Effects of hydrophobicity and molecular weight on the transport permeability of oligopeptides across Caco-2 cell monolayers

Xanthan gum and pectin as beverage stabilizers reduce the digestive enzyme hydrolysis of antioxidant and antihypertensive peptides obtained from a brewery byproduct

An acidic beverage was formulated with xanthan gum (XG), pectin (P) and brewer spent grain (BSG) peptides with antioxidant and antihypertensive properties. The impact of hydrocolloids levels on peptide bioaccessibility was studied. Peptides were obtained from BSG using Purazyme and Flavourzyme enzymes. BSG peptides were fractionated by ultrafiltration (UF) and four fractions were obtained: F1 (>10 kDa), F2 (10-5 kDa), F3 (1-5 kDa), and F4 (<1 kDa). F3 showed the highest protein purity, ferulic acid content, proportion of amphipathic peptides, and bioactive properties (ABTS+ radical scavenging and ACE-I inhibitory activity). The identified peptides from F3 by tandem mass spectrometry were 138. In silico analysis showed that 26 identified peptides had ABTS+ inhibitory activity, while 59 ones presented good antihypertensive properties. The effect of XG and P levels on bioaccessibility of F3 peptides in the formulated beverages was studied by a central composite experimental design. It was observed that F3 peptides interacted with hydrocolloids by electrostatic forces at pH of formulated beverages. The addition of hydrocolloids to formulation modulated the release of the antioxidant peptides and protected the degradation of ACE-I inhibitory peptides from F3 during simulated gastrointestinal digestion. Finally, the level of hydrocolloids that produced intermediate viscosities in the formulated beverages improved the bioaccessibility of the F3 peptides.

Protein oxidation affected the digestibility and modification sites of myofibrillar proteins from bighead carp fillets treated with hydroxyl radicals and endogenous oxidizing system

This study aimed to investigate the effect of hydroxyl radical oxidizing system (HROS) and endogenous oxidizing system (EOS, i.e., frozen storage at -20 °C) on protein oxidation, digestive properties, and peptide modification of myofibrillar proteins (MPs) in bighead carp (Hypophthalmichthys nobilis) fillets. The oxidation degree increased with the frozen time and H₂O₂ concentration as evidenced by carbonyl group generation and sulfhydryl group loss in MPs. The digestibility of protein declined gradually during frozen storage, while it increased after treatment with 5 mM H₂O₂ compared with no H₂O₂ intervention. More modification numbers and types were observed in the EOS group than HROS in digested MPs peptides, which might be due to the complexity of the frozen fillet system such as the presence of lipid. The potential conversion of α-aminoadipic semialdehyde (AAS) to α-aminoadipic acids (AAA) was observed in HROS. Additionally, the myosin heavy chain was more susceptible to oxidation among all MPs by EOS oxidation.

Potential of Food Protein-Derived Bioactive Peptides against Sarcopenia: A Comprehensive Review

Sarcopenia is an age-related progressive muscle disorder characterized by accelerated loss of muscle mass, strength, and function, which are important causes of physiological dysfunctions in the elderly. At present, the main alleviating method includes protein supplements to stimulate synthesis of muscle proteins. Food protein-derived peptides containing abundant branched-chain amino acids have a remarkable effect on the improvement of sarcopenia. Understanding the underlying molecular mechanism and clarifying the structure-activity relationship is essential for the mitigation of sarcopenia. This present review recaps the epidemiology, pathogenesis, diagnosis, and treatment of sarcopenia, which facilitates a comprehensive understanding of sarcopenia. Moreover, the latest research progress on food-derived antisarcopenic peptides is reviewed, including their antisarcopenic activity, molecular mechanism as well as structural characteristics. Food-derived bioactive peptides can indeed alleviate/mitigate sarcopenia. These antisarcopenic peptides play a pivotal role mainly by activating the PI3K/Akt/mTOR and MAPK pathways and inhibiting the ubiquitin-proteasome system and AMPK pathway, thus promoting the synthesis of muscle proteins and inhibiting their degradation. Antisarcopenic peptides alleviate sarcopenia via specific peptides, which may be absorbed into the circulation and exhibit their bioactivity in intact forms. The present review provides a theoretical reference for mitigation and prevention of sarcopenia by food protein-derived bioactive peptides.

