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The inhibition of dipeptidyl peptidase-IV (DPP-IV) is a promising approach for regulating the blood glucose levels in patients with type 2 diabetes (T2D). Oysters, rich in functional peptides, contain peptides capable of inhibiting DPP-IV activity. This study aims to identify the hypoglycemic peptides from oysters and investigate their potential anti-T2D targets and mechanisms. This research utilized virtual screening for the peptide selection, followed by in vitro DPP-IV activity assays to validate the chosen peptide. Network pharmacology was employed to identify the potential targets, GO terms, and KEGG pathways. Molecular docking and molecular dynamics simulations were used to provide virtual confirmation. The virtual screening identified LRGFGNPPT as the most promising peptide among the screened oyster peptides. The in vitro studies confirmed its inhibitory effect on DPP-IV activity. Network pharmacology revealed that LRGFGNPPT exerts an anti-T2D effect through multiple targets and signaling pathways. The key hub targets are AKT1, ACE, and REN. Additionally, the molecular docking results showed that LRGFGNPPT exhibited a strong binding affinity with targets like AKT1, ACE, and REN, which was further confirmed by the molecular dynamics simulations showcasing a stable peptide-target interaction. This study highlights the potential of LRGFGNPPT as a natural anti-T2D peptide, providing valuable insights for potential future pharmaceutical or dietary interventions in T2D management.

Pearl and nacre powders have been valuable traditional Chinese medicines with whitening properties for thousands of years. We utilized a high-temperature and high-pressure method along with compound enzyme digestion to prepare the enzymatic hydrolysates of nacre powder of Pinctada martensii (NP-PMH). The peptides were identified using LC-MS/MS and screened through molecular docking and molecular dynamics simulations. The interactions between peptides and tyrosinase were elucidated through enzyme kinetics, circular dichroism spectropolarimetry, and isothermal titration calorimetry. Additionally, their inhibitory effects on B16F10 cells were explored. The results showed that a tyrosinase-inhibitory peptide (Ala-His-Tyr-Tyr-Asp, AHYYD) was identified, which inhibited tyrosinase with an IC 50 value of 2.012 ± 0.088 mM. The results of the in vitro interactions showed that AHYYD exhibited a mixed-type inhibition of tyrosinase and also led to a more compact enzyme structure. The binding reactions of AHYYD with tyrosinase were spontaneous, leading to the formation of a new set of binding sites on the tyrosinase. The B16F10 cell-whitening assay revealed that AHYYD could reduce the melanin content of the cells by directly inhibiting the activity of intracellular tyrosinase. Additionally, it indirectly affects melanin production by acting as an antioxidant. These results suggest that AHYYD could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals.

Ultrasonic-assisted treatment is an eco-friendly and cost-effective emulsification method, and the acoustic cavitation effect produced by ultrasonic equipment is conducive to the formation of stable emulsion. However, its effect on the underlying stability of low-molecular-weight oyster peptides (LOPs) functional-nutrition W 1 /O/W 2 double emulsion has not been reported. The effects of different ultrasonic power (50, 75, 100, 125, and 150 W) on the stability of double emulsions and the ability to mask the fishy odor of LOPs were investigated. Low ultrasonic power (50 W and 75 W) treatment failed to form a well-stabilized double emulsion, and excessive ultrasound treatment (150 W) destroyed its structure. At an ultrasonic power of 125 W, smaller particle-sized double emulsion was formed with more uniform distribution, more whiteness, and a lower viscosity coefficient. Meanwhile, the cavitation effect generated by 125 W ultrasonic power improved storage, and oxidative stabilities, emulsifying properties of double emulsion by reducing the droplet size and improved sensorial acceptability by masking the undesirable flavor of LOPs. The structure of the double emulsion was further confirmed by optical microscopy and confocal laser scanning microscopy. The ultrasonic-assisted treatment is of potential value for the industrial application of double emulsion in functional-nutrition foods., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)

