Gut motility and hormone changes after bariatric procedures

PURPOSE OF REVIEW

Metabolic and bariatric surgery (MBS) and endoscopic bariatric therapies (EBT) are being increasingly utilized for the management of obesity. They work through multiple mechanisms, including restriction, malabsorption, and changes in the gastrointestinal hormonal and motility.

RECENT FINDINGS

Roux-en-Y gastric bypass (RYGB) and laparoscopic sleeve gastrectomy (LSG) cause decrease in leptin, increase in GLP-1 and PYY, and variable changes in ghrelin (generally thought to decrease). RYGB and LSG lead to rapid gastric emptying, increase in small bowel motility, and possible decrease in colonic motility. Endoscopic sleeve gastroplasty (ESG) causes decrease in leptin and increase in GLP-1, ghrelin, and PYY; and delayed gastric motility.

SUMMARY

Understanding mechanisms of action for MBS and EBT is critical for optimal care of patients and will help in further refinement of these interventions.

Gut hormones and appetite regulation

PURPOSE OF REVIEW

Various gut hormones interact with the brain through delicate communication, thereby influencing appetite and subsequent changes in body weight. This review summarizes the effects of gut hormones on appetite, with a focus on recent research.

RECENT FINDINGS

Ghrelin is known as an orexigenic hormone, whereas glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), cholecystokinin (CCK), postprandial peptide YY (PYY), and oxyntomodulin (OXM) are known as anorexigenic hormones. Recent human studies have revealed that gut hormones act differently in various systems, including adipose tissue, beyond appetite and energy intake, and even involve in high-order thinking. Environmental factors including meal schedule, food contents and quality, type of exercise, and sleep deprivation also play a role in the influence of gut hormone on appetite, weight change, and obesity. Recently published studies have shown that retatrutide, a triple-agonist of GLP-1, GIP, and glucagon receptor, and orforglipron, a GLP-1 receptor partial agonist, are effective in weight loss and improving various metabolic parameters associated with obesity.

SUMMARY

Various gut hormones influence appetite, and several drugs targeting these receptors have been reported to exert positive effects on weight loss in humans. Given that diverse dietary and environmental factors affect the actions of gut hormones and appetite, there is a need for integrated and largescale long-term studies in this field.

Dietary L-Glu sensing by enteroendocrine cells adjusts food intake via modulating gut PYY/NPF secretion

Amino acid availability is monitored by animals to adapt to their nutritional environment. Beyond gustatory receptors and systemic amino acid sensors, enteroendocrine cells (EECs) are believed to directly percept dietary amino acids and secrete regulatory peptides. However, the cellular machinery underlying amino acid-sensing by EECs and how EEC-derived hormones modulate feeding behavior remain elusive. Here, by developing tools to specifically manipulate EECs, we find that Drosophila neuropeptide F (NPF) from mated female EECs inhibits feeding, similar to human PYY. Mechanistically, dietary L-Glutamate acts through the metabotropic glutamate receptor mGluR to decelerate calcium oscillations in EECs, thereby causing reduced NPF secretion via dense-core vesicles. Furthermore, two dopaminergic enteric neurons expressing NPFR perceive EEC-derived NPF and relay an anorexigenic signal to the brain. Thus, our findings provide mechanistic insights into how EECs assess food quality and identify a conserved mode of action that explains how gut NPF/PYY modulates food intake.

Satiety: a gut-brain-relationship

Many hormones act on the hypothalamus to control hunger and satiety through various pathways closely associated with several factors. When food is present in the gastro intestinal (GI) tract, enteroendocrine cells (EECs) emit satiety signals such as cholecystokinin (CCK), glucagon like peptide-1 (GLP-1) and peptide YY (PYY), which can then communicate with the vagus nerve to control food intake. More specifically, satiety has been shown to be particularly affected by the GLP-1 hormone and its receptor agonists that have lately been acknowledged as a promising way to reduce weight. In addition, there is increasing evidence that normal flora is also involved in the peripheral, central, and reward system that impact satiety. Moreover, neurologic pathways control satiety through neurotransmitters. In this review, we discuss the different roles of each of the GLP-1 hormone and its agonist, gut microbiomes, as well as neurotransmitters and their interconnected relation in the regulation of body's satiety homeostasis.

Diabetes Remission After LRYGBP With and Without Fundus Resection: a Randomized Clinical Trial

BACKGROUND

Glycemic control, after metabolic surgery, is achieved in two stages, initially with neuroendocrine alterations and in the long-term with sustainable weight loss. The resection of the gastric fundus, as the major site of ghrelin production, is probably related with optimized glucose regulation. The aim of the present study is to investigate whether the modification of laparoscopic Roux-en-Y gastric bypass (LRYGBP) with fundus resection offers superior glycemic control, compared to typical LRYGBP.

MATERIALS AND METHODS

Participants were 24 patients with body mass index (BMI) ≥40kg/m2 and type II diabetes mellitus (T2DM), who were randomly assigned to undergo LRYGBP and LRYGBP with fundus resection (LRYGBP+FR). Gastrointestinal (GI) hormones [ghrelin, glucagon-like-peptide-1 (GLP-1), peptide-YY (PYY)] and glycemic parameters (glucose, insulin, HbA1c, C-peptide, insulinogenic index, HOMA-IR) were measured preoperatively, at 6 and 12 months during an oral glucose tolerance test (OGTT).

RESULTS

Ninety-five percent of patients showed complete remission of T2DM after 12 months. LRYGBP+FR was not related with improved glycemic control, compared to LRYGBP. Ghrelin levels were not significantly reduced at 6 and 12 months after LRYGBP+FR. GLP-1 and PYY levels were remarkably increased postprandially in both groups at 6 and 12 months postoperatively (p<0.01). Patients who underwent LRYGBP+FR achieved a significantly lower BMI at 12 months in comparison to LRYGBP (p<0.05).

CONCLUSION

Fundus resection is not associated with improved glycemic regulation, compared to typical LRYGBP and the significant decrease in BMI after LRYGBP+FR has to be further confirmed with longer follow-up.

Gut epithelium modulates fungal pathogenesis

Specialized epithelium secretes an antifungal peptide.

Peptide YY: A Paneth cell antimicrobial peptide that maintains Candida gut commensalism

The mammalian gut secretes a family of multifunctional peptides that affect appetite, intestinal secretions, and motility whereas others regulate the microbiota. We have found that peptide YY (PYY1-36), but not endocrine PYY3-36, acts as an antimicrobial peptide (AMP) expressed by gut epithelial paneth cells (PC). PC-PYY is packaged into secretory granules and is secreted into and retained by surface mucus, which optimizes PC-PYY activity. Although PC-PYY shows some antibacterial activity, it displays selective antifungal activity against virulent Candida albicans hyphae-but not the yeast form. PC-PYY is a cationic molecule that interacts with the anionic surfaces of fungal hyphae to cause membrane disruption and transcriptional reprogramming that selects for the yeast phenotype. Hence, PC-PYY is an antifungal AMP that contributes to the maintenance of gut fungal commensalism.

The metabolic interplay between dietary carbohydrate and exercise and its role in acute appetite regulation in males: a randomized controlled study

An understanding of the metabolic determinants of postexercise appetite regulation would facilitate development of adjunctive therapeutics to suppress compensatory eating behaviours and improve the efficacy of exercise as a weight-loss treatment. Metabolic responses to acute exercise are, however, dependent on pre-exercise nutritional practices, including carbohydrate intake. We therefore aimed to determine the interactive effects of dietary carbohydrate and exercise on plasma hormonal and metabolite responses and explore mediators of exercise-induced changes in appetite regulation across nutritional states. In this randomized crossover study, participants completed four 120 min visits: (i) control (water) followed by rest; (ii) control followed by exercise (30 min at ∼75% of maximal oxygen uptake); (iii) carbohydrate (75 g maltodextrin) followed by rest; and (iv) carbohydrate followed by exercise. An ad libitum meal was provided at the end of each 120 min visit, with blood sample collection and appetite assessment performed at predefined intervals. We found that dietary carbohydrate and exercise exerted independent effects on the hormones glucagon-like peptide 1 (carbohydrate, 16.8 pmol/L; exercise, 7.4 pmol/L), ghrelin (carbohydrate, -48.8 pmol/L; exercise: -22.7 pmol/L) and glucagon (carbohydrate, 9.8 ng/L; exercise, 8.2 ng/L) that were linked to the generation of distinct plasma 1 H nuclear magnetic resonance metabolic phenotypes. These metabolic responses were associated with changes in appetite and energy intake, and plasma acetate and succinate were subsequently identified as potential novel mediators of exercise-induced appetite and energy intake responses. In summary, dietary carbohydrate and exercise independently influence gastrointestinal hormones associated with appetite regulation. Future work is warranted to probe the mechanistic importance of plasma acetate and succinate in postexercise appetite regulation. KEY POINTS: Carbohydrate and exercise independently influence key appetite-regulating hormones. Temporal changes in postexercise appetite are linked to acetate, lactate and peptide YY. Postexercise energy intake is associated with glucagon-like peptide 1 and succinate levels.

