Simulated GI digestion of dietary protein: Release of new bioactive peptides involved in gut hormone secretion

Acid-active proteases to optimize dietary protein digestibility: a step towards sustainable nutrition

Introduction

Historically, prioritizing abundant food production often resulted in overlooking nutrient quality and bioavailability, however, environmental concerns have now propelled sustainable nutrition and health efficacy to the forefront of global attention. In fact, increasing demand for protein is the major challenge facing the food system in the 21st century with an estimation that 70% more food is needed by 2050. This shift has spurred interest in plant-based proteins for their sustainability and health benefits, but most alternative sources of protein are poorly digestible. There are two approaches to solve digestibility: improve the digestibility of food proteins or improve the digestive capacity of consumers. Enhancing nutrient digestibility and bioavailability across diverse protein sources is crucial, with proteases presenting a promising avenue. Research, inspired by the proteases of human breast milk, has demonstrated that exogenous microbial proteases can activate within the human digestive tract and substantially increase the digestion of targeted proteins that are otherwise difficult to fully digest.

Methods

Here, we introduce the use of an acid-active family of bacterial proteases (S53) to improve the digestibility and nutritional quality of a variety of protein sources, evaluated using the INFOGEST 2.0 protocol.

Results

Results from in vitro digestibility indicate that the most effective protease in the S53 family substantially improves the digestibility of an array of animal and plant-derived proteins-soy, pea, chickpea, rice, casein, and whey. On average, this protease elevated protein digestibility by 115% during the gastric phase and by 15% in the intestinal phase, based on the degree of hydrolysis.

Discussion

The widespread adoption of these proteases has the potential to enhance nutritional value and contribute to food security and sustainability. This approach would complement ongoing efforts to improve proteins in the food supply, increase the quality of more sustainable protein sources and aid in the nourishment of patients with clinically compromised, fragile intestines and individuals like older adults and high-performance athletes who have elevated protein needs.

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.

In vitro gastrointestinal digestion of highland barley protein: identification and characterization of novel bioactive peptides involved in gut cholecystokinin secretion

BACKGROUND

The satiety hormone cholecystokinin (CCK) plays an important role in food intake inhibition. Its secretion is regulated by dietary components. The search for bioactive compounds that induce CCK secretion is currently an active area of research. The objective of this study was to evaluate the ability of highland barley protein digest (HBPD) to stimulate CCK secretion in vitro and in vivo and identify the responsible peptide sequences.

RESULTS

HBPD was prepared by in vitro gastrointestinal digestion model. Peptides of <1000 Da in HBPD accounted for 82%. HBPD was rich in essential amino acids Leu, Phe and Val, but lack in sulfur amino acids Met and Cys. HBPD treatment at a concentration of 5 mg mL-1 significantly stimulated CCK secretion from enteroendocrine STC-1 cells (P < 0.05). Moreover, oral gavage with HBPD in mice significantly increased plasma CCK level. Chromatographic separation was performed to isolate peptide fractions involved in CCK secretion and peptide sequence was determined by ultra-performance liquid chromatography-tandem mass spectrometry. Two novel CCK-releasing peptides, PDLP and YRIVPL, were pointed out for their outstanding CCK secretagogue activity.

CONCLUSION

This study demonstrated for the first time that HBPD had an ability to stimulate CCK secretion in vitro and in vivo and determined the bioactive peptides exerting CCK secretagogue activity in HBPD. © 2023 Society of Chemical Industry.

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.

Wheat Alkylresorcinols Modulate Glucose Homeostasis through Improving GLP-1 Secretion in High-Fat-Diet-Induced Obese Mice

