Towards the improved discovery and design of functional peptides: common features of diverse classes permit generalized prediction of bioactivity

Enhancing bioactive peptide release and identification using targeted enzymatic hydrolysis of milk proteins

Milk proteins have been extensively studied for their ability to yield a range of bioactive peptides following enzymatic hydrolysis/digestion. However, many hurdles still exist regarding the widespread utilization of milk protein-derived bioactive peptides as health enhancing agents for humans. These mostly arise from the fact that most milk protein-derived bioactive peptides are not highly potent. In addition, they may be degraded during gastrointestinal digestion and/or have a low intestinal permeability. The targeted release of bioactive peptides during the enzymatic hydrolysis of milk proteins may allow the generation of particularly potent bioactive hydrolysates and peptides. Therefore, the development of milk protein hydrolysates capable of improving human health requires, in the first instance, optimized targeted release of specific bioactive peptides. The targeted hydrolysis of milk proteins has been aided by a range of in silico tools. These include peptide cutters and predictive modeling linking bioactivity to peptide structure [i.e., molecular docking, quantitative structure activity relationship (QSAR)], or hydrolysis parameters [design of experiments (DOE)]. Different targeted enzymatic release strategies employed during the generation of milk protein hydrolysates are reviewed herein and their limitations are outlined. In addition, specific examples are provided to demonstrate how in silico tools may help in the identification and discovery of potent milk protein-derived peptides. It is anticipated that the development of novel strategies employing a range of in silico tools may help in the generation of milk protein hydrolysates containing potent and bioavailable peptides, which in turn may be used to validate their health promoting effects in humans. Graphical abstract The targeted enzymatic hydrolysis of milk proteins may allow the generation of highly potent and bioavailable bioactive peptides.

Utilization of blood by-products: An in silico and experimental combined study for BSA usage

In order to exploit industrial discards, protein enzymatic hydrolysis is a currently popular methodology for obtaining bioactive peptides. However, once released, most promising peptides have to be selected from the mixture. In this work, the suitability of pepsin (EC 3.4.23.1) to hydrolyse serum albumin in order to obtain bioactive peptides was assessed. Then, a suitable process to obtain best separation of bioactive peptides was evaluated, using polyethersulfone membranes at different pH values. Serum albumin was easily hydrolysed by pepsin, reaching a DH value of the 65.64 ± 1.57% of the maximum possible. A 23.25% of the identified peptides possessed high bioactivity scores (greater than 0.5), and one of them had reported bioactivity (LLL). Charge mechanisms always predominated over the sieve effect, and best transmission was accomplished at pH values close to the peptides isoelectric points. Basic and neutral peptides with the highest scores were always the most transmitted. Membrane material had greater influence than NMWCO in determining peptide transmission. In order to obtain purified fractions rich in peptides with high bioactivity scores from serum albumin, polyethersulfone membranes (applicable to industrial scale) of 5 kDa MWCO should be used at basic pH values after pepsin digestion.

Predicted Release and Analysis of Novel ACE-I, Renin, and DPP-IV Inhibitory Peptides from Common Oat (Avena sativa) Protein Hydrolysates Using in Silico Analysis

The renin-angiotensin-aldosterone system (RAAS) plays an important role in regulating hypertension by controlling vasoconstriction and intravascular fluid volume. RAAS itself is largely regulated by the actions of renin (EC 3.4.23.15) and the angiotensin-I-converting enzyme (ACE-I; EC 3.4.15.1). The enzyme dipeptidyl peptidase-IV (DPP-IV; EC 3.4.14.5) also plays a role in the development of type-2 diabetes. The inhibition of the renin, ACE-I, and DPP-IV enzymes has therefore become a key therapeutic target for the treatment of hypertension and diabetes. The aim of this study was to assess the bioactivity of different oat (Avena sativa) protein isolates and their ability to inhibit the renin, ACE-I, and DPP-IV enzymes. In silico analysis was carried out to predictthe likelihood of bioactive inhibitory peptides occurring from oat protein hydrolysates following in silico hydrolysis with the proteases papain and ficin. Nine peptides, including FFG, IFFFL, PFL, WWK, WCY, FPIL, CPA, FLLA, and FEPL were subsequently chemically synthesised, and their bioactivities were confirmed using in vitro bioassays. The isolated oat proteins derived from seven different oat varieties were found to inhibit the ACE-I enzyme by between 86.5 ± 10.7% and 96.5 ± 25.8%, renin by between 40.5 ± 21.5% and 70.9 ± 7.6%, and DPP-IV by between 3.7 ± 3.9% and 46.2 ± 28.8%. The activity of the synthesised peptides was also determined.

