Food-derived peptides unleashed: emerging roles as food additives beyond bioactivities

Innovating food additives stands as a cornerstone for the sustainable evolution of future food systems. Peptides derived from food proteins exhibit a rich array of physicochemical and biological attributes crucial for preserving the appearance, flavor, texture, and nutritional integrity of foods. Leveraging these peptides as raw materials holds great promise for the development of novel food additives. While numerous studies underscore the potential of peptides as food additives, existing reviews predominantly focus on their biotic applications, leaving a notable gap in the discourse around their abiotic functionalities, such as their physicochemical properties. Addressing this gap, this review offers a comprehensive survey of peptide-derived food additives in food systems, accentuating the application of peptides' abiotic properties. It furnishes a thorough exploration of the underlying mechanisms and diverse applications of peptide-derived food additives, while also delineating the challenges encountered and prospects for future applications. This well-time review will set the stage for a deeper understanding of peptide-derived food additives.

Intestinal absorption of bioactive oligopeptides: paracellular transport and tight junction modulation

Bioactive oligopeptides have gained increasing attention due to their diverse physiological functions, and these can be transported into the vasculature via transcellular and paracellular pathways. Among these, paracellular transport through the intercellular space is a passive diffusion process without energy consumption. It is currently the most frequently reported absorption route for food-derived bioactive oligopeptides. Previous work has demonstrated that paracellular pathways are mainly controlled by tight junctions, but the mechanism by which they regulate paracellular absorption of bioactive oligopeptides remains unclear. In this review, we summarized the composition of paracellular pathways across the intercellular space and elaborated on the paracellular transport mechanism of bioactive oligopeptides in terms of the interaction between oligopeptides and tight junction proteins, the protein expression level of tight junctions, the signaling pathways regulating intestinal permeability, and the properties of oligopeptides themselves. These findings contribute to a more profound understanding of the paracellular absorption of bioactive oligopeptides.

Egg white hydrolysate protects white adipose tissue against metabolic insult in deoxycorticosterone acetate-salt rats

The purpose of this study was to investigate the effect of an egg white hydrolysate (EWH) to protect white adipose tissue damage from cardiometabolic changes induced by severe hypertension. Male Wistar rats were uninephrectomised and divided: SHAM (weekly subcutaneous vehicle (mineral oil + propylene glycol, 1:1)), SHAM + EWH (subcutaneous vehicle plus EWH via gavage, 1 g/kg per day), DOCA (deoxycorticosterone acetate diluted in vehicle subcutaneously weekly in subsequent doses of 20 mg/kg -1st week, 12 mg/kg - 2–3th week, and 6 mg/kg -4–8th week, respectively, plus 1 % NaCl and 0·2 % KCl in drinking water), and DOCA + EWH. Body weight gain, food and water intake, glucose and lipid metabolism were evaluated. Oxidative stress was assessed by biochemical assay and immunofluorescence for NOX-1, nuclear factor kappa B (NFκB), and caspase-3 in retroperitoneal white adipose tissue (rtWAT). Proinflammatory cytokines (IL-6 and 1β), CD163+ macrophage infiltration, and immunohistochemistry for TNFα and uncoupling protein-1 were evaluated, as well as histological analysis on rtWAT. Glutathione peroxidase and reductase were also determined in plasma. EWH showed hypocholesterolemic, antioxidant, anti-inflammatory, and anti-apoptotic properties in the arterial hypertension DOCA-salt model. The results demonstrated the presence of functional changes in adipose tissue function by a decrease in macrophage infiltration and in the fluorescence intensity of NFκB, NOX-1, and caspase-3. A reduction of proinflammatory cytokines and restoration of antioxidant enzymatic activity and mitochondrial oxidative damage by reducing uncoupling protein-1 fluorescence intensity were also observed. EWH could be used as a potential alternative therapeutic strategy in the treatment of cardiometabolic complications associated with malignant secondary arterial hypertension.

Investigating the Transepithelial Transport and Enzymatic Stability of Lactononadecapeptide (NIPPLTQTPVVVPPFLQPE), a 19-Amino Acid Casein-Derived Peptide in Caco-2 Cells

Lactononadecapeptide (LNDP; NIPPLTQTPVVVPPFLQPE), a casein-derived peptide comprising 19 residues, is known for its capacity to enhance cognitive function. This study aimed to explore the transepithelial transport and stability of LNDP. Results showed that LNDP retained over 90% stability after 2 h of treatment with gastrointestinal enzymes. The stability of LNDP on Caco-2 cell monolayers ranged from 93.4% ± 0.9% to 101.1% ± 1.2% over a period of 15-60 min, with no significant differences at each time point. The permeability of LNDP across an artificial lipid membrane was very low with the effective permeability of 3.6 × 10-11 cm/s. The Caco-2 assay demonstrated that LNDP could traverse the intestinal epithelium, with an apparent permeability of 1.22 × 10-6 cm/s. Its transport was significantly inhibited to 67.9% ± 5.0% of the control by Gly-Pro, a competitor of peptide transporter 1 (PEPT1). Furthermore, PEPT1 knockdown using siRNA significantly inhibited LNDP transport by 77.6% ± 1.9% in Caco-2 cell monolayers. The LNDP uptake in PEPT1-expressing HEK293 cells was significantly higher (54.5% ± 14.6%) than that in mock cells. These findings suggest that PEPT1 plays a crucial role in LNDP transport, and LNDP exhibits good resistance to gastrointestinal enzymes.

Encapsulation of short-chain bioactive peptides (BAPs) for gastrointestinal delivery: a review

The majority of known peptides with high bioactivity (BAPs) such as antihypertensive, antidiabetic, antioxidant, hypocholesterolemic, anti-inflammatory and antimicrobial actions, are short-chain sequences of less than ten amino acids. These short-chain BAPs of varying natural and synthetic origin must be bioaccessible to be capable of being adsorbed systemically upon oral administration to show their full range of bioactivity. However, in general, in vitro and in vivo studies have shown that gastrointestinal digestion reduces BAPs bioactivity unless they are protected from degradation by encapsulation. This review gives a critical analysis of short-chain BAP encapsulation and performance with regard to the oral delivery route. In particular, it focuses on short-chain BAPs with antihypertensive and antidiabetic activity and encapsulation methods via nanoparticles and microparticles. Also addressed are the different wall materials used to form these particles and their associated payloads and release kinetics, along with the current challenges and a perspective of the future applications of these systems.

