Oxalate toxicity in renal epithelial cells: characteristics of apoptosis and necrosis

Nephro-protective effect of Daphnetin in hyperoxaluria-induced rat renal injury via alterations of the gut microbiota

It is well proved that hyperoxaluria induces the renal injury and finally causes the end stage kidney disease. Daphnetin (coumarin derivative) already confirmed renal protective effect in renal model, but hyperoxaluria protective effect still unexplore. The objective of this research was to scrutinize the renal protective effect of daphnetin against ethylene glycol (GC)-induced hyperoxaluria via altering the gut microbiota. GC (1% v/v) was used for the induction of hyperoxaluria in the rats and the rats were received the oral administration of daphnetin (5, 10 and 15 mg/kg). The body and renal weight were assessed. Urine, renal, inflammatory cytokines, antioxidant, inflammatory parameters, and gut microbiota were appraised. Daphnetin effectually improved the body weight and reduced the renal weight. Its also remarkably boosted the magnesium, calcium, citrate level and suppressed the level of uric acid and oxalate formation. Daphnetin significantly (p < .001) ameliorate the level of urinary kidney injury molecule 1 (KIM-1), blood urea nitrogen (BUN), urea, serum creatinine (Scr), neutrophil gelatinase-associated lipocalin (NGAL) and uric acid along with inflammatory cytokines and inflammatory mediators. Daphnetin considerably repressed the malonaldehyde (MDA) level, protein carbonyl and improved the level of glutathione reductase (GR), superoxide dismutase (SOD), glutathione (GSH) and catalase (CAT). Daphnetin treatment considerably altered the microbial composition of different bacteria at phylum, genus and family level. Daphnetin significantly suppressed the Firmicutes relative abundance and boosted the Bacteroidetes relative abundance. Our result clearly indicated that daphnetin remarkably ameliorates the GC induced hyperoxaluria in rats via altering the oxidative stress, inflammatory reaction and gut microbiota. PRACTICAL APPLICATION: Nephrotoxicity is a serious health disease worldwide. We induce the renal toxicity in the experimental rats using the ethylene glycol and scrutinized the renal protective effect of daphnetin. Daphnetin considerably suppress the renal, urine parameters. For estimation the underlying mechanism, we estimated the gut microbiota in all group rats. Daphnetin remarkably altered the level of gut microbiota and suggesting the renal protective effect.

Ceramides and Acute Kidney Injury

Altered lipid metabolism is a characteristic feature and potential driving factor of acute kidney injury (AKI). Of the lipids that accumulate in injured renal tissues, ceramides are potent regulators of metabolism and cell fate. Up-regulation of ceramide synthesis is a common feature shared across several AKI etiologies in vitro and in vivo. Furthermore, ceramide accumulation is an early event in the natural history of AKI that precedes cell death and organ dysfunction. Emerging evidence suggests that inhibition of ceramide accumulation may improve renal outcomes in several models of AKI. This review examines the landscape of ceramide metabolism and regulation in the healthy and injured kidney. Furthermore, we discuss the body of literature regarding ceramides as therapeutic targets for AKI and consider potential mechanisms by which ceramides drive kidney pathogenesis.

A Rheostat of Ceramide and Sphingosine-1-Phosphate as a Determinant of Oxidative Stress-Mediated Kidney Injury

Reactive oxygen species (ROS) modulate sphingolipid metabolism, including enzymes that generate ceramide and sphingosine-1-phosphate (S1P), and a ROS-antioxidant rheostat determines the metabolism of ceramide-S1P. ROS induce ceramide production by activating ceramide-producing enzymes, leading to apoptosis, while they inhibit S1P production, which promotes survival by suppressing sphingosine kinases (SphKs). A ceramide-S1P rheostat regulates ROS-induced mitochondrial dysfunction, apoptotic/anti-apoptotic Bcl-2 family proteins and signaling pathways, leading to apoptosis, survival, cell proliferation, inflammation and fibrosis in the kidney. Ceramide inhibits the mitochondrial respiration chain and induces ceramide channel formation and the closure of voltage-dependent anion channels, leading to mitochondrial dysfunction, altered Bcl-2 family protein expression, ROS generation and disturbed calcium homeostasis. This activates ceramide-induced signaling pathways, leading to apoptosis. These events are mitigated by S1P/S1P receptors (S1PRs) that restore mitochondrial function and activate signaling pathways. SphK1 promotes survival and cell proliferation and inhibits inflammation, while SphK2 has the opposite effect. However, both SphK1 and SphK2 promote fibrosis. Thus, a ceramide-SphKs/S1P rheostat modulates oxidant-induced kidney injury by affecting mitochondrial function, ROS production, Bcl-2 family proteins, calcium homeostasis and their downstream signaling pathways. This review will summarize the current evidence for a role of interaction between ROS-antioxidants and ceramide-SphKs/S1P and of a ceramide-SphKs/S1P rheostat in the regulation of oxidative stress-mediated kidney diseases.

Probiotic Lactiplantibacillus plantarum N-1 could prevent ethylene glycol-induced kidney stones by regulating gut microbiota and enhancing intestinal barrier function

Defective permeability barrier is considered to be an incentive of hyperuricemia, however, the link between them has not been proven. Here, we evaluated the potential preventive effects of Lactiplantibacillus plantarum N-1 (LPN1) on gut microbiota and intestinal barrier function in rats with hyperoxaluria-induced kidney stones. Male rats were supplied with 1% ethylene glycol (EG) dissolved in drinking water for 4 weeks to develop hyperoxaluria, and some of them were administered with LPN1 for 4 weeks before EG treatment as a preventive intervention. We found that EG not only resulted hyperoxaluria and kidney stone formation, but also promoted the intestinal inflammation, elevated intestinal permeability, and gut microbiota disorders. Supplementation of LPN1 inhibited the renal crystalline deposits through reducing urinary oxalic acid and renal osteopontin and CD44 expression and improved EG-induced intestinal inflammation and barrier function by decreasing the serum LPS and TLR4/NF-κB signaling and up-regulating tight junction Claudin-2 in the colon, as well as increasing the production of short-chain fatty acid (SCFAs) and the abundance of beneficial SCFAs-producing bacteria, mainly from the families of Lachnospiraceae and Ruminococcaceae. Probiotic LPN1 could prevent EG-induced hyperoxaluria by regulating gut microbiota and enhancing intestinal barrier function.

