Intestinal Signaling of Proteins and Digestion-Derived Products Relevant to Satiety

Fully Organic Sensors for Continuous Real-Time Digestion Monitoring

Monitoring the gastric digestive function is important for the diagnosis of gastric disorders and drug development. However, there is no report on the in situ and real-time monitoring of digestive functions. Herein, we report a flexible fully organic sensor to effectively monitor protein digestion in situ in a simulated gastric environment for the first time. The sensors are made of a blend of gluten that is a protein and poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) that is a conducting polymer. During the protein digestion, the breakdown of the polypeptides increases the level of separation among the PEDOT chains, thereby increasing the resistance. The resistance variation is sensitive to various conditions, including the concentration of pepsin that is the enzyme for protein digestion, temperature, pH value, and digestive drugs. Hence, these sensors can provide real-time information about the digestion and efficacy of digestive drugs. In addition, the signals can be collected via a convenient wireless communication manner.

Current advances for in vitro protein digestibility

Protein is an essential macronutrient in our diet, source of nitrogen and essential amino acids, but the biological utilization of dietary protein depends on its digestibility and the absorption of amino acids and peptides in the gastrointestinal tract. The methods to define the amount and the quality of protein to meet human nutritional needs, such as the Digestible Indispensable Amino Acid Score (DIAAS), require the use of animal models or human studies. These in vivo methods are the reference in protein quality evaluation, but they are expensive and long-lasting procedures with significant ethical restrictions. Therefore, the development of rapid, reproducible and in vitro digestion methods validated with in vivo data is an old demand. This review describes the challenges of the in vitro digestion methods in the evaluation of the protein nutritional quality. In addition to the technical difficulties to simulate the complex and adaptable processes of digestion and absorption, these methods are affected by similar limitations as the in vivo procedures, i.e., analytical techniques to accurately determine bioavailable amino acids and the contribution of the endogenous nitrogen. The in vitro methods used for the evaluation of protein digestibility, with special attention on those showing comparative data, are revised, emphasizing their pros and cons. The internationally harmonized digestion protocol proposed by the INFOGEST network is being adapted to evaluate protein and amino acid digestibility. The inter-laboratory reproducibility of this protocol was demonstrated for dairy products. The in vivo/in vitro comparability results obtained to date with this protocol for several plant and animal sources are promising, but it requires an extensive validation with a wider range of foods and substrates with known in vivo digestibility. These in vitro methods will probably not be applicable to all foods, and therefore, it is important to identify their limitations, not to elude their use, but to apply them within the limits, by using the appropriate standards and references, and always as a complementary tool to in vivo tests to reduce their number.

Metabolic Syndrome and Biotherapeutic Activity of Dairy (Cow and Buffalo) Milk Proteins and Peptides: Fast Food-Induced Obesity Perspective-A Narrative Review

Metabolic syndrome (MS) is defined by the outcome of interconnected metabolic factors that directly increase the prevalence of obesity and other metabolic diseases. Currently, obesity is considered one of the most relevant topics of discussion because an epidemic heave of the incidence of obesity in both developing and underdeveloped countries has been reached. According to the World Obesity Atlas 2023 report, 38% of the world population are presently either obese or overweight. One of the causes of obesity is an imbalance of energy intake and energy expenditure, where nutritional imbalance due to consumption of high-calorie fast foods play a pivotal role. The dynamic interactions among different risk factors of obesity are highly complex; however, the underpinnings of hyperglycemia and dyslipidemia for obesity incidence are recognized. Fast foods, primarily composed of soluble carbohydrates, non-nutritive artificial sweeteners, saturated fats, and complexes of macronutrients (protein-carbohydrate, starch-lipid, starch-lipid-protein) provide high metabolic calories. Several experimental studies have pointed out that dairy proteins and peptides may modulate the activities of risk factors of obesity. To justify the results precisely, peptides from dairy milk proteins were synthesized under in vitro conditions and their contributions to biomarkers of obesity were assessed. Comprehensive information about the impact of proteins and peptides from dairy milks on fast food-induced obesity is presented in this narrative review article.

Assessment of genetically modified maize DP202216 for food and feed uses, under Regulation (EC) No 1829/2003 (application EFSA-GMO-NL-2019-159)

Genetically modified maize DP202216 was developed to confer tolerance to glufosinate-ammonium-containing herbicides and to provide an opportunity for yield enhancement under field conditions. These properties were achieved by introducing the mo-pat and zmm28 expression cassettes. The molecular characterisation data and bioinformatic analyses do not identify issues requiring food/feed safety assessment. None of the identified differences in the agronomic/phenotypic and compositional characteristics tested between maize DP202216 and its comparator needs further assessment, except for the levels of stearic acid (C18:0), which do not raise nutritional and safety concerns. The GMO Panel does not identify safety concerns regarding the toxicity and allergenicity of the PAT and ZMM28 proteins as expressed in maize DP202216, and finds no evidence that the genetic modification would change the overall allergenicity of maize DP202216. In the context of this application, the consumption of food and feed from maize DP202216 does not represent a nutritional concern in humans and animals. The GMO Panel concludes that maize DP202216 is as safe as the comparator and non-GM reference varieties tested, and no post-market monitoring of food/feed is considered necessary. In the case of accidental release of viable maize DP202216 grains into the environment, this would not raise environmental safety concerns. The post-market environmental monitoring plan and reporting intervals are in line with the intended uses of maize DP202216. The GMO Panel concludes that maize DP202216 is as safe as its comparator and the tested non-GM reference varieties with respect to potential effects on human and animal health and the environment.

Identification and target of action of cholecystokinin-releasing peptides from simulated digestion hydrolysate of wheat protein

BACKGROUND

Wheat protein intake leads to improved appetite control. However, the active components causing appetite in wheat have not been fully clarified. Gut cholecystokinin (CCK) plays a vital role in appetite control. This study aimed to investigate the ability of wheat protein digest (WPD) to stimulate CCK secretion and clarify the active components and target of action.

RESULTS

WPD was prepared by a simulated gastrointestinal digestion model. WPD treatment with a concentration of 5 mg mL-1 significantly stimulated CCK secretion in enteroendocrine STC-1 cells (P < 0.05). Furthermore, oral gavage with WPD in mice significantly increased plasma CCK level at 60 min (P < 0.01). Preparative C18 column separation was used to isolate peptide fractions associated with CCK secretion and peptide sequences were identified by liquid chromatography-tandem mass spectrometry. A new CCK-releasing peptide, RYIVPL, that potently stimulated CCK secretion was successfully identified. After pretreatment with a specific calcium-sensing receptor (CaSR) antagonist, NPS 2143, CCK secretion induced by WPD or RYIVPL was greatly suppressed, suggesting that CaSR was involved in WPD- or RYIVPL-induced CCK secretion.

CONCLUSION

The present study demonstrated that WPD has an ability to stimulate CCK secretion in vitro and in vivo, and determined that peptide RYIVPL in WPD could stimulate CCK secretion through CaSR. © 2023 Society of Chemical Industry.

