Effects of angiotensin II subtype 1 receptor blockade by losartan on tubulointerstitial lesions caused by hyperoxaluria

A prospective case-control study on the evaluation of oxidative stress in renal stone formers

Association of increased oxidative stress (OS) with the pathophysiology of renal stone formation has not been explored greatly in the field of urolithiasis. In this prospective case-control study, we measured 24-h urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in patients with urolithiasis and compared them with matched healthy controls. We also measured 24-h urinary uric acid, calcium, oxalate, and citrate levels in patients with renal stone disease and studied their relation with urinary 8-OHdG levels. Seventy-five cases of renal stone disease and 75 well-matched controls were included. Median 24-h urinary 8-OHdG levels were significantly higher in cases compared to controls (7.6 vs. 3.7 µg/g of creatinine; p < 0.000). Receiver-operating curve (ROC) analysis for 8-OHdG between cases and controls revealed an area under the curve of 0.90. At 8-OHdG (µg/g of creatinine) value of 5 or more, a sensitivity and a specificity of 84% each were obtained. A positive correlation between 8-OHdG (µg/g of creatinine) and 24-h urinary oxalate level was noted (r = 0.461, p = 0.000). No correlation between 8-OHdG (µg/g of creatinine) and other variables was noted. On multivariate linear regression analysis, we noted 24-h urinary oxalate levels to be an independent predictor of urinary 8-OHdG levels. OS is significantly higher in patients with renal stone diseases compared to healthy controls. Urinary oxalate levels were significantly correlated with urinary 8-OHdG levels.

Inhibition of AT1R/IP3/IP3R-mediated Ca2+ release protects against calcium oxalate crystals-induced renal oxidative stress

Calcium oxalate (CaOx) stones are the most prevalent type of kidney stones. CaOx crystals can stimulate reactive oxygen species (ROS) generation and induce renal oxidative stress to promote stone formation. Intracellular Ca2+ is an important signaling molecule, and an elevation of cytoplasmic Ca2+ levels could trigger oxidative stress. Our previous study has revealed that upregulation of Ang II/AT1R promoted renal oxidative stress during CaOx exposure. IP3/IP3R/Ca2+ signaling pathway activated via Ang II/AT1R is involved in several diseases, but its role in stone formation has not been reported. Herein, we focus on the role of AT1R/IP3/IP3R-mediated Ca2+ release in CaOx crystals-induced oxidative stress and explore whether inhibition of this pathway could alleviate renal oxidative stress. NRK-52E cells were exposed to CaOx crystals pretreated with AT1R inhibitor losartan or IP3R inhibitor 2-APB, and glyoxylic acid monohydrate-induced CaOx stone-forming rats were treated with losartan or 2-APB. The intracellular Ca2+ levels, ROS levels, oxidative stress indexes, and the gene expression of this pathway were detected. Our results showed that CaOx crystals activated AT1R to promote IP3/IP3R-mediated Ca2+ release, leading to increased cytoplasmic Ca2+ levels. The Ca2+ elevation was able to stimulate NOX2 and NOX4 to generate ROS, induce oxidative stress, and upregulate the expression of stone-related proteins. 2-APB and losartan reversed the referred effects, reduced CaOx crystals deposition and alleviated tissue injury in the rat kidneys. In summary, our results indicated that CaOx crystals promoted renal oxidative stress by activating the AT1R/IP3/IP3R/Ca2+ pathway. Inhibition of AT1R/IP3/IP3R-mediated Ca2+ release protected against CaOx crystals-induced renal oxidative stress. 2-APB and losartan might be promising preventive and therapeutic agents for the treatment of kidney stone disease.

Exploring the Therapeutic Mechanism of Desmodium styracifolium on Oxalate Crystal-Induced Kidney Injuries Using Comprehensive Approaches Based on Proteomics and Network Pharmacology

Purpose: As a Chinese medicinal herb, Desmodium styracifolium (Osb.) Merr (DS) has been applied clinically to alleviate crystal-induced kidney injuries, but its effective components and their specific mechanisms still need further exploration. This research first combined the methods of network pharmacology and proteomics to explore the therapeutic protein targets of DS on oxalate crystal-induced kidney injuries to provide a reference for relevant clinical use.

Methods: Oxalate-induced kidney injury mouse, rat, and HK-2 cell models were established. Proteins differentially expressed between the oxalate and control groups were respectively screened using iTRAQ combined with MALDI-TOF-MS. The common differential proteins of the three models were further analyzed by molecular docking with DS compounds to acquire differential targets. The inverse docking targets of DS were predicted through the platform of PharmMapper. The protein–protein interaction (PPI) relationship between the inverse docking targets and the differential proteins was established by STRING. Potential targets were further validated by western blot based on a mouse model with DS treatment. The effects of constituent compounds, including luteolin, apigenin, and genistein, were investigated based on an oxalate-stimulated HK-2 cell model.

Results: Thirty-six common differentially expressed proteins were identified by proteomic analysis. According to previous research, the 3D structures of 15 major constituents of DS were acquired. Nineteen differential targets, including cathepsin D (CTSD), were found using molecular docking, and the component-differential target network was established. Inverse-docking targets including p38 MAPK and CDK-2 were found, and the network of component-reverse docking target was established. Through PPI analysis, 17 inverse-docking targets were linked to differential proteins. The combined network of component-inverse docking target-differential proteins was then constructed. The expressions of CTSD, p-p38 MAPK, and p-CDK-2 were shown to be increased in the oxalate group and decreased in kidney tissue by the DS treatment. Luteolin, apigenin, and genistein could protect oxalate-stimulated tubular cells as active components of DS.

Conclusion: The potential targets including the CTSD, p38 MAPK, and CDK2 of DS in oxalate-induced kidney injuries and the active components (luteolin, apigenin, and genistein) of DS were successfully identified in this study by combining proteomics analysis, network pharmacology prediction, and experimental validation.

