Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined the protective effect of cellular superoxide dismutase against extracellular hydrogen peroxide in cultured bovine aortic endothelial cells. 51Cr-labeled cells were exposed to hydrogen peroxide generated by glucose oxidase/glucose. Glucose oxidase caused a dose-dependent increase of 51Cr release. Pretreatment with diethyldithiocarbamate enhanced injury induced by glucose oxidase, corresponding with the degree of inhibition of endogenous superoxide dismutase activity. Inhibition of cellular superoxide dismutase by diethyldithiocarbamate was not associated either with alteration of other antioxidant defenses or with potentiation of nonoxidant injury. Enhanced glucose oxidase damage by diethyldithiocarbamate was prevented by chelating cellular iron. Inhibition of cellular xanthine oxidase neither prevented lysis by hydrogen peroxide nor diminished enhanced susceptibility by diethyldithiocarbamate. These results suggest that, in cultured endothelial cells: 1) cellular superoxide is involved in mediating hydrogen peroxide-induced damage; 2) superoxide, which would be generated upon exposure to excess hydrogen peroxide independently of cellular xanthine oxidase, promotes the Haber-Weiss reaction by initiating reduction of stored iron (Fe3+) to Fe2+; 3) cellular iron catalyzes the production of a more toxic species from these two oxygen metabolites; 4) cellular superoxide dismutase plays a critical role in preventing hydrogen peroxide damage by scavenging superoxide and consequently by inhibiting the generation of the toxic species.
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PMID:Role of cellular superoxide dismutase against reactive oxygen metabolite injury in cultured bovine aortic endothelial cells. 132 16

Using the isolated perfused rat liver, we examined the effect of stimulation of mitochondrial respiration by 2,4-dinitrophenol (2,4-DNP) and adrenaline on reactive oxygen species (ROS) production, liver damage and lipid peroxidation. ROS production was monitored by luminol- and lucigenin-enhanced chemiluminescence and oxygen uptake was measured simultaneously. Liver damage and lipid peroxidation were evaluated by measuring hepatic lactate dehydrogenase (LDH) and thiobarbituric acid reacting substances (TBARS) release. Tissue ROS level decreased and oxygen uptake increased soon after 2,4-DNP infusion. On termination of 2,4-DNP infusion, there was a sharp increase in lucigenin-enhanced chemiluminescence, which declined slowly, but luminol-enhanced chemiluminescence did not change prominently. Hepatic LDH and TBARS release increased gradually during 2,4-DNP infusion and were manifested by termination of the infusion. Allopurinol did not affect ROS production and TBARS release, but delayed increases in LDH release after termination of 2,4-DNP infusion. Adrenaline, which stimulates mitochondrial respiration without uncoupling caused similar but smaller ROS changes observed in 2,4-DNP. LDH and TBARS release were not affected significantly by adrenaline infusion. These results indicate that uncoupling of oxidative phosphorylation decreases ROS production and restoration of oxidative phosphorylation enhances ROS production and liver damage. Xanthine oxidase is unlikely to contribute to enhanced ROS production after termination of 2,4-DNP but has some protective effect during uncoupling.
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PMID:Comparison of the effect of a mitochondrial uncoupler, 2,4-dinitrophenol and adrenaline on oxygen radical production in the isolated perfused rat liver. 132 18

Ultraweak chemiluminescence (CL) from bilirubin occurs in the presence of triplet oxygen and is stimulated by the addition of aldehydes. Active oxygen species also enhance bilirubin CL, in the absence of aldehydes. An inhibitory effect of active oxygen scavengers on the CL indicated that active oxygens generated from the decomposition of added hydrogen peroxide or from the xanthine-xanthine oxidase reaction contributed to the CL from bilirubin molecules. However, the contribution of singlet oxygen to the CL disappeared in the presence of formaldehyde. This suggested that the scission of tetrapyrrole bonds via a dioxetane intermediate or the production of triplet carbonyls from the oxidation of aldehydes by singlet oxygen was not involved in the CL, at least in the presence of formaldehyde. The spectrum of CL induced by the generation of active oxygen was the same as that from the aldehyde-enhanced CL reaction. We propose that the formation of a hydroperoxide (and/or hydroxide) bilirubin intermediate, but not a dioxetane, may be involved in the excitation of bilirubin molecules for CL.
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PMID:Bilirubin chemiluminescence induced by the attack of active oxygen species. 132 33

