Hyperoxaluria-induced oxidative stress and antioxidants for renal protection

Do "inhibitors of crystallisation" play any role in the prevention of kidney stones? A critique

A critical examination of data in the literature and in as yet unpublished laboratory records on the possible role of so-called inhibitors of crystallisation in preventing the formation of calcium-containing kidney stones leads to the following conclusions. So-called inhibitors of spontaneous "self-nucleation" are unlikely to play any role in the initiation of the crystallisation of CaOx or CaP in urine because excessive urinary supersaturation of urine with respect to these salts dominates the onset of "self-nucleation" within the normal time frame of the transit of tubular fluid through the nephron (3-4 min). Inhibitors of the crystal growth of CaOx crystals may or may not play a significant role in the prevention of CaOx stone-formation since once again excessive supersaturation of urine can overwhelm any potential effect of the inhibitors on the growth process. However, they may play a role as inhibitors of crystal growth at lower levels of metastable supersaturation when the balance between supersaturation and inhibitors is more equal. Inhibitors of CaOx crystal aggregation may play a significant role in the prevention of stones, since they do not appear to be strongly affected by excessive supersaturation, either in vitro or in vivo. Inhibitors of CaOx crystal binding to renal tubular epithelium may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones in the renal tubules. Inhibitors of CaOx crystal binding to Randall's Plaques and Randall's Plugs may exist but further studies are necessary to elucidate their importance in reducing the risk of initiating stones on renal papillae. There may be an alternative explanation other than a deficiency in the excretion of inhibitors for the observations that there is a difference between CaOx crystal size and degree of aggregation in the fresh, warm urines of normal subjects compared those in urine from patients with recurrent CaOx stones. This difference may depend more on the site of "self-nucleation" of CaOx crystals in the renal tubule rather than on a deficiency in the excretion of so-called inhibitors of crystallisation by patients with CaOx stones. The claim that administration of potassium citrate, potassium magnesium citrate or magnesium hydroxide reduces the rate of stone recurrence may be due to the effect of these forms of medication on the supersaturation of urine with respect to CaOx and CaP rather than to any increase in "inhibitory activity" attributed to these forms of treatment. In summary, there is a competition between supersaturation and so-called inhibitors of crystallisation which ultimately determines the pattern of crystalluria in stone-formers and normals. If the supersaturation of urine with respect to CaOx reaches or exceeds the 3-4 min formation product of that salt, then it dominates the crystallisation process both in terms of "self-nucleation" and crystal growth but appears to have little or no effect on the degree of aggregation of the crystals produced. At supersaturation levels of urine with respect to CaOx well below the 3-4 min formation product of that salt, the influence of inhibitors increases and some may affect not only the degree of aggregation but also the crystal growth of any pre-formed crystals of CaOx at these lower levels of metastability.

Metformin Prevents Renal Stone Formation through an Antioxidant Mechanism In Vitro and In Vivo

Oxidative stress is a causal factor and key promoter of urolithiasis associated with renal tubular epithelium cell injury. The present study was designed to investigate the preventive effects of metformin on renal tubular cell injury induced by oxalate and stone formation in a hyperoxaluric rat model. MTT assays were carried out to determine the protection of metformin from oxalate-induced cytotoxicity. The intracellular superoxide dismutase (SOD) activities and malondialdehyde (MDA) levels were measured in vitro. Male Sprague-Dawley rats were divided into control group, ethylene glycol (EG) treated group, and EG + metformin treated group. Oxidative stress and crystal formations were evaluated in renal tissues after 8-week treatment. Metformin significantly inhibited the decrease of the viability in MDCK cells and HK-2 cells induced by oxalate. Besides, metformin markedly prevented the increased concentration of MDA and the decreased tendency of SOD in oxalate-induced MDCK cells and HK-2 cells. In vivo, the increased MDA levels and the reduction of SOD activity were detected in the EG treated group compared with controls, while these parameters reversed in the EG + metformin treated group. Kidney crystal formation in the EG + metformin treated group was decreased significantly compared with the EG treated group. Metformin suppressed urinary crystal deposit formation through renal tubular cell protection and antioxidative effects.

Urinary MCP-1、HMGB1 increased in calcium nephrolithiasis patients and the influence of hypercalciuria on the production of the two cytokines

The study aims to observe the urinary excretion of monocyte chemoattractant-1 (MCP-1) and high-mobility group box 1 (HMGB1) in patients with calcium nephrolithiasis and to determine the influence of hypercalciuria on the production of the two cytokines. 81 cases of patients with calcium nephrolithiasis (group CN) and 30 healthy controls (group C) were involved in this study. To observe the influence of urinary calcium on the excretion of those cytokines, the patients were subdivided according to their 24-h urinary calcium level: ≥4 mg/kg/day (group H) and <4 mg/kg/day (group N). MCP-1 and HMGB1 in urina sanguinis were determined for all subjects. In addition, in vitro study was done to determine the production of the two cytokines and index of apoptosis and oxidative injuries in human kidney epithelial cells (HK-2) exposed to three high levels of calcium. Data showed that both urinary MCP-1 and HMGB1 in group CN were higher than that of group C. When the patients were subdivided, comparisons among the three groups showed that both MCP-1 and HMGB1 in group H and group N were higher than group C, but there was no significant statistical difference between the two stone groups. In vitro study, the apoptosis rate of cells, the lactate dehydrogenase activities, the hydrogen peroxide, and 8-isoprostane concentrations in the medium all increased in accordance with the increased concentration of calcium supplemented. Compared with the control, mRNA expressions of MCP-1 and HMGB1 in cells and the protein concentrations of the two cytokines in the medium of calcium-supplemented groups increased significantly. Results showed that urinary MCP-1 and HMGB1 increased in calcium nephrolithiasis patients and hypercalciuria might affect the identical pathways (through the reactive oxygen species) with other factors in stimulating the production of MCP-1 and HMGB1 in vivo.

Reinjury risk of nano-calcium oxalate monohydrate and calcium oxalate dihydrate crystals on injured renal epithelial cells: aggravation of crystal adhesion and aggregation

BACKGROUND

Renal epithelial cell injury facilitates crystal adhesion to cell surface and serves as a key step in renal stone formation. However, the effects of cell injury on the adhesion of nano-calcium oxalate crystals and the nano-crystal-induced reinjury risk of injured cells remain unclear.

METHODS

African green monkey renal epithelial (Vero) cells were injured with H2O2 to establish a cell injury model. Cell viability, superoxide dismutase (SOD) activity, malonaldehyde (MDA) content, propidium iodide staining, hematoxylin-eosin staining, reactive oxygen species production, and mitochondrial membrane potential (Δψm) were determined to examine cell injury during adhesion. Changes in the surface structure of H2O2-injured cells were assessed through atomic force microscopy. The altered expression of hyaluronan during adhesion was examined through laser scanning confocal microscopy. The adhesion of nano-calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) crystals to Vero cells was observed through scanning electron microscopy. Nano-COM and COD binding was quantitatively determined through inductively coupled plasma emission spectrometry.

