Association of plasma xanthine oxidoreductase activity with severity and clinical outcome in patients with chronic heart failure

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.

Serum uric acid to eGFR ratio correlates with adverse outcomes in elderly hospitalized for acute heart failure

BACKGROUND

Serum uric acid (SUA) is a known biomarker of severity in acute heart failure (AHF), reflecting the intricate interplay between cardiovascular and metabolic dysfunction. Since SUA can increase in response to worsening kidney function, and subjects with AHF often have cardiorenal syndrome or are on diuretic therapy, we tested whether the ratio of SUA to eGFR might provide prognostic value in elderly hospitalized for AHF.

METHODS

The BOTERO-AHF Study (BOlogna study of Therapies, Epidemiology and Radiodiagnostic Outcomes in Acute Heart Failure patients) included 293 patients admitted for AHF who were consecutively enrolled from January 2020 onwards. We compared the baseline characteristics of participants who had a composite outcome (CO) (n = 203) of death or re-hospitalization for AHF within 12 months from discharge to those without CO (n = 90), and we assessed the prognostic impact of SUA/eGFR for 12-months CO.

RESULTS

SUA/eGFR was significantly higher in participants who experienced a CO within 12 months from discharge for AHF, compared to those who did not experience any CO (17.8 (16.6) vs. 13.7 (12.1) mg/dl/ml/min*100, p = 0.008). SUA/eGFR, and not SUA alone, was associated with an increase in the rate of CO (unadjusted HR 1.011, CI 95% 1.004-1.019, p = 0.003). This association lost significance in participants under treatment with xanthine oxidase inhibitors but remained significant after adjustment for multiple confounders.

CONCLUSION

The SUA/ eGFR ratio provides prognostic value in elderly patients hospitalized for AHF. Future studies may clarify if SUA/eGFR and XOI may represent novel diagnostic and therapeutic approaches for subgroups of patients with AHF.

Nanozyme as a rising star for metabolic disease management

Nanozyme, characterized by outstanding and inherent enzyme-mimicking properties, have emerged as highly promising alternatives to natural enzymes owning to their exceptional attributes such as regulation of oxidative stress, convenient storage, adjustable catalytic activities, remarkable stability, and effortless scalability for large-scale production. Given the potent regulatory function of nanozymes on oxidative stress and coupled with the fact that reactive oxygen species (ROS) play a vital role in the occurrence and exacerbation of metabolic diseases, nanozyme offer a unique perspective for therapy through multifunctional activities, achieving essential results in the treatment of metabolic diseases by directly scavenging excess ROS or regulating pathologically related molecules. The rational design strategies, nanozyme-enabled therapeutic mechanisms at the cellular level, and the therapies of nanozyme for several typical metabolic diseases and underlying mechanisms are discussed, mainly including obesity, diabetes, cardiovascular disease, diabetic wound healing, and others. Finally, the pharmacokinetics, safety analysis, challenges, and outlooks for the application of nanozyme are also presented. This review will provide some instructive perspectives on nanozyme and promote the development of enzyme-mimicking strategies in metabolic disease therapy.

The Effects of Pharmacological Urate-Lowering Therapy on Cardiovascular Disease in Older Adults with Gout

Cardiovascular disease is an important cause of mortality in older patients. In addition to the traditional risk factors for cardiovascular disease, hyperuricemia has been increasingly associated with an elevated risk of cardiovascular disease. Uric acid itself has several unfavorable effects on the cardiovascular system, and hyperuricemia can lead to the development of gout. Gout is the most prevalent inflammatory rheumatic disease. Older patients with gout have an increased risk of cardiovascular morbidity and mortality due to an increased prevalence of traditional risk factors, as well as the inflammatory burden of gout activity. As the prevalence of traditional risk factors and the prevalence of both hyperuricemia and gout are increasing in older adults, cardiovascular risk management in these patients is very important. This risk management consists of, on the one hand, treatment of individual traditional risk factors and, on the other hand, of urate lowering, thereby decreasing inflammatory burden of gout. However, there is insufficient evidence to conclude that urate-lowering therapy reduces the risk of cardiovascular events. Moreover, from a cardiovascular point of view, there is no preference for one urate lowering drug over another in patients with gout, nor is there enough evidence to support a preference in patients with gout with increased cardiovascular risk. Personalized treatment in older patients with gout should be aimed at optimizing serum uric acid levels, as well as targeting traditional cardiovascular risk factors. Further prospective randomized trials are needed to support the hypothesis that urate lowering reduces cardiovascular risk in older patients with gout.

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

The Association Between Oxidative Stress and the Progression of Heart Failure: A Systematic Review

Chronic heart failure (CHF) is a progressive multifactorial condition where the role of oxidative stress may have implications in the pathogenesis of the disease. Despite growing interest among researchers and clinicians, the limited, unorganized, and divergent findings regarding the association between oxidative stress and the progression of heart failure (HF) have prompted us to conduct this study. Drawing upon the evolving nature of this research domain, this study is one of the first of its kind to present a systematic and comprehensive overview of the existing evidence regarding the role of oxidative stress production in the progression of HF. This study systematically reviews peer-reviewed empirical studies published in English, particularly focusing on the association between oxidative stress and the progression of HF. Parameters, such as publication year, study design, population demographics (size, age, and gender), types of HF, and characterization of markers in the existing studies, were reviewed. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) procedure, a thorough search was conducted on PubMed, Cochrane, Embase, and Sage databases, without any restrictions on the publication dates of articles, which yielded a total of 1,808 records on the association of oxidative stress production with clinical outcomes in HF patients. The analysis of the content of 17 articles offered a robust observation of this phenomenon, providing insights into the levels of oxidative stress, antioxidant markers, and the enzymes involved in the production of reactive oxygen species (ROS), and their association with the progression and severity of HF. The findings highlighted various knowledge gaps and future research priorities are recommended in the areas of interest and unexplored areas.

Hyperuricemia and Gout Reduction by SGLT2 Inhibitors in Diabetes and Heart Failure: JACC Review Topic of the Week

Gout is characterized by increased production of purines (through the pentose phosphate pathway), which is coupled with reduced renal or intestinal excretion of urate. Concurrent upregulation of nutrient surplus signaling (mammalian target of rapamycin and hypoxia-inducible factor-1a) and downregulation of nutrient deprivation signaling (sirtuin-1 and adenosine monophosphate-activated protein kinase) redirects glucose toward anabolic pathways (rather than adenosine triphosphate production), thus promoting heightened oxidative stress and cardiomyocyte and proximal tubular dysfunction, leading to cardiomyopathy and kidney disease. Hyperuricemia is a marker (rather than a driver) of these cellular stresses. By inducing a state of starvation mimicry in a state of nutrient surplus, sodium-glucose cotransporter-2 inhibitors decrease flux through the pentose phosphate pathway (thereby attenuating purine and urate synthesis) while promoting renal urate excretion. These convergent actions exert a meaningful effect to lower serum uric acid by ≈0.6 to 1.5 mg/dL and to reduce the risk of gout by 30% to 50% in large-scale clinical trials.

Serum uric acid and outcome in hospitalized elderly patients with chronic heart failure through the whole spectrum of ejection fraction phenotypes

INTRODUCTION

Elevated serum uric acid (SUA) levels have been associated with poor outcome in patients with heart failure (HF). Uric acid is associated with inflammation and microvascular dysfunction, which may differentially affect left ventricular ejection fraction (EF) phenotypes. We aimed to identify the role of SUA across EF phenotypes in hospitalized elderly patients with chronic HF.

