Mitochondrial superoxide production during oxalate-mediated oxidative stress in renal epithelial cells

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

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

Dietary oxalate-calcium balance and the incidence of hypertension and chronic kidney disease: a prospective study among an Asian population

Background

The potential effects of dietary oxalate (Ox) intake on cardio-renal function have remained unestablished. We evaluated the effect of usual Ox intake and its interaction with dietary calcium (Ca) on incident hypertension (HTN) and chronic kidney disease (CKD).

Methods

Adult men and women, free of HTN and CKD at baseline (2006–2008), were recruited. Dietary intakes were assessed using a validated food frequency questionnaire, and the outcomes were documented up to 2014–2017. Multivariate Cox proportional hazard regression models were used to estimate the development of HTN and CKD in relation to Ox intakes. Repeated-measures generalized estimating equation (GEE) linear regression models were used to assess possible effect of Ox-intake on the estimated glomerular filtration rate (eGFR) and blood pressure levels over eight years.

Results

Dietary Ox intakes were positively associated with incident CKD (HR = 2.59, 95% CI = 1.46–4.64) and HTN (HR = 1.79, 95% CI = 1.05–3.04). Compared to high-Ca consumers, subjects who had lower Ca intakes (< 990 vs. 1580 mg/d) had a higher incidence of CKD and HTN (HR = 2.43, 95% CI = 1.06–5.55, and HR = 1.72, 95% CI = 0.76–3.78). Participants with higher intakes of Ox (> 220 vs. < 150 mg/d) had lower eGFR values (75.3, 95% CI = 75.0–76.5 vs. 77.3, 95% CI = 76.6–78.1 mL/min/1.73m², P_time×group = 0.004) and higher SBP levels (112, 95% CI = 111–113 vs. 109, 95% CI = 108–110 mmHg, P_time×group = 0.007) overtime.

Conclusion

Higher dietary Ox intake may increase the risk of HTN and CKD. The relation between dietary Ox and risk of HTN and CKD seems to be varied by Ca intake, and subjects with lower Ca intakes may be more burdened by excessive amounts of dietary Ox.

Dietary oxalate to calcium ratio and incident cardiovascular events: a 10-year follow-up among an Asian population

Background and aim

The potential cardiovascular impact of usual intakes of oxalate (Ox) is uninvestigated. We evaluated the effect of dietary Ox and its interaction with dietary calcium (Ca) on incident cardiovascular disease (CVD).

Methods

We included 2966 adult men and women aged 19–84 y without known CVD during baseline enrollment (2006–2008) of the Tehran Lipid and Glucose Study. Dietary intakes were assessed using a validated FFQ, and incident CVD (i.e., coronary heart disease, stroke, and CVD mortality) were documented through March 2018.

Results

A 7.1% incident of CVD occurred during a median follow-up of 10.6 y. After multivariable adjustment for traditional risk factors and key dietary nutrients, including total fat and fiber, Ox intakes ≥220 mg/d increased incident CVD (HR T3 vs. T1 = 1.47, 95% CI = 1.02–2.12). This association was potentiated (HR T3 vs. T1 = 2.42, 95% CI = 1.19–4.89) in subjects who had a lower intake of Ca (< 981 mg/d); in a low-Ca diet, an even lower amount of dietary Ox (second tertile, 148–220 mg/d) was related to increased CVD events by 92% (HR = 1.92, 95% CI = 1.00–3.70). No association was observed between dietary Ox and CVD events in the presence of medium- and high levels of Ca intakes. The critical cut-off point of Ox-to-Ca for predicting CVD events was 0.14, which was related to an increased risk of CVD by 37% (HR = 1.37, 95% CI = 1.02–1.84).

Conclusion

Higher dietary Ox intake appeared to be associated with a modestly elevated risk of incident CVD, especially in a diet with a lower amount of Ca.

The role of reactive oxygen species derived from different NADPH oxidase isoforms and mitochondria in oxalate-induced oxidative stress and cell injury

Hyperoxaluria is a risk factor for urolithiasis and can cause renal epithelial cell injury secondary to oxidative stress. Reactive oxygen species (ROS) produced during cell damage originate from different sources and play different roles. Here, we explored the potential sources of ROS production and investigated the role of ROS from various sources in oxalate-induced oxidative stress and cell injury in normal rat kidney-52 epithelial (NRK-52E) cells. Oxalate-induced injury was assessed by lactate dehydrogenase (LDH) release experiments. 2,7-dichlorodihydrofluorescein diacetate and mitoSOX Red were used to determine the intracellular and mitochondrial ROS (mtROS) production, respectively. The expression level of Nox4, Nox2, and p22 protein was detected by Western blotting to observe the effect of oxalate on nicotinamide adenine dinucleotide phosphate oxidase (NADPH) oxidase (Nox). Furthermore, a specific NADPH oxidase subtype inhibitor and targeted mitochondrial antioxidants were used to preliminarily identify the role of ROS from different sources in renal tubular epithelial cell injury induced by oxalate. We found that oxalate inhibited cell viability, induced LDH release, and prompted intracellular and mitochondrial ROS (mtROS) production. Oxalate also decreased the protein expression level of Nox4 and increased the protein expression level of p22. Mitochondria were also a source of ROS production. In addition, Nox2 inhibitor or mtROS scavenging prevented oxalate-induced cell injury, reversed by an inhibitor of Nox4/1. We concluded that ROS from different sources might play different roles in oxalate-induced renal tubular epithelial cell injury. We also identified new potential targets for preventing or alleviating oxalate-induced renal tubular epithelial cell injury.

