Structure–activity relationship of antioxidant dipeptides: Dominant role of Tyr, Trp, Cys and Met residues

Soybean meal peptide Gly-Thr-Tyr-Trp could protect mice from acute alcoholic liver damage: A study of protein-protein interaction and proteomic analysis

Alcoholic liver disease (ALD) is a serious health threat. Soybean meal peptide (SMP) supplementation may protect against this damage; however, the potential mechanism underlying the specific sequence of SMPs is unclear. Protein-protein interaction and proteomic analyses are effective methods for studying functional ingredients in diseases. This study aimed to investigate the potential mechanism of action of the peptide Gly-Thr-Tyr-Trp (GTYW) on ALD using protein-protein interaction and proteomic analyses. These results demonstrate that GTYW influenced the targets of glutathione metabolism (glutathione-disulfide reductase, glutathione S-transferase pi 1, and glutathione S-transferase mu 2). It also regulated the expression of targets related to energy metabolism and amino acid conversion (trypsin-2, cysteine dioxygenase type-1, and F6SJM7). Amino acid and lipid metabolisms were identified based on Gene Ontology annotation. These results indicate that GTYW might affect alcohol-related liver disease signaling pathways. This study provides evidence of the protective and nutritional benefits of SMPs in ALD treatment.

A Comparative Study of the Stability, Transport, and Structure-Activity Relationship of Round Scad Derived Peptides with Antineuroinflammatory Ability

Our previous study identified round scad neuroprotective peptides with different characteristics. However, the intrinsic relationship between their structure and bioactivity, as well as their bioavailability, remains unclear. The aim of this study is to elucidate the bioavailability of these peptides and their structure-activity relationship against neuroinflammation. Results showed that the SR and WCP peptides were resistant to gastrointestinal digestion. Additionally, peptides SR, WCP, and WCPF could transport Caco-2 monolayers as intact peptides. The permeability coefficients (Papp) of SR, WCP, and WCPF in Caco-2 monolayer were (1.53 ± 0.01) × 10-5, (2.12 ± 0.01) × 10-5, and (8.86 ± 0.03) × 10-7 cm/s, respectively. Peptides SR, WCP, and WCPF, as promising inhibitors of JAK2 and STAT3, could attenuate the levels of pro-inflammatory cytokines and regulate the NFκB and JAK2/STAT3 signaling pathway in LPS-treated BV-2 cells. WCPF exerted the highest anti-inflammatory activity. Moreover, bioinformatics, molecular docking, and quantum chemistry studies indicated that the bioactivity of SR was attributed to Arg, whereas those of WCP and WCPF were attributed to Trp. This study supports the application of round-scad peptides and deepens the understanding of the structure-activity relationship of neuroprotective peptides.

Identification, in silico selection, and mechanistic investigation of antioxidant peptides from corn gluten meal hydrolysate

Seven novel antioxidant peptides (AWF, LWQ, WIY, YLW, LAYW, LPWG, and LYFY) exhibiting a superior activity compared to trolox were identified through in silico screening. Among these, the four peptides (WIY, YLW, LAYW, and LYFY) displayed notably enhanced performance, with ABTS activity 2.58-3.26 times and ORAC activity 5.19-8.63 times higher than trolox. Quantum chemical calculations revealed that the phenolic hydroxyl group in tyrosine and the nitrogen-hydrogen bond in the indole ring of tryptophan serve as the critical sites for antioxidant activity. These findings likely account for the potent chemical antioxidant activity. The corn peptides also exerted a protective effect against AAPH-induced cytomorphologic changes in human erythrocytes by modulating the antioxidant system. Notably, LAYW exhibited the most pronounced cytoprotective effects, potentially due to its high content of hydrophobic amino acids.

Glutamine-derived peptides: Current progress and future directions

Glutamine, the most abundant amino acid in the body, plays a critical role in preserving immune function, nitrogen balance, intestinal integrity, and resistance to infection. However, its limited solubility and instability present challenges for its use a functional nutrient. Consequently, there is a preference for utilizing glutamine-derived peptides as an alternative to achieve enhanced functionality. This article aims to review the applications of glutamine monomers in clinical, sports, and enteral nutrition. It compares the functional effectiveness of monomers and glutamine-derived peptides and provides a comprehensive assessment of glutamine-derived peptides in terms of their classification, preparation, mechanism of absorption, and biological activity. Furthermore, this study explores the potential integration of artificial intelligence (AI)-based peptidomics and synthetic biology in the de novo design and large-scale production of these peptides. The findings reveal that glutamine-derived peptides possess significant structure-related bioactivities, with the smaller molecular weight fraction serving as the primary active ingredient. These peptides possess the ability to promote intestinal homeostasis, exert hypotensive and hypoglycemic effects, and display antioxidant properties. However, our understanding of the structure-function relationships of glutamine-derived peptides remains largely exploratory at current stage. The combination of AI based peptidomics and synthetic biology presents an opportunity to explore the untapped resources of glutamine-derived peptides as functional food ingredients. Additionally, the utilization and bioavailability of these peptides can be enhanced through the use of delivery systems in vivo. This review serves as a valuable reference for future investigations of and developments in the discovery, functional validation, and biomanufacturing of glutamine-derived peptides in food science.

Effects of hypo-osmotic stress on osmoregulation, antioxidant response, and energy metabolism in sea cucumber Holothuria moebii under desalination environment

With global climate changing, hypo-salinity events are increasing in frequency and duration because of continuous rainfall and freshwater inflow, which causes reduced cytosolic osmolarity and cellular stress responses in aquatic animals. Sea cucumbers are considered stenohaline because they lack osmoregulatory organs and are vulnerable to salinity fluctuations. In this study, we performed multiple biochemical assays, de novo transcriptomics, and widely targeted metabolomics to comprehensively explore the osmoregulatory mechanisms and physiological responses of sea cucumber Holothuria moebii to hypo-osmotic stress, which is a representative specie that is frequently exposed to hypo-saline intertidal zones. Our results found that H. moebii contracted their ambulacral feet and oral tentacles, and the coelomic fluid ion concentrations were reduced to be consistent with the environment. The microvilli of intestines and respiratory trees underwent degeneration, and the cytoplasm exhibited swelling and vacuolation. Moreover, the Na+, K+, and Cl- concentrations and Na+/K+-ATPase activity were significantly reduced under hypo-osmotic stress. The decrease in protein kinase A activity and increase in 5'-AMP level indicated a significant inhibition of the cAMP signaling pathway to regulate ion concentrations. And small intracellular organic molecules (amino acids, nucleotides and their derivatives) also play crucial roles in osmoregulation through oxidative deamination of glutamate, nucleotide catabolism, and nucleic acid synthesis. Moreover, lysosomes and peroxisomes removed oxidative damage, whereas antioxidant metabolites, such as N-acetyl amino acids and glutathione, were increased to resist oxidative stress. With prolonged hypo-osmotic stress, glycerophospholipid metabolism was enhanced to maintain membrane stability. Furthermore, acyl-CoA-binding protein activity was significantly inhibited, and only a small amount of acylcarnitine was significantly accumulated, which indicated a disruption in energy metabolism. PPAR signaling pathway and choline content were up-regulated to promote fatty acid metabolism under hypo-osmotic stress. Overall, our results provide new insights into the osmoregulatory mechanisms and physiological responses of sea cucumbers to hypo-osmotic stress.

