Profiling the Gut Microbiota in Obese Children with Formula Feeding in Early Life and Selecting Strains against Obesity

Formula feeding, obesity and the gut microbiota are closely related. The present investigation explored the profiles of the intestinal microbiota in obese children over 5 years old with formula feeding in early life. We identified functional bacteria with anti-obesity potential through in vitro and in vivo experiments, elucidating their mechanisms. The results indicated that, in the group of children over 5 years old who were fed formula in early life, obese children exhibited distinct gut microbiota, which were characterized by diminished species diversity and reduced Bifidobacterium levels compared to normal-weight children. As a result, Lactobacillus acidophilus H-68 (H-68) was isolated from the feces of the N-FF group and recognized as a promising candidate. H-68 demonstrated the ability to stimulate cholecystokinin (CCK) secretion in STC-1 cells and produce bile salt hydrolase. In vivo, H-68 promoted CCK secretion, suppressing food intake, and regulated bile acid enterohepatic circulation, leading to increased deoxycholic acid and lithocholic acid levels in the ileum and liver. This regulation effectively inhibited the diet-induced body weight and body fat gain, along with the liver fat deposition. In conclusion, H-68 was recognized for its prospective anti-obesity impact, signifying an auspicious pathway for forthcoming interventions targeted at averting pediatric obesity in formula-fed children.

In vitro digestibility of proteins from red seaweeds: Impact of cell wall structure and processing methods

This study aimed to assess the nutritional quality and digestibility of proteins in two red seaweed species, Gelidium corneum and Gracilaropsis longissima, through the application of in vitro gastrointestinal digestions, and evaluate the impact of two consecutive processing steps, extrusion and compression moulding, to produce food snacks. The protein content in both seaweeds was approximately 16 %, being primarily located within the cell walls. Both species exhibited similar amino acid profiles, with aspartic and glutamic acid being most abundant. However, processing impacted their amino acid profiles, leading to a significant decrease in labile amino acids like lysine. Nevertheless, essential amino acids constituted 35-36 % of the total in the native seaweeds and their processed products. Although the protein digestibility in both seaweed species was relatively low (<60 %), processing, particularly extrusion, enhanced it by approximately 10 %. Interestingly, the effect of the different processing steps on the digestibility varied between the two species. This difference was mainly attributed to compositional and structural differences. G. corneum exhibited increased digestibility with each processing step, while G. longissima reached maximum digestibility after extrusion. Notably, changes in the amino acid profiles of the processed products affected adversely the protein nutritional quality, with lysine becoming the limiting amino acid. These findings provide the basis for developing strategies to enhance protein quality in these seaweed species, thereby facilitating high-quality food production with potential applications in the food industry.

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.

Impact of In Vitro Digestion on the Digestibility, Amino Acid Release, and Antioxidant Activity of Amaranth (Amaranthus cruentus L.) and Cañihua (Chenopodium pallidicaule Aellen) Proteins in Caco-2 and HepG2 Cells

This study evaluated the impact of in vitro gastrointestinal digestion on the digestibility, amino acid release, and antioxidant activity of proteins from amaranth (Amarantus cruentus L.) and cañihua (Chenopodium pallidicaule Aellen). Antioxidant activity was assessed using ORAC, ABTS, DPPH, and cellular antioxidant activity (CAA) assays in human intestinal Caco-2 and hepatic Hep-G2 cell lines. The results showed that amaranth had higher protein digestibility (79.19%) than cañihua (71.22%). In addition, intestinal digestion promoted the release of essential amino acids, such as leucine, lysine, and phenylalanine, in both protein concentrates. Concentrations of amaranth and cañihua proteins, ranging from 0.125 to 1.0 mg mL-1, were non-cytotoxic in both cell lines. At a concentration of 0.750 mg mL-1, simulated gastrointestinal digestion enhanced cellular antioxidant activity. Intestinal digest fractions containing peptides >5 kDa were the principal contributors to CAA in both cell lines. Notably, cañihua proteins exhibited high CAA, reaching values of 85.55% and 82.57% in Caco-2 and HepG2 cells, respectively, compared to amaranth proteins, which reached 84.68% in Caco-2 and 81.06% in HepG2 cells. In conclusion, both amaranth and cañihua proteins, after simulated gastrointestinal digestion, showcased high digestibility and released peptides and amino acids with potent antioxidant properties, underscoring their potential health benefits.

