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D Reeves, M Lee, D Hatala, TS Kern; Nitroimidazole Derivative as a Histologic Marker for Retinal Ischemia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):785.
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Purpose:Ischemia underlies the pathophysiology of numerous retinal vascular diseases. Methods to objectively assess the localization of hypoxia in the retina are lacking. Nitroimidazole derivatives are selectively retained in areas of low oxygen tension, and have been used in cancer research to identify and target ischemic cells in solid tumors. We used the Hypoxyprobe-1, a substituted nitroimidazole compound (pimonidazole hydrochloride), to assess the distribution of ischemia in experimentally induced retinal ischemia and in long-term hyperglycemia in rodents. Methods:Retinal ischemia was created in one eye of non-diabetic rats by either raising the intraocular pressure (30 inch column height) or injecting intravitreal endothelin-1 (10-6 M, in Emulphor EL-620). The other eye was used as control. Prior to inducing ischemia, all animals were injected intraperitoneally with Hypoxyprobe-1. After varying durations of hypoxia (10-60 minutes), the eyes were enucleated, and hypoxia identified immunohistochemically with an antibody to Hypoxyprobe-1. To determine if 6 months hyperglycemia is sufficient to alter retinal oxygenation grossly, the probe was injected into mice experimentally diabetic and fed a 30% galactose diet. Results:Gross reduction in retinal blood flow (by increased IOP and endothelin-1 injection) for 10-60 minutes resulted in significant accumulation of Hypoxyprobe-1 throughout the retina. At shorter duration of hypoxia, there was noticeably more immunostaining in the inner retinal layers compared to the photoreceptor layer. In contrast, 6 months of severe hyperglycemic stress showed no significant retinal accumulation of Hypoxyprobe-1 immunostain compared to non-diabetic controls. Conclusion:Nitroimidazoles are retained in areas of severe retinal hypoxia, but 6 months of severe hyperglycemic stress did not cause significant marker retention. CR: None Support: Kristin C. Dietrich Diabetic Research Award, NIH-P30-EY11373 Core Grant, RPB and Retina Research Fund
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