The physiological role of GLP-1 in human: incretin, ileal brake or more?

Changes in gastrointestinal motility and gut hormone secretion after Roux-en-Y gastric bypass and sleeve gastrectomy for individuals with severe obesity

BACKGROUND

Bariatric surgery is very effective in long-term weight management. The present study was undertaken to investigate the short-term effects of sleeve gastrectomy (SG) and of Roux-en-Y gastric bypass (RYGB) on (a) gastrointestinal (GI) motility, that is gastric emptying and oro-cecal transit time and (b) secretion of regulatory gut peptides and (c) their interrelationship.

METHODS

Prospective single-centre study in which we assessed gastric emptying, oro-cecal transit time and gut peptide release in 28 severely obese individuals before and 2, respectively, 12 months after bariatric surgery (either SG or RYGB). Plasma PYY, GLP-1, ghrelin, insulin and glucose levels were measured fasting and after intake of a solid standard 459 kcal meal at each occasion. Gastric emptying was measured by 13 C octanoic acid breath testing, and oro-cecal transit time was measured by lactulose H2 breath testing. Satiation was measured using VAS scores.

RESULTS

After both RYGB and SG gastric emptying become significantly accelerated, and postprandial release of the distal gut peptides GLP-1 and PYY becomes significantly increased, pointing to ileal brake activation. Oro-cecal transit time becomes significantly accelerated after SG but not after RYGB. No significant correlations were observed between changes in distal gut peptide release, changes in GI motility and clinical parameters.

CONCLUSION

Both SG and RYGB resulted in significant weight loss and significantly affected GI motility and PYY and GLP-1 secretion. Subtle differences between both procedures were found in effect on oro-cecal transit time and patterns of peptide secretion.

GLP-1 and IL-6 regulates obesity in the gut and brain

Obesity is a chronic metabolic disease characterized by excessive nutrient intake leading to increased subcutaneous or visceral fat, resulting in pathological and physiological changes. The incidence rate of obesity, an important form of metabolic syndrome, is increasing worldwide. Excess appetite is a key pathogenesis of obesity, and the inflammatory response induced by obesity has received increasing attention. This review focuses on the role of appetite-regulating factor (Glucogan-like peptide 1) and inflammatory factor (Interleukin-6) in the gut and brain in individuals with obesity and draws insights from the current literature.

GLP-1 Receptor Agonists: A Promising Therapy for Modern Lifestyle Diseases with Unforeseen Challenges

Modern lifestyle diseases remain a persistent challenge in healthcare. Currently, about 422 million people worldwide are affected by diabetes, while 1 in 8 people are living with obesity. The development of glucagon-like peptide 1 receptor agonists (GLP-1RAs) has marked a significant milestone in treating these conditions. Interest in GLP-1RAs has grown due to evidence that, beyond their established role in diabetes management, these drugs influence other metabolic disorders. This is attributed to the fact that GLP-1 receptors are found in various healthy human tissues. However, a potential cause for concern is the expression of GLP-1 receptors in certain cancers. This review focuses on the most recent findings concerning the actions of GLP-1RAs, detailing their documented impact on the thyroid gland and pancreas. It addresses concerns about the long-term use of GLP-1RAs in relation to the development of pancreatitis, pancreatic cancer, and thyroid neoplasms by exploring the mechanisms and long-term effects in different patient subgroups and including data not discussed previously. This review was conducted through an examination of the literature available in the MedLine (PubMed) database, covering publications from 1978 to 10 May 2024. The collected articles were selected based on their relevance to studies of GLP-1 agonists and their effects on the pancreas and thyroid and assessed to meet the established inclusion criteria. The revised papers suggest that prolonged use of GLP-1RA could contribute to the formation of thyroid tumors and may increase the risk of acute inflammatory conditions such as pancreatitis, particularly in high-risk patients. Therefore, physicians should advise patients on the need for more frequent and detailed follow-ups.

GLP-1 physiology in obesity and development of incretin-based drugs for chronic weight management

The introduction of the highly potent incretin receptor agonists semaglutide and tirzepatide has marked a new era in the treatment of type 2 diabetes and obesity. With normalisation of glycated haemoglobin levels and weight losses around 15-25%, therapeutic goals that were previously unrealistic are now within reach, and clinical trials have documented that these effects are associated with reduced risk of cardiovascular events and premature mortality. Here, I review this remarkable development from the earliest observations of glucose lowering and modest weight losses with native glucagon-like peptide (GLP)-1 and short acting compounds, to the recent development of highly active formulations and new molecules. I will classify these agents as GLP-1-based therapies in the understanding that these compounds or combinations may have actions on other receptors as well. The physiology of GLP-1 is discussed as well as its mechanisms of actions in obesity, in particular, the role of sensory afferents and GLP-1 receptors in the brain. I provide details regarding the development of GLP-1 receptor agonists for anti-obesity therapy and discuss the possible mechanism behind their beneficial effects on adverse cardiovascular events. Finally, I highlight new pharmacological developments, including oral agents, and discuss important questions regarding maintenance therapy.

Spanish Experience with Latero-Lateral Duodeno-Ileostomy + Sleeve Gastrectomy with Magnet Anastomosis System

BACKGROUND

The partial diversion of intestinal contents facilitates achieving and maintaining weight loss and improving glycemic control in patients with obesity and with or without T2DM. The purpose of this study is to report our experience and 1-year follow-up with novel modification of SADI-S.

METHODS

This study is a part of a multicentric trial of patients that underwent primary side-to-side duodeno-ileostomy and sleeve gastrectomy (SG) with GT metabolic solutions magnetic anastomosis system. Feasibility, safety, and initial efficacy were evaluated.

RESULTS

The mean age of the patients included was 48 ± 8.75 years and the preoperative BMI was 43.32 ± 2.82 kg/m2. The complications were present in 30% of patients. The anastomosis patency was confirmed by the passage of radiological contrast under fluoroscopy at a mean of 17 days (17-29 days), and the mean expulsion time was 42 days (32-62). The mean diameter of the anastomosis after the magnet expulsion was 13.8 × 11.4 mm. The percentage of total weight lost at 1 year was 38.68 ± 8.48% (p < 0.001). The percentage of excess weight loss 82.5 ± 18.44% (p < 0.001) and improvements in glucose profiles were observed. Mean baseline HbA1c 5.77 ± 0.31% was reduced to 5.31 ± 0.26% (p < 0.024).

CONCLUSIONS

Latero-lateral duodeno-ileostomy + SG with magnetic duodenal bipartition is afeasible and reasonably safe technique and induces weight loss in patients with obesity and improvement of glycemic control. This modification could be considered as an option to standard SADI-S or as a first step in two stages procedure. However, larger studies are needed.

TRIAL REGISTRATION

Clinicaltrials.gov Identifier: #NCT05322122.

Multifunctional microelectronic fibers enable wireless modulation of gut and brain neural circuits

Progress in understanding brain-viscera interoceptive signaling is hindered by a dearth of implantable devices suitable for probing both brain and peripheral organ neurophysiology during behavior. Here we describe multifunctional neural interfaces that combine the scalability and mechanical versatility of thermally drawn polymer-based fibers with the sophistication of microelectronic chips for organs as diverse as the brain and the gut. Our approach uses meters-long continuous fibers that can integrate light sources, electrodes, thermal sensors and microfluidic channels in a miniature footprint. Paired with custom-fabricated control modules, the fibers wirelessly deliver light for optogenetics and transfer data for physiological recording. We validate this technology by modulating the mesolimbic reward pathway in the mouse brain. We then apply the fibers in the anatomically challenging intestinal lumen and demonstrate wireless control of sensory epithelial cells that guide feeding behaviors. Finally, we show that optogenetic stimulation of vagal afferents from the intestinal lumen is sufficient to evoke a reward phenotype in untethered mice.