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.

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.

The impacts and mechanisms of dietary proteins on glucose homeostasis and food intake: a pivotal role of gut hormones

Glucose and energy metabolism disorders are the main reasons induced type 2 diabetes (T2D) and obesity. Besides providing energy, dietary nutrients could regulate glucose homeostasis and food intake via intestinal nutrient sensing induced gut hormone secretion. However, reviews regarding intestinal protein sensing are very limited, and no accurate information is available on their underlying mechanisms. Through intestinal protein sensing, dietary proteins regulate glucose homeostasis and food intake by secreting gut hormones, such as glucagon-like peptide 1 (GLP-1), cholecystokinin (CCK), peptide YY (PYY) and glucose-dependent insulinotropic polypeptide (GIP). After activating the sensory receptors, such as calcium-sensing receptor (CaSR), peptide transporter-1 (PepT1), and taste 1 receptors (T1Rs), protein digests induced Ca2+ influx and thus triggered gut hormone release. Additionally, research models used to study intestinal protein sensing have been emphasized, especially several innovative models with excellent physiological relevance, such as co-culture cell models, intestinal organoids, and gut-on-a-chips. Lastly, protein-based dietary strategies that stimulate gut hormone secretion and inhibit gut hormone degradation are proposed for regulating glucose homeostasis and food intake.

Optimized LC-MS/MS Method for the Detection of ppCCK(21-44): A Surrogate to Monitor Human Cholecystokinin Secretion

The hormone cholecystokinin (CCK) is secreted postprandially from duodenal enteroendocrine cells and circulates in the low picomolar range. Detection of this digestion and appetite-regulating hormone currently relies on the use of immunoassays, many of which suffer from insufficient sensitivity in the physiological range and cross-reactivity problems with gastrin, which circulates at higher plasma concentrations. As an alternative to existing techniques, a liquid chromatography and mass spectrometry-based method was developed to measure CCK-derived peptides in cell culture supernatants. The method was initially applied to organoid studies and was capable of detecting both CCK8 and an N-terminal peptide fragment (prepro) ppCCK(21-44) in supernatants following stimulation. Extraction optimization was performed using statistical modeling software, enabling a quantitative LC-MS/MS method for ppCCK(21-44) capable of detecting this peptide in the low pM range in human plasma and secretion buffer solutions. Plasma samples from healthy individuals receiving a standardized meal (Ensure) after an overnight fast were analyzed; however, the method only had sensitivity to detect ppCCK(21-44). Secretion studies employing human intestinal organoids and meal studies in healthy volunteers confirmed that ppCCK(21-44) is a suitable surrogate analyte for measuring the release of CCK in vitro and in vivo.

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.

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.

Blue Whiting (Micromesistius poutassou) Protein Hydrolysates Increase GLP-1 Secretion and Proglucagon Production in STC-1 Cells Whilst Maintaining Caco-2/HT29-MTX Co-Culture Integrity

Inducing the feeling of fullness via the regulation of satiety hormones presents an effective method for reducing excess energy intake and, in turn, preventing the development of obesity. In this study, the ability of blue whiting soluble protein hydrolysates (BWSPHs) and simulated gastrointestinal digested (SGID) BWSPHs, to modulate the secretion and/or production of satiety hormones, such as glucagon-like peptide-1 (GLP-1), cholecystokinin (CCK) and peptide YY (PYY), was assessed in murine enteroendocrine STC-1 cells. All BWSPHs (BW-SPH-A to BW-SPH-F) (1.0% w/v dw) increased active GLP-1 secretion and proglucagon production in STC-1 cells compared to the basal control (Krebs–Ringer buffer) (p < 0.05). The signaling pathway activated for GLP-1 secretion was also assessed. A significant increase in intracellular calcium levels was observed after incubation with all BWSPHs (p < 0.05) compared with the control, although none of the BWSPHs altered intracellular cyclic adenosine monophosphate (cAMP) concentrations. The secretagogue effect of the leading hydrolysate was diminished after SGID. Neither pre- nor post-SGID hydrolysates affected epithelial barrier integrity or stimulated interleukin (IL)-6 secretion in differentiated Caco-2/HT-29MTX co-cultured cells. These results suggest a role for BWSPH-derived peptides in satiety activity; however, these peptides may need to be protected by some means to avoid loss of activity during gastrointestinal transit.

