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E Gaillard; A Photochemical Study of HIDD, a Derivative of All-Trans-Retinal and Ethanolamine and HIDD-PE, a Component of Retinal Lipofuscin . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4522.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To determine the photophysical and photochemical reactivities of HIDD and HIDD-PE with an emphasis on the mechanisms by which they may cause photooxidative damage to the retina. Methods: HIDD and HIDD-PE have been synthesized and purified according to previously published methods. Both steady state and time resolved fluorescence and absorption techniques have been used to quantitate the photophysical and photochemical reactivities of HIDD and HIDD-PE. Results: Both HIDD and HIDD-PE are weakly fluorescent and have broad emission spectra ranging from ca. 450 nm to 650 nm depending on the degree of protonation. The absorption spectrum of HIDD-PE is consistent with published spectra from retinal tissue of ABCR knockout mice (Weng, J. et al, Cell 98, 13 (1999)). Time resolved absorption experiments with HIDD and HIDD-PE show that both substances form triplet excited states upon direct excitation (lifetimes = 29 micro-s and 10 micro-s, respectively) with relatively good efficiency (quantum yield ca. 0.25) resulting in both being singlet oxygen sensitizers. Besides singlet oxygen sensitization, the triplet excited states of both compounds are potent photooxidizing agents capable of direct electron abstraction from several substrates and, therefore, they function as both Type I and Type II sensitizers depending on the availability of oxygen. Conclusion: HIDD and HIDD-PE, which has been isolated from retinal tissue of ABCR knockout mice, are both efficient photosentizers of both Type I and Type II photooxidative processes. In the RPE, these initial processes can ultimately lead to damage to the tissue through the formation of peroxides and other oxidized species.
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