The Rise in Tubular pH during Hypercalciuria Exacerbates Calcium Stone Formation.

In calcium nephrolithiasis (CaNL), most calcium kidney stones are identified as calcium oxalate (CaOx) with variable amounts of calcium phosphate (CaP), where CaP is found as the core component. The nucleation of CaP could be the first step of CaP+CaOx (mixed) stone formation. High urinary supersaturation of CaP due to hypercalciuria and an elevated urine pH have been described as the two main factors in the nucleation of CaP crystals. Our previous in vivo findings (in mice) show that transient receptor potential canonical type 3 (TRPC3)-mediated Ca2+ entry triggers a transepithelial Ca2+ flux to regulate proximal tubular (PT) luminal [Ca2+], and TRPC3-knockout (KO; -/-) mice exhibited moderate hypercalciuria and microcrystal formation at the loop of Henle (LOH). Therefore, we utilized TRPC3 KO mice and exposed them to both hypercalciuric [2% calcium gluconate (CaG) treatment] and alkalineuric conditions [0.08% acetazolamide (ACZ) treatment] to generate a CaNL phenotype. Our results revealed a significant CaP and mixed crystal formation in those treated KO mice (KOT) compared to their WT counterparts (WTT). Importantly, prolonged exposure to CaG and ACZ resulted in a further increase in crystal size for both treated groups (WTT and KOT), but the KOT mice crystal sizes were markedly larger. Moreover, kidney tissue sections of the KOT mice displayed a greater CaP and mixed microcrystal formation than the kidney sections of the WTT group, specifically in the outer and inner medullary and calyceal region; thus, a higher degree of calcifications and mixed calcium lithiasis in the kidneys of the KOT group was displayed. In our effort to find the Ca2+ signaling pathophysiology of PT cells, we found that PT cells from both treated groups (WTT and KOT) elicited a larger Ca2+ entry compared to the WT counterparts because of significant inhibition by the store-operated Ca2+ entry (SOCE) inhibitor, Pyr6. In the presence of both SOCE (Pyr6) and ROCE (receptor-operated Ca2+ entry) inhibitors (Pyr10), Ca2+ entry by WTT cells was moderately inhibited, suggesting that the Ca2+ and pH levels exerted sensitivity changes in response to ROCE and SOCE. An assessment of the gene expression profiles in the PT cells of WTT and KOT mice revealed a safeguarding effect of TRPC3 against detrimental processes (calcification, fibrosis, inflammation, and apoptosis) in the presence of higher pH and hypercalciuric conditions in mice. Together, these findings show that compromise in both the ROCE and SOCE mechanisms in the absence of TRPC3 under hypercalciuric plus higher tubular pH conditions results in higher CaP and mixed crystal formation and that TRPC3 is protective against those adverse effects.

Herbo-Mineral Medicine, Lithom Exhibits Anti-Nephrolithiasis Activity in Rat Model of Hyperoxaluria by Attenuating Calcium Oxalate Crystal Formation and Oxidative Stress.

BACKGROUND: Calcium oxalate monohydrate (COM) forms the most common type of kidney stones observed in clinics, elevated levels of urinary oxalate being the principal risk factor for such an etiology. The objective of the present study was to evaluate the anti-nephrolithiatic effect of herbo-mineral formulation, Lithom. METHODS: The in vitro biochemical synthesis of COM crystals in the presence of Lithom was performed and observations were made by microscopy and Scanning Electron Microscope (SEM) based analysis for the detection of crystal size and morphology. The phytochemical composition of Lithom was evaluated by Ultra-High-Performance Liquid Chromatography (UHPLC). The in vivo model of Ethylene glycol-induced hyperoxaluria in Sprague-Dawley rats was used for the evaluation of Lithom. The animals were randomly allocated to 5 different groups namely Normal control, Disease control (ethylene glycol (EG), 0.75%, 28 days), Allopurinol (50 mg/kg, q.d.), Lithom (43 mg/kg, b.i.d.), and Lithom (129 mg/kg, b.i.d.). Analysis of crystalluria, oxalate, and citrate levels, oxidative stress parameters (malondialdehyde (MDA), catalase, myeloperoxidase (MPO)), and histopathology by hematoxylin and eosin (H&E) and Von Kossa staining was performed for evaluation of Lithom. RESULTS: The presence of Lithom during COM crystals synthesis significantly reduced the average crystal area, feret's diameter, and area-perimeter ratio, in a dose-dependent manner. SEM analysis revealed that COM crystals synthesized in the presence of 100 and 300 µg/mL of Lithom exhibited a veritable morphological transition from irregular polygons with sharp edges to smoothened smaller cuboid polygons. UHPLC analysis of Lithom revealed the presence of Trigonelline, Bergenin, Xanthosine, Adenosine, Bohoervinone B, Vanillic acid, and Ellagic acid as key phytoconstituents. In EG-induced SD rats, the Lithom-treated group showed a decrease in elevated urinary oxalate levels, oxidative stress, and renal inflammation. Von Kossa staining of kidney tissue also exhibited a marked reduction in crystal depositions in Lithom-treated groups. CONCLUSION: Taken together, Lithom could be a potential clinical-therapeutic alternative for management of nephrolithiasis.