Wheat alkylresorcinols (ARs) consumption has been evidenced to improve obesity and its associated insulin resistance. However, the effect of ARs on glucagon-like peptide 1 (GLP-1) secretion and the underlying mechanism of action are still unclear. In this study, C57BL/6J mice were fed low-fat diet (LFD), high-fat diet (HFD), and HFD supplemented with 0.4% (w/w) ARs separately for 9 weeks. The results showed that ARs intervention significantly improved glucose homeostasis and restored the serum level of GLP-1 compared with the HFD control group. Moreover, ARs treatment alleviated HFD-induced ileal epithelium damage according to TUNEL staining, immunofluorescence, and transmission electron microscopy observation. The alleviative effect was further verified by apoptosis analysis and mitochondrial function evaluation. Furthermore, palmitic acid (PA) was administered to the intestinal secretin tumor cell line (STC-1) to clarify the protective effect of ARs on GLP-1 secretion in vitro. In consistence with the results of animal studies, ARs treatment could significantly improve GLP-1 secretion in STC-1 cells compared with PA treatment alone in a dose-dependent manner, accompanied by a reduction in apoptosis and mitochondrial dysfunction. In addition, ARs treatment notably enhanced the abundance of SCFA (short-chain fatty acid)-producing bacteria, such as Bacteroides, Bifidobacterium, and Akkermansia. The increased levels of intestinal SCFAs, such as acetic acid, propionic acid, and butyric acid, improved the expression of short-chain fatty acid receptors (FFAR3) and glucagon-like peptide-1 receptor (GLP-1R), enhancing the secretion of the intestinal hormones GLP-1. Thus, this study provides potential clinical implications of whole wheat as a dietary strategy to improve glucose homeostasis for obese populations.

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.

In vitro gastrointestinal digestion of buckwheat (Fagopyrum esculentum Moench) protein: release and structural characteristics of novel bioactive peptides stimulating gut cholecystokinin secretion

Satiety hormone cholecystokinin (CCK) plays a vital role in appetite inhibition. Its secretion is regulated by dietary components. The search for bioactive compounds that stimulate CCK secretion is currently an active area of research. The objective of this study was to evaluate the ability of buckwheat (Fagopyrum esculentum Moench) protein digest (BPD) to stimulate CCK secretion in vitro and in vivo and clarify the structural characteristics of peptides stimulating CCK secretion. BPD was prepared by an in vitro gastrointestinal digestion model. The relative molecular weight of BPD was <10 000 Da, and peptides with <3000 Da accounted for 70%. BPD was rich in essential amino acids Lys, Leu, and Val but lacked sulfur amino acids Met and Cys. It had a stimulatory effect on CCK secretion in vitro and in vivo. Chromatographic separation was performed to isolate peptide fractions involved in CCK secretion, and five novel CCK-releasing peptides including QFDLDD, PAFKEEHL, SFHFPI, IPPLFP, and RVTVQPDS were successfully identified. A sequence length range of 6-8 and marked hydrophobicity (18-28) were observed among the most CCK-releasing peptides. The present study demonstrated for the first time that BPD could stimulate CCK secretion and clarify the structural characteristics of bioactive peptides having CCK secretagogue activity in BPD.

Potential of Human Hemoglobin as a Source of Bioactive Peptides: Comparative Study of Enzymatic Hydrolysis with Bovine Hemoglobin and the Production of Active Peptide α137-141

Cruor, the main component responsible for the red color of mammalian blood, contains 90% haemoglobin, a protein considered to be a rich source of bioactive peptides. The aim of the present study is to assess the potential of human hemoglobin as a source of bioactive peptides, compared with bovine hemoglobin, which has been extensively studied in recent years. More specifically, the study focused on the α137-141 fragment of bovine haemoglobin (TSKYR), a small (653 Da) hydrophilic antimicrobial peptide. In this work, the potential of human hemoglobin to contain bioactive peptides was first investigated in silico in comparison with bovine hemoglobin-derived peptides using bioinformatics tools. The blast results showed a high identity, 88% and 85% respectively, indicating a high similarity between the α and β chains. Peptide Cutter software was used to predict cleavage sites during peptide hydrolysis, revealing major conservation in the number and location of cleavage sites between the two species, while highlighting some differences. Some peptides were conserved, notably our target peptide (TSKYR), while others were specific to each species. Secondly, the two types of hemoglobin were subjected to similar enzymatic hydrolysis conditions (23 °C, pH 3.5), which showed that the hydrolysis of human hemoglobin followed the same reaction mechanism as the hydrolysis of bovine hemoglobin, the 'zipper' mechanism. Concerning the peptide of interest, α137-141, the RP-UPLC analyses showed that its identification was not affected by the increase in the initial substrate concentration. Its production was rapid, with more than 60% of the total α137-141 peptide production achieved in just 30 min of hydrolysis, reaching peak production at 3 h. Furthermore, increasing the substrate concentration from 1% to 10% (w/v) resulted in a proportional increase in α137-141 production, with a maximum concentration reaching 687.98 ± 75.77 mg·L-1, approximately ten-fold higher than that obtained with a 1% (w/v) concentration. Finally, the results of the UPLC-MS/MS analysis revealed the identification of 217 unique peptides in bovine hemoglobin hydrolysate and 189 unique peptides in human hemoglobin hydrolysate. Of these, 57 peptides were strictly common to both species. This revealed the presence of several bioactive peptides in both cattle and humans. Although some had been known previously, new bioactive peptides were discovered in human hemoglobin, such as four antibacterial peptides (α37-46 PTTKTYFPHF, α36-45 FPTTKTYFPH, α137-141 TSKYR, and α133-141 STVLTSKYR), three opioid peptides (α137-141 TSKYR,β31-40 LVVYPWTQRF,β32-40, VVYPWTQRF), an ACE inhibitor (β129-135 KVVAGVA), an anticancer agent (β33-39 VVYPWTQ), and an antioxidant (α137-141 TSKYR). To the best of our knowledge, these peptides have never been found in human hemoglobin before.

