Mammalian xanthine oxidoreductase - mechanism of transition from xanthine dehydrogenase to xanthine oxidase

Effect of febuxostat on biochemical parameters of hyperlipidemia induced by a high-fat diet in rabbits

Febuxostat, a highly potent xanthine oxidase inhibitor with an antioxidant effect, inhibits elevated xanthine oxidase, leading to reduction of reactive oxygen species and oxidative stress, the main causes of vascular inflammation in hyperlipidemia. The aim of this study was to test the potential antioxidant and anti-inflammatory effects of febuxostat and (or) stopping a high-fat diet on the biochemical parameters in rabbits with hyperlipidemia induced by a high-fat diet. Male New Zealand rabbits were distributed into 3 groups: a normal control group fed standard chow for 12 weeks and 2 other groups fed a high-fat diet with 1% cholesterol for 8 weeks, and then shifted to standard chow for 4 weeks. During the last 4 weeks, one high-fat diet group received 0.5% carboxymethyl cellulose, whereas the other group was treated with febuxostat (2 mg/kg per day p.o.). Febuxostat significantly lowered low-density lipoprotein cholesterol (“bad” cholesterol) compared to the untreated group (high-fat diet group). Febuxostat also displayed a potent anti-inflammatory and antioxidant activity by decreasing serum levels of lipid peroxidation index, proinflammatory cytokines, and enhancing antioxidant enzyme activity. Stopping the hyperlipidemic diet in the high-fat diet group did not show improvement. These findings indicate the antioxidant and anti-inflammatory effects of febuxostat that may be common mechanisms of the anti-hyperlipidemic effect of this drug. Stopping a hyperlipidemic diet without treatment is not sufficient once injury has occurred.

Atlas of Circadian Metabolism Reveals System-wide Coordination and Communication between Clocks

Metabolic diseases are often characterized by circadian misalignment in different tissues, yet how altered coordination and communication among tissue clocks relate to specific pathogenic mechanisms remains largely unknown. Applying an integrated systems biology approach, we performed 24-hr metabolomics profiling of eight mouse tissues simultaneously. We present a temporal and spatial atlas of circadian metabolism in the context of systemic energy balance and under chronic nutrient stress (high-fat diet [HFD]). Comparative analysis reveals how the repertoires of tissue metabolism are linked and gated to specific temporal windows and how this highly specialized communication and coherence among tissue clocks is rewired by nutrient challenge. Overall, we illustrate how dynamic metabolic relationships can be reconstructed across time and space and how integration of circadian metabolomics data from multiple tissues can improve our understanding of health and disease.

In Silico and 3D QSAR Studies of Natural Based Derivatives as Xanthine Oxidase Inhibitors

BACKGROUND

A large number of disorders and their symptoms emerge from deficiency or overproduction of specific metabolites has drawn the attention for the discovery of new therapeutic agents for the treatment of disorders. Various approaches such as computational drug design have provided the new methodology for the selection and evaluation of target protein and the lead compound mechanistically. For instance, the overproduction of xanthine oxidase causes the accumulation of uric acid which can prompt gout.

OBJECTIVE

In the present study we critically discussed the various techniques such as 3-D QSAR and molecular docking for the study of the natural based xanthine oxidase inhibitors with their mechanistic insight into the interaction of xanthine oxidase and various natural leads.

CONCLUSION

The computational studies of deferent natural compounds were discussed as a result the flavonoids, anthraquinones, xanthones shown the remarkable inhibitory potential for xanthine oxidase inhibition moreover the flavonoids such as hesperidin and rutin were found as promising candidates for further exploration.

Redox Mechanisms in Neurodegeneration: From Disease Outcomes to Therapeutic Opportunities

SIGNIFICANCE

Once considered to be mere by-products of metabolism, reactive oxygen, nitrogen and sulfur species are now recognized to play important roles in diverse cellular processes such as response to pathogens and regulation of cellular differentiation. It is becoming increasingly evident that redox imbalance can impact several signaling pathways. For instance, disturbances of redox regulation in the brain mediate neurodegeneration and alter normal cytoprotective responses to stress. Very often small disturbances in redox signaling processes, which are reversible, precede damage in neurodegeneration. Recent Advances: The identification of redox-regulated processes, such as regulation of biochemical pathways involved in the maintenance of redox homeostasis in the brain has provided deeper insights into mechanisms of neuroprotection and neurodegeneration. Recent studies have also identified several post-translational modifications involving reactive cysteine residues, such as nitrosylation and sulfhydration, which fine-tune redox regulation. Thus, the study of mechanisms via which cell death occurs in several neurodegenerative disorders, reveal several similarities and dissimilarities. Here, we review redox regulated events that are disrupted in neurodegenerative disorders and whose modulation affords therapeutic opportunities.

CRITICAL ISSUES

Although accumulating evidence suggests that redox imbalance plays a significant role in progression of several neurodegenerative diseases, precise understanding of redox regulated events is lacking. Probes and methodologies that can precisely detect and quantify in vivo levels of reactive oxygen, nitrogen and sulfur species are not available.

FUTURE DIRECTIONS

Due to the importance of redox control in physiologic processes, organisms have evolved multiple pathways to counteract redox imbalance and maintain homeostasis. Cells and tissues address stress by harnessing an array of both endogenous and exogenous redox active substances. Targeting these pathways can help mitigate symptoms associated with neurodegeneration and may provide avenues for novel therapeutics. Antioxid. Redox Signal. 30, 1450-1499.