Graphic abstract

Dietary Oxalate Loading Impacts Monocyte Metabolism and Inflammatory Signaling in Humans

Diet has been associated with several metabolic diseases and may impact immunity. Increased consumption of meals with high oxalate content may stimulate urinary calcium oxalate (CaOx) crystals, which are precursors to CaOx kidney stones. We previously reported that CaOx stone formers have decreased monocyte cellular bioenergetics compared to healthy participants and oxalate reduces monocyte metabolism and redox status in vitro. The purpose of this study was to investigate whether dietary oxalate loading impacts monocyte cellular bioenergetics, mitochondrial complex activity, and inflammatory signaling in humans. Healthy participants (n = 40; 31.1 ± 1.3 years) with a BMI of 24.9 ± 0.6 kg/m² consumed a controlled low oxalate diet for 3 days before drinking a blended preparation of fruits and vegetables containing a large amount of oxalate. Blood and urine were collected before (pre-oxalate) and for 5 h after the oxalate load to assess urinary oxalate levels, monocyte cellular bioenergetics and mitochondrial complex activity, and plasma cytokine/chemokine levels. Urinary oxalate levels significantly increased in post-oxalate samples compared to pre-oxalate samples. Monocyte cellular bioenergetics, mitochondrial complex I activity, and plasma cytokine and chemokine levels were altered to varying degrees within the study cohort. We demonstrate for the first time that dietary oxalate loading may impact monocyte metabolism and immune response in a cohort of healthy adults, but these response are variable. Further studies are warranted to understand oxalate mediated mechanisms on circulating monocytes and how this potentially influences CaOx kidney stone formation.

Effects of Selenized Astragalus Polysaccharide on the Adhesion and Endocytosis of Nanocalcium Oxalate Dihydrate after the Repair of Damaged HK-2 Cells

An oxidative damage model of human proximal renal epithelial cells (HK-2) was established using oxalate damage. The repair effects of Astragalus polysaccharide (APS) and selenized APS (Se-APS) on damaged HK-2 cells were investigated. Differences in the adhesion and endocytosis of HK-2 cells to calcium oxalate dihydrate crystals with a size of approximately 100 nm before and after APS and Se-APS repair were also explored. The results showed that after being repaired by APS and Se-APS, HK-2 cells exhibited increased cell viability, restored cell morphology, reduced reactive oxygen species level, increased mitochondrial membrane potential, reduced phosphatidylserine eversion, and osteopontin expression. Moreover, the amount of adherent crystals on the cell surface decreased, but the amount of endocytic crystals increased. At the same concentration, Se-APS exhibited better repair effects on the damaged HK-2 cells than APS. All these findings revealed that Se-APS may be a potential drug candidate for inhibiting the formation of kidney stones.

Bioavailable wine pomace attenuates oxalate-induced type II epithelial mesenchymal transition and preserve the differentiated phenotype of renal MDCK cells

The functional renal epithelium is composed of differentiated and polarized tubular cells with a strong actin cortex and specialized cell-cell junctions. If, under pathological conditions, these cells have to resist higher kidney osmolarity, they need to activate diverse mechanisms to survive external nephrotoxic agents such as inflammation and oxidative stress. Wine pomace polyphenols exert protective effects on renal cells. In this study, two wine-pomace products and their protective effects upon promotion and preservation of normal cell differentiation and attenuation of oxalate-induced type II epithelial mesenchymal transition (EMT) are evaluated. Treatment with gastrointestinal and colonic bioavailable fractions from red (rWPP) and white (wWPP) wine pomaces, both in the presence and the absence of oxalate, showed similar cell numbers and nuclear size than the non-treated differentiated MDCK cells. Immunofluorescence analysis showed the reduction of morphological changes and the preservation of cellular junctions for the rWPP and wWPP pre-treatment of cells exposed to oxalate injury. Hence, both rWPP and wWPP attenuated oxalate type II EMT in MDCK cells that conserved their epithelial morphology and cellular junctions through the antioxidant activities of grape pomace polyphenols.

Mitochondrial Dysfunction and Kidney Stone Disease

Mitochondrion is a pivotal intracellular organelle that plays crucial roles in regulation of energy production, oxidative stress, calcium homeostasis, and apoptosis. Kidney stone disease (nephrolithiasis/urolithiasis), particularly calcium oxalate (CaOx; the most common type), has been shown to be associated with oxidative stress and tissue inflammation/injury. Recent evidence has demonstrated the involvement of mitochondrial dysfunction in CaOx crystal retention and aggregation as well as Randall’s plaque formation, all of which are the essential mechanisms for kidney stone formation. This review highlights the important roles of mitochondria in renal cell functions and provides the data obtained from previous investigations of mitochondria related to kidney stone disease. In addition, mechanisms for the involvement of mitochondrial dysfunction in the pathophysiology of kidney stone disease are summarized. Finally, future perspectives on the novel approach to prevent kidney stone formation by mitochondrial preservation are discussed.