In vitro dipeptidyl peptidase IV inhibitory activity and in situ insulinotropic activity of milk and egg white protein digests

Dietary proteins are involved in the regulation of glucose homeostasis by different mechanisms. Food protein digestion products are reported to inhibit dipeptidyl peptidase IV (DPP-IV), induce incretin secretion or directly exert an insulinotropic effect in pancreatic β-cells. This study illustrates the DPP-IV inhibitory activity of gastric and intestinal digests of casein, whey and egg white proteins determined in vitro, using Gly-Pro-AMC, and in situ using non-differentiated Caco-2 cells. Comparable trends in the DPP-IV inhibitory profiles were obtained by these two methods although the extent of inhibition in situ was consistently lower than the inhibition observed in vitro. Casein intestinal digests and whey protein gastric and intestinal digests showed potent DPP-IV inhibitory activities in Caco-2 cells with IC₅₀ values ranging from 0.8 to 1.2 mg mL^-1. The absorbed fraction of the intestinal digests from whey and egg white protein induced insulin secretion in BRIN-BD11 cells when determined using a two-tiered cellular model (Caco-2 and BRIN-BD11). However, the gastric digests from the same substrates showed no insulin secretion. This may be related to limited trans-epithelial transport through the Caco-2 monolayer of the gastric digestion products. However, both, gastric and intestinal digests were able to induce insulin secretion in BRIN-BD11 cells when the monolayer was composed of a co-culture of STC-1 and Caco-2 cells. This result may be attributed to the activation of STC-1 cells and subsequent incretin secretion, induced by the gastric digest, as shown by an enhanced intracellular calcium uptake.

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.

Mouse gastric mucosal endocrine cells are sources and sites of action of Phoenixin-20

Energy homeostasis is is determined by food intake and energy expenditure, which are partly regulated by the cross-talk between central and peripheral hormonal signals. Phoenixin (PNX) is a recently discovered pleiotropic neuropeptide with isoforms of 14 (PNX-14) and 20 (PNX-20) amino acids. It is a potent reproductive peptide in vertebrates, regulating the hypothalamo-pituitary-gonadal axis (HPG). It has been identified as a regulator of food intake during light phase when injected intracerebroventricularly in rats. In addition, plasma levels of PNX also increased after food intake in rats, suggesting that it might have possible roles in energy homeostasis. We hypothesized that gut is a source and site of action of PNX in mice. Immunoreactivity for PNX and its putative receptor, super-conserved receptor expressed in brain (SREB3; also known as the G-protein coupled receptor 173/GPR 173) was found in the stomach and intestine of male C57/BL6 J mice, and in MGN3-1 (mouse stomach endocrine) cells and STC-1 (mouse enteroendocrine) cells. In MGN3-1 cells, PNX-20 significantly upregulated ghrelin (10 nM) and ghrelin-O-acyl transferase (GOAT) mRNAs (1000 nM) at 6 h. In STC-1 cells, it significantly suppressed CCK (100 nM) at 2 h. No effects were found on other intestinal hormones tested (glucagon like peptide-1, glucose dependent insulinotropic polypeptide, and peptide YY). Together, these results indicate that PNX-20 is produced in the gut, and it could act directly on gut cells to regulate metabolic hormones.

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.

Glycomacropeptide: A Bioactive Milk Derivative to Alleviate Metabolic Syndrome Outcomes

Significance: Metabolic syndrome (MetS) represents a cluster of cardiometabolic disorders, which accelerate the risk of developing diabetes, nonalcoholic fatty liver disease, and cardiovascular disorders such as atherosclerosis. Oxidative stress (OxS) and inflammation contribute to insulin resistance (IR) that greatly promotes the clinical manifestations of MetS components. Given the growing prevalence of this multifactorial condition, its alerting comorbidities, and the absence of specific drugs for treatment, there is an urgent need of prospecting for alternative nutraceutics as effective therapeutic agents for MetS. Recent Advances: There is a renewed interest in bioactive peptides derived from human and bovine milk proteins given their high potential in magnifying health benefits. Special attention has been paid to glycomacropeptide (GMP), a bioactive and soluble derivative from casein and milk whey, because of the wide range of its health-promoting functions perceived in the MetS and related complications. Critical Issues: In the present review, the challenging issue relative to clinical utility of GMP in improving MetS outcomes will be critically reported. Its importance in alleviating obesity, OxS, inflammation, IR, dyslipidemia, and hypertension will be underlined. The mechanisms of action will be analyzed, and the various gaps of knowledge in this area will be specified. Future Directions: Valuable data from cellular, preclinical, and clinical investigations have emphasized the preventive and therapeutic actions of GMP toward the MetS. However, additional efforts are needed to support its proofs of principle and causative relationship to translate its concept into the clinic. Antioxid. Redox Signal. 34, 201-222.