Emerging uses of glucagon-like peptide 1 (GLP-1) receptor agonists following ileal resection: literature review and case examples

Following ileal resection, the combination of severe bile acid (BA) malabsorption, rapid small bowel transit and unrestricted upper gastrointestinal (GI) secretion results in severe diarrhoea that can prove refractory to pharmacological therapies. While established therapies, including BA sequestrants and antidiarrhoeal drugs seek to ameliorate symptoms, they do not target the underlying pathophysiological mechanisms in this patient group. Their use can also be limited by both intolerance and adverse effects. The novel use of glucagon-like peptide-1 (GLP-1) receptor agonists (RAs) in these patients may allow restoration of the physiological negative feedback mechanisms lost in ileal resection and reduce diarrhoea by prolonging small bowel transit time, limiting upper GI secretions and perhaps by inhibiting hepatic BA synthesis. While recent evidence supports the use of GLP-1 RAs as a safe and effective therapy for bile acid diarrhoea (BAD), it remains uncertain whether those with severe BAD and subsequent short bowel syndrome secondary to extensive ileal resection will benefit. Here, we present three cases of severe diarrhoea secondary to extensive ileal resection in which the use of the GLP-1 RA, liraglutide, was well tolerated and resulted in an objective improvement in diarrhoeal symptoms. We further provide a narrative review of the emerging evidence base supporting the use of GLP therapies in this challenging condition.

The Neurobiology of Eating Behavior in Obesity: Mechanisms and Therapeutic Targets: A Report from the 23rd Annual Harvard Nutrition Obesity Symposium

Obesity is increasing at an alarming rate. The effectiveness of currently available strategies for the treatment of obesity (including pharmacologic, surgical, and behavioral interventions) is limited. Understanding the neurobiology of appetite and the important drivers of energy intake (EI) can lead to the development of more effective strategies for the prevention and treatment of obesity. Appetite regulation is complex and is influenced by genetic, social, and environmental factors. It is intricately regulated by a complex interplay of endocrine, gastrointestinal, and neural systems. Hormonal and neural signals generated in response to the energy state of the organism and the quality of food eaten are communicated by paracrine, endocrine, and gastrointestinal signals to the nervous system. The central nervous system integrates homeostatic and hedonic signals to regulate appetite. Although there has been an enormous amount of research over many decades regarding the regulation of EI and body weight, research is only now yielding potentially effective treatment strategies for obesity. The purpose of this article is to summarize the key findings presented in June 2022 at the 23rd annual Harvard Nutrition Obesity Symposium entitled "The Neurobiology of Eating Behavior in Obesity: Mechanisms and Therapeutic Targets." Findings presented at the symposium, sponsored by NIH P30 Nutrition Obesity Research Center at Harvard, enhance our current understanding of appetite biology, including innovative techniques used to assess and systematically manipulate critical hedonic processes, which will shape future research and the development of therapeutics for obesity prevention and treatment.

Colonic Delivery of Nutrients for Sustained and Prolonged Release of Gut Peptides: A Novel Strategy for Appetite Management

Obesity is one of the major global threats to human health and risk factors for cardiometabolic diseases and certain cancers. Glucagon-like peptide-1 (GLP-1) plays a major role in appetite and glucose homeostasis and recently the USFDA approved GLP-1 agonists for the treatment of obesity and type 2 diabetes. GLP-1 is secreted from enteroendocrine L-cells in the distal part of the gastrointestinal (GI) tract in response to nutrient ingestion. Endogenously released GLP-1 has a very short half-life of <2 min and most of the nutrients are absorbed before reaching the distal GI tract and colon, which hinders the use of nutritional compounds for appetite regulation. The review article focuses on nutrients that endogenously stimulate GLP-1 and peptide YY (PYY) secretion via their receptors in order to decrease appetite as preventive action. In addition, various delivery technologies such as pH-sensitive, mucoadhesive, time-dependent, and enzyme-sensitive systems for colonic targeting of nutrients delivery are described. Sustained colonic delivery of nutritional compounds could be one of the most promising approaches to prevent obesity and associated metabolic diseases by, e.g., sustained GLP-1 release.

An inter-organ neural circuit for appetite suppression

Glucagon-like peptide-1 (GLP-1) is a signal peptide released from enteroendocrine cells of the lower intestine. GLP-1 exerts anorectic and antimotility actions that protect the body against nutrient malabsorption. However, little is known about how intestinal GLP-1 affects distant organs despite rapid enzymatic inactivation. We show that intestinal GLP-1 inhibits gastric emptying and eating via intestinofugal neurons, a subclass of myenteric neurons that project to abdominal sympathetic ganglia. Remarkably, cell-specific ablation of intestinofugal neurons eliminated intestinal GLP-1 effects, and their chemical activation functioned as a GLP-1 mimetic. GLP-1 sensing by intestinofugal neurons then engaged a sympatho-gastro-spinal-reticular-hypothalamic pathway that links abnormal stomach distension to craniofacial programs for food rejection. Within this pathway, cell-specific activation of discrete neuronal populations caused systemic GLP-1-like effects. These molecularly identified, delimited enteric circuits may be targeted to ameliorate the abdominal bloating and loss of appetite typical of gastric motility disorders.

Activation of gastrointestinal ileal brake response with dietary slowly digestible carbohydrates, with no observed effect on subjective appetite, in an acute randomized, double-blind, crossover trial

PURPOSE

To test the hypothesis that oral ingestion of slowly digestible carbohydrates (SDCs) that reach the ileum triggers the ileal brake as indicated by delayed gastric emptying, reduced glycemic response, and decreased subjective appetite.

METHODS

The study was a five-arm, randomized, double-blind, crossover trial with a 1-week washout period between treatments (n = 20; 9 females, 11 males). Five treatments consisted of three SDC ingredients [raw corn starch, isomaltooligosaccharide (IMO), sucromalt], and an IMO/sucromalt combination, shown in vitro to have slow and extended digestion profiles, and a rapidly digestible carbohydrate control (maltodextrin). Carbohydrates (26 g) were incorporated into yogurt [300 g total; carbohydrate (~ 77 g), fat (~ 0.2 g), and protein (~ 9 g)] with closely matched energy content (346 kcal) and viscosity (~ 30,000 cP). Outcomes were measured in a 4 h postprandial period.

RESULTS

Mean gastric half-emptying times were moderately though significantly increased for the raw corn starch and IMO treatments (P < 0.05), but they could be sub-divided into larger effect responder (n = 11) and non-responder groups (n = 9). Longer time for glycemic response to return to baseline was associated with increased gastric half-emptying time in an exploratory subset of data removing gastric half-emptying times > 3.5 h (P = 0.02). No significant differences in appetite ratings were observed.

CONCLUSION

SDCs caused slower gastric emptying rate through activation of the ileal brake, as closely matched semi-solid yogurts were used and only rate of carbohydrate digestion differed. Extending glycemic response through consumption of SDCs was associated with triggering the ileal brake.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03630445, August 2018, retrospectively registered.

Effects of Sitagliptin as Monotherapy and Add-On to Metformin on Weight Loss among Overweight and Obese Patients with Type 2 Diabetes: A Systematic Review and Meta-Analysis

BACKGROUND

Sitagliptin is known as an antidiabetic agent inhibiting the dipeptidyl peptidase-4. Although sitagliptin may influence weight, controversial results have been reported, and there is no general agreement on this issue. Therefore, this study assessed the effect of sitagliptin as monotherapy and add-on therapy to metformin on weight reduction in overweight or obese cases with type 2 diabetes.

METHODS

We reviewed the following databases to identify all relevant papers published until 1st April 2021: Web of Science, MEDLINE, Embase, Scopus, Cochrane Central Register of Controlled Trials Cochrane Library, and Google Scholar. The research included all clinical trials investigating the effect of sitagliptin in obese or overweight adult patients with type 2 diabetes without any language restriction.

RESULTS

In total, eighteen randomized controlled trials with 2009 participants were included in our meta-analysis. Results showed supplementation of sitagliptin has led to weight loss for sitagliptin treated (MD  -0.99; 95% CI; (-1.87, -0.12); p=0.026)) and sitagliptin+metformin treated groups (MD  -1.09; 95% CI; (-1.69, -0.49); p<0.001)). Also, the intervention has influenced body mass index in sitagliptin treated (MD  -0.23; 95% CI; (-0.45, 0.02); p=0.033)) and sitagliptin+metformin treated groups (MD -0.52; 95% CI; (-0.96, 0.08); p=0.020)) comparing to placebo.

CONCLUSION

Our results demonstrated that sitagliptin administration with or without metformin might reduce the body weight and body mass index if these drugs are taken for more than 6 months.

