Showing papers on "Xanthine published in 2002"

The physiology of endothelial xanthine oxidase: from urate catabolism to reperfusion injury to inflammatory signal transduction.

Abstract: Xanthine oxidoreductase (XOR) is a ubiquitous metalloflavoprotein that appears in two interconvertible yet functionally distinct forms: xanthine dehydrogenase (XD), which is constitutively expressed in vivo; and xanthine oxidase (XO), which is generated by the posttranslational modification of XD, either through the reversible, incremental thiol oxidation of sulfhydryl residues on XD or the irreversible proteolytic cleavage of a segment of XD, which occurs at low oxygen tension and in the presence of several proinflammatory mediators. Functionally, both XD and XO catalyze the oxidation of purines to urate. However, whereas XD requires NAD+as an electron acceptor for these redox reactions, thereby generating the stable product NADH, XO is unable to use NAD+as an electron acceptor, requiring instead the reduction of molecular oxygen for this purine oxidation and generating the highly reactive superoxide free radical. Nearly 100 years of study has documented the physiologic role of XD in urate catabolism. Ho...

Anodic Voltammetry of Xanthine, Theophylline, Theobromine and Caffeine at Conductive Diamond Electrodes and Its Analytical Application

Abstract: Boron-doped diamond (BDD) electrodes were used to examine the electrochemical oxidation of xanthine and its naturally occurring N-methyl derivatives, theophylline, theobromine and caffeine. Voltammetric studies showed that the mechanism of the overall reaction is similar to that of the oxidation of purine derivatives at the pyrolytic graphite electrode. The effects of pH, concentration and potential sweep rate on the voltammetric response were thoroughly investigated, and it was found that BDD exhibits excellent behavior, in terms of very well-defined, reproducible oxidation peaks, for xanthine, theophylline, theobromine and caffeine determination. The results enabled the measurement of the oxidation peak current to be used as the basis for a simple, accurate and rapid method for determining the investigated compounds, within a concentration range of 1 to 400 μM for theophylline, theobromine and caffeine, and of 1 to 100 μM for xanthine. Promising results were obtained for caffeine determination in real samples of commercially available products, without separation from the matrix.

Antioxidant activity of Hypericum androsaemum infusion: scavenging activity against superoxide radical, hydroxyl radical and hypochlorous acid.

Abstract: Hypericum androsaemum is a medicinal plant species containing many polyphenolic compounds, namely flavonoids and phenolic acids. Since polyphenolic compounds have high antioxidant potential, the ability of H. androsaemum infusion to act as a scavenger of reactive oxygen species (superoxide radical, hydroxyl radical and hypochlorous acid) was investigated. Superoxide radical was generated by the xanthine/xanthine oxidase and phenazine methosulphate/NADH systems. The infusion-mediated prevention of nitroblue tetrazolium reduction by the superoxide radical was used as the measured endpoint. Hydroxyl radical was generated by the Fe3+-EDTA/ascorbate Fenton system, and assayed by evaluating deoxyribose degradation using the thiobarbituric acid method. Hypochlorous acid scavenging activity was tested by measuring the inhibition of hypochlorous acid-induced 5-thio-2-nitrobenzoic acid oxidation to 5,5′-dithiobis(2-nitrobenzoic acid). The tested infusion mainly exhibited a potent scavenging effect on superoxide radicals (although a noncompetitive inhibitory effect on xanthine oxidase was also observed). The infusion also acted as a moderate scavenger of hydroxyl radicals and hypochlorous acid. A phytochemical study of the infusion was also undertaken, and nine phenolic compounds were identified.

1,8-disubstituted xanthine derivatives: synthesis of potent A2B-selective adenosine receptor antagonists.

