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Showing papers on "Xanthine published in 1991"


Journal ArticleDOI
TL;DR: It is suggested that generation of uric acid during ischemia/reperfusion contributes to atherogenesis and intimal proliferation following arterial injury.

371 citations


Journal ArticleDOI
01 Jan 1991
TL;DR: DHLA is very effective as shown by its dual capability by eliminating both O2- and HO, suggesting that both TA and DHLA possess antioxidant properties.
Abstract: Thioctic acid (TA) and its reduced form dihydrolipoic acid (DHLA) have recently gained somc recognition as useful biological antioxidants. In particular, the ability of DHLA to inhibit lipid peroxidation has been reported. In the present study, the effects of TA and DHLA on reactive oxygen species (ROS) generated in the aqueous phase have been investigated. Xanthine plus xanthine oxidase-generated superoxide radicals (O2), detected by electron spin resonance spectroscopy (ESR) using DMPO as a spin trap. were eliminated by DHLA but not by TA. The sulhydryl content of DHLA, measured using Ellman's reagent decreased subsequent to the incubation with xanthine plus xanthine oxidase confirming the interaction between DHLA and O2-. An increase of hydrogen peroxide concentration accompanied the reaction between DHLA and O2x, suggesting the reduction of O2- by DHLA. Competition of O2- with epinephrine allowed us to estimate a second order kinetic constant of the reaction between O2- and DHLA, which was found to be...

246 citations


Journal ArticleDOI
TL;DR: The target cells employed include the murine macrophage cell line, P388D1, human peripheral lymphocytes, monocytes and neutrophils, rabbit alveolar macrophages, bovine aortic endothelial cells, and GM1380 fibroblasts to study the mechanisms by which the spectrum of oxidants released from stimulated leukocytes injure cells.

187 citations


Journal ArticleDOI
TL;DR: The increase in production of reactive oxygen species such as H2O2 at the G2/M phase of the second cell cycle may be related to the in vitro block to development of mouse 2-cell embryos.
Abstract: The increase in production of reactive oxygen species such as H2O2 at the G2/M phase of the second cell cycle may be related to the in vitro block to development of mouse 2-cell embryos. The occurrence of the H2O2 rise is independent of the activation of the embryonic genome and of passage through the S, G2 and M phases of the first cell cycle and G1 and M phases of the second cell cycle, but does require the activation of the unfertilized oocyte. The H2O2 is produced via dismutation of superoxide by the enzyme superoxide dismutase. Production of superoxide via mitochondrial, NADPH-oxidase and xanthine/xanthine oxidase systems has been investigated. The evidence suggests that superoxide, and thereby H2O2, is produced by the xanthine/xanthine oxidase system, but an involvement of the other superoxide generating systems has not been excluded. The relation between H2O2 and development in vitro is discussed.

142 citations


Journal ArticleDOI
TL;DR: In this paper, the determination of four purine bases (adenine, guanine, hypoxanthine, and xanthine) by reversed-phase high-performance liquid chromatography (RP-HPLC), in combination with real-time surface-enhanced Raman spectroscopy (SERS) detection, is demonstrated.
Abstract: The determination of four purine bases (adenine, guanine, hypoxanthine, and xanthine) by reversed-phase high-performance liquid chromatography (RP-HPLC), in combination with real-time surface-enhanced Raman spectroscopy (SERS) detection, is demonstrated. The goal of this study was to examine several factors (laser irradiation, pH, memory effects, and the construction of the interface between the RP-HPLC system and the Raman spectrometer) that effect SERS detection under flowing conditions. The separation and detection of a mixture of four purine bases was accomplished

