Ginsenoside Rb1 alleviates diabetic kidney podocyte injury by inhibiting aldose reductase activity.

Panax notoginseng, a traditional Chinese medicine, exerts beneficial effect on diabetic kidney disease (DKD), but its mechanism is not well clarified. In this study we investigated the effects of ginsenoside Rb1 (Rb1), the main active ingredients of Panax notoginseng, in alleviating podocyte injury in diabetic nephropathy and the underlying mechanisms. In cultured mouse podocyte cells, Rb1 (10 µM) significantly inhibited high glucose-induced cell apoptosis and mitochondrial injury. Furthermore, Rb1 treatment reversed high glucose-induced increases in Cyto c, Caspase 9 and mitochondrial regulatory protein NOX4, but did not affect the upregulated expression of aldose reductase (AR). Molecular docking analysis revealed that Rb1 could combine with AR and inhibited its activity. We compared the effects of Rb1 with eparestat, a known aldose reductase inhibitor, in high glucose-treated podocytes, and found that both alleviated high glucose-induced cell apoptosis and mitochondrial damage, and Rb1 was more effective in inhibiting apoptosis. In AR-overexpressing podocytes, Rb1 (10 µM) inhibited AR-mediated ROS overproduction and protected against high glucose-induced mitochondrial injury. In streptozotocin-induced DKD mice, administration of Rb1 (40 mg·kg-1·d-1, ig, for 7 weeks) significantly mitigated diabetic-induced glomerular injuries, such as glomerular hypertrophy and mesangial matrix expansion, and reduced the expression of apoptotic proteins. Collectively, Rb1 combines with AR to alleviate high glucose-induced podocyte apoptosis and mitochondrial damage, and effectively mitigates the progression of diabetic kidney disease.

Triptolide ameliorates fine particulate matter-induced podocytes injury via regulating NF-κB signaling pathway.

BACKGROUND: PM2.5 is associated closely with an increased risk of membranous nephropathy (MN), however, whether PM2.5 could induce podocytes injury, the underlying pathology for MN, has not be thoroughly studied. Triptolide, an active component in Tripterygium wilfordii Hook F, is frequently used to treat MN in China, but its effects on PM2.5-induced podocytes injury is still largely unknown. Therefore, we evaluated the effects of PM2.5 on podocytes, and explored whether triptolide could improve PM2.5-induced podocytes injury and the possible underlying mechanisms. RESULTS: Podocytes were incubated with PM2.5 after being pre-treated with triptolide, viability, apoptosis rate and migratory capacity of podocytes were determined by CCK-8 assay, flow cytometry and Transwell assay, respectively. Additionally, the levels of lactate dehydrogenase (LDH), malondialdehyde (MDA), and superoxide dismutase (SOD) in podocytes, the cytoskeleton of podocytes, the protein expressions of nephrin, podocin, Bcl-2, Bax, nuclear factor kappa-B/p65 (NF-κB/p65) and phospho-inhibitor of NF-κB (p-IκBα) were measured. Our data showed that PM2.5 treatment significantly increased the disorganization of F-actin stress fibers, the damaged structural integrity of nucleus, the deranged and dissociated cytoskeleton in podocytes, increased the podocytes apoptosis rate, the levels of MDA and LDH, markedly up-regulated the protein expression of Bax, NF-κB/p65 and p-IκBα, down-regulated the protein expression of nephrin, podocin and Bcl-2, and significantly decreased the level of SOD, the migration rate and the viability of podocytes, compared with those of the untreated podocytes. These effects of PM2.5 on podocytes, however, were reversed by triptolide administration. CONCLUSION: These results suggest that triptolide could prevent against PM2.5-induced podocytes injury via suppressing NF-κB signaling pathway.

Effects of BSF on Podocyte Apoptosis via Regulating the ROS-Mediated PI3K/AKT Pathway in DN.