Exposure of Platelets to Dengue Virus and Envelope Protein Domain III Induces Nlrp3 Inflammasome-Dependent Platelet Cell Death and Thrombocytopenia in Mice

In tropical and subtropical regions, mosquito-borne dengue virus (DENV) infections can lead to severe dengue, also known as dengue hemorrhage fever, which causes bleeding, thrombocytopenia, and blood plasma leakage and increases mortality. Although DENV-induced platelet cell death was linked to disease severity, the role of responsible viral factors and the elicitation mechanism of abnormal platelet activation and cell death remain unclear. DENV and virion-surface envelope protein domain III (EIII), a cellular binding moiety of the virus particle, highly increase during the viremia stage. Our previous report suggested that exposure to such viremia EIII levels can lead to cell death of endothelial cells, neutrophils, and megakaryocytes. Here we found that both DENV and EIII could induce abnormal platelet activation and predominantly necrotic cell death pyroptosis. Blockages of EIII-induced platelet signaling using the competitive inhibitor chondroitin sulfate B or selective Nlrp3 inflammasome inhibitors OLT1177 and Z-WHED-FMK markedly ameliorated DENV- and EIII-induced thrombocytopenia, platelet activation, and cell death. These results suggest that EIII could be considered as a virulence factor of DENV, and that Nlrp3 inflammasome is a feasible target for developing therapeutic approaches against dengue-induced platelet defects.

Dengue Virus Envelope Protein Domain III Induces Nlrp3 Inflammasome-Dependent NETosis-Mediated Inflammation in Mice

Abnormal immune responses and cytokine storm are involved in the development of severe dengue, a life-threatening disease with high mortality. Dengue virus-induced neutrophil NETosis response is associated with cytokine storm; while the role of viral factors on the elicitation of excessive inflammation mains unclear. Here we found that treatments of dengue virus envelope protein domain III (EIII), cellular binding moiety of virion, is sufficient to induce neutrophil NETosis processes in vitro and in vivo. Challenges of EIII in inflammasome Nlrp3-/- and Casp1-/- mutant mice resulted in less inflammation and NETosis responses, as compared to the wild type controls. Blockages of EIII-neutrophil interaction using cell-binding competitive inhibitor or selective Nlrp3 inflammasome inhibitors OLT1177 and Z-WHED-FMK can suppress EIII-induced NETosis response. These results collectively suggest that Nlrp3 inflammsome is a molecular target for treating dengue-elicited inflammatory pathogenesis.

Exposure to Dengue Envelope Protein Domain III Induces Nlrp3 Inflammasome-Dependent Endothelial Dysfunction and Hemorrhage in Mice

Typically occurring during secondary dengue virus (DENV) infections, dengue hemorrhagic fever (DHF) causes abnormal immune responses, as well as endothelial vascular dysfunction, for which the responsible viral factor remains unclear. During peak viremia, the plasma levels of virion-associated envelope protein domain III (EIII) increases to a point at which cell death is sufficiently induced in megakaryocytes in vitro. Thus, EIII may constitute a virulence factor for endothelial damage. In this study, we examined endothelial cell death induced by treatment with DENV and EIII in vitro. Notably, pyroptosis, the major type of endothelial cell death observed, was attenuated through treatment with Nlrp3 inflammasome inhibitors. EIII injection effectively induced endothelial abnormalities, and sequential injection of EIII and DENV-NS1 autoantibodies induced further vascular damage, liver dysfunction, thrombocytopenia, and hemorrhage, which are typical manifestations in DHF. Under the same treatments, pathophysiological changes in the Nlrp3 inflammasome–deficient mice were notably reduced compared with those in the wild-type mice. These results suggest that the Nlrp3 inflammasome constitutes a potential therapeutic target for treating DENV-induced hemorrhage in DHF.

Oxalate-Degrading Bacillus subtilis Mitigates Urolithiasis in a Drosophila melanogaster Model

Kidney stone disease is a morbid condition that is increasing in prevalence, with few nonsurgical treatment options. The majority of stones are composed of calcium oxalate. Unlike humans, some microbes can break down oxalate, suggesting that microbial therapeutics may provide a novel treatment for kidney stone patients. This study demonstrated that Bacillus subtilis 168 (BS168) decreased stone burden, improved health, and complemented the microbiota in a Drosophila melanogaster urolithiasis model, while not exacerbating calcium oxalate aggregation or adhesion to renal cells in vitro. These results identify this bacterium as a candidate for ameliorating stone formation; given that other strains of B. subtilis are components of fermented foods and are used as probiotics for digestive health, strain 168 warrants testing in humans. With the severe burden that recurrent kidney stone disease imposes on patients and the health care system, this microbial therapeutic approach could provide an inexpensive therapeutic adjunct.

Kidney stones affect nearly 10% of the population in North America and are associated with high morbidity and recurrence, yet novel prevention strategies are lacking. Recent evidence suggests that the human gut microbiota can influence the development of nephrolithiasis, although clinical trials have been limited and inconclusive in determining the potential for microbially based interventions. Here, we used an established Drosophila melanogaster model of urolithiasis as a high-throughput screening platform for evaluation of the therapeutic potential of oxalate-degrading bacteria in calcium oxalate (CaOx) nephrolithiasis. The results demonstrated that Bacillus subtilis 168 (BS168) is a promising candidate based on its preferential growth in high oxalate concentrations, its ability to stably colonize the D. melanogaster intestinal tract for as long as 5 days, and its prevention of oxalate-induced microbiota dysbiosis. Single-dose BS168 supplementation exerted beneficial effects on D. melanogaster for as long as 14 days, decreasing stone burden in dissected Malpighian tubules and fecal excreta while increasing survival and behavioral markers of health over those of nonsupplemented lithogenic controls. These findings were complemented by in vitro experiments using the established MDCK renal cell line, which demonstrated that BS168 pretreatment prevented increased CaOx crystal adhesion and aggregation. Taking our results together, this study supports the notion that BS168 can functionally reduce CaOx stone burden in vivo through its capacity for oxalate degradation. Given the favorable safety profile of many B. subtilis strains already used as digestive aids and in fermented foods, these findings suggest that BS168 could represent a novel therapeutic adjunct to reduce the incidence of recurrent CaOx nephrolithiasis in high-risk patients.

IMPORTANCE Kidney stone disease is a morbid condition that is increasing in prevalence, with few nonsurgical treatment options. The majority of stones are composed of calcium oxalate. Unlike humans, some microbes can break down oxalate, suggesting that microbial therapeutics may provide a novel treatment for kidney stone patients. This study demonstrated that Bacillus subtilis 168 (BS168) decreased stone burden, improved health, and complemented the microbiota in a Drosophila melanogaster urolithiasis model, while not exacerbating calcium oxalate aggregation or adhesion to renal cells in vitro. These results identify this bacterium as a candidate for ameliorating stone formation; given that other strains of B. subtilis are components of fermented foods and are used as probiotics for digestive health, strain 168 warrants testing in humans. With the severe burden that recurrent kidney stone disease imposes on patients and the health care system, this microbial therapeutic approach could provide an inexpensive therapeutic adjunct.

