Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Rat left atria or Langendorff hearts were kept at 37 degrees C and stimulated at a rate of 3.33 Hz. They were subjected to hypoxia (deprivation of oxygen) or ischemia (deprivation of oxygen and glucose + acidosis + increased extracellular potassium concentration) for 15 min or 1 h and subsequent reoxygenation for 5 or 15 min. Tissue concentrations of proteins, reduced and oxidized glutathione and conjugated dienes were measured at the end of the experiment. Hypoxia and ischemia decreased the excitability and contractility of the preparations and caused contracture. These effects were partly reversible during reoxygenation. However, in Langendorff hearts reoxygenation caused an increased release of CPK, LDH and glutathione into the perfusion fluid. Ischemia and reoxygenation in atria lowered the tissue concentration of reduced glutathione and increased its oxidized form. Similar changes were seen in atria and Langendorff hearts when oxygen radical production was accelerated by hypoxanthine and xanthine oxidase. No treatment raised significantly the concentration of conjugated dienes. These results seem to exclude an important role of an increased lipid peroxidation for reperfusion injury of isolated heart preparations.
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PMID:No evidence for an increased lipid peroxidation during reoxygenation in Langendorff hearts and isolated atria of rats. 279 63

Recent data suggest that oxygen free radicals are implicated in the pathogenesis of ischemic injury. This study evaluates the effects of allopurinol, a xanthine oxidase (XO) inhibitor, on malonaldehyde generation, free sulfhydryl levels, oxygen consumption, and water contents of rat gastrocnemius muscles of female Sprague-Dawley rats subjected to tourniquet shock and after hind-limb reperfusion. Serum lactic dehydrogenase isozyme patterns after ligature release were also examined. Our results show that the four muscle parameters were not altered during 5 hr of ischemia, but that on hind-limb reperfusion, malonaldehyde production, SH levels, O2 consumption, and water contents were significantly altered in the control animals, but not in those pretreated with allopurinol. LDH serum patterns of the untreated animals showed the presence of all five isoforms; these were much less evident in the drug-protected rats. Our data suggest that following ischemia, the affected muscles are unable to recover their normal function when reperfusion is resumed. The subsequent damage is probably due to the generation of cytotoxic superoxide radicals formed during the XO-catalyzed transformation of hypoxanthine to uric acid on tissue reoxygenation. The severity of tissue damage is related to the duration of the ischemic episode possibly due to hypoxanthine accumulation during ischemia.
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PMID:Tourniquet shock in rats: effects of allopurinol on biochemical changes of the gastrocnemius muscle subjected to ischemia followed by reperfusion. 301 Oct 37

The potential protective effect of N-acetylcysteine against various types of oxidative stress (exposure to hyperoxia, treatment with paraquat, incubation in the presence of the hypoxanthine-xanthine oxidase system) was tested in primary cultures of porcine aortic endothelial cells. It was compared to that of selenomethionine (Se-Met), known to increase glutathione peroxidase activity, when given either alone or in combination with N-acetylcysteine. LDH release, 3H-thymidine (TdR) incorporation into DNA and DNA content were measured to assess the cytotoxic effect of the conditions tested. Total and oxidized glutathione content was also determined. Whereas Se-Met had a partial protective effect on all the conditions but paraquat treatment, N-acetylcysteine administration had no effect on the hyperoxia induced changes and significantly worsened the cytotoxic action of paraquat. On the other hand, LDH release following an incubation in the presence of the hypoxanthine-xanthine oxidase was significantly reduced after N-acetylcysteine treatment. No major change in total nor in oxidized glutathione followed N-acetylcysteine treatment in control and experimental conditions. A dose-dependent protective effect of N-acetylcysteine was obtained when this agent was given concomitantly with the xanthine oxidase system. These data suggest that in cultured endothelial cells a N-acetylcysteine-related protective effect, if present, is most likely to result from the direct scavenging action of N-acetylcysteine.
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PMID:Comparative study on the selenium- and N-acetylcysteine-related effects on the toxic action of hyperoxia, paraquat and the enzyme reaction hypoxanthine-xanthine oxidase in cultured endothelial cells. 368 96

Primary cultures of porcine aortic endothelial cells were used to assess the effects of O2 intermediates produced by 10-40 mU/ml xanthine oxidase (XO; +2 mM hypoxanthine) or 25-100 mU/ml glucose oxidase (GO; +5 mM glucose). A 60-min incubation in the presence of the enzyme systems resulted in a dose-dependent toxic effect with evidence of cytolysis (increased LDH release) and cell loss (decrease in DNA and protein content), when these indexes were measured 24 hr after completion of the enzyme reaction. Decreased [3H]thymidine incorporation into DNA was the most sensitive index of cell dysfunction for both enzyme systems. The effects of various scavengers and enzymes indicated that H2O2 was the main O2 intermediate involved in the cytotoxicity resulting from the XO-hypoxanthine reaction. Increased glutathione peroxidase activity associated with the addition of 2 X 10(-7) M selenomethionine to culture medium had a partial protective effect which could be related to an increased rate of H2O2 degradation. Evidence for increased DNA synthesis after injury was found in cells previously exposed to XO-hypoxanthine, the degree of increase in [3H]thymidine incorporation being dependent on the intensity of the initial cytotoxicity. Cultured endothelial cells provide a useful tool to evaluate the role of O2 intermediates in endothelial cell injury, to test the effects of protective agents, and to study the repair process.
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PMID:Effect of variable glutathione peroxidase activity on H2O2-related cytotoxicity in cultured aortic endothelial cells. 383 24

