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 factors that predispose to the accelerated organ injury that accompanies the hypertensive syndrome have remained speculative and without a firm experimental basis. Indirect evidence has suggested that a key feature may be related to an enhanced oxygen radical production. The purpose of this study was to refine and use a technique to visualize evidence of spontaneous microvascular oxidative stress in vivo in the spontaneously hypertensive rat (SHR) compared with its normotensive control, the Wistar-Kyoto rat (WKY). We investigated the effects of adrenal glucocorticoids on the microvascular oxidative stress sequence. The mesentery was superfused with hydroethidine, a reduced, nonfluorescent precursor of ethidium bromide. In the presence of oxidative challenge, hydroethidine is transformed intracellularly into the fluorescent compound ethidium bromide, which binds to DNA and can be detected by virtue of its red fluorescence. The fluorescent light emission from freshly exteriorized and otherwise unstimulated mesentery microvessels was recorded by digital microscopy. The number of ethidium bromide-positive nuclei along the arteriolar and venular walls in SHR was found to be significantly increased above the level exhibited by WKY. The elevation in ethidium bromide fluorescence in SHR arterioles could be attenuated by a synthetic glucocorticoid inhibitor and in rats subjected to adrenalectomy. The administration of glucocorticoids after adrenalectomy by injection of dexamethasone restored the oxidative reaction in SHR arterioles. Treatment with dimethylthiourea and with a xanthine oxidase inhibitor attenuated the superoxide formation. Although a nitric oxide synthase inhibitor (NG-nitro-L-arginine methyl ester) enhanced the ethidium bromide staining in WKY, it did not affect that in SHR.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:In vivo evidence for microvascular oxidative stress in spontaneously hypertensive rats. Hydroethidine microfluorography. 773 20

One of the objectives of studying endothelial cells in vitro is to evaluate neutrophil-endothelial cell interactions including potential consequences of oxidant-mediated damage to the endothelial cell. Current understanding of endothelial cell oxidative function is derived primarily from the measurement of extracellular products. We utilized 2 dyes, 2',7'-dichlorofluorescein diacetate (DCFH-DA) and hydroethidine (HE), which measure hydrogen peroxide (H2O2) and superoxide anion (O2-) respectively, for their suitability to monitor oxidative mechanisms in endothelial cells and to provide a reliable measure of intracellular oxidants. Endothelial cells stained with DCFH-DA and stimulated with H2O2 exhibited an increase in the fluorescent product 2',7'-dichlorofluorescein (DCF) (measure of intracellular H2O2) which peaked at 10 min. Endothelial cells stained with HE and stimulated with H2O2 exhibited an increase in the fluorescent product ethidium bromide (EB) (measure of intracellular O2-) which lasted for approximately 60 min. Superoxide dismutase increased DCF fluorescence in endothelial cells stimulated with H2O2 by 158%. Allopurinol (xanthine oxidase inhibitor) reduced DCF and EB fluorescence by 48% and 37% respectively in endothelial cells stimulated with H2O2. Catalase completely inhibited an increase in DCF or EB fluorescence in endothelial cells stimulated with H2O2. There was a direct correlation between mean DCF and EB fluorescence intensity and the concentration of H2O2 or the number of phorbol 12-myristate 13-acetate-activated neutrophils added to endothelial cells. We conclude from these studies that DCFH-DA and HE can be used to measure intracellular H2O2 and O2- in endothelial cells and that the xanthine oxidase pathway for intracellular O2- production accounts for approximately 40% of the total intracellular O2- generated in endothelial cells after stimulation with H2O2. The combination of image cytometry and flow cytometry will be important for future evaluations of endothelial cell function.
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PMID:Intracellular hydrogen peroxide and superoxide anion detection in endothelial cells. 830 Dec 22

