Mechanistic insights into xanthine oxidoreductase from development studies of candidate drugs to treat hyperuricemia and gout

Estrogen-mediated inhibition of purine metabolism and cell cycle arrest as a novel therapeutic approach in colorectal cancer

Purine metabolism is upregulated in various cancers including colorectal cancer (CRC). While previous work has elucidated the role of estrogen (E2) in metabolic reprogramming and ATP production, the effect of E2 on purine metabolism remains largely unknown. Herein, the impact of E2 signalling on purine metabolism in CRC cells was investigated using metabolome and transcriptome profiling of cell extracts derived from E2-treated HCT-116 cells with intact or silenced estrogen receptor alpha (ERα). Purine metabolic pathway enrichment analysis showed that 27 genes in the de novo purine synthesis pathway were downregulated in E2-treated CRC cells. Downstream consequences of E2 treatment including the induction of DNA damage, cell cycle arrest, and apoptosis were all shown to be ERα-dependent. These findings demonstrate, for the first time, that E2 exerts a significant anti-growth and survival effect in CRC cells by targeting the purine synthesis pathway in a ERα-dependent manner, meriting further investigation of the therapeutic utility of E2 signalling in CRC.

The potential role of uric acid in women with polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder among women of reproductive age and is associated with a variety of multi-system complications. The prevailing treatment strategy for PCOS is to individualize the interventions based on individual symptoms and patient complaints. However, optimal efficacy in treatment necessitates a focus on addressing the underlying pathogenic mechanisms. Uric acid (UA), the end product of purine metabolism, has been suggested to be involved in the development of several diseases, including PCOS. However, the precise mechanisms by which UA may affect PCOS remain incompletely understood. This literature review aims to investigate the correlation between UA and the various clinical presentations of PCOS, such as hyperandrogenism, insulin resistance (IR), ovulation disorders, obesity, and other related manifestations, through the analysis of epidemiological and clinical studies. The purpose of this study is to improve our comprehension of how UA contributes to each aspect of PCOS and their interrelationship, thus identifying the potential role of UA as a facilitator of PCOS. Furthermore, we explore potential pathways linking UA and PCOS, and propose therapeutic interventions based on these findings to optimize the management of this condition.

Redox-dependent purine degradation triggers postnatal loss of cardiac regeneration potential

Postnatal cardiomyocyte cell cycle withdrawal is a critical step wherein the mammalian heart loses regenerative potential after birth. Here, we conducted interspecies multi-omic comparisons between the mouse heart and that of the opossum, which have different postnatal time-windows for cardiomyocyte cell cycle withdrawal. Xanthine metabolism was activated in both postnatal hearts in parallel with cardiomyocyte cell cycle arrest. The pentose phosphate pathway (PPP) which produces NADPH was found to decrease simultaneously. Postnatal myocardial tissues became oxidized accordingly, and administration of antioxidants to neonatal mice altered the PPP and suppressed the postnatal activation of cardiac xanthine metabolism. These results suggest a redox-driven postnatal switch from purine synthesis to degradation in the heart. Importantly, inhibition of xanthine metabolism in the postnatal heart extended postnatal duration of cardiomyocyte proliferation and maintained postnatal heart regeneration potential in mice. These findings highlight a novel role of xanthine metabolism as a redox-dependent metabolic regulator of cardiac regeneration potential.

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.

Effects of Febuxostat Therapy on Circulating Adipokine Profiles in Patients with Overweight or Obesity and Asymptomatic Hyperuricemia: A Randomized Controlled Study

INTRODUCTION

Elevated levels of serum uric acid (SUA) are strongly associated with several components of the metabolic syndrome, particularly obesity. Previous studies have reported the correlation between SUA levels, xanthine oxidoreductase (XOR) activity, and the imbalanced adipokine levels that are characteristic of obesity. In this study, we explored the effect of febuxostat on circulating adipokine profiles in patients with overweight or obesity and asymptomatic hyperuricemia.

METHODS

This study was a single-center, randomized, and controlled clinical trial that enrolled 130 participants with asymptomatic hyperuricemia and obesity. One hundred seventeen participants were included in the final analysis, with 60 participants in the febuxostat group and 57 in the control group. We compared the circulating adipokine levels at 3 and 6 months, including high molecular weight (HMW) adiponectin, chemerin, omentin, monocyte chemotactic protein-1, asprosin, fibroblast growth factor 21, neuregulin-4, leptin, resistin, vaspin, visfatin, adipsin, and assessed the correlation between changes in adipokine levels (Δadipokines) and changes in XOR activity (ΔXOR) after febuxostat treatment.

RESULTS

The results showed that an increase in HMW adiponectin and omentin levels and a decrease in chemerin and asprosin levels at 3 or 6 months compared to the control group. Additionally, a positive correlation was observed between ΔXOR activity and Δasprosin. Furthermore, after adjusting for triglyceride (ΔTG) and serum uric acid (ΔSUA) in multiple linear regression analyses, we found that ΔXOR activity was independently correlated with Δasprosin.

CONCLUSION

This study may provide important evidence that febuxostat could alleviate the imbalance in circulating adipokine levels in patients with overweight or obesity and asymptomatic hyperuricemia. Furthermore, we observed a positive correlation between changes in asprosin levels and changes in XOR activity after febuxostat treatment.

Xanthine oxidoreductase inhibition ameliorates high glucose-induced glomerular endothelial injury by activating AMPK through the purine salvage pathway

Xanthine oxidoreductase (XOR) contributes to reactive oxygen species production. We investigated the cytoprotective mechanisms of XOR inhibition against high glucose (HG)-induced glomerular endothelial injury, which involves activation of the AMP-activated protein kinase (AMPK). Human glomerular endothelial cells (GECs) exposed to HG were subjected to febuxostat treatment for 48 h and the expressions of AMPK and its associated signaling pathways were evaluated. HG-treated GECs were increased xanthine oxidase/xanthine dehydrogenase levels and decreased intracellular AMP/ATP ratio, and these effects were reversed by febuxostat treatment. Febuxostat enhanced the phosphorylation of AMPK, the activation of peroxisome proliferator-activated receptor (PPAR)-gamma coactivator (PGC)-1α and PPAR-α and suppressed the phosphorylation of forkhead box O (FoxO)3a in HG-treated GECs. Febuxostat also decreased nicotinamide adenine dinucleotide phosphate oxidase (Nox)1, Nox2, and Nox4 expressions; enhanced superoxide dismutase activity; and decreased malondialdehyde levels in HG-treated GECs. The knockdown of AMPK inhibited PGC-1α-FoxO3a signaling and negated the antioxidant effects of febuxostat in HG-treated GECs. Despite febuxostat administration, the knockdown of hypoxanthine phosphoribosyl transferase 1 (HPRT1) also inhibited AMPK-PGC-1α-FoxO3a in HG-treated GECs. XOR inhibition alleviates oxidative stress by activating AMPK-PGC-1α-FoxO3a signaling through the HPRT1-dependent purine salvage pathway in GECs exposed to HG conditions.

Effect of lactation on the distribution of mineral elements in goat milk

The distribution of mineral elements in milk is crucial for their absorption and utilization, however, there has been limited attention given to the status of mineral elements in goat milk. In this study, goat milk was collected at 4 lactation periods (1-3, 90, 150, 240 d) and separated into 4 fractions (fat, casein, whey, and aqueous phase). The concentrations of Mg, Ca, Na, K, Zn, Fe, Cu, Mn, Co, Ni, Mo, and Cr in 4 fractions were analyzed using an inductively coupled plasma emission spectrometer. Our findings reveal that Ca, Zn, Fe, Cu, Mn, and Cr exhibit the highest levels in casein, while Mo demonstrates the highest content in whey. Additionally, Mg, Na, K, and Ni display the highest concentrations in the aqueous phase. Specifically, the contents of Ca, Cu and Fe in casein decrease from 1-3 to 150 d of lactation but increase from 150 to 240 d of lactation. Furthermore, the content of Mg in the aqueous phase decreases from 1-3 to 90 d of lactation but increases from 90 to 240 d of lactation. The content of Na and K in the aqueous phase decreases from 1-3 to 150 d of lactation. Notably, the content of Mo in whey increases from 1-3 to 150 d of lactation and decreases from 150 to 240 d. Our research contributes to the advancement of understanding the bioavailability of mineral elements in goat milk.