Shape-dependent adhesion and endocytosis of hydroxyapatite nanoparticles on A7R5 aortic smooth muscle cells

The interaction between nanohydroxyapatite (HAP) and smooth muscle cells is an important step in vascular calcification. However, the effect of the shape of HAP on adhesion and endocytosis to aortic smooth muscle cells has been rarely reported. Four different morphological HAP crystals (H-Rod, H-Needle, H-Sphere, and H-Plate) were selected to interact with rat aortic smooth muscle cells (A7R5). Fluorescence-labeled HAP was used to detect crystal adhesion and endocytosis and then pretreated with different endocytic inhibitors to explore the pathway of endocytotic crystals. The distribution of crystals inside and outside the cells and the crystal localization in lysosomes was observed through laser confocal microscopy. The effect of crystal on the cell cycle and the changes in the expression of phosphatidylserine, osteopontin, α-actin, core binding factor alpha 1, and osterix on the surface of A7R5 cells were detected. The adhesion and endocytosis of HAP on A7R5 cells were closely related to crystal shapes and ranked as follows: H-Plate > H-Sphere > H-Needle > H-Rod. H-Sphere and H-Needle were internalized into the cells mainly via the clathrin-mediated pathway, whereas H-Plate and H-Rod were internalized into the cells mainly via macropinocytosis. The endocytosed nano-HAP was mainly distributed in the cell lysosome. The adhesion and endocytosis of HAP to A7R5 cells were positively correlated with the specific surface area, and contact area of HAP and negatively correlated with the absolute value of Zeta and contact angle of HAP. This study provided insights into the effect of crystal morphology on vascular calcification and its mechanism.

In Vitro and In Silico Evaluation of Betulin on Calcium Oxalate Crystal Formation

Objective: The medicinal plant Betula alba has been used for prevention and treatment of kidney stones. Betulin is one of the main phytochemicals of Betula alba. The aim of this study is to investigate the antioxidant and antiurolithiatic activity of betulin in vitro and in silico. For antioxidant activity, 2, 2-diphenyl-1-picrylhydrazyl (DPPH), total reducing capacity, nitric oxide (NO) radical scavenging assay, and superoxide radical scavenging assay were studied. Method: In order to study antiurolithiatic activity, three assays such as crystallization, nucleation, and aggregation of oxalate crystal in urine were performed. In silico experiments were performed by using AutoDock 4.2 tools in order to establish affinity of phytochemicals toward antioxidant enzyme and matrix metalloproteinase (MMP-2 and 9). Results: The results obtained clearly demonstrate the significant scavenging activity of betulin and cystone against DPPH, NO, and superoxide radicals in comparison to standard antioxidant L-ascorbate (L-AA). It has also been observed that betulin has the capacity to inhibit the crystallization, nucleation, and aggregation in comparison to cystone. On the other hand, betulin and L-AA showed strong affinity toward antioxidant enzymes and matrix metalloproteinase as determined by in silico experiments. Conclusions: From this, it may be concluded that the antiurolithiatic activity of betulin is, at least in part, mediated by its antioxidant property.

Repair activity and crystal adhesion inhibition of polysaccharides with different molecular weights from red algae Porphyra yezoensis against oxalate-induced oxidative damage in renal epithelial cells

Porphyra yezoensis polysaccharide repaired oxalate-injured renal epithelial cells and decreased COM crystal adhesion on the cell surface.

Protective effect of pentoxifylline on oxidative renal cell injury associated with renal crystal formation in a hyperoxaluric rat model

The aim of the study is to investigate the effects of pentoxifylline (PTX) on the renal tubular cell injury and stone formation in a hyperoxaluric rat model induced by ethylene glycol and its possible underlying mechanisms. The study was performed with 30 male Wistar rats and randomized into three groups of teen. The sham-control (group 1) received only drinking water orally. The EG/untreated (group 2) received drinking water containing 0.75% EG for 4 weeks orally. The EG/PTX treated (group 3) received drinking water containing 0.75% EG for 4 weeks orally and PTX. Urine and blood were collected to determine some parameters. The kidneys were also removed for histological examination. Serum and urinary parameters were significantly improved in the EG/PTX treated. In the EG/PTX-treated group, the MDA, TOS and MPO activity reduced and the TAS, SOD, CAT and GSH-Px activities were increased markedly compared with the group 2. In urine of the group 2 rats, a large number of CaOx crystals were displayed and most tubules that contained crystals were dilated and showed degeneration, necrosis, and desquamation of the lining epithelium. Only few CaOx crystals were r in EG/PTX-treated animal's urine. Mild tissue damage was observed in PTX-treated rats. iNOS expression was significantly elevated in the group 2. In contrast, in the EG/PTX-treated group, eNOS expression in renal tubular epithelial cells was increased. Current study indicates that PTX may partially reduce renal tubular injury resulting from hyperoxaluria-induced oxidative and nitrosative stress.

Calcifying nanoparticles induce cytotoxicity mediated by ROS-JNK signaling pathways

Calcifying nanoparticles (CNPs) play an important role in kidney stone formation, but the mechanism(s) are unclear. CNPs were isolated and cultured from midstream urine of patients with kidney stones. CNP morphology and characteristics were examined by electron microscopy and electrophoresis analysis. Chemical composition was analyzed using energy-dispersive X-ray microanalysis and Western blotting. Human renal proximal convoluted tubule cell (HK-2) cultures were exposed to CNPs for 0, 12 and 72 h, and production of reactive oxygen species (ROS), mitochondrial membrane potential and apoptosis levels were evaluated. CNPs isolated from patients showed classical morphology, the size range of CNPs were 15-500 nm and negative charge; they were found to contain fetuin-A. Exposure of HK-2 cells to CNPs induced ROS production, decreased mitochondrial membrane potential and decreased cell viability. Transmission electron microscopy showed that CNPs can enter the cell by phagocytosis, and micrographs revealed signs of apoptosis and autophagy. CNPs increased the proportion of apoptotic cells, down-regulated Bcl-2 expression and up-regulated Bax expression. CNPs also up-regulated expression of LC3-B, Beclin-1and p-JNK.CNPs are phagocytosed by HK-2 cells, leading to autophagy, apoptosis and ROS production, in part through activation of JNK signaling pathways. ROS and JNK pathways may contribute to CNP-induced cell injury and kidney stone formation.