Exploration of Potentially Bioactive Peptides Generated from the Enzymatic Hydrolysis of Hempseed Proteins

The seed of industrial hemp is an underexploited protein source. In view of a possible use in functional foods, a hempseed protein concentrate was hydrolyzed with pepsin, trypsin, pancreatin, or a mixture of these enzymes. A detailed peptidomic analysis using data-dependent acquisition showed that the numbers of peptides identified ranged from 90 belonging to 33 parent proteins in the peptic hydrolysate to 9 belonging to 6 proteins in the pancreatin digest. The peptic and tryptic hydrolysates resulted to be the most efficient inhibitors of 3-hydroxymethyl-coenzyme A reductase activity when tested on the catalytic domain of the enzyme. Using the open access tools PeptideRanker and BIOPEP, a list of potentially bioactive peptides was generated: the alleged activities included the antioxidant property, the glucose uptake stimulating activity, the inhibition of dipeptidyl peptidase-IV and angiotensin-converting enzyme I.

Peptides Derived from Foods as Supportive Diet Components in the Prevention of Metabolic Syndrome

Metabolic syndrome (MSyn) includes physiological, biochemical, clinical, and metabolic abnormalities, leading to an increase in health problems like obesity, dyslipidemia, cardiovascular diseases, and diabetes, which contribute to an increase in mortality rate. One of the main factors having a key impact on our health is the food we consume. Thus, scientists work towards the discovery of novel bioactive compounds with therapeutic potential to address MSyn. According to scientific reports, peptides derived from food proteins exhibit bioactivities important for the prevention of MSyn diseases; that is, they regulate blood pressure and glycemia; reduce cholesterol level and body mass; and scavenge free radicals. The aim of this review is to study the potential role of peptides in the prevention of MSyn. Particularly peptides which exhibit the following activities: antihypertensive [angiotensin-converting enzyme (ACE) inhibition (EC 3.4.15.1)], antidiabetic [dipeptidyl peptidase IV (DPP-IV) (EC 3.4.14.5)/α-glucosidase (EC 3.2.1.20)/α-amylase (EC 3.2.1.1) inhibition)], cholesterol level reduction, antioxidative, and obesity prevention, were studied. If possible, special attention is paid in the review to the bioactivities of peptides that were measured in vivo. Some examples of peptides showing dual or multiple action against MSyn targets are presented. Moreover, using the database of bioactive peptide sequences (BIOPEP) we made a list of peptides serving simultaneous functions in counteracting MSyn dysfunctions. Such an approach may simplify the discovery of MSyn preventive peptides, as well as highlight some of them as potent bioactive ingredients that may be incorporated into foods. Moreover, the research strategy involving the in silico and in vitro/in vivo methodologies may be useful in the production of food protein hydrolysates supporting the treatment of MSyn dysfunctions.

Peptides Released from Foremilk and Hindmilk Proteins by Breast Milk Proteases Are Highly Similar

Human milk contains active proteases that initiate hydrolysis of milk proteins within the mammary gland. Milk expressed at the beginning of feeding is known as foremilk and that at the end of feeding is known as hindmilk. As hindmilk contains higher fat, vitamins A and E, and higher calories than foremilk, feeding only hindmilk initially and reserving foremilk for later are practiced in some neonatal intensive care units. This study investigated the difference in peptide profiles, predicted milk protease activities, and bioactive peptides between foremilk and hindmilk. Bioactive peptides are short fragments of proteins that influence biological processes. Four mothers pumped 10 mL of their foremilk and 10 mL of their hindmilk into iced containers prepared with antiproteases and the samples were immediately frozen. The peptide profile of each sample was analyzed by liquid chromatography nano-electrospray ionization Orbitrap Fusion tandem mass spectrometry. Peptide abundance (sum of ion intensities) and count (number of unique peptide sequences) in each milk sample were determined from this analysis. The specific enzymes that participated in peptide release were predicted based on the amino acids positioned at each cleavage site. Peptide bioactivity was predicted based on homology to a known functional peptide database and two bioactivity prediction algorithms. Hindmilk contained a higher count of peptides than foremilk. The higher number of unique peptide sequences in hindmilk was related to hydrolysis of β-casein, osteopontin, α_s1-casein and mucin-1 via plasmin and elastase cleavage, and possible aminopeptidase and carboxypeptidase activities. Though hindmilk contained a greater number of peptides than foremilk, the overall peptide abundance did not differ and most of the total peptide abundance derived from peptide sequences that were present in both milk types. The presence of higher numbers of predicted bioactive peptides in the hindmilk could indicate that the practice of providing hindmilk rather than foremilk to premature infants could positively impact health outcomes; however, as there are few differences in overall peptide abundance, the overall effect is likely limited.