Mechanistic insights into iron-sulfur clusters and flavin oxidation of a novel xanthine oxidoreductase from Sulfobacillus acidophilus TPY

Xanthine oxidoreductase (XOR) catalyzes the oxidation of purines (hypoxanthine and xanthine) to uric acid. XOR is widely used in various therapeutic and biotechnological applications. In this study, we characterized the biophysical and mechanistic properties of a novel bacterial XOR from Sulfobacillus acidophilus TPY (SaXOR). Our results showed that SaXOR is a heterotrimer consisting of three subunits, namely XoA, XoB, and XoC, which denote the molybdenum cofactor (Moco), 2Fe-2S, and FAD-binding domains, respectively. XoC was found to be stable when co-expressed with XoB, forming an XoBC complex. Furthermore, we prepared a fusion of XoB and XoC via a flexible linker (fusXoBC) and evaluated its function in comparison to that of XoBC. Spectroscopic analysis revealed that XoB harbors two 2Fe-2S clusters, whereas XoC bears a single-bound FAD cofactor. Electron transfer from reduced forms of XoC, XoBC, and fusXoBC to molecular oxygen (O2 ) during oxidative half-reaction yielded no flavin semiquinones, implying ultrafast single-electron transfer from 2Fe-2Sred to FAD. In the presence of XoA, XoBC and fusXoBC exhibited comparable XoA affinity and exploited a shared overall mechanism. Nonetheless, the linkage may accelerate the two-step, single-electron transfer cascade from 2Fe-2Sred to FAD while augmenting protein stability. Collectively, our findings provide novel insights into SaXOR properties and oxidation mechanisms divergent from prior mammalian and bacterial XOR paradigms.

Distinctive biochemistry profiles associated with hyperuricemia between Tibetans and Hans in China

Purpose

We sought to identify distinct risk factors for hyperuricemia in native Tibetan and immigrant Han populations in Tibet, China.

Methods

Three cohorts of male participants aged between 20 and 40 years were enrolled in this study. Biochemical parameters including serum uric acid (UA), fasting plasma glucose, insulin, lactate dehydrogenase (LDH), thyroxin, blood cell count, aminotransferase, and lipid profiles were analyzed. The association of risk factors with UA levels was evaluated using a multivariable line regression model. The effect of UA level on the biochemical parameters between the Hans and Tibetans was evaluated by two-way ANOVA.

Results

The prevalence of hyperuricemia (≥420 μmol/L) was 24.8% (62/250) in the Hans, similar to 23.8% (29/136) in the Tibetans. In the regression analysis, the risk factors that were significantly associated with UA in Hans did not apply to Tibetans. Tibetans had higher fasting insulin (P<0.05) and LDH (P<0.01) levels, in contrast with lower levels of triglycerides (P<0.05), total cholesterol (P<0.01), and low-density lipoprotein-cholesterol (P<0.01) than Hans in normal UA populations. Biochemistry analysis revealed lower albumin levels (P<0.001) and higher levels of all aminotransaminase and especially alkaline phosphatase (P<0.01) in Tibetans than in Hans in both populations. Compared with Hans, Tibetans had lower serum levels of urea, creatinine, and electrolytes in the normal UA population, which were further exacerbated in the high UA population. Tibetans had comparable white blood cell counts as Hans in both normal and high UA populations. In contrast, the red blood cell count and hemoglobin concentration were much lower in Tibetans than in Hans under high UA conditions.

Conclusions

The distinctive biochemistry between Tibetans and Hans may underlie the different etiologies of hyperuricemia in Tibet, China.

Raman Spectroscopy for the Quantitative Analysis of Solid Dosage Forms of the Active Pharmaceutical Ingredient of Febuxostat

Raman spectroscopy has been used to characterize and quantify the solid dosage forms of the commercially available drug febuxostat. For this purpose, different formulations consisting of the febuxostat (API) and excipients with different concentrations of the API are prepared and analyzed by Raman spectroscopy to identify different spectral features related to the febuxostat API and excipients. Multivariate data analysis tools such as principal component analysis (PCA) and partial least-squares regression (PLSR) analysis are used for qualitative and quantitative analyses. PCA has been found to be useful for the qualitative monitoring of various solid dosage forms. PLSR analysis has led to the successful prediction of API concentration in the unknown samples with a sensitivity and a selectivity of 98 and 99%, respectively. Moreover, the root-mean-square error (RMSE) of calibration and validation of the PLSR model has been found to be 2.9033 and 1.35, respectively. Notably, it is found to be very helpful for the comparison between the self-made formulations of febuxostat and commercially available febuxostat tablets (40 and 80 mg) of two different brands (Gouric and Zurig). These results showed that Raman spectroscopy can be a useful and reliable technique for identifying and quantifying the active pharmaceutical ingredient (API) in commercially available solid dosage forms.

How hypoxia affects microbiota metabolism in mice

Objective

To investigate the relationship between gut microbiota and the fecal metabolites of hypoxic environments in mice.

Methods

High-fat diet-induced obese mice (n = 20) and normal diet-fed mice (n = 20) were randomly divided into four groups: high altitude obese group (HOB), high altitude normal weight group (HN), low altitude obese group LOB (LOB), and low altitude normal weight group (LN). Fecal samples from each group were 16S rRNA gene sequenced, and five samples from each of the four groups above were selected for non-targeted fecal metabolomics analysis using liquid chromatography-mass spectrometry. The relationship between gut microbiota and fecal metabolites was analyzed using SIMCA 14.1, MetaboAnalyst 5.0 and R 4.1.11.

Results

(A) Body weight was significantly lower in the hypoxic obesity group than in the normoxic obesity group. (B) Differences in α-diversity and β-diversity were found in the fecal gut microbiota of mice of different body weights and altitude, and the diversity of gut microbiota was higher in the normal group than in the obese group; the results of the comparison between the two groups showed that Faecalibaculum, Romboutsia, Lactobacillus, and A2 were associated with obesity; Romboutsia was associated with hypoxia. (C) The metabolic profiles of fecal metabolites differed between groups: gut microbiota were associated with nucleotide and amino acid metabolism in the same body groups, while gut microbiota were associated with lipid and amino acid metabolism in the same oxygen concentration groups.

Conclusion

(a) Gut microbiota diversity was reduced in obese groups. Romboutsia was the dominant microbiota in the hypoxia group. (b) Gut microbiota were associated with nucleotide and amino acid metabolism in the same body weight groups, while they were associated with lipid and amino acid metabolism in the same altitude groups.

A novel multi-hyphenated approach to screen and character the xanthine oxidase inhibitors from saffron floral bio-residues

Recently, the incidence of hyperuricemia increased with patient rejuvenation, searching for new xanthine oxidase (XOD) inhibitors from natural products becomes important. In our previous work, a flavonoid extract of saffron floral bio-residues (SFB) was found to alleviate hyperuricemia via inhibiting XOD. In this study, an integrated approach combining two-dimensional liquid chromatography, surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) was developed to online screen and character the potential XOD inhibitors from SFB. The two-dimensional liquid chromatography consisted of affinity chromatography and reverse phase chromatography (2D-AR), in which an XOD column, an inactive XOD column, and a control column were used in the first dimensional liquid chromatography to avoid phenomena of "false positive" and "missing screen of compounds with weak affinity to XOD" that often occur in the screening process, and a C18 column was used in the second dimensional liquid chromatography to separate the mixed XOD binders. Four flavonoid glycosides, i.e., quercetin-3-O-sophoroside (QS), kaempferol-3-O-sophoroside (KS), kaempferol-3-O-rutinoside (KR), and kaempferol-3-O-glucoside (KG), were thus successfully screened and identified from SFB extract by the 2D-AR method. The affinity of QS, KS, KR, KG, kaempferol (aglycone of KS, KR and KG), and quercetin (aglycone of QS) binding to XOD was investigated using SPR method, with KD ranged from 4.8 μM to 47.6 μM. The inhibitor constant (KI) of KS, KR, KG, quercetin and kaempferol were 4.92 mM, 1.11 mM, 0.294 mM, 4.93 μM and 3.27 μM, respectively, determined using ITC method. Finally, the anti-XOD activities of KS, the most abundant flavonoid in SFB extract, and kaempferol in hyperuricemia mice were verified, which suggested that the multi-hyphenated approach established herein can be applied for screen and character the XOD inhibitors in natural products.

