Mechanism of calcium oxalate renal stone formation and renal tubular cell injury

Identification and validation of the biomarkers related to ferroptosis in calcium oxalate nephrolithiasis

Ferroptosis is a specific type of programmed cell death characterized by iron-dependent lipid peroxidation. Understanding the involvement of ferroptosis in calcium oxalate (CaOx) stone formation may reveal potential targets for this condition. The publicly available dataset GSE73680 was used to identify 61 differentially expressed ferroptosis-related genes (DEFERGs) between normal kidney tissues and Randall's plaques (RPs) from patients with nephrolithiasis through employing weighted gene co-expression network analysis (WGCNA). The findings were validated through in vitro and in vivo experiments using CaOx nephrolithiasis rat models induced by 1% ethylene glycol administration and HK-2 cell models treated with 1 mM oxalate. Through WGCNA and the machine learning algorithm, we identified LAMP2 and MDM4 as the hub DEFERGs. Subsequently, nephrolithiasis samples were classified into cluster 1 and cluster 2 based on the expression of the hub DEFERGs. Validation experiments demonstrated decreased expression of LAMP2 and MDM4 in CaOx nephrolithiasis animal models and cells. Treatment with ferrostatin-1 (Fer-1), a ferroptosis inhibitor, partially reversed oxidative stress and lipid peroxidation in CaOx nephrolithiasis models. Moreover, Fer-1 also reversed the expression changes of LAMP2 and MDM4 in CaOx nephrolithiasis models. Our findings suggest that ferroptosis may be involved in the formation of CaOx kidney stones through the regulation of LAMP2 and MDM4.

Pathophysiology and Main Molecular Mechanisms of Urinary Stone Formation and Recurrence

Kidney stone disease (KSD) is one of the most common urological diseases. The incidence of kidney stones has increased dramatically in the last few decades. Kidney stones are mineral deposits in the calyces or the pelvis, free or attached to the renal papillae. They contain crystals and organic components, and they are made when urine is supersaturated with minerals. Calcium-containing stones are the most common, with calcium oxalate as the main component of most stones. However, many of these form on a calcium phosphate matrix called Randall's plaque, which is found on the surface of the kidney papilla. The etiology is multifactorial, and the recurrence rate is as high as 50% within 5 years after the first stone onset. There is a great need for recurrence prevention that requires a better understanding of the mechanisms involved in stone formation to facilitate the development of more effective drugs. This review aims to understand the pathophysiology and the main molecular mechanisms known to date to prevent recurrences, which requires behavioral and nutritional interventions, as well as pharmacological treatments that are specific to the type of stone.

Different Degrees of Sulfated Laminaria Polysaccharides Recovered Damaged HK-2 Cells and Inhibited Adhesion of Nano-COM and Nano-COD Crystals

Purpose

The crystal adhesion caused by the damage of renal tubular epithelial cells (HK-2) is the key to the formation of kidney stones. However, no effective preventive drug has been found. This study aims to explore the recovery effects of four Laminaria polysaccharides (SLPs) with different sulfate (-OSO3-) contents on damaged HK-2 cells and the difference in the adhesion of damaged cells to nanometer calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) before and after recovery.

Methods

Sodium oxalate (2.6 mmol/L) was used to damage HK-2 cells to establish a damaged model. SLPs (LP0, SLP1, SLP2, and SLP3) with -OSO3- contents of 0.73%, 15.1%, 22.8%, and 31.3%, respectively, were used to restore the damaged cells, and the effects of SLPs on the adhesion of COM and COD, with a size of about 100 nm before and after recovery, were measured.

Results

The following results were observed after SLPs recovered the damaged HK-2 cells: increased cell viability, restored cell morphology, decreased reactive oxygen levels, increased mitochondrial membrane potential, decreased phosphatidylserine eversion ratio, increased cell migration ability, reduced expression of annexin A1, transmembrane protein, and heat shock protein 90 on the cell surface, and reduced adhesion amount of cells to COM and COD. Under the same conditions, the adhesion ability of cells to COD crystals was weaker than that to COM crystals.

Conclusions

As the sulfate content in SLPs increases, the ability of SLPs to recover damaged HK-2 cells and inhibit crystal adhesion increases. SLP3 with high -OSO3- content may be a potential drug to prevent kidney stones.

The SOX4/EZH2/SLC7A11 signaling axis mediates ferroptosis in calcium oxalate crystal deposition-induced kidney injury

Epigenetic regulation is reported to play a significant role in the pathogenesis of various kidney diseases, including renal cell carcinoma, acute kidney injury, renal fibrosis, diabetic nephropathy, and lupus nephritis. However, the role of epigenetic regulation in calcium oxalate (CaOx) crystal deposition-induced kidney injury remains unclear. Our study demonstrated that the upregulation of enhancer of zeste homolog 2 (EZH2)-mediated ferroptosis facilitates CaOx-induced kidney injury. CaOx crystal deposition promoted ferroptosis in vivo and in vitro. Usage of liproxstatin-1 (Lip-1), a ferroptosis inhibitor, mitigated CaOx-induced kidney damage. Single-nucleus RNA-sequencing, RNA-sequencing, immunohistochemical and western blotting analyses revealed that EZH2 was upregulated in kidney stone patients, kidney stone mice, and oxalate-stimulated HK-2 cells. Experiments involving in vivo EZH2 knockout, in vitro EZH2 knockdown, and in vivo GSK-126 (an EZH2 inhibitor) treatment confirmed the protective effects of EZH2 inhibition on kidney injury and ferroptosis. Mechanistically, the results of RNA-sequencing and chromatin immunoprecipitation assays demonstrated that EZH2 regulates ferroptosis by suppressing solute carrier family 7, member 11 (SLC7A11) expression through trimethylation of histone H3 lysine 27 (H3K27me3) modification. Additionally, SOX4 regulated ferroptosis by directly modulating EZH2 expression. Thus, this study demonstrated that SOX4 facilitates ferroptosis in CaOx-induced kidney injury through EZH2/H3K27me3-mediated suppression of SLC7A11.

Melatonin exerts a protective effect in ameliorating nephrolithiasis via targeting AMPK/PINK1-Parkin mediated mitophagy and inhibiting ferroptosis in vivo and in vitro

Hyperoxaluria-induced damage to renal tubular epithelial cells (RTECs) is considered the most significant contributor to kidney stone formation. However, the precise regulatory mechanism underlying this damage, particularly its association with mitophagy dysfunction, remains unclear. Additionally, effective preventive medications for kidney stones are lacking. Melatonin, a hormone secreted by the pituitary gland that primarily regulates circadian rhythm, has been found to modulate mitophagy in recent research. Therefore, this investigation aims to examine the impact of melatonin on mitophagy and cellular impairment in the formation of kidney stone. The results of this study reveal that melatonin can alleviate the formation of kidney stones and reduce oxalate-induced renal injuries. In the RTECs of kidney stone model, mitophagy was found to be impaired, leading to increased oxidative stress, inflammation, and ferroptosis both in vivo and in vitro. Melatonin was shown to have a restorative potential in enhancing PINK1-Parkin-regulated mitophagy through AMPK phosphorylation, reducing excessive ROS release and inhibiting oxidative stress, inflammation and ferroptosis. Further experiments demonstrated that the protective effect of melatonin was diminished by PINK1 knockdown and AMPK pathway blockade. This study is the first to reveal the interplay between mitophagy and ferroptosis in kidney stone models and establish the protective role of melatonin in restoring mitophagy to inhibit ferroptosis.