Calcium oxalate crystals and oxalate induce an epithelial-to-mesenchymal transition in the proximal tubular epithelial cells: Contribution to oxalate kidney injury

TGF-β1 is the main mediator of epithelial-to-mesenchymal transition (EMT). Hyperoxaluria induces crystalluria, interstitial fibrosis, and progressive renal failure. This study analyzed whether hyperoxaluria is associated with TGF-β1 production and kidney fibrosis in mice and if oxalate or calcium oxalate (CaOx) could induce EMT in proximal tubule cells (HK2) and therefore contribute to the fibrotic process. Hyperoxaluria was induced by adding hydroxyproline and ethylene glycol to the mice’s drinking water for up to 60 days. Renal function and oxalate and urinary crystals were evaluated. Kidney collagen production and TGF-β1 expression were assessed. EMT was analyzed in vitro according to TGF-β1 production, phenotypic characterization, invasion, cell migration, gene and protein expression of epithelial and mesenchymal markers. Hyperoxaluric mice showed a decrease in renal function and an increase in CaOx crystals and Ox urinary excretion. The deposition of collagen in the renal interstitium was observed. HK2 cells stimulated with Ox and CaOx exhibited a decreased expression of epithelial as well as increased expression mesenchymal markers; these cells presented mesenchymal phenotypic changes, migration, invasiveness capability and TGF-β1 production, characterizing EMT. Treatment with BMP-7 or its overexpression in HK2 cells was effective at preventing it. This mechanism may contribute to the fibrosis observed in hyperoxaluria.

Oxalate nephropathy in systemic sclerosis: Case series and review of the literature

OBJECTIVE

To increase awareness of oxalate nephropathy as a cause of acute kidney injury (AKI) among systemic sclerosis patients with small intestinal dysmotility and malabsorption, and to prompt consideration of dietary modification and early treatment of predisposing causes of oxalate nephropathy in this population.

METHODS

Two cases of biopsy-proven oxalate nephropathy were identified among systemic sclerosis patients in the course of direct clinical care. Subsequently, a retrospective search of the Johns Hopkins Pathology databases identified a third patient with systemic sclerosis who developed oxalate nephropathy.

RESULTS

Among the three patients with qualifying biopsies, all three had systemic sclerosis with lower gastrointestinal involvement. All three presented with diarrhea, malabsorption, and AKI. In two of the three patients, diarrhea was present for at least 2 years before the development of AKI; in the third, incidental oxalate nephropathy was noted 3 years before she developed AKI and extensive oxalate nephropathy in the setting of a prolonged mycobacterium avium-intracellulare enteritis. In the first case, oxalate crystals were present by urinalysis months before diagnosis by biopsy; in the second, hyperoxaluria was diagnosed by urine collection immediately after; and in the third, oxalate crystals had been noted incidentally on post-transplant renal biopsy 3 years before the development of fulminant oxalate nephropathy. All three patients died within a year after diagnosis.

CONCLUSIONS

Patients with systemic sclerosis and bowel dysmotility associated with chronic diarrhea and malabsorption may be at risk for an associated oxalate nephropathy. Regular screening of systemic sclerosis patients with small bowel malabsorption syndromes through routine urinalysis or 24-h urine oxalate collection, should be considered. Further studies defining the prevalence of this complication in systemic sclerosis, the benefit of dietary modification on hyperoxaluria, the effect of treating small intestinal bowel overgrowth with antibiotics, and the effectiveness of probiotics, calcium supplements, or magnesium supplements to prevent hyperoxaluria-associated renal disease in these patients, are warranted.

Enteric hyperoxaluria: an important cause of end-stage kidney disease

Hyperoxaluria is a frequent complication of inflammatory bowel diseases, ileal resection and Roux-en-Y gastric bypass and is well-known to cause nephrolithiasis and nephrocalcinosis. The associated prevalence of chronic kidney disease and end-stage kidney disease (ESKD) is less clear but may be more consequential than recognized. In this review, we highlight three cases of ESKD due to enteric hyperoxaluria following small bowel resections. We review current information on the pathophysiology, complications and treatment of this complex disease.

Antinephrolithiatic and antioxidative efficacy of Dolichos biflorus seeds in a lithiasic rat model

CONTEXT

Dolichos biflorus sensu auct non L. (Fabaceae) is widely used for the treatment of kidney stones, leucorrhoea, urinary disorders, and menstrual troubles, and is known for its antioxidant activity.

OBJECTIVES

To evaluate the preventive effect of hydro-alcoholic extract of Dolichos biflorus seeds (DBE) in ethylene glycol induced nephrolithiasis.

MATERIALS AND METHODS

In vitro antioxidative capacity of DBE was estimated in terms of reducing power, superoxide radical, 2,2- diphenyl-1-picrylhydrazyl radical, and nitric oxide scavenging activity. A validated HPLC method was used for standardization using quercetin as a marker. Adult female Wistar rats were administered with DBE (150 and 300 mg/kg body weight/day) along with ethylene glycol (0.75%, v/v) for 28 d. The various biochemical parameters were measured in urine, serum, and kidney followed by histochemistry.

RESULTS

Ethylene glycol caused a significant increase in calcium, oxalate, phosphate, and total protein in urine as well as in kidney whereas decrease in calcium, sodium, and magnesium in serum was observed (p < 0.001). Ethylene glycol also caused a significant increase in lipid peroxidation and concurrent decrease in activities of antioxidant enzymes in kidney (p < 0.001). However, the seed extract of D. biflorus caused significant restoration of all these parameters (p < 0.001). Histopathological and histochemical studies also showed the reduced calcifications in kidney of seed extract treated rats.

DISCUSSION AND CONCLUSION

These results indicated that seeds of D. biflorus have significant prophylactic effect in preventing the nephrolithiasis, which might be due to the antioxidant activity of the active compounds of the plant.

Antioxidative mechanism involved in the preventive efficacy of Bergenia ciliata rhizomes against experimental nephrolithiasis in rats

CONTEXT

Bergenia ciliata Haw. (Saxifragaceae) is widely used in traditional medicines for renal disorders including kidney stones, inflammation and also well known for its antioxidant activity. Use of traditional herbs proved to be an important strategy for the management of kidney stones by modulating the oxidative stress imposed by calcium oxalate nephrolithiasis.

