Showing papers on "Xanthine published in 1987"
TL;DR: The high EC levels of adenosine during ischemia may turn off spontaneous neuronal firing, counteract excitotoxicity, and inhibit ischemic calcium uptake, thereby exerting neuroprotective effects.
Abstract: Extracellular (EC) adenosine, hypoxanthine, xanthine, and inosine concentrations were monitored in vivo in the striatum during steady state, 15 min of complete brain ischemia, and 4 h of reflow and compared with purine and nucleotide levels in the tissue. Ischemia was induced by three-vessel occlusion combined with hypotension (50 mm Hg) in male Sprague-Dawley rats. EC purines were sampled by microdialysis, and tissue adenine nucleotides and purine catabolites were extracted from the in situ frozen brain at the end of the experiment. ATP, ADP, and AMP were analyzed with enzymatic fluorometric techniques, and adenosine, hypoxanthine, xanthine, and inosine with a modified HPLC system. Ischemia depleted tissue ATP, whereas AMP, adenosine, hypoxanthine, and inosine accumulated. In parallel, adenosine, hypoxanthine, and inosine levels increased in the EC compartment. Adenosine reached an EC concentration of 40 microM after 15 min of ischemia. Levels of tissue nucleotides and purines normalized on reflow. However, xanthine levels increased transiently (sevenfold). In the EC compartment, adenosine, inosine, and hypoxanthine contents normalized slowly on reflow, whereas the xanthine content increased. The high EC levels of adenosine during ischemia may turn off spontaneous neuronal firing, counteract excitotoxicity, and inhibit ischemic calcium uptake, thereby exerting neuroprotective effects.
427 citations
TL;DR: Increased proteolysis seems to occur independently of membrane damage and to be a more sensitive indicator of cell exposure to oxygen radicals than is lipid peroxidation.
410 citations
TL;DR: The excretion of purine derivatives in excess of endogenous contribution was closely related to the theoretically expected values and increased linearly with increasing microbial nucleic acid input in sheep.
Abstract: Two experiments were carried out to determine endogenous excretion of purine derivatives in steers and lambs, and to investigate the relationship between microbial nucleic acid input and urinary excretion of purine nitrogen. The endogenous excretion of allantoin after conversion of hypoxanthine, xanthine and uric acid to allantoin, was calculated to be 72 and 26 mg/kg W 0·75 per day in steers and lambs, respectively, when the dietary protein contained no nucleic acid nitrogen. The excretion of purine derivatives increased linearly with increasing microbial nucleic acid input in lambs. The excretion of purine derivatives in excess of endogenous contribution was closely related to the theoretically expected values. The average recovery was calculated as 0·96 for one sheep and 1·0 for the other.
292 citations
TL;DR: A simple and fast ion pair reversed-phase high-performance liquid chromatographic method has been developed for the simultaneous determination of ATP, ADP, AMP, GTP, GDP, IMP, NADP+, NADPH+, NAD+, NADH,ADP-ribose, inosine, adenosine, hypoxanthine, and xanthine.
186 citations
TL;DR: Of these 9-substituted purines, the guanine derivative 1 showed the highest activity against herpes simplex virus types 1 and 2 in cell cultures, and in some tests it was more active than acyclovir, with no evidence of toxicity for the cells.
Abstract: Alkylation of 2-amino-6-chloropurine with 5-(2-bromoethyl)-2,2-dimethyl-1,3-dioxane (5) provided 2-amino-6-chloro-9-[2,(2,2-dimethyl-1,3-dioxan-5-yl)ethyl]purine (6) in high yield. This aminochloropurine 6 was readily converted to the antiviral acyclonucleoside 9-[4-hydroxy-3-(hydroxymethyl)but-1-yl]guanine (1) and to its 6-chloro (10), 6-thio (11), 6-alkoxy (12-17), 6-amino (20), and 6-deoxy (21) purine analogues. The guanine derivative 1 was converted to its xanthine analogue 9. Similarly, alkylation of 6-chloropurine with 5 provided a route to 8, the hypoxanthine analogue of 1. Of these 9-substituted purines, the guanine derivative 1 showed the highest activity against herpes simplex virus types 1 and 2 in cell cultures, and in some tests it was more active than acyclovir, with no evidence of toxicity for the cells. A series of monoesters (30-33) and diesters (24-27, 29) of 1 were prepared, and some of these also showed antiherpes virus activity in cell cultures, the most active ester being the dihexanoate 27.
