Mitochondrial dysfunction is a primary event in renal cell oxalate toxicity

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.

The protection of polysaccharide from the Brown Seaweed Sargassum graminifolium against ethylene glycol-induced mitochondrial damage

The aim of the present study is to evaluate the protective effect of polysaccharide from the Brown Seaweed Sargassum graminifolium (SGP) on ethylene glycol-induced kidney damage and the mechanism of SGP-mediated protection. Mitochondrial lipid peroxidation, mitochondrial swelling, the activity of succinate dehydrogenase (SDH), ATPases and mitochondrial antioxidant enzymes was observed in hyperoxaluric rats. Administration of SGP (25, 100 and 400 mg·kg-1, intragastrically) increased the activities of antioxidant enzymes, SDH and Na+/K+-ATPases, Ca2+-ATPases, Mg2+-ATPases, also decreased mitochondrial lipid peroxidation and mitochondrial swelling. SGP exhibited a protective effect by improving antioxidant enzymes and restoring mitochondrial dysfunction in the kidney of hyperoxaluric rats. It may be used as a promising therapeutic agent to provide superior renal protection.

Acaricide, fungicide and drug interactions in honey bees (Apis mellifera)

Background

Chemical analysis shows that honey bees (Apis mellifera) and hive products contain many pesticides derived from various sources. The most abundant pesticides are acaricides applied by beekeepers to control Varroa destructor. Beekeepers also apply antimicrobial drugs to control bacterial and microsporidial diseases. Fungicides may enter the hive when applied to nearby flowering crops. Acaricides, antimicrobial drugs and fungicides are not highly toxic to bees alone, but in combination there is potential for heightened toxicity due to interactive effects.

Methodology/Principal Findings

Laboratory bioassays based on mortality rates in adult worker bees demonstrated interactive effects among acaricides, as well as between acaricides and antimicrobial drugs and between acaricides and fungicides. Toxicity of the acaricide tau-fluvalinate increased in combination with other acaricides and most other compounds tested (15 of 17) while amitraz toxicity was mostly unchanged (1 of 15). The sterol biosynthesis inhibiting (SBI) fungicide prochloraz elevated the toxicity of the acaricides tau-fluvalinate, coumaphos and fenpyroximate, likely through inhibition of detoxicative cytochrome P450 monooxygenase activity. Four other SBI fungicides increased the toxicity of tau-fluvalinate in a dose-dependent manner, although possible evidence of P450 induction was observed at the lowest fungicide doses. Non-transitive interactions between some acaricides were observed. Sublethal amitraz pre-treatment increased the toxicity of the three P450-detoxified acaricides, but amitraz toxicity was not changed by sublethal treatment with the same three acaricides. A two-fold change in the toxicity of tau-fluvalinate was observed between years, suggesting a possible change in the genetic composition of the bees tested.

Conclusions/Significance

Interactions with acaricides in honey bees are similar to drug interactions in other animals in that P450-mediated detoxication appears to play an important role. Evidence of non-transivity, year-to-year variation and induction of detoxication enzymes indicates that pesticide interactions in bees may be as complex as drug interactions in mammals.

Aluminum citrate prevents renal injury from calcium oxalate crystal deposition

Calcium oxalate monohydrate crystals are responsible for the kidney injury associated with exposure to ethylene glycol or severe hyperoxaluria. Current treatment strategies target the formation of calcium oxalate but not its interaction with kidney tissue. Because aluminum citrate blocks calcium oxalate binding and toxicity in human kidney cells, it may provide a different therapeutic approach to calcium oxalate-induced injury. Here, we tested the effects of aluminum citrate and sodium citrate in a Wistar rat model of acute high-dose ethylene glycol exposure. Aluminum citrate, but not sodium citrate, attenuated increases in urea nitrogen, creatinine, and the ratio of kidney to body weight in ethylene glycol-treated rats. Compared with ethylene glycol alone, the addition of aluminum citrate significantly increased the urinary excretion of both crystalline calcium and crystalline oxalate and decreased the deposition of crystals in renal tissue. In vitro, aluminum citrate interacted directly with oxalate crystals to inhibit their uptake by proximal tubule cells. These results suggest that treating with aluminum citrate attenuates renal injury in rats with severe ethylene glycol toxicity, apparently by inhibiting calcium oxalate's interaction with, and retention by, the kidney epithelium.

Cyclooxygenase 2 and prostaglandin E2 regulate the attachment of calcium oxalate crystals to renal epithelial cells

OBJECTIVE

To determine the roles of endogenous cyclooxygenase 2 and prostaglandin E(2) in crystal-cell binding, which is considered to be an important step in the development of intratubular nephrocalcinosis.

METHODS

An expression plasmid for human cyclooxygenase 2 was introduced into Madin-Darby canine kidney cells using the lipofection method. Cyclooxygenase activity was measured using thin-layer chromatography, and the prostaglandin E(2) concentration was determined with an enzyme immunoassay. In addition, crystal attachment was evaluated with a liquid scintillation counter using [(14)C] calcium oxalate monohydrate crystals, and immunohistochemistry and an enzyme immunoassay were used to analyze and quantify the expression of hyaluronan, a crystal-binding molecule.