The luteolytic mechanism was investigated in rat corpora lutea (CL). This study focused on the changes that occur in the plasma membrane. Previous experiments with rat luteal cells indicated that in vitro generation of superoxide radicals by xanthine oxidase disrupted LH-stimulated cAMP production and progesterone secretion similar to the effect of prostaglandin F2 alpha, the luteolytic hormone. In the present study, we observed that xanthine oxidase treatment of plasma membrane samples from CL caused a large decrease in fluidity, which also occurs during prostaglandin F2 alpha-induced luteolysis. This fluidity change was blocked by catalase, bromophenacyl bromide, an inhibitor of phospholipase-A activity, indomethacin, and free radical scavengers, and it was reversed by removal of FFA from the membrane. In addition, xanthine oxidase treatment caused phospholipid breakdown, formation of neutral lipids, a burst of inorganic peroxides, and a sustained rise in the level of lipid peroxides. These results indicate that free radical generation causes several changes that disrupt the plasma membrane of CL cells, and they raise the possibility that phospholipid breakdown could be involved in the mechanism that inhibits LH stimulation of steroidogenesis during luteolysis.
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PMID:Plasma membrane changes in the rat corpus luteum induced by oxygen radical generation. 834 94

Guanidinium chloride inhibits xanthine oxidase competitively with respect to xanthine. Although previously attributed solely to the guanidinium cation, it is now apparent that this inhibition owes much to the counter anion. Thus KCl or KBr, which were not themselves inhibitory, markedly increased the inhibitory potency of guanidinium sulfate. Weak binding of the guanidinium cation evidently creates a binding site for a monovalent anion, whose subsequent binding then stabilizes the binding of the guanidinium. In effect the ion pair is bound to the catalytic center. The proportion of univalent reduction of dioxygen by xanthine oxidase, at fixed concentrations of xanthine and dioxygen and at fixed pH, can be markedly increased by addition of a competitive inhibitor such as guanidinium bromide.
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PMID:Competitive inhibition of xanthine oxidase by guanidinium: dependence upon monovalent anions and effects on production of superoxide. 839 58

Experiments have been carried out to explore the use of a tetrazolium salt, MTT(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide in the detection of intracellularly generated superoxide in HeLa cells. From the use of a low molecular weight lipophilic mimic of superoxide dismutase, as well as superoxide dismutase, and inhibitors of superoxide dismutase, it is suggested that at least 20-30% of the intracellular reduction of MTT is due to superoxide. Whilst this may arise from mitochondria another possible intracellular source in HeLa cells may be xanthine oxidase. The overall rate of intracellular MTT reduction in HeLa cells is inversely dependent on levels of serum in the culture medium. Serum components with a modulatory role in this context are those with antioxidant function. Reduced MTT is also detectable extracellularly in cultures of HeLa cells and at least 80% of this is due to superoxide. Use of inhibitors suggest that whilst a small proportion (30%) may arise through an NADPH-oxidase type enzyme, other sources of extracellular superoxide in HeLa cells remain a possibility.
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PMID:Reduction of a tetrazolium salt and superoxide generation in human tumor cells (HeLa). 839 48

Methotrexate, an important agent in the treatment of childhood acute lymphoblastic leukaemia, has generally failed to induce dose-dependent cytotoxicity of patient-derived leukaemic blasts when tested in the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. This effect is apparently due to salvage from the medium, by surviving leukaemic cells, of metabolites such as hypoxanthine and thymidine. In an attempt to address this problem, we have examined the effect, on leukaemic cell populations, of enzymatically depleting these metabolites from the culture medium employed during the MTT assay, using xanthine oxidase and thymidine phosphorylase. Specifically we have assessed methotrexate cytotoxicity in the paediatric acute lymphoblastic T cell leukaemia, GKTL, which is maintained as a xenograft, and like primary leukaemias, has poor viability in vitro. Although little cytotoxicity of GKTL cells was observed when the MTT assay was performed in supplemented RPMI-1640 medium, dose-dependent cytotoxicity of these cells was clearly apparent when the same medium was enzymatically depleted. In contrast, the ID50 for methotrexate of control CCRF-CEM cells was unaltered in enzymatically depleted medium. In the absence of methotrexate, enzymatic depletion of the medium did not affect leukaemic cell survival. We are currently investigating the general applicability of this approach for assaying the response to methotrexate of primary leukaemia samples.
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PMID:Methotrexate cytotoxicity determination using the MTT assay following enzymatic depletion of thymidine and hypoxanthine. 844 66

