Mechanism of tiron as scavenger of superoxide ions and free electrons

Sodium 4,5-dihydroxybenzene-1,3-disulfonate (tiron) has been reported to be an efficient chelator of certain metal ions, and a substrate in several enzyme reactions. Its small size facilitates cell entry and therefore modulates intracellular electron transfer reactions as an antioxidant by scavenging free radicals. Its reduction by electrochemical and enzymatic methods gives identical products; a semiquinone detectable by EPR spectroscopy. In a test of its use as a spin trap, in comparison with DMPO, tiron does not form a molecular spin-adduct but proves more functional as an electron trap. Electron addition to tiron is more facile than reduction of dioxygen as observed by the non-formation of DMPO-OOH spin-adduct in the system XO/HPX/O2/DMPO/tiron. Rather, it is the tiron semiquinone radical which is formed quantitatively with increasing concentration of hypoxanthine independent of oxygen concentration. These results offer explanation for the action of tiron and its suitability for measuring electron release in hypoxic conditions, and also for mitigating redox-induced toxicity in drug regimes by acting as an electron scavenger.