Ommochromes from the Compound Eyes of Insects: Physicochemical Properties and Antioxidant Activity

The objective of this study was screening of ommochromes from the compound eyes of insects and comparison of their antioxidant properties. Ommochromes were isolated in preparative quantities from insects of five different families: Stratiomyidae, Sphingidae, Blaberidae, Acrididae, and Tenebrionidae. The yield of ommochromes (dry pigment weight) was 0.9-5.4% of tissue wet weight depending on the insect species. Isolated pigments were analyzed by high-performance liquid chromatography and represented a mixture of several ommochromes of the ommatin series. The isolated ommochromes displayed a pronounced fluorescence with the emission maxima at 435-450 nm and 520-535 nm; furthermore, the emission intensity increased significantly upon ommochrome oxidation with hydrogen peroxide. The ommochromes produced a stable EPR signal consisting of a singlet line with g = 2.0045-2.0048, width of 1.20-1.27 mT, and high concentration of paramagnetic centers (> 10¹⁷ spin/g dry weight). All the investigated ommochromes demonstrated high antiradical activity measured from the degree of chemiluminescence quenching in a model system containing luminol, hemoglobin, and hydrogen peroxide. The ommochromes strongly inhibited peroxidation of the photoreceptor cell outer segments induced by visible light in the presence of lipofuscin granules from the human retinal pigment epithelium, as well as suppressed iron/ascorbate-mediated lipid peroxidation. The obtained results are important for understanding the biological functions of ommochromes in invertebrates and identifying invertebrate species that could be used as efficient sources of ommochromes for pharmacological preparations to prevent and treat pathologies associated with the oxidative stress development.