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J.R. Trevithick, C.C. Trevithick–Sutton, T. Dzialoszynski, M. Collins, M. Kolenko, Z. Ajami; Radical Scavenging by Lutein and Related Carotenoids May Contribute to Risk Reduction of AMD and Cataract . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3855.
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Purpose: to re–examine the free radical scavenging activity of important dietary carotenoids and antioxidants (lutein, lutein esters, zeaxanthin, beta–carotene, lycopene, ascorbate and ascorbyl palmitate) with respect to their activity in reducing risk of AMD and cataract Methods:the decrease in peroxide–induced luminescent count rate when the carotenoids were present was measured. An IC50 (inhibitory concentration for 50% inhibition) was calculated for each carotenoid to evaluate relative potency of individual carotenoids. ESR–spin trapping (electron spin resonance spin trapping) was used to evaluate the relative scavenging ability of each carotenoid for superoxide radicals (generated by hypoxanthine/xanthine oxidase) or hydroxyl radicals (from hydrogen peroxide). Results:All carotenoids decreased the luminescent counts from hydrogen peroxide: lutein ester and lutein were most potent, but all carotenoids showed micromolar IC50 values similar to ascorbate. All carotenoids significantly decreased the amplitude of the ESR spectra for superoxide anion and hydroxyl radical. Conclusions:The general consensus in the literature that carotenoids cannot scavenge superoxide is based on an unrepresentative example, crocin. The mixtures of all–trans–carotenoids and 15,15’–cis–carotenoids studied here by ESR spectroscopy scavenge both superoxide and hydroxyl radicals. All of the individual carotenoids (lycopene, ß–carotene, zeaxanthin, and lutein) were better hydroxyl radical scavengers than superoxide scavengers. Zeaxanthin, the predominant carotenoid in the fovea, scavenged the hydroxyl radical more effectively than the other retinal carotenoid, lutein, suggesting that scavenging hydroxyl radicals is more important in the central fovea than elsewhere in the retina. The antioxidant activity of lutein may be responsible for its reported cataract risk reduction.
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