RESULTS

The expression of hyaluronan on the cell surface was increased during wound healing because of Vero cell injury. The structure and function of the cell membrane were also altered by cell injury; thus, nano-crystal adhesion occurred. The ability of nano-COM to adhere to the injured Vero cells was higher than that of nano-COD crystals. The cell viability, SOD activity, and Δψm decreased when nano-crystals attached to the cell surface. By contrast, the MDA content, reactive oxygen species production, and cell death rate increased.

CONCLUSION

Cell injury contributes to crystal adhesion to Vero cell surface. The attached nano-COM and COD crystals can aggravate Vero cell injury. As a consequence, crystal adhesion and aggregation are enhanced. These findings provide further insights into kidney stone formation.

Anti-inflammatory effects of royal jelly on ethylene glycol induced renal inflammation in rats

Objective:

In this study, anti-inflammatory effects of Royal Jelly were investigated by inducing renal inflammation in rats with the use of ethylene glycol. For this purpose, the calcium oxalate urolithiasis model was obtained by feeding rats with ethylene glycol in drinking water.

Materials and Methods:

The rats were divided in five study groups. The 1^st group was determined as the control group. The rats in the 2^nd group received ethylene glycol (1%) in drinking water. The rats in the 3^rd group were daily fed with Royal Jelly by using oral gavage. The 4^th group was determined as the preventive group and the rats were fed with ethylene glycol (1%) in drinking water while receiving Royal Jelly via oral gavage. The 5^th group was determined as the therapeutic group and received ethylene glycol in drinking water during the first 2 weeks of the study and Royal Jelly via oral gavage during the last 2 weeks of the study.

Results:

At the end of the study, proinflammatory/anti-inflammatory cytokines, TNF-α, IL-1β and IL-18 levels in blood and renal tissue samples from the rats used in the application were measured.

Conclusion:

The results have shown that ethylene glycol does induce inflammation and renal damage. This can cause the formation of reactive oxygen species. Royal Jelly is also considered to have anti-inflammatory effects due to its possible antiradical and antioxidative effects. It can have positive effects on both the prevention of urolithiasis and possible inflammation during the existing urolithiasis and support the medical treatment.

Diuretic and antiurolithiatic activities of an ethanolic extract of Acorus calamus L. rhizome in experimental animal models

Acorus calamus is a plant commonly used as a traditional herbal medicine and possesses the wide range of pharmacological applications. The present study investigated the diuretic and antiurolithiatic activities of an ethanolic extract of Acorus calamus L. (Family: Araceae) rhizome (EEAC). For diuretic activity, three doses of EEAC (250, 500 and 750 mg/kg) were studied, and measurement of the urinary volume and electrolytes (Na⁺ and K⁺) concentration were taken as evaluation parameters. On the other hand, ethylene glycol induced urolithiasis (0.75% v/v in drinking water for 28 days) was used to study the antiurolithiatic effect of EEAC at the oral dose of 750 mg/kg in male Wistar albino rats. CYSTONE (750 mg/kg, p.o.) was used as a standard reference drug in the present study. After completion of the 28-days respective treatments, the level of various urolithiatic promoters in the biological samples (urine, serum and kidney homogenate) and renal function were used as criteria for assessing the antiurolithiatic effect of EEAC. Results indicate that, the EEAC (750 mg/kg, p.o.) produced significant increase in urine volume (p < 0.001) and urinary excretion of Na⁺ and K⁺ electrolytes (p < 0.05) in a pattern comparable to that of furosemide. In ethylene glycol induced urolithiatic model, EEAC significantly (p < 0.05) decreased excretion and deposition of various urolithiatic promoters as compared to urolithiatic control in a pattern comparable to that of CYSTONE. The EEAC supplementation also prevents the impairment of renal functions. The antiurolithiatic mechanism is mediated possibly through diuretic and nephroprotective actions of the active compounds of rhizomes.

Role of mitochondria and NADPH oxidase derived reactive oxygen species in hyperoxaluria induced nephrolithiasis: therapeutic intervention with combinatorial therapy of N-acetyl cysteine and Apocynin

The interactions between the main cellular sources of ROS, such as mitochondria and NADPH oxidase, are known to play an imperative role in the pathogenesis of hyperoxaluria-induced nephrolithiasis. The present study was designed to investigate the protective effect of a combinatorial therapy based on the attenuation of oxidative stress with antioxidant (N-acetyl cysteine), and NADPH oxidase inhibitor (apocynin), that might be required to effectively eliminate hyperoxaluric manifestations. Hyperoxaluria was induced in male Wistar rats by administering 0.4% ethylene glycol with 1% ammonium chloride in drinking water for 9 days. Hyperoxaluria accentuated renal oxidative stress in terms of increased ROS production and lipid peroxidation. Mitochondrial dysfunction, a central deleterious event in renal stone crystallization, was evident by decreased activities of electron transport chain complex I, II and IV, augmented mitochondrial ROS, reduced GSH/GSSG ratio, which resulted in the mitochondrial permeability transition pore (mPTP) opening as indicated by increased mitochondrial swelling in hyperoxaluric rats. Furthermore, NADPH oxidase activity was significantly increased, with raised expression of NOX1, NOX2, NOX4, p38MAPK and MnSOD, in the renal tissue of hyperoxaluric rats compared to control. However, combinatorial therapy with N-acetyl cysteine (50mg/kg/day) and apocynin (200mg/kg/day), intraperitoneally, significantly improved renal functions in hyperoxaluric rats and considerably ameliorated mitochondrial dysfunction. NAC with apocynin was also found to be effective in reducing the redundant activity of NADPH oxidase in renal tissue of hyperoxaluric rats. Hence, our investigation provides novel mechanistic insights that combinatorial approaches using targeted modulators of ROS offer therapeutic benefits in hyperoxaluria-induced nephrolithiasis.

Oligomeric proanthocyanidins protect against HK-2 cell injury induced by oxalate and calcium oxalate monohydrate crystals

The purpose of the study was to test whether the antioxidants oligomeric proanthocyanidins (OPCs) could provide protection against oxalate and calcium oxalate monohydrate crystals (COM) toxicity in HK-2 cells. Four groups were chosen for the study: negative control group, positive control group (COM + oxalate), OPCs group (OPCs + COM + oxalate), Vit E group (Vit E + COM + oxalate). HK-2 cells were exposed for 4, 8, 12 and 24 h. The activity of HK-2 cell was assessed by MTT. Cellular injury was assessed by activity of Na(+)/K(+) ATP enzyme. Peroxidation level was assessed by malondialdehyde (MDA) content in medium and activity of superoxide dismutase (SOD). Morphological changes of HK-2 cell after exposed for 4 and 12 h in each group were observed under Transmission electron microscope (TEM). The effects of OPCs and VitE on oxalate- and COM-exposed cells were tested. After exposed to oxalate and COM crystals, activity of cells, Na(+)/K(+) ATP enzyme and SOD enzyme showed a significant reduction, and MDA content in medium was significantly increased. OPCs group: the addition of OPCs significantly increased activity of cell, SOD and Na(+)/K(+) ATP enzyme while MDA content was significantly decreased compared with the positive control group. VitE group: compared with the positive control group, activity of HK-2 cell, Na(+)/K(+) ATP enzyme was not significantly changed while SOD activity was restored, and MDA content was significantly decreased after the addition of Vit E. Morphological structure of HK-2 cell was extremely changed as observed under TEM after exposure to high level of COM crystals and oxalate. After the addition of OPCs or Vit E, amounts of cells with vacuoles formed in cytoplasms, karyotheca dissolved and nucleolus disappeared were less than in positive control group. The morphological structure changing in OPCs group was slighter than that in Vit E group. OPCs and vitamin E administration may prevent oxalate- and COM-mediated peroxidative injury, restoring intracellular antioxidant enzyme activity. The protection rendered by OPCs was greater than that of vitamin E.

