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T. Okamoto, S.B. Koevary, S. Roy; Effect of Topically–Applied Insulin on Vascular Changes in Retinas of Diabetic Rats . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3254.
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Purpose: To determine if topically administered insulin prevents vascular apoptosis and cell loss in retinas of diabetic rats. Methods: Lewis rats were randomly divided into six groups: normal, diabetic, diabetic treated with insulin eye drops daily or twice weekly, and normal rats treated with insulin eye drops daily or twice weekly. Diabetes was induced with streptozotocin injection. In the insulin–treated groups, normal and diabetic rats received 0.75% insulin in buffer containing 0.5% Brij–78 as a single eye drop (∼15 ul). After two months, the rats were sacrificed and their retinas isolated, fixed in 10% formaldehyde for 48 h, and subjected to trypsin digestion. Retinal vascular cells undergoing apoptosis were detected by using the TUNEL assay. Retinal trypsin digests were counterstained with hematoxylin, eosin, and periodic acid Schiff (PAS) and examined under the microscope to identify pericyte loss and acellular vessels. Results: The number of TUNEL–positive cells was significantly increased in the retinal trypsin digests of diabetic rats compared to those of non–diabetic controls (2.6±0.8 vs 1.4±0.7 per 0.4 mm2, p=0.008). In retinas of diabetic rats treated with insulin eye drops daily or twice weekly, the number of TUNEL–positive cells was significantly reduced (1.4±0.7 vs 2.6±0.8 per 0.4 mm2, p=0.04; 1.5 ±0.5 vs 2.6±0.8 per 0.4 mm2, p=0.03, respectively). The number of pericyte ghosts and acellular vessels was increased in retinas of diabetic rats compared to those of normal rats (3.1±1.1 vs 1.2±1.2 per 1000 cells, p=0.005 and 2.3±0.2 vs 1.6±0.4 per mm2, p=0.002, respectively). In retinas of diabetic rats treated with insulin eye drops daily or twice weekly, the number of pericyte ghosts was significantly reduced compared to nondiabetic control rats (1.5±0.7 vs 3.1±1.1, p=0.04 and 1.5±1.0 vs 3.1±1.1, p=0.02, respectively); similarly the number of acellular vessels was significantly reduced (1.5±0.2 vs 2.3±0.2 per mm2, p=0.0007 and 1.4±0.3 vs 2.3±0.2 per mm2, p=0.001, respectively). Interestingly, in retinas of nondiabetic rats treated with insulin, a slight increase in TUNEL positive cells, pericyte loss, and acellular vessels was observed. Conclusions: Insulin eye drops may be effective in reducing accelerated cell death and vascular lesions characteristic of diabetic retinopathy.
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