Ascorbyl radical as natural indicator of oxidative stress: quantitative regularities.

The intensity of ESR spectrum associated with ascorbyl free radical (A.) was found to be sensitive to various pathologies and intoxications connected with oxidative stress. For this reason, A. has been suggested to be used as a natural noninvasive ESR indicator of oxidative stress. To specify factors controlling [A.] in biological tissues, the kinetic study of ascorbic acid (AH) oxidation in aqueous solutions catalyzed by Fe ions and methylene blue (MB) has been performed by using ESR and Clark electrode techniques. Concentration, temperature, and pH dependences of [A.] and rate of AH oxidation (R(ox)), effects of additives of biological importance (glutathione, uric acid, proteins, glucose, lipid) as well as that of Na dodecylsulfate (SDS) have been studied. The oxidation of 1 mol of AH is accompanied by the consumption of 1 mol of O2 and the generation of 1 mol of A.. [A.] has been found to be proportional to the square root of R(ox), no matter what reason is for R(ox) variation. A. has been shown to be inactive toward all substances tested and free radicals other than A.. It has been concluded that A. decays in biological tissues mostly by self-disproportionation, a value of [A.] gives the definitive quantitative information on the total rate of AH oxidative transformations (oxidation by O2 plus reactions with free radicals). SDS shows the retarding effect on AH oxidation induced by MB.