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Exposure to ionizing radiation (IR) set a series of deleterious events causing acute radiation syndrome and mortality, posing the need for a potent and safe radio-protective drug. IR induces cell death predominantly by causing oxidative stress and macromolecular damage. The pre-existing antioxidant defence machinery of the cellular system plays a crucial role in protecting the cells against oxidative stress by activation of Nrf2. The current study was undertaken to investigate the radio-protective potential of sphingosine kinase inhibitor (SKI-II), which was demonstrated to activate Nrf2 signaling. The safety and efficacy of SKI-II were evaluated with cell cytotoxicity, proliferation index, and clonogenic survival assays in different cell lines, namely Raw 264.7, INT-407, IEC-6 and NIH/3T3 cell lines. A safe dose of SKI-II was found radio-protective in all the cell lines linked with the activated antioxidant defence system, thereby resulting in the amelioration of IR induced oxidative stress. SKI-II pretreatment also significantly reduced DNA damage, micronuclei expression, and accelerated DNA repair kinetics as compared to IR exposed cells. Reduced oxidative stress and enhanced DNA repair significantly reduced apoptosis and suppressed the pro-death signaling associated with IR exposure. Furthermore, the in-vitro observation was verified in the in-vivo model (C57 BL/6). The Intra-peritoneal (IP) administration of SKI-II, 2 h before a lethal dose of IR exposure (7.5 Gy) resulted in 75% survival. These results imply that SKI-II ameliorates IR-induced oxidative stress and cell death by inducing anti-oxidant defence system and DNA repair pathways, thus strengthening its potential to be used as radiation countermeasure. [ABSTRACT FROM AUTHOR]

Radiation induced cell death is one of the detrimental effects of ionizing radiation causes acute radiation syndrome leading to mortality. The cytotoxic and genotoxic effects caused by ionizing radiation are mainly through the oxidative damage induced by free radical release. IL-6 is known to protect many types of cells from oxidative stress, ischemia/reperfusion injury and other stress induced cell death. Therefore, we tested the hypothesis, if IL-6 treatment before irradiation will protect the cells from radiation induced cell death. First, we tested the radio-protective potential of IL-6 in multiple cell model systems such as hematopoietic (Raw264.7), fibroblast (NIH3T3) and intestinal epithelial (INT407) cells. We treated the cells with pleiotropic IL-6 as a prophylaxis (2hr prior to radiation) and analyzed radiation induced cell death. We found a significant increase in cell survival (30% to 40%). Further, we observed that IL-6 also control the radiation induced oxidative stress by enhancing the Nrf2 levels, which resulted in the reduction of ROS and subsequently ROS mediated macromolecular damage (lipid, protein and DNA).The result of IL-6 mediated reduction in radiation induced cell death substantiated by the reduced levels of pro (Bax, p21, p53, PARP and caspase 3 cleavages) and enhanced anti apoptotic proteins (Mcl-1, Bcl2, Bclxl). Together, we found that IL-6 induced STAT-3 signaling not only reduces the radiation induced cell death but also play important role in early detection of DNA damage and facilitates faster repair. The gamma-H2AX foci and Comet assays suggest faster repair kinetics in IL-6 pre-treated samples. These results were further supported by increased levels of DNA repair proteins ATM, Rad51, NBS1 and Neil-1 & OGG-1 (major mitochondrial DNA repair enzymes) in IL-6 treated samples. Therefore, these findings suggest that IL-6 induced STAT-3 mediated pro-survival signaling, anti-oxidant defense and faster repair kinetics protects the cells from radiation induced cell death. [ABSTRACT FROM AUTHOR]