Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.17.3.2 (xanthine oxidase)
8,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Acute cerebral ischemia increases the generation of free radicals, causing cell damage, and theoretically may decrease the activity of the scavenging enzyme superoxide dismutase. To investigate the role of superoxide dismutase in cerebral ischemia, we used a model of middle cerebral artery occlusion in rats. In this model an infarct is produced in the pyriform and frontoparietal cortices, extending into the lateral basal ganglia. We measured superoxide dismutase activity by using the xanthine oxidase cytochrome c reduction assay in these areas of rat brains. Tissue samples were analyzed 20 minutes, 2, 6, or 24 hours, or 7 days after middle cerebral artery occlusion and 2 or 24 hours or 7 days after sham operation (n = 8-10 at each time). There was no significant change in superoxide dismutase activity relative to control values in any brain area at any time up to 24 hours after surgery. However, 7 days after middle cerebral artery occlusion a significant decline in superoxide dismutase activity, to 55%-68% (p less than 0.05) of that in unoperated controls, was observed in all brain areas. Our results do not support an important role for changes in the activity of endogenous superoxide dismutase during the acute phase of cerebral ischemia. However, the decrease in superoxide dismutase activity 7 days after ischemia could indicate ongoing additional damage to peri-infarct tissue.
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PMID:Effect of ischemia induced by middle cerebral artery occlusion on superoxide dismutase activity in rat brain. 223 56

Since hydrogen peroxide (H2O2) can react with ferrous iron (FE++) to form the more toxic hydroxyl radical (OH) in vitro, and since H2O2 is generated brain xanthine oxidase (XO) during ischemia/reperfusion (I/R), we hypothesized that gerbils depleted of iron by dietary restriction or treated with iron chelators would be less susceptible to I/R injury. We found that gerbils fed a low iron diet for 8 weeks had decreased brain and serum iron levels, less neurologic deficits, and decreased brain edema after temporary unilateral carotid ligation (ischemia) and then reperfusion than gerbils fed a control standard iron diet. In addition, brains from gerbils treated with iron-free deferoxamine (an iron chelator), but not iron-loaded deferoxamine, had decreased (P less than .05) brain edema following ischemia and reperfusion. The results indicate that iron may contribute to cerebral ischemia/reperfusion damage.
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PMID:Iron depletion or chelation reduces ischemia/reperfusion-induced edema in gerbil brains. 230 92

Free radicals have been shown to play an important role in ischemia-reperfusion injury in several organ systems; however, the role of free radicals in central nervous system ischemia has been less well studied. Many potential free radical-generating systems exist. The primary products of these reactions, superoxide and hydrogen peroxide, may combine to produce hydroxyl radicals. Of the many potential sources of free radical generation, the enzyme xanthine oxidase has been shown to be important in ischemia in noncerebral tissue. We investigated the effect of the hydroxyl radical scavenger dimethylthiourea and the xanthine oxidase inhibitor allopurinol on infarct volume in a model of continuous partial ischemia. Male Sprague-Dawley rats were treated with dimethylthiourea or allopurinol before middle cerebral artery occlusion. Infarct volume was measured by triphenyltetrazolium chloride staining of brains removed 3 or 24 hours after occlusion. Stroke volume was reduced by 30% after dimethylthiourea treatment and by 32-35% after allopurinol treatment. At 24 hours after stroke, cortical tissue was more effectively protected than caudate tissue with both agents. Pretreatment with dimethylthiourea and allopurinol also significantly reduced cerebral edema formation and improved blood-brain barrier function as measured by fluorescein uptake. Our results imply that hydroxyl radicals are important in tissue injury secondary to partial cerebral ischemia and that xanthine oxidase may be the primary source of these radicals.
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PMID:Allopurinol and dimethylthiourea reduce brain infarction following middle cerebral artery occlusion in rats. 246 8