Digestion, absorption, and transport properties of soy-fermented douchi hypoglycemic peptides VY and SFLLR under simulated gastrointestinal digestion and Caco-2 cell monolayers

Two novel hypoglycemic peptides VY and SFLLR were identified from douchi as the major peptides responsible for the glucose uptake activity. The present work aimed to elucidate their digestion, absorption and transport properties using simulated digestion and Caco-2 cell monolayers transport models. Besides, the effects of digestion and absorption on the structure and activity were also studied. The results showed that VY was resistant to gastrointestinal tract digestion and could cross Caco-2 cell monolayers intactly via both TJs-mediated passive paracellular pathway and PepT1-mediated active route. In comparison, SFLLR was partially degraded into small fragments of SFLL, SFL, and SF by the digestive system, leading to increased glucose uptake activity. Notably, SFLLR, SFLL, and SFL were partly hydrolyzed by aminopeptidase N or dipeptidyl peptidase IV during transport, but they were transported intact. SFL was transported via both paracellular diffusion and PepT1-mediated routes, while SFLLR and SFLL were via paracellular route only.

Current trends and perspectives on bioaccessibility and bioavailability of food bioactive peptides: in vitro and ex vivo studies

The bioaccessibility and bioavailability of food-derived bioactive compounds are important issues when assessing their in vivo physiological health-promoting effects. Food components such as proteins and peptides are exposed to different proteases and peptidases during gastrointestinal digestion and absorption. Different in vitro approaches have therefore been developed to evaluate the bioaccessibility and stability of bioactive peptides. The static simulated gastrointestinal digestion model (SGD) was widely reported to assess the bioaccessibility of bioactive peptides. On the other hand, although the dynamic SGD model may better simulate human digestion, it has rarely been explored in bioaccessibility studies of food bioactive peptides due to its high cost and lack of standardization. For bioavailability studies, the Caco-2 cell monolayer model has been used extensively for the assessment of food bioactive peptides. In fact, very few reports using alternative methods for determining transepithelial transport of bioactive peptides have been employed. In this sense, ex vivo tissue-based models such as the Ussing chamber and the everted sac gut have been used. Current evidence supports the fact that using SGD with cell-based models for evaluating the bioaccessibility, absorption, and bioavailability of food-derived bioactive peptides, is the most commonly used approach. Nevertheless, SGD with ex vivo tissue-based models such as the everted sac, remains to be further explored because it seems to be the model that better mimics the physiological process - it is also fast and inexpensive, and several compounds may be tested simultaneously. In the present review, we discuss information available on the different in vitro approaches for the determination of bioaccessibility and bioavailability of food-derived bioactive peptides with special emphasis on ex vivo tissue-based models such as the everted sac and the Ussing chamber models. © 2022 Society of Chemical Industry.

Dietary Egg White Hydrolysate Prevents Male Reproductive Dysfunction after Long-Term Exposure to Aluminum in Rats

Aluminum (Al) is a non-essential metal omnipresent in human life and is considered an environmental toxicant. Al increases reactive oxygen production and triggers immune responses, contributing to chronic systemic inflammation development. Here, we have tested whether an egg white hydrolysate (EWH) with potential bioactive properties can protect against changes in reproductive function in rats exposed to long-term Al dietary levels at high and low doses. Male Wistar rats received orally: low aluminum level group-AlCl₃ at 8.3 mg/kg b.w. for 60 days with or without EWH (1 g/kg/day); high aluminum level group-AlCl₃ at 100 mg/kg b.w. for 42 days with or without EWH (1 g/kg/day). The co-administration of EWH prevented the increased Al deposition surrounding the germinative cells, reducing inflammation and oxidative stress in the reproductive organs. Furthermore, the daily supplementation with EWH maintained sperm production and sperm quality similar to those found in control animals, even after Al exposure at a high dietary contamination level. Altogether, our results suggest that EWH could be used as a protective agent against impairment in the reproductive system produced after long-term exposure to Al at low or high human dietary levels.

Advances in the stability challenges of bioactive peptides and improvement strategies

Bioactive peptides are widely used in functional foods due to their remarkable efficacy, selectivity, and low toxicity. However, commercially produced bioactive peptides lack quality stability between batches. Furthermore, the efficacies of bioactive peptides cannot be guaranteed in vivo due to gastrointestinal digestion and rapid plasma, liver, and kidney metabolism. The problem of poor stability has restricted the development of peptides. Bioactive peptide stability assessments use different stability assays, so the results of different studies are not always comparable. This review summarizes the quality stability challenges in the enzymatic hydrolysis production of bioactive peptides and the metabolism stability challenges after oral administration. Future directions on the strategies for improving their stability are provided. It was proposed that we use fingerprinting as a quality control measure using qualitative and quantitative characteristic functional peptide sequences. The chemical modification and encapsulation of bioactive peptides in microcapsules and liposomes are widely used to improve the digestive and metabolic stability of bioactive peptides. Additionally, the establishment of a universal stability test and a unified index would greatly improve uniformity and comparability in research into bioactive peptides. In summary, the reliable evaluation of stability is an essential component of peptide characterization, and these ideas may facilitate further development and utilization of bioactive peptides.

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Stability challenges encountered by bioactive peptides were summarized.

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Strategies to improve the stability of bioactive peptides were provided.

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A universal stability test and unified index would improve uniformity and comparability in research into bioactive peptides.

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It was proposed that we use a method of traditional Chinese medicine fingerprinting as a quality control measure.

