Improved in vitro wound healing in response to a superoxidised solution.

OBJECTIVE: This study assessed wound healing in response to a superoxidised solution using an in vitro wound healing model. METHOD: Prewounded reconstructed full-thickness human skin models were treated with 10µl of either superoxidised solution (Hydrocyn aqua, Bactiguard South East Asia Sdn. Bhd., Malaysia) or Dulbecco's phosphate buffered saline (DPBS) and incubated at 37°C for up to seven days, with additional treatments added every 48 hours. On days 0, 1, 2, 5 and 7, triplicate samples were taken for specific immunostaining against cytokeratin 14 and vimentin. At each timepoint, horizontal and vertical wound diameters were measured to demonstrate wound closure. Maintenance media was taken at the same timepoints for the measurement of secreted proinflammatory cytokines interleukin (IL)-1ß, IL-6 and tumour necrosis factor (TNF)-ɑ. RESULTS: At day 1, the superoxidised solution induced significantly lower diameter measurements compared with baseline data at day 0. Both treatment groups demonstrated significantly lower diameter measurements by day 2 when compared with the baseline; however, the average wound size of samples treated with the superoxidised solution was significantly lower when compared to the DPBS-treated group (p<0.05). No significant difference in expression of any proinflammatory was identified at any timepoint. CONCLUSION: Application of the superoxidised solution resulted in significantly improved wound closure over the first 48 hours in comparison to DPBS-treatment. Furthermore, application of the superoxidised solution did not induce significant proinflammatory effects, despite the significantly reduced wound diameter.

Safety and effectiveness of an antiseptic wound cleansing and irrigation solution containing polyhexamethylene biguanide.

OBJECTIVE: There is currently a wide range of cleansing and irrigation solutions available for wounds, many of which contain antimicrobial agents. The aim of this study was to assess the safety of HydroClean Solution (HARTMANN, Germany), a polyhexamethylene biguanide (PHMB)-containing irrigation solution, in a standard cytotoxicity assay, and to assess its effect in a three-dimensional (3D) full-thickness model of human skin. METHOD: A number of commercially available wound cleansing and irrigation solutions, including the PHMB-containing irrigation solution, were tested in a cytotoxicity assay using L929 mouse fibroblasts (ISO 10993-5:2009). The PHMB-containing irrigation solution was then assessed in an in vitro human keratinocyte-fibroblast 3D full-thickness wounded skin model to determine its effect on wound healing over six days. The effect of the PHMB-containing irrigation solution on tissue viability was measured using a lactate dehydrogenase (LDH) assay, and proinflammatory effects were measured using an interleukin-6 (IL-6) production assay. RESULTS: The PHMB-containing irrigation solution was shown to be equivalent to other commercially available cleansing and irrigation solutions when tested in the L929 fibroblast cytotoxicity assay. When assessed in the in vitro 3D human full-thickness wound healing model, the PHMB-containing irrigation solution treatment resulted in no difference in levels of LDH or IL-6 when compared with levels produced in control Dulbecco's phosphate-buffered saline cultures. There was, however, a pronounced tissue thickening of the skin model in the periwound region. CONCLUSION: The experimental data presented in this study support the conclusion that the PHMB-containing irrigation solution has a safety profile similar to other commercially available cleansing and irrigation solutions. Evidence also suggests that the PHMB-containing irrigation solution does not affect tissue viability or proinflammatory cytokine production, as evidenced by LDH levels or the production of IL-6 in a 3D human full-thickness wound healing model. The PHMB-containing irrigation solution stimulated new tissue growth in the periwound region of the skin model.

Determination of sweetener specificity of horse gut-expressed sweet taste receptor T1R2-T1R3 and its significance for energy provision and hydration.