Abstract: 3-Unsubstituted xanthine derivatives bearing a cyclopentyl or a phenyl residue in the 8-position were synthesized and developed as A2B adenosine receptor antagonists. Compounds bearing polar substituents were prepared to obtain water-soluble derivatives. 1-Alkyl-8-phenylxanthine derivatives were found to exhibit high affinity for A2B adenosine receptors (ARs). 1,8-disubstituted xanthine derivatives were equipotent to or more potent than 1,3,8-trisubstituted xanthines at A2B ARs, but generally less potent at A1 and A2A, and much less potent at A3 ARs. Thus, the new compounds exhibited increased A2B selectivity versus all other AR subtypes. 9-Deazaxanthines (pyrrolo[2,3-d]pyrimidindiones) appeared to be less potent at A2B ARs than the corresponding xanthine derivatives. 1-Propyl-8-p-sulfophenylxanthine (17) was the most selective compound of the present series, exhibiting a K(i) value of 53 nM at human A2B ARs and showing greater than 180-fold selectivity versus human A1 ARs. Compound 17 was also highly selective versus rat A1 ARs (41-fold) and versus the other human AR subtypes (A2A > 400-fold and A3 > 180-fold). The compound is highly water-soluble due to its sulfonate function. 1-Butyl-8-p-carboxyphenylxanthine (10), another polar analogue bearing a carboxylate function, exhibited a K(i) value of 24 nM for A2B ARs, 49-fold selectivity versus human and 20-fold selectivity versus rat A1 ARs, and greater than 150-fold selectivity versus human A2A and A3 ARs. 8-[4-(2-Hydroxyethylamino)-2-oxoethoxy)phenyl]-1-propylxanthine (29) and 1-butyl-8-[4-(4-benzyl)piperazino-2-oxoethoxy)phenyl]xanthine (35) were among the most potent A2B antagonists showing K(i) values at A2B ARs of 1 nM, 57-fold (29) and 94-fold (35) selectivity versus human A1, ca. 30-fold selectivity versus rat A1, and greater than 400-fold selectivity versus human A2A and A3 ARs. The new potent, selective, water-soluble A2B antagonists may be useful research tools for investigating A2B receptor function.

Apolipoprotein A-I(Milano) and apolipoprotein A-I(Paris) exhibit an antioxidant activity distinct from that of wild-type apolipoprotein A-I.

Abstract: Apolipoprotein A-IMilano (apoA-IMilano) and apoA-IParis are rare cysteine variants of apoA-I that produce a HDL deficiency in the absence of cardiovascular disease in humans. This paradox provides the basis for the hypothesis that the cysteine variants possess a beneficial activity not associated with wild-type apoA-I (apoA-IWT). In this study, a unique antioxidant activity of apoA-IMilano and apoA-IParis is described. ApoA-IMilano was twice as effective as apoA-IParis in preventing lipoxygenase-mediated oxidation of phospholipids, whereas apoA-IWT was poorly active. Antioxidant activity was observed using the monomeric form of the variants and was equally effective before and after initiation of oxidative events. ApoA-IMilano protected phospholipid from reactive oxygen species (ROS) generated via xanthine/xanthine oxidase (X/Xo) but failed to inhibit X/Xo-induced reduction of cytochrome c. These results indicate that apoA-IMilano was unable to directly quench ROS in the aqueous phase. There were no diffe...

Antioxidant Activity of Wheat Sprouts Extract In Vitro: Inhibition of DNA Oxidative Damage

Abstract: Wheat sprouts contain a remarkable level of various antioxidants. A fraction containing high amounts of powerful antioxidant glycoside molecules has been isolated. In a dose-dependent manner, this fraction reduces the lucigenin-amplified chemiluminescence produced by the superoxide anion generated from the xanthine/xanthine oxidase system, thus indicating a superoxide-scavenging activity. A protective effect of this wheat sprouts fraction on the oxidative damage of pBR322 plasmid DNA induced by Fenton reaction (Fe2+/H2O2) was subsequently demonstrated. Moreover, the results reported here show that the amount of antioxidant compound strongly increases during the germination phase, while scantly present in the wheat germ, and virtually absent in the young wheat plant.

Ischemic preconditioning: a defense mechanism against the reactive oxygen species generated after hepatic ischemia reperfusion.

