Allopurinol and oxypurinol differ in their strength and mechanisms of inhibition of xanthine oxidoreductase.

Xanthine oxidoreductase is a metalloenzyme that catalyzes the final steps in purine metabolism by converting hypoxanthine to xanthine and then uric acid. Allopurinol, an analog of hypoxanthine, is widely used as an antigout drug, as xanthine oxidoreductase-mediated metabolism of allopurinol to oxypurinol leads to oxypurinol rotation in the enzyme active site and reduction of the molybdenum Mo(VI) active center to Mo(IV), inhibiting subsequent urate production. However, when oxypurinol is administered directly to a mouse model of hyperuricemia, it yields a weaker urate-lowering effect than allopurinol. To better understand its mechanism of inhibition and inform patient dosing strategies, we performed kinetic and structural analyses of the inhibitory activity of oxypurinol. Our results demonstrated that oxypurinol was less effective than allopurinol both in vivo and in vitro. We show that upon reoxidation to Mo(VI), oxypurinol binding is greatly weakened, and reduction by xanthine, hypoxanthine, or allopurinol is required for reformation of the inhibitor-enzyme complex. In addition, we show oxypurinol only weakly inhibits the conversion of hypoxanthine to xanthine and is therefore unlikely to affect the feedback inhibition of de novo purine synthesis. Furthermore, we observed weak allosteric inhibition of purine nucleoside phosphorylase by oxypurinol which has potentially adverse effects for patients. Considering these results, we propose the single-dose method currently used to treat hyperuricemia can result in unnecessarily high levels of allopurinol. While the short half-life of allopurinol in blood suggests that oxypurinol is responsible for enzyme inhibition, we anticipate multiple, smaller doses of allopurinol would reduce the total allopurinol patient load.

Raising serum uric acid with a uricase inhibitor worsens PKD in rat and mouse models.

Humans are predisposed to gout because they lack uricase that converts uric acid to allantoin. Rodents have uricase, resulting in low basal serum uric acid. A uricase inhibitor raises serum uric acid in rodents. There were two aims of the study in polycystic kidney disease (PKD): 1) to determine whether increasing serum uric acid with the uricase inhibitor, oxonic acid, resulted in faster cyst growth and 2) to determine whether treatment with the xanthine oxidase inhibitor, oxypurinol, reduced the cyst growth caused by oxonic acid. Orthologous models of human PKD were used: PCK rats, a polycystic kidney and hepatic disease 1 (Pkhd1) gene model of autosomal recessive PKD (ARPKD) and Pkd1RC/RC mice, a hypomorphic Pkd1 gene model. In PCK rats and Pkd1RC/RC mice, oxonic acid resulted in a significant increase in serum uric acid, kidney weight, and cyst index. Mechanisms of increased cyst growth that were investigated were proinflammatory cytokines, the inflammasome, and crystal deposition in the kidney. Oxonic acid resulted in an increase in proinflammatory cytokines in the serum and kidney in Pkd1RC/RC mice. Oxonic acid did not cause activation of the inflammasome or uric acid crystal deposition in the kidney. In Pkd1RC/RC male and female mice analyzed together, oxypurinol decreased the oxonic acid-induced increase in cyst index. In summary, increasing serum uric acid by inhibiting uricase with oxonic acid results in an increase in kidney weight and cyst index in PCK rats and Pkd1RC/RC mice. The effect is independent of inflammasome activation or crystal deposition in the kidney.NEW & NOTEWORTHY This is the first reported study of uric acid measurements and xanthine oxidase inhibition in polycystic kidney disease (PKD) rodents. Raising serum uric acid with a uricase inhibitor resulted in increased kidney weight and cyst index in Pkd1RC/RC mice and PCK rats, elevated levels of proinflammatory cytokines in the serum and kidney in Pkd1RC/RC mice, and no uric acid crystal deposition or activation of the caspase-1 inflammasome in the kidney.

The presence of xanthine dehydrogenase is crucial for the maturation of the rat kidneys.

