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)

Previous studies have shown that washed human platelets attenuate oxidant oedema in isolated perfused rabbit lungs through mechanisms dependent on platelet glutathione. We hypothesized that the platelet glutathione redox cycle scavenges hydrogen peroxide in this model and thereby protects vascular endothelial cells from oxidant injury. This hypothesis was tested by asking two questions: (1) do glutathione-supplemented platelets demonstrate augmented lung protection compared with control platelets, and (2) does conjugation of platelet glutathione with 1-chloro-2,4-dinitrobenzene or inactivation of catalase with 3-amino-1,2,4-triazole decrease in vitro platelet metabolism of hydrogen peroxide? We incubated washed human platelets with reduced glutathione or glutathione monoester and observed platelet glutathione contents of 181% and 189%, respectively, compared with control values. Incubation of platelets with N-acetylcysteine did not alter platelet glutathione content. Infusion of glutathione-supplemented platelets into isolated lungs injured by purine and xanthine oxidase did not augment platelet protection compared with untreated platelets. We also found that conjugation of platelet glutathione and/or inactivation of platelet catalase did not decrease the rate constant for platelet metabolism of hydrogen peroxide. We conclude that platelets attenuate oxidant lung oedema through glutathione-dependent mechanisms other than direct scavenging of hydrogen peroxide.
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PMID:Platelet prevention of oxidant lung oedema is not mediated through scavenging of hydrogen peroxide. 145 Mar 19

Activation of glutathione transferase activity in rat liver microsomes under a variety of conditions producing oxidative stress was investigated. Neither hydrogen peroxide (10 mM) (added or produced endogenously by glucose + glucose oxidase) nor duroquinone together with an NADPH-regenerating system (which generates the superoxide anion radical) had any significant effect on the glutathione transferase activity towards 1-chloro-2,4-dinitrobenzene. On the other hand, incubation of microsomes with 1 mM noradrenaline (which autooxidizes and generates superoxide anion radical) gave a 160% activation, as shown earlier (Aniya and Anders, J Biol Chem 264: 1998-2002, 1989). This was taken as an indication that microsomal glutathione transferase could be activated by oxidative stress. Here, we demonstrate that activation by this compound is due to covalent binding (presumably of the quinone formed during autooxidation). The xanthine/xanthine oxidase system, which generates the superoxide anion radical and hydrogen peroxide, increases microsomal glutathione transferase activity, but this activation was not dependent on the presence of xanthine. Western blots of microsomes treated with xanthine oxidase revealed that activation was due to proteolysis (presumably by contaminating proteases in the xanthine oxidase). In conclusion, there is no firm evidence that rat liver microsomal glutathione transferase is activated directly by reduced oxygen species in the microsomal system. The possibility remains that oxidative stress triggers secondary mechanisms such as generation of reactive intermediates and/or activation of proteolysis, which can in turn increase enzyme activity.
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PMID:Mechanism of activation of rat liver microsomal glutathione transferase by noradrenaline and xanthine oxidase. 157 69

We investigated the effect of xanthine (X) plus xanthine oxidase (XO) on pulmonary microvascular endothelial permeability in isolated rabbit lungs perfused with Krebs buffer containing bovine serum albumin (5 g/100 ml). Addition of five mU/ml XO and 500 microM X to the perfusate caused a twofold increase in the pulmonary capillary filtration coefficient (Kf,c) 30 min later without increasing the pulmonary capillary pressure. This increase was prevented by allopurinol or catalase but not by superoxide dismutase or dimethyl sulfoxide. Because these data implicated hydrogen peroxide (H2O2) as the injurious agent, we measured its concentration in the perfusate after the addition of X and XO for a 60-min interval. In the absence of lung tissue and albumin, H2O2 increased with time, reaching a concentration of approximately 250 microM by 60 min. If albumin (5 g/100 ml) was added to the perfusate, or in the presence of lung tissue, the corresponding values were 100 microM and less than 10 microM, respectively. To understand the mechanisms of H2O2 scavenging by lung tissue, we added a 250 microM bolus of H2O2 to the lung perfusate. We found that H2O2 was removed rapidly, with a half-life of 0.31 +/- 0.04 (SE) min. This variable was not increased significantly by inhibition of lung catalase activity with sodium azide or inhibition of the lung glutathione redox cycle with 1-chloro-2,4-dinitrobenzene. However, inhibition of both enzymatic systems increased the half-life of H2O2 removal to 0.71 +/- 0.09 (SE) min (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanisms of extracellular reactive oxygen species injury to the pulmonary microvasculature. 160 78