Plant-based meat analogues enhance the gastrointestinal motility function and appetite of mice by specific volatile compounds and peptides

Eating behavior is critical for maintaining energy homeostasis. Previous studies have found that plant-based meat analogues increased diet intake in mice compared with animal meat under a free feeding mode, however the reasons were unclear. To explore the underlying mechanisms of plant-based meat analogues increasing diet intake, mice were fed animal or plant-based pork and beef analogue diets, respectively. Biochemical and histological analyses were performed to evaluate appetite-regulating hormones and gastrointestinal motility function. Peptiomics and GC-IMS were applied to identify key substances. We found that the intake of plant-based meat analogues significantly enhanced the gastrointestinal motility function of mice. The long-term intake (68 days) of plant-based meat analogues significantly increased the muscle layer thickness of the duodenum and jejunum of mice; the activity of gastrointestinal cells of Cajal were also promoted by upregulating the expression of c-kit related signals as compared to animal meat; plant-based meat analogues intake markedly enhanced the signal intensity of the intestinal neurotransmitter 5-hydroxytryptamine (5-HT) by upregulating the expression of 5-HT synthase and receptors but downregulating its transporter and catabolic enzyme in the intestine. Moreover, plant-based meat analogues intake significantly increased levels of appetite-stimulating factors in the peripheral or hypothalamus but reduced levels of appetite-suppressing factors compared with animal meat. Specific volatile compounds were significantly associated with appetite regulating factors. Among them, 7 substances such as linalool have a potential promoting effect on food intake. Besides, different digestive peptides in gastrointestinal tract may affect eating behavior mainly through the neuroactive ligand-receptor interaction pathway, exerting hormone-like effects or influencing endocrine cell secretion. These findings preliminarily clarified the mechanism of plant-based meat analogues promoting diet intake and provided a theoretical basis for a reasonable diet.

Intestinal gluconeogenesis: A translator of nutritional information needed for glycemic and emotional balance

At the interface between the outside world and the self, the intestine is the first organ receiving nutritional information. One intestinal function, gluconeogenesis, is activated by various nutrients, particularly diets enriched in fiber or protein, and thus results in glucose production in the portal vein in the post-absorptive period. The detection of portal glucose induces a nervous signal controlling the activity of the central nuclei involved in the regulation of metabolism and emotional behavior. Induction of intestinal gluconeogenesis is necessary for the beneficial effects of fiber or protein-enriched diets on metabolism and emotional behavior. Through its ability to translate nutritional information from the diet to the brain's regulatory centers, intestinal gluconeogenesis plays an essential role in maintaining physiological balance.

Protein-based nutritional strategies to manage the development of diabetes: evidence and challenges in human studies

Type 2 diabetes mellitus (T2DM) is one of the most prevalent diseases in modern society, governed by both genetic and environmental factors, such as nutritional habits. This metabolic disorder is characterized by insulin resistance, which is related to high blood glucose levels, implying negative health effects in humans, hindering the healthy ageing of people. The relationship between food and health is clear, and the ingestion of specific nutrients modulates some physiological processes, potentially implying biologically relevant changes, which can translate into a health benefit. This review aims to summarize human studies published in which the purpose was to investigate the effect of protein ingestion (in native state or as hydrolysates) on human metabolism. Overall, several studies showed how protein ingestion might induce a decrease of glucose concentration in the postprandial state (area under the curve), although it is highly dependent on the source and the dose. Other studies showed no biological effects upon protein consumption, mostly with fish-derived products. In addition, the major challenges and perspectives in this research field are highlighted, suggesting the future directions, towards which scientists should focus on. The dietary intake of proteins has been proven to likely exert a beneficial effect on diabetes-related parameters, which can have a biological relevance in the prevention and pre-treatment of diabetes. However, the number of well-designed human studies carried out to date to demonstrate the effects of specific proteins or protein hydrolysates in vivo is still scarce.

Enteroendocrine cells and gut hormones as potential targets in the crossroad of the gut-kidney axis communication

Recent studies suggest that disruptions in intestinal homeostasis, such as changes in gut microbiota composition, infection, and inflammatory-related gut diseases, can be associated with kidney diseases. For instance, genomic investigations highlight how susceptibility genes linked to IgA nephropathy are also correlated with the risk of inflammatory bowel disease. Conversely, investigations demonstrate that the use of short-chain fatty acids, produced through fermentation by intestinal bacteria, protects kidney function in models of acute and chronic kidney diseases. Thus, the dialogue between the gut and kidney seems to be crucial in maintaining their proper function, although the factors governing this crosstalk are still emerging as the field evolves. In recent years, a series of studies have highlighted the significance of enteroendocrine cells (EECs) which are part of the secretory lineage of the gut epithelial cells, as important components in gut-kidney crosstalk. EECs are distributed throughout the epithelial layer and release more than 20 hormones in response to microenvironment stimuli. Interestingly, some of these hormones and/or their pathways such as Glucagon-Like Peptide 1 (GLP-1), GLP-2, gastrin, and somatostatin have been shown to exert renoprotective effects. Therefore, the present review explores the role of EECs and their hormones as regulators of gut-kidney crosstalk and their potential impact on kidney diseases. This comprehensive exploration underscores the substantial contribution of EEC hormones in mediating gut-kidney communication and their promising potential for the treatment of kidney diseases.

Interaction mechanism of egg derived peptides RVPSL and QIGLF with dipalmitoyl phosphatidylcholine membrane: microcalorimetric and molecular dynamics simulation studies

BACKGROUND

Egg-derived peptides are becoming increasingly popular due to their biological activity and non-toxic effects. The egg-derived peptides Arg-Val-Pro-Ser-Leu (RVPSL) and Gln-Ile-Gly-Leu-Phe (QIGLF) display strong angiotensin-converting enzyme inhibitory activity and they can be taken up by intestinal epithelial cells. The interaction of the egg-derived peptides RVPSL and QIGLF with the membrane remains unclear.

RESULTS

The position and structure of the peptides in the membrane were calculated. The maximum density values of RVPSL and QIGLF were 2.27 and 1.22 nm from the center of the 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) membrane, respectively, indicating that peptides penetrated the membrane-water interface and were embedded in the membrane. The interaction of RVPSL and QIGLF with the DPPC membrane did not affect the average area per lipid or the lipid sequence parameters. The thermodynamic parameters ΔH, ΔG, and ΔS of the interaction between the peptide RVPSL with the DPPC membrane were 17.91 kJ mol-1 , -17.63 kJ mol-1 , 187.5 J mol-1 ·k-1 , respectively. The thermodynamic parameters ΔH, ΔG, and ΔS of the interaction between peptide QIGLF with DPPC membrane were 17.10 kJ mol-1 , -17.12 kJ mol-1 , 114.8 J mol-1 ·k-1 , respectively.

CONCLUSION

The results indicated that the binding of peptides RVPSL and QIGLF to DPPC is an endothermic, spontaneous, and entropy-driven reaction. The results of the study are relevant to the problem of the low bioavailability of bioactive peptides (BP). © 2023 Society of Chemical Industry.

