Measurement of Density of Hydroxyl radical Generation in Water Induced by Low-LET Radiation

Secondary radical reactions of the hydroxyl radical (•OH) account for 80% of radio-biological effects mediated by the generation of reactive oxygen species (ROS). The regulation of •OH is important for suppressing these indirect actions. In this study, by applying the electron paramagnetic resonance (EPR) spin trapping method, we determined the density of •OH generation when an aqueous sample was irradiate with low-LET radiation such as X-rays or gamma-rays, by using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin trapping agent.Several concentrations (from 0.5 to 1680 mM) of DMPO in aqueous solution were irradiated with 32 Gy X-rays (3.2 Gy/min). The amount of hydroxyl radical adduct (DMPO-OH) generated was measured by X-band EPR. The relationship between the concentration of DMPO in the reaction mixrure and DMPO-OH generation was analyzed.The amount of DMPO-OH generated increased linearly and reached an inflexion point where the amount of DMPO-OH formation decreased substantially for a given amount of DMPO added to solution, as the concentration of DMPO was increased above 3 mM, i.e., the inflexion concetration. This observatino suggests that the concentration of •OH generated was approximately 3.3 mM or more. After the concentration of DMPO-OH formation decrased for a given amount of DMPO added to solution (at approximately 3 mM of DMPO), a linear trend that passed through the origin was observed. From this result, the very high density of •OH generation which could be detected by increasing DMPO concentration, was observed. The extremely high-density of •OH generation can be very difficult to control, however lower densities of •OH generation (~ 3 mM) may well be contralled by antioxidants.APES-IES-SEST 2014 (Joint Conference of 9th Asia-Pacific EPR/ESR Society Symposium, 1st International EPR (ESR) Society Symposium, and 53rd SEST Annual Meeting