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Showing papers on "Xanthine published in 2014"


Journal ArticleDOI
TL;DR: Clinicians and patients could utilize that reference in nutritional therapy for gout and hyperuricemia through an HPLC method for purine analysis and determined purines in a total of 270 foodstuffs.
Abstract: Purines are natural substances found in all of the body’s cells and in virtually all foods. In humans, purines are metabolized to uric acid, which serves as an antioxidant and helps to prevent damage caused by active oxygen species. A continuous supply of uric acid is important for protecting human blood vessels. However, frequent and high intake of purine-rich foods reportedly enhances serum uric acid levels, which results in gout and could be a risk factor for cardiovascular disease, kidney disease, and metabolic syndrome. In Japan, the daily intake of dietary purines is recommended to be less than 400 mg to prevent gout and hyperuricemia. We have established an HPLC method for purine analysis and determined purines in a total of 270 foodstuffs. A relatively small number of foods contained concentrated amounts of purines. For the most part, purine-rich foods are also energy-rich foods, and include animal meats, fish meats, organs such as the liver and fish milt, and yeast. When the ratio of the four purine bases (adenine, guanine, hypoxanthine, and xanthine) was compared, two groups of foods were identified: one that contained mainly adenine and guanine and one that contained mainly hypoxanthine. For patients with gout and hyperuricemia, the amount of total purines and the types of purines consumed, particularly hypoxanthine, are important considerations. In this context, the data from our analysis provide a purine content reference, and thereby clinicians and patients could utilize that reference in nutritional therapy for gout and hyperuricemia.

129 citations


Journal ArticleDOI
TL;DR: The current complex provides a structural basis for the rational design of flavonoid-type inhibitors against xanthine oxidase useful for the treatment of hyperuricemia, gout, and inflammatory disease states.
Abstract: Xanthine oxidase catalyzes the sequential hydroxylation of hypoxanthine to uric acid via xanthine as intermediate. Deposition of crystals of the catalytic product uric acid or its monosodium salt in human joints with accompanying joint inflammation is the major cause of gout. Natural flavonoids are attractive leads for rational design of preventive and therapeutic xanthine oxidase inhibitors due to their beneficial antioxidant, anti-inflammatory, and antiproliferative activities in addition to their micromolar inhibitory activities toward xanthine oxidase. We determined the first complex X-ray structure of mammalian xanthine oxidase with the natural flavonoid inhibitor quercetin at 2.0 A resolution. The inhibitor adopts a single orientation with its benzopyran moiety sandwiched between Phe 914 and Phe 1009 and ring B pointing toward the solvent channel leading to the molybdenum active center. The favorable steric complementarity of the conjugated three-ring structure of quercetin with the active site and ...

82 citations


Journal ArticleDOI
TL;DR: This review article describes the various immobilization methods of XOD and different matrices used for construction of xanthine biosensors, their classification, analytical performance and applications along with their merits and demerits.

52 citations


Journal ArticleDOI
TL;DR: The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and perox isome function, which may be relevant beyond plants.
Abstract: Purine nucleotides can be fully catabolized by plants to recycle nutrients. We have isolated a urate oxidase (uox) mutant of Arabidopsis thaliana that accumulates uric acid in all tissues, especially in the developing embryo. The mutant displays a reduced germination rate and is unable to establish autotrophic growth due to severe inhibition of cotyledon development and nutrient mobilization from the lipid reserves in the cotyledons. The uox mutant phenotype is suppressed in a xanthine dehydrogenase (xdh) uox double mutant, demonstrating that the underlying cause is not the defective purine base catabolism, or the lack of UOX per se, but the elevated uric acid concentration in the embryo. Remarkably, xanthine accumulates to similar levels in the xdh mutant without toxicity. This is paralleled in humans, where hyperuricemia is associated with many diseases whereas xanthinuria is asymptomatic. Searching for the molecular cause of uric acid toxicity, we discovered a local defect of peroxisomes (glyoxysomes) mostly confined to the cotyledons of the mature embryos, which resulted in the accumulation of free fatty acids in dry seeds. The peroxisomal defect explains the developmental phenotypes of the uox mutant, drawing a novel link between uric acid and peroxisome function, which may be relevant beyond plants.