Machine learning methods for unveiling the potential of antioxidant short peptides in goat milk-derived proteins during in vitro gastrointestinal digestion

Milk serves as an important dietary source of bioactive peptides, offering notable benefits to individuals. Among the antioxidant short peptides (di- and tripeptides) generated from gastrointestinal digestion are characterized by enhanced bioavailability and bioaccessibility, while assessing them individually presents a labor-intensive and expensive challenge. Based on 4 distinct types of amino acid descriptors (physicochemical, 3D structural, quantum, and topological attributes) and genetic algorithms for feature selection, 1 and 4 machine learning predicted models separately for di- and tripeptides with ABTS radical scavenging capacity exhibited excellent fitting and prediction ability with random forest regression as machine learning algorithm. Intriguingly, the electronic properties of N-terminal amino acid were considered as only factor affecting the antioxidant capacity of dipeptides containing both tyrosine and tryptophan. Four peptides from the potential di- and tripeptides exhibited highly predicted values by the constructed predicted models. Subsequently, a total of 45 dipeptides and 52 tripeptides were screened by a customized workflow in goat milk during in vitro simulated digestion. In addition to 5 known antioxidant dipeptides, 9 peptides were quantified during digestion, falling within the range of 0.04 to 1.78 mg L-1. Particularly noteworthy was the promising in vivo functionality of antioxidant dipeptides with N-terminal tyrosine, supported by in silico assays. Overall, this investigation explored crucial molecular properties influencing antioxidant short peptides and high-throughput screening potential peptides with antioxidant activity from goat milk aided by machine learning, thereby facilitating the identification of novel bioactive peptides from milk-derived proteins and paving the way for understanding their metabolites during digestion.

Collagen derived Gly-Pro-type DPP-IV inhibitory peptides: Structure-activity relationship, inhibition kinetics and inhibition mechanism

Our previous study has demonstrated that both the amino acid at N3 position and peptide length affected the DPP-IV inhibitory activity of Gly-Pro-type peptides. To further elucidate their molecular mechanism, a combined approach of QSAR modeling, enzymatic kinetics and molecular docking was used. Results showed that the QSAR models of Gly-Pro-type tripeptides and Gly-Pro-type peptides containing 3-12 residues were successfully constructed by 5z-scale descriptor with R2 of 0.830 and 0.797, respectively. The lower values of electrophilicity, polarity, and side-chain bulk of amino acid at N3 position caused higher DPP-IV inhibitory activity of Gly-Pro-type peptides. Moreover, an appropriate increase in the length of Gly-Pro-type peptides did not change their competitive inhibition mode, but decreased their inhibition constants (Ki values) and increased interactions with DPP-IV. More importantly, the interactions between the residues at C-terminal of Gly-Pro-type peptides containing 5 ∼ 6 residues with S2 extensive subsites (Ser209, Phe357, Arg358) of DPP-IV increased the interactions of Gly residue at N1 position with the S2 subsites (Glu205, Glu206, Asn710, Arg125, Tyr662) and decreased the acylation level of DPP-IV-peptide complex, and thereby increasing peptides' DPP-IV inhibitory activity.

Comparison of the Protective Effects of Casein Hydrolysate Containing Tyr-Pro-Val-Glu-Pro-Phe and Casein on the Behaviors and Peripheral and Brain Functions in Mice with Chronic-Stress-Induced Anxiety and Insomnia

Chronic stress is a major inducer of anxiety and insomnia. Milk casein has been studied for its stress-relieving effects. We previously prepared a casein hydrolysate (CP) rich in the sleep-enhancing peptide YPVEPF, and this study aims to systemically investigate the different protective effects of CP and casein on dysfunction and anxiety/insomnia behavior and its underlying mechanisms in chronically stressed mice. Behavioral results showed that CP ameliorated stress-induced insomnia and anxiety more effectively than milk casein, and this difference in amelioration was highly correlated with an increase in GABA, 5-HT, GABAA, 5-HT1A receptors, and BDNF and a decrease in IL-6 and NMDA receptors in stressed mice. Furthermore, CP restored these dysfunctions in the brain and colon by activating the HPA response, modulating the ERK/CREB-BDNF-TrκB signaling pathway, and alleviating inflammation. The abundant YPVEPF (1.20 ± 0.04%) and Tyr-based/Trp-containing peptides of CP may be the key reasons for its different effects compared to casein. Thus, this work revealed the main active structures of CP and provided a novel dietary intervention strategy for the prevention and treatment of chronic-stress-induced dysfunction and anxiety/insomnia behaviors.

Novel antioxidant peptides identified from coix seed by molecular docking, quantum chemical calculations and invitro study in HepG2 cells

The aim of the study was to identify potent antioxidant peptides sourced from coix seed, analyze the structure-activity relationship through molecular docking and quantum chemical calculation. Molecular docking results showed that among thirteen peptides selected in silico, eight had favourable binding interaction with the Keap1-Kelch domain (2FLU). Promising peptides with significant binding scores were further evaluated using quantum calculation. It was shown that peptide FFDR exhibited exceptional stability, with a high energy gap of 5.24 eV and low Highest Occupied Molecular Orbitals (HOMO) and Lowest Unoccupied Molecular Orbitals (LUMO) values. Furthermore, FFDR displayed the capacity to enhance the expression of Nrf2-Keap1 antioxidant genes (CAT, SOD, GSH-Px) and improved cellular redox balance by increasing reduced glutathione (GSH) while reducing oxidized glutathione (GSSG) and malonaldehyde (MDA) levels. These findings highlight the potential of coix seed peptides in developing novel, effective and stable antioxidant-based functional foods.