Dysregulation of stress systems and nitric oxide signaling underlies neuronal dysfunction in Alzheimer's disease

Stress is a multimodal response involving the coordination of numerous body systems in order to maximize the chance of survival. However, long term activation of the stress response results in neuronal oxidative stress via reactive oxygen and nitrogen species generation, contributing to the development of depression. Stress-induced depression shares a high comorbidity with other neurological conditions including Alzheimer's disease (AD) and dementia, often appearing as one of the earliest observable symptoms in these diseases. Furthermore, stress and/or depression appear to exacerbate cognitive impairment in the context of AD associated with dysfunctional catecholaminergic signaling. Given there are a number of homologous pathways involved in the pathophysiology of depression and AD, this article will highlight the mechanisms by which stress-induced perturbations in oxidative stress, and particularly NO signaling, contribute to neurodegeneration.

A role for Vibrio vulnificus PecS during hypoxia

The genus Vibrio includes serious human pathogens, and mollusks are a significant reservoir for species such as V. vulnificus. Vibrio species encode PecS, a member of the multiple antibiotic resistance regulator (MarR) family of transcription factors; pecS is divergently oriented to pecM, which encodes an efflux pump. We report here that Vibrio species feature frequent duplications of pecS-pecM genes, suggesting evolutionary pressures to respond to distinct environmental situations. The single V. vulnificus PecS binds two sites within the pecS-pecM intergenic region with K_d = 0.3 ± 0.1 nM, a binding that is attenuated by the ligands xanthine and urate, except when promoter DNA is saturated with PecS. A unique target is found in the intergenic region between genes encoding the nitric oxide sensing transcription factor, NsrR, and nod; the nod-encoded nitric oxide dioxygenase is important for preventing nitric oxide stress. Reporter gene assays show that PecS-mediated repression of gene expression can be relieved in presence of ligand. Since xanthine and urate are produced as part of the oxidative burst during host defenses and under molluscan hypoxia, we propose that these intermediates in the host purine degradation pathway function to promote bacterial survival during hypoxia and oxidative stress.

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.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

Antenatal melatonin modulates an enhanced antioxidant/pro-oxidant ratio in pulmonary hypertensive newborn sheep

Chronic hypobaric hypoxia during fetal and neonatal life induces neonatal pulmonary hypertension. Hypoxia and oxidative stress are driving this condition, which implies an increase generation of reactive oxygen species (ROS) and/or decreased antioxidant capacity. Melatonin has antioxidant properties that decrease oxidative stress and improves pulmonary vascular function when administered postnatally. However, the effects of an antenatal treatment with melatonin in the neonatal pulmonary function and oxidative status are unknown. Therefore, we hypothesized that an antenatal therapy with melatonin improves the pulmonary arterial pressure and antioxidant status in high altitude pulmonary hypertensive neonates. Twelve ewes were bred at high altitude (3600 m); 6 of them were used as a control group (vehicle 1.4% ethanol) and 6 as a melatonin treated group (10 mg d^-1 melatonin in vehicle). Treatments were given once daily during the last third of gestation (100–150 days). Lambs were born and raised with their mothers until 12 days old, and neonatal pulmonary arterial pressure and resistance, plasma antioxidant capacity and the lung oxidative status were determined. Furthermore, we measured the pulmonary expression and activity for the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase, and the oxidative stress markers 8-isoprostanes, 4HNE and nitrotyrosine. Finally, we assessed pulmonary pro-oxidant sources by the expression and function of NADPH oxidase, mitochondria and xanthine oxidase. Melatonin decreased the birth weight. However, melatonin enhanced the plasma antioxidant capacity and decreased the pulmonary antioxidant activity, associated with a diminished oxidative stress during postnatal life. Interestingly, melatonin also decreased ROS generation at the main pro-oxidant sources. Our findings suggest that antenatal administration of melatonin programs an enhanced antioxidant/pro-oxidant status, modulating ROS sources in the postnatal lung.

Nephromyces Encodes a Urate Metabolism Pathway and Predicted Peroxisomes, Demonstrating That These Are Not Ancient Losses of Apicomplexans

The phylum Apicomplexa is a quintessentially parasitic lineage, whose members infect a broad range of animals. One exception to this may be the apicomplexan genus Nephromyces, which has been described as having a mutualistic relationship with its host. Here we analyze transcriptome data from Nephromyces and its parasitic sister taxon, Cardiosporidium, revealing an ancestral purine degradation pathway thought to have been lost early in apicomplexan evolution. The predicted localization of many of the purine degradation enzymes to peroxisomes, and the in silico identification of a full set of peroxisome proteins, indicates that loss of both features in other apicomplexans occurred multiple times. The degradation of purines is thought to play a key role in the unusual relationship between Nephromyces and its host. Transcriptome data confirm previous biochemical results of a functional pathway for the utilization of uric acid as a primary nitrogen source for this unusual apicomplexan.

MarR Family Transcription Factors from Burkholderia Species: Hidden Clues to Control of Virulence-Associated Genes

Species within the genus Burkholderia exhibit remarkable phenotypic diversity. Genomic plasticity, including genome reduction and horizontal gene transfer, has been correlated with virulence traits in several species. However, the conservation of virulence genes in species otherwise considered to have limited potential for infection suggests that phenotypic diversity may not be explained solely on the basis of genetic diversity. Instead, differential organization and control of gene regulatory networks may underlie many phenotypic differences. In this review, we evaluate how regulation of gene expression by members of the multiple antibiotic resistance regulator (MarR) family of transcription factors may contribute to shaping the physiological diversity of Burkholderia species, with a focus on the clinically relevant human pathogens. All Burkholderia species encode a relatively large number of MarR proteins, a feature common to bacteria that must respond to environmental changes such as those associated with host invasion. However, evolution of gene regulatory networks has likely resulted in orthologous transcription factors controlling disparate sets of genes. Adaptation to, and survival in, diverse habitats, including a human or plant host, is key to the success of Burkholderia species as (opportunistic) pathogens, and recent reports suggest that control of virulence-associated genes by MarR proteins features prominently among the survival strategies employed by these species. We suggest that identification of MarR regulons will contribute significantly to clarification of virulence determinants and phenotypic diversity.