Protective effects of N-acetylcysteine against hyperoxaluria induced mitochondrial dysfunction in male wistar rats

The purpose of the present study was to evaluate the nephro-protective potential of N-acetylcysteine against hyperoxaluria-induced renal mitochondrial dysfunction in rats. Nine days dosing of 0.4 % ethylene glycol +1 % ammonium chloride, developed hyperoxaluria in male wistar rats which resulted in renal injury and dysfunction as supported by increased level of urinary lactate dehydrogenase, calcium, and decreased creatinine clearance. Mitochondrial oxidative strain in hyperoxaluric animals was evident by decreased levels of superoxide dismutase, glutathione peroxidase, glutathione reductase, reduced glutathione, and an increased lipid peroxidation. Declined activities of respiratory chain enzymes and tricarboxylic acid cycle enzymes showed mitochondrial dysfunction in hyperoxaluric animals. N-acetylcysteine (50 mg/kg, i.p.), by virtue of its -SH reviving power, was able to increase the glutathione levels and thus decrease the oxidative stress in renal mitochondria. Hence, mitochondrial damage is, evidently, an essential event in ethylene glycol-induced hyperoxaluria and N-acetylcysteine presented itself as a safe and effective remedy in combating nephrolithiasis.

Size-dependent toxicity and interactions of calcium oxalate dihydrate crystals on Vero renal epithelial cells

Urinary crystals in normal and kidney stone patients often have varying sizes; the interaction between renal epithelial cells and COD crystals generated in the tubular fluid could play an initiating role in the pathophysiology of calcium oxalate nephrolithiasis. This study aims to compare the cytotoxicity of micro/nano-calcium oxalate dihydrate (COD) crystals (50 nm, 100 nm, 600 nm, 3 μm, and 10 μm) toward African green monkey renal epithelial (Vero) cells to reveal the mechanism of kidney stone formation at the molecular and cellular levels.

METHODS

Vero cells were exposed to COD crystals of varying sizes at a concentration of 200 μg mL^-1 for 6 h. The effects of COD crystals on Vero cell viability, apoptosis rate, and cellular biochemical parameters [lactate dehydrogenase (LDH), superoxide dismutase (SOD), reactive oxygen species (ROS), hyaluronic acid (HA), osteopontin (OPN), and mitochondrial membrane potential (Δψ_m)] were determined using biochemical and morphological analyses.

RESULTS

Vero cell viability and apoptotic rate were closely associated with the size of COD crystals; lower cell viability and higher apoptosis rate were observed in cells exposed to smaller COD crystal size. The expression of SOD, ROS, HA and OPN also changed in a size-dependent manner after exposure to the five different sizes of COD crystals. The area ratio of the (100) face with a high density of Ca²⁺ ions to the total surface area was also found to influence the severity of cell injury. Cell injury induced by COD crystals was mainly caused by excessive expression of intracellular ROS and reduction of free-radical scavenger SOD. Moreover, binding of large crystals on the cell membrane surface takes more time to cause cell injury than internalized small-sized crystals. The cell death rate was found to be positively correlated with the amount of internalized COD crystals.

CONCLUSIONS

although the COD toxicity is often disregarded, the size-dependent cytotoxicity of COD crystals toward Vero cells is demonstrated in this study.

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.

Activation of the NLRP3 inflammasome in association with calcium oxalate crystal induced reactive oxygen species in kidneys

PURPOSE

We investigated the association of hyperoxaluria and calcium oxalate crystal induced production of reactive oxygen species with activation of the NLRP3 inflammasome.

MATERIALS AND METHODS

Eight-week-old male rats were given hydroxy-L-proline to induce hyperoxaluria. A group of rats on the hydroxy-L-proline diet also received apocynin, an antioxidant and nonspecific inhibitor of NADPH oxidase. At 28 days the rats were sacrificed and the kidneys were extracted. Microarray analysis was done with the BeadArray™ Reader. Gene ontology and gene pathway analyses were done with the DAVID (Database for Annotation, Visualization of Integrated Discovery) enrichment analysis tool. Quantitative real-time polymerase chain reaction and immunohistochemical staining were performed to confirm microarray results.

RESULTS

Analysis of 22,226 genes revealed that 20 and 24 pathways were highly significant in the cortex and medulla, respectively. In the cortex extracellular matrix-receptor interaction, complement and coagulation cascades, focal adhesion and hypertrophic cardiomyopathy were the most significant pathways. In the medulla complement and coagulation cascades, extracellular matrix-receptor interaction and dilated cardiomyopathy were the major pathways. Genes encoding for PYCARD (ASC), TXNIP, NLRP3, caspase-1, and IL-1β and 18 were significantly up-regulated in hydroxy-L-proline fed rats but in the group that received apocynin these genes were down-regulated in the cortex and medulla. Results were verified by quantitative real-time polymerase chain reaction with SYBR® Green assay and immunohistochemical staining.

CONCLUSIONS

Results indicate a role for reactive oxygen species in activation of the NLRP3 inflammasome via TXNIP. This led to a robust inflammatory response in the kidneys of rats with hyperoxaluria and calcium oxalate nephrolithiasis.

Protective effects of methanolic extract form fruits of Lycium ruthenicum Murr on 2,2'-azobis (2-amidinopropane) dihydrochloride-induced oxidative stress in LLC-PK1 cells

Background:

Fruits of Lycium ruthenicum Murr is a health food and also used as a folk to treat heart disease, abnormal menstruation and menopause in Tibetan, China. However; whether L. ruthenicum Murr fruits methanolic extracts (LFME) protect LLC-PK1 porcine renal tubules cells from AAPH-induced oxidative damage has not been investigated.

Objective:

To investigate the protective effects of L. ruthenicum Murr fruits methanolic extracts (LFME) against 2, 2’- azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidative damage in renal proximal tubule LLC-PK1 cells.

Materials and Methods:

LLC-PK1 cells were co-incubated with AAPH (1mM) and different concentrations of LFMW together for 24 h. Cell viability was determined by MTT assay. Total intercellular reactive oxygen species (ROS) levels and lipid peroxidation were measured using a fluorescent probe 2’, 7’-dichlorfluorescein-diacetate (DCFH-DA) and the TBA reactive substance (TBARS) assay, respectively. The endogenous antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-px) and intercellular glutathione (GSH) levels were determined using commercial assay kits according to the manufacturer's instructions.