The development of the kidney involves essential cellular processes, such as cell proliferation and differentiation, which are led by interactions between multiple signaling pathways. Xanthine dehydrogenase (XDH) catalyzes the reaction producing uric acid in the purine catabolism, which plays a multifaceted role in cellular metabolism. Our previous study revealed that the genetic ablation of the Xdh gene in rats leads to smaller kidneys, kidney damage, decline of renal functions, and failure to thrive. Rats, unlike humans, continue their kidney development postnatally. Therefore, we explored whether XDH plays a critical role in kidney development using SS-/- rats during postnatal development phase. XDH expression was significantly increased from postnatal day 5 to 15 in wild-type but not homozygote rat kidneys. The transcriptomic profile of renal tissue revealed several dysregulated pathways due to the lack of Xdh expression with the remodeling in inflammasome, purinergic signaling, and redox homeostasis. Further analysis suggested that lack of Xdh affects kidney development, likely via dysregulation of epidermal growth factor and its downstream STAT3 signaling. The present study showed that Xdh is essential for kidney maturation. Our data, alongside the previous research, suggests that loss of Xdh function leads to developmental issues, rendering them vulnerable to kidney diseases in adulthood.

Pipeline Therapies for Gout.

PURPOSE OF REVIEW: Despite effective available treatments, gout management is often unsuccessful in getting patients to target serum urate goal and in managing flares in the setting of comorbidities. Studies addressing future treatment options for short- and long-term management are reviewed. RECENT FINDINGS: URAT-1 blocking agents have been helpful but have had limitations related to effects on renal function, lack of efficacy with renal impairment, and potential to increase renal stones. Dotinurad may function in the setting of decreased renal function. Arhalofenate has anti-URAT-1 activity and may also blunt gout flares. A new xanthine oxidase inhibitor (XOI), tigulixostat, is under study. New uricase treatments manufactured in combination with agents that can reduce immunogenicity may make uricase treatment simpler. A unique strategy of inhibiting gut uricase may offer the benefits of avoiding systemic absorption. For gout flares, IL-1ß inhibitor studies in progress include different dosing schedules. Dapansutrile, an oral agent under investigation, inhibits activation of the NLRP3 inflammasome and may be an effective anti-inflammatory. New treatments for gout that are under study may work in the setting of comorbidities, simplify management, utilize new mechanisms, or have reduced side effects.

Rapid screening of xanthine oxidase inhibitors from Ligusticum wallichii by using xanthine oxidase functionalized magnetic metal-organic framework.

In this study, xanthine oxidase was immobilized for the first time using a novel magnetic metal-organic framework material (Fe3O4-SiO2-NH2@MnO2@ZIF-8-NH2). A ligand fishing method was established to rapidly screen XOD inhibitors from Ligusticum wallichii based on the immobilized XOD. Characterization and properties of the immobilized enzyme revealed its excellent stability and reusability. A ligand was screened from Ligusticum wallichii and identified as ligustilide by ultra-high performance liquid chromatography tandem mass spectrometry. The IC50 value of ligustilide was determined to be 27.70 ± 0.13 µM through in vitro inhibition testing. Furthermore, molecular docking verified that ligustilide could bind to amino acid residues at the active site of XOD. This study provides a rapid and effective method for the preliminary screening of XOD inhibitors from complex natural products and has great potential for further discovery of anti-hyperuricemic compounds.

Discovery of digallic acid as XOD/URAT1 dual target inhibitor for the treatment of hyperuricemia.