Studies carried out in several species have demonstrated that detection of low-calorie sweeteners in the lumen of the intestine, by the sweet receptor, T1R2-T1R3, initiates a signaling pathway leading to enhanced expression and activity of intestinal Na+/glucose cotransporter 1, SGLT1. This results in an increased gut capacity to absorb glucose, sodium chloride and water, the basis for oral rehydration therapy. Horses express T1R2, T1R3 and downstream signaling elements in the intestinal tissue. As such, the potential of sweetener-stimulation of T1R2-T1R3 leading to upregulation of SGLT1 allows the provision of more glucose (energy) and hydration for horses. This is especially important when the need for glucose increases during strenuous exercise, pregnancy, and lactation. There are significant differences among species in the ability to detect sweeteners. Amino acid substitutions and pseudogenization of taste receptor genes underlie these variations. Nothing is known about the sweetener specificity of horse T1R2-T1R3. Using heterologous expression methodology, we demonstrate that sweeteners sucralose, stevia and neohesperidin dihydrochalcone (NHDC) activate horse T1R2-T1R3, but cyclamate does not. Determination of sweetener specificity of equine sweet receptor is crucial for developing suitable dietary additives to optimize glucose absorption, hydration and avoiding the intestinal disease brought about by microbial fermentation of unabsorbed carbohydrate reaching the large intestine.

Alterations of mucosa-attached microbiome and epithelial cell numbers in the cystic fibrosis small intestine with implications for intestinal disease.

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Defective CFTR leads to accumulation of dehydrated viscous mucus within the small intestine, luminal acidification and altered intestinal motility, resulting in blockage. These changes promote gut microbial dysbiosis, adversely influencing the normal proliferation and differentiation of intestinal epithelial cells. Using Illumina 16S rRNA gene sequencing and immunohistochemistry, we assessed changes in mucosa-attached microbiome and epithelial cell profile in the small intestine of CF mice and a CF patient compared to wild-type mice and non-CF humans. We found increased abundance of pro-inflammatory Escherichia and depletion of beneficial secondary bile-acid producing bacteria in the ileal mucosa-attached microbiome of CFTR-null mice. The ileal mucosa in a CF patient was dominated by a non-aeruginosa Pseudomonas species and lacked numerous beneficial anti-inflammatory and short-chain fatty acid-producing bacteria. In the ileum of both CF mice and a CF patient, the number of absorptive enterocytes, Paneth and glucagon-like peptide 1 and 2 secreting L-type enteroendocrine cells were decreased, whereas stem and goblet cell numbers were increased. These changes in mucosa-attached microbiome and epithelial cell profile suggest that microbiota-host interactions may contribute to intestinal CF disease development with implications for therapy.

Non-nutritive sweetener activation of the pig sweet taste receptor T1R2-T1R3 in vitro mirrors sweetener stimulation of the gut-expressed receptor in vivo.

The perception of sweet is mediated by the sweet taste receptor T1R2-T1R3 expressed in taste cells of the lingual epithelium. This receptor is also expressed in intestinal enteroendocrine cells and is required for sensing luminal sugars and sweeteners to regulate expression of intestinal Na+-glucose cotransporter 1 (SGLT1). There are some notable differences amongst species in the ability to detect certain non-nutritive (artificial) sweeteners. Amino acid substitutions and pseudogenization of taste receptor genes are responsible for these disparities. Using heterologous expression, we demonstrate that the commonly used non-nutritive sweeteners sucralose, saccharin and acesulfame K activate pig T1R2-T1R3, but that aspartame and cyclamate do not. Furthermore, we show that in vitro sweetener activation of pig T1R2-T1R3 mirrors the sweetener stimulation of the gut-expressed receptor in vivo. Considering that sweeteners are included in animal feed worldwide, determination of taste receptor specificities in different species is essential for the development of scientifically-based dietary formulations.

Consumption of a Natural High-Intensity Sweetener Enhances Activity and Expression of Rabbit Intestinal Na+/Glucose Cotransporter 1 (SGLT1) and Improves Colibacillosis-Induced Enteric Disorders.

Absorption of glucose, via intestinal Na+/glucose cotransporter 1 (SGLT1), activates salt and water absorption and is an effective route for treating Escherichia coli (E. coli)-induced diarrhea. Activity and expression of SGLT1 is regulated by sensing of sugars and artificial/natural sweeteners by the intestinal sweet receptor T1R2-T1R3 expressed in enteroendocrine cells. Diarrhea, caused by the bacterial pathogen E. coli, is the most common post-weaning clinical feature in rabbits, leading to mortality. We demonstrate here that, in rabbits with experimentally E. coli-induced diarrhea, inclusion of a supplement containing stevia leaf extract (SL) in the feed decreases cumulative morbidity, improving clinical signs of disease (p < 0.01). We show that the rabbit intestine expresses T1R2-T1R3. Furthermore, intake of SL enhances activity and expression of SGLT1 and the intestinal capacity to absorb glucose (1.8-fold increase, p < 0.05). Thus, a natural plant extract sweetener can act as an effective feed additive for lessening the negative impact of enteric diseases in animals.