Results:

LFME did not show a significant cytotoxic effect and increased the viability of LLC-PK1 cells in a concentration-dependent manner. LFME also decreased the total intercellular levels of ROS, reduced lipid peroxidation and increased the GSH levels as well as the activities of endogenous antioxidant enzymes to protect LLC-PK1 cells against AAPH-induced oxidative damage.

Conclusion:

The results from the present study indicated that LFME is an effective ROS scavenger to protect LLC-PK1 cells against AAPH-induced oxidative damage through decreasing ROS generation, reducing lipid peroxidation and up-regulation of endogenous GSH levels and antioxidant enzymes.

Resveratrol inhibits the intracellular calcium increase and angiotensin/endothelin system activation induced by soluble uric acid in mesangial cells

Resveratrol (Resv) is natural polyphenol found in grapes. This study evaluated the protective effect of Resv against the effects of uric acid (UA) in immortalized human mesangial cells (ihMCs). ihMCs were preincubated with Resv (12.5 µM) for 1 h and treated with UA (10 mg/dL) for 6 or 12 h. The intracellular calcium concentration [Ca²⁺]i was quantified by fluorescence using flow cytometry. Angiotensinogen (AGT) and pre-pro endothelin-1 (ppET-1) mRNA were assayed by quantitative real-time RT-PCR. Angiotensin II (AII) and endothelin-1 (ET-1) were assayed by ELISA. UA significantly increased [Ca²⁺]i. Pre-incubation with Resv significantly reduced the change in [Ca²⁺]i induced by UA. Incubation with UA for 6 or 12 h also increased AGT mRNA expression and AII protein synthesis. Resv blunted these increases in AGT mRNA expression and AII protein. Incubation with UA in the ihMCs increased ppET-1 expression and ET-1 protein synthesis at 6 and 12 h. When ihMCs were pre-incubated with Resv, UA had a significantly diminished effect on ppET-1 mRNA expression and ET-1 protein synthesis at 6 and 12 h, respectively. Our results suggested that UA triggers reactions including AII and ET-1 production in mesangial cells. The renin-angiotensin system may contribute to the pathogenesis of renal function and chronic kidney disease. Resv can minimize the impact of UA on AII, ET-1 and the increase of [Ca²⁺]i in mesangial cells, suggesting that, at least in part, Resv can prevent the effects of soluble UA in mesangial cells.

The selective NADPH oxidase inhibitor apocynin has potential prophylactic effects on melamine-related nephrolithiasis in vitro and in vivo

The objective of this study is to examine the effects of apocynin on melamine-cyanuric acid mixture (MCM)-induced nephrolithiasis in vitro and in vivo. For the in vitro experiments, changes in oxidative stress (OS) markers and the expression of osteopontin (OPN) and phospho-p38 (p-p38) were measured to assess the effects of apocynin treatment after MCM-induced crystallization in HK-2 cells, a human renal epithelial-derived cell line. For in vivo studies, the potential effects of apocynin in preventing and treating nephrolithiasis were analyzed with a MCM-induced nephrolithiasis rat model, and urea and creatinine levels were measured. Urinary 8-IP (a product of lipid peroxidation) and malondialdehyde levels and superoxide dismutase activity were assessed in the kidneys as markers of renal OS. The kidneys were removed, weighed, and subjected to histopathological examination. The urolithiasis-associated proteins p-p38 and OPN were evaluated by immunohistochemistry and Western blotting. Apocynin treatment prevented the MCM-induced changes in OS and in OPN and p-p38 expression in HK-2 cells. For in vivo experiments, the expression of OS markers, renal OPN, and p-p38 increased after MCM administration, and these increases were diminished by apocynin. In addition, apocynin prevented MCM-induced renal crystallization. Moreover, prophylactic apocynin treatment reduced MCM-induced nephrotoxicity. After therapeutic apocynin treatment in nephrolithic rats, OS decreased, but the other indicators did not improve significantly. Prophylactic apocynin administration reduced renal melamine-related-crystal deposition, potentially by modulating OS and thereby decreasing p-p38 and OPN expression.

A polyherbal formulation attenuates hyperoxaluria-induced oxidative stress and prevents subsequent deposition of calcium oxalate crystals and renal cell injury in rat kidneys

INTRODUCTION

Cystone is an approved Ayurvedic polyherbal proprietary medicine used in India for various urinary disorders, including urolithiasis.

AIM

To evaluate the protective effect of Cystone against hyperoxaluria-induced oxidative stress and calcium oxalate crystal deposition in urolithiasis.

METHODS

Ethylene glycol (EG) (0.75%, V/V) in drinking water was given to rats for 28 days to induce urolithiasis with simultaneous treatment of Cystone (500 and 750 mg/kg body weight), and various urinary risk factors of urolithiasis and antioxidant markers were assessed.

RESULTS

EG treatment lead to increased urine volume and lowered urinary pH, along with increased urinary excretion of oxalate, calcium and phosphate in untreated animals. These changes caused extensive calcium oxalate crystal deposition, increased lipid peroxidation and decreased activity of antioxidant enzymes (SOD, catalase and GPx) in the kidney of untreated rats. Cystone prevented these hyperoxaluric manifestations and inhibited calcium oxalate crystal deposition in treated rats at both doses.

CONCLUSIONS

Cystone therapy provides protection against hyperoxaluria-induced oxidative stress and calcium oxalate crystal deposition by improving renal tissue antioxidant status and diuresis.

Fad diets and their effect on urinary stone formation

The influence of unhealthy dietary habits on urinary stone formation has been widely recognized in literature. Dietary advice is indeed the cornerstone prescription for prevention of nephrolithiasis as well. However, only a small amount of medical literature has addressed the influence of popular or fad diets, often self-prescribed for the management of obesity and overweight or for cultural beliefs, on the risk of kidney stones. Thereby in this paper we analyze the current knowledge on the effects of some popular diets on overall lithogenic risk. High-protein diets, like Dukan diet, raise some concerns, since animal proteins are able to increase urinary calcium and to decrease urinary citrate excretion, thus leading to a high overall lithogenic risk. Low-carbohydrate diets, like Atkins diet or zone diet, may have a protective role against kidney stone formation, but there are also evidences stating that this dietary approach may rise calciuria and decrease citraturia, since it is generally associated to a relatively high intake of animal proteins. Vegan diet can be harmful for urinary stone disease, especially for the risk of hyperuricemia and micronutrient deficiencies, even if only few studies have addressed this specific matter. On the other side, the benefits of a lacto-ovo-vegetarian diet on kidney stone prevention have been largely emphasized, provided that the intake of calcium and oxalate is balanced. Traditional Mediterranean diet should exert a protective effect on nephrolithiasis as well, even if specific studies have not been carried out yet. High phytate and antioxidant content of this diet have however demonstrated to be beneficial in preventing the formation of new or recurrent calculi. Anyway, at the current state of knowledge, the most effective dietary approach to prevent kidney stone disease is a mild animal protein restriction, a balanced intake of carbohydrates and fats and a high intake of fruit and vegetables. Other fundamental aspects, which are often neglected in fad diets, are a normal intake of milk and dairy products and salt restriction. All these nutritional aspects should be greatly taken into account when patients who are willing to undergo fad or commercial diets ask for dietary advice.

