Assessing Hydroxyl Radical density Generated in Aqueous Solution by Low-LET Radiation

Indirect actions account for 80% of radio-biological effects mediated by the generation of reactive oxygen species (ROS). The regulation of hydroxyl radical (•OH) is important for suppressing these indirect actions. In this study, by applying the electron paramagnetic resonance (EPR) spin trapping method using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin traping agent, the density of •OH generation was assessed when an aqueous sample wa irradiate with low-LET radiation such as X-rays or γ-rays.Several concentrations (0.5-1680 mM) of DMPO in aqueous solution were irradiated with 32 Gy low-LET radiation. Experiments were performed with different dose-rate of X-ray (3.2 Gy/min, 4.8 Gy/min, and 6.4 Gy/min) or γ-ray (7.9 Gy/min). The amount of •OH adduct of DMPO (DMPO-OH) generated was measured by X-band EPR spectrometer. The relationship between the molecular density of DMPO in the reaction mixture and DMPO-OH generated was analyzed.The concentration of DMPO-OH in proportion to the molecular density of DMPO was increased linearly and reached a flexion point when the molecular density of DMPO was around 125 /μm (which correspond to 3.3 mM as the concentration). The flexion point was not changed by dose rate or type of ray. The flexion point suggests the relatively "sparse" generation of •OH that was approximately 3 mM or more. Another linear trend that passed through the origin was again observed when DMPO density was extremely high (667-1000 /μm). The extremely "dense" generation which were barely detectable by very high DMPO concentration (1 M~) was suggested.These observations suggest that two different concentrations of •OH generation were existed. One is the "sparse" generation and the other is "dense" generation. The extremely "dense" of •OH generation can not be controlled, however "sparse" of •OH generation could be controlled by appropriate concentration of antioxidants.15th International Congress of Radiation Research (ICRR2015