The development of XOD/URAT1 dual target inhibitors has emerged as a promising therapeutic strategy for the management of hyperuricemia. Here, through virtual screening, we have identified digallic acid as a novel dual target inhibitor of XOD/URAT1 and subsequently evaluated its pharmacological properties, pharmacokinetics, and toxicities. Digallic acid inhibited URAT1 with an IC50 of 5.34 ± 0.65 µM, which is less potent than benzbromarone (2.01 ± 0.36 µM) but more potent than lesinurad (10.36 ± 1.23 µM). Docking and mutation analysis indicated that residues S35, F241 and R477 of URAT1 confer a high affinity for digallic acid. Digallic acid inhibited XOD with an IC50 of 1.04 ± 0.23 µM. Its metabolic product, gallic acid, inhibited XOD with an IC50 of 0.91 ± 0.14 µM. Enzyme kinetic studies indicated that both digallic acid and gallic acid act as mixed-type XOD inhibitors. It shares the same binding mode as digallic acid, and residues E802, R880, F914, T1010, N768 and F1009 contribute to their high affinity. The anion group (carboxyl) of digallic acid contribute significantly to its inhibition activity on both XOD and URAT1 as indicated by docking analysis. Remarkably, at a dosage of 10 mg/kg in vivo, digallic acid exhibited a stronger urate-lowering and uricosuric effect compared to the positive drug benzbromarone and lesinurad. Pharmacokinetic study indicated that digallic acid can be hydrolyzed into gallic acid in vivo and has a t1/2 of 0.77 ± 0.10 h. Further toxicity evaluation indicated that digallic acid exhibited no obvious renal toxicity, as reflected by CCK-8, biochemical analysis (CR and BUN) and HE examination. The findings of our study can provide valuable insights for the development of XOD/URAT1 dual target inhibitors, and digallic acid deserves further investigation as a potential anti-hyperuricemic drug.

Pathology, target discovery, and the evolution of XO inhibitors from the first discovery to recent advances (2020-2023).

Hyperuricemia, a disease characterized by elevation of serum uric acid level beyond 6 mg/dL. This elevation led to appearance of symptoms from joint pain to gout and from gout to difficulty in mobility of the patient. So, in this review, we have summarized the pathology of hyperuricemia, discovery of target and discovery of first XO inhibitor. At last, this review provides in-sights about the recently discovered as natural XO inhibitors, followed by design, structure activity relationship and biological activity of synthetic compounds as XO inhibitors discovered between 2020 and 2023 years. At last, the pharmacophores generated in this study will guide new researchers to design and modify the structure of novel XO inhibitors.

Allopurinol use leading to xanthine nephrolithiasis in pediatric tumor lysis syndrome: a case series.

Tumor lysis syndrome (TLS) is a life-threatening metabolic disorder caused by massive tumor lysis. Allopurinol, a xanthine oxidase inhibitor, is initiated during chemotherapy to prevent hyperuricemia and subsequent acute kidney injury (AKI). We report two cases of xanthine nephrolithiasis during TLS in newly diagnosed hematologic malignancy patients receiving prophylactic allopurinol. Allopurinol use likely promoted xanthine crystallization, stone formation, and AKI.

A comprehensive review of synthetic and semisynthetic xanthine oxidase inhibitors: identification of potential leads based on in-silico computed ADME characteristics.

Xanthine oxidase (XO) inhibitors, both synthetic and semisynthetic, have been developed extensively over the past few decades. The increased level of XO is not only the major cause of gout but is also responsible for various conditions associated with hyperuricemia, such as cardiovascular disorders, chronic kidney disorders, diabetes, Alzheimer's disease and chronic wounds. Marketed available XO inhibitors (allopurinol, febuxostat, and topiroxostat) are used to treat hyperuricemia but they are associated with fatal side effects, which pose serious problems for the healthcare system, rising the need for new, more potent, safer compounds. This review summarizes recent findings on XO and describes their design, synthesis, biological significance in the development of anti-hyperuricemic drugs with ADME profile, structure activity relationship (SAR) and molecular docking studies. The results might help medicinal chemists to develop more efficacious XO inhibitors.

Efficacy and safety of the urate-lowering agent febuxostat in chronic heart failure patients with hyperuricemia: results from the LEAF-CHF study.

