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)

Human polymorphonuclear leucocytes were found to promote peroxidation linolenic acid micelles. The peroxidation was markedly enhanced by addition of ferric iron, either in the form of chloride, ADP-complex or EDTA to the phosphate-buffered reaction mixture. The leucocyte oxygen burst was induced by the addition of the lipid micelles, and no other stimulatory agent was therefore required. Pretreatment of the leucocytes with cytochalasin B did not inhibit t.e lipid peroxidation which indicates that phagocytosis was not part of the peroxidative mechanism. Lipid peroxidation was inhibited by alpha-tocopherol acetate, butylated hydroxytoluene, manganese ions and desferrioxamine but not by superoxide dismutase, catalase or the hydroxyl radical scavenger dimethylsulfoxide. Lipid peroxidation promoted by xanthine oxidase, was studied for comparison. This was inhibited by superoxide dismutase, indicating that xanthine oxidase, in contrast to leucocytes, promotes lipid peroxidation via a superoxide-dependent mechanism. Manganese ions and butylated hydroxytoluene, and to a lesser extent alpha-tocopherol, were also inhibitors. The leucocyte promoted lipid peroxidation is similar to the well-known peroxidation promoted by microsomal NADPH-cytochrome P450 reductase, which also is not induced by superoxide radicals. Peroxidation of lipids may be a mechanism whereby granulocytes express tissue damage in for example inflammation and ischaemia.
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PMID:Peroxidation of linolenic acid promoted by human polymorphonuclear leucocytes. 287 64

Human monocytes require serum components immunoglobulin G, C3/C3b, and B/Bb to exert optimal microbicidal action against ingested microorganisms. The present study was performed to find out whether these factors act by enhancing oxygen-dependent antimicrobial mechanisms. Serum enhanced oxygen consumption and superoxide production by monocytes before phagocytosis, but did not further increase these processes in monocytes that had recently ingested bacteria. Furthermore, serum did not boost iodination during intracellular killing by monocytes. Phorbol myristate acetate, N-formyl-methyonyl-leucyl-phenylalanine, concanavalin A, and concanavalin A-Sephadex all stimulated the conversion of O2 to H2O2 by monocytes, but only concanavalin A augmented intracellular killing. Reactive oxygen intermediates generated by cell-free enzymes (xanthine oxidase or glucose oxidase) in concentrations comparable to those accumulating extracellularly during incubation of monocytes containing bacteria with phorbol myristate acetate did not promote intracellular killing. The presence of catalase during phagocytosis inhibited killing, but had no effect on killing in the postphagocytic state. Monocytes deprived of glucose for 24 h showed markedly impaired O2 consumption, O2- generation, and bacterial killing; all of these effects were rapidly reversed by restoration of glucose. It is concluded that both an intact respiratory burst and extracellular serum factors are necessary for optimal killing of intracellular Staphylococcus aureus by human monocytes. Serum does not appear to act by enhancing the respiratory burst, but rather to have a separate, synergistic role, the biochemical basis of which is unknown.
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PMID:Relationship between extracellular stimulation of intracellular killing and oxygen-dependent microbicidal systems of monocytes. 298 74

