Anti-diabetic and anti-hyperlipidemic effects of sea cucumber (Cucumaria frondosa) gonad hydrolysates in type II diabetic rats

Discovery of novel DPP4 inhibitory peptides from egg yolk by machine learning and molecular docking: In vitro and in vivo validation

DPP4 inhibitors could treat T2DM. Low-cost and accessible egg yolk protein (EYP) has the potential to produce highly bioactive peptides. Therefore, this study was to explore the novel DPP4 inhibitory peptide in EYP. The optimal protease (alcalase and pepsin) was screened using virtual enzymatic digestion. 61 potential peptides were filtered by ultrafiltration, LC-MS/MS, activity prediction and physicochemical property calculations. Then peptides RYHFPEGL, EYF, KFL, YKF and AAQEKIRYW were obtained by machine learning, BIOPEP database and molecular docking. AAQEKIRYW had outstanding hypoglycemia efficacy by in vitro cellular assay and mice plasma assay, with IC50 36.65 μM. Molecular docking and MD revealed that AAQEKIRYW-DPP4 complex was stably bound to S1 and S2' pockets of protein through hydrophilic (hydrogen bonding and electrostatic interactions) and hydrophobic interactions. It will provide a new insight for high-value utilization of EYP and a reference for the efficient screening and mechanism resolution of highly active peptides.

Characteristics and bioinformatics of peptides from natural and cultured sandfish (Holothuria scabra)

This study aimed to investigate the characteristics and bioinformatics identification of peptides in sandfish (Holothuria scabra) protein hydrolysate from natural and cultured sources, with the hypothesis that different sources of sandfish and enzymatic treatments would result in distinct peptide profiles. Sandfish from both sources were subjected to double enzymatic hydrolysis using neutral protease-alcalase (NA), papain-neutral protease (PN), and papain-alcalase (PA) to obtain protein hydrolysates. The hydrolysates were analyzed for amino acid composition, protein molecular weight distribution, functional groups using FTIR spectroscopy, LC-MSMS analysis coupled with bioinformatics for protein and peptide identification, and mineral profile. The resulting hydrolysates exhibited similar amino acid profiles, characterized by high levels of glycine, alanine, glutamic acid, and aspartic acid. The functional groups of the sandfish protein hydrolysates were primarily found at wavenumbers 1658 cm-1 (amide I), 1541 cm-1 (amide II), and 1246 cm-1 (amide III). Peptides with molecular weights below 500 Da predominated in every sample, highlighting their small molecular size. LC-MSMS analysis, coupled with bioinformatics database comparisons, indicated that sandfish from natural and cultured sources, as well as different enzymes used in the hydrolysis process, significantly affect protein and peptide pattern. Of the 2132 identified proteins, 1258 exhibited significant differences (p < 0.05, FDR < 0.05). This study provides insights into how source and enzymatic treatment influence peptide profiles, which could be applied in the development of functional ingredients or bioactive peptides from sandfish.

EPA-enriched lipid from Apostichopus japonicus byproducts mitigates UVB-induced oxidative stress and inflammation by gut-skin axis

The tremendous byproducts from sea cucumber processing discarded as waste bring serious environmental and economic challenges. The abundant EPA in sea cucumber intestines indicates the potential for lipid development. However, there is little study on how these lipids affect skin health. Using REM techniques, this study prepared lipids from Apostichopus japonicus intestines (AJIL) with a 26.63 % EPA content, which displayed DPPH scavenging capacity in vitro. Administration of AJIL showed significant skin repair effects by reducing the symptoms of UVB-induced skin tissue damage, preventing epidermal thickening and increasing hydroxyproline content to protect collagen. AJIL suppressed oxidative stress and inflammation by significantly reducing ROS and MDA levels and enhancing GPx and CAT activity, as well as inhibiting the expression of inflammatory cytokines such as TNF-α, NF-κB, IL-1β and IL-6. By upregulating Nrf2, HO-1 and NQO-1 and downregulating Keap1, AJIL activated the Keap1-Nrf2 signaling pathways. Furthermore, AJIL regulated the composition and structure of gut microbiome, especially significantly increasing the SCFA-producing and anti-inflammatory bacteria like Muribacuclaceae, Alloprevotella, Bacteroides and Prevotellaceae, then improved key metabolic pathways. Overall, AJIL mediated the gut-skin axis to prevent UVB-induced skin damage and revealed potential as a natural skin protection candidate, which transformed discarded sea cucumber intestines into valuable resources for skin health.