132 citations


Journal ArticleDOI
01 Dec 1991-Stroke
TL;DR: Findings confirm marked alterations in purine metabolism following focal ischemia and suggest that xanthine oxidase contributes to the generation of free radicals.
Abstract: Background and Purpose: Increases in uric acid follow experimental stroke, which may be related to free radical formation by xanthine oxidase. The present study examined the time course of changes in xanthine and uric acid and their relationship to changes in the free radical scavengers glutathione, cysteine, and ascorbic acid. Methods: Focal ischemia was induced by occluding the middle cerebral artery, followed by transient occlusion of the common carotid arteries for 60 minutes. At varying time points, animals were sacrificed, and ischemic cortex was dissected. Neurochemical measurements were made by high-performance liquid chromatography with 16-sensor electrochemical detection. Results: Marked increases in uric acid were seen at all time points, with a maximal increase at 1 day and a persistent increase lasting up to 21 days. There were smaller reciprocal decreases in xanthine. Glutathione, cysteine, and ascorbic acid showed significant decreases, consistent with the generation of free radicals. Reductions in levels of cysteine and glutathione were significantly correlated with increases in uric acid levels. Conclusions: These findings confirm marked alterations in purine metabolism following focal ischemia and suggest that xanthine oxidase contributes to the generation of free radicals. (Stroke 1991;22:1548-1553)

128 citations


Journal ArticleDOI
TL;DR: PC12 cells, similar to some smooth muscle fibers but at variance with neurons and other secretory cells, express a single, rapidly exchangingCa2+ store in which two distinct intracellular Ca2+ channels, i.e. the receptors for caffeine-ryanodine and Ins-P3, appear to be colocalized.

120 citations


Journal ArticleDOI
TL;DR: The simultaneous determination of MDA, ascorbic acid, and of ATP and its degradation products gives the opportunity to correlate, by a single chromatographic run, peroxidative damages with the energy state of the cell which is of great importance in studies of ischemic and reperfused tissues.

117 citations


Journal ArticleDOI
TL;DR: Percutaneous transluminal coronary angioplasty provides a unique opportunity to study the time course of alterations in myocardial metabolism in humans early after short and repetitive occlusions of a major coronary artery, as well as the interaction among oxygen-free radicals with polyunsaturated fatty acids.
Abstract: The stunned myocardium has recently become the focus of considerable interest because of its potential role in negating the benefits of reperfusion. A critical but still unresolved issue relates to the mechanism responsible for this contractile abnormality. In recent years an increasing number of studies have provided indirect evidence that postischemic myocardial dysfunction may be mediated in part by the generation of reactive oxygen species, such as superoxide radical, hydrogen peroxide and hydroxyl radical. These oxygen-free radicals could arise from various sources, such as hypoxanthine conversion by xanthine oxidase, catecholamine degradation and mitochondrial electron transport. Direct evidence of injury by free radicals has yet to be shown in the human heart, but many studies of other mammals have linked reactive oxygen metabolites with myocardial injury. l-5 During myocardial ischemia, xanthine dehydrogenase (which appears to be located in the endothelial cells)‘j is converted to xanthine oxidase, an enzyme that produces supcroxide radical, hydrogen peroxide and uric acid from hypoxanthine or xanthine and molecular oxygen.7 At the same time, ischemia is associated with rapid catabolism of adenosine triphosphate.7 This degradation of adenosine triphosphate causes an efflux of breakdown products that are able to pass through the cell membrane, resulting in an accumulation of hypoxanthine, 1 of 2 substrates for xanthine oxidase. The other substrate (molecular oxygen) is provided by reperfusion, which results in a burst of free-radical generation. These free radicals initiate chain reactions causing peroxidative breakdown of polyunsaturated fatty acids in the membrane bilayer.9-12 The interaction among oxygen-free radicals with polyunsaturated fatty acids has been described as lipid pet-oxidation and can be measured by formation of malondialdehyde. Until recently, the assessment of alterations in myocardial metabolism in humans early after short and repetitive occlusions of a major coronary artery has not been feasible. However, percutaneous transluminal coronary angioplasty provides a unique opportunity to study the time course of these metabolic changes during transient interruption of coronary flow by the balloon-occlusion sequence in patients with 1 -vessel disease and without angi

113 citations


Journal ArticleDOI
TL;DR: Plasma protein thiol oxidation was determined to be a more sensitive and specific indication of oxidant stress to the vascular compartment than assessment of lipid oxidation byproducts.