The Effect of Milk Replacer Composition on the Intestinal Microbiota of Pre-ruminant Dairy Calves.

The impact of dietary composition and prebiotics, in promoting the growth of beneficial groups of gut bacteria, is increasingly apparent. Using Illumina MiSeq sequencing of bacterial 16S rRNA genes, this study has aimed to characterize and compare the establishment of the gastrointestinal microbiota in dairy calves given two different commercial milk replacer (MR) diets. MR1 and MR2 contain different levels of macronutrients such as protein and fat. Moreover, differences in manufacturing methods infer that MR2 may contain a greater proportion of conjugated milk oligosaccharides (OS), while MR1 contains more free milk OS. A total of 10 dairy calves, five in each group, were assigned to one of the two MR diets. Freshly voided fecal samples were taken at 0, 7, 14, 28, and 49 days after first consumption of milk replacer. The relative abundance of two individual Bifidobacterium species, which are known to utilize milk OS, and Faecalibacterium prausnitzii were significantly higher at day 7 in the fecal microbiome of calves fed MR2 compared with MR1. These commensal bacteria are widely regarded as probiotic organisms that confer a health benefit on the host. Our findings suggest that the composition of bovine milk replacers can have significant effects on the establishment of the gut microbiota in pre-weaned (neonatal) dairy calves. Better understanding of milk composition-microbiota-host interactions in early life will inform targeted interventions to increase growth and reduce mortality in young animals.

Host selectively contributes to shaping intestinal microbiota of carnivorous and omnivorous fish.

Fish production is increasingly important to global food security. A major factor in maintaining health, productivity and welfare of farmed fish is the establishment and promotion of a stable and beneficial intestinal microbiota. Understanding the effects of factors such as host and environment on gut microbial community structure is essential for developing strategies for stimulating the establishment of a health-promoting gut-microbiota. We compared intestinal microbiota of common carp and rainbow trout, two fish with different dietary habits, sourced from various farm locations. There were distinct differences in the gut microbiota of carp and trout intestine. The microbiota of carp was dominated by Fusobacteriia and Gammaproteobacteria, while the trout microbiota consisted predominantly of Mollicutes and Betaproteobacteria. The majority of bacterial sequences clustered into a relatively low number of operational taxonomic units (OTUs) revealing a comparatively simple microbiota, with Cetobacterium, Aeromonas and Mycoplasma being highly abundant. Within each species, fish from different facilities were found to have markedly similar predominant bacterial populations despite distinctly different rearing environments, demonstrating intra-species uniformity and significant influence of host selectivity. This study demonstrates that in fish the host species imparts substantial impact in shaping the community structure of the intestinal microbiota.

Deregulation of transcription factors controlling intestinal epithelial cell differentiation; a predisposing factor for reduced enteroendocrine cell number in morbidly obese individuals.

Morbidly obese patients exhibit impaired secretion of gut hormones that may contribute to the development of obesity. After bariatric surgery there is a dramatic increase in gut hormone release. In this study, gastric and duodenal tissues were endoscopically collected from lean, and morbidly obese subjects before and 3 months after laparoscopic sleeve gastrectomy (LSG). Tissue morphology, abundance of chromogranin A, gut hormones, α-defensin, mucin 2, Na+/glucose co-transporter 1 (SGLT1) and transcription factors, Hes1, HATH1, NeuroD1, and Ngn3, were determined. In obese patients, the total number of enteroendocrine cells (EEC) and EECs containing gut hormones were significantly reduced in the stomach and duodenum, compared to lean, and returned to normality post-LSG. No changes in villus height/crypt depth were observed. A significant increase in mucin 2 and SGLT1 expression was detected in the obese duodenum. Expression levels of transcription factors required for differentiation of absorptive and secretory cell lineages were altered. We propose that in obesity, there is deregulation in differentiation of intestinal epithelial cell lineages that may influence the levels of released gut hormones. Post-LSG cellular differentiation profile is restored. An understanding of molecular mechanisms controlling epithelial cell differentiation in the obese intestine assists in the development of non-invasive therapeutic strategies.

