Transepithelial transport across Caco-2 cell monolayers of angiotensin converting enzyme (ACE) inhibitory peptides derived from simulated in vitro gastrointestinal digestion of cooked chicken muscles

Progress in Preparation Technology and Functional Research On Marine Bioactive Peptides

Marine bioactive peptides are a class of peptides derived from marine organisms that can optimize the body's metabolic environment and benefit the body's health. These peptides have attracted increasing amounts of attention due to their wide range of health-promoting effects. Additionally, they have the potential to ameliorate diseases such as hypertension, diabetes, influenza viruses, and inflammation and can be used as functional foods or nutritional supplements for the purpose of treating or alleviating diseases. This paper reviews the recent research progress on marine bioactive peptides, focusing on their production technologies and functions in biomaterials and drug development.

The zinc absorption of the novel peptide-Zn complex in Caco-2 cells: effects of soybean peptides charge and hydrophobicity

BACKGROUND

The supplemental effect of zinc depends not only on adequate intake, but also on how efficiently it is absorbed in the small intestine. In the present study, weak hydrophobic peptides (WHP), strong hydrophobic peptides (SHP), positively charged peptides (PCP) and negatively charged peptides (NCP) were isolated from soybean peptides (SP). The peptide-Zn complexes (PCP-Zn, NCP-Zn, WHP-Zn, SHP-Zn and SP-Zn) were prepared to compare their promotion zinc absorption capacity in the Caco-2 cells monolayers model.

RESULTS

We found that the carboxyl, carbonyl and amino groups in peptide were the primary binding sites of Zn. Compared with zinc sulfate, the peptide-Zn complexes with different charge and hydrophobic peptides could improve zinc solubility at different pH. NCP-Zn had a lower Zn-binding capacity but a higher zinc absorption capacity compared to that of PCP-Zn in Caco-2 cells. In addition, the capacity of PCP-Zn to promote zinc absorption was lower than the control group (SP-Zn). There were no significant differences in transport rates, retention rates and uptake rates of WHP-Zn, SHP-Zn and SP-Zn. NCP-Zn could improve the activity of Zn-related enzymes, and the expression levels of PepT1 and ZnT1 were higher than other peptide-Zn complexes.

CONCLUSION

The promotion zinc absorption capacity of peptide-Zn complexes was not completely dependent on the Zn-binding capacity, but also depended on the charge and hydrophobicity of peptides. © 2024 Society of Chemical Industry.

Exploring the Utilization of Bovine Blood as a Source of Antioxidant Peptide: Production, Concentration, Identification, and In Silico Gastrointestinal Digestion

This study delves into the pivotal industrial process of efficiently managing livestock waste. Specifically, the study concentrates on harnessing the potential of bovine blood through enzymatic hydrolysis to produce antioxidant peptides. The whole bovine blood sample, subjected to a 90°C heat treatment for 30 min, underwent hydrolysis utilizing various commercial enzymes, alcalase, neutrase, and papain. Through neutrase hydrolysis (BB-N), we identified optimized conditions crucial for achieving heightened antioxidant activities and 40% protein recovery. Ultrafiltration with a molecular weight cutoff of 3 kDa was employed to concentrate the BB-N peptide, demonstrating the highest antioxidant and protein yield. The gel electrophoresis profile confirmed the denaturation of key proteins like albumin, globulin, and fibrinogen before digestion, while the BB-N derived after digestion contained peptides below 16 kDa. Post-concentration, the permeation of UF-3 kDa underwent purification, and the peptide sequence was discerned using liquid chromatography with tandem mass spectrometry. The exploration identified nine novel peptides- IWAGK, VDLL, MTTPNK, MPLVR, KIII, LPQL, TVIL, DFPGLQ, and VEDVK. Notably, the IWAGK sequence emerged as the most potent antioxidant activity peptide. Subsequent in-silico gastrointestinal digestion predicted structural changes in these peptides. While IWAGK, VDLL, MPLVR, LPQL, TVIL, and DFPGLQ could be fragmented into bioactive dipeptides and tripeptides, MTTPNK, KIII, and VEDVK exhibited resistance, suggesting potential circulation through the bloodstream to reach the target organ. Consequently, our study explores the potential use of BB-N as a novel dietary ingredient with health benefits. In vivo studies are needed to validate and extend our findings.