Cinnamaldehyde Induces Release of Cholecystokinin and Glucagon-Like Peptide 1 by Interacting with Transient Receptor Potential Ankyrin 1 in a Porcine Ex-Vivo Intestinal Segment Model

Cinnamaldehyde and capsaicin have been reported to exert effects on the gastric function, mediated by the interaction with transient receptor potential ankyrin channel 1 (TRPA1) and transient receptor potential vanilloid channel 1 (TRPV1), respectively. This study examined whether these compounds could trigger the release of cholecystokinin (CCK) and/or glucagon-like peptide 1 (GLP-1) in the pig's gut in a porcine ex-vivo intestinal segment model. Furthermore, it was verified whether this response was mediated by TRPA1 or TRPV1 by using the channel's antagonist. These gut peptides play a key role in the "intestinal brake", a feedback mechanism that influences the function of proximal parts of the gut. Structural analogues of cinnamaldehyde were screened as well, to explore structure-dependent activation. Results showed a significant effect of capsaicin on GLP-1 release in the proximal small intestine, TRPV1 independent. TRPA1 showed to be strongly activated by cinnamaldehyde, both in proximal and distal small intestine, evidenced by the release of CCK and GLP-1, respectively. Out of all structural derivates, cinnamaldehyde showed the highest affinity for TRPA1, which elucidates the importance of the α,β-unsaturated aldehyde moiety. In conclusion, cinnamaldehyde as a TRPA1 agonist, is a promising candidate to modulate gastric function, by activating intestinal brake mechanisms.

Sweet Taste Is Complex: Signaling Cascades and Circuits Involved in Sweet Sensation

Sweetness is the preferred taste of humans and many animals, likely because sugars are a primary source of energy. In many mammals, sweet compounds are sensed in the tongue by the gustatory organ, the taste buds. Here, a group of taste bud cells expresses a canonical sweet taste receptor, whose activation induces Ca²⁺ rise, cell depolarization and ATP release to communicate with afferent gustatory nerves. The discovery of the sweet taste receptor, 20 years ago, was a milestone in the understanding of sweet signal transduction and is described here from a historical perspective. Our review briefly summarizes the major findings of the canonical sweet taste pathway, and then focuses on molecular details, about the related downstream signaling, that are still elusive or have been neglected. In this context, we discuss evidence supporting the existence of an alternative pathway, independent of the sweet taste receptor, to sense sugars and its proposed role in glucose homeostasis. Further, given that sweet taste receptor expression has been reported in many other organs, the physiological role of these extraoral receptors is addressed. Finally, and along these lines, we expand on the multiple direct and indirect effects of sugars on the brain. In summary, the review tries to stimulate a comprehensive understanding of how sweet compounds signal to the brain upon taste bud cells activation, and how this gustatory process is integrated with gastro-intestinal sugar sensing to create a hedonic and metabolic representation of sugars, which finally drives our behavior. Understanding of this is indeed a crucial step in developing new strategies to prevent obesity and associated diseases.

Effects of GLP-1 and Its Analogs on Gastric Physiology in Diabetes Mellitus and Obesity

The processing of proglucagon in intestinal L cells results in the formation of glucagon, GLP-1, and GLP-2. The GLP-1 molecule becomes active through the effect of proconvertase 1, and it is inactivated by dipeptidyl peptidase IV (DPP-IV), so that the half-life of endogenous GLP-1 is 2-3 min. GLP-1 stimulates insulin secretion from β cells in the islets of Langerhans. Human studies show that infusion of GLP-1 results in slowing of gastric emptying and increased fasting and postprandial gastric volumes. Retardation of gastric emptying reduces postprandial glycemia. Exendin-4 is a peptide agonist of the GLP-1 receptor that promotes insulin secretion. Chemical modifications of exendin-4 and GLP-1 molecules have been accomplished to prolong the half-life of GLP-1 agonists or analogs. This chapter reviews the effects of GLP-1-related drugs used in treatment of diabetes or obesity on gastric motor functions, chiefly gastric emptying. The literature shows that diverse methods have been used to measure effects of the GLP-1-related drugs on gastric emptying, with most studies using the acetaminophen absorption test which essentially measures gastric emptying of liquids during the first hour and capacity to absorb the drug over 4-6 h, expressed as AUC. The most valid measurements by scintigraphy (solids or liquids) and acetaminophen absorption at 30 or 60 min show that GLP-1-related drugs used in diabetes or obesity retard gastric emptying, and this is associated with reduced glycemia and variable effects on food intake and appetite. GLP-1 agonists and analogs are integral to the management of patients with type 2 diabetes mellitus and obesity. The effects on gastric emptying are reduced with long-acting preparations or long-term use of short-acting preparations as a result of tachyphylaxis. The dual agonists targeting GLP-1 and another receptor (GIP) do not retard gastric emptying, based on reports to date. In summary, GLP-1 agonists and analogs are integral to the management of patients with type 2 diabetes mellitus and obesity, and their effects are mediated, at least in part, by retardation of gastric emptying.

An alternative pathway for sweet sensation: possible mechanisms and physiological relevance

Sweet substances are detected by taste-bud cells upon binding to the sweet-taste receptor, a T1R2/T1R3 heterodimeric G protein-coupled receptor. In addition, experiments with mouse models lacking the sweet-taste receptor or its downstream signaling components led to the proposal of a parallel "alternative pathway" that may serve as metabolic sensor and energy regulator. Indeed, these mice showed residual nerve responses and behavioral attraction to sugars and oligosaccharides but not to artificial sweeteners. In analogy to pancreatic β cells, such alternative mechanism, to sense glucose in sweet-sensitive taste cells, might involve glucose transporters and K_ATP channels. Their activation may induce depolarization-dependent Ca²⁺ signals and release of GLP-1, which binds to its receptors on intragemmal nerve fibers. Via unknown neuronal and/or endocrine mechanisms, this pathway may contribute to both, behavioral attraction and/or induction of cephalic-phase insulin release upon oral sweet stimulation. Here, we critically review the evidence for a parallel sweet-sensitive pathway, involved signaling mechanisms, neural processing, interactions with endocrine hormonal mechanisms, and its sensitivity to different stimuli. Finally, we propose its physiological role in detecting the energy content of food and preparing for digestion.

Feed intake patterns nor growth rates of pigs are affected by dietary resistant starch, despite marked differences in digestion

Current feed evaluation systems often assume that fermented starch (i.e. resistant starch (RS)) yields less energy than digested starch. However, growth rates of pigs fed low and high RS diets are often the same when feed is available ad libitum. This may be explained by its effect on digestive processes changing feeding behavior, and consequently energy utilization. This study aims to investigate the effect of RS on nutrient digestion and digesta passage rate in pigs, in combination with its effect on feeding behavior and growth performance under ad libitum conditions. In experiment 1, 20 male pigs (40 ± 2.82 kg) were fed diets containing either 50% waxy maize starch (low in RS (LRS)) or high-amylose maize starch (high in RS (HRS)), and soluble and insoluble indigestible markers. After 14 days of adaptation to the diets, pigs were fed hourly to reach steady state (6 h), dissected, and digesta were collected from eight segments. From the collected samples, nutrient digestion and passage rate of the solid and liquid digesta fraction were determined. In experiment 2, 288 pigs (80 ± 0.48 kg; sex ratio per pen 1 : 1; boar : gilt) were housed in groups of 6. Pigs were ad libitum-fed one of the experimental diets, and slaughtered at approximately 115 kg. Feed intake, growth and carcass parameters were measured. Ileal starch digestibility was greater for LRS-fed than for HRS-fed pigs (98.0% v. 74.0%; P < 0.001), where the additional undigested starch in HRS-fed pigs was fermented in the large intestine. No effects of RS on digesta passage rate of the solid or liquid digesta fraction and on feeding behavior were observed. Growth rate and feed intake did not differ between diets, whereas feed efficiency of HRS-fed pigs was 1%-unit higher than that of LRS-fed pigs (P = 0.041). The efficiency of feed used for carcass gain did not differ between diets indicating that the difference in feed efficiency was determined by the non-carcass fraction. Despite a 30% greater RS intake (of total starch) with HRS than with LRS, carcass gain and feed efficiency used for carcass gain were unaffected. RS did not affect digesta passage rate nor feeding behavior suggesting that the difference in energy intake between fermented and digested starch is compensated for post-absorptively. Our results indicate that the net energy value of fermented starch currently used in pig feed evaluation systems is underestimated and should be reconsidered.

