Uric acid and xanthine oxidase: future therapeutic targets in the prevention of cardiovascular disease?

Effectiveness of anthocyanin-containing foods and nutraceuticals in mitigating oxidative stress, inflammation, and cardiovascular health-related biomarkers: a systematic review of animal and human interventions

Cardiovascular diseases (CVDs) are a group of chronic health disorders prevalent worldwide that claim millions of lives yearly. Inflammation and oxidative stress are intricately associated with myocardial tissue damage, endothelial dysfunction, and increased odds of heart failure. Thus, dietary strategies aimed at decreasing the odds of CVDs are paramount. In this regard, the consumption of anthocyanins, natural pigments found in edible flowers, fruits, and vegetables, has attracted attention due to their potential to promote cardiovascular health. The main mechanisms of action linked with their protective effects on antioxidant and anti-inflammatory activities, serum lipid profile modulation, and other cardiovascular health parameters are explained and exemplified. However, little is known about the dose-dependency nature of the effects, which anthocyanin has better efficiency, and whether anthocyanin-containing foods display better in vivo efficacy than nutraceuticals (i.e., concentrated extracts containing higher levels of anthocyanins than foods). Thus, this systematic review focused on determining the effects of anthocyanin-containing foods and nutraceuticals on biomarkers associated with CVDs using animal studies and human interventions supported by in vitro mechanistic insights. Overall, the results showed that the regular consumption of anthocyanin-containing foods and nutraceuticals improved vascular function, lipid profile, and antioxidant and anti-inflammatory effects. The daily dosage, the participants' health status, and the duration of the intervention also significantly influenced the results.

Lignan and Phthalide Derivatives from the Rhizome of Ligusticum chuanxiong (Rhizoma chuanxiong) and Evaluation of Their anti-Xanthine Oxidase Activities

The previous research results showed that the extracts of ethyl acetate of the rhizome of Ligusticum chuanxiong (Rhizoma chuanxiong) possessed significant antigout effects in model mice. To explore the active ingredients responsible for the effects, phytochemical studies were performed, which led to the isolation of three rare 8', 9-linked neolignans, ligusticumins A-C (1-3), together with two novel phthalide-phenylpropanoid heterodimers, ligusticumalides A-B (4 and 5). It is noteworthy that 4 possesses an unprecedented 7-styryl phthalide skeleton. The structures and absolute configurations of 1-5 were elucidated by one-dimensional (1D) and two-dimensional (2D) NMR spectroscopy and electron-capture detector (ECD) spectroscopic methods. The bioassay results showed that compounds 1, 2, 3, and 5 presented moderate inhibitory activities against xanthine oxidase (XO) and 4 possessed a significant XO inhibitory effect with an IC50 value of 93.88 μM. This is the first time to investigate the anti-XO active ingredients of R. chuanxiong, which provides valuable information for searching for new antigout agents from natural products.

Bioactivity assays and phytochemical analysis upon Alcea glabrata; focusing on xanthine oxidase inhibitory and antimalarial properties

Alcea glabrata from the family Malvaceae, was selected for evaluating its xanthine oxidase inhibitory, anti-malarial, and antioxidant activities. In addition, some phytochemical analysis upon different extracts of A. glabrata were performed. Aerial parts of the collected A. glabrata plant material were dried and solvent extracted via soxhlet apparatus using different solvents. Various chromatographic techniques were used for extra fractionation of the achieved extracts. Xanthine oxidase (XO) inhibitory, antimalarial and antioxidant activity assays upon different A. glabrata extracts and fractions were carried out and reported in terms of IC_50s. Total phenolic and flavonoid contents of the A. glabrata methanol extract (MeOH) were determined using the 2,2-Di Phenyl-1-Picryl Hydrazyl (DPPH) assay, aluminum chloride colorimetric, and Folin-Ciocalteu reagents, respectively. In addition, A. glabrata essential oil was obtained through hydrodistillation by a Clevenger apparatus. Analysis and identification of essential oil compounds were carried out through gas chromatography mass spectrometry (GC-MS) analysis. MeOH extract showed the highest XO inhibitory activity with the IC₅₀ of 0.37 ± 0.12 μg/mL antioxidant activity with the RC₅₀ of 0.24 ± 0.06 μg/mL. While, chloroform extract revealed the strongest antimalarial activity with the IC₅₀ of 0.4 ± 0.05 μg/mL. The total flavonoid and phenolic contents of the A. glabrata methanol extract were 39.8 mg quercetin equivalent and 6.1 g gallic acid equivalent per 100 g of dry plant material, respectively. GC-MS analysis showed that the monoterpenes were prevailing in A. glabrata essential oil where the major constituents: octacosane (30.7%), eugenol (12.3%), and anethole (12.0%). Concerning the results of this study, A. glabrata extracts and its ingredients could be considered as a novel promising herbal medicine in the design and also treatment of new drugs for the relief of gout and malaria diseases.

A novel γ-lactone isolated from the leaves of Pithecellobium dulce (Roxb.) Benth. and its xanthine oxidase activity

A novel 3-(hydroxymethyl)-4-(methylamino)-dihydrofuran-2(3H)-one (1) was isolated for the first time from the leaves of Pithecellobium dulce (Roxb.) Benth., along with kaempferol (2) and kaempferol-3-rhamnoside (3). It demonstrated a promising xanthine oxidase inhibitory activity with IC₅₀ values of 79.0, 0.38, and 70.4 μg/mL (allopurinol = 0.4 µg/mL). This is the first paper to describe the presence of 3-(hydroxymethyl)-4-(methylamino)dihydrofuran-2(3H)-one (1) in the Fabaceae family. The structure elucidation of 3-(hydroxymethyl)-4-(methylamino)dihydrofuran-2(3H)-one (1), kaempferol (2), and kaempferol-3-rhamnoside (3) was determined primarily based on the analyses of MS and NMR results.

Shikonin derivatives as potent xanthine oxidase inhibitors: in-vitro study

Induction of hypersensitivity reactions (may be fatal too) by specific XO inhibitors has led to development of new molecules that are efficacious and have safer ADME profile. Among natural compounds, biologically active Alkannin/Shikonin (A/S) derivatives have unexplored XO inhibition potential. Therefore, their iso-hexenylnaphthazarin nucleus was studied and found that the nucleus is similar to that of allopurinol, signifying the XO inhibitory potential of these derivatives. For confirmation of their potential, β,β-dimethylacrylshikonin and deoxyshikonin were successfully isolated and characterised from Arnebia euchroma (Royle.) Johnst. (Boraginaceae) and were evaluated for in vitro XO inhibitory potential. β,β-dimethylacrylshikonin and deoxyshikonin showed a good XO inhibition potential with IC₅₀ values of 7.475 ± 1.46 µg/mL and 4.487 ± 0.88 µg/mL, respectively. Results also validated the pharmacophore hypothesis, and it was concluded that nucleus iso-hexenylnaphthazarin can be remodelled for optimising the efficacy.

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.

Platanic acid derived amides are more cytotoxic than their corresponding oximes

Abstract

Albeit platanic acid has been known since 1956, its potential to act as a valuable starting material for the synthesis of cytotoxic agents has been neglected for many years. Hereby we describe the synthesis of a small library of amides and oximes derived from 3-O-acetyl-platanic acid, and the results of their screening as cytotoxic agents for several human tumor cell lines. As a result, while the cytotoxicity of the oximes was diminished as compared to the parent amides, the homopiperazinyl amide 5 held the highest cytoxicity (EC50 = 0.9 μM for A375 human melanoma cells). Extra FACS and cell cycle measurements showed compound 5 to act onto A375 cells rather by apoptosis than by necrosis.

