Intestinal sensing of nutrients

Sequential appetite suppression by oral and visceral feedback to the brainstem

The termination of a meal is controlled by dedicated neural circuits in the caudal brainstem. A key challenge is to understand how these circuits transform the sensory signals generated during feeding into dynamic control of behaviour. The caudal nucleus of the solitary tract (cNTS) is the first site in the brain where many meal-related signals are sensed and integrated1-4, but how the cNTS processes ingestive feedback during behaviour is unknown. Here we describe how prolactin-releasing hormone (PRLH) and GCG neurons, two principal cNTS cell types that promote non-aversive satiety, are regulated during ingestion. PRLH neurons showed sustained activation by visceral feedback when nutrients were infused into the stomach, but these sustained responses were substantially reduced during oral consumption. Instead, PRLH neurons shifted to a phasic activity pattern that was time-locked to ingestion and linked to the taste of food. Optogenetic manipulations revealed that PRLH neurons control the duration of seconds-timescale feeding bursts, revealing a mechanism by which orosensory signals feed back to restrain the pace of ingestion. By contrast, GCG neurons were activated by mechanical feedback from the gut, tracked the amount of food consumed and promoted satiety that lasted for tens of minutes. These findings reveal that sequential negative feedback signals from the mouth and gut engage distinct circuits in the caudal brainstem, which in turn control elements of feeding behaviour operating on short and long timescales.

Protein- and Calcium-Mediated GLP-1 Secretion: A Narrative Review

Glucagon-like peptide 1 (GLP-1) is an incretin hormone produced in the intestine that is secreted in response to nutrient exposure. GLP-1 potentiates glucose-dependent insulin secretion from the pancreatic β cells and promotes satiety. These important actions on glucose metabolism and appetite have led to widespread interest in GLP-1 receptor agonism. Typically, this involves pharmacological GLP-1 mimetics or targeted inhibition of dipeptidyl peptidase-IV, the enzyme responsible for GLP-1 degradation. However, nutritional strategies provide a widely available, cost-effective alternative to pharmacological strategies for enhancing hormone release. Recent advances in nutritional research have implicated the combined ingestion of protein and calcium with enhanced endogenous GLP-1 release, which is likely due to activation of receptors with high affinity and/or sensitivity for amino acids and calcium. Specifically targeting these receptors could enhance gut hormone secretion, thus providing a new therapeutic option. This narrative review provides an overview of the latest research on protein- and calcium-mediated GLP-1 release with an emphasis on human data, and a perspective on potential mechanisms that link potent GLP-1 release to the co-ingestion of protein and calcium. In light of these recent findings, potential future research directions are also presented.

The role of diet in the pathophysiology and management of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic gastrointestinal (GI) disorder that reportedly affects 5% to 20% of the world population. The etiology of IBS is not completely understood, but diet appears to play an important role in its pathophysiology. Asian diets differ considerably from those in Western countries, which might explain differences in the prevalence, sex, and clinical presentation seen between patients with IBS in Asian and Western countries. Dietary regimes such as a low-fermentable oligo-, di-, monosaccharides, and polyols (FODMAP) diet and the modified National Institute for Health and Care Excellence (NICE) diet improve both symptoms and the quality of life in a considerable proportion of IBS patients. It has been speculated that diet is a prebiotic for the intestinal microbiota and favors the growth of certain bacteria. These bacteria ferment the dietary components, and the products of fermentation act upon intestinal stem cells to influence their differentiation into enteroendocrine cells. The resulting low density of enteroendocrine cells accompanied by low levels of certain hormones gives rise to intestinal dysmotility, visceral hypersensitivity, and abnormal secretion. This hypothesis is supported by the finding that changing to a low-FODMAP diet restores the density of GI cells to the levels in healthy subjects. These changes in gut endocrine cells caused by low-FODMAP diet are also accompanied by improvements in symptoms and the quality of life.

GLP-1 Analogues as a Complementary Therapy in Patients after Metabolic Surgery: a Systematic Review and Qualitative Synthesis

The evidence is strong that bariatric surgery is superior to medical treatment in terms of weight loss and comorbidities in patients with severe obesity. However, a considerable part of patients presents with unsatisfactory response in the long term. It remains unclear whether postoperative administration of glucagon-like peptide-1 analogues can promote additional benefits. Therefore, a systematic review of the current literature on the management of postoperative GLP-1 analogue usage after metabolic surgery was performed. From 4663 identified articles, 6 met the inclusion criteria, but only one was a randomized controlled trial. The papers reviewed revealed that GLP-1 analogues may have beneficial effects on additional weight loss and T2D remission postoperatively. Thus, the use of GLP-1 analogues in addition to surgery promises good results concerning weight loss and improvements of comorbidities and can be used in patients with unsatisfactory results after bariatric surgery.

Possible role of intestinal stem cells in the pathophysiology of irritable bowel syndrome

The pathophysiology of irritable bowel syndrome (IBS) is not completely understood. However, several factors are known to play a role in pathophysiology of IBS such as genetics, diet, gut microbiota, gut endocrine cells, stress and low-grade inflammation. Understanding the pathophysiology of IBS may open the way for new treatment approaches. Low density of intestinal stem cells and low differentiation toward enteroendocrine cells has been reported recently in patients with IBS. These abnormalities are believed to be the cause of the low density of enteroendocrine cells seen in patients with IBS. Enteroendocrine cells regulate gastrointestinal motility, secretion, absorption and visceral sensitivity. Gastrointestinal dysmotility, abnormal absorption/secretion and visceral hypersensitivity are all seen in patients with IBS and haven been attributed to the low density the intestinal enteroendocrine cells in these patients. The present review conducted a literature search in Medline (PubMed) covering the last ten years until November 2019, where articles in English were included. Articles about the intestinal stem cells and their possible role in the pathophysiology of IBS are discussed in the present review. The present review discusses the assumption that intestinal stem cells play a central role in the pathophysiology of IBS and that the other factors known to contribute to the pathophysiology of IBS such as genetics, diet gut microbiota, stress, and low-grade inflammation exert their effects through affecting the intestinal stem cells. It reports further the data that support this assumption on genetics, diet, gut microbiota, stress with depletion of glutamine, and inflammation.

Diet in Irritable Bowel Syndrome (IBS): Interaction with Gut Microbiota and Gut Hormones

Diet plays an important role not only in the pathophysiology of irritable bowel syndrome (IBS), but also as a tool that improves symptoms and quality of life. The effects of diet seem to be a result of an interaction with the gut bacteria and the gut endocrine cells. The density of gut endocrine cells is low in IBS patients, and it is believed that this abnormality is the direct cause of the symptoms seen in IBS patients. The low density of gut endocrine cells is probably caused by a low number of stem cells and low differentiation progeny toward endocrine cells. A low fermentable oligo-, di-, monosaccharide, and polyol (FODMAP) diet and fecal microbiota transplantation (FMT) restore the gut endocrine cells to the level of healthy subjects. It has been suggested that our diet acts as a prebiotic that favors the growth of a certain types of bacteria. Diet also acts as a substrate for gut bacteria fermentation, which results in several by-products. These by-products might act on the stem cells in such a way that the gut stem cells decrease, and consequently, endocrine cell numbers decrease. Changing to a low-FODMAP diet or changing the gut bacteria through FMT improves IBS symptoms and restores the density of endocrine cells.

Food Intake Recruits Orosensory and Post-ingestive Dopaminergic Circuits to Affect Eating Desire in Humans

Pleasant taste and nutritional value guide food selection behavior. Here, orosensory features of food may be secondary to its nutritional value in underlying reinforcement, but it is unclear how the brain encodes the reward value of food. Orosensory and peripheral physiological signals may act together on dopaminergic circuits to drive food intake. We combined fMRI and a novel [11C]raclopride PET method to assess systems-level activation and dopamine release in response to palatable food intake in humans. We identified immediate orosensory and delayed post-ingestive dopamine release. Both responses recruit segregated brain regions: specialized integrative pathways and higher cognitive centers. Furthermore, we identified brain areas where dopamine release reflected the subjective desire to eat. Immediate dopamine release in these wanting-related regions was inversely correlated with, and presumably inhibited, post-ingestive release in the dorsal striatum. Our results highlight the role of brain and periphery in interacting to reinforce food intake in humans.