Redox regulation in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most devastating complications of diabetes mellitus, where currently there is no cure available. Several important mechanisms contribute to the pathogenesis of this complication, with oxidative stress being one of the key factors. The past decades have seen a large number of publications with various aspects of this topic; however, the specific details of redox regulation in DKD are still unclear. This is partly because redox biology is very complex, coupled with a complex and heterogeneous organ with numerous cell types. Furthermore, often times terms such as "oxidative stress" or reactive oxygen species are used as a general term to cover a wide and rich variety of reactive species and their differing reactions. However, no reactive species are the same, and not all of them are capable of biologically relevant reactions or "redox signaling." The goal of this review is to provide a biochemical background for an array of specific reactive oxygen species types with varying reactivity and specificity in the kidney as well as highlight some of the advances in redox biology that are paving the way to a better understanding of DKD development and risk.

Investigation of the Inhibition Mechanism of Xanthine Oxidoreductase by Oxipurinol: A Computational Study

Xanthine oxidoreductase (XOR) is an enzyme found in various organisms. It converts hypoxanthine to xanthine and urate, which are crucial steps in purine elimination in humans. Elevated uric acid levels can lead to conditions like gout and hyperuricemia. Therefore, there is significant interest in developing drugs that target XOR for treating these conditions and other diseases. Oxipurinol, an analogue of xanthine, is a well-known inhibitor of XOR. Crystallographic studies have revealed that oxipurinol directly binds to the molybdenum cofactor (MoCo) in XOR. However, the precise details of the inhibition mechanism are still unclear, which would be valuable for designing more effective drugs with similar inhibitory functions. In this study, molecular dynamics and quantum mechanics/molecular mechanics calculations are employed to investigate the inhibition mechanism of XOR by oxipurinol. The study examines the structural and dynamic effects of oxipurinol on the pre-catalytic structure of the metabolite-bound system. Our results provide insights on the reaction mechanism catalyzed by the MoCo center in the active site, which aligns well with experimental findings. Furthermore, the results provide insights into the residues surrounding the active site and propose an alternative mechanism for developing alternative covalent inhibitors.

A Newly Developed Method-Based Xanthine Oxidoreductase Activities in Various Human Liver Diseases

Studies evaluating xanthine oxidoreductase (XOR) activities in comprehensive liver diseases are scarce, and different etiologies have previously been combined in groups for comparison. To accurately evaluate XOR activities in liver diseases, the plasma XOR activities in etiology-based comprehensive liver diseases were measured using a novel, sensitive, and accurate assay that is a combination of liquid chromatography and triple quadrupole mass spectrometry to detect [¹³C₂, ¹⁵N₂]uric acid using [¹³C₂, ¹⁵N₂]xanthine as a substrate. We also mainly evaluated the association between the plasma XOR activities and parameters of liver tests, purine metabolism-associated markers, oxidative stress markers, and an inflammation marker. In total, 329 patients and 32 controls were enrolled in our study. Plasma XOR activities were generally increased in liver diseases, especially in the active phase, such as in patients with hepatitis C virus RNA positivity, those with abnormal alanine transaminase (ALT) levels in autoimmune liver diseases, and uncured hepatocellular carcinoma patients. Plasma XOR activities were numerically highest in patients with acute hepatitis B. Plasma XOR activities were closely correlated with parameters of liver tests, especially serum ALT levels, regardless of etiology and plasma xanthine levels. Our results indicated that plasma XOR activity might reflect the active phase in various liver diseases.

Computational Characterization of the Inhibition Mechanism of Xanthine Oxidoreductase by Topiroxostat

Xanthine oxidase (XO) is a member of the molybdopterin-containing enzyme family. It interconverts xanthine to uric acid as the last step of purine catabolism in the human body. The high uric acid concentration in the blood directly leads to human diseases like gout and hyperuricemia. Therefore, drugs that inhibit the biosynthesis of uric acid by human XO have been clinically used for many years to decrease the concentration of uric acid in the blood. In this study, the inhibition mechanism of XO and a new promising drug, topiroxostat (code: FYX-051), is investigated by employing molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) calculations. This drug has been reported to act as both a noncovalent and covalent inhibitor and undergoes a stepwise inhibition by all its hydroxylated metabolites, which include 2-hydroxy-FYX-051, dihydroxy-FYX-051, and trihydroxy-FYX-051. However, the detailed mechanism of inhibition of each metabolite remains elusive and can be useful for designing more effective drugs with similar inhibition functions. Hence, herein we present the computational investigation of the structural and dynamical effects of FYX-051 and the calculated reaction mechanism for all of the oxidation steps catalyzed by the molybdopterin center in the active site. Calculated results for the proposed reaction mechanisms for each metabolite's inhibition reaction in the enzyme's active site, binding affinities, and the noncovalent interactions with the surrounding amino acid residues are consistent with previously reported experimental findings. Analysis of the noncovalent interactions via energy decomposition analysis (EDA) and noncovalent interaction (NCI) techniques suggests that residues L648, K771, E802, R839, L873, R880, R912, F914, F1009, L1014, and A1079 can be used as key interacting residues for further hybrid-type inhibitor development.

Purine Metabolism Dysfunctions: Experimental Methods of Detection and Diagnostic Potential

Purines, such as adenine and guanine, perform several important functions in the cell. They are found in nucleic acids; are structural components of some coenzymes, including NADH and coenzyme A; and have a crucial role in the modulation of energy metabolism and signal transduction. Moreover, purines have been shown to play an important role in the physiology of platelets, muscles, and neurotransmission. All cells require a balanced number of purines for growth, proliferation, and survival. Under physiological conditions, enzymes involved in purines metabolism maintain a balanced ratio between their synthesis and degradation in the cell. In humans, the final product of purine catabolism is uric acid, while most other mammals possess the enzyme uricase that converts uric acid to allantoin, which can be easily eliminated with urine. During the last decades, hyperuricemia has been associated with a number of human extra-articular diseases (in particular, the cardiovascular ones) and their clinical severity. In this review, we go through the methods of investigation of purine metabolism dysfunctions, looking at the functionality of xanthine oxidoreductase and the formation of catabolites in urine and saliva. Finally, we discuss how these molecules can be used as markers of oxidative stress.

Effect of low dose allopurinol on glycemic control and glycemic variability in patients with type 2 diabetes mellitus: A cross-sectional study

Background

Type 2 diabetes mellitus (DM), gout, and asymptomatic hyperuricemia are inter-connected pathologies. Glycemic control (GC), involving a range of treatments is central to the management of DM, whereas allopurinol continues to be the most widely recommended urate lowering agent. Allopurinol has been shown to possess anti-oxidant properties: this study explores the potential effect of allopurinol on glucose homeostasis.

Methods

This is an observational study with a cross-sectional design performed on patients with type 2 diabetes mellitus (DM), recruited from centers in Saudi Arabia. Patients were divided into two groups; allopurinol users; (for gout or asymptomatic hyperuricemia) and a matching disease control group. Patient demographics, co-morbid conditions, biochemical tests, and pharmacological treatments were extracted from electronic records to investigate the effect of allopurinol therapy on Glycemic control (GC), as assessed by glycated haemoglobin (HbA1c as primary endpoint), and on parameters of glycaemic variability (GV) (secondary endpoints).

