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 effects of cellular mediators that contribute to ischemia-induced neuronal degeneration on gamma-aminobutyric acid (GABAA)-receptor function were studied. In vitro, phospholipase A2 (PLA2) inhibited muscimol-induced 36Cl- uptake in cerebral cortical synaptoneurosomes. The major hydrolysis product of PLA2 activity, arachidonic acid, also inhibited GABA-mediated 36Cl- uptake. The unsaturated nature of arachidonic acid makes it (and its metabolites) highly susceptible to peroxidation by oxygen radicals. Incubation of synaptoneurosomes with the superoxide radical-generating system, xanthine and xanthine oxidase, decreased muscimol-induced 36Cl- uptake, suggesting that the peroxidation of arachidonic acid and/or its metabolites interferes with GABAA-receptor function. Another factor involved in ischemia-induced neuronal degeneration is an increase in intracellular Ca2+. Calcium also inhibited GABA-mediated 36Cl- flux, consistent with its ability to activate PLA2. In contrast, Mg2+, which blocks Ca2+ channels, enhanced muscimol-induced 36Cl- uptake, consistent with its neuroprotective effects. Each of these cellular processes is activated during cerebral ischemia and can lead to neuronal degeneration. We used a model of transient forebrain ischemia in gerbils to determine if GABAA-receptor regulation is altered in vivo at a time when CA1 hippocampal cells have degenerated. Four days after a 5 minute bilateral carotid artery occlusion, receptor autoradiography was performed to measure the binding of [35S]t-butylbicyclophosphorothionate (TBPS) to the GABA-gated chloride channel. Significant decreases in TBPS binding were observed only in the dendritic layers (stratum oriens and lacunosem moleculare) of the CA1 hippocampus. The results suggest that ischemia-induced cellular processes that contribute to cell death can decrease GABA-gated chloride channels on dendrites of CA1 pyramidal cells, and that GABAA receptors may also reside on neurons afferent to or intrinsic to the dendritic layers of CA1 hippocampus.
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PMID:Cellular regulation of the benzodiazepine/GABA receptor: arachidonic acid, calcium, and cerebral ischemia. 131 67

The effects of arachidonic acid and its metabolites on gamma-aminobutyric acid (GABAA) receptor function were determined in rat cerebral cortical synaptoneurosomes. Incubation of synaptoneurosomes with phospholipase A2 decreased muscimol-induced 36Cl- uptake. Arachidonic acid, the major unsaturated fatty acid released by phospholipase A2, also inhibited muscimol-induced 36Cl uptake. Similar inhibition was obtained with other unsaturated fatty acids (docosahexaenoic, oleic) but not with saturated fatty acids (stearic, palmitic). The effect of arachidonic acid on muscimol responses was inhibited by bovine serum albumin (BSA), and BSA enhanced muscimol responses directly, indicating the generation of endogenous arachidonic acid in the synaptoneurosome preparation. The generation of endogenous arachidonic acid was also indicated by the ability of 2 inhibitors of arachidonic acid metabolism, indomethacin and nordihydroguaiaretic acid (NDGA), to inhibit muscimol-induced 36Cl uptake. We conclude that arachidonic acid probably has both direct and indirect actions on muscimol responses since both enzyme inhibitors inhibited muscimol responses but did not prevent the effect of exogenously added arachidonic acid. In additional experiments, arachidonic acid metabolites generated by cyclooxygenase, prostaglandins D2, E2 and F2 alpha, each decreased muscimol responses; prostaglandins F2 alpha was the most potent inhibitor. Since the unsaturated fatty acids and their metabolites are most susceptible to peroxidation, a generating system of superoxide radicals was tested on muscimol responses. A combination of xanthine and xanthine oxidase inhibited muscimol-induced 36Cl uptake in a concentration-dependent manner. We propose that the inhibition of GABAA neurotransmission by arachidonic acid and its metabolites can lead to increased neuronal excitability. This mechanism may play an important role in the development of neuronal damage following seizures or cerebral ischemia.
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PMID:Inhibition of GABA-gated chloride channel function by arachidonic acid. 132 73

