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

Atlantic salmon (Salmo salar) waste as a unique source of biofunctional protein hydrolysates: Emerging productions, promising applications, and challenges mitigation

The Atlantic salmon is an extremely popular fish for its nutritional value and unique taste among several fish species. Researchers are focusing on the utilization of Atlantic salmon waste for generating protein hydrolysates rich in peptides and amino acids and investigating their health benefits. Several technological approaches, including enzymatic, chemical, and the recently developed subcritical water hydrolysis, are currently used for the production of Atlantic salmon waste protein hydrolysates. Hydrolyzing various wastes, e.g., heads, bones, skin, viscera, and trimmings, possessing antioxidant, blood pressure regulatory, antidiabetic, and anti-inflammatory properties, resulting in applications in human foods and nutraceuticals, animal farming, pharmaceuticals, cell culture, and cosmetics industries. Furthermore, future applications, constraints several challenges associated with industrial hydrolysate production, including sensory, safety, and economic constraints, which could be overcome by suggested techno processing measures. Further studies are recommended for developing large-scale, commercially viable production methods, focusing on eradicating sensory constraints and facilitating large-scale application.

Marine collagen: Unveiling the blue resource-extraction techniques and multifaceted applications

Marine organisms such as fish and shellfish are composed of compounds with properties and characteristics that have been proven useful in a variety of sectors such as cosmetics, healthcare (wound healing), food industries, and tissue engineering. Collagen extraction from fish waste as a "blue resource" has attracted research attention over the past decade. Around 75 % of fish waste contains a high concentration of collagen. This has driven research in the conversion of these low-cost by-products into valuable products. Collagen extracted by acidic or/and enzymatic methods is gaining a lot of attention today due to its low cost and high yield. Fermentation and enzymatic hydrolysis stand out as one of the most environmentally sustainable and ecologically friendly methods for collagen extraction. Because of its great biocompatibility, excellent bioactivity, and low antigenicity, marine collagen is receiving more attention. Furthermore, collagen-derived peptides may exhibit interesting antioxidant activity, potent antihypertensive activity, and antimicrobial activity against different strains of bacteria. This review focuses on the advancements in extraction and detection methods of marine collagen, both from a technological and legislative standpoint, in addition to exploring its diverse range of application domains.

Multi-Bioactivity of Protein Digests and Peptides from Oat (Avena sativa L.) Kernels in the Prevention of the Cardiometabolic Syndrome

The aim of this study was to characterize the digests and peptides derived from oat kernel proteins in terms of their major enzyme inhibitory activities related to the prevention of cardiometabolic syndrome. It also entailed the characteristics of antioxidant bioactivity of the analyzed material. The study was carried out using coupled in silico and in vitro methods. The additional goal was to investigate whether identified peptides can pervade Caco-2 cells. Based on the results of bioinformatic analysis, it was found that the selected oat proteins may be a potential source of 107 peptides with DPP-IV and/or ACE inhibitory and/or antioxidant activity. The duodenal digest of oat kernels revealed multiple activities. It inhibited the activities of the following enzymes: DPP-IV (IC₅₀ = 0.51 vs. 10.82 mg/mL of the intact protein), α-glucosidase (IC₅₀ = 1.55 vs. 25.20 mg/mL), and ACE (IC₅₀ = 0.82 vs. 34.52 mg/mL). The DPPH^• scavenging activity was 35.7% vs. 7.93% that of the intact protein. After in silico digestion of oat proteins, 24 peptides were selected for identification using LC-Q-TOF-MS/MS. Among them, 13 sequences were successfully identified. One of them, i.e., VW peptide, exhibited triple activities, i.e., DPP-IV and ACE inhibitory and DPPH^• scavenging activity. The multifunctional peptides: PW, TF, VF, and VW, were identified in the basolateral samples after transport experiments. Both in silico and in vitro analyses demonstrated that oat kernel proteins were the abundant sources of bioactive digests and peptides to be used in a diet for patients suffering from cardiometabolic syndrome.

Enhancing the Biological Activities of Food Protein-Derived Peptides Using Non-Thermal Technologies: A Review

Bioactive peptides (BPs) derived from animal and plant proteins are important food functional ingredients with many promising health-promoting properties. In the food industry, enzymatic hydrolysis is the most common technique employed for the liberation of BPs from proteins in which conventional heat treatment is used as pre-treatment to enhance hydrolytic action. In recent years, application of non-thermal food processing technologies such as ultrasound (US), high-pressure processing (HPP), and pulsed electric field (PEF) as pre-treatment methods has gained considerable research attention owing to the enhancement in yield and bioactivity of resulting peptides. This review provides an overview of bioactivities of peptides obtained from animal and plant proteins and an insight into the impact of US, HPP, and PEF as non-thermal treatment prior to enzymolysis on the generation of food-derived BPs and resulting bioactivities. US, HPP, and PEF were reported to improve antioxidant, angiotensin-converting enzyme (ACE)-inhibitory, antimicrobial, and antidiabetic properties of the food-derived BPs. The primary modes of action are due to conformational changes of food proteins caused by US, HPP, and PEF, improving the susceptibility of proteins to protease cleavage and subsequent proteolysis. However, the use of other non-thermal techniques such as cold plasma, radiofrequency electric field, dense phase carbon dioxide, and oscillating magnetic fields has not been examined in the generation of BPs from food proteins.