Melatonin inhibits oxalate-induced endoplasmic reticulum stress and apoptosis in HK-2 cells by activating the AMPK pathway

Background: Deposition of various crystal and organic substances in the kidney can lead to kidney stone formation. Melatonin is an effective endogenous antioxidant that can prevent crystalluria and kidney damage due to crystal formation and aggregation. In this study, we investigated the mechanism by which melatonin inhibits endoplasmic reticulum (ER) stress and apoptosis. Methods: We treated HK-2 cells with oxalate to establish an in vitro kidney stone model, and treated these cells with different concentrations of melatonin (0, 5, 10, 20 μmol/L) and the AMP-activated protein kinase (AMPK) inhibitor Compound C. We measured levels of stress response markers including reactive oxygen species (ROS), lactate dehydrogenase (LDH), glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), catalase (CAT), and factors in the stress response pathway, such as ATF6, GRP78, DDIT3, PERK, p-PERK, IRE1, p-IRE1, XBP1s, AMPK, and p-AMPK, using real time-PCR, western blot, and immunofluorescence analyzes. We measured mitochondrial membrane potential and caspases-3 activity using the CCK8, enzyme-linked immunosorbent, and flow cytometry assays to assess HK-2 cell viability and apoptosis. Results: Melatonin improved the total antioxidant capacity (T-AOC) of the HK-2 cells, as evidenced by the dose-dependent reduction in apoptosis, ROS levels, and protein expression of ATF6, GRP78, DDIT3, p-PERK, p-IRE1, XBP1s, caspase-12, cleaved caspase-3 and cleaved caspase-9. Addition of the AMPK inhibitor, Compound C, partially reversed the protective effect of melatonin. Conclusion: Our study revealed that the protective effects of melatonin on oxalate-induced ER stress and apoptosis is partly dependent on AMPK activation in HK-2 cells. These findings provide insight into the prevention and treatment of kidney stones.

Inhibiting inflammation and modulating oxidative stress in oxalate-induced nephrolithiasis with the Nrf2 activator dimethyl fumarate

Hyperoxaluria induces oxidative stress, and inflammation causes renal epithelial cell injury in nephrolithiasis, suggesting that reduced oxalate toxicity may be beneficial. This study aimed to investigate whether nuclear factor (erythroid-derived 2)-like 2 (Nrf2, also called Nfe2l2) induced by dimethyl fumarate (DMF) could protect renal epithelial cells against oxalate-mediated injury both in vivo and in vitro. Glyoxylic acid monohydrate was intraperitoneally injected into Sprague-Dawley rats with or without intragastric administration of DMF. We showed that calcium oxalate crystallisation, accompanied by overexpression of oxidant species and inflammatory cytokines and apoptosis in the rat kidney, was partially reversed by treatment with DMF. Furthermore, oxalate induced a reduction in cell viability, cell damage, oxidant species overexpression, mitochondrial dysfunction, and apoptosis in normal rat kidney epithelial-like (NRK-52E) cells, which were reversed by DMF. Pretreatment of NRK-52E cells with DMF significantly increased Nrf2 levels in the nucleus, with subsequent inhibition of the expression of the nicotinamide adenine dinucleotide phosphate subunits Nox4 and P22, canonical inflammation, and osteogenesis-associated differentiation of target genes in the cytoplasm. This effect was partially inhibited by transfection with Nrf2 siRNA and strengthened by transfection with Kelch-like ECH-associated protein 1 siRNA. These results suggest that DMF exerts beneficial effects in nephrolithiasis by inhibiting inflammation and modulating oxidative stress via regulation of Nrf2.

Opportunities for future therapeutic interventions for hyperoxaluria: targeting oxidative stress

INTRODUCTION

Oxalate is a toxic byproduct of metabolism and is normally produced in quantities easily removed from the body. However, under specific circumstances oxalate production is increased resulting in deposition of calcium oxalate (CaOx) crystals in the kidneys as well as other organs causing inflammation and injury. Excessive buildup of crystal deposits in the kidneys causes eventual loss of renal function requiring renal transplantation. Areas covered: Cellular exposure to CaOx crystals induces the production of reactive oxygen species (ROS) with the involvement of renin-angiotensin aldosterone system (RAAS), mitochondria, and NADPH oxidase. Inflammasomes are activated and pro-inflammatory cytokines, such as IL-1β and IL-18 are produced. We reviewed results of experimental and clinical studies of crystal renal epithelial cell interactions with emphasis on cellular injury and ROS production. Expert opinion: Treatment should depend upon the level of hyperoxaluria and whether it is associated with CaOx crystal deposition. Persistent low grade or intermittent hyperoxaluria can be treated with antioxidants, free radical scavengers. Hyperoxaluria associated with CaOx crystal deposition will require administration of angiotensin II receptor blockers, and NADPH oxidase or NLRP3 inflammasome inhibitors. DASH-style diet will be beneficial in both cases.