RESULTS

Cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells produced about 10-fold more prostaglandin E(2) than wild-type Madin-Darby canine kidney cells, and their hyaluronan production was also upregulated. The attachment of calcium oxalate monohydrate crystals to cyclooxygenase 2-overexpressing Madin-Darby canine kidney cells was significantly reduced compared with their attachment to wild-type and mock-transfected Madin-Darby canine kidney cells. Pre-incubation of the cyclooxygenase 2-overexpressing cells, as well as the mock-transfected and wild-type cells with the cyclooxygenase 2 selective inhibitor etodolac, increased the cellular attachment of calcium oxalate monohydrate crystals in a dose-dependent manner.

CONCLUSIONS

These findings suggest that cyclooxygenase 2 expression and the resultant increase in endogenous prostaglandin E(2), leading to increased hyaluronan production, help to prevent nephrocalcinosis by inhibiting the attachment of calcium oxalate monohydrate crystals to the surface of renal epithelial cells.

Mitochondrial permeability transition pore opening induces the initial process of renal calcium crystallization

Renal tubular cell injury induced by oxidative stress via mitochondrial collapse is thought to be the initial process of renal calcium crystallization. Mitochondrial collapse is generally caused by mitochondrial permeability transition pore (mPTP) opening, which can be blocked by cyclosporine A (CsA). Definitive evidence for the involvement of mPTP opening in the initial process of renal calcium crystallization, however, is lacking. In this study, we examined the physiological role of mPTP opening in renal calcium crystallization in vitro and in vivo. In the in vitro study, cultured renal tubular cells were exposed to calcium oxalate monohydrate (COM) crystals and treated with CsA (2 μM). COM crystals induced depolarization of the mitochondrial membrane potential and generated oxidative stress as evaluated by Cu-Zn SOD and 4-HNE. Furthermore, the expression of cytochrome c and cleaved caspase 3 was increased and these effects were prevented by CsA. In the in vivo study, Sprague-Dawley rats were administered 1% ethylene glycol (EG) to generate a rat kidney stone model and then treated with CsA (2.5, 5.0, and 10.0 mg/kg/day) for 14 days. EG administration induced renal calcium crystallization, which was prevented by CsA. Mitochondrial collapse was demonstrated by transmission electron microscopy, and oxidative stress was evaluated by measuring Cu-Zn SOD, MDA, and 8-OHdG generated by EG administration, all of which were prevented by CsA. Collectively, our results provide compelling evidence for a role of mPTP opening and its associated mitochondrial collapse, oxidative stress, and activation of the apoptotic pathway in the initial process of renal calcium crystallization.

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.

MAP4 mechanism that stabilizes mitochondrial permeability transition in hypoxia: microtubule enhancement and DYNLT1 interaction with VDAC1

Mitochondrial membrane permeability has received considerable attention recently because of its key role in apoptosis and necrosis induced by physiological events such as hypoxia. The manner in which mitochondria interact with other molecules to regulate mitochondrial permeability and cell destiny remains elusive. Previously we verified that hypoxia-induced phosphorylation of microtubule-associated protein 4 (MAP4) could lead to microtubules (MTs) disruption. In this study, we established the hypoxic (1% O₂) cell models of rat cardiomyocytes, H9c2 and HeLa cells to further test MAP4 function. We demonstrated that increase in the pool of MAP4 could promote the stabilization of MT networks by increasing the synthesis and polymerization of tubulin in hypoxia. Results showed MAP4 overexpression could enhance cell viability and ATP content under hypoxic conditions. Subsequently we employed a yeast two-hybrid system to tag a protein interacting with mitochondria, dynein light chain Tctex-type 1 (DYNLT1), by hVDAC1 bait. We confirmed that DYNLT1 had protein-protein interactions with voltage-dependent anion channel 1 (VDAC1) using co-immunoprecipitation; and immunofluorescence technique showed that DYNLT1 was closely associated with MTs and VDAC1. Furthermore, DYNLT1 interactions with MAP4 were explored using a knockdown technique. We thus propose two possible mechanisms triggered by MAP4: (1) stabilization of MT networks, (2) DYNLT1 modulation, which is connected with VDAC1, and inhibition of hypoxia-induced mitochondrial permeabilization.

[Primary hyperoxaluria]

Primary hyperoxalurias are rare recessive inherited inborn errors of glyoxylate metabolism. They are responsible for progressive renal involvement, which further lead to systemic oxalate deposition, which can even occur in infants. Primary hyperoxaluria type 1 is the most common form in Europe and is due to alanine-glyoxylate aminostransferase deficiency, a hepatic peroxisomal pyridoxin-dependent enzyme. Therefore primary hyperoxaluria type 1 is responsible for hyperoxaluria leading to aggressive stone formation and nephrocalcinosis. As glomerular filtration rate decreases, systemic oxalate storage occurs throughout all the body, and mainly in the skeleton. The diagnosis is first based on urine oxalate measurement, then on genotyping, which may also allow prenatal diagnosis to be proposed. Conservative measures - including hydration, crystallization inhibitors and pyridoxine - are safe and may allow long lasting renal survival, provided it is given as soon as the diagnosis has been even suspected. No dialysis procedure can remove enough oxalate to compensate oxalate overproduction from the sick liver, therefore a combined liver and kidney transplantation should be planned before advanced renal disease has occurred, in order to limit/avoid systemic oxalate deposition. In the future, primary hyperoxaluria type 1 may benefit from hepatocyte transplantation, chaperone molecules, etc.

