Showing papers on "Xanthine published in 1989"

Superoxide anion is an endothelium-derived contracting factor

Abstract: The calcium ionophore A23187 causes endothelium-dependent contractions in canine basilar arteries. Removal of the endothelium, or treatment with indomethacin or superoxide dismutase (SOD), prevented the endothelium-dependent excitatory effect of the calcium ionophore. Catalase and deferoxamine were without effect. Superoxide anion generated by xanthine plus xanthine oxidase in the presence of catalase caused contractions of the vascular smooth muscle, which were abolished by SOD or heat inactivation of xanthine oxidase. The A23187-induced production of prostaglandins F2 alpha and E2 and thromboxane B2 was abolished by the removal of endothelium and by treatment with indomethacin but was not affected by the presence of SOD plus catalase. These observations are consistent with the hypothesis that superoxide anion, rather than prostaglandins generated by hydroperoxidase activity of cyclooxygenase, is an endothelium-derived contracting factor in canine cerebral arteries.

CGS 21680C, an A2 selective adenosine receptor agonist with preferential hypotensive activity.

Abstract: CGS 21680C (2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethyl-carboxamido adenosine) a 2-substituted analog of the riboside uronamide, 5'-N-ethylcarboxamido adenosine and the related analog CGS 21577 (2-phenethylamino-5'-N-ethylcarboxamido adenosine), have high in vitro affinity for brain striatal adenosine A2 receptors (IC50 values = 22 and 13 nM, respectively). Both compounds were considerably less active at A1 receptors with CGS 21577 and CGS 21680C having respective IC50 values of 0.76 and 3.1 microM. The former compound was thus 59-fold selective for A2 receptors whereas CGS 21680C was 140-fold selective. In contrast, the reference A2 selective ligand, CV 1808 (2-phenylaminoadenosine), showed only 8-fold selectivity as an A2 ligand, having an IC50 of 115 nM in the [3H]-5'N-ethylcarboxamide adenosine assay and an IC50 of 910 nM at the N6-[3H] cyclohexyladenosine site. Further examination of CGS 21680C showed that the compound was without effect on binding to 17 other putative neurotransmitter/neuromodulator sites indicating its selectivity as an adenosine receptor ligand. In an isolated perfused working rat heart model, CGS 21680C effectively increased coronary flow with an ED25 value of 1.8 nM. The corresponding value for CGS 21577 was 3 nM whereas that for CV 1808 was 110 nM. The EC25 for eliciting bradycardia for all three compounds was greater than 1000 nM. The effects of all three compounds could be reversed by treatment with the xanthine adenosine antagonist, xanthine amine congener.(ABSTRACT TRUNCATED AT 250 WORDS)

Contractions to oxygen-derived free radicals are augmented in aorta of the spontaneously hypertensive rat.

Abstract: 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.

Xanthine oxidase activity in rat pulmonary artery endothelial cells and its alteration by activated neutrophils.

Abstract: The possibility that endothelial cell-derived oxidants could contribute to neutrophil-mediated endothelial cell injury and cytotoxicity has been a subject of speculation. Rat pulmonary artery endothelial cells (RPAECs) were examined for the presence of xanthine oxidase (XO) activity, a well-known source of O2-. Using a sensitive assay based on measurements of radioactive xanthine conversion to uric acid by high performance liquid chromatography (HPLC), RPAEC extracts were found to contain both XO and xanthine dehydrogenase (XD) activities. Extracts from early passage cells have 55.3 +/- 11.7 (mean +/- SE) units/10(6) cells of total (XO + XD) activity, one unit of activity being defined as the conversion of 1% of substrate to product in 30 minutes of incubation. XO comprised 31.6 +/- 3.1% of this total activity. Addition of human neutrophils stimulated with phorbol myristate acetate (PMA) caused a rapid and dose-dependent increase in RPAEC XO activity from 31.6 +/- 3.1% to 71.7 +/- 4.8% of total without altering total (XO + XD) activity. The neutrophil dose-response curve for increase in XO paralleled closely the curve for neutrophil-mediated RPAEC cytotoxicity. The basal XO and XD activities and the neutrophil-induced increase in XO activity were inhibited by treating RPAECs with allopurinol, oxypurinol, and lodoxamide, which also inhibited cytotoxicity, but not by catalase, superoxide dismutase, or deferoxamine. Addition of H2O2 failed to cause an increase in RPAEC XO activity or XD to XO conversion. The results suggest that during neutrophil-mediated injury, rapid conversion of RPAEC XD to XO occurs, resulting in increased XO, catalyzed endogenous oxidant production, which may contribute to the oxidant burden in the killing mechanism initiated by activated neutrophils. Although the mechanism for conversion of XD to XO is uncertain, it appears that neutrophil-derived H2O2 is not sufficient to cause this phenomenon. Furthermore, neither O2- nor chelatable iron is required for neutrophil-induced XD to XO conversion. Supernatant fluids from activated neutrophils failed to induce XD to XO conversion in RPAECs. This in vitro system provides an opportunity to define the cellular and molecular mechanisms underlying the in vivo phenomenon of XD to XO conversion associated with ischemic/reperfusion or inflammatory tissue injury.