Results

A total of 194 patients with type 2 DM were recruited (97 in both groups). The two groups were matched for age, sex, and duration of DM: mean age: 59.4 years, 73% males, and 122 months in the allopurinol group vs 59.6 years, 73% males, and 113 months in the control group. Antidiabetic medications were matched between the two groups. In the allopurinol group, it was prescribed with a daily dose of 100 mg, for 77% of the patients, with median duration of 39.5 months. HbA1c values were; 6.90% (6.20, 7.80) in the allopurinol group vs 7.30% (6.60, 8.40) in the control group (P = 0.010). Parameters of GV were calculated from 3 consecutive fasting blood sugar (FBS) readings: variability independent of the mean (VIM) was 0.140 in the allopurinol group vs 0.987 in the control group (P < 0.001).

Conclusion

Concomitant low-dose allopurinol therapy in patients with type 2 DM was associated with modest but significant improvements in GC and GV.

Immune Modulation by Myeloid-Derived Suppressor Cells in Diabetic Kidney Disease

Diabetic kidney disease (DKD) frequently leads to end-stage renal disease and other life-threatening illnesses. The dysregulation of glomerular cell types, including mesangial cells, endothelial cells, and podocytes, appears to play a vital role in the development of DKD. Myeloid-derived suppressor cells (MDSCs) exhibit immunoregulatory and anti-inflammatory properties through the depletion of L-arginine that is required by T cells, through generation of oxidative stress, interference with T-cell recruitment and viability, proliferation of regulatory T cells, and through the promotion of pro-tumorigenic functions. Under hyperglycemic conditions, mouse mesangial cells reportedly produce higher levels of fibronectin and pro-inflammatory cytokines. Moreover, the number of MDSCs is noticeably decreased, weakening inhibitory immune activities, and creating an inflammatory environment. In diabetic mice, immunotherapy with MDSCs that were induced by a combination of granulocyte-macrophage colony-stimulating factor, interleukin (IL)-1β, and IL-6, reduced kidney to body weight ratio, fibronectin expression, and fibronectin accumulation in renal glomeruli, thus ameliorating DKD. In conclusion, MDSCs exhibit anti-inflammatory activities that help improve renal fibrosis in diabetic mice. The therapeutic targeting of the proliferative or immunomodulatory pathways of MDSCs may represent an alternative immunotherapeutic strategy for DKD.

Ten Years Milestones in Xanthine Oxidase Inhibitors Discovery: Febuxostat-Based Inhibitors Trends, Bifunctional Derivatives, and Automatized Screening Assays

Xanthine oxidase (XO) is an enzyme involved in the oxidative process of hypoxanthine and xanthine to uric acid (UA). This process also produces reactive oxygen species (ROS) as byproducts. Both UA and ROS are dangerous for human health, and some health conditions trigger upregulation of XO activity, which results in many diseases (cancer, atherosclerosis, hepatitis, gout, and others) given the worsened scenario of ROS and UA overproduction. So, XO became an attractive target to produce and discover novel selective drugs based on febuxostat, the most recent XO inhibitor out of only two approved by FDA. Under this context, high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) have been successfully applied to rapidly and easily screen for bioactive compounds, isolated or in complex natural matrixes, that act as enzyme inhibitors through the use of an immobilized enzyme reactor (IMER). This article’s goal is to present advances comprising febuxostat-based XO inhibitors as a new trend, bifunctional moieties capable of inhibiting XO and modulating ROS activity, and in-flow techniques employing an IMER in HPLC and CE to screen for synthetic and natural compounds that act as XO inhibitors.

Metabolomic Characteristics of Liver and Cecum Contents in High-Fat-Diet-Induced Obese Mice Intervened with Lactobacillus plantarum FRT10

Obesity has become a major social problem related to health and quality of life. Our previous work demonstrated that Lactobacillus plantarum FRT10 alleviated obesity in high-fat diet (HFD)-fed mice by alleviating gut dysbiosis. However, the underlying functions of FRT10 in regulating liver and cecum contents metabolism remain unknown. Liver and cecum contents metabonomics combined with pathway analysis based on ultraperformance liquid chromatography-quadrupole-time-of-flight mass spectrometry (UHPLC-Q-TOF/MS) were performed to evaluate the alterations of metabolic profiles between obese control mice and obese mice in FRT10-treated groups. The orthogonal partial least squares discriminant analysis (OPLS-DA) score plots showed that there were significant differences in cecum contents and liver markers between experimental groups. In total, 26 potential biomarkers were identified in the liver and 15 in cecum contents that could explain the effect of FRT10 addition in HFD-fed mice. In addition, gut–liver axis analysis indicated that there was a strong correlation between cecum contents metabolites and hepatic metabolites. The mechanism of FRT10 against obesity might be related to the alterations in glycerophospholipid metabolism, primary bile acid biosynthesis, amino metabolism, and purine and pyrimidine metabolism. Studies on these metabolites could help us better understand the role of FRT10 in obesity induced by HFD.

Xanthine Oxidoreductase Activity in Marathon Runners: Potential Implications for Marathon-Induced Acute Kidney Injury

Excess activation of circulating xanthine oxidoreductase (XOR) may contribute to the pathogenesis of widespread remote organ injury, including kidney injury. The purpose of this study was to determine the acute impact of marathon running on plasma XOR activity and to examine whether plasma XOR activity is associated with marathon-induced elevations in biomarkers of acute kidney injury (AKI). Twenty-three young men (aged 20-25 years) who participated in the 38th Tsukuba Marathon were included. Blood and urine samples were collected before, immediately, 2 h (only blood sample), and 24 h after a full marathon run. Plasma XOR activity was evaluated using a highly sensitive assay utilizing a combination of [13C2,15N2] xanthine and liquid chromatography-triple quadrupole mass spectrometry. The levels of several AKI biomarkers, such as serum creatinine and urinary liver-type fatty acid-binding protein (L-FABP) were measured in each participant. Marathon running caused a transient elevation in plasma XOR activity and levels of purine degradation products (hypoxanthine, xanthine, and uric acid) as well as serum creatinine, urinary albumin, and urinary L-FABP levels. Immediately after the marathon, individual relative changes in plasma XOR activity were independently correlated with corresponding changes in serum creatinine and urinary L-FABP levels. In addition, the magnitude of marathon-induced elevation in plasma XOR activity and levels of purine degradation products were higher in individuals who developed AKI. These findings collectively suggest that marathon running substantially influences the purine metabolism pathway including XOR activity. Moreover, activated circulating XOR can be partly associated with elevated biomarkers of AKI after marathon running.

Serum uric acid level is associated with an increase in systolic blood pressure over time in female subjects: Linear mixed-effects model analyses

Whether hyperuricemia is a true risk factor for elevated blood pressure (BP) is controversial, and the sex-specific effects of serum uric acid (SUA) on BP during a follow-up period remain unclear. We investigated whether the association of SUA level with systolic or diastolic BP during a 10-year period differs by sex in a Japanese general population of individuals who received annual health examinations (n = 28,990). After exclusion of subjects who had no BP or SUA data at baseline, a total of 22,994 subjects (male/female: 14,603/8391, age: 47 ± 11 years) were recruited. After adjustment for age; body mass index; BP; SUA level; use of drugs for hyperuricemia and hypertension; diagnosis of diabetes mellitus, dyslipidemia, and chronic kidney disease; family history of hypertension; habits of current smoking and alcohol consumption at baseline; the duration of the observation period; and the interaction between each covariate and the duration of the observation period indicated a significant association of SUA level with change in systolic or diastolic BP over time. There was a significant interaction between sex and SUA level for the change in systolic BP (P = 0.003) but not the change in diastolic BP (P = 0.081). The SUA level at baseline (per 1 mg/dL) was significantly associated with a change in systolic BP over time in females (estimate: 0.073 mmHg/year, P = 0.003) but not in males (estimate: 0.020 mmHg/year, P = 0.160). In conclusion, a high SUA level at baseline is significantly associated with an increase in systolic BP over time in female individuals but not in male individuals.