Clinical trial registration

No clinical trials are associated with this study

Anti-Diabetes, Anti-Gout, and Anti-Leukemia Properties of Essential Oils from Natural Spices Clausena indica, Zanthoxylum rhetsa, and Michelia tonkinensis

Essential oils (EOs) of Clausena indica fruits, Zanthoxylum rhetsa fruits, and Michelia tonkinensis seeds were analyzed for their phytochemical profiles and biological activities, including anti-diabetes, anti-gout, and anti-leukemia properties. Sixty-six volatile compounds were identified by gas chromatography–mass spectrometry (GC–MS), in which, myristicin (68.3%), limonene (44.2%), and linalool (49.3%) were the most prominent components of EOs extracted from C. indica, Z. rhetsa, and M. tonkinensis, respectively. In addition, only EOs from C. indica inhibited the activities of all tested enzymes comprising α-amylase (IC₅₀ = 7.73 mg/mL), α-glucosidase (IC₅₀ = 0.84 mg/mL), and xanthine oxidase (IC₅₀ = 0.88 mg/mL), which are related to type 2 diabetes and gout. Remarkably, all EOs from C. indica, Z. rhetsa (IC₅₀ = 0.73 mg/mL), and M. tonkinensis (IC₅₀ = 1.46 mg/mL) showed a stronger anti-α-glucosidase ability than acarbose (IC₅₀ = 2.69 mg/mL), a known anti-diabetic agent. Moreover, the growth of leukemia cell Meg-01 was significantly suppressed by all EOs, of which, the IC₅₀ values were recorded as 0.32, 0.64, and 0.31 mg/mL for EOs from C. indica, Z. rhetsa, and M. tonkinensis, respectively. As it stands, this is the first report about the inhibitory effects of EOs from C. indica and Z. rhetsa fruits, and M. tonkinensis seeds on the human leukemia cell line Meg-01 and key enzymes linked to diabetes and gout. In conclusion, the present study suggests that EOs from these natural spices may be promising candidates for pharmaceutical industries to develop nature-based drugs to treat diabetes mellitus or gout, as well as malignant hematological diseases such as leukemia.

Xanthine oxidase inhibitor febuxostat reduces atrial fibrillation susceptibility by inhibition of oxidized CaMKII in Dahl salt-sensitive rats

Oxidative stress could be a possible mechanism and a therapeutic target of atrial fibrillation (AF). However, the effects of the xanthine oxidase (XO) inhibition for AF remain to be fully elucidated. We investigated the effects of a novel XO inhibitor febuxostat on AF compared with allopurinol in hypertension rat model. Five-week-old Dahl salt-sensitive rats were fed either low-salt (LS) (0.3% NaCl) or high-salt (HS) (8% NaCl) diet. After 4 weeks of diet, HS diet rats were divided into three groups: orally administered to vehicle (HS-C), febuxostat (5 mg/kg/day) (HS-F), or allopurinol (50 mg/kg/day) (HS-A). After 4 weeks of treatment, systolic blood pressure (SBP) was significantly higher in HS-C than LS, and it was slightly but significantly decreased by treatment with each XO inhibitor. AF duration was significantly prolonged in HS-C compared with LS, and significantly suppressed in both HS-F and HS-A (LS; 5.8 ± 3.5 s, HS-C; 33.9 ± 23.7 s, HS-F; 15.0 ± 14.1 s, HS-A; 20.1 ± 11.9 s: P<0.05). Ca2+ spark frequency was obviously increased in HS-C rats and reduced in the XO inhibitor-treated rats, especially in HS-F group. Western blotting revealed that the atrial expression levels of Met281/282-oxidized Ca2+/Calmodulin-dependent kinase II (CaMKII) and Ser2814-phosphorylated ryanodine receptor 2 were significantly increased in HS-C, and those were suppressed in HS-F and HS-A. Decreased expression of gap junction protein connexin 40 in HS-C was partially restored by treatment with each XO inhibitor. In conclusion, XO inhibitor febuxostat, as well as allopurinol, could reduce hypertension-related increase in AF perpetuation by restoring Ca2+ handling and gap junction.

Suppression of Adenosine Deaminase and Xanthine Oxidase Activities by Mineralocorticoid and Glucocorticoid Receptor Blockades Restores Renal Antioxidative Barrier in Oral Contraceptive-Treated Dam

OBJECTIVE

We tested the hypothesis that postpartum combined oral contraceptive (COC) treatment would induce oxidative stress via the adenosine deaminase-xanthine oxidase pathway in the kidney. We also sought to determine whether mineralocorticoid receptor (MR) or glucocorticoid receptor (GR ) blockade would suppress the activities of ADA and xanthine oxidase caused by postpartum COC treatment in the kidney.

METHODS

Twenty-four Wistar dams were randomly assigned to 4 groups (n = 6/group). Dams received vehicle (po), COC (1.0 μg ethinylestradiol and 5.0 μg levonorgestrel; po), COC with GR blockade (mifepristone; 80.0 mg/kg; po), and COC with MR blockade (spironolactone; 0.25 mg/kg; po) daily between 3rd and 11th week postpartum.

RESULTS

Data showed that postpartum COC caused increased plasma creatinine and urea, increased renal triglyceride/high-density lipoprotein ratio, free fatty acid accumulation, alanine aminotransferase, gamma-glutamyltransferase, uric acid, and activities of renal XO and ADA. On the other hand, postpartum COC resulted in decreased plasma albumin, renal glutathione, and Na+-K+-ATPase activity with no effect on lactate production. However, MR or GR blockade ameliorated the alterations induced by postpartum COC treatment. The present results demonstrate that MR or GR blockade ameliorates postpartum COC-induced increased activities of ADA and xanthine oxidase and restores glutathione-dependent antioxidative defense.

CONCLUSION

These findings implicate the involvements of GR and MR in renal dysfunctions caused by COC in dams via disrupted glutathione antioxidative barrier.

Natural Products and Extracts as Xantine Oxidase Inhibitors - A Hope for Gout Disease?

Xanthine oxidase (EC 1.17.3.2) (XO) is one of the main enzymatic sources that create reactive oxygen species (ROS) in the living system. It is a dehydrogenase enzyme that performs electron transfer to nicotinamide adenine dinucleotide (NAD+), while oxidizing hypoxanthin, which is an intermediate compound in purine catabolism, first to xanthine and then to uric acid. XO turns into an oxidant enzyme that oxidizes thiol groups under certain stress conditions in the tissue. The last metabolic step, in which hypoxanthin turns into uric acid, is catalyzed by XO. Uric acid, considered a waste product, can cause kidney stones and gouty-type arthritis as it is crystallized, when present in high concentrations. Thus, XO inhibitors are one of the drug classes used against gout, a purine metabolism disease that causes urate crystal storage in the joint and its surroundings caused by hyperuricemia. Urate-lowering therapy includes XO inhibitors that reduce uric acid production as well as uricosuric drugs that increase urea excretion. Current drugs that obstruct uric acid synthesis through XO inhibition are allopurinol, febuxostat, and uricase. However, since the side effects, safety and tolerability problems of some current gout medications still exist, intensive research is ongoing to look for new, effective, and safer XO inhibitors of natural or synthetic origins for the treatment of the disease. In the present review, we aimed to assess in detail XO inhibitory capacities of pure natural compounds along with the extracts from plants and other natural sources via screening Pubmed, Web of Science (WoS), Scopus, and Google Academic. The data pointed out to the fact that natural products, particularly phenolics such as flavonoids (quercetin, apigenin, and scutellarein), tannins (agrimoniin and ellagitannin), chalcones (melanoxethin), triterpenes (ginsenoside Rd and ursolic acid), stilbenes (resveratrol and piceatannol), alkaloids (berberin and palmatin) have a great potential for new XO inhibitors capable of use against gout disease. In addition, not only plants but other biological sources such as microfungi, macrofungi, lichens, insects (silk worms, ants, etc) seem to be the promising sources of novel XO inhibitors.