Effects of Bioactive Peptides from Atlantic Salmon Processing By-Products on Oxyntopeptic and Enteroendocrine Cells of the Gastric Mucosa of European Seabass and Gilthead Seabream

The present study was designed to evaluate the effects of dietary levels of bioactive peptides (BPs) derived from salmon processing by-products on the presence and distribution of peptic cells (oxyntopeptic cells, OPs) and enteric endocrine cells (EECs) that contain GHR, NPY and SOM in the gastric mucosa of European seabass and gilthead seabream. In this study, 27 seabass and 27 seabreams were divided into three experimental groups: a control group (CTR) fed a control diet and two groups fed different levels of BP to replace fishmeal: 5% BP (BP5%) and 10% BP (BP10%). The stomach of each fish was sampled and processed for immunohistochemistry. Some SOM, NPY and GHR-IR cells exhibited alternating "open type" and "closed type" EECs morphologies. The BP10% group (16.8 ± 7.5) showed an increase in the number of NPY-IR cells compared to CTR (CTR 8.5 ± 4.8) and BP5% (BP10% vs. CTR p ≤ 0.01; BP10% vs. BP5% p ≤ 0.05) in the seabream gastric mucosa. In addition, in seabream gastric tissue, SOM-IR cells in the BP 10% diet (16.8 ± 3.5) were different from those in CTR (12.5 ± 5) (CTR vs. BP 10% p ≤ 0.05) and BP 5% (12.9 ± 2.5) (BP 5% vs. BP 10% p ≤ 0.01). EEC SOM-IR cells increased at 10% BP (5.3 ± 0.7) compared to 5% BP (4.4 ± 0.8) (5% BP vs. 10% BP p ≤ 0.05) in seabass. The results obtained may provide a good basis for a better understanding of the potential of salmon BPs as feed ingredients for seabass and seabream.

CCK and GLP-1 response on enteroendocrine cells of semi-dynamic digests of hydrolyzed and intact casein

A semi-dynamic gastrointestinal device was employed to explore the link between protein structure and metabolic response upon digestion for two different substrates, a casein hydrolysate and the precursor micellar casein. As expected, casein formed a firm coagulum that remained until the end of the gastric phase while the hydrolysate did not develop any visible aggregate. Each gastric emptying point was subjected to a static intestinal phase where the peptide and amino acid composition changed drastically from that found during the gastric phase. Gastrointestinal digests from the hydrolysate were characterized by a high abundancy of resistant peptides and free amino acids. Although all gastric and intestinal digests from both substrates induced the secretion of cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) in STC-1 cells, GLP-1 levels were maximum in response to gastrointestinal digests from the hydrolysate. The enrichment of protein ingredients with gastric-resistant peptides by enzymatic hydrolysis is proposed as strategy to deliver protein stimuli to the distal gastrointestinal tract to control food intake or type 2 diabetes.

A multi-centre peptidomics investigation of food digesta: current state of the art in mass spectrometry analysis and data visualisation

Mass spectrometry has become the technique of choice for the assessment of a high variety of molecules in complex food matrices. It is best suited for monitoring the evolution of digestive processes in vivo and in vitro. However, considering the variety of equipment available in different laboratories and the diversity of sample preparation methods, instrumental settings for data acquisition, statistical evaluations, and interpretations of results, it is difficult to predict a priori the ideal parameters for optimal results. The present work addressed this uncertainty by executing an inter-laboratory study with samples collected during in vitro digestion and presenting an overview of the state-of-the-art mass spectrometry applications and analytical capabilities available for studying food digestion. Three representative high-protein foods - skim milk powder (SMP), cooked chicken breast and tofu - were digested according to the static INFOGEST protocol with sample collection at five different time points during gastric and intestinal digestion. Ten laboratories analysed all digesta with their in-house equipment and applying theirconventional workflow. The compiled results demonstrate in general, that soy proteins had a slower gastric digestion and the presence of longer peptide sequences in the intestinal phase compared to SMP or chicken proteins, suggesting a higher resistance to the digestion of soy proteins. Differences in results among the various laboratories were attributed more to the peptide selection criteria than to the individual analytical platforms. Overall, the combination of mass spectrometry techniques with suitable methodological and statistical approaches is adequate for contributing to the characterisation of the recently defined digestome.

Membrane filtration processing of infant milk formula alters protein digestion in young pigs

Reducing heat treatment (HT) during processing of infant milk formula (IMF) is desirable to produce a product that more closely resembles breast milk. By employing membrane filtration (MEM), we produced an IMF (60:40 whey to casein ratio) at pilot scale (250 kg). MEM-IMF had a significantly higher content of native whey (59.9 %) compared to HT-IMF (4.5 %) (p < 0.001). Pigs, at 28 days old, were blocked by sex, weight and litter origin and assigned to one of two treatments (n = 14/treatment): (1) starter diet containing 35 % of HT-IMF powder or (2) starter diet containing 35 % of MEM-IMF powder for 28 days. Body weight and feed intake were recorded weekly. Pigs at day 28 post weaning were sacrificed 180 min after their final feeding, for the collection of gastric, duodenal, jejunum and ileal contents (n = 10/treatment). MEM-IMF diet resulted in more water-soluble proteins and higher levels of protein hydrolysis in the digesta at various gut locations compared to HT-IMF (p < 0.05). In the jejunal digesta, a higher concentration of free amino acids were present post MEM-IMF consumption (247 ± 15 µmol g^-1 of protein in digesta) compared to HT-IMF (205 ± 21 µmol g^-1 of protein). Overall, average daily weight gain, average dairy feed intake and feed conversion efficiency were similar for pigs fed either MEM-IMF or HT-IMF diets, but differences and trends to difference of these indicators were determined in particular intervention periods. In conclusion, reducing heat treatment during processing of IMF influenced protein digestion and revealed minor effects on growth parameters providing in vivo evidence that babies who are fed with IMF processed by MEM are likely to have different protein digestion kinetics but minimal effect on overall growth trajectories as babies fed IMF processed by traditional thermal processing.

Enhanced secretion of satiety-promoting gut hormones in healthy humans after consumption of white bread enriched with cellular chickpea flour: A randomized crossover study

BACKGROUND

Dietary intake of pulses is associated with beneficial effects on body weight management and cardiometabolic health, but some of these effects are now known to depend on integrity of plant cells, which are usually disrupted by flour milling. Novel cellular flours preserve the intrinsic dietary fiber structure of whole pulses and provide a way to enrich preprocessed foods with encapsulated macronutrients.

OBJECTIVES

This study aimed to determine the effects of replacing wheat flour with cellular chickpea flour on postprandial gut hormones, glucose, insulin, and satiety responses to white bread.

METHODS

We conducted a double-blind randomized crossover study in which postprandial blood samples and scores were collected from healthy human participants (n = 20) after they consumed bread enriched with 0%, 30%, or 60% (wt/wt) cellular chickpea powder (CCP, 50 g total starch per serving).

RESULTS

Bread type significantly affected postprandial glucagon-like peptide-1 (GLP-1) and peptide YY (PYY) responses (time × treatment, P = 0.001 for both). The 60% CCP breads elicited significantly elevated and sustained release of these anorexigenic hormones [between 0% and 60% CPP-GLP-1: mean difference incremental area under the curve (iAUC), 3101 pM/min; 95% CI: 1891, 4310; P-adjusted < 0.001; PYY: mean difference iAUC, 3576 pM/min; 95% CI: 1024, 6128; P-adjusted = 0.006] and tended to increase fullness (time × treatment, P = 0.053). Moreover, bread type significantly influenced glycemia and insulinemia (time × treatment, P < 0.001, P = 0.006, and P = 0.001 for glucose, insulin, and C-peptide, respectively), with 30% CCP breads eliciting a >40% lower glucose iAUC (P-adjusted < 0.001) than the 0% CCP bread. Our in vitro studies revealed slow digestion of intact chickpea cells and provide a mechanistic explanation for the physiologic effects.

CONCLUSIONS

The novel use of intact chickpea cells to replace refined flours in a white bread stimulates an anorexigenic gut hormone response and has potential to improve dietary strategies for prevention and treatment of cardiometabolic diseases. This study was registered at clinicaltrials.gov as NCT03994276.