Cell death-based approaches in treatment of the urinary tract-associated diseases: a fight for survival in the killing fields

Urinary tract-associated diseases comprise a complex set of disorders with a variety of etiologic agents and therapeutic approaches and a huge global burden of disease, estimated at around 1 million deaths per year. These diseases include cancer (mainly prostate, renal, and bladder), urinary tract infections, and urolithiasis. Cell death plays a key role in the pathogenesis and therapy of these conditions. During urinary tract infections, invading bacteria may either promote or prevent host cell death by interfering with cell death pathways. This has been studied in detail for uropathogenic E. coli (UPEC). Inhibition of host cell death may allow intracellular persistence of live bacteria, while promoting host cell death causes tissue damage and releases the microbes. Both crystals and urinary tract obstruction lead to tubular cell death and kidney injury. Among the pathomechanisms, apoptosis, necroptosis, and autophagy represent key processes. With respect to malignant disorders, traditional therapeutic efforts have focused on directly promoting cancer cell death. This may exploit tumor-specific characteristics, such as targeting Vascular Endothelial Growth Factor (VEGF) signaling and mammalian Target of Rapamycin (mTOR) activity in renal cancer and inducing survival factor deprivation by targeting androgen signaling in prostate cancer. An area of intense research is the use of immune checkpoint inhibitors, aiming at unleashing the full potential of immune cells to kill cancer cells. In the future, this may be combined with additional approaches exploiting intrinsic sensitivities to specific modes of cell death such as necroptosis and ferroptosis. Here, we review the contribution of diverse cell death mechanisms to the pathogenesis of urinary tract-associated diseases as well as the potential for novel therapeutic approaches based on an improved molecular understanding of these mechanisms.

Modeling time-series data from microbial communities

As sequencing technologies have advanced, the amount of information regarding the composition of bacterial communities from various environments (for example, skin or soil) has grown exponentially. To date, most work has focused on cataloging taxa present in samples and determining whether the distribution of taxa shifts with exogenous covariates. However, important questions regarding how taxa interact with each other and their environment remain open thus preventing in-depth ecological understanding of microbiomes. Time-series data from 16S rDNA amplicon sequencing are becoming more common within microbial ecology, but methods to infer ecological interactions from these longitudinal data are limited. We address this gap by presenting a method of analysis using Poisson regression fit with an elastic-net penalty that (1) takes advantage of the fact that the data are time series; (2) constrains estimates to allow for the possibility of many more interactions than data; and (3) is scalable enough to handle data consisting of thousands of taxa. We test the method on gut microbiome data from white-throated woodrats (Neotoma albigula) that were fed varying amounts of the plant secondary compound oxalate over a period of 22 days to estimate interactions between OTUs and their environment.

Serum creatinine and cystatin C provide conflicting evidence of acute kidney injury following acute ingestion of potassium permanganate and oxalic acid

AIM

Acute kidney injury (AKI) is common following deliberate self-poisoning with a combination washing powder containing oxalic acid (H₂C₂O₄) and potassium permanganate (KMnO₄). Early and rapid increases in serum creatinine (sCr) follow severe poisoning. We investigated the relationship of these increases with direct nephrotoxicity in an ongoing multicenter prospective cohort study in Sri Lanka exploring AKI following poisoning.

METHODS

Multiple measures of change in kidney function were evaluated in 48 consenting patients who had serial sCr and serum cystatin C (sCysC) data available.

RESULTS

Thirty-eight (38/48, 79%) patients developed AKI (AKIN criteria). Twenty-eight (58%) had AKIN stage 2 or 3. Initial increases in urine creatinine (uCr) excretion were followed by a substantial loss of renal function. The AKIN stage 2 and 3 (AKIN2/3) group had very rapid rises in sCr (a median of 118% at 24 h and by 400% at 72 h post ingestion). We excluded the possibility that the rapid rise resulted from the assay used or muscle damage. In contrast, the average sCysC increase was 65% by 72 h.

CONCLUSIONS

In most AKI, sCysC increases to the same extent but more rapidly than sCr, as sCysC has a shorter half-life. This suggests either a reduction in Cystatin C production or, conversely, that the rapid early rise of sCr results from increased production of creatine and creatinine to meet energy demands following severe oxidative stress mediated by H₂C₂O₄ and KMnO₄. Increased early creatinine excretion supports the latter explanation, since creatinine excretion usually decreases transiently in AKIN2/3 from other causes.

Cytoprotective and anti-apoptotic role of Terminalia arjuna on oxalate injured renal epithelial cells

Urolithiasis is one of the painful multifactorial disorders caused by metabolic abnormalities influencing the composition of body fluids and urine. The bark of Terminalia arjuna (T. arjuna), very well known in Ayurveda for the treatment of cardiovascular diseases, possesses antioxidant and diuretic activity. The present study was undertaken to investigate the antiurolithiatic efficacy of aqueous extract of bark of T. arjuna on oxalate-induced injury to renal tubular epithelial cells. Madin-Darby canine kidney (MDCK) cells were exposed to 2 mM oxalate for 48 h to evaluate the protective effect of T. arjuna aqueous extract on cell viability, CaOx crystal adherence and apoptotic changes caused by oxalate. The results confirmed that oxalate injured MDCK cells were protected by T. arjuna extract. On treatment with a range concentrations, the cell viability increased in a concentration dependent manner. Moreover, the extract prevented the interaction of the calcium oxalate (CaOx) crystals with the cell surface and reduced the number of apoptotic cells. The current data suggests that T. arjuna bark confers a cytoprotective role and based on our results it could be a potential candidate from natural plant sources against urolithiasis.

Calcium oxalate toxicity in renal epithelial cells: the mediation of crystal size on cell death mode

The cytotoxicity of calcium oxalate (CaOx) in renal epithelial cells has been studied extensively, but the cell death mode induced by CaOx with different physical properties, such as crystal size and crystal phase, has not been studied in detail. In this study, we comparatively investigated the differences of cell death mode induced by nano-sized (50 nm) and micron-sized (10 μm) calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD) to explore the cell death mechanism. The effect of the exposure of nano-/micron-sized COM and COD crystals toward the African green monkey renal epithelial (Vero) cells were investigated by detecting cell cytoskeleton changes, lysosomal integrity, mitochondrial membrane potential (Δψm), apoptosis and/or necrosis, osteopontin (OPN) expression, and malondialdehyde (MDA) release. Nano-/micron-sized COM and COD crystals could cause apoptosis and necrosis simultaneously. Nano-sized crystals primarily caused apoptotic cell death, leading to cell shrinkage, phosphatidylserine ectropion, and nuclear shrinkage, whereas micron-sized crystals primarily caused necrotic cell death, leading to cell swelling and cell membrane and lysosome rupture. Nano-sized COM and COD crystals induced much greater cell death (sum of apoptosis and necrosis) than micron-sized crystals, and COM crystals showed higher cytotoxicity than the same-sized COD crystals. Both apoptosis and necrosis could lead to mitochondria depolarization and elevate the expression of OPN and the generation of lipid peroxidation product MDA. The amount of expressed OPN and generated MDA was positively related to cell injury degree. The physicochemical properties of crystals could affect the cell death mode. The results of this study may provide a basis for future studies on cell death mechanisms.

