Luminal glucose concentrations in the gut under normal conditions

Red rice bran aqueous extract ameliorate diabetic status by inhibiting intestinal glucose transport in high fat diet/STZ-induced diabetic rats

Red rice (Oryza sativa L.) consumption has grown recently, partly due to its potential health benefits in several disease prevention. The impact of red rice bran aqueous extract (RRBE) on intestinal glucose uptake and diabetes mellitus (DM) progression has not been thoroughly investigated. This study aimed to evaluate the effect of RRBE on ex vivo intestinal glucose absorption and its potential as an antihyperglycemic compound using a high-fat diet and streptozotocin (STZ)-induced diabetic rats. High-fat diet/STZ-induced diabetic rats were supplemented with either 1000 mg/kg body weight (BW) of RRBE, 70 mg/kg BW of metformin (Met), or a combination of RRBE and Met for 3 months. Plasma parameters, intestinal glucose transport, morphology, liver and soleus muscle glycogen accumulation were assessed. Treatment with RRBE, metformin, or combination markedly reversed hyperglycemia, hypertriglyceridemia, insulin resistance, and pancreatic morphology changes associated with T2DM. Correspondingly, all supplements effectively downregulated glucose transporters, resulting in a reduction of intestinal glucose transport-additionally, liver and soleus muscle glycogen accumulation was reduced in RRBE + Met treated group. Taken together, RRBE potentially suppressed intestinal glucose transporters' function and expression, reducing diabetic status.

Enhancing probiotic impact: engineering Saccharomyces boulardii for optimal acetic acid production and gastric passage tolerance

Saccharomyces boulardii has been a subject of growing interest due to its potential as a probiotic microorganism with applications in gastrointestinal health, but the molecular cause for its probiotic potency has remained elusive. The recent discovery that S. boulardii contains unique mutations causing high acetic acid accumulation and inhibition of bacterial growth provides a possible clue. The natural S. boulardii isolates Sb.P and Sb.A are homozygous for the recessive mutation whi2S270* and accumulate unusually high amounts of acetic acid, which strongly inhibit bacterial growth. However, the homozygous whi2S270* mutation also leads to acetic acid sensitivity and acid sensitivity in general. In the present study, we have constructed a new S. boulardii strain, derived from the widely therapeutically used CMCN I-745 strain (isolated from the pharmaceutical product Enterol), producing even higher levels of acetic acid while keeping the same tolerance toward low pH as the parent Enterol (ENT) strain. This newly engineered strain, named ENT3, has a homozygous deletion of ACH1 and strong overexpression of ALD4. It is also able to accumulate much higher acetic acid concentrations when growing on low glucose levels, in contrast to the ENT wild-type and Sb.P strains. Moreover, we show the antimicrobial capacity of ENT3 against gut pathogens in vitro and observed that higher acetic acid production might correlate with better persistence in the gut in healthy mice. These findings underscore the possible role of the unique acetic acid production and its potential for improvement of the probiotic action of S. boulardii.IMPORTANCESuperior variants of the probiotic yeast Saccharomyces boulardii produce high levels of acetic acid, which inhibit the growth of bacterial pathogens. However, these strains also show increased acid sensitivity, which can compromise the viability of the cells during their passage through the stomach. In this work, we have developed by genetic engineering a variant of Saccharomyces boulardii that produces even higher levels of acetic acid and does not show enhanced acid sensitivity. We also show that the S. boulardii yeasts with higher acetic acid production persist longer in the gut, in agreement with a previous work indicating competition between probiotic yeast and bacteria for residence in the gut.

Spatial structure, chemotaxis and quorum sensing shape bacterial biomass accumulation in complex porous media

Biological tissues, sediments, or engineered systems are spatially structured media with a tortuous and porous structure that host the flow of fluids. Such complex environments can influence the spatial and temporal colonization patterns of bacteria by controlling the transport of individual bacterial cells, the availability of resources, and the distribution of chemical signals for communication. Yet, due to the multi-scale structure of these complex systems, it is hard to assess how different biotic and abiotic properties work together to control the accumulation of bacterial biomass. Here, we explore how flow-mediated interactions allow the gut commensal Escherichia coli to colonize a porous structure that is composed of heterogenous dead-end pores (DEPs) and connecting percolating channels, i.e. transmitting pores (TPs), mimicking the structured surface of mammalian guts. We find that in presence of flow, gradients of the quorum sensing (QS) signaling molecule autoinducer-2 (AI-2) promote E. coli chemotactic accumulation in the DEPs. In this crowded environment, the combination of growth and cell-to-cell collision favors the development of suspended bacterial aggregates. This results in hot-spots of resource consumption, which, upon resource limitation, triggers the mechanical evasion of biomass from nutrients and oxygen depleted DEPs. Our findings demonstrate that microscale medium structure and complex flow coupled with bacterial quorum sensing and chemotaxis control the heterogenous accumulation of bacterial biomass in a spatially structured environment, such as villi and crypts in the gut or in tortuous pores within soil and filters.

Vagal interoception of microbial metabolites from the small intestinal lumen

The vagus nerve is proposed to enable communication between the gut microbiome and brain, but activity-based evidence is lacking. Herein, we assess the extent of gut microbial influences on afferent vagal activity and metabolite signaling mechanisms involved. We find that mice reared without microbiota (germ-free, GF) exhibit decreased vagal afferent tone relative to conventionally colonized mice (specific pathogen-free, SPF), which is reversed by colonization with SPF microbiota. Perfusing non-absorbable antibiotics (ABX) into the small intestine of SPF mice, but not GF mice, acutely decreases vagal activity, which is restored upon re-perfusion with bulk lumenal contents or sterile filtrates from the small intestine and cecum of SPF, but not GF, mice. Of several candidates identified by metabolomic profiling, microbiome-dependent short-chain fatty acids, bile acids, and 3-indoxyl sulfate stimulate vagal activity with varied response kinetics, which is blocked by co-perfusion of pharmacological antagonists of FFAR2, TGR5, and TRPA1, respectively, into the small intestine. At the single-unit level, serial perfusion of each metabolite class elicits more singly responsive neurons than dually responsive neurons, suggesting distinct neuronal detection of different microbiome- and macronutrient-dependent metabolites. Finally, microbial metabolite-induced increases in vagal activity correspond with activation of neurons in the nucleus of the solitary tract, which is also blocked by co-administration of their respective receptor antagonists. Results from this study reveal that the gut microbiome regulates select metabolites in the intestinal lumen that differentially activate chemosensory vagal afferent neurons, thereby enabling microbial modulation of interoceptive signals for gut-brain communication.

HIGHLIGHTS

Microbiota colonization status modulates afferent vagal nerve activityGut microbes differentially regulate metabolites in the small intestine and cecumSelect microbial metabolites stimulate vagal afferents with varied response kineticsSelect microbial metabolites activate vagal afferent neurons and brainstem neurons via receptor-dependent signaling.

Attempts to limit sporulation in the probiotic strain Bacillus subtilis BG01-4TM through mutation accumulation and selection

The use of bacterial spores in probiotics over viable loads of bacteria has many advantages, including the durability of spores, which allows spore-based probiotics to effectively traverse the various biochemical barriers present in the gastrointestinal tract. However, the majority of spore-based probiotics developed currently aim to treat adults, and there is a litany of differences between the adult and infant intestinal systems, including the immaturity and low microbial species diversity observed within the intestines of infants. These differences are only further exacerbated in premature infants with necrotizing enterocolitis (NEC) and indicates that what may be appropriate for an adult or even a healthy full-term infant may not be suited for an unhealthy premature infant. Complications from using spore-based probiotics for premature infants with NEC may involve the spores remaining dormant and adhering to the intestinal epithelia, the out-competing of commensal bacteria by spores, and most importantly the innate antibiotic resistance of spores. Also, the ability of Bacillus subtilis to produce spores under duress may result in less B. subtilis perishing within the intestines and releasing membrane branched-chain fatty acids. The isolate B. subtilis BG01-4^TM is a proprietary strain developed by Vernx Biotechnology through accumulating mutations within the BG01-4^TM genome in a serial batch culture. Strain BG01-4^TM was provided as a non-spore-forming B. subtilis , but a positive sporulation status for BG01-4^TM was confirmed through in vitro testing and suggested that selection for the sporulation defective genes could occur within an environment that would select against sporulation. The durability of key sporulation genes was ratified in this study, as the ability of BG01-4^TM to produce spores was not eliminated by the attempts to select against sporulation genes in BG01-4^TM by the epigenetic factors of high glucose and low pH. However, a variation in the genes in isolate BG01-4-8 involved in the regulation of sporulation is believed to have occurred during the mutation selection from the parent strain BG01-4^TM. An alteration in selected sporulation regulation genes is expected to have occurred from BG01-4^TM to BG01-4-8, with BG01-4-8 producing spores within 24 h, ~48 h quicker than BG01-4^TM.

Metabolite-induced in vivo fabrication of substrate-free organic bioelectronics

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo-fabricated electronics within the nervous system.