162 citations
TL;DR: This chapter discusses the biological distribution and substrate-inhibitor specificity of molybdenum hydroxylases, which may provide a biochemical barrier against ingested purines and pyrimidines, rendering them harmless.
Abstract: Publisher Summary This chapter discusses the biological distribution and substrate-inhibitor specificity of molybdenum hydroxylases. Aldehyde oxidase and xanthine oxidase are molybdenum-containing enzymes that catalyze the oxidation of many aldehydes and nitrogen heterocycles. They have also been shown to catalyze, under in vitro conditions, a number of reductions. Although aldehyde oxidase is known to oxidize physiological compounds, such as N 1 -methylnicotinamide and pyridoxal, there does not yet appear to be a specific endogenous role for this enzyme. Xanthine oxidase is involved in endogenous purine catabolism, catalyzing the oxidation of hypoxanthine and xanthine to uric acid. This enzyme also has wide substrate specificity, and different functions have been assigned to it. One of the most plausible proposals is that both molybdenum hydroxylases may provide a biochemical barrier against ingested purines and pyrimidines, rendering them harmless. This is similar to the view put forward in a recent review on the role of the molybdenum hydroxylases as drug-metabolizing enzymes, except that the substrate specificity is not restricted to purines and pyrimidines.
135 citations
TL;DR: Two types of compounds may be useful as antioxidants in vivo, although 2-imidazolthiones were more reactive than 2-IMIDazolones in the assays using DPPH and the oxidation of oxyhemoglobin.
117 citations
TL;DR: Results strongly support a variety of chemical studies with model molybdenum complexes suggesting that the oxygen atom of the Mo = O group known to be present at the active site of xanthine oxidase is transferred to product in the course of catalysis.
102 citations
TL;DR: The presence of both circulating xanthine oxidase and its substrate demonstrates the potential for intravascular oxygen metabolite production, which may then cause tissue injury in ARDS.
101 citations
TL;DR: An in vitro model of alveolar epithelial oxidant injury was developed based on exposure of cultured rat type II pneumocytes to superoxide and hydrogen peroxide enzymatically generated in the culture medium and partial and complete protection against oxidation injury was achieved by pretreatment of cells with catalase liposomes.
Abstract: Oxidant injury to the alveolar epithelium can be mediated by exposure to oxidant gases such as O2 at high concentrations and O3, inflammatory cell-derived reactive O2 species, and the intracellular metabolism of xenobiotics such as paraquat. An in vitro model of alveolar epithelial oxidant injury was developed based on exposure of cultured rat type II pneumocytes to superoxide and hydrogen peroxide (H2O2) enzymatically generated in the culture medium. Cytotoxicity was assessed by the release of lactate dehydrogenase (LDH) into the culture medium, which was a more reliable indicator of damage than release of 51Cr by prelabeled cells. Incubation of cells for 6–8 h with xanthine plus xanthine oxidase and glucose plus glucose oxidase induced the release of greater than 50% of total intracellular LDH. Oxidant exposure also resulted in significant detachment of cells from culture dishes. Modulation of oxidant damage was accomplished using liposomes as vectors for the delivery of catalase. Treatment of cells with catalase liposomes for 2 h resulted in augmentation of cellular catalase specific activities up to 631% of controls. Catalase was partitioned into intracellular and surface-associated compartments in catalase liposome-treated cells. Partial and complete protection against oxidant injury, induced by xanthine plus xanthine oxidase and glucose plus glucose oxidase, respectively, was achieved by pretreatment of cells with catalase liposomes. LDH release during oxidant exposure was inversely related to augmentation of cellular catalase activities. Catalase liposome-treated cells also exhibited an enhanced ability to scavenge enzymatically generated H2O2 from the culture medium. These observations suggest a useful approach to modulation of alveolar injury induced by reactive O2 species.