This study aimed to purify and characterize immunoregulatory peptides from Sipunculus nudus L. and to explore the underlying mechanisms. Ultrafiltration, gel filtration chromatography, and reverse phase high‐performance liquid chromatography (RP‐HPLC) were used to purify the peptide following enzymatic hydrolysis. Rates of lymphocyte proliferation and phagocytosis as well as nitric oxide (NO) production levels were used as indicators of immunoregulatory activity to screen the fractions. The amino acid sequence of the peptide, designated as SNLP, was identified as Arg–Val–Lys–Gly–Lys–Ile–Leu–Ala–Lys–Arg–Leu–Asn (RVKGKILAKRLN) by liquid chromatography–tandem mass spectrometry (LC–MS/MS). Treatment with the synthetic SNLP increased the proliferation and phagocytosis of RAW 264.7 macrophages and promoted the secretion of tumor necrosis factor‐ɑ (TNF‐α), interleukin‐6 (IL‐6), interleukin‐1β (IL‐1β), and NO levels. The mRNA levels of these cytokines and iNOS were also increased by SNLP. Our results provide preliminary evidence suggesting that SNLP acts as a dual immunomodulatory peptide with immunostimulatory and anti‐inflammatory activities. In summary, SNLP derived from Sipunculus nudus L. is a potent immunoregulatory peptide and represents a potential functional food or immunoregulatory drug. [ABSTRACT FROM AUTHOR]

In order to realize the multi-level utilization of marine shellfish resources and to develop the potential biological activity of processing by-products of Atrina pectinata, gelatin was extracted from the mantle and the potential whitening effect of its enzymatic peptides was explored. Taking tyrosinase inhibitory activity as the evaluation index, the enzyme hydrolysate process was optimized by response-surface methodology, and the optimal enzyme hydrolysate conditions were as follows: pH 5.82, 238 min enzyme hydrolysate time, and temperature of 54.5 °C. Under these conditions, the tyrosinase inhibition activity of Atrina pectinata mantle gelatin peptide (APGP) was 88.6% (IC50 of 3.268 ± 0.048 mg/mL). The peptides obtained from the identification were separated by ultrafiltration and LC–MS/MS, and then four new peptides were screened by molecular docking, among which the peptide Tyr-Tyr-Pro (YYP) had the strongest inhibitory effect on tyrosinase with an IC50 value of 1.764 ± 0.025 mM. The molecular-docking results indicated that hydrogen bonding is the main driving force for the interaction of the peptide YYP with tyrosinase. From the Lineweaver–Burk analysis, it could be concluded that YYP is inhibitory to tyrosinase and exhibits a mixed mechanism of inhibition. These results suggest that YYP could be widely used as a tyrosinase inhibitor in whitening foods and pharmaceuticals. [ABSTRACT FROM AUTHOR]

The increasing threat posed by antibiotic-resistant pathogens has prompted a shift to the use of naturally-derived antimicrobial peptides (AMPs) in place of chemical preservatives in controlling foodborne pathogens. In this study, ten peptides were identified from salt-fermented shrimps (Penaeus vannamei) using ultra-performance liquid chromatography-mass spectrometry. One of the peptides, designated PV-Q5 (QVRNFPRGSAASPSALASPR), with most features of an AMP, was further explored and found to possess strong antibacterial activity against Vibrio parahaemolyticus and Escherichia coli, with a minimum inhibitory concentration of 31.25 μg/mL. Moreover, PV-Q5 increased bacterial cell membrane permeability and ruptured bacteria cell membranes, as revealed by transmission electron microscopy. Circular dichroism analysis showed that the conformation of PV-Q5 was a random coil in phosphate-buffered saline and α-helical in sodium dodecyl sulfate, which is conducive for interaction with bacteria cell membranes. These findings indicated that PV-Q5 could find potential use in food preservation to control foodborne pathogenic bacteria. [ABSTRACT FROM AUTHOR]