Bioavailability of Peptides Derived from the In Vitro Digestion of Human Milk Assessed by Caco-2 Cell Monolayers

Human milk-protein-derived peptides exhibit an array of bioactivities. Certain bioactivities cannot be exerted unless the peptides are absorbed across the gastrointestinal lumen into the bloodstream. The purpose of study was to determine which peptides derived from in vitro digestion of human milk could cross human intestinal Caco-2 cell monolayers. Our results showed that the numbers of peptides absorbed by the Caco-2 cell monolayer were different at different concentrations (44 peptides out of 169 peptides detected at 10 μg/mL, 124 peptides out of 204 peptides detected at 100 μg/mL, and 175 peptides out of 236 peptides detected at 1000 μg/mL). Four peptides (NLHLPLP (β-casein [138-144]), PLAPVHNPI (β-casein [216-224]), PLMQQVPQPIPQ (β-casein [148-159]), and FDPQIPK (β-casein [126-132])) crossed to the basolateral chamber of the Caco-2 monolayer incubated with peptides at all three concentrations. Among the peptides identified in the basolateral chambers, three peptides (NLHLPLP (β-casein [138-144]), LENLHLPLP (β-casein [136-144]), and QVVPYPQ (β-casein [182-188])) are known ACE-inhibitors; one peptide (LLNQELLLNPTHQIYPV (β-casein [197-213])) is antimicrobial, and another peptide (QVVPYPQ (β-casein [182-188])) has antioxidant activity. These findings indicate that specific milk peptides may be able to reach the bloodstream and exert bioactivity.

Transport, Stability, and In Vivo Hypoglycemic Effect of a Broccoli-Derived DPP-IV Inhibitory Peptide VPLVM

Diabetes is a major metabolic disease that requires long-term pharmacotherapy. Bioactive peptides have unique advantages such as higher potency, selectivity, and safety over small molecules and have achieved great success in the treatment of diabetes. We previously isolated a dipeptidyl peptidase-IV (DPP-IV) inhibitory peptide VPLVM with IC₅₀ = 99.68 μM from the protein hydrolysates of broccoli stems and leaves. Here, we evaluated the interaction with DPP-IV, transport, stability, and in vivo hypoglycemic effects of VPLVM. VPLVM interacted closely and steadily with DPP-IV at S1 and S2 pockets. VPLVM had a good gastrointestinal enzyme resistance and was transported through the Caco-2 cell monolayer via paracellular diffusion and by the PepT1 with a P_app of 6.96 × 10^-7 cm/s. VPLVM has a t_1/2 of 12.56 ± 0.41 min in vitro plasma stability. In the oral glucose tolerance test, VPLVM showed an excellent hypoglycemic effect at 30 min after administration. VPLVM has potential as a candidate for the treatment of hyperglycemia.

Investigation of the intestinal trans-epithelial transport and antioxidant activity of two hempseed peptides WVSPLAGRT (H2) and IGFLIIWV (H3)

A preceding paper has shown that a hempseed peptic hydrolysate displays a cholesterol-lowering activity with a statin-like mechanism of action in HepG2 cells and a potential hypoglycemic activity by the inhibition of dipeptidyl peptidase-IV in Caco-2 cells. In the framework of a research aimed at fostering the multifunctional behavior of hempseed peptides, we present here the identification and evaluation of some antioxidant peptides from the same hydrolysate. After evaluation of its diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, a trans-epithelial transport experiment was performed using differentiated Caco-2 cells that permitted the identification of five transported peptides that were synthesized and evaluated by measuring the oxygen radical absorbance capacity (ORAC), the ferric reducing antioxidant power (FRAP), and the 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic) acid (ABTS), and diphenyl-2-picrylhydrazyl radical DPPH assays. The most active peptides, i.e. WVSPLAGRT (H2) and IGFLIIWV (H3), were then tested in cell assays. Both peptides were able to reduce the H₂O₂-induced reactive oxygen species (ROS), lipid peroxidation, and nitric oxide (NO) production levels in HepG2 cells, via the modulation of Nrf-2 and iNOS pathways, respectively.

Enzymatic hydrolysis and microbial fermentation: The most favorable biotechnological methods for the release of bioactive peptides

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Peptide release methods influence its bioactivity by generating different sequences.

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The absorption, toxicity and taste of peptides is influenced by the production method.

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The most used methods are enzymatic hydrolysis and microbial fermentation.

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The most used methods are biotechnological and differ in their process.

Bioactive peptides are biomolecules derived from proteins. They contain anywhere from 2 to 20 amino acids and have different bioactivities. For example, they have antihypertensive activity, antioxidant activity, antimicrobial activity, etc. However, bioactive peptides are encrypted and inactive in the parental protein, so it is necessary to release them to show their bioactivity. For this, there are different methods, where biotechnological methods are highly favorable, highlighting enzymatic hydrolysis and microbial fermentation.

The choice of the method to be used depends on different factors, which is why it is essential to know about the process, its principle, and its advantages and disadvantages. The process of peptide release is critical to generate various peptide sequences, which will produce different biological effects in the hydrolysate. This review focuses on providing extensive information on the enzymatic method and microbial fermentation to facilitate selecting the method that provides the most benefits.

Current findings support the potential use of bioactive peptides in enhancing zinc absorption in humans

More than two billion people around the world are affected by zinc deficiency, mainly due to the inadequate intake and absorption of zinc. Based on recent research findings, the bioactive peptides could potentially be used to combat zinc deficiency particularly due to their Zinc chelating ability. The main aim of this review was to present current findings, supporting the potential use of bioactive peptides based on their ability to enhance zinc absorption. In-vivo, in-vitro, and ex-vivo studies have demonstrated that zinc chelating peptides can enhance the retention, transportation, and absorption of zinc. Comparative studies on zinc bioavailability from protein hydrolysates and zinc salts have demonstrated that the protein hydrolysates-zinc complexes are more bioavailable than the zinc salts. Data from the structure-function relationship of zinc chelating peptides suggest that the zinc chelating capacities of peptides increase in the following order; the position of zinc chelator > zinc chelator strength > abundance of zinc chelators > net charge > molecular weight. In addition, the transport mechanism of peptide-zinc complex is hypothesized, and the potential use of bioactive peptides based on their safety and taste and limitations to their commercialization are also discussed.