Lycopene from tomatoes and tomato products exerts renoprotective effects by ameliorating oxidative stress, apoptosis, pyroptosis, fibrosis, and inflammatory injury in calcium oxalate nephrolithiasis: the underlying mechanisms.

Several mechanisms underlying nephrolithiasis, one of the most common urological diseases, involve calcium oxalate formation, including oxidative stress, inflammatory reactions, fibrosis, pyroptosis, and apoptosis. Although lycopene has strong antioxidant activity, its protective effects against CaOx-induced injury have not yet been reported. This study aimed to systematically investigate the protective effects of lycopene and explore its mechanisms and molecular targets. Crystal deposition, renal function, oxidative stress, inflammatory response, fibrosis, pyroptosis, and apoptosis were assessed to evaluate the renoprotective effects of lycopene against crystal formation in a CaOx rat model and oxalate-stimulated NRK-52E and HK-2 cells. Lycopene markedly ameliorated crystal deposition, restored renal function, and suppressed kidney injury by reducing oxidative stress, apoptosis, inflammation, fibrosis, and pyroptosis in the rats. In cell models, lycopene pretreatment reversed reactive oxygen species increase, apoptotic damage, intracellular lactate dehydrogenase release, cytotoxicity, pyroptosis, and extracellular matrix deposition. Network pharmacology and proteomic analyses were performed to identify lycopene target proteins under CaOx-exposed conditions, and the results showed that Trappc4 might be a pivotal target gene for lycopene, as identified by cellular thermal shift assay and surface plasmon resonance analyses. Based on molecular docking, molecular dynamics simulations, alanine scanning mutagenesis, and saturation mutagenesis, we observed that lycopene directly interacts with Trappc4 via hydrophobic bonds, which may be attributed to the PHE4 and PHE142 residues, preventing ERK1/2 or elevating AMPK signaling pathway phosphorylation events. In conclusion, lycopene might ameliorate oxalate-induced renal tubular epithelial cell injury via the Trappc4/ERK1/2/AMPK pathway, indicating its potential for the treatment of nephrolithiasis.

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.

Critical role of VHL/BICD2/STAT1 axis in crystal-associated kidney disease.

Nephrolithiasis is highly prevalent and associated with the increased risk of kidney cancer. The tumor suppressor von Hippel-Lindau (VHL) is critical for renal cancer development, however, its role in kidney stone disease has not been fully elucidated until now. Here we reported VHL expression was upregulated in renal epithelial cells upon exposure to crystal. Utilizing Vhl+/mu mouse model, depletion of VHL exacerbated kidney inflammatory injury during nephrolithiasis. Conversely, overexpression of VHL limited crystal-induced lipid peroxidation and ferroptosis in a BICD2-depdendent manner. Mechanistically, VHL interacted with the cargo adaptor BICD2 and promoted itsd K48-linked poly-ubiquitination, consequently resulting in the proteasomal degradation of BICD2. Through promoting STAT1 nuclear translocation, BICD2 facilitated IFNγ signaling transduction and enhanced IFNγ-mediated suppression of cystine/glutamate antiporter system Xc-, eventually increasing cell sensitivity to ferroptosis. Moreover, we found that the BRAF inhibitor impaired the association of VHL with BICD2 through triggering BICD2 phosphorylation, ultimately causing severe ferroptosis and nephrotoxicity. Collectively, our results uncover the important role of VHL/BICD2/STAT1 axis in crystal kidney injury and provide a potential therapeutic target for treatment and prevention of renal inflammation and drug-induced nephrotoxicity.