106 citations


Journal ArticleDOI
TL;DR: The results indicate that luminol chemiluminescence in phorbol-ester-activated Kupffer cells largely depends on L-arginine metabolism by NO synthase, requiring the concurrent formation of NO and O2-/H2O2.
Abstract: Phorbol 12-myristate 13-acetate-induced luminol chemiluminescence in rat Kupffer cells was doubled by the addition of L-arginine and significantly (up to 70%) inhibited by NG-nitro-L-arginine and NG-monomethyl-L-arginine, competitive inhibitors of L-arginine-dependent nitric oxide (NO) formation. The release of superoxide anion (O2-) by NADPH oxidase was neither affected by L-arginine nor by the inhibitors. Only very slight luminol chemiluminescence was detectable in lipopolysaccharide-pretreated Kupffer cells, a condition in which significant amounts of NO were formed but no O2-. In a cell-free system, significant luminol chemiluminescence only occurred when both authentic NO and the O2-/H2O2- generating system xanthine/xanthine oxidase were present. The results indicate that luminol chemiluminescence in phorbol-ester-activated Kupffer cells largely depends on L-arginine metabolism by NO synthase, requiring the concurrent formation of NO and O2-/H2O2.

Journal ArticleDOI
TL;DR: The failure of deoxycoformycin to attenuate amino acid neurotransmitter release, even though it markedly enhancedAdenosine levels in the extracellular space, implies that the amino acid release during ischemia occurs via an adenosine‐insensitive mechanism.
Abstract: The effects of a potent adenosine deaminase inhibitor, deoxycoformycin, on purine and amino acid neuro-transmitter release from the ischemic rat cerebral cortex were studied with the cortical cup technique. Cerebral ischemia (20 min) was elicited by four-vessel occlusion. Purine and amino acid releases were compared from control ischemic animals and deoxycoformycin-pretreated ischemic rats. Ischemia enhanced the release of glutamate, aspartate, and gamma-aminobutyric acid into cortical perfusates. The levels of adenosine, inosine, hypoxanthine, and xanthine in the same perfusates were also elevated during and following ischemia. Deoxycoformycin (500 micrograms/kg) enhanced ischemia-evoked release of adenosine, indicating a marked rise in the adenosine content of the interstitial fluid of the cerebral cortex. Inosine, hypoxanthine, and xanthine levels were depressed by deoxycoformycin. Deoxycoformycin pretreatment failed to alter the pattern of amino acid neurotransmitter release from the cerebral cortex in comparison with that observed in control ischemic animals. The failure of deoxycoformycin to attenuate amino acid neurotransmitter release, even though it markedly enhanced adenosine levels in the extracellular space, implies that the amino acid release during ischemia occurs via an adenosine-insensitive mechanism. Inhibition of excitotoxic amino acid release is unlikely to be responsible for the cerebroprotective actions of deoxycoformycin in the ischemic brain.

Journal ArticleDOI
TL;DR: The results suggest that marked changes in myofibrillar ATPase activities by different species of oxygen free radicals may be mediated by the oxidation of SH groups.

Patent
30 Oct 1991
TL;DR: A combined preparation for simultaneous combined, simultaneous separate, or sequential use in the therapy or prophylaxis of disorders associated with undesirably high levels of TNF, e.g. septic or endotoxic shock and immunoregulatory and inflammatory disorders, which comprises an antibody to TNF or a TNF binding fragment thereof and a xanthine derivative is described in this paper.
Abstract: A combined preparation for simultaneous combined, simultaneous separate, or sequential use in the therapy or prophylaxis of disorders associated with undesirably high levels of TNF, e.g. septic or endotoxic shock and immunoregulatory and inflammatory disorders, which comprises an antibody to TNF or a TNF binding fragment thereof and a xanthine derivative. Particular preferred xanthine derivatives are 3,7-dimethyl-1-(5-oxo-hexyl)xanthine (known as Pentoxifylline or Trental) and 1-(5-hydroxy-5-methylhexyl)-3-methylxanthine and similar compounds. The anti-TNF antibody or fragment is preferably monospecific especially a humanised recombinant antibody or fragment. The ratio of xanthine derivative to anti-TNF antibody component used may be in the range between 450:1 and 1:10 and doses of anti-TNF component in the range 0.001-30mg/kg/day and doses of xanthine derivative in the range 0.5 to 100mg/kg/day may be administered during treatment of human or animal subjects. It has been found that when an anti-TNF antibody and a xanthine derivative are used together in some experimental models of septic shock, a surprising combination effect is observed.