Abstract: Background. Preconditioning protects against both liver and lung damage after hepatic ischemia-reperfusion (I/R). Xanthine and xanthine oxidase (XOD) may contribute to the development of hepatic I/R. Objective. To evaluate whether preconditioning could modulate the injurious effects of xanthine/XOD on the liver and lung after hepatic I/R. Methods. Hepatic I/R or preconditioning previous to I/R was induced in rats. Xanthine and xanthine dehydrogenase/xanthine oxidase (XDH/XOD) in liver and plasma were measured. Hepatic injury and inflammatory response in the lung was evaluated. Results. Preconditioning reduced xanthine accumulation and conversion of XDH to XOD in liver during sustained ischemia. This could reduce the generation of reactive oxygen species (ROS) from XOD, and therefore, attenuate hepatic I/R injury. Inhibition of XOD prevented postischemic ROS generation and hepatic injury. Administration of xanthine and XOD to preconditioned rats led to hepatic MDA and transaminase levels similar to those found after hepatic I/R. Preconditioning, resulting in low circulating levels of xanthine and XOD activity, reduced neutrophil accumulation, oxidative stress, and microvascular disorders seen in lung after hepatic I/R. Inhibition of XOD attenuated the inflammatory damage in lung after hepatic I/R. Administration of xanthine and XOD abolished the benefits of preconditioning on lung damage. Conclusions. Preconditioning, by blocking the xanthine/XOD pathway for ROS generation, would confer protection against the liver and lung injuries induced by hepatic I/R.

Multianalyte sensor for the simultaneous determination of hypoxanthine, xanthine and uric acid based on a preanodized nontronite-coated screen-printed electrode

Abstract: Simultaneous determinations of purine bases of hypoxanthine (Hx), xanthine (X), and uric acid (UA) were demonstrated on preanodized nontronite-coated screen-printed carbon electrodes (NSPEs∗). Good enhancement in the electrochemical sensitivity was noticed upon preanodization at 2.0 V versus Ag/AgCl. The measured interaction parameter “r” reveals a strong attractive force of the purine bases to the NSPE∗. Cyclic voltammetric studies show different charge transfer behavior among the purine bases on the NSPE∗. The experimental parameters were systematically optimized for each analyte of Hx, X, and UA. The calibration curves were all linear in the range of 4–30, 2–40, and 2–40 μM with detection limits (S/N=3) of 0.34, 0.07, and 0.42 μM for Hx, X, and UA, respectively. The analytical performance of the NSPE∗ was demonstrated for the simultaneous determination of Hx, X, and UA in blood plasma and urine samples. The estimation of the fish freshness by monitoring the Hx content was also established with very good reproducibility.

The Effect of Caffeine on Renal Epithelial Cells from Patients with Autosomal Dominant Polycystic Kidney Disease

Abstract: Autosomal dominant polycystic kidney disease (ADPKD) is a hereditary disorder characterized by the progressive enlargement of cysts derived from tubules. Tubule cell proliferation and chloride-dependent fluid accumulation, mechanisms underlying cyst expansion, are accelerated by adenosine 3':5'-cyclic monophosphate (cAMP). This study examined the extent to which caffeine may stimulate the production of cAMP by cyst epithelial cells, thereby adversely increasing proliferation and fluid secretion. Mural epithelial cells from ADPKD cysts and normal human kidney cortex cells (HKC) were cultured, and cAMP levels were determined in response to caffeine and receptor-mediated agonists linked to adenylyl cyclase. Caffeine, a methylxanthine, slightly increased basal levels of cAMP, as did other nonselective phosphodiesterase (PDE) inhibitors, 1-methyl-3- isobutyl xanthine and theophylline and rolipram, a specific PDE IV inhibitor. More importantly, clinically relevant concentrations of caffeine (10 to 50 micro M) potentiated the effects of desmopressin (DDAVP), prostaglandin E(2) (PGE(2)), and isoproterenol to increase cAMP levels in both ADPKD and HKC cells. By contrast, at concentrations that augmented the DDAVP response, caffeine attenuated cAMP accumulation by adenosine, implicating an action apart from the inhibition of PDE. Caffeine enhanced the effect of DDAVP to stimulate transepithelial short-circuit current of polarized ADPKD monolayers, reflecting an increase in chloride secretion. Caffeine potentiated the effect of DDAVP and PGE(2) to increase the levels of phosphorylated extracellular signal-regulated kinase (P-ERK). By contrast, P-ERK levels in HKC cells were not raised by increased intracellular concentrations of cAMP. It is concluded that PDE inhibition by caffeine increases the accumulation of cAMP, and through this mechanism activates the ERK pathway to cellular proliferation and increases transepithelial fluid secretion in ADPKD cystic epithelium. Caffeine is, therefore, a risk factor for the promotion of cyst enlargement in patients with ADPKD.

