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)

Active oxygen species cause gastric mucosal damage in vivo. However, it is not known if these species are directly cytotoxic toward gastric cells. Prostaglandins have important physiological roles in the gastric mucosa, including direct cell protection against damaging factors. So, to find if active oxygen species affect prostaglandin synthesis in gastric mucosal cells is important, but this also is not known. This study was done to investigate the effects of such species on damage to and prostaglandin synthesis in cultured mucus-producing cells from rat gastric mucosa. Active oxygen species were produced by the addition of xanthine and xanthine oxidase to the culture medium. Cytotoxicity was assayed by 51Cr release. Xanthine (1 mM) and xanthine oxidase (100 mU/ml) increased specific 51Cr release as the thiobarbituric acid reactants increased. This increase in 51Cr release was inhibited by catalase, a scavenger of hydrogen peroxide, or dimethyl sulfoxide, a scavenger of hydroxyl radicals, but not by superoxide dismutase, a scavenger of superoxide, nor deferoxamine, an inhibitor of hydroxyl radical generation. Catalase, dimethyl sulfoxide, and superoxide dismutase each had no effect on prostaglandin E2 synthesis when xanthine and xanthine oxidase were not added. In the presence of xanthine and xanthine oxidase, catalase and dimethyl sulfoxide stimulated the synthesis of prostaglandin E2 and superoxide dismutase inhibited it. Indomethacin, a prostaglandin synthetase inhibitor, did not affect the decrease in 51Cr release caused by catalase in the presence of xanthine and xanthine oxidase, but it abolished the decrease caused by dimethyl sulfoxide. These results suggest that hydrogen peroxide, but not superoxide nor hydroxyl radicals, is involved in damage to cultured rat gastric cells, and that superoxide stimulates prostaglandin E2 synthesis, but that hydrogen peroxide inhibits it. Protection of the cells by dimethyl sulfoxide may be related to stimulation of prostaglandin E2 synthesis in the cells, but not via scavenging hydroxyl radicals.
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PMID:Effects of active oxygen species on damage to and prostaglandin synthesis in cultured rat gastric cells. 132 36

Unstimulated polymorphonuclear leukocytes (PMNLs) release nitric oxide or a like material that relaxes vascular tissues. To determine the effects of activated PMNLs on vascular tone, precontracted rat aortic rings were exposed to ionophore A23187-treated PMNLs. Whereas "unstimulated" PMNLs caused 29 +/- 4% relaxation, "stimulated" PMNLs caused initial contraction followed by 90 +/- 7% relaxation of aortic rings. Indomethacin or the 5-lipoxygenase blocker piriprost had no effect on PMNL-induced initial contraction or subsequent relaxation. However, initial contraction was abolished and the subsequent vasorelaxation attenuated (22 +/- 5%) by the superoxide radical scavenger superoxide dismutase (SOD), suggesting that release of superoxide radicals may have induced vascular contraction and caused endothelial damage that would permit unopposed vasorelaxant effect of PMNLs. To examine this hypothesis, aortic rings were exposed to superoxide radicals (generated by xanthine plus xanthine oxidase, X + XO) or manually deendothelialized. These rings revealed marked relaxation (78 +/- 6 and 85 +/- 6%, respectively) in response to unstimulated PMNLs. These observations suggest that stimulated PMNLs exert an initial vasoconstrictor effect and a subsequent vasorelaxant effect in response to release of superoxide radicals and nitric oxide, respectively. Arachidonate metabolites or 5-lipoxygenase products do not appear to be important in the actions of PMNLs on vascular smooth muscle.
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PMID:Effects of activated polymorphonuclear leukocytes on vascular smooth muscle tone. 165 10

Toxic oxygen metabolites (TOM) released from stimulated phagocytes and lung tissue have been shown to injure the pulmonary microcirculation. In the present study we evaluated microvascular injury caused by TOM in rat lungs perfused with plasma. The injury, as indicated by an increase in vascular permeability, was assessed by determining the fluid filtration rate (FFR) after paralysing the pulmonary vascular bed with papaverine (0.1 mg/ml). TOM were generated by adding xanthine oxidase (XO) (0.05-0.125 U/ml) and hypoxanthine (HX) (1 mmol/l) to the perfusate. FFR was measured before, 30 and 60 min after addition of XO and HX. The following interventions were done: 1. the H2O2-scavenger catalase, 2. substitution of the perfusate after 30 min, 3. BW 755 C, a combined lipoxygenase and cyclooxygenase inhibitor, and 4. indomethacin, a cyclooxygenase inhibitor. Addition of XO and HX caused FFR to increase from 14 +/- 4 mg/min (mean +/- s.e. mean) at the onset to 56 +/- 7 mg/min and 86 +/- 10 mg/min after 30 and 60 min, respectively. Replacing the perfusate with fresh plasma after 30 min caused a significant reduction in FFR at 60 min, from 86 +/- 11 mg/min to 58 +/- 10 mg/min. Catalase prevented the increase in FFR. Indomethacin and BW 755 C had no effect on the increase in FFR. We conclude that TOM induced a partly reversible increase in microvascular permeability of isolated rat lungs. From previous studies, the activity of XO was expected to cease after 30 min. Therefore it is suggested that secondary products of TOM propagate the lung injury. The increase in permeability was not mediated by arachidonic acid metabolites.
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PMID:Increased microvascular permeability caused by toxic oxygen metabolites is partly reversed by exchanging the perfusate in isolated rat lungs. 251 Apr 45