Trp-Tyr is a dipeptide structure that potently stimulates GLP-1 secretion in a murine enteroendocrine cell model, identified by comprehensive analysis

Dietary peptides potently stimulate glucagon-like peptide-1 (GLP-1) secretion, however, the underlying molecular mechanisms, such as structure-activity relationships and sensing mechanisms are only partly elucidated. In this study, we used a dipeptide library to identify dipeptides that potently stimulate GLP-1 release and to clarify the underlying structure-activity relationship. Murine enteroendocrine GLUTag cells were exposed to 339 dipeptides for 60 min, and the concentration of GLP-1 released into the supernatant was measured. Subsequently, selected dipeptides were examined for their reproducibility and dose responsiveness. In addition, we investigated the role of constituent amino acids in the secretion of GLP-1, and whether tripeptides containing the active dipeptide structures maintained their activity. In a concentration range of 1-5 mg/mL, twelve dipeptides had reproducible and concentration-dependent GLP-1-releasing activity. Among them, nine dipeptides (FY, KF, NI, PM, QL, QY, WF, WN, WY) were novel, with WY exhibiting the most potent activity. The reverse sequences and most free amino acids did not induce GLP-1 secretion, indicating that GLP-1-producing cells recognize the structure of each peptide to induce GLP-1 secretion. However, no apparent similarities were found between the active peptides. A comparison between the six tripeptides composed of F, W, and Y revealed the further potent tripeptides FWY and WYF, than WY. In the present study, a comprehensive analysis revealed nine novel dipeptides with high potential to stimulate GLP-1 secretion. Furthermore, the results indicate that 'WY' is a specific dipeptide sequence that potently stimulates GLP-1 secretion.

In Vivo and In Vitro Comparison of the DPP-IV Inhibitory Potential of Food Proteins from Different Origins after Gastrointestinal Digestion

Dipeptidyl-peptidase IV (DPP-IV) plays an essential role in glucose metabolism by inactivating incretins. In this context, food-protein-derived DPP-IV inhibitors are promising glycemic regulators which may act by preventing the onset of type 2 diabetes in personalized nutrition. In this study, the DPP-IV-inhibitory potential of seven proteins from diverse origins was compared for the first time in vitro and in vivo in rat plasma after the intestinal barrier (IB) passage of the indigested proteins. The DPP-IV-inhibitory potentials of bovine hemoglobin, caseins, chicken ovalbumin, fish gelatin, and pea proteins were determined in rat plasma thirty minutes after oral administration. In parallel, these proteins, together with bovine whey and gluten proteins, were digested using the harmonized INFOGEST protocol adapted for proteins. The DPP-IV half-maximal inhibitory concentration (IC50) was determined in situ using Caco-2 cells. The DPP-IV-inhibitory activity was also measured after IB passage using a Caco2/HT29-MTX mixed-cell model. The peptide profiles were analyzed using reversed-phase high-performance liquid chromatography tandem mass spectrometry (RP-HPLC-MS/MS) with MS data bioinformatics management, and the IC50 of the identified peptides was predicted in silico. The in vitro and in vivo DPP-IV-inhibitory activity of the proteins differed according to their origin. Vegetable proteins and hemoglobin yielded the highest DPP-IV-inhibitory activity in vivo. However, no correlation was found between the in vivo and in vitro results. This may be partially explained by the differences between the peptidome analysis and the in silico predictions, as well as the study complexity.