OBJECTIVES

To evaluate the antinephrolithiatic and antioxidative activity of B. ciliata rhizomes as a preventive agent on ethylene glycol (EG)-induced nephrolithiasis.

MATERIALS AND METHODS

The hydro-methanol extract (30:70, v/v) of B. ciliata rhizomes was orally administrated simultaneously at a dose of 150 and 300 mg/kg body weight/day, to adult female Wistar rats for 28 d along with EG (0.75%, v/v) in drinking water. The results were compared to a parallel study conducted with marketed polyherbal drug cystone under identical dosage conditions. The biochemical parameters were measured in urine, serum and kidney followed by histochemistry. A validated HPLC method was used for standardization using gallic acid as a marker.

RESULTS

EG caused a significant increase in calcium, oxalate and phosphate levels in urine and kidney and concurrent decrease in calcium, sodium and magnesium in serum (p<0.001). EG also caused an increase in lipid peroxidation and a decrease in activities of antioxidative enzymes in kidney. Co-treatment with B. ciliata rhizomes extract caused restoration of all these parameters (p<0.001). Histochemical studies showed reduced calcifications with extract treatment.

CONCLUSION

B. ciliata has a significant prophylactic effect in preventing the nephrolithiasis, which might be mediated through antioxidant activity of these active compounds.

Osteopontin knockdown in the kidneys of hyperoxaluric rats leads to reduction in renal calcium oxalate crystal deposition

Osteopontin (OPN) expression is increased in kidneys of rats with ethylene glycol (EG) induced hyperoxaluria and calcium oxalate (CaOx) nephrolithiasis. The aim of this study is to clarify the effect of OPN knockdown by in vivo transfection of OPN siRNA on deposition of CaOx crystals in the kidneys. Hyperoxaluria was induced in 6-week-old male Sprague-Dawley rats by administering 1.5% EG in drinking water for 2 weeks. Four groups of six rats each were studied: Group A, untreated animals (tap water); Group B, administering 1.5% EG; Group C, 1.5% EG with in vivo transfection of OPN siRNA; Group D, 1.5% EG with in vivo transfection of negative control siRNA. OPN siRNA transfections were performed on day 1 and 8 by renal sub-capsular injection. Rats were killed at day 15 and kidneys were removed. Extent of crystal deposition was determined by measuring renal calcium concentrations and counting renal crystal deposits. OPN siRNA transfection resulted in significant reduction in expression of OPN mRNA as well as protein in group C compared to group B. Reduction in OPN expression was associated with significant decrease in crystal deposition in group C compared to group B. Specific suppression of OPN mRNA expression in kidneys of hyperoxaluric rats leads to a decrease in OPN production and simultaneously inhibits renal crystal deposition.

Is oxidative stress, a link between nephrolithiasis and obesity, hypertension, diabetes, chronic kidney disease, metabolic syndrome?

Epidemiological studies have provided the evidence for association between nephrolithiasis and a number of cardiovascular diseases including hypertension, diabetes, chronic kidney disease, metabolic syndrome. Many of the co-morbidities may not only lead to stone disease but also be triggered by it. Nephrolithiasis is a risk factor for development of hypertension and have higher prevalence of diabetes mellitus and some hypertensive and diabetic patients are at greater risk for stone formation. An analysis of the association between stone disease and other simultaneously appearing disorders, as well as factors involved in their pathogenesis, may provide an insight into stone formation and improved therapies for stone recurrence and prevention. It is our hypothesis that association between stone formation and development of co-morbidities is a result of certain common pathological features. Review of the recent literature indicates that production of reactive oxygen species (ROS) and development of oxidative stress (OS) may be such a common pathway. OS is a common feature of all cardiovascular diseases (CVD) including hypertension, diabetes mellitus, atherosclerosis and myocardial infarct. There is increasing evidence that ROS are also produced during idiopathic calcium oxalate (CaOx) nephrolithiasis. Both tissue culture and animal model studies demonstrate that ROS are produced during interaction between CaOx/calcium phosphate (CaP) crystals and renal epithelial cells. Clinical studies have also provided evidence for the development of oxidative stress in the kidneys of stone forming patients. Renal disorders which lead to OS appear to be a continuum. Stress produced by one disorder may trigger the other under the right circumstances.

Aqueous extract of Boerhaavia diffusa root ameliorates ethylene glycol-induced hyperoxaluric oxidative stress and renal injury in rat kidney

INTRODUCTION

Boerhaavia diffusa Linn. (Nyctaginaceae) is widely used in traditional Indian medicines against renal afflictions including calcium oxalate (CaOx) urolithiasis and is known for antioxidant activity.

OBJECTIVE

The present study was designed to investigate the ameliorating effect of aqueous extract of B. diffusa roots (BDE) in hyperoxaluric oxidative stress and renal cell injury.

MATERIAL AND METHODS

In vitro antioxidant activity of BDE was estimated in terms of total phenolic content and 1,1-diphenyl-2-picryl hydrazyl free radical scavenging activity. Wistar albino rats were given 0.75% v/v ethylene glycol in drinking water to induce chronic hyperoxaluria and simultaneously BDE was given to nephrolithiasic treated rats at the dose of 100 and 200 mg/kg b.w. orally for 28 days. Urinary volume, oxalate, serum creatinine, blood urea nitrogen (BUN), malondialdehyde (MDA) and antioxidant enzyme (SOD, CAT, GST, GPx) were evaluated.

RESULTS AND DISCUSSION

BDE extract was found to posses a high total phenolic content and exhibited significant free radicals scavenging activity. Oxalate excretion significantly increased in hyperoxaluric animals as compared to control which was protected in BDE-treated animals. BDE treatment significantly reduced level of MDA and improved the activity of antioxidant enzymes followed by reduction in BUN and serum creatinine. In addition, BDE reduced the number of CaOx monohydrate crystals in the urine. Histological analysis depicted that BDE treatment inhibited deposition of CaOx crystal and renal cell damage.

