Immunomodulatory peptides from sturgeon cartilage: Isolation, identification, molecular docking and effects on RAW264.7 cells

Sturgeons (Acipenseridae), ancient fish known for their caviar, produce underutilized by-products like protein-rich cartilage, which is a source of high-quality bioactive peptides. This study investigates immunomodulatory peptides from sturgeon cartilage hydrolysates mechanisms. The study found that sturgeon cartilage hydrolysate F2-7 and its key peptides(DHVPLPLP and HVPLPLP)significantly promoted RAW267.4 cell proliferation, NO release, and phagocytosis (P < 0.001).Additionally, western blotting confirmed that F2-7 enhances immune response by increasing the expression of P-IKKα/β, IΚΚ, p65, and P-p65 proteins in the NF-κB signalling pathway (P < 0.01). Molecular docking further demonstrated that DHVPLPLP and HVPLPLP bind to NF-κB pathway proteins via hydrogen bonding, with low estimated binding energies (-2.75 and -1.64; -6.04 and -4.75 kcal/mol), thus establishing their role as key immune peptides in F2-7. Therefore, DHVPLPLP and HVPLPLP have the potential to be developed as dietary supplements for immune enhancement. Their ability to enhance immune function provides a theoretical basis for novel immune supplements.

Novel casein-derived immunomodulatory peptide PFPEVFG: Activity assessment, molecular docking, activity site, and mechanism of action

Presently, there is a gap in the knowledge of the structure-activity relationship of immunomodulatory peptides. In this study, PFPEVFG was selected as a peptide with immunomodulatory activity from casein hydrolysate by virtual screening, and its immunomodulatory activity was verified by the phagocytosis, proliferation, and expression of cytokines (IL-6, IL-1β, TNF-α) and chemokines (CXCL1, CXCL2) in RAW 264.7 macrophages. Next, molecular docking and double-stranded small interfering RNA mutually verified that the immunomodulatory activity of PFPEVFG was mediated by TLR2 and TLR4. Furthermore, the highest occupied molecular orbital (HOMO) analysis showed that the C19=O20 site with a HOMO contribution of 32.22988% was its active site, and the phenylalanine, where the C19=O20 site was located, was its active amino acid. Finally, the combination of pathway inhibitors and western blot revealed that PFPEVFG activated macrophages through the nuclear factor-κB signaling pathway. In summary, this study provided a new perspective on deeply understanding the structure-activity relationship of casein-derived immunomodulatory peptides, as well as a further theoretical and technological basis for the application of immunomodulatory peptides.

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

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

Gastrointestinal digestion of food proteins: Anticancer, antihypertensive, anti-obesity, and immunomodulatory mechanisms of the derived peptides

Food proteins and their peptides play a significant role in the important biological processes and physiological functions of the body. The peptides show diverse biological benefits ranging from anticancer to antihypertensive, anti-obesity, and immunomodulatory, among others. In this review, an overview of food protein digestion in the gastrointestinal tract and the mechanisms involved was presented. As some proteins remain resistant and undigested, the multifarious factors (e.g. protein type and structure, microbial composition, pH levels and redox potential, host factors, etc.) affecting their colonic fermentation, the derived peptides, and amino acids that evade intestinal digestion are thus considered. The section that follows focuses on the mechanisms of the peptides with anticancer, antihypertensive, anti-obesity, and immunomodulatory effects. As further considerations were made, it is concluded that clinical studies targeting a clear understanding of the gastrointestinal stability, bioavailability, and safety of food-based peptides are still warranted.

