Cinnamon Attenuated Long-Term IGT-Induced Retinal Abnormalities via Regulation of Glucose Homeostasis in Neonatal Streptozotocin Induced Rat Model

Abstract

Diabetic retinopathy (DR) is one of the major causes of blindness all over the world. According to the previous studies, impaired glucose tolerance (IGT) has been linked to retinal dysfunction/vascular damage. Decreased retinal function is an initial event of early DR. Although the biochemical and molecular events are not fully understood, glial activation, angiogenesis and oxidative stress are some of the pathways associated with early retinal abnormalities. Since IGT is associated with development of retinal dysfunction/vascular damage; as a preventive strategy, we have studied beneficial effect of Cinnamon as a hypoglycaemic agent on long-term IGT induced retinal abnormalities using neonatal streptozotocin (nSTZ) rat model. Control, IGT rats were maintained on AIN-93M diet alone and another set of IGT rats were maintained on AIN-93M diet with 3% Cinnamon for 8 months. At the end of the study, untreated IGT rats developed retinal functional abnormalities as assessed by electroretinogram (ERG) and the retinal structure did not alter as assessed by H&E staining. Further, increase in expressions of GFAP, VEGF and decreased expression of rhodopsin in untreated IGT rat retinas. 4-HNE, a marker of oxidative stress was also elevated in IGT state. Supplementation of Cinnamon to IGT rats had lowered fasting and postprandial glucose levels and also prevented retinal functional abnormalities. Further, Cinnamon protected photoreceptor cell damage, suppressed glial activation, angiogenesis and oxidative stress as there was an improved rhodopsin expression, inhibited elevated expressions of GFAP, VEGF and 4-HNE respectively. In conclusion, Cinnamon attenuated IGT induced retinal abnormalities probably through its hypoglycemic property.