Exploration of the molecular interactions between angiotensin-I-converting enzyme (ACE) and the inhibitory peptides derived from hazelnut (Corylus heterophylla Fisch.)

Probiotic survival, biological functionality and untargeted metabolomics of the bioaccessible compounds in fermented camel and bovine milk after in vitro digestion

This study investigated probiotic survival and biological functionality of the bioaccessible fraction of fermented camel milk (FCM) and fermented bovine milk (FBM) after in vitro digestion. Furthermore, untargeted metabolomic analysis was performed to identify the bioaccessible compounds in FCM and FBM, which were produced using starter bacteria (SC), a potential probiotic (Pro) or a combination thereof (SC + Pro), followed by storage (21 d). Survival of Pro and SC + Pro bacteria in FCM was higher than in FBM throughout in vitro digestion. The antioxidant activities of the bioaccessible fractions differed slightly between culture types, whereas the antiproliferative activity of SC was highest, followed by SC + Pro. Antiproliferative activity of the bioaccessible fractions of FCM was greater than for FBM. Untargeted metabolomics of FCM demonstrated discrimination between cultures and from FBM. FCM produced with SC + Pro and Pro had closer clustering than with SC. The bioaccessible fraction of FCM exhibited higher biological functionality compared to FBM.

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.

Molecular dynamics investigation on the interaction of human angiotensin-converting enzyme with tetrapeptide inhibitors

Angiotensin-converting enzyme (ACE) is a well-known zinc metalloenzyme whose physiological functions are vital to blood pressure regulation and management of hypertension. The development of more efficient peptide inhibitors is of great significance for the prevention and treatment of hypertension. In this research, molecular dynamics (MD) simulations were implemented to study the specific binding mechanism and interaction between human ACE (hACE) and tetrapeptides, YIHP, YKHP, YLVR, and YRHP. The calculation of relative binding free energy on the one hand verified that YLVR, an experimentally identified inhibitor, has a stronger inhibitory effect and, on the other hand, indicated that YRHP is the "best" inhibitor with the strongest binding affinity. Inspection of atomic interactions discriminated the specific binding mode of each tetrapeptide inhibitor with hACE and explained the difference of their affinity. Moreover, in-depth analysis of the MD production trajectories, including clustering, principal component analysis, and dynamic network analysis, determined the dynamic correlation between tetrapeptides and hACE and obtained the communities' distribution of a protein-ligand complex. The present study provides essential insights into the binding mode and interaction mechanism of the hACE-peptide complex, which paves a path for designing effective anti-hypertensive peptides.

Novel ACE Inhibitory Peptides Derived from Yeast Hydrolysates: Screening, Inhibition Mechanisms and Effects on HUVECs

The antihypertensive activity of yeast hydrolysate (YH) was confirmed in our previous study. However, the critical peptides in YH and the underlying mechanisms have not been fully elucidated. This study aimed to explore the angiotensin-converting enzyme (ACE) inhibitory peptides in YH and illustrate their molecular and cellular mechanisms. The potential of YH-derived peptides was evaluated by in silico methods, followed by in vitro verification. A new competitive ACE inhibitory peptide, VIPVPFF (V7), with an IC₅₀ value of 10.27 μM, was screened. YH and V7 increased the nitric oxide (NO) levels, upregulated GUCY1A1 gene expression (approximately 15-fold), and functioned in several hypertension-related pathways in human umbilical vein endothelial cells (HUVECs). This study revealed the antihypertensive mechanisms of YH and V7, laying down a theoretical basis for their application.

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.

Antihypertensive effect of quinoa protein under simulated gastrointestinal digestion and peptide characterization

BACKGROUND

Quinoa protein is a potential source of bioactive peptides. Although some studies have demonstrated its angiotensin converting enzyme (ACE) inhibitory properties, research into its in vivo effect on blood-pressure regulation and peptide characterization remains limited.