Composition and diversity of mucosa-associated microbiota along the entire length of the pig gastrointestinal tract; dietary influences.

Mucosa-associated microbial populations of the gastrointestinal tract are in intimate contact with the outer mucus layer. This proximity offers these populations a higher potential, than lumenal microbiota, in exerting effects on the host. Functional characteristics of the microbiota and influences of host-physiology shape the composition and activity of the mucosa-associated bacterial community. We have shown previously that inclusion of an artificial sweetener, SUCRAM, included in the diet of weaning piglets modulates the composition of lumenal-residing gut microbiota and reduces weaning-related gastrointestinal disorders. In this study, using Illumina sequencing we characterised the mucosa-associated microbiota along the length of the intestine of piglets, and determined the effect of SUCRAM supplementation on mucosa-associated populations. There were clear distinctions in the composition of mucosa-associated microbiota, between small and large intestine, concordant with differences in regional oxygen distribution and nutrient provision by the host. There were significant differences in the composition of mucosa-associated compared with lumenal microbiota in pig caecum. Dietary supplementation with SUCRAM affected mucosa-associated bacterial community structure along the length of the intestinal tract. Most notably, there was a substantial reduction in predominant Campylobacter populations proposing that SUCRAM supplementation of swine diet has potential for reducing meat contamination and promoting food safety.

Low calorie sweeteners and gut microbiota.

Studies dating back to 1980s, using bacterial cultures, have reported associations between low calorie sweeteners (LCS) and alterations in bacterial composition, raising the potential that LCS might exert effects on the host via interactions with gut microbiota. However, the results of a few recent studies carried out in this area have produced controversies. There is evidence that human fecal samples, used in most human microbiome studies, may provide a poor representation of microbial contents of the proximal intestine. Furthermore, fecal short chain fatty acid levels do not exemplify the amount of short chain fatty acids produced in the intestine. Short chain fatty acids are largely absorbed in the intestine by a tightly regulated mechanism. Here we present an exemplar study showing that the determination of the molecular mechanism(s) underlying the precise mode of action of a LCS on gut microbiota allows for rational and scientifically-based recommendations.

Bacterial sensing underlies artificial sweetener-induced growth of gut Lactobacillus.

Disruption in stable establishment of commensal gut microbiota by early weaning is an important factor in susceptibility of young animals to enteric disorders. The artificial sweetener SUCRAM [consisting of neohesperidin dihydrochalcone (NHDC) and saccharin] included in piglets' feed reduces incidence of enteric disease. Pyrosequencing of pig caecal 16S rRNA gene amplicons identified 25 major families encompassing seven bacterial classes with Bacteroidia, Clostridia and Bacilli dominating the microbiota. There were significant shifts in microbial composition in pigs maintained on a diet containing SUCRAM, establishing SUCRAM as a major influence driving bacterial community dynamics. The most notable change was a significant increase of Lactobacillaceae population abundance, almost entirely due to a single phylotype, designated Lactobacillus 4228. The sweetener-induced increase in Lactobacillaceae was observed in two different breeds of pigs signifying a general effect. We isolated Lactobacillus 4228, sequenced its genome and found it to be related to Lactobacillus amylovorus. In vitro analyses of Lactobacillus 4228 growth characteristics showed that presence of NHDC significantly reduces the lag phase of growth and enhances expression of specific sugar transporters, independently of NHDC metabolism. This study suggests that sensing of NHDC by a bacterial plasma membrane receptor underlies sweetener-induced growth of a health promoting gut bacterium.

Dietary supplementation with lactose or artificial sweetener enhances swine gut Lactobacillus population abundance.

