Walnut (Juglans regia L.) is unique for its extensive biological activities and pharmaceutical properties. There are few studies on walnut oligopeptides (WOPs), which are small molecule peptides extracted from walnuts. This study aimed to evaluate the anti-fatigue effects of WOPs on ICR mice and explore the possible underlying mechanism. Mice were randomly divided into four experimental sets and each set of mice were then randomly divided into four groups. The vehicle group was administered distilled water, and the three WOP intervention groups were orally administered WOP solution at a dose of 110, 220, and 440 mg/kg of body weight, respectively. After 30 days of WOP intervention, the anti-fatigue activity of WOPs were evaluated using the weight-loaded swimming test and by measuring the change of biochemical parameters, glycogen storage and energy metabolism enzymes, anti-oxidative capacity and mitochondrial function. It was observed that WOPs could significantly prolong the swimming time, decrease the accumulation of lactate dehydrogenase (LDH), creatine kinase (CK), blood urea nitrogen (BUN) and blood lactic acid (BLA), and increased the glycogen storage of liver and gastrocnemius muscle. WOPs also markedly inhibited fatigue induced oxidative stress by increasing the activity of superoxide dismutase (SOD), glutathione peroxidase (GPX) and decreasing the content malondialdehyde (MDA). Notably, WOPs improved the activity of pyruvate kinase (PK), succinate dehydrogenase (SDH), Na+-K+-ATPase, and enhanced the mRNA expression of mitochondrial biogenesis factors and mitochondrial DNA content in skeletal muscles of mice. These results suggest that WOPs have beneficial anti-fatigue effects, which may be attributed to their positive effects on increasing glycogen storage, improving energy metabolism, inhibiting oxidative stress, enhancing mitochondrial function in skeletal muscle, and ameliorating the cell damage and the muscular injury.

The study investigated the protective effect of walnut oligopeptides (WOPs) against ethanol-induced gastric injury using Sprague-Dawley (SD) rats. Rats were randomly divided into seven groups based on body weight (10/group), normal group, ethanol group, whey protein group (220 mg/kg body weight), omeprazole group (20 mg/kg body weight), and three WOPs groups (220, 440, 880 mg/kg body weight). After 30 days of treatment with WOPs, rats were given 5 mL/kg absolute ethanol by gavage to induce gastric mucosal injury. Gastric ulcer index (GUI) were determined and the following measured; gastric content pH, gastric mucin, endogenous pepsinogens (PG), prostaglandin E2 (PGE2), inflammatory cytokines, oxidative stress indicators, and the expression of apoptosis-related proteins were measured to evaluate the gastroprotective effect of WOPs. The results showed that the administration with WOPs markedly mitigated the hemorrhagic gastric lesions caused by ethanol in rats, and decreased the GUI, the gastric content pH, PG1, PG2, and NO levels, enhanced mucin and PGE2. Also, WOPs repressed gastric inflammation through the reduction of TNF-α, IL-6, IL-1β and increase IL-10 levels, and revealed antioxidant properties with the enhancement of superoxide dismutase, glutathione, and catalase activity, while reduction of malondialdehyde. Moreover, WOPs treatment significantly down-regulated Bax, caspase-3 and nuclear factor-κB p65 (NF-κB p65) expression, while up-regulating the expression of Bcl-2 and inhibitor kappa Bα (IκBα) protein. These results indicated that WOPs have protective effects against ethanol-induced gastric mucosal injury in rats through anti-inflammatory, anti-oxidation, and anti-apoptosis mechanisms.

Panax ginseng C.A. Meyer (ginseng) is an edible and traditional medicinal herb, which is reported to have a wide range of biological activity and pharmaceutical properties. There were more studies on ginsenoside and polysaccharides, but fewer on ginseng oligopeptides (GOPs), which are small molecule oligopeptides extracted from ginseng. The present study was designed to investigate the effects and underlying mechanism of ginseng oligopeptide (GOPs) on binge drinking-induced alcohol damage in rats. Sprague Dawley rats were randomly assigned to six groups (n = 10), rats in normal control group and alcohol model group was administered distilled water; rats in four GOPs intervention groups (at a dose of 0.0625, 0.125, 0.25, 0.5 g/kg of body weight, respectively) were administered GOPs once a day for 30 days. Experiment rats were intragastrically administered ethanol at a one-time dose of 7 g/kg of body weight after 30 days. The liver injury was measured through traditional liver enzymes, inflammatory cytokines, expression of oxidative stress markers, and histopathological examination. We found that the GOPs treatment could significantly improve serum alanine aminotransferase and aspartate aminotransferase, plasma lipopolysaccharide, and inflammatory cytokine levels, as well as the oxidative stress markers that were altered by alcohol. Moreover, GOPs treatment inhibited the protein expression of toll-like receptor 4, and repressed the inhibitor kappa Bα and nuclear factor-κB p65 in the liver. These findings suggested that GOPs have a significant protective effect on binge drinking-induced liver injury, and the mechanism possibly mediated by the partial inhibition of lipopolysaccharide—toll-like receptor 4-nuclear factor-κB p65 signaling in the liver.