Hydroxycitric acid prevents hyperoxaluric-induced nephrolithiasis and oxidative stress via activation of the Nrf2/Keap1 signaling pathway

Nephrolithiasis is a common and frequently-occurring disease in the urinary system with high recurrence. The present study aimed to explore the protective effect and underlying mechanism of hydroxycitric acid (HCA) in hyperoxaluria-induced nephrolithiasis in vitro and in vivo. Crystal deposition and pathophysiological injury in rat models of glyoxylate-induced nephrolithiasis were examined using H&E staining. Cell models of nephrolithiasis were established by oxalate-treated renal tubular epithelial cells. The levels of oxidative stress indexes were determined by ELISA kits. Cell proliferation in vivo and in vitro was evaluated using a cell counting kit-8 (CCK-8) assay and Ki-67 cell proliferation detection kit. Cell apoptosis was measured by flow cytometry and TUNEL staining. The protein levels were examined by western blotting. Our results showed that HCA administration significantly reduced crystal deposition and kidney injury induced by glyoxylate. HCA also alleviated oxidative stress via upregulating the antioxidant enzyme activities of superoxide dismutase (SOD) and catalase (CAT) and reducing the malondialdehyde (MDA) content. Moreover, HCA treatment promoted cell proliferation and inhibited apoptosis of renal tubular epithelial cells exposed to hyperoxaluria. Of note, Nrf2 activator dimethyl fumarate (DMF) exerted the same beneficial effects as HCA in nephrolithiasis. Mechanistically, HCA prevented crystal deposition and oxidative stress induced by hyperoxaluria through targeting the Nrf2/Keap1 antioxidant defense pathway, while knockdown of Nrf2 significantly abrogated these effects. Taken together, HCA exhibited antioxidation and anti-apoptosis activities in nephrolithiasis induced by hyperoxaluria via activating Nrf2/Keap1 pathway, suggesting that it may be an effective therapeutic agent for the prevention and treatment of nephrolithiasis.

Studies on phytochemical, mineral content, in vitro anti-urolithiatic and anti-diabetic activities of horse gram flour extracts and its biosynthesized Ag nanoparticles

The current study aims to examine the use of horse gram flour and its extracts as a low-cost source of mineral content with anti-urolithiatic, anti-diabetic properties and to compare the biological activities with its biosynthesized AgNPs. The secondary metabolites and the macro and micronutrients present in the selected herbal product, reinforces the utility of the horse gram as a promising herbal. Present investigation reveals that the biomass chosen for the study as a cheap natural source with valuable mineral content of calcium (43.06 mg/L), followed by potassium (13.78 mg/L) and sodium (6.94 mg/L). The grain's water extracts found to contain carbohydrate as dominating component with the value of (65.10 ± 0.95 mg g^-1 equivalent). Whereas both water and ethanol extract contain TPC (phenol) viz; 60.13 ± 2.45 mg g^-1, 68.24 ± 1.33 mg g^-1, TTC (terpenoids)53.21 ± 1.4 mg g^-1,51.27 ± 2.65 mg g^-1, followed by TSC (sterol)as 45.58 ± 1.7 mg g^-1, 57.27 ± 1.65 mg g^-1 in moderate amounts respectively. The aqueous extract of Horse gram was used for the synthesis the AgNPs through a straightforward green approach and characterized by FESEM, TEM, zeta potential, X-ray diffraction, UV spectroscopy and particle size measurement. These studies demonstrate the production of AgNPs with an average particle size of 30 nm-60 nm. Investigation on anti-urolithiatic property with aqueous extract, (HGW), ethanol extract (HGE) and its biosynthesized Ag nanoparticles (HG-Ag) reveal that, among the three samples chosen, the biosynthesized Ag nanoparticles possess the best inhibiting activity. The disintegration of crystals in gel medium further validated the extracts and Ag nanoparticles crystal growth inhibitory activity, at concentrations of 2% for extracts and 200 μg/ml for AgNPs. Further, it is also found that the HG-Ag nanoparticle exhibit good anti-diabetic activity (75.36%) than the other two extracts (HGW Extract-67.18% & HGE Extract-44.29%). Thus, the seed flour extracts and its AgNps demonstrated to be a promising natural herbal product with potential mineral content, antidiabetic and anti-urolithiatic activities which could be a used as a value-added product in the dietary formulations.

Cell Protection and Crystal Endocytosis Inhibition by Sulfated Laminaria Polysaccharides Against Nano-COM-Induced Oxidative Damage in Renal Epithelial Cells

Background: The damage to renal tubular epithelial cells is closely related to the formation of kidney stones. At present, research on drugs that can protect cells from damage remains limited. Methods: This study aims to explore the protective effects of four different sulfate groups (-OSO₃ ^-) of Laminaria polysaccharides (SLPs) on human kidney proximal tubular epithelial (HK-2) cells and determine the difference in the endocytosis of nano-sized calcium oxalate monohydrate (COM) crystals before and after protection. COM with a size of 230 ± 80 nm was used to damage HK-2 cells to establish a damage model. The protection capability of SLPs (LP0, SLP1, SLP2, and SLP3) with -OSO₃ ^- contents of 0.73, 15, 23, and 31%, respectively, against COM crystal damage and the effect of SLPs on the endocytosis of COM crystals were studied. Results: Compared with that of the SLP-unprotected COM-injured group, the cell viability of the SLP-protected group was improved, healing capability was enhanced, cell morphology was restored, production of reactive oxygen species was reduced, mitochondrial membrane potential and lysosome integrity were increased, intracellular Ca²⁺ level and autophagy were decreased, cell mortality was reduced, and internalized COM crystals were lessened. The capability of SLPs to protect cells from damage and inhibit the endocytosis of crystals in cells enhanced with an increase in the -OSO₃ ^- content of SLPs. Conclusions: SLPs with a high -OSO₃ ^- content may become a potential green drug for preventing the formation of kidney stones.

The mechanisms of alkali therapy in targeting renal diseases

Chronic kidney disease (CKD) is characterized by progressive reduction in kidney function and treatments aiming at stabilizing or slowing its progression may avoid or delay the necessity of kidney replacement therapy and the increased mortality associated with reduced kidney function. Metabolic acidosis, and less severe stages of the acid stress continuum, are common consequences of CKD and some interventional studies support that its correction slows the progression to end-stage kidney disease. This correction can be achieved with mineral alkali in the form of bicarbonate or citrate salts, ingestion of diets with fewer acid-producing food components or more base-producing food components, or a pharmacological approach. In this mini-review article, we summarize the potential mechanisms involved in the beneficial effects of alkali therapy. We also discuss the perspectives in the field and challenges that must be overcome to advance our understanding of such mechanisms.

Network pharmacology and experimental validation to elucidate the pharmacological mechanisms of Bushen Huashi decoction against kidney stones

INTRODUCTION

Kidney stone disease (KS) is a complicated disease with an increasing global incidence. It was shown that Bushen Huashi decoction (BSHS) is a classic Chinese medicine formula that has therapeutic benefits for patients with KS. However, its pharmacological profile and mechanism of action are yet to be elucidated.

METHODS

The present study used a network pharmacology approach to characterize the mechanism by which BSHS affects KS. Compounds were retrieved from corresponding databases, and active compounds were selected based on their oral bioavailability (≥30) and drug-likeness index (≥0.18). BSHS potential proteins were obtained from the Traditional Chinese Medicine Systems Pharmacology (TCMSP) database, whereas KS potential genes were obtained from GeneCards and OMIM, TTD, and DisGeNET. Gene ontology and pathway enrichment analysis were used to determine potential pathways associated with genes. The ingredients of BSHS extract were identified by the ultra-high-performance liquid chromatography coupled with quadrupole orbitrap mass spectrometry (UHPLC-Q/Orbitrap MS). The network pharmacology analyses predicted the potential underlying action mechanisms of BSHS on KS, which were further validated experimentally in the rat model of calcium oxalate kidney stones.

RESULTS

Our study found that BSHS reduced renal crystal deposition and improved renal function in ethylene glycol(EG)+ammonium chloride(AC)-induced rats, and also reversed oxidative stress levels and inhibited renal tubular epithelial cell apoptosis in rats. BSHS upregulated protein and mRNA expression of E2, ESR1, ESR2, BCL2, NRF2, and HO-1 in EG+AC-induced rat kidney while downregulating BAX protein and mRNA expression, consistent with the network pharmacology results.

DISCUSSION

This study provides evidence that BSHS plays a critical role in anti-KS via regulation of E2/ESR1/2, NRF2/HO-1, and BCL2/BAX signaling pathways, indicating that BSHS is a candidate herbal drug for further investigation in treating KS.