RESULTS

Quinoa protein hydrolyzate (QPH) was prepared by simulated gastrointestinal digestion. QPH lowered the systolic blood pressure (SBP) and diastolic blood pressure (DBP) in spontaneously hypertensive model rats (SHRs) from 2 h to10 h after oral administration, effectively controlling blood pressure in these SHRs. An in vitro study showed that QPH is capable of inhibiting ACE activity. This was attributed to the activity of a number of low-molecular-weight peptides. With relatively high scores predicted by PeptideRanker, three promising bioactive peptides, FHPFPR, NWFPLPR, and NIFRPF, were further studied and their ACE-inhibition effects were confirmed with IC₅₀ values of 34.92, 16.77, and 32.40 μM, respectively. A molecular docking study provided insights into the binding of ACE with peptides, and revealed that the presence of specific amino acids in the peptide sequence (Pro, Phe, and Arg at the C-terminal, and Asn at the N-terminal) could contribute to the interaction between ACE and peptides.

CONCLUSION

These results demonstrated the potential of QPH for the management of hypertension, which indicates that it could be a good candidate for inclusion in functional foods to control high blood pressure. © 2020 Society of Chemical Industry.

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

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

Identification of chia seed (Salvia hispanica L.) peptides with enzyme inhibition activity towards skin-aging enzymes

Chia (Salvia hispanica) seed peptides have drawn attention because of their antioxidant, antihypertensive and anti-inflammatory activities, making them ideal candidates for development of cosmeceutical skin products. However, there are no preceding reports that address their aging-related enzyme inhibitory activities. The aim of this study was to investigate the in vitro and in silico inhibitory activity of chia seed peptides towards the main aging-related enzymes. Enzyme-inhibition activity of < 3 kDa chia seed peptides towards collagenase, hyaluronidase, tyrosinase, and elastase was evaluated. Further fractions were obtained by size exclusion chromatography (SEC) and re-tested for enzyme inhibitory activity. Peptide sequences were identified from the most effective fraction and used for in silico analysis. The < 3 kDa peptides exhibited inhibitory activities towards elastase (65.32%, IC₅₀ = 0.43 mg/mL), tyrosinase (58.74%, IC₅₀ = 0.66 mg/mL), hyaluronidase (26.96%, IC₅₀ = 1.28 mg/mL), and collagenase (28.90%, IC₅₀ = 1.41 mg/mL). They showed mixed-type inhibition patterns towards elastase and hyaluronidase, while a non-competitive inhibition pattern was observed towards collagenase and tyrosinase. Fraction II obtained by SEC, showed higher enzyme inhibitory activity. Seven peptides were identified in this fraction (APHWYTN, DQNPRSF, GDAHWAY, GDAHWTY, GDAHWVY, GFEWITF, and KKLKRVYV), which according to in silico analysis, possess 19-29 enzyme-peptide pair interactions towards elastase and three peptide sequences shared homology sequence (GDAHW). These results demonstrate that peptides from chia seeds may contribute in the improvement of skin health by offering protection against aging-related enzymes by preventing degradation of the protein matrix on the skin; however, further in vivo studies are needed to evaluate its actual capability.

Anti-hypertensive and angiotensin-converting enzyme inhibitory effects of Radix Astragali and its bioactive peptide AM-1

ETHNOPHARMACOLOGICAL RELEVANCE

Hypertension is one of the common chronic health problems in the world. Astragalus membranaceus root (AM), also known as Huangqi, is a popular medicinal herb traditionally used to reinforce vital energy and modulate hypertension.

AIM OF THE STUDY

This study was to reveal the anti-hypertensive activities and mechanisms of AM in spontaneously hypertensive rats (SHRs). Moreover, the presence of bioactive components in AM was further identified.

MATERIALS AND METHODS

We analyzed the effects of aqueous extract of AM (AME) on the regulation of blood pressure and angiotensin converting enzyme (ACE), the major target of anti-hypertensive drugs. Proteomic, bioinformatics, and docking analyses were performed to identify the anti-hypertensive bioactive peptides in AME.

RESULTS

Our data showed that AME inhibited ACE activities in a dose-dependent manner, with an IC₅₀ of 1.85 ± 0.01 μg/ml. In comparison with mock, oral administration of AME reduced systolic blood pressure (SBP) levels in SHRs, and the level of SBP was decreased by 22.33 ± 3.61 mmHg at 200 mg/kg AME. Proteomic analysis identified that an abundant 152-amino-acid putative protein kinase fragment accounted for approximately 11.7% of protein spots in AME. AM-1 (LVPPHA), a gastrointestinal enzyme-resistant peptide cleaved from putative protein kinase fragment, inhibited ACE activities, with an IC₅₀ value of 414.88 ± 41.88 μM. Moreover, oral administration of AM-1 significantly decreased SBP levels by 42 ± 2.65 mmHg at 10 μmol/kg. Docking analysis further showed that AM-1 docked into the active site channel of ACE and interacted with Ala-354 in the active site pocket of ACE.

