (e.g., sucrose) or meat (5, 19,
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38, 55). The amounts of some of these vitamins (e.g., biotin, pyridoxine) found in the fecal
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material is similar or greater than that ingested in the diet (55). Knowledge about the bacterial
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species that produce the bulk of these valuable micronutrients has also been forthcoming in
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recent years, and it is now known that it is not necessary that the most abundant bacterial species
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produce the largest amount of WSV (2). We further know that the human intestinal microbial
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communities undergo selective pressure from the host and from other microbial competitors (2,
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19, 25, 102), and that they are also influenced by external factors (e. g., use of antibiotics; 25).
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An interesting recent discovery was the finding that the human gut microbiota is functionally
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clustered into three distinct enterotypes: enterotypes 1, 2, and 3 (2).
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biosynthetic pathways are represented in all these enterotypes, enterotype 1 (enriched in
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Bacteroides) was found to be especially over-represented by enzymes involved in the
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biosynthetic pathway of the WSV biotin as well as that of riboflavin, pantothenic acid and
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ascorbate, while enterotype 2 (enriched in Prevotella) is over-represented by enzymes involved
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in the biosynthetic pathways of thiamine as well as folate (2). The identification of such
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functional differences among enterotypes in different human population groups may have
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nutritional and physiological consequences, but this requires further investigations.
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B) Absorption of WSV in the large intestine:
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While all the WSV
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i) Absorption of vitamin B1 (thiamine):
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Thiamine was the first member of the family of WSV to be described, with reference to
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the effects of its deficiency (beriberi) being suggested some 4000 years ago in the old Chinese
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medical literatures. The vitamin, in its pyrophosphate forms (mainly thiamine pyrophosphate,
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TPP; the most abundant form of vitamin B1 in mammalian cells), is indispensable for oxidative
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energy (sugar) metabolism, ATP production in the mitochondria, and for reducing cellular
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oxidative stress (17, 83); it is also important for maintaining normal mitochondrial structure and
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function (the mitochondria is the major site of accumulation and utilization of thiamine) (13).
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Thus, low intracellular levels of thiamine leads to acute energy failure, propensity for oxidative
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stress, and mitochondrial abnormalities (13, 17, 64, 83, 101). There are two types of thiamine
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deficiencies: systemic and localized (tissue specific). Systemic thiamine deficiency leads to a
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variety of clinical abnormalities including cardiovascular and neurological disorders (reviewed in
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22), and occurs in chronic alcoholism (98, 99), in patients with inflammatory bowel disease (30),
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and those with diabetes mellitus (78), among others.
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deficiency (which occurs despite normal plasma thiamine level) occurs in patients with the
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autosomal recessive thiamine-responsive megaloblastic anemia (TRMA) and thiamine-
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responsive Wernicke’s-like encephalopathy (26, 32, 43, 69) disorder, and leads to tissue-specific
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pathology.
Localized (tissue-specific) thiamine
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The human colonic microbiota synthesize considerable amounts of thiamine and this
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thiamine exists in both the free and phosphorylated (TPP) forms (2, 36, 59, 104). Studies have
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shown that the large intestine is capable of absorbing free thiamine (40), and recent
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investigations using the non-transformed human-derived colonic epithelial NCM460 cells and
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native human colonic mucosa have shown that this occurs via an efficient, specific, Na5
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independent, pH sensitive carrier-mediated mechanism (76). Both of the human thiamine
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transporters 1 and 2 (THTR-1 and THTR-2; products of the SLC19A2 and SLC19A3 genes,
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respectively) are expressed in the human colonocytes, with expression of the former being higher
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than the latter (26, 29, 32, 43, 65). Other studies have used live-cell confocal imaging and
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immunological approaches to show that the hTHTR-1 protein is expressed at both the apical and
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the basolateral membrane domains of absorptive epithelia, while expression of the hTHTR-2
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protein is restricted to the apical membrane domain of these polarized cells (87, 89) (Figure 1).
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The relative contribution of THTR-1 & 2 toward carrier-mediated thiamine absorption has also
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been recently examined in intestinal absorptive epithelia using a gene-silencing approach in vitro
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and a gene knockout (KO) approach in vivo (67, 72), with the results showing a role for both
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systems in the absorption process. Finally, the colonic thiamine uptake process appears to be
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under the regulation of an intracellular Ca2+/calmodulin-mediated pathway, which seems to
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influence its activity and affinity (76).
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With regards to the microbiota-generated TPP in the large intestine, it was considered to
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be of no nutritional value to the host due to the prevailing belief that absorptive epithelia are
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unable to transport such a large, water-soluble, and charged molecule across their phospholipid
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cell membrane prior to its hydrolysis to free thiamine (68). This is especially the case for the
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colon, which has little or no luminal phosphatase activity (11, 18, 24). This belief, however, has
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been recently corrected in studies utilizing human colonic epithelial NCM460 cells and purified
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apical membrane vesicles (AMV) isolated from colonic mucosa of human organ donors (56).
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These studies have shown for the first time that human colonocytes possess a highly efficient
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(apparent Km = 0.16 ± 0.03 µM) carrier-mediated mechanism for TPP uptake (Figure 1). This
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system is pH- and Na+- independent, energy-dependent, and is highly specific for TPP (is not
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affected even by free thiamine and thiamine monophosphate) (56). These studies have also
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shown that the colonic TPP uptake system is influenced by extracellular and intracellular factors
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in that it is adaptively regulated by extracellular TPP levels (via what appears to be a
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transcriptionally-mediated mechanism), and by an intracellular Ca2+/calmodulin-mediated
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pathway (56). The finding that human colonocytes posses efficient uptake mechanisms for free
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thiamine and for its phosphorylated TPP form suggest that the bacterially synthesized vitamin
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contributes to the overall host thiamine nutrition, and especially toward the cellular nutrition and
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health of the local colonocytes.
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Other studies have examined the effect of chronic alcohol exposure on colonic uptake of
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thiamine and showed a significant inhibition of the uptake process (94) (in the setting of chronic
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alcohol exposure, ethanol reaches the colon from the blood side). Part of this inhibition could be
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caused by the alcohol metabolite acetaldehyde, which is generated by the colonic bacteria from
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ethanol that enters the colonic lumen (colonocytes have limited ability to detoxify this metabolite
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as they have low levels of acetaldehyde dehydrogenase activity; 78). The mechanism through
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which alcohol causes this inhibition in colonic thiamine uptake is not clear, but could be similar
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to what has been found in the small intestine mediated (at least in part) via transcriptional
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mechanism(s) (94). Finally, colonic thiamine uptake may also be negatively impacted by
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infection with the gram-negative enteropathogenic Escherichia coli (EPEC), a foodborne
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pathogen (3). EPEC infection of intestinal absorptive epithelia causes a significant inhibition in
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thiamine uptake, an effect that starts with an early onset via reduction in level of THTR-1 & 2
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proteins at the apical membrane, followed by a more prolonged phase of inhibition mediated by
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suppression in transcriptional activity of the SLC19A2 and SLC19A3 promoters.
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ii) Absorption of vitamin B2 (riboflavin):
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Riboflavin (RF), in the form of its metabolically active coenzyme, flavin mononucleotide
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and flavin adenosine dinucleotide, plays an important role in the transfer of electrons in
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biological oxidation-reduction reactions (e. g., carbohydrate, amino acid, and lipid metabolism,
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as well as conversion of folic acid and vitamin B6 to their active forms) (reviewed in 71).