The Peptidome Comes of Age: Mass Spectrometry-Based Characterization of the Circulating Cancer Peptidome

Peptides play a seminal role in most physiological processes acting as neurotransmitters, hormones, antibiotics, and immune regulation. In the context of tumor biology, it is hypothesized that endogenous peptides, hormones, cytokines, growth factors, and aberrant degradation of select protein networks (e.g., enzymatic activities, protein shedding, and extracellular matrix remodeling) are fundamental in mediating cancer progression. Analysis of peptides in biological fluids by mass spectrometry holds promise of providing sensitive and specific diagnostic and prognostic information for cancer and other diseases. The identification of circulating peptides in the context of disease constitutes a hitherto source of new clinical biomarkers. The field of peptidomics can be defined as the identification and comprehensive analysis of physiological and pathological peptides. Like proteomics, peptidomics has been advanced by the development of new separation strategies, analytical detection methods such as mass spectrometry, and bioinformatic technologies. Unlike proteomics, peptidomics is targeted toward identifying endogenous protein and peptide fragments, defining proteolytic enzyme substrate specificity, as well as protease cleavage recognition (degradome). Peptidomics employs "top-down proteomics" strategies where mass spectrometry is applied at the proteoform level to analyze intact proteins and large endogenous peptide fragments. With recent advances in prefractionation workflows for separating peptides, mass spectrometry instrumentation, and informatics, peptidomics is an important field that promises to impact on translational medicine. This review covers the current advances in peptidomics, including top-down and imaging mass spectrometry, comprehensive quantitative peptidome analyses (developments in reproducibility and coverage), peptide prefractionation and enrichment workflows, peptidomic data analyses, and informatic tools. The application of peptidomics in cancer biomarker discovery will be discussed.

Multiplexed Temporal Quantification of the Exercise-regulated Plasma Peptidome

Exercise is extremely beneficial to whole body health reducing the risk of a number of chronic human diseases. Some of these physiological benefits appear to be mediated via the secretion of peptide/protein hormones into the blood stream. The plasma peptidome contains the entire complement of low molecular weight endogenous peptides derived from secretion, protease activity and PTMs, and is a rich source of hormones. In the current study we have quantified the effects of intense exercise on the plasma peptidome to identify novel exercise regulated secretory factors in humans. We developed an optimized 2D-LC-MS/MS method and used multiple fragmentation methods including HCD and EThcD to analyze endogenous peptides. This resulted in quantification of 5,548 unique peptides during a time course of exercise and recovery. The plasma peptidome underwent dynamic and large changes during exercise on a time-scale of minutes with many rapidly reversible following exercise cessation. Among acutely regulated peptides, many were known hormones including insulin, glucagon, ghrelin, bradykinin, cholecystokinin and secretogranins validating the method. Prediction of bioactive peptides regulated with exercise identified C-terminal peptides from Transgelins, which were increased in plasma during exercise. In vitro experiments using synthetic peptides identified a role for transgelin peptides on the regulation of cell-cycle, extracellular matrix remodeling and cell migration. We investigated the effects of exercise on the regulation of PTMs and proteolytic processing by building a site-specific network of protease/substrate activity. Collectively, our deep peptidomic analysis of plasma revealed that exercise rapidly modulates the circulation of hundreds of bioactive peptides through a network of proteases and PTMs. These findings illustrate that peptidomics is an ideal method for quantifying changes in circulating factors on a global scale in response to physiological perturbations such as exercise. This will likely be a key method for pinpointing exercise regulated factors that generate health benefits.

Implications of the Maillard reaction on bovine alpha-lactalbumin and its proteolysis during in vitro infant digestion

This study investigated the functionality and digestibility of Maillard reaction products (MRPs) of alpha-lactalbumin (α-la), a major whey protein and component of infant formulas. The impact of different carbohydrates (glucose, galactose or galacto-oligosaccharides (GOS)) and heating duration was studied. SDS-PAGE, UV and color measurements monitored reaction extent, which varied between carbohydrates whereby galactose reacted more readily than glucose. Surface hydrophobicity and antioxidant capacity were found to be significantly (p < 0.05) higher following Maillard conjugation, with GOS-based MRPs elevating antioxidant capacity ∼50-fold compared to α-la. In addition, the digestive proteolysis of MRPs was evaluated using an infant in vitro gastro-duodenal model. SDS-PAGE analyses of digesta revealed Maillard conjugation generally increased α-la's susceptibility to proteolysis. Interestingly, GOS-based MRPs presented an optimization challenge, since heating for 12 h delayed proteolysis, while extended heating resulted in the highest susceptibility to proteolysis. Proteomic analyses further demonstrated the differences in enzymatic cleavage patterns and helped identify bioactive peptides rendered bioaccessible during the digestion of α-la or its MRPs. Bioinformatic mining of the proteomic data using PeptideRanker also gave rise to two potentially novel bioactive peptides, FQINNKIW and GINYWLAHKALCS. Finally, antioxidant capacity of luminal contents, measured by DPPH, revealed Maillard conjugation increased the antioxidant capacity of both gastric and duodenal digesta. Overall, this work draws a link between the Maillard reaction, digestive proteolysis and the bioaccessibility of bioactive peptides and antioxidant species in the infant alimentary canal. This could help rationally process infant formulas towards improved nutritional and extra-nutritional benefits.

