Retinal and metabolic changes in a high-fat diet (HFD)+STZ model of Type II diabetes

While the high-dose streptozotocin (STZ; 100 mg/kg) rodent model is the gold standard in modeling Type I diabetes, models for Type II diabetes are needed for this more common form of diabetes. We investigated the retinal, cognitive, and metabolic alterations in a Type II diabetic model induced by high-fat diet (HFD) and low-dose STZ (30 mg/kg). Long Evans rats were assigned to naïve control, HFD, or HFD+STZ groups. Diabetic rats were further stratified into Type I and Type II based on metabolic assessments. Optomotor response (OMR, visual function), electroretinograms (retinal function), and Y-maze (cognitive function) were tested. Serum was analyzed for 12 metabolic markers using a multiplex panel. Type I rats showed severe increases in blood glucose accompanied by impairments in insulin and glucose tolerance, reduced bodyweight, and low insulin levels. In contrast, Type II rats showed moderate changes in blood glucose and insulin and glucose tolerance with weights and insulin levels similar to naïve controls. Type I and II rats showed OMR deficits (p<0.05) and electroretinogram changes (p<0.05). No cognitive deficits were observed. Type I rats displayed reduced serum levels of brain-derived neurotrophic factor (BDNF), C-Peptide, and leptin (p<0.05), and alterations in C-Peptide, PYY, and glucagon levels correlated with retinal function changes (p<0.05). Type II rats exhibited a moderate diabetic state while still developing retinal and visual deficits, which recapitulates phenotypes reported in patients.