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)

The murexide (5,5'-nitrilodibarbituric acid, monoammonium salt) is an efficient scavenger for superoxide and hydroxyl radicals. When exposed to oxygen radicals, murexide is converted to a colorless alloxan derivative and its absorbance at 520 nm decreases in proportion to the radicals produced. It is used to detect these reactive oxygen species in biochemical systems such as acetaldehyde oxidation by xanthine oxidase and the respiratory burst of polymorphonuclear leukocytes induced by phorbol 12-myristate, 13-acetate. The method was sensitive enough to allow direct monitoring of the production of superoxides from 10(6) phorbol 12-myristate, 13-acetate polymorphonuclear leukocyte-stimulated cells. Moreover, murexide bleaching is inhibited in the presence of radical scavengers, allowing a comparison of their scavenging activities.
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PMID:Murexide bleaching: a new direct assay method for characterizing reactive oxygen species. 256 47

The passage of circulating tumor cells across vessel walls is an important step in cancer metastasis and is promoted by endothelial injury. Because Walker carcinosarcoma 256 (W256) cells generate oxygen-derived free radicals after cellular activation, the authors tested the hypothesis that these cancer cells can damage endothelial monolayers by producing such reactive oxygen species. To confirm that oxygen-derived radicals can damage endothelial cells, 3H-2-deoxyglucose-labeled human endothelial cell monolayers were exposed to xanthine oxidase in the presence of 0.2 mmol/l xanthine. 3H-2-deoxyglucose release was observed after the addition of xanthine oxidase in concentrations ranging from 6.5 x 10(-3) to 52 x 10(-3) units/ml. The extent of damage correlated with xanthine oxidase-dependent chemiluminescence (r = 0.91). Chemiluminescence assays in the presence of 5 x 10(-5) M luminol confirmed activation of the W256 cells by 1 x 10(-6) M chemotactic peptide fMLP. When fMLP-activated activated W256 cells were incubated with endothelial monolayers, concentrations of 2 x 10(6) to 6 x 10(6) W256 cells/ml were found to cause a 27% increase in the specific release of 2-deoxyglucose after a 90-minute incubation. A small but significant increase in 3H-2-deoxyglucose release also was observed in the absence of fMLP. Detection of 3H-2-deoxyglucose release in the presence of activated or unactivated tumor cells was dependent on preincubating the endothelial cell monolayer with 1 mM buthionine sulfoximine, an inhibitor of glutathione synthesis. Under these conditions, the specific release of 3H-2-deoxyglucose was increased from nondetectable levels to 21%, in the presence of 6.5 x 10(-3) units of the oxidase. Cultured W256 cells promoted isotope release from endothelial cell monolayers when activated with phorbol myristate acetate. Catalase (1000 units/ml) inhibited the tumor cell-induced release of 3H-2-deoxyglucose by 84% whereas superoxide dismutase, even at concentrations of 1 mg/ml, had no effect. A requirement for cell contact was shown because addition of cell-free supernatants from fMLP activated tumor cells did not cause 3H-2-deoxyglucose release and because pretreatment of W256 cells with 1 microM cytochalasin B inhibited their ability to promote isotope release even while increasing tumor cell-generated chemiluminescence threefold. Electron microscopy revealed that fewer cytochalasin B-treated W256 cells were attached to the endothelial cell monolayer than in untreated controls. It is concluded that the W256 tumor cells can damage endothelial cells directly via a mechanism involving production of reactive oxygen species.
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PMID:Walker carcinosarcoma cells damage endothelial cells by the generation of reactive oxygen species. 270 6