The aim of this study was to determine the cellular source of oxygen free radicals generated by isolated hepatocytes during post-anoxic reoxygenation. Superoxide anions (O2.-) were detected by lucigenin chemiluminescence. Cell damage was assessed by LDH release. During anoxia, the chemiluminescence decreased to background levels while LDH release increased 8-fold. During reoxygenation, O2.- formation increased 15-fold within 15 min then declined towards control levels. LDH release increased from 161 to 285 mU/min in the first 30 min of reoxygenation, then declined toward the control rate. Allopurinol, an inhibitor of the xanthine-xanthine oxidase system, did not inhibit O2.- formation nor LDH release. Antimycin, a mitochondrial complex III inhibitor that does not block O2.- formation, increased both O2.- generation and LDH release 82 and 133% respectively. Diphenyleneiodonium (DPI), a mitochondrial and microsomal NADPH oxidase inhibitor, reduced O2.- and LDH release 60-70%. SOD, which catalyzes the dismutation of O2.- to H2O2, was without effect on O2.- and LDH release, but TEMPO, a stable nitroxide which mimics SOD and easily penetrates the cell membrane, decreased O2.-86% without affecting LDH. These results suggest that mitochondria or microsomes are the principal sites of O2.- production during reoxygenation of isolated hepatocytes, whereas the cytosolic xanthine/xanthine oxidase system is apparently not involved.
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PMID:Source of oxygen free radicals produced by rat hepatocytes during postanoxic reoxygenation. 754 22

Oxygen-derived free radicals (ODFR) appear to be involved in the pathogenesis of arthritic disorders. In order to gain new insight on their role in the phenomenon and as a basis for a therapeutic approach, the effect of ODFR (produced by the xanthine oxidase-hypoxantine system) on hyaluronic acid, on two HA ester derivatives, and on pig articular chondrocytes was investigated. High M(r) HA (1.1 x 10(6)) and low M(r) HA (16 x 10(4)) were depolymerized by ODFR but the methyl and hydrocortisone esters of HA (HYAFF 2P50 and HYC13) turned out to be nearly unaffected. When articular chondrocytes were treated with ODFR, a rapid nucleoside triphosphate (NTP) depletion, a transient appearance of pyrophosphate (PPi), and an increase of phosphomonoester and diphosphodiester concentrations have been observed. The NTP depletion and the DPDE increase are related to the concentration of free radicals. Glyceraldehyde-3-phosphate accumulation during ODFR treatment suggests that ATP depletion can occur as a consequence of the blockage of glycolysis at the level of glyceraldehyde-3-P dehydrogenase. The hypothesis is presented that PPi can be produced from the pathway of the FAD-NAD (DPDE) biosynthesis and then either hydrolyzed by endogenous pyrophosphatases or precipitated in the form of insoluble calcium salts. Long-term treatment (16 h) with ODFR causes a loss of chondrocyte membrane integrity which can be revealed both by an increased free LDH activity and by the characteristic signal of free phospholipids in the 31P-NMR spectra. While high M(r) HA shows a significant protective activity for chondrocytes against ODFR action, low M(r) HA and ester derivatives do not. It is suggested that the therapeutic activity of HA ester derivatives can be ascribed to their in vivo hydrolysis products.
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PMID:Oxygen-derived free radical (ODFR) action on hyaluronan (HA), on two HA ester derivatives, and on the metabolism of articular chondrocytes. 773 82

Iron catalyzed free radical formation and lipid peroxidation are accepted mechanisms of heme protein-induced acute renal failure. However, the source(s) of those free radicals which trigger lipid peroxidation in proximal tubular cells remains unknown. This study tested the potential involvement of mitochondrial electron transport, xanthine oxidase activity, and arachidonic acid metabolism in the heme-induced peroxidative state. The impact of cytosolic Ca2+ loading also was assessed. Rhabdomyolysis was induced in mice by glycerol injection, and two hours later heme-laden proximal tubular segments (PTS) were isolated for study. PTS from normal mice served as controls. During 30 to 60 minute incubations, heme loaded PTS developed progressive cytotoxicity (LDH release) and iron-dependent lipid peroxidation (malondialdehyde, MDA, generation; inhibited by deferoxamine). Site 2 (antimycin A) or site 3 (cyanide, hypoxia) mitochondrial respiratory chain inhibition completely blocked lipid peroxidation, whereas site 1 inhibition (rotenone) doubled its extent (presumably by shunting NADH through NADH dehydrogenase, a free radical generating system). Conversely, these agents did not substantially alter MDA in normal PTS. Normal and heme loaded PTS developed comparable degrees of LDH release during respiratory blockade irrespective of increased or decreased MDA production (indicating that lipid peroxidation was not a critical determinant of cell death). Neither increasing free arachidonic acid (PLA2 treatment) nor adding cyclooxygenase/lipoxygenase/cytochrome p450 inhibitors conferred a consistent protective effect. Altering free Ca2+ status (chelators; ionophore addition) and xanthine oxidase inhibition had no discernible impacts. Despite mitochondrial free radical production, mitochondrial function, as assessed by the ATP/ADP ratio, seemingly remained intact. In conclusion, (1) the terminal mitochondrial respiratory chain is the dominant source of free radicals which trigger PTS lipid peroxidation; (2) iron is a required secondary factor; (3) although mitochondria fuel lipid peroxidation, they do not appear to be critical targets of the heme-induced oxidant attack.
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PMID:Mitochondrial free radical production induces lipid peroxidation during myohemoglobinuria. 864 15