Identification of Potent ACE Inhibitory Peptides from Wild Almond Proteins

In this study, the production, fractionation, purification and identification of ACE (angiotensin-I-converting enzyme) inhibitory peptides from wild almond (Amygdalus scoparia) proteins were investigated. Wild almond proteins were hydrolyzed using 5 different enzymes (pepsin, trypsin, chymotrypsin, alcalase and flavourzyme) and assayed for their ACE inhibitory activities. The degree of ACE inhibiting activity obtained after hydrolysis was found to be in the following order: alcalase > chymotrypsin > trypsin/pepsin > flavourzyme. The hydrolysates obtained from alcalase (IC₅₀ = 0.8 mg/mL) were fractionated by sequential ultrafiltration at 10 and 3 kDa cutoff values and the most active fraction (<3 kDa) was further separated using reversed phase high-performance liquid chromatography (RP-HPLC). Peptide sequence identifications were carried out on highly potential fractions obtained from RP-HPLC by means of liquid chromatography coupled to electrospray ionization and tandem mass spectrometry (LC-ESI-MS/MS). Sequencing of ACE inhibitory peptides present in the fraction 26 of RP-HPLC resulted in the identification of 3 peptide sequences (VVNE, VVTR, and VVGVD) not reported previously in the literature. Sequence identification of fractions 40 and 42 from RP-HPLC, which showed the highest ACE inhibitory activities (84.1% and 86.9%, respectively), resulted in the identification of more than 40 potential ACE inhibitory sequences. The results indicate that wild almond protein is a rich source of potential antihypertensive peptides and can be suggested for applications in functional foods and drinks with respect to hindrance and mitigation of hypertension after in vivo assessment.

PRACTICAL APPLICATION

This study has shown the potential of wild almond proteins as good sources for producing ACE-inhibitory active peptides. According to this finding, peptides with higher ACE inhibitory activities could be released during the gastrointestinal digestion and contribute to the health- promoting activities of this natural protein source.

In vivo digestomics of milk proteins in human milk and infant formula using a suckling rat pup model

Human milk is the optimal mode of infant feeding for the first several months of life, and infant formulas serve as an alternative when breast-feeding is not possible. Milk proteins have a balanced amino acid composition and some of them provide beneficial bioactivities in their intact forms. They also encrypt a variety of bioactive peptides, possibly contributing to infant health and growth. However, there is limited knowledge of how milk proteins are digested in the gastrointestinal tract and bioactive peptides are released in infants. A peptidomic analysis was conducted to identify peptides released from milk proteins in human milk and infant formula, using a suckling rat pup model. Among the major milk proteins targeted, α-lactalbumin and β-casein in human milk, and β-lactoglobulin and β-casein in infant formula were the main sources of peptides, and these peptides covered large parts of the parental proteins' sequences. Release of peptides was concentrated to specific regions, such as residues 70-92 of β-casein in human milk, residues 39-55 of β-lactoglobulin in infant formula, and residues 57-96 and 145-161 of β-CN in infant formula, where resistance to gastrointestinal digestion was suggested. In the context of bioactive peptides, release of fragments containing known bioactive peptides was confirmed, such as β-CN-derived opioid and antihypertensive peptides. It is therefore likely that these fragments are of biological significance in neonatal health and development.

Peptigram: A Web-Based Application for Peptidomics Data Visualization

Tandem mass spectrometry (MS/MS) techniques, developed for protein identification, are increasingly being applied in the field of peptidomics. Using this approach, the set of protein fragments observed in a sample of interest can be determined to gain insights into important biological processes such as signaling and other bioactivities. As the peptidomics era progresses, there is a need for robust and convenient methods to inspect and analyze MS/MS derived data. Here, we present Peptigram, a novel tool dedicated to the visualization and comparison of peptides detected by MS/MS. The principal advantage of Peptigram is that it provides visualizations at both the protein and peptide level, allowing users to simultaneously visualize the peptide distributions of one or more samples of interest, mapped to their parent proteins. In this way rapid comparisons between samples can be made in terms of their peptide coverage and abundance. Moreover, Peptigram integrates and displays key sequence features from external databases and links with peptide analysis tools to offer the user a comprehensive peptide discovery resource. Here, we illustrate the use of Peptigram on a data set of milk hydrolysates. For convenience, Peptigram is implemented as a web application, and is freely available for academic use at http://bioware.ucd.ie/peptigram .

Bioactive peptides in beef: Endogenous generation through postmortem aging

The present research was performed to investigate endogenous release of bioactive peptides in beef during postmortem aging times (1, 10 and 20days). Gradually decreased Warner-Bratzler shear force (WBSF) values of longissimus thoracis (LT) and semitendinosus (ST) muscles were observed and the degradation of structural proteins and collagen led to release of low-molecular weight (<3kDa) peptides. These peptides exhibited 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity, ACE- and renin-inhibitory activities. The peptide sequences were identified by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). In silico analysis (PeptideRanker and BIOPEP) of their bioactivity potentials demonstrated peptides with the predicted bioactivity scores (>0.8) as well as collagen peptides with bioactivity scores (0.6-0.8). The present findings provide insights on development of healthy beef through postmortem aging at 4°C.