CONCLUSION

The present study reveals that antioxidant activity of BDE significantly protects against hyperoxaluric oxidative stress and renal cell injury in urolithiasis.

Why does atorvastatin inhibit renal crystal retention?

Recently, we reported that atorvastatin prevents renal tubular cell injury by oxalate and inhibits renal crystal retention. In this study, we investigated the mechanism by which atorvastatin inhibits renal crystal retention. Male Sprague-Dawley rats were separated into four experimental groups, and the ethylene glycol model of hyperoxaluria and the atorvastatin treatment model were analyzed. To clarify the mechanism by which atorvastatin inhibits renal crystal retention, the removed kidneys were used for the quantitative analysis of superoxide dismutase (SOD) and catalase. The subunits of the NADPH oxidase system were evaluated using real-time polymerase chain reaction analysis. Furthermore, the level of transforming growth factor-β (TGF-β) in kidney tissue was compared in each group. Atorvastatin treatment increased the SOD and catalase level compared with the stone-forming control group. Atorvastatin treatment decreased the expression of NOX-1 mRNA. Furthermore, the level of TGF-β was suppressed by atorvastatin treatment. We found that atorvastatin have inhibited calcium oxalate (CaOX) urolithiasis formation. We hypothesize that the mechanism of action of atorvastatin involves inhibiting TGF-β and NADPH oxidase, and increasing the SOD and catalase level. We believe that atorvastatin will be helpful in the treatment of CaOX urolithiasis.

Calcium oxalate crystal deposition in metabolic syndrome model rat kidneys

OBJECTIVE

Although an epidemiological link between the metabolic syndrome and kidney stone formation has been reported, the mechanism by which metabolic syndrome promotes kidney stone formation has yet to be elucidated. We investigated calcium oxalate (CaOx) kidney stone formation in a rat metabolic syndrome model.

METHODS

We induced hyperoxaluria in 8-week-old male Otsuka Long-Evans Tokushima fatty (OLETF) rats, and a control strain, Long-Evans Tokushima Otsuka (LETO) rats, by administering 1.0% ethylene glycol (EG) as their drinking water for 2 weeks. Rats were divided into four groups: LETO-C (control, n = 7); LETO-SF (stone forming, n = 8); OLETF-C (n = 7); and OLETF-SF (n = 8). Urine and blood samples were collected for biochemistry testing, and the kidneys were harvested for estimation of crystal deposition and determinations of the expression of osteopontin (OPN) and monocyte chemoattractant protein-1 (MCP-1).

RESULTS

Administration of EG induced hyperoxaluria to the same degree in both strains. The OLETF-SF group showed a higher grade of renal crystal deposition and significantly higher renal calcium content than the LETO-SF group. Although the OLETF-C group excreted significantly higher amounts of uric acid and more acidic urine than the LETO-C group, similar differences were not observed in rats given EG. Significant upregulation of both OPN and MCP-1 was seen in the kidneys of hyperoxaluric rats, with higher levels of expression in the OLETF-SF group than the LETO-SF group.

CONCLUSIONS

The present results show for the first time that OLETF rats form more renal CaOx crystal deposits compared with control rats under EG-induced hyperoxaluric conditions. The model described here should be useful for investigating the mechanisms by which the metabolic syndrome promotes CaOx kidney stone formation.

Effect of NADPH oxidase inhibition on the expression of kidney injury molecule and calcium oxalate crystal deposition in hydroxy-L-proline-induced hyperoxaluria in the male Sprague-Dawley rats

BACKGROUND

Renal calcium oxalate (CaOx) crystal deposition is associated with epithelial injury and movement of inflammatory cells into the interstitium. We have proposed that oxalate (Ox)- and CaOx crystal-induced injury is most likely caused by reactive oxygen species (ROS) produced by activation of membrane nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.

METHODS

Present study was undertaken to determine the effect of NADPH oxidase inhibitor apocynin on the expression of kidney injury molecule-1 (KIM-1) and renal CaOx crystal deposition in rats with hyperoxaluria. We also investigated the urinary excretion of KIM-1, osteopontin (OPN) and monocyte chemoattractant protein-1 (MCP-1) and renal expression of OPN and ED-1. Male Sprague-Dawley rats were fed a diet containing 5% hydroxyl-L-proline (HLP) and 4 mmol apocynin to drink for 28 days. Urine was collected on Days 7, 14, 21 and 28. After that, rats were sacrificed and their kidneys processed for various microscopic and molecular investigations.

RESULTS

HLP consumption produced heavy deposits of CaOx crystals. Renal expression of KIM-1 and OPN and urinary excretion of KIM-1, OPN, H(2)O(2) and MCP-1 was significantly increased. ED-1-positive cells migrated into renal interstitium. Apocynin treatment caused significant reduction of crystal deposits, injured and dilated tubules; renal expression of KIM-1, OPN and ED-1 and urinary excretion of KIM-1, OPN, MCP-1 and H(2)O(2). Apocynin had no effect on the urinary excretion of Ox.

CONCLUSIONS

This is the first study of urinary excretion and renal expression of KIM-1 in association with renal CaOx crystal deposition, experimental or clinical. The results indicate that NADPH oxidase inhibition leads to reduction in KIM-1 expression and urinary excretion as well as renal CaOx crystal deposition. KIM-1 is an important marker of renal epithelial injury. The results provide further support to our proposal that renal epithelial injury is critical for crystal retention and that injury is in part caused by the production of ROS with the involvement of NADPH oxidase.