CONCLUSIONS

the ACE inhibitory effect of AM and the presence of ACE inhibitory phytopeptide in AME supported the ethnomedical use of AM on hypertension.

Tryptophan targeted pulsed electric field treatment for enhanced immune activity in pine nut peptides

To investigate immune activity of pine nut peptides treated by PEF technology and mechanism of targeting immunoactive sitesits, immune regulatory active was evaluated by RAW 264.7 cells model and the structures of pine nut peptides were researched by fluorescence, CD, and 1D/2D NMR spectrum. These consequences showed the ability of macrophages to phagocytosis neutral red and the production of nitric oxide (NO) were improved after PEF treatment. KWFCT treated by PEF treatment with 40 kV/cm obtained the best immunocompetence. The CD spectroscopy showed that PEF could transform the secondary structures of pine nut peptides. The short-range correlation between C_γ H (1.65 ppm) and C_α H (3.35 ppm), and long-range correlation between C_α H (3.37 ppm) and N_α H (8.07 ppm) were enhanced by PEF treatment. PEF treatment of tryptophan in the pine nut peptides enhanced the immunological activity of the pine nut peptides. PRACTICAL APPLICATIONS: Bioactive peptides derived from food proteins have been extensively studied in recent years. However, little research has been done on the immunoactive peptide of pine nut source. PEF treatment is promising for improving certain properties of foods while maintaining the flavor, color, taste, and nutritional value of the food. This research demonstrated that PEF treatment increased the immunological activity of KWFCT and KWFM. The primary structure of KWFCT and KWFM did not change after PEF treatment, but the secondary structure was transformed into each other. A new perspective on the PEF action site is proposed, which is beneficial to the application of PEF technology.

Immobilized metal affinity chromatography matrix modified by poly (ethylene glycol) methyl ether for purification of angiotensin I-converting enzyme inhibitory peptide from casein hydrolysate

Purification of small bioactive peptides from complex biological samples is a difficult task due to the interference of concentrated large biomolecules. In this study, a magnetic immobilized metal affinity chromatography matrix modified by poly (ethylene glycol) methyl ether (IMACM@mPEG) was prepared and applied for the rapid purification of angiotensin I-converting enzyme (ACE) inhibitory peptides from casein hydrolysate. The proposed IMACM@mPEG considerably reduced the non-specific adsorption of large proteins and exhibited improved purification efficiency towards ACE inhibitory peptides. A novel peptide with moderate ACE inhibitory activity (IC₅₀ value of 274 ± 5 μM) was identified as LLYQEPVLGPVR. Lineweaver-Burk plot confirmed the non-competitive inhibition pattern of LLYQEPVLGPVR. The purified peptide was digested after simulated gastrointestinal digestion and produced shorter peptides which contributed to enhanced ACE inhibitory activity. These results indicated that the IMACM@mPEG is an effective method for the prepurification of ACE inhibitory peptide and the purified peptide LLYQEPVLGPVR may have potential as nutraceutical ingredient in functional foods for hypertension treatments.