Temporal changes in the expression of mRNA of NADPH oxidase subunits in renal epithelial cells exposed to oxalate or calcium oxalate crystals

BACKGROUND

Exposure of renal epithelial cells to oxalate (Ox) or calcium oxalate (CaOx) crystals leads to the production of reactive oxygen species and cell injury. We have hypothesized that Ox and CaOx crystals activate NADPH oxidase through upregulation of its various subunits.

METHODS

Human renal epithelial-derived cell line, HK-2, was exposed to 100 μmol Ox or 66.7 μg/cm(2) CaOx monohydrate crystals for 6, 12, 24 or 48 h. After exposure, the cells and media were processed to determine activation of NADPH oxidase, production of superoxide and 8-isoprostane (8IP), and release of lactate dehydrogenase (LDH). RT-PCR was performed to determine mRNA expression of NADPH subunits p22(phox), p40(phox), p47(phox), p67(phox) and gp91(phox) as well as Rac-GTPase.

RESULTS

Exposure to Ox and CaOx crystals resulted in increase in LDH release, production of 8-IP, NADPH oxidase activity and production of superoxide. Exposure to CaOx crystals resulted in significantly higher NADPH oxidase activity, production of superoxide and LDH release than Ox exposure. Exposure to Ox and CaOx crystals altered the expression of various subunits of NADPH oxidase. More consistent were increases in the expression of membrane-bound p22(phox) and cytosolic p47(phox). Significant and strong correlations were seen between NADPH oxidase activity, the expression of p22(phox) and p47(phox), production of superoxide and release of LDH when cells were exposed to CaOx crystals. The expressions of neither p22(phox) nor p47(phox) were significantly correlated with increased NADPH oxidase activity after the Ox exposure.

CONCLUSIONS

As hypothesized, exposure to Ox or CaOx crystals leads to significant increases in the expression of p22(phox) and p47(phox), leading to activation of NADPH oxidase. Increased NADPH oxidase activity is associated with increased superoxide production and lipid peroxidation. Different pathways appear to be involved in the stimulation of renal epithelial cells by exposure to Ox and CaOx crystals.

Effect of phospholipase A2 hydrolysis products on calcium oxalate precipitation at lipid interfaces

Urinary stones are commonly composed of an inorganic component, calcium oxalate, or calcium phosphate and an organic matrix of lipids, carbohydrates, and proteinaceous matter. Of interest is the role that the organic matrix elements may play as catalysts for the heterogeneous nucleation of the calcium salts, and a number of studies have examined the role of lipids in calcium oxalate monohydrate (COM) formation. In this study, products of lipid hydrolysis from phospholipase A(2) (PLA(2)) are examined for their effect on COM formation using Langmuir monolayers as model lipid membrane assemblies. The enzyme PLA(2) hydrolyzes DPPC monolayers in the presence of a supersaturated calcium oxalate subphase, inducing the rapid and plentiful nucleation of calcium oxalate at the lipid interface. To investigate the cause of increased crystal formation in the presence of the enzyme, Langmuir monolayers modeling the hydrolysis products were investigated. Calcium oxalate crystal growth at a ternary monolayer of dipalmitoylphosphatidylcholine (DPPC), palmitic acid (PA), and a 22-carbon chain lysophospholipid (22:0 Lyso PC) dramatically increases relative to monolayers of just DPPC. Binary monolayers of DPPC with either PA or the 22:0 Lyso PC and single-component monolayers of PA were also studied. It is demonstrated that the fatty acid generated during lipid hydrolysis causes a significant increase in the extent of heterogeneous nucleation of calcium oxalate from supersaturated solutions. The results imply a possible link between increased phospholipase activity, which is associated with hyperoxaluria, and calcium oxalate precipitation.

Renal toxicity of ethylene glycol results from internalization of calcium oxalate crystals by proximal tubule cells

Ethylene glycol exposure can lead to the development of renal failure due to the metabolic formation of calcium oxalate monohydrate (COM) crystals. The renal damage is closely linked to the degree of COM accumulation in the kidney and most likely results from a COM-induced injury to proximal tubule (PT) cells. The present studies have measured the binding and internalization of COM by primary cultures of normal PT cells from humans and from Wistar and Fischer-344 rats in order to examine the roles of these uptake processes in the resulting cytotoxicity. Internalization was determined by incubation of cells with [(14)C]-COM at 37 degrees C, removal of bound COM with an EDTA incubation, followed by solubilization of cells, as well as by transmission electron microscopy of COM-exposed cells. COM crystals were internalized by PT cells in time- and concentration-dependent manners. COM crystals were bound to and internalized by rat cells about five times more than by human cells. Binding and internalization values were similar between PT cells from Wistar and Fischer-344 rats, indicating that a differential uptake of COM does not explain the known strain difference in sensitivity to ethylene glycol renal toxicity. Internalization of COM correlated highly with the degree of cell death, which is greater in rat cells than in human cells. Thus, surface binding and internalization of COM by cells play critical roles in cytotoxicity and explain why rat cells are more sensitive to COM crystals. At the same level of COM accumulation after ethylene glycol exposure or hyperoxaluria in vivo, rats would be more susceptible than humans to COM-induced damage.

Are calcium oxalate crystals involved in the mechanism of acute renal failure in ethylene glycol poisoning?

INTRODUCTION

Ethylene glycol (EG) poisoning often results in acute renal failure, particularly if treatment with fomepizole or ethanol is delayed because of late presentation or diagnosis. The mechanism has not been established but is thought to result from the production of a toxic metabolite.