The primary objective of the study was to test the hypothesis that oxygen radical during initial anoxia stimulate endogenous antioxidant activity in late preconditioning in myocytes. Isolated rat myocytes were preconditioned in one group with two cycles of 5 minutes of anoxia and 5 minutes of reoxygenation and in another group with exogenous superoxide anion (.O2-) generated by reaction of xanthine oxidase with xanthine. Myocytes were kept for 24 hours, after which they were exposed to 60 minutes of anoxia and 60 minutes of reoxygenation. Preconditioned myocytes exhibited decreased LDH release, reduced malondialdehyde formation, increased cell viability, and well-preserved cell structure. .O2- production was increased in myocytes immediately after treatment with repetitive anoxia (1.65 +/- 0.08 nmol/mg protein) or exogenous .O2- (1.42 +/- 0.11 nmol/mg protein). Allopurinol, a xanthine oxidase inhibitor, abolished .O2- production during the initial preconditioning period. Twenty-four hours later, Mn SOD activity declined in anoxic control myocytes (0.38 +/- 0.06 U/mg protein), whereas it increased significantly in myocytes preconditioned with repetitive anoxia (3.25 +/- 0.15 nmol/mg protein) or with exogenous .O2- (2.27 +/- 0.10 nmol/mg protein). The increase in Mn SOD activity and myocardial protective effects observed in preconditioned myocytes were totally blocked by allopurinol. These results indicate that oxygen radicals generated during the initial preconditioning period activate endogenous antioxidant defense (increased Mn SOD activity) 24 hours later, which contributes to the late cardioprotection of preconditioning.
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PMID:Late ischemic preconditioning is mediated in myocytes by enhanced endogenous antioxidant activity stimulated by oxygen-derived free radicals. 890 63

The purpose of this study was to gain direct insights into mechanisms by which myoglobin induces proximal tubular cell death. To avoid confounding systemic and hemodynamic influences, an in vitro model of myoglobin cytotoxicity was employed. Human proximal tubular (HK-2) cells were incubated with 10 mg/ml myoglobin, and after 24 hours the lethal cell injury was assessed (vital dye uptake; LDH release). The roles played by heme oxygenase (HO), cytochrome p450, free iron, intracellular Ca2+, nitric oxide, H2O2, hydroxyl radical (-OH), and mitochondrial electron transport were assessed. HO inhibition (Sn protoporphyrin) conferred almost complete protection against myoglobin cytotoxicity (92% vs. 22% cell viability). This benefit was fully reproduced by iron chelation therapy (deferoxamine). Conversely, divergent cytochrome p450 inhibitors (cimetidine, aminobenzotriazole, troleandomycin) were without effect Catalase induced dose dependent cytoprotection, virtually complete, at a 5000 U/ml dose. Conversely, -OH scavengers (benzoate, DMTU, mannitol), xanthine oxidase inhibition (oxypurinol), superoxide dismutase, and manipulators of nitric oxide expression (L-NAME, L-arginine) were without effect. Intracellular (but not extracellular) calcium chelation (BAPTA-AM) caused approximately 50% reductions in myoglobin-induced cell death. The ability of Ca2+ (plus iron) to drive H2O2 production (phenol red assay) suggests one potential mechanism. Blockade of site 2 (antimycin) and site 3 (azide), but not site 1 (rotenone), mitochondrial electron transport significantly reduced myoglobin cytotoxicity. Inhibition of Na, K-ATPase driven respiration (ouabain) produced a similar protective effect. We conclude that: (1) HO-generated iron release initiates myoglobin toxicity in HK-2 cells; (2) myoglobin, rather than cytochrome p450, appears to be the more likely source of toxic iron release; (3) H2O2 generation, perhaps facilitated by intracellular Ca2+/iron, appears to play a critical role; and (4) cellular respiration/terminal mitochondrial electron transport ultimately helps mediate myoglobin's cytotoxic effect. Formation of poorly characterized toxic iron/H2O2-based reactive intermediates at this site seems likely to be involved.
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PMID:Myoglobin toxicity in proximal human kidney cells: roles of Fe, Ca2+, H2O2, and terminal mitochondrial electron transport. 906 5

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


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