Research Progress on Anti-Hyperlipidemia Peptides Derived from Foods

Hyperlipidemia is a metabolic disorder in which cholesterol (TC) and triglycerides (TGs) in the blood exceed the normal physiological levels. The incidence of the condition has continued to rise in recent years, posing a serious threat to public health. Its clinical treatment mainly relies on drug interventions, such as statins, fibrate, and niacin. Although these drugs have shown some efficacy in the treatment of hyperlipidemia, their adverse effects cannot be ignored. In contrast, naturally derived peptides have gradually become potential candidates for the prevention and treatment of hyperlipidemia due to their strong anti-hyperlipidemic activity and safety; examples of such peptides include those from dairy products, grains, legumes, and seafood. This review systematically summarizes peptides with anti-hyperlipidemic activity and analyzes their mechanisms of action, providing a theoretical basis for further research. In addition, we also outline some challenges facing the application of peptides, hoping to prevent hyperlipidemia and reduce its incidence by encouraging the consumption of foods rich in anti-hyperlipidemia peptides.

High-fat diet promotes type 2 diabetes mellitus by disrupting gut microbial rhythms and short-chain fatty acid synthesis

Diabetes ranks among the top 10 causes of death globally, with over 90% of individuals diagnosed with diabetes having type 2 diabetes mellitus (T2DM). It is acknowledged that a high-fat diet (HFD) poses a serious risk for T2DM. The imbalance of intestinal flora, mediated by HFD, can potentially exacerbate the onset and progression of T2DM. However, the impact of HFD on pathological indicators and the intestinal microbiome in the development of T2DM has not been systematically investigated. Therefore, a HFD mouse model and a T2DM mouse model were established, respectively, in this study. The role of HFD as a driving factor in the development of T2DM was assessed using various measures, including basic pathological indicators of T2DM, lipid metabolism, liver oxidative stress, intestinal permeability, levels of inflammatory factors, gut microbiota, and short-chain fatty acids (SCFAs). The findings indicated that HFD could influence the aforementioned measures to align with T2DM changes, but the contribution of HFD varied across different pathological metrics of T2DM. The impact of HFD on low-density lipoprotein cholesterol, glutathione peroxidase, malondialdehyde, and tumor necrosis factor-α did not show a statistically significant difference from those observed in T2DM during its development. In addition, regarding gut microbes, HFD primarily influenced the alterations in bacteria capable of synthesizing SCFAs. The notable decrease in SCFA content in both serum and cecal matter further underscored the effect of HFD on SCFA-synthesising bacteria in mice. Hence, this research provided a systematic assessment of HFD's propelling role in T2DM's progression. It was inferred that gut microbes, particularly those capable of synthesizing SCFAs, could serve as potential targets for the future prevention and treatment of T2DM instigated by HFD.

Advances in Research on Type 2 Diabetes Mellitus Targets and Therapeutic Agents

Diabetes mellitus is a chronic multifaceted disease with multiple potential complications, the treatment of which can only delay and prolong the terminal stage of the disease, i.e., type 2 diabetes mellitus (T2DM). The World Health Organization predicts that diabetes will be the seventh leading cause of death by 2030. Although many antidiabetic medicines have been successfully developed in recent years, such as GLP-1 receptor agonists and SGLT-2 inhibitors, single-target drugs are gradually failing to meet the therapeutic requirements owing to the individual variability, diversity of pathogenesis, and organismal resistance. Therefore, there remains a need to investigate the pathogenesis of T2DM in more depth, identify multiple therapeutic targets, and provide improved glycemic control solutions. This review presents an overview of the mechanisms of action and the development of the latest therapeutic agents targeting T2DM in recent years. It also discusses emerging target-based therapies and new potential therapeutic targets that have emerged within the last three years. The aim of our review is to provide a theoretical basis for further advancement in targeted therapies for T2DM.