Oyster hydrolysates exhibit promising potential as a zinc supplement for its significant amounts of zinc, however, the zinc chemical speciation which determines zinc nutrition in oyster hydrolysates has not been investigated. This study optimized the oyster hydrolysis conditions using the Response surface methodology (RSM) method, and the zinc chemical speciation, the sequence of zinc-containing peptides, and the binding sites of zinc and peptides were further investigated. Results showed that inorganic and organic zinc in oysters were 60.15% and 36.53% of total zinc respectively, while organic zinc in oysters aqueous extract was 4.54% of which 3.56% was present in the polysaccharide fraction. The zinc yield was 84.20% of total zinc under optimal hydrolysis conditions, while the organic zinc increased to 52.93% of which 38.14% existed in the protein/peptides fraction. Zinc in protein/peptide fraction primarily was bound to low-molecular-weight peptides (Mw < 1000 Da). Further, 42 shared zinc-containing peptides (mainly 3–4 peptides) were identified. Molecular docking indicated that Glu, Leu, and Tyr might be the binding sites for zinc and peptides. These findings provided a theoretical basis for the development of novel and safe zinc dietary supplements. [Display omitted] • The inorganic and organic zinc in oysters were 60.15% and 36.53% respectively. • After hydrolysis, organic zinc was 52.93% which mainly was protein/peptides form. • Zinc in protein/peptides fractions primarily was bound to low-molecule peptides. • Forty-two zinc-containing peptides (mostly 3–4 peptides) were isolated and identified. • Glu, Leu, and Tyr might be the binding sites of zinc and peptides. [ABSTRACT FROM AUTHOR]

Although Vibrio parahaemolyticus infections cause severe diseases of large yellow croaker (Larimichthys crocea), using antibiotics and other chemical agents to treat these infections could result in antimicrobial resistance, environmental pollution, and other associated problems. This study identified seven peptides from Lacticaseibacillus paracasei fermentation broth using ultra-high-performance liquid chromatography-mass spectrometry and screened antimicrobial peptide Y2Fr (VEIKNGLLKLNGKPLLIR) through its net charge, hydrophobicity and predicted secondary structure. Antibacterial activity analysis revealed that Y2Fr had a minimum inhibitory concentration (MIC) of 125 μg/mL, minimum bactericidal concentration (MBC) of 250 μg/mL against V. parahaemolyticus and a time-kill of 3 h. In a bacterial membrane environment, the secondary structure of peptide Y2Fr changed from a random coil to a β-sheet to enhance its membrane permeability and binding to bacteria DNA to exert its antibacterial effect. Further molecular docking analysis revealed that peptide Y2Fr could bind to the membrane protein KKI11460.1 and DNA polymerase A0A0L8TVA4 of V. parahaemolyticus through hydrogen bonds. Meanwhile, treatment of Y2Fr with mammalian red blood cells and plasma revealed that it was noncytotoxic, nonhemolytic, and stable under physiological conditions. Thus, peptide Y2Fr has great potential use in treating and preventing infections caused by V. parahaemolyticus or similar bacteria in aquatic animals. • Peptide Y2Fr is a novel antimicrobial peptide identified from L. paracasei fermentation broth. • The antibacterial activity of Y2Fr against V. parahaemolyticus is stronger than florfenicol, enrofloxacin, and sulfadiazine. • The secondary structure of the Y2Fr changes from random coil to β-sheet in bacterial membrane environment. • Y2Fr exerts its antimicrobial activity by permeabilizing bacteria membrane and binds to DNA. [ABSTRACT FROM AUTHOR]