Targeting Xanthine Oxidase by Natural Products as a Therapeutic Approach for Mental Disorders

Mental disorders comprise diverse human pathologies, including depression, bipolar affective disorder, schizophrenia, and dementia that affect millions of people around the world. The causes of mental disorders are unclear, but growing evidence suggests that oxidative stress and the purine/adenosine system play a key role in their development and progression. Xanthine oxidase (XO) is a flavoprotein enzyme essential for the catalysis of the oxidative hydroxylation of purines -hypoxanthine and xanthine- to generate uric acid. As a consequence of the oxidative reaction of XO, reactive oxygen species (ROS) such as superoxide and hydrogen peroxide are produced and, further, contribute to the pathogenesis of mental disorders. Altered XO activity has been associated with free radical-mediated neurotoxicity inducing cell damage and inflammation. Diverse studies reported a direct association between an increased activity of XO and diverse mental diseases including depression or schizophrenia. Small-molecule inhibitors, such as the well-known allopurinol, and dietary flavonoids, can modulate the XO activity and subsequent ROS production. In the present work, we review the available literature on XO inhibition by small molecules and their potential therapeutic application in mental disorders. In addition, we discuss the chemistry and molecular mechanism of XO inhibitors, as well as the use of structure-based and computational methods to design specific inhibitors with the capability of modulating XO activity.

Association Between Serum Uric Acid Levels and Cognitive Function in Patients with Ischemic Stroke and Transient Ischemic Attack (TIA): A 3-Month Follow-Up Study

PURPOSE

Cognitive impairment is a common complication after stroke and transient ischemic attack (TIA). The relationship between serum uric acid (SUA) and post-stroke cognitive impairment (PSCI) is controversial. This study evaluated the association of different SUA levels in the normal range and PSCI at 3 months.

PATIENTS AND METHODS

A total of 1523 patients with ischemic stroke/TIA were recruited from the Impairment of Cognition and Sleep (ICONS) subgroup of the China National Stroke Registry-3 (CNSR-3). SUA concentration was assessed at baseline. Global cognitive status was evaluated using the Montreal Cognitive Assessment (MoCA). The main clinical outcome was the incidence of PSCI assessed at 3 months after stroke/TIA. The association between SUA status and the risk of PSCI was assessed with multiple regression models adjusted for potential covariates.

RESULTS

Among the 1523 patients (1391 (91.33%) stroke patients and 132 (8.67%) TIA patients), 747 (49.05%) patients had PSCI at 3 months. Compared to the reference group, there was an increased risk of PSCI in males with SUA levels in the first (OR=1.76) and fourth quartiles (OR=1.47). A U-shaped association between SUA levels and the incidence of PSCI with an inflection point of 297 mmol/L was also found in males. However, there was no association between SUA levels and PSCI in females.

CONCLUSION

The association between SUA and PSCI differed between males and females. In males, both low and high SUA levels were associated with relatively higher incidences of PSCI, supporting a U-shaped association between SUA levels and PSCI.

Protective effects of natural compounds against oxidative stress in ischemic diseases and cancers via activating the Nrf2 signaling pathway: A mini review

Oxidative stress, an imbalance between reactive oxygen species and antioxidants, has been seen in the pathological states of many disorders such as ischemic diseases and cancers. Many natural compounds (NCs) have long been recognized to ameliorate oxidative stress due to their inherent antioxidant activities. The modulation of oxidative stress by NCs via activating the Nrf2 signaling pathway is summarized in the review. Three NCs, ursolic acid, betulinic acid, and curcumin, and the mechanisms of their cytoprotective effects are investigated in myocardial ischemia, cerebral ischemia, skin cancer, and prostate cancer. To promote the therapeutic performance of NCs with poor water solubility, the formulation approach, such as the nano drug delivery system, is elaborated as well in this review.

Severe SARS-CoV-2 infection in humans is defined by a shift in the serum lipidome resulting in dysregulation of eicosanoid immune mediators

The COVID-19 pandemic has affected more than 10 million people worldwide with mortality exceeding half a million patients. Risk factors associated with severe disease and mortality include advanced age, hypertension, diabetes, and obesity.1 Clear mechanistic understanding of how these comorbidities converge to enable severe infection is lacking. Notably each of these risk factors pathologically disrupts the lipidome and this disruption may be a unifying feature of severe COVID-19.1-7 Here we provide the first in depth interrogation of lipidomic changes, including structural-lipids as well as the eicosanoids and docosanoids lipid mediators (LMs), that mark COVID-19 disease severity. Our data reveal that progression from moderate to severe disease is marked by a loss of specific immune regulatory LMs and increased pro-inflammatory species. Given the important immune regulatory role of LMs, these data provide mechanistic insight into the immune balance in COVID-19 and potential targets for therapy with currently approved pharmaceuticals.8.

Severe SARS-CoV-2 infection in humans is defined by a shift in the serum lipidome resulting in dysregulation of eicosanoid immune mediators

The COVID-19 pandemic has affected more than 10 million people worldwide with mortality exceeding half a million patients. Risk factors associated with severe disease and mortality include advanced age,hypertension, diabetes, and obesity. Clear mechanistic understanding of how these comorbidities converge to enable severe infection is lacking. Notably each of these risk factors pathologically disrupts the lipidome and this disruption may be a unifying feature of severe COVID-19. Here we provide the first in depth interrogation of lipidomic changes, including structural-lipids as well as the eicosanoids and docosanoids lipid mediators (LMs), that mark COVID-19 disease severity. Our data reveal that progression from moderate to severe disease is marked by a loss of specific immune regulatory LMs and increased pro-inflammatory species. Given the important immune regulatory role of LMs, these data provide mechanistic insight into the immune balance in COVID-19 and potential targets for therapy with currently approved pharmaceuticals.

Oxidative Stress and New Pathogenetic Mechanisms in Endothelial Dysfunction: Potential Diagnostic Biomarkers and Therapeutic Targets

Cardiovascular diseases (CVD), including heart and pathological circulatory conditions, are the world's leading cause of mortality and morbidity. Endothelial dysfunction involved in CVD pathogenesis is a trigger, or consequence, of oxidative stress and inflammation. Endothelial dysfunction is defined as a diminished production/availability of nitric oxide, with or without an imbalance between endothelium-derived contracting, and relaxing factors associated with a pro-inflammatory and prothrombotic status. Endothelial dysfunction-induced phenotypic changes include up-regulated expression of adhesion molecules and increased chemokine secretion, leukocyte adherence, cell permeability, low-density lipoprotein oxidation, platelet activation, and vascular smooth muscle cell proliferation and migration. Inflammation-induced oxidative stress results in an increased accumulation of reactive oxygen species (ROS), mainly derived from mitochondria. Excessive ROS production causes oxidation of macromolecules inducing cell apoptosis mediated by cytochrome-c release. Oxidation of mitochondrial cardiolipin loosens cytochrome-c binding, thus, favoring its cytosolic release and activation of the apoptotic cascade. Oxidative stress increases vascular permeability, promotes leukocyte adhesion, and induces alterations in endothelial signal transduction and redox-regulated transcription factors. Identification of new endothelial dysfunction-related oxidative stress markers represents a research goal for better prevention and therapy of CVD. New-generation therapeutic approaches based on carriers, gene therapy, cardiolipin stabilizer, and enzyme inhibitors have proved useful in clinical practice to counteract endothelial dysfunction. Experimental studies are in continuous development to discover new personalized treatments. Gene regulatory mechanisms, implicated in endothelial dysfunction, represent potential new targets for developing drugs able to prevent and counteract CVD-related endothelial dysfunction. Nevertheless, many challenges remain to overcome before these technologies and personalized therapeutic strategies can be used in CVD management.