Ureterorenoscopic (URS) Lithotripsy and Balloon Dilation Cause Acute Kidney Injury and Distal Renal Tubule Damage: A Prospective Study

Ureterorenoscopy (URS) is believed to be a safe and effective procedure for treating ureteral stones or ureteral strictures. Rapidly increasing intrarenal pressure during URS may have a negative impact on the kidney, but its effect on renal function is not well known. The aim of this study was to evaluate whether URS balloon dilation or lithotripsy could cause acute kidney injury (AKI), which was evaluated using urine neutrophil gelatinase-associated lipocalin (NGAL), and renal tubular damage, which was evaluated using urine α-glutathione S-transferase (GST) and πGST. This prospective study included 207 patients with a mean age of 53.8 years between September 2012 and June 2013. Four groups were included: the ureteral stricture group (group 1), the ureteral stone group (group 2), and two control groups. URS increased urine NGAL (uNGAL) levels on days 1 and 14 in both groups, and only elevated uGST levels were noted on day 14 after URS lithotripsy (URS). On day 14, the difference between low-grade and high-grade hydronephrosis was significant in group 1 (p < 0.001) compared to that in group 2 (p = 0.150). Multivariate logistic regression analysis revealed that age, baseline estimated glomerular filtration rate (eGFR), and stone size > 1.0 cm were associated with the complete recovery of hydronephrosis after URS on day 14. Patients with ureteral stones with preserved renal function had more AKI than those with impaired renal function. However, there was no significant difference in URS-related AKI between the ≤1 cm and >1 cm subgroups. In addition, urine αGST and πGST levels were both significantly higher in the stone > 1 cm subgroup than in the ≤1 cm subgroup. In conclusion, URS laser lithotripsy and balloon dilatation resulted in AKI and renal tubular damage on day 14, although post-URS double-J (DBJ) stenting was performed in every patient.

Dysfunctional peroxisomal lipid metabolisms and their ocular manifestations

Retina is rich in lipids and dyslipidemia causes retinal dysfunction and eye diseases. In retina, lipids are not only important membrane component in cells and organelles but also fuel substrates for energy production. However, our current knowledge of lipid processing in the retina are very limited. Peroxisomes play a critical role in lipid homeostasis and genetic disorders with peroxisomal dysfunction have different types of ocular complications. In this review, we focus on the role of peroxisomes in lipid metabolism, including degradation and detoxification of very-long-chain fatty acids, branched-chain fatty acids, dicarboxylic acids, reactive oxygen/nitrogen species, glyoxylate, and amino acids, as well as biosynthesis of docosahexaenoic acid, plasmalogen and bile acids. We also discuss the potential contributions of peroxisomal pathways to eye health and summarize the reported cases of ocular symptoms in patients with peroxisomal disorders, corresponding to each disrupted peroxisomal pathway. We also review the cross-talk between peroxisomes and other organelles such as lysosomes, endoplasmic reticulum and mitochondria.

Two independent modes of kidney stone suppression achieved by AIM/CD5L and KIM-1

The prevalence of kidney stones is increasing and its recurrence rate within the first 5 years is over 50%. No treatments that prevent the occurrence/recurrence of stones have reached the clinic. Here, we show that AIM (also called CD5L) suppresses stone development and improves stone-associated physical damages. The N-terminal domain of AIM associates with calcium oxalate crystals via charge-based interaction to impede the development of stones, whereas the 2nd and C-terminal domains capture the inflammatory DAMPs to promote their phagocytic removal. Accordingly, when stones were induced by glyoxylate in mice, recombinant AIM (rAIM) injection dramatically reduced stone development. Expression of injury molecules and inflammatory cytokines in the kidney and overall renal dysfunction were abrogated by rAIM. Among various negatively charged substances, rAIM was most effective in stone prevention due to its high binding affinity to crystals. Furthermore, only AIM was effective in improving the physical complaints including bodyweight-loss through its DAMPs removal effect. We also found that tubular KIM-1 may remove developed stones. Our results could be the basis for the development of a comprehensive therapy against kidney stone disease.

The circulating protein apoptosis inhibitor of macrophage (AIM) reduces kidney stone development and prevents build up, providing the basis for kidney stone disease therapy.

Chronic hepatitis B virus infection increases the risk of upper urinary calculi

Background

Although hepatitis B virus (HBV) is a recognized risk factor for renal diseases, little is known about HBV infection in individuals with upper urinary calculi (UUC). We investigated the relationship between chronic HBV infection and UUC.

Methods

We retrospectively analysed data from 1399 patients who were discharged from the Department of Urology (2017–2018). The diagnosis of UUC was determined using urinary tract ultrasonography or computed tomography, and HBV infection was evaluated by a positive hepatitis B surface antigen (HBsAg) test. Data on patients with and without UUC and HBsAg-positive and HBsAg-negative patients were compared by univariate and multivariate analyses.

Results

Data on chronic HBV infection and UUC were available for 1062 patients, including 514 who presented with UUC and 548 who did not. Overall, 5.8% of total patients, 8.0% of UUC patients and 3.8% of non-UUC patients had chronic HBV infection. UUC patients (41/514) had a significantly higher prevalence of HBsAg positivity (OR 2.175; 95% CI 1.267–3.734; P = 0.004) than non-UUC patients (21/548). After stratifying by sex, the relative odds of HBsAg positivity were statistically significant in men (OR 2.156; 95% CI 1.162–4.003; P = 0.015) but not in women (OR 2.947; 95% CI 0.816–10.643; P = 0.099). The incidence of urinary pH > 6 and staghorn stones was significantly higher in HBsAg-positive UUC patients than in HBsAg-negative UUC patients.

Conclusion

This is the first study to demonstrate that chronic HBV infection is strongly associated with UUC, at least in men. The urinary pH > 6 and staghorn stones were more common in UUC patients with chronic HBV infection.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12894-022-01038-z.

Interaction between nanometer calcium oxalate and renal epithelial cells repaired with carboxymethylated polysaccharides

OBJECTIVE

Injury of renal tubular epithelial cells (HK-2) is an important cause of kidney stone formation. In this article, the repairing effect of polysaccharide (PCP0) extracted from the traditional Chinese medicine Poria cocos and its carboxymethylated derivatives on damaged HK-2 cells was studied, and the differences in adhesion and endocytosis of the cells to nanometer calcium oxalate monohydrate (COM) before and after repair were explored.

METHODS

Sodium oxalate (2.8 mmol/L) was used to damage HK-2 cells to establish a damage model, and then Poria cocos polysaccharides (PCPs) with different carboxyl (COOH) contents were used to repair the damaged cells. The changes in the biochemical indicators of the cells before and after the repair and the changes in the ability to adhere to and internalize nano-COM were detected.

RESULTS

The natural PCPs (PCP0, COOH content = 2.56%) were carboxymethylated, and three carboxylated modified Poria cocos with 7.48% (PCP1), 12.07% (PCP2), and 17.18% (PCP3) COOH contents were obtained. PCPs could repair the damaged HK-2 cells, and the cell viability was enhanced after repair. The cell morphology was gradually repaired, the proliferation and healing rate were increased. The ROS production was reduced, and the polarity of the mitochondrial membrane potential was restored. The level of intracellular Ca²⁺ ions decreased, and the autophagy response was weakened.

CONCLUSION

The cells repaired by PCPs inhibited the adhesion to nano-COM and simultaneously promoted the endocytosis of nano-COM. The endocytic crystals mainly accumulated in the lysosome. Inhibiting adhesion and increasing endocytosis could reduce the nucleation, growth, and aggregation of cell surface crystals, thereby inhibiting the formation of kidney stones. With the increase of COOH content in PCPs, its ability to repair damaged cells, inhibit crystal adhesion, and promote crystal endocytosis all increased, that is, PCP3 with the highest COOH content showed the best ability to inhibit stone formation.

Protective effects of interleukin-22 on oxalate-induced crystalline renal injury via alleviating mitochondrial damage and inflammatory response

Oxalate-induced crystalline kidney injury is one of the most common types of crystalline nephropathy. Unfortunately, there is no effective treatment to reduce the deposition of calcium oxalate crystals and alleviate kidney damage. Thus, proactive therapeutic is urgently needed to alleviate the suffering it causes to patient. Here, we investigated whether IL-22 exerted nephroprotective effects to sodium oxalate-mediated kidney damage and its potential mechanism. Crystalline kidney injury models were developed in vitro and in vivo that was often observed in clinic. We provided evidence that IL-22 could effectively decrease the accumulation of ROS and mitochondrial damage in cell and animal models and reduce the death of TECs. Moreover, IL-22 decreased the expression of the NLRP3 inflammasome and mature IL-1β in renal tissue induced by sodium oxalate. Further studies confirmed that IL-22 could play an anti-inflammatory role by reducing the levels of cytokines such as IL-1β, IL-18, and TNF-α in serum. In conclusion, our study confirmed that IL-22 has protective effects on sodium oxalate-induced crystalline kidney injury by reducing the production of ROS, protecting mitochondrial membrane potential, and inhibiting the inflammatory response. Therefore, IL-22 may play a potential preventive role in sodium oxalate-induced acute renal injury. KEY POINTS: • IL-22 could reduce sodium oxalate-mediated cytotoxicity and ameliorate renal injury. • IL-22 could alleviate oxidative stress and mitochondrial dysfunction induced by sodium oxalate. • IL-22 could inhibit inflammatory response of renal injury caused by sodium oxalate.