Is oxidative stress related to childhood urolithiasis?

BACKGROUND

Urolithiasis is a common condition in pediatric populations in Turkey. The role of oxidative stress in renal stone formation in pediatric patients has not been reported to date. The aim of this study was to assess oxidative stress in childhood urolithiasis.

METHODS

Seventy-four children diagnosed with urolithiasis and 72 healthy control subjects were enrolled in the study. Kidney stone formers were evaluated by analysis of metabolic conditions related to urolithiasis, such as hypercalciuria, hyperoxaluria, hypocitraturia and hyperuricosuria. Urine total antioxidant status (TAS), and total oxidant status (TOS) were measured, and oxidative stress index (OSI) was calculated as an indicator of the degree of oxidative stress.

RESULTS

Among the stone formers, metabolic analyses revealed that 30 % had hypercalciuria, 45 % had hypocitraturia, 6 % had hyperoxaluria and 40 % had hyperuricosuria. Elevated levels of the renal tubular damage marker urinary N-acetyl- beta-D-glucosaminidase (NAG) was elevated in 25 % of the patient group, but microalbuminuria was not detected. Total oxidant status and total antioxidant status were significantly higher in stone formers than in the controls (p = 0.023 and 0.004, respectively). In addition, urinary NAG was significantly correlated with TOS (r = 0.427, p = 0.019).

CONCLUSIONS

The results of this study show that oxidative stress may play an important role in the pathogenesis of pediatric stone formers.

Anti-nephrolithic potential of resveratrol via inhibition of ROS, MCP-1, hyaluronan and osteopontin in vitro and in vivo

BACKGROUND

Though resveratrol is known to have anti-cancer, anti-diabetic, anti-oxidant and anti-inflammatory activities, the inhibitory mechanism of resveratrol in kidney stone formation has not been elucidated so far.

METHOD

ELISA, flow cytometry, RT-PCR, and western blotting were performed. Human renal epithelial cells (HRCs) and rats with ethylene glycol (EG)-induced kidney stones were used.

RESULTS

A wound healing assay revealed that resveratrol significantly inhibited the oxalate-mediated migration of HRCs, considering oxalate mediates kidney stone formation. Also, resveratrol suppressed the mRNA expression of nicotinamide adenine dinucleotide phosphate hydrogen (NADPH) oxidase subunits such as p22(phox) and p47(phox), monocyte chemoattractant protein 1 (MCP-1) and osteopontin (OPN) in oxalate-treated HRCs. Furthermore, western blotting showed that resveratrol downregulated the expression of MCP-1-related proteins including transforming growth factor(TGF-β1), TGFR-I or II and hyaluronan in oxalate-treated HRCs. Consistently, resveratrol reduced oxalate-mediated production of reactive oxygen species (ROS) and malondialdehyde (MDA) in oxalate-treated HRCs, while the activities of anti-oxidant enzymes such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were enhanced by resveratrol in HRCs and EG-treated kidneys of rats. Consistently, resveratrol significantly reduced the number of urine calcium oxalate crystals and serum MDA, and attenuated the expression of OPN and hyaluroran in EG-treated rats.

CONCLUSIONS

Our findings suggest that resveratrol exerts anti-nephrolithic potential via inhibition of ROS, MCP-1 hyaluronan and OPN signaling.

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.

Antioxidative effects of fermented sesame sauce against hydrogen peroxide-induced oxidative damage in LLC-PK1 porcine renal tubule cells

BACKGROUND/OBJECTIVES

This study was performed to investigate the in vitro antioxidant and cytoprotective effects of fermented sesame sauce (FSeS) against hydrogen peroxide (H2O2)-induced oxidative damage in renal proximal tubule LLC-PK1 cells.

MATERIALS/METHODS

1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl radical ((•)OH), and H2O2 scavenging assay was used to evaluate the in vitro antioxidant activity of FSeS. To investigate the cytoprotective effect of FSeS against H2O2-induced oxidative damage in LLC-PK1 cells, the cellular levels of reactive oxygen species (ROS), lipid peroxidation, and endogenous antioxidant enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-px) were measured.

RESULTS

The ability of FSeS to scavenge DPPH, (•)OH and H2O2 was greater than that of FSS and AHSS. FSeS also significantly inhibited H2O2-induced (500 µM) oxidative damage in the LLC-PK1 cells compared to FSS and AHSS (P < 0.05). Following treatment with 100 µg/mL of FSeS and FSS to prevent H2O2-induced oxidation, cell viability increased from 56.7% (control) to 83.7% and 75.6%, respectively. However, AHSS was not able to reduce H2O2-induced cell damage (viability of the AHSS-treated cells was 54.6%). FSeS more effectively suppressed H2O2-induced ROS generation and lipid peroxidation compared to FSS and AHSS (P < 0.05). Compared to the other sauces, FSeS also significantly increased cellular CAT, SOD, and GSH-px activities and mRNA expression (P < 0.05).

CONCULUSIONS

These results from the present study suggest that FSeS is an effective radical scavenger and protects against H2O2-induced oxidative damage in LLC-PK1 cells by reducing ROS levels, inhibiting lipid peroxidation, and stimulating antioxidant enzyme activity.

Regulation of macromolecular modulators of urinary stone formation by reactive oxygen species: transcriptional study in an animal model of hyperoxaluria

We used an unbiased approach of gene expression profiling to determine differential gene expression of all the macromolecular modulators (MMs) considered to be involved in stone formation, in hyperoxaluric rats, with and without treatment with the NADPH oxidase inhibitor apocynin. Male rats were fed rat chow or chow supplemented with 5% wt/wt hydroxy-l-proline (HLP) with or without apocynin-supplemented water. After 28 days, rats were euthanized and their kidneys explanted. Total RNA was isolated and microarray analysis was conducted using the Illumina bead array reader. Gene ontology analysis and the pathway analyses of the genes were done using Database for Annotation, Visualization of Integrated Discovery enrichment analysis tool. Quantitative RT-PCR of selected genes was carried out to verify the microarray results. Expression of selected gene products was confirmed using immunohistochemistry. Administration of HLP led to crystal deposition. Genes encoding for fibronectin, CD 44, fetuin B, osteopontin, and matrix-gla protein were upregulated while those encoding for heavy chains of inter-alpha-inhibitor 1, 3, and 4, calgranulin B, prothrombin, and Tamm-Horsfall protein were downregulated. HLP-fed rats receiving apocynin had a significant reversal in gene expression profiles: those that were upregulated came down while those that were downregulated stepped up. Apocynin treatment resulted in near complete absence of crystals. Clearly, there are two types of MMs; one is downregulated while the other is upregulated during hyperoxaluria and crystal deposition. Apparently gene and protein expressions of known macromolecular modulators of CaOx crystallization are likely regulated by ROS produced in part through the activation of NADPH oxidase.

Exposure of Madin-Darby canine kidney (MDCK) cells to oxalate and calcium oxalate crystals activates nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase

OBJECTIVE

To investigate nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase activity in Madin-Darby canine kidney (MDCK) cells and the production of reactive oxygen species on exposure to oxalate (Ox) or calcium oxalate (CaOx) crystals.