Emerging Role of Purine Metabolizing Enzymes in Brain Function and Tumors

The growing evidence of the involvement of purine compounds in signaling, of nucleotide imbalance in tumorigenesis, the discovery of purinosome and its regulation, cast new light on purine metabolism, indicating that well known biochemical pathways may still surprise. Adenosine deaminase is important not only to preserve functionality of immune system but also to ensure a correct development and function of central nervous system, probably because its activity regulates the extracellular concentration of adenosine and therefore its function in brain. A lot of work has been done on extracellular 5′-nucleotidase and its involvement in the purinergic signaling, but also intracellular nucleotidases, which regulate the purine nucleotide homeostasis, play unexpected roles, not only in tumorigenesis but also in brain function. Hypoxanthine guanine phosphoribosyl transferase (HPRT) appears to have a role in the purinosome formation and, therefore, in the regulation of purine synthesis rate during cell cycle with implications in brain development and tumors. The final product of purine catabolism, uric acid, also plays a recently highlighted novel role. In this review, we discuss the molecular mechanisms underlying the pathological manifestations of purine dysmetabolisms, focusing on the newly described/hypothesized roles of cytosolic 5′-nucleotidase II, adenosine kinase, adenosine deaminase, HPRT, and xanthine oxidase.

Human Enzymes for Organic Synthesis

Human enzymes have been widely studied in various disciplines. The number of reactions taking place in the human body is vast, and so is the number of potential catalysts for synthesis. Herein, we focus on the application of human enzymes that catalyze chemical reactions in course of the metabolism of drugs and xenobiotics. Some of these reactions have been explored on the preparative scale. The major field of application of human enzymes is currently drug development, where they are applied for the synthesis of drug metabolites.

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.

Nanoparticles in Medicine: A Focus on Vascular Oxidative Stress

Nanotechnology has had a significant impact on medicine in recent years, its application being referred to as nanomedicine. Nanoparticles have certain properties with biomedical applications; however, in some situations, they have demonstrated cell toxicity, which has caused concern surrounding their clinical use. In this review, we focus on two aspects: first, we summarize the types of nanoparticles according to their chemical composition and the general characteristics of their use in medicine, and second, we review the applications of nanoparticles in vascular alteration, especially in endothelial dysfunction related to oxidative stress. This condition can lead to a reduction in nitric oxide (NO) bioavailability, consequently affecting vascular tone regulation and endothelial dysfunction, which is the first phase in the development of cardiovascular diseases. Therefore, nanoparticles with antioxidant properties may improve vascular dysfunction associated with hypertension, diabetes mellitus, or atherosclerosis.

Anti-hyperuricemic peptides derived from bonito hydrolysates based on in vivo hyperuricemic model and in vitro xanthine oxidase inhibitory activity

Traditional drugs used to treat hyperuricemia have adverse effects. In this study, to identify safer anti-hyperuricemic bioactive peptides isolated from food-derived protein hydrolysates, a hyperuricemia rat model induced by potassium oxonate (PO) was used to evaluate the activity of bonito hydrolysates (BH), dephenolised walnut hydrolysates (DWH), and soybean hydrolysates (SH). The serum uric acid level of rats in the BH group (95.4 ± 27.4 μM, p < 0.01) was significantly reduced compared to that in the model group (212.00 ± 30.00 μM) to a level even lower than that in allopurinol group (114.3 ± 53.0 μM). Furthermore, BH alleviated renal impairment caused by PO in vivo and exhibited the greatest xanthine oxidase (XOD) inhibitory activity (65.5 ± 8.0%) in vitro compared to the other hydrolysates. Two peptides identified from BH bound the catalytic site of XOD, among which the hydrophobic peptide WML entered the active site of XOD more easily compared to the hydrophilic peptide PGACSN, possibly because of hydrophobic interactions. The chemically synthesized WML demonstrated high XOD inhibitory effect compared to PGACSN and a significant change in the secondary structure of XOD. Therefore, hexapeptide PGACSN and tripeptide WML are partially responsible for the anti-hyperuricemic activity of BH, and hydrophobic amino acids play important roles in the XOD inhibitory activity of peptides.