The study was aimed to determine whether treatment with oat oligopeptides (OOPs) could modulate hyperglycemia related to type 2 diabetes mellitus (T2DM) in Sprague–Dawley (SD) rats. Diabetic SD rats modeling by a joint effect of high-calorie diet for 45 days and twice intraperitoneal injection of 30 mg/kg streptozotocin at one-week interval were observed with or without OOPs administration (0.25, 0.50, 1.00, and 2.00 g/kg Body Weight) for 12 weeks. Fasting blood glucose (FBG), oral glucose test tolerance (OGTT), serum insulin, level of antioxidant, and hepatic enzymes were measured. In addition, frequency of micturition was recorded in this study for the first time. It was observed that the administration of OOPs (2.00 g/kg Body Weight) resulted in a significant decrease (p < 0.05) in FBG since 6th week and a significant decrease (p < 0.05) in the OGTT-AUC on 6th and 10th week. In addition, the administration of OOPs (2.00 g/kg Body Weight) reduced HOMA-IR index and 24-h urine volume significantly (p < 0.05) whereas increased SOD activity significantly (p < 0.05). These results suggested that OOPs may have a hypoglycemic effect in diabetic rats.

The study aimed to investigate the immunomodulatory activity of oligopeptides derived from oat (Avena nuda L.) (OOPs). Healthy female BALB/c mice were randomly assigned to five groups, given deionized water (control) and 0.25, 0.5, 1.0, and 2.0 g/kg body weight (BW) of OOPs daily by intragastric administration. Seven assays were performed to determine the immunomodulatory effects of OOPs on immune organ ratios, cellular and humoral immune responses, macrophage phagocytosis, and natural killer (NK) cell activity. Spleen T lymphocyte subpopulations (by flow cytometry), serum cytokine and immunoglobulin levels (by multiplex sandwich immunoassays) were determined to evaluate how OOPs affected the immune system. Our results showed that OOPs could significantly improve innate and adaptive immune responses in mice through the enhancement of cell-mediated and humoral immunity, macrophage phagocytosis capacity, and NK cell activity. We concluded that the immunomodulatory effects might be attributed to increased T and Th cell percentages, serum interferon (IFN)-γ, interleukin (IL)-1 α, IL-2, IL-6, IL-10, IL-12, tumor necrosis factor (TNF)- α, and granulocyte-macrophage colony-stimulating factor (GM-CSF) secretions as well as immunoglobulin (Ig) A, IgG, and IgM productions. These results indicate that dietary OOPs could be considered as promising immunomodulators with dosages ranging from 0.25 to 2.0 g/kg BW.

Walnut oligopeptides (WOPs) intake is associated with the augment of the antioxidant defense system and immune system. The chief object of this study is to evaluate the radioprotective effect of walnut oligopeptides extracted from walnut seed protein against ⁶⁰Coγ-irradiation induced damage in mice. Female BALB/c mice were administered WOPs through drinking water for 14 days until a single dose of whole-body ⁶⁰Coγ-irradiation. The 30-day survival test was carried out in the first group (8 Gy), and the other two groups (3.5 Gy) were sacrificed at 3 days and 14 days post-irradiation. Blood and organ samples of mice in the three groups were collected, the histopathological analysis and immunohistochemistry were conducted. The number of peripheral blood leukocytes, bone marrow DNA content, inflammatory cytokines, antioxidant capacity, and intestinal permeability were measured. We found that the administration of WOPs augmented antioxidant defense system, accelerated hematopoietic recovery and showed the significant trend toward higher survival rate and less weight loss compared with non-administrated control mice. In addition, WOPs administration appeared to be important to limit IR-induced splenocyte apoptosis and inflammatory cascade as well as reduce intestine epithelial barrier dysfunction and promote epithelial integrity. These results suggest that pre and post-treatment of WOPs may help to ameliorate acute damage, which is induced by ionizing radiation in mice and accelerate its recovery.