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A semiquinone glucoside derivative (SQGD) was isolated from a radioresistant bacterium Bacillus sp. INM-1 and its antioxidant and radioprotective activities were evaluated using in vitro assays. Natural stable free radical properties of SQGD in solid as well as in solution form were estimated using Electron Paramagnetic Resonance (EPR) spectrometry. Results of the study were demonstrated high reducing power (1.267 ± 0.03356 U(abs)) and nitric oxide radicals scavenging activity (34.684 ± 2.132%) of SQGD. Maximum lipid peroxidation inhibitory activity of SQGD was found to be 74.09 ± 0.08% at 500 μg/ml concentration. Similarly, significant (39.54%; P < 0.05) protection to the liposomal artificial membrane against gamma radiation was observed by SQGD in terms of neutralization of gamma radiation-induced TBARS radicals in vitro. OH(-) radicals scavenging efficacy of SQGD was estimated in terms of % inhibition in deoxy D: -ribose degradation by non-site-specific and site-specific assay. The maximum (54.01 ± 1.01%) inhibition of deoxy D: -ribose degradation was observed in non-site-specific manner, whereas, site-specific inhibition was observed to be 46.36 ± 0.5% at the same concentration (250 μg/ml) of SQGD. EPR spectroscopic analysis of the SQGD indicated ~80% reduction of DPPH radicals at 6.4% concentration. EPR spectral analysis of SQGD was revealed an appearance of very strong EPR signal of 2.00485 (crystalline form) and 2.00520 (solution form) g(y) tensor value, which were an established characteristic of o-semiquinone radicals. Therefore, it can be concluded that SQGD is a natural stable o-semiquinone-type radical, possessing strong antioxidant activities and can effectively neutralize radiation induced free radicals in biological system.

Present study was undertaken to evaluate radioprotective and immunomodulatory activities of a novel semiquinone glucoside derivative (SQGD) isolated from Bacillus sp. INM-1 in C57 BL/6 mice. Whole body survival study was performed to evaluate in vivo radioprotective efficacy of SQGD. To observe effect of SQGD on immunostimulation, Circulatory cytokine (i.e., interleukin-2 (IL-2), IFN-γ, IL-10, granulocyte colony stimulating factor (G-CSF), granulocyte macrophage colony stimulating factor (GM-CSF), and macrophage colony stimulating factor (M-CSF) expression was analyzed in serum of irradiated and SQGD treated mice at different time intervals using ELISA assay. Results of the present investigation indicated that SQGD pre-treatment (-2 h) to lethally irradiated mice provide ∼ 83% whole body survival compared with irradiated mice where no survival was observed at 30(th) post irradiation day. Significant (p < 0.05) induction in IL-2 and IFN-γ expression was observed at all tested time intervals with SQGD pre-treated irradiated mice as compared with irradiated mice alone. However, sharp increase in IL-10 expression was observed in irradiated mice which were found to be subsidized in irradiated mice pre-treated with SQGD. Similarly, significant (p < 0.05%) induction in G-CSF, M-CSF and GM-CSF expression was observed in irradiated mice treated with SQGD as compared with irradiated control mice at tested time intervals. In conclusion, SQGD pre-treatment to irradiated mice enhanced expression of IL-12 and IFN-γ while down-regulated IL-10 expression and thus modulates cytoprotective pro-inflammatory TH1 type immune response in irradiated mice. Further, SQGD pre-treatment to irradiated mice accelerate G-CSF, GM-CSF and M-CSF expression suggesting improved haematopoiesis and enhanced cellular immune response in immuno-compromised irradiated mice that may contribute to in vivo radiation protection.

This study was focused to evaluate protection of indigenous antioxidant system of mice against gamma radiation-induced oxidative stress using a semiquinone (SQGD)-rich fraction isolated from Bacillus sp. INM-1. Male C57bl/6 mice were administered SQGD (50 mg/kgb.w.i.p.) 2 h before irradiation (10 Gy) and modulation in antioxidant enzymes activities was estimated at different time intervals and compared with irradiated mice which were not pretreated by SQGD. Compared to untreated controls, SQGD pretreatment significantly (p < 0.05) accelerates superoxide dismutase, catalase, GSH, and glutathione-S-transferase activities. Similarly, significant (p < 0.05) increase in the expression of superoxide dismutase, catalase, GSH, and glutathione-S-transferase was observed in irradiated mice pretreated by SQGD, compared to only irradiated groups. Total antioxidant status equivalent to trolox was estimated in renal tissue of the mice after SQGD administration. Significant ABTS(+) radical formation was observed in H2O2-treated kidney homogenate, due to oxidative stress in the tissue. However, significant decrease in the levels of ABTS(+) radical was observed in kidney homogenate of the mice pretreated with SQGD. Therefore, it can be concluded that SQGD neutralizes oxidative stress by induction of antioxidant enzymes activities and thus improved total antioxidant status in cellular system and hence contributes to radioprotection.

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