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.

Different Interactive Effects of Metformin and Acarbose With Dietary Macronutrient Intakes on Patients With Type 2 Diabetes Mellitus: Novel Findings From the MARCH Randomized Trial in China

Antidiabetic oral agents and nutrition management are frequently used together as first-line therapies for type 2 diabetes mellitus (T2DM). However, less is known about their interaction. The interactive effect of two classic antidiabetic medications, namely, acarbose and metformin, with dietary intakes of macronutrients on glycemic control and cardiometabolic risk factors was investigated in the metformin and acarbose in Chinese as the initial hypoglycemic treatment (MARCH) randomized clinical trial. The patients with newly diagnosed T2DM from China were included in the trial. Participants were randomized to receive either metformin or acarbose monotherapy as the initial treatment, followed by a 24-week treatment phase, during which add-on therapy was used if necessary. Dietary intakes of carbohydrate, protein, fat, and total energy were calculated by a 24-h food diary recall method. Linear mixed-effect models combined with a subgroup analysis were used to investigate independent and interactive effects of drugs and diet on clinical outcomes. A data analysis was performed on 551 of the 788 patients randomly assigned to treatment groups. Metformin therapy was independently associated with higher triglycerides (TGs, β = 0.471, P = 0.003), 2 h postprandial plasma glucose (2hPPG, β = 0.381, P = 0.046) but lower low-density lipoprotein cholesterol (LDL-C, β = −0.149, P = 0.013) compared with acarbose therapy. Higher carbohydrates and lower fat intakes were independently associated with poorer glycemic control, less weight loss, and greater insulin secretion. Higher total energy intake was also independently associated with higher fasting (β = 0.0002, P = 0.001) and postprandial blood glucose (β = 0.0004, P = 0.001). Interaction and subgroup analyses demonstrated that glucagon-like peptide-1 (GLP-1) was positively related to total energy (β = 0.268, P = 0.033), carbohydrates intake, and insulin secretion (β = 2,045.2, P = 0.003) only in the acarbose group, while systolic blood pressure (SBP) was negatively related to protein intake in the metformin group (β = 23.21, P = 0.014). The results of this study showed that metformin and acarbose mainly exerted different interactive effects with dietary energy, carbohydrate, and protein intakes on GLP-1 secretion, insulin release, and SBP. The interaction between drug therapy and nutrition intervention in glycemia highlights the complexity of combination therapy.

Dietetic intervention in psoriatic arthritis: the DIETA trial

AIM

To evaluate whether dietary pattern changes, antioxidant supplementation or 5-10% weight loss could improve disease activity (skin and joint) in patients with psoriatic arthritis (PsA).

METHODS

A total of 97 PsA patients were enrolled in this 12-week randomized, double-blinded, placebo-controlled trial. Patients were randomized into three groups: Diet-placebo (hypocaloric diet + placebo supplementation); Diet-fish (hypocaloric diet + 3 g/day of omega-3 supplementation; and Placebo. Food intake (3-day registry, Healthy Eating Index (HEI), and the Dietary Inflammatory Index (DII)), body composition (whole-body dual-energy X-ray absorptiometry (DXA), weight and waist circumference) and disease activity (PASI, BSA, BASDAI, DAS28-ESR, DAS28-CRP and MDA) were evaluated at baseline and after the 12-week intervention. Statistical analysis used the intention-to-treat approach. The P value was considered to indicate significance when below 0.05.

RESULTS

After 12 weeks, DAS28-CRP and BASDAI scores improved, especially in the Diet-placebo group (- 0.6 ± 0.9; p = 0.004 and - 1.39 ± 1.97; p = 0.001, respectively). In addition, a higher proportion of patients achieved minimal disease activity (MDA) in all groups. The Diet-fish group showed significant weight loss (- 1.79 ± 2.4; p = 0.004), as well as waist circumference (- 3.28 ± 3.5, p < 0.001) and body fat (- 1.2 ± 2.2, p = 0.006) reductions. There was no significant correlation between weight loss and disease activity improvement. Each 1-unit increase in the HEI value reduced the likelihood of achieving remission by 4%. Additionally, each 100-cal daily intake increase caused a 3.4-fold DAS28-ESR impairment.

