Dispelling dogma and misconceptions regarding the most pharmacologically targetable source of reactive species in inflammatory disease, xanthine oxidoreductase

Evaluation of the relationship between xanthine oxidase activity and metabolic syndrome in a population group in Bangladesh

Xanthine oxidase (XO) is an enzyme that converts hypoxanthine into xanthine and xanthine into uric acid, which is then eliminated by the kidneys. Serum XO has been linked to diabetes, hypertension, liver dysfunction, and cardiovascular diseases. However, limited information exists on the relationship between serum XO activity and MetS. This study aimed to analyze the relationship between XO activity and metabolic syndrome (MetS) and its components in an adult population group in Bangladesh A total of 601 participants aged ≥18 years were included in the study. MetS was defined based on the criteria set by the National Cholesterol Education Program-Adult Treatment Panel III (NCEP-ATP III). Serum XO activity was measured using the enzyme-linked immunosorbent assay (ELISA), while other biochemical parameters were measured using colorimetric methods. The relationship between serum XO and MetS levels was determined through multivariate logistic regression analysis. Serum XO activity was found to be significantly higher in females (6.17 ± 3.77 U/L) as compared to males (4.00 ± 2.77 U/L) (p < 0.001). Furthermore, participants with MetS had significantly higher mean levels of serum XO (5.34 ± 3.39 U/L) than those without MetS (3.86 ± 2.90 U/L) (p < 0.001). The prevalence of MetS and its components, such as blood pressure and blood glucose increased across the XO quartiles (p < 0.001). Regression analysis indicated that XO activity was significantly and independently associated with the prevalence of MetS (at least p < 0.05 for all cases) and its components, including elevated blood pressure, high blood glucose, and low HDL-C (at least p < 0.05 for all cases). In conclusion, individuals with MetS had significantly higher XO levels than those without MetS. Serum XO activity showed an independent association with MetS and some of its components. Therefore, XO might serve as a useful marker of MetS. Prospective studies are needed to determine the underlying mechanisms linking XO and MetS.

Evaluation of metabolomics-based urinary biomarker models for recognizing major depression disorder and bipolar disorder

BACKGROUND

Major depressive disorder (MDD) and bipolar disorder (BD) are psychiatric disorders with overlapping symptoms, leading to high rates of misdiagnosis due to the lack of biomarkers for differentiation. This study aimed to identify metabolic biomarkers in urine samples for diagnosing MDD and BD, as well as to establish unbiased differential diagnostic models.

METHODS

We utilized a metabolomics approach employing ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) to analyze the metabolic profiles of urine samples from individuals with MDD (n = 50), BD (n = 12), and healthy controls (n = 50). The identification of urine metabolites was verified using MS data analysis tools and online metabolite databases.

RESULTS

Two diagnostic panels consisting of a combination of metabolites and clinical indicators were identified-one for MDD and another for BD. The discriminative capacity of these panels was assessed using the area under the receiver operating characteristic (ROC) curve, yielding an area under the curve (AUC) of 0.9084 for MDD and an AUC value of 0.9017 for BD.

CONCLUSIONS

High-resolution mass spectrometry-based assays show promise in identifying urinary biomarkers for depressive disorders. The combination of urine metabolites and clinical indicators is effective in differentiating healthy controls from individuals with MDD and BD. The metabolic pathway indicating oxidative stress is seen to significantly contribute to depressive disorders.

SNHG12/NFYC-AS1 Acted as the Sponge for hsa-miR-199a-5p to Promote the Expression of S100A8/S100A7/XDH and was Involved in the Progression of Diabetic Foot Ulcers