86 citations
TL;DR: The hypothesis that there is enhanced hypoxanthine salvage in hereditary xanthinuria is supported and degradation of guanine nucleotides to xanthine bypasses the hypox anthine salvage pathway and may explain the predominance of this urinary purine compound in xanth inuria.
Abstract: We tested the hypothesis that there is an enhanced rate of hypoxanthine salvage in two siblings with hereditary xanthinuria. We radiolabeled the adenine nucleotide pool with [8-14C]adenine and examined purine nucleotide degradation after intravenous fructose. The cumulative excretion of radioactivity during a 5-d period was 9.7% and 9.1% of infused radioactivity in the enzyme-deficient patients and 6.0 +/- 0.7% (mean +/- SE) in four normal subjects. Fructose infusion increased urinary radioactivity to 7.96 and 9.16 X 10(6) cpm/g creatinine in both patients and to 4.73 +/- 0.69 X 10(6) cpm/g creatinine in controls. The infusion of fructose increased total urinary purine excretion to a mean of 487% from low-normal baseline values in the patients and to 398 +/- 86% in control subjects. In the enzyme-deficient patients, the infusion of fructose elicited an increase of plasma guanosine from undetectable values to 0.7 and 0.9 microM. With adjustments made for intestinal purine loss, these data support the hypothesis that there is enhanced hypoxanthine salvage in hereditary xanthinuria. Degradation of guanine nucleotides to xanthine bypasses the hypoxanthine salvage pathway and may explain the predominance of this urinary purine compound in xanthinuria.
TL;DR: The results suggest the presence of A1 adenosine receptors on rat ventricular myocytes, which mediate an inhibition of adenylate cyclase, which may be responsible for the effects of adenosines and its analogues on the heart.
Abstract: The aim of the present study was the characterization of adenosine receptors in isolated rat ventricular myocytes The CAMP-levels of rat ventricular myocytes in the presence of 1 μmol/l isoprenaline were reduced by up to 48% by adenosine analogues; the rank order of potency was: R-N6-phenylisopropyladenosine (IC50 60 nmol/1), 5′-N-ethylcarboxamidoadenosine (IC50 360 nmol/l) and S-N6-phenylisopropyladenosine (IC50 16 μol/l) The adenosine receptor antagonist XAC (“xanthine amine congener”) antagonized the effect of R-N6-phenylisopropyladenosine in a concentration-dependent manner with a Ki-value of 20 nmol/l The A1 receptor-selective radioligand R-N6-125I-p-hydroxyphenylisopropyladenosine bound to membranes prepared from rat ventricular myocytes in a saturable manner with a B
max of 177 fmol/mg protein and a K
D-value of 11 nmol/l Adenosine analogues competed for the binding with the same rank order of potency as for the inhibition of the isoprenaline-induced cAMP-increase GTP inhibited radioligand binding with an IC50-value of 73 μol/l These results suggest the presence of A1 adenosine receptors on rat ventricular myocytes, which mediate an inhibition of adenylate cyclase The receptors may be responsible for the effects of adenosine and its analogues on the heart
TL;DR: The effect of adenosine on agonist‐stimulated inositol phospholipid hydrolysis appeared to be selective for histamine H1‐receptor stimulation since it did not augment the phosphoinositide responses to carbachol, noradrenaline, 5‐hydroxytryptamine or elevated KC1.
Abstract: Incubation (45 min) of slices of guinea-pig cerebral cortex with adenosine alone had no significant effect on the accumulation of [3H]-inositol phosphates but enhanced the response to histamine H1-receptor stimulation in a concentration-dependent manner. The effect of adenosine on agonist-stimulated inositol phospholipid hydrolysis appeared to be selective for histamine H1-receptor stimulation since it did not augment the phosphoinositide responses to carbachol, noradrenaline, 5-hydroxytryptamine or elevated KCl. The accumulation of [3H]-inositol phosphates induced by histamine increased linearly between 5 and 45 min incubation with agonist. However, following the simultaneous addition of histamine and adenosine, there was a marked delay in the appearance of the augmentation produced by adenosine. The augmentation of [3H]-inositol phosphate accumulation was mimicked by a number of adenosine analogues. The rank order of potency was; cyclopentyladenosine greater than R-phenyl-isopropyladenosine 5'-N-ethylcarboxamidoadenosine greater than 2-chloroadenosine. This is consistent with the order expected for an adenosine A1-receptor effect but the EC50 values were in the micro- rather than nanomolar range. The response to 2-chloroadenosine was antagonized by the xanthine adenosine-antagonists, cyclopropyltheophylline, 8-phenyltheophylline, 3-isobutyl-1-methylxanthine and theophylline, and the non-xanthine alloxazine.