Current Trends and Applications of Food-derived Antihypertensive Peptides for the Management of Cardiovascular Disease

Abstract:

Food derived Antihypertensive peptides is considered as a natural supplement for controlling the hypertension. Food protein not only serve as a macronutrient but also act as raw material for biosynthesis of physiologically active peptides. Food sources like milk and milk products, animal protein such as meat, chicken, fish, eggs and plant derived proteins from soy, rice, wheat, mushroom, pumpkins contain high amount of antihypertensive peptides. The food derived antihypertensive peptides has ability to supress the action of rennin and Angiotesin converting enzyme (ACE) which is mainly involved in regulation of blood pressure by RAS. The biosynthesis of endothelial nitric oxide synthase is also improved by ACE inhibitory peptides which increase the production of nitric oxide in vascular walls and encourage vasodilation. Interaction between the angiotensin II and its receptor is also inhibited by the peptides which help to reduce hypertension. This review will explore the novel sources and applications of food derived peptides for the management of hypertension.

Production of Dual Inhibitory Hydrolysate by Enzymatic Hydrolysis of Squid Processing By-product

Squid processing by-product contains unutilized abundant proteins. In this study, 6 proteases (pepsin, protamex, trypsin, neutral protease, alkaline protease, and papain) were firstly employed to hydrolyze the squid processing by-product protein. The neutral protease-digested hydrolysate was found to have the most promising ACE (angiotensin-converting enzyme) inhibitory activity. Based on Box-Behnken design, the optimal hydrolysis process was determined to be: 52.4 ℃ of temperature, 5.7 h of time, pH 7.1, and 8151 U/g of enzyme. Under these conditions, the ACE inhibition rate and polypeptide content of the hydrolysate were 84.26% and 229.09 mg/g, respectively. Subsequently, ultrafiltration was performed, and the ACE and renin inhibitory activities of the filtrate (< 1 kDa) were the highest, reaching 87.48 ± 1.76% and 69.72 ± 1.16%, with IC₅₀ values of 1.34 ± 0.12 mg/mL and 1.47 ± 0.06 mg/mL, respectively. However, these activities decreased to 35.15 ± 1.31% and 43.17% ± 1.42%, respectively, after digestion by simulated gastrointestinal juice. Nevertheless, this is the first report representing the neutral protease-digested hydrolysate of squid processing by-product as a potential source of both ACE and renin inhibitors.

Encapsulation of Salmon Peptides in Marine Liposomes: Physico-Chemical Properties, Antiradical Activities and Biocompatibility Assays

Salmon byproducts (Salmo salar) generated by the food chain represent a source of long-chain polyunsaturated fatty acids (eicosapentaenoic acid (EPA): 20:5n-3; docosahexaenoic acid (DHA): 22:6n-3) and peptides that can be used as supplements in food for nutraceutical or health applications, such as in the prevention of certain pathologies (e.g., Alzheimer’s and cardiovascular diseases). The extraction of polar lipids naturally rich in PUFAs by enzymatic processes without organic solvent (controlled by pH-Stat method), coupled with the production of 1 kDa salmon peptides by membrane filtration, allowed the formulation of nanocarriers. The physicochemical properties of the nanoliposomes (size ranging from 120 to 140 nm, PDI of 0.27, zeta potential between −32 and −46 mV and encapsulation efficiency) were measured, and the bioactivity of salmon hydrolysate peptides was assessed (antioxidant and antiradical activity: ABTS, ORAC, DPPH; iron metal chelation). Salmon peptides exhibited good angiotensin-conversion-enzyme (ACE) inhibition activity, with an IC₅₀ value of 413.43 ± 13.12 µg/mL. Cytotoxicity, metabolic activity and proliferation experiments demonstrated the harmlessness of the nanostructures in these experimental conditions.

PTML modeling for peptide discovery: in silico design of non-hemolytic peptides with antihypertensive activity

Hypertension is a medical condition that affects millions of people worldwide. Despite the high efficacy of the current antihypertensive drugs, they are associated with serious side effects. Peptides constitute attractive options for chemical therapy against hypertension, and computational models can accelerate the design of antihypertensive peptides. Yet, to the best of our knowledge, all the in silico models predict only the antihypertensive activity of peptides while neglecting their inherent toxic potential to red blood cells. In this work, we report the first sequence-based model that combines perturbation theory and machine learning through multilayer perceptron networks (SB-PTML-MLP) to enable the simultaneous screening of antihypertensive activity and hemotoxicity of peptides. We have interpreted the molecular descriptors present in the model from a physicochemical and structural point of view. By strictly following such interpretations as guidelines, we performed two tasks. First, we selected amino acids with favorable contributions to both the increase of the antihypertensive activity and the diminution of hemotoxicity. Then, we assembled those suitable amino acids, virtually designing peptides that were predicted by the SB-PTML-MLP model as antihypertensive agents exhibiting low hemotoxicity. The potentiality of the SB-PTML-MLP model as a tool for designing potent and safe antihypertensive peptides was confirmed by predictions performed by online computational tools reported in the scientific literature. The methodology presented here can be extended to other pharmacological applications of peptides.