Biological and behavioral predictors of relative energy intake after acute exercise

Energy intake in the post-exercise state is highly variable and compensatory eating - i.e., (over-) compensation of the expended energy via increased post-exercise energy intake - occurs in some individuals but not others. We aimed to identify predictors of post-exercise energy intake and compensation. In a randomized crossover design, 57 healthy participants (21.7 [SD = 2.5] years; 23.7 [SD = 2.3] kg/m², 75% White, 54% female) completed two laboratory-based test-meals following (1) 45-min exercise and (2) 45-min rest (control). We assessed associations between biological (sex, body composition, appetite hormones) and behavioral (habitual exercise via prospective exercise log, eating behavior traits) characteristics at baseline and total energy intake, relative energy intake (intake - exercise expenditure), and the difference between post-exercise and post-rest intake. We found a differential impact of biological and behavioral characteristics on total post-exercise energy intake in men and women. In men, only fasting (baseline) concentrations of appetite-regulating hormones (peptide YY [PYY, β = 0.88, P < 0.001] and adiponectin [β = 0.66, P = 0.005] predicted total post-exercise energy intake, while in women, only habitual exercise (β = -0.44, P = 0.017) predicted total post-exercise energy intake. Predictors of relative intake were almost identical to those of total intake. The difference in energy intake between exercise and rest was associated with VO_2peak (β = -0.45, P = 0.020), fasting PYY (β = 0.53, P = 0.036), and fasting adiponectin (β = 0.57, P = 0.021) in men but not women (all P > 0.51). Our results show that biological and behavioral characteristics differentially affect total and relative post-exercise energy intake in men and women. This may help identify individuals who are more likely to compensate for the energy expended in exercise. Targeted countermeasures to prevent compensatory energy intake after exercise should take the demonstrated sex differences into account.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Beneficial metabolic effects of recurrent periods of beta-cell rest and stimulation using stable neuropeptide Y1 and glucagon-like peptide-1 receptor agonists

AIM

To examine whether sequential administration of (d-Arg³⁵ )-sea lamprey peptide tyrosine tyrosine (1-36) (SL-PYY) and the glucagon-like peptide-1 (GLP-1) mimetic, liraglutide, has beneficial effects in diabetes.

METHODS

SL-PYY is an enzymatically stable neuropeptide Y1 receptor (NPY1R) agonist known to induce pancreatic beta-cell rest and improve overall beta-cell health. We employed SL-PYY and liraglutide to induce appropriate recurrent periods of beta-cell rest and stimulation, to assess therapeutic benefits in high fat fed (HFF) mice with streptozotocin (STZ)-induced insulin deficiency, namely HFF-STZ mice.

RESULTS

Previous studies confirm that, at a dose of 0.25 nmol/kg, liraglutide exerts bioactivity over an 8-12 hour period in mice. Initial pharmacokinetic analysis revealed that 75 nmol/kg SL-PYY yielded a similar plasma drug time profile. When SL-PYY (75 nmol/kg) and liraglutide (0.25 nmol/kg) were administered sequentially at 08:00 AM and 08:00 PM, respectively, to HFF-STZ mice for 28 days, reductions in energy intake, body weight, circulating glucose, insulin and glucagon were noted. Similarly positive, but slightly less striking, effects were also apparent with twice-daily liraglutide-only therapy. The sequential SL-PYY and liraglutide treatment also improved insulin sensitivity and glucose-induced insulin secretory responses, which was not apparent with liraglutide treatment, although benefits on glucose tolerance were mild. Interestingly, combined therapy also elevated pancreatic insulin, decreased pancreatic glucagon and enhanced the plasma insulin/glucagon ratio compared with liraglutide alone. This was not associated with an enhancement of beneficial changes in islet cell areas, proliferation or apoptosis compared with liraglutide alone, but the numbers of centrally stained glucagon-positive islet cells were reduced by sequential combination therapy.

CONCLUSION

These data show that NPY1R-induced intervals of beta-cell rest, combined with GLP-1R-stimulated periods of beta-cell stimulation, should be further evaluated as an effective treatment option for obesity-driven forms of diabetes.

[Effects of metabolic surgery on islet function in Asian patients with type 2 diabetes]

Type 2 diabetes is a high-profile global public health problem, particularly in Asia. The young age of onset, low body mass index, and early appearance of pancreatic islet dysfunction are characteristics of Asian patients with T2DM. Metabolic surgery has become the standard treatment for T2DM patients and can significantly improve T2DM through a variety of mechanisms including modulation of energy homeostasis and reduction of body fat mass. Indeed, restoration of islet function also plays an integral role in the remission of T2DM. After metabolic surgery, islet function in Asian T2DM patients has improved significantly, with proven short-term and long-term effects. In addition, islet function is an important criterion and reference for patient selection prior to metabolic surgery. The mechanism of islet function improvement after metabolic surgery is not clear, but postoperative anatomical changes in the gastrointestinal tract leading to a number of hormonal changes seem to be the potential cause, including glucagon-like peptide-1, gastric inhibitory polypeptide, peptide YY, ghrelin, and cholecystokinin. The authors analyzed the current retrospective and prospective studies on the effect of metabolic surgery on the islet function of Asian T2DM patients with a low BMI and its mechanism, summarized the clinical evidence that metabolic surgery improved islet function in Asian T2DM patients with a low BMI, and discussed its underlying mechanism. It is of great significance for realizing personalized and precise treatment of metabolic surgery and further improving its clinical benefits.

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.

The role of cholecystokinin and peptide YY in feed intake in Atlantic halibut (Hippoglossus hippoglossus) larvae

Control of appetite and feed intake in fish larvae are still largely unexplored. Two of the key players in controlling vertebrate's feed intake are cholecystokinin (CCK) and peptide YY (PYY). Here we investigated the mRNA expression of pyy, cck and cck receptors (cckr) in the brain (head) and gut of Atlantic halibut larvae in response to three consecutive meals. We used Artemia nauplii cysts that are commonly ingested by halibut larvae when present as inert feed, and three water-soluble extracts as attractants to stimulate appetite. Cyst intake was not affected by the use of attractants and overall ingestion rate was low. Differences in mRNA expression of cck and pyy were observed between the halibut larvae that had eaten and those that had not despite readily available feed (cysts), supporting that mechanisms for control of feed intake are at least partly functional. All genes analysed were present in the brain and gut, however the different expression profiles between paralogues suggest potential divergent functions. In the gut, cck2 and pyyb mRNA expression was significantly higher in the larvae that ate cysts compared to larvae that decided to not eat, indicating that these genes play a satiety function in the halibut larvae similar to the general vertebrate scheme. However, cck2, cck2r1, and pyy mRNA expression in the brain were lower in the fed-filled larvae group compared to larvae before eating, which contrasts with the presumable anorectic function of these genes. Further research is required to fully evaluate how PYY and CCK affect the feeding biology in halibut larvae, contributing to formulate inert diets that can stimulate appetite and feed intake.

A Potential Synbiotic Strategy for the Prevention of Type 2 Diabetes: Lactobacillus paracasei JY062 and Exopolysaccharide Isolated from Lactobacillus plantarum JY039

The disturbance of intestinal microorganisms and the exacerbation of type 2 diabetes (T2D) are mutually influenced. In this study, the effect of exopolysaccharides (EPS) from Lactobacillus plantarum JY039 on the adhesion of Lactobacillus paracasei JY062 was investigated, as well as their preventive efficacy against T2D. The results showed that the EPS isolated from L. plantarum JY039 effectively improved the adhesion rate of L. paracasei JY062 to Caco-2 cells (1.8 times) and promoted the proliferation of L. paracasei JY062. In the mice experiment, EPS, L. paracasei JY062 and their complex altered the structure of the intestinal microbiota, which elevated the proportion of Bifidobacterium, Faecalibaculum, while inversely decreasing the proportion of Firmicutes, Muribaculaceae, Lachnospiraceae and other bacteria involved in energy metabolism (p < 0.01; p < 0.05); enhanced the intestinal barrier function; promoted secretion of the gut hormone peptide YY (PYY) and glucagon-like peptide-1 (GLP-1); and reduced inflammation by balancing pro-inflammatory factors IL-6, TNF-α and anti-inflammatory factor IL-10 (p < 0.01; p < 0.05). These results illustrate that EPS and L. paracasei JY062 have the synbiotic potential to prevent and alleviate T2D.

