Abstract
In the present study, peptide fractions of Cyclina sinensis hydrolysates, with molecular weight (MW) < 3 kDa and highest relative proliferation rate of murine macrophage cell line RAW 264.7, were purified by a series of chromatographic purification methods, to obtain peptide fractions with immunomodulatory activity. The amino acid sequence of the peptide was identified to be Arg-Val-Ala-Pro-Glu-Glu-His-Pro-Val-Glu-Gly-Arg-Tyr-Leu-Val (RVAPEEHPVEGRYLV) with MW of 1750.81 Da, and the novel pentadecapeptide (named SCSP) was synthesized for subsequent immunomodulatory activity experiments. Results showed the SCSP enhanced macrophage phagocytosis, increased productions of nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), and up-regulated the protein level of inducible nitric oxide synthase (iNOS), nuclear factor κB (NF-κB), and NOD-like receptor protein 3 (NLRP3) in RAW 264.7 cells. Furthermore, the expression of inhibitor of nuclear factor κB-α (IκB-α) was down-regulated. These findings suggest that SCSP might stimulate macrophage activities by activating the NF-κB signaling pathway and can be used as a potential immunomodulatory agent in functional food or medicine.
Highlights
The immune system plays a crucial role in maintaining human health by identifying and killing pathogens, aging cells, and tumor cells
The protein levels of inducible nitric oxide synthase (iNOS) increased remarkably increased remarkably after SCSP treatment ( < 0.05) (Figure 7b). These results demonstrated that after SCSP treatment (P < 0.05) (Figure 7b). These results demonstrated that SCSP up-regulated the SCSP up-regulated the protein levels of iNOS and nitric oxide (NO) secretion in RAW 264.7 cells in a protein levels of iNOS and NO secretion in RAW 264.7 cells in a dose-dependent manner, which is dose-dependent manner, which is consistent with that previously demonstrated for oviductus ranae consistent with that previously demonstrated for oviductus ranae [36], yellow field pea seeds [41] and
Artemisia sphaerocephala Krasch seed [45], and the immunomodulatory protein PEP 1b from Pleurotus eryngii [46] on macrophage activation and secretion of IL-6, tumor necrosis factor-α (TNF-α), and IL-1β. These results indicated that SCSP displays significant immunomodulatory activities as it increases the secretion of NO, IL-6, IL-1β, and TNF-α in RAW 264.7 cells
Summary
The immune system plays a crucial role in maintaining human health by identifying and killing pathogens, aging cells, and tumor cells. Activated macrophages have been reported to directly kill and eliminate pathogens, necrotic cell fragments, and foreign substances via phagocytosis, and indirectly participate in immune regulation through the secretion and release of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) and inflammatory molecules (reactive oxygen species (ROS), NO) [2] Macrophage activation is considered a promising strategy for enhancing host immune function. Several drugs such as levamisole, imiquimod, pidotimod, tilorone, and cyclosporine are being clinically used for regulating human immune function.
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