Hyperuricemia is an independent predictor of mortality in patients with chronic heart failure (CHF). To determine whether febuxostat, a urate-lowering agent, may improve clinical outcomes in CHF patients, we conducted a multicenter, prospective, randomized, open-label, blinded endpoint study with a treatment period of 24 weeks. We randomly assigned Japanese outpatients diagnosed with both CHF with reduced left ventricular ejection fraction (LVEF < 40%) and asymptomatic hyperuricemia (serum uric acid [UA] levels > 7.0 mg/dl and < 10.0 mg/dl) to either a febuxostat group (n = 51) or a control group (n = 50). The primary efficacy endpoint was the change in log-transformed plasma B-type natriuretic peptide (BNP) levels from baseline to week 24 (or at discontinuation). The secondary efficacy endpoints were the changes in LV systolic or diastolic function evaluated by echocardiography, New York Heart Association (NYHA) class, hemoglobin, and estimated glomerular filtration rate from baseline to week 24, and the change in log-transformed plasma BNP levels or serum UA levels from baseline to weeks 4, 8, 12, 16 and 20 (BNP) or weeks 4, 8, 12, 16, 20 and 24 (serum UA). The primary safety endpoints were occurrence of all-cause death or major cardiovascular events. The mean age of participants was 70 years; 14% were female. The febuxostat group and the control group did not differ with respect to the primary efficacy endpoint (p = 0.13), although the decrease in log-transformed plasma BNP levels from baseline to each of weeks 4, 8, 12, 16 and 20 was greater in the febuxostat group. There were no significant differences between the two groups in the primary safety endpoints or the secondary efficacy endpoints except reduced serum UA levels in the febuxostat group. Febuxostat did not reduce plasma BNP levels at week 24 in patients with CHF, but it appeared safe with no increase in major cardiovascular events and all-cause or cardiovascular mortality.

Screening, isolation, and activity evaluation of potential xanthine oxidase inhibitors in Poria Cum Radix Pini and mechanism of action in the treatment of gout disease.

Poria Cum Radix Pini is a rare medicinal fungus that contains several potential therapeutic ingredients. On this basis, a particle swarm mathematical model was used to optimize the extraction process of total triterpenes from P. Cum Radix Pini, and xanthine oxidase inhibitors were screened using affinity ultrafiltration mass spectrometry. Meanwhile, the accuracy of the ultrafiltration assay was verified by molecular docking experiments and molecular dynamics analysis, and the mechanism of action of the active compounds for the treatment of gout was analyzed by enzymatic reaction kinetics and network pharmacology. A high-speed countercurrent chromatography method combined with the consecutive injection and the economical two-phase solvent system preparation using functional activity coefficient of universal quasichemical model (UNIFAC) mathematical model was developed for increasing the yield of target compound. In addition, dehydropachymic acid and pachymic acid were used as competitive inhibitors, and 3-O-acetyl-16alpha-hydroxydehydrotrametenolic acid and dehydrotrametenolic acid were used as mixed inhibitors. Then, activity-oriented separation and purification were performed by high-speed countercurrent chromatography combined with semi-preparative high-performance liquid chromatography and the purity of the four compounds isolated was higher than 90%. It will help to provide more opportunities to discover and develop new potential therapeutic remedies from health care food resources.

Enhanced hypoxanthine utilization for cAMP salvage synthesis efficiently by Arthrobacter sp. CCTCC 2013431 via xanthine oxidase inhibition.