Bioactive peptides as a novel strategy to prevent alcoholic liver injury

Alcohol intake has become one of the leading risks to human health and wellness, among which acute and/or chronic alcohol-induced liver injury is a leading threaten, with few therapeutic options other than abstinence. In recent years, studies suggested that certain bioactive peptides from food sources could represent natural and safe alternatives for the prevention of alcoholic liver injury. Hence, this chapter focus on the advanced research on bioactive peptides exerting hepatoprotective activity against alcoholic liver injury. The main sources of protein, strategies for the preparation of hepatoprotective hydrolysates and peptides, underlying mechanisms of peptides on hepatoprotection, and possible structure-activity relationship between peptides and hepatoprotective activity were summarized and discussed, aiming to give a systematic insight into the research progress of hepatoprotective peptides. However, more efforts would be needed to give a clearer insight into the underlying mechanisms and structure-activity relationship before using hepatoprotective peptides as functional food ingredients or dietary supplements.

Effects of Mactra chinenesis Peptides on Alcohol-Induced Acute Liver Injury and Intestinal Flora in Mice

Food-borne bioactive peptides have shown promise in preventing and mitigating alcohol-induced liver injury. This study was the first to assess the novel properties of Mactra chinenesis peptides (MCPs) in mitigating acute alcoholic liver injury in mice, and further elucidated the underlying mechanisms associated with this effect. The results showed that MCPs can improve lipid metabolism by modulating the AMPK signaling pathway, decreasing fatty acid synthase activity, and increasing carnitine palmitoyltransferase 1a activity. Meanwhile, MCPs ameliorate inflammation by inhibiting the NF-κB activation, leading to reduced levels of pro-inflammatory cytokines (tumor necrosis factor-α and interleukin-1β). Additionally, a 16S rDNA sequencing analysis revealed that MCPs can restore the balance of gut microbiota and increase the relative abundance of beneficial bacteria. These findings suggest that supplementation of MCPs could attenuate alcohol intake-induced acute liver injury, and, thus, may be utilized as a functional dietary supplement for the successful treatment and prevention of acute liver injury.

Advances in Research on the Activity Evaluation, Mechanism and Structure-Activity Relationships of Natural Antioxidant Peptides

Antioxidant peptides are a class of biologically active peptides with low molecular weights and stable antioxidant properties that are isolated from proteins. In this review, the progress in research on the activity evaluation, action mechanism, and structure-activity relationships of natural antioxidant peptides are summarized. The methods used to evaluate antioxidant activity are mainly classified into three categories: in vitro chemical, in vitro cellular, and in vivo animal methods. Also, the biological effects produced by these three methods are listed: the scavenging of free radicals, chelation of metal ions, inhibition of lipid peroxidation, inhibition of oxidative enzyme activities, and activation of antioxidant enzymes and non-enzymatic systems. The antioxidant effects of natural peptides primarily consist of the regulation of redox signaling pathways, which includes activation of the Nrf2 pathway and the inhibition of the NF-κB pathway. The structure-activity relationships of the antioxidant peptides are investigated, including the effects of peptide molecular weight, amino acid composition and sequence, and secondary structure on antioxidant activity. In addition, four computer-assisted methods (molecular docking, molecular dynamics simulation, quantum chemical calculations, and the determination of quantitative structure-activity relationships) for analyzing the structure-activity effects of natural peptides are summarized. Thus, this review lays a theoretical foundation for the development of new antioxidants, nutraceuticals, and cosmetics.

Molecular Interactions Between Egg White Peptides and Giant Unilamellar Vesicle Membranes: Effect of Peptide Localization on Membrane Fluidity

Bioactive peptides have been shown to affect cell membrane fluidity, which is an important indicator of the cell membrane structure and function. However, the underlying mechanism of egg white-derived bioactive peptide regulation of cell membrane fluidity has not been elucidated yet. The cell membrane fluidity was investigated by giant unilamellar vesicles in the present study. The results showed that peptides TCNW, ADWAK, ESIINF, VPIEGII, LVEEY, and WKLC connect to membranes through intermolecular interactions, such as hydrogen bonding and regulated membrane fluidity, in a concentration-dependent way. In addition, peptides prefer to localize in the hydrophobic core of the bilayers. This study provides a theoretical basis for analyzing the localization of egg white bioactive peptides in specific cell membrane regions and their influence on the cell membrane fluidity.

Effects of collagen hydrolysates on UV-induced photoaging mice: Gly-Pro-Hyp as a potent anti-photoaging peptide

This work aimed to investigate the protective effects of collagen hydrolysates containing different contents of Gly-Pro-Xaa tripeptides on UV-induced photoaging mice and to identify potent anti-photoaging peptides. Results showed that oral ingestion of collagen hydrolysates with a higher content of Gly-Pro-Xaa tripeptides (∼11.4%, HCH) dramatically enhanced the absorption of Pro-Hyp, Hyp-Gly, and Gly-Pro-Hyp into the body, which were 1.77-, 2.18-, and 65.07-fold higher in area under the concentration-time curve (AUC) values than that of collagen hydrolysates with a lower content of Gly-Pro-Xaa tripeptides (∼3.8%, LCH), respectively. Furthermore, the protective effects of HCH on the photo-aged skin of mice were significantly stronger than those of LCH in terms of increases in the contents of hyaluronic acid and collagen, improvement in skin elasticity and epidermal thickness, alleviation in inflammation, and decreases in the contents of matrix metalloproteinase-1 (MMP-1) and MMP-3. More importantly, Gly-Pro-Hyp displayed potent anti-photoaging activities comparable to HCH based on an equivalent amount of Hyp. Network pharmacology analysis for potential mechanisms further indicated that Gly-Pro-Hyp might interact with JUN and FOS and regulate IL-17 and TNF signaling pathways. Collectively, our results suggested that HCH had great potential to be applied in functional foods for skin health and Gly-Pro-Hyp was found to be a potent collagen-derived anti-photoaging peptide, which might contribute to the excellent anti-photoaging effects of HCH.

Isolation, identification of antioxidant peptides from earthworm proteins and analysis of the structure-activity relationship of the peptides based on quantum chemical calculations

Earthworms are emerging sources of edible animal proteins. Earthworm extracts exhibit good in vivo antioxidant activity after oral administration. To better understand the antioxidant activity of earthworms, antioxidant peptides derived from earthworm proteins after gastrointestinal digestion were isolated and identified, and their structure-activity relationships were analysed in this research. Results showed that earthworm protein gastrointestinal digestion products exhibited good antioxidant activity, and 6030 peptide sequences were identified after separation using ion-exchange and gel-chromatography columns. Eleven peptides were screened using computer simulation activity scores, among which AFWYGLPCKL, WPWQMSLY, and GCFRYACGAFY showed the best antioxidant activities. Highest Occupied Molecular Orbital (HOMO) analysis indicated that N29-H10, O122-H38, and the peptide bond binding sites of serine and leucine were active sites of peptides AFWYGLPCKL, GCFRYACGAFY, and WPWQMSLY, respectively. This study provides a new understanding of substance basis of antioxidant activity in earthworms and contributes to application of earthworm proteins as antioxidants in health-foods.