To determine if oxygen-derived free radicals are mediators of endothelium-dependent contractions to acetylcholine in the aorta of spontaneously hypertensive rats (SHR), the mechanism of contraction to xanthine plus xanthine oxidase was studied. Rings, with and without endothelium, of thoracic aorta from normotensive Wistar-Kyoto (WKY) rats and SHR were suspended in organ chambers for isometric tension recording. Oxygen-derived free radicals caused concentration-dependent contractions; these contractions were twice as large in the aortas of SHR than in WKY rats. Deferoxamine reversed the response to xanthine oxidase to a small relaxation. Either allopurinol, superoxide dismutase, or catalase, or the combination of superoxide dismutase plus catalase reduced the contractions. Diltiazem inhibited the response to xanthine oxidase; in contrast, phentolamine plus propranolol did not affect it. Indomethacin and meclofenamate, but not tranylcypromine or dazoxiben blocked the contractions. Endothelium-dependent contractions to acetylcholine in aortas from the SHR were not affected by deferoxamine or superoxide dismutase plus catalase. These data suggest that hydroxyl radicals cause contractions in the rat aorta, which are dependent on extracellular calcium and mediated by activation of the cyclooxygenase in the vascular smooth muscle. The augmented contractions in the hypertensive strain are due to an increased reactivity of the smooth muscle to oxygen-derived free radicals. However, the lack of effect of the scavengers on endothelium-dependent contractions to acetylcholine suggests that the endothelium-derived contracting factor is chemically different from oxygen-derived free radicals.
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PMID:Contractions to oxygen-derived free radicals are augmented in aorta of the spontaneously hypertensive rat. 256 6

Oxygen radicals have vasoactive properties. The hypoxanthine-xanthine oxidase system generates oxygen radicals. This system relaxes isolated constricted ductus rings from fetal lambs and constricts the pulmonary circulation of adult pigs. Since catalase, and not superoxide dismutase, inhibits the effect of the hypoxanthine-xanthine oxidase system, we believe the effect is caused by the hydroxyl radical. The hydroxyl radical stimulates prostaglandin synthesis in the vessel wall and high concentrations of prostanoids can be measured after hypoxanthine-xanthine oxidase exposure. Indomethacin inhibits the vasoactive effects of the hypoxanthine-xanthine oxidase system. We believe the hypoxanthine-xanthine oxidase system plays an important role in regulating the normal circulation.
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PMID:Circulatory effects of oxygen radicals. 273 Jun 8

In vitro, arachidonic acid depressed calcium transport by sarcoplasmic reticulum (SR) in the homogenate of canine masseter muscle. This effect was inhibited by superoxide dismutase (SOD), a scavenger of the superoxide anion radial ( . O-2), at pH 7.0, and by SOD plus d-mannitol, a scavenger of hydroxyl free radical ( . OH), at pH 5.5. Indomethacin and 2-aminomethyl-4-tert-butyl-6-propionyl phenol (ONO-3144), a compound known to accelerate the conversion of prostaglandin G2 (PGG2) to PGH2 and scavenge free radicals, inhibited the effect of arachidonic acid at both pH 7.0 and pH 5.5. PGG2, but not PGH2, duplicated the effect of arachidonic acid. The effect of PGG2 on SR function was similar to that of exogenous free radicals generated from the xanthine-xanthine oxidase system. Incubation at pH 5.5, in the absence of an exogenous free-radical generating system, depressed SR calcium transport in the homogenate and in isolated SR. This effect in the homogenate was inhibited by indomethacin or by ONO-3144. At 10-min incubation at pH 5.5, SOD partially and temporarily reversed the depressant effect of acidosis. The addition of SOD plus d-mannitol completely reversed the system. d-Mannitol alone was ineffective. Arachidonic acid was able to mimic these effects of acidosis, except that arachidonic acid further depressed isolated SR calcium transport. These results demonstrate that acidosis can depress SR calcium transport in the homogenate of masseter muscle by an oxygen-free radical mechanism by the generation of . O-2 and . OH. Our results also demonstrate that significant oxygen radical generation can occur through the cyclooxygenase pathway of arachidonic acid metabolism at an acidotic pH in the cellular environment outside of the SR of the muscle cell, and seems to be responsible for the generation of the . OH derived from . O-2.
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PMID:Inhibition by free radical scavengers and by cyclooxygenase inhibitors of the effect of acidosis on calcium transport by masseter muscle sarcoplasmic reticulum. 298 87

