Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:1.17.3.2 (xanthine oxidase)
 8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To investigate renal tubular epithelial cell injury mediated by reactive oxygen molecules and to explore the relative susceptibility of epithelial cells and endothelial cells to oxidant injury, we determined cell injury in human umbilical vein endothelial cells and in four renal tubular epithelial cell lines including LLC-PK1, MDCK, OK and normal human kidney cortical epithelial cells (NHK-C). Cells were exposed to reactive oxygen molecules including superoxide anion, hydrogen peroxide and hydroxyl radical generated by xanthine oxidase and hypoxanthine. We determined early sublethal injury with efflux of 3H-adenine metabolites and a decline in ATP levels, while late lytic injury and cell detachment were determined by release of 51chromium. When the cells were exposed to 25, 50, and 100 mU/ml xanthine oxidase with 5.0 mM hypoxanthine, ATP levels were significantly lower (P less than 0.001) in LLC-PK1, NHK-C and OK cells compared to MDCK cells while ATP levels were significantly lower (P less than 0.01) in endothelial cells compared to all tubular cell lines. A similar pattern of injury was seen with efflux of 3H-adenine metabolites. When the cells were exposed to 50 mU/ml xanthine oxidase with 5.0 mM hypoxanthine for five hours, total 51chromium release was significantly (P less than 0.001) greater in LLC-PK1, NHK-C and OK cells compared to MDCK cells, while total 51chromium release was significantly (P less than 0.001) greater in endothelial cells compared to all tubular cells. However, lytic injury was the greatest in LLC-PK1 cells and NHK-C cells while cell detachment was the greatest in endothelial cells. MDCK cells were remarkably resistant to oxidant-mediated cell detachment and cell lysis. In addition, we determined ATP levels, 3H-adenine release and 51chromium release in LLC-PK1, NHK-C and endothelial cells in the presence of superoxide dismutase to dismute superoxide anion, catalase to metabolize hydrogen peroxide, DMPO to trap hydroxyl radical and DMTU to scavenge hydrogen peroxide and hydroxyl radical. We found that catalase and DMTU (scavengers of hydrogen peroxide) provided significant protection from ATP depletion, prevented efflux of 3H-adenine metabolites and cell detachment while DMPO (scavenger of hydroxyl radical) prevented lytic injury. In addition, we found that the membrane-permeable iron chelator, phenanthroline, and preincubation with deferoxamine prevented cell detachment and cell lysis, confirming the role of hydroxyl radical in cell injury.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Reactive oxygen molecule-mediated injury in endothelial and renal tubular epithelial cells in vitro. 217 55

We employed a carbocyanine dye (1,1',3,3,3',3'-hexamethylindocarbocyanine iodide) to measure the plasma membrane potential of LLC-PK1 renal epithelial cells exposed to either xanthine oxidase-generated oxygen radicals or to hydrogen peroxide. Measurements were performed using a fluorescent-activated cell sorter to record fluorescence on a cell by cell basis. Initial exposure of cells to low concentrations of either H2O2 or xanthine oxidase resulted in a transient increase in membrane potential relative to control cells (P less than 0.001), followed by an exponential decline in potential (P less than 0.001). The addition of extracellular catalase diminished the H2O2-related decline in potential, consistent with a role for hydrogen peroxide in producing this effect. Pretreatment of cells with inhibitors of intracellular catalase and superoxide dismutase prior to exposure to xanthine oxidase caused an even larger decline in potential (P less than 0.001). Cells could be partially protected from the radical-mediated loss of potential by incubating them in a hypertonic (400 mosmolal) environment during radical exposure. Similarly, the loss of membrane potential was increased after incubation of cells in a hypotonic (200 mosmolal) environment during radical exposure. These observations are consistent with a reduction in membrane potential effected by exposure to oxygen radicals (including superoxide anion and hydrogen peroxide). This reduction may be prevented, in part, by radical scavenging enzymes and by reducing the degree of cellular swelling in response to oxygen radical exposure.
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PMID:Oxygen radicals alter the cell membrane potential in a renal cell line (LLC-PK1) with differentiated characteristics of proximal tubular cells. 380 79

It has been proposed that cyclosporin (CsA) toxicity may in part be due to the action of oxygen-based free radicals. We compared the response of cultured endothelial (EA) and epithelial (LLC-PK1 and MDCK) cells to CsA, 250 or 1000 ng/mL for 24 or 72 h, with or without the xanthine oxidase inhibitor oxypurinol (Oxy), 10 mg/mL. CsA-induced alterations were seen on phase contrast and electron microscopy. In EA cells, swollen mitochondria and large cytoplasmic vacuoles surrounded by a thin membrane containing ribosomes were present at the periphery of the cell. In LLC-PK1 cells no vacuoles were present while in MDCK cells, the vacuoles were smaller and more centrally located. In both epithelial cell lines, mitochondria were distorted with loss of cristae. In all three cell lines, CsA depressed cell counts and decreased 3H-thymidine incorporation. Also, LDH release was accelerated. The addition of Oxy minimized the morphologic effect of CsA on all three cell lines with the effect more apparent in EA cells. The CsA-induced reduction of cell replication and increase in LDH release were also attenuated by Oxy. These results support the notion that the peroxidative properties of CsA may be responsible in part for CsA-induced nephrotoxicity.
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PMID:Effect of oxypurinol on cyclosporine toxicity in cultured EA, LLC-PK1 and MDCK cells. 950 63