Characterization and Exploration of the Neuroprotective Potential of Oat-Protein-Derived Peptides in PC12 Cells and Scopolamine-Treated Zebrafish

Neurodegenerative disorders pose a substantial risk to human health, and oxidative stress, cholinergic dysfunction, and inflammation are the major contributors. The purpose of this study was to explore the neuroprotective effects of oat protein hydrolysate (OPH) and identify peptides with neuroprotective potential. This study is the first to isolate and identify OPH peptides with neuroprotective potential, including DFVADHPFLF (DF-10), HGQNFPIL (HL-8), and RDFPITWPW (RW-9), by screening via peptidomes and molecular-docking simulations. These peptides showed positive effects on the activity of antioxidant enzymes and thus reduced oxidative stress through regulation of Nrf2-keap1/HO-1 gene expression in vitro and in vivo. The peptides also significantly ameliorated scopolamine-induced cognitive impairment in the zebrafish model. This improvement was correlated with mitigation of MDA levels, AChE activity, and levels of inflammatory cytokines in the brains of zebrafish. Furthermore, these peptides significantly upregulated the mRNA expression of Bdnf, Nrf2, and Erg1 in the brains of zebrafish with neurodegenerative disorders. Collectively, oat peptides have potential for use as active components in nutraceutical applications for the prevention of neurodegenerative diseases.

Protein Hydrolysates from Fishery Processing By-Products: Production, Characteristics, Food Applications, and Challenges

Fish processing by-products such as frames, trimmings, and viscera of commercial fish species are rich in proteins. Thus, they could potentially be an economical source of proteins that may be used to obtain bioactive peptides and functional protein hydrolysates for the food and nutraceutical industries. The structure, composition, and biological activities of peptides and hydrolysates depend on the freshness and the actual composition of the material. Peptides isolated from fishery by-products showed antioxidant activity. Changes in hydrolysis parameters changed the sequence and properties of the peptides and determined their physiological functions. The optimization of the value of such peptides and the production costs must be considered for each particular source of marine by-products and for their specific food applications. This review will discuss the functional properties of fishery by-products prepared using hydrolysis and their potential food applications. It also reviews the structure-activity relationships of the antioxidant activity of peptides as well as challenges to the use of fishery by-products for protein hydrolysate production.

Identification of antioxidant peptides targeting Keap1-Nrf2-ARE pathway from in vitro digestion of pork sausage with partial substitution of NaCl by KCl

The Kelch-like ECH-associated protein 1 (Keap1)-nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response elements (ARE) pathway is one of the most important cellular defense mechanisms against oxidative stress. This study focuses on finding antioxidant peptides from in vitro digestion products of pork sausage with partial substitution of NaCl by KCl by virtual screening. Six antioxidant peptides, LIVGFPAYGH, DWWGSTVR, WNSLLIR, IVGFPAYGH, FDNLWDQGL, and LRSPSWDPF, could activate the Keap1-Nrf2-ARE pathway and protect cells from oxidative stress. DWWGSTVR exhibits the most robust activity among them. Further studies indicated that DWWGSTVR could increase the expression of many antioxidant enzymes by enabling the transfer of Nrf2 from the cytoplasm to the nucleus. In summary, these six peptides are proven to be Nrf2 activators and could be used as functional foods to prevent and treat various oxidative stress-induced diseases.

Preparation, Characterization, and Antioxidant Properties of Selenium-Enriched Tea Peptides

The research on the activity of selenium (Se)-enriched agricultural products is receiving increasing attention since Se was recognized for its antioxidant activities and for its enhancement of immunity in trace elements. In this study, antioxidant Se-containing peptides, namely, Se-TAPepI-1 and Se-TAPepI-2, were optimally separated and prepared from Se-enriched tea protein hydrolysates by ultrafiltration and Sephadex G-25 purification, and subsequently, their physicochemical properties, oligopeptide sequence, and potential antioxidant mechanism were analyzed. Through the optimization of enzymatic hydrolysis conditions, the Se-enriched tea protein hydrolyzed by papain exhibited a better free radical scavenging activity. After separation and purification of hydrolysates, the two peptide fractions obtained showed significant differences in selenium content, amino acid composition, apparent morphology, peptide sequence, and free radical scavenging activity. Therein, two peptides from Se-TAPepI-1 included LPMFG (563.27 Da) and YPQSFIR (909.47 Da), and three peptides from Se-TAPepI-2 included GVNVPYK (775.42 Da), KGGPGG (552.24 Da), and GDEPPIVK (853.45 Da). Se-TAPepI-1 and Se-TAPepI-2 could ameliorate the cell peroxidation damage and inflammation by regulating NRF2/ARE pathway expression. Comparably, Se-TAPepI-1 showed a better regulatory effect than Se-TAPepI-2 due to their higher Se content, typical amino acid composition and sequence, higher surface roughness, and a looser arrangement in their apparent morphology. These results expanded the functional activities of tea peptide and provided the theoretical basis for the development of Se-containing peptides from Se-enriched tea as a potential natural source of antioxidant dietary supplements.

Research Progress on the Preparation and Function of Antioxidant Peptides from Walnuts

Food-derived peptides have good antioxidant activity and are highly safe for humans; consequently, there has been continuous growth in research on antioxidants, with potential applications in food, medicine, cosmetics, and other fields. Among food-derived peptides, walnut-derived peptides have attracted increasing attention as food-derived peptides rich in eight essential amino acids. This review summarizes the progress made in the development and identification of antioxidant peptides in walnut proteins. This article mainly describes the interaction between reactive oxygen species and cellular antioxidant products, modulation of enzyme content and activity, and regulation of the redox signaling pathways and analyzes the mechanisms of reduction in oxidative stress. Finally, the complex structure-activity relationships of walnut-derived peptides are analyzed based on their amino acid composition and secondary structure of the polypeptides. This review provides a theoretical basis for the production of walnut-derived antioxidant peptides and could help promote the development of the walnut industry.