Functional characterization of SGLT1 using SSM-based electrophysiology: Kinetics of sugar binding and translocation

Beside the ongoing efforts to determine structural information, detailed functional studies on transporters are essential to entirely understand the underlying transport mechanisms. We recently found that solid supported membrane-based electrophysiology (SSME) enables the measurement of both sugar binding and transport in the Na⁺/sugar cotransporter SGLT1 (Bazzone et al, 2022a). Here, we continued with a detailed kinetic characterization of SGLT1 using SSME, determining K_M and K_D ^app for different sugars, k_obs values for sugar-induced conformational transitions and the effects of Na⁺, Li⁺, H⁺ and Cl^- on sugar binding and transport. We found that the sugar-induced pre-steady-state (PSS) charge translocation varies with the bound ion (Na⁺, Li⁺, H⁺ or Cl^-), but not with the sugar species, indicating that the conformational state upon sugar binding depends on the ion. Rate constants for the sugar-induced conformational transitions upon binding to the Na⁺-bound carrier range from 208 s^-1 for D-glucose to 95 s^-1 for 3-OMG. In the absence of Na⁺, rate constants are decreased, but all sugars bind to the empty carrier. From the steady-state transport current, we found a sequence for sugar specificity (V_max/K_M): D-glucose > MDG > D-galactose > 3-OMG > D-xylose. While K_M differs 160-fold across tested substrates and plays a major role in substrate specificity, V_max only varies by a factor of 1.9. Interestingly, D-glucose has the lowest V_max across all tested substrates, indicating a rate limiting step in the sugar translocation pathway following the fast sugar-induced electrogenic conformational transition. SGLT1 specificity for D-glucose is achieved by optimizing two ratios: the sugar affinity of the empty carrier for D-glucose is similarly low as for all tested sugars (K_D,K ^app = 210 mM). Affinity for D-glucose increases 14-fold (K_D,Na ^app = 15 mM) in the presence of sodium as a result of cooperativity. Apparent affinity for D-glucose during transport increases 8-fold (K_M = 1.9 mM) compared to K_D,Na ^app due to optimized kinetics. In contrast, K_M and K_D ^app values for 3-OMG and D-xylose are of similar magnitude. Based on our findings we propose an 11-state kinetic model, introducing a random binding order and intermediate states corresponding to the electrogenic transitions detected via SSME upon substrate binding.

The β2-adrenergic receptor in the apical membrane of intestinal enterocytes senses sugars to stimulate glucose uptake from the gut

The presence of sugar in the gut causes induction of SGLT1, the sodium/glucose cotransporter in intestinal epithelial cells (enterocytes), and this is accompanied by stimulation of sugar absorption. Sugar sensing was suggested to involve a G-protein coupled receptor and cAMP - protein kinase A signalling, but the sugar receptor has remained unknown. We show strong expression and co-localization with SGLT1 of the β2-adrenergic receptor (β ₂-AR) at the enterocyte apical membrane and reveal its role in stimulating glucose uptake from the gut by the sodium/glucose-linked transporter, SGLT1. Upon heterologous expression in different reporter systems, the β ₂-AR responds to multiple sugars in the mM range, consistent with estimated gut sugar levels after a meal. Most adrenergic receptor antagonists inhibit sugar signaling, while some differentially inhibit epinephrine and sugar responses. However, sugars did not inhibit binding of I¹²⁵-cyanopindolol, a β ₂-AR antagonist, to the ligand-binding site in cell-free membrane preparations. This suggests different but interdependent binding sites. Glucose uptake into everted sacs from rat intestine was stimulated by epinephrine and sugars in a β ₂-AR-dependent manner. STD-NMR confirmed direct physical binding of glucose to the β ₂-AR. Oral administration of glucose with a non-bioavailable β ₂-AR antagonist lowered the subsequent increase in blood glucose levels, confirming a role for enterocyte apical β ₂-ARs in stimulating gut glucose uptake, and suggesting enterocyte β ₂-AR as novel drug target in diabetic and obese patients. Future work will have to reveal how glucose sensing by enterocytes and neuroendocrine cells is connected, and whether β ₂-ARs mediate glucose sensing also in other tissues.

Surveying the Genetic Design Space for Transcription Factor-Based Metabolite Biosensors: Synthetic Gamma-Aminobutyric Acid and Propionate Biosensors in E. coli Nissle 1917

Engineered probiotic bacteria have been proposed as a next-generation strategy for noninvasively detecting biomarkers in the gastrointestinal tract and interrogating the gut-brain axis. A major challenge impeding the implementation of this strategy has been the difficulty to engineer the necessary whole-cell biosensors. Creation of transcription factor-based biosensors in a clinically-relevant strain often requires significant tuning of the genetic parts and gene expression to achieve the dynamic range and sensitivity required. Here, we propose an approach to efficiently engineer transcription-factor based metabolite biosensors that uses a design prototyping construct to quickly assay the gene expression design space and identify an optimal genetic design. We demonstrate this approach using the probiotic bacterium Escherichia coli Nissle 1917 (EcN) and two neuroactive gut metabolites: the neurotransmitter gamma-aminobutyric acid (GABA) and the short-chain fatty acid propionate. The EcN propionate sensor, utilizing the PrpR transcriptional activator from E. coli, has a large 59-fold dynamic range and >500-fold increased sensitivity that matches biologically-relevant concentrations. Our EcN GABA biosensor uses the GabR transcriptional repressor from Bacillus subtilis and a synthetic GabR-regulated promoter created in this study. This work reports the first known synthetic microbial whole-cell biosensor for GABA, which has an observed 138-fold activation in EcN at biologically-relevant concentrations. Using this rapid design prototyping approach, we engineer highly functional biosensors for specified in vivo metabolite concentrations that achieve a large dynamic range and high output promoter activity upon activation. This strategy may be broadly useful for accelerating the engineering of metabolite biosensors for living diagnostics and therapeutics.

Engineering probiotics to inhibit Clostridioides difficile infection by dynamic regulation of intestinal metabolism

Clostridioides difficile infection (CDI) results in significant morbidity and mortality in hospitalised patients. The pathogenesis of CDI is intrinsically related to the ability of C. difficile to shuffle between active vegetative cells and dormant endospores through the processes of germination and sporulation. Here, we hypothesise that dysregulation of microbiome-mediated bile salt metabolism contributes to CDI and that its alleviation can limit the pathogenesis of CDI. We engineer a genetic circuit harbouring a genetically encoded sensor, amplifier and actuator in probiotics to restore intestinal bile salt metabolism in response to antibiotic-induced microbiome dysbiosis. We demonstrate that the engineered probiotics limited the germination of endospores and the growth of vegetative cells of C. difficile in vitro and further significantly reduced CDI in model mice, as evidenced by a 100% survival rate and improved clinical outcomes. Our work presents an antimicrobial strategy that harnesses the host-pathogen microenvironment as the intervention target to limit the pathogenesis of infection.

Clostridioides difficile infection (CDI) results in significant morbidity and mortality in hospitalised patients. Here the authors engineer probiotics to restore intestinal bile salt metabolism in response to antibiotic-induced microbiome dysbiosis significantly inhibit Clostridioides difficile infection in model mice, presenting a microbiome-based antimicrobial strategy

Understanding the Formation and Mechanism of Anticipatory Responses in Escherichia coli

Microorganisms often live in complex habitats, where changes in the environment are predictable, providing an opportunity for microorganisms to learn, anticipate the upcoming environmental changes and prepare in advance for better survival and growth. One such environment is the mammalian intestine, where the abundance of different carbon sources is spatially distributed. In this study, we identified seven spatially distributed carbon sources in the mammalian intestine and tested whether Escherichia coli exhibits phenotypes that are consistent with an anticipatory response given their spatial order and abundance within the mammalian intestine. Through RNA-Seq and RT-PCR validation measurements, we found that there was a 67% match in the expression patterns between the measured phenotypes and what would otherwise be expected in the case of anticipatory behavior, while 83% and 0% were in agreement with the homeostatic and random response, respectively. To understand the genetic and phenotypic basis of the discrepancies between the expected and measured anticipatory responses, we thoroughly investigated the discrepancy in D-galactose treatment and the expression of maltose operon in E. coli. Here, the expected anticipatory response, based on the spatial distribution of D-galactose and D-maltose, was that D-galactose should upregulate the maltose operon, but it was the opposite in experimental validation. We performed whole genome random mutagenesis and screening and identified E. coli strains with positive expression of maltose operon in D-galactose. Targeted Sanger sequencing and mutation repair identified that the mutations in the promoter region of malT and in the coding region of the crp gene were the factors responsible for the reversion in the association. Further, to identify why positive association in the D-galactose treatment and the expression of the maltose operon did not evolve naturally, fitness measurements were performed. Fitness experiments demonstrated that the fitness of E. coli strains with a positive association in the D-galactose treatment and the expression of the maltose operon was 12% to 20% lower than that of the wild type strain.

The Transcription of Flagella of Enteropathogenic Escherichia coli O127:H6 Is Activated in Response to Environmental and Nutritional Signals

The flagella of enteropathogenic Escherichia coli (EPEC) O127:H6 E2348/69 mediate adherence to host proteins and epithelial cells. What environmental and nutritional signals trigger or down-regulate flagella expression in EPEC are largely unknown. In this study, we analyzed the influence of pH, oxygen tension, cationic and anionic salts (including bile salt), carbon and nitrogen sources, and catecholamines on the expression of the flagellin gene (fliC) of E2348/69. We found that sodium bicarbonate, which has been shown to induce the expression of type III secretion effectors, down-regulated flagella expression, explaining why E2348/69 shows reduced motility and flagellation when growing in Dulbecco’s Minimal Essential Medium (DMEM). Further, growth under a 5% carbon dioxide atmosphere, in DMEM adjusted to pH 8.2, in M9 minimal medium supplemented with 80 mM glucose or sucrose, and in DMEM containing 150 mM sodium chloride, 0.1% sodium deoxycholate, or 30 µM epinephrine significantly enhanced fliC transcription to different levels in comparison to growth in DMEM alone. When EPEC was grown in the presence of HeLa cells or in supernatants of cultured HeLa cells, high levels (4-fold increase) of fliC transcription were detected in comparison to growth in DMEM alone. Our data suggest that nutritional and host signals that EPEC may encounter in the intestinal niche activate fliC expression in order to favor motility and host colonization.