Properties of peptides released from salmon and carp via simulated human-like gastrointestinal digestion described applying quantitative parameters

Apart from the classical (experimental) methods, biologically active peptides can be studied via bioinformatics approach, also known as in silico analysis. This study aimed to verify the following research hypothesis: ACE inhibitors and antioxidant peptides can be released from salmon and carp proteins during simulated in silico human-like gastrointestinal digestion. The potential to release biopeptides was evaluated using the BIOPEP-UWM quantitative criteria including the profile of biological activity, frequency of the occurrence (A)/release (AE) of fragments with an ACE inhibitory or antioxidant activity by selected enzymes, and relative frequency of release of bioactive fragments with a given activity by selected enzymes (W). Salmon collagen and myofibrillar proteins of carp turned out to be the best potential source of the searched peptides-ACE inhibitors and antioxidant peptides. Nonetheless, after digestion, the highest numbers of ACE inhibitors and antioxidant peptides were potentially released from the myofibrillar proteins of salmon and carp. Peptide Ranker Score, Pepsite2, and ADMETlab platform were applied to evaluate peptides' bioactivity potential, their safety and drug-like properties. Among the 63 sequences obtained after the simulated digestion of salmon and carp proteins, 30 were considered potential biopeptides. The amino acid sequences of ACE-inhibiting and antioxidant peptides were predominated by P, G, F, W, R, and L. The predicted high probability of absorption of most analyzed peptides and their low toxicity should be considered as their advantage.

Muscle Protein Hydrolysates and Amino Acid Composition in Fish

Fish muscle, which accounts for 15%-25% of the total protein in fish, is a desirable protein source. Their hydrolysate is in high demand nutritionally as a functional food and thus has high potential added value. The hydrolysate contains physiologically active amino acids and various essential nutrients, the contents of which depend on the source of protein, protease, hydrolysis method, hydrolysis conditions, and degree of hydrolysis. Therefore, it can be utilized for various industrial applications including use in nutraceuticals and pharmaceuticals to help improve the health of humans. This review discusses muscle protein hydrolysates generated from the muscles of various fish species, as well as their amino acid composition, and highlights their functional properties and bioactivity. In addition, the role of the amino acid profile in regulating the biological and physiological activities, nutrition, and bitter taste of hydrolysates is discussed.

Assessment of the biological activity of fish muscle protein hydrolysates using in vitro model systems

The generation of biologically active fish protein hydrolysates (FPH) is a useful technique to produce value-added products with potential application in the functional food and nutraceutical industries. Fish muscle is an attractive substrate for the production of protein hydrolysates due to its rich protein content, containing 15-25% of total fish protein. This paper reviews the production of protein hydrolysates from fish muscle, most commonly via enzymatic hydrolysis, and their subsequent bioactivities including anti-obesity, immunomodulatory, antioxidant, angiotensin I-converting enzyme (ACE)-inhibitory, anti-microbial, and anti-cancer activities as measured by in vitro testing methods. Disease prevention with FPH potentially offers a safe and natural alternative to synthetic drugs. Small molecular weight (MW) FPHs generally exhibit favourable bioactivity than large MW fractions via enhanced absorption through the gastrointestinal tract. This review also discusses the relationship between amino acid (AA) composition and AA sequence of FPH and peptides and their exhibited in vitro bioactivity.

Two novel potent ACEI peptides isolated from Pinctada fucata meat hydrolysates using in silico analysis: identification, screening and inhibitory mechanisms

The aim of this study was to discover potent angiotensin-converting enzyme (ACE) inhibitory (ACEI) peptides from Pinctada fucata (P. fucata) for treating hypertension and to characterize them using in silico analysis. The P. fucata proteins were hydrolyzed by Alcalase®, a serine endopeptidase with broad selectivity, at various times (0, 2, 4, 6, 8, 10 h). The degree of hydrolysis (DH) and ACEI activity of the different hydrolysates were measured. Considering the molecular weight and ACEI activity, the 10 h hydrolysate was purified by a series of traditional separation methods, including ultrafiltration, gel G-25 chromatography, and reversed-phase high-performance liquid chromatography (RP-HPLC), with ACEI activity as a guide. The results showed two fractions, C17 and C18, eluted by means of semi-preparative RP-HPLC, and showed the highest ACEI activities of 80.33 ± 2.70% and 81.66 ± 0.29%, respectively, at 1 mg mL-1. The two fractions were then identified using liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) and their MS/MS spectra data were subjected to de novo sequencing. Subsequently, the potential ACEI peptides were screened by in silico methods, namely, to analyze the average local confidence (ALC) value obtained from the sequencing software and the P-value from the Pepsite 2. In total, 13 potential ACEI peptide sequences were obtained and identified from the two fractions by LC-ESI-MS/MS, and two novel tetrapeptides, FRVW (607.3314 Da) and LPYY (555.2881 Da), were screened for synthesis according to the in silico analysis. The in vitro ACEI tests indicated that FRVW and LPYY had IC50 values of 18.34 and 116.26 μM, respectively. The Lineweaver-Burk plot showed that FRVW was a noncompetitive inhibitor, and LPYY was shown to be a mixed-mode type inhibitor. A stability study against ACE indicated that both peptides were hydrolyzed by ACE to some extent, the higher ACEI activity following incubation with ACE indicating that they should be classified as pro-drug substrates. Molecular docking results showed that hydrophobic amino acids (HAAs) within peptides formed vital interactions including hydrogen bonds, electrostatic forces, van der Waals forces and Pi-Pi interactions with ACE residues, which stabilized the enzyme-peptide complex. Furthermore, the docking results accorded with the inhibition kinetic mode. Our study demonstrated that FRVW and LPYY isolated from P. fucata have potential applications as antihypertensive agents.