METHODS

We analyzed 1355 elderly patients who were diagnosed with chronic HF. All patients had SUA levels measured within the first 24 h following admission. Patients with left ventricle EF were categorized as having HF with reduced EF (HFrEF, EF < 40%), HF with mid-range EF (HFmrEF, 40%≦LVEF ≦ 49%) or HF with preserved EF (HFpEF, LVEF ≥ 50%). Endpoints were cardiovascular death, HF rehospitalization, and their composite. The median follow-up period was 18 months.

RESULTS

Compared with the lowest SUA quartile, the highest SUA quartile was significantly associated with the endpoints (adjusted HR: 2.404, 95% CI: 1.178-4.906, P = 0.016; HR: 1.418, 95% CI: 1.021-1.971, P = 0.037; HR: 1.439, 95% CI: 1.049-1.972, P = 0.024, respectively). After model adjustment, a significant association of SUA with cardiovascular death and the composite endpoint persisted among HFrEF and HFmrEF patients in the highest SUA quartile (P < 0.05 for all).

CONCLUSIONS

In hospitalized elderly patients with chronic HF, SUA is an independent predictor of adverse outcomes, which can be seen in HFrEF and HFmrEF patients.

Association of plasma xanthine oxidoreductase activity with vascular endothelial function independent of serum uric acid level: MedCity21 health examination registry

Background

Xanthine oxidoreductase (XOR) inhibitor administration, known to reduce uric acid and reactive oxygen species (ROS) production, also improves vascular endothelial function (VEF). This cross-sectional study examined our hypothesis that XOR contributes to impaired VEF through ROS but not uric acid production.

Methods

In 395 subjects (196 males, 199 females) without urate-lowering agent administration who underwent a health examination, plasma XOR activity was determined using our highly sensitive assay based on [13C2,15N2] xanthine and liquid chromatography/triple quadrupole mass spectrometry. For VEF evaluation, flow-mediated dilatation (FMD) in the brachial artery was determined by ultrasound, with physical and laboratory measurements also obtained.

Results

The median values for plasma XOR activity, serum uric acid, and FMD were 26.6 pmol/h/mL, 5.4 mg/dL, and 6.2%, respectively. Simple regression analysis showed weak correlations of both log plasma XOR activity and serum uric acid level with FMD (r = -0.213, p < 0.001 and r = -0.139, p = 0.006, respectively). However, multivariable linear regression analyses revealed that log plasma XOR activity but not serum uric acid level remained associated with FMD (β = -0.116, p = 0.037 and β = 0.041, p = 0.549, respectively) after adjustments for various clinical parameters, with no remarkable inconsistencies for the association observed in subgroups divided based on sex or uric acid level. Finally, a series of mediation analyses showed that serum uric acid level did not meet the criteria for mediator of the association of plasma XOR activity with FMD (p = 0.538).

Conclusions

These findings suggest the possibility that XOR contributes to the pathophysiology of impaired VEF through ROS but not uric acid production.

Human Plasma Xanthine Oxidoreductase Activity in Cardiovascular Disease: Evidence from a Population-Based Study

Xanthine oxidoreductase (XOR) and its products contribute to the development of chronic inflammation and oxidative stress. Excessive XOR activity is believed to promote inflammatory responses and atherosclerotic plaque formation, which are major cardiovascular risk factors. The mechanisms of XOR activity in the development and progression of cardiovascular disease (CVD), coupled with the complexity of the relationship between XOR activity and the biological effects of uric acid; reactive oxygen species; and nitric oxide, which are the major products of XOR activity, have long been debated, but have not yet been clearly elucidated. Recently, a system for measuring highly sensitive XOR activity in human plasma was established, and there has been progress in the research on the mechanisms of XOR activity. In addition, there are accumulating findings about the relationship between XOR activity and CVD. In this narrative review, we summarize existing knowledge regarding plasma XOR activity and its relationship with CVD and discuss future perspectives.

Establishment and Validation of Predictive Model of Tophus in Gout Patients

(1) Background: A tophus is a clinical manifestation of advanced gout, and in some patients could lead to joint deformities, fractures, and even serious complications in unusual sites. Therefore, to explore the factors related to the occurrence of tophi and establish a prediction model is clinically significant. (2) Objective: to study the occurrence of tophi in patients with gout and to construct a predictive model to evaluate its predictive efficacy. (3) Methods: The clinical data of 702 gout patients were analyzed by using cross-sectional data of North Sichuan Medical College. The least absolute shrinkage and selection operator (LASSO) and multivariate logistic regression were used to analyze predictors. Multiple machine learning (ML) classification models are integrated to analyze and identify the optimal model, and Shapley Additive exPlanations (SHAP) interpretation was developed for personalized risk assessment. (4) Results: Compliance of urate-lowering therapy (ULT), Body Mass Index (BMI), course of disease, annual attack frequency, polyjoint involvement, history of drinking, family history of gout, estimated glomerular filtration rate (eGFR), and erythrocyte sedimentation rate (ESR) were the predictors of the occurrence of tophi. Logistic classification model was the optimal model, test set area under curve (AUC) (95% confidence interval, CI): 0.888 (0.839-0.937), accuracy: 0.763, sensitivity: 0.852, and specificity: 0.803. (5) Conclusions: We constructed a logistic regression model and explained it with the SHAP method, providing evidence for preventing tophus and guidance for individual treatment of different patients.

Prognostic impact of plasma xanthine oxidoreductase activity in patients with heart failure with atrial fibrillation

BACKGROUND

Xanthine oxidoreductase (XOR) is a rate-limiting enzyme for uric acid (UA) production and plays an important role in generating reactive oxygen species (ROS). Overproduction of ROS is reported to contribute to the pathophysiology of atrial fibrillation (AF), however, the prognostic impact of plasma XOR activity in patients with heart failure (HF) with AF is undetermined.

METHODS

We measured plasma XOR activity in 475 HF patients, including those with sinus rhythm (HF-SR, n = 211), and those with AF (HF-AF, n = 264). The type of AF included paroxysmal (n = 128) and persistent (n = 136) AF. All patients were prospectively followed up for a median period of 804 days.

RESULTS

HF-AF patients had significantly higher plasma XOR activity and serum UA levels compared with HF-SR patients. Both plasma XOR activity and serum UA levels were higher in patients with persistent AF than in those with SR and with paroxysmal AF. Multivariate linear regression analysis showed that persistent AF was independently associated with increased XOR activity. During the follow-up period, there were 79 major adverse cardiovascular events (MACEs). HF-AF patients with MACEs had higher plasma XOR activity compared with those without MACEs, while there were no significant differences in serum UA levels. Multivariate Cox proportional analysis showed that high XOR activity was an independent risk factor for MACEs after adjustment for confounding factors. Kaplan-Meier analysis revealed that the high XOR activity group had a higher risk of MACEs than the low XOR activity group. The prediction model was significantly improved by the addition of XOR activity to the basic predictors.

CONCLUSIONS

HF-AF patients had significantly higher plasma XOR activity compared with HF-SR patients. Plasma XOR activity proved to be a reliable indicator for MACEs in HF-AF patients.

Canagliflozin independently reduced plasma volume from conventional diuretics in patients with type 2 diabetes and chronic heart failure: a subanalysis of the CANDLE trial

Sodium-glucose cotransporter 2 inhibitors (SGLT2is) reduce the risk of heart failure progression and mortality rates. Moreover, osmotic diuresis induced by SGLT2 inhibition may result in an improved heart failure prognosis. Independent of conventional diuretics in patients with type 2 diabetes (T2D) and chronic heart failure, especially in patients with heart failure with preserved ejection fraction (HFpEF), it is unclear whether SGLT2i chronically reduces estimated plasma volume (ePV). As a subanalysis of the CANDLE trial, which assessed the effect of canagliflozin on N-terminal pro-brain natriuretic peptide (NT-proBNP), we examined the change (%) in ePV over 24 weeks of treatment based on the baseline level associated with diuretic usage. In the CANDLE trial, nearly all patients were clinically stable (NYHA class I-II), with approximately 70% of participants presenting a baseline phenotype of HFpEF. A total of 99 (42.5%) patients were taking diuretics (mostly furosemide) at baseline, while 134 (57.5%) were not. Relative to glimepiride, canagliflozin significantly reduced ePV without worsening renal function in patients in both groups: -4.00% vs. 1.46% (p = 0.020) for the diuretic group and -6.14% vs. 1.28% (p < 0.001) for the nondiuretic group. Furthermore, canagliflozin significantly reduced serum uric acid without causing major electrolyte abnormalities in patients in both subgroups. The long-term beneficial effect of SGLT2i on intravascular congestion could be independent of conventional diuretic therapy without worsening renal function in patients with T2D and HF (HFpEF predominantly). In addition, the beneficial effects of canagliflozin are accompanied by improved hyperuricemia without causing major electrolyte abnormalities.

