Prooxidant action of maltol: role of transition metals in the generation of reactive oxygen species and enhanced formation of 8-hydroxy-2'-deoxyguanosine formation in DNA.

Maltol (3-hydroxy-2-methyl-4-pyrone) produced reactive oxygen species as a complex with transition metals. Maltol/iron complex inactivated aconitase the most sensitive enzyme to oxidative stress. The inactivation of aconitase was iron-dependent, and prevented by TEMPOL, a scavenger of reactive oxygen species, suggesting that the maltol/iron-mediated generation of superoxide anion is responsible for the inactivation of aconitase. Addition of maltol effectively enhanced the ascorbate/copper-mediated formation of 8-hydroxy-2'-deoxyguanosine in DNA. Oxidation of ascorbic acid by CuSO(4) was effectively stimulated by addition of maltol, and the enhanced oxidation rate was markedly inhibited by the addition of catalase and superoxide dismutase. These results suggest that maltol can stimulate the copper reduction coupled with the oxidation of ascorbate, resulting in the production of superoxide radical which in turn converts to hydrogen peroxide and hydroxyl radical. Cytotoxic effect of maltol can be explained by its prooxidant properties: maltol/transition metal complex generates reactive oxygen species causing the inactivation of aconitase and the production of hydroxyl radical causing the formation of DNA base adduct.