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Diabetic nephropathy is one of the most common microvascular complications of diabetes and the leading cause of end-stage renal disease. In the present study, we investigated the renoprotective effect of the aqueous extract of Portulaca oleracea (AP) on diabetic nephropathy accelerated by renal fibrosis and inflammation in type 2 diabetic db/db mice. The mice were treated with AP (300 mg/kg/day, p.o.) for ten weeks to examine the long-term effects on diabetic nephropathy and renal dysfunction. We found that AP treatment markedly lowered blood glucose to 412 ± 11.4 mg/dl and plasma creatinine level to 2.3 ± 0.8 mg/dl compared to db/db mice (p < 0.05, p < 0.01, respectively). This study also showed that treatment with AP significantly decreased water intake and urine volume in diabetic db/db mice (p < 0.05). In immunohistological study, the renal expression of transforming growth factor-β1 (TGF-β1), advanced glycation end products (AGE), and intercellular adhesion molecule (ICAM)-1 markedly increased in the renal cortex of untreated db/db mice (p < 0.01). In contrast, AP treatment significantly reduced these expressions to 50 ± 2.1%, 48 ± 2.8%, 61 ± 1.1%, respectively (p < 0.01). Furthermore, NF-κB p65 activation in renal tissues markedly increased in untreated db/db mice, which was significantly suppressed by AP treatment. Taken together, these findings suggest that AP attenuates diabetic nephropathy through inhibition of renal fibrosis and inflammation in db/db mice.

Renal fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) proteins such as type I collagen, fibronectin, and by the increased expression of PAI-1. This study evaluated the anti-fibrotic effect of bee venom and its major compounds (melittin and apamin) on TGF-β-induced pro-fibrotic gene expression. Bee venom and melittin significantly suppressed type I collagen, fibronectin, and PAI-1 protein expression in the TGF-β-treated kidney fibroblast. However, apamin only inhibited the expression of fibronectin and type I collagen. These results indicated that the inhibitory effects of bee venom on TGF-β-induced pro-fibrotic gene expression are caused by melittin. Moreover, we attempted to elucidate mechanisms underlying the anti-fibrotic effect of melittin. Melittin dramatically inhibited the phosphorylation of TGFβRII and Smad2/3. Also, melittin inhibited the phosphorylation of ERK1/2 and JNK, but not the phosphorylation of PI3K, Akt, and p38. These results suggested that melittin inhibits TGF-β-induced pro-fibrotic genes expression through the suppression of TGFβR-Smad2/3, ERK1/2, and JNK phosphorylation, and melittin can be used as a clinical drug for the treatment of fibrosis associated with renal diseases.

Glomerular mesangial cells (GMCs) activation is implicated in the pathogenesis of diabetic nephropathy (DN). Our previous study revealed that high glucose (HG)-treated glomerular endothelial cells (GECs) produce an increased number of TGF-$\beta$1-containing exosomes to activate GMCs through the TGF-$\beta$1/Smad3 signaling pathway. We also identified that Tongxinluo (TXL), a traditional Chinese medicine, has beneficial effects on the treatment of DN in DN patients and type 2 diabetic mice. However, it remained elusive whether TXL could ameliorate renal structure and function through suppression of intercellular transfer of TGF-$\beta$1-containing exosomes from GECs to GMCs. In this study, we demonstrate that TXL can inhibit the secretion of TGF-$\beta$1-containing exosomes from HG-treated GECs. Furthermore, exosomes produced by HG induced-GECs treated with TXL cannot trigger GMC activation, proliferation and extracellular matrix (ECM) overproduction both in vitro and in vivo. These results suggest that TXL can prevent the transfer of TGF-$\beta$1 from GECs to GMCs via exosomes, which may be one of the mechanisms of TXL in the treatment of DN.

Rehmannia glutinosa is widely recognized as a prominent medicinal herb employed by practitioners across various generations for the purpose of fortifying kidney yin. Within Rehmannia glutinosa, the compound known as catalpol (CAT) holds significant importance as a bioactive constituent. However, the protective effects of CAT on kidneys, including ameliorative effects on chronic kidney disease — most prominently renal anemia and renal fibrosis — have not been clearly defined. In this study, the kidney injury model of NRK-52E cells and C57BL/6N male mice was prepared by exposure to aristolochic acid I (AA-I), and it was discovered that CAT could ameliorate oxidative stress injury, inflammatory injury, apoptosis, renal anemia, renal fibrosis, and other renal injuries both in vivo and in vitro. Further treatment of NRK-52E cells with Nrf2 inhibitors (ML385) and activators (ML334), as well as NF-κB inhibitors (PDTC), validated CAT’s ability to target Nrf2 activation. Furthermore, the expression of phosphorylated NF-κB p65, IL-6, and Cleaved-Caspase3 protein was inhibited. CAT also inhibited NF-κB, and then inhibited the expression of IL-6, p-STAS3, TGF-β1 protein. Therefore, CAT can regulate Nrf2/NF-κB signaling pathway, significantly correct renal anemia and renal fibrosis, and is conducive to the preservation of renal structure and function, thus achieving a protective effect on the kidneys.

Diabetic kidney disease (DKD) has become the primary cause of end-stage renal disease (ESRD), causing an urgent need for preventive strategies for DKD. Astragaloside I (ASI), a bioactive saponin extracted from Astragalus membranaceus (Fisch.) Bunge has been demonstrated to possess a variety of biological activities. This study investigates the therapeutic potential of ASI in DKD and the underlying molecular mechanism using db/db mice in vivo and high glucose (HG)-induced SV40-MES-13 cells in vitro. The results indicated that ASI significantly ameliorated renal dysfunction and mitigated the pathological alterations in the renal tissues of db/db mice. Moreover, ASI was found to reduce the levels of renal fibrosis makers and suppress the activation of TGF-β1/Smad2/3 pathway in both db/db mice and HG-induced SV40-MES-13 cells. Furthermore, ASI downregulated HDAC3 expression, upregulated Klotho expression, and enhanced Klotho release. ASI is directly bound to HDAC3, and the beneficial effects of ASI on Klotho/TGF-β1/Smad2/3-mediciated renal fibrosis in DKD were reversed by the HDAC3 agonist ITSA-1. In conclusion, ASI attenuates renal fibrosis in DKD, and may act through concurrently inhibiting HDAC3 and TGF-β1, thereby regulating HDAC3-mediciated Klotho/TGF-β1/Smad2/3 pathway.