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.

Uric acid in advanced heart failure: relation to central haemodynamics and outcome

Objective

The role of hyperuricaemia as a prognostic maker has been established in chronic heart failure (HF) but limited information on the association between plasma uric acid (UA) levels and central haemodynamic measurements is available.

Methods

A retrospective study on patients with advanced HF referred for right heart catherisation. Regression analyses were constructed to investigate the association between UA and haemodynamic variables. Cox models were created to investigate if UA was a significant predictor of adverse outcome where log1.1(UA) was used to estimate the effect on outcome associated with a 10% increase in UA levels.

Results

A total of 228 patients were included (77% males, age 49±12 years, mean left ventricular ejection fraction (LVEF) of 17%±8%). Median UA was 0.48 (0.39–0.61) mmol/L. UA level was associated to pulmonary capillary wedge pressure (PCWP) and cardiac index (CI) in univariable (both p<0.001) and multivariable regression analysis (p<0.004 and p=0.025 for PCWP and CI). When constructing multivariable Cox models including PCWP, CI, central venous pressure, age, estimated glomerular filtration rate (eGFR), use of loop diuretics and LVEF, log1.1(UA) independently predicted the combined endpoint (left ventricular assist device, total artificial heart implantation, heart transplantation or all-cause mortality) (hazard ratio (HR): 1.10 (1.03–1.17), p=0.004) as well as all-cause mortality (HR: 1.15 (1.06–1.25), p=0.001).

Conclusions

Elevated UA is associated with greater haemodynamic impairment in advanced HF. In adjusted Cox models (age, eGFR, LVEF and haemodynamics), UA predicts the combined endpoint and all-cause mortality in long-term follow-up.

Dapagliflozin reduces uric acid concentration, an independent predictor of adverse outcomes in DAPA-HF

AIMS

Blood uric acid (UA) levels are frequently elevated in patients with heart failure and reduced ejection fraction (HFrEF), may lead to gout and are associated with worse outcomes. Reduction in UA is desirable in HFrEF and sodium-glucose cotransporter 2 inhibitors may have this effect. We aimed to examine the association between UA and outcomes, the effect of dapagliflozin according to baseline UA level, and the effect of dapagliflozin on UA in patients with HFrEF in the DAPA-HF trial.

METHODS AND RESULTS

The association between UA and the primary composite outcome of cardiovascular death or worsening heart failure, its components, and all-cause mortality was examined using Cox regression analyses among 3119 patients using tertiles of UA, after adjustment for other prognostic variables. Change in UA from baseline over 12 months was also evaluated. Patients in tertile 3 (UA ≥6.8 mg/dl) versus tertile 1 (<5.4 mg/dl) were younger (66.3 ± 10.8 vs. 68 ± 10.2 years), more often male (83.1% vs. 71.5%), had lower estimated glomerular filtration rate (58.2 ± 17.4 vs. 70.6 ± 18.7 ml/min/1.73 m2 ), and more often treated with diuretics. Higher UA was associated with a greater risk of the primary outcome (adjusted hazard ratio tertile 3 vs. tertile 1: 1.32, 95% confidence interval [CI] 1.06-1.66; p = 0.01). The risk of heart failure hospitalization and cardiovascular death increased by 7% and 6%, respectively per 1 mg/dl unit increase of UA (p = 0.04 and p = 0.07). Spline analysis revealed a linear increase in risk above a cut-off UA value of 7.09 mg/dl. Compared with placebo, dapagliflozin reduced UA by 0.84 mg/dl (95% CI -0.93 to -0.74) over 12 months (p < 0.001). Dapagliflozin improved outcomes, irrespective of baseline UA concentration.

CONCLUSION

Uric acid remains an independent predictor of worse outcomes in a well-treated contemporary HFrEF population. Compared with placebo, dapagliflozin reduced UA and improved outcomes irrespective of UA concentration.

U-shaped association of uric acid to overall-cause mortality and its impact on clinical management of hyperuricemia

Serum uric acid (SUA) is significantly elevated in obesity, gout, type 2 diabetes mellitus, and the metabolic syndrome and appears to contribute to the renal, cardiovascular and pulmonary comorbidities that are associated with these disorders. Most previous studies have focused on the pathophysiologic effects of high levels of uric acid (hyperuricemia). More recently, research has also shifted to the impact of hypouricemia, with multiple studies showing the potentially damaging effects that can be caused by abnormally low levels of SUA. Along with these observations, recent inconclusive data from human studies evaluating the treatment of hyperuricemia with xanthine oxidoreductase (XOR) inhibitors have added to the debate about the causal role of UA in human disease processes. SUA, which is largely derived from hepatic degradation of purines, appears to exert both systemic pro-inflammatory effects that contribute to disease and protective antioxidant properties. XOR, which catalyzes the terminal two steps of purine degradation, is the major source of both reactive oxygen species (O2.-, H2O2) and UA. This review will summarize the evidence that both elevated and low SUA may be risk factors for renal, cardiovascular and pulmonary comorbidities. It will also discuss the mechanisms through which modulation of either XOR activity or SUA may contribute to vascular redox hemostasis. We will address future research studies to better account for the differential effects of high versus low SUA in the hope that this will identify new evidence-based approaches for the management of hyperuricemia.

Impact of serum uric acid levels on cardiovascular events and quality of life in patients with chronic coronary syndromes: Insights from a contemporary, prospective, nationwide registry

BACKGROUND AND AIMS

Hyperuricemia is a metabolic disorder that has been associated with adverse cardiovascular (CV) events. Using the data from a nationwide, prospective registry on patients with chronic coronary syndromes (CCS), we assessed the impact of serum uric acid (SUA) levels on quality of life (QoL) and major adverse CV events (MACE), a composite of CV death and hospitalization for myocardial infarction, heart failure (HF), angina or revascularization at 1-year.

METHODS AND RESULTS

Among the 5070 consecutive CCS patients enrolled in the registry, levels of SUA were available for 2394 (47.2%). Patients with SUA levels available at baseline were grouped as low tertile (n = 860; 4.3 [3.7-4.7] mg/dL), middle tertile (n = 739; 5.6 [5.3-5.9] mg/dL) and high tertile (n = 795; 7.1 [6.7-7.9] mg/dL). At 1 year, the incidence of MACE was 3.7%, 4.1% and 6.8% for low, middle and high tertiles, respectively (p = 0.005 for low vs high tertile). Patients in the high tertile of SUA had a significantly higher rate of CV mortality (1.4% vs 0.4%; p = 0.05) and hospital admission for HF (2.8% vs 1.6%; p = 0.03) compared to the low tertile. However, hyperuricemia did not result as an independent predictor of MACE at multivariable analysis [hazard ratio: 1.27; 95% confidence intervals: 0.81-2.00; p = 0.3].

CONCLUSIONS

In this contemporary, large cohort of CCS, those in the high tertile of SUA had a greater burden of CV disease and worse QoL. However, SUA did not significantly influence the higher rate of CV mortality, hospitalization for HF and MACE observed in these patients during 1-year follow-up.