The relationship between changes in Ca2+-adenosine triphosphatase (ATPase) activity and plasma membrane damage was histochemically studied by enzymatic electron microscopy in rat brains with and without superoxide treatment. The brains were obtained from male Wistar rats after decapitation, and the control brains were examined immediately. Brains not treated with superoxide were incubated at 20 degrees C for 3, 6, or 12 hours. The superoxide-treated brains were immersed in a hypoxanthine-xanthine oxidase system for 20, 60, or 120 minutes. Ca2+-ATPase activity in the cerebral cortex and hippocampal CA1 was studied by the lead citrate method. Control brains showed Ca2+-ATPase activity in the membrane of the nerve cell body and dendrites, the basement membrane of endothelial cells, and the erythrocyte membrane. In untreated brains, enzymatic activity gradually decreased but was still detected after 12 hours. In those treated with superoxide, enzymatic activity gradually decreased but was still observed after 120 minutes in fragments of the plasma membrane. These findings show that the plasma membrane is more affected by treatment with superoxide than by decapitation itself, and that plasma membrane damage precedes the disappearance of Ca2+-ATPase activity. Residual Ca2+-ATPase activity does not necessarily imply reversibility of cerebral ischemia.
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PMID:Ultracytochemical study of Ca2+-ATPase activity in isolated, superoxide-treated rat brains. 247 35

Xanthine oxidase activity in the rat brain was measured by means of high-performance liquid chromatography with electrochemical detection of uric acid. Cerebral ischemia was produced by a four-vessel occlusion method. In the control rat, the enzyme activity was 0.87 +/- 0.13 nmol/gm wet weight/min at 25 degrees C (mean +/- standard deviation), of which 92.4% was associated with the nicotinamide adenine dinucleotide (NAD)-dependent dehydrogenase form and only 7.6% with the oxygen-dependent superoxide-producing oxidase form. However, the ratio of the latter form increased to 43.7% after 30 minutes of global ischemia, despite the total xanthine oxidase activity remaining the same. Thus, it was revealed that uric acid can be synthesized in the rat brain and that cerebral ischemia induced the conversion of xanthine oxidase from an NAD-dependent dehydrogenase to an oxygen-dependent superoxide-producing oxidase. Although the xanthine oxidase pathway has been proposed as a source of oxygen-derived free radicals in various ischemic organs other than brain, the results of the present study suggest the involvement of the oxygen free radicals generated from this pathway in the pathogenesis of the ischemic injury of the rat brain.
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PMID:Changes in xanthine oxidase in ischemic rat brain. 254 24

Oxypurinol, an inhibitor of the enzyme xanthine oxidase, reduced ischemic hippocampal damage and the associated hypermotility in Mongolian gerbils. Cerebral ischemia was induced in unanesthetized gerbils by a bilateral 5-min occlusion of the carotid arteries. Oxypurinol (40 mg/kg, IP), administered 20 min prior to carotid occlusion, prevented the increase in locomotor activity observed in saline-injected ischemic animals and significantly reduced the damage to, and loss of, CA1 hippocampal neurons observed 5 days postischemia. These findings suggest that oxypurinol may be useful for the prevention of cerebral ischemic damage.
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PMID:Oxypurinol attenuates ischemia-induced hippocampal damage in the gerbil. 261 88

To verify whether lipid peroxidation is associated with focal cerebral ischemia, a unilateral middle cerebral artery occlusion was carried out in rats. The concentrations of various endogenous antioxidants in the ischemic center were measured, including alpha-tocopherol and ubiquinones as lipid-soluble antioxidants and ascorbate as a water-soluble antioxidant. At 30 minutes after ischemia, alpha-tocopherol decreased to 79% of baseline, reduced ubiquinone-9 to 73%, ubiquinone-10 to 66%, and reduced ascorbate to 76%. Six hours after ischemia, alpha-tocopherol decreased to 63% and reached a plateau, whereas reduced ubiquinones and reduced ascorbate declined further to 16% and 10%, respectively, 12 hours after ischemia and then reached plateau levels. These results suggest functional and durational differences between antioxidants and lipid peroxidation in this ischemic model. Although the reciprocal increase in oxidized ubiquinones during ischemia was not observed, that of oxidized ascorbate was noted. The complementary antioxidant system between cytoplasmic and membranous components, the combination alpha-tocopherol/ascorbate, was estimated from the calculated consumption ratio of these antioxidants on the basis that the loss of these reduced antioxidants is due to neutralization of free radicals. This system is suggested to play an important role in the early ischemic period. Urate also increased during ischemia. The possible involvement of the xanthine-xanthine oxidase system in initiating free radical reactions in cerebral ischemia is also discussed.
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PMID:Lipid peroxidation in focal cerebral ischemia. 276 92