The interactions between lipid peroxidation and calcium in mediating damage to central nervous system membranes have been examined in several in vitro systems. Using isolated rat brain synaptosomes, brain mitochondria, or cultured fetal mouse spinal cord neurons, Ca2+ was found to markedly enhance lipid peroxidation-induced disruption of membrane function. Gamma-aminobutyric acid (GABA) uptake by synaptosomes was inhibited 25% by either lipid peroxidation (induced with xanthine and xanthine oxidase) or Ca2+ alone, whereas inhibition was 46% with their combination. Ca2+ enhancement of lipid peroxidation-induced damage to synaptosomes was intensified by the Ca2+ ionophore, A23187, and was partially blocked by the Ca2+ channel blocker, verapamil. Similarly, inhibition of state 3 respiration in isolated rat brain mitochondria was observed with Ca2+ and a free radical generating system (xanthine and xanthine oxidase) under conditions where either insult alone failed to cause detectable damage. Na+,K+-ATPase activity of cultured fetal mouse spinal cord neurons was inhibited 32% when cells were incubated for 30 minutes in the presence of both A23187 and a free radical generating system. However, Na+,K+-ATPase was not affected during a 30 minute incubation with either A23187 or radical generating system alone. In further studies, peroxidation of rat brain synaptosomes by ferrous iron (Fe2+) and H2O2 was coupled with a rapid and large (2-7-fold) uptake of Ca2+ by synaptosomes. Fe2+ also enhanced Ca2+ uptake by spinal cord neurons in culture, an effect that was coincident with peroxidation of neuronal membranes and the release of arachidonic acid from cells. Iron-induced Ca2+ uptake was blocked by high concentrations of either desferrioxamine or methylprednisolone, whereas Ca2+ channel blockers did not affect Ca2+ uptake induced by Fe2+. Finally, peroxidation of membrane lipids by Fe2+ was stimulated by Ca2+. Concentrations of Ca2+ as low as 10(-9) M increased peroxidation reactions within brain synaptosomal membranes. The results of these studies indicate that lipid peroxidation and Ca2+ can synergistically act to damage biologic membranes. The findings suggest that Ca2+ and lipid peroxidation cannot be considered as separate entities in the pathophysiology of CNS trauma. A hypothesis proposing an inseparable interplay between lipid peroxidation and Ca2+ in the pathogenesis of traumatic and ischemic cell injury is presented.
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PMID:Interaction of lipid peroxidation and calcium in the pathogenesis of neuronal injury. 242 24

Preincubation of brain membranes with phospholipase A2 (PLA2) has been shown previously to affect the binding characteristics of various recognition sites associated with the gamma-aminobutyric acid (GABA) receptor complex. In the present study, we have investigated the effects of PLA2 (from Naja naja siamensis venom) on the functional activity of the GABA receptor/chloride ion channel. PLA2 (0.001-0.02 U/mg protein) preincubation decreased pentobarbital-induced 36Cl- efflux and muscimol-induced 36Cl- uptake in rat cerebral cortical synaptoneurosomes. The effect of PLA2 was prevented by EGTA and two nonselective PLA2 inhibitors, mepacrine and bromophenacyl bromide. The removal of free fatty acids by addition of bovine serum albumin both prevented and reversed the effect of PLA2. Products of the catalytic activity of PLA2, such as the unsaturated free fatty acids, arachidonic and oleic acids, mimicked the effect of PLA2. However, the saturated fatty acid, palmitic acid, and lysophosphatidyl choline had no effect on pentobarbital-induced 36Cl- efflux. Because unsaturated free fatty acids are highly susceptible to peroxidation by oxygen radicals, the role of oxygen radicals was investigated. Xanthine plus xanthine oxidase, a superoxide radical generating system, mimicked the effect of PLA2, whereas the superoxide radical scavenger, superoxide dismutase, diminished the effects of PLA2 and arachidonic acid on pentobarbital-induced 36Cl- efflux. Similarly, the effect of PLA2 was also inhibited by methanol (1 mM), a scavenger of the hydroxyl radical, and by catalase. These data indicate that exogenously added PLA2 induces alterations in membrane phospholipids, possibly promoting the generation of oxygen radicals and fatty acid peroxides which can ultimately modulate GABA/barbiturate receptor function in brain.
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PMID:Regulation of gamma-aminobutyric acid/barbiturate receptor-gated chloride ion flux in brain vesicles by phospholipase A2: possible role of oxygen radicals. 244 44

Preincubation of rat brain synaptosomes with xanthine and xanthine oxidase (X/XO) in Ca2+-free Krebs buffer resulted in a 27% inhibition of synaptosomal gamma-aminobutyric acid (GABA) uptake. Addition of 1.5 mM CaCl2 increased the inhibition with X/XO to 46%, and inhibition was essentially complete when the calcium ionophore A23187 also was included. In other studies, preincubation of purified rat brain mitochondria with the combination of X/XO and 4 microM CaCl2 produced a significant (38%) decrease in state 3 respiration with glutamate/malate as substrate that was not seen with either X/XO or Ca2+ alone. Similar results were obtained using cultured mouse spinal cord neurons in which incubation with X/XO/ADP/FeCl2 and A23187 produced membrane damage as assessed by a 32% reduction of neuronal Na+, K+-ATPase activity. Neither X/XO/ADP/FeCl2 nor A23187 alone caused detectable inhibition. These results demonstrate the synergistic damaging effect of free radicals and Ca2+ on membrane function. In addition, they suggest that free radical-induced peroxidation of membrane lipid, occurring focally during complete or nearly complete ischemia in vivo, could result in intense cellular perturbation when coupled with increased intracellular Ca2+.
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PMID:Calcium enhances in vitro free radical-induced damage to brain synaptosomes, mitochondria, and cultured spinal cord neurons. 299 23