Role of ROS-Induced NLRP3 Inflammasome Activation in the Formation of Calcium Oxalate Nephrolithiasis

Calcium oxalate nephrolithiasis is a common and highly recurrent disease in urology; however, its precise pathogenesis is still unknown. Recent research has shown that renal inflammatory injury as a result of the cell-crystal reaction plays a crucial role in the development of calcium oxalate kidney stones. An increasing amount of research have confirmed that inflammation mediated by the cell-crystal reaction can lead to inflammatory injury of renal cells, promote the intracellular expression of NADPH oxidase, induce extensive production of reactive oxygen species, activate NLRP3 inflammasome, discharge a great number of inflammatory factors, trigger inflammatory cascading reactions, promote the aggregation, nucleation and growth process of calcium salt crystals, and ultimately lead to the development of intrarenal crystals and even stones. The renal tubular epithelial cells (RTECs)-crystal reaction, macrophage-crystal reaction, calcifying nanoparticles, endoplasmic reticulum stress, autophagy activation, and other regulatory factors and mechanisms are involved in this process.

Hypercalciuria switches Ca2+ signaling in proximal tubular cells, induces oxidative damage to promote calcium nephrolithiasis

Proximal tubule (PT) transports most of the renal Ca2+, which was usually described as paracellular (passive). We found a regulated Ca2+ entry pathway in PT cells via the apical transient receptor potential canonical 3 (TRPC3) channel, which initiates transcellular Ca2+ transport. Although TRPC3 knockout (-/-) mice were mildly hypercalciuric and displayed luminal calcium phosphate (CaP) crystals at Loop of Henle (LOH), no CaP + calcium oxalate (CaOx) mixed urine crystals were spotted, which are mostly found in calcium nephrolithiasis (CaNL). Thus, we used oral calcium gluconate (CaG; 2%) to raise the PT luminal [Ca2+]o further in TRPC3 -/- mice for developing such mixed stones to understand the mechanistic role of PT-Ca2+ signaling in CaNL. Expectedly, CaG-treated mice urine samples presented with numerous mixed crystals with remains of PT cells, which were pronounced in TRPC3 -/- mice, indicating PT cell damage. Notably, PT cells from CaG-treated groups switched their mode of Ca2+ entry from receptor-operated to store-operated pathway with a sustained rise in intracellular [Ca2+] ([Ca2+]i), indicating the stagnation in PT Ca2+ transport. Moreover, those PT cells from CaG-treated groups demonstrated an upregulation of calcification, inflammation, fibrotic, oxidative stress, and apoptotic genes; effects of which were more robust in TRPC3 ablated condition. Furthermore, kidneys from CaG-treated groups exhibited fibrosis, tubular injury and calcifications with significant reactive oxygen species generation in the urine, thus, indicating in vivo CaNL. Taken together, excess PT luminal Ca2+ due to escalation of hypercalciuria in TRPC3 ablated mice induced surplus CaP crystal formation and caused stagnation of PT [Ca2+]i, invoking PT cell injury, hence mixed stone formation.

Ethnomedicinal Plants Used for Treatment of Urolithiasis in India: A Review

Background:

The kidney stone is the most commonly observed and painful disease of the urinary tract in human being. Numerous intrinsic and extrinsic factors are responsible for the formation of kidney stone, for instance, age, sex, heredity (intrinsic factors) and climate, dietary, geography, mineral composition, and water intake (extrinsic factors). The kidney stones are categorized into calcium, struvite or magnesium ammonium phosphate, uric acid or urate, cystine and other types of stones based on chemical composition and pathogenesis. Due to the multifactorial nature of kidney stone disease, the patient may need to rely on complex synthetic medication. However, in ancient Indian history, there are several pieces of evidence where natural resources such as plants were used to remediation this lethal disease.

Objective:

The present review attempts to provide exhaustive information of ethnomedicinal and ethnopharmacological information of medicinal plants used for kidney stone in India.

Result:

Hitherto, there are a total of 258 ethnomedicinal plants from 90 different families reported using for kidney stone application. The majority of the plant species are associated with three important families: Asteraceae, Amaranthaceae, and Fabaceae. Most of the plants are from Andhra Pradesh (43 plants), followed by East Bengal (38), Jammu & Kashmir (36), Uttarakhand (31), Panjab (27), Mizoram (23), Karnataka (20), Maharashtra (20) and Assam (18). The commonly used plant parts for the herbal preparation are roots (21.22 %) followed by leaves/leaf (20.15 %), and sometimes complete plant (17.77 %) is used. The most commonly used method for the formulation is decoction (46.41 %) followed by powder (18.66 %) and then extracts (15.78 %) of different aerial and non-aerial parts of the plant. To date, the in-vitro and in-vivo activities against the kidney stone assessed for more than sixty ethnomedicinal plants.

Conclusion:

The present review epitomizes the ethnomedicinal information of medicinal plants used for kidney stone and pharmacological evidence for anti-urolithiasis activity. Most reported medicinal plants are not yet scientifically explored and need immediate attention before we lose some important species due to excessive deforestation for farming and industrial needs.

Calcium oxalate crystallization in synthetic urinary medium: the impact of resorcinares and calixarenes

The impact of macrocycles on calcium oxalate formation. Calcium oxalate is a major component of kidney stones, an ailment that affects many people globally.

Exploring the Molecular Level Interaction of Human Serum Albumin with Calcium Oxalate Monohydrate Crystals

BACKGROUND

Human serum albumin (HSA) is one of the most abundant proteins in the blood plasma, urine as well as in the organic matrix of renal calculi. Macromolecules present in the urine modulate kidney stone formation either by stimulating or inhibiting crystallization process.

OBJECTIVE

In the present study, effect of HSA protein on the growth of calcium oxalate monohydrate crystal (COM) was investigated.

METHODS

Crystal growth assay was used to measure oxalate depletion in the crystal seeded solution in the presence of HSA. HSA concentrations exhibiting effect on crystal growth were selected for FTIR and XRD analysis. In silico docking was performed on seven different binding sites of HSA.

RESULTS

Albumin is playing dual role in growth of calcium oxalate crystallization. FTIR and XRD studies further revealed HSA exerted strain over crystal thus affecting its structure by interacting with amino acids of its pocket 1. Docking results indicate that out of 7 binding pocket in protein, calcium oxalate interacts with Arg-186 and Lys-190 amino acids of pocket 1.

CONCLUSION

Our study confirms the role of HSA in calcium oxalate crystallization where acidic amino acids arginine and lysine are binding with COM crystals, revealing molecular interaction of macromolecule and crystal in urolithiasis.

Sirt1 inhibits kidney stones formation by attenuating calcium oxalate-induced cell injury

Cell injury is a necessary and critical event during CaOx kidney stone formation. Sirt1 exerts a number of pleiotropic effects, protecting against renal cell injury. This study aims to explore the relationship between Sirt1 and CaOx kidney stone formation and the underlying mechanism. Sirt1 expression in renal tissues or HK-2 cells was detected by Western blot, immunohistochemistry and immunofluorescence. Apoptosis in renal tissues was examined by TUNEL staining. Renal pathological changes and the crystals deposition were detected by hematoxylin-eosin and Von Kossa staining. Crystal-cell adhesion and cell injury in HK-2 cells were assessed by atomic absorption spectrometry and flow cytometry, respectively. Sirt1 expression in nephrolithiasis patients was downregulated and the level of apoptosis was increased. Further study found that Sirt1 expression was decreased in both in vivo and in vitro models. Interestingly, the levels of cell injury were elevated in vivo and in vitro models. Suppressing Sirt1 expression promoted COM-induced crystal-cell adhesion and exacerbated cell injury. In contrast, increasing the expression of Sirt1 by lentivirus transfection in vitro and resveratrol administration in vivo, alleviated crystal deposition and cell damage. Our findings suggest that Sirt1 could inhibit kidney stone formation, at least in part, through attenuating CaOx -induced cell injury.