The protective effect of quercetin against oxidant-induced cell injury (hypoxanthine/xanthine oxidase system) was studied in the renal tubular epithelial cell line LLC-PK1. Pretreatment with quercetin provided protection from structural and functional cell damage in a concentration-dependent manner (10-100 microM). Comparison with structural variants revealed that the protective property of quercetin depends on the number of hydroxyl substituents in the B-ring, the presence of an extended C-ring chromophore, 3-D-planarity and lipophilicity, indicating that membrane affinity is essential for protection. The hypothesis that quercetin exerts its protective effects via inhibition of lipid peroxidation was further examined. Protection by quercetin was found when lipid peroxidation, assessed by the release of malondialdehyde, was initiated by H2O2 or by the combination of 1-chloro-2,4-dinitrobenzene and aminotriazole. In contrast, the bioflavonoid was not protective when oxidative cell damage was induced by menadione and occurred in the absence of lipid peroxidation. These data suggest that cytoprotective effects of quercetin are related to membrane affinity and may be explained by interruption of membrane lipid peroxidation rather than by intracellular scavenging of oxygen free radicals.
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PMID:Inhibition of oxidant-induced lipid peroxidation in cultured renal tubular epithelial cells (LLC-PK1) by quercetin. 992 38

Osmotic diuretics are used successfully to alleviate acute tubular necrosis (ATN) produced by chemotherapeutic agents and aminoglycoside antibiotics. The beneficial action of these agents likely involves rapid elimination of the nephrotoxic agents from the kidney by promoting diuresis. Adenosine A1 receptor (A1AR) subtype present on renal proximal tubular epithelial and cortical collecting duct cells mediates the antidiuretic and cytoprotective actions of adenosine. These receptors are induced by activation of nuclear factor (NF)-kappaB, a transcription factor reported to mediate hyperosmotic stress-induced cytoprotection in renal medullary cells. In this study, we tested the hypothesis that induction of the A1AR in renal proximal tubular cells by NF-kappaB contributes to the cytoprotection afforded by osmotic diuretics. Exposure of porcine renal proximal tubular epithelial (LLC-PK1) cells to mannitol or NaCl produced a significant increase in A1AR. This increase was preceded by adenosine release and NF-kappaB activation. Expression of an IkappaB-alpha mutant, which acts as a superrepressor of NF-kappaB, abrogated the increase in A1AR. Cells exposed to mannitol demonstrated increased reactive oxygen species (ROS) generation, which was attenuated by inhibiting xanthine oxidase with allopurinol. Allopurinol attenuated both the increase in A1AR expression and NF-kappaB activation produced by osmotic diuretics, indicating a role of adenosine metabolites in these processes. Treatment of LLC-PK1 cells with cisplatin (8 microm) resulted in apoptosis, which was attenuated by mannitol but exacerbated by selective A1AR blockade. Administration of mannitol to mice increases A1AR expression and activation of NF-kappaB in renal cortical sections. Taken together, these data provide novel mechanisms of nephroprotection by osmotic diuretics, involving both activation and induction of the A1AR, the latter mediated through activation of a xanthine oxidase pathway leading to ROS generation and promoting activation of NF-kappaB.
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PMID:Osmotic diuretics induce adenosine A1 receptor expression and protect renal proximal tubular epithelial cells against cisplatin-mediated apoptosis. 1527 17

A study was conducted to determine whether the ethanol extract of the roots of Brassica rapa (EBR) ameliorates cisplatin-induced nephrotoxicity in terms of oxidative stress, as characterized by lipid peroxidation, reactive oxygen species (ROS) production, and glutathione (GSH) depletion in LLC-PK1 cells. Pretreatment of cells with EBR prevented cisplatin-induced decreases in cell viability and cellular GSH content. The effect of EBR was then investigated in rats given EBR for 14 d before cisplatin administration. A single dose of cisplatin (7 mg/kg, i.p.) caused kidney damage manifested by an elevation in blood urea nitrogen (BUN), serum creatinine, and urine lactate dehydrogenase (LDH) levels. Also, renal tissue from cisplatin-treated rats showed a significant increase in malondialdehyde (MDA) production, and in the activities of aldehyde oxidase (AO) and xanthine oxidase (XO). Moreover, a significant decrease in the activities of antioxidant enzymes, such as, glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase (CAT) was observed in cisplatin-treated rats versus saline-treated normal group. In contrast, rats given EBR showed lower blood levels of BUN and creatinine, and of urinary LDH. Moreover, EBR prevented the rise of MDA production and the induction of AO and XO activities. This extract also recovered the reduced activities of GPx, SOD and CAT. Taken together, our data indicate that the ethanol extract of the roots of Brassica rapa (EBR) has a protective effect against cisplatin-induced nephrotoxicity because it attenuates oxidative stress.
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PMID:Protective effect of the ethanol extract of the roots of Brassica rapa on cisplatin-induced nephrotoxicity in LLC-PK1 cells and rats. 1714 78