Journal Article•
TL;DR: The results suggest that the increased XO activity detected following TPA treatment is the consequence of TPA-induced XD synthesis, and a conversion of existing and newly synthesized XD to XO.
Abstract: Both xanthine dehydrogenase (XD) and xanthine oxidase (XO) catalyze the conversion of hypoxanthine to xanthine, and xanthine to uric acid. Topical application of a promoting dose of 12- O -tetradecanoylphorbol-13-acetate (TPA) to the dorsal skin of female SENCAR mice resulted in a 3.0–3.5-fold elevation of epidermal XO specific activity. Epidermal XO specific activity was maximally elevated 48–96 h after TPA treatment, and required 11 days to return to control levels. Although TPA increased the XO/(XD + XO) ratio from 0.45 to 0.7, the conversion of preexisting XD to XO could not solely account for the TPA-dependent elevation in XO specific activity since control XD plus XO activity was less than just the XO activity in TPA-treated epidermis. Topical application of cycloheximide simultaneously with, or 12 h after, TPA treatment inhibited the TPA-dependent increases in the XO/(XD + XO) ratio and XO specific activities. Collectively, these results suggest that the increased XO activity detected following TPA treatment is the consequence of TPA-induced XD synthesis, and a conversion of existing and newly synthesized XD to XO. In addition, the in vivo promoting activities of analogues of TPA could be correlated with their abilities to elevate XO activity (TPA > phorbol-12,13-dibenzoate ≫ 4- O -methyl-TPA = phorbol).
01 Jan 1987
TL;DR: Xanthine dehydrogenase is not converted to xanthine oxidase in hypoxic tissue of the isolated perfused rat heart, and that the release of intracellular enzymes upon reoxygenation in this experimental model is mediated by factors other than reactive oxygen generated by xanthin oxidase.
Abstract: The massive leakage of intracellular enzymes which occurs during reoxygenation of heart tissue after hypoxic or ischemic episodes has been suggested to result from the formation of oxygen radicals. One purported source of such radicals is the xanthine oxidase-mediated metabolism of hypoxanthine and xanthine. Xanthine oxidase (O form) has been suggested to be formed in vivo by limited proteolysis of xanthine dehydrogenase (D form) during the hypoxic period (Granger el ai. Gastroenterology 81, 22 (1981)). We measured the activities of xanthine oxidase in both fresh and isolated-perfused (Langendorff) rat heart tissue. Approximately 32% of the total xanthine oxidase was in the O form in fresh and isolated-perfused rat heart. This value was unchanged following 60min of hypoxia and 30 minutes of reoxygenation. The infusion of 250/JM allopurinol throughout the perfusion completely inhibited xanthine oxidase activity but had no effect on the massive release of lactate dehydrogenase (LDH) into the coronary efflue...
Journal Article•
TL;DR: A series of para-substituted N6-phenyladenosines have been synthesized based on a "functionalized congener" approach in which a chemically reactive group, such as an amine or carboxylic acid, is introduced at the terminus of a chain.