Oxalate induces type II epithelial to mesenchymal transition (EMT) in inner medullary collecting duct cells (IMCD) in vitro and stimulate the expression of osteogenic and fibrotic markers in kidney medulla in vivo

EMT occurs in response to a number of stresses conditions as mechanical stretch, cancer, hypoxia, oxidative stress (ROS), among others. EMT describes a phenotypical change induced in epithelial cells. It is characterized by increases in motility, extracellular matrix synthesis, proliferation, and invasiveness. The present study analyzed if oxalate ions (Ox) could induce EMT in IMCD cells. Ox (0.5 mM) and transforming growth factor beta (TGF-β1 20 ng/mL) exposition during 48 hours increased migration and invasiveness, increased mesenchymal marker expression (Vimentin, alpha-smooth muscle actin: α-SMA, TGF-β1) and decreased epithelial marker expression (E-cadherin). IMCD stimulated with Ox and TGF-β1 and then exposed to the osteogenic medium during 15 days significantly increased early osteogenic markers (RUNX-2 and Alkaline Phosphatase) expression. Hyperoxaluric mice fed with trans-4-hydroxy-L-proline (HPL) presented calcium oxalate crystal excretion, increased in TGF-β1 expression and collagen fibers deposition and increased early osteogenic markers (RUNX-2 and Alkaline Phosphatase) at 60 days. Our in vitro and in vivo results suggest that oxalate induces EMT in inner medulla collecting duct cells and it may be involved in fibrotic tissue development, osteogenic differentiation and calcium crystal production both implicated in nephrolithiasis.

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.

Inhibition of autophagy-attenuated calcium oxalate crystal-induced renal tubular epithelial cell injury in vivo and in vitro

Accumulating evidence suggests that autophagy is involved in the pathophysiological processes of kidney diseases. However, the role of autophagy in the formation of calcium oxalate (CaOx) nephrolithiasis remains unclear. In this study, we investigated the effects of autophagy on renal tubular epithelial cell injury induced by CaOx crystals in vivo and in vitro. We first observed that the expression levels of LC3-II and BECN1 and number of autophagic vacuoles were markedly increased in the renal tissue of CaOx stone patients. We subsequently found that exposure of HK-2 cells to CaOx crystals could increase LC3-II and BECN1 expression as well as the number of GFP-LC3 dots and autophagic vacuoles in a dose- and time-dependent manner. In addition, our results suggest that CaOx crystals induced autophagy, at least in part, via activation of the reactive oxygen species (ROS) pathway in HK-2 cells. Furthermore, inhibition of autophagy using 3-methyladenine or siRNA knockdown of BECN1 attenuated CaOx crystal-induced HK-2 cells injury. However, enhancing autophagic activity with rapamycin exerted an opposite effect. Taken together, our results demonstrate that autophagy is essential for CaOx crystal-induced renal tubular epithelial cell injury and that inhibition of autophagy could be a novel therapeutic strategy for CaOx nephrolithiasis.

Transcriptional study of hyperoxaluria and calcium oxalate nephrolithiasis in male rats: Inflammatory changes are mainly associated with crystal deposition

Hyperoxaluria associated with renal deposition of calcium oxalate (CaOx) crystals causes renal injury and inflammation leading to number of diseases including chronic kidney disease (CKD). It is however, not been possible to separate the renal consequences of hyperoxaluria from that of CaOx crystal deposition. We decided to utilize ethylene glycol (EG) model where hyperoxaluria and CaOx crystal deposition can be separated in time. To test our hypothesis, male rats were made hyperoxaluric by administering EG, rats were euthanized and kidneys were extracted on day 14, when occasional crystal is seen in the kidneys and day 28, when all animals have developed renal CaOx crystal deposits. Total RNA was extracted for microarray analysis and genome wide analysis of differentially expressed genes was performed to investigate differences between hyperoxaluria and crystal induced alterations in the kidneys. Immunohistochemical and Hematoxylin and Eosin (H&E) staining was also done for macromolecules with significant role in stone formation. All EG fed rats became hyperoxaluric by day 7, showed a few crystal deposits on day 14, and had heavy crystal deposition by day 28. There were significant changes in the expression of genes encoding for NADPH Oxidases; macromolecular crystallization modulators; genes involved in inflammasome activation; and osteogenic marker genes. Results demonstrate major differences between hyperoxaluria and CaOx crystal induced changes in the kidneys. Injury and inflammation are mainly associated with crystal deposition indicating significant role played by crystal retention.

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.

MitoTEMPO Prevents Oxalate Induced Injury in NRK-52E Cells via Inhibiting Mitochondrial Dysfunction and Modulating Oxidative Stress

As one of the major risks for urolithiasis, hyperoxaluria can be caused by genetic defect or dietary intake. And high oxalate induced renal epithelial cells injury is related to oxidative stress and mitochondrial dysfunction. Here, we investigated whether MitoTEMPO, a mitochondria-targeted antioxidant, could protect against oxalate mediated injury in NRK-52E cells via inhibiting mitochondrial dysfunction and modulating oxidative stress. MitoSOX Red was used to determine mitochondrial ROS (mtROS) production. Mitochondrial membrane potential (Δψm) and quantification of ATP synthesis were measured to evaluate mitochondrial function. The protein expression of Nox4, Nox2, and p22 was also detected to explore the effect of oxalate and MitoTEMPO on NADPH oxidase. Our results revealed that pretreatment with MitoTEMPO significantly inhibited oxalate induced lactate dehydrogenase (LDH) and malondialdehyde (MDA) release and decreased oxalate induced mtROS generation. Further, MitoTEMPO pretreatment restored disruption of Δψm and decreased ATP synthesis mediated by oxalate. In addition, MitoTEMPO altered the protein expression of Nox4 and p22 and decreased the protein expression of IL-6 and osteopontin (OPN) induced by oxalate. We concluded that MitoTEMPO may be a new candidate to protect against oxalate induced kidney injury as well as urolithiasis.