The inhibition of xanthine oxidase by its reaction product, uric acid, was studied by steady state kinetic analysis. Uric acid behaved as an uncompetitive inhibitor of xanthine oxidase with respect to the reducing substrate, xanthine. Under 50 microM xanthine and 210 microM oxygen, the apparent K(i) for uric acid was 70 microM. Uric acid-mediated xanthine oxidase inhibition also caused an increase in the percentage of univalent reoxidation of the enzyme (superoxide radical production). Steady-state rate equations derived by the King-Altman method support the formation of an abortive-inhibitory enzyme-uric acid complex (dead-end product inhibition). Alternatively, inhibition could also depend on the reversibility of the classical ping-pong mechanism present in xanthine oxidase-catalyzed reactions.
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PMID:Inhibition of xanthine oxidase by uric acid and its influence on superoxide radical production. 132 3

The hypothesis that posthypoxic renal injury is mediated by xanthine oxidase-derived oxygen free radical production was tested in an in vitro model of rat proximal tubule epithelial cells in primary culture subjected to 60 min of hypoxia and 30 min of reoxygenation. Hypoxia-reoxygenation-induced injury, measured as lactate dehydrogenase (LDH) release, was 54.0 +/- 7.1%. Inhibition of xanthine oxidase by 10(-4) M allopurinol attenuated injury (LDH release = 35.5 +/- 3.7%; P less than 0.01). Oxypurinol was similarly effective. Alternatively, cells were treated with 50 or 100 microM tungsten to inactivate xanthine oxidase. Tungsten prevented hypoxia-reoxygenation-induced superoxide radical production (basal = 97 +/- 8, hypoxia-reoxygenation = 172 +/- 12, and plus tungsten = 73 +/- 8 nmol/micrograms protein) and attenuated hypoxia-reoxygenation-induced injury (LDH release: basal = 18.8 +/- 3.0%, hypoxia-reoxygenation = 62.0 +/- 4.8%, plus 50 microM tungsten = 24.8 +/- 5.0%, and plus 100 microM tungsten = 6.0 +/- 0.7%). In addition, hypoxia and reoxygenation increased the ratio of xanthine oxidase to total activity (xanthine oxidase + xanthine dehydrogenase) from 73 to 100%. Therefore xanthine oxidase was responsible for hypoxia-reoxygenation-induced superoxide radical formation and hypoxia-reoxygenation-induced injury. Xanthine oxidase is likely to be the major source of oxygen free radicals during renal ischemia and reperfusion.
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PMID:Xanthine oxidase produces O2-. in posthypoxic injury of renal epithelial cells. 132 7

Ischemia-reperfusion is observed in various diseases such as myocardium infarct. Different theories have been proposed to explain the reperfusion injury, among them that the free radical generation plays a crucial role. To study the mechanisms of the reperfusion injury, a hypoxia (H)-reoxygenation (R) model upon human umbilical vein endothelial cells in culture was developed in order to mimic the in vivo situation. Different parameters were quantified and compared under H or H/R, and we found that oxygen readmission led to damage amplification after a short hypoxia period. To estimate the importance of various causes of toxicity, the effects of various protective molecules were compared. Different antioxidant molecules, iron-chelating agent, xanthine oxidase inhibitors, and energy-supplying molecules were very efficient protectors. Synergy could also be observed between the antioxidants and the energy-supplying molecules or the xanthine oxidase inhibitors. The toxic effect of O2.(-) could be lowered by the presence of SOD or glutathione peroxidase in the culture medium, whereas glutathione peroxidase was the most efficient enzyme when injected into the cells. The production of O2.(-) and of H2O2 by endothelial cells was directly estimated to be, respectively, of 0.17 and 0.035 mumol/min/mg prot during the R period. O2.(-) production was completely inhibited when allopurinol was added during H and R. In addition, a xanthine oxidase activity of 21.5 10(-6) U/mg prot could be observed by a direct assay in cells after H but not in control cells, thus confirming the previous conclusions of xanthine oxidase as a potent source of free radicals in these conditions. Thanks to the use of cultured human endothelial cells, a clear picture was obtained of the overall process leading to cell degenerescence during the reoxygenation process. We particularly could stress the importance of the low energetic state of these cells, which is a critical factor acting synergistically with the oxidant molecules to injure the cells. These results also open new possibilities for the development of new therapeutics for ischemia.
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PMID:Human umbilical vein endothelial cells submitted to hypoxia-reoxygenation in vitro: implication of free radicals, xanthine oxidase, and energy deficiency. 132 79