Targeting the Enteroendocrine System for Treatment of Obesity

Mimetics of the anorexigenic gut hormone glucagon-like peptide 1 (GLP-1) were originally developed as insulinotropic anti-diabetic drugs but also evoke significant weight loss, leading to their recent approval as obesity therapeutics. Co-activation of receptors for GLP-1 and other gut hormones which reduce food intake - peptide YY (PYY_3-36), cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) - is now being explored clinically to enhance efficacy. An alternative approach involves pharmacologically stimulating endogenous secretion of these hormones from enteroendocrine cells (EECs) to recapitulate the metabolic consequences of bariatric surgery, where highly elevated postprandial levels of GLP-1 and PYY_3-36 are thought to contribute to improved glycaemia and weight loss.

Colonic Lactulose Fermentation Has No Impact on Glucagon-like Peptide-1 and Peptide-YY Secretion in Healthy Young Men

CONTEXT

The colon houses most of humans' gut microbiota, which ferments indigestible carbohydrates. The products of fermentation have been proposed to influence the secretion of glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) from the many endocrine cells in the colonic epithelium. However, little is known about the colonic contribution to fasting or postprandial plasma levels of L-cell products.

OBJECTIVE

To determine the impact of colonic lactulose fermentation on gut peptide secretion and to evaluate whether colonic endocrine secretion contributes to gut hormone concentrations measurable in the fasting state.

METHODS

Ten healthy young men were studied on 3 occasions after an overnight fast. On 2 study days, lactulose (20 g) was given orally and compared to water intake on a third study day. For 1 of the lactulose visits, participants underwent a full colonic evacuation. Over a 6-h study protocol, lactulose fermentation was assessed by measuring exhaled hydrogen, and gut peptide secretion, paracetamol, and short-chain fatty acid levels were measured in plasma.

RESULTS

Colonic evacuation markedly reduced hydrogen exhalation after lactulose intake (P = 0.013). Our analysis suggests that the colon does not account for the measurable amounts of GLP-1 and PYY present in the circulation during fasting and that fermentation and peptide secretion are not acutely related.

CONCLUSION

Whether colonic luminal contents affect colonic L-cell secretion sufficiently to influence circulating concentrations requires further investigation. Colonic evacuation markedly reduced lactulose fermentation, but hormone releases were unchanged in the present study.

Y1 receptors modulate taste-related behavioral responsiveness in male mice to prototypical gustatory stimuli

Mammalian taste bud cells express receptors for numerous peptides implicated elsewhere in the body in the regulation of metabolism, nutrient assimilation, and satiety. The perturbation of several peptide signaling pathways in the gustatory periphery results in changes in behavioral and/or physiological responsiveness to subsets of taste stimuli. We previously showed that Peptide YY (PYY) - which is present in both saliva and in subsets of taste cells - can affect behavioral taste responsiveness and reduce food intake and body weight. Here, we investigated the contributions of taste bud-localized receptors for PYY and the related Neuropeptide Y (NPY) on behavioral taste responsiveness. Y1R, but not Y2R, null mice show reduced responsiveness to sweet, bitter, and salty taste stimuli in brief-access taste tests; similar results were seen when wildtype mice were exposed to Y receptor antagonists in the taste stimuli. Finally, mice in which the gene encoding the NPY propeptide was deleted also showed reduced taste responsiveness to sweet and bitter taste stimuli. Collectively, these results suggest that Y1R signaling, likely through its interactions with NPY, can modulate peripheral taste responsiveness in mice.

Dynamin regulates L cell secretion in human gut

BACKGROUND

The mechanochemical enzyme dynamin mediates endocytosis and regulates neuroendocrine cell exocytosis. Enteroendocrine L cells co-secrete the anorectic gut hormones glucagon-like peptide 1 (GLP-1) and peptide YY (PYY) postprandially and is a potential therapeutic target for metabolic diseases. In the present study, we aimed to determine if dynamin is implicated in human L cell secretion.

METHODS

Western blot was performed on the murine L cell line GLUTag. Static incubation of human colonic mucosae with activators and inhibitors of dynamin was carried out. GLP-1 and PYY contents of the secretion supernatants were assayed using ELISA.

RESULTS AND CONCLUSION

s: Both dynamin I and II are expressed in GLUTag cells. The dynamin activator Ryngo 1-23 evoked significant GLP-1 and PYY release from human colonic mucosae while the dynamin inhibitor Dynole 3-42 significantly inhibited release triggered by known L cell secretagogues. Thus, the cell signaling regulator dynamin is able to bi-directionally regulate L cell hormone secretion in the human gut and may represent a novel target for gastrointestinal-targeted metabolic drug development.

Ligilactobacillus Salivarius LCK11 Prevents Obesity by Promoting PYY Secretion to Inhibit Appetite and Regulating Gut Microbiota in C57BL/6J Mice

SCOPE

Obesity is a common disease worldwide and there is an urgent need for strategies to preventing obesity.

METHODS AND RESULTS

The anti-obesity effect and mechanism of Ligilactobacillus salivarius LCK11 (LCK11) is studied using a C57BL/6J male mouse model in which obesity is induced by a high-fat diet (HFD). Results show that LCK11 can prevent HFD-induced obesity, reflected as inhibited body weight gain, abdominal and liver fat accumulation and dyslipidemia. Analysis of its mechanism shows that on the one hand, LCK11 can inhibit food intake through significantly improving the transcriptional and translational levels of peptide YY (PYY) in the rectum, in addition to the eventual serum PYY level; this is attributed to the activation of the toll-like receptor 2/nuclear factor-κB signaling pathway in enteroendocrine L cells by the peptidoglycan of LCK11. On the other hand, LCK11 supplementation effectively reduces the Firmicutes/Bacteroidetes ratio and shifts the overall structure of the HFD-disrupted gut microbiota toward that of mice fed on a low-fat diet; this also contributes to preventing obesity.

CONCLUSION

LCK11 shows the potential to be used as a novel probiotic for preventing obesity by both promoting PYY secretion to inhibit food intake and regulating gut microbiota.

Effects of Bacterial CLPB Protein Fragments on Food Intake and PYY Secretion

CLPB (Caseinolytic peptidase B) protein is a conformational mimetic of α-MSH, an anorectic hormone. Previous in vivo studies have already shown the potential effect of CLPB protein on food intake and on the production of peptide YY (PYY) by injection of E. coli wild type (WT) or E. coli ΔClpB. However, until now, no study has shown its direct effect on food intake. Furthermore, this protein can fragment naturally. Therefore, the aim of this study was (i) to evaluate the in vitro effects of CLPB fragments on PYY production; and (ii) to test the in vivo effects of a CLPB fragment sharing molecular mimicry with α-MSH (CLPB25) compared to natural fragments of the CLPB protein (CLPB96). To do that, a primary culture of intestinal mucosal cells from male Sprague-Dawley rats was incubated with proteins extracted from E. coli WT and ΔCLPB after fragmentation with trypsin or after a heat treatment of the CLPB protein. PYY secretion was measured by ELISA. CLPB fragments were analyzed by Western Blot using anti-α-MSH antibodies. In vivo effects of the CLPB protein on food intake were evaluated by intraperitoneal injections in male C57Bl/6 and ob/ob mice using the BioDAQ^® system. The natural CLPB96 fragmentation increased PYY production in vitro and significantly decreased cumulative food intake from 2 h in C57Bl/6 and ob/ob mice on the contrary to CLPB25. Therefore, the anorexigenic effect of CLPB is likely the consequence of enhanced PYY secretion.

Serotonin involvement in okadaic acid-induced diarrhoea in vivo

The consumption of contaminated shellfish with okadaic acid (OA) group of toxins leads to diarrhoeic shellfish poisoning (DSP) characterized by a set of symptoms including nausea, vomiting and diarrhoea. These phycotoxins are Ser/Thr phosphatase inhibitors, which produce hyperphosphorylation in cellular proteins. However, this inhibition does not fully explain the symptomatology reported and other targets could be relevant to the toxicity. Previous studies have indicated a feasible involvement of the nervous system. We performed a set of in vivo approaches to elucidate whether neuropeptide Y (NPY), Peptide YY (PYY) or serotonin (5-HT) was implicated in the early OA-induced diarrhoea. Fasted Swiss female mice were administered NPY, PYY(3-36) or cyproheptadine intraperitoneal prior to oral OA treatment (250 µg/kg). A non-significant delay in diarrhoea onset was observed for NPY (107 µg/kg) and PYY(3-36) (1 mg/kg) pre-treatment. On the contrary, the serotonin antagonist cyproheptadine was able to block (10 mg/kg) or delay (0.1 and 1 mg/kg) diarrhoea onset suggesting a role of 5-HT. This is the first report of the possible involvement of serotonin in OA-induced poisoning.