Sulfate glycosaminoglycan from swim bladder exerts immunomodulatory potential on macrophages via toll-like receptor 4 mediated NF-κB signaling pathways

This study explored the immunomodulatory impact and potential mechanisms on macrophages RAW264.7 using a purified macromolecular sulfate glycosaminoglycan (SBSG) from the swim bladder, whose structure was similar to chondroitin sulfate A. The results showed that SBSG at 0.25-1 mg/mL increased the viability and phagocytosis of RAW264.7 cells. Meanwhile, SBSG promoted the secretion of tumor necrosis factor α (TNF-α), interleukin 10 (IL-10), and nitric oxide (NO), as well as the production of reactive oxygen species (ROS). According to the RT-PCR and Western blot data, SBSG activated TLR4-nuclear factor kappa B (NF-κB) signaling pathways, which decreased the relative mRNA and protein levels of Toll-like receptor 4 (TLR4), IκB kinase β (IKKβ), NF-κB p65, and p-NF-κB p65. The molecular docking and molecular dynamic simulation findings revealed that the main binding force between TLR4 and SBSG was conventional hydrogen bond interaction, resulting in more stable ligand receptor complexes. In summary, SBSG exhibits significant immunomodulatory potential, similar to chondroitin sulfate C. The underlying molecular mechanism involved the binding of SBSG through hydrogen bonding to TLR4 receptors, triggering the NF-κB signaling pathway to downregulate the expression of related genes and proteins. This, in turn, regulated the secretion of various cytokines that were mediated by macrophages to exert the immunity of the body.

Peptidome comparison on the immune regulation effects of different casein fractions in a cyclophosphamide mouse model

The protein composition of human milk plays a crucial role in infant formula milk powder formulation. Notably, significant differences exist between bovine casein and human milk casein. Previous studies have shown that casein hydrolysates could enhance immune function; however, gastrointestinal dyspepsia in infants affects the type and function of peptides. Therefore, the present study used peptidomics to sequence and analyze hydrolyzed peptides from different casein fractions. Additionally, animal experiments were conducted to assess the functionality of these casein fractions and elucidate their differences. The results revealed variations in peptide composition among the different casein fractions of formula milk powder. Interestingly, milk powder formulated with both β- and κ-casein (BK) exhibited significant enrichment of peptides related to the immune system. Moreover, the BK group significantly alleviated immune organ damage in cyclophosphamide-treated mice and regulated serum levels of pro-inflammatory and anti-inflammatory factors. Furthermore, feeding different casein fractions influenced the intestinal microflora of cyclophosphamide-treated mice, with the BK group mitigating the changes caused by cyclophosphamide. In conclusion, the findings suggest that BK formula in milk powder has the potential to positively enhance immunity. This study provides a robust theoretical basis for human-emulsified formula milk powder development.

Protective Effects of Mulberry (Morus atropurpurea Roxb.) Leaf Protein Hydrolysates and Their In Vitro Gastrointestinal Digests on AAPH-Induced Oxidative Stress in Human Erythrocytes

Mulberry leaf protein hydrolysates (HMP), and their in vitro gastrointestinal digests (GHMP), have shown favorable chemical antioxidant activities. The aim of this study is to investigate the potential protective effects of HMP and GHMP against 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced oxidative stress in human erythrocytes. The inhibition rate of hemolysis, the reactive oxygen species (ROS) level, the concentration of malondialdehyde (MDA), the reduced glutathione (GSH) and oxidized glutathione (GSSH), and the enzymatic activities of total superoxide dismutase (SOD), catalase (CAT), and cellular glutathione peroxidase (GSH-Px) were evaluated as the biomarkers of oxidative status in human erythrocytes. The results showed that HMP and GHMP effectively inhibit the occurrence of erythrocyte hemolysis in the range of 0.025-1.0 mg/mL, and the inhibition rates of HMP and GHMP reached 92% and 90% at concentrations of 0.4 mg/mL and 1.0 mg/mL, respectively. HMP and GHMP reduced the AAPH-induced oxidative hemolysis damage via suppressing the generation of ROS by inhibiting the formation of MDA, maintaining the balance of GSH/GSSG, and preserving the activities of the antioxidant enzymes, including SOD, GSH-Px, and CAT. Our findings revealed that both HMP and GHMP could be used as natural antioxidants, and have the potential for further application in the development of functional foods.