Quercetin Mitigates Endothelial Activation in a Novel Intestinal-Endothelial-Monocyte/Macrophage Coculture Setup

Atherosclerosis initiation is associated with a pro-inflammatory state of the endothelium. Quercetin is a flavonoid abundantly present in plant-based foods, with a possible impact on cardiovascular health. In this study, the effects of quercetin on lipopolysaccharide (LPS)-mediated endothelial inflammation and monocyte adhesion and migration, which are initial steps of the atherogenic process, are studied. Novel in vitro multicellular models simulating the intestinal-endothelial-monocytes/macrophages axis allowed to combine relevant intestinal flavonoid absorption, metabolism and efflux, and the consequent bioactivity towards peripheral endothelial cells. In this triple coculture, quercetin exposure decreased monocyte adhesion to and macrophage migration through an LPS-stressed endothelium, and this was associated with significantly lower levels of soluble vascular cell adhesion molecule-1 (sVCAM-1). Furthermore, quercetin decreased the pro-inflammatory cell environment upon LPS-induced endothelial activation, in terms of tumor necrosis factor- α (TNF-α), interleukin-6 (IL-6), interleukin-8 (IL-8), and sVCAM-1 expression. These findings highlight a mode-of-action by which quercetin may positively impact the initial states of atherosclerosis under more physiologically relevant conditions in terms of quercetin concentrations, metabolites, and intercellular crosstalk.

Bacterial Indole as a Multifunctional Regulator of Klebsiella oxytoca Complex Enterotoxicity

Gastrointestinal microbes respond to biochemical metabolites that coordinate their behaviors. Here, we demonstrate that bacterial indole functions as a multifactorial mitigator of Klebsiella grimontii and Klebsiella oxytoca pathogenicity. These closely related microbes produce the enterotoxins tilimycin and tilivalline; cytotoxin-producing strains are the causative agent of antibiotic-associated hemorrhagic colitis and have been associated with necrotizing enterocolitis of premature infants. We demonstrate that carbohydrates induce cytotoxin synthesis while concurrently repressing indole biosynthesis. Conversely, indole represses cytotoxin production. In both cases, the alterations stemmed from differential transcription of npsA and npsB, key genes involved in tilimycin biosynthesis. Indole also enhances conversion of tilimycin to tilivalline, an indole analog with reduced cytotoxicity. In this context, we established that tilivalline, but not tilimycin, is a strong agonist of pregnane X receptor (PXR), a master regulator of xenobiotic detoxification and intestinal inflammation. Tilivalline binding upregulated PXR-responsive detoxifying genes and inhibited tubulin-directed toxicity. Bacterial indole, therefore, acts in a multifunctional manner to mitigate cytotoxicity by Klebsiella spp.: suppression of toxin production, enhanced conversion of tilimycin to tilivalline, and activation of PXR. IMPORTANCE The human gut harbors a complex community of microbes, including several species and strains that could be commensals or pathogens depending on context. The specific environmental conditions under which a resident microbe changes its relationship with a host and adopts pathogenic behaviors, in many cases, remain poorly understood. Here, we describe a novel communication network involving the regulation of K. grimontii and K. oxytoca enterotoxicity. Bacterial indole was identified as a central modulator of these colitogenic microbes by suppressing bacterial toxin (tilimycin) synthesis and converting tilimycin to tilivalline while simultaneously activating a host receptor, PXR, as a means of mitigating tissue cytotoxicity. On the other hand, fermentable carbohydrates were found to inhibit indole biosynthesis and enhance toxin production. This integrated network involving microbial, host, and metabolic factors provides a contextual framework to better understand K. oxytoca complex pathogenicity.

Insight on Glucose and Fructose Absorption and Relevance in the Enterocyte Milieu

Although epidemiological studies indicate a strong correlation between high sugar intake and metabolic diseases, the biological mechanisms underlying this link are still controversial. To further examine the modification and crosstalk occurring in enterocyte metabolism during sugar absorption, in this study we evaluate the diffusion and intestinal metabolism of glucose, fructose and sucrose, which were supplemented in equimolar concentration to Caco-2 cells grown on polyester membrane inserts. At different time points after supplementation, changes in metabolite concentration were evaluated in the apical and basolateral chambers by nuclear magnetic resonance (NMR) and gas-chromatography (GC). Sucrose was only minimally hydrolyzed by Caco-2 cells. Upon supplementation, we observed a faster uptake of fructose than glucose, the pentose sugar being also faster catabolized. Monosaccharide absorption was concomitant to the synthesis/transport of other metabolites, which occurred differently in glucose and fructose supplemented cells. Our results confirm the prominent role of intestinal cells in fructose metabolism and clearance after absorption, representing a further step forward in the understanding of the role of dietary sugars. Future research, including targeted analysis on specific transporters/enzymes and the use of labeled substrates, will be helpful to confirm the present results and their interpretation.

Glucose- and Bile Acid-Stimulated Secretion of Gut Hormones in the Isolated Perfused Intestine Is Not Impaired in Diet-Induced Obese Mice

PURPOSE

Decreased circulating levels of food-intake-regulating gut hormones have been observed in type 2 diabetes and obesity. However, it is still unknown if this is due to decreased secretion from the gut mucosal cells or due to extra-intestinal processing of hormones.

METHODS

We measured intestinal hormone content and assessed morphological differences in the intestinal mucosa by histology and immunohistochemistry. Secretion of hormones and absorption of glucose and bile acids (BA) were assessed in isolated perfused mouse intestine.

RESULTS

GIP (glucose-dependent insulinotropic polypeptide) and SS (somatostatin) contents were higher in the duodenum of control mice (p < 0.001, and <0.01). Duodenal GLP-1 (glucagon-like peptide-1) content (p < 0.01) and distal ileum PYY content were higher in DIO mice (p < 0.05). Villus height in the jejunum, crypt depth, and villus height in the ileum were increased in DIO mice (p < 0.05 and p = 0.001). In the distal ileum of DIO mice, more immunoreactive GLP-1 and PYY cells were observed (p = 0.01 and 0.007). There was no difference in the absorption of glucose and bile acids. Distal secretion of SS tended to be higher in DIO mice (p < 0.058), whereas no difference was observed for the other hormones in response to glucose or bile acids.

CONCLUSION

Our data suggest that differences regarding production and secretion are unlikely to be responsible for the altered circulating gut hormone levels in obesity, since enteroendocrine morphology and hormone secretion capacity were largely unaffected in DIO mice.

Glucose but Not Fructose Alters the Intestinal Paracellular Permeability in Association With Gut Inflammation and Dysbiosis in Mice

A causal correlation between the metabolic disorders associated with sugar intake and disruption of the gastrointestinal (GI) homeostasis has been suggested, but the underlying mechanisms remain unclear. To unravel these mechanisms, we investigated the effect of physiological amounts of fructose and glucose on barrier functions and inflammatory status in various regions of the GI tract and on the cecal microbiota composition. C57BL/6 mice were fed chow diet and given 15% glucose or 15% fructose in drinking water for 9 weeks. We monitored caloric intake, body weight, glucose intolerance, and adiposity. The intestinal paracellular permeability, cytokine, and tight junction protein expression were assessed in the jejunum, cecum, and colon. In the cecum, the microbiota composition was determined. Glucose-fed mice developed a marked increase in total adiposity, glucose intolerance, and paracellular permeability in the jejunum and cecum while fructose absorption did not affect any of these parameters. Fructose-fed mice displayed increased circulation levels of IL6. In the cecum, both glucose and fructose intake were associated with an increase in Il13, Ifnγ, and Tnfα mRNA and MLCK protein levels. To clarify the relationships between monosaccharides and barrier function, we measured the permeability of Caco-2 cell monolayers in response to IFNγ+TNFα in the presence of glucose or fructose. In vitro, IFNγ+TNFα-induced intestinal permeability increase was less pronounced in response to fructose than glucose. Mice treated with glucose showed an enrichment of Lachnospiracae and Desulfovibrionaceae while the fructose increased relative abundance of Lactobacillaceae. Correlations between pro-inflammatory cytokine gene expression and bacterial abundance highlighted the potential role of members of Desulfovibrio and Lachnospiraceae NK4A136 group genera in the inflammation observed in response to glucose intake. The increase in intestinal inflammation and circulating levels of IL6 in response to fructose was observed in the absence of intestinal permeability modification, suggesting that the intestinal permeability alteration does not precede the onset of metabolic outcome (low-grade inflammation, hyperglycemia) associated with chronic fructose consumption. The data also highlight the deleterious effects of glucose on gut barrier function along the GI tract and suggest that Desulfovibrionaceae and Lachnospiraceae play a key role in the onset of GI inflammation in response to glucose.