The objectives of this study were to describe the ultrastructure of granulocyte-Schistosoma mansoni egg interaction and to determine the role of reduced oxygen products as effectors of cell-mediated damage to the parasite target. Granulocytes attached to the parasites and closely applied their plasma membranes to the microspicules of the egg shell 30 min after mixing in the presence of immune serum. By 4 h, the egg shell was fractured and granulocyte pseudopodia extended toward the underlying miracidium. Granulocyte attachment to eggs resulted in release of O2- (0.30-0.52 nmol/min per 2 X 10(6) cells) and accumulation of H2O2 (0.14-0.15 nmol/min) in the presence of antibody or complement. Granulocytes reduced egg tricarboxylic-acid cycle activity and hatching by 28.3 +/- 0.9 and 35.2 +/- 2.8%, respectively (cell-egg ratio of 1,000: 1). Exogenous superoxide dismutase (10 micrograms/ml) inhibited granulocyte toxicity for egg metabolic activity (3.0 +/- 2.1% reduction in acetate metabolism vs. 28.3 +/- 0.9% decrease in controls without superoxide dismutase, P less than 0.0005) and hatching (12.5 +/- 1.8% reduction, P less than 0.0005), whereas catalase and heparin had no effect. Inhibitors of myeloperoxidase (1 mM azide, cyanide, and methimazole) augmented granulocyte-mediated toxicity of egg tricarboxylic-acid cycle activity (44-58% reduction in activity vs. 31 and 35% reduction in controls), suggesting that H2O2 released from cells was degraded before reaching the target miracidium. Oxidants generated by acetaldehyde (2 mM)-xanthine oxidase (10 mU/ml) also decreased egg metabolic activity and hatching by 62.0 +/- 9.0 and 38.7 +/- 7.3%, respectively. Egg damage by the cell-free system was partially prevented by superoxide dismutase (26.5 +/- 4.2% reduction in egg tricarboxylic-acid activity) and completely blocked by catalase (0% reduction in activity). These data suggest that granulocyte-mediated toxicity for S. mansoni eggs is dependent on release of O2- or related molecules. These oxygen products, unlike H2O2, may readily reach the target miracidium where they may be converted to H2O2 or other microbicidal effector molecules.
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PMID:Role of granulocyte oxygen products in damage of Schistosoma mansoni eggs in vitro. 298 56

Examination of the spectra of phagocytosing neutrophils and of myeloperoxidase present in the medium of neutrophils stimulated with phorbol myristate acetate has shown that superoxide generated by the cells converts both intravacuolar and exogenous myeloperoxidase into the superoxo-ferric or oxyferrous form (compound III or MPO2). A similar product was observed with myeloperoxidase in the presence of hypoxanthine, xanthine oxidase and Cl-. Both transformations were inhibited by superoxide dismutase. Thus it appears that myeloperoxidase in the neutrophil must function predominantly as this superoxide derivative. MPO2 autoxidized slowly (t 1/2 = 12 min at 25 degrees C) to the ferric enzyme. It did not react directly with H2O2 or Cl-, but did react with compound II (MP2+ X H2O2). MPO2 catalysed hypochlorite formation from H2O2 and Cl- at approximately the same rate as the ferric enzyme, and both reactions showed the same H2O2-dependence. This suggests that MPO2 can enter the main peroxidation pathway, possibly via its reaction with compound II. Both ferric myeloperoxidase and MPO2 showed catalase activity, in the presence or absence of Cl-, which predominated over chlorination at H2O2 concentrations above 200 microM. Thus, although the reaction of neutrophil myeloperoxidase with superoxide does not appear to impair its chlorinating ability, the H2O2 concentration in its environment will determine whether the enzyme acts primarily as a catalase or peroxidase.
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PMID:Production of the superoxide adduct of myeloperoxidase (compound III) by stimulated human neutrophils and its reactivity with hydrogen peroxide and chloride. 299 50

The effects on neutrophil function of the new immunomodulatory agent fanetizole mesylate were studied. Fanetizole did not affect random or stimulated migration, phagocytosis, or degranulation by normal human neutrophils. Production of superoxide in response to the chemotactic factor formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) was markedly inhibited (41.3 +/- 3.9%) by 250 microM fanetizole. This inhibition was not due to scavenging of superoxide by fanetizole, as there was no impairment of superoxide detection in a cell-free xanthine-xanthine oxidase system. Inhibition was dose dependent (no effect seen with 1 or 10 microM fanetizole) and stimulus specific (no impairment of superoxide production in response to phorbol myristate acetate). Washing the cells after fanetizole treatment partially restored their superoxide response to f-Met-Leu-Phe. Suppression of neutrophil production of toxic oxygen metabolites may partially explain the antiarthritic effect of fanetizole, and study of such selective inhibitors may be useful in probing the contribution of neutrophils to inflammatory tissue damage.
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PMID:Inhibition of neutrophil superoxide production by fanetizole. 299 53