Washed human platelets prevent edema formation in isolated rabbit lungs infused with xanthine oxidase, an enzyme that injures endothelial membranes by generating extracellular oxidants. We hypothesized that platelets would similarly preserve membrane permeability in isolated lungs exposed to ischemia-reperfusion injury, a model that perturbs endothelial cells by the generation of intracellular oxidants. Isolated perfused rabbit lungs (IPL) were exposed to warm ischemia-reperfusion to cause lung edema. The infusion of washed human platelets (1.05 +/- 0.02 x 10(10) cells) prevented edema formation as measured by lung weight gain, wet-to-dry lung weight ratios, histological edema, and preservation of paraendothelial cell tight junctions. Inhibition of the platelet glutathione redox cycle with 1,3-bis(2-chloroethyl)-1-nitrosourea, dehydroepiandrosterone, or 1-chloro-2,4-dinitrobenzene interfered with platelet protective effects. In contrast, inhibition of platelet catalase with aminotriazole and H2O2 had no effect on platelet protection. Lung tissue malonyldialdehyde concentrations were similar in isolated lungs exposed to ischemia-reperfusion with or without the infusion of platelets. These results indicate that platelet attenuation of ischemia-reperfusion lung edema depends on platelet glutathione redox cycle antioxidants but not platelet catalase.
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PMID:Washed human platelets prevent ischemia-reperfusion edema in isolated rabbit lungs. 203 73

This study quantified the ability of freshly isolated alveolar type II (ATII) pneumocytes to reduce extracellularly produced hydrogen peroxide (H2O2) and identify the mechanisms involved. ATII cells were isolated to high purity (greater than 85%) from rabbit lungs by enzymatic digestion and Percoll centrifugation and suspended in Eagle's minimum essential medium (MEM). They were then coincubated with either 500 microM xanthine and 10 mU/ml xanthine oxidase (XO; pH 7.4; 25 degrees C) or 300 microM H2O2. The extracellular H2O2 concentration [H2O2] was measured in the following conditions over a 60-min period: 1) MEM alone, 2) untreated (control), 3) 3-amino-1,2,4-triazole (ATZ)-treated, or 4) 1-chloro-2,4-dinitrobenzene-treated ATII cells. Addition of xanthine and XO to MEM alone resulted in a time-dependent increase in [H2O2], reaching a plateau value of approximately 300 microM after 45 min. In the presence of control ATII cells (1 x 10(6) cells/ml), [H2O2] remained at control levels. When coincubated with 300 microM H2O2, ATII cells cleared H2O2 at a higher rate than an equivalent amount of free catalase. Incubation with ATZ decreased ATII cell catalase activity by 89% and significantly impaired their ability to clear H2O2 (half-life = 18.1 +/- 2.7 vs. 1.3 +/- 0.1 min, P less than 0.01). ATZ-treated cells were more susceptible to oxidant injury, as shown by their decreased ability to exclude trypan blue after 60 min of H2O2 exposure. On the other hand, glutathione-depleted cells scavenged H2O2 at the same rate as controls.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Mechanisms of extracellular hydrogen peroxide clearance by alveolar type II pneumocytes. 207 3

The activities of rat glutathione transferases (GSTs) 3-3, 3-4, 4-4 in Class mu towards 1-chloro-2,4-dinitrobenzene (CDNB) but not 1,2-dichloro-4-nitrobenzene were increased up to 5-fold during preincubation with 0.4 mM xanthine and xanthine oxidase in 50 mM potassium phosphate, pH 7.8, containing 0.1 mM EDTA. The activated GST 3-4, purified by S-hexylglutathione affinity chromatography after the treatment, had a higher specific activity (130 units/mg) than that of the nontreated (35 units/mg), the Km and Vmax values for glutathione or CDNB also were increased. Other rat GSTs in Class alpha and pi were inactivated by the same treatment. In the presence of superoxide dismutase, the activation of GST 3-4 did not occur.
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PMID:Activation of rat glutathione transferases in class mu by active oxygen species. 240 64

