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L.D. Carter–Dawson, Y. Zhang, R.S. Smith, E.L. Smith, III, A. Whitetree, R. Rojas; Oxidative Damage in Retina of Monkeys With Experimental Glaucoma . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2087.
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The retinal ganglion cells in monkeys eyes with experimental glaucoma show increased nitrotyrosine immunolabeling and evidence of oxidized RNA. These changes indicate that increased oxidation contributes to the death of retinal ganglion cells. The purpose of the current study is to investigate whether protein carbonyls, a known indicator of protein oxidation, increase and whether the endogenous levels of antioxidant enzymes, catalase and superoxide dismutase (copper and manganese), are altered in retinas of monkeys with experimental glaucoma.
Experimental glaucoma was induced by argon laser treatments to the trabecular meshwork unilaterally in three rhesus monkeys and bilateral glaucoma induced in two monkeys. Visual field defects were assessed by behavioral perimetry in all five monkeys using a standard clinical field analyzer (Humphrey Field Analyzer) until significant defects were present. Eyes were removed from deeply anesthetized monkeys and retinal samples were quickly frozen in liquid nitrogen and stored at –80ºC. Changes in protein carbonyls were assessed by Western blot using a carbonyl assay (Chemicon) and visualized by chemiluminescence. Protein levels of catalase, and copper and manganese superoxide dismutase were compared between the retinas of control and laser–treated eyes in Western blots using fluorescent secondary antibodies and visualized using a phosphorimager. ß–actin levels were used to normalize loading differences.
Our results showed an increase in protein carbonyls and catalase in retinas of eyes with mild and severe visual field defects compared to control retinas. No significant change was detected in copper and manganese superoxide dismutase between control and glaucomatous retinas regardless of the stage of visual field defects.
The increases of catalase and oxidized proteins (protein carbonyls) in glaucoma retinas signify an increase in the generation of oxidants. The oxidants are most likely both superoxide and hydrogen peroxide. These findings demonstrate that oxidative damage occurs in the retina of monkeys with very mild and severe visual field defects and, thus, oxidation is likely an early event in the pathophysiology of glaucomatous damage.
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