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Systemic RF deficiency leads to a variety of clinical abnormalities that include degenerative
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changes in the nervous system and endocrine dysfunction; such deficiency occurs in patients
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with inflammatory bowel disease and chronic alcoholics, among others (reviewed in 71).
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The normal microflora of the large intestine synthesize considerable amounts of RF and a
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significant portion of this RF exists in the free absorbable form (2, 39, 59). The amount of RF
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produced by the intestinal microbiota varies depending on the type of diet consumed, being
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higher following ingestion of a vegetable-based diet than a diet that is meat-based (39). Previous
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studies have shown that the mammalian colonocytes are capable of absorbing RF (40, 83), with
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recent investigations utilizing the human-derived colonic epithelial NCM460 cells, showing the
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involvement of a highly efficient (apparent Km of 0.14 μM) and specific carrier-mediated
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mechanism (Figure 1) (75).
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transporter- 1 & 3 (RFVT-1 and RFVT-3) are expressed in the large intestine (93, 105, 107),
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with expression and activity of RFVT-3 being significantly higher than that of RFVT-1. These
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findings together with the observation that knocking down RFVT-3 with gene-specific siRNA
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leads to a severe inhibition in RF uptake by absorptive epithelia suggest that this transporter
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plays a prominent role in RF uptake in the gut epithelia (93). Other studies have used live-cell
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confocal imaging to show that the RFVT-1 protein is expressed mainly at the BLM domain of
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absorptive epithelia, while expression of RFVT-3 is exclusively confined to the apical membrane
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domain of these cells (90, 93) (Figure 1).
Also, both of the recently cloned RF transporters, i.e., RF
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Other studies have shown that colonic RF uptake process is adaptively regulated by
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extracellular RF levels with a significant and specific up-regulation and down-regulation in
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uptake occurring in RF-deficient and over-supplemented conditions, respectively (75). This
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adaptive regulation in colonic RF uptake was mediated via changes in the number (and/or
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activity) of the RF uptake carriers and involves transcriptional regulatory mechanism(s) (75).
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Finally, the colonic RF uptake process appears to also be under the regulation of an intracellular
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Ca2+/calmodulin-mediated regulatory pathway (75).
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The effect of chronic exposure to alcohol on colonic RF uptake has also been recently
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examined in a rat model with a significant inhibition being observed (92). The mechanism(s) by
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which alcohol causes this inhibition in colonic RF uptake is not clear but could be similar to
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what has been observed in other intestinal absorptive epithelia (intestinal/renal) being mediated,
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at least in part, via transcriptional mechanism(s) (92).
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iii) Absorption of vitamin B3 (niacin, nicotinic acid/nicotinamide):
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Niacin acts as a precursor for the synthesis of the coenzymes NAD and NADP, which
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participate in a variety of metabolic reactions that maintain cellular redox state. Recent studies
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have also suggested roles for niacin in maintaining normal intestinal homeostasis and reducing
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gut inflammation, in regulating the level of production of intestinal antimicrobial peptides, and in
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regulating the activity of the mammalian target of rapamycin (mTOR) signaling pathway (which
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is involved in cell proliferation, protein synthesis, and transcription) (37). Niacin deficiency
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leads to pellagra, a disease that is characterized by inflammation of mucous membranes, skin
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lesions, diarrhea, and dementia; it is of interest to also mention here that over 90% of patients
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with pellagra develop colitis (79, 86), which demonstrates the important role that niacin plays in
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the maintenance of normal colonic health.
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As with many other WSV, niacin is synthesized in a significant quantity by the large
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intestinal microbiota (20, 60), but until recently this source of the vitamin was assumed to be of
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little or no nutritional value due to the belief that the large intestine is incapable of absorbing the
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vitamin (31 and references therein). Recent studies by Kumar et al (47), however, have directly
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tested the ability of mammalian colonocytes to take up niacin and delineated the mechanism
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involved. Thus, using human colonic epithelial NCM460 cells, as well as native human colonic
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apical membrane vesicles obtained from organ donors, and intact mouse colonic loops in vivo, it
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was shown that uptake of nicotinic acid by colonic cells is via an acidic pH (but not Na+) -
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dependent, specific and high affinity (apparent Km = 2.50 ± 0.80 µM) carrier-mediated process
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(Figure 1) (47). This process is not affected by other bacterially produced monocarboxylic acids,
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nor by substrates of the human organic anion transporter-10 (i.e., urate and p-aminohippurate), a
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system that was believed to play a role in nicotinic acid uptake (6). Other studies have shown
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that, the colonic nicotinic uptake process is regulated by extracellular substrate availability and
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by intracellular PTK- and Ca2+ -calmodulin - mediated regulatory pathways (47). The above
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findings, which establish the existence of a highly efficient carrier-mediated mechanism for
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niacin uptake by colonocytes, support the concept that the bacterially synthesized niacin
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contributes to host niacin nutrition, and especially toward the cellular nutrition and health of the
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local colonocytes. Supporting the latter is the previous reporting of colitis in more than 90
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percent of patients with pellagra (79), a disease caused by niacin deficiency. Also, niacin
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supplementation appears to alleviate the severe colitis that occurs in mice deficient in the
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angiotensin I converting enzyme 2 (37).
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iv) Absorption of vitamin B7 (also known as vitamin H; biotin):
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Biotin acts as a cofactor for five carboxylases that play critical roles in fatty acid and
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amino acid metabolism, and in gluconeogenesis; the vitamin also plays a role in regulating gene
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expression, normal immune function, and cell proliferation (reviewed in 6). Systemic biotin
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deficiency leads to growth retardation, neurological disorders, and dermatological abnormalities;
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also, biotin deficiency during pregnancy (at least in animals) causes embryonic growth
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retardation, congenital malformation, and death (reviewed in 6). Deficiency and sub-optimal
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levels of biotin occur in a variety of conditions including inflammatory bowel diseases, long-
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term parenteral nutrition, and chronic alcoholism (6).
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The large intestinal microbiota synthesize considerable amounts of biotin (estimated to be
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similar or greater than that taken in the diet; 55), and that a significant portion of this biotin
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exists in the free (protein-unbound) form, and thus, available for absorption (59). Recent studies
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that have classified the human gut microbiome into three functional enterotypes have reported
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that enterotype 1 is especially over-represented in enzymes involved in the biotin biosynthetic
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pathway, implying a larger biotin generation in this group (2, 110).