Ceramide-induced apoptosis in renal tubular cells: a role of mitochondria and sphingosine-1-phoshate

Ceramide is synthesized upon stimuli, and induces apoptosis in renal tubular cells (RTCs). Sphingosine-1 phosphate (S1P) functions as a survival factor. Thus, the balance of ceramide/S1P determines ceramide-induced apoptosis. Mitochondria play a key role for ceramide-induced apoptosis by altered mitochondrial outer membrane permeability (MOMP). Ceramide enhances oligomerization of pro-apoptotic Bcl-2 family proteins, ceramide channel, and reduces anti-apoptotic Bcl-2 proteins in the MOM. This process alters MOMP, resulting in generation of reactive oxygen species (ROS), cytochrome C release into the cytosol, caspase activation, and apoptosis. Ceramide regulates apoptosis through mitogen-activated protein kinases (MAPKs)-dependent and -independent pathways. Conversely, MAPKs alter ceramide generation by regulating the enzymes involving ceramide metabolism, affecting ceramide-induced apoptosis. Crosstalk between Bcl-2 family proteins, ROS, and many signaling pathways regulates ceramide-induced apoptosis. Growth factors rescue ceramide-induced apoptosis by regulating the enzymes involving ceramide metabolism, S1P, and signaling pathways including MAPKs. This article reviews evidence supporting a role of ceramide for apoptosis and discusses a role of mitochondria, including MOMP, Bcl-2 family proteins, ROS, and signaling pathways, and crosstalk between these factors in the regulation of ceramide-induced apoptosis of RTCs. A balancing role between ceramide and S1P and the strategy for preventing ceramide-induced apoptosis by growth factors are also discussed.

Observation of superoxide production during catalysis of Bacillus subtilis oxalate decarboxylase at pH 4

This contribution describes the trapping of the hydroperoxyl radical at a pH of 4 during turnover of wild-type oxalate decarboxylase and its T165V mutant using the spin-trap BMPO. Radicals were detected and identified by a combination of EPR and mass spectrometry. Superoxide, or its conjugate acid, the hydroperoxyl radical, is expected as an intermediate in the decarboxylation and oxidation reactions of the oxalate monoanion, both of which are promoted by oxalate decarboxylase. Another intermediate, the carbon dioxide radical anion was also observed. The quantitative yields of superoxide trapping are similar in the wild type and the mutant while it is significantly different for the trapping of the carbon dioxide radical anion. This suggests that the two radicals are released from different sites of the protein.

Krüppel-like factor 5 associates with melamine-cyanurate crystal-induced nephritis in rats

BACKGROUND

Melamine and cyanuric acid (M/CA), when orally administered together to rats, can induce crystal formation within renal tubules and cause acute kidney injury.

METHODS

To investigate the pathomechanism of crystal-induced nephritis, melamine and/or cyanuric acid were administered to 3-week-old (young) and 8-week-old (adult) rats, respectively.

RESULTS

Crystal formation, blood urea nitrogen elevation, tubular cell injury and macrophage infiltration were noted in rats fed with M/CA, but not in rats fed with vehicle, melamine or CA alone. These parameters were significantly higher in young rats than those in adult rats fed with M/CA 200 mg/kg body weight (BW) for 3 days. Krüppel-like factor 5 (KLF5) was expressed on distal tubule cells, especially when crystals deposited within the lumens. Both mRNA and protein levels were higher in young rats than those in adult rats fed with M/CA (200 mg/kg BW). KLF5 expression has been shown to modulate renal tissue cytokine production, and we found that proinflammatory cytokines like monocyte chemoattractant protein-1 and interlukin-6 were increased in kidney tissues of young rats fed with M/CA for 3 days. In contrast, interlukin-10, an anti-inflammatory cytokine, was upregulated in kidneys of adult rats fed with M/CA for 3 days.

CONCLUSIONS

Crystals are prone to deposition in distal tubules of young rats fed with M/CA. M/CA Crystal-related nephritis might be induced by the KLF5 expression, which modulated macrophage recruitment and proinflammatory cytokine production, subsequently leading to renal tubular injury and interstitial inflammation.

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.

Role of TNF-associated cytokines in renal tubular cell apoptosis induced by hyperoxaluria

Crystal-cell interaction has been reported as one of the most crucial steps in urinary stone formation. Hyperoxaluria-induced apoptotic changes in renal tubular epithelial cells is the end-stage of this interaction. We aimed to evaluate the possible pathways responsible in the induction of apoptosis within the involved cells by assessing the receptoral expression of three different pathways. 16 male Spraque-Dowley rats were divided into two groups: Group 1 (n:8) received only distilled water; Group 2 (n:8) received 0.75 % ethylene glycol (EG) in their daily water to induce hyperoxaluria for 2 weeks. After 24 h urine collection, all animals were euthenized and right kidneys were removed and fixed for immunohistochemical evaluation. Oxalate and creatinine levels (in 24 h-urine) and FAS, tumor necrosis factor (TNF), TNF-related apoptosis-inducing ligand (TRAIL) and TRAIL receptor-2 expressions (in tissue) have been assessed. In addition to TNF (p = 0.0007) expression; both FAS (p = 0.0129 ) and FASL (p = 0.032) expressions significantly increased in animals treated with EG. The expressions of TRAIL (p = 0.49) and TRAIL-R2 (p = 0.34) receptors did not change statistically after hyperoxaluria induction. Although a positive correlation with cytokine expression density and 24 h-urinary oxalate expression (mg oxalate/mg creatinine) has been assessed with TNF (p = 0.04, r = 0.82), FAS (p = 0.05, r = 0.80), FAS-L (p = 0.04, r = 0.82); no correlation could be demonstrated between TRAIL and TRAIL R2 expressions. Our results indicate that apoptosis induced by oxalate is possibly mediated via TNF and FAS pathways. However, TRAIL and TRAIL-R2 seemed to have no function in the cascade. Correlation with urinary oxalate levels did further strengthen the findings.

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.