Bergenin attenuates renal injury by reversing mitochondrial dysfunction in ethylene glycol induced hyperoxaluric rat model

Bergenin, isolated from Bergenia ligulata is a potent antioxidant and antilithiatic agent. Present work was designed to establish the biochemical role of bergenin on mitochondrial dysfunction in the ethylene glycol induced hyperoxaluric rat model. Bergenin was administrated at a dose of 10mg/kg body wt i.p. from 14th day of establishing the 28 days hyperoxaluria rat model. α-Tocopherol was given as positive control at a dose of 100mg/kg body wt i.p. Mitochondrial dysfunction was studied by evaluating the activities of respiratory chain complexes, mitochondrial membrane potential and reactive oxygen species. Histopathological analysis of the kidney tissue was done after Pizzolato staining. Also, expression of monocyte chemoattractant protein -1(MCP-1) and kidney injury marker protein (KIM-1) were studied and the levels of IL-1β were evaluated in kidney tissue homogenate. Mitochondrial dysfunction during stone crystallization was evident by decreased activities of electron transport chain complexes I, II and IV and augmented mitochondrial oxidative stress in hyperoxaluric rats. Bergenin treatment significantly (P<0.05) restored the activities of these complexes. Moreover, it curtailed the lipid peroxidation and up regulated antioxidant levels, ameliorating the state of mitochondrial dysfunction. The protective role of bergenin was also reinforced by reducing IL-1β production and expression of KIM-1 and MCP-1 in the renal tissue. The findings of the present study provide evidence that bergenin exerted protective effects in hyperoxaluria through mitochondrial protection that involves attenuation of oxidative stress. Hence, it presented itself as an effective remedy in combating urolithiasis.

Rottlerin, a polyphenolic compound from the fruits of Mallotus phillipensis (Lam.) Müll.Arg., impedes oxalate/calcium oxalate induced pathways of oxidative stress in male wistar rats

BACKGROUND

Oxalate and/or calcium oxalate, is known to induce free radical production, subsequently leading to renal epithelial injury. Oxidative stress and mitochondrial dysfunction have emerged as new targets for managing oxalate induced renal injury.

HYPOTHESIS

Plant products and antioxidants have gained tremendous attention in the prevention of lithiatic disease. Rottlerin, a polyphenolic compound from the fruits of Mallotus phillipensis (Lam.) Müll.Arg., has shown free radical scavenging, antioxidant activity and has been reported to interfere in signaling pathways leading to inflammation and apoptosis. In this study, the potential role of rottlerin, in rats exposed to hyperoxaluric environment was explored.

METHODS

Hyperoxaluria was induced by administering 0.4% ethylene glycol and 1% ammonium chloride in drinking water to male wistar rats for 9 days. Rottlerin was administered intraperitoneally at 1mg/kg/day along with the hyperoxaluric agent. Prophylactic efficacy of rottlerin to diminish hyperoxaluria induced renal dysfunctionality and crystal load was examined along with its effect on free radicals generating pathways in hyperoxaluric rats.

RESULTS

0.4% ethylene glycol and 1% ammonium chloride led to induction of hyperoxaluria, oxiadtive stress and mitochondrial damage in rats. Rottlerin treatment reduced NADPH oxidase activity, prevented mitochondrial dysfunction and maintained antioxidant environment. It also refurbished renal functioning, tissue integrity and diminished urinary crystal load in hyperoxaluric rats treated with rottlerin.

CONCLUSIONS

Thus, the present investigation suggests that rottlerin evidently reduced hyperoxaluric consequences and the probable mechanism of action of this drug could be attributed to its ability to quench free radicals by itself and interrupting signaling pathways involved in pathogenesis of stone formation.

