Does Metformin Protect Against Diabetic Retinopathy in Albino Rats? An Immunohistochemical Study

Background: Metformin (MT) is a widely used oral anti-hyperglycemic agent for Type II diabetes. However, its role in protection against diabetic retinopathy is not clear. Aim of the work: The purpose of this study was to investigate the possible protective effect of MT on the diabetic retinopathy in rat model with special consideration on glial cell activation, neuronal apoptosis and neovascularization. Materials and Methods: Twenty-one male Sprague Dawly rats were divided into control group (n=7) and experimental group (n=14) that developed Type II diabetes by feeding on high fat diet for 8 weeks followed by repeated small doses streptozotocin injections. The experimental group were farther subdivided into Diabetic (DB) group (n=7) were left for another 8 weeks without treatment and MT group (n=7) were left 4 weeks then received MT for another 4 weeks. At the end of the experiment, blood and retinal samples were collected for biochemical, histological and immunohistochemical studies. Results: Metformin administration significantly decreased diabetic induced hyperglycemia and decreased the serum level of oxidative stress markers to the control level. Also, it significantly suppressed the diabetic induced increase of Glial Fibrillary Acidic Protein (GFAP) and Caspase3 expression. On the contrary, it enhanced the diabetic induced increase of vascular endothelial growth factor (VEGF) expression in the retina. Conclusion: This study indicated that MT may have an adjuvant role in prevention of diabetic retinopathy, and future studies are recommended to declare the regulatory mechanisms for its antiangiogenic or proangiogenic effects.