Abstract: Adenosine modulates a variety of physiological functions through interaction with A1 and A2 adenosine receptors, where agonists mediate inhibition and stimulation, respectively, of adenylate cyclase. In the cardiovascular system, A2 receptors mediate vasodilation and reduction in blood pressure, while A1 receptors mediate cardiac depression. The involvement of adenylate cyclase in these responses remains unresolved. Adenosine analogs in particular the N6-substituted compounds are more potent at A1 receptors than at A2 receptors. The subregion of the adenosine receptor that interacts with the N6-substituent is different for A1 and A2 receptors, particularly with respect to phenyl interactions, bulk tolerance and stereoselectivity. A series of para-substituted N6-phenyladenosines have been synthesized based on a "functionalized congener" approach in which a chemically reactive group, such as an amine or carboxylic acid, is introduced at the terminus of a chain. From the "functionalized congener" are synthesized a variety of conjugates each containing a common pharmacophore. Certain of the adenosine conjugates are highly selective for A1 receptors. Xanthines are classical antagonists for adenosine receptors for many of their pharmacological actions may be due to blockade of adenosine receptors. Caffeine and theophylline are virtually non-selective for A2 and A2 receptors. Replacement of the methyl groups of theophylline with n-propyl or larger alkyl groups yields xanthines with selectivity for A1 receptors, particularly when combined with an 8-phenyl moiety. Most 1,3-dialkyl-8-phenyl xanthines are very insoluble, but incorporation of polar aryl substituents, such as sulfo or carboxy to increase solubility, results in marked reduction in potency and selectivity. A new series of more hydrophilic 1,3-dipropyl-8-phenylxanthines has been synthesized using the "functionalized congener" approach. Certain conjugates of 8-[4-(carboxymethyloxy)phenyl 1]1,3-dipropylxanthine display A1 selectivity in biochemical and cardiovascular models. Certain analogs of caffeine in which the methyl group at the 1- or 7-position is replaced with a propargyl or propyl group display selectivity for A2 receptors. The profile of a series of adenosine analogs or of xanthine antagonists can be used to define the nature of adenosine receptors.
TL;DR: The results showed that the pig heart and blood were xanthine oxidase deficient, suggesting that xanthin oxidase-derived free oxygen radicals were not involved in the cytotoxic and arrhythmogenic effects brought about by myocardial ischemia and/or reperfusion in the pig.
Abstract: Xanthine oxidase activities of pig myocardium and blood during and following myocardial ischemia were measured using HPLC, and electrochemical detection of hypoxanthine, xanthine and uric acid. Myocardial ischemia was produced by occluding the anterior descending coronary artery two-thirds of the way from its origin. There was no accumulation of either xanthine orurate in the ischemic pig myocardium during occlusion periods of 90 min, but there was a substantial accumulation of hypoxanthine. Similarly, there was no increase in myocardial xanthine or urate during the 30 min reperfusion following coronary artery occlusion periods of 15, 30, 60 or 90 min. Following in vitro incubation at pH 8 of myocardial homogenates or blood with either hypoxanthine or xanthine and NAD, no urate production was detectable. In contrast, significant amounts of xanthine and/or urate were produced, following addition of xanthine oxidase to the reaction mixtures. Additional in vitro experiments showed that the following pig tissues were lacking xanthine oxidase activity: left and right atrial appendage, left and right ventricle, interventricular septum, anterior descending and circumflex coronary arteries, ascending aorta, lung, and blood. Large amounts of xanthine oxidase (9.3±1.8 SEM mU/g wet weight, n=7) were found in pig liver. In the ischemic pig heart, transmural infarction developed within 60 min of ischemia. Ventricular arrhythmias and fibrillation occured most frequently within 45 min of ischemia and within seconds after reperfusion. These results showed that the pig heart and blood were xanthine oxidase deficient, suggesting that xanthine oxidase-derived free oxygen radicals were not involved in the cytotoxic and arrhythmogenic effects brought about by myocardial ischemia and/or reperfusion in the pig.
TL;DR: It is postulated that the mobile inflamed joint may be subject to cyclical ischaemic reperfusion injury and the detection of Xanthine oxidoreductase is described, and this activity in human synovium is described.
Abstract: It is postulated that the mobile inflamed joint may be subject to cyclical ischaemic reperfusion injury. Xanthine oxidoreductase is an enzyme thought to contribute to oxidative reperfusion injury, and the detection of this activity in human synovium is described. Three normal and five rheumatoid tissues were assayed with a carbon-14 radioassay detecting the conversion of [14C]xanthine to [14C]uric acid. Rheumatoid synovia contained 0.67-305 microU/g tissue (n = 5), while normal synovia contained 1.2-5.0 microU/g tissue (n = 3).