Tracking bioactive peptides and their origin proteins during the in vitro digestion of meat and meat products

Existing reviews address bioactive peptides of meat proteins; however, comprehensive reviews summarizing the released sequences and their corresponding parent meat proteins in the digesta are limited. This review explores the bioactive peptides released during the in vitro gastrointestinal (GI) digestion of meat, connecting with parent proteins. The primary bioactivities of meat-derived peptides include angiotensin-converting enzyme (ACE) and dipeptidyl peptidase (DPP)-IV inhibition and antioxidant effects. Myofibrillar, sarcoplasmic, and stromal proteins play a significant role in peptide release during digestion. The release of bioactive peptides varies according to the parent protein and cryptides had short chains, non-toxicity, and great bioavailability and GI absorption scores. Moreover, the structural stability and bioactivities of peptides can be influenced by the digestive properties and amino acid composition of parent proteins. Investigating the properties and origins of bioactive peptides provides insights for enhancing the nutritional quality of meat and understanding its potential health benefits.

Recent progress in the preparation of bioactive peptides using simulated gastrointestinal digestion processes

Bioactive peptides (BAPs) represent a unique class of peptides known for their extensive physiological functions and their role in enhancing human health. In recent decades, owing to their notable biological attributes such as antioxidant, antihypertensive, antidiabetic, and anti-inflammatory activities, BAPs have received considerable attention. Simulated gastrointestinal digestion (SGD) is a technique designed to mimic physiological conditions by adjusting factors such as digestive enzymes and their concentrations, pH levels, digestion duration, and salt content. Initially established for analyzing the gastrointestinal processing of foods or their constituents, SGD has recently become a preferred method for generating BAPs. The BAPs produced via SGD often exhibit superior biological activity and stability compared with those of BAPs prepared via other methods. This review offers a comprehensive examination of the recent advancements in BAP production from foods via SGD, addressing the challenges of the method and outlining prospective directions for further investigation.

Coupling in vitro food digestion with in vitro epithelial absorption; recommendations for biocompatibility

As food transits the gastrointestinal tract, food structures are disrupted and nutrients are absorbed across the gut barrier. In the past decade, great efforts have focused on the creation of a consensus gastrointestinal digestion protocol (i.e., INFOGEST method) to mimic digestion in the upper gut. However, to better determine the fate of food components, it is also critical to mimic food absorption in vitro. This is usually performed by treating polarized epithelial cells (i.e., differentiated Caco-2 monolayers) with food digesta. This food digesta contains digestive enzymes and bile salts, and if following the INFOGEST protocol, at concentrations that although physiologically relevant are harmful to cells. The lack of a harmonized protocol on how to prepare the food digesta samples for downstream Caco-2 studies creates challenges in comparing inter laboratory results. This article aims to critically review the current detoxification practices, highlight potential routes and their limitations, and recommend common approaches to ensure food digesta is biocompatible with Caco-2 monolayers. Our ultimate aim is to agree a harmonized consensus protocol or framework for in vitro studies focused on the absorption of food components across the intestinal barrier.

Exploration of nutritional and bioactive peptide properties in goat meat from various primal cuts during in vitro gastrointestinal digestion and absorption

OBJECTIVE

This research aims to explore the nutritional and bioactive peptide properties of goat meat taken from various primal cuts, including the breast, shoulder, rib, loin, and leg, to produce these bioactive peptides during in vitro gastrointestinal (GI) digestion and absorption.

METHODS

The goat meat from various primal cuts was obtained from Boer goats with an average carcass weight of 30±2 kg. The meat was collected within 3 h after slaughter and was stored at -80°C until analysis. A comprehensive assessment encompassed various aspects, including the chemical composition, cooking properties, in vitro GI digestion, bioactive characteristics, and the bioavailability of the resulting peptides.

RESULTS

The findings indicate that the loin muscles contain the highest protein and essential amino acid composition. When the meats were cooked at 70°C for 30 min, they exhibited distinct protein compositions and quantities in the sodium dodecyl sulfate-polyacrylamide gel electrophoresis profile, suggesting they served as different protein substrates during GI digestion. Subsequent in vitro simulated GI digestion revealed that the cooked shoulder and loin underwent the most significant hydrolysis during the intestinal phase, resulting in the strongest angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) inhibition. Following in vitro GI peptide absorption using a Caco-2 cell monolayer, the GI peptide derived from the cooked loin demonstrated greater bioavailability and a higher degree of ACE and DPP-IV inhibition than the shoulder peptide.