Effect of Inactivating Mutations on Peptide Conformational Ensembles: The Plant Polypeptide Hormone Systemin

As part of their basal immune mechanism against insect/herbivore attacks, plants have evolved systemic response mechanisms. Such a systemic wound response in tomato was found to involve an 18 amino acid polypeptide called systemin, the first polypeptide hormone to be discovered in plants. Systematic alanine scanning and deletion studies showed differential modulation in its activity, particularly a major loss of function due to alanine substitution at positions 13 and 17 and less extentive loss of function due to substitution at position 12. We have studied the conformational ensembles of wild-type systemin along with its 17 variants by carrying out a total of 5.76 μs of replica-exchange molecular dynamics simulation in an implicit solvent environment. In our simulations, wild-type systemin showed a lack of α-helical and β-sheet structures, in conformity with earlier circular dichroism and NMR data. On the other hand, two regions containing diproline segments showed a tendency to adopt polyproline II structures. Examination of conformational ensembles of the 17 variants revealed a change in the population distributions, suggesting a less flexible structure for alanine substitutions at positions 12 and 13 but not for position 17. Combined with the experimental observations that positions 1-14 of systemin are important for the formation of the peptide-receptor complex, this leads to the hypothesis that loss of conformational flexibility may play a role in the loss of activity of systemin due to the P12A and P13A substitutions, while T17A deactivation probably occurs for a different reason, most likely the loss of the threonine phosphorylation site. We also indicate possible structural reasons why the substitution of the prolines at positions 12 and 13 leads to a loss of conformational freedom in the peptide.

Purification and identification of endogenous antioxidant and ACE-inhibitory peptides from donkey milk by multidimensional liquid chromatography and nanoHPLC-high resolution mass spectrometry

Donkey milk is a valuable product for the food industry due to its nutraceutical, nutritional, and functional properties. In this work, the endogenous peptides from donkey milk were investigated for their antioxidant and ACE-inhibitory activities, combining a two-dimensional peptide fractionation strategy with high-resolution mass spectrometry, bioinformatics analysis, and in vitro assays. After extraction, the endogenous peptides were fractionated twice, first by polymeric reversed phase and then by hydrophilic interaction chromatography. Fractions were screened for the investigated bioactivities and only the most active ones were finally analyzed by nanoRP-HPLC-MS/MS; this approach allowed to reduce the total number of possible bioactive sequences. Results were further mined by in silico analysis using PeptideRanker, BioPep, and PepBank, which provided a bioactivity score to the identified peptides and matched sequences to known bioactive peptides, in order to select candidates for chemical synthesis. Thus, five peptides were prepared and then compared to the natural occurring ones, checking their retention times and fragmentation patterns in donkey milk alone and in spiked donkey milk samples. Pure peptide standards were finally in vitro tested for the specific bioactivity. In this way, two novel endogenous antioxidant peptides, namely EWFTFLKEAGQGAKDMWR and GQGAKDMWR, and two ACE-inhibitory peptides, namely REWFTFLK and MPFLKSPIVPF, were successfully validated from donkey milk. Graphical Abstract Analytical workflow for purification and identification of bioactive peptides from donkey milk sample.

Analytic framework for peptidomics applied to large-scale neuropeptide identification

Large-scale mass spectrometry-based peptidomics for drug discovery is relatively unexplored because of challenges in peptide degradation and identification following tissue extraction. Here we present a streamlined analytical pipeline for large-scale peptidomics. We developed an optimized sample preparation protocol to achieve fast, reproducible and effective extraction of endogenous peptides from sub-dissected organs such as the brain, while diminishing unspecific protease activity. Each peptidome sample was analysed by high-resolution tandem mass spectrometry and the resulting data set was integrated with publically available databases. We developed and applied an algorithm that reduces the peptide complexity for identification of biologically relevant peptides. The developed pipeline was applied to rat hypothalamus and identifies thousands of neuropeptides and their post-translational modifications, which is combined in a resource format for visualization, qualitative and quantitative analyses.

Neuropeptide research is challenged by technical difficulties in identifying new bioactive peptides. Here the authors present an analytical pipeline for large-scale peptidomics applied to the rat hypothalamus, identifying thousands of endogenous neuropeptides and their post-translational modifications.

