The long term objectives of this project are to determine the composition and anatomical distribution of carotenoids in the eyes of a variety of animals, an essential step in elucidating the role of these pigments in vision. The work will be concerned largely with the macular pigments, an area where considerable progress has already been made.
The specific aims are: a) to strengthen the identification of the pigments through electron-impact ionization mass spectrometry, b) to refine a study of the variation with eccentricity in the areal density of the pigments in both humans and non-human primates, c) to examine in greater detail what appears to be an enhancement of macular pigmentation in diabetes, d) to identify the carotenoids in avian cone oil-droplets and compare these with the carotenoids of the turtle retina. The biomedical relevance of our studies of carotenoids centers on their postulated protective capacity against photo-degradation of retinal tissues. Central to this hypothesis would be the ability of there pigments to quench the singlet oxygen excited state and triplet excited states of hosts, believed to be involved in these processes, and/or the simple screening effects of the pigments against short wavelength light. To assess the photoprotection hypothesis, it is important to know exactly that pigments constitute the macular pigment, and how they are distributed in the retinal tissues. Human and other primate retinas will be cut into annuli concentric with the fovea, and their carotenoid content determined by HPLC. Donor information will be recorded as a means of uncovering possible connections between age, disease and pigmentation. Recent evidence suggests the possible existence of a specific mechanism of uptake of lutein and zeaxanthin by rods and cones respectively. To explore this possibility, the carotenoids of the rod-free area will be analyzed and the adult and developing infant eye compared. During the above procedures, macular pigments will be accumulated for final purification by HPLC followed by analysis by mass spectrometry. Fragmentation patterns produced by electron-impact ionization will be compared with those of authentic standards. The results, it is hoped, will confirm initial studies using chemical ionization, and provide an absolute identification of the macular pigments. Work with turtle and avian cone oil-droplets takes advantage of the available expertise in the problem of identifying vary small carotenoid samples. The eventual aim is to further clarify the connection between photoreceptors and carotenoid metabolism.
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