Protective Effects of Total Flavonoids from Lysimachia christinae on Calcium Oxalate-Induced Oxidative Stress in a Renal Cell Line and Renal Tissue

Oxidative stress (OS) in renal tubular epithelial cells (RTECs) is induced by calcium oxalate (CaOx) stones and plays an important role in the pathology of CaOx nephrolithiasis. The nuclear factor-E2-related factor 2 (Nrf2)/antioxidant response element (ARE) pathway is an important endogenous antioxidant pathway. Flavonoids are compounds with 2-phenylchromone as the basic mother nucleus and are natural antioxidant components of Lysimachia christinae. Our previous studies demonstrated that the total flavonoids from L. christinae (TFL) reduced calcium and oxalic acid concentrations in urine, thus inhibiting CaOx stone formation. We also showed that TFL can reduce OS in renal tissue. However, whether TFL inhibit the formation of CaOx stones through the Nrf2/ARE pathway requires further investigation. Here, we found that TFL protected against injury to a renal cell line and renal tissue, reduced CaOx-induced OS in renal tissue, and reduced CaOx crystal formation. In addition, TFL significantly increased nuclear Nrf2 and the expression of the downstream antioxidant genes heme oxygenase 1 (HO-1) and NAD(P)H quinone oxidoreductase 1 (NQO-1). Furthermore, TFL increased superoxide dismutase (SOD) activity and decreased the malondialdehyde (MDA) content, thereby alleviating OS in RTECs. Silencing Nrf2 expression blocked the protective effect of TFL on CaOx-induced OS. Taken together, our findings indicate that TFL reduce CaOx-induced OS in renal tissue by activating the Nrf2/ARE pathway.

Carboxymethylation of Corn Silk Polysaccharide and Its Inhibition on Adhesion of Nanocalcium Oxalate Crystals to Damaged Renal Epithelial Cells

The purpose of this study was to explore the repair effect of carboxymethyl-modified corn silk polysaccharide (CSP) on oxidatively damaged renal epithelial cells and the difference in adhesion between cells and calcium oxalate crystals. The CSP was degraded and modified through carboxymethylation. An oxidatively damaged cell model was constructed by oxalate damage to human kidney proximal tubular epithelial (HK-2) cells. Then, the damaged cells were repaired by modified polysaccharides, and the changes in biochemical indexes and adhesion ability between cells and crystals before and after repair were detected. Four modified polysaccharides with carboxyl group (-COOH) contents of 3.92% (CSP0), 7.75% (CCSP1), 12.90% (CCSP2), and 16.38% (CCSP3) were obtained. Compared with CSP0, CCSPs had stronger antioxidant activity, could repair damaged HK-2 cells, and could reduce phosphorylated serine eversion on the cell membrane, the expression of osteopontin (OPN) and Annexin A1, and crystal adhesion. However, its effect on the expression of hyaluronic acid synthase was not substantial. The carboxymethyl modification of the CSP can improve its ability to repair cells and inhibit crystal adhesion and aggregation. A high carboxymethylation degree results in strong polysaccharide activity. CCSPs are expected to reduce the risk of kidney stone formation and recurrence.

Nano-Sized Hydroxyapatite Induces Apoptosis and Osteogenic Differentiation of Vascular Smooth Muscle Cells via JNK/c-JUN Pathway

Purpose

The deposition of hydroxyapatite (HAp) crystals plays an important role in the development of vascular calcification (VC). This study aimed to demonstrate the effects of nanosized HAp (nHAp) on vascular smooth muscle cells (VSMCs) and VC progression.

Methods

Transmission electron microscopy (TEM) was used to examine cellular uptake of nHAp. Cell viability was determined using CCK-8 assay kit. Mitochondrial impairment and reactive oxygen species were detected by TEM and fluorescence dye staining, respectively. Cell apoptosis was detected by Western blot analysis and Annexin V staining. Mouse model of VC was built via applying nHAp on the surface of abdominal aorta. Calcification was visualized by Alizarin red and von Kossa staining.

Results

We found that nHAp could promote osteogenic transformation of VSMCs by elevating expression of runt-related factor 2 (Runx2), osteopontin (OPN) and alkaline phosphatase (ALP), impairing function and morphology of mitochondria and inducing apoptosis of VSMCs. More phosphorylation of c-Jun N-terminal protein kinase/c-JUN (JNK/c-JUN) in VSMCs was detected after mixing nHAp with VSMCs. HAp-induced osteogenic transformation of VSMCs was blocked by JNK inhibitor SP600125, resulted in decreased ALP activity, less Runx2 and OPN expressions. SP600125 also inhibited apoptosis of VSMCs. Application of nHAp to outside of aorta induced osteogenic transformation and apoptosis of VSMCs, and significant deposition of calcium on the vessel walls of mice, which can be effectively attenuated by SP600125.

Conclusion

JNK/c-JUN signaling pathway is critical for nHAp-induced calcification, which could be a potential therapeutic target for controlling the progression of VC.

Comparison of the Effects of Treadmill Running and Rope Jumping on the Excretion of Mass-Like Urinary Stones Following Extracorporeal Shock Wave Lithotripsy

Background: Extracorporeal shock wave lithotripsy (ESWL) is an effective and relatively safe method for crushing urinary tract stones Objectives: The purpose of this study was to compare the effect of running on treadmill and rope jumping exercises on the excretion of mass-like urinary stones following ESWL in the patients referred to the Asia clinic in the city of Ilam. Methods: This was a quasi-experimental study. The subjects were selected by the convenience sampling method and randomly divided into three groups, including control, treadmill running, and rope jumping (n = 50 per group). Data were collected by a questionnaire to record the sonographic characteristics of the stones before and after lithotripsy and analyzed by SPSS software version 24 using Chi-square, unpaired t-test, and one-way ANOVA at the significance level of 5%. Benieman-Hashberg method was used to correct multiple comparisons. Results: There was a significant difference in the number of excreted stones comparing the control, treadmill running, and rope jumping groups (F = 8.851, P = 0.002). There were significant differences between the control and both treadmill running (P = 0.038) and rope jumping (P = 0.002) groups regarding the rate of stone excretion. However, there was no significant difference between the treadmill running and rope jumping groups regarding the rate of stone excretion (P = 0.293). Conclusions: Rope jumping and treadmill running exercises can help to better and faster expel kidney stones, depending on their location, after lithotripsy.

CREB1 protects against the renal injury in a rat model of kidney stone disease and calcium oxalate monohydrate crystals-induced injury in NRK-52E cells

Kidney stone disease (KSD) is a common urinary disease with increasing prevalence worldwide. In this study, we investigated the effect of cyclic AMP responsive element binding protein (CREB) 1 in a KSD model of rat and calcium oxalate monohydrate (COM) crystals-treated NRK-52E cells. Rats were pretreated with lentivirus (LV)-CREB1 vector or LV-control vector and administrated with ethylene glycol + ammonium chloride to induce KSD. It was found that CREB1 was activated in the renal tissue of non-treated KSD rats. Pretreating with LV-CREB1 vector significantly enhanced CREB1 expression in KSD rats. Biochemical analysis for serum and urine showed that upregulation of CREB1 could improve the renal function of KSD rats. Histological analysis confirmed that upregulation of CREB1 alleviated the renal injury in KSD rats. Moreover, the upregulation of CREB1 suppressed the apoptosis in renal tissue of KSD rats through regulating apoptosis-associated proteins. Further study showed that the upregulation of CREB1 could attenuate the oxidative stress in KSD rats as well. More interestingly, the upregulation of CREB1 enhanced the activity of complex I and complex III and the expression of mitochondrial cytochrome c, implicating the effect of CREB1 on improving mitochondrial function in KSD rats. In vitro study confirmed that upregulation of CREB1 inhibited the apoptosis and oxidative stress, while improved the mitochondrial function of NRK-52E cells treated with COM crystals, demonstrating the protective effect of CREB1 on COM crystals-induced renal epithelial cell injury. Therefore, CREB1 might be served as a promising target in the prophylaxis and treatment of KSD.

Antiurolithic efficacy of a phenolic rich ethyl acetate fraction of the aerial parts of Aerva lanata (Linn) Juss. ex Schult. in ethylene glycol induced urolithic rats

OBJECTIVES

The study was carried out to evaluate the in vivo antiurolithic efficaciousness of an ethyl acetate fraction of Aerva lanata (EAFAL) derived from the hydromethanolic extract of its aerial parts (HMEAL).