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colonocytes can absorb biotin (16, 40, 83), and recent investigations have shown that this occurs
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via an efficient (apparent Km of 19.70 µM) carrier-mediated mechanism (Figure 1) (74). While
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this mechanism is specific for biotin and its close structural analogues (with a free carboxyl
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group), it also transports another water-soluble vitamin, namely pantothenic acid (vitamin B5;
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pantothenic acid plays a central role in energy-yielding metabolic reactions as well as in fat and
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protein metabolism), which is also synthesized by the intestinal microbiota (74). It is for this
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reason that the transport system is referred to as the sodium-dependent multivitamin transporter,
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SMVT. The SMVT protein is a product of the SLC5A6 gene and mRNA of this gene is
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expressed in mammalian small and large intestine. The SMVT protein is exclusively expressed at
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Human and animal
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the apical membrane domain of polarized absorptive epithelia as shown by immunological,
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functional, and live-cell confocal imaging studies (Figure 1) (88). Other studies have described
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the existence of an accessory protein, PDZD11, in human colonic epithelial cells that interact
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with the SMVT (at the C-terminal of the transporter) and affect its function and cell biology
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(Figure 1) (57). While another potential biotin transport system has been suggested in other
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tissues (108), the SMVT system appears to be the only system that operates in the mammalian
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gut. The latter conclusion is based on recent findings utilizing gene-specific silencing (siRNA)
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approach in vitro (10) and conditional (intestinal-specific) SMVT knockout (KO) mouse model
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in vivo (34). In the latter studies, a complete inhibition in gut biotin (and pantothenic acid)
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uptake in the SMVT KO mice was observed. Several interesting phenotypes were also observed
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in these SMVT KO animals (34). The first is that two thirds of the KO animals died prematurely
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prior to reaching the age of 2.5 months due to acute peritonitis. The second is that all the KO
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mice showed severe growth retardation and decreased bone density and length. The third is that
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all the KO animals showed severe histological abnormalities in the large intestine (chronic active
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inflammation, dysplasia) as well as the small intestine (shortened villi, dysplasia) (Figure 2).
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While the mechanism(s) that mediates the distal gut inflammation is not clear, it is likely related
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to the role played by biotin in maintaining normal innate and adaptive immune functions (55).
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Example of the latter is the important role played by biotin in the activity of intestinal NK cells
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(62); these cells play an important role in maintaining normal intestinal epithelial homeostasis
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and in promoting antipathogen response (62, 104). It is interesting to mention here that the
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activity of these cells (as well as the biotin level) is suppressed in patients with Crohn’s disease
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(4, 61, 62, 104).
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The colonic biotin uptake process appears to be under the regulation of an intracellular
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protein kinase C (PKC) - mediated pathway (74). Other studies have shown that chronic alcohol
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exposure leads to a significant inhibition in colonic carrier-mediated biotin uptake (95). The
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mechanism through which chronic alcohol exposure causes inhibition in colonic biotin uptake is
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not clear but could be similar to what has been found in other intestinal epithelia mediated (at
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least in part) via transcriptional mechanism(s) (95). Further studies are needed to confirm this
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suggestion.
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v) Absorption of vitamin B9 (Folate):
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Folate (a term that refers to all derivatives of folic acid) is required for the biosynthesis of
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pyrimidine and purine nucleotides (precursors of DNA and RNA, respectively); it also plays an
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important role in the metabolism of several amino acids like homocysteine. Thus, an adequate
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supply of folate is necessary for normal cellular function and growth/repair. Systemic deficiency
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and sub-optimal levels of folate lead to a variety of clinical abnormalities that include
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megaloblastic anemia, growth retardation, and neural tube defects in the developing embryo.
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Such a deficiency is highly prevalent worldwide and occurs in different conditions like chronic
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alcoholism, patients with intestinal diseases (e. g., celiac disease and tropical sprue), and those
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with the genetic disorder hereditary folate malabsorption syndrome. Existence of a localized
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folate deficiency in tissues like colonic mucosa has also been implied and suggested to play a
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role in the development of pre-malignant changes (23, 48).
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The large intestinal microbiota synthesize folate in amounts that could approach or
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exceed the level in the diet (5, 23, 48), amount of this folate can be modulated by incorporating
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fiber and prebiotics into the diet (5, 41, 44, 99). A number of studies have indicated that the
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microbiota generated folate is of nutritional value to the host. For example, feeding animals a
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folate deficient diet causes growth retardation and severe folate depletion only when sulfa drugs
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are added to the diet (15, 43, 102). Other studies have shown that the introduction of
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radiolabelled p-aminobenzoic acid (a folate precursor) into the lumen of animal large intestine
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leads to the appearance of radiolabelled folate in different tissues (70).
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The mechanism of folate uptake by human colonocytes has been delineated in studies
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using purified membrane vesicles isolated from the colon of organ donors and human-derived
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colonic epithelial NCM460 cells (28, 46). These studies have shown that folate uptake by human
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colonocytes across the apical membrane domain is via an efficient (apparent Km of 8.20 + 2.40
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µM), specific, and pH-dependent carrier-mediated mechanism (Figure 1). This mechanism is
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sensitive to the inhibitory effect of the anion transport inhibitors 4,4'-diisothiocyanostilbene-2,
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2’-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2, 2’-disulfonic acid (SITS)
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(28, 46). Exit of folate out of the human colonocytes across the basolateral membrane has also
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been shown to involve a specific carrier-mediated mechanism (27). Both the reduced folate
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carrier (RFC) and the proton-coupled folate transporter (PCFT) are expressed in the colon, with
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expression of the former being higher than that of the latter (52, 80, 109). This combined with
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the fact that the colonic pH is more favorable for the function of RFC over PCFT, suggests that
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the former system plays a larger role in colonic folate uptake (Figure 1). The colonic folate
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uptake process also appears to be under the regulation of an intracellular cAMP- (through a
310
mechanism independent of protein kinase A), and a protein-tyrosine kinase- mediated pathway
311
(46).
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II) Uptake of WSV by pancreatic cells:
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i) Uptake of vitamin B1 (thiamine):
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As mentioned earlier, thiamine is essential for normal metabolic functions of all cells and
315
that low intracellular levels of the vitamin leads to impairment in energy metabolism, oxidative
316
stress, and mitochondrial abnormalities. The pancreas contains high levels of thiamine (64),
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which it must obtain from its surrounding, as cells of this organ cannot synthesize the vitamin
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endogenously. Thiamine is important for both the exocrine and endocrine functions of the
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pancreas (81). With regards to the exocrine function, thiamine deficiency leads to a severe
320
reduction in its content of digestive enzymes (81). As to the endocrine function, deficiency of
321
this vitamin results in a marked impairment in insulin synthesis and secretion (66). Of relevance
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to the latter is the development of diabetes mellitus in patients with thiamine responsive
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megaloblastic anemia (TRMA) (51, 59), an autosomal recessive disorder caused by mutations in
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THTR-1 (26, 32, 43). These mutations produce impairment in cellular thiamine accumulation
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and the development of localized thiamine deficiency in pancreatic β-cells (and other affected
326
tissues). This in turn leads to derangements in cellular metabolism, cell stress, and apoptosis (59).
327
Supplementation of TRMA patients with high doses of thiamine markedly improves the clinical
328
symptoms of the disease including a reduction or cessation in the need for exogenous insulin (51,
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59).
330
The mechanism of thiamine uptake by pancreatic β-cells and islets, its regulation, and
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how clinically-relevant mutations in THTR-1 found in patients with TRMA patients affect the
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physiology and cell biology of the system have been recently addressed using mouse-derived
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pancreatic β-TC-6 cells and freshly isolated primary mouse and human pancreatic islets (53).