The Role of Oxidative Stress in the Development of Systemic Sclerosis Related Vasculopathy

Systemic sclerosis (SSc) is a rare connective tissue disease characterized by autoimmunity, vasculopathy, and progressive fibrosis typically affecting multiple organs including the skin. SSc often is a lethal disorder, because effective disease-modifying treatment still remains unavailable. Vasculopathy with endothelial dysfunction, perivascular infiltration of mononuclear cells, vascular wall remodeling and rarefaction of capillaries is the hallmark of the disease. Most patients present with vasospastic attacks of the digital arteries referred to as 'Raynaud's phenomenon,' which is often an indication of an underlying widespread vasculopathy. Although autoimmune responses and inflammation are both found to play an important role in the pathogenesis of this vasculopathy, no definite initiating factors have been identified. Recently, several studies have underlined the potential role of oxidative stress in the pathogenesis of SSc vasculopathy thereby proposing a new aspect in the pathogenesis of this disease. For instance, circulating levels of reactive oxygen species (ROS) related markers have been found to correlate with SSc vasculopathy, the formation of fibrosis and the production of autoantibodies. Excess ROS formation is well-known to lead to endothelial cell (EC) injury and vascular complications. Collectively, these findings suggest a potential role of ROS in the initiation and progression of SSc vasculopathy. In this review, we present the background of oxidative stress related processes (e.g., EC injury, autoimmunity, inflammation, and vascular wall remodeling) that may contribute to SSc vasculopathy. Finally, we describe the use of oxidative stress related read-outs as clinical biomarkers of disease activity and evaluate potential anti-oxidative strategies in SSc.

Unique antioxidant effects of herbal leaf tea and stem tea from Moringa oleifera L. especially on superoxide anion radical generation systems

This study aimed to investigate the unique antioxidative effects of Japanese moringa products, herbal leaf tea and stem tea, using established free radical assays, focusing on superoxide anion (O₂^-) radical generation systems. Hot-water extracts from moringa teas resulted in different but lower scavenging activities than Trolox in four synthetic free radical models. Interestingly, these extracts further showed higher O₂^- radical scavenging effects than Trolox in the phenazine methosulfate-NADH-nitroblue tetrazolium and xanthine oxidase assay systems. Incubating human neutrophils in the presence of these tea extracts rather than Trolox effectively suppressed cellular O₂^- radical generation. Among the eight known phenolic constituents of moringa leaves, caffeic acid and chlorogenic acid may be responsible for the O₂^-specific radical scavenging capacity stronger than that of Trolox. These results suggest that moringa herbal teas are a good source of natural antioxidants for preventing O₂^- radical-mediated disorders. Abbreviations: O₂^-: superoxide anion; ROS: reactive oxygen species; H₂O₂: hydrogen peroxide; XOD: xanthine oxidase; DPPH: 1,1-diphenyl-2-picrylhydrazyl; ABTS⁺: 2,2'-azinobis(2-ethylbenzothiazoline-6-sulfonic acid) cation; CPZ⁺: chlorpromazine cation; PMS: phenazine methosulfate; NBT: nitroblue tetrazolium; PMA: phorbol 12-myristate 13-acetate.

Cellular Stresses and Stress Responses in the Pathogenesis of Insulin Resistance

Insulin resistance (IR), a key component of the metabolic syndrome, precedes the development of diabetes, cardiovascular disease, and Alzheimer's disease. Its etiological pathways are not well defined, although many contributory mechanisms have been established. This article summarizes such mechanisms into the hypothesis that factors like nutrient overload, physical inactivity, hypoxia, psychological stress, and environmental pollutants induce a network of cellular stresses, stress responses, and stress response dysregulations that jointly inhibit insulin signaling in insulin target cells including endothelial cells, hepatocytes, myocytes, hypothalamic neurons, and adipocytes. The insulin resistance-inducing cellular stresses include oxidative, nitrosative, carbonyl/electrophilic, genotoxic, and endoplasmic reticulum stresses; the stress responses include the ubiquitin-proteasome pathway, the DNA damage response, the unfolded protein response, apoptosis, inflammasome activation, and pyroptosis, while the dysregulated responses include the heat shock response, autophagy, and nuclear factor erythroid-2-related factor 2 signaling. Insulin target cells also produce metabolites that exacerbate cellular stress generation both locally and systemically, partly through recruitment and activation of myeloid cells which sustain a state of chronic inflammation. Thus, insulin resistance may be prevented or attenuated by multiple approaches targeting the different cellular stresses and stress responses.

Thiopurine-induced toxicity is associated with dysfunction variant of the human molybdenum cofactor sulfurase gene (xanthinuria type II)

BACKGROUND

The aim of our study was to identify the genetic background of thiopurine-induced toxicity in a patient with a wild-type thiopurine methyltransferase genotype and activity. A 38-year-old Caucasian woman presented with cutaneous necrotizing vasculitis pancytopenia one month after starting azathioprine therapy.

METHODS

During a routine biochemical follow-up of the patient, undetectable serum uric acid (<10 μl) was observed. A high performance liquid chromatography analysis of urinary purines revealed increased levels of xanthine (137 mmol/mol creatinine). The suspected diagnosis of hereditary xanthinuria, a rare autosomal recessive disorder of the last two steps of purine metabolism, was confirmed by sequence analysis.

RESULTS

An analysis of XDH/XO and AOX1 revealed common polymorphisms, while analysis of the MOCOS gene identified a rare homozygous variant c.362C > T. Dysfunction of this variant was confirmed by significantly decreased xanthine dehydrogenase/oxidase activity in the patient's plasma (<2% of control mean activity).

CONCLUSIONS

We present a biochemical, enzymatic, and molecular genetic case study suggesting an important association between a hitherto undescribed dysfunction variant in the MOCOS gene and thiopurine-induced toxicity. The identified variant c.362C > T results in slower thiopurine metabolism caused by inhibition of 6-mercaptopurine oxidation (catabolism) to 6-thioxanthine and 6-thiouric acid, which increases the formation of the nucleotide 6-thioguanine, which is toxic. This is the first clinical case to identify the crucial role of the MOCOS gene in thiopurine intolerance and confirm the impact of genetic variability of purine enzymes on different therapeutic outcomes in patients undergoing thiopurine treatment.