The possibility that endothelial cell-derived oxidants could contribute to neutrophil-mediated endothelial cell injury and cytotoxicity has been a subject of speculation. Rat pulmonary artery endothelial cells (RPAECs) were examined for the presence of xanthine oxidase (XO) activity, a well-known source of O2-. Using a sensitive assay based on measurements of radioactive xanthine conversion to uric acid by high performance liquid chromatography (HPLC), RPAEC extracts were found to contain both XO and xanthine dehydrogenase (XD) activities. Extracts from early passage cells have 55.3 +/- 11.7 (mean +/- SE) units/10(6) cells of total (XO + XD) activity, one unit of activity being defined as the conversion of 1% of substrate to product in 30 minutes of incubation. XO comprised 31.6 +/- 3.1% of this total activity. Addition of human neutrophils stimulated with phorbol myristate acetate (PMA) caused a rapid and dose-dependent increase in RPAEC XO activity from 31.6 +/- 3.1% to 71.7 +/- 4.8% of total without altering total (XO + XD) activity. The neutrophil dose-response curve for increase in XO paralleled closely the curve for neutrophil-mediated RPAEC cytotoxicity. The basal XO and XD activities and the neutrophil-induced increase in XO activity were inhibited by treating RPAECs with allopurinol, oxypurinol, and lodoxamide, which also inhibited cytotoxicity, but not by catalase, superoxide dismutase, or deferoxamine. Addition of H2O2 failed to cause an increase in RPAEC XO activity or XD to XO conversion. The results suggest that during neutrophil-mediated injury, rapid conversion of RPAEC XD to XO occurs, resulting in increased XO, catalyzed endogenous oxidant production, which may contribute to the oxidant burden in the killing mechanism initiated by activated neutrophils. Although the mechanism for conversion of XD to XO is uncertain, it appears that neutrophil-derived H2O2 is not sufficient to cause this phenomenon. Furthermore, neither O2- nor chelatable iron is required for neutrophil-induced XD to XO conversion. Supernatant fluids from activated neutrophils failed to induce XD to XO conversion in RPAECs. This in vitro system provides an opportunity to define the cellular and molecular mechanisms underlying the in vivo phenomenon of XD to XO conversion associated with ischemic/reperfusion or inflammatory tissue injury.
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PMID:Xanthine oxidase activity in rat pulmonary artery endothelial cells and its alteration by activated neutrophils. 275 14

Oxygen-derived free radicals are believed to contribute to reperfusion injury based, in part, upon results conferred by the pharmacologic administration of allopurinol. Allopurinol inhibits xanthine oxidase (XO) activity in ischemic tissues. The possible role of XO as a pathologic mediator prompted examination of its effects on isolated peripheral canine neutrophils. In contrast to neutrophils alone, or following stimulation with phorbol myristate acetate (PMA), it was determined that XO affected both the membrane potential and the metabolism significantly. Membrane potential assay showed that at 5-10 min, PMA depolarized 89-96% of the canine neutrophils between 32-48%. Incubation with 0.5 U/ml XO involved fewer cells (54-86%), but at substantially increased cellular depolarization levels (76-90%). Metabolic assay showed that XO concentrations as low as 0.124 U induced significant cellular H2O2 production compared with temperature controls. At 0.25-0.5 U XO/10(6) cells, cytosolic H2O2 increases were almost three times those of PMA.
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PMID:Xanthine oxidase potentiation of reactive oxygen intermediates in isolated canine peripheral neutrophils. 279 91

Phenol and 1-naphthol, products of benzene and naphthalene biotransformation, are metabolized during O2- generation by xanthine oxidase/hypoxanthine and phorbol myristate acetate (PMA)-stimulated human neutrophils. The addition of 1-naphthol to xanthine oxidase/hypoxanthine incubations resulted in the formation of 1,4-naphthoquinone (1,4-NQ) whereas phenol addition yielded only small quantities of hydroquinone, catechol and a unidentified reducible product but not 1,4-benzoquinone. This formation of 1,4-NQ was dependent upon hypoxanthine, xanthine oxidase, and 1-naphthol and was inhibited by the addition of superoxide dismutase (SOD) demonstrating that the conversion was O2-mediated. During O2- generation by PMA-stimulated neutrophils, the addition of phenol interfered with luminol-dependent chemiluminescence and resulted in covalent binding of phenol to protein. Protein binding was 80% inhibited by the addition of azide or catalase to the incubations indicating that bioactivation was peroxidase-mediated. In contrast, the addition of 1-naphthol to PMA-stimulated neutrophils interfered with superoxide-dependent cytochrome c reduction as well as luminol-dependent chemiluminescence and also resulted in protein binding. Protein binding was only partially inhibited by azide or catalase. The addition of SOD in combination with catalase resulted in a significantly greater inhibition of binding when compared to that of catalase alone. The results of these experiments indicate that phenol and 1-naphthol are converted to reactive metabolites during superoxide generating conditions but by different mechanisms. The formation of reactive metabolites from phenol was almost exclusively peroxidase-mediated whereas the bioactivation of 1-naphthol could occur by two different mechanisms, a peroxidase-dependent and a direct superoxide-dependent mechanism.
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PMID:Metabolic activation of 1-naphthol and phenol by a simple superoxide-generating system and human leukocytes. 282 May 96

