The potential of frog skin-derived peptides for development into therapeutically-valuable immunomodulatory agents

The aim of this article is to review the immunoregulatory actions of frog skin-derived peptides in order to assess their potential as candidates for immunomodulatory or anti-inflammatory therapy. Frog skin peptides with demonstrable immunomodulatory properties have been isolated from skin secretions of a range of species belonging to the families Alytidae, Ascaphidae, Discoglossidae, Leptodactylidae, Pipidae and Ranidae. Their effects upon production of inflammatory and immunoregulatory cytokines by target cells have been evaluated ex vivo and effects upon cytokine expression and immune cell activity have been studied in vivo by flow cytometry after injection into mice. The naturally-occurring peptides and/or their synthetic analogues show complex and variable actions on the production of proinflammatory (TNF-α, IL-1β, IL-12, IL-23, IL-8, IFN- and IL-17), pleiotropic (IL-4 and IL-6) and immunosuppressive (IL-10 and TGF-β) cytokines by peripheral and spleen cells, peritoneal cells and/or isolated macrophages. The effects of frenatin 2.1S include enhancement of the activation state and homing capacity of Th1-type lymphocytes and NK cells in the mouse peritoneal cavity, as well as the promotion of their tumoricidal capacities. Overall, the diverse effects of frog skin-derived peptides on the immune system indicate their potential for development into therapeutic agents.