Identification of immunomodulatory peptides from crocodile head protein hydrolysates: Targeted screening and immunomodulatory activity by activating NF-κB signaling pathway

Long-term unhealthy lifestyles are prone to triggering immune disorders, leading to infections and chronic diseases, posing serious health risks. Immunomodulatory peptides, with the advantages of being natural and having low toxicity and few side effects, contribute to maintaining immune balance. However, their mechanism of action remains unclear. It is crucial to conduct in-depth research on immunomodulatory peptides to understand their potential health benefits. This study aims to identify novel immunomodulatory peptides from the crocodile (Crocodylus siamensis) head protein hydrolysates (CHPHs) and explore their intracellular immunomodulatory mechanisms. Four crocodile-derived peptides with potential immunomodulatory activity were screened from CHPHs, i.e., AKLDLEEVIK (AK-10), LEKEKSELK (LEK-9), DFLDLPSIER (DR-10), and LDLEEVIKK (LDK-9), which stably bind to TLR4-MD2 and activate the immune response. These four peptides promoted the proliferative and phagocytic activities of RAW264.7 cells, activated the resting state of the cells, and boosted the expression of NO and cytokines. Peptide DR-10 had the most significant immunomodulatory function and promoted up-regulation of intracellular immune-related factors Acod1, Ccl9, COX2, CD40, NF-κB1, IKKε, and NF-κB2. Additionally, the peptide DR-10 activated the NF-κB signaling pathway, thereby releasing immune effectors and exerting immune effects. These findings suggest that crocodile-derived immunomodulatory peptides may be considered an effective immune supplement, providing new ideas for future research on dietary supplements.