Computational Modelling of Glucose Uptake by SGLT1 and Apical GLUT2 in the Enterocyte

It has been suggested that glucose absorption in the small intestine depends on both constitutively expressed SGLT1 and translocated GLUT2 in the brush border membrane, especially in the presence of high levels of luminal glucose. Here, we present a computational model of non-isotonic glucose uptake by small intestinal epithelial cells. The model incorporates apical uptake via SGLT1 and GLUT2, basolateral efflux into the blood via GLUT2, and cellular volume changes in response to non-isotonic conditions. The dependence of glucose absorption on luminal glucose, blood flow rate, and inlet blood glucose concentration is studied. Uptake via apical GLUT2 is found to be sensitive to all these factors. Under a range of conditions, the maximum apical GLUT2 flux is about half of the SGLT1 flux and is achieved at high luminal glucose (> 50 mM), high blood flow rates, and low inlet blood concentrations. In contrast, SGLT1 flux is less sensitive to these factors. When luminal glucose concentration is less than 10 mM, apical GLUT2 serves as an efflux pathway for glucose to move from the blood to the lumen. The model results indicate that translocation of GLUT2 from the basolateral to the apical membrane increases glucose uptake into the cell; however, the reduction of efflux capacity results in a decrease in net absorption. Recruitment of GLUT2 from a cytosolic pool elicits a 10–20% increase in absorption for luminal glucose levels in the a 20–100 mM range. Increased SGLT1 activity also leads to a roughly 20% increase in absorption. A concomitant increase in blood supply results in a larger increase in absorption. Increases in apical glucose transporter activity help to minimise cell volume changes by reducing the osmotic gradient between the cell and the lumen.

E. coli Nissle 1917 modulates host glucose metabolism without directly acting on glucose

Managing postprandial glycemic response, or the increase in blood sugar following a meal, is a crucial component to maintaining healthy blood sugar in patients with diabetes. To test whether oral probiotics can impact postprandial glycemic response, E. coli Nissle 1917 (EcN) was evaluated in an oral glucose tolerance test. Oral gavage of EcN concurrent with a glucose bolus reduced the post-gavage glycemic response in mice. However, there was no difference in glycemic response when comparing EcN to a mutant deficient in glucose metabolism. This suggests that while EcN can alter glycemic response to a glucose bolus, this effect is not mediated by direct uptake of glucose. Of the possible indirect effects EcN could have, gastric emptying rate was highlighted as a likely cause, but EcN had no effect on gastric emptying rate in mice. This leaves many more possible indirect explanations for the interaction between EcN and host glucose metabolism to be explored in future work.

Mechanisms of Glucose Absorption in the Small Intestine in Health and Metabolic Diseases and Their Role in Appetite Regulation

The worldwide prevalence of metabolic diseases such as obesity, metabolic syndrome and type 2 diabetes shows an upward trend in recent decades. A characteristic feature of these diseases is hyperglycemia which can be associated with hyperphagia. Absorption of glucose in the small intestine physiologically contributes to the regulation of blood glucose levels, and hence, appears as a putative target for treatment of hyperglycemia. In fact, recent progress in understanding the molecular and cellular mechanisms of glucose absorption in the gut and its reabsorption in the kidney helped to develop a new strategy of diabetes treatment. Changes in blood glucose levels are also involved in regulation of appetite, suggesting that glucose absorption may be relevant to hyperphagia in metabolic diseases. In this review we discuss the mechanisms of glucose absorption in the small intestine in physiological conditions and their alterations in metabolic diseases as well as their relevance to the regulation of appetite. The key role of SGLT1 transporter in intestinal glucose absorption in both physiological conditions and in diabetes was clearly established. We conclude that although inhibition of small intestinal glucose absorption represents a valuable target for the treatment of hyperglycemia, it is not always suitable for the treatment of hyperphagia. In fact, independent regulation of glucose absorption and appetite requires a more complex approach for the treatment of metabolic diseases.

The influence of the crowding assumptions in biofilm simulations

Microorganisms are frequently organized into crowded structures that affect the nutrients diffusion. This reduction in metabolite diffusion could modify the microbial dynamics, meaning that computational methods for studying microbial systems need accurate ways to model the crowding conditions. We previously developed a computational framework, termed CROMICS, that incorporates the effect of the (time-dependent) crowding conditions on the spatio-temporal modeling of microbial communities, and we used it to demonstrate the crowding influence on the community dynamics. To further identify scenarios where crowding should be considered in microbial modeling, we herein applied and extended CROMICS to simulate several environmental conditions that could potentially boost or dampen the crowding influence in biofilms. We explore whether the nutrient supply (rich- or low-nutrient media), the cell-packing configuration (square or hexagonal spherical cell arrangement), or the cell growing conditions (planktonic state or biofilm) modify the crowding influence on the growth of Escherichia coli. Our results indicate that the growth rate, the abundance and appearance time of different cell phenotypes as well as the amount of by-products secreted to the medium are sensitive to some extent to the local crowding conditions in all scenarios tested, except in rich-nutrient media. Crowding conditions enhance the formation of nutrient gradient in biofilms, but its effect is only appreciated when cell metabolism is controlled by the nutrient limitation. Thus, as soon as biomass (and/or any other extracellular macromolecule) accumulates in a region, and cells occupy more than 14% of the volume fraction, the crowding effect must not be underestimated, as the microbial dynamics start to deviate from the ideal/expected behaviour that assumes volumeless cells or when a homogeneous (reduced) diffusion is applied in the simulation. The modeling and simulation of the interplay between the species diversity (cell shape and metabolism) and the environmental conditions (nutrient quality, crowding conditions) can help to design effective strategies for the optimization and control of microbial systems.

Development of red genetically encoded biosensor for visualization of intracellular glucose dynamics

Glucose is the main source of energy for organisms, and it is important to understand the spatiotemporal dynamics of intracellular glucose. Single fluorescent protein-based glucose indicators, named "Red Glifons" have been developed that apply to live-cell and dual-color imaging. These indicators exhibited more than 3-fold increase in fluorescence intensity in the presence of 10 mM glucose. The two Red Glifons developed have different half-maximal effective concentration (EC₅₀) values for glucose (300 μM and 3,000 μM) and are able to monitor a wide range of glucose dynamics. Red Glifon combined with green indicators allowing visualization of the interplay between glucose and ATP, lactate, or pyruvate. Glucose influx in the pharyngeal muscle of Caenorhabditis elegans, enteroendocrine cells, and human iPS cell-derived cardiac myocytes was observed using the Red Glifons. Thus these red glucose indicators serve as a multi-color imaging toolkit for investigating complex interactions in energy metabolism.

Nutrient-Induced Cellular Mechanisms of Gut Hormone Secretion

The gastrointestinal tract can assess the nutrient composition of ingested food. The nutrient-sensing mechanisms in specialised epithelial cells lining the gastrointestinal tract, the enteroendocrine cells, trigger the release of gut hormones that provide important local and central feedback signals to regulate nutrient utilisation and feeding behaviour. The evidence for nutrient-stimulated secretion of two of the most studied gut hormones, glucagon-like peptide 1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), along with the known cellular mechanisms in enteroendocrine cells recruited by nutrients, will be the focus of this review. The mechanisms involved range from electrogenic transporters, ion channel modulation and nutrient-activated G-protein coupled receptors that converge on the release machinery controlling hormone secretion. Elucidation of these mechanisms will provide much needed insight into postprandial physiology and identify tractable dietary approaches to potentially manage nutrition and satiety by altering the secreted gut hormone profile.

Glucose confers protection to Escherichia coli against contact killing by Vibrio cholerae

Evolutionary arms races are broadly prevalent among organisms including bacteria, which have evolved defensive strategies against various attackers. A common microbial aggression mechanism is the type VI secretion system (T6SS), a contact-dependent bacterial weapon used to deliver toxic effector proteins into adjacent target cells. Sibling cells constitutively express immunity proteins that neutralize effectors. However, less is known about factors that protect non-sibling bacteria from T6SS attacks independently of cognate immunity proteins. In this study, we observe that human Escherichia coli commensal strains sensitive to T6SS attacks from Vibrio cholerae are protected when co-cultured with glucose. We confirm that glucose does not impair V. cholerae T6SS activity. Instead, we find that cells lacking the cAMP receptor protein (CRP), which regulates expression of hundreds of genes in response to glucose, survive significantly better against V. cholerae T6SS attacks even in the absence of glucose. Finally, we show that the glucose-mediated T6SS protection varies with different targets and killers. Our findings highlight the first example of an extracellular small molecule modulating a genetically controlled response for protection against T6SS attacks. This discovery may have major implications for microbial interactions during pathogen-host colonization and survival of bacteria in environmental communities.

Characterization of SGLT1-mediated glucose transport in Caco-2 cell monolayers, and absence of its regulation by sugar or epinephrine

Caco-2 cells are increasingly used to study the absorption of drugs and nutrients, including D-glucose, an important nutrient that mainly gets absorbed from the intestine by the sodium/glucose cotransporter 1 (SGLT1). However, disadvantages of Caco-2 cells for such studies have been reported, e.g., D-glucose cannot elicit translocation of the intracellular pool of SGLT1 to the apical membrane, the origin of the cells affects glucose uptake, and Caco-2 cells exhibit heterogeneity. This study aimed to characterize SGLT1-mediated glucose transport across Caco-2 cell monolayers. We found that at lower glucose concentrations (5 mM) SGLT1 contributes more to total glucose transport than at higher (10 mM) glucose concentrations, suggesting contributions by another transporter at higher glucose concentrations. This contrasts with the in vivo situation, where SGLT1 dominant glucose transporter at all glucose concentrations. We also tested whether known regulators like sugars or catecholamines can stimulate glucose transport across Caco-2 cell monolayers. Neither epinephrine nor 2-deoxy-D-glucose could stimulate glucose transport. Moreover, the epinephrine could not induce accumulation of cyclic adenosine monophosphate (cAMP) in Caco-2 cells, indicating the absence of a functional β₂-adrenoceptor in Caco-2 cells, which could explain the lack of epinephrine effect on glucose transport. Also, Caco-2 cells may lack some kinases required for increased SGLT1 transport. Overall, SGLT1-mediated glucose transport and its regulation in Caco-2 cells differ from that in vivo, and caution is advised when extrapolating glucose transport results obtained with this model to the in vivo situation.