Peptidomics of Peptic Digest of Selected Potato Tuber Proteins: Post-Translational Modifications and Limited Cleavage Specificity

Bioinformatic tools are useful in predicting bioactive peptides from food proteins. This study was focused on using bioinformatics and peptidomics to evaluate the specificity of peptide release and post-translational modifications (PTMs) in a peptic digest of potato protein isolate. Peptides in the protein hydrolysate were identified by LC-MS/MS and subsequently aligned to their parent potato tuber proteins. Five major proteins were selected for further analysis, namely, lipoxygenase, α-1,4-glucan phosphorylase, annexin, patatin, and polyubiquitin, based on protein coverage, abundance, confidence levels, and function. Comparison of the in silico peptide profile generated with ExPASy PeptideCutter and experimental peptidomics data revealed several differences. The experimental peptic cleavage sites were found to vary in number and specificity from PeptideCutter predictions. Average peptide chain length was also found to be higher than predicted with hexapeptides as the smallest detected peptides. Moreover, PTMs, particularly Met oxidation and Glu/Asp deamidation, were observed in some peptides, and these were unaccounted for during in silico analysis. PTMs can be formed during aging of potato tubers, or as a result of processing conditions during protein isolation and hydrolysis. The findings provide insights on the limitations of current bioinformatics tools for predicting bioactive peptide release from proteins, and on the existence of structural modifications that can alter the peptide bioactivity and functionality.

Addition of an Enzymatic Hydrolysate of Bovine Globulins to Bread and Determination of Hypotensive Effects in Spontaneously Hypertensive Rats

The aim of this study was to develop bread containing a papain hydrolysate of bovine α- and β-globulins (GPH) with in vitro and in vivo antihypertensive activities. The physical characteristics of the formulated bread were assessed over a six day period and results suggested that the overall quality and acceptance of bread was not affected by the inclusion of GPH at a concentration of 4% (w/w). Bright field light microscopy and confocal scanning laser microscopy images were used to visualize the main ingredients of the bread. In addition, the antihypertensive activity of the bread was assessed in spontaneously hypertensive rats (SHRs) over a 24 h period where a maximum significant decrease in systolic blood pressure of 36.2 ± 1.9 mmHg was observed 8 h after oral administration. Results demonstrate that the antihypertensive activity of GPH was resistant to the baking process and shows potential for use as a functional antihypertensive ingredient.

In silico and in vitro analyses of the angiotensin-I converting enzyme inhibitory activity of hydrolysates generated from crude barley (Hordeum vulgare) protein concentrates

Angiotensin-I-converting enzyme (ACE-I) plays a key role in control of hypertension, and type-2 diabetes mellitus, which frequently co-exist. Our current work utilised in silico methodologies and peptide databases as tools for predicting release of ACE-I inhibitory peptides from barley proteins. Papain was the enzyme of choice, based on in silico analysis, for experimental hydrolysis of barley protein concentrate, which was performed at the enzyme's optimum conditions (60 °C, pH 6.0) for 24 h. The generated hydrolysate was subjected to molecular weight cut-off (MWCO) filtration, following which the non-ultrafiltered hydrolysate (NUFH), and the generated 3 kDa and 10 kDa MWCO filtrates were assessed for their in vitro ACE-I inhibitory activities. The 3 kDa filtrate (1 mg/ml), that demonstrated highest ACE-I inhibitory activity of 70.37%, was characterised in terms of its peptidic composition using mass spectrometry and 1882 peptides derived from 61 barley proteins were identified, amongst which 15 peptides were selected for chemical synthesis based on their predicted ACE-I inhibitory properties. Of the synthesized peptides, FQLPKF and GFPTLKIF were most potent, demonstrating ACE-I IC50 values of 28.2 μM and 41.2 μM respectively.

A Bovine Fibrinogen-Enriched Fraction as a Source of Peptides with in Vitro Renin and Angiotensin-I-Converting Enzyme Inhibitory Activities

Bovine fibrinogen is currently used in the food industry as a binding agent in restructured meat products. However, this protein is underused as a source of bioactive peptides. In this study, a number of novel angiotensin-I-converting enzyme (ACE-I) and renin inhibitory peptides were identified and enriched from a bovine fibrinogen fraction. Fibrinogen was isolated and enriched from bovine blood and hydrolyzed with the food-grade enzyme papain, which was selected for use using in silico analysis. The generated hydrolysate was subjected to ultrafiltration and its peptide profile characterized by liquid chromatography-tandem mass spectrometry. A number of peptides were identified and chemically synthesized to confirm their bioactivity in vitro. Identified peptides included the multifunctional tripeptide SLR, corresponding to f(35-37) of the β-chain of bovine fibrinogen with ACE-I and renin IC50 values of 0.17 and 7.2 mM, respectively. Moreover, the resistance of identified peptides to gastrointestinal degradation and their bitterness were predicted using in silico methods.

Cardioprotective cryptides derived from fish and other food sources: generation, application, and future markets

The primary function of dietary protein is to provide amino acids for protein synthesis. However, protein is also a source of latent bioactive peptides or cryptides with potential health benefits including the control and regulation of blood pressure. Hypertension or high blood pressure is one of the major, controllable risk factors in the development of cardiovascular disease (CVD), and it is also implicated in the development of myocardial infarction, heart failure, and end-stage diabetes. Cryptides can act on various systems of the body including the circulatory, gastrointestinal (GI), nervous, skeletal, and respiratory systems. A number of studies carried out to date have examined the health benefits of food protein isolates and hydrolysates. This review provides an overview of existing blood pressure regulating peptides and products derived from fish and other protein sources and hydrolysates. It discusses the methods used currently to generate and identify cryptides from these sources and their application in food and pharmaceutical products. It also looks at the current market for protein-derived peptides and peptide-containing products, legislation governing their use, and the future development of research in this area.