Diabetic nephropathy (DN) is the leading cause of end-stage renal disease (ESRD). The ROS-mediated PI3K/AKT pathway plays a key role in podocyte apoptosis and DN progression. Our previous study demonstrated that Baoshenfang (BSF) can decrease proteinuria and attenuate podocyte injury. However, the effects of BSF on podocyte apoptosis induced by the ROS-mediated PI3K/AKT pathway remain unclear. Herein, in vivo and in vitro studies have been performed. In our in vivo study, BSF significantly decreased 24-h urinary protein, serum creatinine, and blood urea nitrogen levels in DN mice. Meanwhile, BSF significantly inhibited oxidative stress and podocyte apoptosis in our in vivo and in vitro studies. Moreover, BSF significantly decreased the inhibition of the PI3K/AKT pathway induced by HG in DN. More importantly, the effects of BSF on podocyte apoptosis were reversed by PI3K siRNA transfection. In conclusion, BSF can decrease proteinuria and podocyte apoptosis in DN, in part through regulating the ROS-mediated PI3K/AKT pathway.

Puerarin attenuates diabetic kidney injury through the suppression of NOX4 expression in podocytes.

Radix puerariae, a traditional Chinese herbal medication, has been used to treat patients with diabetic nephropathy (DN). Several studies demonstrated that puerarin, the active compound of radix puerariae, reduces diabetic injury in streptozotocin (STZ)-induced diabetic rodent models. However, as STZ injection alone results in mild kidney injury, the therapeutic benefit afforded by puerarin in DN remained inconclusive. Thus we sought to clarify the role of puerarin by employing an accelerated DN model, STZ-induced diabetes in the endothelial nitric oxide synthase-null (eNOS-/-) mice. Puerarin treatment of diabetic eNOS-/- mice significantly attenuated albuminuria and diabetic kidney injury, which were associated with reduced oxidative stress and reduced NAPDH oxidase 4 (NOX4) in glomeruli of diabetic eNOS-/- mice. Puerarin treatment of murine podocytes culture in high glucose conditions led to reduced superoxide production and NOX4 expression. We further determined that that puerarin treatment increased both mRNA and protein levels of SIRT1 in podocytes and that puerarin led to SIRT1-mediated deacetylation of NF-κB and suppression of NOX4 expression. Our findings confirm the renoprotective effects of puerarin in an experimental model of advanced DN and provide a molecular mechanism by which puerarin exerts the anti-oxidative effects in podocytes  in the diabetic milieu.

Role of soluble and membrane-bound dipeptidyl peptidase-4 in diabetic nephropathy.

Diabetic nephropathy is one of the most frequent, devastating and costly complications of diabetes. The available therapeutic approaches are limited. Dipeptidyl peptidase type 4 (DPP-4) inhibitors represent a new class of glucose-lowering drugs that might also have reno-protective properties. DPP-4 exists in two forms: a plasma membrane-bound form and a soluble form, and can exert many biological actions mainly through its peptidase activity and interaction with extracellular matrix components. The kidneys have the highest DPP-4 expression level in mammalians. DPP-4 expression and urinary activity are up-regulated in diabetic nephropathy, highlighting its role as a potential target to manage diabetic nephropathy. Preclinical animal studies and some clinical data suggest that DPP-4 inhibitors decrease the progression of diabetic nephropathy in a blood pressure- and glucose-independent manner. Many studies reported that these reno-protective effects could be due to increased half-life of DPP-4 substrates such as glucagon-like peptide-1 (GLP-1) and stromal derived factor-1 alpha (SDF-1a). However, the underlying mechanisms are far from being completely understood and clearly need further investigations.

Heparanase: another renal player controlled by vitamin D.

Vitamin D deficiency is inevitable in chronic kidney diseases. Clinical and experimental therapies with vitamin D supplements or analogues have demonstrated nephroprotective effects, which vitamin D exerts partly by controlling the renin-angiotensin-aldosterone system, but also by modulating other signalling pathways. In recent work published in the Journal of Pathology, Garsen and colleagues identified heparanase as a novel target of vitamin D and its antiproteinuric activity. Heparanase is an endoglycosidase with a role in remodelling the extracellular matrix through its ability to degrade heparan sulphate, and is involved in the pathogenesis of several proteinuric and fibrotic renal diseases. The new evidence that vitamin D inhibits heparanase expression sets the stage for a better understanding of the vitamin's kidney-protecting effects and its possible application to proteinuric and non-proteinuric chronic kidney diseases.

Vitamin D attenuates proteinuria by inhibition of heparanase expression in the podocyte.