Gut modulation based anti-diabetic effects of carboxymethylated wheat bran dietary fiber in high-fat diet/streptozotocin-induced diabetic mice and their potential mechanisms

We explored the effect of carboxymethylated wheat bran dietary fibers (DFs) on mice with type 2 diabetes (T2D) (induced by HFD combined with STZ) and their possible hypoglycemic mechanism. After feeding the diabetic mice with modified DFs for four weeks, the DFs had lipid lowering and anti-hyperglycemic effect, via increasing the levels of insulin, GLP-1, PYY, and SCFAs in diabetic mice, and improving the histopathology of liver and pancreas. qRT-PCR results showed that the intake of DFs up-regulated the expression levels of G6Pase and Prkce, and down regulated the expression levels of Glut2 and InsR in the liver of diabetic mice. It is suggested that DFs may play a role by inhibiting 1,2-DAG-PKCε pathway, improving insulin receptor activity and insulin signal transduction. 16 S rDNA high-throughput sequencing results showed that the DFs significantly improved the relative abundance of Akkermansia muciniphila, increased the diversity of gut microbiota and reduced the ratio of Firmicutes to Bacteroidetes, thus promoting the hypoglycemic and hypolipidemic effect on diabetic mice. Our study can foster the further understanding of the gut modulatory biomarkers and related metabolites, and may extend the basis for DFs as a potential dietary intervention to prevent or treat the T2D.

The timing of fasting leads to different levels of food consumption and PYY3-36 in nocturnal mice

PURPOSE

The daily circadian cycle is known to modulate both feeding behavior and metabolism. As such, the timing of food consumption can play a role in regulating overall health. The purpose of this study is to determine whether fasting at different times of the day alters subsequent food consumption and levels of PYY_3-36, a hormone secreted after a meal which inhibits appetite.

METHODS

Separate groups of mice were fasted at different times of the day: (1) start of the day, (2) middle of the day, (3) start of the night, and (4) middle of the night, and either injected with vehicle or PYY_3-36 to assess their subsequent food consumption patterns, PYY_3-36 levels, and glucose and insulin levels. We also investigated whether light exposure during the night would alter food consumption and PYY_3-36 levels after fasting.

RESULTS

Mice fasted during the start of the daytime exhibited increased food consumption post-fast compared to mice fasted during the night. Injections of PYY_3-36 during the night were more effective in reducing food consumption compared to PYY_3-36 administration during the day. Constant light exposure suppressed food consumption after fasting and increased fasting PYY_3-36 levels.

CONCLUSIONS

These results indicate that mice exhibit distinct food consumption patterns after being presented with a fast at different times of the day. Light exposure also modulates both food consumption after a fast and levels of PYY_3-36.

Generation and characterisation of C-terminally stabilised PYY molecules with potential in vivo NPYR2 activity

BACKGROUND

Activation of neuropeptide Y2 receptors (NPYR2) by the N-terminally truncated, dipeptidyl peptidase-4 (DPP-4) generated, Peptide YY (PYY) metabolite, namely PYY(3-36), results in satiating actions. However, PYY(3-36) is also subject to C-terminal enzymatic cleavage, which annuls anorectic effects.

METHODS

Substitution of l-Arg³⁵ with d-Arg³⁵ in the DPP-4 stable sea lamprey PYY(1-36) peptide imparts full C-terminal stability. In the current study, we have taken this molecule and introduced DPP-4 susceptibility by Iso³ substitution.

RESULTS

As expected, [Iso³]sea lamprey PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) were N-terminally degraded to respective PYY(3-36) metabolites in plasma. Only [Iso³](d-Arg³⁵)sea lamprey PYY(1-36) was C-terminally stable. Both peptides possessed similar insulinostatic and anti-apoptotic biological actions to native PYY(1-36) in beta-cells. Unlike native PYY(1-36) and [Iso³](d-Arg³⁵)sea lamprey PYY(1-36), [Iso³]sea lamprey PYY(1-36) displayed some proliferative actions in Npyr1 knockout beta-cells. In addition, [Iso³]sea lamprey PYY(1-36) induced more rapid NPYR2-dependent appetite suppressive effects in mice than its C-terminally stable counterpart. Twice daily administration of either peptide to high fat fed (HFF) mice resulted in significant body weight reduction and improvements in circulating triglyceride levels. [Iso³]sea lamprey PYY(1-36) treatment also prevented elevations in glucagon. Both peptides, and especially [Iso³]sea lamprey PYY(1-36), improved glucose tolerance. The treatment interventions also partially reversed the deleterious effects of sustained high fat feeding on pancreatic islet morphology.

CONCLUSION

The present study confirms that sustained NPYR2 receptor activation by [Iso³](d-Arg³⁵)sea lamprey induced significant weight lowering actions. However, identifiable benefits of this peptide over [Iso³]sea lamprey PYY(1-36), which was not protected against C-terminal degradation, were not pronounced.

Metformin improves blood glucose by increasing incretins independent of changes in gluconeogenesis in youth with type 2 diabetes

AIMS/HYPOTHESIS

Metformin is the only approved oral agent for youth with type 2 diabetes but its mechanism of action remains controversial. Recent data in adults suggest a primary role for the enteroinsular pathway, but there are no data in youth, in whom metformin efficacy is only ~50%. Our objectives were to compare incretin concentrations and rates of glucose production and gluconeogenesis in youth with type 2 diabetes before and after short-term metformin therapy compared with peers with normal glucose tolerance (NGT).

METHODS

This is a case-control observational study in youth with type 2 diabetes who were not on metformin (n = 18) compared with youth with NGT (n = 10) who were evaluated with a 2 day protocol. A 75 g OGTT was administered to measure intact glucagon-like 1 peptide (iGLP-1), gastric inhibitory polypeptide (GIP) and peptide YY (PYY). Insulinogenic index (IGI) and whole-body insulin sensitivity were calculated using glucose and insulin levels from the OGTT. Basal rates of gluconeogenesis (²H₂O), glucose production ([6,6-²H₂]glucose) and whole-body lipolysis ([²H₅]glycerol) were measured after an overnight fast on study day 2. Youth with type 2 diabetes (n = 9) were subsequently evaluated with an identical 2 day protocol after 3 months on the metformin study.

RESULTS

Compared with individuals with NGT, those with type 2 diabetes had higher fasting (7.8 ± 2.5 vs 5.1 ± 0.3 mmol/l, mean ± SD p = 0.002) and 2 h glucose concentrations (13.8 ± 4.5 vs 5.9 ± 0.9 mmol/l, p = 0.001), higher rates of absolute gluconeogenesis (10.0 ± 1.7 vs 7.2 ± 1.1 μmol [kg fat-free mass (FFM)]^-1 min^-1, p < 0.001) and whole-body lipolysis (5.2 ± 0.9 vs 4.0 ± 1.4 μmol kg_FFM^-1 min^-1, p < 0.01), but lower fasting iGLP-1 concentrations (0.5 ± 0.5 vs 1.3 ± 0.7 pmol/l, p < 0.01). Metformin decreased 2 h glucose (pre metformin 11.4 ± 2.8 vs post metformin 9.9 ± 1.9 mmol/l, p = 0.04) and was associated with ~20-50% increase in IGI (median [25th-75th percentile] pre 1.39 [0.89-1.47] vs post 1.43 [0.88-2.70], p = 0.04), fasting iGLP-1 (pre 0.3 ± 0.2 vs post 1.0 ± 0.7 pmol/l, p = 0.02), 2 h iGLP (pre 0.4 ± 0.2 vs post 1.2 ± 0.9 pmol/l, p = 0.06), fasting PYY (pre 6.3 ± 2.2 vs post 10.5 ± 4.3 pmol/l, p < 0.01) and 2 h PYY (pre 6.6 ± 2.9 vs post 9.0 ± 4.0 pmol/l, p < 0.01). There was no change in BMI, insulin sensitivity or GIP concentrations pre vs post metformin. There were no differences pre vs post metformin in rates of glucose production (15.0 ± 3.9 vs 14.9 ± 2.2 μmol kg_FFM^-1 min^-1, p = 0.84), absolute gluconeogenesis (9.9 ± 1.8 vs 9.7 ± 1.7 μmol kg_FFM^-1 min^-1, p = 0.76) or whole-body lipolysis (5.0 ± 0.7 vs 5.3 ± 1.3 μmol kg_FFM^-1 min^-1, p = 0.20). Post metformin iGLP-1 and PYY concentrations in youth with type 2 diabetes were comparable to levels in youth with NGT.

CONCLUSIONS/INTERPRETATION

Overall, the improved postprandial blood glucose levels and increase in incretins observed in the absence of changes in insulin sensitivity and gluconeogenesis, support an enteroinsular mechanistic pathway in youth with type 2 diabetes treated with short-term metformin.

