Rehmanniae Radix Iridoid Glycosides Protect Kidneys of Diabetic Mice by Regulating TGF-β1/Smads Signaling Pathway
Objective:To investigate the protective effect of Rehmanniae Radix iridoid glycosides(RIG)on the kidney tissue of streptozotocin(STZ)-induced diabetic mice and explore the underlying mechanism.Methods:Twelve of 72 male C57BL/6J mice were randomly selected as the normal group,and the remaining 60 mice were fed with a high-fat diet for six weeks combined with injection of 60 mg·kg-1 STZ for 4 days to model type 2 diabetes mellitus.The successfully modeled mice were randomized into model,metformin(250 mg·kg-1),catalpol(100 mg·kg-1),low-dose RIG(RIG-L,200 mg·kg-1)and high-dose RIG(RIG-H,400 mg·kg-1)groups(n=11).Mice in each group were administrated with corresponding drugs,while those in the normal group and model group were administrated with the same dose of distilled water by gavage once a day.After 8 weeks of intervention,an oral glucose tolerance test(OGTT)was performed,and the area under the curve(AUC)was calculated.After mice were sacrificed,both kidneys were collected.The body weight,kidney weight,and fasting blood glucose(FBG)were measured.Biochemical assays were performed to measure the serum levels of triglycerides(TG),total cholesterol(TC),serum creatinine(SCr),and blood urea nitrogen(BUN).Enzyme-linked immunosorbent assay(ELISA)was employed to determine the serum level of fasting insulin(FINS),and the insulin sensitivity index(ISI)and homeostatic model assessment for insulin resistance(HOMA-IR)were calculated.The pathological changes in kidneys of mice were observed by hematoxylin-eosin staining and Masson staining.The immunohistochemical method(IHC)was employed to assess the expression of interleukin-1(IL-1),interleukin-6(IL-6),tumor necrosis factor-α(TNF-α),transforming growth factor-β1(TGF-β1),and collagen-3(ColⅢ)in the kidney tissue.The protein levels of TGF-β1,cell signal transduction molecule 3(Smad3),matrix metalloproteinase-9(MMP-9),and Col Ⅲ in kidneys of mice were determined by Western blot.Results:Compared with the normal group,the model group showcased decreased body weight and ISI(P＜0.01),increased kidney weight,FBG,AUC,FINS,HOMA-IR,TC,TG,SCr,and BUN(P＜0.01),glomerular hypertrophy,capsular space narrowing,and collagen deposition in the kidney,up-regulated protein levels of IL-1,IL-6,TNF-α,TGF-β1,Col Ⅲ,and Smad3(P＜0.01),and down-regulated protein level of MMP-9(P＜0.01)in the kidney tissue.Compared with the model group,the treatment groups had no significant difference in the body weight and decreased kidney weight(P＜0.05,P＜0.01).The FBG level declined in the RIG-H group after treatment for 4-8 weeks and in the metformin,catalpol,and RIG-L groups after treatment for 6-8 weeks(P＜0.01).The AUC in the RIG-L,RIG-H,and metformin groups decreased(P＜0.05,P＜0.01).The levels of TC,SCr,and BUN in the serum of mice in each treatment group became lowered(P＜0.05,P＜0.01).The level of TG declined in the RIG-L,RIG-H,and metformin groups(P＜0.05,P＜0.01).The serum level of FINS declined in the catalpol,RIG-L,and metformin groups(P＜0.01).Compared with the model group,the treatment groups showed decreased HOMA-IR(P＜0.01),increased ISI(P＜0.01),alleviated pathological changes in the kidney tissue,and down-regulated expression of IL-1 and TGF-β1.In addition,the protein levels of IL-6,TNF-α,and Col Ⅲ in the RIG-H and metformin groups and IL-6 and TNF-α in the RIG-L group were down-regulated(P＜0.05,P＜0.01),and the protein levels of IL-6,TNF-α,and Col Ⅲ in the catalpol group and Col Ⅲ in the RIG-L group showed a decreasing trend without statistical difference.The protein levels of TGF-β1,Smad3,and Col Ⅲ in the RIG-H and metformin groups were down-regulated(P＜0.01).Compared with that in the model group,the protein level of MMP-9 was up-regulated in each treatment group(P＜0.01).Conclusion:RIG can improve the renal structure and function of diabetic mice by regulating the TGF-β1/Smads signaling pathway.
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