Caco-2/HT29-MTX co-cultured cells as a model for studying physiological properties and toxin-induced effects on intestinal cells

Infectious gastrointestinal diseases are frequently caused by toxins secreted by pathogens which may impair physiological functions of the intestines, for instance by cholera toxin or by heat-labile enterotoxin. To obtain a functional model of the human intestinal epithelium for studying toxin-induced disease mechanisms, differentiated enterocyte-like Caco-2 cells were co-cultured with goblet cell-like HT29-MTX cells. These co-cultures formed a functional epithelial barrier, as characterized by a high electrical resistance and the presence of physiological intestinal properties such as glucose transport and chloride secretion which could be demonstrated electrophysiologically and by measuring protein expression. When the tissues were exposed to cholera toxin or heat-labile enterotoxin in the Ussing chamber, cholera toxin incubation resulted in an increase in short-circuit currents, indicating an increase in apical chloride secretion. This is in line with typical cholera toxin-induced secretory diarrhea in humans, while heat-labile enterotoxin only showed an increase in short-circuit-current in Caco-2 cells. This study characterizes for the first time the simultaneous measurement of physiological properties on a functional and structural level combined with the epithelial responses to bacterial toxins. In conclusion, using this model, physiological responses of the intestine to bacterial toxins can be investigated and characterized. Therefore, this model can serve as an alternative to the use of laboratory animals for characterizing pathophysiological mechanisms of enterotoxins at the intestinal level.

Advancement and prospects of production, transport, functional activity and structure-activity relationship of food-derived angiotensin converting enzyme (ACE) inhibitory peptides

Food-derived antihypertensive peptides have attracted increasing attention in functional foods for health promotion, due to their high biological activity, low toxicity and easy metabolism in the human body. Angiotensin converting enzyme (ACE) is a key enzyme that causes the increase in blood pressure in mammals. However, few reviews have summarized the current understanding of ACE inhibitory peptides and their knowledge gaps. This paper focuses on the food origins and production methods of ACE inhibitory peptides. Compared with conventional methods, the advanced technologies and emerging bioinformatics approaches have recently been applied for efficient and targeted release of ACE inhibitory peptides from food proteins. Furthermore, the transport and underlying mechanisms of ACE inhibitory peptides are emphatically described. Molecular modeling and the Michaelis-Menten equation can provide information on how ACE inhibitors function. Finally, we discuss the structure-activity relationships and other bio-functional properties of ACE inhibitory peptides. Molecular weight, hydrophobic amino acid residues, charge, amino acid composition and sequence (especially at the C-terminal and N-terminal) have a significant influence on ACE inhibitory activity. Some studies are required to increase productivity, improve bioavailability of peptides, evaluate their bio-accessibility and efficiency on reducing blood pressure to provide a reference for the development and application of health products and auxiliary treatment drugs.

Novel Hyp-Gly-containing antiplatelet peptides from collagen hydrolysate after simulated gastrointestinal digestion and intestinal absorption

Bioactive components causing the antiplatelet activity upon collagen hydrolysate (CH) ingestion have not been clarified yet. This study aimed to identify antiplatelet peptides from CH after simulated gastrointestinal digestion and intestinal absorption. Four antiplatelet peptides containing the Hyp-Gly (OG) sequence including OG, Hyp-Gly-Glu (OGE), Pro-Gly-Glu-Hyp-Gly (PGEOG) and Val-Gly-Pro-Hyp-Gly-Pro-Ala (VGPOGPA) were successfully identified. All four peptides exhibited antiplatelet activity, but OGE and PGEOG exerted stronger activity than OG and VGPOGPA. The IC50 value of OGE and PGEOG was 1.076 mM and 1.167 mM, respectively. These four antiplatelet peptides could survive simulated gastrointestinal digestion and be absorbed intact by Caco-2 cells. Furthermore, plasma stability experiments showed that OG and OGE showed a good stability in human plasma, but PGEOG and VGPOGPA showed a relatively poor stability. In vivo studies indicated that OG and OGE were present in blood after the oral administration of CH. Meanwhile, OGE exerted significant in vivo anti-thrombotic activity after its ingestion. The present study clarifies the antiplatelet components causing the CH activity and highlights the potential application of CH or these four peptides as functional foods to combat thrombosis by inhibiting platelet aggregation.

Effect of catechin on dietary AGEs absorption and cytotoxicity in Caco-2 cells

Maillard reaction produces advanced glycation end products (AGEs) that endanger human health. This study investigated the protective effect of (+)-catechin (CC) on different types of dietary AGEs absorption and cytotoxicity in Caco-2 cells. Our results showed that CC had higher inhibitory rate on peptide bound-AGEs absorption than free Nɛ-carboxymethyl lysine (CML), which dropped to 36.24% and 32.21% when treated with 20 and 50 μM CC. The reasons might be that CC could repair the loose tight junction (ZO-1) and down-regulation of protein-coupling peptide carrier 1 (PEPT-1) expression in Caco-2 cells which were in accordance with molecular docking results. Additionally, CC could remarkably decreased the protein levels of receptor of AGEs (RAGE), mitogen-activated protein kinases (MAPK) and nuclear factor-kappa B (NF-κB) that detected by western blotting and immunohistochemical staining method. Taken together, these findings demonstrated that CC may inhibit AGEs absorption and protected Caco-2 cells against RAGE-MAPK-NF-κB signaling suppression.

Trans-Epithelial Transport, Metabolism, and Biological Activity Assessment of the Multi-Target Lupin Peptide LILPKHSDAD (P5) and Its Metabolite LPKHSDAD (P5-Met)

P5 (LILPKHSDAD) is a hypocholesterolemic peptide from lupin protein with a multi-target activity, since it inhibits both 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAR) and proprotein convertase subtilisin/kexin type-9 (PCSK9). This work shows that, during epithelial transport experiments, the metabolic transformation mediated by intestinal peptidases produces two main detected peptides, ILPKHSDAD (P5-frag) and LPKHSDAD (P5-met), and that both P5 and P5-met are linearly absorbed by differentiated human intestinal Caco-2 cells. Extensive comparative structural, biochemical, and cellular characterizations of P5-met and the parent peptide P5 demonstrate that both peptides have unique characteristics and share the same mechanisms of action. In fact, they exert an intrinsically multi-target behavior being able to regulate cholesterol metabolism by modulating different pathways. The results of this study also highlight the dynamic nature of bioactive peptides that may be modulated by the biological systems they get in contact with.

