Xanthine oxidoreductase in atherosclerosis pathogenesis: Not only oxidative stress

Global responses to tris(1-chloro-2-propyl) phosphate and tris(2-butoxyethyl) phosphate in Escherichia coli: Evidences from biomarkers, and metabolic disturbance using GC-MS and LC-MS metabolomics analyses

Tris(1-chloro-2-propyl) phosphate (TCPP) and tris(2-butoxyethyl) phosphate (TBEP) as pollutants of emerging concern have aroused the rising attention due to their potential risks on aquatic ecosystem and public health. Nevertheless, there is a lack of toxicological mechanisms exploration of TCPP and TBEP at molecular levels. Herein, the toxicity effects and molecular mechanism of them were fully researched and summarized on Escherichia coli (E.coli). Acute exposure to them significantly activated antioxidant defense system and caused lipid peroxidation, as proved by the changes of antioxidant enzymes and MDA. The ROS overload resulted in the drop of membrane potential as well as the downregulated synthesis of ATPase, endorsing that E. coli cytotoxicity was ascribed to oxidative stress damage induced by TCPP and TBEP. The combination of GC-MS and LC-MS based metabolomics validated that TCPP and TBEP induced metabolic reprogramming in E.coli. More specifically, the responsive metabolites in carbohydrate metabolism, lipids metabolism, nucleotide metabolism, amino acid metabolism, and organic acids metabolism were significantly disturbed by TCPP and TBEP, confirming the negative effects on metabolic functions and key bioprocesses. Additionally, several biomarkers including PE(16:1(5Z)/15:0), PA(17:1(9Z)/18:2(9Z,12Z)), PE(19:1(9Z)/0:0), and LysoPE(0:0/18:1(11Z)) were remarkably upregulated, verifying that the protection of cellular membrane was conducted by regulating the expression of lipids-associated metabolites. Collectively, this work sheds new light on the potential molecular toxicity mechanism of TCPP and TBEP on aquatic organisms, and these findings using GC-MS and LC-MS metabolomics generate a fresh insight into assessing the effects of OPFRs on target and non-target aquatic organisms.

Targeted Metabolomics Highlights Dramatic Antioxidant Depletion, Increased Oxidative/Nitrosative Stress and Altered Purine and Pyrimidine Concentrations in Serum of Primary Myelofibrosis Patients

To date, little is known concerning the circulating levels of biochemically relevant metabolites (antioxidants, oxidative/nitrosative stress biomarkers, purines, and pyrimidines) in patients with primary myelofibrosis (PMF), a rare form of myeloproliferative tumor causing a dramatic decrease in erythropoiesis and angiogenesis. In this study, using a targeted metabolomic approach, serum samples of 22 PMF patients and of 22 control healthy donors were analyzed to quantify the circulating concentrations of hypoxanthine, xanthine, uric acid (as representative purines), uracil, β-pseudouridine, uridine (as representative pyrimidines), reduced glutathione (GSH), ascorbic acid (as two of the main water-soluble antioxidants), malondialdehyde, nitrite, nitrate (as oxidative/nitrosative stress biomarkers) and creatinine, using well-established HPLC method for their determination. Results showed that PMF patients have dramatic depletions of both ascorbic acid and GSH (37.3- and 3.81-times lower circulating concentrations, respectively, than those recorded in healthy controls, p < 0.0001), accompanied by significant increases in malondialdehyde (MDA) and nitrite + nitrate (4.73- and 1.66-times higher circulating concentrations, respectively, than those recorded in healthy controls, p < 0.0001). Additionally, PMF patients have remarkable alterations of circulating purines, pyrimidines, and creatinine, suggesting potential mitochondrial dysfunctions causing energy metabolism imbalance and consequent increases in these cell energy-related compounds. Overall, these results, besides evidencing previously unknown serum metabolic alterations in PMF patients, suggest that the determination of serum levels of the aforementioned compounds may be useful to evaluate PMF patients on hospital admission for adjunctive therapies aimed at recovering their correct antioxidant status, as well as to monitor patients' status and potential pharmacological treatments.

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.

