Preventive And Therapeutic Effect Of Inonotus Obliquus Polysaccharides And Its Mechanism On Rat Diabetic Retinopathy

ObjectiveTo investigate the preventive and therapeutic effect of Inonotus obliquus polysaccharides in diabetic rats,and to explore the possible mechanism through the Keap1-Nrf2-ARE signaling pathway.MethodsTogether 40 SD rats were divided into four groups in our study and they were control group(CON group),diabetic group(DM group),Inonotus obliquus polysaccharides treatment group(IOP group),IOP+Zn Protoporphrin group(inhibitor group).In addition to the CON group,the other three groups were given a single intraperitoneal injection of streptozotocin to induce the diabetic rat model.The IOP group and the inhibitor group received Inonotus obliquus polysaccharides by intragastric administration once a day(300mg/kg),the inhibitor group received intraperitoneal injection of zinc protoporphyrin(20mg/kg)24h before intragastric administration.After 12 weeks,we measured the rats weight,serum fasting blood glucose,the content of malon dialdehyde(MDA),glutathione(GSH)and superroxide dismutase(SOD)in retina of rats,retinal morphology was observed by HE staining and the density of retinal ganglion cells(RGC)was counted,the expression of heme oxygenase-1(HO-1),NF-E2relatedfactor2(Nrf2)and Cyclooxygenase2(COX-2)were detected by immunohistochemistry and western-blot.Results1.Compared with the CON group,the other groups had significantly lower body weight(all P<0.01)and higher blood glucose(all P<0.01);But the glucose of the IOP group was<16.7mmol/L,lower than DM group and inhibitor group significantly(P<0.01).2.Compared with the CON group,the content of SOD and GSH in the retinal tissues of the DM group decreased,while the content of MDA increased(all P<0.01);Compared with the DM group,the content of SOD and GSH in the IOP group increased significantly,while the content of MDA decreased(all P<0.01);After the addition of the inhibitor,compared with the IOP group,the content of SOD and GSH in the inhibitor group decreased and the content of MDA increased,with statistically significant differences(all P<0.05).3.HE staining results showed that there were no abnormalities in the retinal structures of the CON group and the IOP group.The retinal layers of the rats in the DM group and the inhibitor group were blurred and disordered.The density of retinal ganglion cells in CON group,DM group,inhibitor group and IOP group was(2300±100)/mm~2,(1400±100)/mm~2,(1505±95)/mm~2,(2250±95)/mm~2.Compar ed with the CON group,the density of ganglion cells in the DM group decreased significantly(P<0.01).Compared with the CON group,the density of ganglion cells in the DM group decreased significantly(P<0.01);Compared with DM group,the density of ganglion cells in IOP group increased significantly(P<0.01);Compared with the IOP group,the density of ganglion cells in the inhibitor group decreased significantly(P<0.01),there was no significant difference between the CON group and the IOP group(P>0.05).4.Western-blot results showed that,compared with the CON group,the expression levels of Nrf-2,HO-1 and COX-2 in the DM group were all increased(all P<0.01);Compared with the DM group,the expression of Nrf-2 protein and HO-1 protein in the retinal tissues of the IOP group was significantly increased,while the expression of COX-2 protein was decreased(all P<0.01);Compared with the IOP group,the expression of Nrf-2 protein and HO-1 protein in retinal tissues of the inhibitor group was decreased,while the expression of COX-2 protein was increased(all P<0.01).There was no significant difference between CON group and IOP group(P>0.05).ConclusionsInonotus obliquus polysaccharides can up-regulate the expression of antioxidant stress protein HO-1 and inhibit the expression of inflammatory factor COX-2,so as to protect retinal ganglion cells in diabetic rats,which may be related to the activation of Nrf2 signaling pathway.