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Results of these studies have shown that thiamine uptake is via a specific and pH (but not Na+)-
335
dependent carrier-mediated process that saturates at both the nanomolar (apparent Km of 37.17 ±
336
9.90 nM) and micromolar (apparent Km of 3.26 ± 0.86 μM) ranges. Also, both THTR-1 & -2 are
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expressed in mouse and human pancreatic β-cells with higher expression of the former compared
338
to the latter (91). Other studies have shown that the thiamine uptake process of pancreatic β-cells
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is adaptively regulated by extracellular substrate level via, at least in part, a transcriptional
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mechanism(s) (53); also the process appears to be under the regulation of an intracellular
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Ca2+/calmodulin- and protein-tyrosine kinase- mediated pathway (53). Finally, clinical mutants
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of the THTR-1 were found by live cell confocal imaging to result in mixed expression
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phenotypes of this transporter in β-cells; however, all were functionally impaired (53).
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With regards to the mechanism and regulation of thiamine uptake by pancreatic acinar
345
cells, this issue has also been recently addressed using freshly isolated rodent primary and
346
cultured pancreatic acinar cell lines (rat-derived AR42J and mouse-derived 266-6 pancreatic
347
acinar cells) (91, 96). The results show the involvement of a specific carrier-mediated
348
mechanism, in that both THTR-1 & -2 are expressed in these cells, although at a lower level
349
compared to pancreatic B-cells (91). The relative contribution of these transporters toward total
350
carrier-mediated pancreatic acinar thiamine uptake has also been addressed using a gene-specific
351
(siRNA) silencing approach in vitro, and Slc19a2 and Slc19a3 knockout mouse in vivo (91).
352
Results of both approaches have shown that while both THTR-1 & -2 are involved in thiamine
353
uptake by pancreatic acinar cells, the former transporter plays a larger role than the latter (Figure
354
3) (91).
355
Other studies have examined the effect of chronic alcohol feeding/exposure on thiamine
356
uptake by rodent pancreatic acinar cells and reported significant inhibition compared to pair-fed
357
controls (84, 96). Evidence that this effect is mediated at the level of transcription of the
358
SLC19A2 and SLC19A3 genes was also obtained in studies using transgenic mice carrying the
16
359
human SLC19A2 and SLC19A3 promoters and fed alcohol chronically, and from studies with
360
266-6 cells transfected with the SLC19A2 and SLC19A3 promoters and chronically exposed to
361
alcohol (84, 96). Chronic alcohol feeding was also found to cause a significant inhibition in the
362
level of expression of the thiamine-metabolizing enzymes thiamine phosphokinase (TPKase) and
363
thiamine pyrophosphatase (TPPase) which play important roles in regulating intracellular
364
thiamine levels, as well as in the level of expression of the mitochondrial membrane TPP
365
transporter (a protein that transports cytoplasmic TPP into mitochondria) (96). The negative
366
impact of chronic alcohol exposure on pancreatic acinar thiamine uptake and intracellular
367
metabolism and compartmentalization may contribute to the deleterious effect of ethanol on
368
pancreatic health via altering the resting state of the pancreas and reducing its defense
369
mechanisms.
370
ii) Uptake of vitamin B2 (riboflavin; RF):
371
RF is essential for the normal metabolic activities of pancreatic β-cells; it also has the
372
ability to reduce the level of free radicals and proinflammatory mediators, which these cells are
373
highly sensitive to (14, 21). Pancreatic β-cells obtain RF from their surrounding as they lack the
374
ability to synthesize the vitamin.
375
freshly isolated primary mouse and human pancreatic islets to show that RF uptake by these
376
preparations is via a specific and high affinity (apparent Km of 0.17 ± 0.02 μM) carrier-mediated
377
mechanism (33). All three known mammalian RF transporters, i. e., RF transporters 1, 2, and 3
378
(RFVT-1, -3, and -2) are expressed in pancreatic β-cells/islets. However expression of RFVT-1
379
predominates in mouse pancreatic β-cells/islets while that of RFVT-3 predominates in human
380
pancreatic islets. The uptake process of RF by pancreatic β-cells/islets is adaptively regulated by
Recent studies have used cultured pancreatic β-cells, and
17
381
extracellular substrate level via what appears to be a transcriptional mechanism(s); it also is
382
under the regulation of an intracellular Ca2+/calmodulin-mediated regulatory pathway.
383
iii) Uptake of vitamin B9 (folate):
384
As mentioned earlier, folate is essential for the biosynthesis of precursors of DNA and
385
RNA, metabolism of several amino acids, and for cellular methylation reactions. Thus, an
386
adequate supply of folate is necessary for normal cellular function and growth of pancreatic cells.
387
The pancreas maintains the second highest level of folate after the liver (9, 106), and folate is
388
essential for its normal exocrine function and health. Studies have shown that folate deficiency
389
leads to a decrease in amylase secretion, appearance of immature secretory granules in pancreatic
390
cells, and the disappearance of secreted materials in the pancreatic duct as well as disturbances in
391
methyl
392
adenosylhomocysteine ratio) (9, 7, 8). Other investigations have suggested that disturbance in the
393
folate-dependent methyl group metabolism in the pancreas contributes to the pathogenesis of
394
several pancreatic disorders (reviewed in 49), and that an inverse relationship exists between
395
serum folate level and the risk of development of pancreatic cancer in humans (85).
metabolism
(with
a
significant
reduction
in
S-adenosylmethionine-to-S-
396
Pancreatic acinar cells, like all other mammalian cells, cannot synthesize folate, and thus,
397
must obtain the vitamin from the extracellular environment via transport across the cell
398
membrane. Recent studies have delineated the mechanism of folate uptake by pancreatic acinar
399
cells and showed the involvement of a carrier-mediated mechanism at both acidic and
400
neutral/alkaline pHs (73). Both the reduced folate carrier (RFC) and the proton-coupled folate
401
transporter (PCFT) are expressed in pancreatic acinar cells with expression of RFC being higher
402
than that of PCFT (73); the contribution of these systems toward folate uptake by pancreatic
18
403
acinar cells is not clear but most likely depends on the prevailing extracellular pH.
404
pancreatic folate uptake process is adaptively regulated by the prevailing extracellular folate
405
level, and also appears to be under the regulation of an intracellular cAMP/PKA-mediated
406
pathway (73).
The
407
Finally, chronic feeding of alcohol to animals was found to lead to a significant inhibition
408
in pancreatic acinar folate uptake and suppression in the level of expression of both RFC and
409
PCFT (73). These findings may contribute to the deleterious effects of chronic alcohol exposure
410
on pancreatic health (i. e., acute and chronic pancreatitis; 35), which is multifactorial and
411
involves a reduction in pancreatic defense mechanisms (35, 45, 50).
412
Overall summary and future directions:
413
This review summarized recent findings on the existence of efficient, specific and
414
regulated carrier-mediated mechanisms for uptake of water-soluble vitamins in the large intestine.
415
These findings support a role for the microbiota-generated WSV in host nutrition and especially
416
in the cellular nutrition of the local colonocytes. Further studies are needed to determine the
417
exact contribution of this source of WSV toward overall vitamin body homeostasis under
418
different conditions, and the consequence of disruption of this source by external and internal
419
factors on colonic health in humans.
420
The review also summarized recent finding on the mechanisms involved in the uptake of
421
few WSV by pancreatic cells, and how common environmental factors affect these events.
422
Further studies are needed to delineate the mechanisms of uptake of other WSV, how these
423
events are regulated, and how disruption of these processes could contribute to the development
424
of pancreatic diseases.
19
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References
1.
Alexander B. The Chemical Determination of Thiamine and Cocarboxylase in
Biological Material. J Biol Chem 151: 455-465, 1943.
2.