Effects of Selenium Enrichment on Dough Fermentation Characteristics of Baker's Yeast

In this research, the effect of selenium (Se) enrichment on dough fermentation characteristics of yeast and the possible mechanisms was investigated. Then, the Se-enriched yeast was used as starter to make Se-enriched bread, and the difference between Se-enriched bread and common bread was investigated. It was found Se enrichment increased CO₂ production and sugar consumption rate of Saccharomyces cerevisiae (S. cerevisiae) in dough fermentation, and had positive impacts on final volume and rheological index of dough. The mechanism is possibly related to higher activity and protein expression of hexokinase (HK), phosphofructokinase (PFK), pyruvate kinase (PK), citrate synthase (CS), isocitrate dehydrogenase (ICD), and α-ketoglutarate dehydrogenase (α-KGDHC) in Se-enriched yeast. Moreover, Se-enriched bread (Se content: 11.29 μg/g) prepared by using Se-enriched yeast as starter exhibited higher overall acceptability on sensory, cell density in stomatal morphology, and better elasticity and cohesiveness on texture properties than common bread, which may be due to effect of higher CO₂ production on dough quality. These results indicate Se-enriched yeast could be used as both Se-supplements and starter in baked-foods making.

Investigation of the optimal production conditions for egg white hydrolysates and physicochemical characteristics

This study aimed to investigate the potential of egg white protein hydrolysate (EWH) as a functional food by identifying the optimum production conditions for EWH with response surface methodology (the results of the sensory evaluation were considered as an essential quality indicator). At the same time, its physicochemical and biological activity was also evaluated. The optimal economic production conditions were selected: substrate concentration of 12.5%, enzyme content of 7.5%, and hydrolysis time at 100 min. The degree of hydrolysis (DH %) was 13.51%. In addition, to the better acceptance of the evaluation, it also helps to reduce the production cost of the protein hydrolysate, which is beneficial to future processing and applications. The antioxidant capacity experiments showed that EWH has good antioxidant activity, which presents a dose-dependent relationship. Hence, this study provides a theoretical basis for future research and application of EWH for processing applications, including dietary supplementation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05708-0.

Purification, Identification and Molecular Docking of Immunomodulatory Peptides from the Heads of Litopenaeus vannamei

In order to realize the high-value utilization of Litopenaeus vannamei (L. vannamei) heads, immunomodulatory peptides were prepared from the enzymatic hydrolysate of L. vannamei heads, and the action mechanism of immunomodulatory peptides was determined by molecular docking. The results showed that six proteases were used to hydrolyze L. vannamei head proteins, with the animal protease hydrolysate exhibiting the highest macrophage relative proliferation rate (MRPR). The enzymatic products were then sequentially purified by ultrafiltration, Sephadex G-15 gel chromatography, identified by liquid chromatography-mass spectrometry (LC-MS/MS), and finally selected for six immunomodulatory peptides (PSPFPYFT, SAGFPEGF, GPQGPPGH, QGF, PGMR, and WQR). These peptides maintained good immune activity under heat treatment, pH treatment, and in vitro gastrointestinal digestion. Molecular docking analysis indicated that these peptides showed great binding to both toll-like receptor 2 and 4 (TLR2 and TLR4/MD-2), leading to immunomodulation. The discarded L. vannamei heads in this article are considered to be promising food-borne immunomodulators that contribute to enhancing the immune function of the body.

Effects of low molecular weight peptides from monkfish (Lophius litulon) roe on immune response in immunosuppressed mice

This study aimed to investigate the immunomodulatory activation of low-molecular-weight peptides from monkfish (Lophius litulon) roe (named MRP) on cyclophosphamide (CTX)-induced immunosuppressed mice. Our results indicated that MRP (100 mg/kg/d BW) could significantly increase the body weight and immune organ index, and improve the morphological changes in the spleen and thymus of mice. These effects subsequently enhance the serum levels of interleukin (IL)-6, IL-1β, tumor necrosis factor (TNF)-α, and immunoglobulin (Ig) A, IgM, and IgG. Furthermore, MRP could also improve CTX-induced oxidative stress, and activate the NF-κB and MAPK pathways in the spleen tissues. The findings reported herein indicate that MRP has a good immunomodulatory activation toward immunosuppressed mice, hence can potentially be developed as an immune adjuvant or functional food.