The Structural Characteristics and Bioactivity Stability of Cucumaria frondosa Intestines and Ovum Hydrolysates Obtained by Different Proteases

The study aimed to investigate the effects of alcalase, papain, flavourzyme, and neutrase on the structural characteristics and bioactivity stability of Cucumaria frondosa intestines and ovum hydrolysates (CFHs). The findings revealed that flavourzyme exhibited the highest hydrolysis rate (51.88% ± 1.87%). At pH 2.0, the solubility of hydrolysate was the lowest across all treatments, while the solubility at other pH levels was over 60%. The primary structures of hydrolysates of different proteases were similar, whereas the surface hydrophobicity of hydrolysates was influenced by the types of proteases used. The hydrolysates produced by different proteases were also analyzed for their absorption peaks and antioxidant activity. The hydrolysates of flavourzyme had β-fold absorption peaks (1637 cm^-1), while the neutrase and papain hydrolysates had N-H bending vibrations. The tertiary structure of CFHs was unfolded by different proteases, exposing the aromatic amino acids and red-shifting of the λ-peak of the hydrolysate. The alcalase hydrolysates showed better antioxidant activity in vitro and better surface hydrophobicity than the other hydrolysates. The flavourzyme hydrolysates displayed excellent antioxidant stability and pancreatic lipase inhibitory activity during gastrointestinal digestion, indicating their potential use as antioxidants in the food and pharmaceutical industries.

Antioxidant Peptides from Monkfish Swim Bladders: Ameliorating NAFLD In Vitro by Suppressing Lipid Accumulation and Oxidative Stress via Regulating AMPK/Nrf2 Pathway

In this study, we investigate the ameliorating functions of QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) from monkfish swim bladders on an FFA-induced NAFLD model of HepG2 cells. The lipid-lowering mechanisms revealed that these five oligopeptides can up-regulate the expression of phospho-AMP-activated protein kinase (p-AMPK) proteins to inhibit the expression of the sterol regulatory element binding protein-1c (SREBP-1c) proteins on increasing lipid synthesis and up-regulating the expression of the PPAP-α and CPT-1 proteins on promoting the β-oxidation of fatty acids. Moreover, QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) can significantly inhibit reactive oxygen species' (ROS) production, promote the activities of intracellular antioxidases (superoxide dismutase, SOD; glutathione peroxidase, GSH-PX; and catalase, CAT) and bring down the content of malondialdehyde (MDA) derived from lipid peroxidation. Further investigations revealed that the regulation of these five oligopeptides on oxidative stress was achieved through activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway to raise the expression levels of the heme oxygenase 1 (HO-1) protein and downstream antioxidant proteases. Therefore, QDYD (MSP2), ARW (MSP8), DDGGK (MSP10), YPAGP (MSP13) and DPAGP (MSP18) could serve as candidate ingredients to develop functional products for treating NAFLD.

Antioxidant Potential of Sea Cucumbers and Their Beneficial Effects on Human Health

Sea cucumbers are considered a luxury food item and used locally in traditional medication due to their impressive nutritional profile and curative effects. Sea cucumbers contain a wide range of bioactive compounds, namely phenolics, polysaccharides, proteins (collagen and peptides), carotenoids, and saponins, demonstrating strong antioxidant and other activities. In particular, phenolic compounds, mainly phenolic acids and flavonoids, are abundant in this marine invertebrate and exhibit antioxidant activity. Protein hydrolysates and peptides obtained from sea cucumbers exhibit antioxidant potential, mainly dependent on the amino acid compositions and sequences as well as molecular weight, displayed for those of ≤20 kDa. Moreover, the antioxidant activity of sea cucumber polysaccharides, including fucosylated chondroitin sulfate and fucan, is a combination of numerous factors and is mostly associated with molecular weight, degree of sulfation, and type of major sugars. However, the activity of these bioactive compounds typically depends on the sea cucumber species, harvesting location, food habit, body part, and processing methods employed. This review summarizes the antioxidant activity of bioactive compounds obtained from sea cucumbers and their by-products for the first time. The mechanism of actions, chemical structures, and factors affecting the antioxidant activity are also discussed, along with the associated health benefits.