48 citations


Journal ArticleDOI
TL;DR: In isolated rat basilar arteries, ergothioneine attenuated the reduction in acetylcholine-induced relaxation caused by pyrogallol, xanthine oxidase plusxanthine, or incubation in high glucose, and protected against oxidative stress, curtailing endothelial dysfunction.
Abstract: Ergothioneine is a thiourea derivative of histidine found in food, especially mushrooms. Experiments in cell-free systems and chemical assays identified this compound as a powerful antioxidant. Experiments were designed to test the ability of endothelial cells to take up ergothioneine and hence benefit from protection against oxidative stress. Reverse-transcription polymerase chain reaction and Western blotting demonstrated transcription and translation of an ergothioneine transporter in human brain microvascular endothelial cells (HBMECs). Uptake of [(3)H]ergothioneine occurred by the organic cation transporter novel type-1 (OCTN-1), was sodium-dependent, and was reduced when expression of OCTN-1 was silenced by small interfering RNA (siRNA). The effect of ergothioneine on the production of reactive oxygen species (ROS) in HBMECs was measured using dichlorodihydrofluorescein and lucigenin, and the effect on cell viability was studied using the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. ROS production and cell death induced by pyrogallol, xanthine oxidase plus xanthine, and high glucose were suppressed by ergothioneine. The antioxidant and cytoprotective effects of ergothioneine were abolished when OCTN-1 was silenced using siRNA. The expression of NADPH oxidase 1 was decreased, and those of glutathione reductase, catalase, and superoxide dismutase enhanced by the compound. In isolated rat basilar arteries, ergothioneine attenuated the reduction in acetylcholine-induced relaxation caused by pyrogallol, xanthine oxidase plus xanthine, or incubation in high glucose. Chronic treatment with the compound improved the response to acetylcholine in arteries of rats with streptozotocin-induced diabetes. In summary, ergothioneine is taken up by endothelial cells via OCTN-1, where the compound then protects against oxidative stress, curtailing endothelial dysfunction.

48 citations


Journal ArticleDOI
TL;DR: XDH can be an important redox-regulated source of •O2– generation in ischemic tissue, and conversion to XO is not required to activate radical formation and subsequent tissue injury.
Abstract: The enzyme xanthine oxidoreductase (XOR) is an important source of oxygen free radicals and related postischemic injury. Xanthine dehydrogenase (XDH), the major form of XOR in tissues, can be converted to xanthine oxidase (XO) by oxidation of sulfhydryl residues or by proteolysis. The conversion of XDH to XO has been assumed to be required for radical generation and tissue injury. It is also possible that XDH could generate significant quantities of superoxide, •O₂⁻, for cellular signaling or injury; however, this possibility and its potential ramifications have not been previously considered. To unambiguously determine if XDH can be a significant source of •O₂⁻, experiments were performed to measure and characterize •O²⁻ generation using XDH from chicken liver that is locked in the dehydrogenase conformation. Electron paramagnetic resonance spin trapping experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide demonstrated that XDH in the presence of xanthine produces significant amounts of •O₂⁻. NAD⁺ and NADH inhibited the generation of •O₂⁻ from XDH in a dose-dependent manner, with NAD⁺ exhibiting stronger inhibition than NADH at low physiological concentrations. Decreased amounts of NAD⁺ and NADH, which occur during and following tissue ischemia, enhanced the generation of •O₂⁻ from XDH in the presence of xanthine. It was observed that XDH-mediated oxygen radical generation markedly depressed Ca²⁺-ATPase activity of isolated sarcoplasmic reticulum vesicles from cardiac muscle, and this was modulated by NAD⁺ and NADH. Thus, XDH can be an important redox-regulated source of •O₂⁻ generation in ischemic tissue, and conversion to XO is not required to activate radical formation and subsequent tissue injury.