Combination gut hormones: prospects and questions for the future of obesity and diabetes therapy

Obesity represents an important public health challenge for the twenty-first century: globalised, highly prevalent and increasingly common with time, this condition is likely to reverse some of the hard-won gains in mortality accomplished in previous centuries. In the search for safe and effective therapies for obesity and its companion, type 2 diabetes mellitus (T2D), the gut hormone glucagon-like peptide-1 (GLP-1) has emerged as a forerunner and analogues thereof are now widely used in treatment of obesity and T2D, bringing proven benefits in improving glycaemia and weight loss and, notably, cardiovascular outcomes. However, GLP-1 alone is subject to limitations in terms of efficacy, and as a result, investigators are evaluating other gut hormones such as glucose-dependent insulinotropic peptide (GIP), glucagon and peptide YY (PYY) as possible partner hormones that may complement and enhance GLP-1's therapeutic effects. Such combination gut hormone therapies are in pharmaceutical development at present and are likely to make it to market within the next few years. This review examines the physiological basis for combination gut hormone therapy and presents the latest clinical results that underpin the excitement around these treatments. We also pose, however, some hard questions for the field which need to be answered before the full benefit of such treatments can be realised.

The Effect of Acute Hypohydration on Indicators of Glycemic Regulation, Appetite, Metabolism and Stress: A Systematic Review and Meta-Analysis

Evidence synthesizing the effects of acute body water losses on various markers of glycemic regulation, appetite, metabolism, and stress is lacking. Thus, the purpose of this review was to summarize the response of various hormonal changes involved in these physiologic functions to dehydration. A comprehensive literature search for peer-reviewed research in the databases PubMed, Scopus, CINAHL, and SportDiscus was conducted. Studies were included if they contained samples of adults (>18 years) and experimentally induced dehydration as measured by acute body mass loss. Twenty-one articles were eligible for inclusion. Findings suggested cortisol is significantly elevated with hypohydration (standard mean difference [SMD] = 1.12, 95% CI [0.583, 1.67], p < 0.0001). Testosterone was significantly lower in studies where hypohydration was accompanied by caloric restriction (SMD= -1.04, 95% CI [-1.93, -0.14], p = 0.02), however, there were no changes in testosterone in studies examining hypohydration alone (SMD = -0.17, 95% CI [-0.51 0.16], p = 0.30). Insulin and ghrelin were unaffected by acute total body water losses. Acute hypohydration increases markers of catabolism but has a negligible effect on markers of glycemic regulation, appetite, anabolism and stress. Given the brevity of existing research, further research is needed to determine the impact of hydration on glucagon, leptin, peptide YY and the subsequent outcomes relevant to both health and performance.

Selective stimulation of colonic L cells improves metabolic outcomes in mice

AIMS/HYPOTHESIS

Insulin-like peptide-5 (INSL5) is found only in distal colonic L cells, which co-express glucagon-like peptide-1 (GLP-1) and peptide YY (PYY). GLP-1 is a well-known insulin secretagogue, and GLP-1 and PYY are anorexigenic, whereas INSL5 is considered orexigenic. We aimed to clarify the metabolic impact of selective stimulation of distal colonic L cells in mice.

METHODS

Insl5 promoter-driven expression of Gq-coupled Designer Receptor Exclusively Activated by Designer Drugs (DREADD) was employed to activate distal colonic L cells (LdistalDq). IPGTT and food intake were assessed with and without DREADD activation.

RESULTS

LdistalDq cell stimulation with clozapine N-oxide (CNO; 0.3 mg/kg i.p.) increased plasma GLP-1 and PYY (2.67- and 3.31-fold, respectively); INSL5 was not measurable in plasma but was co-secreted with GLP-1 and PYY in vitro. IPGTT (2 g/kg body weight) revealed significantly improved glucose tolerance following CNO injection. CNO-treated mice also exhibited reduced food intake and body weight after 24 h, and increased defecation, the latter being sensitive to 5-hydroxytryptamine (5-HT) receptor 3 inhibition. Pre-treatment with a GLP1 receptor-blocking antibody neutralised the CNO-dependent improvement in glucose tolerance but did not affect the reduction in food intake, and an independent group of animals pair-fed to the CNO-treatment group demonstrated attenuated weight loss. Pre-treatment with JNJ-31020028, a neuropeptide Y receptor type 2 antagonist, abolished the CNO-dependent effect on food intake. Assessment of whole body physiology in metabolic cages revealed LdistalDq cell stimulation increased energy expenditure and increased activity. Acute CNO-induced food intake and glucose homeostasis outcomes were maintained after 2 weeks on a high-fat diet.

CONCLUSIONS/INTERPRETATION

This proof-of-concept study demonstrates that selective distal colonic L cell stimulation has beneficial metabolic outcomes. Graphical abstract.

Effects of Flavanols on Enteroendocrine Secretion

Some beneficial effects of grape seed proanthocyanidin extract (GSPE) can be explained by the modulation of enterohormone secretion. As GSPE comprises a combination of different molecules, the pure compounds that cause these effects need to be elucidated. The enterohormones and chemoreceptors present in the gastrointestinal tract differ between species, so if humans are to gain beneficial effects, species closer to humans-and humans themselves-must be used. We demonstrate that 100 mg/L of GSPE stimulates peptide YY (PYY) release, but not glucagon-like peptide 1 (GLP-1) release in the human colon. We used a pig ex vivo system that differentiates between apical and basolateral intestinal sides to analyse how apical stimulation with GSPE and its pure compounds affects the gastrointestinal tract. In pigs, apical GSPE treatment stimulates the basolateral release of PYY in the duodenum and colon and that of GLP-1 in the ascending, but not the descending colon. In the duodenum, luminal stimulation with procyanidin dimer B2 increased PYY secretion, but not CCK secretion, while catechin monomers (catechin/epicatechin) significantly increased CCK release, but not PYY release. The differential effects of GSPE and its pure compounds on enterohormone release at the same intestinal segment suggest that they act through chemosensors located apically and unevenly distributed along the gastrointestinal tract.

Gastrointestinal peptides and nonalcoholic fatty liver disease

PURPOSE OF REVIEW

In this review, authors have selected from literature the most recent and suggestive studies on therapy of nonalcoholic fatty liver disease (NAFLD). The selected interventions regulate the action of gastrointestinal peptides, such as gastric inhibitory polypeptide (GIP), nesfatin, peptide YY, cholecystokinin, and glucagon-like peptide 1 (GLP-1). These hormones have been found frequently modified in obesity and/or type 2 diabetes mellitus, morbidities mostly associated with NAFLD. This disease has a very high prevalence worldwide and could evolve in a more severe form, that is, nonalcoholic steatohepatitis, characterized by inflammation and fibrosis. The findings shown by this article describe the metabolic effects of new drugs, mainly but not only, as well of some old substances.

RECENT FINDINGS

Recent approaches, in animal models or in humans, use synthetic GLP-1 receptor agonists, a centrally administered antibody neutralizing GIP receptor, curcumin, compound being active on nesfatin, resveratrol (antiinflammatory agent), and Ginseg, both of them acting on nesfatin, a cholecystokinin receptor analogue, and finally coffee functioning on YY peptide.

SUMMARY

The implications of the presented findings, if they are confirmed in larger clinical trials, likely open the door to future application in clinical practice. In fact, nowadays, patients have only diet and article (incl abstract and keywords) exercise as well accepted recommendations. Thus, there are unmet needs to find substances that could really improve the progression of nonalcoholic steatohepatitis toward liver cirrhosis and hepatocellular carcinoma.

Possible role of peptide YY (PYY) in the pathophysiology of irritable bowel syndrome (IBS)

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder of unknown aetiology for which there is no effective treatment. Although IBS does not increase mortality, it reduces the quality of life and is an economic burden to both the patients themselves and society as a whole. Peptide YY (PYY) is localized in endocrine cells located in the ileum, colon and rectum. The concentration of PYY and the density of PYY cells are decreased in both the colon and rectum but unchanged in the ileum of patients with IBS. The low density of PYY cells in the large intestine may be caused by a decreased number of stem cells and their progeny toward endocrine cells. PYY regulates the intestinal motility, secretion and absorption as well as visceral sensitivity via modulating serotonin release. An abnormality in PYY may therefore contribute to the intestinal dysmotility and visceral hypersensitivity seen in IBS patients. Diet management involving consuming a low-FODMAP diet restores the density of PYY cells in the large intestine and improves abdominal symptoms in patients with IBS. This review shows that diet management appears to be a valuable tool for correcting the PYY abnormalities in the large intestine of IBS patients in the clinic.