Considerations for Docking of Selective Angiotensin-Converting Enzyme Inhibitors

The angiotensin-converting enzyme (ACE) is a two-domain dipeptidylcarboxypeptidase, which has a direct involvement in the control of blood pressure by performing the hydrolysis of angiotensin I to produce angiotensin II. At the same time, ACE hydrolyzes other substrates such as the vasodilator peptide bradykinin and the anti-inflammatory peptide N-acetyl-SDKP. In this sense, ACE inhibitors are bioactive substances with potential use as medicinal products for treatment or prevention of hypertension, heart failures, myocardial infarction, and other important diseases. This review examined the most recent literature reporting ACE inhibitors with the help of molecular modeling. The examples exposed here demonstrate that molecular modeling methods, including docking, molecular dynamics (MD) simulations, quantitative structure-activity relationship (QSAR), etc, are essential for a complete structural picture of the mode of action of ACE inhibitors, where molecular docking has a key role. Examples show that too many works identified ACE inhibitory activities of natural peptides and peptides obtained from hydrolysates. In addition, other works report non-peptide compounds extracted from natural sources and synthetic compounds. In all these cases, molecular docking was used to provide explanation of the chemical interactions between inhibitors and the ACE binding sites. For docking applications, most of the examples exposed here do not consider that: (i) ACE has two domains (nACE and cACE) with available X-ray structures, which are relevant for the design of selective inhibitors, and (ii) nACE and cACE binding sites have large dimensions, which leads to non-reliable solutions during docking calculations. In support of the solution of these problems, the structural information found in Protein Data Bank (PDB) was used to perform an interaction fingerprints (IFPs) analysis applied on both nACE and cACE domains. This analysis provides plots that identify the chemical interactions between ligands and both ACE binding sites, which can be used to guide docking experiments in the search of selective natural components or novel drugs. In addition, the use of hydrogen bond constraints in the S₂ and S₂′ subsites of nACE and cACE are suggested to guarantee that docking solutions are reliable.

ACE inhibitory peptides derived from de-fatted lemon basil seeds: optimization, purification, identification, structure–activity relationship and molecular docking analysis

The study determines optimized process conditions to maximize ACE inhibitory peptide production. The two novel hexa-peptides (LGRNLPPI and GPAGPAGL) from de-fatted lemon basil seeds (DLBS) was achieved.

Peptides from walnut (Juglans mandshurica Maxim.) protect hepatic HepG2 cells from high glucose-induced insulin resistance and oxidative stress

Schematic of the mechanism underlying the protection of hepatic HepG2 cells against high glucose-induced insulin resistance and oxidative stress by walnut-derived peptides.

Isolation and Characterization of Angiotensin Converting Enzyme Inhibitory Peptides from Peach Seed Hydrolysates: In Vivo Assessment of Antihypertensive Activity

A peptide fraction with molecular masses below 3 kDa (PSH-3 kDa) from a peach seed hydrolysate demonstrated high angiotensin converting enzyme (ACE) inhibitory activity (concentration to inhibit 50% ACE (IC₅₀) = 16.4 μg/mL) in our previous work. This work proposes a further study of this highly active fraction. RP-HPLC enabled two fractions (F3 and F4) with high inhibitory activity (IC₅₀ = 2.0 ± 0.5 and 1.2 ± 0.2 μg/mL, respectively) to be isolated. Peptide analysis by LC-Q-TOF-MS/MS using reverse-phase and hydrophilic interaction chromatography enabled 33 peptides within both fractions to be identified. Among them, peptide isoleucine-tyrosine-serine-proline-histidine (IYSPH) showed the highest capacity. The lack of cytotoxicity of peptides was demonstrated in three different cell lines (HeLa, HT-29, and HK-2). Oral administration of PSH-3 kDa fraction or peptide IYSPH caused a significant systolic blood pressure reduction (-30 mmHg) on spontaneously hypertensive rats after 3-6 h treatment.

Evaluation and structure-activity relationship analysis of antioxidant shrimp peptides

The effects of amino acids Gln and Lys on the antioxidant ability of peptides were investigated in this study. The identified peptides Lys-Met-Asp-Asp-Lys (KMDDK), Lys-Met-Asp-Asp-Gln (KMDDQ), Gln-Met-Asp-Asp-Lys (QMDDK), and Gln-Met-Asp-Asp-Gln (QMDDQ) were used to investigate their antioxidant activity and the structure-activity relationship by using UPLC-Q-TOF-MS, flow cytometry, laser scanning confocal microscopy and ¹H NMR spectroscopy. The results indicated that the four pentapeptides significantly increased the viability of PC12 cells and inhibited cell apoptosis and that QMDDQ possessed a stronger survival activity than the others in cell apoptosis. Moreover, the four peptides significantly decreased the scopolamine-induced ROS and LDH content in PC12 cells, and upregulated the SOD activity to the level of the scopolamine group. The DPPH and hydroxyl radical scavenging of QMDDQ were higher than those of the other peptides at 0.5 mg mL^-1 and 1.0 mg mL^-1 (P < 0.05). ¹H NMR spectra revealed that the prominent antioxidant ability of QMDDQ might be attributed to more active hydrogen sites and functional groups. The carboxyl active hydrogen atoms and amino active hydrogen atoms as active sites play a critical role in the antioxidant capacity.