Traditional Chinese medicine has been used to treat diabetic foot ulcer (DFU) for a long time. However, the underlying mechanism of Radix arnebiae seu lithospermi ointment (RAS-ointment) has not been revealed. Effects of RAS-ointment treatment were observed in DFU patients. The endogenous competitive RNA mechanism was constructed based on micro-array sequencing and bioinformatics analysis. RT-PCR was used to detected the expression of genes in DFU ulcerated skins and non-ulcerated skins. Dual luciferase and RT-PCR experiments were used to investigate the endogenous competitive RNA mechanism. Based on micro-array sequencing and bioinformatics analysis, we found that SNHG12/NFYC-AS1, hsa-miR-199a-5p and S100A8/S100A7/XDH might form an endogenous competitive RNA mechanism. RT-PCR assay shown that SNHG12, NFYC-AS1, S100A8, S100A7 and XDH were significantly up-regulated, while hsa-miR-199a-5p was significantly down-regulated in DFU ulcerated skins (N = 10) compared with non-ulcerated skins (N = 10). Dual luciferase and RT-PCR experiments showed that SNHG12 or NFYC-AS1 up-regulated the expression of S100A8, S100A7 and XDH by inhibiting hsa-miR-199a-5p in a direct binding way. After 35 days of RAS-ointment treatment, the wound healing of DFU patients was substantially improved and the expression of S100A7 and XDH were reduced expression in DFU patients. In addition, the monomer composition of RAS-ointment, 49070_FLUKA or auraptenol inhibited the expression of S100A7 and XDH in Te317.sk cells. In conclusion, RAS-ointment may be used as an adjunctive therapy for DFU patients.

Hemin and iron increase synthesis and trigger export of xanthine oxidoreductase from hepatocytes to the circulation

We recently reported a previously unknown salutary role for xanthine oxidoreductase (XOR) in intravascular heme overload whereby hepatocellular export of XOR to the circulation was identified as a seminal step in affording protection. However, the cellular signaling and export mechanisms underpinning this process were not identified. Here, we present novel data showing hepatocytes upregulate XOR expression/protein abundance and actively release it to the extracellular compartment following exposure to hemopexin-bound hemin, hemin or free iron. For example, murine (AML-12 cells) hepatocytes treated with hemin (10 μM) exported XOR to the medium in the absence of cell death or loss of membrane integrity (2.0 ± 1.0 vs 16 ± 9 μU/mL p < 0.0001). The path of exocytosis was found to be noncanonical as pretreatment of the hepatocytes with Vaculin-1, a lysosomal trafficking inhibitor, and not Brefeldin A inhibited XOR release and promoted intracellular XOR accumulation (84 ± 17 vs 24 ± 8 hemin vs 5 ± 3 control μU/mg). Interestingly, free iron (Fe2+ and Fe3+) induced similar upregulation and release of XOR compared to hemin. Conversely, concomitant treatment with hemin and the classic transition metal chelator DTPA (20 μM) or uric acid completely blocked XOR release (p < 0.01). Our previously published time course showed XOR release from hepatocytes likely required transcriptional upregulation. As such, we determined that both Sp1 and NF-kB were acutely activated by hemin treatment (∼2-fold > controls for both, p < 0.05) and that silencing either or TLR4 with siRNA prevented hemin-induced XOR upregulation (p < 0.01). Finally, to confirm direct action of these transcription factors on the Xdh gene, chromatin immunoprecipitation was performed indicating that hemin significantly enriched (∼5-fold) both Sp1 and NF-kB near the transcription start site. In summary, our study identified a previously unknown pathway by which XOR is upregulated via SP1/NF-kB and subsequently exported to the extracellular environment. This is, to our knowledge, the very first study to demonstrate mechanistically that XOR can be specifically targeted for export as the seminal step in a compensatory response to heme/Fe overload.

Evaluation of Plasma Xanthine Oxidoreductase (XOR) Activity in Patients with Cardiopulmonary Arrest