Uric acid and cardiovascular disease

Uric acid (UA) is an end product of purine metabolism in humans and great apes. UA acts as an antioxidant and it accounts for 50% of the total antioxidant capacity of biological fluids in humans. When present in cytoplasm of the cells or in acidic/hydrophobic milieu in atherosclerotic plaques, UA converts into a pro-oxidant agent and promotes oxidative stress and through this mechanism participates in the pathophysiology of human disease including cardiovascular disease (CVD). Most epidemiological studies but not all of them suggested the existence of an association between elevated serum UA level and CVD, including coronary heart disease (CHD), stroke, congestive heart failure, arterial hypertension and atrial fibrillation as well as an increased risk for mortality due to CVD in general population and subjects with confirmed CHD. Evidence available also suggests an association between elevated UA and traditional cardiovascular risk factors, metabolic syndrome, insulin resistance, obesity, non-alcoholic fatty liver disease and chronic kidney disease. Experimental and clinical studies have evidenced several mechanisms through which elevated UA level exerts deleterious effects on cardiovascular health including increased oxidative stress, reduced availability of nitric oxide and endothelial dysfunction, promotion of local and systemic inflammation, vasoconstriction and proliferation of vascular smooth muscle cells, insulin resistance and metabolic dysregulation. Although the causality in the relationship between UA and CVD remains unproven, UA may be pathogenic and participate in the pathophysiology of CVD by serving as a bridging mechanism mediating (enabling) or potentiating the deleterious effects of cardiovascular risk factors on vascular tissue and myocardium.

Regularized Non-Negative Matrix Factorization for Identifying Differentially Expressed Genes and Clustering Samples: A Survey

Non-negative Matrix Factorization (NMF), a classical method for dimensionality reduction, has been applied in many fields. It is based on the idea that negative numbers are physically meaningless in various data-processing tasks. Apart from its contribution to conventional data analysis, the recent overwhelming interest in NMF is due to its newly discovered ability to solve challenging data mining and machine learning problems, especially in relation to gene expression data. This survey paper mainly focuses on research examining the application of NMF to identify differentially expressed genes and to cluster samples, and the main NMF models, properties, principles, and algorithms with its various generalizations, extensions, and modifications are summarized. The experimental results demonstrate the performance of the various NMF algorithms in identifying differentially expressed genes and clustering samples.

The Role of Peroxiredoxins in the Transduction of H2O2 Signals

Hydrogen peroxide (H₂O₂) is produced on stimulation of many cell surface receptors and serves as an intracellular messenger in the regulation of diverse physiological events, mostly by oxidizing cysteine residues of effector proteins. Mammalian cells express multiple H₂O₂-eliminating enzymes, including catalase, glutathione peroxidase (GPx), and peroxiredoxin (Prx). A conserved cysteine in Prx family members is the site of oxidation by H₂O₂. Peroxiredoxins possess a high-affinity binding site for H₂O₂ that is lacking in catalase and GPx and which renders the catalytic cysteine highly susceptible to oxidation, with a rate constant several orders of magnitude greater than that for oxidation of cysteine in most H₂O₂ effector proteins. Moreover, Prxs are abundant and present in all subcellular compartments. The cysteines of most H₂O₂ effectors are therefore at a competitive disadvantage for reaction with H₂O₂. Recent Advances: Here we review intracellular sources of H₂O₂ as well as H₂O₂ target proteins classified according to biochemical and cellular function. We then highlight two strategies implemented by cells to overcome the kinetic disadvantage of most target proteins with regard to H₂O₂-mediated oxidation: transient inactivation of local Prx molecules via phosphorylation, and indirect oxidation of target cysteines via oxidized Prx. Critical Issues and Future Directions: Recent studies suggest that only a small fraction of the total pools of Prxs and H₂O₂ effector proteins localized in specific subcellular compartments participates in H₂O₂ signaling. Development of sensitive tools to selectively detect phosphorylated Prxs and oxidized effector proteins is needed to provide further insight into H₂O₂ signaling. Antioxid. Redox Signal. 28, 537-557.

Moderation of hyperuricemia in rats via consuming walnut protein hydrolysate diet and identification of new antihyperuricemic peptides

Walnut-derived antihyperuricemic peptides were purified and identified based on decreasing serum uric acid level and inhibiting xanthine oxidase.

Targeting Mitochondrial Calcium Handling and Reactive Oxygen Species in Heart Failure

PURPOSE OF REVIEW

In highly prevalent cardiac diseases, new therapeutic approaches are needed. Since the first description of oxidative stress in heart failure, reactive oxygen species (ROS) have been considered as attractive drug targets. Though clinical trials evaluating antioxidant vitamins as ROS-scavenging agents yielded neutral results in patients at cardiovascular risk, the knowledge of ROS as pathophysiological factors has considerably advanced in the past few years and led to novel treatment approaches. Here, we review recent new insights and current strategies in targeting mitochondrial calcium handling and ROS in heart failure.

RECENT FINDINGS

Mitochondria are an important ROS source, and more recently, drug development focused on targeting mitochondria (e.g. by SS-31 or MitoQ). Important advancement has also been made to decipher how the matching of energy supply and demand through calcium (Ca²⁺) handling impacts on mitochondrial ROS production and elimination. This opens novel opportunities to ameliorate mitochondrial dysfunction in heart failure by targeting cytosolic and mitochondrial ion transporters to improve this matching process. According to this approach, highly specific substances as the preclinical CGP-37157, as well as the clinically used ranolazine and empagliflozin, provide promising results on different levels of evidence. Furthermore, the understanding of redox signalling relays, resembled by catalyst-mediated protein oxidation, is about to change former paradigms of ROS signalling. Novel methods, as redox proteomics, allow to precisely analyse key regulatory thiol switches, which may induce adaptive or maladaptive signalling. Additionally, the generation of genetically encoded probes increased the spatial and temporal resolution of ROS imaging and opened a new methodological window to subtle, formerly obscured processes. These novel insights may broaden our understanding of why previous attempts to target oxidative stress have failed, and at the same time provide us with new targets for drug development.