Virtual screening, identification, and potential antioxidant mechanism of novel bioactive peptides during aging by a short-chain peptidomics, quantitative structure-activity relationship analysis, and molecular docking

Antioxidant peptides have received a great deal of attention. However, only a few studies have been conducted on the antioxidant peptides originating from Baijiu. A total of 1490 features deemed potential short-chain peptides (the amino acid number between 2 and 4, SCPs) were screened and analyzed by a customized short-chain peptidomics approach in Feng-flavor Baijiu (FFB) during 14 years of aging, with an obvious discrepancy between FFB aged for 3 years and 6 years being observed. Thirty-nine characteristic SCPs in total were identified and accurately quantified by high-throughput parallel reaction monitoring-based synthetic standards, with the contents ranging from 0.16 to 279.33 μg L-1. Combined with the absorption, distribution, metabolism, excretion, and toxicity analysis model, PGRW, WK, SC, and PAW, four novel antioxidant peptides with high ABTS radical scavenging capacity, were obtained using a customized quantitative structure-activity relationship (QSAR) model based on a two terminal position numbering method, with satisfied coefficients of determination (R2), internal cross-validated R2 (Q2), and external R2 (R2pre) of 0.925, 0.808, and 0.665, respectively. Furthermore, these 4 antioxidant peptides could block the Keap-Nrf2 interaction and promote the accumulation of Nrf2 by molecular docking analysis, and the interaction energy between peptide PGRW and Keap1 was higher than that between epigallocatechin gallate and Keap1 based on CHARMm forced field. Overall, this study facilitated the discovery of functional peptides in Baijiu and the understanding of aging mechanisms.

Design and synthesis of novel carbohydrate-amino acid hybrids and their antioxidant and anti-β-amyloid aggregation activity

Herein we report the synthesis of new furanoid sugar amino acids and thioureas, prepared by coupling aromatic amino acids and dipeptides with isothiocyanato- functionalized ribofuranose ring. Since carbohydrate-derived structures possess many biological activities, synthesized compounds were evaluated as anti-amyloid and antioxidant agents. The anti-amyloid activity of the studied compounds was evaluated based on their potential to destroy amyloid fibrils of intrinsically disordered Aβ₄₀ peptide and globular hen egg-white (HEW) lysozyme. The destructive efficiency of the compounds differed between the studied peptides. While the destruction activity of the compounds on the HEW lysozyme amyloid fibrils was negligible, the effect on Aβ₄₀ amyloid fibrils was significantly higher. Furanoid sugar α-amino acid 1 and its dipeptide derivatives 8 (Trp-Trp) and 11 (Trp-Tyr) were the most potent anti-Aβ fibrils compounds. The antioxidant properties of synthesized compounds were estimated by three complementary in vitro assays (DPPH, ABTS, and FRAP). The ABTS assay was the most sensitive for assessing the radical scavenging activity of all tested compounds compared to the DPPH test. Significant antioxidant activity was detected for compounds in the group of aromatic amino acids depending on the present amino acid, with the highest activity in the case of dipeptides 11 and 12 containing the Tyr and Trp moiety. Regarding the FRAP assay, the best reducing antioxidant potential revealed Trp-containing compounds 5, 10, and 12.

Germination and Simulated Gastrointestinal Digestion of Chickpea (Cicer arietinum L.) in Exhibiting In Vitro Antioxidant Activity in Gastrointestinal Epithelial Cells

Plant-based proteins, in particular pulse proteins, have grown in popularity worldwide. Germination, or sprouting, is an effective method to release peptides and other dietary compounds. However, the combination of germination and gastrointestinal digestion in enhancing the release of dietary compounds with potential health-beneficial biological activity has yet to be entirely elucidated. The present study illustrates the impact of germination and gastrointestinal digestion on the release of dietary compounds with antioxidant activity from chickpeas (Cicer arietinum L.). Germination up to 3 days (D0 to D3) increased the peptide content by denaturing chickpea storage proteins and increased the degree of hydrolysis (DH) in the gastric phase. The antioxidant activity was measured at three different dosages (10, 50, and 100 μg/mL) and compared between D0 and D3 on human colorectal adenocarcinoma cells (HT-29). A significant increase in antioxidant activity was observed in the D3 germinated samples in all three tested dosages. Further analysis identified 10 peptides and 7 phytochemicals differentially expressed between the D0 and D3 germinated samples. Among the differentially expressed compounds, 3 phytochemicals (2',4'-dihydroxy-3,4-dimethoxychalcone, isoliquiritigenin 4-methyl ether, and 3-methoxy-4,2',5'-trihydroxychalcone) and 1 peptide (His-Ala-Lys) were identified only in the D3 samples, indicating their potential contribution towards the observed antioxidant activity.

In Vitro Simulated Gastrointestinal Digestion Stability of a Neuroprotective Octapeptide WCPFSRSF and Prediction of Potential Bioactive Peptides in Its Digestive Fragments by Multiple Bioinformatics Tools

WCPFSRSF, an octapeptide (Trp-Cys-Pro-Phe-Ser-Arg-Ser-Phe), has been reported to improve memory in mice, but its gastrointestinal stability is unclear. The objective of this study was to evaluate the gastrointestinal stability of peptide WCPFSRSF and explore the neuroprotective potential of its digestive fragments. Results showed that the content of WCPFSRSF after gastric and gastrointestinal digestion decreased to 71.64% and less than 1%, respectively. Furthermore, the antioxidant and neuroprotective ability of WCPFSRSF were also affected. Eleven and nine peptides were identified in its gastric and gastrointestinal digestive products, respectively. Multiple bioinformatics tools in combination with principal component analysis were employed to assess the physicochemical and structural properties of peptides. Novel peptides generated after gastrointestinal digestion could be classified into three groups: the first group had high bioactivity and bioavailability; the second group had high amphiphilicity, charge, and net hydrogen; and the third group had a long peptide chain. In addition, the representative peptides WCPF and SR showed neuroprotective ability.

Musculus senhousei as a promising source of bioactive peptides protecting against alcohol-induced liver injury

Alcohol-induced liver injury has become a leading risk for human health, however, effective strategies for the prevention or treatment are still lacking. Hence, the present study explored the potential of Musculus senhousei as a source of hepatoprotective peptides against alcoholic liver injury using in vitro, in vivo and in silico methods. Results indicated that Musculus senhousei peptides (MSP, extracted by simulated gastrointestinal digestion of cooked mussel) exhibited notable antioxidant (ABTS and DPPH assays) and alcohol dehydrogenase (ADH) stabilizing activity in vitro. The ingestion of MSP markedly alleviated alcohol-induced liver injury in mice, as indicated by the decrease of serum transaminases (AST and ALT). In line with in vitro assays, significantly increased hepatic ADH activity and activated antioxidative defense system (GSH, SOD, GSH-Px and CAT) were observed, whereas the oxidative stress (MDA) was decreased. Peptidomic analysis revealed over 6000 peptides with favorable amino acid compositions, and a total of 20 potentially novel peptides with bioactivity and bioavailability were excavated among 746 of the most influential peptides using an in silico strategy. Peptides (i.e. WLPMKL, WLWLPA, RLC and RCL) were further synthesized and validated in vitro to be bioactive. These findings suggest that Musculus senhousei can be an ideal source of bioactive peptides for the prevention of alcoholic liver injury.