Translocation and enhancement of phosphotransferase activity of protein kinase C following exposure in mouse epidermal cells to oxidants.

Abstract: We have studied changes in intracellular localization and phosphorylating activity of protein kinase C (PKC) in mouse epidermal JB6 cells treated with oxidants. Exposure to hydrogen peroxide, reagent grade or generated enzymatically by glucose/glucose oxidase, at concentrations known to result in elevated intracellular free Ca2+ resulted in an increase in binding of [3H]phorbol dibutyrate to intact cells. Ca2+ chelation, either intracellularly by quin 2 or extracellularly by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, abolished the increase in radioligand binding. In contrast to H2O2, superoxide generated extracellularly by xanthine/xanthine oxidase or intracellularly by menadione was inactive. Scatchard plot analysis revealed that the enhancement in binding resulted from both increased receptor affinity and increased maximal binding capacity. Treatment of cells with superoxide, generated extracellularly by xanthine/xanthine oxidase or intracellularly by menadione, diminished the [3H]phorbol dibutyrate-binding capacity of the cytosol fractions prepared at low Ca2+ concentration. This decrease was not accompanied by a compensatory increase in the binding to membrane components. In contrast to superoxide, reagent H2O2, H2O2 produced by glucose/glucose oxidase, and the Ca2+ ionophore A23187 had no significant effect on the [3H]phorbol dibutyrate-binding capacities of either cellular fraction. Exposure of cells to low concentrations of extra- or intracellular superoxide resulted in an increase in the Ca2+- and phospholipid-dependent phosphorylating activity of cytosolic extracts towards adenosine diphosphoribose transferase which has been reported to be a specific substrate for PKC. The increase in phosphorylation could be diminished by the extracellular addition of copper-zinc-containing superoxide dismutase but not catalase suggesting that superoxide rather than H2O2 represents the active oxygen species in this reaction. The observation that reagent H2O2 or glucose/glucose oxidase failed to increase the phosphorylating activity of cytosolic preparations supports this conclusion. Treatment of cells or cytosolic extracts with the sulfhydryl reagent diamide stimulated the Ca2+/phospholipid-dependent phosphorylating activity toward adenosine diphosphoribose transferase. In a reconstituted system containing purified PKC, diamide induced a 25-30% increase in phospholipid-dependent phosphorylation of H1 whereas no change in activity was observed with the reducing agent dithiothreitol. It is concluded that H2O2 but not superoxide induces an increase in the phorbol ester binding, presumably to PKC, of intact JB6 cells. On the other hand

Endotoxin induces bacterial translocation and increases xanthine oxidase activity.

Abstract: Previously, we documented that endotoxin induces bacterial translocation from the gut and that inhibition or inactivation of xanthine oxidase activity reduces endotoxin-induced bacterial translocation. Consequently, experiments were performed to correlate endotoxin-induced bacterial translocation with changes in intestinal mucosal structure and xanthine dehydrogenase and oxidase activity. Segments of the jejunum, ileum, cecum, proximal colon, distal colon, and liver were harvested from ICR mice 24 hr after IP administration of E. coli 0111:B4 endotoxin (0.1 mg). Xanthine dehydrogenase and oxidase activities were measured in these samples and correlated with intestinal morphology. Bacteria translocated from the intestines to extraintestinal organs in 70% of the mice receiving endotoxin, while the organs of control mice were sterile (p less than 0.01). Endotoxin injured primarily the ileal and cecal mucosa and increased ileal and hepatic xanthine dehydrogenase and cecal oxidase activities (p less than 0.05). These results suggest that xanthine oxidase-induced mucosal damage plays a role in endotoxin-induced bacterial translocation.