Activity and bioavailability of food protein-derived angiotensin-I-converting enzyme-inhibitory peptides

Angiotensin-I-converting enzyme (ACE) inhibitory peptides are able to inhibit the activity of ACE, which is the key enzymatic factor mediating systemic hypertension. ACE-inhibitory peptides can be obtained from edible proteins and have the function of antihypertension. The amino acid sequences and the secondary structures of ACE-inhibitory peptides determine the inhibitory activities and stability. The resistance of ACE-inhibitory peptides to digestive enzymes and peptidase affect their antihypertensive bioactivity in vivo. In this paper, the mechanism of ACE-inhibition, sources of the inhibitory peptides, structure-activity relationships, stability during digestion, absorption and transportation of ACE-inhibitory peptides, and consumption of ACE-inhibitory peptides are reviewed, which provide guidance to the development of new functional foods and production of antihypertensive nutraceuticals and pharmaceuticals.

Bioactive Peptides and Hydrolysates from Egg Proteins as a New Tool for Protection Against Cardiovascular Problems

The aim of the present work is to review the potential beneficial effects of dietary supplementation with bioactive egg protein hydrolysates or peptides on cardiometabolic changes associated with oxidative stress. The development of nutritionally improved food products designed to address specific health concerns is of particular interest because many bioactive food compounds can be potentially useful in various physiological functions such as for reducing oxidative stress. The results presented suggest that egg hydrolysates or derived peptides could be included in the diet to prevent and/or reduce some cardiometabolic complications associated with oxidative stress-related diseases.

Antarctic Krill Derived Nonapeptide as an Effective Iron-Binding Ligand for Facilitating Iron Absorption via the Small Intestine

A novel nonapeptide DTDSEEEIR identified from Antarctic krill (Euphausia superba) iron-binding peptides was used in this study to analyze its iron-binding sites and structural changes after iron coordination. The enzymatic resistance and transport of DTDSEEEIR-iron during gastrointestinal digestion and absorption as well as the relationship between the DTDSEEEIR stability and the enhancement of iron absorption were further explored. Results revealed that iron ions spontaneously bound to the carboxyl, hydroxyl, and amino groups of the DTDSEEEIR peptide, which induced the folding of DTDSEEEIR to form a more orderly structure. The DTDSEEEIR peptide remained stable to a certain extent (79.60 ± 0.19%) after gastrointestinal digestion and the coordination of iron improved the digestive stability of the DTDSEEEIR peptide (93.89 ± 1.37%). Moreover, the stability of DTDSEEEIR across intestinal epithelium had a positive effect on iron absorption, which implied that DTDSEEEIR might carry iron ions through intestinal epithelial cells.

Spent Hen Protein Hydrolysate with Good Gastrointestinal Stability and Permeability in Caco-2 Cells Shows Antihypertensive Activity in SHR

Spent hens are a major byproduct of the egg industry but are rich in muscle proteins that can be enzymatically transformed into bioactive peptides. The present study aimed to develop a spent hen muscle protein hydrolysate (SPH) with antihypertensive activity. Spent hen muscle proteins were hydrolyzed by nine enzymes, either individually or in combination; 18 SPHs were assessed initially for their in vitro angiotensin-converting enzyme (ACE) inhibitory activity, and three SPHs, prepared by Protex 26L (SPH-26L), pepsin (SPH-P), and thermoase (SPH-T), showed promising activity and peptide yield. These three hydrolysates were further assessed for their angiotensin-converting enzyme 2 (ACE2) upregulating, antioxidant, and anti-inflammatory activities; only SPH-T upregulated ACE2 expression, while all three SPHs showed antioxidant and anti-inflammatory activities. During simulated gastrointestinal digestion, ACE2 upregulating, ACE inhibitory and antioxidant activities of SPH-T were not affected, but those of SPH-26L and SPH-P were reduced. ACE inhibitory activity of gastrointestinal-digested SPH-T was not affected after the permeability study in Caco-2 cells, while ACE2 upregulating, antioxidant and anti-inflammatory activities were improved; nine novel peptides with five–eight amino acid residues were identified from the Caco-2 permeate. Among these three hydrolysates, only SPH-T reduced blood pressure significantly when given orally at a daily dose of 1000 mg/kg body weight to spontaneously hypertensive rats. SPH-T can be developed into a promising functional food ingredient against hypertension, contributing to a more sustainable utilization for spent hens while generating extra revenue for the egg industry.

A Narrative Review of the Anti-Hyperglycemic and Satiating Effects of Fish Protein Hydrolysates and Their Bioactive Peptides

Prevalence of type 2 diabetes and overweight/obesity are increasing globally. Food supplementation as a preventative option has become an attractive option in comparison to increased pharmacotherapy dependency. Hydrolysates of fish processing waste and by-products have become particularly interesting in a climate of increased food wastage awareness and are rapidly gaining traction in food research. This review summarizes the available research so far on the potential effect of these hydrolysates on diabetes and appetite suppression. Scopus and Web of Science are searched using eight keywords (fish, hydrolysate, peptides, satiating, insulinotropic, incretin, anti-obesity, DPP-4 [dipeptidylpeptidase-4/IV]) returning a total of 2549 results. Following exclusion criteria (repeated appearances, non-fish marine sources [e.g., macroalgae], and irrelevant bioactivities [e.g., immunomodulatory, anti-thrombotic]), 44 relevant publications are included in this review. Stimulation of hormone secretion, regulation of glucose uptake, anorexigenic potential, identified mechanisms of action, and research conducted on the most potent bioactive peptides identified within these hydrolysates are all specifically addressed. Results of this review conclude that despite wide methodological variation between studies, there is significant potential for the application of fish protein hydrolysates in the management of bodyweight and hyperglycemia.