CONCLUSION

This study highlights the potential of goat meat, particularly cooked loin, as a functional meat source for protein, essential amino acids, and bioactive peptides during GI digestion and absorption. These peptides promise to play a role in preventing and treating metabolic diseases due to their dual inhibitory effects on ACE and DPP-IV.

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

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

The modulatory effects on enterohepatic cholesterol metabolism of novel cholesterol-lowering peptides from gastrointestinal digestion of Xuanwei ham

The aim of this study was to investigate the effects and mechanism of in vitro protein digestive products of Xuanwei ham with different ripening periods on cholesterol metabolism and hypercholesterolemia. The results showed that compared with other gastrointestinal digestion (GID) groups, the GID group of Xuanwei ham with 3-year ripening period (XWH3-GID) inhibited the expression of Niemann-Pick C1-like 1 (NPC1L1) and acetyl-CoA acetyltransferase 2 (ACAT2) through hepatocyte nuclear factor 1-alpha (HNF-1α), which in turn effectively inhibited cholesterol absorption in Caco-2 cell monolayers. Following absorption by Caco-2 cell monolayers, the XWH3-GID group suppressed the expression and secretion of proprotein convertase subtilisin/kexin type 9 (PCSK9) via HNF-1α, which enhanced the protein expression and fluorescence intensity of low density lipoprotein receptor (LDLR) on the HepG2 cell membrane, and thus promoted the uptake of low density lipoprotein (LDL). Importantly, three novel peptides (LFP, PKF and VPFP) derived from titin were identified after intestinal epithelial transport in the XWH3-GID group, which could exert cholesterol-lowering effects through inhibiting intestinal cholesterol absorption and promoting peripheral hepatic LDL uptake, and effectively ameliorate western diet-induced hypercholesterolemia in ApoE-/- mice. These results suggest that Xuanwei ham with 3-year ripening period can be used as a source of cholesterol-lowering peptides and has potential to intervene in hypercholesterolemia.

Angiotensin I-Converting Enzyme Inhibitory Activity of Two Peptides Derived from In Vitro Digestion Products of Pork Sausage with Partial Substitution of NaCl by KCl

This study aimed to identify angiotensin I-converting enzyme (ACE) from in vitro digestion products of pork sausage with partial substitution of NaCl by KCl (PSRK). Peptides from in vitro digestion products of PSRK were identified through liquid chromatography with tandem mass spectrometry analysis coupled with de novo sequencing. Subsequently, the ACE inhibitory peptides LIVGFPAYGH and IVGFPAYGH were screened based on PeptideRanker, in silico absorption, molecular docking, and the determination of ACE inhibitory activity. In addition, the ACE inhibitory peptides LIVGFPAYGH and IVGFPAYGH were mixed-type inhibitors; these peptides' ACE inhibitory activities were expressed as the 50% inhibitory concentration (IC₅₀) values in vitro, which were 196.16 and 150.88 μM, respectively. After 2 h of incubation, LIVGFPAYGH and IVGFPAYGH could be transported through Caco-2 cell monolayers with paracellular passive diffusion. Furthermore, LIVGFPAYGH and IVGFPAYGH significantly increased the levels of ACE2 and nitric oxide while decreasing the levels of ACE, angiotensin II, and endothelin-1 in Ang I-treated human umbilical vein endothelial cells, indicating the ACE inhibitory effect of LIVGFPAYGH and IVGFPAYGH. In summary, LIVGFPAYGH and IVGFPAYGH from PSRK can be used as functional foods with antihypertensive activity.

Characterization of the fruit proteolytic system of Bromelia serra Griseb. (Bromeliaceae) and its application in bioactive peptides release

