The Protective Effects of Water-Soluble Alginic Acid on the N-Terminal of Thymopentin

Thymopentin (TP5) has exhibited strong antitumor and immunomodulatory effects in vivo. However, the polypeptide is rapidly degraded by protease and aminopeptidase within a minute at the N-terminal of TP5, resulting in severe limitations for further practical applications. In this study, the protective effects of water-soluble alginic acid (WSAA) on the N-terminal of TP5 were investigated by establishing an H22 tumor-bearing mice model and determining thymus, spleen, and liver indices, immune cells activities, TNF-α, IFN-γ, IL-2, and IL-4 levels, and cell cycle distributions. The results demonstrated that WSAA+TP5 groups exhibited the obvious advantages of the individual treatments and showed superior antitumor effects on H22 tumor-bearing mice by effectively protecting the immune organs, activating CD4⁺ T cells and CD19⁺ B cells, and promoting immune-related cytokines secretions, finally resulting in the high apoptotic rates of H22 cells through arresting them in S phase. These data suggest that WSAA could effectively protect the N-terminal of TP5, thereby improving its antitumor and immunoregulatory activities, which indicates that WSAA has the potential to be applied in patients bearing cancer or immune deficiency diseases as a novel immunologic adjuvant.