45 citations


Journal ArticleDOI
TL;DR: The levels of adenosine, inosine, uric acid, and xanthine may be useful for monitoring the progression of diabetic retinopathy and evaluating the treatment and correlated positively with systolic blood pressure and urea nitrogen.
Abstract: Aims. The purpose of the study was to investigate the differences of adenosine, adenine, inosine, xanthine, hypoxanthine, and uric acid concentrations in patients with type 2 diabetes mellitus and diabetic retinopathy and assess the relationship between purine metabolites and disease. Materials and Methods. The study group consisted of 114 subjects which were divided into three groups: control (), type 2 diabetes without retinopathy (), and type 2 diabetes with retinopathy (). Levels of metabolites were measured in plasma of all participants. Results. There is a significant increase of levels of adenosine ( mg/L versus mg/L, ), inosine ( mg/L versus mg/L, ), xanthine ( mg/L versus mg/L, ), and uric acid ( mg/L versus mg/L, ) with diabetic retinopathy compared to diabetes mellitus. The levels of adenine, hypoxanthine, and xanthine oxidase did not change. Uric acid, xanthine, inosine, and adenosine correlated positively with systolic blood pressure and urea nitrogen. Conclusions. The levels of adenosine, inosine, uric acid, and xanthine may be useful for monitoring the progression of diabetic retinopathy and evaluating the treatment.

44 citations


Journal ArticleDOI
TL;DR: The fabricated biosensor was successfully applied for measurement of fish and chicken meat freshness, which was in agreement with the standard method at the 95% confidence level.

38 citations


Journal ArticleDOI
TL;DR: An on-line high-performance liquid chromatography coupled with post-column dual-bioactivity assay was established and successfully applied to simultaneously screening of XO inhibitors and free radical scavengers from a complex mixture, Oroxylum indicum extract.

37 citations


Journal ArticleDOI
TL;DR: The results suggest that caffeine potentiates d-asp-induced GABA release, which is mediated by GAT-1, via inhibition of adenosine A1 receptor and activation of the PKA pathway.

37 citations



Journal ArticleDOI
TL;DR: Conditioned medium experiments indicated that the protective effect of inosine relies on the release of a protective factor from inOSine-stimulated astrocytes, and raised the possibility that inosines might have a protective effect in PD that is independent of any effects mediated through its metabolite urate.

Journal ArticleDOI
TL;DR: The ambivalent role of xanthine oxido – reductase justifies this review on the basic enzymatic mechanisms involved, derived ROS production, their role in the above mentioned biological processes and especially the interest of the inhibition of this enzyme as a preventive or curative measure in some cardiovascular pathologies.
Abstract: Free radical mediated pathologies occupy a special place in medical semiology and in mechanistic interpretation of diseases. Free radicals, or better reactive oxygen species (ROS) or reactive nitrogen species (RNS) play also an important role in cell signaling. This is the basis of the ambivalent (Jekyll-Hyde) situation of ROS in biology and pathology. Aging itself is attributed by a popular theory to free radicals. A number of ROS-scavenging substances and procedures were described without however reaching credibility for their therapeutic value. An interesting exception is the xanthine oxido-reductase produced ROS and their role in cardiovascular disease. Allopurinol inhibition of xanthine oxido-reductase was shown to be efficient in some cases of cardiovascular diseases. Another important aspect of xanthine oxido-reductase produced ROS is their antibacterial capacity considered to be of importance with newborns fed on milk rich in this enzyme as well as at the gastrointestinal barrier. This ambivalent role of xanthine oxido-reductase justifies this review on the basic enzymatic mechanisms involved, derived ROS production, their role in the above mentioned biological processes and especially the interest of the inhibition of this enzyme as a preventive or curative measure in some cardiovascular pathologies.

Journal ArticleDOI
TL;DR: Investigation of the in vitro metabolism of 6MP to 6-thiouric acid (6TUA) in pooled human liver cytosol found evidence that three enzymes, AO, XO, and XDH, contribute to the production of 6TX intermediate, whereas only XO andXDH are involved in the conversion of 6 TX to 6TUA in pooled HLC.
Abstract: Anticancer agent 6-mercaptopurine (6MP) has been in use since 1953 for the treatment of childhood acute lymphoblastic leukemia (ALL) and inflammatory bowel disease. Despite being available for 60 years, several aspects of 6MP drug metabolism and pharmacokinetics in humans are unknown. Molybdoflavoenzymes such as aldehyde oxidase (AO) and xanthine oxidase (XO) have previously been implicated in the metabolism of this drug. In this study, we investigated the in vitro metabolism of 6MP to 6-thiouric acid (6TUA) in pooled human liver cytosol. We discovered that 6MP is metabolized to 6TUA through sequential metabolism via the 6-thioxanthine (6TX) intermediate. The role of human AO and XO in the metabolism of 6MP was established using the specific inhibitors raloxifene and febuxostat. Both AO and XO were involved in the metabolism of the 6TX intermediate, whereas only XO was responsible for the conversion of 6TX to 6TUA. These findings were further confirmed using purified human AO and Escherichia coli lysate containing expressed recombinant human XO. Xanthine dehydrogenase (XDH), which belongs to the family of xanthine oxidoreductases and preferentially reduces nicotinamide adenine dinucleotide (NAD+), was shown to contribute to the overall production of the 6TX intermediate as well as the final product 6TUA in the presence of NAD+ in human liver cytosol. In conclusion, we present evidence that three enzymes, AO, XO, and XDH, contribute to the production of 6TX intermediate, whereas only XO and XDH are involved in the conversion of 6TX to 6TUA in pooled HLC.

