Cancelation of Hyperthermia Induced Reactive Oxygen Species in Rat Plasma

The relation of reactive oxygen species (ROS) with the effect of hyperthermia has been widely alleged. Several papers have reported evidences of ROS generation in hyperthermal conditions. Combination of hyperthermia and other treatments, such as radiation therapy, chemotherapy, and etc., was investigated for sensitizing the treatment. Interest in hyperthermia for clinical cancer treatment has been increasing recently; however, the detail mechanism of hyperthermal cell killing and/or sensitization to other stresses/treatments has been still in progress. We have previously reported that the temperature dependent reduction of nitroxyl radicals under coexisting GSH was O2- related reaction. In this paper, the effect of X-ray irradiation to the hyperthermal ROS scavenging ability of rat plasma was tested using the temperature and GSH dependent reduction of a nitroxyl radical as an index of O2- generation.A reaction mixture containing 0.1 mM nitroxyl radical (TEMPOL) and 1 mM GSH was prepared using 100 mM phosphate buffer (PB). The reaction mixture was kept in a screw-top vial, and was incubated in a water bath at 37 or 44DegC. The time course of the EPR signal of TEMPOL in the reaction mixture was measured by an X-band EPR spectrometer (JEOL, Tokyo, Japan). The similar experiment was done using rat plasma instead of 100 mM PB. Effect of previous whole body 8 Gy irradiation of X-ray to the rats were tested.ROS generation in an aqueous fluid containing oxygen at hyperthermal temperature was demonstrated. Adding albumin to the reaction mixture could cancel the ROS generation at hyperthermal temperature, since the reduction of TEMPOL in the reaction mixture was restricted. ROS generation in rat plasma at hyperthermal temperature was also restricted. The irradiating X-ray in vivo and/or in vitro could reduce this free radical scavenging ability of plasma.第20回日本学術振興会先端研究拠点事業セミナー：International Redox Core Symposium on In Vivo Magnetic Resonance Imagin