Low glycemic index common bean snack increased satiety without modifying energy intake in adults with normal weight: randomized crossover trials

This study aimed to evaluate the short-term effect of a common bean baked snack (CBBS) and cooked bean consumption on energy intake, satiety, glycemic response, and palatability in subjects with normal weight (Study 1) and overweight (Study 2) and to determine the glycemic index of CBBS (Study 3). For studies 1 and 2, satiety and glycemic response were measured over 45 min after consuming CBBS, cooked beans or white bread preload, and energy intake at an ad libitum test meal was calculated. Energy intake remained similar after consuming the three preloads in both studies. Compared to white bread, CBBS consumption increased fullness by 52% in subjects with normal weight but not in those with overweight. The CBBS calculated glycemic index was considered low (42). Consumption of low glycemic index CBBS increased satiety in adults with a normal weight. Long-term trials assessing the effects on body weight management are necessary.

Bioactive and Sensory Di- and Tripeptides Generated during Dry-Curing of Pork Meat

Dry-cured pork products, such as dry-cured ham, undergo an extensive proteolysis during manufacturing process which determines the organoleptic properties of the final product. As a result of endogenous pork muscle endo- and exopeptidases, many medium- and short-chain peptides are released from muscle proteins. Many of them have been isolated, identified, and characterized, and some peptides have been reported to exert relevant bioactivity with potential benefit for human health. However, little attention has been given to di- and tripeptides, which are far less known, although they have received increasing attention in recent years due to their high potential relevance in terms of bioactivity and role in taste development. This review gathers the current knowledge about di- and tripeptides, regarding their bioactivity and sensory properties and focusing on their generation during long-term processing such as dry-cured pork meats.

The influence of dough kneading time and flour particle size distribution on white bread structure, glycemic response and aspects of appetite

BACKGROUND & AIMS

White bread is widely consumed in many countries despite being a high-glycemic index (GI) food. It has been shown that the "food matrix effect" may help with diabetes and obesity management through lowering GI and appetite. This study aimed at investigating the effects of dough kneading time and flour particle size on white bread structure, glycemic response, and aspects of appetite.

METHODS

A two-phase randomized cross-over design was used in 10 healthy subjects over the course of 2 h. In phase 1, Texture Profile Analysis (TPA) attributes, Scanning Electron Microscope (SEM) image, glycemic response, and appetite aspects of white bread made with a 15-min dough kneading time (K15) were compared with white bread made with a 10-min dough kneading time (K10). In phase 2, TPA, SEM image, glycemic response, and satiety score of white bread made with coarse flour (CF) were compared to white bread made with fine flour (FF).

RESULT

With increasing hardness (force required to compress a food between the molars to a given deformation), total blood glucose IAUC in K15 (IAUC = 119 ± 12; GI = 66) was significantly (p < 0.05) lower than in K10 (IAUC = 154 ± 10; GI = 81). No marked difference was observed between K15 and K10 on aspects of appetite except for hunger. There was no significant (p > 0.05) difference in glycemic response between CF (IAUC = 126 ± 18; GI = 64) and FF (IAUC = 147 ± 12; GI = 81). Similarly, no discernible difference in satiety between CF and FF.

CONCLUSION

Changes in processing conditions can improve blood glucose response relalated to white bread consumption.

Dietary Polyphenols and In Vitro Intestinal Fructose Uptake and Transport: A Systematic Literature Review

Recent evidence links chronic consumption of large amounts of fructose (FRU) with several non-communicable disease. After ingestion, dietary FRU is absorbed into the intestinal tract by glucose transporter (GLUT) 5 and transported to the portal vein via GLUT2. GLUT2 is primarily localized on the basolateral membrane, but GLUT2 may be dislocated post-prandially from the basolateral membrane of intestinal cells to the apical one. Polyphenols (PP) are plant secondary metabolites that exert hypoglycemic properties by modulating intracellular insulin signaling pathways and by inhibiting intestinal enzymes and transporters. Post-prandially, PP may reach high concentrations in the gut lumen, making the inhibition of FRU absorption a prime target for exploring the effects of PP on FRU metabolism. Herein, we have systematically reviewed studies on the effect of PP and PP-rich products on FRU uptake and transport in intestinal cells. In spite of expectations, the very different experimental conditions in the various individual studies do not allow definitive conclusions to be drawn. Future investigations should rely on standardized conditions in order to obtain comparable results that allow a credible rating of polyphenols and polyphenol-rich products as inhibitors of fructose uptake.

Insights into the constellating drivers of satiety impacting dietary patterns and lifestyle

Food intake and body weight regulation are of special interest for meeting today's lifestyle essential requirements. Since balanced energy intake and expenditure are crucial for healthy living, high levels of energy intake are associated with obesity. Hence, regulation of energy intake occurs through short- and long-term signals as complex central and peripheral physiological signals control food intake. This work aims to explore and compile the main factors influencing satiating efficiency of foods by updating recent knowledge to point out new perspectives on the potential drivers of satiety interfering with food intake regulation. Human internal factors such as genetics, gender, age, nutritional status, gastrointestinal satiety signals, gut enzymes, gastric emptying rate, gut microbiota, individual behavioral response to foods, sleep and circadian rhythms are likely to be important in determining satiety. Besides, the external factors (environmental and behavioral) impacting satiety efficiency are highlighted. Based on mechanisms related to food consumption and dietary patterns several physical, physiological, and psychological factors affect satiety or satiation. A complex network of endocrine and neuroendocrine mechanisms controls the satiety pathways. In response to food intake and other behavioral cues, gut signals enable endocrine systems to target the brain. Intestinal and gastric signals interact with neural pathways in the central nervous system to halt eating or induce satiety. Moreover, complex food composition and structures result in considerable variation in satiety responses for different food groups. A better understanding of foods and factors impacting the efficiency of satiety could be helpful in making smart food choices and dietary recommendations for a healthy lifestyle based on updated scientific evidence.

Exploring the Effects of Energy Constraints on Performance, Body Composition, Endocrinological/Hematological Biomarkers, and Immune System among Athletes: An Overview of the Fasting State

The Ramadan fasting period (RFP) means abstaining from consuming food and/or beverages during certain hours of the day—from sunrise to sunset. Engaging in exercise and sports during the RFP leads to the lipolysis of adipose tissue and an increase in the breakdown of peripheral fat, leading to an increase in fat consumption. The effects of the RFP on functional, hematological, and metabolic parameters needs further study as existing studies have reported contradictory results. The differences in the results of various studies are due to the geographical characteristics of Muslim athletes, their specific diets, and their genetics, which explain these variations. In recent years, the attention of medical and sports researchers on the effects of the RFP and energy restrictions on bodily functions and athletic performance has increased significantly. Therefore, this brief article examines the effects of the RFP on the immune system, body composition, hematology, and the functionality of athletes during and after the RFP. We found that most sporting activities were performed during any time of the day without being affected by Ramadan fasting. Athletes were able to participate in their physical activities during fasting periods and saw few effects on their performance. Sleep and nutritional factors should be adjusted so that athletic performance is not impaired.

