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Query: UNIPROT:P47989 (xanthine oxidase)
 8,633 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Heat-induced hepatotoxicity accompanying hyperthermic liver perfusion was studied in the isolated, haemoglobin-free perfused rat liver. Trypan blue uptake, a sensitive indicator of cell death, was used to examine the relationship between the efflux of oxidized glutathione (oxidative stress), the appearance of cytosolic enzymes in the perfusate and cell death. Livers were perfused at 37, 42, 42.5 and 43 degrees C. The efflux of total glutathione (GSH) and oxidized glutathione (GSSG) increased with time and temperature. Differences between temperature groups were significant for both parameters for 37 versus 42, 42.5 and 43 degrees C (p less than 0.05). Temperature-related differences in GSH levels appeared at 15 min for 37 versus 42 degrees C and in GSSG levels at 30 min for 37 versus 42 and 42.5 degrees C. Biliary excretion of total GSH increased from 72 nmol at 37 degrees C to 144 nmol at 42 degrees C, 160 nmol at 42.5 degrees C and 124 nmol at 43 degrees C, which was significant for 37 versus 42 and 42.5 degrees C (p less than 0.05). The release of allantoin into the perfusate, a measure of purine catabolism and flux through xanthine oxidase, was increased at 42, 42.5 and 43 degrees C compared to 37 degrees C (p less than 0.05). Liver injury was assessed by measuring the release of asportate aminotransferase (AST) and lactate dehydrogenase (LDH) and uptake of trypan blue after perfusion at each temperature. There was a pronounced release of LDH and AST into the perfusate after 60 min of perfusion at 42, 42.5 and 43 degrees C, the levels of which were significantly different from the 37 degrees C mean level. There was no uptake of trypan blue after 60 min perfusion at 37 degrees C. Perfusion at 42, 42.5 and 43 degrees C resulted in the uptake of trypan blue in the pericentral areas, but the dye uptake was significant (p less than 0.05) compared to 37 degrees C at 42.5 and 43 degrees C only. These data show that heat-induced pericentral cell death is minimal after 60 min at 42-43 degrees C, and that the biochemical process which occurred during this period suggest 'oxidative stress' as a causative factor in hyperthermic hepatotoxicity. In addition, this liver toxicity is probably related to xanthine oxidase activity or the depletion of GSH as the initiating event which leads to lipid peroxidation and cellular damage.
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PMID:Oxidative stress as a precursor to the irreversible hepatocellular injury caused by hyperthermia. 194 May 10

Excessive stimulation of excitatory amino acid (EAA) receptors and abnormal production of oxygen-derived free radicals have repeatedly been implicated in the series of events linking brain hypoxia or ischemia to neuronal death. We report here that in rat hippocampal slices the KCl-stimulated output of labeled D-3H aspartate or of endogenous aspartate and glutamate significantly increased under in vitro simulated hypoxic, hypoglycemic, or ischemic conditions. In particular, when the slices were incubated for 10 min at 32 degrees C under "ischemic" conditions (namely, lack of oxygen and glucose), endogenous aspartate and glutamate in the supernatant increased by 10 and 20 times, respectively. Since radical scavengers (D-mannitol), drugs reducing free radical formation (indomethacin, corticosteroid), or enzymes able to metabolize them (catalase and superoxide dismutase) significantly reduced this output, it was supposed that free radicals caused EAA release. A direct demonstration of this concept was obtained by showing a significant release of EAA after incubation of hippocampal slices with enzymes and substrates known to cause the formation of free radicals, such as xanthine plus xanthine oxidase or arachidonic acid plus prostaglandin synthase. Neither ischemia nor the enzymatic reactions leading to free radical production increased the activity of the cytoplasmic enzyme lactate dehydrogenase in the incubation medium, thus ruling out a nonspecific cellular lysis. It appears therefore that during ischemic states, brain production of reactive molecules (free radicals) causes an increased output of EAA. This may trigger a series of events which could help to explain the delayed loss of neurons after a transient ischemic period.
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PMID:Excitatory amino acid release and free radical formation may cooperate in the genesis of ischemia-induced neuronal damage. 196 65