Plasma xanthine oxidoreductase (XOR) activity in patients with cardiopulmonary arrest (CPA) has not yet been studied.A total of 1,158 patients who required intensive care and 231 control patients who attended a cardiovascular outpatient clinic were prospectively analyzed. Blood samples were collected within 15 minutes of admission from patients in intensive care patients, which were divided into a CPA group (n = 1,053) and a no-CPA group (n = 105). Plasma XOR activity was compared between the 3 groups and factors independently associated with extremely elevated XOR activity were identified using a multivariate logistic regression model. Plasma XOR activity in the CPA group (median, 1,030.0 pmol/hour/mL; range, 233.0-4,240.0 pmol/hour/mL) was significantly higher than in the no-CPA group (median, 60.2 pmol/hour/mL; range, 22.5-205.0 pmol/hour/mL) and control group (median, 45.2 pmol/hour/mL; range, 19.3-98.8 pmol/hour/mL). The regression model showed that out-of-hospital cardiac arrest (OHCA) (yes, odds ratio [OR]: 2.548; 95% confidence interval [CI]: 1.098-5.914; P = 0.029) and lactate levels (per 1.0 mmol/L increase, OR: 1.127; 95% CI: 1.031-1.232; P = 0.009) were independently associated with high plasma XOR activity (≥ 1,000 pmol/hour/mL). Kaplan-Meier curve analysis indicated that the prognosis, including all-cause death within 30 days, was significantly poorer in high-XOR patients (XOR ≥ 6,670 pmol/hour/mL) than in the other patients.Plasma XOR activity was extremely high in patients with CPA, especially in OHCA. This would be associated with a high lactate value and expected to eventually lead to adverse outcome in patients with CPA.

Disordered Glucose Levels Are Associated with Xanthine Oxidase Activity in Overweight Type 2 Diabetic Women

Oxidative stress plays an important role in vascular complications observed in patients with obesity and Type 2 Diabetes (T2D). Xanthine oxidase (XO) breaks down purine nucleotides into uric acid and contributes to the production of reactive oxygen species (ROS). However, the relationship between XO activity and glucose homeostasis in T2D subjects with obesity is unclear. We hypothesized that disordered glucose levels are associated with serum XO activity in overweight women and men with T2D and without hyperuricemia. We studied serum XO activity in women and men with and without T2D. Our results show that serum XO activity was greater in T2D patients with body mass index (BMI) ≥ 25 kg/m2 than in those with BMI < 25 kg/m2 (p < 0.0001). Sex-based comparative analyses of overweight T2D patients showed that serum XO activity correlated with homeostasis model assessment of β-cell function (HOMA-β), fasting plasma glucose (FPG), and hemoglobin A1C in overweight T2D women but not in overweight T2D men. In addition, as compared to overweight T2D men, women had higher high-sensitivity C-reactive protein (hs-CRP) levels. However, overweight T2D men had higher XO activity and uric acid levels than women. Our results suggest that XO activity is higher in overweight T2D patients, especially in men, but is more sensitive to disordered glucose levels in overweight women with T2D.

The Role of Oxidative Stress in Hyperuricemia and Xanthine Oxidoreductase (XOR) Inhibitors

Uric acid is the end product of purine metabolism in humans. Hyperuricemia is a metabolic disease caused by the increased formation or reduced excretion of serum uric acid (SUA). Alterations in SUA homeostasis have been linked to a number of diseases, and hyperuricemia is the major etiologic factor of gout and has been correlated with metabolic syndrome, cardiovascular disease, diabetes, hypertension, and renal disease. Oxidative stress is usually defined as an imbalance between free radicals and antioxidants in our body and is considered to be one of the main causes of cell damage and the development of disease. Studies have demonstrated that hyperuricemia is closely related to the generation of reactive oxygen species (ROS). In the human body, xanthine oxidoreductase (XOR) catalyzes the oxidative hydroxylation of hypoxanthine to xanthine to uric acid, with the accompanying production of ROS. Therefore, XOR is considered a drug target for the treatment of hyperuricemia and gout. In this review, we discuss the mechanisms of uric acid transport and the development of hyperuricemia, emphasizing the role of oxidative stress in the occurrence and development of hyperuricemia. We also summarize recent advances and new discoveries in XOR inhibitors.