Journal ArticleDOI
TL;DR: Evidence shows that products from xanthine oxidase of endothelial cells are necessary for the toxic effects of hydrogen peroxide or phorbol ester-activated neutrophils, and that ATP levels do not necessarily correlate with cytotoxic events.

Journal ArticleDOI
TL;DR: The results suggest that superoxide is the primary damaging species and a potential role of xanthine oxidase-generated superoxide in oxidative damage to vascular smooth muscle during a number of pathophysiological conditions.
Abstract: Effects of reactive oxygen intermediates generated by hypoxanthine plus xanthine oxidase on the Ca(2+)-adenosinetriphosphatase (ATPase) of sarcoplasmic reticulum from bovine aortic smooth muscle were studied. Exogenous hypoxanthine (0.1-100 microM) plus xanthine oxidase (10 mU/ml) produced an hypoxanthine concentration-dependent inhibition of the Ca(2+)-ATPase. The inhibition could be completely blocked by superoxide dismutase (100 U/ml) but not by either mannitol (20 mM) or deferoxamine (100 microM). Direct addition of hydrogen peroxide in the micromolar range did not cause significant inhibition. These results suggest that superoxide is the primary damaging species. Cysteine blocked this inhibition, suggesting possible involvement of sulfhydryl groups in the inhibition mechanism. Additionally, 1.16 +/- 0.17 mU/g wet wt of xanthine oxidase activity was detected in the postnuclear supernatant of bovine aortic smooth muscle, suggesting the existence of a possible intracellular source of superoxide. This value was calculated to be approximately 5 mU/ml by using a usual value of vascular smooth muscle cellular volume. Thus the level of endogenous xanthine oxidase in vascular smooth muscle is comparable with the level of exogenous xanthine oxidase used in the present study. These findings suggest a potential role of xanthine oxidase-generated superoxide in oxidative damage to vascular smooth muscle during a number of pathophysiological conditions.

Journal Article
TL;DR: Data indicate that H2O2 plays a major role in asbestos-stimulated ODC induction and proliferation of epithelial cells of the respiratory tract by altering the regulation of a gene critical to proliferation.
Abstract: Induction of ornithine decarboxylase (ODC) enzyme activity occurs after exposure of hamster tracheal epithelial (HTE) cells to asbestos and the soluble tumor promoter 12- O -tetradecanoylphorbol-13-acetate. Since active oxygen species are implicated as mediators of asbestos-induced biological responses, studies here were designed to examine whether active oxygen species generated by asbestos or oxidants caused increased ODC activity. In confluent HTE cells, significant blockage of chrysotile or crocidolite asbestos-stimulated ODC activity occurred with simultaneous addition of catalase, but not superoxide dismutase, to medium. The addition of xanthine plus xanthine oxidase caused a dose-dependent increase in ODC activity, which was inhibited significantly after addition of catalase or mannitol, indicating that H2O2 was the principal oxidant produced in that reaction. Addition of phenazine methosulfate, a redox reagent used to generate superoxide, resulted in significant elevation of ODC, which was inhibited by addition of superoxide dismutase but not catalase. Hydrogen peroxide added to culture medium also caused a potent increase in ODC activity inhabitable by catalase. Hypochlorous acid caused increases in ODC activity, although the magnitude of this response was less than that observed with other oxidants. Therefore, although all active oxygen species examined triggered ODC, less reduced species ( \rm O^{\d{-}}_{2} and H2O2) were more proficient than OH or a halogenated oxidant. All oxidants, except HOCl, caused a significant increase in [3H] thymidine incorporation at 24 or 48 h after their addition to HTE cells. In comparative studies, exposure of HTE cells to either asbestos or xanthine plus xanthine oxide increased the level of ODC mRNAs proportionate to oxidant concentration and the extent of enzyme induction. Thus, data indicate that H2O2 plays a major role in asbestos-stimulated ODC induction and proliferation of epithelial cells of the respiratory tract by altering the regulation of a gene critical to proliferation.