A crude extract with proteolytic activity was prepared from edible fruits of Bromelia serra, containing cysteine peptidases with molecular masses between 24.1 and 25.9 kDa. The extract presented an optimal pH range of 6.03-9.05, retained more than 80% of activity after thermal pre-treatments at 23, 37, and 45°C (120 min), but it was rapidly inactivated after 10 min at 75°C. These proteases were employed to hydrolyze soybean proteins, bovine casein and bovine whey, achieving degrees of hydrolysis of 18.3 ± 0.6, 29.1 ± 0.7, and 12.6 ± 0.9% (55°C, 180 min), respectively. The casein 180 min-hydrolysate (55°C) presented the maximum value of antioxidant activity (2.89 ± 0.12 mg/mL Trolox), and the whey protein 180 min-hydrolysate (55°C) showed the highest percentage of angiotensin-converting enzyme inhibition (91.9 ± 1.2%). This low-cost enzymatic preparation would be promising for the food industry because it requires mild working conditions and yields hydrolysates with biological activities useful as ingredients for functional food. PRACTICAL APPLICATION: Proteolytic enzymes are employed in the food industry in a wide variety of processes since they modify the properties of proteins causing beneficial effects such as improvement digestibility, diminution of allergenicity, and release of bioactive peptides. Fruits from Bromelia serra possess cysteine peptidases that could be used in food biotechnology because they are capable to hydrolyze soybean and milk proteins by mild working conditions and to provoke the release of bioactive peptides. These hydrolysates containing antioxidative and ACE-inhibitor activities would be useful as ingredients for functional foods or as nutraceuticals, which are nowadays two products highly required by consumers.

Antihypertensive activity of the ACE-renin inhibitory peptide derived from Moringa oleifera protein

Moringa oleifera (MO) leaf is a potential plant protein resource with high nutritional and medicinal value. The study aims to investigate the hypotensive activity and stability of MO leaf peptides. MO leaf protein was extracted and then hydrolyzed with Alcalase to produce the MO leaf protein hydrolysate (MOPH). The MOPH was separated into peptide fractions with different molecular weights by membrane ultrafiltration. The MOPH and ultrafiltration fractions were evaluated for antihypertensive activity. Inhibition of the angiotensin-converting enzyme (84.71 ± 0.07%) and renin (43.72 ± 0.02%) was significantly higher for <1 kDa peptides when compared to other fractions. Oral administration of the <1 kDa component in spontaneously hypertensive rats positively lowers the blood pressure (∼17 mmHg). The <1 kDa component was isolated and purified subsequently; the final active component was identified by mass spectrometry and amino acid sequence analysis. Two highly active ACE (angiotensin-converting enzyme) and renin dual inhibitory peptides Leu-Gly-Phe-Phe (LGF) and Gly-Leu-Phe-Phe (GLFF) were obtained. The two peptides exhibited a good dual inhibitory activity of ACE and renin with IC50 values of LGF (0.29 ± 0.13 mM, 1.88 ± 0.08 mM) and GLFF (0.31 ± 0.04 mM, 2.80 ± 0.08 mM). Furthermore, in vivo models, LGF and GLFF significantly reduced the systolic blood pressure (19.4 mmHg; 18.2 mmHg) and diastolic blood pressure (12 mmHg; 13.8 mmHg) of SHRs (spontaneously hypertensive rats). The peptide transmembrane transport experiments and simulated gastrointestinal digestion experiments with LGF and GLFF showed that they can resist gastrointestinal digestion in a complete form. Thus, bioactive peptides from MO leaf may possess the potential to be used for treating hypertension in humans.

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.

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

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

Purification and identification of novel antioxidant peptides from silver carp muscle hydrolysate after simulated gastrointestinal digestion and transepithelial transport

Unregulated oxidative reactions occur in human body or food system can cause harmful effects both on food quality and human health. This study aimed to develop novel antioxidant peptides from silver carp muscle hydrolysate after simulated gastrointestinal digestion and transepithelial transport. Results showed that alcalase- and papain-induced hydrolysates had higher antioxidant activities before and after in vitro gastrointestinal digestion. Fractions with molecular weight <1 kDa from these two digestive products (named A-GID-1 and P-GID-1) exhibited the greatest antioxidant capacity, which was ascribed to the large proportion of low-molecular peptides and hydrophobic amino acids. After transepithelial transport analysis, a total of ten peptides were identified from the RP-HPLC fractions with the highest antioxidant activity from both P-GID-1 and A-GID-1 permeates. Among them, LVPVAVF exhibited the highest DPPH radical scavenging and reactive oxygen species (ROS) inhibitory activity. Our findings will provide new knowledge for the development of novel natural antioxidants and the high-value utilization of silver carp protein.

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.