CELF1/p53 axis: a sustained antiproliferative signal leading to villus atrophy under total parenteral nutrition

Intestinal villus atrophy is a major complication of total parenteral nutrition (TPN). Our previous study revealed that TPN-induced villus atrophy is accompanied by elevated expression of CUGBP, Elav-like family member 1 (CELF1); however, its mechanism of action has not been fully understood. Herein, we report a pivotal role of CELF1/p53 axis, which induces a sustained antiproliferative signal, leading to suppressed proliferation of intestinal epithelial cells (IECs). By using a rat model of TPN, we found synchronous upregulation of CELF1 and p53 in jejunum mucosa, accompanied by a 51% decrease in crypt cell proliferation rate. By using HCT-116 cells as an IEC model in vitro, we found that the expression of CELF1 altered dynamically in parallel to proliferation rate, suggesting a self-adaptive expression pattern in IECs in vitro. Furthermore, ectopic overexpression of CELF1 elicited a significant antiproliferative effect in HCT-116, Caco-2, and IEC-6 cells, whereas knockdown of CELF1 elicited a significant proproliferative effect. Moreover, cell-cycle assay revealed that ectopic overexpression of CELF1 induced sustained G2 arrest and G1 arrest in HCT-116 and IEC-6 cells, respectively, which could be abolished by p53 silencing. Mechanistically, polysomal profiling and nascent protein analysis revealed that regulation of p53 by CELF1 was mediated through accelerating its protein translation in polysomes. Taken together, our findings revealed a sustained suppression of IEC proliferation evoked by CELF1/p53 axis, which may be a potential therapeutic target for the treatment of TPN-induced villus atrophy.-Yan, J.-K., Zhang, T., Dai, L.-N., Gu, B.-L., Zhu, J., Yan, W.-H., Cai, W., Wang, Y. CELF1/p53 axis: a sustained antiproliferative signal leading to villus atrophy under total parenteral nutrition.

Sensing of L-Arginine by Gut-Expressed Calcium Sensing Receptor Stimulates Gut Satiety Hormones Cholecystokinin and Glucose-Dependent Insulinotropic Peptide Secretion in Pig Model

Nutrients regulate the secretion of gut satiety hormones, which is related to the modulation of food intake and blood glucose levels. Calcium-sensing receptor (CaSR) is involved in regulating gut hormone secretion in response to l-amino acids and multivalent cations. Rodents are often used to investigate the effect of nutrients on these hormonal release. However, results obtained using rodent models are difficult to be applied in humans, we used pigs as a model in this study because their physiology is similar to that of humans. In this study, we investigated whether l-Arginine (l-Arg) could induce gut hormones cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) secretion in the porcine duodenum and if so, whether CaSR mediated l-Arg-regulated gut satiety hormone secretion. Our data showed that treatment with 20 and 50 mM l-Arg induced CCK and GIP secretion compared with 0 mM l-Arg. However, treatment with d-Arg (an inactive isomer) failed to elicit this response. The potency of l-Arg to induce CCK and GIP secretion was enhanced in the presence of extracellular Ca²⁺ and CaSR agonist cinacalcet. However, the effect of Arg on CCK and GIP secretion was attenuated by blocking CaSR and its downstream signaling molecules adenylate cyclase (AC) and phospholipase C (PLC). Taken all together, pig duodenum provides an appropriate model to explore the effects of l-Arg on the secretion of the satiety-related gut hormones CCK and GIP and the role of CaSR in this effect. Further investigations are needed to verify the effect of l-Arg on food intake and blood glucose in human study. PRACTICAL APPLICATION: l-Arginine is able to modulate cholecystokinin and glucose-dependent insulinotropic peptide secretion through the CaSR in pig model, which has a potential role in regulating food intake and blood glucose levels.

Role of Short Chain Fatty Acid Receptors in Intestinal Physiology and Pathophysiology

Nutrient sensing is a mechanism for organisms to sense their environment. In larger animals, including humans, the intestinal tract is a major site of nutrient sensing for the body, not surprisingly, as this is the central location where nutrients are absorbed. In the gut, bacterial fermentation results in generation of short chain fatty acids (SCFAs), a class of nutrients, which are sensed by specific membrane bound receptors, FFA2, FFA3, GPR109a, and Olfr78. These receptors are expressed uniquely throughout the gut and signal through distinct mechanisms. To date, the emerging data suggests a role of these receptors in normal and pathological conditions. The overall function of these receptors is to regulate aspects of intestinal motility, hormone secretion, maintenance of the epithelial barrier, and immune cell function. Besides in intestinal health, a prominent role of these receptors has emerged in modulation of inflammatory and immune responses during pathological conditions. Moreover, these receptors are being revealed to interact with the gut microbiota. This review article updates the current body of knowledge on SCFA sensing receptors in the gut and their roles in intestinal health and disease as well as in whole body energy homeostasis. © 2017 American Physiological Society. Compr Physiol 8:1091-1115, 2018.

Microbiota promote secretory cell determination in the intestinal epithelium by modulating host Notch signaling

Resident microbes promote many aspects of host development, although the mechanisms by which microbiota influence host tissues remain unclear. We showed previously that the microbiota is required for allocation of appropriate numbers of secretory cells in the zebrafish intestinal epithelium. Because Notch signaling is crucial for secretory fate determination, we conducted epistasis experiments to establish whether the microbiota modulates host Notch signaling. We also investigated whether innate immune signaling transduces microbiota cues via the Myd88 adaptor protein. We provide the first evidence that microbiota-induced, Myd88-dependent signaling inhibits host Notch signaling in the intestinal epithelium, thereby promoting secretory cell fate determination. These results connect microbiota activity via innate immune signaling to the Notch pathway, which also plays crucial roles in intestinal homeostasis throughout life and when impaired can result in chronic inflammation and cancer.

Dynamics of Gut-Brain Communication Underlying Hunger

Communication between the gut and brain is critical for homeostasis, but how this communication is represented in the dynamics of feeding circuits is unknown. Here we describe nutritional regulation of key neurons that control hunger in vivo. We show that intragastric nutrient infusion rapidly and durably inhibits hunger-promoting AgRP neurons in awake, behaving mice. This inhibition is proportional to the number of calories infused but surprisingly independent of macronutrient identity or nutritional state. We show that three gastrointestinal signals-serotonin, CCK, and PYY-are necessary or sufficient for these effects. In contrast, the hormone leptin has no acute effect on dynamics of these circuits or their sensory regulation but instead induces a slow modulation that develops over hours and is required for inhibition of feeding. These findings reveal how layers of visceral signals operating on distinct timescales converge on hypothalamic feeding circuits to generate a central representation of energy balance.

Effect of diet and individual dietary guidance on gastrointestinal endocrine cells in patients with irritable bowel syndrome (Review)

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal (GI) disorder that is characterized by a combination of abdominal pain or discomfort, bloating and alterations in bowel movements. This review presents recent developments concerning the roles of diet and GI endocrine cells in the pathophysiology of IBS and of individual dietary guidance in the management of IBS. Patients with IBS typically report that food aggravates their IBS symptoms. The interactions between specific types of foodstuffs rich in fermentable oligosaccharides, disaccharides, monosaccharides and polyols (FODMAPs) and GI endocrine cells induce changes in cell densities. Providing individual dietary guidance about a low FODMAP intake, high soluble-fiber intake, and changing the proportions of protein, fat and carbohydrates helps to reduce the symptoms experienced by patients with IBS and to improve their quality of life. These improvements are due to restoring the densities of the GI endocrine cells back to normal. The reported observations emphasize the role of GI endocrine cells in the pathophysiology of IBS and support the provision of dietary guidance as a first-line treatment for managing IBS.