Angiotensin-I converting enzyme inhibitory peptide derived from the shiitake mushroom (Lentinula edodes)

Abstract

Angiotensin-I converting enzyme (ACE) inhibitors are widely used to control hypertension. In this study, protein hydrolysates from shiitake mushroom were hydrolyzed to prepare ACE-inhibitory peptides. Optimum process conditions for the hydrolysis of shiitake mushrooms using Alcalase were optimized using response surface methodology. Monitoring was conducted to check the degree of hydrolysis (DH) and ACE inhibitory activity. In the results, the optimum condition with the highest DH value of 28.88% was 50.2 °C, 3-h hydrolysis time, and 1.16 enzyme/substrate ratios. The highest ACE inhibitory activity (IC₅₀ of 0.33 μg/mL) was under 47 °C, 3 h 28 min hydrolysis time, and 0.59 enzyme/substrate ratios. The highest activity was fractionated into 5 ranges of molecular weight, and the fraction below 0.65 kDa showed the highest activity with IC₅₀ of 0.23 μg/mL. This fraction underwent purification using RP-HPLC, meanwhile the peak which offered a retention time of about 37 min showed high ACE inhibitory activity. Mass spectrometry identified the amino acid sequence of this peak as Lys-Ile-Gly-Ser-Arg-Ser-Arg-Phe-Asp-Val-Thr (KIGSRSRFDVT), with a molecular weight of 1265.43 Da. The synthesized variant of this peptide produced an ACE inhibitory activity (IC₅₀) of 37.14 μM. The peptide KIGSRSRFDVT was shown to serve as a non-competitive inhibitor according to the Lineweaver-Burk plot findings. A molecular docking study was performed, which showed that the peptide binding occurred at an ACE non-active site. The findings suggest that peptides derived from shiitake mushrooms could serve either as useful components in pharmaceutical products, or in functional foods for the purpose of treating hypertension.

Graphic abstract

Food-Derived Opioid Peptides in Human Health: A Review

World Health Organization data suggest that stress, depression, and anxiety have a noticeable prevalence and are becoming some of the most common causes of disability in the Western world. Stress-related disorders are considered to be a challenge for the healthcare system with their great economic and social impact. The knowledge on these conditions is not very clear among many people, as a high proportion of patients do not respond to the currently available medications for targeting the monoaminergic system. In addition, the use of clinical drugs is also associated with various side effects such as vomiting, dizziness, sedation, nausea, constipation, and many more, which prevents their effective use. Therefore, opioid peptides derived from food sources are becoming one of the safe and natural alternatives because of their production from natural sources such as animals and plant proteins. The requirement for screening and considering dietary proteins as a source of bioactive peptides is highlighted to understand their potential roles in stress-related disorders as a part of a diet or as a drug complementing therapeutic prescription. In this review, we discussed current knowledge on opioid endogenous and exogenous peptides concentrating on their production, purification, and related studies. To fully understand their potential in stress-related conditions, either as a drug or as a therapeutic part of a diet prescription, the need to screen more dietary proteins as a source of novel opioid peptides is emphasized.

Soybean (Glycine max) Protein Hydrolysates as Sources of Peptide Bitter-Tasting Indicators: An Analysis Based on Hybrid and Fragmentomic Approaches

The aim of this study was to analyze soybean proteins as sources of peptides likely to be bitter using fragmentomic and hybrid approaches involving in silico and in vitro studies. The bitterness of peptides (called parent peptides) was theoretically estimated based on the presence of bitter-tasting motifs, particularly those defined as bitter-tasting indicators. They were selected based on previously published multilinear stepwise regression results. Bioinformatic-assisted analyses covered the hydrolysis of five major soybean-originating protein sequences using bromelain, ficin, papain, and proteinase K. Verification of the results in experimental conditions included soy protein concentrate (SPC) hydrolysis, RP-HPLC (for monitoring the proteolysis), and identification of peptides using RP-HPLC-MS/MS. Discrepancies between in silico and in vitro results were observed when identifying parent peptide SPC hydrolysate samples. However, both analyses revealed that conglycinins were the most abundant sources of parent peptides likely to taste bitter. The compatibility percentage of the in silico and in vitro results was 3%. Nine parent peptides with the following sequences were identified in SPC hydrolysates: LSVISPK, DVLVIPLG, LIVILNG, NPFLFG, ISSTIV, PQMIIV, PFPSIL, DDFFL, and FFEITPEK (indicators are in bold). The fragmentomic idea of research might provide a supportive method for predicting the bitterness of hydrolysates. However, this statement needs to be confirmed experimentally.

