Protective impact of resveratrol in experimental rat model of hyperoxaluria

Resveratrol inhibits calcium oxalate crystal growth, reduces adhesion to renal cells and induces crystal internalization into the cells, but promotes crystal aggregation

Resveratrol is a natural phenolic compound that belongs to stilbenoid group found in diverse plants. Health benefits and therapeutic potentials of resveratrol have been widely recognized in various diseases. In kidney stone disease, it can alleviate oxalate-induced hyperproduction of free radicals in renal epithelial cells. Nevertheless, its direct effects on calcium oxalate (CaOx) crystal, which is the major stone component, remained unclear. This study therefore addressed the direct effects of resveratrol (at 1, 10 or 100 μM) on each step of CaOx kidney stone formation. The results revealed that resveratrol had no significant effects on CaOx crystallization. However, resveratrol significantly decreased CaOx crystal growth and adhesion to renal epithelial cells at all concentrations, and induced crystal internalization into the cells (a process related to crystal degradation by endolysosomes) in a concentration-dependent manner. On the other hand, resveratrol promoted crystal aggregation. These data indicate that resveratrol serves as a dual modulator on CaOx stone formation. While it inhibits CaOx stone development by reducing crystal growth and adhesion to renal cells and by inducing crystal internalization into the cells, resveratrol promotes crystal aggregation, which is one of the mechanisms leading to kidney stone formation.

Polydatin protects against calcium oxalate crystal-induced renal injury through the cytoplasmic/mitochondrial reactive oxygen species-NLRP3 inflammasome pathway

BACKGROUND

Oxidative stress and inflammatory responses are critical factors in calcium oxalate (CaOx) crystal-induced renal injury. Reactive oxygen species (ROS) are usually produced in the cytoplasm and mitochondria and trigger the priming and activation of the NLRP3 inflammasome, thereby regulating cytokines and inflammation. Polydatin is a plant rhizome extract with anti-inflammatory, antioxidant, and antitumor effects. However, it remains not clear whether and how these pathophysiological processes exists in CaOx crystal-induced renal inflammatory injury.

METHODS

Here, we measured the expression of the NLRP3 inflammasome, IL-18, IL-1β, intracellular and mitochondrial ROS (mtROS) levels and relevant morphological changes in treated renal tubular epithelial cells (TECs) and stone-forming rats. The study further explored the action of intracellular ROS and mtROS on these inflammatory damage, and the beneficial effects and pathway of polydatin.

RESULTS

We verified that CaOx crystal-induced cytoplasmic ROS and mtROS upregulation promoted the priming and activation of the NLRP3 inflammasome, thereby stimulating IL-18/1β maturation and activation. Polydatin can relieve oxidative stress and inflammatory damage by decreasing ROS. We further demonstrated that mtROS is the main target for polydatin to exert the NLRP3 inflammasome-regulating function. The inhibition of mtROS can effectively relieve the inflammatory damage to TECs and kidney caused by CaOx crystal.

CONCLUSION

These findings provide new insight into the relationship between mitochondrial damage and inflammation in nephrolithiasis and show that polydatin-mediated anti-inflammatory and antioxidative protection is a therapeutic strategy for, but not limited to, crystalline nephropathy.

The Protective Role of Dietary Polyphenols in Urolithiasis: Insights into Antioxidant Effects and Mechanisms of Action

Urolithiasis is a common urological disease with increasing prevalence and high recurrence rates around the world. Numerous studies have indicated reactive oxygen species (ROS) and oxidative stress (OS) were crucial pathogenic factors in stone formation. Dietary polyphenols are a large group of natural antioxidant compounds widely distributed in plant-based foods and beverages. Their diverse health benefits have attracted growing scientific attention in recent decades. Many literatures have reported the effectiveness of dietary polyphenols against stone formation. The antiurolithiatic mechanisms of polyphenols have been explained by their antioxidant potential to scavenge free radicals and ROS, modulate the expression and the activity of endogenous antioxidant and prooxidant enzymes, regulate signaling pathways associated with OS, and maintain cell morphology and function. In this review, we first describe OS and its pathogenic effects in urolithiasis and summarize the classification and sources of dietary polyphenols. Then, we focus on the current evidence defining their antioxidant potential against stone formation and put forward challenges and future perspectives of dietary polyphenols. To conclude, dietary polyphenols offer potential applications in the treatment and prevention of urolithiasis.

Litholytic Activities of Natural Bioactive Compounds and Their Mechanism Insights

Urolithiasis is a disease characterized by the formation of stones, which are crystalline accretions that form in the urinary tract from minerals dissolved in the urine. Moreover, it is considered to be a complex and multifactorial disease, requiring treatment. Unfortunately, current treatments are insufficient or may induce several side effects. In fact, medicinal plants are among the anti-litholytic treatments that are strongly recommended by many studies. Indeed, these natural resources contain bioactive molecules of different natures, such as flavonoids, terpenoids, alkaloids, and phenolic acids, which have recently demonstrated very important anti-litholytic effects. The molecular mechanisms involved are multiple and variable, and can reach cellular and molecular levels. In this review, we have discussed in depth the work that has studied the bioactive molecules of medicinal plants and their major potential against urolithiasis. Scientific databases, including Web of Science, PubMed, and Google Scholar, were searched from their inception until April 2021.The cellular and molecular mechanisms are presented and discussed. Some mechanisms of action related to these bioactive compounds are highlighted. This review could provide a scientific starting point for further studies on urolithiasis and natural bioactive compounds, especially flavonoids.

