LIGHT-INDUCED OXIDATIVE STRESS PRODUCTION IN THE ROD OUTER SEGMENTS.

Purpose Oxidative stress is involved in retinal diseases such as diabetic retinopathy, age-related macular degeneration and retinal damage by light, characterized by Reactive Oxygen Intermediates (ROI) production. Rod Outer Segments (OS), display a mitochondria-like activity, producing ATP and consuming oxygen through the expression of the electron transfer chain (ETC) complexes I–IV and F1Fo-ATP synthase. As the ETC is a major source of ROI generation, here we investigated the ultimate ROI source in the OS after blue light (BL) or ambient light irradiation. Methods Samples were: purified bovine OS and organotypic model of photoreceptors (from C57BL/6 mice) irradiated with BL (peak, 405 nm). Histochemical assays were conducted on unfixed eye culture sections. To test ROI, 5-(and-6)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate was used both for cyofluorimentric assay in purified OS and for live staining of retinas explanted from eye cultures. Oxidative metabolism was investigated by ATP synthesis and oximetry in purified OS. Malondialdehyd (MDA) concentration in OS homogenates was evaluated. Results Under BL stress, ROI and MDA production increased while O2 consumption and ATP synthesis were impaired in OS after 6 h BL treatment. Impairment of respiratory Complexes I and II after BL exposure, both in the OS and IS was found. In ambient light, purifed OS, even in the absence of respiring substrates, produced a consistent amount of ROI, while in the dark, OS ATP synthesis is negligible. Conclusions Likely, severe malfunctioning of OS aerobic respiratory capacity after BL treatment is secondary to a self-induced damage after initial over-functioning of both phototransduction and respiratory chain, with ROI production. Correlation among ROI production and phototransduction activity as well as possible antioxidant supplementation are discussed.