Effects of 8-phenyl and 8-cycloalkyl substituents on the activity of mono-, di-, and trisubstituted alkylxanthines with substitution at the 1-, 3-, and 7-positions.

Abstract: The effects of 8-phenyl and 8-cycloalkyl substituents on the activity of theophylline, caffeine, 1,3-dipropylxanthine, 1,3-dipropyl-7-methylxanthine, 3-propylxanthine, and 1-propylxanthine at A1 adenosine receptors of rat brain and fat cells and at A2 adenosine receptors of rat pheochromocytoma PC12 cells and human platelets are compared. An 8-phenyl substituent has little effect on the activity of caffeine or 1,3-dipropyl-7-methylxanthine at adenosine receptors, while markedly increasing activity of theophylline, 1,3-dipropylxanthine, 1-isoamyl-3-isobutylxanthine, 1-methylxanthine, and 3-propylxanthine. 8-Phenyl-1-propylxanthine is potent (Ki = 20-70 nM) at all receptors. A p-carboxy or p-sulfo substituent, which is introduced on the 8-phenyl ring to increase water solubility, in most cases decreases the activity and selectivity for the A1 receptor. Among the 8-p-sulfo analogues, only 8-(p-sulfophenyl)theophylline and 1,3-dipropyl-8-(p-sulfophenyl)xanthine are selective for the A1 receptors. 8-p-Sulfophenyl derivatives of caffeine, 1,3-dipropyl-7-methylxanthine, and 3-propylxanthine are somewhat selective for the A2 receptors. 8-Cycloalkyl substituents (cyclopentyl, cyclohexyl) markedly increase activity of caffeine and 1,3-dipropyl-7-methylxanthine at the A2 receptor. 8-Cyclohexylcaffeine is potent (Ki = 190 nM) and very selective for the human platelet A2 receptors, but is not as selective for the rat PC12 cell A2 receptor. Such A2 selectivity is in contrast to the marked A1 selectivity of 8-cycloalkyltheophyllines and 8-cycloalkyl-1,3-dipropulxanthines. The apparent selectivity of certain xanthines is dependent on the assay systems that are compared.

Time course of structure, function, and metabolic changes due to an exogenous source of oxygen metabolites in rat heart.

Abstract: Effects of xanthine (2 mM) and xanthine oxidase (10 U/L) perfusion on myocardial function, lipid peroxide content, high-energy phosphates and their metabolites, and ultrastructure were examined in isolated perfused rat hearts to define the time course of myocardial injury due to exogenous supply of active oxygen species. Peak-developed force and dF/dt showed a decline within 5 min and complete contractile failure was seen at 20 min. Resting tension was higher at 10 min and reached a maximum value of 400% at 40 min. These changes in contractile parameters were reduced by superoxide dismutase (1.2 × 105 U/L), catalase (2 and 4 × 104 U/L), and mannitol (10 and 20 mM). Lipid peroxide content was significantly higher at 5 min and rose continuously with xanthine – xanthine oxidase (X–XO) perfusion. A close correlation was noted (r = 0.935) between increased lipid peroxide content and a decrease in peak-developed force. Creatine phosphate and adensoine triphosphate (ATP) showed a time-dependent decrease due to X...

NADH Induces the Generation of Superoxide Radicals in Leaf Peroxisomes

Abstract: In peroxisomes isolated from pea leaves (Pisum sativum L.) the production of superoxide free radicals (O2−) by xanthine and NADH was investigated. In peroxisomal membranes, 100 micromolar NADH induced the production of O2− radicals. In the soluble fractions of peroxisomes, no generation of O2− radicals was observed by incubation with either NADH or xanthine, although xanthine oxidase was found located predominantly in the matrix of peroxisomes. The failure of xanthine to induce superoxide generation was probably due to the inability to fully suppress the endogenous Mn-superoxide dismutase activity by inhibitors which were inactive against xanthine oxidase. The generation of superoxide radicals in leaf peroxisomes together with the recently described production of these oxygen radicals in glyoxysomes (LM Sandalio, VM Fernandez, FL Ruperez, LA del Rio [1988] Plant Physiol 87: 1-4) suggests that O2− generation could be a common metabolic property of peroxisomes and further supports the existence of active oxygen-related roles for peroxisomes in cellular metabolism.