Losartan inhibits collagen I synthesis and improves the distribution and efficacy of nanotherapeutics in tumors

The dense collagen network in tumors significantly reduces the penetration and efficacy of nanotherapeutics. We tested whether losartan--a clinically approved angiotensin II receptor antagonist with noted antifibrotic activity--can enhance the penetration and efficacy of nanomedicine. We found that losartan inhibited collagen I production by carcinoma-associated fibroblasts isolated from breast cancer biopsies. Additionally, it led to a dose-dependent reduction in stromal collagen in desmoplastic models of human breast, pancreatic, and skin tumors in mice. Furthermore, losartan improved the distribution and therapeutic efficacy of intratumorally injected oncolytic herpes simplex viruses. Finally, it also enhanced the efficacy of i.v. injected pegylated liposomal doxorubicin (Doxil). Thus, losartan has the potential to enhance the efficacy of nanotherapeutics in patients with desmoplastic tumors.

Experimentally induced hyperoxaluria in MCP-1 null mice

Experimental animal model studies suggest that calcium oxalate (CaOx) crystal deposition in the kidneys is associated with the development of oxidative stress, epithelial injury and inflammation. There is increased production of inflammatory molecules including osteopontin (OPN), monocyte chemoattractant protein-1 (MCP-1) and various subunits of inter-alpha-inhibitor such as bikunin. What does the increased production of such molecules suggest? Is it a cause or consequence of crystal deposition? We hypothesized that over-expression and increased production of MCP-1 is a result of the interaction between renal epithelial cells and CaOx crystals after their deposition in the renal tubules. We induced hyperoxaluria in MCP-1 null as well as wild type mice and examined pathological changes in their kidneys and urine. Both wild type and MCP-1 null male mice became hyperoxaluric and demonstrated CaOx crystalluria. Neither of them developed crystal deposits in their kidneys. Both showed some morphological changes in their renal proximal tubules. Significant pathological changes such as cell death and increased urinary excretion of LDH were not seen. Results suggest that at least in mice (1) Increase in oxalate and decrease in citrate excretion can lead to CaOx crystalluria but not CaOx nephrolithiasis; (2) MCP-1 does not play a role in crystal retention within the kidneys; (3) Expression of OPN and MCP-1 is not increased in the kidneys in the absence of crystal deposition; (4) Crystal deposition is necessary for significant pathological changes and movement of monocytes and macrophages into the interstitium.

The tubular epithelium in the initiation and course of intratubular nephrocalcinosis

Intratubular nephrocalcinosis is defined as the histological observation of calcium oxalate and/or calcium phosphate deposits retained within the lumen of the renal tubules. As the tubular epithelium is the primary interaction partner of crystals formed in the tubular fluid, the role of the epithelial cells in nephrocalcinosis has been investigated intensively. This review summarizes our current understanding on how the tubular epithelium mechanistically appears to be involved both in the initiation and in the course of nephrocalcinosis, with emphasis on in vivo observations.

Nephrocalcinosis in animal models with and without stones

Nephrocalcinosis is the deposition of calcium salts in renal parenchyma and can be intratubular or interstitial. Animal model studies indicate that intratubular nephrocalcinosis is a result of increased urinary supersaturation. Urinary supersaturation with respect to calcium oxalate (CaOx) and calcium phosphate (CaP) are generally achieved at different locations in the renal tubules. As a result experimental induction of hyperoxaluria in animals with CaP deposits does not lead to growth of CaOx over CaP. Interstitial nephrocalcinosis has been seen in mice with lack of crystallization modulators Tamm-Horsfall protein and osteopontin. Sodium phosphate co-transporter or sodiumhydrogen exchanger regulator factor-1 null mice also produced interstitial nephrocalcinosis. Crystals plug the tubules by aggregating and attaching to the luminal cell surface. Structural features of the renal tubules also play a role in crystal retention. The crystals plugging the terminal collecting ducts when exposed to the metastable pelvic urine may promote the formation of stone.

Taurine protected kidney from oxidative injury through mitochondrial-linked pathway in a rat model of nephrolithiasis

Hyperoxaluria and crystal deposition induce oxidative stress (OS) and renal epithelial cells injury, both mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are considered as the main sources of reactive oxygen species (ROS). Taurine is known to have antioxidant activity and shows renoprotective effect. We investigate the effect of taurine treatment on renal protection, and the putative source of ROS, in a rat model of calcium oxalate nephrolithiasis. Rats were administered with 2.5% (V/V) ethylene glycol + 2.5% (W/V) ammonium chloride (4 ml/day), with restriction on intake of drinking water (20 ml/day) for 4 weeks. Simultaneous treatment with taurine (2% W/W, mixed with the chow) was performed. At the end of the study, indexes of OS and renal injury were assessed. Renal tubular ultrastructure changes were analyzed under transmission electron microscopy. Crystal deposition in kidney was scored under light microscopy. Angiotensin II in kidney homogenates was determined by radioimmunoassay. Expression of NADPH oxidase subunits p47phox and Nox-4 mRNAs in kidney was evaluated by real time-polymerase chain reaction. The data showed that oxidative injury of the kidney occurred in nephrolithiasis-induced rats. Hyperplasia of mitochondria developed in renal tubular epithelium. The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) in mitochondria decreased and the mitochondrial membrane showed oxidative injury. Taurine treatment alleviated the oxidative injury of the kidney, improved SOD and GSH-Px activities, as well as the mitochondrial membrane injury, with lesser crystal depositions in the kidney. We could not detect statistical changes in the renal angiotensin II level, and the renal p47phox and Nox-4 mRNAs expression in those rats. The results suggest that mitochondria but not NADPH oxidase may account for the OS and taurine protected kidney from oxidative injury through mitochondrial-linked pathway in this rat model.

