Objective: To evaluate the action of Angiotensin II (AngII) on the occurrence and development of diabetic retinopathy and the effect of captopril and valsartan on preventing and treating diabetic retinopathy.
Methods: Male C57BL/KsJ db/+ mice were obtained at 3 weeks of age and maintained on diets enriched animal fat for 4 weeks. After exposure to high-fat diet for 4 weeks, mice were injected intraperitoneally with streptozotocin (STZ) 100 mg/kg body weight. After 2 weeks, nonfasting plasma glucose concentration was measured by nipping the distal part of the tail. Mice whose plasma glucose concentrations were higher than 11.1 mmol/L were selected for the study as model groups. Starting from day 2, captopril 12.5 mg/kg or valsartan 40 mg/kg was given to treatment group via the oral route After treatment for 4, 8, 12 weeks, respectively, eyeballs of mice from each group were enucleated, embedded in paraffin to make tissue sections for immunohistochemistry analysis. The instrument for computer image-analysis was used to analyze the expression of AngII and VEGF in ganglion cell layer. The analyzed indices were mean gray scale value and area density value.
Results: With increased duration of diabetes, the mean gray scale values of AngII and VEGF decreased significantly. At the same time, area density values of AngII and VEGF increased significantly. The area density values of VEGF in captopril treated-group was significantly lower than that in valsartan-treated group for the same duration. Moreover, the area density values of VEGF at 4 weeks was significantly lower than that at 8 weeks or 12 weeks. The area density value in captopril treated-group had a significant negative correlation with diabetes duration. AngII had significant positive correlation with VEGF.
Conclusion: AngII possibly participated directly and/or indirectly in the occurrence and development of diabetic retinopathy via the upregulation the expression of VEGF. Early treatment with angiotensin-converting enzyme inhibitors (ACEi) and angiotensin 1 type receptor (AT1R) antagonists could improve diabetic retinopathy to some degree and protect the retinas. The effect of treatment with ACEi was better than that with AT1R antagonists in short term situation.