METHODS

A literature review utilizing PubMed identified papers dealing with renal toxicity and EG or oxalate. The list of papers was culled to those relevant to the mechanism and treatment of the renal toxicity associated with either compound. ROLE OF METABOLITES: Although the "aldehyde" metabolites of EG, glycolaldehyde, and glyoxalate, have been suggested as the metabolites responsible, recent studies have shown definitively that the accumulation of calcium oxalate monohydrate (COM) crystals in kidney tissue produces renal tubular necrosis that leads to kidney failure. In vivo studies in EG-dosed rats have correlated the severity of renal damage with the total accumulation of COM crystals in kidney tissue. Studies in cultured kidney cells, including human proximal tubule (HPT) cells, have demonstrated that only COM crystals, not the oxalate ion, glycolaldehyde, or glyoxylate, produce a necrotic cell death at toxicologically relevant concentrations. COM CRYSTAL ACCUMULATION: In EG poisoning, COM crystals accumulate to high concentrations in the kidney through a process involving adherence to tubular cell membranes, followed by internalization of the crystals. MECHANISM OF TOXICITY: COM crystals have been shown to alter membrane structure and function, to increase reactive oxygen species and to produce mitochondrial dysfunction. These processes are likely to be involved in the mechanism of cell death.

CONCLUSIONS

Accumulation of COM crystals in the kidney is responsible for producing the renal toxicity associated with EG poisoning. The development of a pharmacological approach to reduce COM crystal adherence to tubular cells and its cellular interactions would be valuable as this would decrease the renal toxicity not only in late treated cases of EG poisoning, but also in other hyperoxaluric diseases such as primary hyperoxaluria and kidney stone formation.

Renal tubular epithelial cell injury and oxidative stress induce calcium oxalate crystal formation in mouse kidney

OBJECTIVES

To clarify the role of renal tubular cell (RTC) injury and oxidative stress in the early stage of renal calcium oxalate crystal formation in a mouse model.

METHODS

Daily intra-abdominal injections of glyoxylate (1.35 mmol/kg/day) into 8-week-old mice were carried out over 6 days. Kidneys were extracted before and at 6, 12 and 24 h and 3 and 6 days after glyoxylate injection. Crystal formation was detected using Pizzolato staining and polarized light optical microscopy. Immunohistochemical staining and western blotting of superoxide dismutase, and 4-hydroxynonenal and malondialdehyde were carried out in order to observe oxidative stress and lipid peroxidation, respectively. RTC microstructural damage and crystal nuclei formation were observed using transmission electron microscopy. To ameliorate RTC injury, mice were treated with green tea 1 week before and 1 week after glyoxylate administration. The number of crystals and RTC damage were observed and comparisons were made between glyoxylate-treated mice with and without green tea administration.

RESULTS

Oxidative stress and lipid peroxidation were observed after 6 h. Crystal nuclei containing collapsed mitochondria and fallen microvilli appeared in the renal distal tubular lumen after 24 h. Crystals occupying the tubular lumen were detected on day 3. The number of crystals in mice receiving green tea was significantly lower than in those receiving glyoxylate alone.

CONCLUSIONS

RTC injury, especially mitochondrial damage, and oxidative stress induce the early stage of calcium oxalate crystal formation in mice.

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.

Emerging epidemic of fatal human self-poisoning with a washing powder in Southern Sri Lanka: a prospective observational study

INTRODUCTION

Self-poisoning is a public health problem in Sri Lanka. A new laundry detergent consisting of a sachet each of 1.2 g of potassium permanganate and 12.5 g of oxalic acid has become a popular agent among the youth for self-poisoning.

METHOD

Prospective clinical data and major outcomes were recorded in all patients admitted to a referring and a referral hospital. Serial biochemistry was performed in 20 patients. Postmortem examinations were performed in some patients.

RESULTS

There were 115 patients. The majority developed symptoms of the gastrointestinal tract within the first 24 h. There were 18 deaths. Ingestion of oxalic acid was associated with a case fatality ratio of 25.4% (95% CI = 14-39), while ingestion of both potassium permanganate and oxalic acid was associated with a case fatality ratio of 9.8% (95% CI = 3.2-21). Ingestion of more than one sachet was associated with a significantly higher risk of death (risk ratio = 13.26, 95% CI = 3.2-54, p < 0.05). Majority of the deaths occurred within an hour since ingestion. Postmortem examinations revealed mucosal ulceration in the majority of deaths.

DISCUSSION

This case series brings to light an emerging epidemic of fatal self-poisoning in Sri Lanka from a compound that is not regulated. As deaths occur soon after ingestion, medical management of these patients is bound to be difficult.

CONCLUSION

This case series highlights a fatal mode of self-poisoning that could be controlled through regulation of the manufacture and sale of the product.

Mitochondrial damage, cytotoxicity and apoptosis in iron-potentiated alcoholic liver fibrosis: amelioration by taurine

Taurine effectively prevents ischemia-induced apoptosis in the cardiomyocytes and hypothalamic nuclei. The present study explores the influence of taurine on mitochondrial damage, oxidative stress and apoptosis in experimental liver fibrosis. Male albino Wistar rats were divided into six groups and maintained for a period of 60 days as follows: Group I, control; Group II, ethanol treatment [6 g/(kg/day)]; Group III, fibrosis induced by ethanol and iron (0.5% w/w); Group IV, ethanol + iron + taurine (2% w/v); Group V, ethanol + taurine treatment and Group VI, control + taurine treatment. Hepatocytes isolated from ethanol plus iron-treated rats showed decreased cell viability and redox ratio, increased reactive oxygen species formation, lipid peroxidation, DNA fragmentation, and formation of apoptotic bodies. Liver mitochondria showed increased susceptibility to swell, diminished activities of mitochondrial respiratory chain complexes and antioxidants. Taurine administration to fibrotic rats restored mitochondrial function, reduced reactive oxygen species formation, prevented DNA damage, and apoptosis. Thus taurine might contribute to the amelioration of the disease process.

