Screening Marine Natural Products to Identify Immunomodulatory Agents

Dysregulated immune responses are increasingly a source of disease, with autoimmune and inflammatory diseases increasing in prevalence globally, causing major financial and health burdens. Immune responses are regulated in large part through immune cell production of cytokines, small protein messengers of the immune system that signal and direct immune responses to clear foreign pathogens during infections, largely through induction of a state known as inflammation. Key producers of cytokines and directors of inflammation are macrophages and T cells. Acute inflammation is essential for appropriate immune responses and is generally followed by a resolution and wound healing phase whereby the body returns to homeostasis. Chronic inflammation, however, is the development of a low-level, constant state of inappropriate inflammation that contributes to the development of many diseases, including autoimmune, cancer and neurodegenerative diseases. Natural products are compounds, often secondary metabolites, produced by numerous organisms, that have historically been a source of new therapeutics due to their evolutionary optimisation for bioactivity. Traditionally, many therapeutical natural products have been isolated from terrestrial organisms, however, the ocean is a vast environment home to an extraordinary number of organisms facing unique environmental pressures that lead to the development of novel, unique marine natural products with great therapeutic potential. One such example is the myxillin class natural products, a group of N-acyl-dopamine glycosides isolated from the marine sponge Myxilla incrustans that were shown to modulate dendritic cell production of inflammatory cytokines. Numerous novel myxillins isolated from Amphilectus fucorum, and myxillin-related, natural products isolated from Myxilla asigmata, totalling a small library of thirteen glycolipid marine natural products, were assessed for immunomodulatory bioactivity. Screening was conducted in ConA-stimulated murine splenocytes to represent longer, adaptive immune responses, and in LPS-stimulated RAW264.7 cells to represent, early, macrophage responses. The isolated compounds demonstrated the capacity for modulating immune responses in both in vitro models. Myxillin A, JB-BS-3 and JB-BS-5 demonstrated anti-proliferative potential against T cells and altered T cell expression of the activation markers CD44 and CD69. All compounds altered the inflammatory cytokine profile of both splenocytes and RAW264.7 cells by modulating leucocyte production of NO, IL-10, IL-6, IFN-γ and TNF-α. Myxillin A displayed strong anti-inflammatory potential while JB-BS-9 induced pro-inflammatory cytokine profiles. The structural variation between compounds, and the immunomodulatory effects they induced, allowed for an analysis of the structure-function relationship to implicate key structural features in immunomodulatory effects. In general, compounds with dopamine moieties, longer acyl chains and higher molecular weight tended to induce anti-inflammatory profiles, whereas shorter, lighter compounds tended to induce more pro-inflammatory responses. Overall, this work demonstrated the capacity for marine glycolipids to modulate inflammatory responses in various immune cells and related immunomodulatory effects to structural features of the compounds. While the mechanisms of action for these compounds have not been determined and require further work, this work increases our understanding of the immunomodulatory effects of marine glycolipids, particularly the myxillin class natural products.