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

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

AgCu@CuO aerogels with peroxidase-like activities and photoelectric responses for sensitive biosensing

Photoelectrochemical (PEC) enzymatic biosensors integrate the excellent selectivity of enzymes and high sensitivity of PEC bioanalysis, but the drawbacks such as high cost, poor stability, and tedious immobilization of natural enzymes on photoelectrodes severely suppress their applications. AgCu@CuO aerogel-based photoelectrode materials with both remarkable enzyme-like activities and outstanding photoelectric properties were innovatively designed and synthesized to evaluate the activity of xanthine oxidase with a wide linear detection range and a low limit of detection.

Gender Differences in the Impact of Plasma Xanthine Oxidoreductase Activity on Coronary Artery Spasm

Xanthine oxidoreductase (XOR) is the rate-limiting enzyme in uric acid (UA) production that plays a pivotal role in generating oxidative stress. Gender differences in the impact of plasma XOR activity on coronary artery spasm (CAS) remain unclear. We investigated plasma XOR activity in 132 patients suspected of having CAS (male, n = 78; female, n = 54) and who underwent an intracoronary acetylcholine provocation test. Plasma XOR activity was significantly lower in female patients compared with male patients. CAS was provoked in 36 male patients and 17 female patients, and both had significantly higher plasma XOR activity than those without. Multivariate logistic regression analysis showed that this activity was independently associated with the incidence of CAS in both sexes after adjusting for confounding factors. The optimal cut-off values for predicting CAS were lower in female patients than in male patients. Multivariate analysis demonstrated that female patients with high XOR activity exhibited a higher incidence of CAS than male patients. Plasma XOR activity was an independent predictor of the incidence of CAS in both sexes. The impact of plasma XOR activity on CAS was stronger in female patients than in male patients.

Xanthine oxidoreductase: A leading actor in cardiovascular disease drama

Cardiovascular diseases (CVD) are the leading cause of global mortality and their pathogenesis lies mainly in the atherosclerotic process. There are close connections linking oxidative stress and inflammation to endothelial dysfunction, atherosclerosis and, consequently, to CVD. This review focuses on the role of xanthine oxidoreductase (XOR) and its products on the development of chronic inflammation and oxidative stress, responsible for atheromatous plaque formation. Evidence is reported that an excessive level of XOR products favors inflammatory response and plaque development, thereby promoting major cardiovascular risk factors. Also, the relationship between hyperuricemia and hypertension as well as between XOR activity and CVD is confirmed. In spite of the increasing number of clinical studies investigating the output of cardiovascular patients treated with urate-lowering therapies (including uricosuric drugs, XOR inhibitors and recombinant uricase) the results are still uncertain. The inhibition of XOR activity appears more promising than just the control of uricemia level in preventing cardiovascular events, possibly because it also reduces the intracellular accumulation of urate, as well as the production of reactive oxygen species. However, XOR inhibition also reduces the availability of the multifaced mediator nitric oxide and, at present, can be recommended only in hyperuricemic patients.

Effect of Topiroxostat on Brain Natriuretic Peptide Level in Patients with Heart Failure with Preserved Ejection Fraction: A Pilot Study

BACKGROUND

Various optimal medical therapies have been established to treat heart failure (HF) with reduced ejection fraction (HFrEF). Both HFrEF and HF with preserved ejection fraction (HFpEF) are associated with poor outcomes. We investigated the effect of topiroxostat, an oral xanthine oxidoreductase inhibitor, for HFpEF patients with hyperuricemia or gout.

METHODS

In this nonrandomized, open-label, single-arm trial, we administered topiroxostat 40-160 mg/day to HFpEF patients with hyperuricemia or gout to achieve a target uric acid level of 6.0 mg/dL. The primary outcome was rate of change in log-transformed brain natriuretic peptide (BNP) level from baseline to 24 weeks after topiroxostat treatment. The secondary outcomes included amount of change in BNP level, uric acid evaluation values, and oxidative stress marker levels after 24 weeks of topiroxostat treatment. Thirty-six patients were enrolled; three were excluded before study initiation.

RESULTS

Change in log-transformed BNP level was -3.4 ± 8.9% (p = 0.043) after 24 weeks of topiroxostat treatment. The rate of change for the decrease in BNP level was -18.0 (-57.7, 4.0 pg/mL; p = 0.041). Levels of uric acid and 8-hydroxy-2'-deoxyguanosine/creatinine, an oxidative stress marker, also significantly decreased (-2.8 ± 1.6 mg/dL, p < 0.001, and -2.3 ± 3.7 ng/mgCr, p = 0.009, respectively).

CONCLUSIONS

BNP level was significantly lower in HFpEF patients with hyperuricemia or gout after topiroxostat administration; however, the rate of decrease was low. Further trials are needed to confirm our findings.

Plasma xanthine oxidoreductase is associated with carotid atherosclerosis in stable kidney transplant recipients

AIM

Xanthine oxidoreductase (XOR) is known as an enzyme related to purine metabolism, catalysing the oxidation of hypoxanthine to xanthine and of xanthine to uric acid. We investigated the relationship between plasma XOR activity in stable kidney transplantation (KT) recipients and carotid artery lesions.

METHODS

A total of 42 KT patients visiting our outpatient clinic on regular basis were recruited. Associations between plasma XOR activity and the existence of plaque in the common carotid artery (CCA) or internal carotid artery (ICA) and maximum intima-medial thickness (IMT) of CCA (max-CIMT) > 0.9 mm were examined using univariate and multivariate analyses.

RESULTS

At blood sampling, the mean and SD patient age was 52.7 ± 13.8 years old. Plasma XOR(pmol/h/ml) activity was significantly higher in patients with CCA/ICA plaque or max-CIMT >0.9 mm than those without. [23.9 (11.8, 38.3) vs. 8.29 (6.67, 17.5), p < .01, 23.9 (16.9, 71.2) vs. 9.16 (6.67, 28.2), p = .01] Univariate and multivariate logistic regression analyses revealed age and plasma XOR activity as independent predictors of CCA/ICA plaque or max-CIMT >0.9 mm. Receiver operator characteristic curve analyses revealed that the cutoff value of plasma XOR activity for the diagnosis of CCA/ICA plaque or CCA-IMT > 0.9 mm was 16.3 pmol/h/ml.

CONCLUSION

Plasma XOR activity is associated independently with atherosclerotic changes in the carotid artery of stable post-KT patients.

Association between plasma xanthine oxidoreductase activity and in-hospital outcomes in patients with stable coronary artery disease after percutaneous coronary intervention

OBJECTIVES

Reactive oxygen species generated by xanthine oxidoreductase (XOR) are associated with the progression of atherosclerosis. However, changes in plasma XOR (pXOR) activity after percutaneous coronary intervention (PCI) for stable coronary artery disease (CAD) remains unknown.

METHODS

Herein, we compared the change in the pXOR activity in patients undergoing PCI with that in patients undergoing coronary angiography (CAG) and further evaluated the relation between changes in pXOR activity and in-hospital and long-term outcomes of patients undergoing PCI. The pXOR activity of 80 consecutive patients who underwent PCI and 25 patients who underwent CAG during the hospitalization was analyzed daily. The percentage changes from baseline regulated time interval was evaluated.

RESULTS

We found that although pXOR activity decreased after PCI, and remained low until discharge, no significant changes were observed in patients undergoing CAG. Furthermore, among the patients undergoing PCI, those who experienced in-hospital adverse events, had a higher percentage of pXOR reduction 3 days after PCI. There was no association between these changes and long-term events.