Prevention of cellular ROS damage by isovitexin and related flavonoids.

Abstract: The antioxidant properties of isovitexin and related flavonoids were studied. Isovitexin inhibited xanthine oxidase with an IC50 value of = 15.2 microM. The flavonoid analogues, apigenin, kaempferol, quercetin, myricetin, and genistein also inhibited xanthine oxidase with IC50 values of 0.58, 2.18, 1.09, 9.90, and 4.83 microM, respectively. Isovitexin protected DNA from the Fenton reaction-induced breakage in a dose-dependent manner with an IC50 value of 9.52 microM. Isovitexin also protected HL-60 cells from the ROS damage induced by the xanthine/xanthine oxidase reaction. Isovitexin exhibited the lowest cytotoxicity toward HL-60 cells (LD50 >400 microM) compared to the other flavonoids examined. In addition, excess hydrogen peroxide induced by cadmium in A2780 ovarian cells was significantly suppressed by isovitexin. These results suggest that isovitexin in rice may protect cells from oxidative stress.

Inosine Mediates the Protective Effect of Adenosine in Rat Astrocyte Cultures Subjected to Combined Glucose-Oxygen Deprivation

Abstract: Preliminary evidence suggests adenosine, a neuromodulator, has neuroprotective properties during cerebral ischemia. It is unclear, however, if adenosine has glioprotective effects. We studied the effect of adenosine on cellular injury in astroglial cultures subjected to combined glucose-oxygen deprivation. Adenosine (100-1,000 microM)dramatically reduced astroglial injury, whereas the adenosine agonists 2-chloroadenosine (10 nM-100 microM), N6-cyclopentyladenosine (1 nM-10 microM), 5'-N-ethylcarboxamidoadenosine (10 nM-100 microM), and N6-2-(4-aminophenyl)ethyladenosine (10 nM-100 microM) had no effect. Furthermore, the adenosine antagonists 8-cyclopentyl-1,3-dipropylxanthine (1 nM-1 microM), xanthine amine congener (10 nM-10 microM), and 8-(p-sulfophenyl)-theophylline (10-300 microM) failed to reverse the protective effect of 200 microM adenosine. Next, adenosine degradation products were studied. Inosine proved to be glioprotective at concentrations nearly identical to those of adenosine, but hypoxanthine and ribose had no effect. The protective effect of 200 microM inosine was not reversed by 8-(p-sulfophenyl)theophylline (10-300 microM). Adenosine deaminase (1 unit/ml) had no effect on protection produced by adenosine, whereas erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride (10 microM) reversed the protective effect of adenosine. Dipyridamole (4 microM) inhibited the protective effect of both adenosine and inosine. We conclude that adenosine dramatically decreases astroglial injury during combined glucose-oxygen deprivation and that this protective effect appears to be mediated by inosine.

Enhanced neuronal damage by co-administration of quinolinic acid and free radicals, and protection by adenosine A2A receptor antagonists.

Abstract: 1. Quinolinic acid may be an important endogenous excitotoxin, but its concentrations in brain are low. We have therefore attempted to determine whether its neurotoxicity can be increased by the simultaneous presence of free radicals. 2. Quinolinic acid was injected into the hippocampus of anaesthetized rats at doses of 40 and 80 nmols which produced little neuronal loss, and 120 nmols which produced over 90% neuronal loss. 3. A mixture of xanthine and xanthine oxidase, a known source of free radical reactive oxygen species, also generated little damage alone, but killed over 80% of CA1 neurons when combined with 80 nmols of quinolinic acid. Similarly, the nitric oxide donor S-nitroso-N-acetylpenicillamine (SNAP) potentiated the damage produced by quinolinic acid. 4. The glutamate antagonist 5,7-dichlorokynurenic acid prevented the damage produced by 120 nmols of quinolinic acid, but not that produced by quinolinic acid plus xanthine/xanthine oxidase, indicating that damage was not simply the result of free radical enhancement of NMDA receptor activation. 5. Three chemically dissimilar antagonists at adenosine A(2A) receptors prevented the damage caused by quinolinic acid and xanthine/xanthine oxidase or by quinolinic acid plus SNAP. 6. It is concluded that reactive oxygen species can potentiate the neurotoxicity of quinolinic acid. The site of interaction is probably distal to the NMDA receptor. Blockade of adenosine A(2A) receptors can protect against this combined damage, suggesting potential value in the prevention of brain damage.

