Quercetin Ameliorates Diabetic Kidney Injury by Inhibiting Ferroptosis via Activating Nrf2/HO-1 Signaling Pathway.

Diabetic nephropathy (DN) is thought to be the major cause of end-stage renal disease. Due to its complicated pathogenesis and the low efficacy of DN treatment, a deep understanding of new etiological factors may be useful. Ferroptosis, a nonapoptotic form of cell death, is characterized by the accumulation of iron-dependent lipid peroxides to lethal levels. Ferroptosis-triggered renal tubular injury is reported to participate in the development of DN, and blocking ferroptosis might be an effective strategy to prevent the development of DN. Quercetin (QCT), a natural flavonoid that is present in a variety of fruits and vegetables, has been reported to ameliorate DN. However, its underlying nephroprotective mechanism is unclear. Herein, we explored the antiferroptosic effect of QCT and verified its nephroprotective effect using DN mice and high glucose (HG)-incubated renal tubular epithelial cell models. We found HG-induced abnormal activation of ferroptosis of renal tubular epithelial cells, and QCT treatment inhibited ferroptosis by downregulating the expression of transferrin receptor 1 (TFR-1) and upregulating the expression of glutathione peroxidase 4 (GPX4), ferritin heavy chain 1 (FTH-1), and the cystine/glutamate reverse antiporter solute carrier family 7 member (SLC7A11) in DN mice and HG-incubated HK-2 cells. Subsequently, both in vitro and in vivo results confirmed that QCT activated the NFE2-related factor 2 (Nrf2)/Heme oxygenase-1(HO-1) signaling pathway by increasing the levels of Nrf2 and HO-1. Therefore, this study supports that QCT inhibits the ferroptosis of renal tubular epithelial cells by regulating the Nrf2/HO-1 signaling pathway, providing a novel insight into the protective mechanism of QCT in DN treatment.

The Expression of Tristetraprolin and Its Relationship with Urinary Proteins in Patients with Diabetic Nephropathy.

OBJECTIVE: Tristetraprolin (TTP), also known as zinc finger protein 36, is an RNA binding protein that has a significant role in regulating the expression of mRNAs containing AU-rich elements. We postulated that TTP might regulate interleukin (IL)-6 and IL-18 expression in diabetes. This study aimed to test the hypothesis that the levels of TTP are correlated with nephropathy in patients with type 2 diabetes. METHODS: Eighty-seven patients (61.3±9.6 years old) who had been diagnosed with type 2 diabetes mellitus and 41 age and sex matched healthy control subjects were enrolled. The diabetes patients were classified into those without proteinuria, with microalbuminuria, and with clinical proteinuria groups according to the ratio of urinary excretion of albumin/creatinine (ACR). RESULTS: Serum and urinary levels of IL-6 and IL-18 were significantly elevated, but those of TTP were significantly decreased in patients with diabetes as compared with control subjects. In addition, serum and urinary levels of IL-6 and IL-18 were significantly higher, but those of TTP were significantly lower in patients with proteinuria than in patients without proteinuria or with microalbuminuria. There was a significant correlation between serum TTP and IL-6/IL-18 (correlation coefficients of -0.572 and -0.685, P < 0.05). CONCLUSION: These results show that diabetes with clinical proteinuria is accompanied by decreased urinary and serum level of TTP and increased levels of IL-6 and IL-18. Decreased TTP expression might occur prior to the increase in IL-6 and IL-18, and decrease of TTP might provide an earlier marker for glomerular dysfunction than IL-6 and IL-18.