Abstract
Colochirus robustus, a species of sea cucumber, has long been used in East and Southeast Asia as nutritious food as well as for certain medicinal purpose. Studies have shown a number of biological functions associated with consumption of sea cucumber, many of which are attributed to its major component, sea cucumber peptides (SCP). However, how SCP impacts immune system, which is critical for host defense, has not been defined. To address this issue, in the present study, we conducted comprehensive analysis of immune function after oral administration of SCP (0, 25, 50, and 75 mg/kg body weigh) for eight weeks in C57BL/6 mice. We found that SCP treatment significantly enhanced lymphocyte proliferation, serum albumin (ALB) levels, and the natural killer (NK) cell activity. Moreover, SCP promoted functions of helper T cells (Th) as indicated by increased production of Th1 type cytokines of Interleukin (IL)-1β, IL-2, Interferon (IFN)-γ and TNF-α and Th2 type cytokines (IL-4, IL-6, and IL-10). To determine the effective components, SCP was hydrolyzed into 16 types of constituent amino acids in simulated gastrointestinal digestion and these hydrolytic amino acids (HAA) were used for the mechanistic studies in the in vitro models. Results showed that HAA enhanced lymphocyte proliferation and production of IL-2, IL-10 and IFN-γ. Furthermore, CD3ζ (CD3ζ) and ζ-chain-associated protein kinase 70 (ZAP-70), the signaling molecules essential for activating T lymphocytes, were significantly up-regulated after HAA treatment. In summary, our results suggest that SCP is effective in enhancing immune function by activating T cells via impacting CD3ζ- and ZAP-70-mediated signaling pathway.