Journal ArticleDOI
TL;DR: Degradation of PGS and PXS is primarily mediated by the action of esterase, with free-radical oxidation playing a secondary role, suggesting that both could synergistically affect the biodegradability of biomaterial implants, under more complex biological conditions.
Abstract: Poly(glycerol sebacate) (PGS) and poly(xylitol sebacate) (PXS) are biodegradable elastomers with tremendous potential in soft tissue engineering. This study was aimed at exploring the enzymatic degradation mechanisms of these polyesters, using biochemical conditions similar to those occurring in vivo. To this end, PGS and PXS (crosslinked at 130℃ for 2 or 7 (PGS)/12 days (PXS)) were incubated in vitro under physiological conditions in tissue culture media supplemented with either a biodegrading enzyme (esterase), an oxidant species (FeSO4/H2O2 with 0.11 molar ratio of Fe2+/H2O2), an oxidant generating enzyme (xanthine oxidase and xanthine) or combinations of these (FeSO4/H2O2 and esterase, or (v) xanthine oxidase/xanthine and esterase), based on their independent effects on polymer degradation. Testing was performed over 35 days of continuous incubation, during which mechanical properties, mass loss, biomaterial thickness and pH value of the culture medium were determined. Degradation kinetics of both PGS...

Journal ArticleDOI
TL;DR: 8‐Benzyl‐substituted tetrahydropyrazino[2,1‐f]purine‐2,4(1H,3H)‐dione was found to be the best triple‐target drug in rat and may serve as a useful tool for preclinical proof‐of‐principle studies.
Abstract: 8-Benzyl-substituted tetrahydropyrazino[2,1-f]purinediones were designed as tricyclic xanthine derivatives containing a basic nitrogen atom in the tetrahydropyrazine ring to improve water solubility. A library of 69 derivatives was prepared and evaluated in radioligand binding studies at adenosine receptor (AR) subtypes and for their ability to inhibit monoamine oxidases (MAO). Potent dual-target-directed A1 /A2A adenosine receptor antagonists were identified. Several compounds showed triple-target inhibition; one of the best compounds was 8-(2,4-dichloro-5-fluorobenzyl)-1,3-dimethyl-6,7,8,9-tetrahydropyrazino[2,1-f]purine-2,4(1H,3H)-dione (72) (human AR: Ki A1 217 nM, A2A 233 nM; IC50 MAO-B: 508 nM). Dichlorinated compound 36 [8-(3,4-dichlorobenzyl)-1,3-dimethyl-6,7,8,9-tetrahydropyrazino[2,1-f]purine-2,4(1H,3H)-dione] was found to be the best triple-target drug in rat (Ki A1 351 nM, A2A 322 nm; IC50 MAO-B: 260 nM), and may serve as a useful tool for preclinical proof-of-principle studies. Compounds that act at multiple targets relevant for symptomatic as well as disease-modifying treatment of neurodegenerative diseases are expected to show advantages over single-target therapeutics.

Journal ArticleDOI
TL;DR: In this paper, a series of halogenated pyridines were used as ligands for the Suzuki-Miyaura cross couplings of a set of anilines with phenylboronic acid.

Journal ArticleDOI
Jinlian Li1, Lin Runxian1, Qian Wang1, Guanggang Gao1, Jiwen Cui1, Jiguang Liu1, Dongmei Wu1 
TL;DR: The results showed that with the increase of genistein dose at the range of 10(-9) to 10(-6)M, the two electrochemical signals of MCF-7 cell suspension increased due to the proliferation, whereas the tendency at the high dosage range of more than 10(-5)M was decreased.