Towards rice bran protein utilization: In silico insight on the role of oryzacystatins in biologically-active peptide production

Rice bran proteins (RBP) have been demonstrated to harbour biologically active peptides, which can be released by proteases and applied in human health promotion. In this study, the roles of rice bran cysteine protease inhibitors, oryzacystatins, were considered for efficient production of bioactive peptides from RBP. In silico evidence demonstrates that aspartate protease (pepsin at pH>2) and metalloproteinase (thermolysin) have strong prospects for use in simultaneously cleaving the QXVXGX motif of oryzacystatins, which can lead to their inactivation, and in releasing bioactive sequences from the protease inhibitors. The cleaved bioactive peptides are known to possess activities that can be applied in the management of hypertension, oxidative stress, type 2 diabetes mellitus and other aberrant cellular processes. Moreover, several potentially bioactive di- and tripeptides were identified in oryzacystatin peptide pools. This study provides an important consideration and a direction that can lead to efficient release of bioactive peptides from rice bran proteins for functional food applications.

ACE Inhibitory and Antioxidant Activities of Collagen Hydrolysates from the Ribbon Jellyfish (Chrysaora sp.)

Collagen isolated from the ribbon jellyfish (Chrysaora sp.) was hydrolysed using three different proteases (i.e. trypsin, alcalase and Protamex) to obtain bioactive peptides. Angiotensin-I-converting enzyme (ACE) inhibitory activity and antioxidant activities (i.e. ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity) of the peptides were measured and compared, and the effect of the duration of hydrolysis on the bioactivity (ACE inhibitory and antioxidant activities) of peptides was also evaluated. FRAP activity was the highest in Protamex-induced (25-27 mM) and trypsin-induced hydrolysates (24-26 mM) at 7 and 9 h, respectively. Conversely, hydrolysates produced by trypsin for 1 and 3 h showed the highest DPPH radical scavenging activities (94 and 92%, respectively). Trypsin-induced hydrolysates (at 3 h) also showed the highest ACE inhibitory activity (89%). The peptide sequences with the highest activities were identified using tandem mass spectrometry, and the results show that the hydrolysates had a high content of hydrophobic amino acids as well as unique amino acid sequences, which likely contribute to their biological activities.

BactPepDB: a database of predicted peptides from a exhaustive survey of complete prokaryote genomes

With the recent progress in complete genome sequencing, mining the increasing amount of genomic information available should in theory provide the means to discover new classes of peptides. However, annotation pipelines often do not consider small reading frames likely to be expressed. BactPepDB, available online at http://bactpepdb.rpbs.univ-paris-diderot.fr, is a database that aims at providing an exhaustive re-annotation of all complete prokaryotic genomes—chromosomal and plasmid DNA—available in RefSeq for coding sequences ranging between 10 and 80 amino acids. The identified peptides are classified as (i) previously identified in RefSeq, (ii) entity-overlapping (intragenic) or intergenic, and (iii) potential pseudogenes—intergenic sequences corresponding to a portion of a previously annotated larger gene. Additional information is related to homologs within order, predicted signal sequence, transmembrane segments, disulfide bonds, secondary structure, and the existence of a related 3D structure in the Protein Databank. As a result, BactPepDB provides insights about candidate peptides, and provides information about their conservation, together with some of their expected biological/structural features. The BactPepDB interface allows to search for candidate peptides in the database, or to search for peptides similar to a query, according to the multiple properties predicted or related to genomic localization.

Database URL:http://www.yeastgenome.org/

Dipeptide Phe-Cys derived from in silico thermolysin-hydrolysed RuBisCO large subunit suppresses oxidative stress in cultured human hepatocytes

A dipeptide (Phe-Cys) was predicted to be bioactive following bioinformatics analysis of the large subunit of plant and microalgae ribulose-1,5-bisphosphate carboxylase (RuBisCO), which was hydrolysed in silico with thermolysin. The peptide was synthesised and found to possess in vitro reducing potential and inhibitory activity against lipid peroxidation, comparable to the activity of glutathione. In cultured Chang human hepatocytes, 2.5-10 μM Phe-Cys was found to induce the suppression of reactive oxygen species formation and membrane lipid peroxidation in oxidative stressed cells. Intracellular glutathione levels were found to increase in the peptide-treated cells under normal condition, which can potentially contribute in protecting the cells from oxidative damage. Furthermore, Western blot analysis showed that the levels of antioxidant enzymes, catalase and superoxide dismutase-1, increased in the hepatic cells when treated with Phe-Cys in the presence of the oxidant. The results show that this peptide has great potential to be used against oxidative stress-induced health conditions.