The glomerular filtration barrier consists of podocytes, the glomerular basement membrane, and endothelial cells covered with a glycocalyx. Heparan sulphate (HS) in the glomerular filtration barrier is reduced in patients with proteinuria, which is associated with increased expression of the HS-degrading enzyme heparanase. Previously, we showed that heparanase is essential for the development of proteinuria in experimental diabetic nephropathy. Vitamin D supplementation reduces podocyte loss and proteinuria in vitro and in vivo. Therefore, we hypothesize that vitamin D reduces proteinuria by reducing glomerular heparanase. Adriamycin-exposed rats developed proteinuria and showed increased heparanase expression, which was reduced by 1,25-dihydroxyvitamin D3 (1,25-D3) treatment. In vitro, adriamycin increased heparanase mRNA in the podocyte, which could be corrected by 1,25-D3 treatment. In addition, 1,25-D3 treatment reduced transendothelial albumin passage after adriamycin stimulation. In line with these results, we showed direct binding of the vitamin D receptor to the heparanase promoter, and 1,25-D3 dose-dependently reduced heparanase promoter activity. Finally, 1,25-D3-deficient 25-hydroxy-1α-hydroxylase knockout mice developed proteinuria and showed increased heparanase, which was normalized by 1,25-D3 treatment. Our data suggest that the protective effect of vitamin D on the development of proteinuria is mediated by inhibiting heparanase expression in the podocyte.

Impact of high glucose and transforming growth factor-ß on bioenergetic profiles in podocytes.

Diabetic nephropathy is the most common cause of chronic renal failure in industrialized countries. Depletion of podocytes plays an important role in the progression of diabetic glomerulopathy. Various factors in the diabetic milieu lead to serious podocyte stress driving the cells toward cell cycle arrest (p27(Kip1)), hypertrophy, detachment, and apoptosis. Mitochondria are responsible for oxidative phosphorylation and energy supply in podocytes. Recent studies indicated that mitochondrial dysfunction is a key factor in diabetic nephropathy. In the present study, we investigated metabolic profiles of podocytes under diabetic conditions. We examined oxygen consumption rates (OCRs) and oxidative phosphorylation complex activities in murine podocytes. Cells were exposed to high glucose for 48 hours, cultured for 10 passages under high-glucose conditions (30 mmol/L), or incubated with transforming growth factor-ß (5 ng/mL) for 24 hours. After prolonged exposure to high glucose, podocytes showed a significantly increased OCR at baseline and also a higher OCR after addition of oligomycin, indicating significant changes in mitochondrial energy metabolism. Higher OCRs after inhibition of respiration by rotenone also indicated changes in nonmitochondrial respiration. Podocytes stimulated with a proapoptotic concentration of transforming growth factor-ß displayed similar bioenergetic profiles, even with decreased citrate synthase activity. In all tested conditions, we found a higher cellular nicotinamide adenine dinucleotide content and changes in activities of respiratory chain complexes. In summary, we provide for the first time evidence that key factors of the diabetic milieu induce changes in glucose metabolism and mitochondrial function in podocytes.

Astragaloside IV attenuates complement membranous attack complex induced podocyte injury through the MAPK pathway.

Membranous nephropathy (MN) is the most common cause of idiopathic nephrotic syndrome in adults and the cause is known to be due to the injury of podocytes located in the glomeruli. Astragalus membranaceus has been used for the treatment of patients with MN in China for a long time. The beneficial effect of Astragalus membranaceus on proteinuria of patients with MN has been well documented. However, the mechanism of astragalus membranaceu in alleviation of MN is still not completely understood. Therefore, in the current study, we employed a podocyte injury model induced by complement membranous attack complex to examine the mechanism of astragalus membraneceus in the treatment of MN. We found that complement membranous attack complex could increase lactate dehydrogenase (LDH) release from podocytes and astragaloside IV (AS-IV) could prevent LDH release from podocytes in a time- and dose-dependent pattern. Moreover, AS-IV restored podocyte morphology and cytoskeleton loss induced by complement membranous attack complex. Furthermore, AS-IV was able to reduce phosphorylation of JNK and ERK1/2 induced by complement membranous attack complex. In conclusion, the mechanism of Astragalus membranaceus in the treatment of MN may be related to its attenuation of podocyte injury through regulation of cytoskeleton and mitogen activated protein kinase.