METHODS

In vivo pharmacological potency of EAFAL was assessed by ethylene glycol (EG) induced urolithiasis model in male Wistar albino rats. Urine samples of the animals were analysed for physical parameters, stone promoters, inhibitors along with an evaluation of the biochemical parameters of serum and kidneys. Histopathological investigation of the kidneys was done. The fraction was further subjected to LC-MS and HPLC for its phytochemical evaluation.

KEY FINDINGS

EAFAL demonstrated a significant antiurolithic effect by a restoration of the balance between urinary promoters and inhibitors along with an amelioration of the urinary pH. The abnormally elevated levels of serum nitrogenous substances, calcium, albumin, globulin, total protein along with altered renal calcium, oxalate and uric acid were also alleviated significantly followed by an improvement of the histopathological aberrancies. Phytochemical analysis showed evidence of phenolic components and flavonoids.

CONCLUSIONS

The current findings prove the beneficial role of phenolic and flavonoid rich EAFAL in ameliorating urolithiasis induced abnormalities of urine, serum and kidneys.

A Prospective, Double-Blind, Randomized, Placebo-Controlled, Crossover Study Using an Orally Administered Oxalate Decarboxylase (OxDC)

BACKGROUND

Hyperoxaluria is typically associated with excessive oxalate intake in the diet, decreased dietary calcium, hyperabsorption of oxalate, or increased endogenous production of oxalate. The disorder spectrum extends from recurrent kidney stones to ESKD. This clinical trial sought to evaluate the effectiveness of an acid stable oxalate decarboxylase (OxDC) to reduce urinary oxalate in healthy subjects on a high-oxalate diet.

METHODS

In this prospective, double-blind, randomized, placebo-controlled, crossover clinical trial, 33 healthy volunteers were randomized into two crossover sequences separated by a 2-day washout period. A controlled high-oxalate diet (750-800 mg oxalate, 500-550 mg calcium daily) was utilized, and six 24-hour urine collections were measured. Subjects were given approximately 1000 U (micromoles per minute per milligram) of OxDC or placebo with meals three times daily during the 4 days of treatment.

RESULTS

Urinary oxalate significantly decreased with OxDC treatment. The baseline corrected within-subject mean reduction in 24-hour urinary excretion (after OxDC dosing versus high-oxalate baseline preceding treatment) was 12.5 mg or 29% (P<0.001). OxDC treatment was effective (>5% reduction) in 31 of 33 subjects (94%). Compared with placebo, OxDC produced a 24% reduction (P<0.001) in 24-hour oxalate excretion. Other urinary parameters (creatinine, uric acid, citrate, magnesium, calcium) were not affected by OxDC. No serious adverse events and no product-related adverse events occurred.

CONCLUSIONS

An orally administered OxDC is capable of significantly reducing urinary oxalate levels in healthy volunteers on a high-oxalate diet without affecting creatinine clearance, urine creatinine, or other solutes related to supersaturation of calcium oxalate.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

Evaluation of Nephure, and the Reduction of Dietary Oxalate, in Healthy Volunteers, NCT03661216.

Specific populations of urinary extracellular vesicles and proteins differentiate type 1 primary hyperoxaluria patients without and with nephrocalcinosis or kidney stones

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is associated with nephrocalcinosis (NC) and calcium oxalate (CaOx) kidney stones (KS). Populations of urinary extracellular vesicles (EVs) can reflect kidney pathology. The aim of this study was to determine whether urinary EVs carrying specific biomarkers and proteins differ among PH1 patients with NC, KS or with neither disease process.

METHODS

Mayo Clinic Rare Kidney Stone Consortium bio-banked cell-free urine from male and female PH1 patients without (n = 10) and with NC (n = 6) or KS (n = 9) and an eGFR > 40 mL/min/1.73 m2 were studied. Urinary EVs were quantified by digital flow cytometer and results expressed as EVs/ mg creatinine. Expressions of urinary proteins were measured by customized antibody array and results expressed as relative intensity. Data were analyzed by ANCOVA adjusting for sex, and biomarkers differences were considered statistically significant among groups at a false discovery rate threshold of Q < 0.20.

RESULTS

Total EVs and EVs from different types of glomerular and renal tubular cells (11/13 markers) were significantly (Q < 0.20) altered among PH1 patients without NC and KS, patients with NC or patients with KS alone. Three cellular adhesion/inflammatory (ICAM-1, MCP-1, and tissue factor) markers carrying EVs were statistically (Q < 0.20) different between PH1 patients groups. Three renal injury (β2-microglobulin, laminin α5, and NGAL) marker-positive urinary EVs out of 5 marker assayed were statistically (Q < 0.20) different among PH1 patients without and with NC or KS. The number of immune/inflammatory cell-derived (8 different cell markers positive) EVs were statistically (Q < 0.20) different between PH1 patients groups. EV generation markers (ANO4 and HIP1) and renal calcium/phosphate regulation or calcifying matrixvesicles markers (klotho, PiT1/2) were also statistically (Q < 0.20) different between PH1 patients groups. Only 13 (CD14, CD40, CFVII, CRP, E-cadherin, EGFR, endoglin, fetuin A, MCP-1, neprilysin, OPN, OPGN, and PDGFRβ) out of 40 proteins were significantly (Q < 0.20) different between PH1 patients without and with NC or KS.

CONCLUSIONS

These results imply activation of distinct renal tubular and interstitial cell populations and processes associated with KS and NC, and suggest specific populations of urinary EVs and proteins are potential biomarkers to assess the pathogenic mechanisms between KS versus NC among PH1 patients.

Human kidney stone matrix proteins alleviate hyperoxaluria induced renal stress by targeting cell-crystal interactions

Increased levels of urinary oxalate also known as hyperoxaluria, increase the likelihood of kidney stone formation through enhanced calcium oxalate (CaOx) crystallization. The management of lithiatic renal pathology requires investigations at the initial macromolecular stages. Hence, the current study was designed to unravel the protein make-up of human kidney stones and its impact on renal cells' altered proteome, induced as the consequence of CaOx injury. CaOx kidney stones were collected from patients; stones were pooled for entire cohort, followed by protein extraction. Immunocytochemistry, RT-PCR and flow-cytometric analysis revealed the promising antilithiatic activity of kidney stone matrix proteins. The iTRAQ analysis of renal cells showed up-regulation of 12 proteins and down-regulation of 41 proteins due to CaOx insult, however, this differential expression was normalized in the presence of kidney stone matrix proteins. Protein network analysis revealed involvement of up-regulated proteins in apoptosis, calcium-binding, inflammatory and stress response pathways. Moreover, seven novel antilithiatic proteins were identified from human kidney stones' matrix: Tenascin-X-isoform2, CCDC-144A, LIM domain kinase-1, Serine/Arginine receptor matrix protein-2, mitochondrial peptide methionine sulfoxide reductase, volume-regulated anion channel subunit-LRRC8A and BMPR2. In silico analysis concluded that these proteins exert antilithiatic potential through crystal binding, thereby inhibiting the crystal-cell interaction, a pre-requisite to initiate inflammatory response. Thus, the outcomes of this study provide insights into the molecular events of CaOx induced renal toxicity and subsequent progression into nephrolithiasis.

Taurine suppresses ROS-dependent autophagy via activating Akt/mTOR signaling pathway in calcium oxalate crystals-induced renal tubular epithelial cell injury

Oxidative stress and autophagy are the key promoters of calcium oxalate (CaOx) nephrolithiasis. Taurine is an antioxidant that plays a protective role in the pathogenesis of kidney disease. Previous studies found that taurine suppressed cellular oxidative stress, and inhibited autophagy activation. However, the effect of taurine on CaOx kidney stone formation remains unknown. In the present work, we explored the regulatory effects of taurine on CaOx crystals-induced HK-2 cell injury. Results showed that pretreatment with taurine significantly enhanced the viability of HK-2 cells and ameliorated kidney tissue injury induced by CaOx crystals. Taurine also markedly reduced the levels of inflammatory cytokines, apoptosis, and CaOx crystals deposition. Furthermore, we observed that taurine supplementation alleviated CaOx crystals-induced autophagy. Mechanism studies showed that taurine reduced oxidative stress via increasing SOD activity, reducing MDA concentration, alleviating mitochondrial oxidative injury, and decreasing the production of intracellular ROS. Taurine treatment also effectively activated Akt/mTOR signaling pathway in CaOx crystals-induced HK-2 cells both in vitro and in vivo. In summary, the current study shows that taurine inhibits ROS-dependent autophagy via activating Akt/mTOR signaling pathway in CaOx crystals-induced HK-2 cell and kidney injury, suggesting that taurine may serve as an effective therapeutic agent for the treatment of CaOx nephrolithiasis.