To determine the mechanism responsible for the enhanced susceptibility of endothelial cells to oxidant injury in the absence of glucose, we induced endothelial cell injury with oxygen radicals in the presence of various oxygen radical scavengers and measured endothelial cell levels of glutathione after oxidant injury in the presence and absence of glucose. Endothelial cells were damaged with toxic oxygen radicals generated by phorbol myristate acetate (PMA)-activated polymorphonuclear leukocytes (PMNs) or xanthine-xanthine oxidase in the presence and absence of glucose and catalase (scavenger of hydrogen peroxide), superoxide dismutase (scavenger of superoxide radical), isoleucine, valine, and serine (scavengers of hypochlorous acid), or mannitol, ethanol, benzoic acid, dimethyl sulfoxide, and dimethyl thiourea (scavengers of hydroxyl radical). Endothelial cell injury was quantitated by 2-deoxy-[1-3H] glucose or chromium 51 release assays or both. In each oxidant-generating system, in the presence and absence of glucose, only catalase significantly protected endothelial cells from oxidant injury (P less than 0.001). When endothelial cells were damaged by hydrogen peroxide generated with xanthine-xanthine oxidase in the presence of glucose, endothelial cell levels of glutathione remained unchanged. In contrast, when endothelial cells were damaged with xanthine-xanthine oxidase in the absence of glucose, endothelial cell levels of glutathione fell to less than 50% of baseline (P less than 0.05). Xanthine-xanthine oxidase-mediated endothelial cell damage and depletion of glutathione in the absence of glucose were similar to results obtained in the presence of glucose when glutathione was depleted with buthionine sulfoximine, diethyl maleate, or 1-chloro-2,4-dinitrobenzene.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of glutathione in protecting endothelial cells against hydrogen peroxide oxidant injury. 309 44

Because platelets contain active antioxidant systems, the capacity of platelets to attenuate oxidant lung injury was investigated. Purine and xanthine oxidase were infused into isolated perfused rabbit lungs (IPL) to generate H2O2, thereby causing increased membrane permeability edema. The coinfusion of washed human platelets (1.20 +/- 0.07 x 10(10) cells) attenuated the degree of edema formation as measured by lung weight gain and lung lavage albumin concentration. Electron microscopy of lung preparations demonstrated platelet adherence to capillary endothelial luminal surfaces of oxidant-injured lungs, but there was no evidence of vascular plugging with platelet macroaggregates. The platelet glutathione redox cycle or platelet catalase were inhibited before infusion of platelets into the IPL with purine and xanthine oxidase. Inhibition of the glutathione redox cycle with 1,3-bis(2-chloroethyl)-1-nitrosourea, 1-chloro-2,4-dinitrobenzene, or buthionine sulfoximine prevented platelet attenuation of lung injury. Inactivation of platelet catalase with 3-amino-1,2,4-triazole, however, did not significantly reduce the platelet-induced lung protection. We conclude that the platelet glutathione redox cycle plays a major role in reducing enzymatically generated toxic O2 metabolites and attenuating lung injury.
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PMID:Human platelets attenuate oxidant injury in isolated rabbit lungs. 318 95

The mechanism for formation of high-affinity binding of 1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine (guanoxabenz) to alpha2-adrenoceptors was studied in particulate fractions from the rat spleen. The proportion of apparent high versus low-affinity alpha2-adrenoceptor binding sites increased with increasing incubation time and was also augmented by Mg2+ ions. The formation of high-affinity guanoxabenz binding seemed to be inhibited by a series of N-hydroxyguanidine analogs to guanoxabenz, as well as by a series of metabolic inhibitors that included allopurinol, 1-chloro-2,4-dinitrobenzene, 5,5'-dithiobis-(2-nitrobenzoic acid), cibacron blue, phenyl-p-benzoquinone, didox, and trimidox. The formation of guanoxabenz high-affinity binding was also inhibited in a time- and concentration-dependent fashion by preincubating the membranes with the LW03 N-hydroxyguanidine analogue of guanoxabenz. Moreover, when the spleen membranes were extensively washed for 30 min with buffers at 25 degrees, the guanoxabenz high-affinity binding disappeared. However, when these washed membranes were supplemented with xanthine, the apparent affinity of guanoxabenz increased four to five-fold. Taken together, all data were compatible with the theory that the formation of high-affinity binding was dependent on the generation of a guanoxabenz metabolite that showed an approximate 100-fold greater affinity for the alpha2-adrenoceptors than guanoxabenz itself. Because the most potent blocker of the formation of high-affinity binding was allopurinol (apart from some N-hydroxyguanidine analogs to guanoxabenz) and since the activity could be restored with xanthine, a likely candidate responsible for the metabolic activation is xanthine oxidase.
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PMID:Characterization of the enzymatic activity for biphasic competition by guanoxabenz (1-(2,6-dichlorobenzylidene-amino)-3-hydroxyguanidine) at alpha2-adrenoceptors. I. Description of an enzymatic activity in spleen membranes. 980 20

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


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