CONCLUSION

A 12-week hypocaloric intervention provided suitable control of joint disease activity in patients with PsA, regardless of weight loss. Adding omega-3 supplementation caused relevant body composition changes but not disease activity improvement.

TRIAL REGISTRATION

The study was recorded on Clinicaltrials.gov (NCT03142503).

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Characteristics of Food Protein-Derived Antidiabetic Bioactive Peptides: A Literature Update

Diabetes, a glucose metabolic disorder, is considered one of the biggest challenges associated with a complex complication of health crises in the modern lifestyle. Inhibition or reduction of the dipeptidyl peptidase IV (DPP-IV), alpha-glucosidase, and protein-tyrosine phosphatase 1B (PTP-1B) enzyme activities or expressions are notably considered as the promising therapeutic strategies for the management of type 2 diabetes (T2D). Various food protein-derived antidiabetic bioactive peptides have been isolated and verified. This review provides an overview of the DPP-IV, PTP-1B, and α-glucosidase inhibitors, and updates on the methods for the discovery of DPP-IV inhibitory peptides released from food-protein hydrolysate. The finding of novel bioactive peptides involves studies about the strategy of separation fractionation, the identification of peptide sequences, and the evaluation of peptide characteristics in vitro, in silico, in situ, and in vivo. The potential of bioactive peptides suggests useful applications in the prevention and management of diabetes. Furthermore, evidence of clinical studies is necessary for the validation of these peptides’ efficiencies before commercial applications.

Slow digestion-oriented dietary strategy to sustain the secretion of GLP-1 for improved glucose homeostasis

Dysregulated glucose metabolism is associated with many chronic diseases such as obesity and type 2 diabetes mellitus (T2DM), and strategies to restore and maintain glucose homeostasis are essential to health. The incretin hormone of glucagon-like peptide-1 (GLP-1) is known to play a critical role in regulating glucose homeostasis and dietary nutrients are the primary stimuli to the release of intestinal GLP-1. However, the GLP-1 producing enteroendocrine L-cells are mainly distributed in the distal region of the gastrointestinal tract where there are almost no nutrients to stimulate the secretion of GLP-1 under normal situations. Thus, a dietary strategy to sustain the release of GLP-1 was proposed, and the slow digestion property and dipeptidyl peptidase IV (DPP-IV) inhibitory activity of food components, approaches to reduce the rate of food digestion, and mechanisms to sustain the release of GLP-1 were reviewed. A slow digestion-oriented dietary approach through encapsulation of nutrients, incorporation of viscous dietary fibers, and enzyme inhibitors of phytochemicals in a designed whole food matrix will be implemented to efficiently reduce the digestion rate of food nutrients, potentiate their distal deposition and a sustained secretion of GLP-1, which will be beneficial to improved glucose homeostasis and health.

Improvement of Glucose Tolerance by Food Factors Having Glucagon-Like Peptide-1 Releasing Activity

Glucagon-like peptide-1 (GLP-1) is a gastrointestinal hormone released from enteroendocrine L cells in response to meal ingestion. GLP-1 receptor agonists and GLP-1 enhancers have been clinically employed to treat diabetes owing to their glucose-dependent insulin-releasing activity. The release of GLP-1 is primarily stimulated by macronutrients such as glucose and fatty acids, which are nutritionally indispensable; however, excessive intake of sugar and fat is responsible for the development of obesity and diabetes. Therefore, GLP-1 releasing food factors, such as dietary peptides and non-nutrients, are deemed desirable for improving glucose tolerance. Human and animal studies have revealed that dietary proteins/peptides have a potent effect on stimulating GLP-1 secretion. Studies in enteroendocrine cell models have shown that dietary peptides, amino acids, and phytochemicals, such as quercetin, can directly stimulate GLP-1 secretion. In our animal experiments, these food factors improved glucose metabolism and increased GLP-1 secretion. Furthermore, some dietary peptides not only stimulated GLP-1 secretion but also reduced plasma peptidase activity, which is responsible for GLP-1 inactivation. Herein, we review the relationship between GLP-1 and food factors, especially dietary peptides and flavonoids. Accordingly, utilization of food factors with GLP-1-releasing/enhancing activity is a promising strategy for preventing and treating obesity and diabetes.