Gastrointestinal neuroendocrine peptides/amines in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic recurrent condition whose etiology is unknown, and it includes ulcerative colitis, Crohn’s disease, and microscopic colitis. These three diseases differ in clinical manifestations, courses, and prognoses. IBD reduces the patients’ quality of life and is an economic burden to both the patients and society. Interactions between the gastrointestinal (GI) neuroendocrine peptides/amines (NEPA) and the immune system are believed to play an important role in the pathophysiology of IBD. Moreover, the interaction between GI NEPA and intestinal microbiota appears to play also a pivotal role in the pathophysiology of IBD. This review summarizes the available data on GI NEPA in IBD, and speculates on their possible role in the pathophysiology and the potential use of this information when developing treatments. GI NEPA serotonin, the neuropeptide Y family, and substance P are proinflammatory, while the chromogranin/secretogranin family, vasoactive intestinal peptide, somatostatin, and ghrelin are anti-inflammatory. Several innate and adaptive immune cells express these NEPA and/or have receptors to them. The GI NEPA are affected in patients with IBD and in animal models of human IBD. The GI NEPA are potentially useful for the diagnosis and follow-up of the activity of IBD, and are candidate targets for treatments of this disease.

Effect of dietary fiber and diet particle size on nutrient digestibility and gastrointestinal secretory function in growing pigs

Reduction of diet particle size (PS) increases feed efficiency due to an increase in the apparent total tract (ATTD) of GE. However, other effects of PS on the gut secretory function are not known. Therefore, the objective of this experiment was to measure the effect of diet composition (DC) and PS on nutrient digestibility, gastrointestinal hormones, total bile acids (TBA), total cholesterol and glucose concentrations in plasma of finishing pigs ( = 8/diet). Pigs were fed finely (374 ± 29 µm) or coarsely (631 ± 35 µm) ground corn-soybean meal (CSB), CSB + 35% corn dried distillers' grains with solubles (DDGS), and CSB with 21% soybean hulls (SBH) diets for 49 d. Diet composition, nutrient digestibility, along with fasting plasma concentrations of gastrin, insulin, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic peptide (GIP), TBA, cholesterol, and glucose were measured. Fine ground diets had greater ( < 0.05) ATTD of GE as well as greater ( < 0.05) ME than coarse ground diets independent on the DC. Fine ground diets also had greater ( < 0.05) ATTD of DM, N, ether extract, and NDF, independent of DC. A decrease in PS also caused an increase ( < 0.05) in ATTD of N, K, and S, but it did not affect ATTD of Ca, P, or Na. The DC and PS affected plasma gastrin, insulin and TBA but not GIP, GLP-1, glucose, and cholesterol. Gastrin concentration was greater ( < 0.05) in pigs fed coarse DDGS compared with feeding coarse CSB and SBH diets. Insulin concentration of pigs fed CSB was greater ( < 0.01) in pigs fed fine compared with coarse DDGS, and was greater ( < 0.05) in coarse compared with fine SBH diets. Pigs fed DDGS had greater ( < 0.05) TBA than those fed SBH and fine CSB diets. Gastrin, insulin, TBA and cholesterol tended ( < 0.10), or correlated ( < 0.05) with P, K and Fe intake. Insulin, TBA, and cholesterol were correlated ( < 0.05) with Na and S intake. In conclusion, a decrease in diet PS increases the ATTD of nutrients independently of DC, while mineral intake affects gastrointestinal secretion of hormones with potential metabolic impacts. Plasma insulin and glucose concentrations were correlated with DM intake, and glucose was associated with lipid and protein intake. Diet energy, nutrient digestibility, and plasma gastrin, insulin and TBA concentrations were affected by DC and PS.

Dietary fiber in irritable bowel syndrome (Review)

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder. It is widely believed that IBS is caused by a deficient intake of dietary fiber, and most physicians recommend that patients with IBS increase their intake of dietary fiber in order to relieve their symptoms. However, different types of dietary fiber exhibit marked differences in physical and chemical properties, and the associated health benefits are specific for each fiber type. Short-chain soluble and highly fermentable dietary fiber, such as oligosaccharides results in rapid gas production that can cause abdominal pain/discomfort, abdominal bloating/distension and flatulence in patients with IBS. By contrast, long-chain, intermediate viscous, soluble and moderately fermentable dietary fiber, such as psyllium results in a low gas production and the absence of the symptoms related to excessive gas production. The effects of type of fiber have been documented in the management of IBS, and it is known to improve the overall symptoms in patients with IBS. Dietary fiber acts on the gastrointestinal tract through several mechanisms, including increased fecal mass with mechanical stimulation/irritation of the colonic mucosa with increasing secretion and peristalsis, and the actions of fermentation byproducts, particularly short-chain fatty acids, on the intestinal microbiota, immune system and the neuroendocrine system of the gastrointestinal tract. Fiber supplementation, particularly psyllium, is both safe and effective in improving IBS symptoms globally. Dietary fiber also has other health benefits, such as lowering blood cholesterol levels, improving glycemic control and body weight management.

Changes in duodenal enteroendocrine cells in patients with irritable bowel syndrome following dietary guidance

The densities of enteroendocrine cells are abnormal in patients with irritable bowel syndrome (IBS); however, they tend to change toward normal levels in stomach, ileum, and colon following dietary guidance. The aim was to identify the types of duodenal enteroendocrine cells affected after receiving dietary guidance in the same group of patients with IBS. Fourteen patients with IBS and 14 control subjects were included. The patients received three sessions of dietary guidance. Both groups underwent gastroscopies at baseline, and again for the patients after 3–9 months (median, four months) from receiving dietary guidance. Tissue biopsies were collected from the descending part of the duodenum and were immunostained for all the types of enteroendocrine cells and were then quantified by using computerized image analysis. Using the Kruskal–Wallis non-parametric test with Dunn’s test as a post-test, the results showed a significant difference in the secretin cell densities between control subjects and patients with IBS prior to and following dietary guidance (P = 0.0001 and 0.011, respectively). The corresponding P values for cholecystokinin (CCK) cell densities were 0.03 and 0.42, respectively; gastric inhibitory peptide (GIP) cell densities were 0.06 and 0.43, respectively; serotonin cell densities were <0.0001 and 0.002, respectively; and for somatostatin cell densities were <0.0001 and 0.052, respectively. The Paired t-test showed a significant difference only in the serotonin (P = 0.03) and somatostatin (P < 0.0001) cell densities between IBS patients prior to and following dietary guidance. The changes in the cell densities of secretin, CCK, and GIP were not significant between IBS patients prior to and following dietary guidance. In conclusion, the densities of several duodenal enteroendocrine cells in IBS patients changed toward the values measured in control subjects following dietary guidance. The changes in serotonin and somatostatin cell densities may have contributed to the improvements in IBS symptoms, particularly pain and diarrhea.

The possible role of gastrointestinal endocrine cells in the pathophysiology of irritable bowel syndrome

The etiology of irritable bowel syndrome (IBS) is unknown, but several factors appear to play a role in its pathophysiology, including abnormalities of the gastrointestinal endocrine cells. The present review illuminates the possible role of gastrointestinal hormones in the pathophysiology of IBS and the possibility of utilizing the current knowledge in treating the disease. Areas covered: Research into the intestinal endocrine cells and their possible role in the pathophysiology of IBS is discussed. Furthermore, the mechanisms underlying the abnormalities in the gastrointestinal endocrine cells in IBS patients are revealed. Expert commentary: The abnormalities observed in the gastrointestinal endocrine cells in IBS patients explains their visceral hypersensitivity, gastrointestinal dysmotility, and abnormal intestinal secretion, as well as the interchangeability of symptoms over time. Clarifying the role of the intestinal stem cells in the pathophysiology of IBS may lead to new treatment methods for IBS.