Characteristics of Patients with an Abnormally Decreased Plasma Xanthine Oxidoreductase Activity in Acute Heart Failure Who Visited the Emergency Department

Background: The factors associated with a low plasma xanthine oxidoreductase (XOR) activity were not elucidated in patients with acute heart failure (AHF). Methods: Two-hundred and twenty-nine AHF patients who visited the emergency department were prospectively analyzed. AHF patients were divided into 3 groups according to the plasma XOR quartiles (Q1 = low-XOR group [n = 57], Q2/Q3 = middle-XOR group [n = 115], and Q4 = high-XOR group [n = 57]). The prognostic nutritional index (PNI) and the controlling nutritional status (CONUT) score were evaluated. Results: The multivariate logistic regression model showed that the nutritional status (PNI: OR 1.044, 95% CI 1.000–1.088; CONUT: OR 3.805, 95% CI 1.158–12.498), age, and serum creatinine level were independently associated with a low plasma XOR activity. The Kaplan-Meier curve showed a significantly lower incidence of heart failure events in the low-XOR group than in the middle + high-XOR group (hazard ratio, HR 1.648, 95% CI 1.061–2.559). In particular, a low XOR activity with an increased serum creatinine level (>1.21 mg/dL) was independently associated with heart failure events (HR 1.937, 95% CI 1.199–3.130). Conclusion: A low plasma XOR activity was associated with malnutrition, renal dysfunction, and aging in AHF. A low XOR activity complicated with renal dysfunction leads to adverse long-term outcomes.

Plasma xanthine oxidoreductase (XOR) activity in patients who require cardiovascular intensive care

Hyperuricemia is known to be associated with adverse outcomes in cardiovascular intensive care patients, but its mechanisms are unknown. A total of 569 emergency department patients were prospectively analyzed and assigned to intensive care (ICU group, n = 431) or other departments (n = 138). Uric acid (UA) levels were significantly higher in the intensive care patients (6.3 [5.1-7.6] mg/dl vs. 5.8 [4.6-6.8] mg/dL). The plasma xanthine oxidoreductase (XOR) activity in the ICU group (68.3 [21.2-359.5] pmol/h/mL) was also significantly higher than that in other departments (37.2 [15.1-93.6] pmol/h/mL). Intensive care patients were divided into three groups according to plasma XOR quartiles (Q1, low-XOR, Q2/Q3, normal-XOR, and Q4, high-XOR group). A multivariate logistic regression model showed that lactate (per 1.0 mmol/L increase, OR 1.326; 95%, CI 1.166-1.508, p < 0.001) and the Acute Physiology and Chronic Health Evaluation II score (per 1.0 point increase, OR 1.095, 95% CI 1.034-1.160, p = 0.002) were independently associated with the high-XOR group. In-hospital mortality was significantly higher in the high-XOR group (n = 28, 26.2%) than in the normal- (n = 11, 5.1%) and low- (n = 9, 8.3%) XOR groups. The high-XOR group (vs. normal-XOR group) was independently associated with the in-hospital mortality (OR 2.934; 95% CI 1.170-7.358; p = 0.022). Serum UA levels and plasma XOR activity were high in patients admitted to intensive care. The enhanced XOR activity may be one of the mechanisms under which hyperuricemia was associated with adverse outcomes in patients requiring cardiovascular intensive care.

Sickle cell disease subjects and mouse models have elevated nitrite and cGMP levels in blood compartments

The hypothesis of decreased nitric oxide (NO) bioavailability in sickle cell disease (SCD) proposes that multiple factors leading to decreased NO production and increased consumption contributes to vaso-occlusion, pulmonary hypertension, and pain. The anion nitrite is central to NO physiology as it is an end product of NO metabolism and serves as a reservoir for NO formation. However, there is little data on nitrite levels in SCD patients and its relationship to pain phenotype. We measured nitrite in SCD subjects and examined its relationship to SCD pain. In SCD subjects, median whole blood, red blood cell and plasma nitrite levels were higher than in controls, and were not associated with pain burden. Similarly, Townes and BERK homozygous SCD mice had elevated blood nitrite. Additionally, in red blood cells and plasma from SCD subjects and in blood and kidney from Townes homozygous mice, levels of cyclic guanosine monophosphate (cGMP) were higher compared to controls. In vitro, hemoglobin concentration, rather than sickle hemoglobin, was responsible for nitrite metabolism rate. In vivo, inhibition of NO synthases and xanthine oxidoreductase decreased nitrite levels in homozygotes but not in control mice. Long-term nitrite treatment in SCD mice further elevated blood nitrite and cGMP, worsened anemia, decreased platelets, and did not change pain response. These data suggest that SCD in humans and animals is associated with increased nitrite/NO availability, which is unrelated to pain phenotype. These findings might explain why multiple clinical trials aimed at increasing NO availability in SCD patients failed to improve pain outcomes.