Listeria monocytogenes, a gram-positive motile bacterium which can cause severe bacterial infection in humans, is considered to be pathogenic by virtue of its ability to resist intracellular killing. Since the mechanism of intracellular survival is poorly understood, we assessed the sensitivity of L. monocytogenes to several potent antibacterial products. Phorbol myristate acetate (PMA)-stimulated polymorphonuclear cells (PMNs) produced extracellular antibacterial products which were inhibited completely by catalase, suggesting a role for oxidative agents in this process. L. monocytogenes in logarithmic (log) growth phase resisted PMA-stimulated PMN extracellular products significantly more than L. monocytogenes in stationary (stat) growth phase or Escherichia coli (three strains) in either phase of growth. The role of oxidative agents was studied further by using xanthine oxidase-xanthine, glucose oxidase-glucose, and myeloperoxidase enzyme systems to generate hydroxyl radical (.OH), hydrogen peroxide (H2O2), and hypochlorous acid (OCl-), respectively. L. monocytogenes in log phase resisted the antibacterial products of these enzyme systems under conditions which produced superoxide (O2-) and H2O2 at concentrations similar to those produced extracellularly by PMA-stimulated PMNs, while stat-growth-phase L. monocytogenes and E. coli in either phase of growth were susceptible. Antibacterial activity could be blocked or inhibited by exogenous catalase (for all oxygen radical-generating systems), mannitol, or desferoxamine (for xanthine oxidase-xanthine) and alanine (for myeloperoxidase), suggesting that .OH and OCl- were responsible for this activity. Log-phase L. monocytogenes had 2.5-fold higher bacteria-associated catalase activity, as compared with stat-phase L. monocytogenes. These experiments, therefore, suggest that log-phase L. monocytogenes resists oxidative antibacterial agents by producing sufficient catalase to inactivate these products. This may contribute to the ability of L. monocytogenes to survive intracellularly.
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PMID:Relationship of bacterial growth phase to killing of Listeria monocytogenes by oxidative agents generated by neutrophils and enzyme systems. 282 83

Evidence has been obtained that implicates the generation of reactive oxygen species as an early and critical event in the promotion of neoplastic transformation in mouse JB6 cells. The time courses for specific inhibition by CuZn-superoxide dismutase (CuZn-SOD) of the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of neoplastic transformation in JB6 cells and for changes in antioxidant enzyme activities associated with TPA-exposure were examined. The antipromoting effect of CuZn-SOD was found to be critically dependent on the time of addition of CuZn-SOD relative to the start of a 14-day exposure of cells to TPA. Treatment of JB6 P+ Clone 22 and Clone 41 cells with CuZn-SOD for 18 h before, simultaneously with or up to 1 h after exposure to TPA, all inhibited promotion of transformation maximally. Delay of addition of CuZn-SOD by 2 h or more after the start of TPA treatment resulted in a marked decrease in the promotion inhibitory effect. CuZn-SOD added 24 or 48 h after TPA had no effect on promotion of transformation. Exposure of JB6 cells to 0.2- (superoxide anion radical) generated exogenously by the aerobic xanthine oxidase reaction resulted in promotion of neoplastic transformation that was prevented by concurrent addition of CuZn-SOD. Taken together these studies provide evidence that increased superoxide anion generation within the first 2 h following TPA exposure is an essential event in promotion of transformation in JB6 cells. Upon TPA exposure, JB6 Clone 41 cells exhibited time-specific activity changes in the cellular SOD, glutathione peroxidase (GSH-Px), and catalase. SOD and GSH-Px activities were reduced to 54% and 26% respectively of basal levels within 2 h of TPA treatment. GSH-Px activity recovered to basal levels within 4 h and CuZn-SOD within 48 h. Catalase activity was maximally reduced to 50% of basal within 1 h after TPA treatment and rebounded to greater than basal levels within 4 h. It is postulated that a c-kinase-dependent event induces rapid elevation of superoxide anion following TPA exposure and that this leads to reduced activity of antioxidant enzymes. Since antipromotion by exogenous CuZn-SOD is effective only during the first 2 h following TPA exposure, this suggests that the promotion-relevant 0.2- elevation is transient.
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PMID:Early superoxide dismutase-sensitive event promotes neoplastic transformation in mouse epidermal JB6 cells. 282 3