TL;DR: It is concluded that in vitro oxygen metabolites, extracellularly generated, have a direct toxic effect on gastric mucosal cells; hydrogen peroxide is a major mediator of oxygen metabolite-induced gastric cell injury; the oxygen-derived superoxide and hydroxyl radicals are less toxic to gastric tissue cells than hydrogenperoxide; and intracellular glutathione, which detoxifies hydrogen peroxy, may be involved in antioxidant defense mechanisms.
Abstract: Reactive oxygen metabolites have been reported to be responsible for the pathogenesis of ischemia-induced gastric mucosal lesion. The authors have investigated the possible protective effect of specific enzymes and oxygen radical scavenging agents on oxygen metabolite-induced injury to cultured gastric mucosal cells. Oxygen-reactive metabolites were generated by 1 mM xanthine and 10-100 mU/ml xanthine oxidase. Cytotoxicity was quantified by measuring /sup 51/Cr release from prelabeled cells. Xanthine oxidase caused a dose-dependent increase of /sup 51/Cr release in the presence of 1 mM xanthine. Catalase diminished xanthine-xanthine oxidase-induced /sup 51/Cr release in a dose-dependent manner. Superoxide dismutase failed to affect the amounts of /sup 51/Cr release induced by xanthine plus xanthine oxidase. Pretreatment with diethyl maleate potentiated oxygen radical-mediated /sup 51/Cr release dose dependently. The presence of ferrous ion or ethylenediaminetetraacetic acid-chelated iron did not alter xanthine-xanthine oxidase-induced cellular injury. They conclude that in vitro (1) oxygen metabolites, extracellularly generated, have a direct toxic effect on gastric mucosal cells; (2) hydrogen peroxide is a major mediator of oxygen metabolite-induced gastric cell injury; (3) the oxygen-derived superoxide and hydroxyl radicals are less toxic to gastric mucosal cells than hydrogen peroxide; and (4) intracellular glutathione, which detoxifies hydrogen peroxide, may be involved inmore » antioxidant defense mechanisms.« less
TL;DR: In this paper, the nanomolar levels of the purines, guanine, hypoxanthine, xanthine and adenine in aqueous solution can be determined by cathodic stripping voltammetry (CSV).
TL;DR: There is species dependency in the myocardial activity of xanthine oxidase or dehydrogenase, that when present it can be inhibited by acute allopurinol pretreatment, and that xanthin oxidase activity and its ability to generate oxygen radicals are not universal contributors to cardiac ischemic damage.
Abstract: Allopurinol is thought to protect hearts against damage due to hypoxia or ischemia by inhibiting xanthine oxidase and oxygen radical generation. We subjected isolated rabbit hearts, equilibrated by perfusion at 37 degrees C, to 1 h of global ischemia at 27 or 37 degrees C with or without brief pretreatment with 100 microM allopurinol. The total absence of xanthine or uric acid in the coronary effluent following ischemia, the presence of hypoxanthine (25 +/- 4 microM peak concentration), and the failure of allopurinol to alter purine washout profiles or postischemic cardiac function suggest that rabbit myocardium lacks xanthine oxidase or dehydrogenase. Data obtained with a similar rat heart preparation showed appreciable formation of xanthine (12 +/- 2 microM peak) and uric acid (10 +/- 3 microM). Allopurinol pretreatment inhibited xanthine and uric acid formation and significantly improved key indicators of postischemic left ventricular function. We conclude that there is species dependency in the myocardial activity of xanthine oxidase or dehydrogenase, that when present it can be inhibited by acute allopurinol pretreatment, and that xanthine oxidase activity and its ability to generate oxygen radicals are not universal contributors to cardiac ischemic damage.
TL;DR: Observations are consistent with a reduction in membrane potential effected by exposure to oxygen radicals (including superoxide anion and hydrogen peroxide) and may be prevented, in part, by radical scavenging enzymes and by reducing the degree of cellular swelling in response to oxygen radical exposure.
TL;DR: A high-performance liquid chromatographic method that makes it possible to separate theophylline and its metabolites from other uric acid or xanthine derivatives, especially 1,7-dimethylxanthine, a metabolite of caffeine.
01 Jan 1987
TL;DR: A series of para-substituted N6-phenyladenosines have been synthesized, on the basis of a “functionalized congener” approach in which a chemically reactive group is introduced at the terminus of a chain.