METHODS

Monolayers of confluent Madin-Darby canine kidney cells were exposed to 100, 300, 500 μmol, 1 mmol Ox or 33, 66, 132 μg/cm(2) CaOx crystals for 15 minutes, 30 minutes, 1 hour, 2 hours, or 3 hours. After specified periods of exposure to Ox and CaOx crystals, lactate dehydrogenase release, trypan blue exclusion, activation of NADPH oxidase, and superoxide production were determined using standard procedures. The production of Nox4, a membrane associated subunit of the NADPH oxidase enzyme, was determined by western blot analysis.

RESULTS

Exposure to Ox and CaOx crystals leads to time- and concentration-dependent activation of NADPH oxidase. Western blot analysis showed an increase in the production of Nox4. The production of superoxide also changed in a time- and concentration-dependent manner, with maximum increases after 30-minute exposure to the highest concentrations of Ox and CaOx crystals. Longer exposures did not change the results or resulted in decreased activities. Exposure to higher concentrations also caused increased lactate dehydrogenase release and trypan blue exclusion indicating cell damage.

CONCLUSION

Results indicate that cells of the distal tubular origin are equipped with NADPH oxidase that is activated by exposures to Ox and CaOx crystals. Higher concentrations of both lead to cell injury, most probably through the increased reactive oxygen species production by the exposed cells.

Renal function in a rat model of neurogenic bladder, effect of statins and phosphodiesterase-5 inhibitors

PURPOSE

Neurogenic bladder is a common complication of several central nervous system injuries. Statins and phosphodiesterase-5 (PDE-5) inhibitors are reportedly beneficial in neural injuries and urinary system dysfunction. The effect of simvastatin, sildenafil and tadalafil on several renal function indices of an animal model of neurogenic bladder was investigated.

METHODS

Forty male rats were assessed in five equal groups. Dura mater and the cord were injured with an aneurysmal clamp at the level of T9-T10 in all rats except in sham group. The sham and control groups (treated by normal saline), simvastatin (4 mg/kg), sildenafil (5 mg/kg), and tadalafil (2 mg/kg) groups received treatment (i.p.) for seven consecutive days following injury. Renal system and motor functions were assessed at day 28 following injury. Data were analyzed by analysis of variance followed by the Student-Newman-Keuls post hoc test.

RESULTS

Simvastatin improved both the renal and the motor function compared with the control group. However, sildenafil and tadalafil could only improve the motor function but could not make any significant differences in renal indices in comparison with the control group.

CONCLUSION

Statins can effectively improve the motor and renal functions in a condition of renal dysfunction in a rat model of neurogenic bladder. PDE-5 inhibitors could help to improve motor function, but are not helpful in renal function, at least in short time.

NADPH oxidase as a therapeutic target for oxalate induced injury in kidneys

A major role of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase family of enzymes is to catalyze the production of superoxides and other reactive oxygen species (ROS). These ROS, in turn, play a key role as messengers in cell signal transduction and cell cycling, but when they are produced in excess they can lead to oxidative stress (OS). Oxidative stress in the kidneys is now considered a major cause of renal injury and inflammation, giving rise to a variety of pathological disorders. In this review, we discuss the putative role of oxalate in producing oxidative stress via the production of reactive oxygen species by isoforms of NADPH oxidases expressed in different cellular locations of the kidneys. Most renal cells produce ROS, and recent data indicate a direct correlation between upregulated gene expressions of NADPH oxidase, ROS, and inflammation. Renal tissue expression of multiple NADPH oxidase isoforms most likely will impact the future use of different antioxidants and NADPH oxidase inhibitors to minimize OS and renal tissue injury in hyperoxaluria-induced kidney stone disease.

Evaluation of anti-urolithiatic activity of Pashanabhedadi Ghrita against experimentally induced renal calculi in rats

Population in an industrialized world is afflicted by urinary stone disease. Kidney stones are common in all kinds of urolithiasis. One distinguished formulation mentioned by Sushruta for management of Ashmari (urolithiasis) is Pashanabhedadi Ghrita (PBG), which is in clinical practice since centuries. Validation of drug is the requirement of time through the experimental study. In this study, trial of PBG has been made against ammonium oxalate rich diet and gentamicin injection induced renal calculi in albino rats. The calculi were induced by gentamicin injection and ammonium oxalate rich diet. Test drug was administered concomitantly in the dose of 900 mg/kg for 15 consecutive days. Rats were sacrificed on the 16^th day. Parameters like kidney weight, serum biochemical, kidney tissue and histopathology of kidney were studied. Concomitant treatment of PBG attenuates blood biochemical parameters non-significantly, where as it significantly attenuated lipid peroxidation and enhanced glutathione and glutathione peroxidase activities. It also decreased crystal deposition markedly into the renal tubules in number as well as size and prevented damage to the renal tubules. The findings showed that PBG is having significant anti-urolithiatic activities against ammonium oxalate rich diet plus gentamicine injection induced urolithiasis in rats.

Cigarette smoking and nephrolitiasis in adult individuals

Background

Nephrolithiasis is a widespread multifactorial disorder. Constitutional, environmental and genetic factors play a role in stone formation. Although important advances have been made in understanding the pathophysiology of stone formation, none of the many theories have given a satisfactory explanation of this process.

Objectives

The objective of study was to evaluate the probable relationship between cigarette smoking and nephrolitiasis in adult men.

Patients and Methods

A total of 102 cases diagnosed with nepholithiasis and 121 age-matched healthy controls were recruited from June 2010 to September 2011. Smoking status and resultant data was obtained from both groups.

Results

Twenty seven (26.5%) of the patients with stones and eighteen (14.9%) of the control group were current cigarette smokers. Our findings showed that smoking significantly increases the risk of nepholithiasis (OR = 2.06, 95% CI: 1.06-4.01, P = 0.034). There was no significant difference in the number of cigarettes smoked (P = 0.830) and years of smoking (P = 0.536) between subjects with and without stones (P = 0.536).

Conclusions

This study suggests that cigarette smoking might be an independent risk factor for the development of nephrolithiasis.

Biomolecular mechanism of urinary stone formation involving osteopontin

Urinary stones consist of two phases-an inorganic (mineral) phase and an organic (matrix) phase. Studies on the organic components of kidney stones have been undertaken later than those on the inorganic components. After osteopontin was identified as one of the matrix components, the biomolecular mechanism of urinary stone formation became clearer. It also triggered the development of new preventive treatments. Osteopontin expression is sporadically observed in normal distal tubular cells and is markedly increased in stone-forming kidneys. Calcium oxalate crystals adhering to renal tubular cells are incorporated into cells by the involvement of osteopontin. Stimulation of crystal-cell adhesion impairs the opening of mitochondrial permeability transition pores (mPTP) in tubular cells and produces oxidative stress, apoptosis, and osteopontin expression. Macrophages phagocytose and digest a small amount of crystals, but many crystals aggregate into a mass containing osteopontin and epithelial cell debris and are excreted into the renal tubular lumen, becoming nuclei of urinary stones. This biomolecular mechanism is similar to atherosclerotic calcification. Based on these findings, new preventive treatments have been developed. Dietary control such as low-cholesterol intake and the ingestion of antioxidative foods and vegetables have successfully reduced the 5-year recurrence rate. Osteopontin antibodies and cyclosporine A, which blocks the opening of mPTP, have markedly inhibited the expression of osteopontin and urinary stone formation in animal models.