Interaction between diet and gastrointestinal endocrine cells

The gastrointestinal endocrine cells are essential for life. They regulate the gastrointestinal motility, secretion, visceral sensitivity, absorption, local immune defense, cell proliferation and appetite. These cells act as sensory cells with specialized microvilli that project into the lumen that sense the gut contents (mostly nutrients and/or bacteria byproducts), and respond to luminal stimuli by releasing hormones into the lamina propria. These released hormones exert their actions by entering the circulating blood and reaching distant targets (endocrine mode), nearby structures (paracrine mode) or via afferent and efferent synaptic transmission. The mature intestinal endocrine cells are capable of expressing several hormones. A change in diet not only affects the release of gastrointestinal hormones, but also alters the densities of the gut endocrine cells. The interaction between ingested foodstuffs and the gastrointestinal endocrine cells can be utilized for the clinical management of gastrointestinal and metabolic diseases, such as irritable bowel syndrome, obesity and diabetes.

Cloning, Phylogenetic Analysis, and Distribution of Free Fatty Acid Receptor GPR120 Expression along the Gastrointestinal Tract of Housing versus Grazing Kid Goats

G-protein-coupled receptor 120 (GPR120) is reported as a long-chain fatty acid (LCFA) receptor that elicits free fatty acid (FFA) regulation on metabolism homeostasis. The study aimed to clone the gpr120 gene of goats (g-GPR120) and subsequently investigate phylogenetic analysis and tissue distribution throughout the digestive tracts of kid goats, as well as the effect of housing versus grazing (H vs G) feeding systems on GPR120 expression. Partial coding sequence (CDS) of g-GPR120 was cloned and submitted to NCBI (accession no. KU161270 ). Phylogenetic analysis revealed that g-GPR120 shared higher homology in both mRNA and amino acid sequences for ruminants than nonruminants. Immunochemistry, real-time PCR, and Western blot analysis showed that g-GPR120 was expressed throughout the digestive tracts of goats. The expression of g-GPR120 was affected by feeding system and age, with greater expression of g-GPR120 in the G group. It was concluded that the g-GPR120-mediated LCFA chemosensing mechanism is widely present in the tongue and gastrointestinal tract of goats and that its expression can be affected by feeding system and age.

Upper gastrointestinal sensitivity to meal-related signals in adult humans - relevance to appetite regulation and gut symptoms in health, obesity and functional dyspepsia

Both the stomach and small intestine play important roles in sensing the arrival of a meal, and its physico-chemical characteristics, in the gastrointestinal lumen. The presence of a meal in the stomach provides a distension stimulus, and, as the meal empties into the small intestine, nutrients interact with small intestinal receptors, initiating the release of gut hormones, associated with feedback regulation of gastrointestinal functions, including gut motility, and signaling to the central nervous system, modulating eating behaviours, including energy intake. Lipid appears to have particularly potent effects, also in close interaction with, and modulating the effects of, gastric distension, and involving the action of gut hormones, particularly cholecystokinin (CCK). These findings have not only provided important, and novel, insights into how gastrointestinal signals interact to modulate subjective appetite perceptions, including fullness, but also laid the foundation for an increasing appreciation of the role of altered gastrointestinal sensitivities, e.g. as a consequence of excess dietary intake in obesity, or underlying the induction of gastrointestinal symptoms in functional dyspepsia (a condition characterized by symptoms, including bloating, nausea and early fullness, amongst others, after meals, particularly those high in fat, in the absence of any structural or functional abnormalities in the gastrointestinal tract). This paper will review the effects of dietary nutrients, particularly lipid, on gastrointestinal function, and associated effects on appetite perceptions and energy intake, effects of interactions of gastrointestinal stimuli, as well as the role of altered gastrointestinal sensitivities (exaggerated, or reduced) in eating-related disorders, particularly obesity and functional dyspepsia.

Changes in small intestinal chromogranin A-immunoreactive cell densities in patients with irritable bowel syndrome after receiving dietary guidance

Chromogranin A (CgA) is a common marker for enteroendocrine cells in the gut, and CgA-immunoreactive cell densities are abnormal in patients with irritable bowel syndrome (IBS). The majority of patients with IBS report that their symptoms develop after consuming certain foodstuffs. In the present study, we investigated the effects of dietary guidance on the total enteroendocrine cell densities in the small intestine, as detected by CgA. A total of 14 patients with IBS underwent a gastroscopy with duodenal biopsies and 11 of them also underwent a colonoscopy, with biopsy samples obtained from the ileum. Fourteen control subjects were also included. Each patient received 3 sessions of dietary guidance. Gastroscopies and colonoscopies were performed on both the controls and patients with IBS (at baseline and at 3–9 months after receiving guidance). Biopsy samples obtained from the duodenum and ileum were immunostained for CgA using the avidin-biotin complex (ABC) method and were quantified using computerized image analysis. The density of CgA-immunoreactive cells in the duodenum (mean ± SEM values) in the control subjects was 235.9±31.9 cells/mm²; in the patients with IBS, the density was 36.9±9.8 and 103.7±16.9 cells/mm² before and after they received dietary guidance, respectively (P=0.007). The density of CgA-immunoreactive cells in the ileum in the control subjects was 47.4±8.3 cells/mm²; in the patients with IBS, the density was 48.4±8.1 and 17.9±4.4 cells/mm², before and after they received dietary guidance, respectively (P=0.0006). These data indicate that changes in CgA-immunoreactive cell densities in patients with IBS after receiving dietary guidance may reflect a change in the densities of the small intestinal enteroendocrine cells, which may contribute to an improvement in the IBS symptoms.

Lipid derivatives activate GPR119 and trigger GLP-1 secretion in primary murine L-cells

AIMS/HYPOTHESIS

Glucagon-like peptide-1 (GLP-1) is an incretin hormone derived from proglucagon, which is released from intestinal L-cells and increases insulin secretion in a glucose dependent manner. GPR119 is a lipid derivative receptor present in L-cells, believed to play a role in the detection of dietary fat. This study aimed to characterize the responses of primary murine L-cells to GPR119 agonism and assess the importance of GPR119 for the detection of ingested lipid.

METHODS

GLP-1 secretion was measured from murine primary cell cultures stimulated with a panel of GPR119 ligands. Plasma GLP-1 levels were measured in mice lacking GPR119 in proglucagon-expressing cells and controls after lipid gavage. Intracellular cAMP responses to GPR119 agonists were measured in single primary L-cells using transgenic mice expressing a cAMP FRET sensor driven by the proglucagon promoter.

RESULTS

L-cell specific knockout of GPR119 dramatically decreased plasma GLP-1 levels after a lipid gavage. GPR119 ligands triggered GLP-1 secretion in a GPR119 dependent manner in primary epithelial cultures from the colon, but were less effective in the upper small intestine. GPR119 agonists elevated cAMP in ∼70% of colonic L-cells and 50% of small intestinal L-cells.

CONCLUSIONS/INTERPRETATION

GPR119 ligands strongly enhanced GLP-1 release from colonic cultures, reflecting the high proportion of colonic L-cells that exhibited cAMP responses to GPR119 agonists. Less GPR119-dependence could be demonstrated in the upper small intestine. In vivo, GPR119 in L-cells plays a key role in oral lipid-triggered GLP-1 secretion.