Identification of novel dipeptidyl peptidase-IV and angiotensin-I-converting enzyme inhibitory peptides from meat proteins using in silico analysis

Angiotensin-I-converting enzyme (ACE-I, EC 3.4.15.1), renin (EC 3.4.23.15), and dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5) play key roles in the control of hypertension and the development of type-2 diabetes and other diseases associated with metabolic syndrome. The aim of this work was to utilize known in silico methodologies, peptide databases and software including ProtParam (http://web.expasy.org/protparam/), Basic Local Alignment Tool (BLAST), ExPASy PeptideCutter (http://web.expasy.org/peptide_cutter/) and BIOPEP (http://www.uwm.edu.pl/biochemia/index.php/pl/biopep) to assess the release of potentially bioactive DPP-IV, renin and ACE-I inhibitory peptides from bovine and porcine meat proteins including hemoglobin, collagen and serum albumin. These proteins were chosen as they are found commonly in meat by-products such as bone, blood and low-value meat cuts. In addition, the bioactivities of identified peptides were confirmed using chemical synthesis and in vitro bioassays. The concentration of peptide required to inhibit the activity of ACE-I and DPP-IV by 50% was determined for selected, active peptides. Novel ACE-I and DPP-IV inhibitory peptides were identified in this study using both in silico analysis and a literature search to streamline enzyme selection for peptide production. These novel peptides included the ACE-I inhibitory tri-peptide Ile-Ile-Tyr and the DPP-IV inhibitory tri-peptide Pro-Pro-Leu corresponding to sequences f (182-184) and f (326-328) of both porcine and bovine serum albumin which can be released following hydrolysis with the enzymes papain and pepsin, respectively. This work demonstrates that meat proteins are a suitable resource for the generation of bioactive peptides and further demonstrates the usefulness of in silico methodologies to streamline identification and generation of bioactive peptides.

Effect of power ultrasound pretreatment on peptidic profiles and angiotensin converting enzyme inhibition of milk protein concentrate hydrolysates

BACKGROUND

The use of power ultrasound as a pretreatment to enhance the hydrolysis of milk protein concentrate (MPC) and subsequent angiotensin converting enzyme (ACE) inhibitory activity has been studied. Liquid chromatography was used to analyse peptide profiles of Neutrase-derived MPC hydrolysates after pretreatment at 0, 1, 3, 5 and 8 min at an ultrasound power level of 800 W.

RESULTS

The peptide profiles indicated an increase in number of peptides when ultrasound pretreatment was applied. There was also an increase in the degree of hydrolysis of MPC hydrolysates. The profiles indicated that new small peptides in ultrasound pretreated samples (1-5 min) which were not present in the control samples and 8 min pretreated samples, could be responsible for increased ACE inhibitory activity. These small peptides were digested in the 8 min pretreated samples.

CONCLUSION

Ultrasound pretreatment of MPC increases the ACE inhibitory activity of the hydrolysates because of the production of new small peptides. This can be used as a means to derive potent ACE inhibitory peptides at industrial scale in complex protein sources.

Angiotensin I-converting enzyme (ACE) inhibitory activity and ACE inhibitory peptides of salmon (Salmo salar) protein hydrolysates obtained by human and porcine gastrointestinal enzymes

The objectives of the present study were two-fold: first, to detect whether salmon protein fractions possess angiotensin I-converting enzyme (ACE) inhibitory properties and whether salmon proteins can release ACE inhibitory peptides during a sequential in vitro hydrolysis (with commercial porcine enzymes) and ex vivo digestion (with human gastrointestinal enzymes). Secondly, to evaluate the ACE inhibitory activity of generated hydrolysates. A two-step ex vivo and in vitro model digestion was performed to simulate the human digestion process. Salmon proteins were degraded more efficiently by porcine enzymes than by human gastrointestinal juices and sarcoplasmic proteins were digested/hydrolyzed more easily than myofibrillar proteins. The ex vivo digested myofibrillar and sarcoplasmic duodenal samples showed IC50 values (concentration required to decrease the ACE activity by 50%) of 1.06 and 2.16 mg/mL, respectively. The in vitro hydrolyzed myofibrillar and sarcoplasmic samples showed IC50 values of 0.91 and 1.04 mg/mL, respectively. Based on the results of in silico studies, it was possible to identify 9 peptides of the ex vivo hydrolysates and 7 peptides of the in vitro hydrolysates of salmon proteins of 11 selected peptides. In both types of salmon hydrolysates, ACE-inhibitory peptides IW, IY, TVY and VW were identified. In the in vitro salmon protein hydrolysates an ACE-inhibitory peptides VPW and VY were also detected, while ACE-inhibitory peptides ALPHA, IVY and IWHHT were identified in the hydrolysates generated with ex vivo digestion. In our studies, we documented ACE inhibitory in vitro effects of salmon protein hydrolysates obtained by human and as well as porcine gastrointestinal enzymes.