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 morphological, biochemical and functional characterization of the vascular endothelium has become possible through the broad use of electron microscopic methods, the successful elaboration and application of techniques for the isolation and cultivation of endothelial cells in vitro and through sophisticated studies on vessel and organ preparations, both in vitro and in vivo. In this survey emphasis is placed on certain methodological aspects of endothelial cell culture as well as on biochemical, physiological and pathophysiological features of the vascular endothelium. Endothelial cells can be propagated in culture dishes, the most commonly applied method, on suspended microbeads (dextrane, polyacrylamide), a technique giving large yields, or on thin porous membranes, a procedure suited for the study of transport processes across the endothelial layer. Different structural, biochemical and functional properties of the luminal (apical) and abluminal (basal) cell membrane determine important polarity features of the endothelium. Endothelial cells exhibit a variety of biochemical pathways and are characterized by high metabolic activities. Of particular interest is the large content of ATP in endothelial cells of different vascular origin. The rapid intracellular degradation of adenine nucleotides to nucleosides and bases, which are constantly released, is balanced by synthesis, mainly via salvage pathways. In endothelial cells of microvascular origin uric acid predominates by far as the final purine degradative because of the presence of xanthine dehydrogenase in these cells; in the macrovascular endothelium purine breakdown proceeds only to hypoxanthine, since xanthine dehydrogenase is lacking. In this connection interrelations between nucleotide catabolism in myocardial tissue and in coronary endothelial cells are discussed, also with respect to the participation of endothelial xanthine oxidase in the formation of oxygen radicals during post-ischemic reperfusion of the heart. Vascular endothelial cells of different origin are also capable of a rapid extracellular degradation of ATP, ADP and AMP to adenosine by means of specific ecto-nucleotidases. The subsequent fate of extracellularly formed adenosine appears to be different for endothelial cells of microvascular (preferential adenosine uptake) and macrovascular origin (preferential extracellular adenosine accumulation), thus implying functional consequences for platelet aggregation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:The vascular endothelium: a survey of some newly evolving biochemical and physiological features. 393 1

The metabolic causes for immune impairment in patients with severe chronic inflammatory diseases have not been clearly defined. Recently, the overproduction of poly(ADP-ribose) in resting lymphocytes with unrepaired DNA strand breaks has been suggested to contribute to immune dysfunction in adenosine deaminase-deficient patients. Our experiments have determined to what extent DNA damage and poly(ADP-ribose) synthesis might also explain the impaired mitogen responsiveness of PBL exposed to toxic oxygen species. Treatment of normal resting human lymphocytes with xanthine oxidase and hypoxanthine dose-dependently induced DNA strand breaks and triggered the rapid synthesis of poly(ADP-ribose). Subsequently, NAD+ and ATP pools decreased precipitously. Lymphocytes exposed previously to the enzymatic oxidizing system did not synthesize DNA after stimulation with PHA. However, if the medium was supplemented with 3-aminobenzamide or nicotinamide, two compounds that inhibit poly(ADP-ribose) formation, cellular NAD+ and ATP pools were preserved, and the lymphocytes responded vigorously to a mitogenic challenge. Excessive poly(ADP-ribose) synthesis, provoked by DNA strand breakage, may represent a common pathway that connects the immunodeficiency syndromes associated with (a) exposure of lymphocytes to toxic oxygen species during chronic inflammatory states, (b) adenosine deaminase deficiency, and (c) certain DNA repair disorders.
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PMID:Lymphocyte dysfunction after DNA damage by toxic oxygen species. A model of immunodeficiency. 395 May 45

Regional intestinal ischemia in cats resulted in an accumulation of hypoxanthine within 2 h, the concentration of which rose from 0.062 to 1.131 nmol/mg protein. A similar rise in AMP content (from 0.5 to 3.2 nmol/mg protein) was observed, but not in the ADP level. In parallel, ATP content decreased from 7.5 to 2.8 nmol/mg protein. Reperfusion of the ischemic tissue was followed by rapid metabolism of the purine metabolites; after 1 h of reperfusion the tissue level of hypoxanthine was 0.186 nmol/mg protein, of AMP 0.7 nmol/mg protein, and of ATP 4.3 nmol/mg protein. The oxidation of hypoxanthine, mediated by xanthine oxidase, is accompanied by the release of superoxide ions. Consequently, the concentration of oxidized glutathione was doubled upon reperfusion, while marked lipid peroxidation took place, as evidenced by the rise in conjugated diene content from 2.8 mumol/g tissue before reperfusion to 5.6 mumol/g tissue after 10 min of reoxygenation. In line with these findings is the fact that histologically observable damage occurred mainly in the presence of oxygen. These data indicate that, at least in our model, rapid reoxygenation is a major cause of "ischemic" tissue damage.
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PMID:Oxidative tissue damage following regional intestinal ischemia and reperfusion in the cat. 609 11