Regulation of appetite, satiation, and body weight by enteroendocrine cells. Part 1: characteristics of enteroendocrine cells and their capability of weight regulation

The gastrointestinal tract is the gateway for food in our body. Food ingestion and the ensuing digestive processes depend on the composition and amount of ingested nutrients. This complex process of nutrient digestion and absorption is effectively regulated by the enteroendocrine system. Enteroendocrine cells (EECs) reside scattered throughout the intestinal epithelium. They express nutrient receptors that face the lumen and secrete peptide hormones in response to food. Besides regulating digestion, gastrointestinal endocrine cells are involved in the regulation of appetite and satiety. The first part of this review describes the anatomical and biological characteristics of EECs and discusses the capability of their hormones to influence appetite, satiety, and body weight. In the second part, we then discuss the therapeutic potential of EECs in the treatment of obesity.

Dietary guidance normalizes large intestinal endocrine cell densities in patients with irritable bowel syndrome

Background/Objectives:

To determine the large intestinal endocrine cell types affected following dietary guidance in patients with irritable bowel syndrome (IBS).

Subjects/Methods:

The study included 13 IBS patients and 13 control subjects. The patients received three sessions of individualized dietary guidance. Both the control subjects and the patients were scheduled for colonoscopies at baseline and again for the patients at 3–9 months after dietary guidance. Biopsy samples were taken from the colon and rectum and were immunostained for all types of large intestinal endocrine cells. The endocrine cells were quantified using computerized image analysis.

Results:

The daily total consumption (mean±s.e.m. values) of fruits and vegetables rich in FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) decreased significantly from 16.2±5.3 g before receiving dietary guidance to 9.2±3.2 g after receiving dietary guidance (P=0.02). In the total colon, the densities of serotonin cells were 46.8±8.9, 10.5±2.1 and 22.6±3.2 cells/mm² in control subjects and in IBS patients before and after receiving dietary guidance, respectively (P=0.007); the corresponding densities of peptide YY cells were 11.6±1.8, 10.8±1.7 and 16.8±2.1 cells/mm², respectively (P=0.06). The cell densities for both serotonin and peptide YY did not change significantly in the rectum. The densities of somatostatin cells in the rectum were 13.5±3.0, 13.2±3.0, and 22.3±3.2 cells/mm² for control subjects and for IBS patients before and after receiving dietary guidance, respectively (P=0.01).

Conclusions:

The densities of the large intestinal endocrine cells tend to normalize following dietary guidance that may have contributed to the improvement of the patients with IBS symptoms.

Transcriptional and Functional Characterization of the G Protein-Coupled Receptor Repertoire of Gastric Somatostatin Cells

In the stomach, somatostatin (SST) acts as a general paracrine negative regulator of exocrine secretion of gastric acid and pepsinogen and endocrine secretion of gastrin, ghrelin, and histamine. Using reporter mice expressing red fluorescent protein (RFP) under control of the SST promotor, we have characterized the G protein-coupled receptors expressed in gastric Sst-RFP-positive cells and probed their effects on SST secretion in primary cell cultures. Surprisingly, besides SST, amylin and PYY were also highly enriched in the SST cells. Several receptors found to regulate SST secretion were highly expressed and/or enriched. 1) The metabolite receptors calcium-sensing receptor and free fatty acid receptor 4 (GPR120) functioned as positive and negative regulators, respectively. 2) Among the neurotransmitter receptors, adrenergic receptors α1a, α2a, α2b, and β1 were all highly expressed, with norepinephrine and isoproterenol acting as positive regulators. The muscarinic receptor M3 acted as a positive regulator, whereas M4 was conceivably a negative regulator. 3) Of the hormone receptors, the GLP-1 and GIP receptors, CCKb (stimulated by both CCK and gastrin) and surprisingly the melanocortin MC1 receptor were all positive regulators. 4) The neuropeptide receptors for calcitonin gene-related peptide, adrenomedullin, and vasoactive intestinal peptide acted as positive regulators, no effect was observed using galanin and nociceptin although transcripts for the corresponding receptors appeared highly expressed. 5) The SST receptors 1 and 2 functioned in an autocrine negative feedback loop. Thus, the article provides a comprehensive map of receptors through which SST secretion is regulated by hormones, neurotransmitters, neuropeptides and metabolites that act directly on the SST cells in the gastric mucosa.

Bile Acids Trigger GLP-1 Release Predominantly by Accessing Basolaterally Located G Protein-Coupled Bile Acid Receptors

Bile acids are well-recognized stimuli of glucagon-like peptide-1 (GLP-1) secretion. This action has been attributed to activation of the G protein-coupled bile acid receptor GPBAR1 (TGR5), although other potential bile acid sensors include the nuclear farnesoid receptor and the apical sodium-coupled bile acid transporter ASBT. The aim of this study was to identify pathways important for GLP-1 release and to determine whether bile acids target their receptors on GLP-1-secreting L-cells from the apical or basolateral compartment. Using transgenic mice expressing fluorescent sensors specifically in L-cells, we observed that taurodeoxycholate (TDCA) and taurolithocholate (TLCA) increased intracellular cAMP and Ca(2+). In primary intestinal cultures, TDCA was a more potent GLP-1 secretagogue than taurocholate (TCA) and TLCA, correlating with a stronger Ca(2+) response to TDCA. Using small-volume Ussing chambers optimized for measuring GLP-1 secretion, we found that both a GPBAR1 agonist and TDCA stimulated GLP-1 release better when applied from the basolateral than from the luminal direction and that luminal TDCA was ineffective when intestinal tissue was pretreated with an ASBT inhibitor. ASBT inhibition had no significant effect in nonpolarized primary cultures. Studies in the perfused rat gut confirmed that vascularly administered TDCA was more effective than luminal TDCA. Intestinal primary cultures and Ussing chamber-mounted tissues from GPBAR1-knockout mice did not secrete GLP-1 in response to either TLCA or TDCA. We conclude that the action of bile acids on GLP-1 secretion is predominantly mediated by GPBAR1 located on the basolateral L-cell membrane, suggesting that stimulation of gut hormone secretion may include postabsorptive mechanisms.

Research Resource: A Chromogranin A Reporter for Serotonin and Histamine Secreting Enteroendocrine Cells

Chromogranin A (ChgA) is an acidic protein found in large dense-core secretory vesicles and generally considered to be expressed in all enteroendocrine cells of the gastrointestinal (GI) tract. Here, we characterize a novel reporter mouse for ChgA, ChgA-humanized Renilla reniformis (hr)GFP. The hrGFP reporter was found in the monoamine-storing chromaffin cells of the adrenal medulla, where ChgA was originally discovered. hrGFP also was expressed in enteroendocrine cells throughout the GI tract, faithfully after the expression of ChgA, as characterized by immunohistochemistry and quantitative PCR analysis of fluorescence-activated cell sorting-purified cells, although the expression in the small intestine was weak compared with that of the stomach and colon. In the stomach, hrGFP was highly expressed in almost all histamine-storing enterochromaffin (EC)-like cells, at a lower level in the majority of serotonin-storing EC cells and ghrelin cells, in a small fraction of somatostatin cells, but was absent from gastrin cells. In the small intestine, the hrGFP reporter was selectively, but weakly expressed in EC cells, although not in any peptide-storing enteroendocrine cells. In the colon, hrGFP was exclusively expressed in EC cells but absent from the peptide-storing enteroendocrine cells. In contrast, in the pancreas, hrGFP was expressed in β-cells, α-cells, and a fraction of pancreatic polypeptide cells. It is concluded that ChgA-hrGFP in the GI tract functions as an effective reporter, particularly for the large populations of still poorly characterized monoamine-storing enteroendocrine cells. Furthermore, our findings substantiate the potential function of ChgA as a monoamine-binding protein that facilitates the regulated endocrine secretion of large amounts of monoamines from enteroendocrine cells.