Antiurolithiatic and antioxidant activity of Hordeum vulgare seeds on ethylene glycol-induced urolithiasis in rats

OBJECTIVE

The objective was to investigate the antiurolithiatic and antioxidant activity of ethanolic extract of Hordeum vulgare seeds (EHV) on ethylene glycol-induced urolithiasis in Wistar albino rats.

MATERIALS AND METHODS

Urolithiasis was produced in Wistar albino rats by adding 0.75% v/v ethylene glycol (EG) to drinking water for 28 days. The ethanolic extract of Hordeum vulgare seeds (EHV) was assessed for its curative and preventive action in urolithiasis. In preventive treatment, the EHV given from 1st day to 28th day, while in the curative regimen, the EHV was given from 15th day to 28th day. Various renal functional and injury markers such as urine volume, calcium, phosphate, uric acid, magnesium, urea, and oxalate were evaluated using urine, serum, and kidney homogenate. Antioxidant parameters such as lipid peroxidation, superoxide dismutase, and catalase were also determined.

RESULTS

The EHV treatment (both preventive and curative) increased the urine output significantly compared to the control. The EHV treatment significantly reduced the urinary excretion of the calcium, phosphate, uric acid, magnesium, urea, and oxalate and increased the excretion of citrate compared to EG control. The increased deposition of stone forming constituents in the kidneys of calculogenic rats were significantly lowered by curative and preventive treatment with EHV. It was also observed that the treatment with EHV produced significant decrease in lipid peroxidation, and increased levels of superoxide dismutase and catalase.

CONCLUSION

These results suggest the usefulness of ethanolic extract of Hordeum vulgare seeds as an antiurolithiatic and antioxidant agent.

Apocynin-treatment reverses hyperoxaluria induced changes in NADPH oxidase system expression in rat kidneys: a transcriptional study

Purpose

We have previously shown that production of reactive oxygen species (ROS) is an important contributor to renal injury and inflammation following exposure to oxalate (Ox) or calcium-oxalate (CaOx) crystals. The present study was conducted, utilizing global transcriptome analyses, to determine the effect of Apocynin on changes in the NADPH oxidase system activated in kidneys of rats fed a diet leading to hyperoxaluria and CaOx crystal deposition.

Approach

Age-, sex- and weight-matched rats were either fed regular rat chow or regular rat chow supplemented with 5% w/w hydroxy-L-proline (HLP). Half of the rats on the HLP diet were also placed on Apocynin-supplemented H₂O. After 28 days, each rat was euthanized, their kidneys freshly explanted and dissected to obtain both cortex and medulla tissues. Total RNA was extracted from each tissue and subjected to genomic microarrays to obtain global transcriptome data. KEGG was used to identify gene clusters with differentially expressed genes. Immunohistochemistry was used to confirm protein expressions of selected genes.

Results

Genes encoding both membrane- and cytosolic-NADPH oxidase complex-associated proteins, together with p21rac and Rap1a, were coordinately up-regulated significantly in both renal medulla and cortex tissues in the HLP-fed rats compared to normal healthy untreated controls. Activation of NADPH oxidase appears to occur via the angiotensin-II/angiotensin-II receptor-2 pathway, although the DAG-PKC pathway of neutrophils may also contribute. Immuno histochemical staining confirmed up-regulated gene expressions. Simultaneously, genes encoding ROS scavenger proteins were down-regulated. HLP-fed rats receiving Apocynin had a complete reversal in the differential-expression of the NADPH oxidase system genes, despite showing similar levels of hyperoxaluria.

Conclusions

A strong up-regulation of an oxidative/respiratory burst involving the NADPH oxidase system, activated via the angiotensin-II and most likely the DAG-PKC pathways, occurs in kidneys of hyperoxaluric rats. Apocynin treatment reversed this activation without affecting the levels of hyperoxaluria.

Reactive oxygen species as the molecular modulators of calcium oxalate kidney stone formation: evidence from clinical and experimental investigations

PURPOSE

Idiopathic calcium oxalate kidney stones form while attached to Randall plaques, the subepithelial deposits on renal papillary surfaces. Plaque formation and growth mechanisms are poorly understood. Plaque formation elsewhere in the body is triggered by reactive oxygen species and oxidative stress. This review explores possible reactive oxygen species involvement in plaque formation and calcium oxalate nephrolithiasis.

MATERIALS AND METHODS

A search of various databases for the last 8 years identified literature on reactive oxygen species involvement in calcium oxalate nephrolithiasis. The literature was reviewed and results are discussed.

RESULTS

Under normal conditions reactive oxygen species production is controlled, increasing as needed and regulating crystallization modulator production. Reactive oxygen species overproduction or decreased antioxidants lead to oxidative stress, inflammation and injury, and are involved in stone comorbidity. All major chronic inflammation markers are detectable in stone patient urine. Patients also have increased urinary excretion of the IαI and the thrombin protein families. Results of a recent study of 17,695 participants in NHANES III (National Health and Nutrition Examination Survey) showed significantly lower antioxidants, carotene and β-cryptoxanthin in those with a kidney stone history. Animal model and tissue culture studies revealed that high oxalate, calcium oxalate and calcium phosphate crystals provoked renal cell reactive oxygen species mediated inflammatory responses. Calcium oxalate crystals induce renin up-regulation and angiotensin II generation. Nonphagocytic NADPH oxidase leads to reactive oxygen species production mediated by protein kinase C. The P-38 MAPK/JNK transduction pathway is turned on. Transcriptional and growth factors, and generated secondary mediators become involved. Chemoattractant and osteopontin production is increased and macrophages infiltrate the renal interstitium around the crystal. Phagocytic NADPH oxidase is probably activated, producing additional reactive oxygen species. Localized inflammation, extracellular matrix and fibrosis develop. Crystallization modulators have a significant role in inflammation and tissue repair.

CONCLUSIONS

Based on available data, Randall plaque formation is similar to extracellular matrix mineralization at many body sites. Renal interstitial collagen becomes mineralized, assisting plaque growth through the interstitium until the mineralizing front reaches papillary surface epithelium. Plaque exposure to pelvic urine may also be a result of reactive oxygen species triggered epithelial sloughing.

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.

Antioxidant properties of polysaccharide from the brown seaweed Sargassum graminifolium (Turn.), and its effects on calcium oxalate crystallization

We investigated the effects of polysaccharides from the brown seaweed Sargassum graminifolium (Turn.) (SGP) on calcium oxalate crystallization, and determined its antioxidant activities. To examine the effects of SGP on calcium oxalate crystallization, we monitored nucleation and aggregation of calcium oxalate monohydrate crystals, using trisodium citrate as a positive control. We assessed antioxidant activities of SGP by determining its reducing power, its ability to scavenge superoxide radicals, and its activity in the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The nucleation inhibition ratio of trisodium citrate and SGP was 58.5 and 69.2%, respectively, and crystal aggregation was inhibited by 71.4 and 76.8%, respectively. Increasing concentrations of SGP resulted in increased scavenging of superoxide anions and DPPH radicals (IC₅₀ = 1.9 and 0.6 mg/mL, respectively). These results suggest that SGP could be a candidate for treating urinary stones because of its ability to inhibit calcium oxalate crystallization and its antioxidant properties.

