The influence of melanins on the photoperoxidation of lipids

The influence of synthetic Dopa-melanin, natural-A, AB-melanin and pheomelanin has been studied for the following processes: (1) microsomal and liposomal lipid peroxidation induced by illumination with UV- and visible light; (2) interaction of melanin with the superoxide anion; and (3) chemiluminescence intensity of phospholipids in the presence and absence of melanins. It has been shown that (a) melanins can function as a scavenger of the superoxide anion radical O2-. (pseudo-superoxide dismutase) and (b) melanins protect microsomes and liposomes against lipid peroxidation which is due to the absorption of light energy (filter effect). Our data show that in the presence of melanins lipid peroxidation is significantly lower in comparison with the phospholipids incubated in the absence of melanins (except pheomelanin). The level of photoperoxidation of lipids was studied by means of the chemiluminescence method and by measurement of the malondialdehyde product. The results obtained by both methods indicate that melanin can effectively influence the process of lipid peroxidation. Mechanisms involved in the physical (optical screening) and photochemical reactions are proposed.