Objective  In order to investigate if puerarin could prevent and therapy diabetic retinopathy in rats, we observed the pathology and apoptosis of diabetic retinopathy in diabetic rats and the mechanism of protected effects of puerarin on diabetic retinopathy.

Methods  72 healthy male Wister rats were randomly divided into the following groups: control group, diabetic group  and diabetic+ puerarin group. Diabetes was induced in the rats by streptozotocin(STZ) administered intraperitoneally. Rats were killed at month 1,3,and5 months, we observed the retinopathy of the rats on different course of the disease by HE ,TNNEL stains,Electron microscopy,RT-PCR and western-blot methods.

Results  By HE stain, we found that the number of ganglion cells reduced, the optical density depressed in internal and external granular cells and the cells were disperse with irregular arrangement and rarefaction in the amphiblestrodes of diabetic rats. While these changes obviously improved in puerarin diabetic group. The apoptosis cells were significantly increased in the amphiblestrodes of diabetic rats by TNNEL stain. After the treatment of puerarin, the number of apoptosis cells were obviously decreased in the amphiblestrodes of diabetic rats. The mRNA level of Bcl-2 was decreased in diabetic rats while Bax was increased, in puerarin-group, treatment with puerarin inhibited downregulation of Bcl-2 and upregulation of Bax. The ratio of Bcl-2 to Bax was significantly reduced in STZ-group and attenuated by treatment with puerarin. Western blot analysis revealed a increased cleavaged caspase-3 level in STZ rats retina, which was prevented by a pretreatment with puerarin .

Conclusion  Puerarin had the preventive and therapeutic effect on the diabetic retinopathy, the mechanism maybe Puerarin inhibited cell apoptosis by decreasing  caspase-3 expression and increasing the Bcl-2/Bax ratio. Western blot analysis revealed a increased cleavaged caspase-3 level in STZ rats retina, which was prevented by a pretreatment with puerarin .