MECHANISMS OF RETINAL PHOTOTOXICITY

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The long-term objective of the proposed research is to identify--and eventually control--the cytotoxic molecule(s) that are formed upon irradiation of the retina with visible light and that cause photosensitive cells to degenerate. The theoretical mechanism of retinal phototoxicity is based on the concept of lipid peroxidation and the formation of intermediates that are toxic to the photosensitive cells and, under certain conditions, to the retinal pigment epithelium (RPE), causing them to degenerate. The specific aims of the proposed research are to (1) determine if light damage to the retina occurs by a mechanism of photosensitized lipid oxidation; (2) use biochemical markers of retinal damage (i.e., lipid oxidation intermediates) to assess primary sites of damage (e.g., photoreceptors vs RPE); (3) determine if nutritional vitamin E or vitamin A are able to modulate the sensitivity of the retina to photic injury; (4) determine if the biochemical markers of lipid oxidation correlate with regional patterns of retinal degeneration; (5) correlate individual animal variation in sensitivity to light damage with levels of biochemical markers; and (6) demonstrate the cytotoxicity of specific lipid oxidation intermediates. To accomplish the above aims, albino and pigmented rats will be maintained on formulated diets containing specific levels of vitamins E and A prior to exposure. Freeze-dried sections of retina will be microdissected into three specific layers: neural retina, photoreceptor cells, and RPE-choroid. Samples of each layer will be analyzed for vitamin E, unsaturated fatty acids, and products of peroxidation by gas chromatography-mass spectrometry (GC-MS). Structural analysis will include light and electron microscopy, and electroretinograms will be used to assess retinal function. As human retinal tissue becomes available from fresh autopsies or surgery, it will be used to develop procedures to handle small retinal biopsies and acquire a data base on the above parameters for possible future studies. It may be that virtually everyone is subjected to subclinical light damage to their retinas. Daily accumulated light damage appears to be aggravated by nutritional deficiencies and extended exposure to light (i.e., electric illumination). This work seeks to understand the basic mechanisms of retinal light damage in order to better evaluate its importance and to open routes to control it, and to preserve retinal health.