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

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

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

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

Osteogenic changes in kidneys of hyperoxaluric rats

Many calcium oxalate (CaOx) kidney stones develop attached to renal papillary sub-epithelial deposits of calcium phosphate (CaP), called Randall's plaque (RP). Pathogenesis of the plaques is not fully understood. We hypothesize that abnormal urinary environment in stone forming kidneys leads to epithelial cells losing their identity and becoming osteogenic. To test our hypothesis male rats were made hyperoxaluric by administration of hydroxy-l-proline (HLP). After 28days, rat kidneys were extracted. We performed genome wide analyses of differentially expressed genes and determined changes consistent with dedifferentiation of epithelial cells into osteogenic phenotype. Selected molecules were further analyzed using quantitative-PCR and immunohistochemistry. Genes for runt related transcription factors (RUNX1 and 2), zinc finger protein Osterix, bone morphogenetic proteins (BMP2 and 7), bone morphogenetic protein receptor (BMPR2), collagen, osteocalcin, osteonectin, osteopontin (OPN), matrix-gla-protein (MGP), osteoprotegrin (OPG), cadherins, fibronectin (FN) and vimentin (VIM) were upregulated while those for alkaline phosphatase (ALP) and cytokeratins 10 and 18 were downregulated. In conclusion, epithelial cells of hyperoxaluric kidneys acquire a number of osteoblastic features but without CaP deposition, perhaps a result of downregulation of ALP and upregulation of OPN and MGP. Plaque formation may additionally require localized increases in calcium and phosphate and decrease in mineralization inhibitory potential.

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

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

Mechanism of cytotoxicity of micron/nano calcium oxalate monohydrate and dihydrate crystals on renal epithelial cells

The toxicity difference and distribution in Vero cells of calcium oxalate with different crystal phases and sizes.

Androgen receptor enhances kidney stone-CaOx crystal formation via modulation of oxalate biosynthesis & oxidative stress

Males develop kidney stones far more frequently than females with a ratio of 2–3:1, suggesting that androgen receptor (AR) signaling might play a key role in the development of nephrolithiasis. Using the cre-loxP system to selectively knock out AR in glyoxylate-induced calcium oxalate (CaOx) crystal mouse models, we found that the mice lacking hepatic AR had less oxalate biosynthesis, which might lead to lower CaOx crystal formation, and that the mice lacking kidney proximal or distal epithelial AR also had lower CaOx crystal formation. We found that AR could directly up-regulate hepatic glycolate oxidase and kidney epithelial NADPH oxidase subunit p22-PHOX at the transcriptional level. This up-regulation might then increase oxalate biosynthesis and oxidative stress that resulted in induction of kidney tubular injury. Targeting AR with the AR degradation enhancer ASC-J9 led to suppression of CaOx crystal formation via modulation of oxalate biosynthesis and oxidative stress in both in vitro and in vivo studies. Taken together, these results established the roles of AR in CaOx crystal formation.

C-phycocyanin confers protection against oxalate-mediated oxidative stress and mitochondrial dysfunctions in MDCK cells

Oxalate toxicity is mediated through generation of reactive oxygen species (ROS) via a process that is partly dependent on mitochondrial dysfunction. Here, we investigated whether C-phycocyanin (CP) could protect against oxidative stress-mediated intracellular damage triggered by oxalate in MDCK cells. DCFDA, a fluorescence-based probe and hexanoyl-lysine adduct (HEL), an oxidative stress marker were used to investigate the effect of CP on oxalate-induced ROS production and membrane lipid peroxidation (LPO). The role of CP against oxalate-induced oxidative stress was studied by the evaluation of mitochondrial membrane potential by JC1 fluorescein staining, quantification of ATP synthesis and stress-induced MAP kinases (JNK/SAPK and ERK1/2). Our results revealed that oxalate-induced cells show markedly increased ROS levels and HEL protein expression that were significantly decreased following pre-treatment with CP. Further, JC1 staining showed that CP pre-treatment conferred significant protection from mitochondrial membrane permeability and increased ATP production in CP-treated cells than oxalate-alone-treated cells. In addition, CP treated cells significantly decreased the expression of phosphorylated JNK/SAPK and ERK1/2 as compared to oxalate-alone-treated cells. We concluded that CP could be used as a potential free radical-scavenging therapeutic strategy against oxidative stress-associated diseases including urolithiasis.

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.

Leishmania amazonensis fails to induce the release of reactive oxygen intermediates by CBA macrophages

CBA mouse macrophages effectively control Leishmania major infection, yet are permissive to Leishmania amazonensis. It has been established that some Leishmania species are destroyed by reactive oxygen species (ROS). However, other species of Leishmania exhibit resistance to ROS or even down-modulate ROS production. We hypothesized that L. amazonensis–infected macrophages reduce ROS production soon after parasite–cell interaction. Employing a highly sensitive analysis technique based on chemiluminescence, the production of superoxide () and hydrogen peroxide (H₂O₂) by L. major- or L. amazonensis-infected CBA macrophages were measured. L. major induces macrophages to release levels of 3·5 times higher than in uninfected cells. This production is partially dependent on NADPH oxidase (NOX) type 2. The level of accumulated H₂O₂ is 20 times higher in L. major-than in L. amazonensis-infected cells. Furthermore, macrophages stimulated with L. amazonensis release amounts of ROS similar to uninfected cells. These findings support previous studies showing that CBA macrophages are effective in controlling L. major infection by a mechanism dependent on both production and H₂O₂ generation. Furthermore, these data reinforce the notion that L. amazonensis survive inside CBA macrophages by reducing ROS production during the phagocytic process.