Use of Tuna Visceral Pepsin in Combination with Trypsin as Digestion Aid: Enhanced Protein Hydrolysis and Bioavailability

Freeze-dried tuna pepsin powder (TPP) was prepared using maltodextrin (10%) and trehalose (5%), while trypsin-loaded beads (TLB) with 5% glycerol were obtained via chitosan/alginate ionotropic gelation. The storage stability of TPP and TLB and their proteolytic activity toward red kidney bean protein (RKB), threadfin bream surimi (TBS) and egg white protein (EWP) in varying simulated in vitro gastrointestinal (GI) tract conditions were studied. The intestinal transepithelial transportation of generated peptides was also carried out through Caco-2 cell monolayers after the cytotoxicity test. Enzyme activity was dropped when TPP and TLB in blister packs were kept for 10 weeks of storage at room (28 °C) and refrigerated (4 °C) temperatures. TPP and TLB at a level of 50% (w/w of proteins) effectively hydrolyzed RKB, TBS and EWP in a simulated in vitro GI tract, as indicated by marked protein degradation and increased degree of hydrolysis. Some peptides generated after GI digestion could transport through Caco-2 cell monolayers. Those peptides had different molecular size distribution and antioxidant activities. The highest antioxidant activity was observed for RKB hydrolysate after passing through the Caco-2 cell monolayer. Therefore, TPP and TLB from skipjack tuna viscera could potentially be used for enzyme supplementation to help digest food proteins. Food-derived bioactive peptides generated after GI digestion could assist in improving human health due to their antioxidant activity.

Use of Fluorescent 2-AB to Explore the Bidirectional Transport Mechanism of Pseudostellaria heterophylla Polysaccharides across Caco-2 Cells

Polysaccharides are abundant in natural resources and perform numerous physiological functions. Polysaccharide structures often lack chromophore groups; thus, current analytical methods cannot distinguish polysaccharide metabolites in the body or polysaccharide prototypes in biological samples. Thus, the measurement of polysaccharides in blood, bodily fluid, and cell-culture medium is difficult. Our early-stage research resulted in the isolation of two homogeneous polysaccharides from Pseudostellaria heterophylla, PHP_0.5MSC-F and PHP_H-1-2, which have anti-hyperglycemia and insulin resistance improvement effects for type 2 diabetes. In this study, the reducing terminal sugars of PHP_0.5MSC-F and PHP_H-1-2 were labeled with 2-aminobenzamide (2-AB) to prepare novel fluorescent probes for HPLC-coupled fluorescence detection (HPLC-FLD). Quantitative analysis was performed in reference to T40, and the detection limit for PHP_0.5MSC-F was found to be 8.84 μg/mL with a linear range of 29.45-683.28 μg/mL. In reference to T70, the detection limit for PHP_H-1-2 was found to be 13.89 μg/mL with a linear range of 46.29-462.76 μg/mL. This method was used to measure the bidirectional transport of polysaccharides across caco-2 cells from apical to basolateral (AP→BL) or from basolateral to apical (BL→AP) directions and to evaluate the polysaccharide bioavailability. The drug absorption capacity was determined based on the apparent permeability coefficient (Papp), and the Papp values for the two polysaccharides were found to be greater than 1 × 10^-6 cm/s, which suggests easy absorption. Regarding bidirectional transport, the AP→BL Papp values were greater than the BL→AP values; thus, PHP_0.5MSC-F and PHP_H-1-2 mainly underwent passive transference. The two membrane permeable polysaccharides were not P-gp efflux transporter substrates. The absorption mechanism of PHP_0.5MSC-F complies with passive diffusion under a concentration gradient, whereas PHP_H-1-2 mainly utilizes a clathrin-mediated endocytic pathway to enter caco-2 cells. This innovative HPLC-FLD method can help to track polysaccharide internalization in vitro and in vivo to facilitate cellular uptake and biodistribution exploration.