Our previous studies had suggested a link between bile salt stimulation of colonic epithelial proliferation and the release and oxygenation of arachidonate via the lipoxygenase pathway. In the present study, we examined the role of reactive oxygen versus end products of arachidonate metabolism via the cyclooxygenase and lipoxygenase pathways in bile salt stimulation of rat colonic epithelial proliferation. Intracolonic instillation of 5 mM deoxycholate increased mucosal ornithine decarboxylase activity and [3H]thymidine incorporation into DNA. Responses to deoxycholate were abolished by the superoxide dismutase mimetic CuII (3,5 diisopropylsalicylic acid)2 (CuDIPS), and by phenidone or esculetin, which inhibit both lipoxygenase and cyclooxygenase activities. By contrast, indomethacin potentiated the response. Phenidone and esculetin suppressed deoxycholate-induced increases in prostaglandin E2 (PGE2), leukotriene B4 (LTB4), and 5, 12, and 15-hydroxyeicosatetraenoic acid (HETE), whereas CuDIPS had no effect. Indomethacin suppressed only PGE2. Deoxycholate (0.5-5 mM) increased superoxide dismutase sensitive chemiluminescence 2-10-fold and stimulated superoxide production as measured by cytochrome c reduction in colonic mucosal scrapings or crypt epithelium. Bile salt-induced increases in chemiluminescence were abolished by CuDIPS, phenidone, and esculetin, but not by indomethacin. Intracolonic generation of reactive oxygen by xanthine-xanthine oxidase increased colonic mucosal ornithine decarboxylase activity and [3H]thymidine incorporation into DNA approximately twofold. These effects were abolished by superoxide dismutase. The findings support a key role for reactive oxygen, rather than more distal products of either the lipoxygenase or cyclooxygenase pathways, in the stimulation of colonic mucosal proliferation by bile salts.
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PMID:Role of reactive oxygen in bile salt stimulation of colonic epithelial proliferation. 300 68

1. Myocardial ischaemia and reperfusion can evoke excitation of cardiac vagal afferent nerve endings and activation of a cardiogenic depressor reflex (Bezold-Jarisch effect). We postulate that oxygen free radicals, which are well known to be produced during ischaemia and reperfusion, contribute to this excitation. 2. Activity from vagal afferent fibres in rats, whose endings were located in the walls of all four chambers of the heart, was recorded in response to topical application of pro-oxidant chemicals to the surface of the heart. Activity was also recorded from vagal afferent fibres, whose endings were located in the left ventricle, in response to occlusion of the left anterior coronary artery (LAC) for 30 min and subsequent reperfusion. A majority of the recorded fibres were classified as chemosensitive C-fibre endings due to their irregular discharge under resting conditions, their activation in response to the topical application of capsaicin (1-10 micrograms) to the surface of the heart encompassing the receptive field and their conduction velocities. 3. Topical application of either H2O2 or xanthine/xanthine oxidase to the heart activated 50% of the chemosensitive endings and did not directly affect cardiac mechanoreceptors. This effect was reproducible, dose-dependent and was not due to [H+]. 4. Administration of the superoxide radical scavenging enzyme, superoxide dismutase (20000 U/kg, i.v.), decreased the response of fibres to xanthine/xanthine oxidase but had no effect on the activation caused by H2O2. The antioxidants deferoxamine (20 mg/kg, i.v.) or dimethylthiourea (10 mg/kg, i.v.), which scavenge the hydroxyl radical, abolished the responses to xanthine/xanthine oxidase and H2O2. Administration of indomethacin (5 mg/kg, i.v.) had no effect on the afferent response to H2O2. 5. In response to ligation of the left anterior coronary (LAC), the activity of chemosensitive endings within the ischaemic zone increased within the first 2 min of occlusion. Endings outside the ischaemic zone were not affected at the beginning of ischaemia. Reperfusion activated only chemosensitive endings responsive to topical H2O2. These reperfusion-sensitive endings were located both within and outside the ischaemic zone of the left ventricle. 6. Indomethacin (5 mg/kg, i.v.) prevented activation of chemosensitive endings at the beginning of LAC occlusion regardless of their sensitivity to H2O2 but had no effect on the response to reperfusion. Conversely, deferoxamine (20 mg/kg, i.v.) had no effect on the activation of chemosensitive fibres at the onset of ischaemia, whereas it completely prevented activation at reperfusion. 7. We propose that there are two different mechanisms that activate chemosensitive afferent vagal fibres in the rat heart during ischaemia and reperfusion. The first causes excitation of these endings at the onset of ischaemia and is mediated by prostaglandin synthesis within the ischaemic zone. The second mechanism leads to a more widespread activation of chemosensitive afferents in the left ventricle during prolonged ischaemia and at the moment of reperfusion and is mediated by oxygen free radical formation.
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PMID:Cardiac vagal afferent stimulation by free radicals during ischaemia and reperfusion. 888 94

