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

Abstract

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-γ, TNF-α, 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 (2 h-48 h) 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-γ levels (∼90%) with significant decrease in TNF-α at 24h as compared to irradiated cells. Further, significant decrease (∼20%) in IL-10 and IL-2 (∼26%) levels was observed in irradiated macrophages pretreated with NATG as compared to only irradiated cells. A sharp improvement in IL-17A (∼92%) and IL-12 (∼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-γ, IL-17A and IL-12 expression, but suppresses TNF-α, IL-10 and IL-2 expressions. Conclusively, NATG pretreatment overcomes radiation-induced Th2 immune response by improving Th1 responsive cytoprotective cytokines IFN-γ, IL-17A and IL-12 in irradiated macrophages possibly by NK-1R antagonistic mechanism, and thus contributes to radioprotection.

Keywords:

• Ionizing radiation
• Th1/Th2 homeostasis
• bacterial metabolite
• cytokines
• radioprotection

Disclosure statement

The authors declare no conflict of interest.

Funding

The authors would like to acknowledge Defence Research and Development Organization, Ministry of Defence, Govt. of India, for providing the financial support for the present study under Project RAKSHAK (No. 1.2 of TP-15/INM-313). Authors would also like to acknowledge UGC for providing research fellowship to Poonam Malhotra.