Conversion of xanthine dehydrogenase (XDH) to xanthine oxidase (XO) and the toxic reactions of subsequent XO-derived superoxide, hydrogen peroxide and hydroxyl radical, have been suggested to be critical factors in several mechanisms of tissue pathophysiology. In the lung, intracellular XO-derived products may modulate type II pneumocyte surfactant turnover and barrier function, jeopardizing the pulmonary air-blood barrier. We characterized total cellular XDH/XO enzymatic activity in freshly isolated and cultured rat pulmonary type II epithelial cells. Type II cells were isolated and cultured on fibronectin-pretreated dishes, with a plating efficiency after 36 h in culture of 40% or 14% when quantified via cellular protein or DNA, respectively. Over the subsequent 96 h in culture, monolayer DNA was unchanged, whereas protein per cell increased continuously. Alterations in different cellular enzymatic activities were also detected in these cultured cells. In culture, total cellular XDH/XO and catalase activities decreased in a logarithmical fashion with respect to time, whether normalized for cellular protein or DNA. The rate of loss of these enzymes was greatest when normalized for cell protein, but was also significant when the activities were normalized for DNA. When compared to freshly isolated type II cells, catalase and total XDH/XO activities normalized for protein decreased 78% and 72%, respectively, during the first 36 h of culture. After 132 h in culture, XDH/XO and catalase activities normalized for protein decreased 93% and 84%, respectively, when compared to freshly isolated cell values. Total cellular XDH/XO activity in the oxidase form (% XO) was initially 31% in freshly isolated type II cells and increased to 67% during the 132 h culture period. In contrast to the loss of total cellular XDH/XO and catalase, no significant change in lactate dehydrogenase (LDH) activity occurred during culture of the type II cells. In type II cells the conversion of XDH to XO, the cytotoxic potential of XO, and the activity of the hydrogen peroxide scavenger, catalase, is expected to be strongly influenced by in vitro culture. Thus, strong consideration should be made before transposing information obtained from cultured type II cells to in vivo situations.
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PMID:Characterization of cultured alveolar epithelial cell xanthine dehydrogenase/oxidase. 200 13

Reactive O2 species appear to be generated both during hypoxia and at reoxygenation, but it has not been established whether these species interact with heart tissue and cause injury. Oxidative changes were evaluated in isolated rat heart perfused with Krebs-Henseleit medium containing 10 mM glucose and 2.5 mM calcium. After 5-10 min hypoxia, tissue glutathione (GSH) decreased while glutathione disulfide (GSSG), protein carbonyls, and thiobarbituric acid reactive substances (TBARS) increased compared with controls. Similarly, sarcolemmal and sarcoplasmic reticular Ca-ATPase activity (an enzyme susceptible to oxidative inactivation) decreased in response to 10 min hypoxia. These changes were more pronounced after 60 min of hypoxia when protein-GSH mixed disulfides were also increased. There were no further oxidative changes after 4 min reoxygenation when the release of lactate dehydrogenase (LDH) was maximal. Myocardial protein thiol and alpha-tocopherol contents were not significantly changed by either hypoxia or reoxygenation. Mitochondria also exhibited oxidative changes but with more pronounced increases in GSSG and mixed disulfides. There was no change in GSH or GSSG efflux into the coronary effluent during hypoxia, although, in parallel with LDH release, both increased after reoxygenation. Diamide (200 microM), t-butylhydroperoxide (20 microM), or purine (2.3 mM) + xanthine oxidase (0.01 U/ml) were infused for 10 min. Except for large diamide-induced changes in protein thiols and mixed disulfides, the magnitude of the changes produced by these oxidants was similar to those produced by hypoxia. These data show that changes consistent with oxidative processes occur in whole heart and mitochondria in response to hypoxia. The absence of marked signs of oxidation at reoxygenation suggest that enzyme release at this time is unrelated to oxidative stress.
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PMID:Oxidative changes in hypoxic rat heart tissue. 203 61