To examine the possible involvement of cytokines in reperfusion injury, we have studied production of IL-1 by human vascular cells, including smooth muscle and mononuclear phagocytes. Exposure of cells to hypoxia (pO2 approximately 14 torr) followed by reoxygenation led to significant release of IL-1 only from the mononuclear phagocytes. Elaboration of IL-1 was dependent on the oxygen tension and duration of hypoxia (optimal at lower pO2s, approximately 14-20 torr, and after 9 h), as well as the time in reoxygenation (maximal IL-1 release at 6-9 h). Although a period of hypoxia was necessary for subsequent IL-1 production during reoxygenation of either peripheral blood monocytes or cultured monocyte-derived macrophages, no IL-1 release occurred during the hypoxic exposure. IL-1 released during reoxygenation was newly synthesized, and its production was triggered by the generation of oxygen free radicals, as it could be blocked by the addition of either allopurinol or free radical scavengers to cultures and could be stimulated in part by low concentrations of hydrogen peroxide or xanthine/xanthine oxidase. The potential pathophysiological effects of IL-1-containing supernatants from reoxygenated macrophages was shown by their induction of endothelial tissue factor and enhancement of endothelial adhesiveness for neutrophils, both of which could be blocked by anti-IL-1 antibody. The relevance of IL-1 to hypoxia/reoxygenation in vivo was suggested by the presence of circulating nanogram amounts of this cytokine in the plasma of mice during the reoxygenation period following a hypoxia.
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PMID:Synthesis and release of interleukin 1 by reoxygenated human mononuclear phagocytes. 132 90

Active oxygen species cause gastric mucosal damage in vivo. However, it is not known if these species are directly cytotoxic toward gastric cells. Prostaglandins have important physiological roles in the gastric mucosa, including direct cell protection against damaging factors. So, to find if active oxygen species affect prostaglandin synthesis in gastric mucosal cells is important, but this also is not known. This study was done to investigate the effects of such species on damage to and prostaglandin synthesis in cultured mucus-producing cells from rat gastric mucosa. Active oxygen species were produced by the addition of xanthine and xanthine oxidase to the culture medium. Cytotoxicity was assayed by 51Cr release. Xanthine (1 mM) and xanthine oxidase (100 mU/ml) increased specific 51Cr release as the thiobarbituric acid reactants increased. This increase in 51Cr release was inhibited by catalase, a scavenger of hydrogen peroxide, or dimethyl sulfoxide, a scavenger of hydroxyl radicals, but not by superoxide dismutase, a scavenger of superoxide, nor deferoxamine, an inhibitor of hydroxyl radical generation. Catalase, dimethyl sulfoxide, and superoxide dismutase each had no effect on prostaglandin E2 synthesis when xanthine and xanthine oxidase were not added. In the presence of xanthine and xanthine oxidase, catalase and dimethyl sulfoxide stimulated the synthesis of prostaglandin E2 and superoxide dismutase inhibited it. Indomethacin, a prostaglandin synthetase inhibitor, did not affect the decrease in 51Cr release caused by catalase in the presence of xanthine and xanthine oxidase, but it abolished the decrease caused by dimethyl sulfoxide. These results suggest that hydrogen peroxide, but not superoxide nor hydroxyl radicals, is involved in damage to cultured rat gastric cells, and that superoxide stimulates prostaglandin E2 synthesis, but that hydrogen peroxide inhibits it. Protection of the cells by dimethyl sulfoxide may be related to stimulation of prostaglandin E2 synthesis in the cells, but not via scavenging hydroxyl radicals.
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PMID:Effects of active oxygen species on damage to and prostaglandin synthesis in cultured rat gastric cells. 132 36

