Purification of novel polypeptides from bee pupae and their immunomodulatory activity in vivo and in vitro

Abstract

Edible insects have been proposed as an understudied food whose cultivation could be increased with global population growth. However, the bioactivators and bioactivities of bee pupae are poorly studied. In this paper, the active ingredients of bee pupa powder were analysed, and novel bee pupa polypeptides (BPP) were obtained through protein hydrolysis with alkaline protease. Two purified polypeptide components (BPP-21 and BPP-22) were isolated and purified on a diethylaminoethyl-sepharose fast flow column and a Sephadex G-25 column, and identified using size exclusion chromatography-high performance liquid chromatography and amino acid composition analyses. Due to its higher cell proliferation activity, BPP-22 was selected for further study of its immunomodulatory activity and mechanism in vivo and in vitro. The analysis of immunomodulatory activity showed that BPP-22 significantly increased the body weight growth rate, organ index, macrophage phagocytosis, delayed-type hypersensitivity reaction, cytokine level (interleukin (IL)-2 and interferon (IFN)-γ), immunoglobulin (Ig) levels (IgA, IgG, and IgM), and routine blood indexes in cyclophosphamide-treated immunosuppressed mice (P<0.01). Mechanistic research in RAW264.7 cells showed that BPP-22 might promote the secretion of cytokines (IL-2, tumour necrosis factor-α and IFN-γ) and the production of nitric oxide by increasing homologous mRNA expression and could exert immunomodulatory activity by increasing the phosphorylation of ERK and p38, and modulating the expression of intranuclear transcription factors (EIK-1, MEF-2 and CREB) in the MAPK signalling pathway. These findings are helpful for promoting the application of bee pupae as potential immunomodulatory agents and protein supplements.