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.

Dynamic change and preventive role of stress response via Keap1-Nrf2 during renal crystal formation.

Oxidative stress is a major risk factor for calcium oxalate nephrolithiasis. Reports suggest that oxidative stress response is induced in animals and humans with kidney stones. Keap1, Nrf2, and HO-1 are known as oxidative stress mediators. However, the association between oxidative stress response and stone formation is unclear. In this study, we analyzed oxidative stress response from the acute to the crystal formation phase when crystal formation was applied to renal crystal mice model and bioimaging mice and investigated the effect on crystal formation. In renal tissues, after glyoxylate administration, HO-1 increased for up to 6 h and returned to baseline at 24 h. This was observed following each daily dose until five days after the crystallization phase; however, the range of increase was attenuated. The possibility that Nrf2 activity influenced the number of crystals was considered in the experiment. Crystal formation increased in Nrf2-deficient mice and could be reduced by Nrf2 activators. In conclusion, the oxidative stress response via the Keap1-Nrf2 pathway may contribute to crystal formation. Particularly, this pathway may be a prospective target for drug development to prevent and cure nephrolithiasis.

Klotho inhibits the formation of calcium oxalate stones by regulating the Keap1-Nrf2-ARE signaling pathway.

PURPOSE: Oxidative damage is important in calcium oxalate (CaOx) stone development but occurs via multiple pathways. Studies have shown that klotho plays an essential role in ameliorating oxidative damage. This study aims to explore the role of klotho in CaOx stones and whether the underlying mechanism is related to the regulation of Keap1-Nrf2-ARE signaling. METHODS: The levels of GSH, SOD, CAT, MDA, and ROS were examined by ELISA. The klotho, Bcl-2, caspase-3, Keap1, Nrf2, HO-1, and NQO1 mRNA levels were measured by qRT‒PCR, and their protein levels were detected by Western blotting. Renal tissue apoptosis was examined by TUNEL staining, and crystal cell adherence and apoptosis in HKC cells were assessed based on the Ca2+ concentrations and by flow cytometry. The renal pathological changes and the adhesion of CaOx crystals in the kidneys were examined by hematoxylin-eosin and von Kossa staining, respectively. RESULTS: We constructed a CaOx kidney stone model in vitro. By regulating the klotho gene, klotho overexpression inhibited the CaOx-induced promotion of crystal cell adherence and apoptosis in HKC cells, and these effects were reversed by klotho knockdown. Moreover, our in vivo assay demonstrated that klotho overexpression alleviated glyoxylate administration-induced renal oxidative damage, renal apoptosis, and crystal deposition in the kidneys of mice, and these effects were also associated with activation of the Keap1-Nrf2-ARE pathway. CONCLUSION: Klotho protein inhibits the oxidative stress response of HKC cells through the Keap1-Nrf2-ARE signaling pathway, reduces the apoptosis of and adhesion of CaOx crystals to HKC cells, and decreases the occurrence of CaOx kidney stones. CLINICAL TRIAL REGISTRATION: 20220304.

CXCR4 inhibition attenuates calcium oxalate crystal deposition-induced renal fibrosis.

Nephrolithiasis is a highly prevalent urological disease and results in a correspondingly heavy socioeconomic and healthcare burden. Calcium oxalate (CaOx) stones are among the most common types of kidney stones. They are associated with renal tubular damage, interstitial fibrosis and chronic kidney disease (CKD). However, the molecular mechanisms in CaOx crystal deposition-induced renal fibrosis remain unclear. Chemokines and their receptors act a crucial role in the progression of renal fibrosis through inflammatory cell infiltration, autophagy activation, and epithelial-mesenchymal transition (EMT). The current work aims to study the action and mechanism of the C-X-C motif chemokine receptor 4 (CXCR4) in CaOx crystal deposition-induced renal fibrosis. Transcriptome RNA sequencing, qPCR, and immunohistochemistry revealed that the expression of CXCR4 was significantly upregulated in patients with nephrolithiasis and hyperoxaluric mice. Renal injury and fibrosis were significantly suppressed by inhibiting CXCR4 with AMD3100 or siRNA in hyperoxaluric mice and oxalate-stimulated HK-2 cells; EMT, reactive oxygen species (ROS) levels, and autophagy were also suppressed. Bioinformatic analysis revealed that the NF-κB pathway was activated in hyperoxaluric mice. Mechanistically, activation of the NF-κB pathway was suppressed by CXCR4 inhibition in CaOx crystal-induced renal fibrosis; this suppression was significantly aggravated by the NF-κB inhibitor BAY-11-7085. Moreover, inhibition of autophagy attenuated EMT progression in vitro. Our results suggest that CXCR4 inhibition attenuates CaOx crystal deposition-induced renal fibrosis by suppressing autophagy and EMT through the NF-κB pathway. Therefore, CXCR4 is a potential target for preventing renal fibrosis in patients with nephrolithiasis.