Assessing the effect of starch digestion characteristics on ileal brake activation in broiler chickens

The objective of this research was to evaluate activation of the ileal brake in broiler chickens using diets containing semi-purified wheat (WS; rapidly and highly digested) and pea (PS; slowly and poorly digested) starch. Diets were formulated to contain six WS:PS ratios (100:0, 80:20, 60:40, 40:60, 20:80, 0:100) and each starch ratio was fed to 236 Ross 308 male broilers housed in 4 litter floor pens. At 28 d of age, the effect of PS concentration was assessed on starch digestion, digestive tract morphology, and digesta pH and short-chain fatty acid (SCFA) concentration. Glucagon-like peptide-1 (GLP-1) and peptide tyrosine-tyrosine (PYY) status were assessed in serum (ELISA) and via gene expression in jejunal and ileal tissue (proglucagon for GLP-1). Data were analyzed using regression analyses, and significance was accepted at P ≤ 0.05. Increasing dietary PS resulted in reduced starch digestibility in the small intestine, but had no effect in the colon. Crop content pH responded quadratically to PS level with an estimated minimum at 55% PS. Total SCFA increased linearly in the crop with PS level, but changed in a quadratic fashion in the ileum (estimated maximum at 62% PS). Ceacal SCFA concentrations were highest for the 80 and 100% PS levels. The relative empty weight (crop, small intestine, colon), length (small intestine) and content (crop jejunum, Ileum) of digestive tract sections increased linearly with increasing PS concentration. Dietary treatment did not affect serum GLP-1 or PYY or small intestine transcript abundance. In conclusion, feeding PS increased the presence of L-cell activators (starch, SCFA) and increased trophic development and content of the digestive tract, suggestive of L-cell activation. However, no direct evidence of ileal brake activation was found by measuring venous blood levels of GLP-1 or PYY or corresponding gene expression in small intestine tissue.

Pigs Ferment Enzymatically Digestible Starch when it Is Substituted for Resistant Starch

BACKGROUND

Feeding behavior is controlled by satiety mechanisms, which are affected by the extent of starch digestion, and thus resistant starch (RS) intake. Alterations in feeding behavior to changes in RS intake may depend on the adaptation of processes involved when shifting from starch digestion to fermentation or vice versa.

OBJECTIVES

The aim of this study was to investigate how growing pigs adapt their feeding behavior in response to increasing and decreasing dietary RS concentrations.

METHODS

Thirty-six groups of 6 pigs (25.4 ± 2.8 kg; Hypor Libra × Hypor Maxter; male:female, 1:1) were fed diets containing 50% high-amylose maize starch (high RS; HRS) or waxy maize starch (low RS; LRS). Over 28 d, diets were exchanged following a 5-step titration (25% per step) that was executed in the upward (LH) or downward direction (HL). Twelve groups received a control diet to correct for changes over time. Individual feeding behavior and total tract starch digestion and fermentation were evaluated. The response in each parameter to increasing dietary HRS inclusion was estimated through the use of linear regression procedures, and tested for titration direction and sex effects.

RESULTS

Complete substitution of LRS with HRS increased the proportion of starch fermented, which was greater in LH pigs than in HL pigs (17.6% compared with 8.18%; P < 0.001), and decreased the feed intake (106 g/d; P = 0.021) and meal size (12.6 g; P < 0.001) of LH pigs, but not of HL pigs. In LH pigs, the size of the starch fermentation response positively correlated with the size of the feed intake response (r = 0.90, P < 0.001).

CONCLUSIONS

The attenuated response in starch fermentation in HL pigs indicates that pigs adapt more slowly to dietary supply of digestible starch than to RS, consequently resulting in fermentation of enzymatically digestible starch. Feed intake and feeding behavior only changed in pigs poorly adapting to RS, indicating that adequacy of adaptation, rather than RS itself, drives feed intake. These findings stress the importance of diet history for nutrient digestion and feeding behavior.

The incretin system in healthy humans: The role of GIP and GLP-1

The incretin effect, the amplification of insulin secretion occurring when glucose is taken in orally as compared to infused intravenously, is one of the factors that help the body to tolerate carbohydrate/glucose ingestion. These include 1) amount and type of carbohydrates; 2) gastric emptying rate; 3) digestion and absorption of the carbohydrates; 4) secretion and effect of the incretin hormones; 5) disposition of absorbed nutrients/glucose. The incretin effect can also be viewed as the fraction of the ingested glucose load handled via gastrointestinal mechanisms (including the incretin effect); it is calculated by comparison of the amount of glucose required to copy, by intravenous infusion, the oral load. Typically, for 75 g of oral glucose, about 25 g are required. This means that the GastroIntestinal Glucose Disposal (GIGD) is 66%. Both the GIGD and the incretin effect depend on the amount of glucose ingested: for higher doses the GIGD may amount to 80%, which shows that this effect is a major contributor to glucose tolerance. The main mechanism behind it is stimulation of insulin secretion by a proportional secretion of the insulinotropic hormones GIP and GLP-1. Recently it has become possible to estimate their contributions in healthy humans using specific and potent receptor antagonists. Both hormones act to improve glucose tolerance (i.e. the antagonists impair tolerance) and their effects are additive. GIP seems to be quantitatively the most important, particularly regarding insulin secretion, whereas the action of GLP-1 is mainly displayed via inhibition of glucagon secretion.

Abnormal absorptive colonic motor activity in germ-free mice is rectified by butyrate, an effect possibly mediated by mucosal serotonin

The role of short-chain fatty acids (SCFAs) in the control of colonic motility is controversial. Germ-free (GF) mice are unable to produce these metabolites and serve as a model to study how their absence affects colonic motility. GF transit is slower than controls, and colonization of these mice improves transit and serotonin [5-hydroxytryptamine (5-HT)] levels. Our aim was to determine the role SCFAs play in improving transit and whether this is dependent on mucosal 5-HT signaling. Motility was assessed in GF mice via spatiotemporal mapping. First, motor patterns in the whole colon were measured ex vivo with or without luminal SCFA, and outflow from the colon was recorded to quantify outflow caused by individual propulsive contractions. Second, artificial fecal pellet propulsion was measured. Motility was then assessed in tryptophan hydroxylase-1 (TPH1) knockout (KO) mice, devoid of mucosal 5-HT, with phosphate buffer, butyrate, or propionate intraluminal perfusion. GF mice exhibited a lower proportion of propulsive contractions, lower volume of outflow/contraction, slower velocity of contractions, and slower propulsion of fecal pellets compared with controls. SCFAs changed motility patterns to that of controls in all parameters. Butyrate administration increased the proportion of propulsive contractions in controls yet failed to in TPH1 KO mice. Propionate inhibited propulsive contractions in all mice. Our results reveal significant abnormalities in the propulsive nature of colonic motor patterns in GF mice, explaining the decreased transit time in in vivo studies. We show that butyrate but not propionate activates propulsive motility and that this may require mucosal 5-HT. NEW & NOTEWORTHY Understanding the role that the microbiota play in governing the physiology of colonic motility is lacking. Here, we offer for the first time, to our knowledge, a detailed analysis of colonic motor patterns and pellet propulsion using spatiotemporal mapping in the absence of microbiota. We show a striking difference in germ-free and control phenotypes and attribute this to a lack of fermentation-produced short-chain fatty acid. We then show that butyrate but not propionate can restore motility and that the butyrate effect likely requires mucosal 5-hydroxytryptamine.

Implication of neurohormonal-coupled mechanisms of gastric emptying and pancreatic secretory function in diabetic gastroparesis

Recently, diabetic gastroparesis (DGP) has received much attention as its prevalence is increasing in a dramatic fashion and management of patients with DGP represents a challenge in the clinical practice due to the limited therapeutic options. DGP highlights an interrelationship between the gastric emptying and pancreatic secretory function that regulate a wide range of digestive and metabolic functions, respectively. It well documented that both gastric emptying and pancreatic secretion are under delicate control by multiple neurohormonal mechanisms including extrinsic parasympathetic pathways and gastrointestinal (GI) hormones. Interestingly, the latter released in response to various determinants that related to the rate and quality of gastric emptying. Others and we have provided strong evidence that the central autonomic nuclei send a dual output (excitatory and inhibitory) to the stomach and the pancreas in response to a variety of hormonal signals from the abdominal viscera. Most of these hormones released upon gastric emptying to provide feedback, and control this process and simultaneously regulate pancreatic secretion and postprandial glycemia. These findings emphasize an important link between gastric emptying and pancreatic secretion and its role in maintaining homeostatic processes within the GI tract. The present review deals with the neurohormonal-coupled mechanisms of gastric emptying and pancreatic secretory function that implicated in DGP and this provides new insights in our understanding of the pathophysiology of DGP. This also enhances the process of identifying potential therapeutic targets to treat DGP and limit the complications of current management practices.

