To investigate the protective effects of an antioxidant tert-butylhydroquinone (tBHQ) on the morphology and function of retina in early-stage experimental diabetic rats, and to explore the mechanism of its protective effect.

Forty-five healthy SD rats of clean degree were randomized into normal control group, diabetes model group and tBHQ intervention group, with 15 rats in each group according to a random number table.The diabetes model was established via a single intraperitoneal injection of streptozotocin (STZ) in diabetes model group and tBHQ intervention group.Normal control group was intraperitoneally administered with an equal-volume injection of sodium citrate buffer.Rats in the tBHQ intervention group maintained a diet with 1% tBHQ for 2 weeks before the STZ injection, and the other two groups were fed with normal rat food only.Blood from tail vein was collected to assay the blood glucose level at 72 hours, 2 weeks and 4 weeks following modeling.Rat electroretinogram (ERG) was detected at 4 weeks after modeling.Morphological changes of rat retina were observed by hematoxylin and eosin staining.The apoptosis of retinal cells in different layers was detected by TUNEL assay.The expression of protein kinase B (Akt), p-Akt, endothelial nitric oxide synthase (eNOS) and p-eNOS was detected by Western blot.Müller cell line rMC-1 cells cultured in vitro were divided into 5 groups, including normal control group (72-hour culturing in normal medium), mannitol control group (72-hour culturing in medium containing 5.5 mmol/L glucose and 24.5 mmol/L mannitol), high glucose group (72-hour culturing in high-glucose medium), tBHQ intervention group (24-hour culturing in normal-glucose medium containing 5 μmol/L tBHQ, 72-hour culturing in high-glucose medium containing 5 μmol/L tBHQ), and phosphoinositide 3-kinase (PI3K) inhibitor group (6-hour culturing in normal medium containing 5 μmol/L LY294002, 24-hour culturing in normal-glucose medium containing 5 μmol/L LY294002 and 5 μmol/L tBHQ, 72-hour culturing in high-glucose medium containing 5 μmol/L LY294002 and 5 μmol/L tBHQ). The expression of Akt, p-Akt, eNOS and p-eNOS in the cells was detected by western blot.The use and care of animals complied with Regulations for the Administration of Laboratory Animals in Southwest Medical University.The study protocol was approved by the Animal Ethics Committee of Southwest Medical University (No.201711189).

The blood glucose level at 72 hours, 2 weeks and 4 weeks after modeling was higher in diabetic model group than tBHQ intervention group and normal control group (all at P<0.01). Four weeks after modeling, the scotopic ERG a-wave and b-wave amplitudes of diabetic model group were lower than those of normal control group and tBHQ intervention group (all at P<0.05). With edema and thickening of inner plexiform layer, thinning of inner nuclear layer and outer nuclear layer, as well as loosely arrangement and disorder of retinal layers, the number of retinal ganglion cells was decreased in diabetic model group in comparison with normal control group, all of which were improved in tBHQ intervention group in comparison with diabetic model group.There were more apoptotic retinal cells in diabetic model group than normal control group and tBHQ intervention group (both at P<0.05), which mainly existed in the outer nuclear layer.The relative expressions of p-Akt/Akt and p-eNOS/eNOS in rat retina of normal control group, diabetic model group and tBHQ intervention group were 0.76±0.11 and 0.83±0.06, 0.52±0.10 and 0.52±0.08, 1.14±0.31 and 1.03±0.13, respectively.The relative expressions of p-Akt/Akt and p-eNOS/eNOS in diabetic model group were lower than those of normal control group and tBHQ intervention group (all at P<0.01). The relative expressions of p-Akt/Akt and p-eNOS/eNOS in normal glucose group, mannitol control group, high glucose group, tBHQ intervention group and PI3K inhibitor group were 0.95±0.38 and 0.86±0.11, 0.94±0.27 and 0.74±0.29, 0.33±0.25 and 0.45±0.29, 1.32±0.37 and 1.28±0.22, 0.24±0.09 and 0.73±0.29, respectively.The relative expressions of p-Akt/Akt and p-eNOS/eNOS were significantly lower in high glucose group than those in normal glucose group and tBHQ intervention group (all at P<0.05), which were significantly lower in PI3K inhibitor group compared with tBHQ intervention group (both at P<0.01).

tBHQ has protective effects on the morphology and function of retina in early diabetic rats, and the mechanism may be related to the activation of Akt/eNOS signaling pathway.

Diabetes mellitus/complications; Retinopathy; Antioxidants/tert-butylhydroquinone; Electroretinogram; Apoptosis; Akt/eNOS