Influence of L-lactate and low glucose concentrations on the metabolism and the toxin formation of Clostridioides difficile

The virulence of Clostridioides difficile (formerly Clostridium difficile) is mainly caused by its two toxins A and B. Their formation is significantly regulated by metabolic processes. Here we investigated the influence of various sugars (glucose, fructose, mannose, trehalose), sugar derivatives (mannitol and xylitol) and L-lactate on toxin synthesis. Fructose, mannose, trehalose, mannitol and xylitol in the growth medium resulted in an up to 2.2-fold increase of secreted toxin. Low glucose concentration of 2 g/L increased the toxin concentration 1.4-fold compared to growth without glucose, while high glucose concentrations in the growth medium (5 and 10 g/L) led to up to 6.6-fold decrease in toxin formation. Transcriptomic and metabolic investigation of the low glucose effect pointed towards an inactive CcpA and Rex regulatory system. L-lactate (500 mg/L) significantly reduced extracellular toxin formation. Transcriptome analyses of the later process revealed the induction of the lactose utilization operon encoding lactate racemase (larA), electron confurcating lactate dehydrogenase (CDIF630erm_01321) and the corresponding electron transfer flavoprotein (etfAB). Metabolome analyses revealed L-lactate consumption and the formation of pyruvate. The involved electron confurcation process might be responsible for the also observed reduction of the NAD⁺/NADH ratio which in turn is apparently linked to reduced toxin release from the cell.

Inulin-grown Faecalibacterium prausnitzii cross-feeds fructose to the human intestinal epithelium

Many chronic diseases are associated with decreased abundance of the gut commensal Faecalibacterium prausnitzii. This strict anaerobe can grow on dietary fibers, e.g., prebiotics, and produce high levels of butyrate, often associated to epithelial metabolism and health. However, little is known about other F. prausnitzii metabolites that may affect the colonic epithelium. Here, we analyzed prebiotic cross-feeding between F. prausnitzii and intestinal epithelial (Caco-2) cells in a "Human-oxygen Bacteria-anaerobic" coculture system. Inulin-grown F. prausnitzii enhanced Caco-2 viability and suppressed inflammation- and oxidative stress-marker expression. Inulin-grown F. prausnitzii produced excess butyrate and fructose, but only fructose efficiently promoted Caco-2 growth. Finally, fecal microbial taxonomy analysis (16S sequencing) from healthy volunteers (n = 255) showed the strongest positive correlation for F. prausnitzii abundance and stool fructose levels. We show that fructose, produced and accumulated in a fiber-rich colonic environment, supports colonic epithelium growth, while butyrate does not.

Sodium-glucose cotransporter 1 as a sugar taste sensor in mouse tongue

AIM

We investigated potential neuron types that code sugar information and how sodium-glucose cotransporters (SGLTs) and T1Rs are involved.

METHODS

Whole-nerve recordings in the chorda tympani (CT) and the glossopharyngeal (GL) nerves and single-fibre recordings in the CT were performed in T1R3-KO and wild-type (WT) mice. Behavioural response measurements were conducted in T1R3-KO mice using phlorizin (Phl), a competitive inhibitor of SGLTs.

RESULTS

Results indicated that significant enhancement occurred in responses to sucrose and glucose (Glc) by adding 10 mmol/L NaCl but not in responses to KCl, monopotassium glutamate, citric acid, quinine sulphate, SC45647(SC) or polycose in both CT and GL nerves. These enhancements were abolished by lingual application of Phl. In single-fibre recording, fibres showing maximal response to sucrose could be classified according to responses to SC and Glc with or without 10 mmol/L NaCl in the CT of WT mice, namely, Phl-insensitive type, Phl-sensitive Glc-type and Mixed (Glc and SC responding)-type fibres. In T1R3-KO mice, Phl-insensitive-type fibres disappeared. Results from behavioural experiments showed that the number of licks and amount of intake for Glc with or without 10 mmol/L NaCl were significantly suppressed by Phl.

CONCLUSION

We found evidence for the contribution of SGLTs in sugar sensing in taste cells of mouse tongue. Moreover, we found T1R-dependent (Phl-insensitive) type, Glc-type and Mixed (SGLTs and T1Rs)-type fibres. SGLT1 may be involved in the latter two types and may play important roles in the glucose-specific cephalic phase of digestion and palatable food intake.

Anthocyanin Bioactivity in Obesity and Diabetes: The Essential Role of Glucose Transporters in the Gut and Periphery

Obesity and type-2 diabetes trends continue to worsen in the United States. Dietary anthocyanins (typically provided by berries and other fruits) are reported to have protective effects against both conditions using a variety of experimental research models including animal and human feeding studies. This review highlights studies that explore the biochemical pathways in both tissue and rodent models which could explain clinical improvements noted with anthocyanin consumption. First, the primary mode of intestinal absorption of anthocyanins is through both sGLT1 and GLUT2 glucose transporters. Stronger binding affinities may allow anthocyanins to be more inhibitive to glucose absorption compared to the reverse, where GLUT2 expression may also be affected. Genetic or chemical inhibition of sGLT1 or GLUT2 demonstrate their essential function in anthocyanin absorption across the enterocyte, where the former interacts with a greater variety of anthocyanins but the latter is the major transporter for specific anthocyanin-glycosides. Once absorbed, anthocyanins positively modulate GLUT4 density and function in both skeletal muscle and adipose tissues via the upregulation of AMPK and restoration of insulin sensitivity. Antioxidant properties and phosphodiesterase inhibition by anthocyanins promote both mitochondrial function and density which could be novel targets for dietary management of obesity and its complications.

Predicting community dynamics of antibiotic-sensitive and -resistant species in fluctuating environments

Microbes occupy almost every niche within and on their human hosts. Whether colonizing the gut, mouth or bloodstream, microorganisms face temporal fluctuations in resources and stressors within their niche but we still know little of how environmental fluctuations mediate certain microbial phenotypes, notably antimicrobial-resistant ones. For instance, do rapid or slow fluctuations in nutrient and antimicrobial concentrations select for, or against, resistance? We tackle this question using an ecological approach by studying the dynamics of a synthetic and pathogenic microbial community containing two species, one sensitive and the other resistant to an antibiotic drug where the community is exposed to different rates of environmental fluctuation. We provide mathematical models, supported by experimental data, to demonstrate that simple community outcomes, such as competitive exclusion, can shift to coexistence and ecosystem bistability as fluctuation rates vary. Theory gives mechanistic insight into how these dynamical regimes are related. Importantly, our approach highlights a fundamental difference between resistance in single-species populations, the context in which it is usually assayed, and that in communities. While fast environmental changes are known to select against resistance in single-species populations, here we show that they can promote the resistant species in mixed-species communities. Our theoretical observations are verified empirically using a two-species Candida community.

Adaptation of the Gut Microbiota to Modern Dietary Sugars and Sweeteners

The consumption of sugar has become central to the Western diet. Cost and health concerns associated with sucrose spurred the development and consumption of other sugars and sweeteners, with the average American consuming 10 times more sugar than 100 y ago. In this review, we discuss how gut microbes are affected by changes in the consumption of sugars and other sweeteners through transcriptional, abundance, and genetic adaptations. We propose that these adaptations result in microbes taking on different metabolic, ecological, and genetic profiles along the intestinal tract. We suggest novel approaches to assess the consequences of these changes on host-microbe interactions to determine the safety of novel sugars and sweeteners.

The microbiome of the upper respiratory tract in health and disease

The human upper respiratory tract (URT) offers a variety of niches for microbial colonization. Local microbial communities are shaped by the different characteristics of the specific location within the URT, but also by the interaction with both external and intrinsic factors, such as ageing, diseases, immune responses, olfactory function, and lifestyle habits such as smoking. We summarize here the current knowledge about the URT microbiome in health and disease, discuss methodological issues, and consider the potential of the nasal microbiome to be used for medical diagnostics and as a target for therapy.

A higher throughput and physiologically relevant two-compartmental human ex vivo intestinal tissue system for studying gastrointestinal processes

A majority of the preclinical intestinal screening models do not properly reflect the complex physiology of the human intestinal tract, resulting in low translational value to the clinical situation. The often used cell lines such as Caco-2 or HT-29 are not well suited to investigate the different processes that predict oral bioavailability in real life, or processes involved in general gut health aspects. Therefore, highly realistic models resembling the human in vivo situation are needed; application of ex vivo intestinal tissue is an interesting and feasible alternative. After previously using porcine intestinal tissue as a predictive model for human intestinal absorption, we now have successfully applied human intestinal tissue into a newly developed InTESTine™ two-compartmental disposable device suitable for standard 6- or 24-well plate format. With this set-up we demonstrated (regional differences in) drug absorption, by using a subset of compounds with known varying F_a (fraction absorbed) values. A rank-order relationship of R² = 0.85 could be established between the F_a and P_app of these commercially available drugs. Additionally, comparison between the InTESTine system and the established Ussing chamber technology showed a correlation of R² = 0.94 (10 drugs) with respect to P_app values, indicating good comparison of both models. Besides absorption, intestinal wall metabolism of testosterone (CYP3A4) was determined by showing a linear formation (R² = 0.99; up to 165 min) of the main metabolites androstenedione and 6Beta-hydroxytestosterone, indicating no loss of metabolic capacity of the intestinal tissue within the system. Enteroendocrine responses were assessed of the satiety hormones GLP-1 and PYY after stimulation with rebaudioside A and casein, resulting in significantly increased secretion to the luminal side as well as to the basolateral side. Incubation with the probiotic strain LGG showed to enhance the viability of the tissue by showing to decrease the LDH secretion compared to blank intestinal tissue. In conclusion, we show that human ex vivo intestinal tissue mounted in the higher throughput InTESTine 6- 24-transwell plate system is easy to handle and a suitable system to study diverse functional GI processes.