Current genetic engineering strategies for the production of antihypertensive ACEI peptides

Hypertension is a major and highly prevalent risk factor for various diseases. Among the most frequently prescribed antihypertensive first-line drugs are synthetic angiotensin I-converting enzyme inhibitors (ACEI). However, since  their use in hypertension therapy has been linked to various side effects, interest in the application of food-derived ACEI peptides (ACEIp) as antihypertensive agents is rapidly growing. Although promising, the industrial production of ACEIp through conventional methods such as chemical synthesis or enzymatic hydrolysis of food proteins has been proven troublesome. We here provide an overview of current antihypertensive therapeutics, focusing on ACEI, and illustrate how biotechnology and bioengineering can overcome the limitations of ACEIp large-scale production. Latest advances in ACEIp research and current genetic engineering-based strategies for heterologous production of ACEIp (and precursors) are also presented. Cloning approaches include tandem repeats of single ACEIp, ACEIp fusion to proteins/polypeptides, joining multivariate ACEIp into bioactive polypeptides, and producing ACEIp-containing modified plant storage proteins. Although bacteria have been privileged ACEIp heterologous hosts, particularly when testing for new genetic engineering strategies, plants and microalgae-based platforms are now emerging. Besides being generally safer, cost-effective and scalable, these "pharming" platforms can perform therelevant posttranslational modifications and produce (and eventually deliver) biologically active protein/peptide-based antihypertensive medicines.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

From biomedicinal to in silico models and back to therapeutics: a review on the advancement of peptidic modeling

Bioactive peptides participate in numerous metabolic functions of living organisms and have emerged as potential therapeutics on a diverse range of diseases. Albeit peptide design does not go without challenges, overwhelming advancements on in silico methodologies have increased the scope of peptide-based drug design and discovery to an unprecedented amount. Within an in silico model versus an experimental validation scenario, this review aims to summarize and discuss how different in silico techniques contribute at present to the design of peptide-based molecules. Published in silico results from 2014 to 2018 were selected and discriminated in major methodological groups, allowing a transversal analysis, promoting a landscape vision and asserting its increasing value in drug design.

Comparative peptidomic profile and bioactivities of cooked beef, pork, chicken and turkey meat after in vitro gastro-intestinal digestion

This study was designed to investigate the potential contribution of bioactive peptides to the biological activities related to the consumption of pork, beef, chicken and turkey meat following in vitro gastro-intestinal digestion. After extraction of the peptidic fractions from digested samples, the bioactivities were evaluated by in vitro antioxidant activity as well as angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) inhibition assays. Pork and turkey meat appeared to be the best sources of antioxidant peptides. Pork was found to be the best source of DPP-IV-inhibitory peptides whereas chicken meat supplied peptides with the highest ACE-inhibitory activity. The comprehensive analysis of the peptidomic profile of digested samples was performed by nano-LC-ESI-QTOF MS/MS analysis. A total of 217, 214, 257 and 248 peptides were identified in digested pork, beef, chicken and turkey meat, respectively. Chicken and turkey meat showed the highest similarity in peptide sequences with 202 common peptides. Sixty-two peptides matched with sequences with previously demonstrated biological activity. In particular, 35 peptides showed ACE-inhibitory activity and 23 DPP-IV inhibitory activity. Twenty-two bioactive peptides were commonly released from the different types of meat. The relative amount of identified bioactive peptides were positively correlated to the biological activities of the different digested meats. BIOLOGICAL SIGNIFICANCE: The present study describes for the first time a comprehensive peptide profile of four types of meat after in vitro gastro-intestinal digestion. The peptide inventory was used to identify 62 bioactive peptides with ACE- and DPPIV-inhibitory and antioxidant activities. The bioactivity analysis revealed interesting and significant differences between the studied meats. The originality of this work lay in the description of intrinsic differences in physiological functions after the ingestion of meat proteins from different species. In a context in which the current research scene relates meat consumption to the onset of chronic pathologies, this peptide profiling and bioactivity analysis shed light on the possible health benefits of peptides released from meat proteins. In fact, this paper represents a sort of detailed peptide list that may help to predict which peptides could be generated after meat intake and detectable at gastro-intestinal level. It also provides a thorough investigation of novel biological activities associated to meat protein hydrolysates, giving a new positive aspect to meat consumption.