Journal ArticleDOI
TL;DR: The synthesis and the adenosine A1 and A2 receptor affinity of substituted 1H-imidazo[4,5-c]quinolin-4-amines are reported on and the structure-activity relationships (SAR) of these compounds are discussed in relation to SAR for otherAdenosine receptor ligands.
Abstract: On the basis of a model we recently developed for the antagonist binding site of the adenosine A1 receptor (J. Med. Chem. 1990, 33, 1708-1713), it was predicted that 1H-imidazo[4,5-c]quinolin-4-amines would be antagonists of the A1 receptor. Furthermore, it was expected that certain hydrophobic substitutions at the 2- and 4-positions would enhance affinity. Here, we report on the synthesis and the adenosine A1 and A2 receptor affinity of substituted 1H-imidazo[4,5-c]quinolin-4-amines. Some of these compounds have nanomolar affinity for the A1 receptor. The structure-activity relationships (SAR) of these compounds are discussed in relation to SAR for other adenosine receptor ligands. The 1H-imidazo[4,5-c]quinolin-4-amines constitute a novel class of non-xanthine adenosine antagonists.

Journal Article
TL;DR: It is demonstrated that caffeine increases base-line renin release primarily by blocking peripheral, cell-surface adenosine receptors and in part by additional central nervous system and/or intracellular mechanism(s) that involve the beta adrenergic system, while DPSPX potentiates vasodilator-induced renin secretion.
Abstract: Previous studies strongly suggest that adenosine receptors on juxtaglomerular cells function to restrain the secretion of renin induced by a variety of stimuli. The clinical significance of this is that caffeine, a widely consumed adenosine receptor antagonist, could augment renin release responses to diseases such as renovascular hypertension, liver cirrhosis and heart failure and to therapeutic maneuvers such as salt restriction, diuretics and vasodilators. Caffeine may be particularly troublesome in this regard because this methylxanthine has central nervous system effects and intracellular actions that also might contribute to the overall ability of caffeine to potentiate renin secretion. The purpose of this study was to document the effects of caffeine on renin release responses to a vasodilator and to investigate what mechanisms were responsible for any augmentation of vasodilator-induced renin secretion. Accordingly, we compared the effects of caffeine vs. 1,3-dipropyl-8-p-sulfophenylxanthine (DPSPX; a xanthine that we documented in this study not to significantly enter the brain or penetrate cell membranes) on base-line and hydralazine-induced renin release in both normal and beta adrenoceptor-blocked (propranolol, 15 mg/kg) rats. Both xanthines (at a dose of 10 mg/kg plus 150 micrograms/min) attenuated adenosine-mediated hypotension and bradycardia, and DPSPX was at least as effective as caffeine in antagonizing peripheral adenosine receptors. Caffeine and DPSPX increased base-line plasma renin activity to a similar extent regardless of whether the animals were pretreated with propranolol. In rats with an intact beta adrenergic system, caffeine, but not DPSPX, increased the renin release response to low-dose hydralazine (1 mg/kg). Although both xanthines augmented the renin release response to high-dose hydralazine (10 mg/kg), caffeine was more efficacious in this regard. In beta adrenoceptor-blocked rats, neither caffeine nor DPSPX augmented the renin release response to low-dose hydralazine, whereas both xanthines equally potentiated the renin release response to high-dose hydralazine. These data demonstrate that caffeine increases base-line renin release primarily by blocking peripheral (most likely renal), cell-surface adenosine receptors; however, caffeine potentiates vasodilator-induced renin secretion in part by blocking peripheral (most likely renal), cell-surface adenosine receptors and in part by additional central nervous system and/or intracellular mechanism(s) that involve the beta adrenergic system.

