Comprehensive assessment of peptide derived from pig spleen: Preparation, bioactivity and structure-activity relationships

Pig spleens, as the by-products of pig resources, were often discarded as waste or used for low-value. Therefore, we tried to isolate bioactive peptide from protein hydrolysate of pig spleens to increase their added value. In this study, the low molecular weight peptides (<3000 Da) were prepared by enzyme hydrolysis and its structure-activity relationship was discussed. The main secondary structures of the pig spleen peptide (PSP) were beta-turn and random coil by Fourier transform infrared (FT-IR) analysis. Hydrophobic amino acids accounted for half of the total amino acid content. In vitro, PSP had no inhibition effect on HepG2, HCT116, H22 and S180 cells. While PSP exhibited scavenging capacities of PSP on 2,2 '-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), superoxide anion (O2-) and hydroxyl (OH) radicals. In vivo, the activity of antioxidant enzymes (superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX)) increased and the level of malondialdehyde (MDA) decreased in PSP-treated mice. PSP displayed obvious immunomodulatory effects including stimulation of multiple immune cells to proliferate, production of cytokines (IFN-gamma, IL-2, IL-4 and TNF-alpha) and increase the level of IgG, IgM and IgA antibodies. It induced solid tumor cells apoptosis and arrested at S phase of cell cycle. In conclusion, PSP had significant immunomodulatory effects and antioxidant activity. These results provided theoretical and data support for bioactive peptides derived from meat by-products used as the functional foods.