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.

Voltammetry at Hexamethyl-P-Terphenyl Poly(Benzimidazolium) (HMT-PMBI)-Coated Glassy Carbon Electrodes: Charge Transport Properties and Detection of Uric and Ascorbic Acid

We describe the voltammetric behavior of an anion-exchange membrane, hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI). The anion-exchange properties of HMT-PMBI chemically modified electrodes were investigated using K4Fe(CN)6 and K2IrCl6 as redox probes. The permselectivity properties of HMT-PMBI chemically modified electrodes were ascertained using tris(2-2')bipyridyl-ruthenium(II) chloride Ru(bpy)32+. Cyclic voltammetry and chronoamperometry were utilized to extract parameters such as the concentration of the redox mediators inside the films and the apparent diffusion coefficients. We found the concentration of K4Fe(CN)6 and K2IrCl6 redox species within HMT-PMBI-coated films to be on the order of 0.04-0.1 mol·dm-3, and values of Dapp ca. 10-10-10-9 cm2·s-1. To evaluate the possibility of using such a polymer coating in electroanalysis, HMT-PMBI-modified electrodes were utilized for the voltammetric detection of uric acid in artificial urine, Surine® and ascorbic acid in Vitamin C samples. The results showed that HMT-PMBI-coated electrodes can detect uric acid in Surine® with a limit of detection (LoD) of 7.7 µM, sensitivity of 0.14 µA·µM-1·cm-2, and linear range between 5 μM and 200 μM, whereas for Vitamin C tablets, the LoD is 41.4 µM, the sensitivity is 0.08 µA·µM-1·cm-2, and the linear range is between 25 μM and 450 μM.

Antioxidant, Anti-Melanogenic and Anti-Wrinkle Effects of Phellinus vaninii

In this study, the antioxidant, anti-xanthine oxidase, anti-melanogenic and anti-wrinkle effects of methanol (ME) and hot water (HE) extracts from the fruiting bodies of Phellinus vaninii were investigated. The 1,1-diphenyl-2-picryl-hydrazyl free radical scavenging activity of 2.0 mg/mL HE (95.38%) was comparable to that of butylated hydroxytoluene (96.97%), the reference standard. The hydroxyl radical scavenging activities of ME (98.19%) and HE (97.55%) were higher than that of butylated hydroxytoluene (92.66%) at 2.0 mg/mL. Neither ME nor HE was cytotoxic to murine melanoma B16-F10 cells at 25-750 µg/mL. Although the xanthine oxidase (XO) inhibitory effects of ME and HE were significantly lower than that of allopurinol, the values were higher than 84 percent. The in vitro tyrosinase inhibitory activities of ME and HE were comparable to kojic acid at 2.0 mg/mL. The cellular tyrosinase and melanin synthetic activities of ME and HE on B16-F10 melanoma cells at 500 µg/mL were higher than arbutin, indicating that the inhibitory effects of arbutin on the tyrosinase and melanin synthesis were higher than those of ME and HE. The collagenase inhibitory activity of HE was comparable to EGCG at 2.0 mg/mL, however, the elastase inhibitory activity of ME and HE was lower than EGCG at the concentration tested. The study results demonstrated that the fruiting bodies of Ph. vaninii possessed good antioxidant, anti-xanthine oxidase, cell-free anti-tyrosinase, cellular anti-tyrosinase, anti-collagenase, and moderate anti-elastase activities, which might be used for the development of novel anti-gout, skin-whitening, and skin anti-wrinkle agents.

In silico design and synthesis of hesperitin derivatives as new xanthine oxidase inhibitors

Background

Hesperitin, a naturally occurring flavonoid was hybridized with phenolic acids to evaluate its potential to inhibit the activity of xanthine oxidase (XO), a key enzyme which catalyses xanthine to uric acid which is found to be associated with gout and many life style related disorders.

Objective

To develop new xanthine oxidase inhibitors from natural constituents along with antioxidant potential.

Method

In this report, we designed and synthesized hesperitin derivatives hybridized with natural phenolic acids to form ester linkage with the help of molecular docking. The synthesized compounds were evaluated for their antioxidant and xanthine oxidase inhibitory potential.

Results

The in vitro xanthine oxidase inhibitory activity and enzyme kinetics studies showed that hesperitin derivatives displayed a potential inhibition against XO in competitive manner with IC₅₀ value ranging from 9.0 to 23.15 µM and HET4 was revealed as most active derivative. Molecular simulation revealed that new hesperitin derivatives interacted with the amino acid residues SER1080, PHE798, GLN1194, ARG912, THR1083, ALA1078 and MET1038 located within the active cavity of XO. Results of antioxidant activity revealed that all the derivatives showed very good antioxidant potential.

Conclusion

Taking advantage of molecular docking, this hybridization of two natural constituent could lead to desirable xanthine oxidase inhibitors with improved activity.

In silico design and synthesis of targeted rutin derivatives as xanthine oxidase inhibitors

Background

Xanthine oxidase is an important enzyme of purine catabolism pathway and has been associated directly in pathogenesis of gout and indirectly in many pathological conditions like cancer, diabetes and metabolic syndrome. In this research rutin, a bioactive flavonoid was explored to determine the capability of itself and its derivatives to inhibit xanthine oxidase.

Objective

To develop new xanthine oxidase inhibitors from natural constituents along with antioxidant potential.

Method

In this report, we designed and synthesized rutin derivatives hybridized with hydrazines to form hydrazides and natural acids to form ester linkage with the help of molecular docking. The synthesized compounds were evaluated for their antioxidant and xanthine oxidase inhibitory potential.

Results

The enzyme kinetic studies performed on rutin derivatives showed a potential inhibitory effect on XO ability in competitive manner with IC₅₀ value ranging from 04.708 to 19.377 µM and RU3a₃ was revealed as most active derivative. Molecular simulation revealed that new rutin derivatives interacted with the amino acid residues PHE798, GLN1194, ARG912, GLN 767, ALA1078 and MET1038 positioned inside the binding site of XO. Results of antioxidant activity revealed that all the derivatives showed very good antioxidant potential.

Conclusion

Taking advantage of molecular docking, this hybridization of two natural constituent could lead to desirable xanthine oxidase inhibitors with improved activity.

Electronic supplementary material

The online version of this article (10.1186/s13065-019-0585-8) contains supplementary material, which is available to authorized users.

The relationship between serum uric acid and lipid profile in Bangladeshi adults

Background

Although the link between elevated uric acid and metabolic syndrome has been reported in some studies; the relationship of serum uric acid (SUA) with lipid profile has not well studied or little is known so far. This study was conducted to assess the relationship between SUA and lipid profile among the general adults in Bangladesh.