Tissue changes consistent with oxidative damage in hypoxic/reoxygenated heart tissue have not been well documented. We recently reported that oxidative perturbations were evident in isolated-perfused rat heart tissue subjected to as little as 10 min hypoxia and that these changes were not exacerbated by reoxygenation. The mechanism and species specificity of this finding is not known. Rabbit hearts, which lack measurable xanthine oxidase activity, were examined for evidence of hypoxia-induced injury. The release of lactate dehydrogenase into the coronary effluent gradually increased during the retrograde perfusion of isolated rabbit hearts with hypoxic medium (containing 10 mM glucose and 2.5 mM calcium), and was slightly enhanced upon reoxygenation after 60 min hypoxia. Cardiac glutathione content decreased significantly while glutathione disulfide, protein-glutathione mixed disulfides, thiobaribturic acid reactive substances (TBARS), and protein carbonyl contents increased significantly after 60 min of hypoxia, compared to oxygenated controls. These values were unaltered after 4 min of reoxygenation except for a loss of TBARS. The oxidative changes observed in hypoxic rabbit hearts may be caused by energy deficiency impairing normal reductive processes or by the generation of reactive oxygen species as a result of abnormal cell functions, but cannot be related to xanthine oxidase activity.
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PMID:Oxidative changes in hypoxic-reoxygenated rabbit heart: a consequence of hypoxia rather than reoxygenation. 206 Aug 63

A number of investigations have implicated free radicals in the progression of ischemic/reperfusion injury. alpha-Tocopherol has been found to attenuate alterations due to ischemia and reperfusion in an isolated heart model. The present study was intended to directly examine neonatal rat cardiac ventricular cell cultures exposed to a free radical generating system catalyzed by xanthine oxidase. The effectiveness of alpha-tocopherol in the attenuation of the resultant changes and the mechanism by which the effects of alpha-tocopherol may be exerted were evaluated. Cultures were either nontreated or pretreated for 18 h with 20 microM alpha-tocopherol or the subcomponents of the alpha-tocopherol molecule, phytol and Trolox. Exposure of cell cultures to free radicals resulted in significant increases in lipid peroxidation products, release of both lactate dehydrogenase and 3H-arachidonate, and structural alterations. Pretreatment with alpha-tocopherol showed significant attenuation of the changes associated with exposure to free radicals. Trolox and phytol at equal molar doses were not as effective as alpha-tocopherol in protecting the myocytes against injury. Thus, alpha-tocopherol seems beneficial in its ability to reduce free radical-mediated changes by functioning as a lipophilic antioxidant. Additionally, the intact, native alpha-tocopherol molecule exceeded the protective capabilities of either of its subcomponents.
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PMID:Free radical damage in neonatal rat cardiac myocyte cultures: effects of alpha-tocopherol, Trolox, and phytol. 212 18

Oxygen-derived free radicals have been implicated in damage to membrane phospholipids leading to alterations in membrane function. The purpose of this study was to investigate alterations in intracellular ionic calcium (Ca2+) levels and Ca2+ transients, cellular morphology, conjugated diene levels, arachidonate release, and lactate dehydrogenase release resulting from the exposure of cultured neonatal rat ventricular myocytes to a xanthine oxidase catalyzed free radical generating system capable of producing superoxide and hydroxyl radicals. The ability of alpha-tocopherol to prevent alterations due to free radical exposure was investigated. For measurements of Ca2+, myocytes grown on coverslips for 3-4 days were loaded with fura-2/AM and studied by microspectrofluorometry. Control myocytes superfused with a physiological buffer or buffer containing purine and iron-loaded transferrin exhibited Ca2+ transients associated with spontaneous contractions. For control, buffer perfused myocytes (n = 4), the fura-2 340/380 ratios were 0.5 +/- 0.1 (mean +/- S.E.) and 1.6 +/- 0.03 at the minimum and maximum, respectively, of the Ca2+ transient, after 1 h of perfusion. Exposure to the free radical generating solution (n = 14) altered intracellular Ca2+. The 340/380 minimum ratio was 639% of the control value after approximately 30-70 mins with cessation of normal Ca2+ transients. Bleb development was associated with increased Ca2+. Myocytes reperfused with control medium continued to exhibit an elevated minimum fura-2 ratio at 687% of control. Myocytes pretreated with 10 microM alpha-tocopherol (n = 13) for 18-24 h and exposed to free radicals did not exhibit increases in intracellular Ca2+, having a minimum 340/380 ratio of 0.5 +/- 0.1 after 60-90 mins, and although myocytes often ceased contracting, they resumed spontaneous Ca2+ transients with control medium reperfusion and also maintained normal structure. Exposure of myocyte cultures to free radical generating solutions resulted in increased levels of conjugated dienes and increased release of [3H]arachidonate and lactate dehydrogenase compared to control values after 1 h. alpha-Tocopherol treatment attenuated the increase in conjugated diene levels, and the release of [3H]arachidonate and lactate dehydrogenase. Thus, free radicals alter intracellular Ca2+, conjugated dienes and membrane structure indicating their ability to induce altered ionic homeostasis in association with myocardial membrane damage. alpha-Tocopherol decreased free radical mediated injury.
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PMID:Free radicals alter ionic calcium levels and membrane phospholipids in cultured rat ventricular myocytes. 212 94