Recent developments in the pathophysiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder, the pathophysiology of which is not completely known, although it has been shown that genetic/social learning factors, diet, intestinal microbiota, intestinal low-grade inflammation, and abnormal gastrointestinal endocrine cells play a major role. Studies of familial aggregation and on twins have confirmed the heritability of IBS. However, the proposed IBS risk genes are thus far nonvalidated hits rather than true predisposing factors. There is no convincing evidence that IBS patients suffer from food allergy/intolerance, with the effect exerted by diet seemingly caused by intake of poorly absorbed carbohydrates and fiber. Obesity is a possible comorbidity of IBS. Differences in the microbiota between IBS patients and healthy controls have been reported, but the association between IBS symptoms and specific bacterial species is uncertain. Low-grade inflammation appears to play a role in the pathophysiology of a major subset of IBS, namely postinfectious IBS. The density of intestinal endocrine cells is reduced in patients with IBS, possibly as a result of genetic factors, diet, intestinal microbiota, and low-grade inflammation interfering with the regulatory signals controlling the intestinal stem-cell clonogenic and differentiation activities. Furthermore, there is speculation that this decreased number of endocrine cells is responsible for the visceral hypersensitivity, disturbed gastrointestinal motility, and abnormal gut secretion seen in IBS patients.

Does nutrient sensing determine how we "see" food?

The ability to "see" both incoming and circulating nutrients plays an essential role in the maintenance of energy homeostasis. As such, nutrient-sensing mechanisms in both the gastrointestinal tract and the brain have been implicated in the regulation of energy intake and glucose homeostasis. The intestinal wall is able to differentiate individual nutrients through sensory machinery expressed in the mucosa and provide feedback signals, via local gut peptide action, to maintain energy balance. Furthermore, both the hypothalamus and hindbrain detect circulating nutrients and respond by controlling energy intake and glucose levels. Conversely, nutrient sensing in the intestine plays a role in stimulating food intake and preferences. In this review, we highlight the emerging evidence for the regulation of energy balance through nutrient-sensing mechanisms in the intestine and the brain, and how disruption of these pathways could result in the development of obesity and type 2 diabetes.

Increased chromogranin a cell density in the large intestine of patients with irritable bowel syndrome after receiving dietary guidance

The large intestine contains five types of endocrine cells that regulate its functions by sensing its luminal contents and releasing specific hormones. Chromogranin A (CgA) is a common marker for the gastrointestinal endocrine cells, and it is abnormal in irritable bowel syndrome (IBS) patients. Most IBS patients relate their symptoms to certain food elements. The present study investigated the effect of dietary guidance on the total endocrine cells of the large intestine as detected by CgA in 13 IBS patients. Thirteen control subjects were also included. Each patient received three sessions of dietary guidance. Colonoscopies were performed on controls and patients (at baseline and at 3–9 months after receiving guidance). Biopsy samples from the colon and rectum were immunostained for CgA and quantified by computerized image analysis. The densities of CgA cells in the total colon (mean ± SEM) among the controls and the IBS patients before and after receiving dietary guidance were 83.3 ± 10.1, 38.6 ± 3.7, and 64.7 ± 4.2 cells/mm², respectively (P = 0.0004), and were unchanged in the rectum. In conclusion, the increase in CgA cell density after receiving dietary guidance may reflect a change in the densities of the large intestinal endocrine cells causing an improvement in the IBS symptoms.

Deoxynivalenol (Vomitoxin)-Induced Cholecystokinin and Glucagon-Like Peptide-1 Release in the STC-1 Enteroendocrine Cell Model Is Mediated by Calcium-Sensing Receptor and Transient Receptor Potential Ankyrin-1 Channel

Food refusal is a hallmark of exposure of experimental animals to the trichothecene mycotoxin deoxynivalenol (DON), a common foodborne contaminant. Although studies in the mouse suggest that DON suppresses food intake by aberrantly inducing the release of satiety hormones from enteroendocrine cells (EECs) found in the gut epithelium, the underlying mechanisms for this effect are not understood. To address this gap, we employed the murine neuroendocrine tumor STC-1 cell line, a widely used EEC model, to test the hypothesis that DON-induced hormone exocytosis is mediated by G protein-coupled receptor (GPCR)-mediated Ca(2+) signaling. The results indicate for the first time that DON elicits Ca(2)-dependent secretion of cholecystokinin (CCK) and glucagon-like peptide-1(7-36) amide (GLP-1), hormones that regulate food intake and energy homeostasis and that are products of 2 critical EEC populations--I cells of the small intestine and L cells of the large intestine, respectively. Furthermore, these effects were mediated by the GPCR Ca(2+)-sensing receptor (CaSR) and involved the following serial events: (1)PLC-mediated activation of the IP3 receptor and mobilization of intracellular Ca(2+) stores, (2) activation of transient receptor potential melastatin-5 ion channel and resultant L-type voltage-sensitive Ca(2+) channel-facilitated extracellular Ca(2+) entry, (3) amplification of extracellular Ca(2+) entry by transient receptor potential ankyrin-1 channel activation, and finally (4) Ca(2+)-driven CCK and GLP-1 excytosis. These in vitro findings provide a foundation for future investigation of mechanisms by which DON and other trichothecenes modulate EEC function in ex vivo and in vivo models.

Sensing of triacylglycerol in the gut: different mechanisms for fatty acids and 2-monoacylglycerol

Sensing of dietary triacylglycerol in the proximal small intestine results in physiological, hormonal and behavioural responses. However, the exact physiological pathways linking intestinal fat sensing to food intake and the activation of brain circuits remain to be identified. In this study we examined the role of triacylglycerol digestion for intestinal fat sensing, and compared the effects of the triacylglycerol digestion products, fatty acids and 2-monoacylglycerol, on behavioural, hormonal and dopaminergic responses in behaving mice. Using an operant task in which mice are trained to self-administer lipid emulsions directly into the stomach, we show that inhibiting triacylglycerol digestion disrupts normal behaviour of self-administration in mice, indicating that fat sensing is conditional to digestion. When administered separately, both digestion products, 2-monoacylglycerol and fatty acids, were sensed by the mice, and self-administration patterns of fatty acids were affected by the fatty acid chain length. Peripheral plasma concentrations of the gut hormones GLP-1, GIP, PYY, CCK and insulin did not offer an explanation of the differing behavioural effects produced by 2-monoacylglycerol and fatty acids. However, combined with behavioural responses, striatal dopamine effluxes induced by gut infusions of oleic acid were significantly greater than those produced by equivalent infusions of 2-oleoylglycerol. Our data demonstrate recruitment of different signalling pathways by fatty acids and 2-monoacylglycerol, and suggest that the structural properties of fat rather than total caloric value determine intestinal sensing and the assignment of reward value to lipids.

SCFA transport in rat duodenum

Bacterial or ingested food-derived short-chain fatty acids (SCFAs) are present in the duodenal lumen. Acetate, the most abundant SCFA in the foregut lumen, is absorbed immediately after ingestion, although the mechanism by which this absorption occurs is not fully understood. We investigated the distribution and function of candidate SCFA transporters in rat duodenum. The Na(+)-coupled monocarboxylate transporter-1 (SMCT1) was localized to the brush border, whereas the pH-dependent monocarboxylate transporter (MCT) 1 and MCT4 were localized to the duodenocyte basolateral membrane. In Ussing chambered duodenal mucosa, luminal acetate dose-dependently increased short-circuit current (Isc) in the presence of serosal bumetanide and indomethacin by a luminal Na(+)-dependent, ouabain-sensitive mechanism. The Isc response was inhibited dose-dependently by the SMCT1 nonsubstrate inhibitor ibuprofen, consistent with net electrogenic absorption of acetate via SMCT1. Other SCFAs and lactate also increased Isc. Furthermore, duodenal loop perfusion of acetate increased portal venous acetate concentration, inhibited by coperfusion of ibuprofen or a MCT inhibitor. Luminal acetate perfusion increased duodenal HCO3 (-) secretion via capsaicin-sensitive afferent nerve activation and cyclooxygenase activity, consistent with absorption-mediated HCO3 (-) secretion. These results suggest that absorption of luminal SCFA via SMCT1 and MCTs increases duodenal HCO3 (-) secretion. In addition to SCFA sensing via free fatty acid receptors, the presence of rapid duodenal SCFA absorption may be important for the suppression of luminal bacterial colonization and implicated in the generation of functional dyspepsia due to bacterial overgrowth.

