Photoprotective and radioprotective properties of nitroxides and their application in magnetic resonance imaging.

Nitroxides are a group of stable organic radicals of low molecular weight having a nitroxyl group > N-.O, which has an unpaired electron. The presence of this group allows a nitroxide to participate in redox reactions. They serve as mimics of superoxide dismutase (SOD) and have stimulative properties towards haemoproteins with catalase-like activity. Nitroxides oxidize Fe (II) to Fe (III) preventing the Fenton and Haber-Weiss reactions. As the radicals have the ability to scavenge other free radicals. Nitroxides are not immunogenic, and mutagenic and do not show toxicity to the human cells. The review discusses the use of nitroxide in protecting cells and tissues from the effects of UVA radiation. Preliminary studies indicate that they are more effective than conventionally used vitamins C and E and UV filters. They also protect the biological material from the effects of ionizing radiation. Nitroxides protect healthy cells and simultaneously they do not protect cancer cells from ionizing radiation. The differences in the nitroxide activity are associated with conditions prevailing in the oxidizing environment of the tumor as opposed to reducing conditions in normal cells. Nitroxides can be used as contrast agents in the magnetic resonance imaging (MR). They have ability of detection of subtle changes in redox equilibrium in the tumor tissue. Application of nitroxides in MR method allow to distinguish normal and pathological state of tissue. Successful investigations using this technique were conducted in mice with colon and brain cancer.