Potential Dangers of Serum Urate-Lowering Therapy

In observational studies, high serum urate levels are associated with adverse outcomes, including mortality. However, the hypothesis that urate-lowering may improve nongout outcomes has not been confirmed by placebo-controlled clinical trials. On the contrary, 7 recent placebo-controlled trials of urate-lowering drugs with different mechanisms of action (uricosuric: lesinurad; xanthine oxidase inhibition: febuxostat; uricase: pegloticase) have observed higher mortality or trends to higher mortality in gout patients, with the largest decreases in serum urate. Because all urate-lowering mechanisms were implicated, this raises safety concerns about urate-lowering itself. Far from unexpected, the higher mortality associated with more intense urate-lowering is in line with the U-shaped association of urate with mortality in some observational studies. Urate accounts for most of the antioxidant capacity of plasma, and strategies to increase urate are undergoing clinical trials in neurological disease. Post hoc analysis of recent trials should explore whether the magnitude of urate-lowering is associated with adverse outcomes, and safety trials are needed before guidelines recommend lowering serum urate below certain thresholds.

Mechanisms impairing blood pressure responses to nitrite and nitrate

Hypertension is a multifactorial disease associated with impaired nitric oxide (NO) production and bioavailability. In this respect, restoring NO activity by using nitrite and nitrate has been considered a potential therapeutic strategy to treat hypertension. This possibility is justified by the understanding that both nitrite and nitrate may be recycled back to NO and also promote the generation of other bioactive species. This process involves a complex biological circuit known as the enterosalivary cycle of nitrate, where this anion is actively taken up by the salivary glands and converted to nitrite by nitrate-reducing bacteria in the oral cavity. Nitrite is then ingested and reduced to NO and other nitroso species under the acid conditions of the stomach, whereas reminiscent nitrite that escapes gastric reduction is absorbed systemically and can be converted into NO by nitrite-reductases in tissues. While there is no doubt that nitrite and nitrate exert antihypertensive effects, several agents can impair the blood pressure responses to these anions by disrupting the enterosalivary cycle of nitrate. These agents include dietary and smoking-derived thiocyanate, antiseptic mouthwash, proton pump inhibitors, ascorbate at high concentrations, and xanthine oxidoreductase inhibitors. In this article, we provide an overview of the physiological aspects of nitrite and nitrate bioactivation and the therapeutic potential of these anions in hypertension. We also discuss mechanisms by which agents counteracting the antihypertensive responses to nitrite and nitrate mediate their effects. These critical aspects should be taken into consideration when suggesting nitrate or nitrite-based therapies to patients.

Plasma xanthine oxidoreductase activity in patients with decompensated acute heart failure requiring intensive care

Aims

Plasma xanthine oxidoreductase (XOR) activity during the acute phase of acute heart failure (AHF) requires further elucidation.

Methods and results

One hundred eighteen AHF patients and 231 control patients who attended a cardiovascular outpatient clinic were prospectively analysed. Blood samples were collected within 15 min of admission from AHF patients (AHF group) and control patients who visited a daily cardiovascular outpatient clinic (control group). Plasma XOR activity was compared between the two groups, and factors independently associated with extremely elevated XOR activity were identified using a multivariate logistic regression model. Plasma XOR activity in the AHF group (median, 104.0 pmol/h/mL; range, 25.9–423.5 pmol/h/mL) was significantly higher than that in the control group (median, 45.2 pmol/h/mL; range, 19.3–98.8 pmol/h/mL). The multivariate logistic regression model showed that serum uric acid (per 1.0 mg/dL increase, odds ratio: 1.280; 95% confidence interval: 1.066–1.536; P = 0.008) and lactate levels (per 1.0 mmol/L increase, odds ratio: 1.239; 95% confidence interval: 1.040–1.475; P = 0.016) were independently associated with high plasma XOR activity (>300 pg/h/mL) during the acute phase of AHF.

