Superoxide-dependent reduction of free Fe3+ and release of Fe2+ from ferritin by the physiologically-occurring Cu(I)-glutathione complex

The intracellularly-occurring Cu(I)-glutathione complex (Cu(I)-[GSH]2) has the ability to reduce molecular oxygen into superoxide radicals (O2·-). Based on such ability, we addressed the potential of this complex to generate the redox-active Fe2+ species, during its interaction with free Fe3+ and with ferritin-bound iron. Results show that: (i) the complex reduces free Fe3+ through a reaction that totally depends on its O2·--generating capacity; (ii) during its interaction with ferritin, the complex reduces and subsequently releases iron through a largely (77%) SOD-inhibitable reaction; the remaining fraction is accounted for by a direct effect of GSH molecules contained within the complex. The O2·--dependent iron-releasing efficiency of the complex was half that of its iron-reducing efficiency; (iii) the ability of the complex to release ferritin-bound iron was increased, concentration-dependently, by the addition of GSH and totally prevented by SOD; (iv) in the presence of added H2O2, the Fe2+ ions generated through (i) or (ii) were able to catalyze the generation of hydroxyl radicals. Thus, the present study demonstrates the ability of the Cu(I)-[GSH]2 complex to generate the redox-active Fe2+ species and suggest that by favouring the occurrence of superoxide-driven Fenton reactions, its pro-oxidant potential could be increased beyond its initial O2·--generating capacity.