PURPOSE. To determine whether minocycline, a compound known to protect the retina against light-induced damage in rodent models, and its structurally related analogues would protect photoreceptor cells in primary bovine retinal cell culture against light and oxidative stress. METHODS. Minocycline and its analogues were tested in primary retinal cell culture to see whether they would inhibit light or oxidative stress-induced cell death. Primary cell cultures composed of photoreceptors, bipolar

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... lls, and glial cells were prepared from bovine retinas. The extent of cell death induced by light or oxidative stress was assessed by using Sytox Green (Invitrogen-Molecular Probes, Eugene, OR) a nucleic acid dye uptake assay. Differential protection of photoreceptor cells from stress were examined using immunocytochemistry. RESULTS. Minocycline and methacycline were cytoprotective against light-or oxidative stress-induced damage of bovine primary photoreceptors in culture with an EC 50 Ͻ 10 M. In contrast, structurally related analogues such as demeclocycline, meclocycline, and doxycycline were phototoxic at Ͼ3 to Ͼ10 M. Though demeclocycline was found to be phototoxic, it was cytoprotective (EC 50 ϭ 5 M) against oxidative stress in the absence of exposure to light. CONCLUSIONS. The protective action of minocycline against light-induced damage in the cell-based assays agrees with earlier reports in animal models and suggests that the in vitro assay using bovine primary retinal cell culture is a suitable model for evaluating compounds for retinal protection. Cellular protection or toxicity produced by structurally related compounds show that minor structural modifications can alter the function of minocycline and lead to potent retinal protective compounds. (Invest Ophthalmol Vis Sci. 2007;48:412-421)