The mobilization of ferritin iron by liver cytosol. A comparison of xanthine and NADH as reducing substrates.

Abstract: Considerable evidence suggests that the release of iron from ferritin is a reductive process. A role in this process has been proposed for two hepatic enzymes, namely xanthine oxidoreductase and an NADH oxidoreductase. The abilities of xanthine and NADH to serve as a source of reducing power for the enzyme-mediated release of ferritin iron (ferrireductase activity) were compared with turkey liver and rat liver homogenates. The maximal velocity (Vmax.) for the reaction with NADH was 50 times greater than with xanthine; however, the substrate concentration required to achieve half-maximal velocity (Km) was 1000 times less with xanthine than with NADH. NADPH could be substituted for NADH with little loss in activity. Dicoumarol did not inhibit the reaction with NADH or NADPH, demonstrating that the ferrireductase activity with those substrates was not the result of the liver enzyme 'DT-diaphorase' [NAD(P)H dehydrogenase (quinone)]. A flavin nucleotide was required for ferrireductase activity with rat and turkey liver cytosol when xanthine, NADH or NADPH was used as the reducing substrate. FMN yielded twice the activity with NADH or NADPH, whereas FAD was twice as effective with xanthine as substrate. Kinetic comparisons, differences in lability and partial chromatographic resolution of the ferrireductase activities with the two types of reducing substrates strongly indicate that the ferrireductase activities with xanthine and NADH are catalysed by separate enzyme systems contained in liver cytosol. Complete inhibition by allopurinol of the ferrireductase activity endogenous to undialysed liver cytosol preparations and the ability of xanthine to restore equivalent activity to dialysed preparations indicate that the source of reducing power for the endogenous activity is xanthine. These studies suggest that xanthine, NADH or NADPH can serve as a source of reducing power for the enzyme-mediated reduction of ferritin iron, with a flavin nucleotide serving as the shuttle of electrons from the enzymes to the ferritin iron.

Cardiovascular effects of two xanthines and the relation to adenosine antagonism.

Abstract: We hypothesize that the hemodynamic effects of xanthine derivatives depend on their ability to antagonize the vasodilating effects of endogenous adenosine. In a randomized, double-blind, and placebo-controlled study of 10 normotensive volunteers caffeine, a xanthine with in vitro adenosine antagonistic properties, increased mean arterial pressure by 5.6 ± 0.9 mm Hg and lowered heart rate by 5.3 ±1.1 beats/min. After administration of enprofylline, a xanthine without adenosine antagonism, forearm vascular resistance decreased by 5.6 ± 3.4 IU, heart rate increased by 10.6 ± 2.6 beats/min, and plasma adrenaline, plasma noradrenaline, and renin activity increased by 178 ± 86%, 14 ± 8%, and 36 ± 13%, respectively. Adenosine infusion alone induced a dose-related increase in pulse pressure and heart rate, and it increased plasma adrenaline and noradrenaline by 186 ± 77% and 132 ± 55%, respectively. This response to adenosine was reduced by pretreatment with caffeine but not enprofylline. Thus opposite circulatory responses to caffeine and enprofylline occurred, with signs of vasoconstriction and vasodilation, respectively. In addition, caffeine, but not enprofylline, reduced the cardiovascular response to exogenous adenosine. Clinical Pharmacology and Therapeutics (1989) 45, 593–599; doi:10.1038/clpt.1989.79

Role of xanthine oxidase in postischemic microvascular injury in skeletal muscle.