Antioxidant and immunomodulatory potency of Lacticaseibacillus rhamnosus NCDC24 fermented milk-derived peptides: A computationally guided in-vitro and ex-vivo investigation

Infections of microbial and non-microbial origins have been associated with significant immunological manifestations, thereby underscoring the need for a thorough understanding and investigation of novel immunomodulatory and antioxidant molecules that could prevent these incidences. To this end, we herein aim to identify fermented milk peptides with antioxidant and immunomodulatory properties that could be exploited for specific future applications. Our computational prediction models indicate that these peptides are non-toxic and possess considerable hydrophobicity (19.82-38.96 %) and functionality. Further analyses reveal that two of the four peptides, i.e., Pep 1 (AGWNIPM) and Pep 4 (YLGYLEQLLR), possess higher in-vitro antioxidant activity. The immunomodulatory potential of these two peptides (Pep 1 and Pep 4) is further demonstrated by using a combination of molecular simulation trajectory and ex-vivo approaches. Both peptides demonstrate ability to control the production of pro- inflammatory (TNF-α, IL-1, and IL-6) and anti-inflammatory (IL-10) cytokines as well as nitric oxide release in LPS-stimulated murine peritoneal macrophages. Similarly, peptide interferences also lead to significant (P < 0.05) improvement in macrophage phagocytic capacity. Taken together, these findings highlight the antioxidant and immunomodulatory properties of fermented milk peptides (Pep 1 and Pep 4) within the cellular environment and should facilitate prospective studies exploring such bioactive peptides and related functional molecules mediating the benefits of fermented milk products on human health.

C-Terminal Modification on the Immunomodulatory Activity, Antioxidant Activity, and Structure–Activity Relationship of Pulsed Electric Field (PEF)-Treated Pine Nut Peptide

In this study, a novel peptide VNAVL was synthesized by removing the C-terminal histidine on the basis of a bioactive peptide VNAVLH obtained from pine nut (Pinus koraiensis Sieb. et Zucc) protein. The effects of removing histidine on antioxidant activity, immunomodulatory activity, and secondary structure of the PEF-treated peptide were discussed. Compared with VNAVLH, VNAVL only exhibited lower antioxidant activity, but no immunomodulatory activity to release TNF-α, IL-6, and NO by activating RAW 264.7 cells. In addition, both antioxidant and immune activities of VNAVLH were significantly more sensitive to treatment with 40 kV/cm than other field intensities, whereas VNAVL was not sensitive to field strength changes. CD spectra and DSSP analysis verified that both peptides consisted of a β structure and random coil, but the ability of VNAVL to transform the random coil via PEF treatment is weaker than that of VNAVLH. Therefore, PEF treatment might expose the key active site located on the C-terminal histidine by altering the secondary structure of the peptide.

Isolation, Identification, and Immunomodulatory Mechanism of Peptides from Lepidium meyenii (Maca) Protein Hydrolysate

Maca is a protein-enriched edible plant with immunomodulatory activity. However, the role of proteins in the immunomodulatory activity of maca is unclear. In this study, peptide products of maca proteins obtained through in vitro gastrointestinal digestion were isolated and purified, and the immunomodulatory activities of these peptides were assessed in macrophages (RAW 264.7 cells). The results show that the maca protein hydrolysate enhanced the phagocytic capacity and NO, TNF-α, and IL-6 secretion of RAW 264.7 cells. Forty-five peptides from known proteins of maca or the cruciferous family were identified by ultraperformance liquid chromatography-tandem mass spectrometry in the hydrolysate, and the peptide RNPFLP exhibited the strongest immunomodulatory activity. Antibody blocking, siRNA, pathway inhibitors, and western blot assays showed that RNPFLP-activated RAW 264.7 cells through the NF-κB and MAPK signaling pathways mediated by TLR2 and TLR4 receptors. An analysis of the structure-activity relationship showed that the N₉-H₆₀ active site in arginine plays an important role in the immunomodulatory activity of RNPFLP. This study provides a new understanding of the immunomodulatory activity of maca.