In this study, we attempted to elucidate the metabolic pathway and enzymes actually involved in oxalate formation from glycolate in rat and human liver. In rat liver, the formation of oxalate from glycolate appeared to take place predominantly via glyoxylate. The oxalate formation from glycolate observed with crude enzyme preparations was almost entirely accounted for by the sequential actions of glycolate oxidase and xanthine oxidase (XOD) or lactate dehydrogenase (LDH). Under the conditions used, no significant activity was attributable to glycolate dehydrogenase, an enzyme reported to catalyze the direct oxidation of glycolate to oxalate. Among the three enzymes known to catalyze the oxidation of glyoxylate to oxalate, glycolate oxidase and XOD showed much lower activities (a higher Km and lower Vmax) toward glyoxylate than those with the respective primary substrates. As to LDH, none of the LDH subunit-deficient patients examined showed profoundly lowered urinary oxalate excretion. Based on the results obtained, the presumed efficacies in vivo of individual enzymes, as catalysts of glyoxylate oxidation, and the in vivo conditions assumed to allow their catalysis of oxalate production are discussed.
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PMID:The formation of oxalate from glycolate in rat and human liver. 222 23

Toxic oxygen metabolites can damage endothelial cells and may play an important role in the initiation and progression of atherosclerotic lesions. Since the antithrombotic drug heparin, interacts with endothelium, we wished to determine if heparin would protect endothelial cells from free radical injury. Endothelial cell injury was produced by the addition of xanthine and xanthine oxidase to cultured cells and assessed by changes in cell viability and release of lactate dehydrogenase (LDH) to the media. Pretreatment with heparin 24 h prior to addition of xanthine and xanthine oxidase significantly decreased cell damage. We suggest that heparin (and related compounds) can protect endothelium from free radical damage, and is therefore prophylactic for ischemic and inflammatory injury, and the development and progression of atheroma.
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PMID:Heparin protects cultured arterial endothelial cells from damage by toxic oxygen metabolites. 239 Jan 35

Isolated Langendorff-perfused rat hearts after 10 minutes preperfusion, were subjected to a substrate-free anoxic perfusion (20 minutes) followed by 20 minutes reperfusion with a glucose-containing oxygen-balanced medium. Under the same perfusion conditions, the effect of exogenous 5mM fructose-1,6-bisphosphate has been investigated. The xanthine dehydrogenase to xanthine oxidase ratio, concentrations of high-energy phosphates and of TBA-reactive material (TBARS) were determined at the end of each perfusion period in both control and fructose-1,6-bisphosphate-treated hearts. Results indicate that anoxia induces the irreversible transformation of xanthine dehydrogenase into oxidase as a consequence of the sharp decrease of the myocardial energy metabolism. This finding is supported by the protective effect exerted by exogenous fructose-1,6-bisphosphate which is able to maintain the correct xanthine dehydrogenase/oxidase ratio by preventing the depletion of phosphorylated compounds during anoxia. Moreover, in control hearts, the release of lactate dehydrogenase during reperfusion, is paralleled by a 50% increase in the concentration of tissue TBARS. On the contrary, in fructose-1,6-bisphosphate-treated hearts this concentration does not significantly change after reoxygenation, while a slight but significant increase of lactate dehydrogenase activity in the perfusates is observed. On the whole these data indicate a direct contribution of oxygen-derived free radicals to the worsening of post-anoxic hearts. A hypothesis on the mechanism of action of fructose-1,6-bisphosphate in anoxic and reperfused rat heart and its possible application in the clinical therapy of myocardial infarction are presented.
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PMID:Oxygen radical injury and loss of high-energy compounds in anoxic and reperfused rat heart: prevention by exogenous fructose-1,6-bisphosphate. 239 20


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