Bi-enzymatic and capillary electrophoretic analysis of non-fluorescent compounds in microfluidic devices. Determination of xanthine

Abstract: This report describes general investigations for xanthine determination in microfluidic devices. Xanthine is chosen as a model analyte for the detection of compounds via bi-enzymatic systems on one hand, and via capillary electrophoresis (CE) of non-fluorescent analytes on the other. The bi-enzyme system comprises xanthine oxidase (XOD) and horseradish peroxidase (HRP) with XOD giving the specificity for the analyte and HRP allowing chemiluminescent (CL) detection. Studies include the use of enzyme solutions, as well as enzyme coated beads pumped continuously through the device or trapped in a 330 pL cavity. In a second approach, indirect laser-induced fluorescence (LIF) is used as a detection method for microchip-based CE separations. Although the detection methods are not optimised, this report demonstrates general new possibilities for a fast determination of such compounds, in particular xanthine, in microfluidic devices.

Determination of trace xanthine by anodic stripping voltammetry with carbon nanotube modified glassy carbon electrode

Abstract: The electrochemistry of xanthine (Xa) was studied by CV at a glassy carbon electrode modified with carbon nanotubes. A well defined, sensitive oxidation wave of xanthine and a small reduction wave were obtained. Based on the oxidation peak, a method for determination of xanthine with semi-derivative anodic stripping voltammetry at a glassy carbon electrode modified with carbon nanotubes was investigated. The stripping peak current is proportional to the concentration of Xa over the range 2.0 × 10−7–2.0 × 10−5 M with 1-min accumulation. The detection limit is 4.0 × 10−9 mol/L with 3-min accumulation. The method has been successfully applied to the determination of xanthine in human serum.

Pyrido[2,1-f]purine-2,4-dione derivatives as a novel class of highly potent human A(3) adenosine receptor antagonists.

Abstract: 1H,3H-Pyrido[2,1-f]purine-2,4-diones, which can be described as fused xanthine structures, have been synthesized by a novel synthetic procedure, and their affinities for the human adenosine A1, A2A...

Direct simultaneous determination of uremic toxins: creatine, creatinine, uric acid, and xanthine in human biofluids by hplc

Abstract: The determination of creatine, creatinine, uric acid, and xanthine in urine and blood serum is very important in clinical assays as they are most widely used as markers to assess renal function. A simple and direct method for the routine analysis of uremic toxins: creatine, creatinine, uric acid, and xanthine in human blood serum and urine is described. Low wavelength UV detection is achieved at 200 nm using 10 mmol/L KH2PO4, as mobile phase, at a flow rate 0.8 mL/min and a Kromasil C8, 250 × 4 mm, analytical column. Analysis was achieved within approximately 8 min. The limits of detection were 4 pg for creatine and creatinine, 20 pg for uric acid, and 6 pg for xanthine, while the limits of quantitation were 10 pg for creatine and creatinine, 60 pg for uric acid, and 20 pg for xanthine, when 20 μL were injected onto column. A rectilinear relationship was observed up to 2 ng/μL for creatine and creatinine, 12 ng/μL for uric acid, and 5 ng/μL for xanthine. The statistical evaluation of the method was examin...

Effect of beer on the plasma concentrations of uridine and purine bases.