Baijiu vinasse as a new source of bioactive peptides with antioxidant and anti-inflammatory activity

During production in Chinese baijiu fermentation process, huge amounts of the by-product vinasse are generated and generally utilized as low-value animal feed. We applied alkaline extraction in combination with ultrasonication to recover vinasse proteins, which were then hydrolyzed by complex protease Corolase PP for 8 h to obtain peptide fractions (VPH-1, -2, -3) displaying high DPPH radical scavenging activity. VPH-3 (<3 kDa) separated by ultrafiltration had EC₅₀ values lower than those of VPH-1 and -2 for reactive oxygen species (ROS) and reactive nitrogen species (RNS) radicals, and significantly inhibited production of NO and pro-inflammatory cytokines in LPS-stimulated RAW264.7 macrophage cells. Active peptides and their amino acid sequences were identified by LC-MS/MS analysis, and five synthesized peptides (particularly KLPDHPKLPK and VDVPVKVPYS) displayed strong anti-inflammatory activity at concentration 0.25 mg/mL. These findings will be useful in future commercial development of baijiu vinasse, including application as a new source of bioactive peptides.

Structural Evidence for Antihypertensive Effect of an Antioxidant Peptide Purified from the Edible Marine Animal Styela clava

This study investigated the antihypertensive effects of an antioxidant peptide, Leu-Trp-His-Thr-His (LWHTH), purified from Styela clava peptic hydrolysate, to assess the bioactivity of the peptide and verify the value of S. clava as a health-promoting food. Also, the study presented structural evidence for the effects of LWHTH. The inhibitory effect of LWHTH on angiotensin I-converting enzyme (ACE) was assessed using enzyme reaction methods and the simulation methods in computational space. LWHTH inhibited ACE with an IC₅₀ value of 16.42 ± 0.45 μM. The LWHTH structure was stable, and its ACE inhibitory effect was retained under simulated gastrointestinal conditions. In silico simulations revealed that LWHTH binds the active site of ACE, with residues LW making the ACE-LWHTH complex stable and residues HTH making the complex strong. Furthermore, LWHTH significantly reduced blood pressure in spontaneously hypertensive rats. These results demonstrate that LWHTH has the potential to be a healthy functional food with antihypertensive effects. Therefore, S. clava consumption may be beneficial for human health.

Implication of Opioid Receptors in the Antihypertensive Effect of a Novel Chicken Foot-Derived Peptide

The peptide AVFQHNCQE demonstrated to produce nitric oxide-mediated antihypertensive effect. This study investigates the bioavailability and the opioid-like activity of this peptide after its oral administration. For this purpose, in silico and in vitro approaches were used to study the peptide susceptibility to GI digestion. In addition, AVFQHNCQE absorption was studied both in vitro by using Caco-2 cell monolayers and in vivo evaluating peptide presence in plasma from Wistar rats by ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and by ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS). Both in vivo and in vitro experiments demonstrated that peptide AVFQHNCQE was not absorbed. Thus, the potential involvement of opioid receptors in the BP-lowering effect of AVFQHNCQE was studied in the presence of opioid receptors-antagonist Naloxone. No changes in blood pressure were recorded in rats administered Naloxone, demonstrating that AVFQHNCQE antihypertensive effect is mediated through its interaction with opioid receptors. AVFQHNCQE opioid-like activity would clarify the antihypertensive properties of AVFQHNCQE despite its lack of absorption.

Yak (Bos grunniens) bones collagen-derived peptides stimulate osteoblastic proliferation and differentiation via the activation of Wnt/β-catenin signaling pathway

BACKGROUND

As the world's population is transitioning gradually to an ageing stage, the incidence of osteoporosis is increasing annually. Yak bone is one of the major components of Tibetan medicine and it has mainly been associated with an improvement in bone health, for example against osteoporosis. However, the functional bioactive ingredients and the underlying mechanisms are still unclear.

RESULTS

Sequential purification of yak-bone hydrolysates was achieved by ultrafiltration, size exclusion chromatography, and semi-preparative reverse-phase high-performance liquid chromatography. After this, 35 novel peptides were identified by mass spectrometry analysis, of which peptide GPAGPPGPIGNV (GP-12) displayed the highest osteoblast proliferation-promoting activity, with an increase of 42.7% in cell growth. An in vitro stability study demonstrated that GP-12 was digested into smaller peptides (GP-9, GV-9, AV-10 and GP-11) after simulated gastrointestinal digestion and absorption (Caco-2 cell monolayers) experiments. However, some of them still can be absorbed intact through the (Caco-2 cell monolayers by a paracellular route (Papp: 5.36 ± 0.34 cm s^-1 ). Flow cytometry results indicated that GP-12 enhanced osteoblastic proliferation by inducing the alteration of the cell-cycle progression both from the G0/G1 to the S phase and from the S to the G2/M phase. Quantitative real-time polymerase chain reaction (PCR) and western blot results revealed that GP-12 induced osteoblastic proliferation and differentiation in a dose-response manner through the activation of a Wnt/β-catenin signaling pathway.

CONCLUSION

These findings highlighted that such peptides hold the promise of discovering candidates for functional and health-promoting foods, which could be potentially used for the treatment of osteoporosis. © 2020 Society of Chemical Industry.

Egg White Hydrolysate: A new putative agent to prevent vascular dysfunction in rats following long-term exposure to aluminum

Aluminum (Al) is toxic for humans and animals. Here, we have tested the potential for Egg White Hydrolysate (EWH) to protect against cardiovascular changes in rats exposed to both high and low dietary levels of Al. Indeed, EWH has been previously shown to improve cardio metabolic dysfunctions induced by chronic exposure to heavy metals. Male Wistar rats received orally: Group 1) Low aluminum level (AlCl₃ at a dose of 8.3 mg/kg b.w. during 60 days) with or without EWH treatment (1 g/kg/day); Group 2) High aluminum level (AlCl₃ at a dose of 100 mg/kg b.w. during 42 days) with or without EWH treatment. After Al treatment, rats co-treated with EWH did not show vascular dysfunction or increased blood pressure as was observed in non EWH-cotreated animals. Indeed, co-treatment with EWH prevented the following effects observed in both aorta and mesenteric arteries: the increased vascular responses to phenylephrine (Phe), the decreased ACh-induced relaxation, the reduction on endothelial modulation of vasoconstrictor responses and the nitric oxide bioavailability, as well as the increased reactive oxygen species production from NAD(P)H oxidase. Altogether, our results suggest that EWH could be used as a protective agent against the harmful vascular effects after long term exposure to Al.