Novel ACE inhibitory tripeptides from ovotransferrin using bioinformatics and peptidomics approaches

Food-derived ACE inhibitory peptides have recently attracted increased attention. This work focused on a more efficient in silico method to find ACE inhibitory peptides from ovotransferrin. In this work, ovotransferrin was digested into peptides by virtual enzymolysis. Subsequently, in vitro ACE inhibitory activity of potential tripeptides was conducted following the peptide score, toxicity, and water solubility prediction. Both pharmacophore study and flexible docking were applied to analyze ACE inhibition mechanism of tripeptides. Our results demonstrated that EWL was a potent ACE inhibitory tripeptide with IC₅₀ value of 380 ± 10 μM. Besides, pharmacophore and flexible docking showed that the pi interaction and hydrogen bond were the key interactions in ACE-EWL complex. It appears that the in vitro ACE inhibitory activity of tripeptide EWL was consistent with its molecular modeling.

Structure⁻Activity Prediction of ACE Inhibitory/Bitter Dipeptides-A Chemometric Approach Based on Stepwise Regression

Forward and backward stepwise regression (FR and BR, respectively) was applied for the structure⁻bioactivity prediction of angiotensin converting enzyme (ACE)-inhibitory/bitter-tasting dipeptides. The datasets used in this study consisted of 28 sequences and numerical variables reflecting dipeptides' physicochemical nature. The data were acquired from the BIOPEP-UWM, Biological Magnetic Resonance Databank, ProtScale, and AAindex databases. The calculations were computed using STATISTICA®13.1. FR/BR models differed in R² (0.91/0.76, respectively). The impact of C-atC(-) and N-Molw(+) on the dual function of dipeptides was observed. Positive (+) and negative (-) correlations with log IC50 are presented in parens. Moreover, C-Bur(+), N-atH(+), and N-Pol(-) were also found to be important in the FR model. The additional statistical significance of N-bul(-), N-Bur(-), and N-Hdr(+) was reported in the BR model. These attributes reflected the composition of the dipeptides. We report that the "ideal" bitter ACE inhibitor should be composed of P, Y, F (C-end) and G, V, I, L (N-end). Functions: log Rcaf. = f (observed log IC50) and log Rcaf. = f (predicted log IC50) revealed no direct relationships between ACE inhibition and the bitterness of the dipeptides. It probably resulted from some structural discrepancies between the ACE inhibitory/bitter peptides and/or the measure of activity describing one of the two bioactivities. Our protocol can be applicable for the structure⁻bioactivity prediction of other bioactivities peptides.

Cod Residual Protein Prevented Blood Pressure Increase in Zucker fa/fa Rats, Possibly by Inhibiting Activities of Angiotensin-Converting Enzyme and Renin

Hypertension is the leading risk factor for cardiovascular disease, and prevention of high blood pressure through diet and lifestyle should be a preferred approach. High intake of fish is associated with lower blood pressure, possibly mediated through the proteins since peptides with angiotensin-converting enzyme (ACE) inhibiting capacities have been identified in fish skin, backbone, and fillet. The effects of cod meals made from residual materials and fillet on blood pressure were investigated in obese Zucker fa/fa rats which spontaneously develop high blood pressure. Rats were fed diets containing water-soluble (stickwater) or water-insoluble (presscake) fractions of protein-rich meals from cod residual materials (head, gut, backbone with muscle residuals, skin, trimmings) or fillet. Rats were fed diets containing 25% of total protein from cod meal and 75% of protein from casein, or casein as the sole protein source (control group) for four weeks. Results show that a diet containing residual presscake meal with high gut content prevented blood pressure increase, and this cod residual meal also showed the strongest in vitro inhibitions of ACE and renin activities. In conclusion, a diet containing water-insoluble proteins (presscake meal) with high gut content prevented increase in blood pressure in obese Zucker fa/fa rats.

The potential peptides against angiotensin-I converting enzyme through a virtual tripeptide-constructing library

