Abstract
Abstract: :
Purpose: To identify the products derived from the oxidative breakdown of the macular pigment carotenoids, lutein and zeaxanthin. Recent interest has focused on dietary supplementation with high dose macular pigment carotenoids to reduce the risks for cataract and age-related macular degeneration. Previous clinical trials with structurally related ß-carotene revealed unsuspected toxicity and products derived from its autoxidation were implicated. Therefore before lutein/and or zeaxanthin dietary supplementation becomes extensive it would be prudent to analyze and characterize their breakdown products. Methods: The carotenoids, lutein and zeaxanthin, were subjected to different forms of physical and chemical-induced oxidative stress, such as heat, light exposure, cigarette smoke, and hypochlorite. The carotenoid decomposition reactions were accomplished in methanolic solution. After oxidation, the degraded products were extracted in dichloromethane and analyzed by gas chromatography-mass spectrometry using electron ionization. Results: One of the most commonly identified products was 4-hydroxy-ß-ionone. Zeaxanthin generated only the 4-hydroxy ß-ionone isomer, whereas lutein generated an isomeric mixture of 4 hydroxy-α- and -ß-ionones. Other products that were identified included 4-hydroxy analogs of ß-cyclocitral, dihydroactinidiolide, 5,6, epoxy-α- and ß-ionones and ß-apo-13'carotenone. Conclusion: Oxidation of the macular pigment carotenoids yields a mixture of aldehydic breakdown products, which can be readily identified by gas chromatography-mass spectrometry. The asymmetry in the lutein molecule causes formation of specific products such as 4-hydroxy-α-ionone, derived only from this carotenoid.
Keywords: 308 age-related macular degeneration • 462 macular pigment • 337 carotenoids/carotenoid binding proteins