Dominant negative mutation in oxalate transporter SLC26A6 associated with enteric hyperoxaluria and nephrolithiasis.

BACKGROUND: Nephrolithiasis (NL) is a complex multifactorial disease affecting up to 10%-20% of the human population and causing a significant burden on public health systems worldwide. It results from a combination of environmental and genetic factors. Hyperoxaluria is a major risk factor for NL. METHODS: We used a whole exome-based approach in a patient with calcium oxalate NL. The effects of the mutation were characterised using cell culture and in silico analyses. RESULTS: We identified a rare heterozygous missense mutation (c.1519C>T/p.R507W) in the SLC26A6 gene that encodes a secretory oxalate transporter. This mutation cosegregated with hyperoxaluria in the family. In vitro characterisation of mutant SLC26A6 demonstrated that Cl--dependent oxalate transport was dramatically reduced because the mutation affects both SLC26A6 transport activity and membrane surface expression. Cotransfection studies demonstrated strong dominant-negative effects of the mutant on the wild-type protein indicating that the phenotype of patients heterozygous for this mutation may be more severe than predicted by haploinsufficiency alone. CONCLUSION: Our study is in line with previous observations made in the mouse showing that SLC26A6 inactivation can cause inherited enteric hyperoxaluria with calcium oxalate NL. Consistent with an enteric form of hyperoxaluria, we observed a beneficial effect of increasing calcium in the patient's diet to reduce urinary oxalate excretion.

SLC26A6 and NADC­1: Future direction of nephrolithiasis and calculus­related hypertension research (Review).

Nephrolithiasis is the most common type of urinary system disease in developed countries, with high morbidity and recurrence rates. Nephrolithiasis is a serious health problem, which eventually leads to the loss of renal function and is closely related to hypertension. Modern medicine has adopted minimally invasive surgery for the management of kidney stones, but this does not resolve the root of the problem. Thus, nephrolithiasis remains a major public health issue, the causes of which remain largely unknown. Researchers have attempted to determine the causes and therapeutic targets of kidney stones and calculus­related hypertension. Solute carrier family 26 member 6 (SLC26A6), a member of the well­conserved solute carrier family 26, is highly expressed in the kidney and intestines, and it primarily mediates the transport of various anions, including OXa2­, HCO3­, Cl­ and SO42­, amongst others. Na+­dependent dicarboxylate­1 (NADC­1) is the Na+­carboxylate co­transporter of the SLC13 gene family, which primarily mediates the co­transport of Na+ and tricarboxylic acid cycle intermediates, such as citrate and succinate, amongst others. Studies have shown that Ca2+ oxalate kidney stones are the most prevalent type of kidney stones. Hyperoxaluria and hypocitraturia notably increase the risk of forming Ca2+ oxalate kidney stones, and the increase in succinate in the juxtaglomerular device can stimulate renin secretion and lead to hypertension. Whilst it is known that it is important to maintain the dynamic equilibrium of oxalate and citrate in the kidney, the synergistic molecular mechanisms underlying the transport of oxalate and citrate across kidney epithelial cells have undergone limited investigations. The present review examines the results from early reports studying oxalate transport and citrate transport in the kidney, describing the synergistic molecular mechanisms of SLC26A6 and NADC­1 in the process of nephrolithiasis formation. A growing body of research has shown that nephrolithiasis is intricately associated with hypertension. Additionally, the recent investigations into the mediation of succinate via regulation of the synergistic molecular mechanism between the SLC26A6 and NADC­1 transporters is summarized, revealing their functional role and their close association with the inositol triphosphate receptor­binding protein to regulate blood pressure.

The Molecular Aspect of Nephrolithiasis Development.