Journal ArticleDOI
TL;DR: The synthesized nanoconjugate was found be to efficient selective xanthine and urease inhibitors in comparison to Ag and AR, and required less amount of AR than standard drugs, pure ligand and silver.
Abstract: Conjugated and drug loaded silver nanoparticles are getting an increased attention for various biomedical applications. Nanoconjugates showed significant enhancement in biological activity in comparison to free drug molecules. In this perspective, we report the synthesis of bioactive silver capped with 5-Amino-?-resorcylic acid hydrochloride dihydrate (AR). The in vitro antimicrobial (antibacterial, antifungal), enzyme inhibition (xanthine oxidase, urease, carbonic anhydrase, ?-chymotrypsin, cholinesterase) and antioxidant activities of the developed nanostructures was investigated before and after conjugation to silver metal. The conjugation of AR to silver was confirmed through FTIR, UV-vis and TEM techniques. The amount of AR conjugated with silver was characterized through UV-vis spectroscopy and found to be 9% by weight. The stability of synthesized nanoconjugates against temperature, high salt concentration and pH was found to be good. Nanoconjugates, showed significant synergic enzyme inhibition effect against xanthine and urease enzymes in comparison to standard drugs, pure ligand and silver. Our synthesized nanoconjugate was found be to efficient selective xanthine and urease inhibitors in comparison to Ag and AR. On a per weight basis, our nanoconjugates required less amount of AR (about 11 times) for inhibition of these enzymes.

Journal ArticleDOI
TL;DR: The screening strategy allows for rapid analysis of small molecules with almost no sample preparation and can be completed within a week, making it a useful assay to identify unstable compounds and provide the empirical foundation for E. obtusifolia as a natural remedy for gout and oxidative-stress-related diseases.
Abstract: As a final step of the purine metabolism process, xanthine oxidase catalyzes the oxidation of hypoxanthine and xanthine into uric acid. Our research has demonstrated that Erycibe obtusifolia has xanthine oxidase inhibitory properties. The purpose of this paper is to describe a new strategy based on a combination of multiple mass spectrometric platforms and thin-layer chromatography bioautography for effectively screening the xanthine oxidase inhibitory and antioxidant properties of E. obtusifolia. This strategy was accomplished through the following steps. (i) Separate the extract of E. obtusifolia into fractions by an autopurification system controlled by liquid chromatography with mass spectrometry. (ii) Determine the active fractions of E. obtusifolia by thin-layer chromatography bioautography. (iii) Identify the structure of the main active compounds with the information provided by direct analysis in real time mass spectrometry. (iv) Calculate the IC50 value of each compound against xanthine oxidase using high-performance liquid chromatography. Using the caulis of E. obtusifolia as the experimental material, seven target peaks were screened out as xanthine oxidase inhibitors or antioxidants. Our screening strategy allows for rapid analysis of small molecules with almost no sample preparation and can be completed within a week, making it a useful assay to identify unstable compounds and provide the empirical foundation for E. obtusifolia as a natural remedy for gout and oxidative-stress-related diseases.

Journal ArticleDOI
TL;DR: Addition of exogenous uric acid increased the influx of heterophils into rabbit intestinal loops, as measured by myeloperoxidase activity and white blood cells adhered avidly to uric Acid crystals, forming large aggregates of cells.
Abstract: Uric acid can be generated in the gastrointestinal (GI) tract from the breakdown of nucleotides ingested in the diet or from purines released from host cells as a result of pathogen-induced cell damage. Xanthine oxidase (XO) is the enzyme that converts hypoxanthine or xanthine into uric acid, a reaction that also generates hydrogen peroxide. It has been assumed that the product of XO responsible for the pro-inflammatory effects of this enzyme is hydrogen peroxide. Recent literature on uric acid, however, has indicated that uric acid itself may have biological effects. We tested whether uric acid itself has detectable pro-inflammatory effects using an in vivo model using ligated rabbit intestinal segments ("loops") as well as in vitro assays using cultured cells. Addition of exogenous uric acid increased the influx of heterophils into rabbit intestinal loops, as measured by myeloperoxidase activity. In addition, white blood cells adhered avidly to uric acid crystals, forming large aggregates of cells. Uric acid acts as a leukocyte chemoattractant in the GI tract. The role of uric acid in enteric infections and in non-infectious disorders of the GI tract deserves more attention.