Flavor preference conditioning by different sugars in sweet ageusic Trpm5 knockout mice

Knockout (KO) mice missing the taste signaling protein Trpm5 have greatly attenuated sweetener preferences but develop strong preferences for glucose in 24-h tests, which is attributed to post-oral sugar conditioning. Trpm5 KO mice express mild preferences for galactose but no preferences for fructose in 24-h tests, which suggests that these sugars differ in their post-oral reinforcing effects. Here we investigated sugar-conditioned flavor preferences in Trpm5 KO and C57BL/6J wildtype (B6) mice. The mice were trained to consume a flavored (CS+, e.g. grape) 8% sugar solution and flavored (CS-, e.g., cherry) water on alternating days followed by two-bottle choice tests with CS+ vs. CS- flavors in water and with unflavored sugar vs. water. The KO mice displayed strong preferences (>80%) for the CS+ glucose and CS+ galactose but not for the CS+ fructose flavor. They also preferred glucose and galactose, but not fructose to water. In contrast, the B6 mice preferred all three CS+ flavors to the CS- flavor, and all three sugars to water. In tests with the non-metabolizable sugar α-methyl-d-glucopyranoside (MDG), the KO and B6 mice preferred 8% MDG to water but did not prefer the CS+ 8% MDG to CS-. However, they preferred a CS+ flavor mixed with 4% MDG over the CS- flavor. Trpm5 KO mice also preferred galactose and MDG to fructose in direct choice tests. The Trpm5 KO data indicate that glucose and, to a lesser extent, galactose and MDG have post-oral reinforcing actions that stimulate intake and preference while fructose has a much weaker effect. The CS+ flavor and sugar preferences of B6 mice may be mediated by the sweet taste and/or post-oral actions of the various sugars. Glucose, galactose, and MDG, but not fructose, are ligands for the sodium-glucose transporter 1 (SGLT1) which is implicated in post-oral sugar conditioning in B6 mice.

Differential acute postprandial effects of processed meat and isocaloric vegan meals on the gastrointestinal hormone response in subjects suffering from type 2 diabetes and healthy controls: a randomized crossover study

BACKGROUND

The intake of meat, particularly processed meat, is a dietary risk factor for diabetes. Meat intake impairs insulin sensitivity and leads to increased oxidative stress. However, its effect on postprandial gastrointestinal hormone (GIH) secretion is unclear. We aimed to investigate the acute effects of two standardized isocaloric meals: a processed hamburger meat meal rich in protein and saturated fat (M-meal) and a vegan meal rich in carbohydrates (V-meal). We hypothesized that the meat meal would lead to abnormal postprandial increases in plasma lipids and oxidative stress markers and impaired GIH responses.

METHODS

In a randomized crossover study, 50 patients suffering from type 2 diabetes (T2D) and 50 healthy subjects underwent two 3-h meal tolerance tests. For statistical analyses, repeated-measures ANOVA was performed.

RESULTS

The M-meal resulted in a higher postprandial increase in lipids in both groups (p<0.001) and persistent postprandial hyperinsulinemia in patients with diabetes (p<0.001). The plasma glucose levels were significantly higher after the V-meal only at the peak level. The plasma concentrations of glucose-dependent insulinotropic peptide (GIP), peptide tyrosine-tyrosine (PYY) and pancreatic polypeptide (PP) were higher (p<0.05, p<0.001, p<0.001, respectively) and the ghrelin concentration was lower (p<0.001) after the M-meal in healthy subjects. In contrast, the concentrations of GIP, PYY and PP were significantly lower after the M-meal in T2D patients (p<0.001). Compared with the V-meal, the M-meal was associated with a larger increase in lipoperoxidation in T2D patients (p<0.05).

CONCLUSION/INTERPRETATION

Our results suggest that the diet composition and the energy content, rather than the carbohydrate count, should be important considerations for dietary management and demonstrate that processed meat consumption is accompanied by impaired GIH responses and increased oxidative stress marker levels in diabetic patients.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01572402.

Gut microbiota, nutrient sensing and energy balance

The gastrointestinal (GI) tract is a highly specialized sensory organ that provides crucial negative feedback during a meal, partly via a gut-brain axis. More specifically, enteroendocrine cells located throughout the GI tract are able to sense and respond to specific nutrients, releasing gut peptides that act in a paracrine, autocrine or endocrine fashion to regulate energy balance, thus controlling both food intake and possibly energy expenditure. Furthermore, the gut microbiota has been shown to provide a substantial metabolic and physiological contribution to the host, and metabolic disease such as obesity has been associated with aberrant gut microbiota and microbiome. Interestingly, recent evidence suggests that the gut microbiota can impact the gut-brain axis controlling energy balance, at both the level of intestinal nutrient-sensing mechanisms, as well as potentially at the sites of integration in the central nervous system. A better understanding of the intricate relationship between the gut microbiota and host energy-regulating pathways is crucial for uncovering the mechanisms responsible for the development of metabolic diseases and for possible therapeutic strategies.

Steviol glycoside rebaudioside A induces glucagon-like peptide-1 and peptide YY release in a porcine ex vivo intestinal model

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) are hormones important for satiation and are involved in the process called "ileal brake". The aim of this study was to investigate the GLP-1- and PYY-stimulating efficacy of rebaudioside A, casein, and sucrose. This was studied using tissue segments collected from various regions of the pig small intestine. GLP-1 release was strongest from the distal ileum. There, control release was 0.06 ± 0.01 (GLP-1) and 0.07 ± 0.01 (PYY) pmol/cm(2) of tissue. Rebaudioside A (2.5, 12.5, and 25 mM) stimulated GLP-1 release (0.14 ± 0.02, 0.16 ± 0.02, and 0.13 ± 0.02 pmol/cm(2) of tissue, p < 0.001) and PYY release (0.19 ± 0.02, 0.42 ± 0.06, and 0.27 ± 0.03 pmol/cm(2) of tissue, p < 0.001). Sucrose stimulated GLP-1 release (0.08 ± 0.01 pmol/cm(2) of tissue, p < 0.05) only at 10 mM. Casein (0.5%, 1%, and 2.5%, w/v) stimulated GLP-1 release (0.15 ± 0.03, 0.13 ± 0.02, and 0.14 ± 0.01 pmol/cm(2) of tissue, p < 0.001) and PYY release (0.13 ± 0.02, 0.20 ± 0.03, and 0.27 ± 0.03 pmol/cm(2) of tissue, p < 0.01). These findings may help in developing dietary approaches for weight management.

Increased gastric chromogranin A cell density following changes to diets of patients with irritable bowel syndrome

The gut endocrine cells control and regulate several functions of the gastrointestinal tract. They have been reported to be abnormal in irritable bowel syndrome (IBS), with alterations occurring in several functions regulated by these cells. Furthermore, it has been established that gut endocrine cells interact with the gut lumen contents, particularly the nutrients. The present study was undertaken to establish whether the positive outcome of dietary guidance observed in patients suffering from IBS is associated with a change in gastric endocrine cells. A total of 46 patients with IBS participated in the present study, of which 14 completed all aspects. These patients included nine females and five males with a mean age of 34 years (range, 20–45 years). In the healthy control group, nine females and five males, with a mean age of 54 years (range 26–70 years) were selected. The patients and controls underwent gastroscopy with biopsy samples taken from the corpus and antrum of the stomach. Each patient attended three sessions that lasted ~45 min each, and received individual guidance on their dietary management. The patients followed the diet prescribed for a minimum of three months, then further samples were taken using a method similar to that used for the initial biopsies. The biopsy samples were immunostained using the avidin-biotin complex method for chromogranin A (CgA) and quantified by computerized image analysis. The patients with IBS presented a low density of CgA compared with the controls. The density of CgA increased in these patients following dietary guidance and changes in food intake. The present observations emphasized the interaction between food intake and gut endocrine cells. The current study also suggests that the positive effects of dietary guidance may be attributed to changes in gut endocrine cell density.