Human umbilical vein endothelial cells accelerate oxalate-induced apoptosis of human renal proximal tubule epithelial cells in co-culture system which is prevented by pyrrolidine dithiocarbamate

Oxalate is the most common component of kidney stones and elevated urinary levels induce renal tubular cell toxicity and death which is essential for crystal attachment. Endothelial cells, in some studies have been shown to regulate certain functions of renal proximal tubule cells. The aim of this study was to evaluate the effect of endothelial cells on tubular cell apoptosis in a co-culture system mimicking the in vivo renal physiological settings. The human umbilical vein endothelial cells (HUVEC) and human renal proximal tubule epithelial cells (RPTEC) were exposed to increasing concentrations (0-1.0 mM) of oxalate with or without 10 μM PDTC pretreatment for 24 h. In HUVEC, RPTEC and HUVEC-RPTEC co-cultures, the cell viability was measured using the WST-1 assay and cell death with the TUNEL analysis using the flow cytometry. The treatment of RPTECs with oxalate lead to 8.9-26.2% cell death which was reduced to 0-1.6% with the PDTC pretreatment. The death rate of RPTECs was significantly increased by 15-19% at different oxalate concentrations when co-cultured with HUVECs. In contrast, cell viability was not substantially altered in PDTC pretreated RPTECs that were co-cultured with HUVECs. Apoptosis was the way of cell death as similar rate of apoptosis was observed in cell culture systems. Although cell viability of RPTECs was further reduced when co-cultured with HUVECs, it was restored with the pretreatment of PDTC. This is the first study focusing on the role of endothelial cells on RPTEC apoptosis following hyperoxaluria.

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.

Simultaneous impedimetric and amperometric interrogation of renal cells exposed to a calculus-forming salt

The complexity of the cellular response, induced even by the simplest experimental stimulus, requires an increased number of cellular parameters to be simultaneously monitored. An all electrochemical system allowing the simultaneous and real-time monitoring of both cell adherence and superoxide release into the extracellular space was developed to address this challenge. Cell adherence (to neighboring cells and to substrate) was monitored using non-faradaic impedance spectroscopy while the superoxide release was monitored using a cytochrome c-based amperometric biosensor. The system was used to observe for the first time how these two cellular parameters are changing in real-time for renal cells exposed to calcium oxalate, a calculus-forming salt. It was discovered that calcium oxalate crystals decrease cell adherence and in the same time induce oxidative stress by an overproduction of superoxide. Subconfluent cells, without fully developed tight junctions, appear to be more vulnerable than confluent cells with tight junctions indicating the important protective role of these junctions.

Preparation and investigation of bioactive transferrin-iron complexes formed with different synergistic anions

Human serum transferrin has a potential for drug-delivery systems. Oxalate and aziridine-carboxylate was conjugated to serum transferrin in order to transport into the targeted cancer cells via transferrin-receptor mediated endocytosis. Capillary zone electrophoresis and capillary isoelectric focusing were used to analyze the effectiveness of complexation reactions. The electropherograms show the differences between iron-free- and iron-complexed molecular forms of human serum transferrin. The iron-complexed transferrin sample containing the different anions as synergistic complexing agents were characterized by different electrophoretic parameters.

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.

Oxidative Decomposition of Vitamin C in Drinking Water

We have previously shown that vitamin C (ascorbic acid) can initiate hydroxyl radical formation in copper contaminated household drinking water. In the present study, we have examined the stability of vitamin C in copper and bicarbonate containing household drinking water. In drinking water samples, contaminated with copper from the pipes and buffered with bicarbonate, 35% of the added vitamin C was oxidized to dehydroascorbic acid within 15 min. After 3h incubation at room temperature, 93% of the added (2 mM) ascorbic acid had been oxidized. The dehydroascorbic acid formed was further decomposed to oxalic acid and threonic acid by the hydrogen peroxide generated from the copper (I) autooxidation in the presence of oxygen. A very modest oxidation of vitamin C occurred in Milli-Q water and in household water samples not contaminated by copper ions. Moreover, addition of vitamin C to commercially sold domestic bottled water samples did not result in vitamin C oxidation. Our results demonstrate that ascorbic acid is rapidly oxidized to dehydroascorbic acid and further decomposed to oxalic- and threonic acid in copper contaminated household tap water that is buffered with bicarbonate. The impact of consuming ascorbic acid together with copper and bicarbonate containing drinking water on human health is discussed.

Mechanisms of star fruit-induced acute renal failure

We have previously discovered that star fruit can induce oliguric acute renal failure. To investigate the mechanisms of star fruit-associated acute oxalate nephropathy, the nephrotoxic effect of star fruit was examined in both cellular experiments and animal models. We evaluated renal function, pathological changes in kidney tissues and apoptotic effects using terminal deoxynucleotidyl transferase nick-end labeling (TUNEL) assay in four groups of rats -- a control group (CG), fed with tap water (1); a star fruit group (SG), fed with star fruit juice naturally containing 0.2M oxalate (2); and oxalate groups (OxG), fed with 0.2M (3) or 0.4M (4) oxalate solution. The effects of both star fruit juice and oxalate on MDCK cells were also analyzed by flow cytometry. We found that the mean creatinine clearance was significantly lower in the SG, 0.2M OxG and 0.4M OxG. Dose-dependent apoptotic effects were evident from the TUNEL assay, and flow cytometry analysis of treated MDCK cells showed dose- and time-dependent effects. Our findings suggest that star fruit juice produces acute renal injury, not only through the obstructive effect of calcium oxalate crystals, but also by inducing apoptosis of renal epithelial cells, which may be caused by the levels of oxalate in the fruit.

Stability of oxaliplatin in infusion bags containing 5% dextrose injection

PURPOSE

The stability of oxaliplatin in infusion bags containing 5% dextrose injection was studied.

METHODS

Solutions of oxaliplatin 0.7 mg/mL were prepared in polyolefin infusion bags containing 5% dextrose injection and stored at 3-7 degrees C in a lightproof bag, at 20-24 degrees C with continuous exposure to artificial light, and at 20-24 degrees C with continuous exposure to fluorescent light in a lightproof bag. Samples were analyzed at 1, 2, 3, 4, 5, 7, 14, and 30 days and assayed in duplicate. Stability was measured using a stability-indicating high-performance liquid chromatographic method. Samples were also examined for changes in color and pH and for the presence of particulate matter.

RESULTS

All samples retained over 90% of their initial concentration over the study period. No color changes or visible precipitation was observed, and the pH of all samples remained stable. Neither temperature nor artificial light had any significant effect on the stability of oxaliplatin.