Peptides derived from food proteins are promising bioactive source for inhibiting Angiotensin-I converting enzyme (ACE) activity. Bioactive peptides (BP) have received much attention, particularly from the pharmaceutical industry. As they not only own potent properties but also possess less side-effects than synthetic drugs. In this work, an 8000 possible tripeptides library was constructed to predict the potential ACE inhibitory peptides by using in silico tools. GOLD molecular docking was then applied to determine the binding mode of action between ACE and each of tripeptide from this in-house library. The first 662 high-ranking tripeptides by ChemScore were chosen to create association rules of tripeptides-ACE complexes. An orientation pattern of amino acid in the binding tunnel of ACE has been examined by frequency analysis. The association rules (confident values over 90%) illustrated that hydrophobic factor has been displayed as main components in the ACE tripeptides inhibitor from four factors in equation, hydrophobic, aromatic, polar, charged. According to in silico output, five tripeptides were chosen to test in vitro study of ACE-inhibitory activity. The half-maximal inhibitory concentration (IC₅₀) of these selective five peptides, WCW, IWW, WWW, WWI and WLW for inhibiting ACE were 49.50 ± 3.88 μM, 489.14 ± 8.84 μM, 536.02 ± 38.57 μM, 752.91 ± 41.89 μM and 1783 ± 0.113 μM, respectively. Molecular dynamics simulations approach was applied to study the interaction of WCW (Trp-Cys-Trp) within ACE pocket site. This ligand was stabilized by strong hydrogen bonding interactions with ACE active site, Tyr523-Trp'1 (99.76%) and His353-Trp'1 (95.68%). Our computational protocol could be considered as a new tool for identifying active peptide against ACE from hydrolysated peptides of natural sources.

Antihypertensive activity of fish protein hydrolysates and its peptides

The rising interest to utilize nutritionally exorbitant fish proteins has instigated research activities in fish waste utilization. The development of newer technologies to utilize fish waste has fostered use of bioactive value-added products for specific health benefits. Enzymatically obtained Fish Protein Hydrolysate (FPH) is a rich source of biologically active peptides possessing anti-oxidant, anticancer, antimicrobial and anti-hypertensive activity. Isolating natural remedies to combat alarming negative consequences of synthetic drugs has been the new trend in current research promoting identification of antihypertensive peptides from FPH. In this review, we aim to culminate data available to produce antihypertensive peptides from FPH, its composition and potential to be used as a therapeutic agent. These purified peptides are known to be rich in arginine, valine and leucine. Reports reveal peptides with low molecular weight (<1 kDa) and shorter chain length (<20 amino acids) exhibited higher antihypertensive activity. As these peptides have proven Angiotensin Converting Enzyme - I inhibitory activity in vitro and in vivo, their potential to be used as antihypertensive drugs is outrageous. However, current focus on research in the field of molecular docking is necessary to have improved understanding of interaction of the peptides with the enzyme.

Biotechnological production of the angiotensin-converting enzyme inhibitory dipeptide isoleucine-tryptophan

Peptides with angiotensin-converting enzyme (ACE)-inhibitory and antihypertensive effects are suggested as innovative food additives to prevent or treat hypertension. Currently, these substances are isolated from food proteins following nonselective hydrolysis as a mixture of ACE-inhibitory peptides and other protein fragments. This study presents an innovative biotechnological method, based on recombinant DNA technology that was established to specifically produce the ACE-inhibitory dipeptide isoleucine-tryptophan. In a first step, a repetitive isoleucine-tryptophan construct fused to the maltose-binding protein was generated and expressed in Escherichia coli BL21 cells. The chromatographically purified recombinant fusion protein was enzymatically hydrolyzed using α-chymotrypsin to liberate the dipeptide isoleucine-tryptophan. The identity of the liberated isoleucine-tryptophan was confirmed by MS and derivatization of its N-terminus. The ACE-inhibitory effect of the recombinant dipeptide on soluble and membrane bound ACE was found to be indistinguishable from the inhibitory potential of the chemically produced commercially available dipeptide. The established experimental strategy represents a promising approach to the biotechnical production of sufficient amounts of recombinant peptide-based ACE-inhibitory and antihypertensive substances that are applicable as functional food additives to delay or even prevent hypertension.

Structural Basis of Bioactivity of Food Peptides in Promoting Metabolic Health

Bioactive peptides have many structural features that enable them to become functional in controlling several biological processes in the body, especially those related to metabolic health. This chapter provides an overview of the multiple targets of food-derived peptides against metabolic health problems (e.g., hypertension, dyslipidemia, hyperglycemia, oxidative stress) and discusses the importance of structural chemistry in determining the bioactivities of peptides and protein hydrolysates.

Identification and Antithrombotic Activity of Peptides from Blue Mussel (Mytilus edulis) Protein

The blue mussel (Mytilus edulis) reportedly contains many bioactive components of nutritional value. Water-, salt- and acid-soluble M. edulis protein fractions were obtained and the proteins were trypsinized. The resultant peptides were analyzed by ultra-performance liquid chromatography quadrupole time of flight tandem mass spectrometry (UPLC-Q-TOF-MS/MS). 387 unique peptides were identified that matched 81 precursor proteins. Molecular mass distributions of the proteins and peptides were analyzed by sodium dodecyl sulfate-polyacryl amide gel electrophoresis (SDS-PAGE). The differences between the three protein samples were studied by Venn diagram of peptide and protein compositions. Toxicity, allergic and antithrombotic activity of peptides was predicted using database website and molecular docking respectively. The antithrombotic activity of enzymatic hydrolysate from water-, salt- and acid-soluble M. edulis protein were 40.17%, 85.74%, 82.00% at 5 mg/mL, respectively. Active mechanism of antithrombotic peptide (ELEDSLDSER) was also research about amino acid binding sites and interaction, simultaneously.