Arumugam M, Raes J, Pelletier E, Le Paslier D, Yamada T, Mende DR,
Fernandes GR, Tap J, Bruls T, Batto JM, Bertalan M, Borruel N, Casellas F,
Fernandez L, Gautier L, Hansen T, Hattori M, Hayashi T, Kleerebezem M,
Kurokawa K, Leclerc M, Levenez F, Manichanh C, Nielsen HB, Nielsen T, Pons N,
Poulain J, Qin J, Sicheritz-Ponten T, Tims S, Torrents D, Ugarte E, Zoetendal EG,
Wang J, Guarner F, Pedersen O, de Vos WM, Brunak S, Doré J; MetaHIT
Consortium, Antolín M, Artiguenave F, Blottiere HM, Almeida M, Brechot C, Cara
C, Chervaux C, Cultrone A, Delorme C, Denariaz G, Dervyn R, Foerstner KU, Friss
C, van de Guchte M, Guedon E, Haimet F, Huber W, van Hylckama-Vlieg J, Jamet
A, Juste C, Kaci G, Knol J, Lakhdari O, Layec S, Le Roux K, Maguin E, Mérieux A,
Melo Minardi R, M'rini C, Muller J, Oozeer R, Parkhill J, Renault P, Rescigno M,
Sanchez N, Sunagawa S, Torrejon A, Turner K, Vandemeulebrouck G, Varela E,
Winogradsky Y, Zeller G, Weissenbach J, Ehrlich SD and Bork P. Enterotypes of the
human gut microbiome. Nature 473:174-180, 2011.
3.
Ashokkumar B, Kumar JS, Hecht GA and Said HM. Enteropathogenic
escherichia coli inhibits intestinal vitamin B1 (thiamine) uptake: studies with humanderived intestinal epithelial Caco-2 cells. Am J Physiol 297: G825-833, 2009.
4.
Auer IO, Ziemer E and Sommer H. Immune status in Crohn’s disease. V.
Decreased in vitro natural killer cell activity in peripheral blood. Clin Exp Immunol 42:
41-49, 1980.
5.
Aufreiter S, Kim JH and O’Connor DL. Dietary oligosaccharides increase
colonic weight and the amount but not concentration of bacterially synthesized folate in
the colon of piglets. J Nutr 141: 366-372, 2011.
6.
Bahn A, Hagos Y, Reuter S, Balen D, Brzica H, Krick W, Burckhardt BC,
Sabolic I and Burckhardt G. Identification of a New Urate and High Affinity
Nicotinate Transporter, hOAT10 (SLC22A13). J Biol Chem 283: 16332-16341, 2008.
7.
Balaghi M and Wager C. Folate deficiency inhibits pancreatic amylase secretion
in rats. Am J Clin Nutr 61: 90-96, 1995.
8.
Balaghi M and Wagner C. Methyl group metabolism in the pancreas of folate
deficient rats. J Nutr 122: 1391-1396, 1992.
9.
Balaghi M, Horne DW, Woodward SC and Wagner C. Pancreatic one-carbon
metabolism in rats. Am J Clin Nutr 58: 198-203, 1993.
10.
Balamurugan K, Ortiz A and Said HM. Biotin uptake by human intestinal and
liver epithelial cells: role of the SMVT system. Am J Physiol Gastrointest Liver Physiol
285: G73-77, 2003.
11.
Barrow BJ, Ortiz-Reyes R, O'Riordan MA and Pretlow TP. In situ
localization of enzymes and mucin in normal rat colon embedded in plastic. Histochem J
21: 289-295, 1989.
12.
Berdanier CD. Trace Minerals. Adv Nutr Micronutr 183-219, 1998.
20
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
13.
Bettendorff L, Goessens G, Sluse F, Wins P, Bureau M, Laschet J and Grisar
T.Thiamine deficiency in cultured neuroblastoma cells: effect on mitochondrial function
and peripheral benzodiazepine receptors. J Neurochem 64: 2013-2021, 1995.
14.
Betz Al, Ren XD, Ennis SR, Hultquist DE. Riboflavin reduces edema in focal
cerebral ischemia. Acta Neurochir Suppl (Wien) 60: 314-317, 1944.
15.
Black S, McKibbin JM and Elvehjem CA. Use of sulfaguanidine in nutrition
experiments. Proc Soc Exp Biol Med 47:308-310, 1941.
16.
Bowman BB & Rosenberg IH. Biotin absorption by distal rat intestine. J Nutr
117: 2121-2126, 1987.
17.
Calingasan N, Chun W, Park L, Uchida K and Gibson GE. Oxidative stress is
associated with region-specific neuronal death during thiamine deficiency. J Neuropath
Exp Neurol 58: 946-958, 1999.
18.
Chernobilsky B and Tsou KC. Adenocarcinoma, adenomas and polyps of the
colon. Histochemical study. Cancer 21:165-177, 1968.
19.
Claesson MJ, Jeffery IB, Conde S, Power SE, O'Connor EM, Cusack S,
Harris HM, Coakley M, Lakshminarayanan B, O'Sullivan O, Fitzgerald GF, Deane
J, O'Connor M, Harnedy N, O'Connor K, O'Mahony D, van Sinderen D, Wallace
M, Brennan L, Stanton C, Marchesi JR, Fitzgerald AP, Shanahan F, Hill C, Ross
RP and O'Toole PW. Gut microbiota composition correlates with diet and health in the
elderly. Nature 488: 178-184, 2012.
20.
Coates ME, Ford JE and Harrison GF. Intestinal synthesis of vitamins of the
B complex in chicks. Br J Nutr 22: 493-500, 1968.
21.
Cobianchi L, Fornoni A, Pileggi A, Molano RD, Sanabria NY, GonzalezQuintana J, Bocca N, Marzorati S, Zahr E, Hogan AR, Ricordi C and Inverardi L.
Riboflavin inhibits IL-6 expression and p38 activation in islet cells. Cell Transplant 17:
559-566, 2008.
22.
Cooper EA. On the protective and curative properties of certain foodstuffs
against polyneuritis induced in birds by a diet of polished rice: Part II. J Hyg 14: 12-22,
1914
23.
Cravo ML, Mason JB, Selhub J and Rosenberg IH. Use of deoxyuridine
suppression test to evaluate localized folate deficiency in rat colonic epithelium. Am J
Clin Nutr 53: 1450-1454, 1991.
24.
Dawson I and Pryse-Davies J. The distribution of certain enzyme systems in the
normal human gastrointestinal tract. Gastroenterology 44: 745-760, 1963.
25.
Dethlefsen L, Huse S, Sogin M and Relman DA. The pervasive effects of an
antibiotic on the human gut microbiota, as revealed by deep 16S rRNA sequencing. PloS
Biol 6: e280, 2008.
26.
Diaz GA, Banikazemi M, Oishi K, Desnick RJ and Gelb BD. Mutations in a
new gene encoding a thiamine transporter cause thiamine-responsive megaloblastic
anaemia syndrome. Nature Genetics 22: 309-312, 1999.
27.
Dudeja PK, Kode A, Alnounou M, Tyagi S, Torania S, Subramanian VS and
Said HM. Mechanism of folate transport across the human colonic basolateral membrane.
Am J Physiol 281: G54-60, 2001.
28.
