Long term features of diabetic retinopathy in streptozotocin-induced diabetic Wistar rats

Diabetic retinopathy is a complication of diabetes and a leading cause of vision loss among working-age adults. To assess whether the Wistar rat with Streptozotocin (STZ)-induced diabetes is a suitable animal model of human proliferative diabetic retinopathy we evaluated the vascular changes to assess the diabetic retinopathy (DR) stages in this model. After two weeks of intraperitoneal STZ (55 mg/kg) injection in male Wistar rats (270-300 g), they were considered diabetic with persistent blood glucose levels >= 16.65 mmol/L. The diabetic and control rats were investigated after 1, 3, 6 and 9 months by electroretinography, Evans blue assay, dextran fluorescence retinal angiography, and retinal histopathological studies. Retinal vascular permeability in the diabetic groups increased significantly in all diabetic groups. The amplitude of a- and b-waves decreased significantly in all diabetic groups compared with the age-matched control groups. The latent time of a-waves in the diabetic groups was delayed at 3 months of diabetes and this delay remained relatively constant till 9 months following the onset of diabetes. Although the latent time of b-wave in the diabetic groups increased slightly, a significant difference was found right at 9 months of diabetes. Vascular density and branching point numbers significantly decreased in the diabetic eyes at 3 and 6 months while they increased at 9 months, which was not significant. Intraretinal hemorrhage and ischemic changes were detected in the half of diabetic rats after 6 months and considered as preproliferative stage of diabetic retinopathy. Although preproliferative changes were detected in all diabetic rats at 9 months, half of them showed vitreous neovascularization attached to retina and retinal folds which can be considered as proliferative stage of DR. Intraretinal hemorrhage, extensive leakage of fluorescein, retinal folds, and vitreous neovascularization were the most prominent findings of severe and proliferative diabetic retinopathy in a fraction of the STZ-induced diabetic rats which were comparable to that of the human patients. STZ-induced diabetic rats can be considered to be a potentially useful model for studies on pathogenesis and treatment of diabetic retinopathy in human.