Absorption and immune-modulating effects of active peptides from Hericium erinaceus proteins in an in vitro gastrointestinal model

The mechanism by which fungal proteins retain immunomodulatory activity after gastrointestinal digestion remains unknown. To shed light on the mechanism, the proteins and peptides from Hericium erinaceus were explored through in vitro digestion using a Caco-2/RAW264.7 co-culture model. Protein hydrolysate with different molecular weights exhibited varying immunomodulatory activities, wherein a smaller molecular weight correlated with stronger immune-enhancing activity. Four active peptides with good intestinal absorption and immunomodulatory potential were screened from the peptide library of Hericium erinaceus. FPLLTK and PLLTKF peptides with hydrophobic nature and smaller molecular weight mainly utilized a sodium-coupled oligopeptide transporter, while the hydrophilic peptides LYEELKPWF and YLEELKPWF, carrying amino acid side chains with negative charges, primarily used paracellular transport. The transport ratio and the apparent permeability coefficient of PLLTKF and FPLLTK were significantly higher than those of LYEELKPWF and YLEELKPWF owing to a decrease in occludin mRNA expression. FPLLTK exhibited the best intestinal absorption capability and immunomodulatory activity, with the apparent permeability coefficient of 1.12 × 10^-6 cm s^-1. It could promote the phosphorylation of NF-κB p65 via the release of TNF-α, thereby enhancing the transcription and production of cytokines (interleukin-6 and interleukin-10). This study uncovered the transmembrane transport mechanism and immune-modulating effects of active peptides from Hericium erinaceus.