Inhibition of lipid peroxidation by S-nitrosoglutathione and copper

The antioxidant properties of S-nitrosoglutathione, a nitric oxide-derived product were studied in different experimental systems. By using the crocin bleaching test, S-nitrosoglutathione, in the presence of copper ions, shows an antioxidant capacity about six times higher than that of Trolox c and referable to the interception of peroxyl radicals by nitric oxide. Copper alone shows a modest inhibitory action, which is about seven times lower than that of Trolox c. S-nitrosoglutathione prevents lipid peroxidation induced by the well-known Fe2+/ascorbate system (IC50 = 450 microM) and the inhibitory effect is strongly reinforced by the presence of copper ions (IC50 = 6.5 microM). In addition, cumene hydroperoxide-induced lipid peroxidation is markedly decreased by S-nitrosoglutathione, provided that copper ions, maintained reduced by ascorbate, are present. Decomposition of S-nitrosoglutathione through metal catalysis and/or the presence of reducing agents and the consequent release of nitric oxide are of crucial importance for eliciting the antioxidant power. In this way, copper ions and/or reducing species with low antioxidant potency are able to promote the formation of an extremely strong antioxidant species such as nitric oxide.