Abstract: Adenosine modulates a variety of physiological functions through interaction with A1 and A2 adenosine receptors, where agonists can mediate inhibition and stimulation, respectively, of adenylate cyclase. Adenosine analogues, in particular the N6-substituted compounds, are more potent at A1 receptors than at A2 receptors. The subregion of the adenosine receptor that interacts with the N6-substituent is different for A1 and A2 receptors, particularly with respect to phenyl interactions, bulk tolerance, and stereoselectivity. A series of para-substituted N6-phenyladenosines have been synthesized, on the basis of a “functionalized congener” approach in which a chemically reactive group, such as an amine or carboxylic acid, is introduced at the terminus of a chain. From the functionalized congener are synthesized a variety of conjugates, each containing a common pharmacophore. Certain of the adenosine conjugates are highly selective for A1 receptors. Xanthines are classic antagonists for adenosine receptors, and many of their pharmacological actions may be due to blockade of adenosine receptors. Caffeine and theophylline are virtually nonselective for A1 and A2 receptors. Replacement of the methyl groups of theophylline with n-propyl or larger alkyl groups yields xanthines with selectivity for A1 receptors, particularly when combined with an 8-phenyl moiety. Most 1,3-dialky1-8-phenyl-xanthines are highly water-insoluble, but incorporation of polar aryl substituents, such as parasulfo or para-carboxy, to increase solubility results in a marked reduction in potency and selectivity. A new series of more hydrophilic 1,3-dipropy1-8-phenylxanthines has been synthesized using the functionalized congener approach. Certain conjugates of 8-[4-(carboxymethyloxy)phenyl]-1,3-dipropylxanthine display A1 selectivity in biochemical and cardiovascular models and in radioactive form provide an antagonist ligand for both A1 and A2 receptors. Certain analogues of caffeine in which the methyl group at the 1- or 7-position is replaced with a propargyl or propyl group display selectivity for A2 receptors. The profile of a series of adenosine analogues or of xanthine antagonists can be used to define the class of adenosine receptors.
TL;DR: The effects of singlet oxygen- and oxygen radical-induced lipid peroxidation on cell membrane integrity were compared, using the human erythrocyte ghost as a model system, indicating O2−/H2O2 intermediacy and a free radical mechanism.
Abstract: The effects of singlet oxygen- and oxygen radical-induced lipid peroxidation on cell membrane integrity were compared, using the human erythrocyte ghost as a model system. Resealed ghosts underwent lipid peroxidation and lysis (release of trapped glucose-6-P) when irradiated in the presence of uroporphyrin (UP) or when incubated with xanthine (X), xanthine oxidase (XO) and iron. The UP-sensitized process was inhibited by azide but not by phenolic antioxidants, consistent with singlet oxygen (nonradical) involvement. This was confirmed by showing that the predominant photoproduct of membrane cholesterol was the 5α-hydroperoxide. Total hydroperoxide (LOOH) content in UP-photooxidized ghosts increased linearly during the prelytic lag and throughout the period of rapid lysis. Unlike the photoreaction, X/XO/iron-dependent peroxidation and lysis was inhibited by catalase, superoxide dismutase and phenolic antioxidants, indicating O2
−/H2O2 intermediacy and a free radical mechanism. Correspondingly, only radical reactions products of cholesterol were formed, notably the 7α-, 7β-hydroperoxide pair. Membranes lysis had a distinct lag as in photooxidation; however, the LOOH profile was more complex, with an initial lag followed by a sharp increase and then slow decline. X/XO/iron-induced lysis commenced when LOOH levels were 2–3 times higher than in photosensitized lysis, suggesting that the pathways of membrane lesion formation are different in the two systems. In low concentrations, ascorbate exacerbated the damaging effects of photoperoxidation, switching the reaction from primarily singled oxygen- to oxygen radical-dependence, as indicated by cholesterol product analysis.
TL;DR: Peroxisomes in the rosy-506 mutants show less intense cytochemical staining for catalase than those in wild-type flies, and biochemical assays indicate thatCatalase in therosy mutant is much more accessible to substrate in the absence of detergent than in the wild type.