The hepatic metabolism of hypoxanthine was investigated by studying both the fate of labelled hypoxanthine, added at micromolar concentrations to isolated rat hepatocyte suspensions, and the kinetic properties of purified hypoxanthine/guanine phosphoribosyltransferase from rat liver. More than 80% of hypoxanthine was oxidized towards allantoin; less than 5% of the label was incorporated into the purine mononucleotides, and a similar proportion appeared transiently in inosine. The maximal velocity of oxidation (approx. 750nmol/min per g of cells) was in close agreement with the known activity of xanthine oxidase in liver extracts. In contrast, the maximal velocity of the incorporation of labelled hypoxanthine into mononucleotides reached only 30nmol/min per g of cells, compared with an activity of hypoxanthine/guanine phosphoribosyltransferase, measured at substrate concentrations analogous to those prevailing intracellularly, of 500nmol/min per g of cells. Hypoxanthine incorporation into the mononucleotides was decreased by allopurinol, anoxia and ethanol, despite inhibition of its oxidation under these conditions; it was increased by incubation of the cells in supraphysiological concentrations of Pi. Allopurinol and anoxia decreased the concentration of phosphoribosyl pyrophosphate inside the cells by respectively 40 and 60%, ethanol had no effect on the concentration of this metabolite and Pi increased its concentration up to 10-fold. The kinetic study of purified hypoxanthine/guanine phosphoribosyltransferase showed that a mixture of ATP, IMP, GMP and GTP, at the concentrations prevailing in the liver cell, decreased the V max. of the enzyme 6-fold, increased its Km for hypoxanthine from 1 to 4 microM and its Km for phosphoribosyl pyrophosphate from 2.5 to 25 microM. In the presence of 5 microM-hypoxanthine and 2.5 microM-phosphoribosyl pyrophosphate, the mixture of nucleotides inhibited the activity of purified hypoxanthine/guanine phosphoribosyltransferase by 95%. It is concluded that this inhibition results in a limited participation of hypoxanthine/guanine phosphoribosyltransferase in the control of the production of allantoin by the liver.
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PMID:Metabolism of hypoxanthine in isolated rat hepatocytes. 620 48

Superoxide (.O-2) is demonstrated to participate at the prostaglandin phase swelling (2-4 h) of carrageenan paw edema. Superoxide production is inhibited in vitro by typical anti-inflammatory drugs, but these drugs did not scavenge superoxide which was produced by xanthine oxidase. Phosphate, pyrophosphate, ATP, ADP and sulfate were essential for superoxide production by macrophages. These anions can induce paw swelling and are reported to increase in rheumatic patients. A mixture of macrophages and lymphocytes from BCG sensitized guinea-pigs was cultured for 2 days with SOD or D-mannitol. Nitroblue tetrazolium reduction (formazan formation) was inhibited by these agents, suggesting that the hydroxyl radical (.OH) is necessary for metabolic activation of macrophage. Lympholine-like factor of which production or release is enhanced by hydroxyl radical, activates macrophage. Production of oxygen radicals may increase rapidly by this chain cycle reaction. Possible relations of oxygen radicals to prostaglandin(s) biosyntheses, chemotaxis, lysosomal enzyme release protease participation, were discussed. Endogenous SOD, epinephrine, ceruloplasmin, blood plasma proteins, inflammatory fluid, may modulate the amount of superoxide by their superoxide scavenging capacities.
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PMID:Inflammation and superoxide production by macrophages. 626 69

The superoxide radical plays major roles in the neutrophil-medicated acute inflammatory response and in postischemic tissue injury, although the sources and actions of the radical are quite different in these two pathological states. While neutrophils produce superoxide for the primary purpose of aiding in the killing of ingested microbes, a second useful function has evolved. The superoxide released from actively phagocytosing neutrophils serves to attract more neutrophils by reacting with, and activating, a latent chemotactic factor present in plasma. Superoxide dismutase, by preventing the activation of this superoxide-dependent chemotactic factor, exerts potent anti-inflammatory action. During ischemia, energy-starved tissues catabolize ATP to hypoxanthine. Calcium transients in these cells appear to activate a calmodulin regulated protease which attacks the enzyme xanthine dehydrogenase, converting it to a xanthine oxidase capable of superoxide generation. When the tissue is reperfused and reoxygenated, all the necessary components are present (xanthine oxidase, hypoxanthine, and oxygen) to produce a burst of superoxide which results in extensive tissue damage. Ischemic tissues are protected by superoxide dismutase or allupurinol, an inhibitor of xanthine oxidase.
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PMID:The pathophysiology of superoxide: roles in inflammation and ischemia. 629 73