Purification, Identification and Evaluation of Antioxidant Peptides from Pea Protein Hydrolysates

Food-derived antioxidant peptides can be explored as natural antioxidants due to their potential health benefits. In this study, antioxidant peptides were isolated and purified from pea protein hydrolysates (PPH). The DPPH and ABTS radical scavenging activities were used as indexes to purify the antioxidant peptides by a series of purification steps including ultrafiltration, ion exchange chromatography, G25 gel filtration chromatography, and reversed-phase chromatography. Three novel antioxidant peptides YLVN, EEHLCFR and TFY were identified, which all exhibited strong antioxidant activity in vitro. EEHLCFR showed stronger DPPH scavenging activity with an IC50 value of 0.027 mg/mL. YLVN showed stronger ABTS scavenging activity with an IC50 value of 0.002 mg/mL and higher ORAC values of 1.120 ± 0.231 μmol TE/μmol, which is even better than that of GSH. Three novel antioxidant peptides significantly elevated LO2 cells viability even at the concentration of 0.025 mg/mL, and cell viability enhanced to 53.42 ± 1.19%, 55.78 ± 1.03%, and 51.09 ± 1.06% respectively, compared to that of H2O2 injury group (48.35 ± 0.96%), and prevented the accumulation of ROS by enhancing the activities of antioxidant enzymes in H2O2-induced oxidative stress LO2 cells. The molecular docking results showed that the potential molecular mechanism of the three novel antioxidant peptides may be in high correlation with the activation of the Keap1-Nrf2 pathway by occupying the Keap1-Nrf2 binding site. These results demonstrate that the three novel antioxidant peptides are potential natural antioxidants that can be devoted to medicine or functional food ingredients.

Prediction of antioxidant peptides using a quantitative structure-activity relationship predictor (AnOxPP) based on bidirectional long short-term memory neural network and interpretable amino acid descriptors

Antioxidant peptides can protect against free radical-mediated diseases, especially food-derived antioxidant peptides are considered as potential competitors among synthetic antioxidants due to their safety, high activity and abundant sources. However, wet experimental methods can not meet the need for effectively screening and clearly elucidating the structure-activity relationship of antioxidant peptides. Therefore, it is particularly important to build a reliable prediction platform for antioxidant peptides. In this work, we developed a platform, AnOxPP, for prediction of antioxidant peptides using the bidirectional long short-term memory (BiLSTM) neural network. The sequence characteristics of peptides were converted into feature codes based on amino acid descriptors (AADs). Our results showed that the feature conversion ability of the combined-AADs optimized by the forward feature selection method was more accurate than that of the single-AADs. Especially, the model trained by the optimal descriptor SDPZ27 significantly outperformed the existing predictor on two independent test sets (Accuracy = 0.967 and 0.819, respectively). The SDPZ27-based AnOxPP learned four key structure-activity features of antioxidant peptides, with the following importance as steric properties > hydrophobic properties > electronic properties > hydrogen bond contributions. AnOxPP is a valuable tool for screening and design of peptide drugs, and the web-server is accessible at http://www.cqudfbp.net/AnOxPP/index.jsp.

White Wine Antioxidant Metabolome: Definition and Dynamic Behavior during Aging on Lees in Oak Barrels

White wines' oxidative stability is related to a flow of chemical reactions involving a number of native wine compounds comprising their antioxidant metabolome. By applying the combination of powerful and modern analytical approaches (EPR, DPPH, and UPLC-qToF-MS-based metabolomics), we could define wine antioxidant metabolome as the sum of molecular antioxidant markers (AM) characterized by their radical scavenging (AM-RS) and nucleophilic (AM-Nu) properties. The impact of on-lees barrel aging of chardonnay wines on the antioxidant metabolome was studied for two consecutive vintages. The identification of wines' antioxidant metabolome allows for a detailed understanding of the transient chemical interplays involved in the antioxidant chemistry associated with well-known antioxidants and opens an avenue towards personalized winemaking. The present study gathers for the first time the dynamics of wines' antioxidant metabolome during on-lees aging. Monitoring the variations of the wine antioxidant metabolome can provide an avenue to better control the winemaking process using the knowledge of how to optimize the wine aging potential.

Abalone visceral peptides containing Cys and Tyr exhibit strong in vitro antioxidant activity and cytoprotective effects against oxidative damage

The in vitro antioxidation and cytoprotection of abalone visceral peptides against oxidative damage were investigated. Results show that the DPPH· scavenging activities of the 16 chemically synthesized peptides were significantly and positively correlated with their reducing power. Their scavenging activities against ABTS·⁺ were positively correlated with their ability to inhibit linoleic acid oxidation. Only Cys containing peptides exhibited good DPPH· scavenging activity, while only Tyr containing peptides showed significant ABTS·⁺ scavenging activity. In the cytoprotection assay, all four representative peptides significantly increased the viability of H₂O₂-damaged LO2 cells and the activities of GSH-Px, CAT, and SOD, and all decreased MDA levels and LDH leakage, in which the Cys-containing peptides were more effective at increasing the activities of antioxidant enzymes, while the Tyr-containing peptides were more effective at decreasing MDA levels and LDH leakage. Abalone visceral peptides containing both Cys and Tyr exhibit strong in vitro and cellular antioxidation.

Freshwater Clam Extract Attenuates Indomethacin-Induced Gastric Damage In Vitro and In Vivo

Contemporary pharmacological studies have reported that freshwater clam (Corbicula fluminea) can provide a broad spectrum of bioactivities, including antioxidant, anticancer, antihypertensive, hepatoprotective, and hypocholesterolemic effects. The aim of this study was to evaluate the gastroprotective effects of water extract of freshwater clam (WEC) on indomethacin (IND)-induced gastric mucosal cell damage in vitro and gastric ulcer in vivo. The cell viability of rat gastric mucosa RGM-1 cells was markedly decreased by 0.8 mM of IND treatment, and pre-treated with various concentration of WEC significantly restored IND-induced cell damage in a dose-dependent manner. WEC also significantly attenuated the elevated reactive oxygen species (ROS) levels, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression, and nuclear factor-κB (NF-κB) p65 nuclear translocation induced by IND. In the in vivo study, IND caused severe gastric ulcer in Wistar rats, while WEC pretreatment effectively reduced the ulcer area and edema in the submucosa. We found that WEC significantly restored glutathione (GSH) content in gastric mucosa in a dose-dependent manner (p < 0.05). The reduction of prostaglandin E2 (PGE2) caused by IND was also improved with higher doses of WEC administration. Moreover, the overexpression of COX-2, iNOS, and tumor necrosis factor-α (TNF-α) proteins in gastric mucosa was downregulated by administration of WEC. Consequently, WEC can be used as a potential nutritional supplement to improve NSAIDs-caused gastric mucosal lesions.