Xanthine oxidase inhibitory activity of natural and hemisynthetic flavonoids from Gardenia oudiepe (Rubiaceae) in vitro and molecular docking studies

Xanthine oxidase (XO), an enzyme widely distributed among mammalian tissues, is associated with the oxidation of xanthine and hypoxanthine to form uric acid. Reactive oxygen species are also released during this process, leading to oxidative damages and to the pathology called gout. Available treatments mainly based on allopurinol cause serious side effects. Natural products such as flavonoids may represent an alternative. Thus, a series of polymethoxyflavones isolated and hemisynthesized from the bud exudates of Gardenia oudiepe has been evaluated for in vitro XO inhibitory activity. Compounds 1, 2 and 3 were more active than the reference inhibitor, Allopurinol (IC₅₀ = 0.25 ± 0.004 μM) with IC₅₀ values of (0.004 ± 0.001) μM, (0.05 ± 0.01) μM and (0.09 ± 0.003) μM, respectively. Structure-activity relationships were established. Additionally, a molecular docking study using MOE™ tool was carried out to establish the binding mode of the most active flavones with the enzyme, showing important interactions with its catalytic residues. These promising results, suggest the use of these compounds as potential leads for the design and development of novel XO inhibitors.

Generation of a new mouse model of glaucoma characterized by reduced expression of the AP-2β and AP-2δ proteins

We generated 6 transgenic lines with insertion of an expression plasmid for the R883/M xanthine dehydrogenase (XDH) mutant protein. Approximately 20% of the animals deriving from one of the transgenic lines show ocular abnormalities and an increase in intra-ocular pressure which are consistent with glaucoma. The observed pathologic phenotype is not due to expression of the transgene, but rather the consequence of the transgene insertion site, which has been defined by genome sequencing. The insertion site maps to chromosome 1qA3 in close proximity to the loci encoding AP-2β and AP-2δ, two proteins expressed in the eye. The insertion leads to a reduction in AP-2β and AP-2δ levels. Down-regulation of AP-2β expression is likely to be responsible for the pathologic phenotype, as conditional deletion of the Tfap2b gene in the neural crest has recently been shown to cause defective development of the eye anterior segment and early-onset glaucoma. In these conditional knock-out and our transgenic mice, the morphological/histological features of the glaucomatous pathology are surprisingly similar. Our transgenic mouse represents a model of angle-closure glaucoma and a useful tool for the study of the pathogenesis and the development of innovative therapeutic strategies.

Xanthine oxidoreductase and its inhibitors: relevance for gout

Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in purine catabolism and converts hypoxanthine to xanthine, and xanthine into uric acid. When concentrations of uric acid exceed its biochemical saturation point, crystals of uric acid, in the form of monosodium urate, emerge and can predispose an individual to gout, the commonest form of inflammatory arthritis in men aged over 40 years. XOR inhibitors are primarily used in the treatment of gout, reducing the formation of uric acid and thereby, preventing the formation of monosodium urate crystals. Allopurinol is established as first-line therapy for gout; a newer alternative, febuxostat, is used in patients unable to tolerate allopurinol. This review provides an overview of gout, a detailed analysis of the structure and function of XOR, discussion on the pharmacokinetics and pharmacodynamics of XOR inhibitors-allopurinol and febuxostat, and the relevance of XOR in common comorbidities of gout.

Oxidative Stress-Mediated Atherosclerosis: Mechanisms and Therapies

Atherogenesis, the formation of atherosclerotic plaques, is a complex process that involves several mechanisms, including endothelial dysfunction, neovascularization, vascular proliferation, apoptosis, matrix degradation, inflammation, and thrombosis. The pathogenesis and progression of atherosclerosis are explained differently by different scholars. One of the most common theories is the destruction of well-balanced homeostatic mechanisms, which incurs the oxidative stress. And oxidative stress is widely regarded as the redox status realized when an imbalance exists between antioxidant capability and activity species including reactive oxygen (ROS), nitrogen (RNS) and halogen species, non-radical as well as free radical species. This occurrence results in cell injury due to direct oxidation of cellular protein, lipid, and DNA or via cell death signaling pathways responsible for accelerating atherogenesis. This paper discusses inflammation, mitochondria, autophagy, apoptosis, and epigenetics as they induce oxidative stress in atherosclerosis, as well as various treatments for antioxidative stress that may prevent atherosclerosis.