CONCLUSIONS

A significant change in pXOR activity was observed in patients undergoing PCI than in patients undergoing CAG, and there seems to be a correlation between the in-hospital outcomes and the percentage reduction from baseline in pXOR activity.

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

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

Serum uric acid and outcomes in patients with chronic heart failure through the whole spectrum of ejection fraction phenotypes: Analysis of the ESC-EORP Heart Failure Long-Term (HF LT) Registry

BACKGROUND

Retrospective analyses of clinical trials indicate that elevated serum uric acid (sUA) predicts poor outcome in heart failure (HF). Uric acid can contribute to inflammation and microvascular dysfunction, which may differently affect different left ventricular ejection fraction (LVEF) phenotypes. However, role of sUA across LVEF phenotypes is unknown.

OBJECTIVES

We investigated sUA association with outcome in a prospective cohort of HF patients stratified according to LVEF.

METHODS

Through the Heart Failure Long-Term Registry of the European Society of Cardiology (ESC-EORP-HF-LT), 4,438 outpatients were identified and classified into: reduced (<40% HFrEF), mid-range (40-49% HFmrEF), and preserved (≥50% HFpEF) LVEF. Endpoints were the composite of cardiovascular death/HF hospitalization, and individual components.

RESULTS

Median sUA was 6.72 (IQ:5.48-8.20) mg/dl in HFrEF, 6.41 (5.02-7.77) in HFmrEF, and 6.30 (5.20-7.70) in HFpEF. At a median 372-day follow-up, the composite endpoint occurred in 648 (13.1%) patients, with 176 (3.6%) deaths and 538 (10.9%) HF hospitalizations. Compared with lowest sUA quartile (Q), Q-III and Q-IV were significantly associated with the composite endpoint (adjusted HR 1.68: 95% CI 1.11-2.54; 2.46: 95% CI 1.66-3.64, respectively). By univariable analyses, HFrEF and HFmrEF patients in Q-III and Q-IV, and HFpEF patients in Q-IV, showed increased risk for the composite endpoint (P<0.05 for all); after model-adjustment, significant association of sUA with outcome persisted among HFrEF in Q-IV, and HFpEF in Q-III-IV.

CONCLUSIONS

In a large, contemporary-treated cohort of HF outpatients, sUA is an independent prognosticator of adverse outcome, which can be appreciated in HErEF and HFpEF patients.

Plasma Xanthine Oxidoreductase Activity Associated with Glycemic Control in Patients with Pre-Dialysis Chronic Kidney Disease

INTRODUCTION

Xanthine oxidoreductase (XOR) activity plays an important role as a pivotal source of reactive oxygen species, which is associated with cardiovascular disease (CVD) events. Patients with CKD have increased risk of CVD events. In the present study, factors associated with plasma XOR activity in pre-dialysis CKD patients were investigated.

METHODS

In this cross-sectional study, plasma XOR activity in 118 pre-dialysis CKD patients (age 68 [57-75] years; 64 males, 26 with diabetes mellitus [DM]) was determined using a newly established highly sensitive assay based on (13C2,15N2) xanthine and liquid chromatography/triple quadrupole mass spectrometry.

RESULTS

Plasma glucose, hemoglobin A1c, and estimated glomerular filtration (eGFR) were significantly and positively correlated with plasma logarithmically transformed XOR (ln-XOR) activity. In multiple regression analyses, eGFR and hemoglobin A1c or plasma glucose were significantly, independently, and positively associated with plasma ln-XOR activity after adjusting for several confounders. Plasma XOR activity was significantly higher in CKD patients with (n = 26) than in those without (n = 92) DM (62.7 [32.3-122] vs. 25.7 [13.4-45.8] pmol/h/mL, p < 0.001). A total of 38 patients were taking uric acid-lowering drugs. Multiple regression analysis of CKD patients not administered uric acid-lowering drugs (n = 80) showed no significant association between eGFR and plasma ln-XOR activity. In contrast, association between glycemic control and plasma ln-XOR activity was significant even in CKD patients without uric acid-lowering drug treatment.

CONCLUSIONS

These results indicate the importance of glycemic control in CKD patients in regard to decreased XOR, possibly leading to a decrease in CVD events.

Pharmacokinetics/pharmacometabolomics-pharmacodynamics reveals the synergistic mechanism of a multicomponent herbal formula, Baoyuan decoction against cardiac hypertrophy

Multicomponent herbal formulas (MCHFs) have earned a wide reputation for their definite efficacy in preventing or treating chronic complex diseases. However, holistic elucidation of the causal relationship between the bioavailable ingredients of MCHFs and their multitarget interactions is very challenging. To solve this problem, pharmacokinetics/pharmacometabolomics-pharmacodynamics (PK/PM-PD) combined with a multivariate biological correlation-network strategy was developed and applied to a classic MCHF, Baoyuan decoction (BYD), to clarify its active components and synergistic mechanism against cardiac hypertrophy (CH). First, multiple plasma metabolic biomarkers for β-adrenergic agonist-induced CH rats were identified by using untargeted metabolomic profiling, and then, these CH-associated endogenous metabolites and the absorbed BYD-compounds in plasma at different treatment stages after oral administration of BYD were analyzed by using targeted PK and PM. Second, the dynamic relationship of BYD-related compounds and CH-associated endogenous metabolites and signaling pathways was built by using multivariate and bioinformatic correlation analysis. Finally, metabolic-related PD indicators were predicted and further verified by biological tests. The results demonstrated that the bioavailable BYD-compounds, such as saponins and flavonoids, presented differentiated and distinctive metabolic features and showed positive or negative correlations with various CH-altered metabolites and PD-indicators related to gut microbiota metabolism, amino acid metabolism, lipid metabolism, energy homeostasis, and oxidative stress at different treatment stages. This study provides a novel strategy for investigating the dynamic interaction between BYD and the biosystem, providing unique insight for disclosing the active components and synergistic mechanisms of BYD against CH, which also supplies a reference for other MCHF related research.

Inhibition of xanthine oxidase in the acute phase of myocardial infarction prevents skeletal muscle abnormalities and exercise intolerance

AIMS

Exercise intolerance in patients with heart failure (HF) is partly attributed to skeletal muscle abnormalities. We have shown that reactive oxygen species (ROS) play a crucial role in skeletal muscle abnormalities, but the pathogenic mechanism remains unclear. Xanthine oxidase (XO) is reported to be an important mediator of ROS overproduction in ischaemic tissue. Here, we tested the hypothesis that skeletal muscle abnormalities in HF are initially caused by XO-derived ROS and are prevented by the inhibition of their production.

METHODS AND RESULTS

Myocardial infarction (MI) was induced in male C57BL/6J mice, which eventually led to HF, and a sham operation was performed in control mice. The time course of XO-derived ROS production in mouse skeletal muscle post-MI was first analysed. XO-derived ROS production was significantly increased in MI mice from Days 1 to 3 post-surgery (acute phase), whereas it did not differ between the MI and sham groups from 7 to 28 days (chronic phase). Second, mice were divided into three groups: sham + vehicle (Sham + Veh), MI + vehicle (MI + Veh), and MI + febuxostat (an XO inhibitor, 5 mg/kg body weight/day; MI + Feb). Febuxostat or vehicle was administered at 1 and 24 h before surgery, and once-daily on Days 1-7 post-surgery. On Day 28 post-surgery, exercise capacity and mitochondrial respiration in skeletal muscle fibres were significantly decreased in MI + Veh compared with Sham + Veh mice. An increase in damaged mitochondria in MI + Veh compared with Sham + Veh mice was also observed. The wet weight and cross-sectional area of slow muscle fibres (higher XO-derived ROS) was reduced via the down-regulation of protein synthesis-associated mTOR-p70S6K signalling in MI + Veh compared with Sham + Veh mice. These impairments were ameliorated in MI + Feb mice, in association with a reduction of XO-derived ROS production, without affecting cardiac function.