Stability, Bioavailability, and Structure-Activity Relationship of Casein-Derived Peptide YPVEPF with a Sleep-Enhancing Effect

YPVEPF (Tyr-Pro-Val-Glu-Pro-Phe) is an outstanding sleep-enhancing peptide derived from casein. This study aimed to evaluate the bioavailability of YPVEPF in vitro and in vivo and to explore its structure-activity relationship through a sleep test and cheminformatics. Our results showed that YPVEPF was unstable against gastrointestinal enzymes and almost totally degraded to YPVEP in vitro. However, the pharmaco-kinetics results in vivo showed that the C_max of YPVEPF was 10.38 ± 4.01 ng/mL at 5 min, and YPVEPF could be detected in the stomach, intestine, and brain at 12.89 ± 0.55, 10.26 ± 0.23, and 2.47 ± 0.55 ng/g, respectively. The main metabolites including YPVEP, YP, PVEPF, and PVEP were identified. We first explored whether the fragment YPVEP also had a strong sleep-enhancing effect, and the sleep-enhancing effects of PVEPF and PVEP (lacking a Tyr residue) significantly decreased compared with those of YPVEPF and YPVEP. Moreover, molecular docking and quantum calculations revealed that the N-terminus Tyr played a dominant role in YPVEPF and YPVEP. They had distinctive self-folding structures and varying electron-withdrawing properties of the groups at the N terminus, allowing different binding modes and electron/proton transfer.

Food Protein-Derived Antioxidant Peptides: Molecular Mechanism, Stability and Bioavailability

The antioxidant activity of protein-derived peptides was one of the first to be revealed among the more than 50 known peptide bioactivities to date. The exploitation value associated with food-derived antioxidant peptides is mainly attributed to their natural properties and effectiveness as food preservatives and in disease prevention, management, and treatment. An increasing number of antioxidant active peptides have been identified from a variety of renewable sources, including terrestrial and aquatic organisms and their processing by-products. This has important implications for alleviating population pressure, avoiding environmental problems, and promoting a sustainable shift in consumption. To identify such opportunities, we conducted a systematic literature review of recent research advances in food-derived antioxidant peptides, with particular reference to their biological effects, mechanisms, digestive stability, and bioaccessibility. In this review, 515 potentially relevant papers were identified from a preliminary search of the academic databases PubMed, Google Scholar, and Scopus. After removing non-thematic articles, articles without full text, and other quality-related factors, 52 review articles and 122 full research papers remained for analysis and reference. The findings highlighted chemical and biological evidence for a wide range of edible species as a source of precursor proteins for antioxidant-active peptides. Food-derived antioxidant peptides reduce the production of reactive oxygen species, besides activating endogenous antioxidant defense systems in cellular and animal models. The intestinal absorption and metabolism of such peptides were elucidated by using cellular models. Protein hydrolysates (peptides) are promising ingredients with enhanced nutritional, functional, and organoleptic properties of foods, not only as a natural alternative to synthetic antioxidants.

Arginine-Containing Peptides Derived from Walnut Protein Against Cognitive and Memory Impairment in Scopolamine-Induced Zebrafish: Design, Release, and Neuroprotection

The purpose of this study was to investigate the neuroprotective effect of Arg-containing peptides from walnut storage protein sequences in scopolamine-induced zebrafish and further to validate the potential neuroprotection of Arg-containing peptide enriched walnut hydrolysates prepared by in silico hydrolysis and controlled enzymatic release. Results showed that walnut derived Arg-containing peptides with high abundance and great bioactivity predicted by bioinformatics displayed potent neuroprotection in scopolamine-induced zebrafish, and regulation of neurotransmitter level and antioxidant enzyme activity might be the main target for Arg-containing peptides to exert neuroprotection. Notably, Arg-containing peptides (not free arginine) contributed greater neuroprotection, and the positive charge and cell-penetrating properties also affected their neuroprotection. Subsequently, Arg-containing peptides could be released efficiently from walnut protein following hydrolysis by trypsin, pepsin, papain, and thermolysin (bound arginine content: ranging from 110.43 ± 1.58 to 121.82 ± 1.02 mg/g). Among them, trypsin had excellent potential for releasing Arg-containing peptides in silico hydrolysis, and its hydrolysate was confirmed to have neuroprotective capacity, indicating that the combination of in silico hydrolysis and controlled enzymatic release might be an effective approach to obtain Arg-containing neuroprotective peptides.

Preparation and Antioxidant Activities of High Fischer’s Ratio Oligopeptides from Goat Whey

This study aimed to obtain high Fischer’s ratio oligopeptides from goat whey (HFO) and investigate antioxidant property of it. Hydrolysis of goat whey was done with the approach of sequential digestion of pepsin and flavourzyme. With the adsorption of aromatic amino acids by activated carbon, HFO with a Fischer’s ratio of 27.070 and a molecular weight of 200–1,000 Da were obtained, and the branched-chain amino acids accounted for 22.87%. Then the antioxidant activity of HFO was evaluated. At the concentrations of 2.0 mg/mL and 0.50 mg/mL, HFO scavenged 77.27% and 99.63% of 1,1-diphenyl-2-picrylhydrazyl and 3-ethylbenzthiazoline-6-sulphonate free radicals respectively. The scavenging rate of HFO against hydroxyl radicals reached 92.31% at the concentration of 0.25 mg/mL. Animal experiments demonstrated that HFO could moderate the changes of malondialdehyde, superoxide dismutase and glutathione peroxidase caused by CCl₄-induced oxidative stress in vivo. This study indicated that HFO from goat whey was capable of oxidation resistance both in vivo and in vitro, which provided a scientific basis for the high-value processing and application of goat milk whey.

Enhancing organic selenium content and antioxidant activities of soy sauce using nano-selenium during soybean soaking

Nano-selenium has a greater potential than inorganic selenium in preventing selenium-deficiency diseases due to its higher safety. In this study, spherical nano-selenium particles (53.8 nm) were prepared using sodium selenite, ascorbic acid and chitosan. Selenium-enriched soy sauces were prepared by soaking soybean in nano-selenium and sodium selenite solutions (2–10 mg/L), respectively. Total selenium and organic selenium contents of soy sauces prepared by nano-selenium and sodium selenite were increased by 32–191-fold and 29–173-fold compared to the control (without selenium), and organic selenium accounted for over 90% of total selenium. Soy sauce prepared using 6 mg/L nano-selenium had the strongest antioxidant activities, which were 9.25–28.02% higher than the control. Nano-selenium (6 mg/L) markedly enhanced the koji's enzyme activities (9.76–33.59%), then the latter promoted the release of total phenolics (27.54%), total flavonoids (27.27%) and the formation of free amino acids (16.19%), Maillard reaction products (24.50%), finally the antioxidant activities of selenium-enriched soy sauce were enhanced.