Urolithiasis is the third most common urological disease after urinary tract infections and prostate diseases, and it is characterised by an occurrence rate of about 15%, which continues to rise. The increase in the incidence of kidney stones observed in recent decades, is most likely caused by modifications in dietary habits (high content of protein, sodium and sugar diet) and lifestyle (reduced physical activity) in all industrialised countries. Moreover, men are more likely than women to be diagnosed with kidney stones. A growing body of evidence suggests that inflammation, oxidant-antioxidant imbalance, angiogenesis, purine metabolism and urea cycle disorders may play a crucial role in nephrolithiasis development. Patients with urolithiasis were characterised by an increased level of reactive oxygen species (ROS), the products of lipid peroxidation, proinflammatory cytokines as well as proangiogenic factors, compared to controls. Furthermore, it has been shown that deficiency and disorders of enzymes involved in purine metabolism and the urea cycle might be causes of deposit formation. ROS generation suggests that the course of kidney stones might be additionally potentiated by inflammation, purine metabolism and the urea cycle. On the other hand, ROS overproduction may induce activation of angiogenesis, and thus, allows deposit aggregation.

A 3D Renal Proximal Tubule on Chip Model Phenocopies Lowe Syndrome and Dent II Disease Tubulopathy.

Lowe syndrome and Dent II disease are X-linked monogenetic diseases characterised by a renal reabsorption defect in the proximal tubules and caused by mutations in the OCRL gene, which codes for an inositol-5-phosphatase. The life expectancy of patients suffering from Lowe syndrome is largely reduced because of the development of chronic kidney disease and related complications. There is a need for physiological human in vitro models for Lowe syndrome/Dent II disease to study the underpinning disease mechanisms and to identify and characterise potential drugs and drug targets. Here, we describe a proximal tubule organ on chip model combining a 3D tubule architecture with fluid flow shear stress that phenocopies hallmarks of Lowe syndrome/Dent II disease. We demonstrate the high suitability of our in vitro model for drug target validation. Furthermore, using this model, we demonstrate that proximal tubule cells lacking OCRL expression upregulate markers typical for epithelial-mesenchymal transition (EMT), including the transcription factor SNAI2/Slug, and show increased collagen expression and deposition, which potentially contributes to interstitial fibrosis and disease progression as observed in Lowe syndrome and Dent II disease.

Lead (Pb2+)-induced calcium oxalate crystallization ex vivo is ameliorated via inositol 1,4,5-trisphosphate receptor (InsP3R) knockdown in a Drosophila melanogaster model of nephrolithiasis.

Nephrolithiasis causes severe pain and is a highly recurrent pathophysiological state. Calcium-containing stones, specifically calcium oxalate (CaOx), is the most common type accounting for approximately 75 % of stone composition. Genetic predisposition, gender, geographic region, diet, and low fluid intake all contribute to disease pathogenesis. However, exposure to environmental pollutants as a contribution to kidney stone formation remains insufficiently studied. Lead (Pb2+) is of particular interest as epidemiological data indicate that low-level exposure (BLL = 0.48-3.85 µM) confers a 35 % increased risk of developing CaOx nephrolithiasis. However, mechanisms underlying this association have yet to be elucidated. Drosophila melanogaster provide a useful genetic model where major molecular pathophysiological pathways can be efficiently studied. Malpighian tubules (MT) were isolated from either Wild-Type or InsP3R knockdown flies and treated with oxalate (5 mM) ± Pb2+ (2µM) for 1 h. Following exposure, MTs were imaged and crystals quantified. CaOx crystal number and total area were significantly increased (˜5-fold) in Pb2+(pre-treatment) + oxalate-exposed MTs when compared to oxalate alone controls. However, CaOx crystal number and total crystal area in Pb2+ + oxalate-exposed InsP3R knockdown MTs were significantly decreased (˜3-fold) indicating the role for principal cell-specific InsP3R-mediated Ca2+ mobilization as a mechanism for Pb2+-induced increases in CaOx crystallization inset model of nephrolithiasis.

Effect of Carnosine on the Course of Experimental Urate Nephrolithiasis.

The prospect of using the antioxidant dipeptide carnosine for the treatment of urate nephrolithiasis was evaluated. Urate nephrolithiasis was modeled in rats by intragastric administration of a mixture of oxonic and uric acids. Carnosine was administered intragastrically through a tube in a dose of 15 mg/kg. In rats treated with carnosine, the concentration of TBA-reactive products decreased by 1.4 times, the total antioxidant activity increased by 1.4 times, and catalase activity increased by 1.3 times. By the end of the experiment, the lactate dehydrogenate level in experimental rats was 2-fold lower than in the control, and the number of urate deposits decreased by 1.6 times with a concomitant alleviation of the inflammatory processes. Thus, the use of direct peptide antioxidant carnosine attenuated the manifestations of urate nephrolithiasis.