Reversal of Hyperoxaluria-Induced Alteration in Rat Liver by Administration ofN-Acetylcysteine

The current work was designed to study the potential of N-acetylcysteine (NAC) in modulating hyperoxaluric manifestations induced by acute oxalate dose in rat liver. Hyperoxaluric conditions were induced by giving a single dose of sodium oxalate (70 mg/kg body weight) in one group, and in the other group, hyperoxaluric rats were administered NAC (200 mg/kg body weight) after 30 min of the oxalate dose. After 12 h of the above treatment, blood was taken from the orbital sinus for testing serum oxalate, and animals were sacrificed. To exploit the potential of NAC, various oxidative stress parameters [lipid peroxidation (LP) and activity of antioxidant enzymes], lipid content, and histologic analysis of rat liver were performed. The increased level of LP and activities of superoxide dismutase and catalase in hyperoxaluric rats were restored after NAC treatment. Not only the decreased amount of total lipids and phospholipids but also the increased ratio of cholesterol/phospholipid (showing decreased membrane fluidity) in hyperoxaluric rats were balanced by NAC treatment. Further restored histologic changes of liver tissue confirmed the protective antioxidant effects of the given drug. Thus, N-acetylcysteine being an extraneous antioxidant showed curative properties toward hyperoxaluric manifestations in liver.

Glyoxylate induces renal tubular cell injury and microstructural changes in experimental mouse

Crystal formation in mice could not be induced either by the administration of ethylene glycol or by glycolate. To clarify the reasons for the difference among these oxalate precursors in mice, we studied renal tubular epithelial injury by immunohistochemical staining of oxidative stress and observing microstructures. Daily intra-abdominal injection of saline solution [10 ml/(kg day)], ethylene glycol[(48.3 mmol/(kg day)], glycolate [1.31 mmol/(kg day)], and glyoxylate [1.35 mmol/(kg day)] into C57BL/6 male mice (8 weeks) was performed for 7 days. Immunohistochemical staining of superoxide dismutase (SOD) and malondialdehyde (MDA), and transmission electron microscopy (TEM) of renal tubular epithelial cells were performed to observe oxidative stress and morphological changes, respectively. Decreased SOD and increased MDA were shown only in glyoxylate-treated mouse kidneys. The TEM study with glyoxylate-treated mouse kidneys demonstrated that the internal structure of mitochondria in renal tubular cells underwent destruction and vacuolization, and microvilli density decreased. These changes in renal tubular cells were located in the crystal-forming area. However, such changes were not detected in the other groups. Each precursor of oxalate induces different changes in renal epithelial cells regarding oxidative stress and the microstructural changes. It is suggested that calcium oxalate crystal formation requires cell injury and morphological changes of renal epithelial tubular cells induced by glyoxylate administration in the mouse kidney.

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.

Renal cell apoptosis induced by nephrotoxic drugs: cellular and molecular mechanisms and potential approaches to modulation

Apoptosis plays a central role not only in the physiological processes of kidney growth and remodeling, but also in various human renal diseases and drug-induced nephrotoxicity. We present in a synthetic fashion the main molecular and cellular pathways leading to drug-induced apoptosis in kidney and the mechanisms regulating it. We illustrate them using three main nephrotoxic drugs (cisplatin, gentamicin, and cyclosporine A). We discuss the main regulators and effectors that have emerged as key targets for the design of therapeutic strategies. Novel approaches using gene therapy, antisense strategies, recombinant proteins, or compounds obtained from both classical organic and combinatorial chemistry are examined. Finally, key issues that need to be addressed for the success of apoptosis-based therapies are underlined.

Mitochondrial dysfunction in an animal model of hyperoxaluria: a prophylactic approach with fucoidan

Oxalate/calcium oxalate toxicity is mediated through generation of reactive oxygen species in a process that partly depends upon events that induce mitochondrial damage. Mitochondrial dysfunction is an important event favoring stone formation. The objective of the present study was to investigate whether mitochondria is a target for oxalate/calcium oxalate and the plausible role of naturally occurring glycosaminoglycans from edible seaweed, fucoidan in ameliorating mitochondrial damage. Male albino rats of Wistar strain were divided into four groups and treated as follows: Group I: vehicle treated control, Group II: hyperoxaluria was induced with 0.75% ethylene glycol in drinking water for 28 days, Group III: fucoidan from F. vesiculosus (5 mg/kg b.wt, s.c) from the 8th day of the experimental period, Group IV: ethylene glycol+fucoidan treated rats. The tricarboxylic acid (TCA) cycle enzymes like succinate dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase and respiratory complex enzyme activities were assessed to evaluate mitochondrial function. Oxidative stress was assessed based on the activities of antioxidant enzymes, level of reactive oxygen species, lipid peroxidation and reduced glutathione. Mitochondrial swelling was also analyzed. Ultra structural changes in renal tissue were analyzed with electron microscope. Hyperoxaluria induced a decrease in the activities of TCA cycle enzymes and respiratory complex enzymes. The oxidative stress was evident by the decrease in antioxidant enzymes, glutathione and an increase in reactive species and lipid peroxidation in mitochondria. Mitochondrial damage was evident by increased mitochondrial swelling. Administration of fucoidan, decreased reactive oxygen species, lipid peroxidation (P<0.05), mitochondrial swelling and increased the activities of antioxidant enzymes and glutathione levels (P<0.05) and normalized the activities of mitochondrial TCA cycle and respiratory complex enzymes (P<0.05). From the present study, it can be concluded that mitochondrial damage is an essential event in hyperoxaluria, and fucoidan was able to effectively prevent it and thereby the renal damage in hyperoxaluria.