Journal ArticleDOI
TL;DR: The addition of exogenous PGI2 (150 mM) to platelet-endothelial systems did not completely prevent the enhanced platelet adherence, suggesting that a lack of P GI2 was not completely responsible for the adherence of platelets to O2(-).-injured cells.
Abstract: This study was directed to the ability of oxygen free radicals to cause reversible vascular endothelial cell dysfunction. A well-characterized system for the production of the superoxide anion radical (O2(-).) and hydrogen peroxide (H2O2), employing xanthine and xanthine oxidase, was used to sublethally injure human umbilical vein endothelial (HUVE) cells in vitro. We examined the effects of a 15-minute incubation of HUVE cells with xanthine (50 microM) and xanthine oxidase (2.5-100 munits) on platelet adherence and prostacyclin (PGI2) release. All experiments were conducted in a serum-free N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid)-Tyrode buffer (pH 7.4) incubation system. Exposure of HUVE cells to sublethal concentrations of oxygen free radicals caused significant enhancement of platelet adherence (65 +/- 6.3%) to injured endothelium. A 12-fold increase in PGI2 release resulted after a 15-minute treatment with xanthine and xanthine oxidase. The addition of exogenous PGI2 (150 mM) to platelet-endothelial systems did not completely prevent the enhanced platelet adherence, suggesting that a lack of PGI2 was not completely responsible for the adherence of platelets to O2(-).-injured cells. When superoxide dismutase (SOD) and catalase, scavengers of O2(-). and H2O2, were added in combination to treated cells, platelet adherence decreased by 42-77% and PGI2 release approached that of control cultures. No decrease in either platelet adherence or PGI2 release occurred when chemically inactivated forms of SOD and catalase or bovine serum albumin were added to oxidant-treated cultures.

Journal ArticleDOI
TL;DR: In this article, an amperometric sensor for xanthine oxidase was constructed on a carbon paste electrode and physically entrapped with a semipermeable membrane, and the product of the enzymatic reaction was oxidized electrochemically at +0.4 V vs. Ag/AgCl.

Journal ArticleDOI
TL;DR: This study was designed to clarify the mechanism of ischemia-reperfusion-induced rat liver injury and to evaluate the effect of long-acting superoxide dismutase (SOD-POE) on mitochondrial function and liver mitochondrial functional indices.

Journal ArticleDOI
TL;DR: These purine derivatives suppress calcitriol synthesis and inhibit receptor binding affinity for DNA in rats infused with either theophylline or urate.
Abstract: The effects of theophylline and sodium urate on metabolic production (PR) and clearance rate (MCR) of calcitriol were determined by the constant isotope infusion method in normal rats. Calcitriol PR was significantly reduced after infusion for 20 h of either theophylline (1 mg/h, PR = 22.3 +/- 1.6 ng.kg-1.day-1, P less than 0.001, n = 5) or sodium urate (0.5 mg/h, PR = 18.6 +/- 1.2 ng.kg-1.day-1, P less than 0.001, n = 5) compared with control rats infused with saline (PR = 32.0 +/- 1.5 ng.kg-1.day-1, n = 5). Renal 1 alpha-hydroxylase activity of kidney homogenate was significantly inhibited in rats infused with theophylline or urate. Suppression of 1 alpha-hydroxylase activity was also observed when the kidney homogenate was preincubated for 3 h with various concentrations of xanthine (0.11-3.0 mg/dl). In addition, the MCR of calcitriol was decreased in rats infused with either theophylline (MCR = 21.0 +/- 0.88 microliter.min-1.100 g-1, P less than 0.005) or urate (MCR = 22.9 +/- 0.91 microliter.min-1.100 g-1, P less than 0.05) compared with saline-infused control rats (MCR = 25.2 +/- 0.41 microliter.min-1.100 g-1). Because calcitriol degradation is a receptor-mediated process that requires binding of the receptor-hormone complex to chromatin, we studied the binding affinity of labeled calcitriol receptor for DNA-cellulose in the presence of theophylline or urate. Both theophylline and urate inhibited receptor binding affinity for DNA-cellulose. We conclude that these purine derivatives suppress calcitriol synthesis and inhibit receptor binding affinity for DNA. The altered receptor binding affinity could explain the decreased MCR of calcitriol.