Mechanisms of angiotensin II-enhanced connecting tubule glomerular feedback

Increasing Na delivery to the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation, a process we call CNT glomerular feedback (CTGF). Angiotensin II (ANG II) in the CNT lumen enhances CTGF via PKC. We hypothesized that luminal ANG II stimulates CTGF via activation of protein kinase C (PKC), NADPH oxidase 2 (NOX2), and enhanced production of superoxide (O(2)(-)). Rabbit Af-Arts and adherent CNTs were microdissected and microperfused in vitro. Dilation of the Af-Art was induced by increasing luminal CNT NaCl from 0 to 5, 10, 30, 45, and 80 mM, and the concentration of NaCl that elicited a half-maximal response (EC(50)) was calculated. Compared with vehicle, adding ANG II (10(-9) M) to the CNT lumen reduced EC(50) from 37 ± 3 to 14 ± 1 mM (P < 0.001), indicating ANG II potentiates CTGF. In the presence of ANG II, the O(2)(-) scavenger tempol (10(-4) M) increased EC(50) from 20 ± 4 to 41 ± 3 mM (P < 0.01), the NOX inhibitor apocynin (10(-5) M) increased EC(50) from 17 ± 2 to 39 ± 4 mM (P < 0.01), and the specific NOX2 inhibitor gp91ds-tat (10(-5) M) increased EC(50) from 19 ± 2 to 34 ± 2 mM (P < 0.01). However, tempol, apocynin, and gp91ds-tat had no effect on CTGF in the absence of ANG II. Compared with vehicle, the PKC activator PMA (2 × 10(-7) M) decreased EC(50) from 35 ± 2 to 14 ± 1 (P < 0.001). In the presence of PMA, tempol increased EC(50) from 14 ± 2 to 35 ± 2 mM (P < 0.01). We conclude the PKC/NOX2/O(2)(-) pathway mediates the enhancement of CTGF by luminal ANG II but it does not participate in CTGF in the absence of ANG II.

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.

A case of renal oxalosis in a 3-month-old cat raised under controlled conditions

The kidneys of a 3-month-old female cat were examined. The cat which had been raised under controlled conditions with no history of any poisoning showed progressive weight loss with increases in blood BUN and creatinine concentrations. At necropsy, both kidneys were firm in consistency with formation of focal scars. Histopathologically, widespread deposition of crystals was observed in the renal tubules (in both dilated lumina and degenerative epithelia) accompanying mild interstitial fibrosis with lymphocyte infiltration. The crystals were colorless or basophilic on the hematoxilin and eosin-stained section and could be visualized with polarized light as doubly fractile crystals. The crystals were identified as calcium oxalate crystals by histochemical examinations using von Kossa stain and alizarin red S stain under different conditions and by ultrastructural examination. Judging from the above-mentioned findings, the present renal lesion detected in an infant cat was diagnosed as renal oxalosis which was suspected to be hereditary in nature.

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.

Oxygen gradients for open well cellular cultures via microfluidic substrates

Controlling oxygen concentration at a microscale level can benefit experimental investigations involving oxidative stress, ischemia, and reactive oxygen species (ROS) mediated cellular pathways. Here, we report the application of microfluidic gradient generation in an open-well culture model, in which a gradient of gas is delivered via diffusion through a gas permeable substrate that separates cells from the gas microchannels below. By using diffusion to localize oxygen delivery, microgradients of oxygen concentrations can be rapidly and controllably applied without exposing cells to mechanical stresses or reducing culture volumes inside microfluidic culture chambers. Furthermore, we demonstrate the modulation of intracellular ROS levels in Madin-Darby Canine Kidney (MDCK) cells by applying these oxygen microgradients. Increases in ROS levels consistent with both oxidative stress and hypoxic exposures were observed in MDCK cells. The measured ROS increases were comparable to 100 microM hydrogen peroxide exposure in a control comparison, which is within the range of standard ROS induction methods. Incubation with 200 microM vitamin C was able to demodulate the ROS response at both hypoxic and hyperoxic exposures. By providing microfluidic controlled gradients, constant ROS exposure, and a shear-free open well design, the devices introduced here greatly improve upon standard oxygen-based culturing methods.

The oxygen tension modulates acetaminophen-induced mitochondrial oxidant stress and cell injury in cultured hepatocytes

Oxidative stress and mitochondrial dysfunction play an important role in acetaminophen (APAP)-induced hepatocyte cell death. However, exact mechanisms involved in the process are controversial, in part, because of the disparity in findings between in vitro and in vivo studies. A major difference in this context is the oxygen tension, with cells in culture being exposed to 21% oxygen, whereas those in the liver experience a gradient from 3 to 9% oxygen. To determine if oxygen tensions could modulate hepatocyte responses to APAP, primary mouse hepatocytes were treated with 5mM APAP for up to 15 h under various oxygen tensions and mitochondrial dysfunction (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxyanilide inner salt assay, 5,5',6,6'-tetrachloro-1,1,3,3-tetraethylbenzimidazolylcarbocyanine iodide [JC-1] fluorescence ratio) and cell death (lactate dehydrogenase release) was evaluated. Mitochondrial reactive oxygen and reactive nitrogen species were measured using Mitosox Red or dihydrorhodamine fluorescence and nitrotyrosine staining, respectively. Exposure of hepatocytes to 5mM APAP at 21% O(2) resulted in mitochondrial oxidant stress formation, deterioration of mitochondrial function, and loss of membrane potential as early as 6 h and massive cell death at 15 h. Culture of cells at 10% O(2) resulted in no increase in mitochondrial oxidant stress and better preserved mitochondrial function at 6 h and significant protection against cell death at 15 h. Furthermore, dihydrorhodamine fluorescence was significantly attenuated at 10% oxygen. Cells cultured at 5% oxygen were also protected but showed evidence of hypoxia (accumulation of lactate and nuclear translocation of hypoxia-inducing factor-1α). These results suggest that oxygen tension can modulate hepatocyte responses to APAP, with low physiological levels (10%) decreasing mitochondrial oxidant stress and delaying hepatocyte cell death.