CONCLUSION

Oxaliplatin 0.7 mg/mL in infusion bags containing 5% dextrose injection was chemically stable for at least 30 days at both 3-7 degrees C and 20-24 degrees C without regard to light exposure.

Calcium oxalate, and not other metabolites, is responsible for the renal toxicity of ethylene glycol

Ethylene glycol (EG) is nephrotoxic due to its metabolism. Many studies suggest that the toxicity is due to oxalate accumulation, but others have conversely suggested that toxicity results from effects of metabolites such as glycolaldehyde or glyoxylic acid on proximal tubule cells. In vivo studies have indicated that accumulation of calcium oxalate monohydrate (COM) corresponds closely with development of toxicity in renal tissue. The present studies were therefore designed to clarify the roles of various metabolites in the mechanism for EG toxicity in vitro by comparing the relative cytotoxicity of EG metabolites using three measures of cell death, ethidium homodimer uptake, lactate dehydrogenase (LDH) release and the conversion of the tetrazolium salt XTT to a colorimetric dye. Human proximal tubule cells in culture were incubated in physiologic buffers for 6h at 37 degrees C with COM (147-735microg/ml, an oxalate equivalence of 1-5mM), glycolate (5-25mM), glyoxylate (0.2-5mM) and glycolaldehyde (0.2-2mM). To assess the effects of acidity on the cytotoxicity, incubations were carried out at pH 6-7.4. The results show that COM dose-dependently increased LDH release and ethidium homodimer uptake, while the other metabolites did not. Conversely, COM had no effect on the XTT assay, while high concentrations of glycolaldehyde and glyoxylate decreased XTT activity, but the latter only at acidic pH. The correlation between the uptake of ethidium homodimer and the release of LDH suggest that COM is cytotoxic to human kidney cells in culture, while the XTT assay does not validly measure cytotoxicity in this system. These results indicate that COM, and not glyoxylate or glycolaldehyde, is the toxic metabolite responsible for the acute tubular necrosis and renal failure that is observed in EG-poisoned patients.

Prediction of rodent carcinogenic potential of naturally occurring chemicals in the human diet using high-throughput QSAR predictive modeling

Consistent with the U.S. Food and Drug Administration (FDA) Critical Path Initiative, predictive toxicology software programs employing quantitative structure-activity relationship (QSAR) models are currently under evaluation for regulatory risk assessment and scientific decision support for highly sensitive endpoints such as carcinogenicity, mutagenicity and reproductive toxicity. At the FDA's Center for Food Safety and Applied Nutrition's Office of Food Additive Safety and the Center for Drug Evaluation and Research's Informatics and Computational Safety Analysis Staff (ICSAS), the use of computational SAR tools for both qualitative and quantitative risk assessment applications are being developed and evaluated. One tool of current interest is MDL-QSAR predictive discriminant analysis modeling of rodent carcinogenicity, which has been previously evaluated for pharmaceutical applications by the FDA ICSAS. The study described in this paper aims to evaluate the utility of this software to estimate the carcinogenic potential of small, organic, naturally occurring chemicals found in the human diet. In addition, a group of 19 known synthetic dietary constituents that were positive in rodent carcinogenicity studies served as a control group. In the test group of naturally occurring chemicals, 101 were found to be suitable for predictive modeling using this software's discriminant analysis modeling approach. Predictions performed on these compounds were compared to published experimental evidence of each compound's carcinogenic potential. Experimental evidence included relevant toxicological studies such as rodent cancer bioassays, rodent anti-carcinogenicity studies, genotoxic studies, and the presence of chemical structural alerts. Statistical indices of predictive performance were calculated to assess the utility of the predictive modeling method. Results revealed good predictive performance using this software's rodent carcinogenicity module of over 1200 chemicals, comprised primarily of pharmaceutical, industrial and some natural products developed under an FDA-MDL cooperative research and development agreement (CRADA). The predictive performance for this group of dietary natural products and the control group was 97% sensitivity and 80% concordance. Specificity was marginal at 53%. This study finds that the in silico QSAR analysis employing this software's rodent carcinogenicity database is capable of identifying the rodent carcinogenic potential of naturally occurring organic molecules found in the human diet with a high degree of sensitivity. It is the first study to demonstrate successful QSAR predictive modeling of naturally occurring carcinogens found in the human diet using an external validation test. Further test validation of this software and expansion of the training data set for dietary chemicals will help to support the future use of such QSAR methods for screening and prioritizing the risk of dietary chemicals when actual animal data are inadequate, equivocal, or absent.

Detrimental role of homocysteine in renal ischemia-reperfusion injury

Ischemia followed by reperfusion is a major cause for renal injury in both native kidney and renal allografts. Hyperhomocysteinemia, a condition of elevated plasma homocysteine (Hcy) level, is associated with cardiovascular diseases. Recent evidence suggests that Hcy, at higher levels, may be harmful to other organs such as the kidney. In this study, we investigated the role of Hcy in ischemia-reperfusion-induced renal injury. The left kidney of a Sprague-Dawley rat was subjected to either 30-min or 1-h ischemia followed by 1- or 24-h reperfusion. Ischemia-reperfusion caused a significant increase in peroxynitrite formation and lipid peroxidation in kidneys, which reflected oxidative stress. The number of apoptotic cells in those kidneys was also markedly increased. Hcy levels were elevated 2.9- and 1.5-fold in kidneys subjected to ischemia alone or ischemia-reperfusion, respectively. Further investigation revealed that elevation of Hcy level in the kidney upon ischemia-reperfusion was due to reduced activity of cystathionine-beta-synthase, a key enzyme in Hcy metabolism. Administration of anti-Hcy antibodies into the kidney not only abolished ischemia-reperfusion-induced oxidative stress and cell death in the kidneys but also restored renal function after 1 h of reperfusion. However, such a protective effect was not sustained after 24 h of reperfusion. In conclusion, ischemia-reperfusion impairs Hcy metabolism in the kidney. Hcy, at elevated levels, is capable of inducing oxidative stress and renal injury. Neutralization of Hcy with antibodies offers transient functional benefit against ischemia-reperfusion-induced oxidative stress and renal injury. These results suggest that Hcy may play a detrimental role in the kidney during ischemia-reperfusion.

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.