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.

Compared digestibility of plant protein isolates by using the INFOGEST digestion protocol

The use of ingredients based on plant protein isolates is being promoted due to sustainability and health reasons. However, it is necessary to explore the behaviour of plant protein isolates during gastrointestinal digestion including the profile of released free amino acids and the characterization of resistant domains to gastrointestinal digestion. The aim of the present study was to monitor protein degradation of four legume protein isolates: garden pea, grass pea, soybean and lentil, using the harmonized Infogest in vitro digestion protocol. In vitro digests were characterized regarding protein, peptide and free amino acid content. Soybean was the protein isolate with the highest percentage of insoluble nitrogen at the end of the digestion (12%), being this fraction rich in hydrophobic amino acids. Free amino acids were mainly released during the intestinal digestion, comprising 21-24% of the total nitrogen content, while the percentage of nitrogen corresponding to peptides ranged from 66 to 76%. Legume globulins were resistant to gastric digestion whereas they were hydrolysed into peptides and amino acids during the intestinal phase. However, the molecular weight (MW) distribution demonstrated that all intestinal digests, except those from soybean, contained peptides with MW > 4 kDa at the end of gastrointestinal digestion. The profile of free amino acids released during digestion supports legume protein isolates as an excellent source of essential amino acids to be used in protein-rich food products. Peptides released during digestion matched with previously reported epitopes from the same plant species or others, explaining the ability to induce allergic reactions and cross-linked reactivity.

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.

Peptidomic data of egg white gastrointestinal digests prepared using the Infogest Harmonized Protocol

These data are related to the research article entitled “Induction of CCK and GLP-1 release in enteroendocrine cells by egg white peptides generated during gastrointestinal digestion”. In this article, the peptide and free amino acid profile of egg white gastrointestinal in vitro digests is shown. Egg white proteins were digested following the INFOGEST gastrointestinal digestion protocol. Different time points of gastric and intestinal digestion were characterized regarding protein, peptide and amino acid content. Protein degradation was followed by SDS-PAGE where some electrophoretic bands were identified by MALDI-TOF/TOF after tryptic digestion. Moreover, the molecular weight distribution of egg white peptides found at different times of gastrointestinal digestion was performed using MALDI-TOF. Peptides identified from the most abundant egg white proteins by tandem mass spectrometry were represented using a peptide profile tool and raw data are given in table format. These results reveal the protein regions resistant to digestion and illustrate the free amino acid profile of egg white protein at the end of the digestion process. These data can be used for nutritional purposes and to identify allergen epitopes or bioactive sequences.

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.

Evaluation and Exploration of Potentially Bioactive Peptides in Casein Hydrolysates against Liver Oxidative Damage in STZ/HFD-Induced Diabetic Rats

Hyperglycemia-induced oxidative stress can cause liver damage in diabetes, and protein hydrolysates with antidiabetic and antioxidant properties are emerging as a potential therapy. In this study, protective effects of casein hydrolysates against live oxidative damage in streptozotocin/high-fat-induced diabetic rats were studied and potentially bioactive peptides were explored by an integrated approach of differential peptide and in silico analysis. Results showed that different casein hydrolysates significantly alleviated liver oxidative damage (p < 0.05) via different mechanisms. Particularly, casein hydrolyzed by a papain-flavourzyme combination (P-FCH) treatment significantly improved liver antioxidant enzyme activities by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) transcription (p < 0.05). Furthermore, 18 peptides were screened as potential bioactive peptides by analyzing differential peptides among different hydrolysates combined with in silico prediction. Among them, the dipeptide WM might directly inhibit the Kelch-like ECH-associated protein 1 (Keap1)-Nrf2 interaction as potential Nrf2 activators. These results suggested that P-FCH might be an alternative way to treat liver damage in diabetes.

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.

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.