Role of Nrf2-antioxidant in radioprotection by root extract of Inula racemosa

Purpose:Inula racemosa, a Trans-Himalayan plant is an important medicinal herb. In this study, the radio-modulatory efficacy of aqueous root extract of I. racemosa was investigated. Materials and methods: Normal Kidney Epithelium cells were treated with extract (50-200 μg/ml) and exposed to 3 Gy of γ-radiation, while C57BL/6 mice were administered with extract (300-600 mg/kg BW) intraperitoneally prior to exposure to 7.5 Gy of γ-radiation to assess radiation modulatory efficacy. Results: The administration of extract (30 min and 1 h) prior to radiation exposure improved the survival of NKE cells (as measured by proliferation), restored MMP and ROS levels as compared to radiation-exposed alone cells. These cells showed up-regulated Nrf2 protein levels at 7 h and increased expression of HO-1 and NOQ1 protein at 24 h In mice, the 30 days whole body survival study demonstrated that extract pre-treatment increases survival or delays the onset of radiation-induced mortality as against 70% mortality of 7.5 Gy of γ-radiation. Conclusions: The aqueous extract of roots of I. racemosa enhanced the survival of irradiated NKE cells and rescued C57BL/6 mice against WBI-induced mortality. The radiation modulation efficacy was mediated through cumulative activation of HO-1 and NQO1 downstream of Nrf2 translocation in NKE cells. Abbreviations: ARE: Antioxidant Response Element; FITC: Fluorescein isothiocyanate; GCS: Glutamylcysteine synthase; HO-1: Heme oxygenase-1; LPS: Lipopolysacharide; MRP: Multidrug Resistance-Associated Proteins; NQO1: NAD(P)H Quinone Dehydrogenase 1; NRH: Quinone Oxidoreductase 2 (NQO2); PBS: Phosphate Buffer Saline; PKA: Protein Kinase A; PKC: Protein Kinase C; PI3-kinase: Phosphatidylinositol 3-Kinase; SRB: Sulforhodamine B; UV: Ultra-Violet radiation.