Protecting effects and mechanism of tert-butyl hydroquinone on retinal cells in type 2 diabetic rats

Abstract

Background Apoptosis is a primary clinical pathological mechanism of diabetic retinopathy (DR). Oxidative stress and high glucose can activate cell apoptosis pathway and thus leads to cellular damage.It is confirmed that tert-butyl hydroquinone (tBHQ) plays an antioxidation effect, however, whether it has a protective role on retinal cells in DR is still unelucidated. Objective This study was to investigate the effect of tBHQ on vascular endothelial growth factor (VEGF) and bcl-2 expressions in retina of type 2 diabetic rats and its possible mechanism via nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) signal pathway. Methods Fifty clean healthy male SD rats were included in this experimental study.Ten rats were fed with normal diet as the normal control group, and other rats were fed with high fatty and high sugar food for 4 weeks.After 12 hours of fasting, streptozotoin (STZ) (30 mg/kg) was intraperitoneally injected to induce the type 2 diabetic models.The model rats were randomly divided into the diabetic control group and tBHQ group and 1% tBHQ was added into the high fatty and sugar food 1 week after modeling in the tBHQ group.Fasting plasma glucose (FPG) level, blood total cholesterol (TC) level, blood triglyceride (TG) level, high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C) and fasting serum insulin (FINs) were detected 4 and 12 weeks after modeling, respectively, and radio immunoassay was used to detect the FIN levels of the rats.The relative expression of VEGF and bcl-2 in retinas of the rats were assayed by immunohistochemistry and fluorescence real-time quantitative PCR (qRT-PCR). The use of the animals complied with the Regulations for the Administration of Affairs Concerning Experimental Animals by State and Technology Commission. Results Type 2 diabetic models were successfully established in 35 rats with successful rate 92.1%.The FIN levels were significantly different among different groups and time points (Fgroup=22.480, P=0.000; Ftime=7.636, P=0.008). The FPG, TC, TG and LDL-C levels were significantly different among the groups (FPG: Fgroup=78.531, P=0.000; TC: Fgroup=28.049, P=0.000; TG: Fgroup=13.108, P=0.000; LDL-C: Fgroup=6.804, P<0.05). Immunohistochemistry showed that VEGF and bcl-2 were mainly expressed in retinal ganglion cell layer, inner plexiform layer and outer plexiform layer.The expressions of VEGF and bcl-2 proteins were significantly different among different groups (VEGF: Fgroup=11.805, P=0.000; bcl-2: Fgroup=22.943, P=0.000); the expression level of bcl-2 protein was higher in 12 weeks after modeling than that in 4 weeks after modeling in the tBHQ group (P<0.05). The expressions of VEGF and Bcl-2 mRNA in rat retinas were significantly different among different groups and time points (VEGF: Fgroup=79.220, P=0.000; Ftime=6.090, P<0.05; Bcl-2: Fgroup=105.000, P=0.000; Ftime=13.170, P=0.001). Four and eight weeks after modeling, the expressions of VEGF and Bcl-2 mRNA in the diabetic control group and tBHQ group were significantly higher than that in the normal control group, and the expressions of Bcl-2 mRNA in the tBHQ group were significantly higher than that in the model control group (all at P<0.05); the expression of Bcl-2 mRNA was higher at 12 weeks after modeling than that at 4 weeks in the tBHQ group (P<0.05). Conclusions tBHQ produces anti-oxidative-damage and anti-apoptosis effects on retinal cells by up-regulating VEGF expression and down-regulating bcl-2 expression in DR rats.In addition, tBHQ may have effects on lowering high blood sugar, regulating insulin and blood lipid levels. Key words: Diabetes mellitus/complication; Retinopathy; Vascular endothelial growth factor; Bcl-2/metabolism; Disease models, animal; SD rats; Tert-butyl hydroquinone