Associations of circulating xanthine oxidoreductase activity with cardiometabolic risk markers in overweight and obese Japanese men: a cross-sectional pilot study

Circulating xanthine oxidoreductase (XOR) activity may contribute to the pathogenesis of obesity-related adverse cardiometabolic profiles. This pilot study aimed to examine the cross-sectional associations between plasma XOR activity and cardiometabolic risk (CMR) markers in overweight and obese men. In 64 overweight and obese Japanese men (aged 31–63 years), plasma XOR activity and several CMR markers, such as homeostasis model assessment of insulin resistance (HOMA-IR), and clustered CMR score were measured in each participant. Clustered CMR score was constructed based on waist circumference, triglyceride, blood pressure, fasting plasma glucose, and high-density lipoprotein cholesterol. Plasma XOR activity in overweight and obese men was positively associated with the body mass index, waist circumference, visceral fat area, body fat mass, hemoglobin A1c, serum 8-hydroxy-2'-deoxyguanosine, HOMA-IR, and clustered CMR score and was inversely associated with handgrip strength and high-density lipoprotein cholesterol. Multiple linear regression analysis further demonstrated that the associations of plasma XOR activity with HOMA-IR and the clustered CMR score remained significant after adjustment for covariates including uric acid. Our data demonstrate that circulating XOR activity was independently associated, albeit modestly, with HOMA-IR and the clustered CMR score. These preliminary findings suggest that circulating XOR activity can potentially be one of the preventive targets and biomarkers of cardiometabolic disorders in over­weight and obese men.

Sulfide and transition metals - A partnership for life

Sulfide and transition metals often came together in Biology. The variety of possible structural combinations enabled living organisms to evolve an array of highly versatile metal-sulfide centers to fulfill different physiological roles. The ubiquitous iron‑sulfur centers, with their structural, redox, and functional diversity, are certainly the best-known partners, but other metal-sulfide centers, involving copper, nickel, molybdenum or tungsten, are equally crucial for Life. This review provides a concise overview of the exclusive sulfide properties as a metal ligand, with emphasis on the structural aspects and biosynthesis. Sulfide as catalyst and as a substrate is discussed. Different enzymes are considered, including xanthine oxidase, formate dehydrogenases, nitrogenases and carbon monoxide dehydrogenases. The sulfide effect on the activity and function of iron‑sulfur, heme and zinc proteins is also addressed.

Association of Mutations Identified in Xanthinuria with the Function and Inhibition Mechanism of Xanthine Oxidoreductase

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the two-step reaction from hypoxanthine to xanthine and from xanthine to uric acid in purine metabolism. XOR generally carries dehydrogenase activity (XDH) but is converted into an oxidase (XO) under various pathophysiologic conditions. The complex structure and enzymatic function of XOR have been well investigated by mutagenesis studies of mammalian XOR and structural analysis of XOR-inhibitor interactions. Three XOR inhibitors are currently used as hyperuricemia and gout therapeutics but are also expected to have potential effects other than uric acid reduction, such as suppressing XO-generating reactive oxygen species. Isolated XOR deficiency, xanthinuria type I, is a good model of the metabolic effects of XOR inhibitors. It is characterized by hypouricemia, markedly decreased uric acid excretion, and increased serum and urinary xanthine concentrations, with no clinically significant symptoms. The pathogenesis and relationship between mutations and XOR activity in xanthinuria are useful for elucidating the biological role of XOR and the details of the XOR reaction process. In this review, we aim to contribute to the basic science and clinical aspects of XOR by linking the mutations in xanthinuria to structural studies, in order to understand the function and reaction mechanism of XOR in vivo.

Constitutive Oxidative Stress by SEPHS1 Deficiency Induces Endothelial Cell Dysfunction

The primary function of selenophosphate synthetase (SEPHS) is to catalyze the synthesis of selenophosphate that serves as a selenium donor during selenocysteine synthesis. In eukaryotes, there are two isoforms of SEPHS (SEPHS1 and SEPHS2). Between these two isoforms, only SEPHS2 is known to contain selenophosphate synthesis activity. To examine the function of SEPHS1 in endothelial cells, we introduced targeted null mutations to the gene for SEPHS1, Sephs1, in cultured mouse 2H11 endothelial cells. SEPHS1 deficiency in 2H11 cells resulted in the accumulation of superoxide and lipid peroxide, and reduction in nitric oxide. Superoxide accumulation in Sephs1-knockout 2H11 cells is due to the induction of xanthine oxidase and NADPH oxidase activity, and due to the decrease in superoxide dismutase 1 (SOD1) and 3 (SOD3). Superoxide accumulation in 2H11 cells also led to the inhibition of cell proliferation and angiogenic tube formation. Sephs1-knockout cells were arrested at G2/M phase and showed increased gamma H2AX foci. Angiogenic dysfunction in Sephs1-knockout cells is mediated by a reduction in nitric oxide and an increase in ROS. This study shows for the first time that superoxide was accumulated by SEPHS1 deficiency, leading to cell dysfunction through DNA damage and inhibition of cell proliferation.

Independent association of plasma xanthine oxidoreductase activity with hypertension in nondiabetic subjects not using medication

Xanthine oxidoreductase (XOR), a rate-limiting and catalyzing enzyme of uric acid formation in purine metabolism, is involved in reactive oxygen species generation. Plasma XOR activity has been shown to be a novel metabolic biomarker related to obesity, liver dysfunction, hyperuricemia, dyslipidemia, and insulin resistance. However, the association between plasma XOR activity and hypertension has not been fully elucidated. We investigated the association of hypertension with plasma XOR activity in 271 nondiabetic subjects (male/female: 119/152) who had not taken any medications in the Tanno-Sobetsu Study, a population-based cohort. Males had higher plasma XOR activity than females. Plasma XOR activity was positively correlated with mean arterial pressure (r = 0.128, P = 0.036). When the subjects were divided by the presence and absence of hypertension into an HT group (male/female: 34/40) and a non-HT group (male/female: 85/112), plasma XOR activity in the HT group was significantly higher than that in the non-HT group (median: 39 vs. 28 pmol/h/mL, P = 0.028). There was no significant difference in uric acid levels between the two groups. Multivariable logistic regression analysis showed that plasma XOR activity (odds ratio: 1.091 [95% confidence interval: 1.023-1.177] per 10 pmol/h/mL, P = 0.007) was an independent determinant of the risk for hypertension after adjustment for age, sex, current smoking and alcohol consumption, estimated glomerular filtration rate, brain natriuretic peptide, and insulin resistance index. The interaction of sex with plasma XOR activity was not significant for the risk of hypertension. In conclusion, plasma XOR activity is independently associated with hypertension in nondiabetic individuals who are not taking any medications.

Xanthine Oxidoreductase Is Involved in Chondrocyte Mineralization and Expressed in Osteoarthritic Damaged Cartilage

Pathologic calcification of cartilage consists of the formation of basic calcium phosphate (BCP) and/or calcium pyrophosphate dihydrate (CPPD) containing calcium crystals in mature hyaline or articular cartilage and is associated with aging, cartilage injury and likely plays a role in accelerating the pathology of osteoarthritis (OA). The pathways regulating joint calcification, in particular cartilage calcification, are not completely understood, but inflammation and the formation of reactive oxygen species (ROS) are contributory factors. The xanthine oxidase (XO) form of xanthine oxidoreductase (XOR), the key enzyme in xanthine and uric acid metabolism, is a major cellular source of superoxide. We hypothesized that XOR could be implicated in chondrocyte mineralization and cartilage calcification and degradation in OA. We showed both in murine primary chondrocyte and chondrogenic ATDC5 cells, that mineralization was inhibited by two different XOR inhibitors, febuxostat and allopurinol. In addition, XOR inhibition reduced the expression of the pro-mineralizing cytokine interleukin-6 (IL-6). We next generated XOR knock-out chondrocyte cell lines with undetectable XOR expression and XO activity. XOR knock-out chondrocyte cells showed decreased mineralization and reduced alkaline phosphatase (Alp) activity. To assess the precise form of XOR involved, primary chondrocytes of XOR mutant mice expressing either the XDH form (XDH ki) or the XO form (XO ki) were studied. We found that XO ki chondrocytes exhibited increased mineralization compared to XDH ki chondrocytes, and this was associated with enhanced Alp activity, ROS generation and IL-6 secretion. Finally, we found increased XOR expression in damaged vs. undamaged cartilage obtained from OA patients and XOR expression partially co-localized with areas showing pathologic calcification. Altogether, our results suggest that XOR, via its XO form, contribute to chondrocyte mineralization and pathological calcification in OA cartilage.