The effects on rat aorta of EUK-8, a salen-manganese complex with high superoxide dismutase and catalase activities, were investigated. EUK-8 protected the acetylcholine-induced relaxation of rat aortic rings from inhibition by superoxide anions and reduced H2O2-induced relaxation. Moreover, EUK-8 dose-dependently relaxed rat aorta precontracted with phenylephrine (10(-6) M) and decreased the vascular tone of noncontracted aortic rings. The relaxant effect of EUK-8 was significantly potentiated by endothelium abrasion and/or preincubation with N-nitro-L-arginine methyl ester (10(-5) M and 5 x 10(-4) M), an inhibitor of nitric oxide synthase. Indomethacin (10(-5) M) had no effect on the action of EUK-8, showing that it was not dependent on prostacyclin synthesis. Methylene blue (10(-5) M), an inhibitor of soluble guanylate cyclase, partly abolished relaxation induced by EUK-8. Incubation of rat aorta with EUK-8 (10(-4) M) induced an increase in vascular cyclic AMP content. The lack of inhibition by dl-propranolol showed that adenylate cyclase activation by EUK-8 was not mediated through beta-adrenergic receptors. The inhibition of the effects of EUK-8 by tetraethylammonium (10(-2) M) and glibenclamide (10(-5) and 2 x 10(-5) M) showed the implication of potassium channels in the intracellular cascade triggered by EUK-8. The vasorelaxant activity of EUK-8 was neither affected by xanthine oxidase inhibition (incubation with oxypurinol 25 microM) nor by superoxide anion scavenging (incubation with oxypurinol 125 microM). Finally, the ligand for EUK-8 (EUK-8 without manganese), which has the same aromatic structure as EUK-8 without its antioxidant activities because of the absence of manganese, conversely potentiated phenylephrine-induced contraction of aortic rings. We conclude that the vasorelaxant effect of EUK-8 observed under our experimental conditions is essentially mediated through an activation of adenylate cyclase and soluble guanylate cyclase of smooth muscle cells and is different from a classical antioxidant effect of protection of nitric oxide.
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PMID:Vasodilatory effects of a salen-manganese complex with potent oxyradical scavenger activities. 907 25

The aim of the study was to investigate the time course of neutrophil activation after skeletal muscle ischemia in humans and to assess the effect of xanthine oxidase inhibitor allopurinol or cyclooxygenase inhibitor indomethacin. In patients undergoing tourniquet ischemia of the upper limb, polymorphonuclear neutrophils (PMN) were simultaneously isolated from antecubital vein blood of both the contralateral control arm and the tourniquet arm. PMN-superoxide production (PMN-SOP) was determined by a cytochrome C reduction assay, PMN-myeloperoxidase activity (PMN-MPO) by guaiacol oxidation and serum PMN-elastase concentration by an enzyme immunoassay. At 60 min after release of the tourniquet, significant increases of PMN-SOP, PMN-MPO, and serum elastase concentrations were observed in tourniquet arms as compared with control arms (p < .05). Allopurinol (300 mg orally, 12 and 2 h before ischemia) significantly inhibited the increase of PMN-SOP, PMN-MPO, and serum elastase (p < .05). Indomethacin (50 mg orally, 2 h before ischemia) prevented increased PMN-MPO and serum elastase, but prevented increased PMN-SOP only when neutrophils were incubated in the presence of their autologous plasma. These findings suggest that ischemia/reperfusion of human skeletal muscle involves both xanthine oxidase-dependent oxygen free radicals and cyclooxygenase metabolites. These pathways could activate circulating neutrophils which potentially inflict local and remote endothelial injury.
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PMID:Neutrophil activation after skeletal muscle ischemia in humans. 946 69


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