Journal ArticleDOI
23 Oct 2014-Nature
TL;DR: It is demonstrated that purified circularly permuted yellow fluorescent protein (cpYFP) exhibits a twofold fluorescence increase after oxygenation, and an additional twofold increase after the subsequent addition of X plus XO, which could not be accounted for by solvent (potassium hydroxide)-induced alkalization.
Abstract: Replying to M. Schwarzlander et al. , 10.1038/nature13858 (2014) In the accompanying Comment1, Schwarzlander challenged our recent study2 because they failed to reproduce our previous finding that the fluorescence intensity of purified circularly permuted yellow fluorescent protein (cpYFP) increases in response to oxygen and superoxide anions produced by xanthine (X) plus xanthine oxidase (XO)3. Starting from a ‘fully reduced’ state (incubation with 10 mM dithiothreitol for >3 h) and in the presence of 75 mM HEPES, we demonstrated that cpYFP exhibits a twofold fluorescence increase after oxygenation, and an additional twofold increase after the subsequent addition of X plus XO, which could not be accounted for by solvent (potassium hydroxide)-induced alkalization. Furthermore, the xanthine plus xanthine oxidase-induced increase in cpYFP fluorescence was reversed by Cu/Zn superoxide dismutase (600 U ml−1). We also found that the fluorescence intensity of fully reduced cpYFP increased >fourfold after incubation with 1 mM aldrithiol. Notably, recombinant cpYFP purified in the absence of dithiothreitol treatment exhibits a high fluorescence comparable to that of the fully oxidized state, indicating the high susceptibility of cpYFP to oxidation in non-reducing environments3. Therefore, ensuring a fully reduced state of cpYFP is essential for the probe to sense superoxide in vitro. This property is probably the reason that the probe functions readily as a reversible superoxide biosensor when targeted to the reduced environment of the mitochondrial matrix. Unfortunately, from the brief description of the methods and limited data provided by Schwarzlander et al.1, it is not possible to determine whether cpYFP was fully reduced in their experiments, or whether sufficient precautions were taken to prevent oxidation of the probe. Moreover, in our experiments cpYFP was expressed in Escherichia coli BL21(DE3)LysS cells, whereas Schwarzlander et al.1 used E. coli Origami, a trxB (thioredoxin reductase) mutant strain that also lacks glutathione reductase needed to fully limit cysteine oxidation4, which could result in an increased oxidative status of their purified cpYFP rendering it non-responsive to superoxide.

Journal ArticleDOI
TL;DR: The advantages of combining NQR, DFT/QTAIM, and Hirshfeld surface analysis to extract detailed information on electron density distribution and complex H-bonding networks in crystals of purinic type heterocycles, relevant in pharmacological processes are demonstrated.
Abstract: Allopurinol (1,5-dihydro-4H-pyrazolo [3,4-d]pyrimidin-4-one), the active pharmaceutical ingredient (API) of the drugs applied for the treatment of gout and tumor lysis syndrome, recently discovered to have multifaceted therapeutic potential, and hypoxanthine which is a naturally occurring purine have been studied experimentally in the solid state by (1)H-(14)N NMR-NQR double resonance. Twelve (14)N resonance frequencies have been detected at 295 K and assigned to two pairs of two kinds of nitrogen sites (-N═ and -NH) in each compound. The experimental results are supported by and interpreted with the help of quantum theory of atoms in molecules (QTAIM)/density functional theory (DFT) calculations. The factors, such as the substituent effect, in particular the shift of nitrogen from position 7 (as in hypoxanthine) to position 8 (as in allopurinol), hybridization, possible prototropic tautomerism, and the pattern of intermolecular bonding, have been taken into account in (1)H-(14)N NMR-NQR spectra interpretation. This study demonstrates the advantages of combining NQR, DFT/QTAIM, and Hirshfeld surface analysis to extract detailed information on electron density distribution and complex H-bonding networks in crystals of purinic type heterocycles, relevant in pharmacological processes. In the absence of X-ray data for xanthine, the NQR parameters supported by DFT/QTAIM calculations and Hirshfeld surface analysis were proved to be valuable tools for clarifying the details of crystalline packing and predicting an unsolved crystalline structure of xanthine. The influence of a decrease in purine ring conjugation level upon oxidation on the biological activity of allopurinol, a xanthine oxidase (XO) enzyme inhibitor, which blocks the conversion of hypoxanthine to xanthine and subsequently xanthine to uric acid, is also discussed.