Plant-derived proteins as a sustainable source of bioactive peptides: recent research updates on emerging production methods, bioactivities, and potential application

The development of novel protein sources to compensate for the expected future shortage of traditional animal proteins due to their high carbon footprint is a major contemporary challenge in the agri-food industry currently. Therefore, both industry and consumers are placing a greater emphasis on plant proteins as a sustainable source of protein to meet the growing nutritional demand of ever increasing population. In addition to being key alternatives, many plant-based foods have biological properties that make them potentially functional or health-promoting foods, particularly physiologically active peptides and proteins accounting for most of these properties. This review discusses the importance of plant-based protein as a viable and sustainable alternative to animal proteins. The current advances in plant protein isolation and production and characterization of bioactive hydrolysates and peptides from plant proteins are described comprehensively. Furthermore, the recent research on bioactivities and bioavailability of plant protein-derived bioactive peptides is reviewed briefly. The limitations of using bioactive peptides, regulatory criteria, and the possible future applications of plant protein-derived bioactive peptides are highlighted. This review may help understand plant proteins and their bioactive peptides and provide valuable suggestions for future research and applications in the food industry.

Characterization of DPP-IV Inhibitory Peptides Using an In Vitro Cell Culture Model of the Intestine

Here, we characterize the activities of two depeptidyl peptidase-IV (DPP-IV) inhibitory peptides, VLATSGPG and LDKVFER, using the Caco-2 monolayer model for the intestine. VLATSGPG and LDKVFR inhibited the DPP-IV in the cells via a mixed-type inhibition mode, with in situ IC₅₀ values of 207.3 and 148.5 μM, respectively. Furthermore, VLATSGPG and LDKVFR were transported intact across the cells, with P_app values of 2.41 ± 0.16 and 4.23 ± 0.29 × 10^-7 cm/s, respectively. Fragmented peptides were identified in the basolateral side of the membrane. Two of these, GPG and VLA, exhibited high inhibitory activities of 83.6 ± 3.3 and 58.5 ± 2.5%, respectively, at 100 μM concentration. Although 3 mM VLATSGPG and LDKVFR were transported across the epithelium in a concentration-dependent manner, their transport did not damage the tight junction proteins, ZO-1 and occludin. This study demonstrates that the two peptides potentially regulate DPP-IV activity in the intestine.

Using Peptidomics and Machine Learning to Assess Effects of Drying Processes on the Peptide Profile within a Functional Ingredient

Bioactive peptides are known to have many health benefits beyond nutrition; yet the peptide profile of high protein ingredients has been largely overlooked when considering the effects of different processing techniques. Therefore, to investigate whether drying conditions could affect the peptide profile and bioactivity within a functional ingredient, we examined the effects of spray (SD) and freeze (FD) drying on rice natural peptide network (NPN), a characterised functional ingredient sourced from the Oryza sativa proteome, which has previously been shown to effectively modulate circulating cytokines and improve physical performance in humans. In the manufacturing process, rice NPN was either FD or SD. Employing a peptidomic approach, we investigated the physicochemical characteristics of peptides common and unique to FD and SD preparations. We observed similar peptide profiles regarding peptide count, amino acid distribution, weight, charge, and hydrophobicity in each sample. Additionally, to evaluate the effects of drying processes on functionality, using machine learning, we examined constituent peptides with predicted anti-inflammatory activity within both groups and identified that the majority of anti-inflammatory peptides were common to both. Of note, key bioactive peptides validated within rice NPN were recorded in both SD and FD samples. The present study provides an important insight into the overall stability of the peptide profile and the use of machine learning in assessing predicted retention of bioactive peptides contributing to functionality during different types of processing.