Incretin hormones: Their role in health and disease

Incretin hormones are gut peptides that are secreted after nutrient intake and stimulate insulin secretion together with hyperglycaemia. GIP (glucose-dependent insulinotropic polypeptide) und GLP-1 (glucagon-like peptide-1) are the known incretin hormones from the upper (GIP, K cells) and lower (GLP-1, L cells) gut. Together, they are responsible for the incretin effect: a two- to three-fold higher insulin secretory response to oral as compared to intravenous glucose administration. In subjects with type 2 diabetes, this incretin effect is diminished or no longer present. This is the consequence of a substantially reduced effectiveness of GIP on the diabetic endocrine pancreas, and of the negligible physiological role of GLP-1 in mediating the incretin effect even in healthy subjects. However, the insulinotropic and glucagonostatic effects of GLP-1 are preserved in subjects with type 2 diabetes to the degree that pharmacological stimulation of GLP-1 receptors significantly reduces plasma glucose and improves glycaemic control. Thus, it has become a parent compound of incretin-based glucose-lowering medications (GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase-4 or DPP-4). GLP-1, in addition, has multiple effects on various organ systems. Most relevant are a reduction in appetite and food intake, leading to weight loss in the long term. Since GLP-1 secretion from the gut seems to be impaired in obese subjects, this may even indicate a role in the pathophysiology of obesity. Along these lines, an increased secretion of GLP-1 induced by delivering nutrients to lower parts of the small intestines (rich in L cells) may be one factor (among others like peptide YY) explaining weight loss and improvements in glycaemic control after bariatric surgery (e.g., Roux-en-Y gastric bypass). GIP and GLP-1, originally characterized as incretin hormones, have additional effects in adipose cells, bone, and the cardiovascular system. Especially, the latter have received attention based on recent findings that GLP-1 receptor agonists such as liraglutide reduce cardiovascular events and prolong life in high-risk patients with type 2 diabetes. Thus, incretin hormones have an important role physiologically, namely they are involved in the pathophysiology of obesity and type 2 diabetes, and they have therapeutic potential that can be traced to well-characterized physiological effects.

The nutritional property of endosperm starch and its contribution to the health benefits of whole grain foods

Purported health benefits of whole grain foods in lowering risk of obesity, type 2 diabetes, cardiovascular disease, and cancer are supported by epidemiological studies and scientific researches. Bioactive components including dietary fibers, phytochemicals, and various micronutrients present in the bran and germ are commonly considered as the basis for such benefits. Endosperm starch, as the major constituent of whole grains providing glucose to the body, has been less investigated regarding its nutritional property and contribution to the value of whole grain foods. Nutritional quality of starch is associated with its rate of digestion and glucose absorption. In whole grain foods, starch digestion and glucose delivery may vary depending on the form in which the food is delivered, some with starch being rapidly and others slowly digested. Furthermore, there are other inherent factors in whole grain products, such as phenolic compounds and dietary fibers, that may moderate glycemic profiles. A good understanding of the nutritional properties of whole grain starch is important to the development of food processing technologies to maximize their health benefits.

Effect of Liraglutide Treatment on Jejunostomy Output in Patients With Short Bowel Syndrome: An Open-Label Pilot Study

BACKGROUND

An impaired hormonal "ileo-colonic brake" may contribute to rapid gastric emptying, gastric hypersecretion, high ostomy losses, and the need for parenteral support in end-jejunostomy short bowel syndrome (SBS) patients with intestinal failure (IF). Liraglutide, a glucagon-like peptide 1 receptor agonist, may reduce gastric hypersecretion and dampen gastric emptying, thereby improving conditions for intestinal absorption.

MATERIALS AND METHODS

In an 8-week, open-label pilot study, liraglutide was given subcutaneously once daily to 8 end-jejunostomy patients, aged 63.4 ± 10.9 years (mean ± SD) and with small bowel lengths of 110 ± 66 cm. The 72-hour metabolic balance studies were performed before and at the end of treatment. Food intake was unrestricted. Oral fluid intake and parenteral support volume were kept constant. The primary end point was change in the ostomy wet weight output.

RESULTS

Liraglutide reduced ostomy wet weight output by 474 ± 563 g/d from 3249 ± 1352 to 2775 ± 1187 g/d (P = .049, Student t test). Intestinal wet weight absorption tended to increase by 464 ± 557 g/d (P = .05), as did urine production by 765 ± 759 g/d (P = .02). Intestinal energy absorption improved by 902 ± 882 kJ/d (P = .02).

CONCLUSION

Liraglutide reduced ostomy wet weight output in end-jejunostomy patients with SBS-IF and increased their intestinal wet weight and energy absorption. If larger, randomized, placebo-controlled studies confirm these effects, it adds to the hypothesis that many ileo-colonic brake hormones in conjunction may be involved in the process of intestinal adaptation. By identification of key hormones and addressing their potential synergistic effects, better treatments may be provided to patients with SBS-IF. This trial was registered at clinicaltrialsregister.eu as 2013-005499-16.

Impact of Metabolic Hormones Secreted in Human Breast Milk on Nutritional Programming in Childhood Obesity

Obesity is the most common metabolic disease whose prevalence is increasing worldwide. This condition is considered a serious public health problem due to associated comorbidities such as diabetes mellitus and hypertension. Perinatal morbidity related to obesity does not end with birth; this continues affecting the mother/infant binomial and could negatively impact on metabolism during early infant nutrition. Nutrition in early stages of growth may be essential in the development of obesity in adulthood, supporting the concept of "nutritional programming". For this reason, breastfeeding may play an important role in this programming. Breast milk is the most recommended feeding for the newborn due to the provided benefits such as protection against obesity and diabetes. Health benefits are based on milk components such as bioactive molecules, specifically hormones involved in the regulation of food intake. Identification of these molecules has increased in recent years but its action has not been fully clarified. Hormones such as leptin, insulin, ghrelin, adiponectin, resistin, obestatin and insulin-like growth factor-1 copeptin, apelin, and nesfatin, among others, have been identified in the milk of normal-weight women and may influence the energy balance because they can activate orexigenic or anorexigenic pathways depending on energy requirements and body stores. It is important to emphasize that, although the number of biomolecules identified in milk involved in regulating food intake has increased considerably, there is a lack of studies aimed at elucidating the effect these hormones may have on metabolism and development of the newborn. Therefore, we present a state-of-the-art review regarding bioactive compounds such as hormones secreted in breast milk and their possible impact on nutritional programming in the infant, analyzing their functions in appetite regulation.

Effects of GW002, a novel recombinant human glucagon-like peptide-1 (GLP-1) analog fusion protein, on CHO recombinant cells and BKS-db mice

AIMS

GLP-1-based strategies have many advantages in treatment of type 2 diabetes mellitus (T2DM), but native GLP-1 has a short half-life in the circulation, which limits its clinical application. The purpose of this study was to evaluate the effects of GW002, a novel recombinant GLP-1 analog fusion protein produced by linking the human GLP-1 analog C-terminus to the N-terminus of human serum albumin via a linker, in vitro and in BKS-db mice.

METHODS

To determine whether GW002 can activate the GLP-1 receptor in cells, the level of luciferase expression was evaluated in vitro. In vivo, body weight, food intake, non-fasting and fasting blood glucose, oral glucose tolerance test, blood glucose and insulin levels, liver histology, liver function parameters and antibody levels in BKS-db mice were investigated to evaluate the effects of GW002. Albiglutide was chosen as a positive comparator.

RESULTS

Cyclic adenosine monophosphate levels were increased in a dose-dependent manner in cells. In vivo studies demonstrated that GW002 lowers non-fasting and fasting blood glucose levels and improves glucose tolerance and insulin secretion in BKS-db mice. The degree of hepatic steatosis and hepatic biochemical indexes was also decreased. In this study, the mice body weight was not reduced significantly.

CONCLUSIONS

The above results showed that the efficacy of GW002 in BKS-db mice displayed a significant hypoglycemic effect, which indicated that GW002 might be a potential candidate for the treatment of T2DM.