Abstract: This study shows that peroxisomes are abundant in the Malpighian tubule and gut of wild-type Oregon R Drosophila melanogaster and that the peroxisomal population of the rosy-506 eye-color mutant differs from that of the wild type. Catalase activity in wild-type flies is demonstrable in bodies of appearance and centrifugal behavior comparable to the peroxisomes of vertebrate tissues. Xanthine oxidase (xanthine:oxygen oxidoreductase, EC 1.1.3.22) activity of the Malpighian tubule of wild-type flies is demonstrable cytochemically in bodies like those containing catalase. The rosy-506 mutant flies, with a deletion in the structural gene for xanthine dehydrogenase (xanthine:NAD+ oxidoreductase, EC 1.1.1.204), lack cytochemically demonstrable peroxisomal xanthine oxidase activity. In addition, peroxisomes in the rosy-506 mutants show less intense cytochemical staining for catalase than those in wild-type flies, and biochemical assays indicate that catalase in the rosy mutant is much more accessible to substrate in the absence of detergent than in the wild type. Thus, the rosy-506 mutation appears to affect peroxisomes and may mimic aspects of the defects of peroxisomes in some human metabolic disorders.
TL;DR: A fully automatic method for analysis of adenosine, inosine, and hypoxanthine/xanthine which combines the specificity of enzymatic catalysis and sensitivity of chemiluminescence is presented.
TL;DR: Activation of ureagenesis by both nucleosides had the following characteristics: it was observed with either glutamine or (NH4)2CO3, provided that glucose was present, and it was dependent on Ca2+.
Abstract: Adenosine and inosine produced a dose-dependent stimulation of ureagenesis in isolated rat hepatocytes. Hypoxanthine, xanthine and uric acid were without effect. Half-maximally effective concentrations were 0.08 microM for adenosine and 5 microM for inosine. Activation of ureagenesis by both nucleosides had the following characteristics: (a) it was observed with either glutamine or (NH4)2CO3, provided that glucose was present; (b) it was not detected when glucose was replaced by lactate plus oleate; (c) it was mutually antagonized by glucagon, but not by adrenaline; and (d) it was dependent on Ca2+. We suggest that the action of adenosine and inosine on ureagenesis might be of physiological significance.
TL;DR: Cultured rat mesangial cells were exposed to a reactive oxygen species (ROS) generating system (xanthine plus xanthine oxidase) to explore the effect of ROS on their metabolism of arachidonic acid (AA), which suggested that H2O2 was the responsible metabolite.
Abstract: Cultured rat mesangial cells were exposed to a reactive oxygen species (ROS) generating system (xanthine plus xanthine oxidase) to explore the effect of ROS on their metabolism of arachidonic acid (AA). Cell viability, as assessed by 51Cr release, was not affected by the concentrations of xanthine plus xanthine oxidase used. Prostaglandin E2 (PGE2) production following exposure to increasing quantities of xanthine plus xanthine oxidase was significantly decreased to 38.1 +/- 9.7 or 30.8 +/- 6.9% of control levels (P less than 0.05) when cells were stimulated with the calcium ionophore A23187 (1 microgram/ml) or AA (10(-6) M), respectively. Maximum suppression of production was seen within 10 min of ROS exposure. Thromboxane B2 production was similarly decreased to 83.1 +/- 7.6 (0.05 less than P less than 0.10) or 54.9 +/- 2.5% (P less than 0.05). This effect was reversed by addition of catalase to the ROS generating system but not by superoxide dismutase or mannitol, which suggested that H2O2 was the responsible metabolite. High levels of H2O2 (5 x 10(-4) M) suppressed PGE2 production to 44.0 +/- 4.1 or 17.4 +/- 6.2% of A23187- or AA-stimulated production (P less than 0.05). Lower levels of H2O2 resulted in significant stimulation of base-line PGE2 production. Analysis of release of [3H]AA-labeled metabolites from A23187-stimulated cells showed no effect of H2O2 on phospholipase activity. Thus ROS can stimulate or inhibit AA metabolism in the glomerular mesangium, which may have important effects on glomerular hemodynamics during glomerular injury.