Mechanism of Calf thymus DNA radioprotection by sucrose: A combined effect of scavenging action and altered water

Background: Development of safe radioprotector is a challenging task. In this study radioprotective effect of sucrose has been demonstrated in calf thymus DNA (CtDNA). Sucrose is a free radical scavenger and also acts as osmolyte and therefore can influence the water activity around DNA and effects of radiation on DNA. Hoechst 33258 was used to probe the possible alteration in physicochemical properties due to altered hydration induced by sucrose in irradiated CtDNA. Materials and Methods: Calf thymus DNA (CtDNA), sucrose and Hoechst 33258 were obtained from Sigma Chemicals, USA. 60Co Gamma source (Gamma5000, BRIT India) was used for irradiation. Radiation induced structural destabilization was monitored spectrophotometrically (Cary Bio 100, Varian, Australia) by measuring CtDNA melting temperature. Changes in physicochemical properties (altered water activity, minor groove binding characteristics) were investigated using absorption and fluorescence spectroscopic properties of Hoechst 33258-CtDNA interactions in presence of sucrose. Results: The CtDNA melting temperature data suggest that sucrose reduced the effect of &gamma-irradiation on CtDNA. Thermodynamics of binding interaction of Hoechst 33258 with irradiated CtDNA suggested favorable energetics accompanied by displacement of water molecules. Binding affinity in presence of sucrose was altered marginally at low concentration (<0.5Osm). The marginal changes in absorption and fluorescence spectroscopic properties of Hoechst 33258-CtDNA interactions at higher concentration of sucrose suggested unaltered functional capability of CtDNA. Conclusion: This study suggests that sucrose can provide structural protection in &gamma irradiated CtDNA. Both scavenging and altered water activities by sucrose contributed in the observed radioprotection. These physicochemical properties of sucrose can be considered for designing better radioprotector. The observations at low concentrations of sucrose appears important lead for further validation studies.