Sugars, Sweet Taste Receptors, and Brain Responses

Sweet taste receptors are composed of a heterodimer of taste 1 receptor member 2 (T1R2) and taste 1 receptor member 3 (T1R3). Accumulating evidence shows that sweet taste receptors are ubiquitous throughout the body, including in the gastrointestinal tract as well as the hypothalamus. These sweet taste receptors are heavily involved in nutrient sensing, monitoring changes in energy stores, and triggering metabolic and behavioral responses to maintain energy balance. Not surprisingly, these pathways are heavily regulated by external and internal factors. Dysfunction in one or more of these pathways may be important in the pathogenesis of common diseases, such as obesity and type 2 diabetes mellitus.

Effect of GLP-1 receptor agonist on gastrointestinal tract motility and residue rates as evaluated by capsule endoscopy

AIM

This study evaluated the effects of a glucagon-like peptide-1 receptor agonist on gastrointestinal (GI) tract motility and residue rates by examining GI transit time and lumen using capsule endoscopy.

MATERIAL AND METHODS

GI motility and lumen were assessed by capsule endoscopy before and after liraglutide administration in 14 patients with type 2 diabetes mellitus (T2DM).

RESULTS

Gastric transit time in the group with diabetic neuropathy (DN) was 1:12:36±1:04:30h before liraglutide administration and 0:48:40±0:32:52h after administration (nonsignificant difference, P=0.19). Gastric transit time in the non-DN group was 1:01:30±0:52:59h before administration and 2:33:29±1:37:24h after administration (significant increase, P=0.03). Duodenal and small intestine transit time in the DN group was 4:10:34±0:25:54h before and 6:38:42±3:52:42h after administration (not significant, P=0.09) and, in the non-DN group, 3:51:03±0:53:47h before and 6:45:31±2:41:36h after administration (significant increase, P=0.03). The GI residue rate in the DN group was 32.1±24% before administration and 90.0±9.1% after administration (significant increase, P<0.001), and increased in all patients; in the non-DN group, it was 32.1±35.3% before and 78.3±23.9% after administration (significant increase, P<0.001), and also increased in all patients.

CONCLUSION

Liraglutide causes delayed gastric emptying and inhibits duodenal and small intestine motility. However, these GI movement-inhibiting effects may be decreased or absent in patients with DN-associated dysautonomia.

Gastrointestinal actions of glucagon-like peptide-1-based therapies: glycaemic control beyond the pancreas

The gastrointestinal hormone glucagon-like peptide-1 (GLP-1) lowers postprandial glucose concentrations by regulating pancreatic islet-cell function, with stimulation of glucose-dependent insulin and suppression of glucagon secretion. In addition to endocrine pancreatic effects, mounting evidence suggests that several gastrointestinal actions of GLP-1 are at least as important for glucose-lowering. GLP-1 reduces gastric emptying rate and small bowel motility, thereby delaying glucose absorption and decreasing postprandial glucose excursions. Furthermore, it has been suggested that GLP-1 directly stimulates hepatic glucose uptake, and suppresses hepatic glucose production, thereby adding to reduction of fasting and postprandial glucose levels. GLP-1 receptor agonists, which mimic the effects of GLP-1, have been developed for the treatment of type 2 diabetes. Based on their pharmacokinetic profile, GLP-1 receptor agonists can be broadly categorized as short- or long-acting, with each having unique islet-cell and gastrointestinal effects that lower glucose levels. Short-acting agonists predominantly lower postprandial glucose excursions, by inhibiting gastric emptying and intestinal glucose uptake, with little effect on insulin secretion. By contrast, long-acting agonists mainly reduce fasting glucose levels, predominantly by increased insulin and reduced glucagon secretion, with potential additional direct inhibitory effects on hepatic glucose production. Understanding these pharmacokinetic and pharmacodynamic differences may allow personalized antihyperglycaemic therapy in type 2 diabetes. In addition, it may provide the rationale to explore treatment in patients with no or little residual β-cell function.

Expression of the Bitter Taste Receptor, T2R38, in Enteroendocrine Cells of the Colonic Mucosa of Overweight/Obese vs. Lean Subjects

Bitter taste receptors (T2Rs) are expressed in the mammalian gastrointestinal mucosa. In the mouse colon, T2R138 is localized to enteroendocrine cells and is upregulated by long-term high fat diet that induces obesity. The aims of this study were to test whether T2R38 expression is altered in overweight/obese (OW/OB) compared to normal weight (NW) subjects and characterize the cell types expressing T2R38, the human counterpart of mouse T2R138, in human colon. Colonic mucosal biopsies were obtained during colonoscopy from 35 healthy subjects (20 OW/OB and 15 NW) and processed for quantitative RT-PCR and immunohistochemistry using antibodies to T2R38, chromogranin A (CgA), glucagon like peptide-1 (GLP-1), cholecystokinin (CCK), or peptide YY (PYY). T2R38 mRNA levels in the colonic mucosa of OW/OB were increased (> 2 fold) compared to NW subjects but did not reach statistical significance (P = 0.06). However, the number of T2R38 immunoreactive (IR) cells was significantly increased in OW/OB vs. NW subjects (P = 0.01) and was significantly correlated with BMI values (r = 0.7557; P = 0.001). In both OW/OB and NW individuals, all T2R38-IR cells contained CgA-IR supporting they are enteroendocrine. In both groups, T2R38-IR colocalized with CCK-, GLP1- or PYY-IR. The overall CgA-IR cell population was comparable in OW/OB and NW individuals. This study shows that T2R38 is expressed in distinct populations of enteroendocrine cells in the human colonic mucosa and supports T2R38 upregulation in OW/OB subjects. T2R38 might mediate host functional responses to increased energy balance and intraluminal changes occurring in obesity, which could involve peptide release from enteroendocrine cells.

Dumping Syndrome: A Review of the Current Concepts of Pathophysiology, Diagnosis, and Treatment

Gastric surgery has long been known to be a cause of dumping syndrome (DS). However, the increasing incidence of gastric bypass surgery, as well as reports of DS unrelated to previous gastric surgeries, has increased the importance of understanding DS in recent years. DS is due to the gastrointestinal response to voluminous and hyperosmolar chyme that is rapidly expelled from the stomach into the small intestine. This response involves neural and hormonal mechanisms. This review encompasses the symptoms, diagnosis, and treatment approaches of DS and also focuses on the current research status of the pathophysiology of DS.

Psyllium fiber improves glycemic control proportional to loss of glycemic control: a meta-analysis of data in euglycemic subjects, patients at risk of type 2 diabetes mellitus, and patients being treated for type 2 diabetes mellitus

BACKGROUND

A number of health benefits are associated with intake of soluble, viscous, gel-forming fibers, including reduced serum cholesterol and the attenuation of postprandial glucose excursions.

OBJECTIVE

We assess the effects of psyllium, which is a soluble, gel-forming, nonfermented fiber supplement, on glycemic control in patients who were being treated for type 2 diabetes mellitus (T2DM) and in patients who were at risk of developing T2DM.

DESIGN

A comprehensive search was performed of available published literature (Scopus scientific database) and clinical records stored by Procter & Gamble with the use of key search terms to identify clinical studies that assessed the glycemic effects of psyllium in nondiabetic, pre-T2DM, and T2DM patients.

RESULTS

We identified 35 randomized, controlled, clinical studies that spanned 3 decades and 3 continents. These data were assessed in 8 meta-analyses. In patients with T2DM, multiweek studies (psyllium dosed before meals) showed significant improvement in both the fasting blood glucose (FBG) concentration (-37.0 mg/dL; P < 0.001) and glycated hemoglobin (HbA1c) [-0.97% (-10.6 mmol/mol); P = 0.048]. Glycemic effects were proportional to baseline FBG; no significant glucose lowering was observed in euglycemic subjects, a modest improvement was observed in subjects with pre-T2DM, and the greatest improvement was observed in subjects who were being treated for T2DM.

CONCLUSIONS

These data indicate that psyllium would be an effective addition to a lifestyle-intervention program. The degree of psyllium's glycemic benefit was commensurate with the loss of glycemic control. Because the greatest effect was seen in patients who were being treated for T2DM, additional studies are needed to determine how best to incorporate psyllium into existing prevention and treatment algorithms with concomitant hypoglycemic medications.

GLP-1: a mediator of the beneficial metabolic effects of bariatric surgery?

There has been increasing interest in the role that gut hormones may play in contributing to the physiological changes produced by certain bariatric procedures, such as Roux-en-Y gastric bypass and sleeve gastrectomy. Here, we review the evidence implicating one such gut hormone, glucagon-like peptide-1, as a mediator of the metabolic benefits of these two procedures.

