3-carbamoyl-2-2-5-5-tetramethyl-1-pyrrolidinyl-n-oxyl and 6-hydroxy-2-5-7-8-tetramethylchroman-2-carboxylic-acid

Previously, we reported that X-irradiation enhanced the signal decay of a spin probe injected into whole mice measured by in vivo ESR, and that the observed enhancement was suppressed by the pre-administration of cysteamine, a radioprotector [Miura, Y., Anzai, K., Urano, S. and Ozawa, T. (1997) Free Rad. Biol. Med. 23: 533-540]. In the present study, the suppression activity of the X-ray-induced increase in the ESR signal decay rate (termed suppression index, SI) was measured for several radioprotectors: 5-hydroxytryptamine (5-HT), S-2-(3-aminopropylamino)-ethylphosphorothioic acid (WR-2721), 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl (TEMPOL), cimetidine, interleukin-1 beta (IL-1 beta) and stem cell factor (SCF). The enhancement of the ESR signal decay of carbamoyl-PROXYL due to X-irradiation was suppressed by a treatment with all of the radioprotectors examined, showing positive SI values. However, a dose-dependency of 5-HT or WR-2721 was not observed, suggesting that several mechanisms exist for radioprotection and a modification of the signal decay rate. Although the in vivo ESR system cannot be used in place of the 30-day survival method for the assessment of radioprotectors, this system might be applicable to in vivo, non-invasive screening prior to using the 30-day survival method.

Topics: Amifostine; Animals; Ascorbic Acid; Chromans; Cimetidine; Cyclic N-Oxides; Dose-Response Relationship, Drug; Electron Spin Resonance Spectroscopy; Interleukin-1; Mice; Nitrogen Oxides; Oxidation-Reduction; Oxidative Stress; Pyrrolidines; Radiation-Protective Agents; Recombinant Proteins; Serotonin; Spin Labels; Stem Cell Factor; Vitamin E; Whole-Body Irradiation

The noninvasive, real time technique of in vivo electron spin resonance (ESR) spectroscopy was used to evaluate free radical reactions catalyzed by iron in living mice. The spectra and signal decay of a nitroxyl probe, carbamoyl-PROXYL, were observed in the upper abdomen of mice. The signal decay was significantly enhanced in mice subcutaneously loaded with ferric citrate (0.2 micromol/g body wt) and the enhancement was suppressed by pre-treatment with either desferrioxamine (DF) or the chain breaking antioxidant Trolox, but only slightly suppressed by the hydroxyl radical scavenger DMSO. To determine the catalytic form of iron, DF was administered at different times with respect to iron loading: before, simultaneously, and after 20 and 50 min. The effect of DF on signal decay, liver iron content, iron excretion, and lipid peroxidation (TBARs) depended on the time of the treatment. There was a good correlation between the signal decay, iron content, and lipid peroxidation, indicating that "chelatable iron" contributed to the enhanced signal decay. The nitroxyl probe also exhibited in vivo antioxidant activity, implying that the process responsible for the signal decay of the nitroxyl probe is involved in free radical oxidative stress reactions catalyzed by iron.

Topics: Animals; Antioxidants; Chelating Agents; Chromans; Cyclic N-Oxides; Deferoxamine; Dimethyl Sulfoxide; Electron Spin Resonance Spectroscopy; Evaluation Studies as Topic; Female; Free Radical Scavengers; Free Radicals; Iron; Lipid Peroxidation; Liver; Mice; Oxidative Stress; Pyrrolidines; Reactive Oxygen Species; Spin Labels; Thiobarbituric Acid Reactive Substances