Effects of Dietary Peptides From Essence of Chicken on Neuroinflammation and Their Synergism in Neuroprotection

Objective: Neuroinflammation is a chronic disease of the nervous system, and timely prevention and treatment could effectively prevent its progression to severe diseases. Essence of chicken (EC) is a mixture of peptides and amino acids extracted from whole chickens which has been proven to alleviate neuroinflammation and improve cognition. The aim of the present study was to screen for potential peptides possessing excellent effects in alleviating neuroinflammation and to explore their synergistic effects. Methods: BV2 cells were treated with 0.1, 1, or 10 mM dietary peptides found in EC in the presence of 1 μg/mL lipopolysaccharide (LPS) for 16 h to screen for potent compounds. LPS-treated BV2 cells were then cultured with 0.03 or 0.1 mM potent bioactive compounds alone or in combination with 0.1 mM carnosine (CAR) for 16 h to determine their synergistic effects. These synergistically treated BV2 cells were further cocultured with HT-22 cells for 24 h to clarify their neuroprotective effects. Results: Among the eight bioactives of EC, CAR, pyroglutamic acid (PA), and cyclo(Gly-Pro) exerted notable anti-inflammatory and antioxidative effects on BV2 cells, as evidenced by the downregulation of inflammatory cytokine and chemokine expression (10 mM treatment group vs. LPS: p < 0.05), attenuation of the inflammatory pathway (all treatment group vs. LPS: p < 0.05), and increase in activity of superoxide dismutase (SOD) (p < 0.01), catalase (CAT) (p < 0.05), and the content of glutathione (GSH) (p < 0.01). The experiment was conducted in triplicate. Interestingly, PA and cyclo(Gly-Pro) showed a marked synergistic effect with CAR on neuroinflammation. For example, the content of inflammation markers, tumor necrosis factor-α (TNF-α) (CAR + PA vs. CAR: p = 0.030, CAR + cyclo(Gly-Pro) vs. CAR: p = 0.008) and monocyte chemoattractant protein-1 (MCP-1) (CAR + PA vs. CAR: p = 0.039, CAR + cyclo(Gly-Pro) vs. CAR: p = 0.020), were decreased markedly. The coculture of BV2 microglia with HT-22 neurons revealed that CAR, PA, and cyclo(Gly-Pro) also worked synergistically to reduce LPS-induced cytotoxicity in BV2 cells to protect the growth of HT-22 cells (all treated groups vs. LPS: p < 0.05). The protective effect of these dietary peptides might be regulated by the Phosphatidylinositol 3-kinase/Protein Kinase B (PI3K/AKT) pathway-mediated inhibition of apoptosis. Conclusion: CAR, PA, and cyclo(Gly-Pro) exhibited potent anti-inflammatory and antioxidant effects, suggesting that EC dietary peptides are neuroprotective candidates and that the intake of a mixture rather than individual peptides confers more beneficial effects in maintaining healthy neuron function.