The commensal bacteria Lactobacillus are widely used as probiotic organisms conferring a heath benefit on the host. They have been implicated in promoting gut health via the stimulation of host immunity and anti-inflammatory responses, as well as protecting the intestinalmucosa against pathogen invasion. Lactobacilli grow by fermenting sugars and starches and produce lactic acid as their primary metabolic product. For efficient utilisation of varied carbohydrates, lactobacilli have evolved diverse sugar transport and metabolic systems, which are specifically induced by their own substrates. Many bacteria are also capable of sensing and responding to changes in their environment. These sensory responses are often independent of transport or metabolism and are mediated through membrane-spanning receptor proteins. We employed DNA-based pyrosequencing technology to investigate the changes in the intestinal microbiota of piglets weaned to a diet supplemented with either a natural sugar, lactose or an artificial sweetener (SUCRAM®, consisting of saccharin and neohesperidin dihydrochalcone (NHDC); Pancosma SA). The addition of either lactose or saccharin/NHDC to the piglets' feed dramatically increased the caecal population abundance of Lactobacillus, with concomitant increases in intraluminal lactic acid concentrations. This is the first report of the prebiotic-like effects of saccharin/NHDC, an artificial sweetener, being able to influence the commensal gut microbiota. The identification of the underlying mechanism(s) will assist in designing nutritional strategies for enhancing gut immunity and maintaining gut health.

Role of nutrient-sensing taste 1 receptor (T1R) family members in gastrointestinal chemosensing.

Luminal nutrient sensing by G-protein-coupled receptors (GPCR) expressed on the apical domain of enteroendocrine cells activates intracellular pathways leading to secretion of gut hormones that control vital physiological processes such as digestion, absorption, food intake and glucose homeostasis. The taste 1 receptor (T1R) family of GPCR consists of three members: T1R1; T1R2; T1R3. Expression of T1R1, T1R2 and T1R3 at mRNA and protein levels has been demonstrated in the intestinal tissue of various species. It has been shown that T1R2-T1R3, in association with G-protein gustducin, is expressed in intestinal K and L endocrine cells, where it acts as the intestinal glucose (sweet) sensor. A number of studies have demonstrated that activation of T1R2-T1R3 by natural sugars and artificial sweeteners leads to secretion of glucagon-like peptides 1&2 (GLP-1 and GLP-2) and glucose dependent insulinotropic peptide (GIP). GLP-1 and GIP enhance insulin secretion; GLP-2 increases intestinal growth and glucose absorption. T1R1-T1R3 combination co-expressed on the apical domain of cholecystokinin (CCK) expressing cells is a luminal sensor for a number of L-amino acids; with amino acid-activation of the receptor eliciting CCK secretion. This article focuses on the role of the gut-expressed T1R1, T1R2 and T1R3 in intestinal sweet and L-amino acid sensing. The impact of exploiting T1R2-T1R3 as a nutritional target for enhancing intestinal glucose absorption and gut structural maturity in young animals is also highlighted.

Sensing of amino acids by the gut-expressed taste receptor T1R1-T1R3 stimulates CCK secretion.

CCK is secreted by endocrine cells of the proximal intestine in response to dietary components, including amino acids. CCK plays a variety of roles in digestive processes, including inhibition of food intake, consistent with a role in satiety. In the lingual epithelium, the sensing of a broad spectrum of L-amino acids is accomplished by the heteromeric amino acid (umami) taste receptor (T1R1-T1R3). T1R1 and T1R3 subunits are also expressed in the intestine. A defining characteristic of umami sensing by T1R1-T1R3 is its potentiation by IMP or GMP. Furthermore, T1R1-T1R3 is not activated by Trp. We show here that, in response to L-amino acids (Phe, Leu, Glu, and Trp), but not D-amino acids, STC-1 enteroendocrine cells and mouse proximal small intestinal tissue explants secrete CCK and that IMP enhances Phe-, Leu-, and Glu-induced, but not Trp-induced, CCK secretion. Furthermore, small interfering RNA inhibition of T1R1 expression in STC-1 cells results in significant diminution of Phe-, Leu-, and Glu-stimulated, but not Trp-stimulated, CCK release. In STC-1 cells and mouse intestine, gurmarin inhibits Phe-, Leu-, and Glu-induced, but not Trp-stimulated, CCK secretion. In contrast, the Ca(2+)-sensing receptor antagonist NPS2143 inhibits Phe-stimulated CCK release partially and Trp-induced CCK secretion totally in mouse intestine. However, NPS2143 has no effect on Leu- or Glu-induced CCK secretion. Collectively, our data demonstrate that functional characteristics and cellular location of the gut-expressed T1R1-T1R3 support its role as a luminal sensor for Phe-, Leu-, and Glu-induced CCK secretion.