The activity of antimicrobial peptides (AMPs) can be enhanced by sodium chloride (NaCl), but whether this applies to halotolerant bacteria, such as Staphylococcus aureus , is unknown. Ten peptides with antimicrobial potential were identified from Penaeus vannamei using ultra-performance liquid chromatography-mass spectrometry and in silico analysis. One of the peptides, designated GPCR10 (LGLLLPALTLGTTHASGASGRR), was further explored against S. aureus in combination with NaCl treatment. Peptide GPCR10 had a minimum inhibitory concentration (MIC) of 62.5 μg/mL against S. aureus but when combined with NaCl (3.5% (w/v)), the MIC decreased to 3.9 μg/mL. Besides, the destruction of bacteria ultrastructure by GPCR10 was enhanced by NaCl, and its random coil structure was transformed to the α-helical form, thereby increasing its binding with bacteria membranes and permeability. These changes in GPCR10 resulted in bacteria destruction, extrusion of cellular content, and binding to bacteria DNA. Thus, low NaCl concentration could enhance the antibacterial activity of AMPs in food preservation. • Peptide GPCR10 is a novel antimicrobial peptide isolated from P. vannamei. • NaCl enhances the antibacterial activity of GPCR10 against S. aureus. • The permeability of GPCR10 across S. aureus increases with NaCl treatment. • Peptide GPCR10 binds bacterial genomic DNA to exert its antibacterial activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • An oyster peptide (OPs)-loaded composite nanogel (CMC@CMCS@OPs) was fabricated. • CMC@CMCS@OPs enhanced the thermal and digestive stabilities of individual OPs. • CMC@CMCS@OPs improved the hypoglycemic activity retention rate of OPs in vitro. • CMC@CMCS@OPs could help OPs achieve targeted and controlled release in the intestine. • CMC@CMCS@OPs could facilitate the absorption and transport of OPs. An oyster peptide (OPs)-loaded composite nanogel based on carboxymethyl cellulose and carboxymethyl chitosan (CMC@CMCS@OPs) was prepared, and the characterization, absorption and transport mechanism were further investigated. CMC@CMCS@OPs, a dense spherical microstructure with a diameter of ∼64 nm, which enhanced the thermal and digestive stabilities of individual OPs and improved its retention rate of hypoglycemic activity in vitro. The swelling response and in-vitro release profiles showed that CMC@CMCS@OPs could help OPs achieve targeted and controlled release in the intestine. In addition, CMC@CMCS@OPs had no cytotoxicity on Caco-2 cells, and its apparent permeability coefficients increased 4.70–7.45 times compared with OPs, with the absorption rate increased by 129.38 %. Moreover, the transcytosis of CMC@CMCS@OPs nanogel occurred primarily through the macropinocytosis pathway, endocytosis pathway and intestinal efflux transporter-mediated efflux. Altogether, these results suggested that CMC@CMCS@OPs nanogel could be as an effective OPs delivery device for enhancing its stability and absorption. [ABSTRACT FROM AUTHOR]

Antifreeze peptides from fish byproducts have the potential to act as suitable and safe cryoprotectants, replacing synthetic additives currently utilized in the food industry. The main focus of this study was to explore the cryoprotective activity of antifreeze peptides from collagen hydrolysate of tilapia (Oreochromis niloticus) skin and deduce the relationship between its physio-chemical characteristics and antifreeze activity. Our results showed that the antifreeze peptides from tilapia skin collagen hydrolysate (TSCP) by alcalase had a lower molecular weight of <2500 Da, higher content of hydrophilic amino acids, and thermal hysteresis activity was 0.50 °C. TSCP 33 , the identified novel cryoprotectant peptide with a molecular weight of 454.26 Da, and the amino acid sequence -NHGK showed remarkable thermal hysteresis activity (THA) of 2.63 °C. Frozen scallop muscles treated with 3 g/100g TSCP exhibited higher salt soluble protein concentration, total sulfhydryl content, Ca2+-ATPase activity, and water-holding capacity during the 8 weeks storage period. The cryoprotective effect of 3 g/100g TSCP was equivalent to that of the commercial phosphorus antifreeze. Our findings provide a theoretical basis for developing safe peptide-based cryoprotectants which will maintain and improve the quality of frozen foods. • Tilapia skin collagen hydrolysate by alcalase showed good cryoprotective activity in the frozen scallop muscles. • A cryoprotectant peptide was characterized by the amino acid sequence of NHGK. • NHGK showed remarkable thermal hysteresis activity of 2.63 °C. [ABSTRACT FROM AUTHOR]