Current trends and perspectives of bioactive peptides

The remarkable growth of therapeutic peptide development in the past decade has led to a large number of market approvals and the market value is expected to hit $25 billion by 2018. This significant market increase is driven by the increasing incidences of metabolic and cardiovascular diseases and technological advancements in peptide synthesis. For this reason, the search for bioactive peptides has also increased exponentially. Many bioactive peptides from food and nonfood sources have shown positive health effects yet, obstacles such as the need to implement efficient and cost-effective strategies for industrial scale production, good manufacturing practices as well as well-designed clinical trials to provide robust evidence for supporting health claims continue to exist. Several other factors such as the possibility of allergenicity, toxicity and the stability of biological functions of the peptides during gastrointestinal digestion would need to be addressed.

Mechanism of antihypertensive effect of Mucuna pruriens L. seed extract and its isolated compounds

Background In the search of safe and effective lead molecules from natural sources, Mucuna pruriens (MP) L. (Fabaceae) seeds were utilized for exploring the antihypertensive potential. Traditionally, it is used as diuretic and hypotensive. Methods Bioassay-guided fractions were utilized for the isolation of active compounds by column chromatography. IC50 value, enzyme kinetics and inhibition mechanism were determined. In vivo time and dose-dependent hypotensive study followed by changes in mean arterial pressure (MAP) induced by angiotensin I (3 nmol/kg), angiotensin II (3 nmol/kg), and bradykinin (10 nmol/kg) in anesthetized rats was done. Plasma and tissue angiotensin I-converting enzyme (ACE) activities were also determined. Results Phytochemical analysis by spectroscopic techniques revealed the presence of known compounds like genistein, ursolic acid and L-DOPA from the ethyl acetate and water fraction, respectively. In vitro study revealed MP ethyl acetate (MPEA) fraction and genistein as the most active fraction (IC50 156.45 µg/mL) and compound (IC50 253.81 µM), respectively. Lineweaver-Burk plots revealed a non-competitive mode of inhibition. ACE protein precipitation was the suggested mechanism for inhibition. The extract showed a time- and dose-dependent decrease in MAP. Genistein was able to dose-dependently reduce the MAP, up to 53±1.5 mmHg (40 mg/kg, i.v.). As compared to control, it showed a dose-dependent decrease in plasma ACE activity of 40.61 % and 54.76 % at 10 mg/kg and 20 mg/kg, respectively. It also decreased the ACE activity in the aorta (107.67nM/ml min at 10 mg, p<0.001; 95.33nM/ml min at 20 mg p<0.001). Captopril was used as a standard for various in vitro and in vivo assays. Conclusions The study revealed the antihypertensive potential of MP seed compounds via ACE inhibition.

Antioxidant properties of salmon (Salmo salar L.) protein fraction hydrolysates revealed following their ex vivo digestion and in vitro hydrolysis

BACKGROUND

Salmon (Salmo salar L.) myofibryllar protein (MP) and sarcoplasmic protein (SP) were digested with human gastric and duodenal juices and hydrolysed in vitro with commercial pepsin and Corolase PP.

RESULTS

The digestion after duodenal juice/Corolase PP caused almost complete breakdown of peptide bonds in MP and SP. The DPPH(•) scavenging activity of proteins decreased during both ex vivo digestion and in vitro hydrolysis. The highest value of DPPH(•) scavenging activity was shown for the gastric digest of SP (8.88 ± 0.87%). The ABTS(+•) scavenging activity of MP and SP increased during digestion/hydrolysis. The duodenal digest of SP was characterised by the highest value of ABTS(+•) scavenging activity (72.7 ± 1.2%). In turn, the highest value of ferric-reducing power was determined for the gastric digest of SP (84.8 ± 0.2%). Salmon antioxidant peptides Phe-Ile-Lys-Lys, His-Leu, Ile-Tyr, Pro-His-Leu, Pro-Trp, Val-Pro-Trp were identified in both ex vivo digested and in vitro hydrolysed MP and SP. An antioxidant peptide, Val-Tyr, was additionally detected in the in vitro hydrolysate of SP.

CONCLUSION

The results indicate the salmon myofibrillar and sarcoplasmic protein fractions as potential sources of antioxidant peptides that could be released in the gastrointestinal tract but their amino acid sequence and quantification vary. © 2015 Society of Chemical Industry.

Gastrointestinal Endogenous Protein-Derived Bioactive Peptides: An in Vitro Study of Their Gut Modulatory Potential