Competition among Nasal Bacteria Suggests a Role for Siderophore-Mediated Interactions in Shaping the Human Nasal Microbiota

Resources available in the human nasal cavity are limited. Therefore, to successfully colonize the nasal cavity, bacteria must compete for scarce nutrients. Competition may occur directly through interference (e.g., antibiotics) or indirectly by nutrient sequestration. To investigate the nature of nasal bacterial competition, we performed coculture inhibition assays between nasal Actinobacteria and Staphylococcus spp. We found that isolates of coagulase-negative staphylococci (CoNS) were sensitive to growth inhibition by Actinobacteria but that Staphylococcus aureus isolates were resistant to inhibition. Among Actinobacteria, we observed that Corynebacterium spp. were variable in their ability to inhibit CoNS. We sequenced the genomes of 10 Corynebacterium species isolates, including 3 Corynebacterium propinquum isolates that strongly inhibited CoNS and 7 other Corynebacterium species isolates that only weakly inhibited CoNS. Using a comparative genomics approach, we found that the C. propinquum genomes were enriched in genes for iron acquisition and harbored a biosynthetic gene cluster (BGC) for siderophore production, absent in the noninhibitory Corynebacterium species genomes. Using a chrome azurol S assay, we confirmed that C. propinquum produced siderophores. We demonstrated that iron supplementation rescued CoNS from inhibition by C. propinquum, suggesting that inhibition was due to iron restriction through siderophore production. Through comparative metabolomics and molecular networking, we identified the siderophore produced by C. propinquum as dehydroxynocardamine. Finally, we confirmed that the dehydroxynocardamine BGC is expressed in vivo by analyzing human nasal metatranscriptomes from the NIH Human Microbiome Project. Together, our results suggest that bacteria produce siderophores to compete for limited available iron in the nasal cavity and improve their fitness.IMPORTANCE Within the nasal cavity, interference competition through antimicrobial production is prevalent. For instance, nasal Staphylococcus species strains can inhibit the growth of other bacteria through the production of nonribosomal peptides and ribosomally synthesized and posttranslationally modified peptides. In contrast, bacteria engaging in exploitation competition modify the external environment to prevent competitors from growing, usually by hindering access to or depleting essential nutrients. As the nasal cavity is a nutrient-limited environment, we hypothesized that exploitation competition occurs in this system. We determined that Corynebacterium propinquum produces an iron-chelating siderophore, and this iron-sequestering molecule correlates with the ability to inhibit the growth of coagulase-negative staphylococci. Furthermore, we found that the genes required for siderophore production are expressed in vivo Thus, although siderophore production by bacteria is often considered a virulence trait, our work indicates that bacteria may produce siderophores to compete for limited iron in the human nasal cavity.

Roles of the Transcription Factors Sfl2 and Efg1 in White-Opaque Switching in a/α Strains of Candida albicans

Candida albicans remains the most pervasive fungal pathogen colonizing humans. The majority of isolates from hosts are heterozygous at the mating type locus (MTL a/α), and a third of these have recently been shown to be capable of switching to the opaque phenotype. Here we have investigated the roles of two transcription factors (TFs) Sfl2 and Efg1, in repressing switching in a/α strains. Deleting either gene results in the capacity of a/α cells to switch to opaque en masse under facilitating environmental conditions, which include N-acetylglucosamine (GlcNAc) as the carbon source, physiological temperature (37°C), and high CO₂ (5%). These conditions are similar to those in the host. Our results further reveal that while glucose is a repressor of sfl2Δ and efg1Δ switching, GlcNAc is an inducer. Finally, we show that when GlcNAc is the carbon source, and the temperature is low (25°C), the efg1Δ mutants, but not the sfl2Δ mutants, form a tiny, elongate cell, which differentiates into an opaque cell when transferred to conditions optimal for a/α switching. These results demonstrate that at least two TFs, Sfl2 and Efg1, repress switching in a/α cells and that a/α strains with either an sfl2Δ or efg1Δ mutation can switch en masse but only under physiological conditions. The role of opaque a/α cells in commensalism and pathogenesis must, therefore, be investigated.IMPORTANCE More than 95% of Candida albicans strains isolated from humans are MTL a/α, and approximately a third of these can undergo the white-to-opaque transition. Therefore, besides being a requirement for MTL-homozygous strains to mate, the opaque phenotype very likely plays a role in the commensalism and pathogenesis of nonmating, a/α populations colonizing humans.

High fructose-induced metabolic changes enhance inflammation in human dendritic cells

Dendritic cells (DCs) are critical antigen-presenting cells which are the initiators and regulators of the immune response. Numerous studies support the idea that dietary sugars influence DC functions. Increased consumption of fructose has been thought to be the leading cause of metabolic disorders. Although evidence supports their association with immune dysfunction, the specific mechanisms are not well understood. Fructose is one of the main dietary sugars in our diet. Therefore, here we compared the effect of fructose and glucose on the functions of human DCs. High levels of D-fructose compared to D-glucose led to activation of DCs in vitro by promoting interleukin (IL)-6 and IL-1β production. Moreover, fructose exposed DCs also induced interferon (IFN)-γ secretion from T cells. Proinflammatory response of DCs in high fructose environment was found to be independent of the major known metabolic regulators or glycolytic control. Instead, DC activation on acute exposure to fructose was via activation of receptor for advanced glycation end product (RAGE) in response to increased accumulation of advanced glycation end products (AGE). However, chronic exposure of DCs to high fructose environment induced a shift towards glycolysis compared to glucose cultured DCs. Further investigations revealed that the AGEs formed by fructose induced increased levels of inflammatory cytokines in DCs compared to AGEs from glucose. In summary, understanding the link between metabolic changes and fructose-induced DC activation compared to glucose has broad implications for immune dysfunction associated with metabolic disorders.

Recent insights into the role of ChREBP in intestinal fructose absorption and metabolism

Fructose in the form of sucrose and high fructose corn syrup is absorbed by the intestinal transporter and mainly metabolized in the small intestine. However, excess intake of fructose overwhelms the absorptive capacity of the small intestine, leading to fructose malabsorption. Carbohydrate response element-binding protein (ChREBP) is a basic helix-loop-helix leucine zipper transcription factor that plays a key role in glycolytic and lipogenic gene expression in response to carbohydrate consumption. While ChREBP was initially identified as a glucose-responsive factor in the liver, recent evidence suggests that ChREBP is essential for fructoseinduced lipogenesis and gluconeogenesis in the small intestine as well as in the liver. We recently identified that the loss of ChREBP leads to fructose intolerance via insufficient induction of genes involved in fructose transport and metabolism in the intestine. As fructose consumption is increasing and closely associated with metabolic and gastrointestinal diseases, a comprehensive understanding of cellular fructose sensing and metabolism via ChREBP may uncover new therapeutic opportunities. In this mini review, we briefly summarize recent progress in intestinal fructose metabolism, regulation and function of ChREBP by fructose, and delineate the potential mechanisms by which excessive fructose consumption may lead to irritable bowel syndrome.

NanI Sialidase Is an Important Contributor to Clostridium perfringens Type F Strain F4969 Intestinal Colonization in Mice

Clostridium perfringens type F (formerly enterotoxigenic C. perfringens type A) strains produce an enterotoxin (CPE) to cause acute cases of food poisoning and chronic nonfoodborne human gastrointestinal diseases (NFD), e.g., antibiotic-associated diarrhea (AAD). NFD strains also produce NanI sialidase, an extracellular enzyme that releases sialic acids from sialyated host macromolecules. Recent in vitro studies suggested that NanI may contribute to NFD strain intestinal colonization by enhancing the adherence of such strains to intestinal cells and promoting their bacterial growth using generated sialic acid as an energy source. The current study tested this hypothesis by developing a mouse intestinal colonization model involving clindamycin pretreatment to produce conditions mimicking those during AAD. In this model, the type F NFD strain F4969 persisted for at least 4 days in the small intestine, cecum, and colon. When clindamycin-pretreated mice were challenged by oral gavage with equivalent numbers of F4969 bacteria or its isogenic nanI null mutant, significantly lower numbers of the nanI mutant were recovered from all intestinal segments, and it was completely cleared from the small intestine by day 4. Complementation of the mutant to restore NanI production also promoted colonization. When the same nanI null mutant strain was coinoculated into the mouse model together with a nanI-producing strain, the numbers of this mutant were restored to wild-type F4969 levels in all intestinal segments. This result suggests that sialidases produced by other bacteria might also provide some support for C. perfringens intestinal colonization. Collectively, these in vivo findings identify NanI to be the first known significant contributor to chronic intestinal colonization by NFD strains.