Transepithelial Transport Characteristics of the Cholesterol- Lowing Soybean Peptide, WGAPSL, in Caco-2 Cell Monolayers

Recent studies have shown that soybean protein and its peptides have cholesterol-lowering activities. However, it is not clear whether these peptides could overcome physiological barriers, such as phase II metabolism in gastrointestinal tract and poor permeability, to reach the blood stream in its intact form. Therefore, the transepithelial transport characteristics of soybean peptide Trp-Gly-Ala-Pro-Ser-Leu (WGAPSL) with cholesterol- lowering activity were investigated in Caco-2 cells. In this study; the transepithelial absorption of WGAPSL was studied using human intestinal Caco-2 cell monolayers. The results showed that WGAPSL had good stability (83.9% ±1.98%) after simulated gastric and intestinal digestion. During the apical (AP) side to basolateral (BL) side transport, WGAPSL was absorbed intact through Caco-2 cell monolayers with apparent permeability coefficient (Papp) values of 4.4 × 10-8 to 1.2 × 10-8 cm/s. Cytochalasin D loosened the tight junctions of Caco-2 cell monolayers and significantly (p < 0.05) improved the transport process. Sodium azide, wortmannin, and Gly-Pro had minimal effects on transport, demonstrating that the major transport route of WGAPVL was paracellular via tight junctions. Finally, LC-MS analysis showed that Gly-Ala-Pro (GAP) was the important part for the intact absorption of WGAPVL and Trp (W) was the most unstable amino acid residue.

Preparation, Bioavailability, and Mechanism of Emerging Activities of Ile-Pro-Pro and Val-Pro-Pro

Ile-Pro-Pro and Val-Pro-Pro are two most well-known food-derived bioactive peptides, initially identified as inhibitors of angiotensin I-converting enzyme (ACE) from a sample of sour milk. These two peptides were identified in fermented and enzymatic hydrolyzed cow and non-cow (that is, goat, sheep, buffalo, yak, camel, mare, and donkey) milk, as well as sourdough prepared from wheat, rye, and malt. Similar to other bioactive peptides, bioavailability of these peptides is low (about 0.1%), reaching picomolar concentration in human plasma; they showed blood pressure lowering activity in animals and in human, via improved endothelial function, activation of ACE2, and anti-inflammatory property. Emerging bioactivities of these two peptides toward against metabolic syndrome and bone-protection received limited attention, but may open up new applications of these peptides as functional food ingredients. Further studies are warranted to determine the best source as well as to identify novel enzymes (particularly from traditional fermented milk products) to improve the efficiency of production, to characterize possible peptide receptors using a combination of omics technology with molecular methods to understand if these two peptides act as signal-like molecules, to improve their bioavailability, and to explore new applications based on emerging bioactivities.

Hydrolysis and Transport of Egg White-Derived Peptides in Caco-2 Cell Monolayers and Everted Rat Sacs

The objective of this paper was to investigate the hydrolysis and transepithelial transport of egg white peptides in Caco-2 cell monolayers and everted rat sacs. Results showed that egg white peptides had higher permeability but lower degradation in Caco-2 cell monolayers than found for everted rat sacs. Peptides LGAKDSTRT, DGSRQPVDN, VNDLQGKTS, and GKKDPVLKD were identified from not only the basolateral (BL) side of Caco-2 cell monolayers but also the serous side of everted rat sacs, suggesting that these four peptides could be transported intact in both model systems. In addition, there were 24 peptides identified from the apical (AP) side of Caco-2 cell monolayers and the mucosal side of everted rat sacs, indicating potential resistance to hydrolysis by brush border membrane peptidases. Among these, peptides IRDLLER, YAEERYP, and IRNVLQPS were demonstrated as having dipeptidyl peptidase IV (DPP-IV) inhibitory activities with IC₅₀ values of 186.23 ± 15.25, 340.62 ± 4.73, and 598.28 ± 15.12 μM ( P < 0.05), respectively. Furthermore, molecular docking revealed that the DPP-IV inhibitory peptides were predicted to form hydrogen-bonds, π-π bonds, and charge interactions with the activity sites, especially the amino acid residues located in the S2 pocket of DPP-IV, potentially contributing to their DPP-IV inhibitory activities.

Egg White Hydrolysate as a functional food ingredient to prevent cognitive dysfunction in rats following long-term exposure to aluminum

Aluminum (Al), which is omnipresent in human life, is a potent neurotoxin. Here, we have tested the potential for Egg White Hydrolysate (EWH) to protect against changes in cognitive function in rats exposed to both high and low levels of Al. Indeed, EWH has been previously shown to improve the negative effects induced by chronic exposure to heavy metals. Male Wistar rats received orally: Group 1) Low aluminum level (AlCl3 at a dose of 8.3 mg/kg b.w. during 60 days) with or without EWH treatment (1 g/kg/day); Group 2) High aluminum level (AlCl3 at a dose of 100 mg/kg b.w. during 42 days) with or without EWH treatment (1 g/kg/day). After 60 or 42 days of exposure, rats exposed to Al and EWH did not show memory or cognitive dysfunction as was observed in Al-treated animals. Indeed, co-treatment with EWH prevented catalepsy, hippocampal oxidative stress, cholinergic dysfunction and increased number of activated microglia and COX-2-positive cells induced by Al exposure. Altogether, since hippocampal inflammation and oxidative damage were partially prevented by EWH, our results suggest that it could be used as a protective agent against the detrimental effects of long term exposure to Al.