Digestion characteristics of quinoa, barley and mungbean proteins and the effects of their simulated gastrointestinal digests on CCK secretion in enteroendocrine STC-1 cells

The demand for plant-based proteins has been rapidly increasing due to sustainability, ethical and health reasons. The present study aimed to investigate the digestion characteristics of three plant proteins (quinoa, barley and mungbean) based on an in vitro digestion model and the effect of their simulated gastrointestinal digests on satiety hormone cholecystokinin (CCK) secretion in enteroendocrine STC-1 cells. The nitrogen distribution in the digestion process, the relative molecular weight (MW) of peptides and the amino acid composition in simulated gastrointestinal digests were characterized. Quinoa protein had the highest proportion of soluble nitrogen after gastrointestinal digestion (85.79%), followed by barley protein (74.98%) and mungbean protein (64.14%), suggesting that quinoa protein was more easily digested than barley and mungbean proteins. The peptides but not free amino acids were the main components in the gastrointestinal digests of quinoa, barley, and mungbean proteins. The gastrointestinal digest of quinoa protein had a well balanced amino acid pattern, whereas that of barley protein was lacking Lys, and that of the mungbean protein was short of sulfur amino acids (Phe + Tyr) but rich in Lys. In terms of the ability to stimulate CCK secretion, the gastrointestinal digest of barley protein had a strong stimulatory effect on CCK secretion, while that of quinoa and mungbean proteins had only a weak stimulatory effect. After pretreatment with a specific calcium-sensing receptor (CaSR) antagonist NPS 2143, CCK secretion induced by the barley protein digest was greatly suppressed, indicating that CaSR was involved in barley protein digest-induced CCK secretion. These results show that quinoa protein has good nutritional quality, while barley protein is an excellent plant protein source to stimulate CCK secretion and has a potential application as a dietary supplement for obesity management.

Soybean protein hydrolysate stimulated cholecystokinin secretion and inhibited feed intake through calcium-sensing receptors and intracellular calcium signalling in pigs

Although soybean protein is the major component in livestock feeds, its effect on pigs' appetites is largely unknown. Recently, the importance of gut nutrient-sensing for appetite modulation by regulating anorectic gut hormone release has been recognised. This study investigates the roles of soybean proteins in appetite regulation, anorectic gut hormone secretion, and underlying mechanisms. The duodenal-cannulated piglets were used to evaluate the effects of soybean protein hydrolysate (SPH) on feed intake and anorectic hormone release, including cholecystokinin (CCK), peptide YY (PYY), glucagon-like peptide 1 (GLP-1), and glucose-dependent insulinotropic polypeptide (GIP) in the hepatic vein by infusing SPH. Identifying which nutrient-sensing receptor in pig duodenum response to SPH stimulation for gut hormone release was conducted. Using its antagonist, the role of the identified receptor in feed intake and anorectic hormone release was also investigated. Combination with an ex vivo perfusion system, the possible mechanism by which SPH exerts the effects in porcine duodenum was further illustrated. Results in vivo showed that intraduodenal infusion of SPH inhibited short-term feed intake in pigs and promoted CCK, PYY, and GIP secretion in the hepatic vein. SPH also increased duodenum calcium-sensing receptor (CaSR) expression. Pre-treated with CaSR antagonist NPS 2143, the feed intake of pigs tended to be attenuated by SPH (P = 0.09), and CCK release was also suppressed (P < 0.05), indicating that CaSR was involved in SPH-stimulated CCK release and inhibited feed intake in pigs. The ex vivo perfused duodenum tissues revealed that SPH-triggered CCK secretion was likeliest due to the activation of the intracellular Ca²⁺/TRPM5 pathway. Overall, this study's result illustrates that the diet soybean protein might decrease appetite in pigs by triggering duodenum CCK secretion by activating CaSR and the intracellular Ca²⁺/TRPM5 pathway.

Physiology of Taste Processing in the Tongue, Gut, and Brain

The gustatory system detects and informs us about the nature of various chemicals we put in our mouth. Some of these have nutritive value (sugars, amino acids, salts, and fats) and are appetitive and avidly ingested, whereas others (atropine, quinine, nicotine) are aversive and rapidly rejected. However, the gustatory system is mainly responsible for evoking the perception of a limited number of qualities that humans taste as sweet, umami, bitter, sour, salty, and perhaps fat [free fatty acids (FFA)] and starch (malto-oligosaccharides). The complex flavors and mouthfeel that we experience while eating food result from the integration of taste, odor, texture, pungency, and temperature. The latter three arise primarily from the somatosensory (trigeminal) system. The sensory organs used for detecting and transducing many chemicals are found in taste buds (TBs) located throughout the tongue, soft palate esophagus, and epiglottis. In parallel with the taste system, the trigeminal nerve innervates the peri-gemmal epithelium to transmit temperature, mechanical stimuli, and painful or cooling sensations such as those produced by changes in temperature as well as from chemicals like capsaicin and menthol, respectively. This article gives an overview of the current knowledge about these TB cells' anatomy and physiology and their trigeminal induced sensations. We then discuss how taste is represented across gustatory cortices using an intermingled and spatially distributed population code. Finally, we review postingestion processing (interoception) and central integration of the tongue-gut-brain interaction, ultimately determining our sensations as well as preferences toward the wholesomeness of nutritious foods. © 2021 American Physiological Society. Compr Physiol 11:1-35, 2021.

Deoxynivalenol (Vomitoxin)-Induced Anorexia Is Induced by the Release of Intestinal Hormones in Mice

Deoxynivalenol (DON), also known as vomitoxin, is a mycotoxin that can cause antifeeding and vomiting in animals. However, the mechanism of DON inducing anorexia is complicated. Studies have shown that intestinal hormones play a significant part in the anorexia caused by DON. We adopted the “modeling of acute antifeeding in mice” as the basic experimental model, and used two methods of gavage and intraperitoneal injection to explore the effect of intestinal hormones on the antifeedant response induced by DON in mice. We found that 1 and 2.5 mg/kg·bw of DON can acutely induce anorexia and increase the plasma intestinal hormones CCK, PYY, GIP, and GLP-1 in mice within 3 h. Direct injection of exogenous intestinal hormones CCK, PYY, GIP, and GLP-1 can trigger anorexia behavior in mice. Furthermore, the PYY receptor antagonist JNJ-31020028, GLP-1 receptor antagonist Exendin(9-39), CCK receptor antagonist Proglumide, GIP receptor antagonist GIP(3-30)NH₂ attenuated both intestinal hormone and DON-induced anorectic responses. These results indicate that intestinal hormones play a critical role in the anorexia response induced by DON.

In vitro protein and starch digestion kinetics of individual chickpea cells: from static to more complex in vitro digestion approaches

Attention has been given to more (semi-)dynamic in vitro digestion approaches ascertaining the consequences of dynamic in vivo aspects on in vitro digestion kinetics. As these often come with time and economical constraints, evaluating the consequence of stepwise increasing the complexity of static in vitro approaches using easy-to-handle digestion set-ups has been the center of our interest. Starting from the INFOGEST static in vitro protocol, we studied the influence of static gastric pH versus gradual gastric pH change (pH 6.3 to pH 2.5 in 2 h) on macronutrient digestion in individual cotyledon cells derived from chickpeas. Little effect on small intestinal proteolysis was observed comparing the applied digestion conditions. Contrary, the implementation of a gradual gastric pH change, with and without the addition of salivary α-amylase, altered starch digestion kinetics rates, and extents by 25%. The evaluation of starch and protein digestion, being co-embedded in cotyledon cells, did not only confirm but account for the interdependent digestion behavior. The insights generated in this study demonstrate the possibility of using a hypothesis-based approach to introduce dynamic factors to in vitro models while sticking to simple and cost-efficient set-ups.