CONCLUSION

XO inhibition during the acute phase post-MI can prevent skeletal muscle abnormalities and exercise intolerance in mice with HF.

Plasma Xanthine Oxidoreductase Activity Is Associated with a High Risk of Cardiovascular Disease in a General Japanese Population

The purpose of this study was to investigate the association between xanthine oxidoreductase (XOR) activity and a high risk of cardiovascular disease (CVD) in a general Japanese population. The Iwate Tohoku Medical Megabank Organization pooled individual participant data from a general population-based cohort study in Iwate prefecture. The cardiovascular risk was calculated using the Framingham Risk Score (FRS). A total of 1605 of the 1631 participants (98.4%) had detectable XOR activity. Multiple regression analysis demonstrated that XOR activity was independently associated with body mass index (β = 0.26, p < 0.001), diabetes (β = 0.09, p < 0.001), dyslipidemia (β = 0.08, p = 0.001), and uric acid (β = 0.13, p < 0.001). Multivariate analysis showed that the highest quartile of XOR activity was associated with a high risk for CVD (FRS ≥ 15) after adjustment for baseline characteristics (OR 2.93, 95% CI 1.16-7.40). The area under the receiver operating characteristic curves of the FRS with XOR activity was 0.81 (p = 0.008). XOR activity is associated with a high risk for CVD, suggesting that high XOR activity may indicate cardiovascular risk in a general Japanese population.

Association of the plasma xanthine oxidoreductase activity with the metabolic parameters and vascular complications in patients with type 2 diabetes

Xanthine oxidoreductase (XOR) catalyzes the oxidation of hypoxanthine to xanthine, and of xanthine to uric acid. XOR also enhances the production of reactive oxygen species and causes endothelial dysfunction. In this study, we evaluated the association of XOR and its substrate with the vascular complications in 94 Japanese inpatients with type 2 diabetes (T2DM). The plasma XOR activity and plasma xanthine levels were positively correlated with the body mass index, aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-GTP, fasting plasma insulin, and the homeostasis model of assessment of insulin resistance (HOMA-IR), and negatively correlated with the high density lipoprotein cholesterol. The plasma XOR activity also showed a positive correlation with the serum triglyceride. Multivariate analyses identified AST, ALT, fasting plasma insulin and HOMA-IR as being independently associated with the plasma XOR activity. The plasma XOR activity negatively correlated with the duration of diabetes, and positively correlated with the coefficient of variation of the R-R interval and sensory nerve conduction velocity. Furthermore, the plasma XOR activity was significantly decreased in patients with coronary artery disease. Thus, the plasma XOR activity might be a surrogate marker for the development of vascular complications, as well as liver dysfunction and insulin resistance, in T2DM.

Trial registration: This study is registered at the UMIN Clinical Trials Registry (UMIN000029970; https://www.umin.ac.jp/ctr/index-j.htm). The study was conducted from Nov 15, 2017.

Xanthine oxidase inhibition attenuates doxorubicin-induced cardiotoxicity in mice

Accumulating evidence suggests that high serum uric acid (UA) is associated with left ventricular (LV) dysfunction. Although xanthine oxidase (XO) activation is a critical regulatory mechanism of the terminal step in ATP and purine degradation, the pathophysiological role of cardiac tissue XO in LV dysfunction remains unclear. We herein investigated the role and functional significance of tissue XO activity in doxorubicin-induced cardiotoxicity. Either doxorubicin (10 mg/kg) or vehicle was intraperitonially administered in a single injection to mice. Mice were treated with or without oral XO-inhibitors (febuxostat 3 mg/kg/day or topiroxostat 5 mg/kg/day) for 8 days starting 24 h before doxorubicin injection. Cardiac tissue XO activity measured by a highly sensitive assay with liquid chromatography/mass spectrometry and cardiac UA content were significantly increased in doxorubicin-treated mice at day 7 and dramatically reduced by XO-inhibitors. Accordingly, XO-inhibitors substantially improved LV ejection fraction (assessed by echocardiography) and LV developed pressure (assessed by ex vivo Langendorff heart perfusion) impaired by doxorubicin administration. This was associated with an increase in XO-derived hydrogen peroxide production with concomitant upregulation of apoptotic and ferroptotic pathways, all of which were reduced by XO-inhibitors. Furthermore, metabolome analyses revealed enhanced purine metabolism in doxorubicin-treated hearts, and XO-inhibitors suppressed the serial metabolic reaction of hypoxanthine-xanthine-UA, the paths of ATP and purine degradation. In summary, doxorubicin administration induces cardiac tissue XO activation associated with impaired LV function. XO-inhibitors attenuate doxorubicin-induced cardiotoxicity through inhibition of XO-derived oxidative stress and cell death signals as well as the maintenance of cardiac energy metabolism associated with modulation of the purine metabolic pathway.

Evaluation of Enhanced Lipid Oxidation and Compensatory Suppression using Natriuretic Peptide in Patients with Cardiovascular Diseases

Malondialdehyde-modified low-density lipoprotein (MDA-LDL) is recognized as a surrogate marker of lipid oxidation and is associated with arteriosclerosis. However, there are limited reports on the relationship between heart failure and MDA-LDL. Therefore, we aimed to determine whether MDA-LDL is activated in patients with left ventricular (LV) dysfunction and examine our hypothesis that the B-type natriuretic peptide (BNP) masks the enhancement of MDA-LDL in patients with LV dysfunction by its strong antioxidative action. The study population comprised 2,976 patients with various cardiovascular diseases. Patients were divided into four groups depending on the LV ejection fraction (LVEF) or plasma BNP level. A nonparametric analysis with the Kruskal-Wallis test was used to perform an interquartile comparison. In addition, structural equation modeling and Bayesian estimation were used to compare the effects of LVEF and BNP on MDA-LDL. MDA-LDL levels did not significantly change (P > 0.05) with respect to the degree of LVEF among the four groups. In contrast, MDA-LDL levels were significantly decreased (P < 0.001) with respect to the degree of BNP among the four groups. A path model based on structural equation modeling clearly showed a significant effect of LVEF (standardized regression coefficient; β: -0.107, P < 0.001) and BNP (β: -0.114, P < 0.001) on MDA-LDL, with a significant inverse association between LVEF and BNP (correlation coefficient -0.436, P < 0.001). MDA-LDL should be activated in patients with LV dysfunction; however, BNP is thought to exert a strong compensatory suppression on lipid oxidation, masking the relationship between heart failure and lipid oxidation.

Time-dependent changes in plasma xanthine oxidoreductase during hospitalization of acute heart failure

Aims

The aim of present study is to evaluate the clinical significance of the time‐dependent changes in xanthine oxidoreductase (XOR) activity during hospitalization for acute heart failure (AHF).

Methods and results

A total of 229 AHF patients who visited to emergency room were prospectively enrolled, and 187 patients were analysed. Blood samples were collected within 15 min of admission (Day 1), after 48–72 h (Day 3), and between Days 7 and 21 (Day 14). The AHF patients were divided into two groups according to the XOR activity on Day 1: the high‐XOR group (≥100 pmol/h/mL, n = 85) and the low‐XOR group (<100 pmol/h/mL, n = 102). The high‐XOR patients were assigned to two groups according to the rate of change in XOR from Day 1 to Day 14: the decreased group (≥50% decrease; n = 70) and the non‐decreased group (<50% decrease; n = 15). The plasma XOR activity significantly decreased on Days 3 and 14 [23.6 (9.1 to 63.1) pmol/h/mL and 32.5 (10.2 to 87.8) pmol/h/mL, respectively] in comparison with Day 1 [78.5 (16.9 to 340.5) pmol/h/mL]. A Kaplan–Meier curve indicated that the prognosis, including heart failure (HF) events (all‐cause death and readmission by HF) within 365 days, was significantly poorer in the low‐XOR patients than in the high‐XOR patients and was also significantly poorer in the non‐decreased group than in the decreased group.