Resveratrol Attenuates Oxalate-Induced Renal Oxidative Injury and Calcium Oxalate Crystal Deposition by Regulating TFEB-Induced Autophagy Pathway

The oxidative injury of renal tubular epithelial cells caused by inflammation and oxidative stress induced by hyperoxaluria is an important factor in the kidney calcium oxalate (CaOx) stone formation. Resveratrol (RSV) has been reported to reduce oxidative injury to renal tubular epithelial cells, and autophagy is critical for the protective effect of resveratrol. However, the protective mechanism of RSV in oxalate-induced oxidative injury of renal tubular cells and the role of autophagy in this process are still unclear. In our study, glyoxylic acid monohydrate-induced rats were treated with or without resveratrol, and it was detected that the overexpression of oxidant species, CaOx crystal deposition, apoptosis level, inflammatory cytokines and osteoblastic-associated protein expression were reversed by resveratrol. Additionally, Resveratrol pretreatment significantly reversed oxalate -induced decline in cell viability, cell damage, oxidant species overexpression, and osteogenic transformation in normal rat kidney epithelial-like (NRK-52E) cells. Furthermore, we found that RSV pretreatment promoted intracellular LC3II upregulation, p62 downregulation, and autophagosome formation, whereas 3-methyladenine treatment reduced this effect. Moreover, RSV induced the expression of transcription factor EB (TFEB) in the nucleus of NRK-52E cells in a concentration-dependent manner. After transfection of NRK-52E cells with TFEB siRNA, we showed that the RSV-induced increase in TFEB expression and autophagosome formation were inhibited. Simultaneously, RSV-induced NRK-52E cells protection was partially reversed. These results suggested that RSV regulates oxalate-induced renal inflammation, oxidative injury, and CaOx crystal deposition in vitro and in vivo through the activation of a TFEB-induced autophagy.

Oxidative stress and endoplasmic stress in calcium oxalate stone disease: the chicken or the egg?

Crystal modulators play a significant role in the formation of calcium oxalate stone disease. When renal cells are subjected to oxalate stress, the loss in cell integrity leads to exposure of multiple proteins that assist and/or inhibit crystal attachment and retention. Contact between oxalate and calcium oxalate with urothelium proves fatal to cells as a result of reactive oxygen species generation and onset of oxidative stress. Hence, as a therapeutic strategy it was hypothesised that supplementation of antioxidants would suffice. On the contrary to popular belief, the detection of oxalate induced endoplasmic reticulum mediated apoptosis proved the ineffectiveness of antioxidant therapy alone. Thus, the inadequacy of antioxidant supplementation in oxalate stress invoked the presence of an alternative pathway for the induction of kidney fibrosis in hyperoxaluric rats. In addition to settling this query, the link between oxidative stress and ER stress is not well understood, especially in urolithiasis.

Protective effect of pentoxifylline on oxidative renal cell injury associated with renal crystal formation in a hyperoxaluric rat model

The aim of the study is to investigate the effects of pentoxifylline (PTX) on the renal tubular cell injury and stone formation in a hyperoxaluric rat model induced by ethylene glycol and its possible underlying mechanisms. The study was performed with 30 male Wistar rats and randomized into three groups of teen. The sham-control (group 1) received only drinking water orally. The EG/untreated (group 2) received drinking water containing 0.75% EG for 4 weeks orally. The EG/PTX treated (group 3) received drinking water containing 0.75% EG for 4 weeks orally and PTX. Urine and blood were collected to determine some parameters. The kidneys were also removed for histological examination. Serum and urinary parameters were significantly improved in the EG/PTX treated. In the EG/PTX-treated group, the MDA, TOS and MPO activity reduced and the TAS, SOD, CAT and GSH-Px activities were increased markedly compared with the group 2. In urine of the group 2 rats, a large number of CaOx crystals were displayed and most tubules that contained crystals were dilated and showed degeneration, necrosis, and desquamation of the lining epithelium. Only few CaOx crystals were r in EG/PTX-treated animal's urine. Mild tissue damage was observed in PTX-treated rats. iNOS expression was significantly elevated in the group 2. In contrast, in the EG/PTX-treated group, eNOS expression in renal tubular epithelial cells was increased. Current study indicates that PTX may partially reduce renal tubular injury resulting from hyperoxaluria-induced oxidative and nitrosative stress.

Aldosterone is involved in the pathogenesis of obesity-related glomerulopathy through activation of Wnt/β-catenin signaling in podocytes

Obesity-related glomerulopathy (ORG) is morphologically characterized by glomerulomegaly with or without observable focal segmental glomerulosclerosis under light microscope, with decreased podocyte density and number, and with increased foot‑process width observed under electron microscope. The severity of podocyte injury is correlated with the degree of proteinuria and renal dysfunction. However, the pathogenesis of ORG is not well understood. The aim of the present study was to explore the possible pathogenic role of aldosterone (ALDO) in ORG. In the in vivo animal experiments, body weight, Lee's obesity index, abdominal fat index, urinary protein excretion, average glomerular diameter were significantly increased, the mRNA and protein expression of podocyte‑associated molecules including nephrin, podocin, podoplanin and podocalyxin were significantly reduced, and the Wnt/β‑catenin signaling pathway was activated in ORG model mice compared with the Control mice, whereas the administration of spironolactone significantly ameliorated these effects. In the in vitro experiments on cultured podocytes, the mRNA and protein expression levels of the aforementioned podocyte‑associated molecules were significantly downregulated and the Wnt/β‑catenin signaling pathway was activated following ALDO stimulation, whereas eplerenone significantly attenuated all the above effects. Dickkopf‑related protein 1 (DKK1), an inhibitor of Wnt/β‑catenin signaling pathway, also reduced the effects of ALDO exposure on the expression of podocyte‑associated molecules. The present study hypothesized that ALDO may be involved in the pathogenesis of ORG through the activation of Wnt/β‑catenin signaling pathway in podocytes.