Sleeve gastrectomy effects on hunger, satiation, and gastrointestinal hormone and motility responses after a liquid meal test

BACKGROUND

The relation between hunger, satiation, and integrated gastrointestinal motility and hormonal responses in morbidly obese patients after sleeve gastrectomy has not been determined.

OBJECTIVE

The objective was to assess the effects of sleeve gastrectomy on hunger, satiation, gastric and gallbladder motility, and gastrointestinal hormone response after a liquid meal test.

DESIGN

Three groups were studied: morbidly obese patients (n = 16), morbidly obese patients who had had sleeve gastrectomy (n = 8), and nonobese patients (n = 16). The participants fasted for 10 h and then consumed a 200-mL liquid meal (400 kcal + 1.5 g paracetamol). Fasting and postprandial hunger, satiation, hormone concentrations, and gastric and gallbladder emptying were measured several times over 4 h.

RESULTS

No differences were observed in hunger and satiation curves between morbidly obese and nonobese groups; however, sleeve gastrectomy patients were less hungry and more satiated than the other groups. Antrum area during fasting in morbidly obese patients was statistically significant larger than in the nonobese and sleeve gastrectomy groups. Gastric emptying was accelerated in the sleeve gastrectomy group compared with the other 2 groups (which had very similar results). Gallbladder emptying was similar in the 3 groups. Sleeve gastrectomy patients showed the lowest ghrelin concentrations and higher early postprandial cholecystokinin and glucagon-like peptide 1 peaks than did the other participants. This group also showed an improved insulin resistance pattern compared with morbidly obese patients.

CONCLUSIONS

Sleeve gastrectomy seems to be associated with profound changes in gastrointestinal physiology that contribute to reducing hunger and increasing sensations of satiation. These changes include accelerated gastric emptying, enhanced postprandial cholecystokinin and glucagon-like peptide 1 concentrations, and reduced ghrelin release, which together may help patients lose weight and improve their glucose metabolism after surgery. This trial was registered at clinicaltrials.gov as NCT02414893.

NUTRALYS(®) pea protein: characterization of in vitro gastric digestion and in vivo gastrointestinal peptide responses relevant to satiety

BACKGROUND

Pea protein (from Pisum sativum) is under consideration as a sustainable, satiety-inducing food ingredient.

OBJECTIVE

In the current study, pea-protein-induced physiological signals relevant to satiety were characterized in vitro via gastric digestion kinetics and in vivo by monitoring post-meal gastrointestinal hormonal responses in rats.

DESIGN

Under in vitro simulated gastric conditions, the digestion of NUTRALYS(®) pea protein was compared to that of two dairy proteins, slow-digestible casein and fast-digestible whey. In vivo, blood glucose and gastrointestinal hormonal (insulin, ghrelin, cholecystokinin [CCK], glucagon-like peptide 1 [GLP-1], and peptide YY [PYY]) responses were monitored in nine male Wistar rats following isocaloric (11 kcal) meals containing 35 energy% of either NUTRALYS(®) pea protein, whey protein, or carbohydrate (non-protein).

RESULTS

In vitro, pea protein transiently aggregated into particles, whereas casein formed a more enduring protein network and whey protein remained dissolved. Pea-protein particle size ranged from 50 to 500 µm, well below the 2 mm threshold for gastric retention in humans. In vivo, pea-protein and whey-protein meals induced comparable responses for CCK, GLP-1, and PYY, that is, the anorexigenic hormones. Pea protein induced weaker initial, but equal 3-h integrated ghrelin and insulin responses than whey protein, possibly due to the slower gastric breakdown of pea protein observed in vitro. Two hours after meals, CCK levels were more elevated in the case of protein meals compared to that of non-protein meals.

CONCLUSIONS

These results indicate that 1) pea protein transiently aggregates in the stomach and has an intermediately fast intestinal bioavailability in between that of whey and casein; 2) pea-protein- and dairy-protein-containing meals were comparably efficacious in triggering gastrointestinal satiety signals.

Evidence-Based Approach to Fiber Supplements and Clinically Meaningful Health Benefits, Part 1: What to Look for and How to Recommend an Effective Fiber Therapy

Dietary fiber that is intrinsic and intact in fiber-rich foods (eg, fruits, vegetables, legumes, whole grains) is widely recognized to have beneficial effects on health when consumed at recommended levels (25 g/d for adult women, 38 g/d for adult men). Most (90%) of the US population does not consume this level of dietary fiber, averaging only 15 g/d. In an attempt to bridge this “fiber gap,” many consumers are turning to fiber supplements, which are typically isolated from a single source. Fiber supplements cannot be presumed to provide the health benefits that are associated with dietary fiber from whole foods. Of the fiber supplements on the market today, only a minority possess the physical characteristics that underlie the mechanisms driving clinically meaningful health benefits. The first part (current issue) of this 2-part series will focus on the 4 main characteristics of fiber supplements that drive clinical efficacy (solubility, degree/rate of fermentation, viscosity, and gel formation), the 4 clinically meaningful designations that identify which health benefits are associated with specific fibers, and the gel-dependent mechanisms in the small bowel that drive specific health benefits (eg, cholesterol lowering, improved glycemic control). The second part (next issue) of this 2-part series will focus on the effects of fiber supplements in the large bowel, including the 2 mechanisms by which fiber prevents/relieves constipation (insoluble mechanical irritant and soluble gel-dependent water-holding capacity), the gel-dependent mechanism for attenuating diarrhea and normalizing stool form in irritable bowel syndrome, and the combined large bowel/small bowel fiber effects for weight loss/maintenance. The second part will also discuss how processing for marketed products can attenuate efficacy, why fiber supplements can cause gastrointestinal symptoms, and how to avoid symptoms for better long-term compliance.

Wholegrain barley β-glucan fermentation does not improve glucose tolerance in rats fed a high-fat diet

Fermentation of oat and barley β-glucans is believed to mediate in part their metabolic health benefits, but the exact mechanisms remain unclear. In this study, we sought to test the hypothesis that barley β-glucan fermentation raises circulating incretin hormone levels and improves glucose control, independent of other grain components. Male Sprague-Dawley rats (n = 30) were fed a high-fat diet for 6 weeks and then randomly allocated to 1 of 3 dietary treatments for 2 weeks. The low- (LBG, 0% β-glucan) and high- (HBG, 3% β-glucan) β-glucan diets contained 25% wholegrain barley and similar levels of insoluble dietary fiber, available carbohydrate, and energy. A low-fiber diet (basal) was included for comparison. Immediately prior to the dietary intervention, gastric emptying rate (using the (13)C-octanoic breath test) and postprandial glycemic response of each diet were determined. At the end of the study, circulating gut hormone levels were determined; and a glucose tolerance test was performed. The rats were then killed, and indices of cecal fermentation were assessed. Diet did not affect live weight; however, the HBG diet, compared to basal and LBG, reduced food intake, tended to slow gastric emptying, increased cecal digesta mass and individual and total short-chain fatty acid pools, and lowered digesta pH. In contrast, circulating levels of glucose, insulin, gastric-inhibitory peptide, and glucagon-like peptide-1, and glucose tolerance were unaffected by diet. In conclusion, wholegrain barley β-glucan suppressed feed intake and increased cecal fermentation but did not improve postprandial glucose control or insulin sensitivity.

GLP-1: benefits beyond pancreas

INTRODUCTION

Glucagon-like peptide 1 (GLP-1) is an intestinal hormone secreted after the ingestion of various nutrients. The main role of GLP-1 is to stimulate insulin secretion in a glucose-dependent manner. However, the expression of GLP-1 receptor was found to be expressed in a variety of tissues beyond pancreas such as lung, stomach, intestine, kidney, heart and brain. Beyond pancreas, a beneficial effect of GLP-1 on body weight reduction has been shown, suggesting its role for the treatment of obesity. In addition, GLP-1 has been demonstrated to reduce cardiovascular risk factors and to have a direct cardioprotective effect, fostering heart recovery after ischemic injury. Further, data from both experimental animal models and human studies have shown beneficial effect of GLP-1 on bone metabolism, either directly or indirectly on bone cells.

MATERIALS AND METHODS

We review here the recent findings of the extra-pancreatic effects of GLP-1 focusing on both basic and clinical studies, thus opening future perspectives to the use of GLP-1 analogs for the treatment of disease beyond type 2 diabetes.

