Inhibition of vitreoretinal VEGF elevation and blood-retinal barrier breakdown in streptozotocin-induced diabetic rats by brimonidine

Purpose To determine whether long-term brimonidine (BRI) treatment prevents the hyperglycemia-induced increase in vitreoretinal vascular endothelial growth factor (VEGF) expression and breakdown of the blood-retinal barrier (BRB) in streptozotocin (STZ)-induced diabetic rats. Methods Brown Norway/Long-Evans rats were divided into three groups with similar distributions of blood glucose and body weight. Two groups received a single intravenous injection of STZ (65 mg/kg) and the remaining control group received vehicle. Drug treatment administered via miniosmotic pumps was initiated 1 or 6 weeks later. The STZ-induced diabetic rats were treated with BRI (1 mg/kg/d) or vehicle (VEH) and control nondiabetic rats were treated with VEH for 4 weeks. Vitreoretinal VEGF protein, vitreal glutamate, and BRB breakdown were then measured. Results At 5 weeks after STZ treatment, STZ-treated diabetic rats demonstrated significantly elevated vitreoretinal VEGF expression, vitreal glutamate concentrations, and BRB leakage compared with nondiabetic control rats. Chronic BRI treatment had no effect on vitreal glutamate concentrations in diabetic animals but significantly decreased vitreoretinal VEGF expression and BRB breakdown to levels similar to those observed in control rats. BRI also significantly reduced BRB breakdown in aged diabetic rats at 10 weeks after STZ treatment. Conclusions BRI produced marked decreases in vitreoretinal VEGF and inhibition of BRB breakdown in diabetic rats. The mechanism for these effects may involve attenuation of retinal NMDA receptor activity by BRI. The results suggest that BRI would be useful for treatment of ocular diseases associated with BRB leakage, such as diabetic macular edema and retinopathy.