New Strategy That Delays Progression of Amyotrophic Lateral Sclerosis in G1H-G93A Transgenic Mice: Oral Administration of Xanthine Oxidoreductase Inhibitors That Are Not Substrates for the Purine Salvage Pathway

Amyotrophic lateral sclerosis (ALS), Lou Gehrig's disease, is a progressive fatal neurodegenerative disease that involves both upper and lower motor neurons. We orally administered 4 xanthine oxidoreductase (XOR) inhibitors to G1H-G93A mice carrying 25 transgene copy numbers of human mutant G93A superoxide dismutase 1, from 80 days of age. Three nonpurine-analogue inhibitors (TEI-6720: Febuxostat, Y-700 and FYX-051), but not allopurinol with a purine analogue ring (pyrazolo pyrimidine ring), significantly delayed disease onset, prolonged survival and the duration of disease stages, improved clinical signs, and alleviated weight loss. Exercise testing (extension reflex, inclined plane, footprint, rotarod, and beam balance tests) showed significantly improved motor function in the G1H-G93A mice treated with these 3 inhibitors. Significant amelioration of disease was seen even when TEI-6720 or Y-700 was administered after the appearance of early signs. Histopathological evaluation in the late stage revealed that G1H-G93A mice treated with TEI-6720 had well-preserved motor neurons and fewer inclusion bodies, compared with mice treated with placebo or with allopurinol. Our results indicate that these 3 nonpurine-analogue XOR inhibitors might increase the supply of high-energy compounds via the purine salvage pathway, thereby protecting motor neurons against death. This strategy may be applicable for oral therapy of ALS patients.

Measurement and Clinical Significance of Biomarkers of Oxidative Stress in Humans

Oxidative stress is the result of the imbalance between reactive oxygen species (ROS) formation and enzymatic and nonenzymatic antioxidants. Biomarkers of oxidative stress are relevant in the evaluation of the disease status and of the health-enhancing effects of antioxidants. We aim to discuss the major methodological bias of methods used for the evaluation of oxidative stress in humans. There is a lack of consensus concerning the validation, standardization, and reproducibility of methods for the measurement of the following: (1) ROS in leukocytes and platelets by flow cytometry, (2) markers based on ROS-induced modifications of lipids, DNA, and proteins, (3) enzymatic players of redox status, and (4) total antioxidant capacity of human body fluids. It has been suggested that the bias of each method could be overcome by using indexes of oxidative stress that include more than one marker. However, the choice of the markers considered in the global index should be dictated by the aim of the study and its design, as well as by the clinical relevance in the selected subjects. In conclusion, the clinical significance of biomarkers of oxidative stress in humans must come from a critical analysis of the markers that should give an overall index of redox status in particular conditions.

Oxidative stress and reactive oxygen species in endothelial dysfunction associated with cardiovascular and metabolic diseases

Reactive oxygen species (ROS) are reactive intermediates of molecular oxygen that act as important second messengers within the cells; however, an imbalance between generation of reactive ROS and antioxidant defense systems represents the primary cause of endothelial dysfunction, leading to vascular damage in both metabolic and atherosclerotic diseases. Endothelial activation is the first alteration observed, and is characterized by an abnormal pro-inflammatory and pro-thrombotic phenotype of the endothelial cells lining the lumen of blood vessels. This ultimately leads to reduced nitric oxide (NO) bioavailability, impairment of the vascular tone and other endothelial phenotypic changes collectively termed endothelial dysfunction(s). This review will focus on the main mechanisms involved in the onset of endothelial dysfunction, with particular focus on inflammation and aberrant ROS production and on their relationship with classical and non-classical cardiovascular risk factors, such as hypertension, metabolic disorders, and aging. Furthermore, new mediators of vascular damage, such as microRNAs, will be discussed. Understanding mechanisms underlying the development of endothelial dysfunction is an important base of knowledge to prevent vascular damage in metabolic and cardiovascular diseases.

Xanthine oxidase inhibitors beyond allopurinol and febuxostat; an overview and selection of potential leads based on in silico calculated physico-chemical properties, predicted pharmacokinetics and toxicity

Xanthine oxidase (XO), a versatile metalloflavoprotein enzyme, catalyzes the oxidative hydroxylation of hypoxanthine and xanthine to uric acid in purine catabolism while simultaneously producing reactive oxygen species. Both lead to the gout-causing hyperuricemia and oxidative damage of the tissues where overactivity of XO is present. Over the past years, significant progress and efforts towards the discovery and development of new XO inhibitors have been made and we believe that not only experts in the field, but also general readership would benefit from a review that addresses this topic. Accordingly, the aim of this article was to overview and select the most potent recently reported XO inhibitors and to compare their structures, mechanisms of action, potency and effectiveness of their inhibitory activity, in silico calculated physico-chemical properties as well as predicted pharmacokinetics and toxicity. Derivatives of imidazole, 1,3-thiazole and pyrimidine proved to be more potent than febuxostat while also displaying/possessing favorable predicted physico-chemical, pharmacokinetic and toxicological properties. Although being structurally similar to febuxostat, these optimized inhibitors bear some structural freshness and could be adopted as hits for hit-to-lead development and further evaluation by in vivo studies towards novel drug candidates, and represent valuable model structures for design of novel XO inhibitors.

Fructose Intake, Serum Uric Acid, and Cardiometabolic Disorders: A Critical Review

There is a direct relationship between fructose intake and serum levels of uric acid (UA), which is the final product of purine metabolism. Recent preclinical and clinical evidence suggests that chronic hyperuricemia is an independent risk factor for hypertension, metabolic syndrome, and cardiovascular disease. It is probably also an independent risk factor for chronic kidney disease, Type 2 diabetes, and cognitive decline. These relationships have been observed for high serum UA levels (>5.5 mg/dL in women and >6 mg/dL in men), but also for normal to high serum UA levels (5-6 mg/dL). In this regard, blood UA levels are much higher in industrialized countries than in the rest of the world. Xanthine-oxidase inhibitors can reduce UA and seem to minimize its negative effects on vascular health. Other dietary and pathophysiological factors are also related to UA production. However, the role of fructose-derived UA in the pathogenesis of cardiometabolic disorders has not yet been fully clarified. Here, we critically review recent research on the biochemistry of UA production, the relationship between fructose intake and UA production, and how this relationship is linked to cardiometabolic disorders.

