ABSTRACT
Background The pathogenesis of diabetic retinopathy (DR) might be related with oxidative stress and its mechanism has not been fully elucidated.Grape seed proanthocyanidin extracts (GSPE),a powerful antioxidant,plays roles in some systemic diseases.However,the effect and mechanism of GSPE in DR has not been illuminated clearly.Objective This study was to investigate whether GSPE has a protective effect on the retinas of diabetic subjects and explore its mechanism.Methods Thirty SPF adult Wistar rats were divided into the control group,diabetic group and diabetes + GSPE group according to the randomized number table.Diabetic models were induced by intraperitoneal injection of 100 mg/kg strebtozotocin (STZ) prepared with citrate buffer,and only the equal amount of citrate buffer was used in the same way in the control group.GSPE solution was intragastrally used 250 mg/kg daily in the rats of the diabetes+GSPE group from injective day through 8 weeks,and distilled water was used in the same way in the rats of the control and diabetic groups.The rats were sacrificed in the eighth week after injection and the retinas were isolated.The morphology of the retina were examined by hematoxylin and eosin stain.Retinal homogenatewas prepared for the assay of superoxide dismutase (SOD),glutathione peroxidase (GSH-Px) activity and malonaldehyde (MDA) content.The expressions and location of nuclear erythroid related factor 2 (Nrf2) was determined by immunochemistry,and the expressions of Nrf2 and heme oxygenase-1 (HO-1) were quantitatively analyzed by Western blot.The apoptosis of retinal cells was detected by TUNEL.Results In the eighth week after modeling,the blood glucose levels were significantly higher and the body weight was lower in the rats of the diabetic group and diabetes+GSPE group compared with the control group (all at P＜0.01).Retinal structure was normal in the rats of the control group.However,loose tissue,irregular arrangement of cells and thickness decrease of retinal fiber layer,retinal ganglion cell layer and inner plexiform layer were exhibited in the rats of the diabetic group,while the morphology abnormality was slight in the rats of the diabetes+GSPE group.The SOD and GSH-Px activities and MDA content were significantly different among the 3 groups (F =11.010,P =0.001 ; F =12.072,P =0.000 ; F =25.224,P=0.000),and activities of SOD and GSH-Px in the retinas were significantly lower,and the MDA level was higher in the rats of diabetic group than those of the diabetes+GSPE group and the control group (all at P＜0.01).The relative expressing levels of Nrf2 were (165.5±29.4) ％ and (134.8 ±7.8) ％ in the diabetes+ GSPE group and diabetic group,with a significant difference between them (t=2.450,P=0.044).Compared with the diabetic group,the expressing level of the HO-1 was sigficantly increased ([170.2±22.0)％ versus [125.3±9.2] ％,t =2.360,P =0.002).TUNEL showed that the retinal apoptotic cells of diabetic rats were mainly located in the retinal fiber layer,RGCs layer,inner and outer nuclear layer,and the number of apoptotic cells was less in the diabetes+GSPE group compared with the diabetic group under the fluorescence microscope.Conclusions GSPE can play a protective role on diabetic rats by activating Nrf2 pathway and therefore improving retinal oxidative stress and decreasing apoptosis.