Dudeja PK, Torania SA and Said HM. Evidence for the existence of an
electroneutral, pH-dependent, DIDS-sensitive carrier-mediated folate uptake mechanism
in the human colonic luminal membrane vesicles. Am J Physiol 272: G1408-1415, 1991.
21
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
29.
Dutta B, Huang W, Molero M, Kekuda R, Leibach FH, Devoe LD,
Ganapathy V and Prasad PD. Cloning of the human thiamine transporter, a member of
the folate transporter family. J Biol Chem 45: 31925-31929, 1999.
30.
Fernandez-Banares F, Abad-Lacruz A and Xiol X. Vitamin status in patients
with inflammatory bowel disease. Am J Gastroenterol 84: 744-748, 1989.
31.
Flachowsky G. Niacin in Dairy and Beef Cattle Nutrition. Arch Anim Nutr 43:
195-213, 1993.
32.
Fleming JC, Tartaglini E, Steinkamp MP, Schorderet DF, Cohen N and
Neufeld EJ. The gene mutated in thiamine-responsive anaemia with diabetes and
deafness (TRMA) encodes a functional thiamine transporter. Nature Genetics 22: 305308, 1999
33.
Ghosal A and Said HM. Mechanism and regulation of vitamin B2 (riboflavin)
uptake by mouse and human pancreatic B-cells/islets: physiological and molecular
aspects. Am J Physiol Gastrointest Liver Physiol 303: G1052-1058, 2012.
34.
Ghosal A, Lambrecht N, Subramanya SB, Kapadia R and Said HM.
Conditional knockout of the Slc5a6 gene in mouse intestine impairs biotin absorption.
Am J Physiol Gastrointest Liver Physiol 304: G64-71, 2012.
35.
Greensberger NJ and Toskes PP. Acute and chronic pancreatic. In: Harrison’s
Principles of Internal Medicine, edited by Kasper DL. New York: McGraw- Hill, 2005.
36.
Gurerrant NB, Dutcher RA and Brown RA. Further studies concerning
formation of B vitamins in digestive tract of rat. J Nutr 13: 305-315, 1937.
37.
Hashimoto T, Perlot T, Rehman A, Trichereau J, Ishiguro H, Paolino M, Sigl
V, Hanada T, Hanada R, Lipinski S, Wild B, Camargo SMR, Singer D, Andreas R,
Kuba K, Fukamizu A, Schreiber S, Clevers H, Verrey F, Rosenstiel P and Penninger
JM. ACE2 links amino acid malnutrition to microbial ecology and intestinal
inflammation. Nature 487: 477-481, 2012.
38.
Iinuma S. Synthesis of riboflavin by intestinal bacteria. J Vitaminol (Kyoto) 10:
6-13, 1955.
39.
Iinuma S. Synthesis of riboflavin by intestinal bacteria. J Vitamin 2: 6-13, 1955.
40.
Kasper H. Vitamin absorption in the colon. Am J Protocol 21, 341-345, 1970.
41.
Keagy PM and Oace SM. Folic acid utilization from high fiber diets in rats. J
Nutr 114: 1252-1259, 1984.
42.
Kono S, Miyajima H, Yoshida K, Togawa A, Shirakawa K and Suzuki H.
Mutations in thiamine-transporter gene and Wernickes-like encephalopathy. N Engl J
Med 360: 1792-1794, 2009
43.
Kornberg A, Daft FS and Sebrell WH. Production and treatment of
granulocytopenia and anemia in rats fed sulfonamides in purified diets. Science 98: 20-22,
1944.
22
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
44.
Krause LJ, Forsberg CW and O’Connor DL. Feeding human milk to rats
increases Bifidobacterium in the cecum and colon which correlates with enhanced folate
status. J Nutr 126: 1505-1511, 1996.
45.
Kubisch CH, Gukovsky I, Lugea A, Pandol SJ, Kuick R, Misek DE, Hanash
SM and Logsdon CD. Long-term ethanol consumption alters pancreatic gene expression
in rats: a possible connection to pancreatic injury. Pancreas 33: 66-76, 2006.
46.
Kumar CK, Moyer MP, Dudeja PK and Said HM. A protein-tyrosine kinase
regulated, pH-dependent carrier-mediated uptake system for folate by human normal
colonic epithelial cell line NCM 460. J Biol Chem 272: 6226-6231, 1997.
47.
Kumar JS, Subramanian VS, Kapadia R, Kashyap ML and Said HM.
Mammalian colonocytes possess a carrier-mediated mechanism for uptake of vitamin B3
(niacin): Studies utilizing human and mouse colonic preparations. Am J Physiol
Gastrointest Liver Physiol, 2013 (in press).
48.
Lashner BA, Heidenreich PA, Su GL, Kane SV and Hanauer SB. The effect
of folate supplementation on the incidence of dysplasia and cancer in chronic ulcerative
colitis: A case control study. Gastroenterol 97: 255-259, 1989.
49.
Longnecker DS. Abnormal methyl metabolism in pancreatic toxicity and
diabetes. J Nutr 132: 2373S-2376, 2002.
50.
Lu Z, Karne S, Kolodecik T and Gorelick FS. Alcohols enhance caeruleininduced zymogen activation in pancreatic acinar cells. Am J Physiol 282: G501-507,
2002.
51.
Mandel H, Berant M, Hazani A and Naveh Y. Thiamine-dependent beriberi in
the "thiamine-responsive anemia syndrome". N Engl J Med 311: 836-838, 1984.
52.
Matherly LH and Hou Z. Structure and function of the reduced folate carrier a
paradigm of a major facilitator superfamily mammalian nutrient transporter. Vitam Horm
79: 145-184, 2008.
53.
Mee L, Nabokina SM, Sekar VT, Subramanian VS, Maedler K and Said
HM. Pancreatic beta cells and islets take up thiamine by a regulated carrier-mediated
process: studies using mice and human pancreatic preparations. Am J Physiol
Gastrointest Liver Physiol 297: G197-206, 2009.
54.
Mitchell HK and Isbell ER. Intestinal bacterial synthesis as a source of B
vitamins for the rat. University of Texas at Austin- University of Texas Publication 4237:
125-134, 1942.
55.
Mock DM. Biotin, In: Handbook of Vitamins, edited by Zempleni J, McCormick
DB, and Suttie JW. New York: CRC Press; 2006. p 361-377.
56.
Nabokina SM and Said HM. A high affinity and specific carrier-mediated
mechanism for uptake of thiamine pyrophosphate by human colonic epithelial cells. Am J
Physiol Gastrointest Liver Physiol 2012; 303: G389-395.
57.
Nabokina SM, Subramanian VS and Said HM. Association of PDZ-containing
proteinPDZD11 with the human sodium dependent multivitamin transporter gene. Am J
Physiol 280: C548-555, 2010.
58.
Najjar VA and Holt LE. The biosynthesis of thiamine in man and its implication
in human nutrition. JAMA 123: 683-684, 1943
23
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
59.
Neufeld EJ, Fleming JC, Tartaglini E and Steinkamp MP. Thiamineresponsive megaloblastic anemia syndrome: a disorder of high-affinity thiamine
transport. Blood Cells Mol Dis 27:135-138, 2001.
60.
O’Sullivan MG, Thornton G, O’Sullivan GC and Collins JK. Probiotic
bacteria: myth or reality? Food Sci & Tech 3: 309-314, 1992.
61.