Effect of Gazpacho, Hummus and Ajoblanco on Satiety and Appetite in Adult Humans: A Randomised Crossover Study

Nowadays, overweight and obesity has reached an epidemic level around the world. With the aim to tackle them, an interesting strategy is the study of food and ingredients with satiety properties. In addition to reducing food and/or calorie intake, this type of foods must be included as part of a healthy diet. With regard to this, it is well known that the Mediterranean Diet (MD) is a feeding pattern that helps us to maintain good health, providing an adequate intake of micronutrients and active compounds. With this background, the main aim of this research was to identify MD foods with a high satiating potential capacity. For this purpose, three typical foods of the Mediterranean region, mainly based on vegetables, were selected: hummus, ajoblanco and gazpacho. As a control, white bread was used. Twenty-four human healthy volunteers consumed a standard breakfast followed by the different typical Mediterranean foods, and then the subjective sensation of hunger and satiety for each food was assessed by visual analogue scales (VAS) during 3 h. Subsequently, volunteers had ad libitum access to a standard meal. The results indicate that gazpacho showed the highest satiating scores, despite the fact that it was not the food that provided the highest protein or fibre amount. More studies of this type are needed to determine the proportion and/or combination of ingredients from these classical Mediterranean recipes that could enhance human satiety.

A Review on the Role of Food-Derived Bioactive Molecules and the Microbiota-Gut-Brain Axis in Satiety Regulation

Obesity is a chronic disease resulting from an imbalance between energy intake and expenditure. The growing relevance of this metabolic disease lies in its association with other comorbidities. Obesity is a multifaceted disease where intestinal hormones such as cholecystokinin (CCK), glucagon-like peptide 1 (GLP-1), and peptide YY (PYY), produced by enteroendocrine cells (EECs), have a pivotal role as signaling systems. Receptors for these hormones have been identified in the gut and different brain regions, highlighting the interconnection between gut and brain in satiation mechanisms. The intestinal microbiota (IM), directly interacting with EECs, can be modulated by the diet by providing specific nutrients that induce environmental changes in the gut ecosystem. Therefore, macronutrients may trigger the microbiota-gut-brain axis (MGBA) through mechanisms including specific nutrient-sensing receptors in EECs, inducing the secretion of specific hormones that lead to decreased appetite or increased energy expenditure. Designing drugs/functional foods based in bioactive compounds exploiting these nutrient-sensing mechanisms may offer an alternative treatment for obesity and/or associated metabolic diseases. Organ-on-a-chip technology represents a suitable approach to model multi-organ communication that can provide a robust platform for studying the potential of these compounds as modulators of the MGBA.

Gut-adipose tissue crosstalk: A bridge to novel therapeutic targets in metabolic syndrome?

The gut is one of the main endocrine organs in our body, producing hormones acknowledged to play determinant roles in controlling appetite, energy balance and glucose homeostasis. One of the targets of such hormones is the adipose tissue, a major energetic reservoir, which governs overall metabolism through the secretion of adipokines. Disturbances either in nutrient and metabolic sensing and consequent miscommunication between these organs constitute a key driver to the metabolic complications clustered in metabolic syndrome. Thus, it is essential to understand how the disruption of this crosstalk might trigger adipose tissue dysfunction, a strong characteristic of obesity and insulin resistance. The beneficial effects of metabolic surgery in the amelioration of glucose homeostasis and body weight reduction allowed to understand the potential of gut signals modulation as a treatment for metabolic syndrome-related obesity and type 2 diabetes. In this review, we cover the effects of gut hormones in the modulation of adipose tissue metabolic and endocrine functions, as well as their impact in tissue plasticity. Furthermore, we discuss how the modulation of gut secretome, either through surgical procedures or pharmacological approaches, might improve adipose tissue function in obesity and metabolic syndrome.

Glucagon-like peptide-1 regulation by food proteins and protein hydrolysates

Glucagon-like peptide-1 (GLP-1) is an enterohormone with a key role in several processes controlling body homeostasis, including glucose homeostasis and food intake regulation. It is secreted by the intestinal cells in response to nutrients, such as glucose, fat and amino acids. In the present review, we analyse the effect of protein on GLP-1 secretion and clearance. We review the literature on the GLP-1 secretory effects of protein and protein hydrolysates, and the mechanisms through which they exert these effects. We also review the studies on protein from different sources that has inhibitory effects on dipeptidyl peptidase-4 (DPP4), the enzyme responsible for GLP-1 inactivation, with particular emphasis on specific sources and treatments, and the gaps there still are in knowledge. There is evidence that the protein source and the hydrolytic processing applied to them can influence the effects on GLP-1 signalling. The gastrointestinal digestion of proteins, for example, significantly changes their effectiveness at modulating this enterohormone secretion in both in vivo and in vitro studies. Nevertheless, little information is available regarding human studies and more research is required to understand their potential as regulators of glucose homeostasis.

New Bioactive Peptides Identified from a Tilapia Byproduct Hydrolysate Exerting Effects on DPP-IV Activity and Intestinal Hormones Regulation after Canine Gastrointestinal Simulated Digestion

Like their owners, dogs and cats are more and more affected by overweight and obesity-related problems and interest in functional pet foods is growing sharply. Through numerous studies, fish protein hydrolysates have proved their worth to prevent and manage obesity-related comorbidities like diabetes. In this work, a human in vitro static simulated gastrointestinal digestion model was adapted to the dog which allowed us to demonstrate the promising effects of a tilapia byproduct hydrolysate on the regulation of food intake and glucose metabolism. Promising effects on intestinal hormones secretion and dipeptidyl peptidase IV (DPP-IV) inhibitory activity were evidenced. We identify new bioactive peptides able to stimulate cholecystokinin (CCK) and glucagon-like peptide 1 (GLP-1) secretions, and to inhibit the DPP-IV activity after a transport study through a Caco-2 cell monolayer.

Role of Bioactive Peptide Sequences in the Potential Impact of Dairy Protein Intake on Metabolic Health

For years, there has been an increasing move towards elucidating the complexities of how food can interplay with the signalling networks underlying energy homeostasis and glycaemic control. Dairy foods can be regarded as the greatest source of proteins and peptides with various health benefits and are a well-recognized source of bioactive compounds. A number of dairy protein-derived peptide sequences with the ability to modulate functions related to the control of food intake, body weight gain and glucose homeostasis have been isolated and characterized. Their being active in vivo may be questionable mainly due to expected low bioavailability after ingestion, and hence their real contribution to the metabolic impact of dairy protein intake needs to be discussed. Some reports suggest that the differential effects of dairy proteins-in particular whey proteins-on mechanisms underlying energy balance and glucose-homeostasis may be attributed to their unique amino acid composition and hence the release of free amino acid mixtures enriched in essential amino acids (i.e., branched-chain-amino acids) upon digestion. Actually, the research reports reviewed in this article suggest that, among a number of dairy protein-derived peptides isolated and characterized as bioactive compounds in vitro, some peptides can be active in vivo post-oral administration through a local action in the gut, or, alternatively, a systemic action on specific molecular targets after entering the systemic circulation. Moreover, these studies highlight the importance of the enteroendocrine system in the cross talk between food proteins and the neuroendocrine network regulating energy balance.