Vitamin E attenuates crystal formation in rat kidneys: Roles of renal tubular cell death and crystallization inhibitors

We previously reported that oxidative stress and renal tubular damage occur in chronic hyperoxaluric rats. However, the in vivo responses of renal epithelial cells after vitamin E administration and their correlations with calcium oxalate (CaOx) crystal formation have not been evaluated. Male Wistar rats received 0.75% ethylene glycol (EG) for 7, 21, or 42 days to induce CaOx deposition (EG group). Another group of EG-treated rats received 200 mg kg(-1) of vitamin E intraperitoneally (EG+E group) to evaluate its effect on hyperoxaluria. Urinary electrolytes and biochemistry and levels of lipid peroxides and enzymes were examined, together with serum vitamin E levels. Levels of the tubular markers, alpha and mu glutathione S-transferase, proliferating cell nuclear antigen (PCNA), osteopontinin (OPN), and Tamm-Horsfall protein (THP) were also measured, and TUNEL staining was performed to examine the viability of the tubular epithelium. There were no significant differences between the two age-matched controls either untreated or given vitamin E. Compared to untreated controls, tubular cell death was increased at all time points in EG rats with a gradual increase in CaOx crystals, whereas the number of PCNA-positive cells was only significantly increased on day 21. In EG+E rats, tubular cell death was decreased compared to the EG group, and cell proliferation was seen at all time points, while CaOx crystal deposition was decreased, but hyperoxaluria, urinary lipid peroxides, and enzymuria were unaffected. Vitamin E supplement prevented the loss of OPN and THP in renal tissues by EG and the reduction in their levels in the urine. The beneficial effect of vitamin E in reducing CaOx accumulation is due to attenuation of tubular cell death and enhancement of the defensive roles of OPN and THP.

Impact of hypoxia and hypercapnia on calcium oxalate toxicity in renal epithelial and interstitial cells

Although there is an ongoing controversy about the primary site of calcium oxalate stone (CaOx) formation, there is some evidence for extratubular crystallization. However, the mechanisms leading to such interstitial calcifications are not clear. Anatomical studies have demonstrated a close association between the renal vasculature and renal tubules. It has been hypothesized that disorders of the vasculature may contribute to renal stone formation. The exceptional papillary environment with low oxygen and high carbon dioxide is of interest in this context and its impact on CaOx toxicity to renal cells has to be evaluated. LLC-PK1, Madin-Darby canine kidney (MDCK), human umbilical vein endothelial (HUVEC) and fibroblast cell lines were exposed to hypoxia (3% O2) alone, hypercapnia combined with hypoxia (3% O2, 18% CO2) or standard culture conditions (20% O2) for 72 h. Cell survival rates were determined microscopically after 4 h of incubation with CaOx at final concentrations of 1, 2 and 4 mM. DAPI staining and western blot were used to evaluate the induction of apoptosis. We confirmed that CaOx leads to concentration-dependent effects on the viability of the cell lines. HUVECs were most vulnerable to CaOx among the four cell lines. Incubation under hypoxia alone had no impact on CaOx toxicity to any of the cell lines in terms of survival. However, under combined hypoxic and hypercapnic conditions, all cell lines displayed a significant reduction of cell survival compared to room air incubation. Again, this effect was most pronounced for HUVECs. The induction of apoptosis could not be demonstrated in any experimental setting. Combined hypoxia and hypercapnia clearly aggravate CaOx toxicity to renal cell lines. As we could not demonstrate the induction of apoptosis, this effect may be a result of toxic necrosis. Especially the CaOx effect on interstitial cell lines might be of interest in the chronic ischemic papillary environment. An increased toxicity may lead to recurrent stone formation, and vice versa, diseases of the vasculature, like arteriosclerosis, may further promote stone formation by induction of local ischemia. This issue has to be clarified by further studies.

Urinary macromolecules and renal tubular cell protection from oxalate injury: Comparison of normal subjects and recurrent stone formers

AIM

To determine whether urinary macromolecules (UMM), which are the high molecular weight substances in urine, can provide protection against the oxalate-associated injury to the renal tubular cells.

METHODS

UMM were extracted from 24-h urine of 12 healthy adult male volunteers and 13 recurrent-stone-former male patients. Urine parameters in relation to urolithiasis were measured, including the level of glycosaminoglycans (GAG) in the UMM. Madin-Darby canine kidney (MDCK) cells were used to evaluate the protective activity of UMM from oxalate-induced cytotoxicity by LDH release measurement and methyl-thiazolyl tertrazolium (MTT) assay.

RESULTS

Considering urinary parameters, citrate was significantly higher in urine from normal subjects than stone-former subjects; the other parameters show no differences between the groups. Total UMM and the level of GAG in the UMM were also significantly higher in the normal subject group. Compared with normal subject and stone-former subject UMM, after cells were treated with the UMM and then exposed to oxalate solution, LDH release was significantly higher in stone-former group. In the MTT assay, we found that more viable cells were observed after treatment with UMM compared to control in both groups. Moreover, UMM from the normal subjects showed higher protective activity against oxalate-related cytotoxicity than UMM from the stone-former subjects.

CONCLUSION

UMM protected renal epithelial cells from oxalate-related injury. This protective activity was found to be higher in normal subject UMM than stone-former UMM. Among other factors, a higher concentration of GAG and citrate in normal subject UMM might affect some parts in this finding.

Hepatocyte growth factor has protective effects on crystal-cell interaction and crystal deposits

OBJECTIVES

To investigate whether hepatocyte growth factor (HGF) has a protective role against crystal-cell interaction and crystal deposits in a stone-forming rat model kidney. Crystal-cell interaction is an important step during the early stages of stone formation. High oxalate levels induce cell injuries and increase adhesion of calcium oxalate monohydrate (COM) crystals to renal tubular cells. HGF was initially identified as the most potent growth factor for hepatocytes and is well known as a mesenchyme-derived pleiotropic factor for various types of cells. HGF has mitogenic, morphogenic, and anti-apoptotic effects on renal tubular cells.

METHODS

Madin-Darby canine kidney cells were exposed to potassium oxalate or COM crystals in the presence or absence of HGF. We measured lactate dehydrogenase activity in the medium and analyzed apoptosis by FACScan. COM crystal formation was induced by administration of 0.5% ethylene glycol in the drinking water and forced feeding of 0.5 microg of 1alpha-OH-D3 every other day to male Sprague-Dawley rats. Plasmid vector encoding HGF was transferred to stone-forming rats on day 1, and the kidneys were excised on day 8.

RESULTS

Exposure of Madin-Darby canine kidney cells to both potassium oxalate (KOX) and COM crystals resulted in an increase in lactate dehydrogenase release and the proportion of apoptotic cells, but these effects were reduced by HGF. HGF had inhibitory activity against the adhesion of COM crystals to Madin-Darby canine kidney cells. HGF gene transfer significantly reduced crystal deposits on the renal tubules in stone-forming rats.

CONCLUSIONS

These findings suggest that HGF might play an important role in stone formation.