Okabe N, Fujita K & Yao T. Immunological studies on Crohn’s disease. III.
Defective natural killer activity. J Clin Lab Immunol 17: 143-146, 1985.
62.
Okabe N, Urabe K, Fujita K, Yamamoto T, Yao T and Doi S. Biotin effects in
Crohn’s disease. Dig Dis Sci 33: 1495-1496, 1988.
63.
Portari GV, Marchini JS, Vannucchi H and Jordao AA. Antioxidant effect of
thiamine on acutely alcoholized rats and lack of efficacy using thiamine or glucose to
reduce blood alcohol content. Basic Clin Pharacol Toxicol 103: 482-486, 2008.
64.
Prasannan KG, Sundaresan R and Venkatesan K. Thiamine deficiency and
protein secretion by pancreatic slices in vitro. Experentia 33: 169-170, 1977.
65.
Rajgopal A, Edmondson A, Goldman D and Zhao R. SLC19A3 encodes a
second thiamine transporter ThTr2. Biochim Biophys Acta 1537: 175-178, 2001
66.
Rathanaswami P, Pourany A and Sundaresan R. Effects of thiamine
deficiency on the secretion of insulin and the metabolism of glucose in isolated rat
pancreatic islets. Biochem Int 25: 577-583, 1991.
67.
Reidling JC, Lambrecht N, Kassir M and Said HM. Impaired intestinal
vitamin B1 (thiamine) uptake in thiamine transporter-2-deficient mice. Gastroenterology
138: 1802-1809, 2010.
68.
Rindi G & Laforenza U. Thiamine intestinal transport and related issues: recent
aspects. Proc Soc Exp Biol Med 224: 246-255, 2000
69.
Rindi G, Patrini C, Laforenza U, Mandel H, Berant M, Viana MB, Poggi V
and Zarra AN. Further studies on erythrocytes thiamine transport and phosphorylation
in seven patients with thiamine-responsive megaloblastic anaemia. J Inherit Meta Dis 17:
667-667, 1994.
70.
Rong N, Selhub J, Goldin BR and Rosenberg IH. Bacterially synthesized folate
in rat large intestine is incorporated into host tissue folyl polyglutamates. J Nutr 121:
1955-1959, 1991.
71.
Said HM and Ross C. Riboflavin. In: Modern Nutrition in Health and Disease.
ROSS C, Caballero B, Cousins RJ, Tucker KL, Ziegler TR, editors; 11th edition, pp 325330, 2011
72.
Said HM, Balamurugan K, Subramanian VS and Marchant JS. Expression
and functional contribution of hTHTR-2 in thiamine absorption in human intestine. Am J
Physiol 286: G491-498, 2003.
73.
Said HM, Mee L, Sekar VT, Ashokkumar B and Pandol SJ. Mechanism and
regulation of folate uptake by pancreatic acinar cells: effect of chronic alcohol
consumption. Am J Physiol Gastrointest Liver Physiol 298: G985-993, 2010.
74.
Said HM, Ortiz A, McCloud E, Dyer D, Moyer MP and Rubin S. Biotin
uptake by the human colonic epithelial cells NCM460: A carrier-mediated process shared
with pantothenic acid. Am J Physiol 275: C1365-1371, 1998.
75.
Said HM, Ortiz A, Moyer MP and Yanagawa N. Riboflavin uptake by humanderived colonic epithelial NCM460 cells. Am J Physiol 278: C270-276, 2000.
24
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
76.
Said HM, Ortiz A, Subramanian VS, Neufeld EJ, Moyer MP and Dudeja PK.
Mechanism of thiamine uptake by human coloncytes: studies with cultured colonic
epithelial cell line NCM460. Am J Physiol 281: G144-150, 2001
77.
Saito N, Kimura M, Kuchiba A and Itokawa Y. Blood thiamine levels in
outpatients with diabetes mellitus. J Nutr Sci Vitaminol (Tokyo) 33: 421-430, 1987.
78.
Salaspuro M. Bacteriocolonic pathway for ethanol oxidation: characteristics and
implications. Ann Med 28: 195-200, 1996.
79.
Segal I, Ou TL, Demetriou A, Paterson A, Hale M and Lerios M. Rectal
manifestations of pellagra. Int J Colorectal Dis 1: 238-243, 1986.
80.
Shayeghi M, Latunde-Dada GO, Oakhill JS, Laftah AH, Takeuchi K,
Halliday N, Khan Y, Warley A, McCann FE, Hider RC, Frazer DM, Anderson GJ,
Vulpe CD, Simpson RJ and McKie AT. Identification of an intestinal heme transporter.
Cell 122: 789-801, 2005.
81.
Singh M. Effect of thiamine deficiency on pancreatic acinar cell function. Am J
Clin Nutr 36: 500-504, 1982.
82.
Singleton CK and Martin PR. Molecular mechanisms of thiamine utilization.
Curr Mol Med 1: 197-207, 2001.
83.
Sorell MF, Frank O and Thomsom AD. Absorption of vitamins from the large
intestine. Nutr Res Int 3, 143-48, 1971.
84.
Srinivasan P, Subramanian VS and Said HM. Effect of chronic alcohol
feeding on physiological and molecular parameters of thiamine uptake by pancreatic
acinar cells of transgenic reporter mice carrying the human SLC19A2 and SLC19A3
promoters. FASEB J 27: Lb722, 2013.
85.
Stolzenberg-Solomon RZ, Albanes D, Nieto FJ, Hartman TJ, Tangrea JA,
Rautalahti M, Sehlub J, Virtamo J and Taylor PR. Pancreatic cancer risk and
nutrition-related methyl-group availability indicators in male smokers. J Natl Cancer Inst
91: 535-541, 1999.
86.
Stratigos JD and Katsambas A. Pellagra: a still existing disease. Br J Dermatol
96: 99-106, 1977.
87.
Subramanian VS, Marchant JS and Said HM. Targeting and trafficking of the
human thiamine transporter-2 in epithelial cells. J Biol Chem 281: 5233-5245, 2006.
88.
Subramanian VS, Marchant JS, Boulware MJ, Ma TY and Said HM.
Membrane targeting and intracellular trafficking of the human sodium-dependent
multivitamin transporter in polarized epithelial cells. Am J Physiol 296: C663-671, 2009.
89.
Subramanian VS, Marchant JS, Parker I and Said HM. Cell Biology of the
human thiamine transporter-1 (htHTR1): intracellular trafficking and membrane targeting
mechanisms. J Biol Chem 278: 3976-3984, 2003.
90.
Subramanian VS, Rapp L, Marchant JS and Said HM. Role of cysteine
residues in cell surface expression of the human riboflavin transporter-2 (hRFT2) in
intestinal epithelial cells. Am J Physiol Gastrointest Liver Physiol 301: G100-109, 2011
25
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
91.
Subramanian VS, Subramanya SB and Said HM. Relative contribution of
THTR-1 and THTR-2 in thiamine uptake by pancreatic acinar cells: studies utilizing
Slc19a2 and Slc19a3 knockout mouse models. Am J Physiol Gastrointest Liver Physiol
302: G572-578, 2012.
92.
Subramanian VS, Subramanya SB, Ghosal A and Said HM. Chronic alcohol
feeding inhibits physiological and molecular parameters of intestinal and renal riboflavin
transport. Am J Physiol Cell Physiol, 2013 (in press).
93.
