Abstract: Objective  To investigate the protective effects of curcumin on rat with diabetic nephropathy(DN) as well as the functional mechanism. 
Methods  The SD rats were randomly divided into control group(N group), DN model group(DN group) and curcumin treatment group(CT group). At 4 weeks after treatment, pathological changes of renal tissues were detected and changes of nephrin protein were detected. The expression of miR-146a, pro-inflammatory factors and fibrogenic factors was detected by real-time quantitative polymerase chain reaction(RT-qPCR). HBZY-1 cells under different culture conditions were collected and the mRNA expression of miR-146a was detected. Using transfection technique, miR-146a minics was transfected into HBZY-1 cells under high-glucose culture conditions. The mRNA expression of miR-146a, Traf6, pro-inflammatory factors and fibrogenic factors as well as the change of nuclear factor kappa-B(NF-kappa B) p65 protein were detected. 
Results  Compared with the control group, blood glucose(BG), blood urea nitrogen(BUN), serum creatinine(SCr) and urine albumin creatine ratio(UACR) were significantly increased in the DN group. After curcumin intervention treatment, the content of BG, BUN, SCr and UACR were decreased, and the difference was statistically significant. Pathological sections of kidney and Western blot results showed that compared with the control group, there was the kidney tissue damage in the DN group, which, however, was alleviated in the CT group. RT-qPCR results showed that compared with the control group, the expression of miR-146a was reduced and the expressions of tumor necrosis factor-α(TNF-α), interleukin-1β(IL-1β), transforming growth factor-β(TGF-β) and collagenⅠwere increased in the DN group. Compared with the DN group, the expression of miR-146a was increased, while the expression of cytokine was decreased in the CT group, suggesting significant difference. After stimulating HBZY-1 cells with curcumin at concentrations of 0, 5 μmol/L, 15 μmol/L and 25 μmol/L for 24 h, the mRNA expression of miRNA-146a was gradually increased. Cells were cultured with culture medium containing 4.5 mmol/L(L-HC group) , 15 mmol/L(M-HC group) and 25 mmol/L(H-HC group) glucose, respectively, and the expression of miRNA-146a was gradually decreased. When miR-146a minics and negative control(NC) were transfected into HBZY-1 cells under high-glucose culture conditions, the mRNA expression of miR-146a in H-HC miR-146a group was significantly higher than that in H-HC miR-NC group, but there was no difference between the HC group and the H-HC miR-NC group. Compared with the H-HC miR-NC group, the target genes Traf6 and proinflammatory factors(TNF-α and IL-1β) and fibrosis factors(TGF-β and collagen Ⅰ) were reduced in the H-HC miR-146a group, and the difference was statistically significant. The expression level of p65 protein in H-HC miR-146a group was significantly lower than that in H-HC miR-NC group and H-HC group. 
Conclusion  Curcumin alleviates kidney damage in rats with DN by promoting the expression of miR-146a and inhibiting the NF-κB signaling pathway.

Key words: curcumin, diabetic nephropathy, nuclear factor κB