Isolation and Characterization of Three Antihypertension Peptides from the Mycelia of Ganoderma Lucidum (Agaricomycetes)

Ganoderma lucidum (G. lucidum) has been widely used in Asia to treat hypertension, but the active substances responsible for its antihypertensive effects remain unclear. Using the well-established angiotensin I-converting enzyme (ACE) as a target, we identified three ACE inhibitory peptides (ACEIPs), Gln-Leu-Val-Pro (QLVP), Gln-Asp-Val-Leu (QDVL), and Gln-Leu-Asp-Leu (QLDL), which account for the antihypertensive activity of G. lucidum. Notably, QLVP worked in a mixed-type manner against ACE with an IC₅₀ value of 127.9 μmol/L. Molecular dynamics simulation suggested that the potent charge energy of QLVP, which interacted with Gln242 and Lys472 of ACE via a hydrogen bond and a salt bridge, potentially contributed to ACE inhibitory activity. Moreover, QLVP markedly activated angiotensin I-mediated phosphorylation of endothelial nitric oxide synthase in human umbilical vein endothelial cells and partly reduced mRNA and protein expression of the vasoconstrictor factor endothelin-1. This is the first report of the antihypertensive activity of small ACEIPs originating from G. lucidum mycelia, paving the way for the possible application of these peptides as potent drug candidates for treating hypertension.

FeptideDB: A web application for new bioactive peptides from food protein

BACKGROUND

Bioactive peptides derived from food are important sources for alternative medicine and possess therapeutic activity. Several biochemical methods have been achieved to isolate bioactive peptides from food, which are tedious and time consuming. In silico methods are an alternative process to reduce cost and time with respect to bioactive peptide production. In this paper, FeptideDB was used to collect bioactive peptide (BP) data from both published research articles and available bioactive peptide databases. FeptideDB was developed to assist in forecasting bioactive peptides from food by combining peptide cleavage tools and database matching. Furthermore, this application was able to predict the potential of cleaved peptides from 'enzyme digestion module' to identify new ACE (angiotensin converting enzyme) inhibitors using an automatic molecular docking approach.

RESULTS

The FeptideDB web application contains tools for generating all possible peptides cleaved from input protein by various available enzymes. This database was also used for analysis and visualization to assist in bioactive peptide discovery. One module of FeptideDB has the ability to create 3-dimensional peptide structures to further predict inhibitors for the target protein, ACE (angiotensin converting enzyme).

CONCLUSIONS

FeptideDB is freely available to researchers who are interested in exploring bioactive peptides. The FeptideDB interface is easy to use, allowing users to rapidly retrieve data based on desired search criteria. FeptideDB is freely available at http://www4g.biotec.or.th/FeptideDB/. Ultimately, FeptideDB is a computational aid for assessing peptide bioactivities.

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.

Structural and molecular basis of angiotensin-converting enzyme by computational modeling: Insights into the mechanisms of different inhibitors

Angiotensin-I converting enzyme (ACE) is a two-domain dipeptidylcarboxypeptidase involved in regulating blood pressure via the kallikrein-kininand renin-angiotensin-aldosterone complex. Therefore, ACE is a key drug target for the treatment of cardiovascular system diseases. At present many works are focus on searching for new inhibitory peptides of ACE to control the blood pressure. In order to exploit the interactions between ACE and its inhibitors, molecular dynamics simulations were used. The results showed that (a) the secondary structures of the three inhibitor-protein complexes did not change significantly; (b) root-mean-square deviation (RMSD), radius of gyration (Rg), and solvent-accessible surface area (SASA) values of Leu-Ile-Val-Thr (LIVT)-ACE complexes were significantly higher than that of other systems; (c) the backbone movement of LIVT was vigorous in Asp300-Val350, compared with that in Tyr-Leu-Val-Pro-His (YLVPH) and Tyr-Leu-Val-Arg(YLVR), as shown by the center-of-mass distance; and (d) the backbone movement of Asp300-Val350 may contribute to the interaction between ACE and its inhibitors. Our theoretical results will be helpful to further the design of specific inhibitors of ACE.