Species differences in Cl- affinity and in electrogenicity of SLC26A6-mediated oxalate/Cl- exchange correlate with the distinct human and mouse susceptibilities to nephrolithiasis

The mouse is refractory to lithogenic agents active in rats and humans, and so has been traditionally considered a poor experimental model for nephrolithiasis. However, recent studies have identified slc26a6 as an oxalate nephrolithiasis gene in the mouse. Here we extend our earlier demonstration of different anion selectivities of the orthologous mouse and human SLC26A6 polypeptides to investigate the correlation between species-specific differences in SLC26A6 oxalate/anion exchange properties as expressed in Xenopus oocytes and in reported nephrolithiasis susceptibility. We find that human SLC26A6 mediates minimal rates of Cl(-) exchange for Cl(-), sulphate or formate, but rates of oxalate/Cl(-) exchange roughly equivalent to those of mouse slc2a6. Both transporters exhibit highly cooperative dependence of oxalate efflux rate on extracellular [Cl(-)], but whereas the K(1/2) for extracellular [Cl(-)] is only 8 mM for mouse slc26a6, that for human SLC26A6 is 62 mM. This latter value approximates the reported mean luminal [Cl(-)] of postprandial human jejunal chyme, and reflects contributions from both transmembrane and C-terminal cytoplasmic domains of human SLC26A6. Human SLC26A6 variant V185M exhibits altered [Cl(-)] dependence and reduced rates of oxalate/Cl(-) exchange. Whereas mouse slc26a6 mediates bidirectional electrogenic oxalate/Cl(-) exchange, human SLC26A6-mediated oxalate transport appears to be electroneutral. We hypothesize that the low extracellular Cl(-) affinity and apparent electroneutrality of oxalate efflux characterizing human SLC26A6 may partially explain the high human susceptibility to nephrolithiasis relative to that of mouse. SLC26A6 sequence variant(s) are candidate risk modifiers for nephrolithiasis.

Lanthanum suppresses arachidonic acid-induced cell death and mitochondrial depolarization in PC12 cells

Within the framework of studying the mechanisms of acute toxicity of arachidonic acid and the role of ambient cations, we have investigated the effects of extracellular La(3+) on arachidonic acid-induced death (lactate dehydrogenase release) and mitochondrial depolarization (rhodamine 123 fluorescence) in PC12 cells. Micromolar La(3+) profoundly suppressed arachidonic acid toxicity and this effect was dependent on the presence of other cations. Whereas in the cation-free solution 10-20 microM La(3+) protected most cells from death caused by a 2 hour-long exposure to 20 microM arachidonic acid, the cytoprotective effect of 100 microM La(3+) was reduced to approximately 70% in the presence of a normal complement of monovalent cations and was hardly detectable with 5 mM Ca(2+) in the bath. Increasing the concentration of arachidonic acid could defeat La(3+) cytoprotection. In fluorescence experiments, arachidonic acid caused a decrease in the mitochondrial membrane potential, with the rate and extent of depolarization increasing with an increase in the concentration of arachidonic acid. La(3+) countered the depolarizing effect of arachidonic acid in a manner consistent with a decrease in the effective arachidonic acid concentration. The results suggest that extracellular cations modulate cellular effects of arachidonic acid by reducing its ability to pass through the plasma membrane, possibly by binding the fatty acid. The similarities of the La(3+) effects on arachidonic acid-induced cell death and arachidonic acid-induced mitochondrial depolarization strongly support the causal relations between the two events and suggest that mitochondria are the primary target of arachidonic acid at the cellular level.

Mitochondria are the major targets in albumin-induced apoptosis in proximal tubule cells

Nephrotic-range proteinuria is considered a poor prognostic factor. A correlation between tubulointerstitial injury and the degree of proteinuria is well established. In an attempt to explain the tubular atrophy that is observed in advanced glomerulonephritides, this study investigated apoptotic mechanisms in cultured human proximal tubule cells (HKC-8) that were exposed to endotoxin-free albumin (5, 10, and 20 mg/ml). Apoptosis was detected by Hoechst 33342; annexin staining; and assays for caspases 3, 8, and 9. The apoptotic effect of albumin was maximal at 10 mg/ml albumin, and necrosis prevailed in cells that were incubated with 20 mg/ml. Increase in caspase-9 and -3 activity was observed starting at 6 and maximally at 16 to 24 h. The proapoptotic Bcl-2 protein Bax was upregulated at 6 h, associated with translocation of cytochrome-c from mitochondria to cytosol and alteration in the mitochondrial membrane potential. Production of reactive oxygen species (ROS) was significant at 6 h but declined at 16 and 24 h. Treatment with ROS scavenger dimethylthiourea or antioxidant N-acetylcysteine did not alleviate caspase-3 production. Pan protein kinase C inhibitor bisindolylmaleimide-1 protected the cells from apoptosis. It is concluded that albumin induces apoptosis in human proximal tubule cells by stimulating mitochondrial apoptotic pathway independent of ROS production.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

