[Inhibitory effects of ursolic acid on diabetic retinopathy in mice]

To explore the protective effect and its mechanisms of intravitreal injection of ursolic acid (UA) on retinal injury in diabetic retinopathy (DR) mice.

DR model was set up by using alloxan. 60 C57BL/6 male mice (clean animal, aged 12 weeks) were randomly and evenly divided into 6 groups: blank control group, DR model group, positive control group (triamcinolone acetonide), UA intervention groups (low, moderate and high dose). Mice were killed one week after drug intervention and the eyeballs were removed to prepare paraffin section. Retinal new blood vessel was examined by histopathological methods. The mRNA and protein expressions of vascular endothelial growth factor (VEGF), cyclooxygenase 2 (COX-2), and Matrix Metalloproteinase 2 (MMP-2) in retinal tissues were detected by real-time PCR and Western blotting, respectively. The superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were detected by related kits.

The HE and PAS staining showed uniform inner limiting membrane structure and orderly vascular endothelial cells in blank control group, and neovascularization was seldom detected. In DR model group, numerous new blood vessels were formed beyond inner limiting membrane. UA intervention group with low dose had almost the same results with DR group, while the results of UA intervention group with high dose were similar with positive control group, in which the inner limiting membrane structure was uniform and new blood vessels were seldom seen. The mRNA expressions of VEGF, COX-2, and MMP-2 in DR model group were significantly higher than those of blank control group (P<0.001) and UA intervention group with moderate and high dose (P<0.001). The protein expressions of VEGF, COX-2 and MMP-2 in DR model group were significantly higher than those of blank control group (P<0.001) and UA intervention group with low, moderate and high dose (all P<0.05). The MDA content of retinal tissue in DR model group was significantly higher than those of blank control group (P=0.001) and UA intervention groups with moderate and high dose (P=0.026, 0.007). The activity of SOD was significantly lower in DR model group than those of blank control group (P<0.001) and UA intervention groups with low, moderate and high dose (P=0.040, 0.021, 0.003).

UA may inhibit the formation of new blood vessels through reducing the expressions of VEGF, COX-2 and MMP-2 in retinal tissues, and promote a remission from DR by obvious resistance to oxidative stress.