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Daniel T. Organisciak, Ruth M. Darrow, Christine M. Rapp, Rekha Rangarajan, John C. Lang; Prevention of Retinal Light Damage by the Trace Element Zinc and the Natural Antioxidant Rosemary. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2560.
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To assess protective mechanisms and potential synergistic effects between a natural antioxidant and an essential trace element in an animal model of light-induced retinal degeneration.
Weanling male Sprague-Dawley rats were maintained in darkness until P60 and then exposed to intense visible light for 4 hours, beginning at 9 am. One hour before light exposure some animals were injected 1X IP with various doses of zinc oxide, or a Tween detergent extract of Rosemary powder. Other rats received combined doses of zinc plus Rosemary prior to light treatment. Following light exposure all animals were returned to the dark environment for 2 weeks to allow for removal of dead photoreceptor cells and recovery of surviving photoreceptors. To determine the extent of visual cell survival photoreceptor cell DNA and rhodopsin levels were measured. Retinal histology and western analysis were performed to confirm antioxidant efficacy and to assess changes in protein levels.
Dose response curves for zinc oxide and Rosemary powder indicate that each is effective in preventing retinal light damage. Compared to vehicle injected rats, over 50% visual cell recovery occurred with zinc oxide at the AREDS formulation recommended dose (1.3 mg/kg). Detergent extracts of Rosemary powder (17 mg/kg) were equally effective. Zinc combined with Rosemary extract was effective at one-half the dose of the individual compounds. Retinal histology confirmed the beneficial effects of combined treatment. By western analysis, immunoreactivity for heme oxygenase and carboxyethylpyrrole, were reduced by either zinc or Rosemary treatment.
The protective efficacy of zinc combined with Rosemary indicates that their effects on photoreceptor cell survival are additive. The levels of two protein markers of oxidative stress were decreased by treatment with either zinc or Rosemary, suggesting that their mechanisms of action may also be complementary. The antioxidants present in Rosemary may also reduce potential toxicity associated with high doses of zinc.
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