Melatonin inhibits oxalate-induced endoplasmic reticulum stress and apoptosis in HK-2 cells by activating the AMPK pathway

Background: Deposition of various crystal and organic substances in the kidney can lead to kidney stone formation. Melatonin is an effective endogenous antioxidant that can prevent crystalluria and kidney damage due to crystal formation and aggregation. In this study, we investigated the mechanism by which melatonin inhibits endoplasmic reticulum (ER) stress and apoptosis. Methods: We treated HK-2 cells with oxalate to establish an in vitro kidney stone model, and treated these cells with different concentrations of melatonin (0, 5, 10, 20 μmol/L) and the AMP-activated protein kinase (AMPK) inhibitor Compound C. We measured levels of stress response markers including reactive oxygen species (ROS), lactate dehydrogenase (LDH), glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), and factors in the stress response pathway, such as ATF6, GRP78, DDIT3, PERK, p-PERK, IRE1, p-IRE1, XBP1s, AMPK, and p-AMPK, using real time-PCR, western blot, and immunofluorescence analyzes. We measured mitochondrial membrane potential and caspases-3 activity using the CCK8, enzyme-linked immunosorbent, and flow cytometry assays to assess HK-2 cell viability and apoptosis. Results: Melatonin improved the total antioxidant capacity (T-AOC) of the HK-2 cells, as evidenced by the dose-dependent reduction in apoptosis, ROS levels, and protein expression of ATF6, GRP78, DDIT3, p-PERK, p-IRE1, XBP1s, caspase-12, cleaved caspase-3 and cleaved caspase-9. Addition of the AMPK inhibitor, Compound C, partially reversed the protective effect of melatonin. Conclusion: Our study revealed that the protective effects of melatonin on oxalate-induced ER stress and apoptosis is partly dependent on AMPK activation in HK-2 cells. These findings provide insight into the prevention and treatment of kidney stones.

Hydroxycitric Acid Inhibits Renal Calcium Oxalate Deposition by Reducing Oxidative Stress and Inflammation

Objective:

The study aimed to evaluate the preventive effects of hydroxycitric acid（HCA） for stone formation in the glyoxylate-induced mouse model.

Materials and methods:

Male C57BL/6J mice were divided into a control group, glyoxylate(GOX) 100 mg/kg group, a GOX+HCA 100 mg/kg group, and a GOX+HCA 200 mg/kg group. Blood samples and kidney samples were collected on the eighth day of the experiment. We used Pizzolato staining and a polarized light microscope to examine crystal formation and evaluated oxidative stress via the levels of malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) was used to detect the expression of monocyte chemotactic protein-1(MCP-1), nuclear factor-kappa B (NF κ B), interleukin-1 β (IL-1 β) and interleukin-6 (IL-6) messenger RNA (mRNA). The expression of osteopontin (OPN) and a cluster of differentiation-44(CD44) were detected by immunohistochemistry and qRT-PCR. In addition, periodic acid Schiff (PAS) staining and TUNEL assay were used to evaluate renal tubular injury and apoptosis.

Results:

HCA treatment could reduce markers of renal impairment (Blood Urea Nitrogen and serum creatinine). There was significantly less calcium oxalate crystal deposition in mice treated with HCA. Calcium oxalate crystals induced the production of reactive oxygen species and reduced the activity of antioxidant defense enzymes. HCA attenuated oxidative stress induced by calcium oxalate crystallization. HCA had inhibitory effects on calcium oxalate-induced inflammatory cytokines, such as MCP-1, IL- 1 β, and IL-6. In addition, HCA alleviated tubular injury and apoptosis caused by calcium oxalate crystals.

Conclusion:

HCA inhibits renal injury and calcium oxalate crystal deposition in the glyoxylate-induced mouse model through antioxidation and anti-inflammation.

Size-Dependent Cytotoxicity of Hydroxyapatite Crystals on Renal Epithelial Cells

Background

Hydroxyapatite (HAP) is a common component of most idiopathic calcium oxalate (CaOx) stones and is often used as a nidus to induce the formation of CaOx kidney stones.

Methods

This work comparatively studies the cytotoxicity of four kinds of HAP crystals with different sizes (40 nm to 2 μm), namely, HAP-40 nm, HAP-70 nm, HAP-1 μm, and HAP-2 μm, on human renal proximal tubular epithelial cells (HK-2).

Results

HAP crystals reduce the viability and membrane integrity of HK-2 cells in a concentration-dependent manner and consequently cause cytoskeleton damage, cell swelling, increased intracellular reactive oxygen species level, decreased mitochondrial membrane potential, increased intracellular calcium concentration, blocked cell cycle and stagnation in G0/G1 phase, and increased cell necrosis rate. HAP toxicity to HK-2 cells increases with a decrease in crystal size.

Conclusion

Cell damage caused by HAP crystals increases the risk of kidney stone formation.

MiR-21 promotes calcium oxalate-induced renal tubular cell injury by targeting PPARA

Kidney stone disease is a crystal concretion formed in the kidneys that has been associated with an increased risk of chronic kidney disease. MicroRNAs are functionally involved in kidney injury. Data mining using a microRNA array database suggested that miR-21 may be associated with calcium oxalate monohydrate (COM)-induced renal tubular cell injury. Here, we confirmed that COM exposure significantly upregulated miR-21 expression, inhibited proliferation, promoted apoptosis, and caused lipid accumulation in an immortalized renal tubular cell line (HK-2). Moreover, inhibition of miR-21 enhanced proliferation and decreased apoptosis and lipid accumulation in HK-2 cells upon COM exposure. In a glyoxylate-induced mouse model of renal calcium oxalate deposition, increased miR-21 expression, lipid accumulation, and kidney injury were also observed. In silico analysis and subsequent experimental validation confirmed the peroxisome proliferator-activated receptor (PPAR)-α gene (PPARA) a key gene in fatty acid oxidation, as a direct miR-21 target. Suppression of miR-21 by miRNA antagomiR or activation of PPAR-α by its selective agonist fenofibrate significantly reduced renal lipid accumulation and protected against renal injury in vivo. In addition, miR-21 was significantly increased in urine samples from patients with calcium oxalate renal stones compared with healthy volunteers. In situ hybridization of biopsy samples from patients with nephrocalcinosis revealed that miR-21 was also significantly upregulated compared with normal kidney tissues from patients with renal cell carcinoma who underwent radical nephrectomy. These results suggested that miR-21 promoted calcium oxalate-induced renal tubular cell injury by targeting PPARA, indicating that miR-21 could be a potential therapeutic target and biomarker for nephrolithiasis.

Biodegradable shape memory polymer foams with appropriate thermal properties for hemostatic applications

Shape memory polymer (SMP) foams are a promising material for hemostatic dressings due to their biocompatibility, high surface area, excellent shape recovery, and ability to quickly initiate blood clotting. Biodegradable SMP foams could eliminate the need for a secondary removal procedure of hemostatic material from the patients' wound, further facilitating wound healing. In this study, we developed hydrolytically and oxidatively biodegradable SMP foams by reacting polyols (triethanolamine or glycerol) with 6-aminocaproic acid or glycine to generate foaming monomers with degradable ester bonds. These monomers were used in foam synthesis to provide highly crosslinked SMP foam structures. The ester-containing foams showed clinically relevant thermal properties that were comparable to controls and excellent shape recovery within eight min. Triethanolamine-based ester-containing foams showed interconnected porous structure along with increased mechanical strength. Faster hydrolytic and oxidative biodegradation rates were achieved in ester-containing foams in comparison to controls. These biodegradable SMP foams with clinically applicable thermal properties possess great potential as an effective hemostatic device for use in hospitals or on battlefields.

Repair of Tea Polysaccharide Promotes the Endocytosis of Nanocalcium Oxalate Monohydrate by Damaged HK-2 Cells

Endocytosis is a protective mechanism of renal epithelial cells to eliminate retained crystals. This research investigated the endocytosis of 100 nm calcium oxalate monohydrate crystals in human kidney proximal tubular epithelial (HK-2) cells before and after repair by four kinds of tea polysaccharides with molecular weights (MWs) of 10.88 (TPS0), 8.16 (TPS1), 4.82 (TPS2), and 2.31 kDa (TPS3), respectively. When HK-2 cells were repaired by TPSs after oxalic acid injury, the cell viability, wound healing ability, mitochondrial membrane potential, percentage of cells with endocytosed crystals, and dissolution rate of the endocytosed crystals increased; the cell morphology recovered; and the reactive oxygen level and lactate dehydrogenase release decreased. Most of the endocytosed crystals were found in the lysosomes. The repair effects of the four TPSs were ranked in the following order: TPS2>TPS1>TPS3>TPS0. TPS2 with moderate MW presented the optimal repair ability and strongest ability to promote endocytosis.