Luminal Na+ homeostasis has an important role in intestinal peptide absorption in vivo

Intestinal cell line studies indicated luminal Na⁺ homeostasis is essential for proton-coupled peptide absorption, because the driving force of PepT1 activity is supported by the apical Na⁺/H⁺ exchanger NHE3. However, there is no direct evidence demonstrating the importance of in vivo luminal Na⁺ for peptide absorption in animal experiments. To investigate the relationship between luminal Na⁺ homeostasis and peptide absorption, we took advantage of claudin 15-deficient (cldn15^-/-) mice, whereby Na⁺ homeostasis is disrupted. We quantitatively assessed the intestinal segment responsible for peptide absorption using radiolabeled nonhydrolyzable dipeptide (glycylsarcosine, Gly-Sar) and nonabsorbable fluid phase marker polyethylene glycol (PEG) 4000 in vivo. In wild-type (WT) mice, the concentration ratio of Gly-Sar to PEG 4000 decreased in the upper jejunum, suggesting the upper jejunum is responsible for peptide absorption. Gly-Sar absorption was decreased in the jejunum of cldn15^-/- mice. To elucidate the mechanism underlining these impairments, a Gly-Sar-induced short-circuit ( I_sc) current was measured. In WT mice, increments of Gly-Sar-induced I_sc were inhibited by the luminal application of a NHE3-specific inhibitor S3226 in a dose-dependent fashion. In contrast to in vivo experiments, robust Gly-Sar-induced I_sc increments were observed in the jejunal mucosa of cldn15^-/- mice. Gly-Sar-induced I_sc was inhibited by S3226 or a reduction of luminal Na⁺ concentration, which mimics low luminal Na⁺ concentrations in vivo . Our study demonstrates that luminal Na⁺ homeostasis is important for peptide absorption in native epithelia and that there is a cooperative functional relationship between PepT1 and NHE3. NEW & NOTEWORTHY Our study is the first to demonstrate that luminal Na⁺ homeostasis is important for proton-coupled peptide absorption in in vivo animal experiments.

On the relationship between glucose absorption and glucose-stimulated secretion of GLP-1, neurotensin, and PYY from different intestinal segments in the rat

Ingested glucose powerfully stimulates the secretion of appetite‐ and metabolism‐regulating peptide hormones from the gut – including glucagon‐like peptide‐1 (GLP‐1), neurotensin (NT), and polypeptide YY (PYY). However, the regional origin of these secretions after glucose stimulation is not well characterized, and it remains uncertain how their secretion is related to glucose absorption. We isolated and perfused either the upper (USI) or the lower (LSI) small intestine or the colon from rats and investigated concomitant glucose absorption and secretory profiles of GLP‐1, NT, and PYY. In the USI and LSI luminal glucose (20%, w/v) increased GLP‐1 and NT secretion five to eightfold compared to basal secretion. Compared to the USI, basal and stimulated GLP‐1 secretion from the colon was 8–10 times lower and no NT secretion was detected. Luminal glucose stimulated secretion of PYY four to fivefold from the LSI and from the USI and colon, but the responses in the USI and colon were 5‐ to 15‐fold lower than in the LSI. Glucose was absorbed to a comparable extent in the USI and LSI by mechanisms that partly depended on both SGLT1 and GLUT2 activity, whereas the absorption in the colon was 80–90% lower. The absorption rates were, however, similar when adjusted for segmental length. Glucose absorption rates and NT, PYY and in particular GLP‐1 secretion were strongly correlated (P < 0.05). Our results indicate that the rate of secretion of GLP‐1, NT, and PYY in response to glucose, regardless of the involved molecular machinery, is predominantly regulated by the rate of glucose absorption.

Enterocyte glycosylation is responsive to changes in extracellular conditions: implications for membrane functions

Epithelial cells in the lining of the intestines play critical roles in maintaining homeostasis while challenged by dynamic and sudden changes in luminal contents. Given the high density of glycosylation that encompasses their extracellular surface, environmental changes may lead to extensive reorganization of membrane-associated glycans. However, neither the molecular details nor the consequences of conditional glycan changes are well understood. Here we assessed the sensitivity of Caco-2 and HT-29 membrane N-glycosylation to variations in (i) dietary elements, (ii) microbial fermentation products and (iii) cell culture parameters relevant to intestinal epithelial cell growth and survival. Based on global LC-MS glycomic and statistical analyses, the resulting glycan expression changes were systematic, dependent upon the conditions of each controlled environment. Exposure to short chain fatty acids produced significant increases in fucosylation while further acidification promoted hypersialylation. Notably, among all conditions, increases of high mannose type glycans were identified as a major response when extracellular fructose, galactose and glutamine were independently elevated. To examine the functional consequences of this discrete shift in the displayed glycome, we applied a chemical inhibitor of the glycan processing mannosidase, globally intensifying high mannose expression. The data reveal that upregulation of high mannose glycosylation has detrimental effects on basic intestinal epithelium functions by altering permeability, host-microbe associations and membrane protein activities.

NanI Sialidase Can Support the Growth and Survival of Clostridium perfringens Strain F4969 in the Presence of Sialyated Host Macromolecules (Mucin) or Caco-2 Cells

Enterotoxin-producing Clostridium perfringens type A strains cause human gastrointestinal (GI) infections, including a very common food poisoning and 5 to 10% of all cases of antibiotic-associated diarrhea. This bacterium can utilize free sialic acid for growth, but most sialic acids in the GI tract are sequestered on macromolecules, such as the mucin proteins of mucus or glycoconjugates in host cells. However, many C. perfringens strains produce sialidases that might promote growth and survival by generating free sialic acid from those sialyated host macromolecules or by exposing underlying carbohydrates or proteins for digestion by other enzymes. The current study tested that possibility and found that the C. perfringens nonfoodborne human GI disease strain F4969 can use either a mucin preparation or Caco-2 cells, which are human enterocyte-like cells, to support its growth and survival. An isogenic nanI null mutant and complemented strain were used to show that this enhanced growth and survival using mucin or Caco-2 cells involved NanI, which is the major exosialidase of F4969 and many other C. perfringens strains. Experiments also suggested that, at least in part, this growth promotion involves utilization of NanI-generated sialic acid. In addition, a sialidase inhibitor named siastatin B reduced the growth and survival of F4969 growing with either the mucin preparation or Caco-2 cells. These findings suggest that, when produced, NanI may be a significant contributor to C. perfringens human GI infections by promoting the intestinal growth and survival of this bacterium. They also suggest the possibility that sialidase inhibitors might inhibit C. perfringens infections.

NanR Regulates nanI Sialidase Expression by Clostridium perfringens F4969, a Human Enteropathogenic Strain

Clostridium perfringens can produce up to three different sialidases, including NanI, its major exosialidase. The current study first showed that human intestinal strains of C. perfringens can grow by utilizing either glucose or sialic acids, such as N-acetylneuraminic acid (Neu5Ac), which are the end products of sialidase activity. For the human enteropathogenic strain F4969, it was then determined that culture supernatant sialidase activity and expression of exosialidase genes, particularly nanI, are influenced by the presence of Neu5Ac or glucose. Low Neu5Ac concentrations increased culture supernatant sialidase activity, largely by stimulating nanI transcription. In contrast, low glucose concentrations did not affect exosialidase activity or nanI transcription. However, either high Neu5Ac or high glucose concentrations repressed F4969 culture supernatant sialidase activity and nanI transcription levels. Furthermore, high glucose levels repressed F4969 culture sialidase activity and nanI expression even in the presence of low Neu5AC concentrations. To begin to evaluate the mechanistic basis for nanI expression, a nanR null mutant was used to demonstrate that NanR, a member of the RpiR family of regulatory proteins, decreases exosialidase activity and nanI transcription in the absence of sialic acid. The ability of C. perfringens to regulate its exosialidase activity, largely by controlling nanI expression, may affect intestinal pathogenesis by affecting the production of NanI, which may affect C. perfringens growth, adhesion, and toxin binding in vivo.

Structure-function analysis of human sucrase-isomaltase identifies key residues required for catalytic activity

Sucrase-isomaltase (SI) is an intestinal membrane-associated α-glucosidase that breaks down di- and oligosaccharides to absorbable monosaccharides. SI has two homologous functional subunits (sucrase and isomaltase) that both belong to the glycoside hydrolase family 31 (GH31) and differ in substrate specificity. All GH31 enzymes share a consensus sequence harboring an aspartic acid residue as a catalytic nucleophile. Moreover, crystallographic structural analysis of isomaltase predicts that another aspartic acid residue functions as a proton donor in hydrolysis. Here, we mutagenized the predicted proton donor residues and the nucleophilic catalyst residues in each SI subunit. We expressed these SI variants in COS-1 cells and analyzed their structural, transport, and functional characteristics. All of the mutants revealed expression levels and maturation rates comparable with those of the wild-type species and the corresponding nonmutated subunits were functionally active. Thereby we determined rate and substrate specificity for each single subunit without influence from the other subunit. This approach provides a model for functional analysis of the single subunits within a multidomain protein, achieved without the necessity to express the individual subunits separately. Of note, we also found that glucose product inhibition regulates the activities of both SI subunits. We experimentally confirmed the catalytic function of the predicted proton donor residues, and sequence analysis suggested that these residues are located in a consensus region in many GH31 family members. In summary, these findings reveal the kinetic features specific for each human SI subunit and demonstrate that the activities of these subunits are regulated via product inhibition.