Endogenous polyamines with anti-inflammatory activity scavenge superoxide and possibly other oxy-radicals produced by xanthine oxidase or from stimulated polymorphonuclear leucocytes. Polyamines incubated with stimulated cells are in part metabolised. Putrescine is converted to metabolites tentatively identified as gamma-aminobutyraldehyde, delta'-pyrolline and gamma-aminobutyric acid. The metabolism of spermidine, spermine and cadaverine was not as extensively studied but metabolites were formed that gave positive reaction to Schiffs reagent on tlc plates. The possible relevance of the results to the anti-inflammatory action of polyamines is discussed.
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PMID:In vitro interactions between endogenous polyamines and superoxide anion. 302 Sep 41

Incubation of rat brain synaptosomes with xanthine and xanthine oxidase (X/XO) resulted in an inhibition of gamma-aminobutyric acid (GABA) uptake. The inhibitory effects of X/XO were temperature- and time-dependent, and were characterized by an increased Km for GABA and a decreased Vmax. Inhibition of GABA uptake by X/XO was associated with both the formation of malonyldialdehyde (MDA) and conjugated dienes, indicating that lipid peroxidation was involved. Studies with catalase, superoxide dismutase (SOD), mannitol, and chelated iron suggested that hydroxyl radical (OH X) was probably responsible for the initiation of lipid peroxidation. Both the peroxidation of synaptosomal membranes and the inhibition of GABA uptake by X/XO were enhanced by the addition of ADP and FeCl2. The X/XO-induced inhibition of GABA uptake by synaptosomes could be prevented by preincubation of synaptosomes with certain glucocorticoids prior to X/XO exposure. Methylprednisolone sodium succinate (MPSS), dexamethasone sodium phosphate (DMSP), and prednisolone sodium succinate (PSS) all prevented the inhibition of GABA uptake by X/XO. MPSS was most effective at concentrations around 100 microM, DMSP was slightly more potent, and PSS was optimal at around 300 microM. On the other hand, hydrocortisone sodium succinate (HCSS) was ineffective at preventing X/XO-induced inhibition of GABA uptake at concentrations up to 3 mM. The steroids are presumed to work through a mechanism that blocked the formation of lipid peroxides, as MPSS inhibited the formation of conjugated dienes in synaptosomes exposed to X/XO at a concentration that also protected GABA uptake.
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PMID:Lipid peroxidation-induced inhibition of gamma-aminobutyric acid uptake in rat brain synaptosomes: protection by glucocorticoids. 388 88

Incubation with the oxygen radical-generating enzyme, xanthine oxidase, dramatically reduced striatal dopamine transporter activity, but was unexpectedly without effect on rat hippocampal norepinephrine uptake. To determine whether environmental differences between the striatum and hippocampus contributed to this lack of oxidative effect on norepinephrine transporters, synaptosomal gamma-aminobutyric acid (GABA) uptake was assessed in both regions. Xanthine oxidase similarly decreased [3H]GABA uptake in both the striatum and hippocampus, supporting the conclusion that environmental differences did not account for the lack of effect on norepinephrine transport. These data suggest that norepinephrine transporters are less vulnerable than other Na+/Cl(-)-dependent transporters to oxidative inactivation.
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PMID:Oxygen radicals differentially affect Na+/Cl(-)-dependent transporters. 1049 78

The accumulation of reactive oxygen species during cellular injury leads to oxidative stress. This can have profound effects on ionic homeostasis and neuronal transmission. Gamma-aminobutyric acid (GABA) neurotransmission is sensitive to reactive oxygen species, but most studies have indicated that this is due to alterations in GABA release. Here, we determined whether reactive oxygen species can alter GABA(A) receptor-gated Cl- channels in the adult hippocampus. First, we measured the effects of hydrogen peroxide on intracellular Cl- using UV laser scanning confocal microscopy and the Cl(-)-sensitive probe, 6-methoxy-N-ethylquinolium iodide (MEQ). Superfusion of adult rat hippocampal slices with hydrogen peroxide for 10 min decreased MEQ fluorescence (elevation in [Cl-]i) significantly in area CA1 pyramidal cell soma. Alterations in [Cl-]i were prevented by the vitamin E analog Trolox, an antioxidant that scavenges free radicals. After exposure of slices to hydrogen peroxide, the ability of the GABA agonist muscimol to increase [Cl-]i was attenuated. To determine if GABA(A) receptors were sensitive to oxidative insults, the effect of hydrogen peroxide on the binding of [35S]t-butylbicyclophosphorothionate (TBPS) to GABA-gated Cl- channels was measured using receptor autoradiography and homogenate binding assays. Hydrogen peroxide inhibited [35S]TBPS binding in a regionally selective manner, with the greatest inhibition in cerebral cortex, hippocampus and striatum, areas vulnerable to oxidative stress. Similarly, xanthine and xanthine oxidase, which generate superoxide radicals, reduced [35S]TBPS binding in these regions. The effect of hydrogen peroxide on [35S]TBPS binding was non-competitive and was prevented by Trolox and the iron chelator, deferoxamine. We conclude that reactive oxygen species may compromise GABA(A)-mediated neuronal inhibition via interaction with pre and postsynaptic sites. A reduction in GABA(A)-gated Cl- channel function during periods of oxidative stress may contribute to the development of neuronal damage.
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PMID:Modulation of the GABA(A)-gated chloride channel by reactive oxygen species. 1190 87