Optimization of overexpression of a chaperone protein of steroid C25 dehydrogenase for biochemical and biophysical characterization

Molybdenum is an essential nutrient for metabolism in plant, bacteria, and animals. Molybdoenzymes are involved in nitrogen assimilation and oxidoreductive detoxification, and bioconversion reactions of environmental, industrial, and pharmaceutical interest. Molybdoenzymes contain a molybdenum cofactor (Moco), which is a pyranopterin heterocyclic compound that binds a molybdenum atom via a dithiolene group. Because Moco is a large and complex compound deeply buried within the protein, molybdoenzymes are accompanied by private chaperone proteins responsible for the cofactor's insertion into the enzyme and the enzyme's maturation. An efficient recombinant expression and purification of both Moco-free and Moco-containing molybdoenzymes and their chaperones is of paramount importance for fundamental and applied research related to molybdoenzymes. In this work, we focused on a D1 protein annotated as a chaperone of steroid C25 dehydrogenase (S25DH) from Sterolibacterium denitrificans Chol-1S. The D1 protein is presumably involved in the maturation of S25DH engaged in oxygen-independent oxidation of sterols. As this chaperone is thought to be a crucial element that ensures the insertion of Moco into the enzyme and consequently, proper folding of S25DH optimization of the chaperon's expression is the first step toward the development of recombinant expression and purification methods for S25DH. We have identified common E. coli strains and conditions for both expression and purification that allow us to selectively produce Moco-containing and Moco-free chaperones. We have also characterized the Moco-containing chaperone by EXAFS and HPLC analysis and identified conditions that stabilize both forms of the protein. The protocols presented here are efficient and result in protein quantities sufficient for biochemical studies.

Oxidative metabolism of curcumin-glucuronide by peroxidases and isolated human leukocytes

Conjugation with glucuronic acid is a prevalent metabolic pathway of orally administrated curcumin, the bioactive diphenol of the spice turmeric. The major in vitro degradation reaction of curcumin is autoxidative transformation resulting in oxygenation and cyclization of the heptadienedione chain to form cyclopentadione derivatives. Here we show that curcumin-glucuronide is much more stable than curcumin, degrading about two orders of magnitude slower. Horseradish peroxidase-catalyzed oxidation of curcumin-glucuronide occurred at about 80% of the rate with curcumin, achieving efficient transformation. Using LC-MS and NMR analyses the major products of oxidative transformation were identified as glucuronidated bicyclopentadione diastereomers. Cleavage into vanillin-glucuronide accounted for about 10% of the products. Myeloperoxidase and lactoperoxidase oxidized curcumin-glucuronide whereas tyrosinase and xanthine oxidase were not active. Phorbol ester-activated primary human leukocytes showed increased oxidative transformation of curcumin-glucuronide which was inhibited by the peroxidase inhibitor sodium azide. These studies provide evidence that the glucuronide of curcumin is not an inert product and may undergo further enzymatic and non-enzymatic metabolism. Oxidative transformation by leukocyte myeloperoxidase may represent a novel metabolic pathway of curcumin and its glucuronide conjugate.

CVD and Oxidative Stress

Nowadays, it is known that oxidative stress plays at least two roles within the cell, the generation of cellular damage and the involvement in several signaling pathways in its balanced normal state. So far, a substantial amount of time and effort has been expended in the search for a clear link between cardiovascular disease (CVD) and the effects of oxidative stress. Here, we present an overview of the different sources and types of reactive oxygen species in CVD, highlight the relationship between CVD and oxidative stress and discuss the most prominent molecules that play an important role in CVD pathophysiology. Details are given regarding common pharmacological treatments used for cardiovascular distress and how some of them are acting upon ROS-related pathways and molecules. Novel therapies, recently proposed ROS biomarkers, as well as future challenges in the field are addressed. It is apparent that the search for a better understanding of how ROS are contributing to the pathophysiology of CVD is far from over, and new approaches and more suitable biomarkers are needed for the latter to be accomplished.

Roles of Vascular Oxidative Stress and Nitric Oxide in the Pathogenesis of Atherosclerosis

Major reactive oxygen species (ROS)–producing systems in vascular wall include NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase, xanthine oxidase, the mitochondrial electron transport chain, and uncoupled endothelial nitric oxide (NO) synthase. ROS at moderate concentrations have important signaling roles under physiological conditions. Excessive or sustained ROS production, however, when exceeding the available antioxidant defense systems, leads to oxidative stress. Animal studies have provided compelling evidence demonstrating the roles of vascular oxidative stress and NO in atherosclerosis. All established cardiovascular risk factors such as hypercholesterolemia, hypertension, diabetes mellitus, and smoking enhance ROS generation and decrease endothelial NO production. Key molecular events in atherogenesis such as oxidative modification of lipoproteins and phospholipids, endothelial cell activation, and macrophage infiltration/activation are facilitated by vascular oxidative stress and inhibited by endothelial NO. Atherosclerosis develops preferentially in vascular regions with disturbed blood flow (arches, branches, and bifurcations). The fact that these sites are associated with enhanced oxidative stress and reduced endothelial NO production is a further indication for the roles of ROS and NO in atherosclerosis. Therefore, prevention of vascular oxidative stress and improvement of endothelial NO production represent reasonable therapeutic strategies in addition to the treatment of established risk factors (hypercholesterolemia, hypertension, and diabetes mellitus).