Sweet Taste Receptor Activation in the Gut Is of Limited Importance for Glucose-Stimulated GLP-1 and GIP Secretion

Glucose stimulates the secretion of the incretin hormones: glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). It is debated whether the sweet taste receptor (STR) triggers this secretion. We investigated the role of STR activation for glucose-stimulated incretin secretion from an isolated perfused rat small intestine and whether selective STR activation by artificial sweeteners stimulates secretion. Intra-luminal administration of the STR agonists, acesulfame K (3.85% w/v), but not sucralose (1.25% w/v) and stevioside (2.5% w/v), stimulated GLP-1 secretion (acesulfame K: 31 ± 3 pmol/L vs. 21 ± 2 pmol/L, p < 0.05, n = 6). In contrast, intra-arterial administration of sucralose (10 mM) and stevioside (10 mM), but not acesulfame K, stimulated GLP-1 secretion (sucralose: 51 ± 6 pmol/L vs. 34 ± 4 pmol/L, p < 0.05; stevioside: 54 ± 6 pmol/L vs. 32 ± 2 pmol/L, p < 0.05, n = 6), while 0.1 mM and 1 mM sucralose did not affect the secretion. Luminal glucose (20% w/v) doubled GLP-1 and GIP secretion, but basolateral STR inhibition by gurmarin (2.5 µg/mL) or the inhibition of the transient receptor potential cation channel 5 (TRPM5) by triphenylphosphine oxide (TPPO) (100 µM) did not attenuate the responses. In conclusion, STR activation does not drive GIP/GLP-1 secretion itself, nor does it have a role for glucose-stimulated GLP-1 or GIP secretion.

RNA-Based Stable Isotope Probing Suggests Allobaculum spp. as Particularly Active Glucose Assimilators in a Complex Murine Microbiota Cultured In Vitro

RNA-based stable isotope probing (RNA-SIP) and metabolic profiling were used to detect actively glucose-consuming bacteria in a complex microbial community obtained from a murine model system. A faeces-derived microbiota was incubated under anaerobic conditions for 0, 2, and 4 h with 40 mM [U¹³C]glucose. Isopycnic density gradient ultracentrifugation and fractionation of isolated RNA into labeled and unlabeled fractions followed by 16S rRNA sequencing showed a quick adaptation of the bacterial community in response to the added sugar, which was dominated by unclassified Lachnospiraceae species. Inspection of distinct fractions of isotope-labeled RNA revealed Allobaculum spp. as particularly active glucose utilizers in the system, as the corresponding RNA showed significantly higher proportions among the labeled RNA. With time, the labeled sugar was used by a wider spectrum of faecal bacteria. Metabolic profiling indicated rapid fermentation of [U¹³C]glucose, with lactate, acetate, and propionate being the principal ¹³C-labeled fermentation products, and suggested that "cross-feeding" occurred in the system. RNA-SIP combined with metabolic profiling of ¹³C-labeled products allowed insights into the microbial assimilation of a general model substrate, demonstrating the appropriateness of this technology to study assimilation processes of nutritionally more relevant substrates, for example, prebiotic carbohydrates, in the gut microbiota of mice as a model system.

The Sweetener-Sensing Mechanisms of the Ghrelin Cell

Carbohydrate administration decreases plasma levels of the 'hunger hormone' ghrelin. The ghrelin cell is co-localized with the sweet taste receptor subunit, TAS1R3, and the gustatory G-protein, gustducin, both involved in the sensing of sweeteners by entero-endocrine cells. This study investigated the role of gustducin-mediated sweet taste receptor signaling on ghrelin secretion in a gastric ghrelinoma cell line, tissue segments and mice. The monosaccharide d-glucose and low-intensity sweetener oligofructose (OFS) decreased (p < 0.001) ghrelin secretion while the high-intensity sweetener sucralose increased (p < 0.001) ghrelin secretion in vitro. These effects were not mediated via the sweet taste receptor or glucose transporters (the sodium-dependent glucose cotransporter SGLT-1 and GLUT2). The effect of these compounds was mimicked ex vivo in gastric and jejunal segments from both wild type (WT) and α-gustducin knockout (α-gust-/-) mice. In vivo, the sensing of d-glucose was polarized since intragastric but not intravenous administration of d-glucose decreased (p < 0.05) ghrelin levels in an α-gustducin independent manner which involved inhibition of duodenal ghrelin release. In contrast, neither OFS nor sucralose affected ghrelin secretion in vivo. In conclusion, α-gustducin-mediated sweet taste receptor signaling does not play a functional role in the sensing of carbohydrates, or low- or high-intensity sweeteners by the ghrelin cell.

A computer model simulating human glucose absorption and metabolism in health and metabolic disease states

A computer model designed to simulate integrated glucose-dependent changes in splanchnic blood flow with small intestinal glucose absorption, hormonal and incretin circulation and hepatic and systemic metabolism in health and metabolic diseases e.g. non-alcoholic fatty liver disease, (NAFLD), non-alcoholic steatohepatitis, (NASH) and type 2 diabetes mellitus, (T2DM) demonstrates how when glucagon-like peptide-1, (GLP-1) is synchronously released into the splanchnic blood during intestinal glucose absorption, it stimulates superior mesenteric arterial (SMA) blood flow and by increasing passive intestinal glucose absorption, harmonizes absorption with its distribution and metabolism. GLP-1 also synergises insulin-dependent net hepatic glucose uptake (NHGU). When GLP-1 secretion is deficient post-prandial SMA blood flow is not increased and as NHGU is also reduced, hyperglycaemia follows. Portal venous glucose concentration is also raised, thereby retarding the passive component of intestinal glucose absorption.   Increased pre-hepatic sinusoidal resistance combined with portal hypertension leading to opening of intrahepatic portosystemic collateral vessels are NASH-related mechanical defects that alter the balance between splanchnic and systemic distributions of glucose, hormones and incretins.The model reveals the latent contribution of portosystemic shunting in development of metabolic disease. This diverts splanchnic blood content away from the hepatic sinuses to the systemic circulation, particularly during the glucose absorptive phase of digestion, resulting in inappropriate increases in insulin-dependent systemic glucose metabolism.  This hastens onset of hypoglycaemia and thence hyperglucagonaemia. The model reveals that low rates of GLP-1 secretion, frequently associated with T2DM and NASH, may be also be caused by splanchnic hypoglycaemia, rather than to intrinsic loss of incretin secretory capacity. These findings may have therapeutic implications on GLP-1 agonist or glucagon antagonist usage.

Time-resolved amino acid uptake of Clostridium difficile 630Δerm and concomitant fermentation product and toxin formation

Background

Clostridium difficile is one of the major nosocomial threats causing severe gastrointestinal infections. Compared to the well documented clinical symptoms, little is known about the processes in the bacterial cell like the regulation and activity of metabolic pathways. In this study, we present time-resolved and global data of extracellular substrates and products. In a second part, we focus on the correlation of fermentation products and substrate uptake with toxin production.

Results

Formation of different fermentation products during growth in a comparison between the two different media in a global approach was studied using non-targeted gas chromatography–mass spectrometry (GC-MS) based analysis. During cultivation in a casamino acids medium and minimal medium, the clinical isolate C. difficile 630Δerm showed major differences in amino acid utilization: In casamino acids medium, C. difficile preferred proline, leucine and cysteine as carbon and energy sources while glutamate and lysine were not or hardly used. In contrast, proline and leucine were consumed at a significantly later stage in minimal medium. Due to the more complex substrate mixture more fermentation products were detectable in the casamino acids medium, accompanied by major changes in the ratios between oxidative and reductive Stickland products. Different glucose consumption dynamics were observed in presence of either casamino acids or the minimal set of amino acids, accompanied by major changes in butanoate formation. This was associated with a variation in both the toxin yield and a change in the ratio of toxin A to toxin B.

Conclusions

Since in all media compositions, more than one substrate was available as a suitable carbon source, availability of different carbon sources and their metabolic fate appears to be the key factor for toxin formation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0614-2) contains supplementary material, which is available to authorized users.

Potential mechanism of enhanced postprandial glucagon-like peptide-1 release following treatment with a diacylglycerol acyltransferase 1 inhibitor

Studies have demonstrated that blockade of diacylglycerol acyltransferase 1 (DGAT1) leads to prolonged release of glucagon‐like peptide 1 (GLP‐1) after meal challenge. The current study was undertaken to investigate the mechanism of action underlying the elevated levels of GLP‐1 release following pharmacological inhibition of DGAT1. We utilized a potent, specific DGAT1 inhibitor, compound A, to investigate the changes in intestinal lipid profile in a mouse model after oral administration of the compound and challenge with tracer containing fatty meal. [¹³C₁₈]‐oleic acid and LC‐MS were employed to trace the fate of dietary fatty acids provided as part of a meal challenge in lean mice. Lipid profiles in plasma, proximal to distal segments of intestine, and feces were evaluated at various times following the meal challenge to study the kinetics of fatty acid absorption, synthesis into complex lipids, and excretion. Pharmacological inhibition of DGAT1 led to reduction of postprandial total and newly synthesized triglyceride (TG) excursion and significant increases in TG and FFA levels in the distal portion of intestine enriched with enteroendocrine L cells. Enhanced levels of FFA and cholesteryl ester were observed via fecal fat profiling. DGAT1 inhibition leads to enhancement of carbon flow to the synthesis of phosphatidylcholine within the intestine. DGAT1 inhibition markedly increases levels of TG and FFA in the distal intestine, which could be the predominant contributor to the prolonged and enhanced postprandial GLP‐1 release. Inactivation of DGAT1 could provide potential benefit in the treatment of dysmetabolic diseases.