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.

Development of analytical method of melamine in placenta from pregnant women by isotope-dilution liquid chromatography/tandem mass spectrometry

RATIONALE

Melamine is ubiquitously present in our daily life. It has a known effect on the kidneys, but it may also adversely affect the reproduction system. We have developed an analytical method for measuring melamine levels in maternal placenta and correlated these levels with melamine concentrations in urine, a necessary step in finding out if melamine might cross the placenta and enter the circulation of the fetus.

METHODS

We used liquid-liquid extraction, clean up by solid-phase extraction (SPE), and isotope-dilution liquid chromatography/tandem mass spectrometry (LC/MS/MS) to measure melamine in placenta specimens. The results of this method were assessed for linearity, limits of quantitation (LOQs), and intra- and inter-assay precision as well as accuracy, matrix effect, and recovery rate.

RESULTS

Calibration curves indicated good linearity (r >0.995) over concentrations ranging from 5 to 500 ng/mL in placenta specimens, intra- and inter-assay precision from 0.89% to 27.07%, and accuracy from 92.4% to123.5%. Recovery ranged from 63.9 to 83.9%, and the LOQ was 5 ng/mL in placenta (0.2 g). Placental melamine levels ranged from 7.87 to19.64 ng/mL, all detectable (n = 8). Pregnant women with higher levels of urinary melamine had higher placenta melamine levels than those with non-detectable urinary melamine, though the results were not significantly different (p = 0.149, n = 4 in each group).

CONCLUSIONS

The results of this study suggest that pregnant women were exposed to low doses of melamine in their daily lives as measured in urine samples and placenta specimens. It is unclear whether placenta melamine concentrations can better represent long-term exposure than urine or whether melamine in the uterus can enter the fetus via this route.

Preparation and characterization of selenized Astragalus polysaccharide and its inhibitory effect on kidney stones

Astragalus polysaccharide (APS) was modified using the Na₂SeO₃/HNO₃ method to obtain selenized APS (Se-APS) with a selenium content of 1.75 mg/g. The structure and physicochemical properties of APS and Se-APS were investigated through transmission electron microscopy-energy dispersive spectroscopy mapping, fourier transform infrared spectroscopy, nuclear magnetic resonance, nano-zetasizer analysis, atomic force microscopy, and scanning electron microscopy. APS and Se-APS did not exhibit toxic effects on human kidney proximal tubular epithelial (HK-2) cells and were able to remove hydroxyl and DPPH radicals, alleviate the damage caused by calcium oxalate (CaOx) monohydrate (COM) crystals to HK-2 cells, reduce intracellular reactive oxygen species levels, and restore cell viability and morphology. Both APS and Se-APS could inhibit COM growth, induce calcium oxalate dihydrate formation, and increase the absolute zeta potential of the crystals to inhibit crystal aggregation. However, the ability of Se-APS to regulate CaOx crystals and protect the cells from COM-induced damage was better than that of APS. These results suggested that Se-APS might be a candidate drug for the treatment and prevention of kidney stones.

Roles for Exosome in Various Kidney Diseases and Disorders

Exosome is a nanoscale vesicle with a size range of 30–100 nm. It is secreted from cell to extracellular space by exocytosis after fusion of multivesicular body (MVB) (formed by endocytic vesicles) with plasma membrane. Exosome plays several important roles in cellular homeostasis and intercellular communications. During the last two decades, exosome has acquired a wide attention to explore its additional roles in various aspects of cell biology and function in several organ systems. For the kidney, several lines of evidence have demonstrated 1that exosome is involved in the renal physiology and pathogenic mechanisms of various kidney diseases/disorders. This article summarizes roles of the exosome as the potential source of biomarkers, pathogenic molecules, and therapeutic biologics that have been extensively investigated in many kidney diseases/disorders, including lupus nephritis (LN), other glomerular diseases, acute kidney injury (AKI), diabetic nephropathy (DN), as well as in the process of renal fibrosis and chronic kidney disease (CKD) progression, in addition to polycystic kidney disease (PKD), kidney transplantation, and renal cell carcinoma (RCC). Moreover, the most recent evidence has shown its emerging role in kidney stone disease (or nephrolithiasis), involving inflammasome activation and inflammatory cascade frequently found in kidney stone pathogenesis.

High-phosphorus environment promotes calcification of A7R5 cells induced by hydroxyapatite nanoparticles

This study simulated the high-phosphorus (Pi) environment in patients with chronic kidney disease. Nano-hydroxyapatite (HAP) crystals were used to damage rat aortic smooth muscle cells (A7R5) pre-damaged with different concentrations of Pi solution to compare the differences in HAP-induced calcification in A7R5 cells before and after injury by high-Pi condition. After the A7R5 cells were damaged by high-Pi environment, the following were observed. HAP resulted in declined cell viability and lysosomal integrity, release of lactate dehydrogenase, and increased reactive oxygen species production. The ability of high-Pi damaged cells to internalize HAP crystals declined; crystal adhesion and calcium deposition on the cell surface and alkaline phosphatase activities increased. Osteopontin expression and level of Runt-related transcription factor 2 were increased, and HAP-induced osteogenic transformation was enhanced. High-Pi condition promoted the adhesion of A7R5 cells to nano-HAP crystals and inhibited HAP endocytosis, increasing the risk of calcification.

miRNA-34a inhibits cell adhesion by targeting CD44 in human renal epithelial cells: implications for renal stone disease

Nephrolithiasis is a very common disease in which cell-crystal adhesion is an essential mechanism for kidney stone formation. This study has explored the anti-adhesion function of the microRNA, miR-34a, by targeting CD44, a cell surface receptor, in human renal epithelial (HK-2) cells. The expression of CD44 was monitored by qPCR and western blot. A luciferase assay validated the target of miR-34a in CD44 3' UTR. Immunofluorescence staining under confocal microscopy was used to detect the cell-crystal adhesion effects in vitro. Pizzolato staining was performed to examine the adhesion role of miR-34a in vivo. In HK-2 cells, miR-34a was down-regulated and CD44 was up-regulated when exposed to calcium oxalate monohydrate crystals. Moreover, miR-34a negatively regulated the expression of CD44. According to the luciferase report assay, miR-34a direct targeted a binding site in the CD44 3'UTR. In vitro experiments, miR-34a overexpression inhibited CD44 expression and cell-crystals adhesion; whereas CD44 overexpression showed reversed results. Furthermore, miR-34a suppressed cell-crystals adhesion and stone formation in vivo. These findings indicate that miR-34a targets CD44 in HK-2 cells and inhibits cell-crystal adhesion both in vitro and in vivo. Based on these results, miR-34a may be a potential therapeutic target for renal stone disease.

Comparison of the adhesion of calcium oxalate monohydrate to HK-2 cells before and after repair using tea polysaccharides

Background: Kidney stone formation is closely related to renal epithelial cell damage and the adhesion of calcium oxalate crystals to cells. Methods: In this research, the adhesion of human kidney proximal tubular epithelial cells (HK-2) to calcium oxalate monohydrate crystals with a size of approximately 100 nm was studied. In addition, the inhibition of crystal adhesion by four tea polysaccharides (TPS0, TPS1, TPS2, and TPS3) with the molecular weights of 10.88, 8.16, 4.82, and 2.31 kDa, respectively were compared. Results: When oxalic acid-damaged HK-2 cells were repaired, cell viability increased. By contrast, reactive oxygen species level, phosphatidylserine eversion, and osteopontin expression decreased, thus indicating that tea polysaccharides have a repairing effect on damaged HK-2 cells. Moreover, after repairing the damaged cells, the amount of adherent crystals was reduced. The repair effect of tea polysaccharides is closely related to molecular weight, and TPS2 with the moderate molecular weight displayed the best repair effect. Conclusion: These results suggest that tea polysaccharides, especially TPS2, may inhibit the formation and recurrence of calcium oxalate kidney stones.