Macrophage Function in Calcium Oxalate Kidney Stone Formation: A Systematic Review of Literature.

Background: The global prevalence and recurrence rate of kidney stones is very high. Recent studies of Randall plaques and urinary components in vivo, and in vitro including gene manipulation, have attempted to reveal the pathogenesis of kidney stones. However, the evidence remains insufficient to facilitate the development of novel curative therapies. The involvement of renal and peripheral macrophages in inflammatory processes offers promise that might lead to the development of therapeutic targets. The present systematic literature review aimed to determine current consensus about the functions of macrophages in renal crystal development and suppression, and to synthesize evidence to provide a basis for future immunotherapy. Methods: We systematically reviewed the literature during February 2021 according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Articles investigating the relationship between macrophages and urolithiasis, particularly calcium oxalate (CaOx) stones, were extracted from PubMed, MEDLINE, Embase, and Scopus. Study subjects, languages, and publication dates were unrestricted. Two authors searched and screened the publications. Results: Although several studies have applied mixed modalities, we selected 10, 12, and seven (total, n = 29) of 380 articles that respectively described cultured cells, animal models, and human samples.The investigative trend has shifted to macrophage phenotypes and signaling pathways, including micro (m)-RNAs since the discovery of macrophage involvement in kidney stones in 1999. Earlier studies of mice-associated macrophages with the acceleration and suppression of renal crystal formation. Later studies found that pro-inflammatory M1- and anti-inflammatory M2-macrophages are involved. Studies of human-derived and other macrophages in vitro and ex vivo showed that M2-macrophages (stimulated by CSF-1, IL-4, and IL-13) can phagocytose CaOx crystals, which suppresses stone development. The signaling mechanisms that promote M2-like macrophage polarization toward CaOx nephrocalcinosis, include the NLRP3, PPARγ-miR-23-Irf1/Pknox1, miR-93-TLR4/IRF1, and miR-185-5p/CSF1 pathways.Proteomic findings have indicated that patients who form kidney stones mainly express M1-like macrophage-related proteins, which might be due to CaOx stimulation of the macrophage exosomal pathway. Conclusions: This systematic review provides an update regarding the current status of macrophage involvement in CaOx nephrolithiasis. Targeting M2-like macrophage function might offer a therapeutic strategy with which to prevent stones via crystal phagocytosis.

Novel Dent disease 1 cellular models reveal biological processes underlying ClC-5 loss-of-function.

Dent disease 1 (DD1) is a rare X-linked renal proximal tubulopathy characterized by low molecular weight proteinuria and variable degree of hypercalciuria, nephrocalcinosis and/or nephrolithiasis, progressing to chronic kidney disease. Although mutations in the electrogenic Cl-/H+ antiporter ClC-5, which impair endocytic uptake in proximal tubule cells, cause the disease, there is poor genotype-phenotype correlation and their contribution to proximal tubule dysfunction remains unclear. To further discover the mechanisms linking ClC-5 loss-of-function to proximal tubule dysfunction, we have generated novel DD1 cellular models depleted of ClC-5 and carrying ClC-5 mutants p.(Val523del), p.(Glu527Asp) and p.(Ile524Lys) using the human proximal tubule-derived RPTEC/TERT1 cell line. Our DD1 cellular models exhibit impaired albumin endocytosis, increased substrate adhesion and decreased collective migration, correlating with a less differentiated epithelial phenotype. Despite sharing functional features, these DD1 cell models exhibit different gene expression profiles, being p.(Val523del) ClC-5 the mutation showing the largest differences. Gene set enrichment analysis pointed to kidney development, anion homeostasis, organic acid transport, extracellular matrix organization and cell-migration biological processes as the most likely involved in DD1 pathophysiology. In conclusion, our results revealed the pathways linking ClC-5 mutations with tubular dysfunction and, importantly, provide new cellular models to further study DD1 pathophysiology.

Human kidney stones: a natural record of universal biomineralization.