Expression of sweet receptor components in equine small intestine: relevance to intestinal glucose transport.

The heteromeric sweet taste receptor T1R2-T1R3 is expressed on the luminal membrane of certain populations of enteroendocrine cells. Sensing of sugars and other sweet compounds by this receptor activates a pathway in enteroendocrine cells, resulting in secretion of a number of gut hormones, including glucagon-like peptide 2 (GLP-2). This subsequently leads to upregulation in the expression of intestinal Na(+)/glucose cotransporter, SGLT1, and increased intestinal glucose absorption. On the basis of the current information available on the horse genome sequence, it has been proposed that the gene for T1R2 (Tas1R2) is absent in the horse. We show here, however, that horses express both the mRNA and protein for T1R2. Equine T1R2 is most closely homologous to that in the pig and the cow. T1R2 protein, along with T1R3, α-gustducin, and GLP-2 proteins are coexpressed in equine intestinal endocrine cells. Intravenous administration of GLP-2, in rats and pigs, leads to an increase in the expression of SGLT1 in absorptive enterocytes and enhancement in blood glucose concentrations. GLP-2 receptor is expressed in enteric neurons, excluding the direct effect of GLP-2 on enterocytes. However, electric stimulation of enteric neurons generates a neural response leading to SGLT1 upregulation, suggesting that sugar in the intestine activates a reflex increase in the functional expression of SGLT1. Horses possess the ability to upregulate SGLT1 expression in response to increased dietary carbohydrates, and to enhance the capacity of the gut to absorb glucose. The gut sweet receptor provides an accessible target for manipulating the equine gut to absorb glucose (and water), allowing greater energy uptake and hydration for hard-working horses.

Alterations in microbiota and fermentation products in equine large intestine in response to dietary variation and intestinal disease.

We aimed to determine the effects of variations in dietary composition on equine gut microbiota and their fermentation products, and proposed that dietary modifications profoundly affect microbial ecosystems and their metabolites. Bacterial communities within the large intestine of three groups of horses were compared using oligonucleotide-RNA hybridisation methodology. Each group consisting of six horses was maintained on (1) a grass-only diet, (2) a concentrate diet (i.e. supplemented with hydrolysable carbohydrates) and (3) a concentrate diet but horses were affected by simple colonic obstruction and distension (SCOD), a prevalent form of dietary-induced intestinal disease. We show that in response to dietary change and intestinal disease, there is a progressive and significant increase in Lachnospiraceae, the Bacteroidetes assemblage and the lactic acid-producing, Bacillus-Lactobacillus-Streptococcus (BLS) group. In contrast, there is a corresponding decrease in the proportion of obligate fibrolytic, acid-intolerant bacteria, Fibrobacter and Ruminococcaceae. Assessment of monocarboxylic acids indicated that there are significantly higher concentrations of lactic acid in the colonic contents of horses maintained on a concentrate diet and those suffering from SCOD, correlating with the observed increase in the population abundance of the BLS group. However, the population size of the Veillonellaceae (lactate utilisers) remained constant in each study group. The inability of this group to respond to increased lactic acid may be a contributory factor to the build-up of lactic acid observed in horses fed a concentrate diet and those suffering from SCOD.

Expression of Na+/glucose co-transporter 1 (SGLT1) is enhanced by supplementation of the diet of weaning piglets with artificial sweeteners.

