Protection of Retinal Vascular and Neuronal Cells from Apoptosis as an Approach for the Treatment of Early Diabetic Retinopathy

Abstract

Purpose: : To explore a new treatment for early diabetic retinopathy, G165, a glycoprotein, that has demonstrated protective functions for vascular and neuronal cells, was tested in vivo.

Methods: : Diabetes was induced, by Streptozotocin (i.p. injection), in rats. At the onset of diabetes, a single injection of G165 (5 to 200 ng/eye) was given intravitreally. During the following 6 weeks (ws), the blood–retinal barrier (BRB) was monitored by Evans blue quantification. Retinal cells death was detected by TUNEL staining. The retinal thickness and cell counts in different layers were evaluated by light microscopy. Electron microscopy (EM) was used to scrutinize retinal vascular and neuronal injury. A pharmacokinetic study of G165 was also conducted.

Results: : BRB breakdown was detected as early as 4 days after diabetes onset, peaked at 2 ws (63% increase compared with non–diabetic eyes) and then reached a plateau at 2 to 4 ws. In the G165–treated diabetic eyes, BRB permeability was maintained at the non–diabetic control level. A dose–dependency of G165 for BRB protection was observed. TUNEL–positive cells significantly increased in outer nuclear layer (ONL) at 1 w and reached the peak at 4 to 6 ws after diabetes onset. In the G165 injected eyes there was no evident TUNEL–positive cells detected in ONL until 4 ws. The retinal thickness, specifically, that of the ONL, was reduced significantly in diabetic rats, correlating with the decrease in the cell number of ONL. Treatment with G165 prevented the cell loss and maintained a normal thickness of ONL up to 4 ws. EM observations demonstrated vascular and neuronal death starting early after the onset of diabetes. After G165 administration, the death of photoreceptors and the injury of capillary endothelial cells were undetectable by EM until 4 ws after the onset of diabetes. The pharmacokinetic profile of G165 in the vitreous fits the first order kinetics with a half–life elimination period ranging 24 to 36 hours.

Conclusions: : Apoptosis is an important constituent of vascular and neuronal cell death in the early course of diabetic retinopathy. G165 intravitreal injection in early stage prevented the retinal cell death and the BRB malfunction, and therefore, appears to be a novel approach for treatment of early diabetic retinopathy.

Keywords: diabetic retinopathy • neuroprotection • apoptosis/cell death