Digestion of micellar casein in duodenum cannulated pigs. Correlation between in vitro simulated gastric digestion and in vivo data

Correlation and validation of the results of simulated gastrointestinal digestion of food compounds towards in vivo data is essential. The objective of this work was to monitor the digestion of milk micellar casein in the porcine upper intestinal tract and to match the outcome with the gastric in vitro digestion following the Infogest harmonized protocol. In pig duodenum, small amounts of intact caseins were present in all samples, while caseins were observed up to 60 min of gastric in vitro digestion. The peptide profile generated after in vitro and in vivo digestion showed clear similarities with specific overrepresented regions rich in proline and other hydrophobic residues. The statistical comparison of the in vivo and in vitro peptidome resulted in satisfactory correlation coefficients, up to 0.8. Therefore, the in vitro protocol used was a robust and simple model that provides a similar peptide profile than that found in porcine duodenum.

Gastrointestinal Digestion of Food Proteins under the Effects of Released Bioactive Peptides on Digestive Health

The gastrointestinal tract represents a specialized interface between the organism and the external environment. Because of its direct contact with lumen substances, the modulation of digestive functions by dietary substances is supported by a growing body of evidence. Food-derived bioactive peptides have demonstrated a plethora of activities in the organism with increasing interest toward their impact over the digestive system and related physiological effects. This review updates the biological effects of food proteins, specifically milk and soybean proteins, associated to gastrointestinal health and highlights the study of digestion products and released peptides, the identification of the active form/s, and the evaluation of the mechanisms of action underlying their relationship with the digestive cells and receptors. The approach toward the modifications that food proteins and peptides undergo during gastrointestinal digestion and their bioavailability is a crucial step for current investigations on the field. The recent literature on the regulation of digestive functions by peptides has been mostly considered in terms of their influence on gastrointestinal motility and signaling, oxidative damage and inflammation, and malignant cellular proliferation. A final section regarding the actual challenges and future perspectives in this scientific topic is critically discussed.

Functional Dyspepsia and Food: Immune Overlap with Food Sensitivity Disorders

PURPOSE OF REVIEW

Functional dyspepsia (FD) is a chronic functional gastrointestinal disorder characterised by upper gastrointestinal symptoms. Here, we aimed to examine the evidence for immune responses to food in FD and overlap with food hypersensitivity conditions.

RECENT FINDINGS

A feature of FD in a subset of patients is an increase in mucosal eosinophils, mast cells, intraepithelial cytotoxic T cells and systemic gut-homing T cells in the duodenum, suggesting that immune dysfunction is characteristic of this disease. Rates of self-reported non-celiac wheat/gluten sensitivity (NCW/GS) are higher in FD patients. FD patients commonly report worsening symptoms following consumption of wheat, fermentable oligosaccharides, disaccharides, monosaccharides, or polyols (FODMAPs), high-fat foods and spicy foods containing capsaicin. Particularly, wheat proteins and fructan in wheat may drive symptoms. Immune mechanisms that drive responses to food in FD are still poorly characterised but share key effector cells to common food hypersensitivities including non-IgE-mediated food allergy and eosinophilic oesophagitis.

Milk whey from different animal species stimulates the in vitro release of CCK and GLP-1 through a whole simulated intestinal digestion

Milk whey is effective in enhancing satiety mainly due to its protein composition. Peptides and amino acids derived from digestion of whey protein can act as suppressants of appetite by stimulation of receptors of satiety gut hormones. But, the protein fraction of whey can vary depending on species of animal, season, lactation period, etc. The aim of this study is to evaluate the satiety effect of milk whey from different species of ruminants (cow, sheep, goat and a mixture of them) through a simulated in vitro digestion, which performed the whole gastrointestinal process, from oral digestion to colonic fermentation. The satiety effect of each sample was measured by the production of satiating hormones (CCK and GLP-1) secreted by enteroendocrine cell line (STC-1) after 2 hours of incubation with non-digested, digested and fermented whey. Digested samples have shown to be potent CCK and GLP-1 secretagogues followed by fermented and non-digested samples, showing that the last one showed a weak hormone stimulation. Digested goat whey was the most efficient stimulator of GLP-1 (86.33 ± 4.55 pg mL^-1) and fermented mixture whey produced the major release of CCK (80.78±1.81 pg mL^-1). This study demonstrates that milk whey is a suitable ingredient to stimulate satiety through the effect of peptides, amino acids produced from digestion, and metabolites released by fermentation.

Antidiabetic Food-Derived Peptides for Functional Feeding: Production, Functionality and In Vivo Evidences

Bioactive peptides released from the enzymatic hydrolysis of food proteins are currently a trending topic in the scientific community. Their potential as antidiabetic agents, by regulating the glycemic index, and thus to be employed in food formulation, is one of the most important functions of these peptides. In this review, we aimed to summarize the whole process that must be considered when talking about including these molecules as a bioactive ingredient. In this regard, at first, the production, purification and identification of bioactive peptides is summed up. The detailed metabolic pathways described included carbohydrate hydrolases (glucosidase and amylase) and dipeptidyl-peptidase IV inhibition, due to their importance in the food-derived peptides research field. Then, their characterization, concerning bioavailability in vitro and in situ, stability and functionality in food matrices, and ultimately, the in vivo evidence (from invertebrate animals to humans), was described. The future applicability that these molecules have due to their biological potential as functional ingredients makes them an important field of research, which could help the world population avoid suffering from several diseases, such as diabetes.

Neuropod Cells: The Emerging Biology of Gut-Brain Sensory Transduction

Guided by sight, scent, texture, and taste, animals ingest food. Once ingested, it is up to the gut to make sense of the food's nutritional value. Classic sensory systems rely on neuroepithelial circuits to convert stimuli into signals that guide behavior. However, sensation of the gut milieu was thought to be mediated only by the passive release of hormones until the discovery of synapses in enteroendocrine cells. These are gut sensory epithelial cells, and those that form synapses are referred to as neuropod cells. Neuropod cells provide the foundation for the gut to transduce sensory signals from the intestinal milieu to the brain through fast neurotransmission onto neurons, including those of the vagus nerve. These findings have sparked a new field of exploration in sensory neurobiology-that of gut-brain sensory transduction.

Neuropod Cells: The Emerging Biology of Gut-Brain Sensory Transduction

Guided by sight, scent, texture, and taste, animals ingest food. Once ingested, it is up to the gut to make sense of the food's nutritional value. Classic sensory systems rely on neuroepithelial circuits to convert stimuli into signals that guide behavior. However, sensation of the gut milieu was thought to be mediated only by the passive release of hormones until the discovery of synapses in enteroendocrine cells. These are gut sensory epithelial cells, and those that form synapses are referred to as neuropod cells. Neuropod cells provide the foundation for the gut to transduce sensory signals from the intestinal milieu to the brain through fast neurotransmission onto neurons, including those of the vagus nerve. These findings have sparked a new field of exploration in sensory neurobiology-that of gut-brain sensory transduction.

A review of the short- and long-term impact of weight loss on appetite in youth: what do we know and where to from here?