Subramanian VS, Subramanya SB, Rapp L, Marchant JS, Ma TY and Said
HM. Differential expression of human riboflavin transporters -1, -2, and -3 in polarized
epithelia: a key role for hRFT -2 in intestinal riboflavin uptake. Biochim Biophys Acta
1808: 3016-3021, 2011.
94.
Subramanya SB, Subramanian VS and Said HM. Chronic alcohol
consumption and intestinal thiamine absorption: effects on physiological and molecular
parameters of the uptake process. Am J Physiol 299:G23-31, 2010.
95.
Subramanya SB, Subramanian VS, Kumar JS, Hoiness R and Said HM.
Inhibition of intestinal biotin absorption by chronic alcohol feeding: Cellular and
molecular mechanisms. Am J Physiol Gastrointest Liver Physiol G494-501, 2010.
96.
Subramanya SB, Subramanian VS, Sekar VT and Said HM. Thiamine uptake
by pancreatic acinar cells: effect of chronic alcohol feeding/exposure. Am J Gastrointest
Liver Physiol 301: G896-904, 2011.
97.
Tallaksen CM, Bell H and Bohmer T. Thiamine and thiamine phosphate ester
deficiency assessed by high performance liquid chromatography in four clinical cases of
Werincke encephalopathy. Alcohol Clin Exp Res 17: 712-716, 1993.
98.
Tallaksen CME, Bohmer T and Bell H. Blood serum thiamine and thiamine
phosphate esters concentrations in patients with alcohol dependence syndrome before and
after thiamine treatment. Alcohol Clin Exp Res16: 320-325, 1992.
99.
Thoma C, Green TJ and Ferguson LR. Citrus pectin and oligofructose improve
folate status and lower serum total homocysteine in rats. Int J Vitam Nutr Res 73: 403409, 2003.
100. Todd K and Butterworth R. Early microglial response in experimental thiamine
deficiency: an immunohistochemical analysis. Glia 25: 190-198, 1999.
101. Walker A. Say hello to our little friends. Nature Rev Microbiol 5: 572-573, 2007.
102. Walzem RL and Clifford AJ. Folate deficiency in rats fed diets containing free
amino acids or intact proteins. J Nutr 118: 1089-1096, 1988.
103. Wrong OM, Edmonds CJ and Chadwich VS. Vitamins in the large intestine;
its role in Mammmlian Nutrition and Homeostasis. In: Wiley and Sons, editors. New
York: 1981. p 157-166.
104. Yadav PK, Chen C and Lui Z. Potential role of NK cells in the pathogenesis of
inflammatory bowel disease. J Biomed Biotechnol 2011: 348530, 2011
105. Yamamoto S, Inoue K, Ohta KY, Fukatsu R, Maeda JY, Yoshida Y and
Yuasa H. Identification and functional characterization of rat riboflavin transporter 2. J
Biochem 145: 437-443, 2009.
106. Yeo EJ and Wagner C. Tissue distribution of glycine N-methyltransferase, a
major folate binding protein of liver. Proc Natl Acad Sci 91: 210-214, 1994.
26
723
724
725
726
727
728
729
730
731
732
733
734
735
107. Yonezawa A, Masuda S, Katsura T and Inui K. Identification and functional
characterization of a novel human and rat riboflavin transporter, RRT1. Am J Physiol
295: C632-641, 2008.
108. Zempleni J and Mock DM. Uptake and metabolism of biotin by human
peripheral blood mononuclear cells. Am J Physiol 275: C382-388, 1998
109. Zhao R, Matherly LH and Goldman ID. Membrane transporters and folate
homeostatis: intestinal absorption and transport into systemic compartments and tissues.
Exper Rev Mol Med 11: 1-27, 2009.
110. Zoetenal EG, Raes J, van den Bogert B, Arumugam M, Booijink CC, Troost
FJ, Bork P, Wels M, de Vos WM and Kleerebezem M. The human small intestinal
microbiota is driven by rapid uptake and conversion of simple carbohydrates. ISME J 6:
1415-1426, 2012.
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Figure Legends
741
Figure 1: Diagrammatic representation of the transport systems that appear to be involved
742
in the absorption of the microbiota-generated WSV.
743
Abbreviations: SMVT, sodium-dependent multivitamin transporter; RFC, reduced folate
744
carrier; MDR-3, multi-drug resistance protein-3; PDZD11, PDZ-containing protein 11; RFVT-1,
745
riboflavin transporter-1; RFVT-3, riboflavin transporter-3; THTR-1, thiamine transporter-1;
746
THTR-2, thiamine transporter-2; TPP, thiamine pyrophosphate.
747
pyridoxine and TPP have been functionally identified, but their molecular identity has not been
748
determined. PDZD11 is an accessory protein that interacts with SMVT and affects its function
749
and cell biology (65). The dashed lines are inserted to separate the transporter(s) of a specific
750
vitamin from those of other vitamins.
751
Figure 2: Histology of the small intestine (A-C) and cecum (D-F) of conditional (intestinal-
752
specific) SMVT Knockout (KO) mice and their littermates.
Transporters for niacin,
753
Small bowel: (A) shows normal morphology of the small gut of wild-type (sex-matched)
754
littermates; (B) shows shortening of the villi and focal dysplastic changes (B insert); (C) Small
755
gut villi length in mm (left y-axis) and total area of dysplasia as percentage (right y-axis). (* P <
756
0.01, n=5).
757
Large bowel: A representative section of wild-type (sex-matched) cecum (D) and that of
758
SMVT KO mouse showing significant sub-mucosal edema (open arrow) and acute inflammation
759
involving surface (closed arrows) and crypts (D insert) regions. (F) Number of neutrophils in 10
28
760
high power fields (400x, left y-axis), and total area of dysplasia and sub-mucosal edema as
761
percentage (right y-axis). (* P < 0.01, n=5). Adopted from ref. 34.
762
Figure 3: Carrier-mediated thiamine uptake by freshly isolated primary pancreatic acinar
763
cells of Slc19a2 and Slc19a3 knockout mice, and their littermates. *P < 0.01. Adopted from
764
ref. 91.
765
766
29
Fig. 1
Lumen
Niacin
Riboflavin
Pyridoxine
Thiamine
TPP
Biotin/
Pantothanic acid
Folate
THTR2
??
RFVT-3
PCFT
??
?
THTR1
RFC
SMVT
PDZD11
RFVT-1
Blood
MDR-3
THTR1
Fig.2
Small Bowel Histology
Cecum Histology
A
D
B
E
Dysplasia
Dysplasia
75
1.5
1.0
0.5
*
*
50
25
Neutrophils (#/10 hpf)
2.0
0.0
C
100
Dyspllasia (%)
Length of V
Villi (mm)
2.5
Dysplasia
LP Edema
Neutrophils
50
F
100
75
40
30
*
50
20
10
0
0
*
25
*
0
Dysplasia/LP Ed
dema (% area)
Lenght of
of Villi
Villi
Length
Carrieer-mediated 3[H]]-thiamin uptakee
(fmol/mg proteein/7 min)
5
4
3
3
2
2
1
*
0
Control
KO
(littermate)
Slc19a2
Carrieer-mediated 3[H]-thiamin uptake
(fmol/mg proteiin/7 min)
Fig. 3
A
B
4
*
1
0
Control
(li
(littermate)
)
Slc19a3 KO