It has now been firmly established that, not only ischemia/reperfusion, but also cold itself causes damage during kidney transplantation. Iron chelators or anti-oxidants applied during the cold plus rewarming phase are able to prevent this damage. At present, it is unknown if these measures act only during the cold, or whether application during the rewarming phase also prevents damage. We aimed to study this after cold normoxic and hypoxic conditions. LLC-PK1 cells were incubated at 4 degrees C in Krebs-Henseleit buffer for 6 or 24h, followed by 18 or 6h rewarming, respectively. Cold preservation was performed under both normoxic (95% air/5% CO2) and hypoxic (95% N2/5% CO2) conditions. The iron chelator 2,2'-DPD (100 microM), anti-oxidants BHT (20 microM) or sibilinin (200 microM), and xanthine oxidase inhibitor allopurinol (100 microM) were added during either cold preservation plus rewarming, or rewarming alone. Cell damage was assessed by LDH release (n=3-9). Addition of 2,2'-DPD and BHT during cold hypoxia plus rewarming did, but during rewarming alone did not prevent cell damage. When added during rewarming after 6h cold normoxic incubation, BHT and 2,2'-DPD inhibited rewarming injury compared to control (p<0.05). Allopurinol did not prevent cell damage in any experimental set-up. Our data show that application of iron chelators or anti-oxidants during the rewarming phase protects cells after normoxic but not hypoxic incubation. Allopurinol had no effect. Since kidneys are hypoxic during transplantation, measures aimed at preventing cold-induced and rewarming injury should be taken during the cold.
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PMID:Iron chelation or anti-oxidants prevent renal cell damage in the rewarming phase after normoxic, but not hypoxic cold incubation. 1739 62

We hypothesize that superoxide (O(2)(*-)) accumulation is not a crucial causative factor in inducing nitroglycerin (NTG) tolerance. In LLC-PK1 cells, pre-exposure to NTG resulted in increased O(2)(*-) accumulation and reduced cGMP response to NTG versus vehicle control. O(2)(*-) stimulated by NTG was reduced by oxypurinol (100 microM), a xanthine oxidase inhibitor. Exposure to angiotensin II (Ang II) increased O(2)(*-) but did not reduce cGMP response. The O(2)(*-) scavenger tiron reduced Ang II-induced O(2)(*-) production but did not increase NTG-stimulated cGMP production. Using p47(phox-/-) and gp91(phox-/-) mice versus their respective wild-type controls (WT), we showed that aorta from mice null of these critical NADPH oxidase subunits exhibited similar vascular tolerance after NTG dosing (20 mg/kg s.c., t.i.d. for 3 days), as indicated by their ex vivo pEC(50) and cGMP accumulation upon NTG challenge. In vitro aorta O(2)(*-) production was enhanced by NTG incubation in both p47(phox) null and WT mice. Pre-exposure of isolated mice aorta to 100 microM NTG for 1 h resulted in vascular tolerance toward NTG and increased O(2)(*-) accumulation. Oxypurinol (1 mM) reduced O(2)(*-) but did not attenuate vascular tolerance. These results suggest that O(2)(*-) does not initiate either in vitro and in vivo NTG tolerance, and that the p47(phox) and gp91(phox) subunits of NADPH oxidase are not critically required. Increased O(2)(*-) accumulation may be an effect, rather than an initiating cause, of NTG tolerance.
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PMID:Dissociation between superoxide accumulation and nitroglycerin-induced tolerance. 1865 25

We hypothesize that nitroglycerin (NTG) causes direct oxidation of multiple cellular sulfhydryl (SH) proteins and that manipulation of SH redox status affects NTG tolerance. In LLC-PK1 cells, we found that nitrate tolerance, as indicated by cGMP accumulation toward NTG, was accompanied by increased protein [(35)S]cysteine incorporation, significant S-glutathionylation of multiple proteins, and decreased metabolic activity of several SH-sensitive enzymes, including creatine kinase, xanthine oxidoreductase, and glutaredoxin (GRX). Cells overexpressing GRX exhibited reduced cellular protein S-glutathionylation (PSSG) and absence of NTG tolerance, whereas those with silenced GRX showed increased extent of NTG-induced tolerance. Incubation of LLC-PK1 cells with oxidized glutathione led to several major observations associated with nitrate tolerance, namely, reduced cGMP accumulation, PSSG formation, superoxide accumulation, and the attenuation of these events by vitamin C. Aortic S-glutathionylated proteins increased approximately 3-fold in rats made tolerant in vivo to NTG and showed significant negative correlation with vascular responsiveness ex vivo. NTG incubation in EA.hy926 endothelial cells and LLC-PK1 cells led to increased S-glutathionylation and activity of p21(ras), a known mediator of cellular signaling. These results indicate that the hallmark events of NTG tolerance, such as reduced bioactivation and redox signaling, are associated with GRX-dependent protein deglutathionylation.
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PMID:Role of glutaredoxin-mediated protein S-glutathionylation in cellular nitroglycerin tolerance. 1922 66