Abstract: We conducted the present study to determine whether beer, both with and without ethanol content, increases the plasma concentration and urinary excretion of purine bases and uridine. Because 10 mL of regular beer (with ethanol) was found to contain 0.34 g of freeze-dried beer (without ethanol) and 0.5 mg of uridine, 5 healthy males were given regular beer (10 mL/kg of body weight) and freeze-dried beer (0.34 g/kg of body weight) or uridine (0.5 mg/kg of body weight). The plasma concentrations of hypoxanthine, xanthine, and uridine increased by 3.5-fold (P <.05), 4.7-fold (P <.05), and 1.8-fold (P <.05), respectively, 30 minutes after regular beer ingestion, and the urinary excretion of hypoxanthine, xanthine, and uridine increased by 4.0-fold (P <.05), 4.5-fold (P <.01), and 1.7-fold (P <.05), respectively, when measured 1 hour after ingestion. The plasma concentrations of uric acid and total purine bases increased by 6.5% (P <.05) and 7.6% (P <.05), respectively, 30 minutes after regular beer ingestion, whereas the urinary excretion of uric acid did not increase, while that of total purine bases increased by 1.3-fold (P <.05) when measured 1 hour after ingestion. As for freeze-dried beer, the plasma concentrations of uric acid total purine bases increased by 4.4% (P <.05) and 4.6% (P <.05), respectively, and that of uridine by 1.5-fold (P <.01) 30 minutes after ingestion, while the urinary excretion of uridine increased by 1.4-fold (P <.01) 1 hour after ingestion. However, the plasma concentrations and urinary excretion of hypoxanthine and xanthine and the urinary excretion of uric acid and total purine bases did not change significantly. As for uridine ingestion, the plasma concentration of uridine increased by 1.37-fold (P <.01) 30 minutes after ingestion, and the urinary excretion of uridine increased by 1.3-fold (P <.01) 1 hour after ingestion. However, the plasma concentrations and urinary excretion of hypoxanthine, xanthine, uric acid, and total purine bases did not change significantly. These results suggest that the purines in beer played a major role in the increase in the plasma concentration of uric acid, while both uridine and ethanol in beer had a significant effect on the increase in plasma concentration of uridine.

2-styrylchromones as novel inhibitors of xanthine oxidase. A structure-activity study.

Abstract: The purpose of this study was the evaluation of the xanthine oxidase (XO) inhibition produced by some synthetic 2-styrylchromones. Ten polyhydroxylated derivatives with several substitution patterns were synthesised, and these and a positive control, allopurinol, were tested for their effects on XO activity by measuring the formation of uric acid from xanthine. The synthesised 2-styrylchromones inhibited xanthine oxidase in a concentration-dependent and non-competitive manner. Some IC 50 values found were as low as 0.55 μM, which, by comparison with the IC 50 found for allopurinol (5.43 μM), indicates promising new inhibitors. Those 2-styrylchromones found to be potent XO inhibitors should be further evaluated as potential agents for the treatment of pathologies related to the enzyme's activity, as is the case of gout, ischaemia/reperfusion damage, hypertension, hepatitis and cancer.

Oxo, sulfido, and tellurido Mo-enedithiolate models for xanthine oxidase: understanding the basis of enzyme reactivity.

Abstract: The active site of the mononuclear molybdenum enzyme xanthine oxidase has an LMoOS(OH) center that catalyzes the hydroxylation of substrate (L representing an enedithiolate ligand contributed by a pterin cofactor in the enzyme). Reaction of the enzyme with cyanide results in the replacement of the Mo=S group with a second Mo=O group, which results in loss of enzyme activity. To understand the basis for this loss of activity, we have computationally examined the interaction of a model for the LMoO2(OH) as well the LMoOTe(OH) congener of the enzyme with formamide (a substrate for the enzyme). Our electronic structure calculations for the oxo congener indicate a reduced electron density on the hydrogen being transferred from substrate in the course of the reaction, a shorter O-H bond in the transition state, and a longer nascent O-C bond of product, factors which combine to account for the loss of reactivity in the LMoO2(OH) species. Interestingly, our calculations indicate that the Te congener is characterized by an increased electron density on the hydrogen species being transferred, a longer Te-H bond in the transition state, and a shorter O-C nascent bond in the product and suggest that a Te congener of xanthine oxidase, were it to be prepared experimentally, should exhibit catalytic activity.

Superoxide anion impairs contractility in cultured aortic smooth muscle cells

Abstract: We examined the effects of superoxide anion (O 2 − ) generated by xanthine plus xanthine oxidase (X/XO) on the intracellular Ca2+ concentration ([Ca2+]i) and muscle contractility in cultured bovine...