Different Temperature Treatments of Millet Grains Affect the Biological Activity of Protein Hydrolyzates and Peptide Fractions

The objective of this study was to analyze millet protein hydrolyzates and peptide fractions with molecular mass under 3.0 kDa obtained from grains treated with different temperature values as inhibitors of angiotensin-converting enzyme (ACE), α-amylase, and α-glucosidase activity. The protein fractions were hydrolyzed in vitro in gastrointestinal conditions and the highest degree of hydrolysis was noted for globulin 7S obtained from control grains (98.33%). All samples were characterized by a high peptide bioaccessibility index, which was 23.89 for peptides obtained from globulin 11S after treatment with 100 °C. The highest peptide bioavailability index was noted for peptides obtained from globulin 11S after the treatment with 65 °C (2.12). The highest potential metabolic syndrome inhibitory effect was determined for peptide fractions obtained from the prolamin control (IC50 for ACE and α-amylase was 0.42 and 0.11 mg/mL, respectively) and after the 100 °C treatment (IC50 for ACE and α-glucosidase was 0.33 and 0.12 mg/mL, respectively) and from globulin 11S after the 65 °C treatment (IC50 0.38 and 0.05 for ACE and α-glucosidase, respectively). The effect of these samples on endothelial cell HECa10 was determined. The sequences of potential inhibitory peptides were identified as GEHGGAGMGGGQFQPV, EQGFLPGPEESGR, RLARAGLAQ, YGNPVGGVGH, and GNPVGGVGHGTTGT.

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

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

Three Novel ACE Inhibitory Peptides Isolated From Ginkgo biloba Seeds: Purification, Inhibitory Kinetic and Mechanism

Alcalase, dispase, trypsin, and flavourzyme were used to hydrolyze the extracted Ginkgo biloba seeds protein isolate (GPI). The Ginkgo protein hydrolyzates (GPHs) with the maximum degree of hydrolysis (DH) and ACE inhibitory activity were selected, and ultra-filtered to obtain components with different molecular weights (MW) (<1 kDa, 1-3, 3-5, and 5-10 kDa). The components with MW of <1 kDa showed better ACE inhibition (IC50:0.2227 mg/mL). Purification and identification by Sephadex G-15 gel chromatography and LC-MS/MS conferred three new potential ACE inhibitory peptides [TNLDWY (non-competitive suppression mode), IC50: 1.932 mM; RADFY (competitive inhibition modes), IC50:1.35 mM; RVFDGAV (competitive inhibition modes), IC50:1.006 mM]. Molecular docking depicting the inhibitory mechanism for ACE inhibitory peptides indicated that the peptides bound well to ACE and interacted with amino acid residues at the ACE active site.

In vitro effect of oxidized and reduced glutathione peptides on angiotensin converting enzyme purified from human plasma

Angiotensin converting enzyme (ACE, peptidyldipeptidase A, EC 3.4.15.1) plays an important role in the regulation of blood pressure. In this study, ACE was purified from human plasma by affinity chromatography in single step. The enzyme purified in 5367-fold from human plasma and specific activity was found to be 1208 EU/mg protein. The purity and molecular weight of ACE were determined by SDS-PAGE, which indicated two bands at around 60 kDa and 70 kDa on the gel. Effect of oxidized glutathione (GSSG) peptide and reduced glutathione (GSH) peptide on purified ACE activity were also investigated in which lisinopril was used as reference inhibitor. GSSG showed activation effect on ACE activity whereas GSH provided inhibition effect. In the lights of activity (%) versus activator graph for GSSG and activity (%) versus inhibitor graphs for GSH and lisinopril; IC₅₀ values for GSH and lisinopril were determined to be 16.2 μM and 0.781 nM, respectively. Type of inhibition for GSH and lisinopril from graph Lineweaver-Burk was found to be reversible non-competitive inhibition and K_i constants for GSH and lisinopril were calculated as 11.7 μM and 0.662 nM, respectively.