When hypoxanthine was utilized as the activator for the salvage pathway in cAMP synthesis, xanthine oxidase would generate in quantity leading to low hypoxanthine conversion ratios and cell viability. To enhance cAMP salvage synthesis, fermentations with citrate/luteolin and hypoxanthine coupling added were conducted in a 7 L bioreactor and then multiple physiological indicators of fermentation with luteolin addition were assayed. Due to hypoxanthine feeding, cAMP productivity reached 0.066 g/(L·h) with 43.5% higher than control, however, cAMP synthesis, cell growth and glucose uptake all ceased at 50 h which was shortened by 22 h in comparison to control. The addition of citrate resulted in the cessation of fermentation at 61 h, on the contrary, owing to luteolin addition, cAMP fermentation performance was enhanced significantly during the whole fermentation period (72 h) with higher hypoxanthine conversion ratios and cAMP contents when compared with citrate and only hypoxanthine added batches. Multiple physiological indicators revealed that luteolin inhibited xanthine oxidase activity reducing hypoxanthine decomposition and ROS generation. ATP/AMP, NADH/NAD+ and NADPH/NADP+ were significantly increased especially at the late phase. Moreover, HPRT, PUP expression contents and corresponding gene transcription levels were also elevated. Luteolin could inhibit xanthine oxidase activity and further decrease hypoxanthine decomposition and ROS generation leading to higher hypoxanthine conversion and less cell damage for cAMP salvage synthesis efficiently.

Synthesis and Biological Evaluation of Novel Chlorogenic Acid-Apigenin Conjugates as Anti-acute Gout Agents.

Gout is the second largest metabolic disease worldwide after diabetes, with acute gouty arthritis as most common symptom. Xanthine oxidase (XOD) and the NOD like receptor-3 (NLRP3) inflammasome are the key targets for acute gout treatment. Chlorogenic acid has been reported with a good anti-inflammatory activity, and Apigenin showed an excellent potential in XOD inhibition. Therefore, a series of chlorogenic acid-apigenin (CA) conjugates with varying linkers were designed and synthesized as dual XOD/NLRP3 inhibitors, and their activities both in XOD and NLRP3 inhibition were evaluated. An in vitro study of XOD inhibitory activity revealed that the majority of CA conjugates exhibited favorable XOD inhibitory activity. Particularly, the effects of compounds 10c and 10d, with an alkyl linker on the apigenin moiety, were stronger than that of allopurinol. The selected CA conjugates also demonstrated a favorable anti-inflammatory activity in RAW264.7 cells. Furthermore, compound 10d, which showed the optimal activity both in XOD inhibition and anti-inflammatory, was chosen and its inhibitory ability on NLRP3 and related proinflammatory cytokines was further tested. Compound 10d effectively reduced NLRP3 expression and the secretion of interluekin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) with an activity stronger than the positive control isoliquiritigenin (ISL). Based on these findings, compound 10d exhibits dual XOD/NLRP3 inhibitory activity and, therefore, the therapeutic effects on acute gout is worthy of further study.

Phytochemical Analysis, and Antioxidant and Hepatoprotective Activities of Chamaerops humilis L. Leaves; A Focus on Xanthine Oxidase.

Chamaerops humilis L. is clumping palm of the family Arecaceae with promising health-promoting effects. Parts of this species are utilized as food and employed in folk medicine to treat several disorders. This study investigated the phytochemical constituents of C. humilis leaves and their antioxidant and xanthine oxidase (XO) inhibitory activities in vitro and in vivo in acetaminophen (APAP)-induced hepatotoxicity in rats. The chemical structure of the isolated phytochemicals was determined using data obtained from UV, MS, IR, and 1H-, 13C-NMR spectroscopic tools as well as comparison with authentic markers. Eleven compounds, including tricin 7-O-ß-rutinoside, vicenin, tricin, astragalin, borassoside D, pregnane-3,5,6,16-tetrol, oleanolic acid, ß-sitosterol and campesterol were isolated from C. humilis ethanolic extract (CHEE). CHEE and the butanol, n-hexane, and dichloromethane fractions exhibited in vitro radical scavenging and XO inhibitory efficacies. The computational findings revealed the tendency of the isolated compounds towards the active site of XO. In vivo, CHEE ameliorated liver function markers and prevented tissue injury induced by APAP in rats. CHEE suppressed hepatic XO, decreased serum uric acid and liver malondialdehyde (MDA), and enhanced reduced glutathione (GSH), superoxide dismutase (SOD), and catalase in APAP-treated rats. CHEE ameliorated serum tumor necrosis factor alpha (TNF-α) and interleukin (IL)-1ß in APAP-treated rats. Thus, C. humilis is rich in beneficial phytochemicals that possess binding affinity towards XO. C. humilis exhibited potent in vitro antioxidant and XO inhibitory activities, and prevented APAP hepatotoxicity by attenuating tissue injury, oxidative stress and inflammation.

