Simulated Gastrointestinal Digestion Enhances the Immunomodulatory Activity of Ovalbumin Peptide NVMEERKIK: Mechanistic Insights into TLR4/MAPK/NF-κB Signaling Modulation

NVMEERKIK, a peptide derived from ovalbumin, exhibited remarkable immunomodulatory activity. This study investigated the effect of simulated gastrointestinal digestion on its structure and bioactivity. NVMEERKIK was found to be unstable against gastrointestinal enzymes and completely degraded into NVME, NVMEE, KIK, K, and R. Among these, NVME, which constituted 90.90% of the digest, was synthesized and demonstrated a superior immune-enhancing activity than NVMEERKIK. Specifically, NVME improved phagocytosis, NO production, and TNF-α content in RAW264.7 cells by 1.31–15.86%, 17.17–122.08%, and 0.36–16.76%, respectively. TLR4 inhibition and immunofluorescence assays revealed the strong TLR4 activation and recognition capacities of both peptides. Furthermore, the Western blot results showed that NVMEERKIK and NVME activated the MAPK/NF-κB pathway by upregulating ERK, JNK, p38, and p65, leading to enhanced activation of RAW264.7 cells. The improved immune-enhancing activity of NVMEERKIK after digestion highlighted its potential as an immunomodulatory peptide for functional food applications.