Journal ArticleDOI
TL;DR: It is concluded that the modification of the NaB3H4 reduction assay is a useful postlabeling method for monitoring free radical action in vivo and postulated that free radical damage in estrogen-treated hamster kidney plays a role inosterone-induced carcinogenesis.

Journal ArticleDOI
TL;DR: Results indicated that hydroxyl radical can effect the cleavage of methylenedioxy group on MDPs.
Abstract: The oxidative demethylenation reactions of (methylendioxy)phenyl compounds (MDPs), (methylenedioxy)benzene (MDB), (methylenedioxy)amphetamine (MDA), and (methylenedioxy)methamphetamine (MDMA), were evaluated by using two hydroxyl radical generating systems, the autoxidation of ascorbate in the presence of iron-EDTA and the iron-catalyzed Haber-Weiss reaction conducted by xanthine/xanthine oxidase with iron-EDTA. Reaction products generated when MDB, MDA, and MDMA were incubated with the ascorbate or xanthine oxidase system were catechol, dihydroxyamphetamine (DHA), and dihydroxymethamphetamine (DHMA), respectively. The reaction required the presence of either ascorbic acid or xanthine oxidase. Levels of each catechol increased in proportion to ferric ion concentration and were suppressed by desferrioxamine B methanesulfonate (desferal). Catalase (CAT) inhibited the oxidation by the ascorbate system whereas superoxide dismutase (SOD) had little effect. The addition of hydrogen peroxide to the reaction mixture stimulated the oxidation, but the reaction was not initiated by hydrogen peroxide alone, suggesting that hydrogen peroxide acts as a precursor of hydroxyl radical. SOD and CAT suppressed the demethylenation reactions in the xanthine oxidase system. Hydroxyl radical scavenging agents such as ethanol, benzoate, DMSO, and thiourea effectively inhibited the oxidation by both systems. Urea, which has little effect on hydroxyl radical, was without any effect. These results indicated that hydroxyl radical can effect the cleavage of methylenedioxy group on MDPs.

Journal ArticleDOI
TL;DR: The results suggest that the observed electrophysiological actions of adenine nucleotides in cardiomyocytes are mediated by adenosine and are consistent with activation of A1-adenosine receptors.
Abstract: Adenosine and adenine nucleotides shorten the action potential duration of atrial myocytes and activate a specific acetylcholine and adenosine receptor-operated potassium outward current referred to as IKACh,Ado. The objective of this study was to determine whether adenine nucleotides shorten the action potential duration and increase IKACh,Ado in guinea pig atrial myocytes by directly activating adenosine receptors. The potency and efficacy of AMP and adenosine in increasing IKACh,Ado and shortening atrial action potential duration were similar; the EC50 values for AMP and adenosine were 3.4 +/- 0.8 and 3.1 +/- 0.4 microM, respectively. Likewise, the maximum increases in IKACh,Ado caused by AMP and adenosine were similar (122 +/- 11% versus 123 +/- 9%). In comparison, ATP and the stable analogue of AMP, adenosine monophosphorothioate (AMPS), were significantly less potent and efficacious than adenosine and AMP, and adenosine receptor antagonist 8-(p-sulfophenyl)theophylline and abolished in the presence of adenosine deaminase and alpha, beta-methylene-ADP (APCP, an inhibitor of AMP degradation). Binding of the A1-adenosine antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine (DPCPX) to guinea pig atrial membranes treated with adenosine deaminase and APCP was reduced up to 60% by 100 microM concentrations of AMP, AMPS, and adenosine. Inosine inhibited binding by 43 +/- 3% at 100 microM, whereas hypoxanthine and xanthine had little (5-10% inhibition) and uric acid had no effect. Only 3% of AMP and 35% of AMPS were recovered intact after a 90-minute incubation at 21 degrees C with preparations of guinea pig atrial membranes. Percent displacement of [3H]DPCPX binding to atrial membranes by 100 microM AMP was significantly less in the presence of nucleoside phosphorylase and xanthine oxidase (to degrade inosine, hypoxanthine, and xanthine to uric acid) than in their absence (12.4 +/- 3.1% versus 49.7 +/- 1.5%). The results suggest that the observed electrophysiological actions of adenine nucleotides in cardiomyocytes are mediated by adenosine and are consistent with activation of A1-adenosine receptors.