Single substrate-functionalized molybdenum oxide nanozyme for specific colorimetric monitoring of xanthine oxidase activity.

Xanthine-functionalized molybdenum oxide nanodots (X-MoO3-x NDs) with peroxidase (POD)-like activity were developed for selective, sensitive, and facile colorimetric quantification of xanthine oxidase (XO). Xanthine functionalization can not only be favorable for the successful nanozyme preparation, but also for the specific recognition of XO as well as the simultaneous generation of hydrogen peroxide, which was subsequently transformed into hydroxyl radical to oxidize the chromogenic reagent based on the POD-like catalysis. Under the optimized conditions, the colorimetric biosensing platform was established for XO assay without addition of further substrates, showing good linearity relationship between absorbance difference (ΔA) and XO concentrations in the range 0.05-0.5 U/mL (R2 = 0.998) with a limit of detection (LOD) of 0.019 U/mL. The quantification of XO occurs in 25 min, which is superior to the previously reported and commercial XO assays. The proposed method has been successfully used in the assay of human serum samples, showing its high potential in the field of clinical monitoring.

Triazole derivatives as potential xanthine oxidase inhibitors: Design, enzyme inhibition potential, and docking studies.

Considerable ingenuity has been shown in the recent years in the discovery of novel xanthine oxidase (XO) inhibitors that fall outside the purine scaffold. The triazole nucleus has been the cornerstone for the development of many enzyme inhibitors for the clinical management of several diseases, where hyperuricemia is one of them. Here, we give a critical overview of significant research on triazole-based XO inhibitors, with respect to their design, synthesis, inhibition potential, toxicity, and docking studies, done till now. Based on these literature findings, we can expect a burst of modifications on triazole-based scaffolds in the near future by targeting XO, which will treat hyperuricemics, that is, painful conditions like gout that at present are hard to deal with.

Discovery of 4-(isopentyloxy)-3-nitrobenzamide derivatives as xanthine oxidase inhibitors through a non-anthraquinone exploration.

In our previous study, we reported a series of N-(9,10-anthraquinone-2-carbonyl) amino acid derivatives as novel inhibitors of xanthine oxidase (XO). Recognizing the suboptimal drug-like properties associated with the anthraquinone moiety, we embarked on a nonanthraquinone medicinal chemistry exploration in the current investigation. Through systematic structure-activity relationship (SAR) studies, we identified a series of 4-(isopentyloxy)-3-nitrobenzamide derivatives exhibiting excellent in vitro potency against XO. The optimized compound, 4-isopentyloxy-N-(1H-pyrazol-3-yl)-3-nitrobenzamide (6k), demonstrated exceptional in vitro potency with an IC50 value of 0.13 µM. Compound 6k showed favorable drug-like characteristics with ligand efficiency (LE) and lipophilic ligand efficiency (LLE) values of 0.41 and 3.73, respectively. In comparison to the initial compound 1d, 6k exhibited a substantial 24-fold improvement in IC50, along with a 1.6-fold enhancement in LE and a 3.7-fold increase in LLE. Molecular modeling studies provided insights into the strong interactions of 6k with critical amino acid residues within the active site. Furthermore, in vivo hypouricemic investigations convincingly demonstrated that 6k significantly reduced serum uric acid levels in rats. The MTT results revealed that compound 6k is nontoxic to healthy cells. The gastric and intestinal stability assay demonstrated that compound 6k exhibits good stability in the gastric and intestinal environments. In conclusion, compound 6k emerges as a promising lead compound, showcasing both exceptional in vitro potency and favorable drug-like characteristics, thereby warranting further exploration.

