Himalayan Bioresource Rhodiola imbricata as a promising radioprotector for nuclear and radiological emergencies.

In recent years, a lot of interest has been generated world over in the area of radioprotection for first responders going to work in the hot zones at the incident site. A large number of molecular drugs have been screened for radioprotective efficacy, but with little success. The requirement of differential radioprotection necessitates a holistic approach, which can be realized using herbs in view of their multifaceted mode of action. Our earlier studies showed the radioprotective potential of Rhodiola imbricata, a Himalayan high-altitude plant. In this study, our focus has been to compare the pro-oxidant/antioxidant activities of three fractionated extracts of R. imbricata. The aqueous fraction exhibited significant (P < 0.05) pro-oxidant activity (up to 100 μg/ml) under metal ion-induced stress ± flux [transition metal (Fe/Cu) ± 0.25 kGy]. A decrease in the dielectric constant of the solvent system utilized for extraction, exhibited a significant (P < 0.05) negative correlation (-0.955) with mean protection potential of lipid against radiation flux. Such an effect was visualized as a significant shift from pro-oxidant to antioxidant activity in methanolic fraction (dielectric constant = 33), as compared to aqueous fraction (dielectric constant = 80). Aqueous fraction is predominantly pro-oxidant at maximal concentrations, indicating its anticancer potential. The presence of transition metals modulates such a biphasic activity differentially in various fractions, i.e., the conversion of Fe(III) or Cu(II) to Fe(II) or Cu(I), respectively, due to the presence of certain bioactive constituents (electron donation at lower concentrations), favors pro-oxidant activity. On the other hand, certain other active constituents involved in metal ion chelation contributed to the overall antioxidant activity. The methanolic fraction exhibited significant antioxidant activity up to 250 μg/ml, which contributed to its radioprotective efficacy. The aquo-methanolic fraction exhibited (disparate properties), i.e., concentration-dependant cytotoxicity (up to 250 μg/ml) and cytoprotection at 1000 μg/ml. R. imbricata, in general, exhibited a significant solvent-dependant variation in radioprotective efficacy. In conclusion, solvent extraction and dose are crucial in bioactivity modulation and R. imbricata could be developed as a potential prophylactic radiation countermeasure for use in nuclear and radiological emergencies.