Conclusions

Plasma XOR activity was extremely high in patients with severely decompensated AHF. This would be associated with a high lactate value and would eventually lead to hyperuricaemia in patients with AHF.

Activity of xanthine oxidase in plasma correlates with indices of insulin resistance and liver dysfunction in patients with type 2 diabetes mellitus and metabolic syndrome: A pilot exploratory study

Aims/Introduction

There is controversy as to whether hyperuricemia is an independent risk factor for cardiometabolic diseases. The serum level of uric acid is affected by a wide variety of factors involved in its production and excretion. In contrast, evidence has accumulated that locally‐ and systemically‐activated xanthine oxidase (XO), a rate‐limiting enzyme for production of uric acid, is linked to metabolic derangement in humans and rodents. We therefore explored the clinical implication of plasma XO activity in patients with type 2 diabetes mellitus and metabolic syndrome (MetS).

Materials and Methods

We enrolled 60 patients with type 2 diabetes mellitus and MetS. MetS was defined according to the 2005 International Diabetes Federation guidelines. Plasma XO activity was measured by highly‐sensitive fluorometric assay measuring the conversion of pterin to isoxanthopterin, and explored associations between the value of plasma XO activity and metabolic parameters.

Results

The value of plasma XO activity was correlated with indices of insulin resistance and the level of circulating liver transaminases. In contrast, the level of serum uric acid was not correlated with indices of insulin resistance. The value of plasma XO activity was not correlated with the serum uric acid level.

Conclusions

Plasma XO activity correlates with indices of insulin resistance and liver dysfunction in Japanese patients with type 2 diabetes mellitus and MetS. Through assessing the plasma XO activity, patients showing normal levels of serum uric acid with higher activity of XO can be screened, thereby possibly providing a clue to uncovering metabolic risks in type 2 diabetes mellitus and MetS patients.

Alcohol abuse is associated with enhanced pulmonary and systemic xanthine oxidoreductase activity

Acute respiratory distress syndrome (ARDS) is a common and devastating disorder. Alcohol use disorders (AUDs) increase ARDS risk and worsen outcomes through mechanisms that may include enhancement of pulmonary oxidative stress. Alcohol consumption increases activity of the enzyme xanthine oxidoreductase (XOR) that contributes to production of both reactive oxygen species (ROS) and uric acid, a damage-associated molecular pattern. These by-products have the potential to modulate proinflammatory pathways, such as those involving cyclooxygenase (COX)-2, and to activate the nucleotide-binding domain, leucine-rich-containing family, pyrin-domain containing-3 (NLRP3) inflammasome. We sought to determine if pulmonary and systemic XOR activity was altered by AUDs. Bronchoscopy with bronchoalveolar lavage (BAL) and blood sampling was performed in otherwise healthy human subjects with AUDs and controls. Uric acid in epithelial-lining fluid, derived from BAL, was substantially higher among individuals with AUDs and did not normalize after 7 days of abstinence; serum uric acid did not differ across groups. XOR enzyme activity in fresh BAL cells and serum was significantly increased in subjects with AUDs. XOR protein in BAL cells from AUD subjects was increased in parallel with COX-2 expression, and furthermore, mRNA expression of NLRP3 inflammasome components was sustained in LPS-stimulated BAL cells from AUD subjects in conjunction with increased IL-1β. Our data suggest that AUDs augment pulmonary and systemic XOR activity that may contribute to ROS and uric acid generation, promoting inflammation. Further investigations will be necessary to determine if XOR inhibition can mitigate alcohol-associated pulmonary oxidative stress, diminish inflammation, and improve ARDS outcomes.

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.