Abstract: Previous reports indicate that allopurinol, a xanthine oxidase inhibitor, attenuates the microvascular injury produced by reperfusion of ischemic skeletal muscle. To further assess the role of xanthine oxidase in ischemia/reperfusion (I/R) injury, we examined the effect of xanthine oxidase depletion or inhibition on the increase in microvascular permeability produced by I/R. Changes in vascular permeability were assessed by measurement of the solvent drag reflection coefficient for total plasma proteins (sigma) in rat hindquarters subjected to 2 h of ischemia and 30 min of reperfusion in xanthine oxidase-replete and -depleted animals and in animals pretreated with the xanthine oxidase inhibitor oxypurinol. Xanthine oxidase depletion was accomplished by administration of a tungsten-supplemented (0.7 g/kg diet), molybdenum-deficient diet. In animals fed the tungsten diet, muscle total xanthine dehydrogenase plus xanthine oxidase activity was decreased to less than 10% of control values. Estimates of sigma averaged 0.85 +/- 0.04 in nonischemic (continuous perfusion for 2.5 h) hindquarters, whereas muscle xanthine oxidase activity averaged 3.3 +/- 0.4 mU/g wet wt. I/R was associated with a marked decrease in sigma (0.54 +/- 0.02), whereas xanthine oxidase activity was increased to 5.8 +/- 0.5 mU/g wet wt. These results indicate that I/R produced a dramatic increase in vascular permeability coincident with an increase in muscle xanthine oxidase activity. Xanthine oxidase depletion with the tungsten diet or pretreatment with oxypurinol attenuated this permeability increase (sigma = 0.72 +/- 0.03 and 0.77 +/- 0.7, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Role of purines and xanthine oxidase in reperfusion injury in perfused rat liver.

Abstract: The purpose of this study was to evaluate the possible involvement of xanthine and xanthine oxidase in reperfusion injury in a low-flow, reflow model of liver perfusion. Livers were perfused at flow rates around 25% of normal for 90 min and then at normal flow rates (4 ml/g/min) for 30 min. When flow was restored to normal, malondialdehyde and lactic dehydrogenase (LDH) were released into the effluent perfusate. Malondialdehyde production rapidly reached values of 300 nmol/g/hr whereas LDH increased from basal levels of 100 to 600 U/l upon reperfusion. Trypan blue was taken up exclusively in cells in pericentral regions of the liver lobule under these conditions. Xanthine and hypoxanthine in the effluent perfusate increased steadily during the low-flow period reaching values around 5 and 10 microM, respectively, and decreased rapidly after the flow was restored to normal. Perfusion with nitrogen-saturated buffer for 3 min before restoration of normal flow rates or infusion of the radical scavenger catechin (400 microM) reduced cell damage by about 50%. Infusion of allopurinol (2-6 mM), an inhibitor of xanthine oxidase, prevented reperfusion injury in a dose-dependent manner. Taken together, these data indicate that a reperfusion injury occurs in liver upon reintroduction of oxygen which is initiated by oxidation of xanthine and hypoxanthine via xanthine oxidase and ultimately leads to production of lipid peroxides. Surprisingly, infusion of xanthine (4 mM), substrate for xanthine oxidase, reduced hepatocellular injury on reperfusion. LDH release was decreased from values around 700 to less than 200 U/l and trypan blue uptake in pericentral region was prevented totally by xanthine.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmaceutical containing tnf inhibitor

Abstract: Pharmaceuticals which contain a substance releasing tumor necrosis factor (TNF) are better tolerated and can be given in higher doses when they contain a TNF inhibitor, especially a xanthine derivative.

Genetic susceptibility to mucosal damage leads to bacterial translocation in a murine burn model.

Abstract: Since genetic factors may be important in host resistance to infections after thermal injury, we screened the susceptibility of three mouse strains (CD-1, Balb/c, and C57/bl) to thermally induced bacterial translocation from the GI tract Bacteria translocated to the MLNs of Balb/c but not the CD-1 or C57/bl mice receiving 25% body burns The increased incidence of bacterial translocation in the burned Balb/c mice appeared to be due to a burn-induced gut mucosal injury, since the intestinal mucosa of the Balb/c but not the CD-1 or C57/bl mice was damaged 24 hr after the thermal injury The mucosal injury appears to be mediated, at least in part, by xanthine oxidase-generated oxygen-free radicals, since inhibition of xanthine oxidase activity with allopurinol, or inactivation of xanthine oxidase activity by a molybdenum-free tungsten diet, prevented the mucosal injury and reduced the extent of bacterial translocation