Human neutrophils (PMN), when stimulated with such chemotaxins as phorbol myristate acetate (PMA), destroy erythrocytes and other targets. Cytotoxicity depends on PMN-generated reactive oxygen metabolites, yet the exact toxic specie and its mode of production is a matter of some dispute. Using 51Cr-labeled erythrocytes as targets, we compared various reactive-O2 generating systems for their abilities to lyse erythrocytes as well as to oxidize hemoglobin to methemoglobin. PMA-activated PMNs or xanthine oxidase plus acetaldehyde were added to target erythrocytes in amounts that provided similar levels of superoxide. PMNs lysed 68.3 +/- 2.9% (SEM) of targets, whereas the xanthine oxidase system was virtually impotent (2.3 +/- 0.8%). In contrast, methemoglobin formation by xanthine oxidase plus acetaldehyde was significantly greater than that caused by stimulated PMNs (P less than 0.001). A similar dichotomy was noted with added reagent H2O2 or the H2O2-generating system, glucose plus glucose oxidase; neither of these caused 51Cr release, but induced 10-70% methemoglobin formation. Thus, although O2- and H2O2 can cross the erythrocyte membrane and rapidly oxidize hemoglobin, they do so evidently without damaging the cell membrane. That a granule constituent of PMNs is required to promote target cell lysis was suggested by the fact that agranular PMN cytoplasts (neutroplasts), although added to generate equal amounts of O2- as intact PMNs, were significantly less lytic to target erythrocytes (P less than 0.01). Iron was shown to be directly involved in lytic efficiency by supplementation studies with 2 microM iron citrate; such supplementation increased PMN cytotoxicity by approximately 30%, but had much less effect on erythrocyte lysis by neutroplasts (approximately 3% increase), and no effect on lysis in the enzymatic oxygen radical-generating systems. These results suggest a critical role for an iron-liganding moiety that is abundantly present in PMN, marginally so in neutroplasts, and not at all in purified enzymatic systems--a moiety that we presume catalyzes very toxic O2 specie generation in the vicinity of juxtaposed erythrocyte targets. The obvious candidate is lactoferrin (LF), and indeed, antilactoferrin IgG, but not nonspecific IgG, reduced PMN cytotoxicity by greater than 85%. Re-adding 10(-8) M pure LF to neutroplasts increased their ability to promote hemolysis by 48.4 +/- 0.9%--to a level near that of intact PMNs. We conclude that O-2 and H2O2 are not sufficient to mediate target cell lysis, but require iron bound to LF, which, in turn, probably generates and focuses toxic O2 radicals, such as OH, to target membrane sites.
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PMID:Oxygen radical-induced erythrocyte hemolysis by neutrophils. Critical role of iron and lactoferrin. 299 52

Recent studies examining the effect of allopurinol on bacterial killing by leukocytes [Tubaro et al., Biochem. Pharmac. 29, 3018 (1980); Tritsch and Neiswander, Life Sci. 32, 1359 (1983)] have been interpreted by those authors as proof that xanthine oxidase is the major superoxide producing enzyme in activated leukocytes. To test the assertion that xanthine oxidase is involved in the production of superoxide by activated human neutrophils, the xanthine oxidase content of neutrophils was measured, and the effect of allopurinol on neutrophil functions, including superoxide production, was studied. Neutrophils were found to contain a level of xanthine oxidase insufficient to account for the flux of superoxide associated with neutrophil activation. Allopurinol did not inhibit superoxide production induced by opsonized zymosan, phorbol myristic acetate, or formylmethionylleucylphenylalanine. Furthermore, neither chemotaxis nor degranulation was affected by allopurinol. Allopurinol was also found ineffective in blocking superoxide-mediated carrageenan-induced foot edema in the rat. These studies are interpreted as evidence that xanthine oxidase is not a major superoxide-generating system in activated neutrophils as has been suggested by others.
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PMID:Effect of allopurinol on neutrophil superoxide production, chemotaxis, or degranulation. 299 56