In an intensive livestock production, a shorter suckling period allows more piglets to be born. However, this practice leads to a number of disorders including nutrient malabsorption, resulting in diarrhoea, malnutrition and dehydration. A number of strategies have been proposed to overcome weaning problems. Artificial sweeteners, routinely included in piglets' diet, were thought to enhance feed palatability. However, it is shown in rodent models that when included in the diet, they enhance the expression of Na+/glucose co-transporter (SGLT1) and the capacity of the gut to absorb glucose. Here, we show that supplementation of piglets' feed with a combination of artificial sweeteners saccharin and neohesperidin dihydrochalcone enhances the expression of SGLT1 and intestinal glucose transport function. Artificial sweeteners are known to act on the intestinal sweet taste receptor T1R2/T1R3 and its partner G-protein, gustducin, to activate pathways leading to SGLT1 up-regulation. Here, we demonstrate that T1R2, T1R3 and gustducin are expressed together in the enteroendocrine cells of piglet intestine. Furthermore, gut hormones secreted by the endocrine cells in response to dietary carbohydrates, glucagon-like peptides (GLP)-1, GLP-2 and glucose-dependent insulinotrophic peptide (GIP), are co-expressed with type 1 G-protein-coupled receptors (T1R) and gustducin, indicating that L- and K-enteroendocrine cells express these taste elements. In a fewer endocrine cells, T1R are also co-expressed with serotonin. Lactisole, an inhibitor of human T1R3, had no inhibitory effect on sweetener-induced SGLT1 up-regulation in piglet intestine. A better understanding of the mechanism(s) involved in sweetener up-regulation of SGLT1 will allow the identification of nutritional targets with implications for the prevention of weaning-related malabsorption.

Down-regulation of the monocarboxylate transporter 1 is involved in butyrate deficiency during intestinal inflammation.

BACKGROUND & AIMS: Butyrate oxidation is impaired in intestinal mucosa of patients with inflammatory bowel diseases (IBD). Butyrate uptake by colonocytes involves the monocarboxylate transporter (MCT) 1. We aimed to investigate the role of MCT1 in butyrate oxidation deficiency during colonic inflammation. METHODS: Colonic tissues were collected from patients with IBD or healthy controls and from rats with dextran sulfate sodium (DSS)-induced colitis. The intestinal epithelial cell line HT-29 was treated with interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha). MCT1 expression was analyzed by real-time reverse-transcription polymerase chain reaction, Western blot, and immunofluorescence. Butyrate uptake and oxidation in HT-29 cells was assessed using [(14)C]-butyrate. The mechanism of MCT1 gene regulation was analyzed by nuclear run-on and reporter gene assays. RESULTS: MCT1 messenger RNA (mRNA) and protein levels were markedly decreased in inflamed colonic mucosa of IBD patients and rats. In HT-29 cells, down-regulation of MCT1 mRNA and protein abundance by IFN-gamma and TNF-alpha correlated with a decrease in butyrate uptake and subsequent oxidation. IFN-gamma and TNF-alpha did not affect MCT1 mRNA stability but rather down-regulated gene transcription. We demonstrate that the cytokine response element is located in the proximal -111/+213 core region of the MCT1 promoter. CONCLUSIONS: The data suggest that butyrate oxidation deficiency in intestinal inflammation is a consequence of reduction in MCT1-mediated butyrate uptake. This reinforces the proposition that butyrate oxidation deficiency in IBD is not a primary defect.

T1R3 and gustducin in gut sense sugars to regulate expression of Na+-glucose cotransporter 1.

Dietary sugars are transported from the intestinal lumen into absorptive enterocytes by the sodium-dependent glucose transporter isoform 1 (SGLT1). Regulation of this protein is important for the provision of glucose to the body and avoidance of intestinal malabsorption. Although expression of SGLT1 is regulated by luminal monosaccharides, the luminal glucose sensor mediating this process was unknown. Here, we show that the sweet taste receptor subunit T1R3 and the taste G protein gustducin, expressed in enteroendocrine cells, underlie intestinal sugar sensing and regulation of SGLT1 mRNA and protein. Dietary sugar and artificial sweeteners increased SGLT1 mRNA and protein expression, and glucose absorptive capacity in wild-type mice, but not in knockout mice lacking T1R3 or alpha-gustducin. Artificial sweeteners, acting on sweet taste receptors expressed on enteroendocrine GLUTag cells, stimulated secretion of gut hormones implicated in SGLT1 up-regulation. Gut-expressed taste signaling elements involved in regulating SGLT1 expression could provide novel therapeutic targets for modulating the gut's capacity to absorb sugars, with implications for the prevention and/or treatment of malabsorption syndromes and diet-related disorders including diabetes and obesity.