Antioxidant effect of copper(II) on photosensitized lipid peroxidation

Unilamellar liposomes (LH) of phosphatidylcholine (PC), dispersed in phosphate buffer at pH 7 (PB), underwent lipid peroxidation and lysis with release of entrapped glucose-6-phosphate when irradiated with UVA light in the presence of 2-(3-benzoylphenyl)propionic acid (ketoprofen, KPF) or 2-(6-methoxy-2-naphthyl)propionic acid (naproxen, NAP), which were used as photosensitizers. Lipid photoperoxidation and consequent lysis were reduced when copper(II), up to 5 microM, was present in the irradiated samples. Suitable experiments were performed to evidence the species responsible for the lipid peroxidation, the copper effect on the drug photodegradation, and the mechanism of the copper antioxidant activity. The overall results suggest that the photoperoxidation was probably initiated by organic radicals obtained from the irradiation of KPF and NAP and the inhibition by copper could be attributed to its interaction with the peroxyl radicals of the drug and/or the liposomes, breaking the propagation of the radical chain.