Maintenance of an acidic intralysosomal compartment may be relevant to multiple aspects of neutrophil function. The effect of lysosomal alkalinization on the neutrophil respiratory burst was studied by measuring cytochrome c reduction in response to soluble stimuli in the presence of lysosomotropic weak bases. The weak bases chloroquine, ammonium chloride, methylamine, and clindamycin all raised the intralysosomal pH and inhibited neutrophil oxidative metabolism at concentrations ranging from 0.1 to 100 mmol/L. Inhibition was dose dependent for each base and correlated significantly with the degree of lysosomal alkalinization. Concentrations that did not alkalinize the lysosome did not inhibit the respiratory burst. Inhibition by weak bases was seen when oxidative metabolism was stimulated by phorbol myristate acetate, calcium ionophore A23187, formyl-methionyl-leucyl-phenylalanine, opsonized zymosan, or sodium fluoride. Increasing the stimulus concentration (from 5 ng/mL to 5 micrograms/mL phorbol myristate acetate and from 0.5 to 1 mumol/L A23187) diminished or abolished inhibition by weak bases. Washing the cells after incubation with bases and before stimulation substantially reversed the inhibition. None of the bases impaired detection of superoxide in a cell-free xanthine-xanthine oxidase assay. Other indexes of oxidative metabolism, including oxygen consumption and hydrogen peroxide release, were also inhibited by weak bases. Analysis of particulate NADPH oxidase activity from neutrophils stimulated in the presence of bases suggested that these cells assemble a subnormal amount of an enzyme complex with normal kinetic characteristics. Lysosomotropic weak bases alkalinized the neutrophil lysosome and produced inhibition of oxidative metabolism that was dose related, was not stimulus specific, and was largely reversed by washing the cells before stimulation. A possible explanation would be altered assembly of the enzyme complex involved in respiratory burst activation as a consequence of impaired granule/plasma membrane fusion in the presence of diminished transmembrane pH gradients.
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PMID:Inhibition of neutrophil oxidative metabolism by lysosomotropic weak bases. 300 23

Hydroxyl radicals have been generated from hydrogen peroxide and superoxide (produced with xanthine oxidase), and an iron (EDTA) catalyst, and detected with deoxyribose, or in some cases with benzoate or alpha-keto-gamma-methiolbutyric acid. Purified myeloperoxidase, and neutrophils stimulated with fMet-Leu-Phe and cytochalasin B, strongly inhibited this hydroxyl radical production in a concentration-dependent manner. Supernatants from stimulated cells also inhibited, and inhibition by cells or supernatant was prevented by azide. There was much less inhibition by myeloperoxidase-deficient neutrophils. Inhibition thus was due to myeloperoxidase released by the cells. With neutrophils stimulated with phorbol myristate acetate, which release very little myeloperoxidase, hydroxyl radical production was enhanced due to the additional superoxide produced by the cells. It is concluded that under conditions where neutrophils release myeloperoxidase as well as superoxide and hydrogen peroxide, breakdown of hydrogen peroxide by myeloperoxidase would make conditions unfavorable for hydroxyl radical production.
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PMID:Myeloperoxidase as an effective inhibitor of hydroxyl radical production. Implications for the oxidative reactions of neutrophils. 301 31

The effects of antirheumatic drugs on superoxide anion (O2-.) production by human polymorphonuclear leukocytes (PMNL) activated in vitro with phorbol myristate acetate (PMA) or N-formyl-methionyl-leucyl-phenylalanine (fMLP) were investigated. Chloroquine (CLQ), auranofin (AF) and chlorotriethylphosphine gold (CTEP-G) at 10(-6) to 10(-4) M inhibited PMA and fMLP induced O2-. production in a dose dependent fashion. These drugs had no effect on O2-. production by the hypoxanthine/xanthine oxidase system, indicating that their inhibitory effects were directed at the O2-. generating mechanism and that they were not scavengers of the O2-. formed. AF and CTEP-G inhibited the specific binding of 3H fMPL to PMNL membrane receptors, whereas CLQ had no effect. Colchicine (COL) and gold sodium thiomalate (GSTM) on the other hand did not significantly affect PMA and fMLP induced O2-. production or the specific binding of the ligands to PMNL. The antirheumatic drugs had no effect on isolated neutrophil membrane protease, a chymotrypsin-like enzyme that has been implicated in the activation of NAD(P)H oxidase. However, several of the drugs inhibited the enzymatic activity of a subcellular preparation of PMNL NAD(P)H oxidase, the order of potency being GSTM greater than CLQ greater than penicillamine greater than COL greater than AF approximately equal to CTEP-G. The isolated NAD(P)H oxidase was also inhibited by the thiol compounds--thiomalic acid and dithiothreitol, suggesting that the mechanism of inhibition may involve sulfhydryl-disulfide interchange reactions.
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PMID:Interactions of antirheumatic drugs with the superoxide generation system of activated human polymorphonuclear leukocytes. 301 58


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