Multiple Selection Criteria for Probiotic Strains with High Potential for Obesity Management

Since alterations of the gut microbiota have been shown to play a major role in obesity, probiotics have attracted attention. Our aim was to identify probiotic candidates for the management of obesity using a combination of in vitro and in vivo approaches. We evaluated in vitro the ability of 23 strains to limit lipid accumulation in adipocytes and to enhance the secretion of satiety-promoting gut peptide in enteroendocrine cells. Following the in vitro screening, selected strains were further investigated in vivo, single, or as mixtures, using a murine model of diet-induced obesity. Strain Bifidobacterium longum PI10 administrated alone and the mixture of B. animalis subsp. lactis LA804 and Lactobacillus gasseri LA806 limited body weight gain and reduced obesity-associated metabolic dysfunction and inflammation. These protective effects were associated with changes in the hypothalamic gene expression of leptin and leptin receptor as well as with changes in the composition of gut microbiota and the profile of bile acids. This study provides crucial clues to identify new potential probiotics as effective therapeutic approaches in the management of obesity, while also providing some insights into their mechanisms of action.

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.

Explorative Screening of Bioactivities Generated by Plant-Based Proteins after In Vitro Static Gastrointestinal Digestion

The gastrointestinal digestion of food proteins can generate peptides with a wide range of biological activities. In this study, we screened various potential bioactivities generated by plant-based proteins. Whey protein as an animal protein reference, five grades of pea protein, two grades of wheat protein, and potato, fava bean, and oat proteins were submitted to in vitro SGID. They were then tested in vitro for several bioactivities including measures on: (1) energy homeostasis through their ability to modulate intestinal hormone secretion, to inhibit DPP-IV activity, and to interact with opioid receptors; (2) anti-hypertensive properties through their ability to inhibit ACE activity; (3) anti-inflammatory properties in Caco-2 cells; (4) antioxidant properties through their ability to inhibit production of reactive oxygen species (ROS). Protein intestinal digestions were able to stimulate intestinal hormone secretion by enteroendocrine cells, to inhibit DPP-IV and ACE activities, to bind opioid receptors, and surprisingly, to decrease production of ROS. Neither pro- nor anti-inflammatory effects have been highlighted and some proteins lost their pro-inflammatory potential after digestion. The best candidates were pea, potato, and fava bean proteins.

Integrated Continuous Bioprocess Development for ACE-Inhibitory Peptide Production by Lactobacillus helveticus Strains in Membrane Bioreactor

Production of bioactive peptides (BAPs) by Lactobacillus species is a cost-effective approach compared to the use of purified enzymes. In this study, proteolytic Lactobacillus helveticus strains were used for milk fermentation to produce BAPs capable of inhibiting angiotensin converting enzyme (ACE). Fermented milks were produced in bioreactors using batch mode, and the resulting products showed significant ACE-inhibitory activities. However, the benefits of fermentation in terms of peptide composition and ACE-inhibitory activity were noticeably reduced when the samples (fermented milks and non-fermented controls) were subject to simulated gastrointestinal digestion (GID). Introducing an ultrafiltration step after fermentation allowed to prevent this effect of GID and restored the effect of fermentation. Furthermore, an integrated continuous process for peptide production was developed which led to a 3 fold increased peptide productivity compared to batch production. Using a membrane bioreactor allowed to generate and purify in a single step, an active ingredient for ACE inhibition.

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.

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.

Identification and Quantification of DPP-IV-Inhibitory Peptides from Hydrolyzed-Rapeseed-Protein-Derived Napin with Analysis of the Interactions between Key Residues and Protein Domains

Previously reported peptides derived from napin of rapeseed ( Brassica napus) have been shown to inhibit DPP-IV in silico. In the present study, napin extracted from rapeseed was hydrolyzed by commercial enzymes and filtered by an ultrafiltration membrane. The napin hydrolysate was then purified by a Sephadex G-15 gel-filtration column and preparative RP-HPLC. A two-enzyme-combination approach with alcalase and trypsin was the most favorable in terms of the DPP-IV-inhibitory activity (IC₅₀ = 0.68 mg/mL) of the napin hydrolysate. Three peptides and one modified peptide (pyroglutamate mutation at the N-terminus) were identified using HPLC-triple-TOF-MS/MS. DPP-IV-inhibitory activity and the types of enzyme inhibition were also determined. Meanwhile, key residues associated with the interactions between the selected peptides and DPP-IV were investigated by molecular docking. IPQVS has key amino acid residues (Tyr547, Glu205, and Glu206) that are consistent with Diprotin A. ELHQEEPL could form a better covalent bond with Arg358 in the S3 pocket of DPP-IV.