A recently proposed paradigm suggests that, like their dietary counterparts, digestion of gastrointestinal endogenous proteins (GEP) may also produce bioactive peptides. With an aim to test this hypothesis, in vitro digests of four GEP namely; trypsin (TRYP), lysozyme (LYS), mucin (MUC), serum albumin (SA) and a dietary protein chicken albumin (CA) were screened for their angiotensin-I converting (ACE-I), renin, platelet-activating factor-acetylhydrolase (PAF-AH) and dipeptidyl peptidase-IV inhibitory (DPP-IV) and antioxidant potential following simulated in vitro gastrointestinal digestion. Further, the resultant small intestinal digests were enriched to obtain peptides between 3-10 kDa in size. All in vitro digests of the four GEP were found to inhibit ACE-I compared to the positive control captopril when assayed at a concentration of 1 mg/mL, while the LYS < 3-kDa permeate fraction inhibited renin by 40% (±1.79%). The LYS < 10-kDa fraction inhibited PAF-AH by 39% (±4.34%), and the SA < 3-kDa fraction inhibited DPP-IV by 45% (±1.24%). The MUC < 3-kDa fraction had an ABTS-inhibition antioxidant activity of 150 (±24.79) µM trolox equivalent and the LYS < 10-kDa fraction inhibited 2,2-Diphenyl-1-picrylhydrazyl (DPPH) by 54% (±1.62%). Moreover, over 190 peptide-sequences were identified from the bioactive GEP fractions. The findings of the present study indicate that GEP are a significant source of bioactive peptides which may influence gut function.

The Use of Peptide Markers of Carp and Herring Allergens as an Example of Detection of Sequenced and Non-Sequenced Proteins

The objective of this study is to identify fish protein markers for detecting multiple species based on a comparative proteomic approach that relies on fragments with identical sequences. The possibilities and challenges of the use of peptides obtained from carp (Cyprinus carpio) and herring (Clupea harengus) proteins are discussed. A bioinformatic analysis was followed by an LC-MS/MS experiment to identify markers predicting the presence of fish allergenic proteins. Selected myosin peptides were found in carp protein hydrolysates with known sequences and in herring protein hydrolysates with unknown sequences. The results obtained for carp and herring proteins myosin and parvalbumin indicate that proteins with unknown sequences can be identified by peptide markers. Such markers can be designed by disregarding the principle that peptides should be unique (present in one sequence). The challenge is to determine a group of proteins that can be detected by peptide identification.

Kinetics of the inhibition of renin and angiotensin I-converting enzyme by cod (Gadus morhua) protein hydrolysates and their antihypertensive effects in spontaneously hypertensive rats

Background

Cod muscle has a balanced protein profile that contains potentially bioactive amino acid sequences. However, there is limited information on release of these peptides from the parent proteins and their ability to modulate mammalian blood pressure.

Objective

The aim of this study was to generate cod antihypertensive peptides with potent in vitro inhibitory effects against angiotensin-converting enzyme (ACE) and renin. The most active peptides were then tested for systolic blood pressure (SBP)-reducing ability in spontaneously hypertensive rats (SHRs).

Design

Cod protein hydrolysate (CPH) was produced by subjecting the muscle proteins to proteolysis first by pepsin and followed by trypsin+chymotrypsin combination. In order to enhance peptide activity, the CPH was subjected to reverse-phase (RP)-HPLC separation to yield four fractions (CF1, CF2, CF3, and CF4). The CPH and RP-HPLC fractions were each tested at 1 mg/mL for ability to inhibit in vitro ACE and renin activities. CPH and the most active RP-HPLC fraction (CF3) were then used for enzyme inhibition kinetics assays followed by oral administration (200 and 30 mg/kg body weight for CPH and CF3, respectively) to SHRs and SBP measurements within 24 h.

Results

The CPH, CF3, and CF4 had similar ACE-inhibitory activities of 84, 85, and 87%, which were significantly (p<0.05) higher than the values for CF1 (69%) and CF2 (79%). Conversely, the CF3 had the highest (63%) renin-inhibitory activity (p<0.05) when compared to CPH (43%), CF1 (15%), and CF4 (44%). CPH and CF3 exhibited uncompetitive mode of ACE inhibition, whereas renin inhibition was non-competitive. Even at a 6.7-fold lower dosage, the CF3 significantly (p<0.05) reduced SBP (maximum −40.0 mmHg) better than CPH (maximum −19.1 mmHg).

Conclusions

RP-HPLC fractionation led to enhanced antihypertensive effects of cod peptides, which may be due to a stronger renin-inhibitory activity.

Common Amino Acid Subsequences in a Universal Proteome--Relevance for Food Science

A common subsequence is a fragment of the amino acid chain that occurs in more than one protein. Common subsequences may be an object of interest for food scientists as biologically active peptides, epitopes, and/or protein markers that are used in comparative proteomics. An individual bioactive fragment, in particular the shortest fragment containing two or three amino acid residues, may occur in many protein sequences. An individual linear epitope may also be present in multiple sequences of precursor proteins. Although recent recommendations for prediction of allergenicity and cross-reactivity include not only sequence identity, but also similarities in secondary and tertiary structures surrounding the common fragment, local sequence identity may be used to screen protein sequence databases for potential allergens in silico. The main weakness of the screening process is that it overlooks allergens and cross-reactivity cases without identical fragments corresponding to linear epitopes. A single peptide may also serve as a marker of a group of allergens that belong to the same family and, possibly, reveal cross-reactivity. This review article discusses the benefits for food scientists that follow from the common subsequences concept.

Marine protein hydrolysates: their present and future perspectives in food chemistry – a review

Marine protein hydrolysates are usually prepared by the enzymatic digestion with different proteases at controlled pH and temperature.