Methods

In total, 280 blood samples were collected from general adult participants (male, n = 150 and female, n = 130) and analyzed for serum lipid profile (TC, TG, HDL and LDL) and SUA levels. The study subjects were divided by quartiles based on SUA levels (Q1: ≤225 μmol/L, Q2: 226–285 μmol/L, Q3: 286–340 μmol/L and Q4: > 340 μmol/L). Linear regression modeling was used to evaluate the relationship between SUA and lipid levels.

Results

The prevalence of hyperuricemia was 9.2% in males and 10.4% in females. The mean level of SUA was significantly higher in male (317 ± 90 μmol/L) than in the female (255 ± 65 μmol/L) subjects (p < 0.001). An increasing trend for elevated lipid profile was observed in both gender with increasing levels of SUA in the quartiles (p < 0.05). In regression analysis, a significant positive correlation was found between SUA and TG, TC and LDL (p < 0.01) while an inverse correlation was observed between SUA and HDL (p < 0.01). After adjusting for potential confounders, lipid profile was linearly associated with SUA levels (p < 0.01 for trend).

Conclusions

Present study showed a significant positive relationship for SUA with TG, TC and LDL levels, and an inverse relationship for SUA with HDL. Early prevention of hyperuricemia and dyslipidemia may be helpful to reduce the incidence of associated cardiovascular diseases.

Redox and NF-κB signaling in osteoarthritis

Human cells have to deal with the constant production of reactive oxygen species (ROS). Although ROS overproduction might be harmful to cell biology, there are plenty of data showing that moderate levels of ROS control gene expression by maintaining redox signaling. Osteoarthritis (OA) is the most common joint disorder with a multi-factorial etiology including overproduction of ROS. ROS overproduction in OA modifies intracellular signaling, chondrocyte life cycle, metabolism of cartilage matrix and contributes to synovial inflammation and dysfunction of the subchondral bone. In arthritic tissues, the NF-κB signaling pathway can be activated by pro-inflammatory cytokines, mechanical stress, and extracellular matrix degradation products. This activation results in regulation of expression of many cytokines, inflammatory mediators, transcription factors, and several matrix-degrading enzymes. Overall, NF-κB signaling affects cartilage matrix remodeling, chondrocyte apoptosis, synovial inflammation, and has indirect stimulatory effects on downstream regulators of terminal chondrocyte differentiation. Interaction between redox signaling and NF-κB transcription factors seems to play a distinctive role in OA pathogenesis.

Uric Acid Level and New-Onset Atrial Fibrillation in the Japanese General Population - Longitudinal Study

BACKGROUND

The independent role of uric acid (UA) as a risk factor for atrial fibrillation (AF) has not been fully elucidated. Methods and Results: We studied 111,566 subjects (53,416 men; 58,150 women) who underwent annual health check-ups. We divided them by sex into tertile of baseline UA. To investigate the predictive power of UA for new-onset AF, we performed Cox proportional hazard analysis including UA tertiles, body mass index, creatinine, smoking and drinking status, and presence of hypertension, diabetes, and dyslipidemia. During 4.1 years, 467 men (0.87%) and 180 women (0.31%) had AF (P<0.001). Cut-off points for tertiles of UA were as follows: women, ≤3.9, 4.0-4.8, and ≥4.9 mg/dL; men, ≤5.4, 5.5-6.4, and ≥6.5 mg/dL. Hazard ratio (HR) for third to first tertile was 1.74 (95% CI: 1.15-2.70; P=0.008), whereas there were no differences between tertiles in men. Rate of new-onset AF was significantly higher in the group with initially increased UA (ΔUA ≥0.3 mg/dL) than that with unchanged UA (ΔUA, -0.2 or +0.2 mg/dL) in the third tertile of baseline UA in both sexes.

CONCLUSIONS

Higher baseline UA was significantly associated with higher AF incidence in women. Initial increase in UA was significantly associated with AF incidence when baseline UA was ≥6.5 mg/dL in men, and ≥4.9 mg/dL in women.

An integrated portable system for single chip simultaneous measurement of multiple disease associated metabolites

Metabolites, the small molecules that underpin life, can act as indicators of the physiological state of the body when their abundance varies, offering routes to diagnosis of many diseases. The ability to assay for multiple metabolites simultaneously will underpin a new generation of precision diagnostic tools. Here, we report the development of a handheld device based on complementary metal oxide semiconductor (CMOS) technology with multiple isolated micro-well reaction zones and integrated optical sensing allowing simultaneous enzyme-based assays of multiple metabolites (choline, xanthine, sarcosine and cholesterol) associated with multiple diseases. These metabolites were measured in clinically relevant concentration range with minimum concentrations measured: 25 μM for choline, 100 μM for xanthine, 1.25 μM for sarcosine and 50 μM for cholesterol. Linking the device to an Android-based user interface allows for quantification of metabolites in serum and urine within 2 min of applying samples to the device. The quantitative performance of the device was validated by comparison to accredited tests for cholesterol and glucose.

Metabolic syndrome: an update on diagnostic criteria, pathogenesis, and genetic links

Metabolic syndrome (MetS), today a major global public health problem, is a cluster of clinical, metabolic, and biochemical abnormalities, such as central adiposity, hypertension, insulin resistance, and dyslipidemias. These MetS-related traits significantly increase the risk of type 2 diabetes mellitus, adverse cardiac events, stroke, and hepatic steatosis. The pathogenesis of MetS is multifactorial, with the interplay of environmental, nutritional, and genetic factors. Chronic low-grade inflammation together with visceral adipose tissue, adipocyte dysfunction, and insulin resistance plays a major role in the progression of the syndrome by impairing lipid and glucose homeostasis in insulin-sensitive tissues, such as the liver, muscle, and adipocytes. Adipose-derived inflammatory cytokines and non-esterified fatty acids establish the link between central obesity IR, inflammation, and atherogenesis. Various studies have reported an association between MetS and related traits with single-nucleotide polymorphisms of different susceptibility genes. Modulation of cytokine levels, pro-oxidants, and disturbed energy homeostasis, in relation to the genetic variations, is described in this review of the recent literature, which also provides updated data regarding the epidemiology, diagnostic criteria, and pathogenesis of MetS.

Left ventricular ejection fraction as therapeutic target: is it the ideal marker?

Heart failure (HF) consists the fastest growing clinical cardiac disease. HF patients are categorized on the basis of underlying left ventricular ejection fraction (LVEF) into HF with preserved EF (HFpEF), reduced LVEF (HFrEF), and mid-range LVEF (HFmrEF). While LVEF is the most commonly used surrogate marker of left ventricular (LV) systolic function, the implementation of two-dimensional echocardiography in estimating this parameter imposes certain caveats on current HF classification. Most importantly, LVEF could fluctuate in repeated measurements or even recover after treatment, thus blunting the borders between proposed categories of HF and enabling upward classification of patients. Under this prism, we sought to summarize possible procedures to improve systolic function in patients with HFrEF either naturally or by the means of pharmacologic and non-pharmacologic treatment and devices. Therefore, we reviewed established pharmacotherapy, including beta-blockers, inhibitors of renin-angiotensin-aldosterone axis, statins, and digoxin as well as novel treatments like sacubitril-valsartan, ranolazine, and ivabradine. In addition, we assessed evidence in favor of cardiac resynchronization therapy and exercise training programs. Finally, innovative therapeutic strategies, including stem cells, xanthine oxidase inhibitors, antibiotic regimens, and omega-3 polyunsaturated fatty acids, were also taken into consideration. We concluded that LVEF is subject to changes in HF after intervention and besides the aforementioned HFrEF, HFpEF, and HFmrEF categories, a new entity of HF patients with recovered LVEF should be acknowledged. An improved global and refined LV function assessment by sophisticated imaging modalities and circulating biomarkers is expected to render HF classification more accurate and indicate patients with viable-yet dysfunctional-myocardium and favorable characteristics as the ideal candidates for LVEF recovery by individualized HF therapy.