Antihypertensive Effects of Two Novel Angiotensin I-Converting Enzyme (ACE) Inhibitory Peptides from Gracilariopsis lemaneiformis (Rhodophyta) in Spontaneously Hypertensive Rats (SHRs)

A variety of biologically active products have been isolated from Gracilariopsis lemaneiformis. In the present study, two novel angiotensin-converting enzyme (ACE) inhibitory peptides, FQIN [M(O)] CILR, and TGAPCR, were screened and identified from G. lemaneiformis protein hydrolysates by LC-MS/MS. The IC50 values of FQIN [M(O)] CILR and TGAPCR were 9.64 ± 0.36 μM and 23.94 ± 0.82 μM, respectively. In the stability study, both peptides showed stabilities of pH, temperature, simulated gastrointestinal digestion, and ACE hydrolysis. The Lineweaver–Burk plot showed that the two peptides were noncompetitive inhibitors of ACE. Molecular docking simulated the intermolecular interactions of two peptides and ACE, and the two peptides formed hydrogen bonds with the active pockets of ACE. However, FQIN [M(O)] CILR was more closely linked to the active pockets of ACE, thereby exerting better ACE inhibition. Spontaneously hypertensive rats (SHRs) were studied with an oral dose of 10 mg/kg body weight. Both peptides reduced systolic blood pressure (SBP) and diastolic blood pressure (DBP) in SHRs, of which FQIN [M(O)] CILR was able to reduce the systolic blood pressure by 34 mmHg (SBP) (p < 0.05). Therefore, FQIN [M(O)] CILR was an excellent ACE inhibitory peptide.

Novel Angiotensin-Converting Enzyme Inhibitory Peptides Derived from Oncorhynchus mykiss Nebulin: Virtual Screening and In Silico Molecular Docking Study

Excessive concentrations of angiotensin-converting enzyme (ACE) can give rise to high blood pressure, and is harmful to the body. ACE inhibitory peptides from food proteins are considered good sources of function food. However, the preparation of ACE inhibitory peptides by classical method faces many challenges. Three novel ACE inhibitory peptides were identified by in silico methods, and showed potent activity against ACE in vitro. The simulation hydrolysis of nebulin was performed with ExPASy PeptideCutter program. Potential activity, solubility, and absorption, distribution, metabolism, excretion, and toxicity properties of generated peptides were predicted using program online. Molecular docking displayed that EGF, HGR, and VDF were docked into the S₁ and S₂ pockets of ACE. Meanwhile, Phe and Arg at the C-terminal enhance ACE affinity. The IC₅₀ values of EGF, HGR, and VDF were 474.65 ± 0.08, 106.21 ± 0.52, and 439.27 ± 0.09 μM, respectively. Three peptides EGF, HGR, and VDF from Oncorhynchus mykiss nebulin were identified, and the molecular mechanism between ACE and peptides was clarified using in silico methods. The results suggested that Oncorhynchus mykiss nebulin would be an attractive raw material of antihypertensive nutraceutical ingredients.

PRACTICAL APPLICATION

This study has shown the potential of Oncorhynchus mykiss nebulin as good sources for producing ACE inhibitory peptides. According to this finding, in silico approach is the feasible way for prediction and identification of food-derived ACE inhibitory peptides in emerging nutraceutical field.

Processing Optimization and Characterization of Angiotensin-Ι-Converting Enzyme Inhibitory Peptides from Lizardfish (Synodus macrops) Scale Gelatin

Hypertension can cause coronary heart disease. Synthetic angiotensin-converting enzyme (ACE) inhibitors are effective antihypertensive drugs but often cause side effects. The aim of this study was to prepare potential ACE inhibitors from scales. Gelatin was extracted from lizardfish scales. Then, scale gelatin was enzymolyzed to prepare ACE inhibitory peptides using response surface methodology. Proteolytic conditions after optimization were as follows: pH 7.0, enzyme substrate ratio 3.2%, temperature 47 °C, and proteolysis lasting 2 h and 50 min. The experimental ACE inhibitory activity under optimal conditions was 86.0 ± 0.4%. Among the 118 peptides identified from gelatin hydrolysates, 87.3% were hydrophilic and 93.22% had a molecular weight <2000 Da. Gelatin peptides had high stability upon exposure to high temperature and pH as well as gastrointestinal tract enzymes. Gelatin peptides showed an antihypertensive effect in spontaneously hypertensive rats at a dosage of 2 g/kg in the long-term experiments. A new ACE inhibitory peptide was isolated from gelatin hydrolysates, and was identified as AGPPGSDGQPGAK with an IC₅₀ value of 420 ± 20 μM. In this way, ACE inhibitory peptides derived from scale gelatin have the potential to be used as healthy ACE-inhibiting drug raw materials.