Superoxide from NADPH oxidase as second messenger for the expression of osteopontin and monocyte chemoattractant protein-1 in renal epithelial cells exposed to calcium oxalate crystals

OBJECTIVE To test the hypothesis that exposure of a renal epithelial cell line, NRK52E, to calcium oxalate monohydrate crystals (COM) would up-regulate NADPH oxidase subunit p47(phox), enhance superoxide production and increase monocyte chemoattractant protein-1 (MCP-1) and osteopontin mRNA levels. MATERIALS AND METHODS Confluent cultures of NRK52E cells were exposed to COM (66.7 microg/cm(2)) with or with no pretreatment with diphenileneiodium chloride (DPI, 10 x 10(-6)m) an inhibitor for NADPH oxidase, under serum-free conditions. The conditioned medium was collected and total cellular RNA isolated from the cells, and subjected to enzyme-linked immunosorbent assay and real-time polymerase chain reaction (PCR). Production of reactive oxygen species (ROS) was estimated by dihydroethidium (DHE) staining using a fluorescence microscope. Immunohistochemistry and real-time PCR were used to analyse p47(phox) in NRK52E cells. RESULTS In COM treated NRK52E cells there was enhanced expression of p47(phox) and production of superoxide. COM-induced production of MCP-1 and osteopontin was significantly reduced after treatment with DPI. CONCLUSIONS While the generation of a lot of ROS might play a major role in tissue injury or death, the regulated generation of low concentration of ROS, possibly by NADPH oxidase, may represent a second messenger system for generation of COM-induced MCP-1 and osteopontin production in the renal tubules.

Oxalate in renal stone disease: the terminal metabolite that just won't go away

The incidence of calcium oxalate nephrolithiasis in the US has been increasing throughout the past three decades. Biopsy studies show that both calcium oxalate nephrolithiasis and nephrocalcinosis probably occur by different mechanisms in different subsets of patients. Before more-effective medical therapies can be developed for these conditions, we must understand the mechanisms governing the transport and excretion of oxalate and the interactions of the ion in general and renal physiology. Blood oxalate derives from diet, degradation of ascorbate, and production by the liver and erythrocytes. In mammals, oxalate is a terminal metabolite that must be excreted or sequestered. The kidneys are the primary route of excretion and the site of oxalate's only known function. Oxalate stimulates the uptake of chloride, water, and sodium by the proximal tubule through the exchange of oxalate for sulfate or chloride via the solute carrier SLC26A6. Fecal excretion of oxalate is stimulated by hyperoxalemia in rodents, but no similar phenomenon has been observed in humans. Studies in which rats were treated with (14)C-oxalate have shown that less than 2% of a chronic oxalate load accumulates in the internal organs, plasma, and skeleton. These studies have also demonstrated that there is interindividual variability in the accumulation of oxalate, especially by the kidney. This Review summarizes the transport and function of oxalate in mammalian physiology and the ion's potential roles in nephrolithiasis and nephrocalcinosis.

Positron-Emission Tomography Imaging of the Angiotensin II Subtype 1 Receptor in Swine Renal Artery Stenosis

The angiotensin II subtype 1 receptor (AT 1 R) has been linked to the development and progression of renovascular hypertension. In this study we applied a pig model of renovascular hypertension to investigate the AT 1 R in vivo with positron-emission tomography (PET) and in vitro with quantitative autoradiography. AT 1 R PET measurements were performed with the radioligand [ 11 C]KR31173 in 11 control pigs and in 13 pigs with hemodynamically significant renal artery stenosis; 4 were treated with lisinopril for 2 weeks before PET imaging. The radioligand impulse response function was calculated by deconvolution analysis of the renal time-activity curves. Radioligand binding was quantified by the 80-minute retention of the impulse response function. Median values and interquartile ranges were used to illustrate group statistics. Radioligand retention was significantly increased ( P =0.044) in hypoperfused kidneys of untreated (0.225; range: 0.150 to 0.373) and lisinopril-treated (0.237; range:0.224 to 0.272) animals compared with controls (0.142; range:0.096 to 0.156). Increased binding of [ 11 C]KR31173 documented by PET in vivo was confirmed by in vitro autoradiography. Both in vivo and in vitro binding measurements showed that the effect of renal artery stenosis on the AT 1 R was not abolished by lisinopril treatment. These studies provide insight into kidney biology as the first in vivo/in vitro experimental evidence about AT 1 R regulation in response to reduced perfusion of the kidney. The findings support the concept of introducing AT 1 R PET as a diagnostic biomarker of renovascular disease.

Continuous infusion of oxalate by minipumps induces calcium oxalate nephrocalcinosis

It is hypothesized that oxalate plays an active role in calcium oxalate (CaOx) nephrocalcinosis and oxalate driven nephrolithiasis by interacting with the kidney. We developed an adjustable, nonprecursor, continuous infusion model of hyperoxaluria and CaOx nephrocalcinosis to investigate this hypothesis. Minipumps containing PBS or KOx (60-360 micromol/day; n = 5-7/dose) were implanted subcutaneously in male Sprague-Dawley rats on D0 and D6. Rats were killed on D13. Oxalate excretion and CaOx crystalluria were monitored by 20+4 h urine collections. Localization and content of intrarenal crystals were determined on frozen sections using polarization and microFTIR. Oxalate excretion was significantly elevated in all KOx rats (P < or = 0.005). CaOx crystalluria was most persistent in the 240-360 micromol/day KOx rats, but even 60 micromol/day KOx rats showed sporadic crystalluria. One hundred percent of KOx rats had CaOx nephrocalcinosis as confirmed by microFTIR. Most crystals were localized to the lumens of the corticomedullary collecting ducts. A few crystals are localized just under the papillar urothelium. The minipump model is the first model of hyperoxaluria to provide continuous infusion of oxalate. It permits control of the levels of hyperoxaluria, crystalluria and CaOx nephrocalcinosis. The level of sustained hyperoxaluria and CaOx nephrocalcinosis induced by treatment with 360 micromol/day KOx for 13D models the conditions frequently observed in jejunoileal bypass patients. Adjustments in the length of treatment and level of hyperoxaluria may allow this model to also be used to study the oxalate driven CaOx-nephrolithiasis common in patients with hyperoxaluria due to other causes.