Current Evidence on the Bioavailability of Food Bioactive Peptides

Food protein-derived bioactive peptides are recognized as valuable ingredients of functional foods and/or nutraceuticals to promote health and reduce the risk of chronic diseases. However, although peptides have been demonstrated to exert multiple benefits by biochemical assays, cell culture, and animal models, the ability to translate the new findings into practical or commercial uses remains delayed. This fact is mainly due to the lack of correlation of in vitro findings with in vivo functions of peptides because of their low bioavailability. Once ingested, peptides need to resist the action of digestive enzymes during their transit through the gastrointestinal tract and cross the intestinal epithelial barrier to reach the target organs in an intact and active form to exert their health-promoting properties. Thus, for a better understanding of the in vivo physiological effects of food bioactive peptides, extensive research studies on their gastrointestinal stability and transport are needed. This review summarizes the most current evidence on those factors affecting the digestive and absorptive processes of food bioactive peptides, the recently designed models mimicking the gastrointestinal environment, as well as the novel strategies developed and currently applied to enhance the absorption and bioavailability of peptides.

Assessment of the DPP-IV inhibitory activity of a novel octapeptide derived from rapeseed using Caco-2 cell monolayers and molecular docking analysis

The Octapeptide ELHQEEPL, which was identified from the rapeseed protein napin showed prominent Dipeptidyl peptidase-IV (DPP-IV) inhibitory activity. The objective of this study was to investigate the DPP-IV inhibitory activity and transepithelial transport of ELHQEEPL in an approaching intestinal condition using Caco-2 cell monolayers. ELHQEEPL and its degraded fragments EL, HQEEP, and methylated ELHQEEPL were transported across Caco-2 cell monolayers through different pathways. Compared with the nonbiological enzyme inhibition test, the in vitro experiment on Caco-2 cell monolayers showed that the IC50 value of DPP-IV inhibition increased by 43.11% for ELHQEEPL. There was no significant change in DPP-IV gene expression in the Caco-2 cell monolayers upon treatment with ELHQEEPL. Furthermore, molecular docking predicted that the weaker binding between inhibitory peptide and enzyme for the degradation products from ELHQEEPL during transepithelial transport greatly limited its role in inhibiting DPP-IV. PRACTICAL APPLICATIONS: The DPP-IV inhibitory activity of ELHQEEPL was confirmed using Caco-2 cell monolayers as a novel assessment tool, although its potency was reduced by metabolic degradation. In general, this study reported the use of Caco-2 cell monolayers as a tool for comprehensively studying peptides as sources of DPP-IV inhibitors. A Caco-2 cell-based approach with molecular docking can be adapted for the investigation of intestinal absorption and activity attenuation of food peptides being considered for enzymatic action. Moreover, since the Caco-2 cells express a wide range of enzymes, this method can be used for screening for other active food peptides such as for the inhibitors of ACE and a-glucosidase.

Bioactive Peptides and Dietary Polyphenols: Two Sides of the Same Coin

The call for health-promoting nutraceuticals and functional foods containing bioactive compounds is growing. Among the great diversity of functional phytochemicals, polyphenols and, more recently, bioactive peptides have stood out as functional compounds. The amount of an ingested nutrient able to reach the bloodstream and exert the biological activity is a critical factor, and is affected by several factors, such as food components and food processing. This can lead to unclaimed interactions and/or reactions between bioactive compounds, which is particularly important for these bioactive compounds, since some polyphenols are widely known for their ability to interact and/or precipitate proteins/peptides. This review focuses on this important topic, addressing how these interactions could affect molecules digestion, absorption, metabolism and (biological)function. At the end, it is evidenced that further research is needed to understand the true effect of polyphenol-bioactive peptide interactions on overall health outcomes.