Journal ArticleDOI
TL;DR: This work decouple DPPIV and FAP potency and identified the first selective xanthine-based FAP inhibitors with low micromolar potency, which are the only known FAP-inhibitors that do not rely on a warhead functionality to obtain potencies in this range.
Abstract: Fibroblast activation protein (FAP) is a serine protease that is selectively expressed in many diseases involving activated stroma, including cancer, arthritis and hepatic and pulmonary fibrosis. FAP is closely related to dipeptidyl peptidase IV (DPPIV), of which many inhibitors are known and several are marketed as drugs. One of these is the xanthine derivative linagliptin. In a broad literature screen amongst reported DPPIV inhibitors, linagliptin was the only druglike compound identified that possessed significant FAP potency. Hence, this compound served as a starting point for a SAR study that aimed to identify structural determinants that selectively increase FAP-potency of linagliptin analogues. By investigating the influence of the substitution pattern on N1, N7 and C8 of the xanthine scaffold, we managed to decouple DPPIV and FAP potency and identified the first selective xanthine-based FAP inhibitors with low micromolar potency. Furthermore, these compounds are the only known FAP-inhibitors that do not rely on a warhead functionality to obtain potencies in this range.

Journal ArticleDOI
TL;DR: The analysis of local environment of the nitrogen nucleus permitted drawing some conclusions on the nature of the interactions required for effective processes of recognition and binding of a given methylxanthine to A1-A(2A) receptor.
Abstract: Three anhydrous methylxanthines: caffeine (1,3,7-trimethylxanthine; 1,3,7-trimethyl-1H-purine-2,6-(3H,7H)-dione) and its two metabolites theophylline (1,3-dimethylxanthine; 1,3-dimethyl-7H-purine-2,6-dione) and theobromine (3,7-dimethyl-xanthine; 3,7-dimethyl-7H-purine-2,6-dione), which reveal multifaceted therapeutic potential, have been studied experimentally in solid state by (1)H-(14)N NMR-NQR (nuclear magnetic resonance-nuclear quadrupole resonance) double resonance (NQDR). For each compound the complete NQR spectrum consisting of 12 lines was recorded. The multiplicity of NQR lines indicates the presence of a stable β form of anhydrous caffeine at 233 K and stable form II of anhydrous theobromine at 213 K. The assignment of signals detected in NQR experiment to particular nitrogen atoms was made on the basis of quantum chemistry calculations performed for monomer, cluster, and solid at the DFT/GGA/BLYP/DPD level. The shifts due to crystal packing interactions were evaluated, and the multiplets detected by NQR were assigned to N(9) in theobromine and N(1) and N(9) in caffeine. The ordering theobromine > theophylline > caffeine site and theophylline < theobromine < caffeine according to increasing electric field gradient (EFG) at the N(1) and N(7) sites, respectively, reflects the changes in biological activity profile of compounds from the methylxanthines series (different pharmacological effects). This difference is elucidated on the basis of the ability to form intra- and intermolecular interactions (hydrogen bonds and π···π stacking interactions). The introduction of methyl groups to xanthine restricts the ability of nitrogen atoms to participate in strong hydrogen bonds; as a result, the dominating effect shifts from hydrogen bond (theobromine) to π···π stacking (caffeine). Substantial differences in the intermolecular interactions in stable forms of methylxanthines differing in methylation (site or number) were analyzed within the Hirshfeld surface-based approach. The analysis of local environment of the nitrogen nucleus permitted drawing some conclusions on the nature of the interactions required for effective processes of recognition and binding of a given methylxanthine to A1-A(2A) receptor (target for caffeine in the brain). Although the interactions responsible for linking neighboring methylxanthines molecules in crystals and methylxanthines with targets in the human organism can differ significantly, the knowledge of the topology of interactions provides reliable preliminary information about the nature of this binding.

Journal ArticleDOI
TL;DR: In this article, the HPLC-DAD methodology was used to detect dominant xanthine derivatives (theobromine and caffeine with HPLC DAD and caffeine by USE/GC-MS/FID). Phenylacetaldehyde was the major headspace compound.
Abstract: Coffea spp. honey was screened by UV/VIS, HS-SPME/GC-MS/FID, USE/GC-MS/FID and HPLC-DAD. The direct HPLC-DAD methodology overcame the major limitations of the other methods used. The obtained results constitute a breakthrough since dominant xanthine derivatives were found (theobromine and caffeine with HPLC-DAD and caffeine by USE/GC-MS/FID). Phenylacetaldehyde was the major headspace compound.