Rapid screening, isolation, and activity evaluation of potential xanthine oxidase inhibitors in Polyporus umbellatus and mechanism of action in the treatment of gout.

INTRODUCTION: Studies show that Polyporus umbellatus has some pharmacological effects in enhancing immunity and against gout. OBJECTIVES: We aimed to establish new techniques for extraction, biological activity screening, and preparation of xanthine oxidase inhibitors (XODIs) from P. umbellatus. METHODS: First, the extraction of P. umbellatus was investigated using the back propagation (BP) neural network genetic algorithm mathematical regression model, and the extraction variables were optimised to maximise P. umbellatus yield. Second, XODIs were rapidly screened using ultrafiltration, and the change of XOD activity was tested by enzymatic reaction kinetics experiment to reflect the inhibitory effect of active compounds on XOD. Meanwhile, the potential anti-gout effects of the obtained active substances were verified using molecular docking, molecular dynamics simulations, and network pharmacology analysis. Finally, with activity screening as guide, a high-speed countercurrent chromatography (HSCCC) method combined with consecutive injection and two-phase solvent system preparation using the UNIFAC mathematical model was successfully developed for separation and purification of XODIs, and the XODIs were identified using MS and NMR. RESULTS: The results verified that polyporusterone A, polyporusterone B, ergosta-4,6,8(14),22-tetraen-3-one, and ergosta-7,22-dien-3-one of P. umbellatus exhibited high biological affinity towards XOD. Their structures have been further identified by NMR, indicating that the method is effective and applicable for rapid screening and identification of XODIs. CONCLUSION: This study provides new ideas for the search for natural XODIs active ingredients, and the study provide valuable support for the further development of functional foods with potential therapeutic benefits.

A derivative of trihydroxynaphthalenone and a pyrone metabolite from the endophytic fungus Talaromyces purpurpgenus.

A newly discovered trihydroxynaphthalenone derivative, epoxynaphthalenone (1) involving the condensation of ortho-hydroxyl groups into an epoxy structure, and a novel pyrone metabolite characterized as pyroneaceacid (2), were extracted from Talaromyces purpurpgenus, an endophytic fungus residing in Rhododendron molle. The structures of these compounds were elucidated through a comprehensive analysis of their NMR and HRESIMS data. The determination of absolute configurations was accomplished using electronic circular dichroism (ECD) calculations and CD spectra. Notably, these recently identified metabolites exhibited a moderate inhibitory activity against xanthine oxidase (XOD).

Interaction of Tri-Cyclic Nucleobase Analogs with Enzymes of Purine Metabolism: Xanthine Oxidase and Purine Nucleoside Phosphorylase.

Fluorescent markers play important roles in spectroscopic and microscopic research techniques and are broadly used in basic and applied sciences. We have obtained markers with fluorescent properties, two etheno derivatives of 2-aminopurine, as follows: 1,N2-etheno-2-aminopurine (1,N2-ε2APu, I) and N2,3-etheno-2-aminopurine (N2,3-ε2APu, II). In the present paper, we investigate their interaction with two key enzymes of purine metabolism, purine nucleoside phosphorylase (PNP), and xanthine oxidase (XO), using diffraction of X-rays on protein crystals, isothermal titration calorimetry, and fluorescence spectroscopy. Crystals were obtained and structures were solved for WT PNP and D204N-PNP mutant in a complex with N2,3-ε2APu (II). In the case of WT PNP-1,N2-ε2APu (I) complex, the electron density corresponding to the ligand could not be identified in the active site. Small electron density bobbles may indicate that the ligand binds to the active site of a small number of molecules. On the basis of spectroscopic studies in solution, we found that, in contrast to PNP, 1,N2-ε2APu (I) is the ligand with better affinity to XO. Enzymatic oxidation of (I) leads to a marked increase in fluorescence near 400 nm. Hence, we have developed a new method to determine XO activity in biological material, particularly suitable for milk analysis.