Current state of art after twenty years of the discovery of bioactive peptide lunasin

Non-communicable diseases have become the medical challenge of the 21st century because of their high incidence and mortality rates. Accumulating evidence has suggested that the modulation of diet and other lifestyle habits is the best strategy for the prevention of these diseases. An increasing number of dietary compounds have been found to exert health promoting benefits beyond their nutritional effects. Among them, lunasin is considered one of the most studied bioactive peptides. Since its discovery in soybean twenty years ago, many researchers around the world have focused their studies on demonstrating the chemopreventive and chemotherapeutic activity of lunasin. Moreover, in the last years, promising protective effects of this peptide against hypercholesterolemia, obesity, metabolic syndrome and associated cardiovascular disorders, and inflammatory and immune-regulated diseases have been described. This review summarizes recent remarkable advances on the use of peptide lunasin as a potential functional ingredient to provide health benefits. Moreover, novel aspects related to the influence of lunasin's digestion and bioavailability, the mechanisms of action proposed to explain the underlying biological properties, and the incorporation of this peptide into nutritional supplements are critically discussed.

Whey Proteins Reduce Appetite, Stimulate Anorexigenic Gastrointestinal Peptides and Improve Glucometabolic Homeostasis in Young Obese Women

Introduction: Proteins, particularly whey proteins, represent the most satiating macronutrient in animals and humans. A dietetic regimen based on proteins enriched preload before eating might be a strategy to counteract obesity. Aims and Methods: The aim of the present study was to evaluate the effects of an isocaloric drink containing whey proteins or maltodextrins (preload) on appetite (satiety/hunger measured by a visual analogue scale or VAS), glucometabolic control (blood glucose/insulin), and anorexigenic gastrointestinal peptides (pancreatic polypeptide or PP, glucagon-like peptide 1 or GLP-1 and peptide YY or PYY) in a cohort of obese young women (n = 9; age: 18.1 ± 3.0 years; body mass index, BMI: 38.8 ± 4.5 kg/m²). After two and a half hours, they were administered with a mixed meal at a fixed dose; satiety and hunger were measured by VAS. Results: Each drink significantly augmented satiety and reduced hunger, and the effects were more evident with whey proteins than maltodextrins. Similarly, there were significant increases in GLP-1 and PYY levels (but not PP) after the ingestion of each drink; these anorexigenic responses were higher with whey proteins than maltodextrins. While insulinemia identically increased after each drink, whey proteins induced a lower glycemic response than maltodextrins. No differences in satiety and hunger were found after the meal, which is presumably due to the late administration of the meal test, when the hypophagic effect of whey proteins was disappearing. Conclusions: While whey proteins actually reduce appetite, stimulate anorexigenic gastrointestinal peptides, and improve glucometabolic homeostasis in young obese women, further additional studies are mandatory to demonstrate their hypophagic effects in obese subjects, when administered as preload before eating.

Casein materials show different digestion patterns using an in vitro gastrointestinal model and different release of glucagon-like peptide-1 by enteroendocrine GLUTag cells

Physicochemical properties of casein (CN) materials manufactured using different processes are well studied; however, data on their bioaccessibility or bioactivity are limited. We compared the digestion patterns and glucagon-like peptide-1 (GLP-1)-releasing activities of micellar CN concentrate (MCC) and sodium caseinate (SCN). MCC and SCN mixed with whey protein isolate (SCN + WPI) were subjected to in vitro gastrointestinal digestion; the digestibility of MCC was higher than that of SCN + WPI, and both CN materials showed different patterns of peptides released after in vitro digestion. A comparison of GLP-1-releasing activities showed that MCC induced GLP-1 secretion to a greater extent than SCN + WPI. Candidate peptides identified from CN digesta were chemically synthesized to test their GLP-1-releasing activity. GPVRGPFPIIV identified only in the MCC digesta, could stimulate GLP-1 release. In conclusion, the digestion patterns and GLP-1-releasing activity of CN materials depend on the production process.