Journal ArticleDOI
TL;DR: The data suggest that O2- and H2O2, whether created by stimulated neutrophils or an enzyme-generating system, are damaging to isolated enterocytes.

Journal ArticleDOI
TL;DR: Data indicate that adrenergic receptors in the sarcolemmal membranes are modified by oxygen free radicals.
Abstract: To examine the effects of oxygen free radicals on alpha- and beta-adrenergic receptors, rat heart crude membranes were incubated with xanthine plus xanthine oxidase, H2O2, or H2O2 plus Fe2+. The assay of beta-adrenergic receptors involving [3H]dihydroalprenolol (DHA) binding revealed that the maximal number of binding sites (Bmax) and dissociation constant (Kd) were increased by xanthine plus xanthine oxidase. H2O2 increased the Kd value for [3H]DHA binding. When a hydrophilic ligand, [3H]CGP-12177, was used for the beta-adrenergic receptor assay, an increase in Kd value without any changes in Bmax value was evident on treating the membranes with xanthine plus xanthine oxidase. The assay of alpha-adrenergic receptors involving [3H]prazosin binding showed a decrease in the number of binding sites and an increase in Kd value only after a prolonged period of incubation. Both H2O2 and H2O2 plus Fe2+ increased the Kd value for [3H]prazosin without changes in Bmax. Changes in both alpha- and beta-adrenergic receptors similar to those with crude membranes were also seen by employing the purified heart sarcolemmal membranes. These data indicate that adrenergic receptors in the sarcolemmal membranes are modified by oxygen free radicals.

Journal ArticleDOI
TL;DR: The results suggest that OH.

Journal ArticleDOI
TL;DR: In addition to guanine, xanthine and hypoxanthine were identified in white spherules in excreta of five species ofArgas andOrnithodoros ticks by a reverse-phase high-performance liquid chromatography (HPLC) and a gas chromatographic method with mass spectrometric detection, (GC/MS) as mentioned in this paper.
Abstract: In addition to guanine, xanthine and hypoxanthine were identified in white spherules in excreta of five species ofArgas andOrnithodoros ticks by a reverse-phase high-performance liquid chromatography (HPLC) and a gas chromatographic method with mass spectrometric detection, (GC/MS). The mutual relationships of these purines in excreta ofArgas (Persicargas) persicus were found to be less than 1.5% for hypoxanthine, less than 9.0% for xanthine and 89.8–98.6%, for guanine. In excreta of other species, the relationships of purines were similar, with the exception ofArgas (A.) reflexus andA. (A.) polonicus, where the amount of hypoxanthine was rather elevated. Uric acid was also identified in some cases. The assembly efficacy of xanthine and hypoxanthine is similar to that of guanine, but xanthine significantly enhances the assembly efficacy of commercial guanine when mixed in ratio of about 1∶25. Thus, xanthine seems to be the second important component of assembly pheromone of argasid ticks.