CONCLUSION

Finally, the GLP-1 has been demonstrated to have a beneficial effect on both vascular, degenerative diseases of central nervous system and psoriasis.

Evaluation of intragastric vs intraperitoneal glucose tolerance tests in the evaluation of insulin resistance in a rodent model of burn injury and glucagon-like polypeptide-1 treatment

Evaluation of glucose tolerance in rodent models is usually performed after intraperitroneal administration of glucose (intraperitoneal glucose tolerance test [IPGTT]), whereas in humans the test is performed with oral glucose. Hyperglycemia is a major clinical manifestation of burn injury. Our previous studies using IPGTT have demonstrated burn injury-induced insulin resistance and the beneficial effects of glucagon-like polypeptide-1 (GLP-1) in improving insulin resistance. The goal of the present study is to compare the results of these two procedures under 1) burn injury-induced insulin resistance and 2) GLP-1 treatment after burn. Male CD rats were divided into three groups: sham burn, burn, and burn with GLP-1. Blood glucose and plasma insulin levels were measured during intragastric glucose tolerance test (IGGTT) on day 6 after 40% of full-thickness burn injury. The results were compared with our previous IPGTT. Blood glucose curves for IGGTT and IPGTT showed a similar pattern. However, IGGTT demonstrated a significant lower level of maximal blood glucose when compared with IPGTT. This was accompanied by higher peak insulin levels in sham burn and burn groups. In contrast, peak insulin levels of each burn with GLP-1 group were similar. 1) Both IPGTT and IGGTT demonstrated burn injury-induced insulin resistance and the efficacy of GLP-1 for reducing hyperglycemia after burn injury. 2) The observed differences in the plasma glucose and insulin levels between IGGTT and IPGTT suggest that endogenously produced GLP-1 during the IGGTT may play a role in ameliorating insulin resistance after burn injury.

Effects of sitagliptin on glycemia, incretin hormones, and antropyloroduodenal motility in response to intraduodenal glucose infusion in healthy lean and obese humans and patients with type 2 diabetes treated with or without metformin

The impact of variations in gastric emptying, which influence the magnitude of glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) secretion, on glucose lowering by dipeptidyl peptidase-4 (DPP-4) inhibitors is unclear. We evaluated responses to intraduodenal glucose infusion (60 g over 120 min [i.e., 2 kcal/min], a rate that predominantly stimulates GIP but not GLP-1) after sitagliptin versus control in 12 healthy lean, 12 obese, and 12 type 2 diabetic subjects taking metformin 850 mg b.i.d. versus placebo. As expected, sitagliptin augmented plasma-intact GIP substantially and intact GLP-1 modestly. Sitagliptin attenuated glycemic excursions in healthy lean and obese but not type 2 diabetic subjects, without affecting glucagon or energy intake. In contrast, metformin reduced fasting and glucose-stimulated glycemia, suppressed energy intake, and augmented total and intact GLP-1, total GIP, and glucagon in type 2 diabetic subjects, with no additional glucose lowering when combined with sitagliptin. These observations indicate that in type 2 diabetes, 1) the capacity of endogenous GIP to lower blood glucose is impaired; 2) the effect of DPP-4 inhibition on glycemia is likely to depend on adequate endogenous GLP-1 release, requiring gastric emptying >2 kcal/min; and 3) the action of metformin to lower blood glucose is not predominantly by way of the incretin axis.

Effects of exenatide on metabolic parameters/control in obese Japanese patients with type 2 diabetes

The effects of exenatide on glycemic control, lipid metabolism, blood pressure, and gastrointestinal symptoms were investigated in obese Japanese patients with type 2 diabetes mellitus. Twenty-six outpatients were enrolled and administered 5 μg of exenatide twice daily. If there was insufficient weight loss and/or insufficient improvement in glycemic control, the dose was increased to 10 μg twice daily. Follow-up was continued until the 12th week of administration. Hemoglobin A1c, glycoalbumin, fasting plasma glucose, body weight, fasting serum C-peptide, serum lipids, blood pressure, and pulse rate were measured before and after the observation period. In the initial phase of exenatide therapy, each patient received a diary to record gastrointestinal symptoms. During treatment with exenatide, hemoglobin A1c decreased significantly and serum C-peptide increased significantly. Body weight, low-density lipoprotein cholesterol, and systolic blood pressure decreased significantly. Nausea was the most frequent gastrointestinal symptom and occurred in 16 patients. Its onset was noted at a mean of 1.7 h after injection, the mean duration was 1.1 h, and it continued for a mean of 9.3 days after the initiation of administration. Patients with nausea showed a significant decrease in hemoglobin Alc, glycoalbumin, or body weight compared with those without nausea. These findings suggest that a more marked improvement in metabolic parameters by exenatide can be partly dependent on the manifestation of gastrointestinal symptoms.

Lipids, CHOs, proteins: can all macronutrients put a 'brake' on eating?

The gastrointestinal (GI) tract and specifically the most distal part of the small intestine, the ileum, has become a renewed focus of interest for mechanisms targeting appetite suppression. The 'ileal brake' is stimulated when energy-containing nutrients are delivered beyond the duodenum and jejunum and into the ileum, and is named for the feedback loop which slows or 'brakes' gastric emptying and duodeno-jejunal motility. More recently it has been hypothesized that the ileal brake also promotes secretion of satiety-enhancing GI peptides and suppresses hunger, placing a 'brake' on food intake. Postprandial delivery of macronutrients to the ileum, other than unavailable carbohydrates (CHO) which bypass absorption in the small intestine en route to fermentation in the large bowel, is an uncommon event and hence this brake mechanism is rarely activated following a meal. However the ability to place a 'brake' on food intake through delivery of protected nutrients to the ileum is both intriguing and challenging. This review summarizes the current clinical and experimental evidence for activation of the ileal brake by the three food macronutrients, with emphasis on eating behavior and satiety as well as GI function. While clinical studies have shown that exposure of the ileum to lipids, CHOs and proteins may activate GI components of the ileal brake, such as decreased gut motility, gastric emptying and secretion of GI peptides, there is less evidence as yet to support a causal relationship between activation of the GI brake by these macronutrients and the suppression of food intake. The predominance of evidence for an ileal brake on eating comes from lipid studies, where direct lipid infusion into the ileum suppresses both hunger and food intake. Outcomes from oral feeding studies are less conclusive with no evidence that 'protected' lipids have been successfully delivered into the ileum in order to trigger the brake. Whether CHO or protein may induce the ileal brake and suppress food intake has to date been little investigated, although both clearly have GI mediated effects. This review provides an overview of the mechanisms and mediators of activation of the ileal brake and assesses whether it may play an important role in appetite suppression.

Effects of a D-xylose preload with or without sitagliptin on gastric emptying, glucagon-like peptide-1, and postprandial glycemia in type 2 diabetes

OBJECTIVE

Macronutrient "preloads" can reduce postprandial glycemia by slowing gastric emptying and stimulating glucagon-like peptide-1 (GLP-1) secretion. An ideal preload would entail minimal additional energy intake and might be optimized by concurrent inhibition of dipeptidyl peptidase-4 (DPP-4). We evaluated the effects of a low-energy D-xylose preload, with or without sitagliptin, on gastric emptying, plasma intact GLP-1 concentrations, and postprandial glycemia in type 2 diabetes.

RESEARCH DESIGN AND METHODS

Twelve type 2 diabetic patients were studied on four occasions each. After 100 mg sitagliptin (S) or placebo (P) and an overnight fast, patients consumed a preload drink containing either 50 g D-xylose (X) or 80 mg sucralose (control [C]), followed after 40 min by a mashed potato meal labeled with (13)C-octanoate. Blood was sampled at intervals. Gastric emptying was determined.

RESULTS

Both peak blood glucose and the amplitude of glycemic excursion were lower after PX and SC than PC (P < 0.01 for each) and were lowest after SX (P < 0.05 for each), while overall blood glucose was lower after SX than PC (P < 0.05). The postprandial insulin-to-glucose ratio was attenuated (P < 0.05) and gastric emptying was slower (P < 0.01) after D-xylose, without any effect of sitagliptin. Plasma GLP-1 concentrations were higher after D-xylose than control only before the meal (P < 0.05) but were sustained postprandially when combined with sitagliptin (P < 0.05).

CONCLUSIONS

In type 2 diabetes, acute administration of a D-xylose preload reduces postprandial glycemia and enhances the effect of a DPP-4 inhibitor.