CCK-1 and CCK-2 receptor agonism do not stimulate GLP-1 and neurotensin secretion in the isolated perfused rat small intestine or GLP-1 and PYY secretion in the rat colon

Gastrin and cholecystokinin (CCK) are hormones released from endocrine cells in the antral stomach (gastrin), the duodenum, and the jejunum (CCK). Recent reports, based on secretion experiments in an enteroendocrine cell line (NCI-H716) and gastrin receptor expression in proglucagon-expressing cells from the rat colon, suggested that gastrin could be a regulator of glucagon-like peptide-1 (GLP-1) secretion. To investigate these findings, we studied the acute effects of CCK-8 (a CCK1/CCK2 (gastrin) receptor agonist) and gastrin-17 (a CCK2(gastrin) receptor agonist) in robust ex vivo models: the isolated perfused rat small intestine and the isolated perfused rat colon. Small intestines from Wistar rats (n = 6), were perfused intraarterially over 80 min. During the perfusion, CCK (1 nmol/L) and gastrin (1 nmol/L) were infused over 10-min periods separated by washout/baseline periods. Colons from Wistar rats (n = 6) were perfused intraarterially over 100 min. During the perfusion, CCK (1 nmol/L), vasoactive intestinal peptide (VIP) (10 nmol/L), and glucose-dependent insulinotropic polypeptide (GIP) (1 nmol/L) were infused over 10-min periods separated by washout/baseline periods. In the perfused rat small intestines neither CCK nor gastrin stimulated the release of GLP-1 or neurotensin. In the perfused rat colon, neither CCK or VIP stimulated GLP-1 or peptide YY (PYY) release, but GIP stimulated both GLP-1 and PYY release. In both sets of experiments, bombesin, a gastrin-releasing peptide analog, served as a positive control. Our findings do not support the suggestion that gastrin or CCK participate in the acute regulation of intestinal GLP-1 secretion, but that GIP may play a role in the regulation of hormone secretion from the colon.

Mechanisms controlling hormone secretion in human gut and its relevance to metabolism

The homoeostatic regulation of metabolism is highly complex and involves multiple inputs from both the nervous and endocrine systems. The gut is the largest endocrine organ in our body and synthesises and secretes over 20 different hormones from enteroendocrine cells that are dispersed throughout the gut epithelium. These hormones include GLP-1, PYY, GIP, serotonin, and CCK, each of whom play pivotal roles in maintaining energy balance and glucose homeostasis. Some are now the basis of several clinically used glucose-lowering and weight loss therapies. The environment in which these enteroendocrine cells exist is also complex, as they are exposed to numerous physiological inputs including ingested nutrients, circulating factors and metabolites produced from neighbouring gut microbiome. In this review, we examine the diverse means by which gut-derived hormones carry out their metabolic functions through their interactions with different metabolically important organs including the liver, pancreas, adipose tissue and brain. Furthermore, we discuss how nutrients and microbial metabolites affect gut hormone secretion and the mechanisms underlying these interactions.

A new action of peptide hormones for survival in a low-nutrient environment

Malnutrition occurs when nutrient intake is too low for any reason and occurs regardless of gender or age. Therefore, besides loss of eating or digestive functionality due to illness, malnutrition can occur when a healthy individual undergoes an extreme diet and biases their nutrition, or when athletes exerts more energy than they can replenish through food. It has recently been reported that in Japan, the mortality rate of leaner individuals is equal to or higher than that of obese people. It is important to understand what homeostatic maintenance mechanism is behind this when the body is under hypotrophic conditions. Such mechanisms are generally endocranially controlled. We address this fundamental concern in this paper by focusing on peptide hormones. We introduce a mechanism for survival in a malnourished state via the regulation of food intake and temperature. Additionally, we will discuss the latest findings and future prospects for research on changes in the endocrine environment associated with malnutrition associated with exercise. We also review changes in next-generation endocrine environments when caused by malnutrition brought on by dieting.

Review: Chemosensing of nutrients and non-nutrients in the human and porcine gastrointestinal tract

The gastrointestinal tract (GIT) is an interface between the external and internal milieus that requires continuous monitoring for nutrients or pathogens and toxic chemicals. The study of the physiological/molecular mechanisms, mediating the responses to the monitoring of the GIT contents, has been referred to as chemosensory science. While most of the progress in this area of research has been obtained in laboratory rodents and humans, significant steps forward have also been reported in pigs. The objective of this review was to update the current knowledge on nutrient chemosensing in pigs in light of recent advances in humans and laboratory rodents. A second objective relates to informing the existence of nutrient sensors with their functionality, particularly linked to the gut peptides relevant to the onset/offset of appetite. Several cell types of the intestinal epithelium such as Paneth, goblet, tuft and enteroendocrine cells (EECs) contain subsets of chemosensory receptors also found on the tongue as part of the taste system. In particular, EECs show specific co-expression patterns between nutrient sensors and/or transceptors (transport proteins with sensing functions) and anorexigenic hormones such as cholecystokinin (CCK), peptide tyrosine tyrosine (PYY) or glucagon-like peptide-1 (GLP-1), amongst others. In addition, the administration of bitter compounds has an inhibitory effect on GIT motility and on appetite through GLP-1-, CCK-, ghrelin- and PYY-labelled EECs in the human small intestine and colon. Furthermore, the mammalian chemosensory system is the target of some bacterial metabolites. Recent studies on the human microbiome have discovered that commensal bacteria have developed strategies to stimulate chemosensory receptors and trigger host cellular functions. Finally, the study of gene polymorphisms related to nutrient sensors explains differences in food choices, food intake and appetite between individuals.

PYY is a negative regulator of bone mass and strength

OBJECTIVE

Bone loss in anorexia nervosa and following bariatric surgery is associated with an elevated circulating concentration of the gastrointestinal, anorexigenic hormone, peptide YY (PYY). Selective deletion of the PYY receptor Y1R in osteoblasts or Y2R in the hypothalamus results in high bone mass, but deletion of PYY in mice has resulted in conflicting skeletal phenotypes leading to uncertainty regarding its role in the regulation of bone mass. As PYY analogs are under development for treatment of obesity, we aimed to clarify the relationship between PYY and bone mass.

METHODS

The skeletal phenotype of Pyy knockout (KO) mice was investigated during growth (postnatal day P14) and adulthood (P70 and P186) using X-ray microradiography, micro-CT, back-scattered electron scanning electron microscopy (BSE-SEM), histomorphometry and biomechanical testing.

RESULTS

Bones from juvenile and Pyy KO mice were longer (P < 0.001), with decreased bone mineral content (P < 0.001). Whereas, bones from adult Pyy KO mice had increased bone mineral content (P < 0.05) with increased mineralisation of both cortical (P < 0.001) and trabecular (P < 0.001) compartments. Long bones from adult Pyy KO mice were stronger (maximum load P < 0.001), with increased stiffness (P < 0.01) and toughness (P < 0.05) compared to wild-type (WT) control mice despite increased cortical vascularity and porosity (P < 0.001). The increased bone mass and strength in Pyy KO mice resulted from increases in trabecular (P < 0.01) and cortical bone formation (P < 0.05).

CONCLUSIONS

These findings demonstrate that PYY acts as a negative regulator of osteoblastic bone formation, implicating increased PYY levels in the pathogenesis of bone loss during anorexia or following bariatric surgery.

Effects of Macronutrients on the In Vitro Production of ClpB, a Bacterial Mimetic Protein of α-MSH and Its Possible Role in Satiety Signaling

Gut microbiota can influence the feeding behavior of the host, but the underlying mechanisms are unknown. Recently, caseinolytic protease B (ClpB), a disaggregation chaperon protein of Escherichia coli, was identified as a conformational mimetic of α-melanocyte-stimulating hormone (α-MSH), an anorexigenic neuropeptide. Importantly, ClpB was necessary for E. coli to have an anorexigenic effect in mice, suggesting that it may participate in satiety signaling. To explore this further, we determined the short-term (2 h) effects of three macronutrients: protein (bovine serum albumin), carbohydrate (D-fructose) and fat (oleic acid), on the production of ClpB by E. coli and analyzed whether ClpB can stimulate the secretion of the intestinal satiety hormone, peptide YY (PYY). Isocaloric amounts of all three macronutrients added to a continuous culture of E. coli increased ClpB immunoreactivity. However, to increase the levels of ClpB mRNA and ClpB protein in bacteria and supernatants, supplementation with protein was required. A nanomolar concentration of recombinant E. coli ClpB dose-dependently stimulated PYY secretion from the primary cell cultures of rat intestinal mucosa. Total proteins extracted from E. coli but not from ClpB-deficient E. coli strains also tended to increase PYY secretion. These data support a possible link between E. coli ClpB and protein-induced satiety signaling in the gut.