Acute myocardial ischemia results in a decrease in developed tension and an increase in resting tension. A breakdown of the excitation-contraction coupling system can explain the behavior of the ischemic muscle at a subcellular level. We have identified a specific defect in the sarcoplasmic reticulum (SR) from the ischemic myocardium; i.e., the uncoupling of calcium transport from ATP hydrolysis. The mediators of this excitation-contraction uncoupling process have not been identified. It is now established that the intracellular pH of the ischemic myocardium is in the range of 6.4 but the role of protons and potential role of free radicals have not been identified. We have hypothesized that protons and free radicals may interact to produce the excitation-contraction uncoupling of the ischemic myocardium. Cardiac SR was isolated from the wall of canine left ventricle and calcium uptake velocity and Ca2+ stimulated-Mg2+ dependent ATPase activity determined. Increasing proton concentration between pH 7.0 and 6.4 significantly reduced calcium uptake rates (pH 7.0 = 0.95 +/- 0.02; 6.4 = 0.50 +/- 0.02 mumoles Ca2+/mg-min; p less than 0.01) with no effect on ATPase activity. Calculated coupling ratios (mumoles Ca2+/mumoles Pi) decreased from 0.87 +/- 0.06 at pH 7.0 to 0.51 +/- 0.05 at pH 6.4. At pH 7.0, the generation of exogenous free radicals from the xanthine-xanthine oxidase system significantly depressed both calcium uptake rates (Control = 0.95 +/- 0.02; X+XO = 0.15 +/- 0.02) and ATPase activity (Control = 1.05 +/- 0.02; X+XO + 0.30 +/- 0.01 mumoles Pi/mg-min; p less than 0.01). The decreases in calcium uptake and in ATPase activity were completely reversible with superoxide dismutase (SOD). At pH 6.4 in the presence of xanthine and xanthine oxidase, there is a further depression of calcium uptake rates (Control = 0.50 +/- 0.02; X+XO = 0.11 +/- 0.01; p less than 0.05) but there is no SOD reversible component. The addition of SOD + 20mM mannitol normalized calcium transport at pH 6.4. The calculated coupling ratio at pH 6.4 in the presence of free radicals was 0.13. In contrast sarcoplasmic reticulum isolated from ischemic myocardium demonstrated a significant depression of calcium uptake rates at pH 7.1 which was further accentuated at pH 6.4. Ca2+-ATPase was significantly depressed at pH 7.1 but there was no accentuation at pH 6.4. It is concluded that no single species of free radical can explain the intracellular excitation-contraction uncoupling of the ischemic myocardium. The system can be explained by the interaction of hydrogen ions and superoxide anions producing both injury to the sarcoplasmic reticulum and the formation of lipid free radicals with hydroxyl-like activity.
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PMID:Mediation of sarcoplasmic reticulum disruption in the ischemic myocardium: proposed mechanism by the interaction of hydrogen ions and oxygen free radicals. 630 8

Uninduced rat liver microsomes and NADPH-Cytochrome P-450 reductase, purified from phenobarbital-treated rats, catalyzed an NADPH-dependent oxidation of hydroxyl radical scavenging agents. This oxidation was not stimulated by the addition of ferric ammonium sulfate, ferric citrate, or ferric-adenine nucleotide (AMP, ADP, ATP) chelates. Striking stimulation was observed when ferric-EDTA or ferric-diethylenetriamine pentaacetic acid (DTPA) was added. The iron-EDTA and iron-DTPA chelates, but not unchelated iron, iron-citrate or iron-nucleotide chelates, stimulated the oxidation of NADPH by the reductase in the absence as well as in the presence of phenobarbital-inducible cytochrome P-450. Thus, the iron chelates which promoted NADPH oxidation by the reductase were the only chelates which stimulated oxidation of hydroxyl radical scavengers by reductase and microsomes. The oxidation of aminopyrine, a typical drug substrate, was slightly stimulated by the addition of iron-EDTA or iron-DTPA to the microsomes. Catalase inhibited potently the oxidation of scavengers under all conditions, suggesting that H2O2 was the precursor of the hydroxyl radical in these systems. Very high amounts of superoxide dismutase had little effect on the iron-EDTA-stimulated rate of scavenger oxidation, whereas the iron-DTPA-stimulated rate was inhibited by 30 or 50% in microsomes or reductase, respectively. This suggests that the iron-EDTA and iron-DTPA chelates can be reduced directly by the reductase to the ferrous chelates, which subsequently interact with H2O2 in a Fenton-type reaction. Results with the reductase and microsomal systems should be contrasted with results found when the oxidation of hypoxanthine by xanthine oxidase was utilized to catalyze the production of hydroxyl radicals. In the xanthine oxidase system, ferric-ATP and -DTPA stimulated oxidation of scavengers by six- to eightfold, while ferric-EDTA stimulated 25-fold. Ferric-desferrioxamine consistently was inhibitory. Superoxide dismutase produced 79 to 86% inhibition in the absence or presence of iron, indicating an iron-catalyzed Haber-Weiss-type of reaction was responsible for oxidation of scavengers by the xanthine oxidase system. These results indicate that the ability of iron to promote hydroxyl radical production and the role that superoxide plays as a reductant of iron depends on the nature of the system as well as the chelating agent employed.
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PMID:The role of iron chelates in hydroxyl radical production by rat liver microsomes, NADPH-cytochrome P-450 reductase and xanthine oxidase. 633 21