The non-12-O-tetadecanoylphorbol-13-acetate (TPA)-type tumor promoters, okadaic acid (OA) and calyculin-A (CAL-A), which neither interact with the phorbol ester receptor nor directly activate protein kinase C, mimic the stimulatory effects of and thapsigargin on hydroperoxide (HPx) production in mouse epidermis in vivo. The time course and dose dependency for the stimulation of HPx production by O and TPA are similar. HPx production is maximally stimulated 16 h after two applications of 2 nmol of OA at a 48-h interval. However CAL-A is a stimulator of HPx production about 4 times more potent than OA or TPA. Combinations of TPA and OA or CAL-A have subadditive effects on HPx production. The discrepancies between the abilities of various serine/threonine protein phosphatase (PP) inhibitors to stimulate HPx production suggest that PP inhibition alone is not sufficient for this response. Cycloheximide, Ca2+ antagonists, oxypurinol, diphenyliodonium, nordihydroguaiaretic acid, bromophenacyl bromide, antiinflammatory agents, and antihistamines block or decrease OA-stimulated HPx production. Although most of these inhibitors may have more than one action, their effects suggest that protein synthesis, Ca2+, xanthine oxidase and NADPH oxidase activities, the lipoxygenase pathway of arachidonic acid metabolism, and vascular permeability may be involved in the inflammatory and HPx responses that occur after tumor promoter treatment. The increased HPx-producing activity of the epidermis, therefore, may be a common event resulting from the inflammatory and tumor-promoting actions of diverse TPA- and non-TPA-type agents.
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PMID:Ability of okadaic acid and other protein phosphatase inhibitors to mimic the stimulatory effects of 12-O-tetradecanoylphorbol-13-acetate on hydroperoxide production in mouse epidermis in vivo. 855 15

In the present study we investigated the effect of metabolic activation on the susceptibility of isolated rat pancreatic islet cells to the alkylating beta-cell toxin streptozocin (SZ), reactive oxygen intermediates (ROI), and nitric oxide (NO). The latter two represent physiologically occurring mediators involved in the autoimmune destruction of islet cells. ROI were generated by the enzyme xanthine oxidase, and NO was released from sodium nitroprusside. During 18 h of culture at a physiological glucose concentration (5 mmol/L), 75% of the islet cells were lysed by SZ, 81% by ROI, and 74% by NO, as determined by the trypan blue exclusion assay. Increasing concentrations of glucose or the nonnutrient stimulators theophylline and glibenclamide dose-dependently reduced SZ- and ROI-mediated islet cell lysis. In the presence of 29 mmol/L glucose, 5.5 mmol/L theophylline, or 10 micrograms/mL glibenclamide, SZ-induced lysis was reduced to 15%, 22%, or 15%, and ROI-induced lysis was reduced to 20%, 34%, or 15%, respectively. In contrast, stimulation by glucose, theophylline, or glibenclamide did not improve resistance against NO. The protection against SZ and ROI was associated with preserved mitochondrial activity, as determined by the ability of the islet cells to convert the tetrazolium salt 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide into its formazan. Elevation of the glucose concentration from 5.5 to 29 mmol/L increased the residual mitochondrial activity from 45% to 80% in SZ-exposed islet cells and from 21% to 78% in ROI-exposed cells. Conversely, the lack of protection against NO correlated with no preservation of mitochondrial activity in the presence of high concentrations of glucose, theophylline, or glibenclamide. In conclusion, our results show that metabolic stress does not render islet cells more susceptible to inflammatory insults in vitro. Rather, an increased mitochondrial energy supply improves the resistance against SZ and ROI, whereas the toxicity of NO was independent of islet cell activity.
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PMID:Metabolic activation of islet cells improves resistance against oxygen radicals or streptozocin, but not nitric oxide. 892 45