Molecular Mechanisms in Early Diabetic Kidney Disease: Glomerular Endothelial Cell Dysfunction

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease (ESRD), with prevalence increasing at an alarming rate worldwide and today, there are no known cures. The pathogenesis of DKD is complex, influenced by genetics and the environment. However, the underlying molecular mechanisms that contribute to DKD risk in about one-third of diabetics are still poorly understood. The early stage of DKD is characterized by glomerular hyperfiltration, hypertrophy, podocyte injury and depletion. Recent evidence of glomerular endothelial cell injury at the early stage of DKD has been suggested to be critical in the pathological process and has highlighted the importance of glomerular intercellular crosstalk. A potential mechanism may include reactive oxygen species (ROS), which play a direct role in diabetes and its complications. In this review, we discuss different cellular sources of ROS in diabetes and a new emerging paradigm of endothelial cell dysfunction as a key event in the pathogenesis of DKD.

New insights into purine metabolism in metabolic diseases: role of xanthine oxidoreductase activity

Xanthine oxidoreductase (XOR) consists of two different forms, xanthine dehydrogenase and xanthine oxidase (XO), and is a rate-limiting enzyme of uric acid production from hypoxanthine and xanthine. Uric acid is the end product of purine metabolism in humans and has a powerful antioxidant effect. The lack of ascorbic acid, known as vitamin C, in hominoids has been thought to cause a compensatory increase in uric acid as an antioxidant by unfunctional gene mutation of uricase to a pseudogene. Because XO is involved in an increase in reactive oxygen species (ROS) by generating superoxide and hydrogen peroxide, inadequate activation of XOR promotes oxidative stress-related tissue injury. Plasma XOR activity is associated with obesity, smoking, liver dysfunction, hyperuricemia, dyslipidemia, insulin resistance, and adipokines, indicating a novel biomarker of metabolic disorders. However, XOR activity in adipose tissue is low in humans unlike in rodents, and hypoxanthine is secreted from human adipose tissue. The concentration of hypoxanthine, but not xanthine, is independently associated with obesity in a general population, indicating differential regulation of hypoxanthine and xanthine. Treatment with an XOR inhibitor can decrease uric acid for preventing gout, reduce production of XO-related ROS, and promote reutilization of hypoxanthine and ATP production through the salvage pathway. It has recently been suggested that discontinuation of an XOR inhibitor causes adverse cardiovascular outcomes as XOR inhibitor withdrawal syndrome, possibly due to cardiac disturbance of conduction and contraction by reduced ATP production. New insights into purine metabolism, including the role of XOR activity in the past 5 yr, are mainly discussed in this review.

U-shaped relationship between serum uric acid level and decline in renal function during a 10-year period in female subjects: BOREAS-CKD2

While hyperuricemia is recognized as a risk factor for chronic kidney disease (CKD), the risk of CKD in subjects with a low level of serum uric acid (UA) remains controversial. Here, we examined whether the association of CKD risk with serum UA level differs depending on the sex and age of subjects in a general population. Of subjects who received annual health checkups, we enrolled 6,779 subjects (male/female: 4,454/2,325; age: 45 ± 9 years) with data from a 10-year follow-up after excluding subjects taking anti-hyperuricemic drugs and those with CKD at baseline. During the follow-up period, 11.4% of the males and 11.7% of the females developed CKD. A significant interaction of sex, but not age, with the effect of baseline UA level on CKD risk was found. A restricted cubic spline analysis showed a U-shaped association of the baseline UA level with the risk of CKD in females. Multivariable Cox proportional hazard analyses for females showed that baseline UA levels in the 5th quintile (Q5, ≥5 mg/dL; HR: 1.68) and the 1st quintile (Q1, ≤3.5 mg/dL; HR: 1.73) were independent risk factors for CKD when compared with UA levels in the 4th quintile (Q4, 4.5-4.9 mg/dL). In males, restricted cubic spline analysis indicated increased CKD risk in subjects with a higher baseline UA level but not in those with a low UA level. In conclusion, a low UA level is a significant risk factor for CKD in females, while an elevated UA level increases the risk of CKD in both sexes.

Differential regulation of hypoxanthine and xanthine by obesity in a general population

AIMS/INTRODUCTION

Uric acid is synthesized by oxidation of hypoxanthine and xanthine using a catalyzing enzyme, xanthine oxidoreductase (XOR), which can be a source of reactive oxygen species. Plasma XOR activity is a metabolic biomarker associated with obesity, hyperuricemia, liver dysfunction and insulin resistance. However, it has recently been reported that XOR activity in fat tissue is low in humans, unlike in rodents, and that hypoxanthine is secreted from human fat tissue.

MATERIALS AND METHODS

The associations of obesity with hypoxanthine, xanthine and plasma XOR activity were investigated in 484 participants (men/women: 224/260) of the Tanno-Sobetsu Study.

RESULTS

Levels of hypoxanthine, xanthine and plasma XOR activity were significantly higher in men than in women. In 59 participants with hyperuricemia, 11 (men/women: 11/0) participants were being treated with an XOR inhibitor and had a significantly higher level of xanthine, but not hypoxanthine, than that in participants without treatment. In all of the participants, hypoxanthine concentration in smokers was significantly higher than that in non-smokers. Stepwise and multivariate regression analyses showed that body mass index, smoking habit and xanthine were independent predictors of hypoxanthine after adjustment of age, sex and use of antihyperuricemic drugs. Whereas, alanine transaminase, hypoxanthine and plasma XOR activity were independent predictors for xanthine, and alanine transaminase, triglycerides and xanthine were independent predictors for plasma XOR activity.

CONCLUSIONS

The concentration of hypoxanthine, but not that of xanthine, is independently associated with obesity and smoking habit, indicating differential regulation of hypoxanthine and xanthine in a general population.

In Silico Design and Synthesis of Targeted Curcumin Derivatives as Xanthine Oxidase Inhibitors

BACKGROUND

Curcumin is a well-known pharmacophore and some of its derivatives are shown to target xanthine oxidase (XO) to alleviate disorders caused by the excess production of uric acid.

OBJECTIVE

Curcumin based derivatives were designed, synthesized and evaluated for their antioxidant and xanthine oxidase inhibitory potential.

METHOD

In this report, we designed and synthesized two series of curcumin derivatives modified by inserting pyrazole and pyrimidine ring to central keto group. The synthesized compounds were evaluated for their antioxidant and xanthine oxidase inhibitory potential.

RESULTS

Results showed that pyrazole analogues of curcumin produced excellent XO inhibitory potency with the IC50 values varying from 06.255 µM to 10.503 µM. Among pyrimidine derivatives compound CU3a1 having ortho nitro substitution exhibited more potent xanthine oxidase inhibitory activity than any other curcumin derivative of this series.

CONCLUSION

Curcumin derivatives CU5b1, CU5b2, CU5b3, and CU3a1 showed a potent inhibitory activity against xanthine oxidase along with good antioxidant potential.

