To explore the protective effects of folic acid on retinas and its anti-oxidative stress mechanism in diabetic mice.

Thirty-two 16-week-old SPF degree male db/db mice were randomized into model group and folic acid group, and 16 matched C57BL/KsJ mice were used as controls.Folic acid was used to the mice by oral gavage once per day with the dose of 71 μg/kg (2 ml) for 60 days in the folic acid group, and the same volume of normal saline solution was used in the model group and control group in the same way.The activities, mental state, body weight, and fasting plasma glucose (FPG) of the mice were recorded during experiment.At the end of the intervention, the mice were sacrificed and the retinas and blood sample were obtained.The histopathology of the retinas was examined with hematoxylin- eosin staining; serum homocysteine (Hcy) was detected by ELISA assay; the relative expressions of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) mRNA were detected in the retinas by real-time fluorescence quantitative PCR; the relative expressions of B lymphoma 2 protein (bcl-2), bcl-2 related X protein (bax), 3-nitrotyrosine (3-NT) and 4-Hydroxynonine (4-HNE) proteins were assayed by Western blot assay; superoxide dismutase (SOD), 8-hydroxydeoxyguanosine (8-OHdG) and malondialdehyde (MDA) levels in the retinas were detected by biochemical kits, and immunofluorescence assay was used to detect the expression of NADPH oxidation 4 (NOX4) in the retinas.The use and care of the experimental animals adhered to the ARVO Statement by the American Association for Vision and Ophthalmology Research and this study protocol was approved by Ethic Committee of Qinghai University (QHDX 2018-35).

Over the experimental period, The FPG was normal and body weight was gradually increased in the mice of control group.The FPG>16.7 mmol/L and the mice appeared obese.In the folic acid group, both body mass and FPG of the mice were gradually reduced.At the end of drug administration, serum Hcy concentration of the mice was (27.18±3.18)μmol/L in the model group, which was significantly higher than (8.28±2.18)μmol/L in the control group and (13.73±2.54)μmol/L in the folic acid group (all at P<0.05). The retinal structure was intact in the control group, and the retinas were thinning with more capillaries and inflammatory cells in the model group, the thickness of the retinas was increased and the capillaries and inflammatory cells were decreased in the folic acid group.The relative expressions of TNF-α and IL-6 mRNA in the retinas were significantly higher in the model group than those in the control group, and those in the folic acid group were reduced in comparison with the model group (all at P<0.05). The relative expression of bcl-2 protein in the retinas of folic acid group was lower than that in the control group and higher than that in the model group, and the relative expressions of bax, 3-NT and 4-HNE proteins in the retinas of the folic acid group were significantly higher than those in the control group and lower than those in the model group (all at P<0.05 ). The T-SOD activity in the folic acid group was significantly stronger than that in the control group and weaker than that in the model group, and the concentrations of 8-OHdG and MDA in the retinas of the folic acid group were significantly reduced in comparison with those of the control group and elevated in comparison with those of the model group (all at P<0.05). The expressing intensity of NOX4 protein in the retinas of the folic acid group was significantly weaker than that of the model group.

Folic acid appears aprotective effect on retinal tissue in diabetic mice by reducing serum Hcy, inhibiting oxidative stress and cell apoptosis.

Diabetes/complication; Retina; Protective effect; Folic acid; Oxidative stress; Disease model; Mice