The abilities of angiotensin converting-enzyme (ACE) inhibitors to suppress superoxide anion formation in vitro and to improve postischemic cardiac function in vivo were examined. Three sulfhydryl-containing ACE inhibitors, captopril, its stereoisomer SQ 14,534, and an analog, zofenopril (SQ 26,703) were compared with enalaprilat and teprotide, which lack the sulfhydryl group but inhibit ACE, and two compounds, N-2-mercaptopropionylglycine (MPG) and N-acetylcysteine (NAC), which contain a thiol moiety but are not ACE inhibitors, for suppression of free radical formation in vitro. The autooxidation of epinephrine to adrenochrome is mediated by superoxide anions and inhibited by captopril, SQ 14,534, and zofenopril, with similar IC50 values of 8 to 10 microM, but not by enalaprilat or teprotide (IC50 greater than 1000 microM). This reaction is also inhibited by MPG and NAC with IC50 values of 19 and 17 microM, respectively. In addition, captopril, MPG, or NAC, but not teprotide or enalaprilat, scavenge superoxide anion production by the purine-xanthine oxidase reaction and by canine neutrophils activated with phorbol myristate acetate. These results indicate that captopril scavenges superoxide anions in vitro independent of an action on ACE, which is probably related to the presence of a sulfhydryl moiety. Myocardial segmental function in the anesthetized, open-chest dog is altered during ischemia from active shortening to passive lengthening. Reperfusion after 15 min of ischemia does not restore active shortening within a 3 hr experimental period. Pretreatment of dogs with captopril intravenously (5 mg/kg) results in a 40% to 60% return to active shortening within 60 min of reperfusion. In contrast, equihypotensive doses of enalaprilat do not improve segmental function during reperfusion. Dogs given captopril immediately before restoring coronary blood flow show a similar return of function as that observed in animals treated with the drug before occlusion. SQ 14,534, the isomer of captopril, which is 100-fold less potent as an ACE inhibitor but equipotent in scavenging superoxide anions, also improves reperfusion-induced cardiac dysfunction when administered at reperfusion (5 mg/kg). Thus captopril improves postischemic contractile derangements by a mechanism independent of ACE inhibition. Restoration of blood supply to the ischemic myocardium provokes ventricular fibrillation in 37.5% of control dogs but in only 9% of those administered enalaprilat and 0% of captopril-treated animals. SQ 14,534 does not reduce the incidence of ventricular fibrillation (40%), indicating that the antifibrillatory actions may be related to ACE inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Does captopril attenuate reperfusion-induced myocardial dysfunction by scavenging free radicals? 283 9

In this study we examined the leukocytic oxidant species that induce oxidant damage of DNA in whole cells. H2O2 added extracellularly in micromolar concentrations (10-100 microM) induced DNA strand breaks in various target cells. The sensitivity of a specific target cell was inversely correlated to its catalase content and the rate of removal of H2O2 by the target cell. Oxidant species produced by xanthine oxidase/purine or phorbol myristate acetate-stimulated monocytes induced DNA breakage of target cells in proportion to the amount of H2O2 generated. These DNA strand breaks were prevented by extracellular catalase, but not by superoxide dismutase. Cytotoxic doses of HOCl, added to target cells, did not induce DNA strand breakage, and myeloperoxidase added extracellularly in the presence of an H2O2-generating system, prevented the formation of DNA strand breaks in proportion to its H2O2 degrading capacity. The studies also indicated that H2O2 formed hydroxyl radical (.OH) intracellularly, which appeared to be the most likely free radical responsible for DNA damage: .OH was detected in cells exposed to H2O2; the DNA base, deoxyguanosine, was hydroxylated in cells exposed to H2O2; and intracellular iron was essential for induction of DNA strand breaks.
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PMID:Oxidant-induced DNA damage of target cells. 284 65

Exposure of isolated SENCAR mouse epidermal cells to the tumor promoter 12-0-tetradecanoylphorbol-13-acetate (TPA) in vitro resulted in the production of oxidant species detected as chemiluminescence. This oxidant response can be inhibited by superoxide dismutase and copper complexes but not catalase or scavengers of hydroxyl radical or singlet oxygen, suggesting that the oxidant is superoxide anion. Inhibitors of various parts of the arachidonate cascade affect the TPA-induced oxidant response in a manner that corresponds to their effects on in vivo tumor promotion experiments. Agents that inhibit lipoxygenase activity, i.e. nordihydroguaiaretic acid, benoxaprofen, but not agents that are cyclooxygenase inhibitors, i.e. indomethacin, are effective in suppressing the oxidant response to TPA. Phospholipase C but not phospholipase A2 or D produced an oxidant response kinetically similar to that elicited by TPA. The inhibitors of TPA-induced oxidants inhibited the phospholipase C response to the same extent, suggesting that TPA and phospholipase C may produce an oxidant species through a common mechanism, via phospholipid turnover-protein kinase C activation. The relevance of oxidant production to the tumor promotion process is suggested by the ability of exogenous xanthine/xanthine oxidase, a superoxide anion-generating system, to induce ornithine decarboxylase, a characteristic of TPA-treated cells. In addition, oxidant production is significantly lower in cells from the TPA-promotion resistant C57BL/6J mouse. These studies provide further support for a role for reactive oxygens in the tumor promotion process.
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PMID:Reactive oxygen in the tumor promotion stage of skin carcinogenesis. 284 22


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