The responses of pig aortic endothelial cells to sublethal doses of potentially toxic stimuli were investigated by monitoring K+ efflux, prostaglandin production, and the release of cytoplasmic purines. Xanthine plus xanthine oxidase reversibly stimulated these three parameters of endothelial cell function at doses that were not cytotoxic, as measured by chromium release, adenine uptake, and vital dye exclusion. The effects of xanthine plus xanthine oxidase were inhibited by catalase but not by superoxide dismutase, suggesting that H2O2 was responsible. Reagent H2O2 also reversibly stimulated K+ efflux, prostaglandin production, and the release of purines. The threshold concentration of H2O2 for these effects was approximately 10 microM, which was at least 30-fold lower than that which caused cytotoxicity. In addition to the direct effect of H2O2 in stimulating prostaglandin production (PGI2 and PGE2), prior exposure of endothelial cells to lower doses of H2O2 (less than 0.1 microM) at high oxygen tension inhibited the subsequent stimulation of prostaglandin production by ATP, A23187, and H2O2 itself. We conclude that H2O2 has substantial effects on endothelial physiology at doses up to 3,000-fold lower than those which induce cytotoxicity.
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PMID:Differential effects of hydrogen peroxide on indices of endothelial cell function. 636 99

During renal ischemia, ATP is degraded to hypoxanthine. When xanthine oxidase converts hypoxanthine to xanthine in the presence of molecular oxygen, superoxide radical (O-2) is generated. We studied the role of O-2 and its reduction product OH X in mediating renal injury after ischemia. Male Sprague-Dawley rats underwent right nephrectomy followed by 60 min of occlusion of the left renal artery. The O-2 scavenger superoxide dismutase (SOD) was given 8 min before clamping and before release of the renal artery clamp. Control rats received 5% dextrose instead. Plasma creatinine was lower in SOD treated rats: 1.5, 1.0, and 0.8 mg/dl vs. 2.5, 2.5, and 2.1 mg/dl at 24, 48, and 72 h postischemia. 24 h after ischemia inulin clearance was higher in SOD treated rats than in controls (399 vs. 185 microliter/min). Renal blood flow, measured after ischemia plus 15 min of reflow, was also greater in SOD treated than in control rats. Furthermore, tubular injury, judged histologically in perfusion fixed specimens, was less in SOD treated rats. Rats given SOD inactivated by prior incubation with diethyldithiocarbamate had plasma creatinine values no different from those of control rats. The OH X scavenger dimethylthiourea (DMTU) was given before renal artery occlusion. DMTU treated rats had lower plasma creatinine than did controls: 1.7, 1.7, and 1.3 mg/dl vs. 3.2, 2.2, and 2.4 mg/dl at 24, 48, and 72 h postischemia. Neither SOD nor DMTU caused an increase in renal blood flow, urine flow rate, or solute excretion in normal rats. The xanthine oxidase inhibitor allopurinol was given before ischemia to prevent the generation of oxygen free radicals. Plasma creatinine was lower in allopurinol treated rats: 2.7, 2.2, and 1.4 mg/dl vs. 3.6, 3.5, and 2.3 mg/dl at 24, 48, and 72 h postischemia. Catalase treatment did not protect against renal ischemia, perhaps because its large size limits glomerular filtration and access to the tubular lumen. Superoxide-mediated lipid peroxidation was studied after renal ischemia. 60 min of ischemia did not increase the renal content of the lipid peroxide malondialdehyde, whereas ischemia plus 15 min reflow resulted in a large increase in kidney lipid peroxides. Treatment with SOD before renal ischemia prevented the reflow-induced increase in lipid peroxidation in renal cortical mitochondria but not in crude cortical homogenates. In summary, the oxygen free radical scavengers SOD and DMTU, and allopurinol, which inhibits free radical generation, protected renal function after ischemia. Reperfusion after ischemia resulted in lipid peroxidation; SOD decreased lipid peroxidation in cortical mitochondria after renal ischemia and reflow. We concluded that restoration of oxygen supply to ischemic kidney results in the production of oxygen free radicals, which causes renal injury by lipid peroxidation.
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PMID:Oxygen free radicals in ischemic acute renal failure in the rat. 643 91


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