Metformin Triggers PYY Secretion in Human Gut Mucosa

CONTEXT

The antidiabetic drug metformin causes weight loss, but the underlying mechanisms are unclear. Recent clinical studies show that metformin increases plasma levels of the anorectic gut hormone, peptide YY (PYY), but whether this is through a direct effect on the gut is unknown.

OBJECTIVE

We hypothesized that exposure of human gut mucosal tissue to metformin would acutely trigger PYY secretion.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Mucosal tissue was prepared from 46 human colonic and 9 ileal samples obtained after surgical resection and ex vivo secretion assays were performed. Tissue was exposed to metformin, as well as a series of other compounds as part of our mechanistic studies, in static incubations. Supernatant was sampled after 15 minutes.

MAIN OUTCOME MEASURES

PYY levels in supernatant, measured using ELISA.

RESULTS

Metformin increased PYY secretion from both ileal (P < 0.05) and colonic (P < 0.001) epithelia. Both basal and metformin-induced PYY secretion were unchanged across body mass index or in tissues obtained from individuals with type 2 diabetes. Metformin-dependent PYY secretion was blocked by inhibitors of the plasma membrane monoamine transporter (PMAT) and the serotonin reuptake transporter (SERT), as well as by an inhibitor of AMP kinase (AMPK).

CONCLUSIONS

This is a report of a direct action of metformin on the gut epithelium to trigger PYY secretion in humans, occurring via cell internalization through PMAT and SERT and intracellular activation of AMPK. Our results provide further support that the role of metformin in the treatment of metabolic syndrome has a gut-based component.

Central Nervous System and Peripheral Hormone Responses to a Meal in Children

CONTEXT

Behavioral studies suggest that responses to food consumption are altered in children with obesity (OB).

OBJECTIVE

To test central nervous system and peripheral hormone response by functional MRI and satiety-regulating hormone levels before and after a meal.

DESIGN AND SETTING

Cross-sectional study comparing children with OB and children of healthy weight (HW) recruited from across the Puget Sound region of Washington.

PARTICIPANTS

Children (9 to 11 years old; OB, n = 54; HW, n = 22), matched for age and sex.

INTERVENTION AND OUTCOME MEASURES

Neural activation to images of high- and low-calorie food and objects was evaluated across a set of a priori appetite-processing regions that included the ventral and dorsal striatum, amygdala, substantia nigra/ventral tegmental area, insula, and medial orbitofrontal cortex. Premeal and postmeal hormones (insulin, peptide YY, glucagon-like peptide-1, active ghrelin) were measured.

RESULTS

In response to a meal, average brain activation by high-calorie food cues vs objects in a priori regions was reduced after meals in children of HW (Z = -3.5, P < 0.0001), but not in children with OB (z = 0.28, P = 0.78) despite appropriate meal responses by gut hormones. Although premeal average brain activation by high-calorie food cues was lower in children with OB vs children of HW, postmeal activation was higher in children with OB (Z = -2.1, P = 0.04 and Z = 2.3, P = 0.02, respectively). An attenuated central response to a meal was associated with greater degree of insulin resistance.

CONCLUSIONS

Our data suggest that children with OB exhibit an attenuated central, as opposed to gut hormone, response to a meal, which may predispose them to overconsumption of food or difficulty with weight loss.

Hormonal and metabolic effects of carbohydrate restriction in children with Prader-Willi syndrome

OBJECTIVE

Macronutrient regulation of hyperphagia and adiposity in Prader-Willi syndrome (PWS) is poorly understood. We compared fasting and postprandial concentrations of hormones and metabolites in eight PWS children (age 9-18 years) fed, in random order, low carbohydrate, high-fat (LC, 15% carb; 65% fat; 20% protein) and low-fat, high carbohydrate (LF, 65% carb, 15% fat, 20% protein) diets matched for calories and protein.

METHODS

Participants were randomized to consume either the LC or LF diet during a first hospital admission and the second diet during a subsequent admission. Blood samples were obtained after overnight fasting and 1 hour after a mixed meal.

RESULTS

Relative to subjects consuming the LF diet, subjects consuming the LC diet had: lower postprandial insulin concentrations (P = 0.02); higher fasting GLP-1 AND GIP concentrations and increased postprandial GLP-1 (P < 0.02); reduced ratio of fasting ghrelin to GLP-1 (P = 0.0078); increased FFA and fatty acid oxidation, as assessed by concentrations of even-chain acylcarnitines (P < 0.001); lower fasting TG and TG/HDL ratio (P < 0.01); and higher concentrations of branch chain amino acids (P < 0.01). There were no changes in glucose, PYY, or adiponectin. CRP, AST and ALT were all higher (P < 0.01) on the LC diet.

CONCLUSIONS

Increases in GLP-1 with low carbohydrate feeding and reductions in the ratio of ghrelin to GLP-1 might limit food intake and improve glycaemic control in PWS. Other potential benefits of carbohydrate restriction may include fat mobilization and oxidation and reductions in the TG/HDL ratio, a marker of insulin resistance. However, increases in CRP, AST and ALT necessitate longer-term studies of low carbohydrate efficacy and safety.

Short communication: Expression of transcripts for proglucagon, glucose-dependent insulinotropic peptide, peptide YY, and their cognate receptors, in feline peripheral tissues

Gastrointestinal hormone based therapies are being investigated for treating diabetes in cats; however, the tissue distribution of these hormones and their cognate receptors remain largely understudied. We determined the distribution of transcripts for the gut hormones proglucagon (Gcg), glucose-dependent insulinotropic peptide (Gip), peptide YY (Pyy), and their receptors (Glp1r, Gipr, Npy2r), in feline peripheral tissues. The Gcg, Gip and Pyy mRNA were expressed in the gut, with higher Gcg and Pyy abundance in the lower gut. Interestingly, Glp1r and Npy2r mRNA were expressed in multiple peripheral tissues including the gut, pancreas and liver, whereas, Gipr mRNA was restricted to the stomach and adipose tissues. The localized mRNA expression of Gcg and Pyy in the gut, but the extensive distribution of Glp1r and Npy2r in several peripheral tissues suggests that these hormones may have pleiotropic physiological functions in cats.

Important Role of the GLP-1 Axis for Glucose Homeostasis after Bariatric Surgery

Bariatric surgery is widely used to treat obesity and improves type 2 diabetes beyond expectations from the degree of weight loss. Elevated post-prandial concentrations of glucagon-like peptide 1 (GLP-1), peptide YY (PYY), and insulin are widely reported, but the importance of GLP-1 in post-bariatric physiology remains debated. Here, we show that GLP-1 is a major driver of insulin secretion after bariatric surgery, as demonstrated by blocking GLP-1 receptors (GLP1Rs) post-gastrectomy in lean humans using Exendin-9 or in mice using an anti-GLP1R antibody. Transcriptomics and peptidomics analyses revealed that human and mouse enteroendocrine cells were unaltered post-surgery; instead, we found that elevated plasma GLP-1 and PYY correlated with increased nutrient delivery to the distal gut in mice. We conclude that increased GLP-1 secretion after bariatric surgery arises from rapid nutrient delivery to the distal gut and is a key driver of enhanced insulin secretion.

PYY plays a key role in the resolution of diabetes following bariatric surgery in humans

BACKGROUND

Bariatric surgery leads to early and long-lasting remission of type 2 diabetes (T2D). However, the mechanisms behind this phenomenon remain unclear. Among several factors, gut hormones are thought to be crucial mediators of this effect. Unlike GLP-1, the role of the hormone peptide tyrosine tyrosine (PYY) in bariatric surgery in humans has been limited to appetite regulation and its impact on pancreatic islet secretory function and glucose metabolism remains under-studied.

METHODS

Changes in PYY concentrations were examined in obese patients after bariatric surgery and compared to healthy controls. Human pancreatic islet function was tested upon treatment with sera from patients before and after the surgery, in presence or absence of PYY. Alterations in intra-islet PYY release and insulin secretion were analysed after stimulation with short chain fatty acids (SCFAs), bile acids and the cytokine IL-22.

FINDINGS

We demonstrate that PYY is a key effector of the early recovery of impaired glucose-mediated insulin and glucagon secretion in bariatric surgery. We establish that the short chain fatty acid propionate and bile acids, which are elevated after surgery, can trigger PYY release not only from enteroendocrine cells but also from human pancreatic islets. In addition, we identify IL-22 as a new factor which is modulated by bariatric surgery in humans and which directly regulates PYY expression and release.

INTERPRETATION

This study shows that some major metabolic benefits of bariatric surgery can be emulated ex vivo. Our findings are expected to have a direct impact on the development of new non-surgical therapy for T2D correction.