Effects of vitamin E ingestion on plasma and urinary risk factors for calcium oxalate urolithiasis in two population groups having different stone-risk profiles: evidence of different physiological handling mechanisms

It has been demonstrated that vitamin E supplementation reduces calciuria and oxaluria and that it may also prevent oxalate-mediated peroxidative injury, all of which reduce the risk of calcium oxalate urolithiasis. In view of the significant difference in stone occurrence in black (B) and white (W) South Africans, we undertook to investigate the effects of vitamin E supplementation in subjects from these two groups. Five healthy males from each group ingested one capsule (400 IU) of vitamin E daily for 60 days. Blood and 24 h urine samples were collected at baseline and on day 60; 24 h dietary questionnaires were simultaneously completed. Urine composition was determined by routine analyses. Urinary and plasma TBARS were determined using a commercially available assay kit while plasma vitamin E was determined by reverse phase HPLC. Plasma vitamin E increased significantly in W but not in B. Urinary and plasma TBARS did not increase in either group. Urinary citrate increased significantly in both groups but the percentage increase in W (169%) was greater than that in B (82%). No other urinary parameter changed significantly. The increase in plasma vitamin E in W but not in B suggests either that the mechanism by which it is packaged into chylomicrons, which are secreted into the systemic circulation, is suppressed in the latter group or that it is differentially absorbed in the two groups. Similarly, to explain the greater increase in citraturia in W compared to B, we speculate that inhibition of lipogenesis of arachidonic acid by vitamin E, ultimately leading to an increase in citraturia, occurs to a lesser extent in B than in W.

Crucial role of the cryptic epitope SLAYGLR within osteopontin in renal crystal formation of mice

Osteopontin plays a crucial role in the formation of renal calcium crystals, which are primarily induced by renal tubular cell injury, especially mitochondrial damage. We have previously shown that the impaired Arg-Gly-Asp (RGD) sequence of osteopontin inhibits renal crystal formation by using OPN-transgenic mice and OPN-knockout (OPN-KO) mice. Here, we investigated the effects of an antimurine osteopontin antibody (35B6-Ab) that specifically reacts with the (162) SLAYGLR(168) sequence, which is exposed by thrombin cleavage and is located adjacent to the RGD sequence, on renal crystal formation. Renal crystals induced by daily administration of glyoxylate over 9 days (from days 1 to 9) in a murine model were sporadically detected in the renal tubular cells at the corticomedullary junction, where thrombin-cleaved osteopontin expression was also coincidentally detected. On days 0, 3, 6, and 9, 35B6-Ab administration inhibited renal crystal formation and induced significant morphological changes in a dose-dependent manner (250, 500, and 1000 µg per mouse). Scanning electron microscopy showed that the crystals in 35B6-Ab-treated mice were aberrantly formed and their density was low; in contrast, the crystals in untreated mice that were not administered 35B6-Ab had a radial pattern of growth (rosette petal-like crystals), and their density was high. Microstructure analysis of renal tubular cells by transmission electron microscopy revealed that untreated mice showed collapsed mitochondria in the flattened cytoplasm of renal tubular cells, unlike the corresponding structures in 35B6-Ab-treated mice, in which renal tubular cell injury was inhibited. In vitro, 35B6-Ab was found to inhibit the attachment of (14) C-labeled crystals to renal tubular culture cells and reduce morphological damage to these cells. We conclude that thrombin-cleaved osteopontin plays an important role in formation of renal calcium crystals and that 35B6-Ab contributes to the remarkable inhibition of early-stage renal crystal formation by preventing renal tubular cell injury and crystal-cell attachment.

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.

Phytotherapy in a rat model of hyperoxaluria: the antioxidant effects of quercetin involve serum paraoxonase 1 activation

Serum paraoxonase 1 (PON1) has been reported to be an important contributor to the antioxidant and anti-inflammatory activities of HDL, avoiding LDL oxidation. The activity of this enzyme is reduced in patients with renal insufficiency, caused by elevated oxidative stress and disturbances of apolipoprotein metabolism. Therapeutic utilization of antioxidants to control renal oxidative stress may be an effective therapy in renal protection. The aim was to investigate the protective effects of several antioxidant compounds against the oxidative stress associated to renal failure induced by ethylene glycol (EG), focusing on the possible role of serum PON1 activity. Fifty-four male Wistar rats were randomly assigned to six groups (n = 9): an untreated control (C) group, an EG-treated group, a catechin (CAT)-treated group, an epicatechin (EPI)-treated group, a quercetin (QUE)-treated group and a folk herbal extract (FHE)-treated group. After 16 d of treatment, calcium oxalate lithiasis was induced in the rats using EG. After eight days (treatment + EG), the animals were sacrificed. EG treatment impaired kidney composition, increased oxidative damage, and decreased serum paraoxonase and arylesterase activities. CAT, QUE and the FHE Fagolitos improved oxidative status by enhancing antioxidant defenses - superoxide dismutase and PON1 activities - and reducing oxidative damage, thus reinforcing the idea of a possible role of PON1 in the protective effects of QUE against the deleterious consequences of oxidative stress in kidney.

Selective Rac1 inhibition protects renal tubular epithelial cells from oxalate-induced NADPH oxidase-mediated oxidative cell injury

Oxalate-induced oxidative cell injury is one of the major mechanisms implicated in calcium oxalate nucleation, aggregation and growth of kidney stones. We previously demonstrated that oxalate-induced NADPH oxidase-derived free radicals play a significant role in renal injury. Since NADPH oxidase activation requires several regulatory proteins, the primary goal of this study was to characterize the role of Rac GTPase in oxalate-induced NADPH oxidase-mediated oxidative injury in renal epithelial cells. Our results show that oxalate significantly increased membrane translocation of Rac1 and NADPH oxidase activity of renal epithelial cells in a time-dependent manner. We found that NSC23766, a selective inhibitor of Rac1, blocked oxalate-induced membrane translocation of Rac1 and NADPH oxidase activity. In the absence of Rac1 inhibitor, oxalate exposure significantly increased hydrogen peroxide formation and LDH release in renal epithelial cells. In contrast, Rac1 inhibitor pretreatment, significantly decreased oxalate-induced hydrogen peroxide production and LDH release. Furthermore, PKC α and δ inhibitor, oxalate exposure did not increase Rac1 protein translocation, suggesting that PKC resides upstream from Rac1 in the pathway that regulates NADPH oxidase. In conclusion, our data demonstrate for the first time that Rac1-dependent activation of NADPH oxidase might be a crucial mechanism responsible for oxalate-induced oxidative renal cell injury. These findings suggest that Rac1 signaling plays a key role in oxalate-induced renal injury, and may serve as a potential therapeutic target to prevent calcium oxalate crystal deposition in stone formers and reduce recurrence.