Conclusions

The plasma XOR activity was rapidly decreased by the appropriate treatment of AHF. Although high‐XOR activity on admission was not associated with increased HF events in AHF, high‐XOR activity that was not sufficiently reduced during appropriate treatment was associated with increased HF events.

Greater coronary lipid core plaque assessed by near-infrared spectroscopy intravascular ultrasound in patients with elevated xanthine oxidoreductase: a mechanistic insight

Elevated serum uric acid level was reportedly associated with greater coronary lipid plaque. Xanthine oxidoreductase (XOR) is a rate-limiting enzyme in purine metabolism and believed to play an important role in coronary atherosclerosis. However, the relation of XOR to coronary lipid plaque and its mechanism are unclear. Patients with stable coronary artery disease undergoing elective percutaneous coronary intervention under near-infrared spectroscopy intravascular ultrasound (NIRS-IVUS) guidance were prospectively enrolled. They were divided into three groups according to serum XOR activities: low, normal, and high. Coronary lipid core plaques in non-target vessels were evaluated by NIRS-IVUS with lipid core burden index (LCBI) and a maximum LCBI in 4 mm (maxLCBI_4mm). Systemic endothelial function and inflammation were assessed with reactive hyperemia index (RHI) and high-sensitivity C-reactive protein, neutrophil-to-lymphocyte ratio, and platelet-to-lymphocyte ratio. Of 68 patients, 26, 31, and 11 were classified as low, normal, and high XOR activity groups. LCBI (474.4 ± 171.6 vs. 347.4 ± 181.6 vs. 294.0 ± 155.9, p = 0.04) and maxLCBI_4mm (102.1 ± 56.5 vs. 65.6 ± 48.5 vs. 55.6 ± 37.8, p = 0.04) were significantly higher in high XOR group than in normal and low XOR groups. Although RHI was significantly correlated with body mass index, diabetes, current smoking, and high-density lipoprotein cholesterol, no relation was found between XOR activity and RHI. There were also no relations between XOR activity and C-reactive protein, neutrophil-to-lymphocyte ratio, or platelet-to-lymphocyte ratio. In conclusion, elevated XOR activity was associated with greater coronary lipid core plaque in patients with stable coronary artery disease, without significant relations to systemic endothelial function and inflammation.

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

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

Network Meta-Analysis of Drug Therapies for Lowering Uric Acid and Mortality Risk in Patients with Heart Failure

PURPOSE

This network meta-analysis aimed to assess the current efficacy of decreasing the uric acid (UA) level with drugs to reduce mortality in patients with heart failure (HF).

METHODS

Electronic literature searches using EMBASE and MEDLINE of studies published from 1 Jan 1950 to 26 Dec 2019 were conducted for randomized controlled trials or non-randomized cohort studies that included at least one group of patients who took UA-lowering drugs and with a study outcome of all-cause mortality. A random-effects network meta-analysis was performed within a frequentist framework. Hierarchy of treatments was expressed as the surface under the cumulative ranking curve (SUCRA) value, which is in proportion to mean rank (best is 100%).

RESULTS

Nine studies, which included seven different types of groups, were eligible for analysis. The "untreated uricemia" group in which patients had hyperuricemia but without treatment had a significantly higher risk of mortality than the "no uricemia" group in which patients had no hyperuricemia (relative risk (RR)(95% confidence interval (CI), 1.43 (1.08-1.89)). The "start-allo" group wherein patients started to take allopurinol did not have a significantly lower risk of mortality than the "untreated uricemia" group (RR (95% CI), 0.68 (0.45-1.01)). However, in the "start-allo" group the SUCRA value was comparable to that in the "no uricemia" group (SUCRA: 65.4% for "start-allo"; 64.1% for "no uricemia").

CONCLUSIONS

Results suggested that allopurinol therapy was not associated with a significantly improved prognosis in terms of mortality but could potentially counteract the adverse effects associated with longstanding hyperuricemia in HF patients.

Uric Acid Is a Biomarker of Oxidative Stress in the Failing Heart: Lessons Learned from Trials With Allopurinol and SGLT2 Inhibitors

Hyperuricemia increases the risk of heart failure, and higher levels of serum uric acid are seen in patients who have worse ventricular function, functional capacity, and prognosis. Heart failure is also accompanied by an upregulation of xanthine oxidase, the enzyme that catalyzes the formation of uric acid and a purported source of reactive oxygen species. However, the available evidence does not support the premise that either uric acid or the activation of xanthine oxidase has direct injurious effects on the heart in the clinical setting. Xanthine oxidase inhibitors (allopurinol and oxypurinol) have had little benefit and may exert detrimental effects in patients with chronic heart failure in randomized controlled trials, and the more selective and potent inhibitor febuxostat increases the risk of cardiovascular death more than allopurinol. Instead, the available evidence indicates that changes in xanthine oxidase and uric acid are biomarkers of oxidative stress (particularly in heart failure) and that xanthine oxidase may provide an important source of nitric oxide that quenches the injurious effects of reactive oxygen species. A primary determinant of the cellular redox state is nicotinamide adenine dinucleotide, whose levels drive an inverse relationship between xanthine oxidase and sirtuin-1, a nutrient deprivation sensor that exerts important antioxidant and cardioprotective effects. Interestingly, sodium-glucose cotransporter 2 inhibitors induce a state of nutrient deprivation that includes activation of sirtuin-1, suppression of xanthine oxidase, and lowering of serum uric acid. The intermediary role of sirtuin-1 in both uric acid-lowering and cardioprotection may explain why, in mediation analyses of large-scale cardiovascular trials, the effect of sodium-glucose cotransporter 2 inhibitors to decrease serum uric acid is a major predictor of the ability of these drugs to decrease serious heart failure events.

Serum uric acid, predicts heart failure in a large Italian cohort: search for a cut-off value the URic acid Right for heArt Health study

OBJECTIVE

To assess the prognostic cut-off values of serum uric acid (SUA) in predicting fatal and morbid heart failure in a large Italian cohort in the frame of the Working Group on Uric Acid and Cardiovascular Risk of the Italian Society of Hypertension.

METHODS

The URic acid Right for heArt Health (URRAH) study is a nationwide, multicentre, cohort study involving data on individuals aged 18-95 years, recruited on a community basis from all regions of Italy under the patronage of the Italian Society of Hypertension with a mean follow-up period of 128 ± 65 months. Incident heart failure was defined on the basis of International Classification of Diseases Tenth Revision codes and double-checked with general practitioners and hospital files. Multivariate Cox regression models having fatal and morbid heart failure as dependent variables, adjusted for sex, age, SBP, diabetes, estimated glomerular filtration rate, smoking habit, ethanol intake, BMI, haematocrit, LDL cholesterol, previous diagnosis of heart failure and use of diuretics as possible confounders, were used to search for an association between SUA as a continuous variable and heart failure. By means of receiver operating characteristic curves, two prognostic cut-off values (one for all heart failure and one for fatal heart failure) were identified as able to discriminate between individuals doomed to develop the event. These cut-off values were used as independent predictors to divide individuals according to prognostic cut-off values in a multivariate Cox models, adjusted for confounders.