A meta-analysis of the efficacy of allopurinol in reducing the incidence of myocardial infarction following coronary artery bypass grafting

Background

The xanthine oxidase inhibitor allopurinol that is commonly used to treat gout, has been suggested to have pleiotropic effects that are likely to reduce the incidence of myocardial infarction (MI) in at risk individuals. The aim of this meta-analysis was to assess the efficacy of allopurinol treatment in reducing the incidence of MI.

Method

MEDLINE, Scopus, Web of Science, and Cochrane Library databases were searched for randomised controlled trials examining the efficacy of allopurinol in reducing the incidence of MI. The quality of study methodology was assessed by two independent reviewers using the Cochrane Collaboration’s tool for assessing risk of bias. This meta-analysis was conducted using a fixed-effects model, and heterogeneity was assessed with the I² index.

Results

One thousand one hundred twenty-three citations were screened and only six studies satisfied the inclusion criterion. Published between 1988 and 1995, all studies examined the cardioprotective efficacy of allopurinol in the setting of coronary artery bypass graft (CABG). From a total pooled sample size of 229, MI was reported in 2 (1.77%) allopurinol and 14 (12.07%) control patients. A fixed-effects meta-analysis (I² = 0%) identified a statistically significant reduced incidence of myocardial infarction (RR 0.21, 95% CI: 0.06, 0.70, p = 0.01) in patients allocated to allopurinol. However, in the leave-one-out sensitivity analyses, the treatment effect became non-significant with the removal of one of the studies.

Conclusion

Based on the limited evidence available, allopurinol appears to reduce the incidence of perioperative MI following CABG. Further research is required to confirm these findings.

Electronic supplementary material

The online version of this article (10.1186/s12872-018-0881-6) contains supplementary material, which is available to authorized users.

Evaluation of a pharmacokinetic-pharmacodynamic model for hypouricaemic effects of febuxostat using datasets obtained from real-world patients

AIM

Febuxostat is an active xanthine oxidase (XO) inhibitor which is widely used in the treatment of hyperuricaemia. We aimed to evaluate the predictive performance of a pharmacokinetic-pharmacodynamic (PK-PD) model of the hypouricaemic effects of febuxostat.

METHODS

Previously, we formulated a PK-PD model for predicting the hypouricaemic effects of febuxostat as a function of baseline serum urate levels, body weight, renal function and drug dose, using datasets reported in preapproval studies. Using an updated model with a sensitivity analysis, we examined the predictive performance of the PK-PD model, using datasets obtained from the medical records of patients who received febuxostat from March 2011 to December 2015 at Tokyo Women's Medical University Hospital. Multivariate regression analysis was performed to explore clinical variables to improve the predictive performance of the model.

RESULTS

A total of 1199 serum urate values were retrieved from 168 patients (age: 60.5 ± 17.7 years; 71.4% male) who were receiving febuxostat as a treatment for hyperuricaemia. There was a significant correlation (r = 0.68; P < 0.01) between the serum urate levels observed and those predicted by the modified PK-PD model. A multivariate regression analysis revealed that the predictive performance of the model could be improved further by considering comorbidities (such as diabetes mellitus), estimated glomerular filtration rate (eGFR) and the coadministration of loop diuretics (r = 0.77, P < 0.01).

CONCLUSIONS

The PK-PD model may be useful for predicting individualized maintenance doses of febuxostat in real-world patients.

Sex-Dependent Associations of Serum Uric Acid with Brain Function During Aging

Serum uric acid (SUA) is an abundant natural antioxidant capable of reducing cellular oxidation, a major cause of neurodegenerative disease. In line with this, SUA levels are lower in Alzheimer's disease; however, the association between SUA and cognition remains unclear. Results from studies examining the effects of SUA on cognition may be difficult to interpret in the context of normal versus pathological aging. This study examined sex-specific associations of baseline SUA with cognition during aging. Data from dementia-free participants initially aged 26-99 (N = 1,451) recruited for the Baltimore Longitudinal Study of Aging (BLSA), were used in the current analyses. SUA was assessed using blood samples collected during research visits. Cognition was measured using five composite scores (verbal memory, attention, executive function, language, and visuospatial ability). At the first study visit, compared with women, men were older, more likely to be White, had more years of education, higher baseline SUA levels, and higher cardiovascular risk scores. Higher baseline SUA was associated with attenuated declines in attention (β= 0.006; p = 0.03) and visuospatial abilities (β= 0.007; p = 0.01) in men. There was a trend to suggest higher baseline SUA in men was associated with attenuated declines in language, but this finding did not reach statistical significance (p = 0.09). There were no significant findings with SUA and cognition in women. In this sample of cognitively healthy, community-dwelling adults, we found that higher SUA levels at baseline were associated with attenuated declines in attention and visuospatial abilities in men. SUA was not associated with cognition or change in cognition over time in women.

Diabetic nephropathy: Is there a role for oxidative stress?

Oxidative stress has been implicated in the pathophysiology of diabetic nephropathy. Studies in experimental animal models of diabetes strongly implicate oxidant species as a major determinant in the pathophysiology of diabetic kidney disease. The translation, in the clinical setting, of these concepts have been quite disappointing, and new theories have challenged the concepts that oxidative stress per se plays a role in the pathophysiology of diabetic kidney disease. The concept of mitochondrial hormesis has been introduced to explain this apparent disconnect. Hormesis is intended as any cellular process that exhibits a biphasic response to exposure to increasing amounts of a substance or condition: specifically, in diabetic kidney disease, oxidant species may represent, at determined concentration, an essential and potentially protective factor. It could be postulated that excessive production or inhibition of oxidant species formation might result in an adverse phenotype. This review discusses the evidence underlying these two apparent contradicting concepts, with the aim to propose and speculate on potential mechanisms underlying the role of oxidant species in the pathophysiology of diabetic nephropathy and possibly open future more efficient therapies to be tested in the clinical settings.

Maternal serum uric acid levels and blood pressure during pregnancy: A community-based cohort study

OBJECTIVE

Studies find both very low and high serum uric acid (UA) levels are related to oxidative stress and to conditions such as cardiovascular diseases and chronic kidney disease in the general population. Pregnancy studies have focused only on high maternal UA. In present study, we tested whether unusually high and low levels of maternal serum UA are associated with increases in blood pressure (BP) during pregnancy.

STUDY DESIGN

The Pregnancy Outcomes and Community Health Study enrolled 3019 pregnant women between their 16th-27th week of pregnancy from 52 clinics in 5 Michigan communities (1998-2004). UA levels were measured in maternal blood collected at enrollment from a sub-cohort of 1223 participants. BP was abstracted from prenatal medical records; these analyses used highest recorded diastolic BP (DBP) and its companion systolic BP (SBP). Mean arterial pressure (MAP) was calculated using the formula of (2 × DBP + SBP)/3. Covariates, including maternal race/ethnicity, age at enrollment, education level, medical insurance status, body mass index before pregnancy, parity, smoking during pregnancy, alcohol use during pregnancy, and gestational week at blood collection, were considered as potential confounding variables. Associations between UA levels and BP were evaluated with linear spline or multiple linear regression models. Models' robustness was examined with bootstrap estimation of variance, sensitivity analysis, and 10-fold cross-validation.