Metabolomics and biochemical assays reveal the metabolic responses to hypo-salinity stress and osmoregulatory role of cAMP-PKA pathway in Mercenaria mercenaria

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Metabolomics reveals the metabolic responses of hard clam to hypo-salinity stress.

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cAMP-PKA pathway and NKA play osmoregulatory roles in hard clams.

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Activated antioxidant responses and reorganized membrane lipids occurred at 5 d.

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Alaine and lactate accumulation suggest the onset of anaerobic metabolism at 1 d.

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Fatty acids β-oxidation is promoted to provide energy for osmoregulation.

Hypo-salinity events frequently occur in marine ecosystem due to persistent rainfall and freshwater inflow, reducing the cytosol osmolarity and triggering cellular stress responses in aquatic organisms. Euryhaline bivalves have developed sophisticated regulatory mechanisms to adapt to salinity fluctuations over a long period of evolution. In this study, we performed multiple biochemical assays, widely targeted metabolomics, and gene expression analysis to investigate the comprehensive metabolic responses to hypo-salinity stress and osmoregulation mechanisms in hard clam Mercenaria mercenaria, which is a euryhaline bivalve species widely cultured in China. During hypo-salinity stress, increased vacuoles appeared in gill filaments. The Na⁺ and Cl^- concentrations in gills significantly decreased because of the up-regulation of Na⁺/K⁺-ATPase (NKA) activity. The cAMP content dramatically decreased at 5 d post hypo-salinity stress. Meanwhile, the gene expression levels of adenylate cyclase, proteinkinase A, and sodium and calcium channel proteins were evidently down-regulated, suggesting that cAMP-PKA pathway was inhibited to prevent ambient inorganic ions from entering the gill cells. Antioxidant metabolites, such as serine and Tyr-containing dipeptides, were significantly up-regulated to resist oxidative stress. Glycerolipid metabolism was strengthened to stabilize membrane structure when hypo-salinity stress was prolonged to 5 days. At 1 d post hypo-salinity stress, an increase in alanine and lactate contents marked the initiation of anaerobic metabolism. Acylcarnitines accumulation indicated that fatty acids β-oxidation was promoted to provide energy for osmoregulation. The potential biomarkers of hypo-salinity stress were identified in hard clams. This study provides novel insights into the metabolic regulatory mechanisms to hypo-salinity stress in euryhaline bivalves.

Comprehensive Evaluation and Comparison of Machine Learning Methods in QSAR Modeling of Antioxidant Tripeptides

Due to their multiple beneficial effects, antioxidant peptides have attracted increasing interest. Currently, the screening and identification of bioactive peptides, including antioxidative peptides based on wet-chemistry methods are time-consuming and highly rely on many advanced instruments and trained personnel. Quantitative structure-activity relationship (QSAR) analysis as an in silico method can be more efficient and cost-effective. However, model performance of QSAR studies on antioxidant peptides was still poor due to limited attempts in model development approaches. The objective of this study was to compare popular machine learning methods for antioxidant activity modeling and screening of tripeptides and identify the critical amino acid features that determine the antioxidant activity. 533 numerical indices of amino acids were adopted to characterize 130 tripeptides with known antioxidant activity from the published literature, and then 7 feature selection strategies plus pairwise correlation were used to screen the most important indices for antioxidant activity and model building. 14 machine learning methods were used to build models based on the feature selection strategies, respectively. Among the 98 models, non-linear regression methods tended to perform better, and the best model with an R ² _Test of 0.847 and RMSE_Test of 0.627 for tripeptide antioxidants was obtained by combining random forest for feature selection and tree-based extreme gradient boost regression for model development. Based on the predicted antioxidant values of 7870 unknown tripeptides, potentially high antioxidant activity tripeptides all have a tyrosine, tryptophan, or cysteine residue at the C-terminal position. Furthermore, the predicted antioxidant activity of six synthesized tripeptides was confirmed through experimental determination, and for the first time, the cysteine or tyrosine residue at the C-terminal was found to be critical to the antioxidant activity based on both QSAR models and experimental observations.

Biochemical Reactions and Their Biological Contributions in Honey

Honey is known for its content of biomolecules, such as enzymes. The enzymes of honey originate from bees, plant nectars, secretions or excretions of plant-sucking insects, or from microorganisms such as yeasts. Honey can be characterized by enzyme-catalyzed and non-enzymatic reactions. Notable examples of enzyme-catalyzed reactions are the production of hydrogen peroxide through glucose oxidase activity and the conversion of hydrogen peroxide to water and oxygen by catalase enzymes. Production of hydroxymethylfurfural (HMF) from glucose or fructose is an example of non-enzymatic reactions in honey.

Antioxidative, cytotoxic, and antibacterial properties of self-assembled glycine-histidine-based dipeptides with or without silver nanoparticles in bio-inspired film

Recent years have seen much attention being given to self-assembly of dipeptide-based structures, especially to self-regulation of dipeptide structures with different amino acid sequences. In this study we investigated the effects of varying solvent environments on the self-assembly of glycine-histidine (Gly-His) dipeptide structures. First we determined the morphological properties of Gly-His films formed in different solvent environments with scanning electron microscopy and then structural properties with Fourier-transform infrared (FTIR) spectroscopy. In addition, we studied the effects of Gly-His films on silver nanoparticle (AgNP) formation and the antioxidant and cytotoxic properties of AgNPs obtained in this way. We also, assessed antibacterial activities of Gly-His films against Gram-negative Escherichia coli and Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. Silver nanoparticle-decorated Gly-His films were not significantly cytotoxic at concentrations below 2 mg/mL but had antibacterial activity. We therefore believe that AgNP-decorated Gly-His films at concentrations below 2 mg/mL can be used safely against bacteria.

Biological Functions of Antioxidant Dipeptides

In the history of modern nutritional science, understanding antioxidants is one of the major topics. In many cases, food-derived antioxidants have π conjugate or thiol group in their molecular structures because π conjugate stabilizes radical by its delocalization and two thiol groups form a disulfide bond in its antioxidative process. In recent years, antioxidant peptides have received much attention because for their ability to scavenge free radicals, inhibition of lipid peroxidation, chelation of transition metal ions, as well as their additional nutritional value. Among them, dipeptides are attracting much interest as post-amino acids, which have residues in common with amino acids, but also have different physiological properties and functions from those of amino acids. Especially, dipeptides containing moieties of several amino acid (tryptophan, tyrosine, histidine, cysteine, and methionine) possess potent antioxidant activity. This review summarizes previous details of structural property, radical scavenging activity, and biological activity of antioxidant dipeptide. Hopefully, this review will help provide a new insight into the study of the biological functions of antioxidant dipeptides.