Noninvasive evaluation of in vivo free radical reactions catalyzed by ironusing in vivo ESR spectroscopy

The noninvasive, real time technique of in vivo electron spin resonance (ES R) spectroscopy was used to evaluate free radical reactions catalyzed by ir on in living mice. The spectra and signal decay of a nitroxyl probe, carbam oyl-PROXYL, were observed in the upper abdomen of mice. The signal decay wa s significantly enhanced in mice subcutaneously loaded with ferric citrate (0.2 mu mol/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 det ermine the catalytic form of iron, DF was administered at different times w ith respect to iron loading: before, simultaneously, and after 20 and 50 mi n. The effect of DF on signal decay, liver iron content, iron excretion, an d lipid peroxidation (TBARs) depended on the time of the treatment. There w as a good correlation between the signal decay, iron content, and lipid per oxidation, indicating that "chelatable iron" contributed to the enhanced si gnal 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. (C) 1999 Elsevier Science Inc.