RESULTS

Both DBP and MAP had a J-shaped relationship with maternal UA; the breakpoints (nadirs) were 0.153 and 0.161 mmol/L UA, respectively. For DBP versus UA, adjusted regression coefficient (β) = -95.67 (standard error (SE) = 37.67 and p = 0.01) for the left and adjusted β = 48.95 (SE = 9.56 and p < 0.01) for the right; for MAP versus UA, adjusted β = -58.48 (SE = 31.42 and p = 0.06) for the left and adjusted β = 52.23 (SE = 11.39 and p < 0.01) for the right. Maternal SBP followed a positive linear trend with UA levels (adjusted β = 37.75, SE = 12.93, and p < 0.01). All results were robust.

CONCLUSION

Extreme high and low maternal serum UA levels may be informative in studying maternal blood pressure during pregnancy.

Oxygen-Sensing Nox4 Generates Genotoxic ROS to Induce Premature Senescence of Nucleus Pulposus Cells through MAPK and NF-κB Pathways

Senescence is a crucial driver of intervertebral disc degeneration (IDD). Disc cells are exposed to high oxygen tension due to neovascularization in degenerative discs. However, the effect of oxygen tension on disc cell senescence was unknown. Herein, rat nucleus pulposus (NP) cells were cultured under 20% O₂ or 1% O₂. Consequently, ROS induced by 20% O₂ caused DNA damage and then activated p53-p21-Rb and p16-Rb pathways via ERK signaling to induce NP cell senescence. It also induced catabolic and proinflammatory phenotype of NP cells via MAPK and NF-κB pathways. Furthermore, 20% O₂ was found to upregulate Nox4 in NP cells. Small interfering RNA against Nox4 reduced ROS production induced by 20% O₂ and consequently suppressed premature senescence of NP cells. On the contrary, NP cells overexpressing Nox4 produced more ROS and rapidly developed senescent signs. In consistent with the in vitro studies, the expression of Nox4, p21, and Rb was upregulated in rat degenerative discs. This study, for the first time, demonstrates that Nox4 is an oxygen-sensing enzyme and a main ROS source in NP cells. Nox4-dependent ROS are genotoxic and a potent trigger of NP cell senescence. Nox4 is a potential therapeutic target for disc cell senescence and IDD.

ROS: Crucial Intermediators in the Pathogenesis of Intervertebral Disc Degeneration

Excessive reactive oxygen species (ROS) generation in degenerative intervertebral disc (IVD) indicates the contribution of oxidative stress to IVD degeneration (IDD), giving a novel insight into the pathogenesis of IDD. ROS are crucial intermediators in the signaling network of disc cells. They regulate the matrix metabolism, proinflammatory phenotype, apoptosis, autophagy, and senescence of disc cells. Oxidative stress not only reinforces matrix degradation and inflammation, but also promotes the decrease in the number of viable and functional cells in the microenvironment of IVDs. Moreover, ROS modify matrix proteins in IVDs to cause oxidative damage of disc extracellular matrix, impairing the mechanical function of IVDs. Consequently, the progression of IDD is accelerated. Therefore, a therapeutic strategy targeting oxidative stress would provide a novel perspective for IDD treatment. Various antioxidants have been proposed as effective drugs for IDD treatment. Antioxidant supplementation suppresses ROS production in disc cells to promote the matrix synthesis of disc cells and to prevent disc cells from death and senescence in vitro. However, there is not enough in vivo evidence to support the efficiency of antioxidant supplementation to retard the process of IDD. Further investigations based on in vivo and clinical studies will be required to develop effective antioxidative therapies for IDD.

Xanthine Oxidase Induces Foam Cell Formation through LOX-1 and NLRP3 Activation

PURPOSE

Xanthine oxidase catalyzes the oxidation of xanthine to uric acid. This process generates excessive reactive oxygen species (ROS) that play an important role in atherogenesis. Recent studies show that LRR and PYD domains-containing protein 3 (NLRP3), a component of the inflammasome, may be involved in the formation of foam cells, a hallmark of atherosclerosis. This study was designed to study the role of various scavenger receptors and NLRP3 inflammasome in xanthine oxidase and uric acid-induced foam cell formation.

METHODS AND RESULTS

Human vascular smooth muscle cells (VSMCs) and THP-1 macrophages were treated with xanthine oxidase or uric acid. Xanthine oxidase treatment (of both VSMCs and THP-1 cells) resulted in foam cell formation in concert with generation of ROS and expression of cluster of differentiation 36 (CD36) and oxidized low density lipoprotein (lectin-like) receptor 1 (LOX-1), but not of scavenger receptor A (SRA). Uric acid treatment resulted in foam cell formation, ROS generation and expression of CD36, but not of LOX-1 or SRA. Further, treatment of cells with xanthine oxidase, but not uric acid, activated NLRP3 and its downstream pro-inflammatory signals- caspase-1, interleukin (IL)-1β and IL-18. Blockade of LOX-1 or NLRP3 inflammasome with specific siRNAs reduced xanthine oxidase-induced foam cell formation, ROS generation and activation of NLRP3 and downstream signals.

CONCLUSIONS

Xanthine oxidase induces foam cell formation in large part through activation of LOX-1 - NLRP3 pathway in both VSMCs and THP-1 cells, but uric acid-induced foam cell formation is exclusively through CD36 pathway. Further, LOX-1 activation is upstream of NLRP3 activation. Graphical Abstract Steps in the formation of foam cells in response to xanthine oxidase and uric acid. Xanthine oxidase stimulates LOX-1 expression on the cell membrane of macrophages and vascular smooth muscle cells (VSMCs) and increases generation of ROS, which activate NLRP3 inflammasome and downstream pro-inflammatory mediators such as Caspase-1, IL-1β and IL-18. Xanthine oxidase also induces CD36 expression. Activation of both LOX-1 and CD36 (LOX-1> > CD36) participates in the transformation of macrophages and VSMCs into foam cells. Uric acid formed from xanthine-xanthine oxidase interaction stimulates CD36 expression and triggers foam cell formation independent of NLRP3 activation.

ROS: Crucial Intermediators in the Pathogenesis of Intervertebral Disc Degeneration

Excessive reactive oxygen species (ROS) generation in degenerative intervertebral disc (IVD) indicates the contribution of oxidative stress to IVD degeneration (IDD), giving a novel insight into the pathogenesis of IDD. ROS are crucial intermediators in the signaling network of disc cells. They regulate the matrix metabolism, proinflammatory phenotype, apoptosis, autophagy, and senescence of disc cells. Oxidative stress not only reinforces matrix degradation and inflammation, but also promotes the decrease in the number of viable and functional cells in the microenvironment of IVDs. Moreover, ROS modify matrix proteins in IVDs to cause oxidative damage of disc extracellular matrix, impairing the mechanical function of IVDs. Consequently, the progression of IDD is accelerated. Therefore, a therapeutic strategy targeting oxidative stress would provide a novel perspective for IDD treatment. Various antioxidants have been proposed as effective drugs for IDD treatment. Antioxidant supplementation suppresses ROS production in disc cells to promote the matrix synthesis of disc cells and to prevent disc cells from death and senescence in vitro. However, there is not enough in vivo evidence to support the efficiency of antioxidant supplementation to retard the process of IDD. Further investigations based on in vivo and clinical studies will be required to develop effective antioxidative therapies for IDD.