Milk xanthine oxidase (XO) has been prepared in a dehydrogenase form (XDH) by purifying the enzyme in the presence of 2.5 mM dithiothreitol. Unlike XO, which reacts rapidly only with oxygen and not with NAD, the XDH form of the enzyme reacts rapidly with NAD. XDH has a turnover number for the NAD-dependent conversion of xanthine to urate of 380 mol/min/mol at pH 7.5, 25 degrees C, with a Km = < or = 1 microM for xanthine and a Km = 7 microM for NAD, but has very little O2-dependent activity. There is evidence that the two forms of the enzyme have different flavin environments: XDH stabilizes the neutral form of the flavin semiquinone and XO does not. Further, XDH binds the artificial flavin 8-mercapto-FAD in its neutral form, shifting the pK of this flavin by 5 pH units, while XO binds 8-mercapto-FAD in its benzoquinoid anionic form. XDH can be converted back to the XO form by the addition of three to four equivalents of the disulfide-forming reagent 4,4'-dithiodipyridine, suggesting that, in the XDH form of the enzyme, disulfide bonds are broken; this may cause a conformational change which creates a binding site for NAD and changes the protein structure near the flavin.
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PMID:Purification and properties of milk xanthine dehydrogenase. 132 33

The acute phase protein, C-reactive protein (CRP), when heat-aggregated (Agg-CRP), potentiates immunoglobulin G (IgG) Fc receptor-mediated luminol-enhanced chemiluminescence (CL) in human monocytes and neutrophils. Luminol-CL is a sensitive measure of phagocyte respiratory burst activity; however, the nature of oxidative products contributing to the light emission and their site of generation remain incompletely defined. To more precisely describe the oxidative burst of monocytes and neutrophils to Agg-CRP, superoxide anion release was measured by cytochrome c reduction. In addition, the extracellular release of hydrogen peroxide was distinguished from hydrogen peroxide generation using a phenol red oxidation assay. Finally, a flow cytometric determination of dichlorofluorescein (DCFH) oxidation was employed as an index of intracellular peroxide production. Although Agg-CRP alone did not stimulate hydrogen peroxide generation by either monocytes or neutrophils, it significantly enhanced hydrogen peroxide generation in response to heat-aggregated IgG (Agg-IgG). In contrast, Agg-CRP did not enhance the extracellular release of either hydrogen peroxide or superoxide anion from Agg-IgG-stimulated cells. The capacity of Agg-CRP to enhance selectively intracellular oxidative product generation was confirmed when measuring DCFH oxidation in Agg-IgG-stimulated cells. To evaluate whether this selective enhancement of intracellular oxidative events could be attributed, at least in part, to a scavenging effect of Agg-CRP, a cell-free oxygen radical-generating system was employed. Agg-CRP did not significantly diminish the lucigenin-amplified CL response induced by the xanthine/xanthine oxidase reaction. These results indicate that although Agg-CRP enhances the intracellular generation of reactive oxygen intermediates by monocytes and neutrophils, extracellular release of those products is not influenced by cell interaction with Agg-CRP. It is tempting to speculate that CRP can selectively boost the microbicidal activities of monocytes and neutrophils within an inflammatory site by amplifying the intracellular generation of reactive oxygen products without increasing damage to surrounding normal tissues.
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PMID:C-reactive protein selectively enhances the intracellular generation of reactive oxygen products by IgG-stimulated monocytes and neutrophils. 132 45


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