Xanthine oxidoreductase inhibition – A review of computational aspect

Xanthine Oxidoreductase (XOR) exists in a variety of organisms from bacteria to humans and catalyzes the oxidation of hypoxanthine to xanthine and from xanthine to uric acid. Excessive uric acid could lead to gout and hyperuricemia. In this paper, we have reviewed the recent computational studies on xanthine oxidase inhibition. Computational methods, such as molecular dynamics (molecular mechanics), quantum mechanics, and quantum mechanics/molecular mechanics (QM/MM), have been employed to investigate the binding affinity of xanthine oxidase with synthesized and isolated nature inhibitors. The limitations of different computational methods for xanthine oxidase inhibition studies were also discussed. Implications of the computational approach could be used to help to understand the existing arguments on substrate/product orientation in xanthine oxidase inhibition, which allows designing new inhibitors with higher efficacy.

A pharmacokinetic-pharmacodynamic study of a single dose of febuxostat in healthy subjects

AIMS

To examine the pharmacokinetic-phamacodynamic (PK-PD) relationships of plasma febuxostat and serum urate and the effect of a single dose of the drug on renal excretion and fractional clearance of urate (FCU).

METHODS

Blood and urine samples were collected at baseline and up to 145 hours following administration of febuxostat (80 mg) to healthy subjects (n = 9). Plasma febuxostat and serum and urinary urate and creatinine concentrations were determined. Febuxostat pharmacokinetics were estimated using a two-compartment model with first-order absorption. An Emax PK-PD model was fitted to mean febuxostat and urate concentrations. Urinary urate excretion and FCU were calculated pre- and post-dose.

RESULTS

Maximum mean plasma concentration of febuxostat (2.7 mg L^-1 ) was observed 1.2 hours after dosage. Febuxostat initial and terminal half-lives were 2.0 ± 1.0 and 14.0 ± 4.7 hours (mean ± SD), respectively. The majority (81%) of the drug was eliminated in the 9 hours after dosing. Serum urate declined slowly achieving mean nadir (0.20 mmol L^-1 ) at 24 hours. The IC₅₀ (plasma febuxostat concentration that inhibits urate production by 50%) was 0.11 ± 0.09 mg L^-1 (mean ± SD). Urinary urate excretion changed in parallel with serum urate. There was no systematic or significant change in FCU from baseline.

CONCLUSION

The PK-PD model could potentially be used to individualise febuxostat treatment and improve clinical outcomes. A single dose of febuxostat does not affect the efficiency of the kidney to excrete urate. Further investigations are required to confirm the present results following multiple dosing with febuxostat.

Xanthine Oxidase Inhibitors Screening, Antioxidation, and DNA Protection Properties of Geranium wilfordii Maxim

Geranium wilfordii Maxim is a commonly used traditional medicine and as decoction pieces in drinks for treating acute and chronic rheumatalgia. Earlier research showed it could inhibit xanthine oxidase and had a strong antioxidative activity. In this study, four compounds namely, corilagin, geraniin, ellagic acid, and myricetrin were screened and identified as xanthine oxidase inhibitors and antioxidants using ultrafiltration combined liquid chromatography–mass spectrometry (LC–MS) and 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) spiking combined LC–MS methods. Ellagic acid showed the greatest inhibition with IC50 of 0.018 ± 0.001 mM better than that of allopurinol. The kinetic parameters exhibited the mode of xanthine oxidase inhibitions by corilagin, geraniin, and myricetrin were the competitive types, whereas the ellagic acid was found as an uncompetitive inhibitor. In vitro DNA nicking assay showed these four compounds protected DNA from reactive oxygen species. Correlation analysis and partial least squares analysis showed there was a moderate correlation between ellagic acid and DPPH· scavenging activity. Our findings revealed four compounds in G. wilfordii Maxim contributed satisfied radicals scavenging, xanthine oxidase inhibition, and DNA damage protective activities. More comprehensive research on pharmaceutical applications and phytochemical profile of G. wilfordii Maxim could be further studied.

Beneficial Effects of Macroporous Resin Extract of Dendrobium candidum Leaves in Rats with Hyperuricemia Induced by a High-Purine Diet

Objectives. The incidence of hyperuricemia (HUA) is increasing year by year, and there are no ideal drugs for the treatment; the existing ones can cause serious liver and kidney damage. We have confirmed that the water extract of Dendrobium candidum leaves could reduce the level of uric acid in rats, but the active ingredients remain unknown, and the mechanism is not well understood. This research investigated the therapeutic effect of the macroporous resin extract of the Dendrobium candidum leaf (DLE) on hyperuricemia. In this study, hyperuricemia was induced in rats by a 5-week high-purine diet. After that, DLE was administered continuously for 9 weeks. The result showed that biochemical parameters of liver and kidney function, especially serum uric acid (UA) levels, were significantly improved with DLE, which may relate to the reduction of xanthine oxidase (XOD) and adenosine deaminase (ADA) in the liver. Moreover, DLE could significantly prevent kidney and liver from damage, and intestinal injury and reduce inflammation in hyperuricemic rats by inhibiting the expression of both NF-κB and TLR4 proteins. These results showed that the macroporous resin extract of the Dendrobium candidum leaves may be effective for the treatment of hyperuricemia in rats by inhibiting uric acid production and decreasing inflammation.

Revisiting prochirality

We propose a new model for prochirality that satisfies all known examples: the prochiral plane. This plane contains the prochiral carbon and defines two separate faces for chemical modification. We extend this to enzyme catalysis, replacing the "three point attachment" hypothesis and its variants. Once a prochiral substrate is fixed on an enzyme surface, the asymmetry of the enzyme provides reactants exclusively on one side of the prochiral plane, producing an enantiomerically pure chiral product. The aconitase reaction is detailed as an example, using molecular modeling and its known enzymatic mechanism. We show that the prochiral substrate for this enzyme is not citrate, but rather cis-aconitate. The number of interaction points of cis-aconitate is not relevant to prochirality, but rather to substrate specificity. A second detailed example is the enzyme fumarase; here the substrate fumarate has only two binding sites, but is nonetheless fixed onto the enzyme and has a defined prochiral plane. We also provide a literature survey of more prochiral substrates, all of which have sp² hybridized carbon and contain a prochiral plane. An example of a prochiral unnatural substrate for sphingosine kinase 2, fingolimod, has an sp³ hybridized prochiral carbon and also contains a prochiral plane. Finally, we provide an intuitive example of a prochiral physical object, a coffee cup, interacting with one hand and lip.

Anti-hyperuricemia activity and toxicity prediction of a novel xanthine oxidoreductase inhibitor

A potent xanthine oxidoreductase inhibitor (LS087) was recently proved to exhibit a similar hypouricemic potency to febuxostat. A hyperuricemia model induced by potassium oxonate and hypoxanthine was proposed in specific pathogen-free male Kunming mice, and the serum urea nitrogen, creatinine and uric acid levels were measured after oral administration of LS087. Furthermore, renal histopathology was conducted by staining with hematoxylin and eosin, periodic acid-Schiff and Masson's trichrome stains, respectively. The results showed that the levels of serum urea nitrogen and uric acid significantly decreased compared with the model group, but the level of creatinine showed no significant changes. The pathological abnormalities in kidney tubules were improved after LS087 administration. Ten metabolites (M1-M10) of LS087 were identified after a single oral dosing of 10 mg/kg in rats. M6 was the primary LS087 metabolite in vivo with a pathway of methylation. The toxicity and potential risks of LS087 and its metabolites were predicted using the ProTox-II software. LS087 and the major metabolites (M2, M3, M5, M6, M7 and M8) were predicted to have no potential hepatotoxicity, but some metabolites with a total rate of <1% (M1, M4, M9, and M10) showed potential hepatotoxicity. M1 and M8 showed potential carcinogenicity. The LS087 biotransformation pathway in rat was well characterized.

