In order to further realize the resource reuse of walnut meal after oil extraction, walnut meal was used as raw material to prepare polypeptide, and its angiotensin-converting enzyme (ACE) inhibitory activity was investigated. The ACE inhibitory peptides were prepared from walnut meal protein by alkaline solution and acid precipitation. The hydrolysis degree and ACE inhibition rate were used as indexes to optimize the preparation process by single-factor experiment and response surface method. The components with the highest ACE activity were screened by ultrafiltration, and their antioxidant activities were evaluated in vitro. The effect of gastrointestinal digestion on the stability of walnut peptide was analyzed by measuring molecular weight and ACE inhibition rate. The results showed that the optimal extraction conditions were pH 9.10, hydrolysis temperature 54.50 °C, and hydrolysis time 136 min. The ACE inhibition rate of walnut meal hydrolysate (WMH) prepared under these conditions was 63.93% ± 0.43%. Under the above conditions, the fraction less than 3 kDa showed the highest ACE inhibitory activity among the ACE inhibitory peptides separated by ultrafiltration. The IC₅₀ value of scavenging ·OH free radical was 1.156 mg/mL, the IC₅₀ value of scavenging DPPH free radical was 0.25 mg/mL, and the IC₅₀ value of scavenging O₂⁻ was 3.026 mg/mL, showing a strong total reducing ability. After simulated gastrointestinal digestion in vitro, the ACE inhibitory rate of walnut peptide decreased significantly, but it still maintained over 90% ACE inhibitory activity. This study provides a reference for the application of low-molecular-weight walnut peptide as a potential antioxidant and ACE inhibitor.

Background/Aims: The present study aimed to analyze the mechanisms by which periodic mechanical stress is translated into biochemical signals, and to verify the important role of signaling molecules including phosphatidylinositol-3-kinase (PI3K)-Akt, protein kinase C (PKC), and epidermal growth factor receptor (EGFR) in chondrocyte proliferation. The effects of periodic mechanical stress on the mitogenesis of chondrocytes have been studied extensively in recent years. However, the mechanisms underlying the ability of chondrocytes to sense and respond to periodic mechanical stress need further investigation. Methods: Two steps were undertaken in the experiment. In the first step, the cells were pretreated with shRNA targeted to Akt or EGFR or PKCδ or control scrambled shRNA. Moreover, they were pretreated with LY294002, GF109203X, Gö6976, rottlerin, and AG1478. They were maintained under static conditions or periodic mechanical stress for 3 days, 8 h per day, prior to direct cell counting and CCK-8 assay, respectively. In the second step, the cells were pretreated with shRNA targeted to Akt or EGFR or PKCδ or control scrambled shRNA. Moreover, they were pretreated with LY294002, AG1478, and rottlerin. They were maintained under static conditions or periodic mechanical stress for 1 h prior to Western blot analysis. Results: Proliferation was inhibited by pretreatment with PKC or PKCδ inhibitor GF109203X or rottlerin and by short hairpin RNA (shRNA) targeted to PKCδ, but not by PKCα inhibitor Gö6976 in chondrocytes in response to periodic mechanical stress. Meantime, rottlerin and shRNA targeted to PKCδ also attenuated EGFR, Akt, and ERK1/2 activation. Furthermore, inhibiting EGFR activity by AG1478 and shRNA targeted to EGFR abrogated chondrocyte proliferation and phosphorylation levels of Akt and extracellular signal-regulated kinase (ERK)1/2 subjected to periodic mechanical stress, while the phosphorylation site of PKCδ was not affected. In addition, pretreatment with the PI3K-Akt-selective inhibitor LY294002 and shRNA targeted to Akt reduced periodic mechanical stress-induced chondrocyte proliferation and phosphorylation of ERK1/2, while the phosphorylation levels of EGFR and PKCδ were not inhibited. Conclusion: These findings suggested that periodic mechanical stress promoted chondrocyte proliferation through PKCδ-EGFR-PI3K-Akt-ERK1/2. They provide a stronger viewpoint for further investigations into chondrocyte mechanobiology under periodic mechanical stress and the ways to improve the quality of tissue-engineered cartilage.

Previously, research adopted an ultrasound-assisted extraction method to isolate crude polysaccharide from blackened jujube, followed by preliminary structural identification of the purified polysaccharide (BJP). This manuscript analyzed the accurate structure and immunomodulatory activity of BJP. Further structural identification indicated that BJP was mainly composed of →3)-α-L-Araf-(1→, →3,5)-α-L-Araf-(1→, →3)-β-D-GalpA-(1→, →2,4)-β-D-Galp-(1→, →4)-β-D-GalpA-(1→, →3)-α-L-Rhap-(1→ and →3,4)-α-L-Rhap-(1→. The immunomodulatory effects of BJP were examined using a mouse model with immunosuppression induced by cyclophosphamide. The findings suggested that BJP could relieve the condition of immunosuppressed mice. BJP could inhibit decreases in the body weight and organ index of mice, and HE staining showed that BJP could alleviate the harm to spleen and thymus tissues. BJP enhanced the secretion of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α), interleukin-2 (IL-2), interleukin-6 (IL-6), immunoglobulin A (IgA), and immunoglobulin G (IgG) in serum. It also reduced liver oxidative stress by increasing superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) activities, while lowering malondialdehyde (MDA) levels. Moreover, BJP contributed to the maintenance of gut homeostasis by stimulating the generation of short-chain fatty acids in the cecal contents. The study aims to establish a solid basis for the comprehensive development of blackened jujube and furnish a theoretical framework for its polysaccharides’ role in immune modulation.