Journal ArticleDOI
TL;DR: The inhibition of XO is recognized as one of the therapeutic approaches to treat gout and the developed online system was applicable to complex mixtures.
Abstract: Xanthine oxidase (XO) catalyzes the metabolism of hypoxanthine and xanthine to uric acid, the overproduction and/or underexcretion of which could cause the incidence of hyperuricemia such as gout. Herein, the inhibition of XO is recognized as one of the therapeutic approaches to treat gout. In the present study, an off-line fluorescence-based microplate method was first developed for an XO assay in which the enzyme converted pterin to its fluorescent metabolite isoxanthopterin. Then, a postcolumn continuous XO assay as a means of bioactivity assessment was coupled to HPLC separation to establish the online HPLC with diode array detection, biochemical detection, and MS/MS system for the screening of XO inhibitors. The availability of the online system was first tested with a positive drug, allopurinol, a well-known XO inhibitor, and subsequent analysis of Scutellaria baicalensis extract showed that two main bioactive compounds with XO inhibitory activities were observed, indicating that the developed online system was applicable to complex mixtures.

Journal ArticleDOI
TL;DR: The function of uric acid is summarized in alleviating oxidative damage and providing protection to neural cells during injury and disease.
Abstract: Uric acid, a potent antioxidant for humans, birds, reptiles, and some primate species, is the end-product of purine degradation that is formed in the xanthine/hypoxanthine reactions catalyzed by xanthine oxidase. Associated with the evolutionary loss of urate oxidase (the enzyme that oxidizes uric acid resulting in the formation of allantoin) and resulting increase in concentrations of uric acid is a prolonged life span. Uric acid is known to scavenge peroxynitrite and other free radicals that can cause an imbalance of oxidants leading to oxidative stress. Uric acid also has a role in protecting DNA from single-strand breaks caused by free radicals in the body leading to a protective effect in neurodegenerative diseases. The brain is particularly vulnerable to oxidative stress as it is considered an ‘expensive tissue’ with a particularly high metabolic rate and comparatively increased utilization of oxygen. Brain tissue is also high in unsaturated lipids, which makes it more susceptible to free radical damage. Oxidative stress is thus linked to the pathogenesis of neurodegenerative diseases and also ischemic brain injury. In this review, we summarize the function of uric acid in alleviating oxidative damage and providing protection to neural cells during injury and disease.

Journal ArticleDOI
TL;DR: Theobromine is a xanthine derivative analogous to caffeine and theophylline and is an effective central nervous system stimulant as mentioned in this paper, but it has a lower aqueous solubility than caffeine.
Abstract: Theobromine, a xanthine derivative analogous to caffeine and theophylline, is an effective central nervous system stimulant. It has lower aqueous solubility than caffeine and theophylline. Salts of theobromine with hydrochloric acid, phosphoric acid, methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid were prepared using liquid-assisted grinding (LAG). Proton transfer from the strong acid to the weak base imidazole N resulted in N+–H ⋯O− hydrogen-bonded supramolecular assemblies of theobromine salts. The mesylate salt is polymorphic with amide N–H ⋯O dimer and catemer synthons for the theobromine cations. A variable stoichiometry for phosphate salts (1:3 and 1:2.5) were observed with the latter being more stable. All new salts were characterized by FT-IR, PXRD, DSC and finally single crystal X-ray diffraction. In terms of stability, these salts transformed to theobromine within 1 h of dissolution in water. Remarkably, the besylate and tosylate salts are 88 and 58 times more soluble than theobromine, but they dissociated within 1 h. In contrast, theobromine co-crystals with gallic acid, anthranilic acid and 5-chlorosalicylic acid were found to be stable for more than 24 h in the aqueous slurry conditions, except malonic co-crystal which transformed to theobromine within 1 h. Water mediated phase transformation of theobromine salts and co-crystal may be due to the incongruency (high solubility difference) between the components. These results suggest that even though traditional salts are highly soluble compared to co-crystals, co-crystals can be superior in terms of stability.

Journal ArticleDOI
TL;DR: In this paper, the authors evaluated Xanthine, caffeine and three isomeric dimethyl xanthines (theobromine, theophylline and paraxanthine) on various criteria.