Albumin Redox Modifications Promote Cell Calcification Reflecting the Impact of Oxidative Status on Aortic Valve Disease and Atherosclerosis

Calcific aortic valve disease (CAVD) and coronary artery disease (CAD) are related cardiovascular diseases in which common mechanisms lead to tissue calcification. Oxidative stress plays a key role in these diseases and there is also evidence that the redox state of serum albumin exerts a significant influence on these conditions. To further explore this issue, we used multimarker scores (OxyScore and AntioxyScore) to assess the global oxidative status in patients with CAVD, with and without CAD, also evaluating their plasma thiol levels. In addition, valvular interstitial cells were treated with reduced, oxidized, and native albumin to study how this protein and its modifications affect cell calcification. The differences we found suggest that oxidative status is distinct in CAVD and CAD, with differences in redox markers and thiol levels. Importantly, the in vitro interstitial cell model revealed that modified albumin affects cell calcification, accelerating this process. Hence, we show here the importance of the redox system in the development of CAVD, emphasizing the relevance of multimarker scores, while also offering evidence of how the redox state of albumin influences vascular calcification. These data highlight the relevance of understanding the overall redox processes involved in these diseases, opening the door to new studies on antioxidants as potential therapies for these patients.

Xanthine Oxidoreductase in the Pathogenesis of Endothelial Dysfunction: An Update

Xanthine oxidoreductase (XOR) is a rate-limiting enzyme in the formation of uric acid (UA) and is involved in the generation of reactive oxygen species (ROS). Overproduction of ROS has been linked to the pathogenesis of hypertension, atherosclerosis, and cardiovascular disease, with multiple studies over the last 30 years demonstrating that XOR inhibition is beneficial. The involvement of XOR and its constituents in the advancement of chronic inflammation and ROS, which are responsible for endothelial dysfunction, is the focus of this evidence-based review. An overabundance of XOR products and ROS appears to drive the inflammatory response, resulting in significant endothelium damage. It has also been demonstrated that XOR activity and ED are connected. Diabetes, hypertension, and cardiovascular disease are all associated with endothelial dysfunction. ROS mainly modifies the activity of vascular cells and can be important in normal vascular physiology as well as the development of vascular disease. Suppressing XOR activity appears to decrease endothelial dysfunction, probably because it lessens the generation of reactive oxygen species and the oxidative stress brought on by XOR. Although there has long been a link between higher vascular XOR activity and worse clinical outcomes, new research suggests a different picture in which positive results are mediated by XOR enzymatic activity. Here in this study, we aimed to review the association between XOR and vascular endothelial dysfunction. The prevention and treatment approaches against vascular endothelial dysfunction in atherosclerotic disease.

Temporal change of serum xanthine oxidase levels and its relation to clinical outcome of severe traumatic brain injury: a prospective cohort study

Xanthine oxidase (XO) may be involved in the induction of oxidative stress and inflammation. We measured serum XO levels at multiple days to determine whether it is associated with the severity and prognosis of severe traumatic brain injury (sTBI). In this prospective cohort study, we quantified serum XO levels in 112 sTBI patients and 112 controls. Serum XO levels of patients were measured at admission and at days 1, 3, 5, 7, and 10 after sTBI. Extended Glasgow outcome scale scores of 1-4 at post-trauma 180 days were defined as a poor prognosis. Multivariate analysis was employed to determine the relationship between poor prognosis and serum XO levels at multiple days. Serum XO levels were significantly increased at admission among patients, afterwards elevated gradually, peaked at day 3, and then diminished gradually until day 10, and were substantially higher during 10 days in patients than in controls. Serum XO levels at 6 different days were all correlated with admission Rotterdam computed tomography (CT) scores and Glasgow coma scale (GCS) scores. Serum XO levels at 6 different days were all substantially higher in patients with poor prognosis than in those with good prognosis. Serum XO levels at days 7 and 10, but not at days 1, 3, and 5, had significantly lower area under receiver operating characteristic (AUC) than those at admission. Serum XO levels at admission and at days 1 and 3, but not at day 5, were independently associated with 180-day poor prognosis. Prognostic prediction model containing GCS scores, Rotterdam CT scores, and serum XO levels at admission (or at days 1 and 3) showed substantially higher AUC than GCS scores and Rotterdam CT scores alone. The models were visually described using nomograms, which were comparatively stable under calibration curve and were relatively of clinical benefit under decision curve. Elevated serum XO levels during early period of sTBI are more closely associated with trauma severity and clinical adverse outcomes, assuming that serum XO may serve as a potential prognostic biomarker in sTBI.