The Not So ‘Mighty Chondrion’: Emergence of Renal Diseases due to Mitochondrial Dysfunction

Mitochondria are intracellular organelles with a variety of vital functions, including the provision of energy in the form of adenosine 5'-triphosphate. Increasingly, we are becoming more aware of the importance of mitochondrial dysfunction in a number of common medical conditions. In this review and overview, we focus on the growing evidence that mitochondrial dysfunction is involved in either the etiology or underlying pathophysiology of a broad spectrum of renal diseases, including acute renal injury due to ischemia-reperfusion injury, renal Fanconi syndrome, and glomerular disorders such as focal segmental glomerulosclerosis. In addition, mitochondrial dysfunction may also contribute to the growing burden of chronic kidney disease seen in our aging population, which is still largely unexplained. Unfortunately, at present, our ability to diagnose and treat renal disorders related to mitochondrial dysfunction is limited, and further work in this field is needed.

Renal oxidative vulnerability due to changes in mitochondrial-glutathione and energy homeostasis in a rat model of calcium oxalate urolithiasis

Calcium oxalate monohydrate (COM) crystals are the commonest component of kidney stones. Oxalate and COM crystals in renal cells are thought to contribute to pathology via prooxidant events. Using an in vivo rat model of crystalluria induced by hyperoxaluria plus hypercalciuria [ethylene glycol (EG) plus 1,25-dihydroxycholecalciferol (DHC)], we measured glutathione and energy homeostasis of kidney mitochondria. Hyperoxaluria or hypercalciuria without crystalluria was also investigated. After 1–3 wk of treatment, kidney cryosections were analyzed by light microscopy. In kidney subcellular fractions, glutathione and antioxidant enzymes were measured. In mitochondria, oxygen consumption and superoxide formation as well as cytochrome c content were measured. EG plus DHC treatment increased formation of renal birefringent crystal. Histology revealed increased renal tubular pathology characterized by obstruction, distension, and interstitial inflammation. Crystalluria at all time points led to oxidative stress manifest as decreased cytosolic and mitochondrial glutathione and increased activity of the antioxidant enzymes glutathione reductase and -peroxidase (mitochondria) and glucose-6-phosphate dehydrogenase (cytosol). These changes were followed by a significant decrease in mitochondrial cytochrome c content at 2–3 wk, suggesting the involvement of apoptosis in the renal pathology. Mitochondrial oxygen consumption was severely impaired in the crystalluria group without increased mitochondrial superoxide formation. Some of these changes were also evident in hyperoxaluria at week 1 but were absent at later times and in all calciuric groups. Our data indicate that impaired electron flow did not cause superoxide formation; however, mitochondrial dysfunction contributes to pathological events when tubular crystal-cell interactions are uncontrolled, as in kidney stones disease.

Concomitant real-time monitoring of intracellular reactive oxygen species and mitochondrial membrane potential in individual living promonocytic cells

Reactive oxygen species (ROS) have recently been shown to be involved in multiple physiological responses through modulation of signaling pathways. Inappropriate production of these radicals, and their metabolites, leads to the development of various pathologies. Free radicals can induce both positive and negative effects in cells, and their metabolic pathways are very complex. Hence, it is crucial to be able to simultaneously and directly determine their production dynamics and concentrations in individual living cells, in physiological or pathological states, and in response to drugs. The aim of the present study was to monitor in real time the rates of ROS generation in promonocytic cells upon stimulation with hydrogen peroxide and oxidized lipid. Quantitative detection of intracellular ROS concentration in intact living U937 cells was performed by fluorescence intensity (FI) and polarization (FP) measurements utilizing the Optical LiveCell Array technology. The "dihydro" derivative probes of fluorescein (DCF-DA) and rhodamine (DHR123) were used to assess the intracellular levels of ROS. Each probe molecule exhibited a characteristic FI and FP in its non-fluorescent or oxidized form. Analysis of the temporal relationship between the kinetics of ROS generation and the onset of changes in mitochondrial membrane potential shows high variability within a cell population with regard to both processes. The data demonstrated that temporal measurement of ROS generation, in identifiable individual cells, reveals kinetic behavior that otherwise would be undetected.

Lipid peroxidation is not the underlying cause of renal injury in hyperoxaluric rats

BACKGROUND

Hyperoxaluria is a major risk factor of calcium oxalate stone disease and renal injury is thought to be a significant initiating event. However, the relationship among oxidative stress, renal tubule injury and hyperoxaluria in the progression of nephrolithiasis is unclear, especially in animal models. In the current study, we assess the role of oxidative stress in renal tubular damage in a rat model of chronic hyperoxaluria (HYP) and chronic renal failure induced by hyperoxaluria (HRF) compared to control rats.

METHODS

Urinary excretion of renal tubular enzymes, including lactate dehydrogenase (LDH), alkaline phosphatase (AP), N-acetyl-beta-D-glucosaminidase (NAG), and alpha- and mu-glutathione-S-transferase (alpha-GST and mu-GST, respectively) was quantified in four groups of Sprague-Dawley rats. The study included normal controls, those made hyperoxaluric with ethylene glycol administration (HYP), unilateral nephrectomized controls, and unilateral nephrectomized rats administered ethylene glycol (HRF). Levels of catalase, superoxide dismutase (SOD), glutathione peroxidase (GP), and glutathione transferase (GST) in the renal cortex were measured after 4 weeks and lipid peroxidation was assessed by measuring 8-isoprostane in the urine and lipid hydroperoxide in the renal cortex.