Effect of calcium oxalate on renal cells as revealed by real-time measurement of extracellular oxidative burst

Calcium oxalate is one of the main constituents of kidney stones and has a proved deleterious effect on renal cells that is mediated by oxidative stress. However, the subcellular source of this oxidative stress, and whether it is extending to the extracellular space or not, is still disputed. Therefore, an electrochemical superoxide biosensor was constructed, positioned above A6 renal cells, and used to measure in real-time the extracellular oxidative burst following addition of calcium oxalate crystals. It was observed that A6 cells do secrete superoxide into their extracellular space in few minutes after encountering calcium oxalate crystals. The amount of released superoxide peaks at about 20 min. Superoxide is cleared away from the extracellular space after approximately 3h. Superoxide secretion depends on the presence of superoxide-scavenging enzyme superoxide dismutase, the age of the cells, the amount of calcium oxalate crystals, and the temperature. Moreover, the effect of calcium oxalate crystals was mimicked by phorbol 12-myristate 13-acetate. The developed sensing system can be a useful tool for biologists investigating nephrolithiasis at cellular level.

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.

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

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

The effect of calcium on calcium oxalate monohydrate crystal-induced renal epithelial injury

Since hypercalciuria is a common feature of idiopathic calcium oxalate (CaOx) nephrolithiasis, renal epithelial cells of stone patients are exposed to various crystals in the presence of high calcium. This study was performed to determine the effect of high calcium levels on CaOx crystal-induced cell injury. We exposed human renal epithelial cell line, HK2 in vitro to CaOx monohydrate crystals at a concentration of 133 microg/cm(2) for 1, 3, 6 or 12 h in the presence or absence of 5 or 10 mM/L calcium Ca(++). We determined the release of lactate dehydrogenase as marker of injury and hydrogen peroxide (H(2)O(2)) and 8-isoprostane (8-IP) as sign of oxidative stress. Cells were also examined after trypan blue and nuclear DNA staining with 4',6-diamidino-2-phenylindole to determine their membrane integrity and apoptosis respectively. Exposure of cells to 5 or 10 mM/L of Ca(++,) for up-to 6 h, resulted in increased trypan blue and DAPI staining and production of H(2)O(2). Similarly an exposure to CaOx crystals also resulted in increased trypan blue and DAPI staining and H(2)O(2) production. An exposure to 5 mM/L Ca or CaOx crystals also resulted in increased production of 8-IP. A combination of the two treatments, Ca and CaOx crystals, did not show anymore changes than exposure to high Ca or CaOx crystals alone, except in the case of a longer exposure of 12 h. Longer exposures of 12 h resulted in cells sloughing from the substrate. These results indicate that exposure to high levels of Ca or CaOx crystals is injurious to renal epithelial cells but the two do not appear to work synergistically. On the other hand, results of our earlier studies suggest that oxalate and CaOx crystals work in synergy, i.e., CaOx crystals are more injurious in the presence of high oxalate. Perhaps Ox and CaOx crystals activate different biochemical pathways while Ca and CaOx crystals affect the identical pathways.

Differential patterns of peroxynitrite mediated apoptosis in proximal tubular epithelial cells following ATP depletion recovery

Ischemia-reperfusion injury (IRI) is characterized by ATP depletion in the ischemic phase, followed by a rapid increase in reactive oxygen species, including peroxynitrite in the reperfusion phase. In this study, we examined the role of peroxynitrite on cytotoxicity and apoptosis in an in vitro model of ATP depletion-recovery. Porcine proximal tubular epithelial (LLC-PK(1)) cells were ATP depleted for either 2 h (2/2) or 4 h (4/2) followed by recovery in serum free medium for 2 h. A subset of cells was treated with 100 microM of the peroxynitrite scavenger, iron (III) tetrakis (N-methyl-4'pyridyl) porphyrin pentachloride (FeTMPyP) 30 min prior to and during treatment/recovery. Treatment with FeTMPyP reduced cytotoxicity and superoxide levels at both the 2/2 and 4/2 time points, however FeTMPyP decreased nitric oxide only at the 2/2 time point. FeTMPyP also partially blocked caspase-3 and caspase-8 activation at both 2/2 and 4/2 time points. At the 4/2 time point, FeTMPyP also partially inhibited the ATP depletion mediated increase in tumor necrosis factor alpha (TNF-alpha) and decreased Bax and FasL gene expression. These data show that peroxynitrite induces apoptosis by activation of multiple pathways depending on length and severity of insult following ATP depletion-recovery.

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.

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.