Eating peptides: biomarkers of neurodegeneration in amyotrophic lateral sclerosis and frontotemporal dementia

Objective

Physiological changes potentially influence disease progression and survival along the Amyotrophic Lateral Sclerosis (ALS)-Frontotemporal dementia (FTD) spectrum. The peripheral peptides that regulate eating and metabolism may provide diagnostic, metabolic, and progression biomarkers. The current study aimed to examine the relationships and biomarker potential of hormonal peptides.

Methods

One hundred and twenty-seven participants (36 ALS, 26 ALS- cognitive, patients with additional cognitive behavioral features, and 35 behavioral variant FTD (bvFTD) and 30 controls) underwent fasting blood analyses of leptin, ghrelin, neuropeptide Y (NPY), peptide YY (PYY), and insulin levels. Relationships between endocrine measures, cognition, eating behaviors, and body mass index (BMI) were investigated. Biomarker potential was evaluated using multinomial logistic regression for diagnosis and correlation to disease duration.

Results

Compared to controls, ALS and ALS-cognitive had higher NPY levels and bvFTD had lower NPY levels, while leptin levels were increased in all patient groups. All groups had increased insulin levels and a state of insulin resistance compared to controls. Lower NPY levels correlated with increasing eating behavioral change and BMI, while leptin levels correlated with BMI. On multinomial logistic regression, NPY and leptin levels were found to differentiate between diagnosis. Reduced Neuropeptide Y levels correlated with increasing disease duration, suggesting it may be useful as a potential marker of disease progression.

Interpretation

ALS-FTD is characterized by changes in NPY and leptin levels that may impact on the underlying regional neurodegeneration as they were predictive of diagnosis and disease duration, offering the potential as biomarkers and for the development of interventional treatments.

Specific Microbiota Dynamically Regulate the Bidirectional Gut-Brain Axis Communications in Mice Fed Meat Protein Diets

The purpose of this study was to characterize the dynamic changes of different protein diets to gut microbiota and explore the influence on communications between the gut and the brain. C57BL/6J mice were fed casein, soy protein, and four kinds of processed meat proteins at a normal dose of 20% for 8 months. Bacteroidales S24-7 abundance increased from 4 to 8 months, whereas the abundances of six genera including Akkermansia decreased remarkably. Lachnospiraceae Unclassified abundance in the emulsion-type sausage protein and stewed pork protein groups showed an opposite change from 4 to 8 months. Twenty-eight and 48 specific operational taxonomy units in cecum and colon respectively were involved in regulating serotonin, peptide YY, leptin, and insulin levels. Specific microbiota was involved, directly or indirectly through signaling molecules, in the regulation of body metabolism, which may affect the communications between the gut and brain and cause different growth performances.

Secretion of Gut Hormones and Expression of Sweet Taste Receptors and Glucose Transporters in a Rat Model of Obesity

OBJECTIVES

This study was undertaken to compare gut hormone secretion between high-fat-fed and control rats, and to examine the corresponding changes in the expression of sweet taste receptors and glucose transporters in the small intestine and hypothalamus.

METHODS

Four-week-old male Sprague Dawley rats were fed a standard or high-fat diet for 8 weeks (10 in each group), followed by an oral glucose tolerance test (50% glucose solution, 2 g/kg). Blood was sampled for glucose, insulin, glucagon-like peptide-1 (GLP-1) and polypeptide YY (PYY) assays. One week later, small intestinal and hypothalamic tissue were analyzed for sweet taste receptor and glucose transporter expression by real-time PCR.

RESULTS

After oral glucose, plasma GLP-1 concentrations were higher in high-fat-fed than standard-fat-fed rats (group × time interaction, p < 0.01) with significant differences at t = 15 min (p < 0.01) and 30 min (p < 0.05). Plasma PYY concentrations were lower in high-fat-fed than control rats at t = 0, 15 min (p < 0.05, respectively) and 120 min (p < 0.01). There were no differences in the expression of sweet taste receptors or glucose transporters between high-fat-fed and control rats in the duodenum, ileum, or hypothalamus.

CONCLUSIONS

Changes in GLP-1 and PYY secretion after a high-fat diet appear unrelated to any changes in the expression of sweet taste receptors or glucose transporters. Impaired PYY secretion with high-fat feeding suggests that PYY analogues may provide a potential therapy in the treatment of obesity.

Postprandial gut hormone responses to Hass avocado meals and their association with visual analog scores in overweight adults: A randomized 3 × 3 crossover trial

OBJECTIVE

To evaluate changes in postingestive gut hormone concentrations from the consumption of Hass avocado by addition or inclusion to lunch test meals, and to examine their association with measures of appetite sensation.

METHODS

A randomized 3 × 3 crossover study was conducted with 26 healthy overweight adults. Participants consumed one of three test meals: avocado-free control (C); isoenergic avocado inclusive (AI); and, energy increased avocado added (AA) one week apart. Ghrelin, peptide YY_3-36 (PYY_3-36), gastric inhibitory peptide (GIP) and glucagon-like peptide-1 (GLP-1) concentrations were measured at specific times before and following the test meals. Appetite sensations (Hunger, Fullness, Satisfied, Desire, How Much) were self-assessed using a visual analog scale (VAS) tool at matching time points and a Composite VAS score was computed. Mixed models and repeated measures analysis were used to compare differences among the test meals for VAS measurements and gut hormones, and their associations were evaluated using regression analysis.

RESULTS

A decrease in the 3-hour GLP-1 area under the curve (AUC) was observed in the AA meal compared to the C meal (P = 0.03). Negative associations were found for PYY_3-36 and GIP for Hunger, Desire and How Much, and positive associations for Fullness, Satisfied and the Composite VAS score (all P < 0.001). For GLP-1, a negative association for Hunger and a positive association for Satisfied and the Composite VAS score (all P < 0.05) were noted.

CONCLUSIONS

Postprandial responses to PYY_3-36, GIP and GLP-1 concentrations were associated with VAS measures and the Composite VAS score following consumption of test meals in overweight adults.

Novel ex Vivo Experimental Setup to Assay the Vectorial Transepithelial Enteroendocrine Secretions of Different Intestinal Segments

The enteroendocrine system coordinates gastrointestinal (GI) tract functionality and the whole organism. However, the scarcity of enteroendocrine cells and their scattered distribution make them difficult to study. Here, we glued segments of the GI wall of pigs to a silicon tube, keeping the apical and the basolateral sides separate. The fact that there was less than 1% of 70-kDa fluorescein isothiocyanate (FITC)-dextran on the basolateral side proved that the gluing was efficient. Since the lactate dehydrogenase leakage at basolateral side was lower than 0.1% (1.40 ± 0.17 nKatals) it proved that the tissue was viable. The intestinal barrier function was maintained as it is in segments mounted in Ussing chambers (the amount of Lucifer Yellow crossing it, was similar between them; respectively, % LY, 0.48 ± 0.13; 0.52 ± 0.09; p > 0.05). Finally, apical treatments with two different extract produced differential basolateral enterohormone secretions (basolateral PYY secretion vs control; animal extract, 0.35 ± 0.16; plant extract, 2.5 ± 0.74; p < 0.05). In conclusion, we report an ex vivo system called "Ap-to-Bas" for assaying vectorial transepithelial processes that makes it possible to work with several samples at the same time. It is an optimal device for enterohormone studies in the intestine.

Effects of chronic heat exposure on growth performance, intestinal epithelial histology, appetite-related hormones and genes expression in broilers

BACKGROUND

Heat stress often occurs in the modern poultry industry, which impairs growth performance, particularly via reducing appetite. This study was aimed to investigate the mechanism of attenuating appetite by chronic heat exposure in broilers. A total of 144 broilers (28 days old) were allocated to normal control (NC, 22 °C), heat stress (32 °C), and pair-fed (22 °C) groups.

RESULTS

Chronic heat exposure significantly increased cloacal temperatures and respiration rates, decreased the average daily feed intake and average daily gain, increased feed-to-gain ratio compared with the NC group, and elevated the concentrations of ghrelin and cholecystokinin (CCK) both in serum and intestine, as well as peptide YY and somatostatin in intestine on 35- or 42-day-old broilers. Moreover, heat exposure decreased villi height (VH) and the ratio of VH to crypt depth (CD), while it increased CD in the jejunum on 35- and 42 day-olds, increased (P < 0.05) the concentrations of valine and isoleucine in plasma on 42 days, and upregulated (P < 0.05) the expression of taste receptor type 1 members 1 and 3 (T1R1 and T1R3), CCK, and ghrelin in the intestine on 35- or 42-day-old broilers.

CONCLUSION

Chronic heat exposure impairs the performance, intestinal morphology and appetite, which may be correlated with the increased secretion or gene expression of appetite-related hormones and genes, and the higher expression of nutrient-sensing receptors (T1R1 and T1R3) in broilers. © 2018 Society of Chemical Industry.