In Vitro and in Vivo Studies on the Angiotensin-Converting Enzyme Inhibitory Activity Peptides Isolated from Broccoli Protein Hydrolysate

In the present study we purified and identified peptides from broccoli protein hydrolysates and evaluated their angiotensin-converting enzyme (ACE) inhibitory activity in vitro and hypotensive effect in vivo. Three ACE inhibitory peptides were isolated and identified as IPPAYTK, LVLPGELAK, and TFQGPPHGIQVER, and their inhibitory IC₅₀ values were 23.5, 184.0, and 3.4 μM, respectively. We then investigated the effect of gastrointestinal digestion on ACE inhibitory activity. We detected almost two times the ACE inhibitory activity of the peptide LVLPGELAK following simulated digestion than prior to digestion. LVLPGE and LAK, two novel peptides exhibiting high ACE inhibitory activity, were discovered following digestion and possessed IC₅₀ values of 13.5 and 48.0 μM, respectively. The hypotensive effect of the peptides was assessed after oral administration to spontaneous hypertensive rats (SHRs). We found that LVLPGE and LAK demonstrated a significant hypotensive effect in vivo. Protein from broccoli may thus constitute a potential antihypertensive peptide source.

A Novel Natural Influenza A H1N1 Virus Neuraminidase Inhibitory Peptide Derived from Cod Skin Hydrolysates and Its Antiviral Mechanism

In this paper, a novel natural influenza A H1N1 virus neuraminidase (NA) inhibitory peptide derived from cod skin hydrolysates was purified and its antiviral mechanism was explored. From the hydrolysates, novel efficient NA-inhibitory peptides were purified by a sequential approach utilizing an ultrafiltration membrane (5000 Da), sephadex G-15 gel column and reverse-phase high-performance liquid chromatography (RP-HPLC). The amino acid sequence of the pure peptide was determined by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) was PGEKGPSGEAGTAGPPGTPGPQGL, with a molecular weight of 2163 Da. The analysis of the Lineweacer–Burk model indicated that the peptide was a competitive NA inhibitor with Ki of 0.29 mM and could directly bind free enzymes. In addition, docking studies suggested that hydrogen binding might be the driving force for the binding affinity of PGEKGPSGEAGTAGPPGTPGPQGL to NA. The cytopathic effect reduction assay showed that the peptide PGEKGPSGEAGTAGPPGTPGPQGL protected Madin–Darby canine kidney (MDCK) cells from viral infection and reduced the viral production in a dose-dependent manner. The EC₅₀ value was 471 ± 12 μg/mL against H1N1. Time-course analysis showed that PGEKGPSGEAGTAGPPGTPGPQGL inhibited influenza virus in the early stage of the infectious cycle. The virus titers assay indicated that the NA-inhibitory peptide PGEKGPSGEAGTAGPPGTPGPQGL could directly affect the virus toxicity and adsorption by host cells, further proving that the peptide had an anti-viral effect with multiple target sites. The activity of NA-inhibitory peptide was almost inactivated during the simulated in vitro gastrointestinal digestion, suggesting that oral administration is not recommended. The peptide PGEKGPSGEAGTAGPPGTPGPQGL acts as a neuraminidase blocker to inhibit influenza A virus in MDCK cells. Thus, the peptide PGEKGPSGEAGTAGPPGTPGPQGL has potential utility in the treatment of the influenza virus infection.

Novel Natural Angiotensin Converting Enzyme (ACE)-Inhibitory Peptides Derived from Sea Cucumber-Modified Hydrolysates by Adding Exogenous Proline and a Study of Their Structure⁻Activity Relationship

Natural angiotensin converting enzyme (ACE)-inhibitory peptides, which are derived from marine products, are useful as antihypertensive drugs. Nevertheless, the activities of these natural peptides are relatively low, which limits their applications. The aim of this study was to prepare efficient ACE-inhibitory peptides from sea cucumber-modified hydrolysates by adding exogenous proline according to a facile plastein reaction. When 40% proline (w/w, proline/free amino groups) was added, the modified hydrolysates exhibited higher ACE-inhibitory activity than the original hydrolysates. Among the modified hydrolysates, two novel efficient ACE-inhibitory peptides, which are namely PNVA and PNLG, were purified and identified by a sequential approach combining a sephadex G-15 gel column, reverse-phase high-performance liquid chromatography (RP-HPLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS), before we conducted confirmatory studies with synthetic peptides. The ACE-inhibitory activity assay showed that PNVA and PNLG exhibited lower IC₅₀ values of 8.18 ± 0.24 and 13.16 ± 0.39 μM than their corresponding truncated analogs (NVA and NLG), respectively. Molecular docking showed that PNVA and PNLG formed a larger number of hydrogen bonds with ACE than NVA and NLG, while the proline at the N-terminal of peptides can affect the orientation of the binding site of ACE. The method developed in this study may potentially be applied to prepare efficient ACE-inhibitory peptides, which may play a key role in hypertension management.