The existence of uric acid in mammalian brain was recently reported, but it has not yet become a consensus. The mammalian brain has been thought to lack xanthine oxidase, which catalyzes hypoxanthine to xanthine and xanthine to uric acid as the last steps of ATP degradation in other tissue. Using high-performance liquid chromatography, we performed assays for hypoxanthine, xanthine, and uric acid in rat brain after cerebral ischemia. It was confirmed that all three substances showed significant augmentation in the removed brains and that the chronological order of those increases corresponded to the order in the metabolic pathway. Allopurinol, a specific inhibitor of xanthine oxidase, significantly suppressed the increases in uric acid and xanthine, and a compensatory accumulation of hypoxanthine was observed. From these results, it was concluded that uric acid does exist in the brain, increases after ischemia, and is possibly the end product of purine degradation in the brain. Furthermore, it is suggested that xanthine oxidase exists in the brain and catalyzes the reaction from hypoxanthine to xanthine and then to uric acid. These reactions catalyzed by xanthine oxidase are considered to be a source of free radicals and may play important roles in the pathogenesis of cerebral ischemic injury.
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PMID:Cerebral uric acid, xanthine, and hypoxanthine after ischemia: the effect of allopurinol. 279 98

To verify the lipid peroxidation in the focal cerebral ischemia, the levels of alpha-tocopherol, ubiquinone and ascorbate were measured in the ischemic center in rats. The former two were endogeneous lipid soluble antioxidants and the last was a water soluble antioxidant. alpha-Tocopherol, reduced ubiquinone-9 and -10, and reduced ascorbate decreased to 79%, 73%, 66%, and 76% 0.5 hour after ischemia, respectively. alpha-Tocopherol decreased to 63% 6 hours after ischemia, and then reached a plateau, while reduced ubiquinones and reduced ascorbate declined further to 16% and 10% 12 hours after ischemia, respectively, and then reached plateau levels. These results suggest their functional and durational differences as antioxidants against lipid peroxidation in this ischemic model. Although the reciprocal increase in oxidized ubiquinones during ischemia was not observed, that in oxidized ascorbate was noted. The complementary antioxidant system between cytoplasmic and membranous components, the combination alpha-tocopherol/ascorbate, was estimated from the calculated consumption ratio of these antioxidants, assuming that the loss of these reduced antioxidants is due to neutralization of free radicals. This system was suggested to play an important role in an early ischemic period. Urate also markedly increased during ischemia. Therefore, xanthine oxidase activity was measured in rats both in normal brain and in ischemic brain induced by four-vessel occlusion method. In the control rat, the enzyme activity was 0.87 +/- 0.13 nmol/g wet brain/min at 25 degrees C (mean +/- S.D.): 92.4% was associated with the NAD-dependent dehydrogenase form and only 7.6% with the oxygen-dependent superoxide-producing oxidase form. However, the ratio of the latter form increased to 43.7% after 0.5 hour of global ischemia despite the same level in total xanthine oxidase activity. This result suggests the involvement of the oxygen free radicals generated from the xanthine oxidase pathway in the pathogenesis of the ischemic injury of the rat brain.
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PMID:[Lipid peroxidation and changes in xanthine oxidase in cerebral ischemia]. 280 15

The contribution of toxic O2 metabolites to cerebral ischemia reperfusion injury has not been determined. We found that gerbils subjected to temporary unilateral carotid artery occlusion (ischemia) consistently developed neurologic deficits during ischemia with severities that correlated with increasing degrees of brain edema and brain H2O2 levels after reperfusion. In contrast, gerbils treated just before reperfusion (after ischemia) with dimethylthiourea (DMTU), but not urea, had decreased brain edema and brain H2O2 levels. In addition, gerbils fed a tungsten-rich diet for 4, 5, or 6 wk developed progressive decreases in brain xanthine oxidase (XO) and brain XO + xanthine dehydrogenase (XD) activities, brain edema, and brain H2O2 levels after temporary unilateral carotid artery occlusion and reperfusion. In contrast to tungsten-treated gerbils, allopurinol-treated gerbils did not have statistically significant decreases in brain XO or XO + XD levels, and reduced brain edema and brain H2O2 levels occurred only in gerbils developing mild but not severe neurologic deficits during ischemia. Finally, gerbils treated with DMTU or tungsten all survived, while greater than 60% of gerbils treated with urea, allopurinol, or saline died by 48 h after temporary unilateral carotid artery occlusion and reperfusion. Our findings indicate that H2O2 from XO contributes to reperfusion-induced edema in brains subjected to temporary ischemia.
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PMID:Xanthine oxidase-derived hydrogen peroxide contributes to ischemia reperfusion-induced edema in gerbil brains. 313 Mar 95


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