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

Luminal nutrients stimulate enteroendocrine cells through the activation of specific receptors to release hormones that inhibit appetite and promote glucose homeostasis. While food protein is the macronutrient with the highest effect on satiety, the signaling on the protein digestion products at the gut is poorly understood. This perspective aims to highlight the existing gaps in the study of protein digestion products as signaling molecules in gastrointestinal enteroendocrine cells. Because dietary protein digestion can be modulated by the technological processes applied to food, it is possible to target gut receptors to control food intake by formulating specific food ingredients or protein preloads.

Chicory Roots for Prebiotics and Appetite Regulation: A Pilot Study in Mice

The objectives of this work are to address the prebiotic effects of chicory ( Cichorium intybus) together with its possible role in appetite control. We compared nine chicory genotypes in order to determine if variations in the content of metabolites in the roasted roots would lead to modifications in release of satiety hormones and in composition of gut microbiota. To this aim, a 5-week dietary-intervention study was achieved using mice fed with distinct chicory-based preparations. A 16S rRNA gene-based metagenetic analysis of fecal microbiota was performed. In vitro gastrointestinal digestions were performed in order to study the effect of chicory intestinal digests on gut hormone regulation in enteroendocrine cells. Firmicutes/Bacteroidetes ratio and gut bacterial groups, such as Alloprevotella, Blautia, Alistipes, and Oscillibacter, were found to be modulated by chicory. On the other hand, CCK and GLP-1 satiety hormones were demonstrated to be significantly increased by chicory in vitro.

Molecular targets and mechanisms of bioactive peptides against metabolic syndromes

Bioactive peptides are present in all living organisms and have critical roles ranging from protection against infection as the key element of innate immunity, regulating blood pressure and glucose levels, to reducing signs of ageing by killing senescent cells. Bioactive peptides are also encrypted within food protein sequences that can be released during proteolysis or food processing. These specific food protein fragments are reported to have potential for improving human health and preventing metabolic diseases through their impact on inflammation, blood pressure, obesity, and type-2 diabetes. This review mainly focuses on the molecular targets and the underlying mechanisms of bioactive peptides against various metabolic syndromes including inflammation, high blood pressure, obesity, and type-2 diabetes, to provide new insights and perspectives on the potential of bioactive peptides for management of metabolic syndromes.

Combined in vivo and in silico approaches for predicting the release of bioactive peptides from meat digestion

We studied the kinetics of peptide release during the gastric digestion of meat proteins in vivo, in view to predicting the release of bioactive peptides further on in the digestive tract. Six mini pigs fitted with gastric cannulas received a meal with cooked beef as protein source. Digesta was collected at regular time intervals up to 5½ h. The peptides generated by the gastric digestion of meat were identified and quantified using label-free LC MS, thereafter subjected to in silico digestion mimicking the action of intestinal enzymes. Three clusters of proteins presenting similar evolutions according to their dynamic hydrolysis were obtained. This study clearly improves the in silico prediction of the intestinal release of bioactive peptides by mapping meat protein degradation in the stomach in an in vivo model. Knowledge of the conformation of the peptides released in the stomach further improves this prediction.

Stimulation of CCK and GLP-1 secretion and expression in STC-1 cells by human jejunal contents and in vitro gastrointestinal digests from casein and whey proteins

The present study evaluates casein and whey protein gastrointestinal digests as inducers of CCK and GLP-1 secretion and expression in STC-1 cells.

Protein Digestion-Derived Peptides and the Peripheral Regulation of Food Intake

The gut plays a central role in energy homeostasis. Food intake regulation strongly relies on the gut-brain axis, and numerous studies have pointed out the significant role played by gut hormones released from enteroendocrine cells. It is well known that digestive products of dietary protein possess a high satiating effect compared to carbohydrates and fat. Nevertheless, the processes occurring in the gut during protein digestion involved in the short-term regulation of food intake are still not totally unraveled. This review provides a concise overview of the current data concerning the implication of food-derived peptides in the peripheral regulation of food intake with a focus on the gut hormones cholecystokinin and glucagon-like peptide 1 regulation and the relationship with some aspects of glucose homeostasis.