Preparation and identification of novel inhibitory angiotensin-I-converting enzyme peptides from tilapia skin gelatin hydrolysates: inhibition kinetics and molecular docking

Tilapia skin gelatin was hydrolyzed by successive simulated gastrointestinal digestion, and the hydrolysates were further separated by transport across a Caco-2 cell monolayer. Angiotensin-I-converting enzyme inhibitory (ACEI) peptides were separated by successive chromatographic steps from the transport hydrolysates. We have identified two key ACEI peptides, namely VGLPNSR (741.4133 Da) and QAGLSPVR (826.4661 Da) with IC50 values of ACEI activity of 80.90 and 68.35 μM, respectively. Lineweaver-Burk plots indicated that the inhibitory ACE kinetics of the two peptides were noncompetitive. Molecular docking simulation showed that the two peptides could interact with the ACE site via hydrogen bonds with high binding power. However, the hydrogen bonds were not formed with the key amino acid residues in the active site of ACE. This finding was in accordance with the noncompetitive inhibition. This study established a novel approach to identify key ACEI peptides and suggested the use of tilapia peptides as functional food ingredients to prevent hypertension.

Stability and Transport of Spent Hen-Derived ACE-Inhibitory Peptides IWHHT, IWH, and IW in Human Intestinal Caco-2 Cell Monolayers

Ile-Trp-His-His-Thr (IWHHT), initially identified as an ACE inhibitory peptide, was shown to have antioxidant and anti-inflammatory activities in cells and blood pressure lowering activity in animals. IWHHT was degraded into IWH and IW during simulated gastrointestinal digestion. The purpose of this study was to investigate the stability, permeability, and transport pathways of IWHHT, IWH, and IW across intestinal epithelium using human intestinal Caco-2 cell monolayers. IWHHT, IWH, and IW were partly degraded by aminopeptidase N or dipeptidyl peptidase IV, but they were transported intact, with apparent permeability coefficients of (22.0 ± 1.42) × 10^-8, (37.5 ± 1.11) × 10^-8, and (19.6 ± 0.62) × 10^-8 cm s^-1, respectively. The results firstly evidenced an important role of aminopeptidase N in cleaving small ACE inhibitory peptides during transport. IWH was transported via both peptide transporter 1 (PepT1) and paracellular route, while IW was via PepT1 and IWHHT was via paracellular route only. Transport of IW implied that hydrophobic peptides (even with a small size), consisting of only highly hydrophobic amino acid residues, might not be transported via paracellular diffusion. This study suggested that all three peptides could pass through the intestinal epithelium and that the degraded IWH and IW might also contribute to the antihypertensive activity of IWHHT.

Transport of ACE Inhibitory Peptides Ile-Gln-Pro and Val-Glu-Pro Derived from Spirulina platensis Across Caco-2 Monolayers

This study evaluated transepithelial transport mechanisms of Ile-Gln-Pro (IQP) and Val-Glu-Pro (VEP), two ACE-inhibitory peptides derived from Spirulina platensis, using human intestinal Caco-2 cell monolayers. IQP and VEP were absorbed intact through Caco-2 cell monolayers with P_app values of 7.48 ± 0.58 × 10^-6 and 5.05 ± 0.74 × 10^-6 cm/s, respectively. The transport of IQP and VEP were affected neither by Gly-Pro nor by wortmannin, indicating that they were not PepT1-mediated and did not involve endocytosis. However, transport of IQP and VEP were increased significantly by sodium deoxycholate, suggesting that the major transport mechanism was paracellular. In addition, the increased transport of VEP and IQP were followed with the addition of sodium azide, suggesting influence of energy to the process. The transport of VEP was also increased by verapamil, indicating an apical-to-basolateral flux mediated by P-gp.

PRACTICAL APPLICATION

Bioactive peptides derived from food proteins have been considered as potentially ideal products to reduce hypertension because of their safety and positive impacts on health. IQP and VEP are the 2 ACE inhibitory peptides derived from Spirulina platensis, a kind of edible cyanobacteria with rich nutrition and multiple physiological functions, and were demonstrated to inhibit ACE and lower blood pressure in spontaneously hypertensive rats. However, it is prerequisite that such bioactive peptides must be absorbed intact across the intestinal epithelium, so as to exert antihypertensive effects in vivo. This study evaluated transepithelial transport mechanisms of IQP and VEP. It contributes to the study of Spirulina in lowering blood pressure and supports the development of bioactive peptide products.

Functions and Applications of Bioactive Peptides From Corn Gluten Meal

Corn protein has been identified as an important source of bioactive peptides. Such peptides can be released during hydrolysis induced by proteolytic enzymes or microbial fermentation. Corn peptides have been found to exhibit different functions in vitro and in vivo such as antihypertensive, hepatoprotective, anti-obesity, antimicrobial, antioxidative, mineral-binding and accelerating alcohol metabolism. To date, 22 sequences of bioactive corn peptides have already been identified. There is an increasing commercial interest in the production of corn peptides with the purpose of using them as active ingredients, which may find use in the treatment of liver injury, hypertension, dental carries, oxidative stress, mineral malabsorption and obesity. These bioactive peptides may be used in formulation of functional foods, nutraceuticals, and natural drugs because of their health benefit effects.

Molecular interactions, bioavailability, and cellular mechanisms of angiotensin-converting enzyme inhibitory peptides

Food-derived angiotensin-converting enzyme inhibitory (ACEi) peptides have gained substantial interest as potential alternatives to synthetic drugs in the management of hypertension. Peptide size and sequence are two critical factors that determine their potency, bioavailability, and cellular mechanisms. Molecular interaction studies between ACE and ACEi peptides support that potent ACEi peptides are generally composed of hydrophobic, positively charged, and aromatic or cyclic amino acid residues at the third, second, and first position from the C-terminus, respectively. Small peptides containing N-terminal Tyr and/or C-terminal Pro could improve their stability against enterocyte peptidases, thus their bioavailability. Different ACEi peptides can reduce aberrant cellular proliferation, excessive inflammation, and oxidative stress but through different mechanisms. Further understanding the structure-activity-bioavailability relationships will help design novel potent ACEi peptides with improved bioavailability and in vivo efficacy. PRACTICAL APPLICATIONS: ACEi peptides have the potential for uses as functional food ingredients against hypertension.