This review seeks to synthesise our knowledge about changes in hunger and satiety that occur during diet-induced weight loss and during weight loss maintenance, with a particular focus on youth with obesity. Mechanisms of appetite responses to weight loss rely heavily on the adult literature. Physiological mechanisms that control appetite and satiety via the gut-brain axis have been elucidated but we have an incomplete picture of changes in gut hormones and peptides in youth with obesity. In adolescents, the role of the brain in long-term sensing of body composition and modifying appetite and satiety changes is easily over-ridden by hedonic influences for the reward of highly palatable sweet foods and encourages over-consumption. Accordingly, reward cues and hyper-responsiveness to palatable foods lead to a pattern of food choices. Different reward systems are necessary that are substantial enough to reward the continued individual effort required to sustain new behaviours, that need to be adopted to support a reduced body weight. Periods of growth and development during childhood provide windows of opportunity for interventions to influence body weight trajectory but long-term studies are lacking. More emphasis needs to be placed on anticipatory guidance on how to manage powerful hedonic influences of food choice, essential to cope with living in our obesogenic environment and managing hunger which comes with the stronger desire to eat after weight has been lost.

Induction of CCK and GLP-1 release in enteroendocrine cells by egg white peptides generated during gastrointestinal digestion

The effect of dietary protein on the induction of intestinal hormones is recognised. However, little is known about the nature of the digestion products involved in this intestinal signalling. Our aim was to characterise egg white protein digestion products and study their ability to induce CCK and GLP-1 release in enteroendocrine STC-1 cells. Intestinal digests triggered GLP-1 release at a higher rate than gastric digests. Peptides, but not free amino acids, showed a potent GLP-1 secretagogue effect, while proteins only had a modest effect. CCK was released in response to peptides and free amino acids but not proteins. Two hydrophobic negatively charged peptides triggered CCK release, while the highest GLP-1 response was found with a hydrophobic positively charged peptide, pointing to the involvement of different receptors or active sites. Identifying peptide sequences and receptors involved in hormonal secretion could open up new ways to control food intake and glucose metabolism.

Branched chain amino acids stimulate gut satiety hormone cholecystokinin secretion through activation of the umami taste receptor T1R1/T1R3 using an in vitro porcine jejunum model

Branched chain amino acids (BCAAs) are essential amino acids involved in regulation of feed intake. The function of BCAAs on the central nervous system has been extensively studied, but effects of BCAAs on secretion of gut satiety hormones and their underlying mechanisms are largely unknown. In this study, we evaluated the distribution of gut hormones and amino acid receptors in the porcine GI tract and found cholecystokinin (CCK) and taste dimeric receptor type 1 member 1/3 (T1R1/T1R3) were predominantly expressed in the jejunum and functionally interrelated. We further evaluated the effects of l-leucine, l-isoleucine, l-valine, and BCAAs on CCK and T1R1/T1R3 expression in porcine jejunum tissue. Our data demonstrated that stimulation of porcine jejunum tissue with 10 mM l-leucine, l-isoleucine or BCAAs mix (l-leucine : l-isoleucine : l-valine = 1 : 0.51 : 0.63) for 2 hours significantly increased mRNA expression and protein abundance of T1R1/T1R3 and secretion of CCK (P < 0.05). However, the l-valine treatment only increased the mRNA and protein abundance of T1R1 and T1R3 (P < 0.05), but not CCK secretion (P > 0.10). l-Leucine-, l-isoleucine- or BCAAs mix-induced CCK secretion was significantly decreased after tissues were pretreated with lactisole, a T1R1/T1R3 inhibitor (P < 0.05). Furthermore, the increased mRNA and protein abundance of T1R1/T1R3 were also largely attenuated by blocking T1R1/T1R3 with lactisole (P < 0.05). l-Leucine, l-isoleucine and BCAAs mix appeared to induce the gut satiety hormone CCK secretion through jejunal T1R1/T1R3. These results indicate over-supplementation with BCAAs in the diet might decrease food intake in swine and humans through gastrointestinal feedback.

Distribution and localization of porcine calcium sensing receptor in different tissues of weaned piglets1

Taste receptors including calcium sensing receptor (CaSR) are expressed in various animal tissues, and CaSR plays important roles in nutrient sensing and the physiology, growth, and development of animals. However, molecular distribution of porcine CaSR (pCaSR) in different tissues, especially along the longitudinal axis of the digestive tract in weaned piglets, is still unknown. In the present study, we investigated the distribution and localization of pCaSR in the different tissues including intestinal segments of weaned piglets. Six male pigs were anesthetized and euthanized. Different tissues such as intestinal segments were collected. The pCaSR mRNA abundance, protein abundance, and localization were measured by real-time PCR, Western blotting, and immunohistochemistry, respectively. The mRNA and protein of pCaSR were detected in the kidney, lung, liver, stomach, duodenum, jejunum, ileum, and colon. The pCaSR mRNA was much higher (five to 180 times) in the kidney when compared with other tissues (P < 0.05). The ileum had higher pCaSR mRNA and protein abundances than the stomach, duodenum, jejunum, and colon (P < 0.05). Immunohistochemical staining results indicated that the pCaSR protein was mostly located in the epithelia of the stomach, duodenum, jejunum, ileum, and colon. These results demonstrate that pCaSR is widely expressed in different tissues including intestinal segments in weaned piglets and the ileum has a higher expression level of pCaSR. Further research is needed to confirm the expression of CaSR in the different types of epithelial cells isolated from weaned piglets and characterize the functions of pCaSR, its potential ligands and cell signaling pathways related to CaSR activation in enteroendocrine cells and potentially in enterocytes.

L-phenylalanine Increased Gut Hormone Secretion through Calcium-Sensing Receptor in the Porcine Duodenum

Simple Summary

The proper modulation of feed intake not only meets the nutrient requirement for the maximum growth rate in pigs, but also avoids feed waste. A complete understanding of how dietary factors affect the appetite in pigs will provide a strategy to modulate the feed intake of pigs. L-phenylalanine (L-Phe) has been demonstrated to induce satiety through stimulating anorectic hormone secretion in rodents. However, whether L-Phe has similar effects in pigs is unknown. Here, we aimed to investigate how L-Phe affects gut hormone secretion, along with insight into the underlying mechanism in porcine duodenum by using an in vitro perfusion system. Results showed that 80 mM L-Phe triggered glucose-dependent insulinotropic peptide (GIP) and cholecystokinin (CCK) release, and also upregulated calcium-sensing receptor (CaSR) and its downstream molecules, such as protein kinase C (PKC) and inositol 1,4,5-triphosphate receptor (IP₃R) expression. However, these effects were attenuated by treatment with a CaSR antagonist. Our findings show that CaSR participates in Phe-induced hormone secretion in pig duodenum, indicating that CaSR may be a potential target in the food intake regulation of pigs.

Abstract

Luminal amino acids have a pivotal role in gut hormone secretion, and thereby modulate food intake and energy metabolism. However, the mechanisms by which amino acids exert this effect remains unknown. The purpose of this research was to investigate the response of L-phenylalanine (L-Phe) to gut hormone secretion and its underlying mechanisms by perfusing the pig duodenum. Eighty mM L-Phe and extracellular Ca²⁺ stimulated cholecystokinin (CCK) and glucose-dependent insulinotropic peptide (GIP) release, and upregulated the mRNA expression of the calcium-sensing receptor (CaSR), CCK, and GIP. Western blotting results showed that L-Phe also elevated the protein levels of CaSR, the inositol 1,4,5-triphosphate receptor (IP₃R), and protein kinase C (PKC). However, the CaSR inhibitor NPS 2143 reduced the mRNA expression of CaSR, CCK, and GIP, and the secretion of CCK and GIP, as well as the protein level of CaSR, IP₃R, and PKC. These results indicated that Phe stimulated gut secretion through a CaSR-mediated pathway and its downstream signaling molecules, PKC and IP₃R.