RESULTS

Urinary excretion of NAG, AP, and LDH was elevated after 2 and 4 weeks in the HYP and HRF groups. Urinary levels of mu-GST, a marker of distal tubule damage, were elevated in HRF rats after 4 weeks. alpha-GST levels were similar between control and HYP rats but were lower in HRF rats. Levels of catalase, SOD, GP, and GST in the renal cortex were similar among control, HYP, and unilateral nephrectomized control rats, but were attenuated in the HRF rats after 4 weeks. Renal cortical content of lipid hydroperoxide and urinary 8-isoprostane levels were similar among all groups after 4 weeks.

CONCLUSION

Ethylene glycol-induced hyperoxaluria in Sprague-Dawley rats is accompanied by enzymuria, which is suggestive of renal tubular damage. The antioxidant capacity of the renal cortex in HYP rats is similar to that of control rats after 4 weeks of treatment; however, this capacity is significantly attenuated in rats that are in renal failure induced by hyperoxaluria, although significant lipid peroxidation is not evident. These results suggest that lipid peroxidation is not the underlying cause of renal injury in hyperoxaluric rats.

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.

Counteraction of oxalate induced nitrosative stress by supplementation of l-arginine, a potent antilithic agent

BACKGROUND

Our understanding of nitrosative stress in the process of urolithiasis is far from complete. Earlier studies carried out in our laboratory demonstrate the presence of nitrated THP in stone formers, l-arginine (l-arg) a precursor of nitric oxide (NO), attenuates the endothelial dysfunction caused by reactive nitrogen species. We investigated the role of l-arg in ethylene glycol (EG)-induced urolithic rat model and observed its antilithic and antioxidative properties.

METHODS

Hyperoxaluria was induced using 0.75% EG in drinking water. l-arg [1.25 g/kg body weight] was given orally for a period of 28 days.

RESULTS

EG-treated rats showed significant loss in body weight and increase in the activities of oxalate synthesizing enzymes such as glycollic acid oxidase in liver. Lactate dehydrogenase activity in liver and kidney was increased. The activity of the free radical producing enzyme xanthine oxidase, tissue oxalate and calcium levels were significantly increased in EG-treated rats. Depletion in the antioxidant enzymes, membrane bound ATPases and thiol status was observed in these rats. l-arg co-supplementation to EG-treated rats maintained the activities of the oxalate synthesizing enzymes and free radical producing enzymes with in the normal range. Tissue oxalate and calcium levels were also maintained near normal in l-arg treated hyperoxaluric rats. l-arg, by its cytoprotective effect, maintained the thiol status, thereby preserving the activities of the membrane bound ATPases and preventing proteinuria and subsequent weight loss in EG-treated rats.

CONCLUSION

l-arg feeding prevents the retention of calcium oxalate crystals in hyperoxaluric rats by way of protecting the renal cells from oxidative injury and also by providing a second line of defense through the normalization of the oxalate metabolism. It reduces the risk of stone formation, by curtailing free radicals and hyperoxaluria as both of them have to work in close association to form stones.

Diphenyleneiodium (DPI) reduces oxalate ion- and calcium oxalate monohydrate and brushite crystal-induced upregulation of MCP-1 in NRK 52E cells

BACKGROUND

Our earlier studies have demonstrated upregulation of monocyte chemoattractant protein-1 (MCP-1) in NRK52E rat renal epithelial cells by exposure to oxalate (Ox) ions and crystals of calcium oxalate monohydrate (COM) or the brushite (Br) form of calcium phosphate. The upregulation was mediated by reactive oxygen species (ROS). This study was performed to investigate whether NADPH oxidase is involved in ROS production.

METHODS

Confluent cultures of NRK52E cells were exposed to Ox ions or COM and Br crystals. They were exposed for 1, 3, 6, 12, 24 and 48 h for isolation of MCP-1 mRNA and 24 h for enzyme-linked immunosorbent assay (ELISA) to determine the secretion of protein into the culture medium. We also investigated the effect of free radical scavenger, catalase, and the NADPH oxidase inhibitor diphenyleneiodium (DPI) chloride, on the Ox- and crystal-induced expression of MCP-1 mRNA and protein. The transcription of MCP-1 mRNA in the cells was determined using real-time polymerase chain reaction. Hydrogen peroxide and 8-isoprostane were measured to investigate the involvement of ROS.

RESULTS

Exposure of NRK52E cells to Ox ions as well as the crystals resulted in increased expression of MCP-1 mRNA and production of the chemoattractant. Treatment with catalase reduced the Ox- and crystal-induced expression of both MCP-1 mRNA and protein. DPI reduced the crystal-induced gene expression and protein production but not Ox-induced gene expression and protein production.

CONCLUSIONS

Exposure to Ox ions, and COM and Br crystals stimulates a ROS-mediated increase in MCP-1 mRNA expression and protein production. Reduction in ROS production, lipid peroxidation, low-density lipoprotein release, and inducible MCP-1 gene and protein in the presence of DPI indicates an involvement of NADPH oxidase in the production of ROS.