Serum uric acid and impaired cognitive function in community-dwelling elderly in Beijing

The relationship between serum uric acid (sUA) and cognitive function is contradictory. This study assessed the association between sUA and cognitive impairment in 10,039 community-dwelling subjects aged ≥55years living in Beijing, China. Participants underwent determination of sUA and an evaluation of cognitive function using the scholarship-adjusted Mini-Mental State Examination (MMSE): MMSE ≤17 for illiterates; MMSE≤20 for primary school graduates (≥6years of education); and MMSE≤24 for junior school graduates or above (≥9years of education). Among the 10016 persons with valid MMSE scores, the prevalence of cognitive impairment was 9.14%. A multivariate logistic regression model including demographic, clinical and genetic parameters was performed to assess the relationship between sUA and cognitive impairment. Persons with cognitive impairment had lower sUA levels than those with normal cognitive function: (302.30±82.80 vs. 312.20±84.01μmol/L, p=0.001). After adjusting for age, sex, lifestyle, relevant diseases and the apolipoprotein E (APOE) ε4 allele, stepwise logistic regression showed that participants with higher levels of sUA had a lower risk of cognitive impairment (hazard ratio (HR): 0.78; 95% confidence interval (CI): 0.62-0.96; p=0.022). In this baseline cross-sectional population-based sample, high levels of sUA were associated with a decreased risk of cognitive impairment.

Systemic Redox Imbalance in Chronic Kidney Disease: A Systematic Review

Patients with chronic kidney disease (CKD) experience imbalance between oxygen reactive species (ROS) production and antioxidant defenses leading to cell and tissue damage. However, it remains unclear at which stage of renal insufficiency the redox imbalance becomes more profound. The aim of this systematic review was to provide an update on recent advances in our understanding of how the redox status changes in the progression of renal disease from predialysis stages 1 to 4 to end stage 5 and whether the various treatments and dialysis modalities influence the redox balance. A systematic review was conducted searching PubMed and Scopus by using the Cochrane and PRISMA guidelines. In total, thirty-nine studies met the inclusion criteria and were reviewed. Even from an early stage, imbalance in redox status is evident and as the kidney function worsens it becomes more profound. Hemodialysis therapy per se seems to negatively influence the redox status by the elevation of lipid peroxidation markers, protein carbonylation, and impairing erythrocyte antioxidant defense. However, other dialysis modalities do not so far appear to confer advantages. Supplementation with antioxidants might assist and should be considered as an early intervention to halt premature atherogenesis development at an early stage of CKD.

Is Xanthine oxidase activity in polycystic ovary syndrome associated with inflammatory and cardiovascular risk factors?

The aim of this study is to examine women with polycystic ovary syndrome (PCOS) to determine the relationship between xanthine oxidase (XO) and oxidative stress, inflammatory status, and various clinical and biochemical parameters. In this cross-sectional study a total of 83 women including 45 PCOS patients and 38 healthy women were enrolled. We collected blood samples for XO and superoxide dismutase (SOD) activity, hormone levels, cholesterol values, and inflammatory markers. Body mass index (BMI) , waist-to-hip ratio (WHR), and blood pressure were assessed. Blood samples were taken for hormonal levels, cholesterol levels, fasting plasma glucose (FPG), fasting plasma insulin (FPI), homeostatic model assessment-insulin resistance (HOMA-IR) index, quantitative insulin sensitivity check index (QUICKI), C-reactive protein (CRP), white blood cell and neutrophil counts, XO and SOD activities. The basal hormone levels, triglyceride (TG) levels, TG/HDL-C (high density lipoprotein-cholesterol) ratios FPG, FPI and HOMA-IR levels were higher in PCOS patients compared to controls (p<0.05). Platelet and plateletcrit (PCT) values, CRP, and XO activity were significantly increased, however SOD activity was decreased in PCOS patients (p<0.001). XO activity was positively correlated with LH/FSH and TG/HDL ratios, CRP, PCT, FPG, FPI, and HOMA-IR, and negatively correlated with QUICKI levels. In conclusion, XO is a useful marker to assess oxidative stress in PCOS patients. Positive correlations between XO and inflammatory markers and cardiovascular disease risk factors suggest that XO plays an important role in the pathogenesis of PCOS and its metabolic complications.

Elevated Serum Uric Acid Is Associated with Greater Bone Mineral Density and Skeletal Muscle Mass in Middle-Aged and Older Adults

Background and objective

Previous studies have suggested a positive link between serum uric acid (UA) and bone mineral density (BMD). In this study, we re-examined the association between UA and BMD and further explored whether this was mediated by skeletal muscle mass in a general Chinese population.

Method

This community-based cross-sectional study was conducted among 3079 (963 men and 2116 women) Chinese adults aged 40–75 years. Face-to-face interviews and laboratory analyses were performed to determine serum UA and various covariates. Dual-energy X-ray absorptiometry was used to assess the BMD and appendicular skeletal muscle mass. The skeletal muscle mass index (SMI = ASM/Height², kg/m²) for the total limbs, arms, and legs was then calculated.

Results

The serum UA was graded and, in general, was significantly and positively associated with the BMD and muscle mass, after adjustment for multiple covariates in the total sample. Compared with participants in lowest quartile of UA, those participants in highest quartile showed a 2.3%(whole body), 4.1%(lumbar spine), 2.4%(total hip), and 2.0% (femoral neck) greater BMDs. The mean SMIs in the highest (vs. lowest) quartile increased by 2.7% (total), 2.5% (arm), 2.7% (leg) respectively. In addition, path analysis suggested that the favorable association between UA and BMD might be mediated by increasing SMI.

Conclusion

The elevated serum UA was associated with a higher BMD and a greater muscle mass in a middle-aged and elderly Chinese population and the UA-BMD association was partly mediated by muscle mass.

GWAS and transcriptional analysis prioritize ITPR1 and CNTN4 for a serum uric acid 3p26 QTL in Mexican Americans

Background

The variation in serum uric acid concentrations is under significant genetic influence. Elevated SUA concentrations have been linked to increased risk for gout, kidney stones, chronic kidney disease, and cardiovascular disease whereas reduced serum uric acid concentrations have been linked to multiple sclerosis, Parkinson’s disease and Alzheimer’s disease. Previously, we identified a novel locus on chromosome 3p26 affecting serum uric acid concentrations in Mexican Americans from San Antonio Family Heart Study. As a follow up, we examined genome-wide single nucleotide polymorphism data in an extended cohort of 1281 Mexican Americans from multigenerational families of the San Antonio Family Heart Study and the San Antonio Family Diabetes/Gallbladder Study. We used a linear regression-based joint linkage/association test under an additive model of allelic effect, while accounting for non-independence among family members via a kinship variance component.

Results

Univariate genetic analysis indicated serum uric acid concentrations to be significant heritable (h² = 0.50 ± 0.05, p < 4 × 10⁻³⁵), and linkage analysis of serum uric acid concentrations confirmed our previous finding of a novel locus on 3p26 (LOD = 4.9, p < 1 × 10⁻⁵) in the extended sample. Additionally, we observed strong association of serum uric acid concentrations with variants in following candidate genes in the 3p26 region; inositol 1,4,5-trisphosphate receptor, type 1 (ITPR1), contactin 4 (CNTN4), decapping mRNA 1A (DCP1A); transglutaminase 4 (TGM4) and rho guanine nucleotide exchange factor (GEF) 26 (ARHGEF26) [p < 3 × 10⁻⁷; minor allele frequencies ranged between 0.003 and 0.42] and evidence of cis-regulation for ITPR1 transcripts.

Conclusion

Our results confirm the importance of the chromosome 3p26 locus and genetic variants in this region in the regulation of serum uric acid concentrations.