Duodenal luminal nutrient sensing

The gastrointestinal mucosa is exposed to numerous chemical substances and microorganisms, including macronutrients, micronutrients, bacteria, endogenous ions, and proteins. The regulation of mucosal protection, digestion, absorption and motility is signaled in part by luminal solutes. Therefore, luminal chemosensing is an important mechanism enabling the mucosa to monitor luminal conditions, such as pH, ion concentrations, nutrient quantity, and microflora. The duodenal mucosa shares luminal nutrient receptors with lingual taste receptors in order to detect the five basic tastes, in addition to essential nutrients, and unwanted chemicals. The recent 'de-orphanization' of nutrient sensing G protein-coupled receptors provides an essential component of the mechanism by which the mucosa senses luminal nutrients. In this review, we will update the mechanisms of and underlying physiological and pathological roles in luminal nutrient sensing, with a main focus on the duodenal mucosa.

Stomach antral endocrine cells in patients with irritable bowel syndrome

To the best of our knowledge, stomach antral endocrine cells have not previously been investigated in patients with irritable bowel syndrome (IBS). Thus, in the present study, 76 patients with IBS were examined (designated as IBS-total). Diarrhoea was the predominant symptom in 26 of these patients (IBS-D), while in 21 patients, the predominant symptoms were both diarrhoea and constipation (IBS-M) and in 29 patients the predominant symptom was constipation (IBS-C). Forty-three healthy subjects were enrolled as the controls. Stomach antral biopsy samples obtained from all of the subjects were immunostained using the avidin-biotin-complex method for serotonin, gastrin, somatostatin and serotonin transporter (SERT). The immunopositive cell densities and immunoreactivity intensities were determined by computer-aided image analysis. The density of the serotonin-immunoreactive cells was significantly decreased in the IBS-M patients and increased in the IBS-C patients relative to the controls. The immunoreactivity intensity did not differ significantly between the controls and IBS-total. The density of the gastrin-immunoreactive cells was significantly greater in the IBS-D, IBS-M and IBS-C patients than in the controls. The immunoreactivity intensity of gastrin was significantly greater in the IBS-D patients than in the controls. The density of the somatostatin-immunoreactive cells cells was significantly lower in the IBS-total, IBS-D, IBS-M and IBS-C patients than in the controls. The immunoreactivity intensities of both somatostatin and SERT did not differ significantly between the controls and IBS-total. The increase in gastrin cell density and the decrease in somatostatin cell density in all IBS subtypes may cause high levels of gastric secretion, which may in turn contribute to the high incidence of dyspepsia and gastro-oesophageal reflux observed in patients with IBS.

Interaction between ingested nutrients and gut endocrine cells in patients with irritable bowel syndrome (review)

Several endocrine cell abnormalities have been reported in different segments of the gastrointestinal tract of patients with irritable bowel syndrome (IBS). These cells have specialized microvilli that project into the lumen; they function as sensors for the gut contents and respond to luminal stimuli (mostly ingested nutrients) by releasing hormones into the lamina propria, where they exert their effects via a paracrine/endocrine mode of action. Certain food items trigger the symptoms experienced by IBS patients, including those rich in fermentable oligo-, di- and monosaccharides, and polyols (FODMAPs). In this review, we present the argument that the effects of both FODMAPs and the proportional intake of proteins, fats and carbohydrates on IBS symptoms may be caused by an interaction with the gut endocrine cells. Since the gut hormones control and regulate gastrointestinal motility and sensation, this interaction may be responsible for abnormal gastrointestinal motility and the visceral hypersensitivity observed in these patients. There is no consistent evidence that IBS patients suffer from food allergy. The role of gluten intolerance in the development of IBS symptoms in these patients remains a matter of controversy. Individual guidance on food management, which includes restrictions in the intake of FODMAP-rich foods and testing diets with different proportions of proteins, fats and carbohydrates has been found to reduce the symptoms, improve the quality of life, and make the habitual diet of IBS patients more healthy.

Insulin-like peptide 5 is an orexigenic gastrointestinal hormone

The gut endocrine system is emerging as a central player in the control of appetite and glucose homeostasis, and as a rich source of peptides with therapeutic potential in the field of diabetes and obesity. In this study we have explored the physiology of insulin-like peptide 5 (Insl5), which we identified as a product of colonic enteroendocrine L-cells, better known for their secretion of glucagon-like peptide-1 and peptideYY. i.p. Insl5 increased food intake in wild-type mice but not mice lacking the cognate receptor Rxfp4. Plasma Insl5 levels were elevated by fasting or prolonged calorie restriction, and declined with feeding. We conclude that Insl5 is an orexigenic hormone released from colonic L-cells, which promotes appetite during conditions of energy deprivation.

Long-lived intestinal tuft cells serve as colon cancer-initiating cells

Doublecortin-like kinase 1 protein (DCLK1) is a gastrointestinal tuft cell marker that has been proposed to identify quiescent and tumor growth-sustaining stem cells. DCLK1⁺ tuft cells are increased in inflammation-induced carcinogenesis; however, the role of these cells within the gastrointestinal epithelium and their potential as cancer-initiating cells are poorly understood. Here, using a BAC-CreERT-dependent genetic lineage-tracing strategy, we determined that a subpopulation of DCLK1⁺ cells is extremely long lived and possesses rare stem cell abilities. Moreover, genetic ablation of Dclk1 revealed that DCLK1⁺ tuft cells contribute to recovery following intestinal and colonic injury. Surprisingly, conditional knockdown of the Wnt regulator APC in DCLK1⁺ cells was not sufficient to drive colonic carcinogenesis under normal conditions; however, dextran sodium sulfate-induced (DSS-induced) colitis promoted the development of poorly differentiated colonic adenocarcinoma in mice lacking APC in DCLK1⁺ cells. Importantly, colonic tumor formation occurred even when colitis onset was delayed for up to 3 months after induced APC loss in DCLK1⁺ cells. Thus, our data define an intestinal DCLK1⁺ tuft cell population that is long lived, quiescent, and important for intestinal homeostasis and regeneration. Long-lived DCLK1⁺ cells maintain quiescence even following oncogenic mutation, but are activated by tissue injury and can serve to initiate colon cancer.

Role of anorectic N-acylethanolamines in intestinal physiology and satiety control with respect to dietary fat

Anandamide is a well-known agonist for the cannabinoid receptors. Along with endogenous anandamide other non-endocannabinoid N-acylethanolamines are also formed, apparently in higher amounts. These include mainly oleoylethanolamide (OEA), palmitoyelethanolamide (PEA) and linoleoylethanolamide (LEA), and they have biological activity by themselves being anorectic and anti-inflammatory. It appears that the major effect of dietary fat on the level of these molecules is in the gastrointestinal system, where OEA, PEA and LEA in the enterocytes may function as homeostatic signals, which are decreased by prolonged consumption of a high-fat diet. These lipid amides appear to mediate their signaling activity via activation of PPARα in the enterocyte followed by activation of afferent vagal fibers leading to the brain. Through this mechanism OEA, PEA and LEA may both reduce the consumption of a meal as well as increase the reward value of the food. Thus, they may function as homeostatic intestinal signals involving hedonic aspects that contribute to the regulation of the amounts of dietary fat to be ingested.