Annual change in plasma xanthine oxidoreductase activity is associated with changes in liver enzymes and body weight

Xanthine oxidoreductase (XOR), an enzyme of uric acid formation from hypoxanthine and xanthine, is recognized as a source of oxidative stress. Plasma activity of XOR has been reported to be a biomarker of metabolic disorders associated with obesity, liver dysfunction, insulin resistance, hyperuricemia and adipokines. We investigated longitudinal change in plasma XOR activity, which was determined by using mass spectrometry and liquid chromatography to detect [¹³C₂, ¹⁵N₂]-uric acid using [¹³C₂, ¹⁵N₂]-xanthine as a substrate, in 511 subjects (male/female: 244/267) of the Tanno-Sobetsu Study in the years 2016 and 2017. Plasma XOR activity in a basal state was significantly higher in men than in women, but no significant sex difference was observed in annual change in plasma XOR activity. Annual change in plasma activity of XOR was positively correlated with changes in each parameter, including body weight (r = 0.203, p < 0.001), body mass index, diastolic blood pressure, aspartate transaminase (AST) (r = 0.772, p < 0.001), alanine transaminase (r = 0.647, p < 0.001), γ-glutamyl transpeptidase, total cholesterol, triglycerides, uric acid, fasting glucose and HbA1c. Multivariate regression analysis demonstrated that change in AST and that in body weight were independent predictors of change in plasma XOR activity after adjustment of age, sex and changes in each variable with a significant correlation without multicollinearity. In conclusion, annual change in plasma XOR activity is independently associated with changes in liver enzymes and body weight in a general population. Improvement of liver function and reduction of body weight would decrease plasma XOR activity and its related oxidative stress as a therapeutic strategy.

Independent links between plasma xanthine oxidoreductase activity and levels of adipokines

AIMS/INTRODUCTION

Xanthine oxidoreductase (XOR) is a rate-limiting enzyme that catalyzes uric acid formation in the purine metabolism, is involved in an increase in reactive oxygen species. Plasma XOR activity has been shown to be associated with obesity, smoking, liver dysfunction, hyperuricemia, dyslipidemia and insulin resistance.

MATERIALS AND METHODS

The association between plasma XOR activity, measured by using liquid chromatography and mass spectrometry, and levels of adipokines, including adiponectin, fatty acid-binding protein 4 (FABP4) and fibroblast growth factor 21 (FGF21), was investigated in 282 participants (male/female: 126/156) of the Tanno-Sobetsu Study who were not taking medication.

RESULTS

Women had lower plasma XOR activity than did men. Smoking habit was associated with increased activity. Plasma XOR activity was positively correlated with concentrations of FABP4 (r = 0.192, P < 0.001) and FGF21 (r = 0.208, P < 0.001), homeostasis model assessment of insulin resistance as an index of insulin resistance and uric acid, and was negatively correlated with adiponectin level (r = -0.243, P = 0.001). Multivariate regression analyses showed that levels of adiponectin, FABP4 and FGF21 were independent determinants of plasma XOR activity after adjusting age, sex, uric acid and homeostasis model assessment of insulin resistance. With additional adjustment of smoking habit, the level of FABP4, but not that of adiponectin or FGF21, remained as an independent predictor of plasma XOR activity.

CONCLUSIONS

Plasma XOR activity was independently associated with levels of adipokines in a general population of individuals not taking medication.

Allantoin reduces cell death induced by cisplatin: possible implications for tumor lysis syndrome management

Massive lysis of tumor mass in cancer patients under chemotherapy regimens generates high levels of uric acid, leading to what is known as tumor lysis syndrome (TLS). Rasburicase, a recombinant urate oxidase, converts urate to allantoin, which is readily excreted by the kidneys. Even though there is a high production of allantoin from urate in cancer patients following rasburicase treatment, there are no studies on how allantoin excess could interfere with chemotherapy. We have evaluated allantoin interference with cisplatin efficiency on the lung cancer cell line H460 in vitro. The cells were treated with cisplatin (33 µM), with or without allantoin, for 48 h, in the presence or absence of UV light, and N-acetyl-L-cysteine (NAC) for 24 h. Cell viability, cell cycle, ROS production, apoptosis and immunoblot assays were performed. We showed that allantoin reduced the apoptosis induced by cisplatin in the H460 cell line. However, the activity of carboplatin and oxaliplatin, betulinic acid, TIBA, UV and H₂O₂ was not affected by allantoin. NMR spectroscopy showed that allantoin reduces cisplatin activity through direct interaction with cisplatin.

Shortage of Cellular ATP as a Cause of Diseases and Strategies to Enhance ATP

Germline mutations in cellular-energy associated genes have been shown to lead to various monogenic disorders. Notably, mitochondrial disorders often impact skeletal muscle, brain, liver, heart, and kidneys, which are the body’s top energy-consuming organs. However, energy-related dysfunctions have not been widely seen as causes of common diseases, although evidence points to such a link for certain disorders. During acute energy consumption, like extreme exercise, cells increase the favorability of the adenylate kinase reaction 2-ADP -> ATP+AMP by AMP deaminase degrading AMP to IMP, which further degrades to inosine and then to purines hypoxanthine -> xanthine -> urate. Thus, increased blood urate levels may act as a barometer of extreme energy consumption. AMP deaminase deficient subjects experience some negative effects like decreased muscle power output, but also positive effects such as decreased diabetes and improved prognosis for chronic heart failure patients. That may reflect decreased energy consumption from maintaining the pool of IMP for salvage to AMP and then ATP, since de novo IMP synthesis requires burning seven ATPs. Similarly, beneficial effects have been seen in heart, skeletal muscle, or brain after treatment with allopurinol or febuxostat to inhibit xanthine oxidoreductase, which catalyzes hypoxanthine -> xanthine and xanthine -> urate reactions. Some disorders of those organs may reflect dysfunction in energy-consumption/production, and the observed beneficial effects related to reinforcement of ATP re-synthesis due to increased hypoxanthine levels in the blood and tissues. Recent clinical studies indicated that treatment with xanthine oxidoreductase inhibitors plus inosine had the strongest impact for increasing the pool of salvageable purines and leading to increased ATP levels in humans, thereby suggesting that this combination is more beneficial than a xanthine oxidoreductase inhibitor alone to treat disorders with ATP deficiency.

Fatty Acid-Binding Protein 4 in Cardiovascular and Metabolic Diseases

Fatty acid-binding proteins (FABPs), a family of lipid chaperones, contribute to systemic metabolic regulation via several lipid signaling pathways. Fatty acid-binding protein 4 (FABP4), known as adipocyte FABP (A-FABP) or aP2, is mainly expressed in adipocytes and macrophages and plays important roles in the development of insulin resistance and atherosclerosis in relation to metabolically driven low-grade and chronic inflammation, referred to as ‘metaflammation’. FABP4 is secreted from adipocytes in a non-classical pathway associated with lipolysis and acts as an adipokine for the development of insulin resistance and atherosclerosis. Circulating FABP4 levels are associated with several aspects of metabolic syndrome and cardiovascular disease. Ectopic expression and function of FABP4 in cells and tissues are also related to the pathogenesis of several diseases. Pharmacological modification of FABP4 function by specific inhibitors, neutralizing antibodies or antagonists of unidentified receptors would be novel therapeutic strategies for several diseases, including obesity, diabetes mellitus, atherosclerosis and cardiovascular disease. Significant roles of FABP4 as a lipid chaperone in physiological and pathophysiological conditions and the possibility of FABP4 being a therapeutic target for metabolic and cardiovascular diseases are discussed in this review.

Putting xanthine oxidoreductase and aldehyde oxidase on the NO metabolism map: Nitrite reduction by molybdoenzymes

Nitric oxide radical (NO) is a signaling molecule involved in several physiological and pathological processes and a new nitrate-nitrite-NO pathway has emerged as a physiological alternative to the "classic" pathway of NO formation from L-arginine. Since the late 1990s, it has become clear that nitrite can be reduced back to NO under hypoxic/anoxic conditions and exert a significant cytoprotective action in vivo under challenging conditions. To reduce nitrite to NO, mammalian cells can use different metalloproteins that are present in cells to perform other functions, including several heme proteins and molybdoenzymes, comprising what we denominated as the "non-dedicated nitrite reductases". Herein, we will review the current knowledge on two of those "non-dedicated nitrite reductases", the molybdoenzymes xanthine oxidoreductase and aldehyde oxidase, discussing the in vitro and in vivo studies to provide the current picture of the role of these enzymes on the NO metabolism in humans.