Age-related macular degeneration (AMD) is the leading cause of blindness among older Americans. Why is the central (especially the parafoveal) region of the human retina so prone to damage? The basic hypothesis of this proposal is that the uniqueness of the macula is to be found not only in its unusual anatomy but also in its biochemistry, particularly in the detailed spatial distributions of protective agents. A secondary hypothesis that active biochemical proc~ may be responsible for the specific patterns displayed by retinal antioxidants and by other compounds conferring protection. The long-term goal is to increase our understanding of macular biochemistry and how it relates to macular degeneration. Focus will be placed on micronutrients, because of the possibility or preventive dietary intervention.
Specific Aims are to answer the following questions: l) What is the mechanism by which the macular-pigment carotenoids, lutein and zeaxanthin, shown to be protective against AMD, are selectively accumulated in the foveal region of the primate (and human) retina? We hypothesize that specific macular pigment-binding proteins in the macula are responsible for this accretion. These will be identified and isolated through tracking endogenous ligands by their characteristic, visible, carotenoid spectra. Physical and ligand-binding properties will be measured. Determination of partial amino-acid sequences will allow comparison to carotenoid-binding proteins of other organisms, and also to foveal cDNA libraries. 2) What is the mechanism by which meso-zeaxanthin comes to be in the human fovea as part Or the macular pigment? It is not in the blood. We hypothesize that there are specific converting enzymes in the macula that change lutein into this stereoisomer. If so, what are their substrate specificities, localizations, and mechanisms of action? 3) Vitamin E, a potent membrane antioxidant, displays a dramatic dip in concentration in the monkey neural retina, at the radial position of the foveal crest, just outside the fovea. Does a similar minimum exist in a map Or vitamin E in the human retina? The importance Or such a biochemical vulnerability lies in the observation that its position would coincide with the initial location of geographic atrophy -- the common, """"""""dry"""""""" form Or sight-threatening AMD. 4) Do other antioxidants, present in membranes and in soluble compartments Or the primate and human retina, compensate for (or perhaps exacerbate) the deficiency of vitamin E at the foveal crest? Previous studies have lacked the spatial resolution for a detailed antioxidant map. The radial distributions of vitamin C, glutathione, ubiquinols, and bilirubin will be examined. The methodology for these projects is that of analytical biochemistry, chiefly HPLC separations and analyses. In addition, Aim 1 will require collaborations for molecular-biology techniques, and Aim 2 involves short- term tissue culture.
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