beta(2)-Agonists are known to have anti-inflammatory efficacy. In this context, beta(2)-agonists are also capable of inhibiting oxidant production of cultured inflammatory cells. As the mechanisms of this function still remain speculative, the purpose of this study was to quantify the efficacy of beta(2)-agonists in vitro to inhibit superoxide anion (O2-), hydrogen peroxide (H2O2), hydroxyl radical (OH.) and hypochlorous acid (HOCl). We tested the following antiasthma drugs: ipratropium bromide, salbutamol (salbutamol base), fenoterol (fenoterol hydrobromide), terbutaline (terbutaline sulfate), isoproterenol, prednisolone (prednisolone hydrogensuccinate), beclomethasone (beclomethasone dipropionate) and theophylline (theophylline sulfate). Antioxidant function was quantified by using the following assay systems: O2- (ferricytochrome c + xanthine/xanthine oxidase), H2O2 (phenol red + 5.10(-6) M H2O2), OH. (deoxyribose assay) and HOCI (HOCl/OCl- in luminol-dependent chemiluminescence). At 10(-4) M, the anti-H2O2 and anti-O2- capacity was as follows: salbutamol/terbutaline < fenoterol < isoproterenol. All beta(2)-agonists (10(-4) M) tested reduced HOCl activity by > 50% (p < 0.01). In contrast, moderate OH. reduction (10-30%) by the beta(2)-agonists is regarded as an nonspecific effect, due to the high concentrations needed (10(-3) M). Corticosteroids and theophylline had no antioxidant effect. These results demonstrate the different redox potentials of different phenol types within the molecular structure of the beta(2)-agonists. The good antioxidative function of isoproterenol is related to ortho formation of the phenol ring, whereas fenoterol has tow phenol rings which can be oxidized. A direct oxidant scavenger function may explain the ability of beta(2)-agonists to reduce the oxidant production of inflammatory cells in vitro.
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PMID:Beta-2-agonists have antioxidant function in vitro. 1. Inhibition of superoxide anion, hydrogen peroxide, hypochlorous acid and hydroxyl radical. 904 70

A prominent feature of cell damage caused by oxidative stress is morphological and functional changes in the mitochondria. The present study looked at the effect of free radical exposure on intestinal mitochondrial lipids. Free radical exposure did not alter neutral lipids, but among the phospholipids, phosphatidylethanolamine (PE) content was decreased on exposure to superoxide anion, generated by xanthine-xanthine oxidase or menadione with a concomitant increase in the level of phosphatidic acid (PA), suggesting activation of phospholipase D (PLD). This enzyme did not show transphosphatidylation activity in the presence of ethanol or butanol, and the product formed was phosphatidic acid (PA). This was confirmed by separation of reaction products by HPLC. This alteration in mitochondrial phospholipid was abolished by the presence of superoxide dismutase. Exposure to H2O2 did not have any significant effect. Activation of PLD by free radicals was further confirmed by quantitation of ethanolamine released from PE. Absence of any change in the content of lysophospholipid or diglyceride following exposure of mitochondria to superoxide ruled out the involvement of phospholipase A2 or C in the altered lipid composition. Moreover, inclusion of phospholipase A2 inhibitors, chlorpromazine, or p-bromophenacyl bromide did not prevent the generation of PA on exposure to free radicals. These findings suggest that superoxide anion stimulates intestinal mitochondrial PLD resulting in PE degradation and PA formation. These alterations in mitochondrial lipids may play a role in causing the functional alteration seen in oxidative stress.
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PMID:Phospholipase D activity in the intestinal mitochondria: activation by oxygen free radicals. 919 89


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