Purpose. Aerobic photoexcitation of melanin leads to consumption of oxygen with stoichiometric formation of hydrogen peroxide. However, we have found recently that this product of oxygen reduction accounts for only a fraction of oxygen consumed by melanin granules from human RPE upon irradiation with blue light (Rozanowska et al., 1995). We measured selected products of aerobic photoreactions of melanin, melanolipofuscin and lipofuscin granules isolated from RPEs of human donors of different age, to determine whether aging modifies oxygen-dependent photochemistry of retinal pigment granules. Methods. Photoconsumption of oxygen and photoformation of hydrogen peroxide in aqueous suspension of pigment granules were measured electrochemically using specific electrodes. Lipid hydroperoxides were determined by iodometric method after chloroform-methanol extraction. Results. While the rate of oxygen photoconsumption was highest in lipofuscin and lowest in melanin granules, the corresponding yield of photoformation of hydrogen peroxide was found to be inversly related, i.e. it was significantly lower in lipofuscin than in melanin. We also found an increased photoformation of lipid hydroperoxides in pigment granules from aged human RPEs such as lipofuscin and melanolipofuscin. Conclusions. Lipofuscin and complex pigment granules that are apparent in aged human RPE, apper to be susceptible to photoinduced peroxidation of lipids and may generate potentially cytotoxic species.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience