Showing papers on "Xanthine published in 2013"
TL;DR: It was found that luteolin reversibly inhibited XO in a competitive manner with inhibition constant (Ki) value of (2.38±0.05)×10(-6) mol l(-1).
131 citations
TL;DR: The modified electrode successfully separates the voltammetric signals of the four purine derivatives in a mixture and hence used for the simultaneous determination of them and was demonstrated by simultaneously determining the concentrations of UA, XN, HXN and CAF in human blood plasma and urine samples.
124 citations
TL;DR: In this article, a poly l -methionine modified GC electrode was fabricated by electrochemical polymerization of the l-methionsine on a glassy carbon electrode, which exhibited excellent electrocatalytic activity toward the oxidation of uric acid, xanthine and hypoxanthine.
Abstract: A poly l -methionine modified GC electrode was fabricated by electrochemical polymerization of the l -methionine on a glassy carbon electrode. The electrochemical behaviors of uric acid, xanthine and hypoxanthine at the modified electrode were studied by cyclic voltammetry and differential pulse voltammetry. The results showed that this modified electrode exhibited excellent electrocatalytic activity toward the oxidation of the uric acid, xanthine and hypoxanthine. Also, electrode was used for simultaneous determination of uric acid, xanthine and hypoxanthine. This modified electrode possesses high sensitivity, and the detection limits as values 0.007, 0.004 and 0.008 μM for uric acid, xanthine and hypoxanthine, respectively. Finally, the poly l -methionine modified electrode was successfully employed to detect uric acid, xanthine and hypoxanthine in the serum samples with good selectivity and high sensitivity.
92 citations
TL;DR: It is suggested that uric acid decreased eNOS activity and NO production through reducing the binding between eN OS and CaM in EC and this result may provide molecular mechanism by which uric Acid induces endothelial dysfunction.
88 citations
TL;DR: In this paper, the ability of alternative aqueous biphasic systems (ABS) composed of polyethylene glycol and imidazolium-based ionic liquids (ILs) to selectively separate similar biomolecules was investigated.
85 citations
TL;DR: Although formation of NO from nitrite or formation of xanthine from urate by XOR is chemically feasible, it is not yet clear whether these reactions have any physiological significance since the reactions are catalyzed at a slow rate even under anaerobic conditions.
Abstract: Xanthine oxidoreductase (XOR), a complex flavoprotein, catalyzes the metabolic reactions leading from hypoxanthine to xanthine and from xanthine to urate, and both reactions take place at the molybdenum cofactor. The enzyme is a target of drugs for therapy of gout or hyperuricemia. We review the chemical nature and reaction mechanisms of the molybdenum cofactor of XOR, focusing on molybdenum-dependent reactions of actual or potential medical importance, including nitric oxide (NO) synthesis. It is now generally accepted that XOR transfers the water-exchangeable -OH ligand of the molybdenum atom to the substrate. The hydroxyl group at OH-Mo(IV) can be replaced by urate, oxipurinol and FYX-051 derivatives and the structures of these complexes have been determined by xray crystallography under anaerobic conditions. Although formation of NO from nitrite or formation of xanthine from urate by XOR ischemically feasible, it is not yet clear whether these reactions have any physiological significance since the reactions are catalyzed at a slow rate even under anaerobic conditions.
64 citations
TL;DR: Findings indicate that inhibition of cGMP-preferring PDE is involved in the locomotor activating effects of the acute administration of paraxanthine, which might contribute to the reinforcing effects of caffeine in humans.
59 citations
TL;DR: In this article, an amperometric xanthine biosensor based on covalent Immobilization of Xanthine oxidase (XOD) onto citrate capped silver nanoparticles deposited on Au electrode surface through cysteine self assembled monolayers (SAM) was described.
56 citations
TL;DR: The results support the contention that the distantly related transporters of COG2233 and COG2252 use topologically similar side chain determinants to dictate their function and the distinct purine selectivity profiles.
38 citations
TL;DR: Sol-gel droplets deposited onto a porous silicon chip are employed to entrap a purine metabolite, xanthine, which was found at lower levels in urine samples from patients with non-Hodgkin lymphoma, and specific aptamers with sensitivity of detection at as low as 1 μM were isolated.
Abstract: Sensitive detection of the metabolites indicative of a particular disease contributes to improved therapy outcomes. Developing binding reagents for detection of low molecular weight metabolites is hampered by the difficulty with immobilization of targets through appropriate covalent chemical linkage while ensuring that selected reagents retain specificity to unmodified metabolites. To circumvent chemical modification of targets, we employed sol-gel droplets deposited onto a porous silicon chip to entrap a purine metabolite, xanthine, which was found at lower levels in urine samples from patients with non-Hodgkin lymphoma. By sol-gel SELEX (systematic evolution of ligands by exponential enrichment) against xanthine, specific aptamers (KD ∼ 10 μM) with sensitivity of detection at as low as 1 μM were isolated, which bound to other purine metabolites at more than 100-fold lower affinity. In contrast, we failed to isolate xanthine-specific aptamers when SELEX was performed against xanthine covalently linked to...
35 citations
TL;DR: Molecular modeling investigations indicate that caffeine binds primarily in the catalytic site (Ser203, Glu334 and His447) region of hAChE whereas pentoxifylline and propentofylline are able to bind to both the catalysttic site and peripheral anionic site due to their increased bulk/size, thereby exhibiting superior AChE inhibition relative to caffeine.
TL;DR: It is demonstrated that the N7-demethylation reaction absolutely requires a unique, tightly bound protein complex composed of NdmC, NdmD, and NdmE, a novel glutathione-S-transferase (GST).
Abstract: Caffeine and other N -methylated xanthines are natural products found in many foods, beverages, and pharmaceuticals. Therefore, it is not surprising that bacteria have evolved to live on caffeine as sole carbon and nitrogen source. The caffeine degradation pathway of Pseudomonas putida CBB5 utilizes an unprecedented glutathione- S -transferase-dependent Rieske oxygenase for demethylation of 7-methylxanthine to xanthine, the final step in caffeine N -demethylation. The gene coding this function is unusual, in that the iron-sulfur and non-heme iron domains that compose the normally functional Rieske oxygenase (RO) are encoded by separate proteins. The non-heme iron domain is located in the monooxygenase, ndmC , while the Rieske [2Fe-2S] domain is fused to the RO reductase gene, ndmD . This fusion, however, does not interfere with the interaction of the reductase with N 1 and N 3 -demethylase RO oxygenases, involved in the initial reactions of caffeine degradation. We demonstrate that the N 7 -demethylation reaction absolutely requires a unique, tightly bound protein complex composed of NdmC, NdmD, and NdmE, a novel glutathione- S -transferase (GST). NdmE is proposed to function as a non-catalytic subunit that serves a structural role in the complexation of the oxygenase (NdmC) and Rieske domains (NdmD). Genome analyses found this gene organization of a split RO and GST gene cluster to occur more broadly, implying a larger function for RO-GST protein partners.
TL;DR: An improved HPLC method that is based on a method reported by Kaneko et al. and that is more sensitive yet simple, and suitable for determining the purine content of beer and beer-like alcoholic beverages is developed.
Abstract: Several methods for quantifying the purine content in food and drink have been described using high-performance liquid chromatography (HPLC). We have developed an improved HPLC method that is based on a method reported by Kaneko et al. and that is more sensitive yet simple, and suitable for determining the purine content of beer and beer-like alcoholic beverages. Quantitative HPLC separation was performed on a Shodex Asahi Pak GS-320HQ column with an isocratic elution of 150 mmol/L sodium phosphate buffer (H(3)PO(4)/NaH(2)PO(4) = 20:100 (v/v)). The retention times for the four analytes, namely, adenine, guanine, hypoxanthine and xanthine, were 19.9, 25.0, 29.3 and 43.0 min, respectively. The resolution was good, and there was no excessive interference from the other compounds in the beverages at these retention times. Furthermore, the detection limit for all the analytes was improved to less than 0.0075 mg/L, and all the calibration curves showed good linearity (r(2) > 0.999) between 0.013 and 10 mg/L for adenine and guanine, and between 0.025 and 10 mg/L for hypoxanthine and xanthine. The pretreatment was simplified by removing some procedures and optimizing the perchloric acid hydrolysis and the enzymatic peak-shift assay. We reduced the sample dilution rate by almost 50%, and the time spent on pretreatment from 4 days to only 180 min. The recovery of the analytes from spiked samples was 94.8 - 103.8%. This method may be useful for evaluating quantitative and qualitative differences in the purine content of beer and beer-like alcoholic beverages.
TL;DR: The in vitro, cell free metabolism of a pro-fluorescent substrate, 6-nitroquinoline, under both aerobic and hypoxic conditions provides evidence for multiple oxygen-sensitive steps in the enzymatic conversion of nitroaryl compounds to the corresponding amino derivatives.
Abstract: There is substantial interest in small molecules that can be used to detect or kill the hypoxic (low oxygen) cells found in solid tumors. Nitroaryl moieties are useful components in the design of hypoxia-selective imaging agents and prodrugs because one-electron reductases can convert the nitroaryl group to nitroso, hydroxylamino, and amino metabolites selectively under low oxygen conditions. Here, we describe the in vitro, cell free metabolism of a pro-fluorescent substrate, 6-nitroquinoline (1) under both aerobic and hypoxic conditions. Both LC-MS and fluorescence spectroscopic analyses provided evidence that the one-electron reducing enzyme system, xanthine/xanthine oxidase, converted the nonfluorescent parent compound 1 to the known fluorophore 6-aminoquinoline (2) selectively under hypoxic conditions. The presumed intermediate in this reduction process, 6-hydroxylaminoquinoline (6), is fluorescent and can be efficiently converted by xanthine/xanthine oxidase to 2 only under hypoxic conditions. This finding provides evidence for multiple oxygen-sensitive steps in the enzymatic conversion of nitroaryl compounds to the corresponding amino derivatives. In a side reaction that is separate from the bioreductive metabolism of 1, xanthine oxidase converted 1 to 6-nitroquinolin-2(1H)-one (5). These studies may enable the use of 1 as a fluorescent substrate for the detection and profiling of one-electron reductases in cell culture or biopsy samples. In addition, the compound may find use as a fluorogenic probe for the detection of hypoxia in tumor models. The occurrence of side products such as 5 in the enzymatic bioreduction of 1 underscores the importance of metabolite identification in the characterization of hypoxia-selective probes and drugs that employ nitroaryl units as oxygen sensors.
TL;DR: Adenoviral-mediated gene transfer of SOD3, but not SOD1, protects the aorta from xanthine/XO-mediated endothelial dysfunction, providing important insight into the location and enzymatic source of O2•− production in vascular disease.
Abstract: Superoxide (O2•−) contributes to the development of cardiovascular disease. Generation of O2•− occurs in both the intracellular and extracellular compartments. We hypothesized that the gene transfer of cytosolic superoxide dismutase (SOD1) or extracellular SOD (SOD3) to blood vessels would differentially protect against O2•−-mediated endothelial-dependent dysfunction. Aortic ring segments from New Zealand rabbits were incubated with adenovirus (Ad) containing the gene for Escherichia coli β-galactosidase, SOD1, or SOD3. Activity assays confirmed functional overexpression of both SOD3 and SOD1 isoforms in aorta 24 h following gene transfer. Histochemical staining for β-galactosidase showed gene transfer occurred in the endothelium and adventitia. Next, vessels were prepared for measurement of isometric tension in Kreb's buffer containing xanthine. After precontraction with phenylephrine, xanthine oxidase impaired relaxation to the endothelium-dependent dilator acetylcholine (ACh, max relaxation 33±4% with XO vs. 64±3% without XO, p<0.05), whereas relaxation to the endothelium-independent dilator sodium nitroprusside was unaffected. In the presence of XO, maximal relaxation to ACh was improved in vessels incubated with AdSOD3 (55±2%, p<0.05 vs. control) but not AdSOD1 (34±4%). We conclude that adenoviral-mediated gene transfer of SOD3, but not SOD1, protects the aorta from xanthine/XO-mediated endothelial dysfunction. These data provide important insight into the location and enzymatic source of O2•− production in vascular disease.
TL;DR: P perturbations in purine and neurotransmitter metabolism observed in early SZ are reviewed to suggest that purine catabolism strongly associates with the TRP pathways leading to serotonin and kynurenine metabolites, and the lack of a significant correlation between purine metabolites and 5-HIAA, suggests alterations in key 5-HT pathways.
Abstract: Schizophrenia (SZ) is a biochemically complex disorder characterized by widespread defects in multiple metabolic pathways whose dynamic interactions, until recently, have been difficult to examine. Rather, evidence for these alterations has been collected piecemeal, limiting the potential to inform our understanding of the interactions amongst relevant biochemical pathways. We herein review perturbations in purine and neurotransmitter metabolism observed in early SZ using a metabolomic approach. Purine catabolism is an underappreciated, but important component of the homeostatic response of mitochondria to oxidant stress. We have observed a homeostatic imbalance of purine catabolism in first-episode neuroleptic-naive patients with SZ (FENNS). Precursor and product relationships within purine pathways are tightly correlated. Although some of these correlations persist across disease or medication status, others appear to be lost among FENNS suggesting that steady formation of the antioxidant uric acid (UA) via purine catabolism is altered early in the course of illness. As is the case for within-pathway correlations, there are also significant cross-pathway correlations between respective purine and tryptophan (TRP) pathway metabolites. By contrast, purine metabolites show significant cross-pathway correlation only with tyrosine, and not with its metabolites. Furthermore, several purine metabolites (UA, guanosine, or xanthine) are each significantly correlated with 5-hydroxyindoleacetic acid (5-HIAA) in healthy controls, but not in FENNS at baseline or 4-week after antipsychotic treatment. Taken together, the above findings suggest that purine catabolism strongly associates with the TRP pathways leading to serotonin (5-hydroxytryptamine, 5-HT) and kynurenine metabolites. The lack of a significant correlation between purine metabolites and 5-HIAA, suggests alterations in key 5-HT pathways that may both be modified by and contribute to oxidative stress via purine catabolism in FENNS.
TL;DR: The development and validation of a reversed-phase HPLC method combining electrochemical and UV detection after a short gradient run to measure seven purine metabolites from the entire purine metabolic pathway, which determined basal levels of these metabolites in mouse brain and serum, as well as in post-mortem human brain.
Abstract: The purine metabolic pathway has been implicated in neurodegeneration and neuroprotection. High-performance liquid chromatography (HPLC) is widely used to determine purines and metabolites. However, methods for analysis of multiple purines in a single analysis have not been standardized, especially in brain tissue. We report the development and validation of a reversed-phase HPLC method combining electrochemical and UV detection after a short gradient run to measure seven purine metabolites (adenosine, guanosine, inosine, guanine, hypoxanthine, xanthine and urate) from the entire purine metabolic pathway. The limit of detection (LoD) for each analyte was determined. The LoD using UV absorption was 0.001 mg/dL for hypoxanthine (Hyp), inosine (Ino), guanosine (Guo) and adenosine (Ado), and those using coulometric electrodes were 0.001 mg/dL for guanine (Gua), 0.0001 mg/dL for urate (UA) and 0.0005 mg/dL for xanthine (Xan). The intra- and inter-day coefficient of variance was generally <8%. Using this method, we determined basal levels of these metabolites in mouse brain and serum, as well as in post-mortem human brain. Peak identities were confirmed by enzyme degradation. Spike recovery was performed to assess accuracy. All recoveries fell within 80-120%. Our HPLC method provides a sensitive, rapid, reproducible and low-cost method for determining multiple purine metabolites in a single analysis in serum and brain specimens.
TL;DR: In this article, a sensitive electrochemical biosensor based on a double stranded DNA immobilized on a xanthine oxidase (XOD)-modified glassy carbon electrode (denoted as DNA-XOD/GCE) has been developed to explore the rapid detection of DNA damage.
Abstract: Oxidative DNA damage is one of the most critical factors implicated in carcinogenesis and other disorders. Sensitive and reliable detection of oxidative DNA damage remains a significant challenge. In this work, a sensitive electrochemical biosensor based on a double stranded DNA immobilized on a xanthine oxidase (XOD)-modified glassy carbon electrode (denoted as DNA–XOD/GCE) has been developed to explore the rapid detection of DNA damage. Co(bpy)33+ was used as a redox indicator to monitor DNA damage induced by hydroxyl radical ( OH), which is a reactive oxygen species generated by a XOD-catalyzed Fenton reaction in xanthine/FeSO4 system. The produced OH was validated by UV–vis spectroscopy. The electrochemical behavior of the underlying electrodes was characterized by square wave voltammetry and electrochemical impedance spectroscopy. Optimization of the concentrations of FeSO4 and XA, and the incubation time in terms of DNA damage was explored. Moreover, the protection of DNA from damage by antioxidants, such as ascorbic acid, aloe-emodin, and rutin was investigated. The conclusions demonstrate that the proposed electrochemical method is expected to be of use in further application for DNA damage studies.
TL;DR: Isolation and characterization of xanthine oxidoreductase and its application in the production of food with low purine content is studied.
Abstract: Aims: Isolation and characterization of xanthine oxidoreductase and itsapplication in the production of food with low purine content.Methods and Results: The A. adeninivorans xanthine oxidoreductase is aninducible enzyme. The best inducers were identified by enzyme activity testsand real-time PCR and used to produce large amounts of the protein.Xanthine oxidoreductase was partially purified and biochemically characterized,showing pH and temperature optimum of 8 5 and 43°C, respectively. Theenzyme decreased xanthine and hypoxanthine concentrations in yeast extractand was active simultaneously with other purine-degrading enzymes so that allof the substrates for uric acid production were reduced in a single step.Conclusions: It was shown that induced A. adeninivorans can producesufficient amount of xanthine dehydrogenase and that the enzyme is able toreduce xanthine and hypoxanthine content in food, and when used inconjunction with other enzymes of the pathway, uric acid concentration issignificantly reduced.Significance and Impact of the Study: Reduction in dietary purines isrecommended to people suffering from hyperuricemia. Elimination of mostpurine-rich foods may affect balanced nutrition. Food with lowered purineconcentration will assist in controlling the disease. This study is a continuationof previous studies that characterized and overexpressed other enzymes of thepurine degradation pathway.IntroductionPurine degradation occurs in all living organisms and fol-lows the route from purines to CO
TL;DR: It can be concluded that flavonoids could be a promising remedy for the treatment of gout and related inflammatory disorders and further in-vivo studies are required to develop potential compounds with lesser side effects.
Abstract: Allopurinol, the xanthine oxidase inhibitor, is the only drug available for the treatment of gout. We examined the xanthine oxidase inhibitory activity of some commercially available flavonoids such asepigallocatechin, acacatechin, myricetin, naringenin, daidzein and glycitein by virtual screening and in-vitro studies. The interacting residues within the complex model and their contact types were identified. The virtual screening analysis were carried out using AutoDock 4.2 and in-vitro xanthine oxidase inhibitory activity was carried out using xanthine as the substrate. In addition, enzyme kinetics was performed using LineweaverBurkplot analysis. Allopurinol, a known xanthine oxidase inhibitor was used as the standard. The docking energy ofglycitein was found to be -8.49 kcal/mol which was less than that of the standard (-4.47 kcal/ mol). All the selected flavonoids were found to exhibit lower binding energy (-8.08 to -6.03 kcal/ mol) than allopurinol. The docking results confirm that flavonoids showed greater inhibition of xanthine oxidase due to their active binding sites and lesser binding energies compared to allopurinol. This may be attributed to the presence of benzopyran ring in the flavonoids. In the xanthine oxidase assay, IC 50 value of glycitein was found to be 12±0.86 µg/mL, whereas that of allopurinol was 24±0.28 µg/mL. All the remaining compounds exhibited IC 50 values ranging between 22±0.64 to 62±1.18 µg/mL. In the enzyme kinetic studies, flavonoids showed competitive type of enzyme inhibition. It can be concluded that flavonoids could be a promising remedy for the treatment of gout and related inflammatory disorders. Further in-vivo studies are required to develop potential compounds with lesser side effects.
TL;DR: The results from the spectra of IR, (1)H NMR and ESR and the measurement of molecular weight demonstrated that PAP is an oligomer with the free radicals and exhibited good redox activity in a wide pH range from pH<1-9.0 and can effectively catalyze xanthine oxidation due to the presence of thefree radicals and the reversible redox groups in the copolymer chain.
TL;DR: Long-term stability analysis revealed that G411VΔ1-11 was the most stable construct and the most suited to downstream structural studies, but showed that Q408E is unstable under these conditions.
Abstract: Despite detailed genetic and mutagenic analysis and a recent high-resolution structure of a bacterial member of the nucleobase-ascorbate transporter (NAT) family, understanding of the mechanism of action of eukaryotic NATs is limited. Preliminary studies successfully expressed and purified wild-type UapA to high homogeneity; however, the protein was extremely unstable, degrading almost completely after 48 h at 4°C. In an attempt to increase UapA stability we generated a number of single point mutants (E356D, E356Q, N409A, N409D, Q408E and G411V) previously shown to have reduced or no transport activity, but correct targeting to the membrane. The mutant UapA constructs expressed well as GFP fusions in Saccharomyces cerevisiae and exhibited similar fluorescent size exclusion chromatography (FSEC) profiles to the wild-type protein, following solubilization in 1% DDM, LDAO or OM + 1 mM xanthine. In order to assess the relative stabilities of the mutants, solubilized fractions prepared in 1% DDM + 1 mM xanthine were heated at 45°C for 10 min prior to FSEC. The Q408E and G411V mutants gave markedly better profiles than either wild-type or the other mutants. Further FSEC analysis following solubilization of the mutants in 1% NG ± xanthine confirmed that G411V is more stable than the other mutants, but showed that Q408E is unstable under these conditions. G411V and an N-terminally truncated construct G411VΔ1-11 were submitted to large-scale expression and purification. Long-term stability analysis revealed that G411VΔ1-11 was the most stable construct and the most suited to downstream structural studies.
TL;DR: It is shown that the addicted strain can be used as a biosensor to measure the caffeine content of common beverages and could be useful for reclaiming nutrient-rich byproducts of coffee bean processing and for the cost-effective bioproduction of methylxanthine drugs.
Abstract: The widespread use of caffeine (1,3,7-trimethylxanthine) and other methylxanthines in beverages and pharmaceuticals has led to significant environmental pollution We have developed a portable caffeine degradation operon by refactoring the alkylxanthine degradation (Alx) gene cluster from Pseudomonas putida CBB5 to function in Escherichia coli In the process, we discovered that adding a glutathione S-transferase from Janthinobacterium sp Marseille was necessary to achieve N 7 -demethylation activity E coli cells with the synthetic operon degrade caffeine to the guanine precursor, xanthine Cells deficient in de novo guanine biosynthesis that contain the refactored operon are ″addicted″ to caffeine: their growth density is limited by the availability of caffeine or other xanthines We show that the addicted strain can be used as a biosensor to measure the caffeine content of common beverages The synthetic N-demethylation operon could be useful for reclaiming nutrient-rich byproducts of coffee bean processing and for the cost-effective bioproduction of methylxanthine drugs
TL;DR: The data suggest that caffeine and theophylline have anticancer effects and can improve the treatment effect in canine hemangiosarcoma patients and both drugs may enhance doxorubicin-induced cytotoxicity by inhibiting ATM/ATR kinases.
TL;DR: Serum purine metabolite concentrations in patients affected by fibromyalgia syndrome are evaluated and a negative correlation between adenosine and Fibromyalgia Impact Questionnaire (FIQ) is shown.
TL;DR: The assay allows precise quantification of IMPDH activity, hypoxanthine, guanine, and adenine in lymphocytes and seems as an intriguing pharmacodynamic biomarker for MPA.
Abstract: Background The development of biomarkers describing the individual responses to the immunosuppressant mycophenolic acid (MPA) has focused on the target enzyme activity [inosine 5'-monophosphate dehydrogenase (IMPDH)]. An extended strategy is to quantify the metabolic consequences of IMPDH inhibition. The aim of this study was to develop an assay for quantification of IMPDH activity and related purine bases and to provide preliminary data on the behavior of these biomarkers during clinical exposure to MPA. Methods Liquid chromatography-mass spectrometry was used to determine xanthine (IMPDH activity in incubated cell lysate), hypoxanthine, guanine, and adenine derived from free nucleotides in lymphocytes. Analytical performance was assessed, and the biomarkers were examined in CD4⁺ cells from 2 groups: Healthy individuals in a single-dose MPA study (n = 5) and liver transplant recipients on MPA therapy (n = 15). Results Coefficients of variation between series were below 10% and 15% for measurement of the purines and IMPDH activity, respectively. Although IMPDH was inhibited, the purine levels increased in response to MPA in 3 of the 5 healthy individuals, and this positive response seemed to be associated with IMPDH1 c.579 + 119 G/G and c.580 - 106 G/G. In the liver transplant study, guanine was not reduced in response to the transient drop in IMPDH activity after MPA dosing. However, there were trends toward decrease in guanine and elevation of hypoxanthine during prolonged MPA therapy. The guanine/hypoxanthine ratio (median) was 37% lower and the adenine level was 21% lower at day 17 compared with day 4 after transplantation. Conclusions The assay allows precise quantification of IMPDH activity, hypoxanthine, guanine, and adenine in lymphocytes. Some individuals may possess a counteracting purine response to the MPA-mediated inhibition of IMPDH. Reduction of the guanine/hypoxanthine ratio may be related to prolonged inhibition of IMPDH and seems as an intriguing pharmacodynamic biomarker for MPA.
TL;DR: Genetic and physiological evidence and genetic evidence suggest that the allopurinol translocation pathway is distinct from, but probably overlapping with, that of physiological UapA substrates, and evidence was obtained supporting that accelerated influx of xanthine is triggered through exchange with cytoplasmically accumulated allopURinol.
TL;DR: The developed fragmentation scheme may serve as a valuable tool for the interpretation of ESI-CID fragmentation spectra of more complex xanthine derivatives and their respective metabolites.
Abstract: RATIONALE
In order to deepen the understanding of electrospray ionisation collision-induced dissociation (ESI-CID) fragmentation reactions of xanthine derivatives for the identification of metabolites using low-resolution liquid chromatography/mass spectrometry (LC/MS) analysis, basic experiments using caffeine (1,3,7-trimethylxanthine) as model compound have been performed.
METHODS
Six deuterium isotopomers and one N1-ethylated homologue of caffeine have been synthesized and their ESI fragmentation spectra have been obtained by using LC/MS in combination with either standard or perdeuterated eluent mixtures.
RESULTS
One result of these studies is the finding that the positive charges of the ESI-CID caffeine fragments are caused by the addition of protons. Furthermore, the performed experiments allow the determination of all molecular formulae of each ESI-CID caffeine fragment.
CONCLUSIONS
As basic CID reactions of caffeine have been elucidated in this work, the developed fragmentation scheme may serve as a valuable tool for the interpretation of ESI-CID fragmentation spectra of more complex xanthine derivatives and their respective metabolites. Copyright © 2013 John Wiley & Sons, Ltd.
TL;DR: Data suggest that hormone-mediated modulation of CuZnSOD is related to subtle changes in protein conformation, possibly related to Trp and Phe residues, and it is proposed that this effect may account for the physiological regulation of enzyme activity during conditions where steroid hormones undergo alterations as the ovulatory cycle.
Abstract: This study aimed to evaluate whether natural or synthetic steroid hormones could directly modulate the activity of the different superoxide dismutase (SOD) isoforms found in human blood fractions without changing enzyme expression. Enzyme samples of human erythrocytes, the human platelet-rich plasma fraction (PRP) or isolated CuZnSOD, which was purified from human erythrocytes were pre-incubated with natural steroids (17β-estradiol 17-acetate and progesterone) and their synthetic derivatives (β-estradiol 3-benzoate and medroxyprogesterone 17-acetate). Then, CuZn and MnSOD activities were measured using the xanthine/xanthine oxidase/nitroblue tetrazolium method. Hormones had no effect on MnSOD activity from the PRP, but we show for the first time that natural and synthetic steroid hormones have a direct, bell-shaped effect on the activity of CuZnSOD from both male and female human erythrocytes. Low (physiological) hormone concentrations caused a dose-dependent increase in enzyme activity, which dis...
TL;DR: A series of xanthine derivatives was synthesized and evaluated as inhibitors of dipeptidyl peptidase 4 (DPP-4) for the treatment of type 2 diabetes, and the compounds with 4-methyl-quinazoline-2-yl-methyl group at N-1 position and 2-aminoethylaminomethyl group gave better activities.
Abstract: A series of xanthine derivatives in which a methylene was inserted at position 8 of xanthine scaffold was synthesized and evaluated as inhibitors of dipeptidyl peptidase 4 (DPP-4) for the treatment of type 2 diabetes. As the results of structure-activity relationship (SAR) study of the series, the compounds with 4-methyl-quinazoline-2-yl-methyl group at N-1 position and 2-aminoethylaminomethyl group gave better activities. Compounds H4 and H9 showed good DPP-4 inhibition and more than 100-fold selectivity over DPP-7 and DPP-8.