Protection Of Exendin-4 Analogue In Early Diabetic Retinopathy

Purpose To explore the protective effect of exendin-4 analogue(E4a) on early DR. Methods(1).Exendin-4 analogue was injected subcutaneous(sc.) and intravitreally with different doses to find the best one of protecting the diabetic retinopathy. Expression of GLP-1R was detected at both mRNA and protein levels and verified by immunohistochemistry.(2).Thirty six Sprague-Dawley(SD) rats were included in the experiment,Diabetes was induced by intraperitoneal injection(ip) of streptozotocin (STZ).The rats were divided into 3 groups:normal control(N),diabetic control(D) and E4a-treated diabetic(E4a) group.For E4a group,the rats were treated with E4a (sc.0.05μg/g BW/day);for N and D groups,the rats were treated with normal saline (NS,sc),accordingly.Blood glucose levels and body weight were measured weekly. Electroretinogram(ERG) was performed 1 and 3 months after diabetes onset.The retinal thickness and cell counts in each layer were evaluated under light microscopy after ERG examination.(3).Experimental diabetic rats were injected E4a intravitreally.Electroretinogram(ERG) was performed 1 month after diabetes onset. The retinal thickness and cell counts in each layer were evaluated under light microscopy after ERG examination.The concentration of glutamate in vitreous was tested by HPLC.(4).Expression of GS and GLAST were detected at both mRNA and protein levels and verified by immunohistochemistry.Retinal M(u|¨)ller cell was cultured in medium with high-glucose,and Gene expression of the GS and GLAST were studied with RT-PCR.Western blotting assay was performed to explore the level of GLAST on cell total proteins.Results(1).E4a can reduce the blood glucose level of diabetic rats to the normal control level when it was injected subcutaneously.GLP-1R was expressed at both mRNA and protein levels in retina of SD rats.Immunostaining of the rat retina revealed that GLP-1R was predominantly expressed in inner layer of the retina.(2). B-wave amplitudes and OPs decreased with the progress of diabetes,and E4a injected whether subcutaneous(sc.) or intravitreally prevent the loss of b-wave amplitude and OPs caused by diabetic rats.The retinal thickness was reduced with a diabetes-duration dependent fashion.The cell counts of both ONL and INL were reduced accordingly in the diabetic rats.E4a prevented the cell loss and maintained a normal thickness.The concentration of glutamate in vitreous in E4a injected intravitreally group was significantly reduced compared with the diabetic control.(3). GS and GLAST were expressed at mRNA level in retina of SD rats and M(u|¨)ller cells. Immunostaining of the rat retina revealed that GLAST was predominantly expressed in M(u|¨)ller cells and RGC cells.The protein level of GLAST in E4a group expressed more than diabetic control.Conclusions GLP-1R was expressed in rat retina.Apoptosis is an important constituent of retinal cell death in early DR.E4a administration can reverse the changes of ERG,prevent the retinal cell death and maintain normal retinal thickness in diabetic rats.It can reduce the concentration of glutamate in retina through upregulating the expression of GLAST.Therefore,this is a potent approach for treatment of early DR.