N-acetyl tryptophan glucopyranoside (NATG) as a countermeasure against gamma radiation-induced immunosuppression in murine macrophage J774A.1 cells

Radiation exposure to immune system induces imbalance in cytokines expression involved in Th1/Th2 homeostasis perturbations. In the present study, N-acetyl tryptophan glucoside (NATG), a bacterial secondary metabolite, was evaluated for its possible radioprotective potential to immune system using J774A.1 murine macrophages. In this study, expression of IFN-, TNF-, IL-10, IL-2, IL-12, IL-13 and IL-17A cytokines was analyzed in irradiated and NATG pretreated cells using ELISA assay. Results of the study indicated that irradiated macrophages (NK-1R(+)cells) pretreated with NATG showed higher (p<.05) survival at all observed time-intervals (2h-48h) as compared to irradiated (20Gy) cells that were not pretreated with NATG. However, NATG pretreatment to irradiated HEK293T cells (that did not express NK-1Receptor) did not provide significant survival, suggesting NK-1R involvement in NATG-mediated radioprotection. Cytokine expression analysis demonstrated that NATG pre-treated plus irradiated J774A.1 murine macrophages exhibited increased IFN- levels (approximate to 90%) with significant decrease in TNF- at 24h as compared to irradiated cells. Further, significant decrease (approximate to 20%) in IL-10 and IL-2 (approximate to 26%) levels was observed in irradiated macrophages pretreated with NATG as compared to only irradiated cells. A sharp improvement in IL-17A (approximate to 92%) and IL-12 (approximate to 116%) expression was observed in irradiated macrophages pretreated with NATG as compared to only irradiated cells. Hence, NATG pre-treatment to irradiated macrophages induced IFN-, IL-17A and IL-12 expression, but suppresses TNF-, IL-10 and IL-2 expressions. Conclusively, NATG pretreatment overcomes radiation-induced Th2 immune response by improving Th1 responsive cytoprotective cytokines IFN-, IL-17A and IL-12 in irradiated macrophages possibly by NK-1R antagonistic mechanism, and thus contributes to radioprotection.