Identification and characterization of immunomodulatory peptides from pepsin-soy protein hydrolysates

To obtain immunomodulatory peptides from isolated soy protein (ISP), pepsin was selected to prepare hydrolysates and 4-h treatment (Pepsin-ISPH4h) showed the highest yield and immunomodulatory activities. The Pepsin-ISPH4h was sequentially fractionated by 30, 10 and 1-kDa molecular weight cut-off (MWCO) membranes, in which 1-kDa MWCO permeate (1P) exhibited the most significant enhancement of phagocytosis activity without causing excessive inflammation as compared with Pepsin-ISPH4h. To further purify and enhance the immunomodulatory activity, 1P was distinct by high-performance liquid chromatography equipped with a reverse-phase column and in vivo immunomodulatory activity of fractions was examined in mice. Fraction 1 (F1) significantly elevated phagocytosis activity of mice spleen macrophages and neutrophils. However, increase of phagocytosis activity did not result from the induction of macrophages M1 or M2 polarization. The immunomodulatory peptide sequence, EKPQQQSSRRGS, from F1 was identified by LC-MS/MS. Phagocytosis activity and macrophage M1 polarization were elevated by synthetic peptide treatment. Hence, our results indicated that isolated soy protein hydrolysates prepared by pepsin could provide a source of peptides with immunomodulatory effects.

VF-4 and DR-8 Derived from Salted Egg White Inhibit Inflammatory Activity via NF-κB/PI3K-Akt/MAPK Signal Transduction Pathways in HT-29 Cells Induced by TNF-α

SCOPE

Inflammation is the pathological basis of many chronic diseases, and persistent intestinal inflammation is a key factor in the further development of colon cancer. Egg-derived peptides have been proven to have anti-intestinal inflammation activity. Egg white treated with salt contains a lot of rich protein, whether its peptides have anti-inflammatory activity and how their mechanism of action is still unclear.

METHODS AND RESULTS

In this study, ELISA is used to determine the anti-inflammatory activity of the peptides (VF-4 and DR-8 from salted egg white), and then RNA-seq is used to explore the mechanism of their anti-inflammatory activity, and then verified by western blotting and inhibitors. The results show that VF-4 and DR-8 significantly inhibit TNF-α-induced IL-8 secretion in HT-29 cells in a concentration-dependent manner, and VF-4 show a more significant anti-inflammatory effect than DR-8. The anti-inflammatory mechanism of VF-4 and DR-8 is through inhibiting the activation of Nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK), and phosphatidylinositol 3' -kinase(PI3K)-Akt pathways, reducing the production of inflammatory mediators.

CONCLUSION

VF-4 and DR-8 have obvious anti-inflammatory activity, which can reduce intestinal inflammation and inhibit its further development into colon cancer.

Neuromodulatory peptides: Orally active anxiolytic-like and antidepressant-like peptides derived from dietary plant proteins

Mental disorders are a severe health problem, and the number of patients is growing worldwide. Increased anxiety and decreased motivation due to excessive mental stress further accelerated the severity of the problem. Enzymatic digestion of food proteins produces bioactive peptides with various physiological functions, some of which exhibit neuromodulatory effects with oral administration. Recently, studies reported that some peptides produced from plant proteins such as soybeans, leaves, and grains exhibit emotional regulatory functions such as strong anxiolytic-like and antidepressant-like effects comparable to pharmaceuticals. Conventionally, researchers investigated bioactive peptides by fractionation of protein hydrolysates and structure-activity relationship. As a novel methodology for analyzing bioactive peptides, the information obtained by peptidomics simultaneous analysis of the digested fractions of proteins using mass spectrometry has been effectively utilized. Some small-sized peptides such as dipeptides and tripeptides released food-derived proteins show emotional regulating effects. Moreover, some middle-sized peptides produced after intestinal digestion may exhibit the emotional regulating effect via the vagus nerve, and the importance of the gut-brain axis is also focused. As the central mechanism of emotional regulation, it has been found that these plant-derived peptides regulated monoamine neurotransmitter signaling and hippocampal neurogenesis.