Reactive oxygen species mediated calcium oxalate crystal-induced expression of MCP-1 in HK-2 cells

Under severe hyperoxaluric conditions calcium oxalate crystals often deposit in the renal interstitium and produce localized inflammation. We have proposed that renal epithelial cells exposed to CaOx crystals produce chemoattractants such as monocyte chemoattractant protein-1 (MCP-1). MCP-1 synthesis is mediated by reactive oxygen species (ROS). HK-2 cells of human renal epithelial line were exposed to CaOx crystals for different lengths of time. The culture media was tested for cell injury marker LDH, and subjected to enzyme-linked immunosorbent assay to determine the secretion of MCP-1 protein. Cell expression of MCP-1 was assessed by Western blot analysis. Gene expression was determined by reverse transcriptase-polymerase chain reaction. The data clearly showed that the HK-2 cells express MCP-1 gene and protein. The MCP-1 mRNA expression was increased following exposure to CaOx crystals, which was reduced upon treatment with free radical scavengers, catalase and superoxide dismutase. Results indicate that CaOx crystals strongly induce MCP-1 synthesis and secretion by the HK-2 cells and production is mediated by intracellular ROS production. Based on these and other data, antioxidant therapy and blockade of rennin-angiotensin system may prove beneficial for the prevention of end stage renal disease caused by hyperoxaluria and CaOx crystal deposition.

Oxalate is toxic to renal tubular cells only at supraphysiologic concentrations

BACKGROUND

Oxalate-induced tissue damage may play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. The concentration of oxalate is higher in the renal collecting ducts ( approximately 0.1 to 0.5 mmol/L) than in the proximal tubule ( approximately 0.002 to 0.1 mmol/L). In the present investigation, we studied the damaging effect of oxalate to renal proximal and collecting tubule cells in culture.

METHODS

Studies were performed with the renal proximal tubular cell lines, LLC-PK1 and Madin Darby canine kidney II (MDCK-II), and the renal collecting duct cell lines, rat renal cortical collecting duct (RCCD1) and MDCK-I. Confluent monolayers cultured on permeable growth substrates in a two-compartment culture system were apically exposed for 24 hours to relatively low (0.2, 0.5, and 1.0 mmol/L) and high (5 and 10 mmol/L) oxalate concentrations, after which several cellular responses were studied, including monolayer morphology (confocal microscopy), transepithelial electrical resistances (TER), prostaglandin E(2) (PGE(2)) secretion, lactate dehydrogenase (LDH) release, DNA synthesis ([(3)H]-thymidine incorporation), total cell numbers, reactive oxygen species (H(2)O(2)) generation, apoptotic (annexin V and DNA fragmentation), and necrotic (propidium iodide influx) cell death.

RESULTS

Visible morphologic alterations were observed only at high oxalate concentrations. TER was concentration-dependently decreased by high, but not by low, oxalate. Elevated levels of PGE(2), LDH, and H(2)O(2) were measured in both cell types after exposure to high, but not to low oxalate. Exposure to high oxalate resulted in elevated levels of DNA synthesis with decreasing total cell numbers. High, but not low, oxalate induced necrotic cell death without signs of programmed cell death.

CONCLUSION

This study shows that oxalate is toxic to renal tubular cells, but only at supraphysiologic concentrations.

Hyperoxaluria-induced oxidative stress and antioxidants for renal protection

Renal cellular exposure to oxalate (Ox) and/or CaOx crystals leads to the production of reactive oxygen species (ROS), development of oxidative stress followed by injury and inflammation. Renal injury and inflammation appear to play a significant role in stone formation. ROS are produced from many sources and involve a variety of signaling pathways. Tissue culture and animal model studies show that treatments with anti-oxidants and free radical scavengers reduce Ox/CaOx crystal induced injuries. In addition, CaOx crystal deposition in kidneys is significantly reduced by treatments with antioxidants and free radical scavengers, indicating their efficacy. These results point towards a great potential for the therapeutic application of antioxidants and free radical scavengers to reduce stone recurrence particularly after shock wave lithotripsy, which is itself known to generate ROS and cause renal damage.

Oxalate toxicity in renal cells

Exposure to oxalate, a constituent of the most common form of kidney stones, generates toxic responses in renal epithelial cells, including altered membrane surface properties and cellular lipids, changes in gene expression, disruption of mitochondrial function, formation of reactive oxygen species and decreased cell viability. Oxalate exposure activates phospholipase A2 (PLA2), which increases two lipid signaling molecules, arachidonic acid and lysophosphatidylcholine (Lyso-PC). PLA2 inhibition blocks, whereas exogenous Lyso-PC or arachidonic acid reproduce many of the effects of oxalate on mitochondrial function, gene expression and cell viability, suggesting that PLA2 activation plays a role in mediating oxalate toxicity. Oxalate exposure also elicits potentially adaptive or protective changes that increase expression of proteins that may prevent crystal formation or attachment. Additional adaptive responses may facilitate removal and replacement of dead or damaged cells. The presence of different inflammatory cells and molecules in the kidneys of rats with hyperoxaluria and in stone patients suggests that inflammatory responses play roles in stone disease. Renal epithelial cells can synthesize a variety of cytokines, chemoattractants and other molecules with the potential to interface with inflammatory cells; moreover, oxalate exposure increases the synthesis of these molecules. The present studies demonstrate that oxalate exposure upregulates cyclooxygenase-2, which catalyzes the rate-limiting step in the synthesis of prostanoids, compounds derived from arachidonic acid that can modify crystal binding and may also influence inflammation. In addition, renal cell oxalate exposure promotes rapid degradation of IkappaBalpha, an endogenous inhibitor of the NF-kappaB transcription factor. A similar response is observed following renal cell exposure to lipopolysaccharide (LPS), a bacterial cell wall component that activates toll-like receptor 4 (TLR4). While TLRs are primarily associated with immune cells, they are also found on many other cell types, including renal epithelial cells, suggesting that TLR signaling could directly impact renal function. Prior exposure of renal epithelial cells to oxalate in vitro produces endotoxin tolerance, i.e. a loss of responsiveness to LPS and conversely, prior exposure to LPS elicits a similar heterologous desensitization to oxalate. Renal cell desensitization to oxalate stimulation may have profound effects on the outcome of renal stone disease by impairing protective responses.