GeoBioMed - a new transdisciplinary approach that integrates the fields of geology, biology and medicine - reveals that kidney stones composed of calcium-rich minerals precipitate from a continuum of repeated events of crystallization, dissolution and recrystallization that result from the same fundamental natural processes that have governed billions of years of biomineralization on Earth. This contextual change in our understanding of renal stone formation opens fundamentally new avenues of human kidney stone investigation that include analyses of crystalline structure and stratigraphy, diagenetic phase transitions, and paragenetic sequences across broad length scales from hundreds of nanometres to centimetres (five Powers of 10). This paradigm shift has also enabled the development of a new kidney stone classification scheme according to thermodynamic energetics and crystalline architecture. Evidence suggests that ≥50% of the total volume of individual stones have undergone repeated in vivo dissolution and recrystallization. Amorphous calcium phosphate and hydroxyapatite spherules coalesce to form planar concentric zoning and sector zones that indicate disequilibrium precipitation. In addition, calcium oxalate dihydrate and calcium oxalate monohydrate crystal aggregates exhibit high-frequency organic-matter-rich and mineral-rich nanolayering that is orders of magnitude higher than layering observed in analogous coral reef, Roman aqueduct, cave, deep subsurface and hot-spring deposits. This higher frequency nanolayering represents the unique microenvironment of the kidney in which potent crystallization promoters and inhibitors are working in opposition. These GeoBioMed insights identify previously unexplored strategies for development and testing of new clinical therapies for the prevention and treatment of kidney stones.

Theaflavin protects against oxalate calcium-induced kidney oxidative stress injury via upregulation of SIRT1.

Renal tubular cell injury induced by calcium oxalate (CaOx) is a critical initial stage of kidney stone formation. Theaflavin (TF) has been known for its strong antioxidative capacity; however, the effect and molecular mechanism of TF against oxidative stress and injury caused by CaOx crystal exposure in kidneys remains unknown. To explore the potential function of TF on renal crystal deposition and its underlying mechanisms, experiments were conducted using a CaOx nephrocalcinosis mouse model established by glyoxylate intraperitoneal injection, and HK-2 cells were subjected to calcium oxalate monohydrate (COM) crystals, with or without the treatment of TF. We discovered that TF treatment remarkably protected against CaOx-induced kidney oxidative stress injury and reduced crystal deposition. Additionally, miR-128-3p expression was decreased and negatively correlated with SIRT1 level in mouse CaOx nephrocalcinosis model following TF treatment. Moreover, TF suppressed miR-128-3p expression and further abolished its inhibition on SIRT1 to attenuate oxidative stress in vitro. Mechanistically, TF interacted with miR-128-3p and suppressed its expression. In addition, miR-128-3p inhibited SIRT1 expression by directly binding its 3'-untranslated region (UTR). Furthermore, miR-128-3p activation partially reversed the acceerative effect of TF on SIRT1 expression. Taken together, TF exhibits a strong nephroprotective ability to suppress CaOx-induced kidney damage through the recovery of the antioxidant defense system regulated by miR-128-3p/SIRT1 axis. These findings provide novel insights for the prevention and treatment of renal calculus.

Crosstalk between Renal and Vascular Calcium Signaling: The Link between Nephrolithiasis and Vascular Calcification.

Calcium (Ca2+) is an important mediator of multicellular homeostasis and is involved in several diseases. The interplay among the kidney, bone, intestine, and parathyroid gland in Ca2+ homeostasis is strictly modulated by numerous hormones and signaling pathways. The calcium-sensing receptor (CaSR) is a G protein-coupled receptor, that is expressed in calcitropic tissues such as the parathyroid gland and the kidney, plays a pivotal role in Ca2+ regulation. CaSR is important for renal Ca2+, as a mutation in this receptor leads to hypercalciuria and calcium nephrolithiasis. In addition, CaSR is also widely expressed in the vascular system, including vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs) and participates in the process of vascular calcification. Aberrant Ca2+ sensing by the kidney and VSMCs, owing to altered CaSR expression or function, is associated with the formation of nephrolithiasis and vascular calcification. Based on emerging epidemiological evidence, patients with nephrolithiasis have a higher risk of vascular calcification, but the exact mechanism linking the two conditions is unclear. However, a dysregulation in Ca2+ homeostasis and dysfunction in CaSR might be the connection between the two. This review summarizes renal calcium handling and calcium signaling in the vascular system, with a special focus on the link between nephrolithiasis and vascular calcification.