RESULTS

A total of 21 386 individuals were included in the analysis. In Cox analyses, SUA as a continuous variable was a significant predictor of all [hazard ratio 1.29 (1.23-1.359), P < 0.0001] and fatal [hazard ratio 1.268 (1.121-1.35), P < 0.0001] incident heart failure. Cut-off values of SUA able to discriminate all and fatal heart failure status were identified by mean of receiver operating characteristic curves in the whole database: SUA more than 5.34 mg/dl (confidence interval 4.37-5.6, sensitivity 52.32, specificity 63.96, P < 0.0001) was the univariate prognostic cut-off value for all heart failure, whereas SUA more than 4.89 mg/dl (confidence interval 4.78-5.78, sensitivity 68.29, specificity 49.11, P < 0.0001) for fatal heart failure. The cut-off for all heart failure and the cut-off value for fatal heart failure were accepted as independent predictors in the Cox analysis models, the hazard ratios being 1.645 (1.284-2.109, P < 0.0001) for all heart failure and 1.645 (1.284-2.109, P < 0.0001) for fatal heart failure, respectively.

CONCLUSION

The results of the current study confirm that SUA is an independent risk factor for all heart failure and fatal heart failure, after adjusting for potential confounding variables and demonstrate that a prognostic cut-off value can be identified for all heart failure (>5.34 mg/dl) and for fatal heart failure (>4.89 mg/dl).

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.

Electrochemical strategy with zeolitic imidazolate framework-8 and ordered mesoporous carbon for detection of xanthine

An accurate, safe, environmentally friendly, fast and sensitive electrochemical biosensors were developed to detect xanthine in serum. The metal-organic framework ZIF-8 was synthesised and elemental gold was supported on the surface of ZIF-8 by reduction method to synthesise Ag-ZIF-8. The mesoporous carbon material and the synthesised Ag-ZIF-8 were, respectively, applied to a glassy carbon electrode to construct biosensors. The constructed biosensor has a good linear relation in the range of 1-280 μmol l^-1 of xanthine and the detection limit is 0.167 μmol l^-1. The relative standard deviation value in serum samples was <5%, and the recoveries were 96-106%, indicating the good selectivity, stability and reproducibility of this electrochemical biosensor.

Impact of plasma xanthine oxidoreductase activity in patients with heart failure with preserved ejection fraction

AIMS

Reactive oxygen species are reportedly involved in the mechanism underlying heart failure with preserved ejection fraction (HFpEF); however, the disease pathophysiology remains poorly understood. Xanthine oxidoreductase (XOR), the rate-limiting enzyme of purine metabolism, plays an important role in uric acid production and generates reactive oxygen species. However, the impact of plasma XOR activity on the clinical outcomes of patients with HFpEF remains unclear. The aim of this study was to investigate whether plasma XOR activity is associated with major adverse cardiovascular events (MACEs) in patients with HFpEF.

METHODS AND RESULTS

The plasma XOR activity was measured in 257 patients with HFpEF, who were then divided into three groups according to the activity levels: low XOR group (<33 pmol/h/mL, n = 45), normal XOR group (33-120 pmol/h/mL, n = 160), and high XOR group (>120 pmol/h/mL, n = 52). During the median follow-up period of 809 days, there were 74 MACEs. Kaplan-Meier analysis revealed that the high XOR group was at the highest risk for MACEs. Multivariate analysis by Cox's proportional hazard regression approach showed that high XOR activity was significantly associated with MACEs, after adjustment for confounding factors. The patients were also divided into four groups according to the absence/presence of high XOR activity and/or hyperuricaemia. According to the multivariate Cox regression analysis, high XOR activity was associated with MACEs, regardless of the hyperuricaemia status.

CONCLUSIONS

Elevated plasma XOR activity is significantly associated with adverse clinical outcomes in patients with HFpEF.

Biomarkers in heart failure: the past, current and future

Despite the enhanced knowledge of the pathophysiology of heart failure (HF), it still remains a serious syndrome with substantial morbidity, mortality, and frequent hospitalizations. These are due to the current improvements in other cardiovascular diseases (like myocardial infarction), the aging population, and growing prevalence of comorbidities. Biomarker-guided management has brought a new dimension in prognostication, diagnosis, and therapy options. Following the recommendation of natriuretic peptides (B-type natriuretic peptide and N-terminal-proBNP), many other biomarkers have been thoroughly studied to reflect different pathophysiological processes (such as fibrosis, inflammation, myocardial injury, and remodeling) in HF and some of them (like cardiac troponins, soluble suppression of tumorigenesis-2, and galectin 3) have subsequently been recommended to aid in the diagnosis and prognostication in HF. Consequently, multi-marker approach has also been approved owing to the varied nature of HF syndrome. In this review, we discussed the guidelines available for HF biomarkers, procedures for evaluating novel markers, and the utilities of both emerging and established biomarkers for risk stratification, diagnosis, and management of HF in the clinics. We later looked at how the rapidly emerging field-OMICs, can help transform HF biomarkers discoveries and establishment.

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.

Obstructive sleep apnea and the risk of gout: a population-based case-control study

Background

Patients with obstructive sleep apnea (OSA) might be at risk of gout because of pathophysiological mechanisms that can lead to hyperuricemia and eventually gout or because of shared risk factors between both diseases. The objective of the present study was to investigate the risk of gout in patients with OSA.

Methods

A population-based case-control study using the UK Clinical Practice Research Datalink GOLD including all patients aged 40 years and older with a first diagnosis of gout between 1987 and 2014. Gout cases were matched by year of birth, sex, and practice to non-gout controls. Conditional logistic regression estimated the risk of gout with an earlier diagnosis of OSA. Analyses were adjusted for lifestyle factors, comorbidities, and recent drug use.

Results

One hundred eleven thousand five hundred nine cases were matched with 210,241 controls. Patients with OSA were at increased risk of gout (OR 1.86; 95%CI (1.71–2.02). However, this association disappeared (OR 1.05; 95% CI 0.96–1.16) after adjustment for smoking status, body mass index (BMI), alcohol use, a history of heart failure, diabetes mellitus, renal function, and recent use of diuretics and other medications. Among females with OSA and patients with OSA associated with heart failure, renal impairment, or higher BMI, the risk of gout was however still increased when compared to the total control population.

Conclusion

This study showed that the observed association between OSA and gout disappeared after adjustment.

Relation of Plasma Xanthine Oxidoreductase Activity to Coronary Lipid Core Plaques Assessed by Near-Infrared Spectroscopy Intravascular Ultrasound in Patients With Stable Coronary Artery Disease

Previous studies reported that elevated serum uric acid level was associated with greater coronary lipid plaque. Xanthine oxidoreductase (XOR) is a rate-limiting enzyme in purine metabolism and is believed to play important roles in coronary atherosclerosis. However, the relation between XOR and coronary lipid plaque is unclear. Patients with stable coronary artery disease who underwent elective percutaneous coronary intervention under near-infrared spectroscopy intravascular ultrasound (NIRS-IVUS) guidance were prospectively included. They were divided into 3 groups according to plasma XOR activities based on a previous report: low, normal, and high. Quantitative coronary angiography and gray-scale IVUS were analyzed. The primary end point was coronary lipid plaques in a nontarget vessel assessed by NIRS-IVUS with lipid core burden index (LCBI) and maximum LCBI in 4 mm (maxLCBI_4mm). Out of 68 patients, 26, 31, and 11 patients were classified as low, normal, and high XOR activity groups. Quantitative coronary angiography demonstrated that the high XOR activity group had longer lesion length, smaller minimum lumen diameter, and higher percentage of diameter stenosis in a nontarget vessel among the 3 groups. Gray-scale IVUS analysis also showed smaller lumen area in the high XOR activity group than the others. LCBI (102.1 ± 56.5 vs 65.6 ± 48.5 vs 55.6 ± 37.8, p = 0.04) and maxLCBI_4mm (474.4 ± 171.6 vs 347.4 ± 181.6, 294.0 ± 155.9, p = 0.04) in a nontarget vessel were significantly higher in the high XOR group than in the normal and low groups. In conclusion, elevated XOR activity was associated with coronary lipid-rich plaque in a nontarget vessel in patients with stable coronary artery disease.