NF-kappaB and chemokine-cytokine expression in renal tubulointerstitium in experimental hyperoxaluria. Role of the renin-angiotensin system

Recent evidence indicates that the renin-angiotensin system (RAS) seems to play a considerable role in the development of tubulointerstitial (TI) lesions caused by hyperoxaluria (Hox). The purpose of the present study was to evaluate the specific mechanism by which Hox involving RAS induces chemokine and cytokine expression and, therefore, renal TI damage in the ethylene-glycol (ETG) induced hyperoxaluric rat model. Sprague-Dawley rats, separated into five groups, received: G1 regular water, and G2, G3, G4 and G5 1% ETG (a precursor for oxalates) in their drinking water for 4 weeks. An angiotensin converting enzyme inhibitor, benazepril (BZ) 10 mg/kg/day, angiotensin II receptor antagonists, subtype 1 (AT1) losartan (LOS) 40 mg/kg/day and subtype 2 (AT2) PD 123,319 (PD) 10 mg/kg/day, were administered daily to G3, G4 and G5, respectively. At the end of the study, the inflammatory response to Hox was evaluated using anti-NF-kappaB (p50), anti-IL-6, anti-MCP-1; anti-RANTES and anti-ED1 (monocytes/macrophages) in each group. In spite of the same urine oxalate levels, rats belonging to the hyperoxaluric groups treated with either BZ or LOS showed significantly (P<0.01) less TI lesions together with a lower immunoexpression of inflammatory mediators when compared with untreated hyperoxaluric animals. NF-kappaB (p50) was increased in tubular cells in the ETG group (43.6+/-8.7 positive cells/mm(2)) and was significantly (P<0.01) reduced by LOS (11.2+/-4 positive cells/mm(2)) and even more by BZ (6.1+/-2.4 positive cells/mm(2)). There was a significant (P<0.01) correlation between NF-kappaB (p50) positive cells and ED1 cells in the ETG group (r=0.88) and in the ETG+LOS group (r=0.92). LOS showed better control on IL-6 and MCP-1 with respect to untreated rats, while BZ showed the best control on RANTES and ED1 cells in comparison with untreated animals. Renal function was significantly (P<0.01) better preserved in BZ and LOS treated groups compared to both untreated animals and rats with PD, as indicated by creatinine clearance values. These results suggest that Hox stimulates the NF-kappaB cascade and, therefore, induces the overexpression of inflammatory mediators like IL-6, MCP-1, and RANTES. This pathway seems to be mediated not only by AT1 but also by AT2 receptors of angiotensin II.

Citrate provides protection against oxalate and calcium oxalate crystal induced oxidative damage to renal epithelium

PURPOSE

Oxalate and calcium oxalate (CaOx) crystals are injurious to renal epithelial cells. The injury is caused by the production of reactive oxygen species (ROS). Citrate is a well-known inhibitor of CaOx crystallization and as such it is one of the major therapeutic agents prescribed. Since citrate increases cellular reduced nicotinamide adenine dinucleotide phosphate and glutathione (GSH), we hypothesized that exogenously administered citrate should act as an antioxidant and protect cells from oxalate induced injury.

MATERIALS AND METHODS

We exposed LLC-PK1 and MDCK cells to 500 microM/ml oxalate or 150 mug/cm calcium oxalate crystals for 30, 60 and 180 minutes with or without 3 mg/ml citrate in the medium. We determined cell viability by lactate dehydrogenase release and trypan blue exclusion, ROS involvement by changes in hydrogen peroxide and GSH, and lipid peroxidation by quantifying 8-isoprostane.

RESULTS

The presence of citrate was associated with significant decrease in lactate dehydrogenase release (p <0.001) and staining with trypan blue (p <0.05). In addition, there was a significant increase in GSH (p <0.005) and a decrease in the production of hydrogen peroxide (p <0.05) and 8-isoprostane (p <0.0005) secretion into the culture medium when citrate was present in the medium.

CONCLUSIONS

Citrate protects cells from oxalate and CaOx crystal induced injury by preventing lipid peroxidation through a decrease in ROS production. The results provide additional data for the beneficial role of citrate therapy for CaOx nephrolithiasis.

ACE inhibitor and angiotensin type I receptor antagonist in combination reduce renal damage in obese Zucker rats

BACKGROUND

In this study, we evaluated whether a combination of an angiotensin-converting enzyme (ACE) inhibitor, benazepril (B), with an angiotensin type I receptor antagonist (AT1RA), irbesartan (I), is as effective or more than drugs as monotherapy in controlling renal damage in obese Zucker rats (OZR), a model of metabolic syndrome.

METHODS

During six months, G1 (OZR receiving no treatment); G2 (OZR with B 10 mg/kg/day); G3 (OZR with I 50mg/kg/day); and G4 (OZR with B 5mg/kg/day + I 25 mg/kg/day). Kidneys were processed for light microscopy (LM) and immunohistochemistry, including antibodies against interstitial alpha-smooth-muscle-actin (alpha-SMA), plasminogen activator inhibitor-1 (PAI-1), transforming growth factor-beta(1)(TGF-beta 1), and collagen (COL) I, III, and IV.

RESULTS

All treated groups presented similar reduction in blood pressure compared with untreated OZR. However, animals from G4 (B + I) showed better control on proteinuria together with a higher creatinine clearance. Additionally, G4 showed a significant (P < 0.05) lower kidney weight; smaller glomerular area; lower glomerulosclerosis score; lower percentage of tubular atrophy, interstitial fibrosis, and interstitial alpha-SMA; lower tubular PAI-1 score; lower percentage of COL I, III, and IV in renal interstitium; and lower wall/lumen ratio in renal vessels, when compared with the other groups. OZR treated with B and/or I showed a better outcome (P < 0.01) in the carbohydrate and lipid metabolism in comparison with untreated OZR.

CONCLUSION

These results suggest that combined therapy using B and I is more effective than therapy with either drug at monotherapy for controlling renal damage in this animal model. In addition, data presented here reaffirm the benefit of interacting against renin-angiotensin-system (RAS) in the metabolic syndrome.