Effects of acute aerobic exercise on arterial stiffness in transgender men

Testosterone replacement therapy (TRT) in transgender men (TM) results in side effects such as elevated triglycerides and increased arterial stiffness. Exercise may be useful to ameliorate such effects, but no studies have examined the effects of acute aerobic exercise in TM. This study aimed to investigate the effects of acute aerobic exercise on arterial stiffness in TM. Thirty-six participants were included, comprising 12 TM (duration of TRT: 57.4 ± 30.3 months), 12 males and 12 females. All participants performed acute aerobic exercise on a treadmill at 50% heart rate reserve for 30 min. Arterial stiffness as measured by brachial-ankle pulse wave velocity (baPWV) was measured before exercise (Pre), 30 min after exercise (Post30), and 60 min after exercise (Post60). Serum sex hormone levels, and serum lipid profile were determined only before exercise. Serum low-density lipoprotein cholesterol (LDL-C) levels before exercise were significantly higher in TM than in males or females (males: p < 0.01; females: p < 0.05). At all points, baPWV in TM was significantly higher than in females (p < 0.05) and significantly lower than in males (p < 0.05). However, when comparing changes in baPWV over time in each group, significant decreases in Post30 and Post60 were seen in males compared to Pre (both p < 0.05), but no significant change after aerobic exercise was seen in TM or females. These results suggest that acute aerobic exercise yield different effects in TM than in males, but is unlikely to reduce arterial stiffness in TM receiving TRT.

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.

NADPH Oxidases: From Molecular Mechanisms to Current Inhibitors

NADPH oxidases (NOXs) form a family of electron-transporting membrane enzymes whose main function is reactive oxygen species (ROS) generation. Strong evidence suggests that ROS produced by NOX enzymes are major contributors to oxidative damage under pathologic conditions. Therefore, blocking the undesirable actions of these enzymes is a therapeutic strategy for treating various pathological disorders, such as cardiovascular diseases, inflammation, and cancer. To date, identification of selective NOX inhibitors is quite challenging, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. The aim of this Perspective is to furnish an updated outlook about the small-molecule NOX inhibitors described over the last two decades. Structures, activities, and in vitro/in vivo specificity are discussed, as well as the main biological assays used.

Novel Insights into the Molecular Mechanisms of Atherosclerosis

Atherosclerosis is one of the most fatal diseases in the world. The associated thickening of the arterial wall and its background and consequences make it a very composite disease entity with many mechanisms that lead to its creation. It is an active process, and scientists from various branches are engaged in research, including molecular biologists, cardiologists, and immunologists. This review summarizes the available information on the pathophysiological implications of atherosclerosis, focusing on endothelium dysfunction, inflammatory factors, aging, and uric acid, vitamin D, and miRNA expression as recent evidence of interactions of the molecular and cellular elements. Analyzing new discoveries for the underlying causes of this condition assists the general research to improve understanding of the mechanism of pathophysiology and thus prevention of cardiovascular diseases.

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.

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.

Inhibition of Xanthine Oxidase Protects against Diabetic Kidney Disease through the Amelioration of Oxidative Stress via VEGF/VEGFR Axis and NOX-FoxO3a-eNOS Signaling Pathway

Xanthine oxidase (XO) is an important source of reactive oxygen species. This study investigated whether XO inhibition exerts renoprotective effects by inhibiting vascular endothelial growth factor (VEGF) and NADPH oxidase (NOX) in diabetic kidney disease (DKD). Febuxostat (5 mg/kg) was administered to streptozotocin (STZ)-treated 8-week-old male C57BL/6 mice via intraperitoneal injection for 8 weeks. The cytoprotective effects, its mechanism of XO inhibition, and usage of high-glucose (HG)-treated cultured human glomerular endothelial cells (GECs) were also investigated. Serum cystatin C, urine albumin/creatinine ratio, and mesangial area expansion were significantly improved in febuxostat-treated DKD mice. Febuxostat reduced serum uric acid, kidney XO levels, and xanthine dehydrogenase levels. Febuxostat suppressed the expression of VEGF mRNA, VEGF receptor (VEGFR)1 and VEGFR3, NOX1, NOX2, and NOX4, and mRNA levels of their catalytic subunits. Febuxostat caused downregulation of Akt phosphorylation, followed by the enhancement of dephosphorylation of transcription factor forkhead box O3a (FoxO3a) and the activation of endothelial nitric oxide synthase (eNOS). In an in vitro study, the antioxidant effects of febuxostat were abolished by a blockade of VEGFR1 or VEGFR3 via NOX-FoxO3a-eNOS signaling in HG-treated cultured human GECs. XO inhibition attenuated DKD by ameliorating oxidative stress through the inhibition of the VEGF/VEGFR axis. This was associated with NOX-FoxO3a-eNOS signaling.

Effect of Topiroxostat on Reducing Oxidative Stress in the Aorta of Streptozotocin-Induced Diabetic Rats

Xanthine oxidoreductase exists both intracellularly and extracellularly and induces vascular injury by producing reactive oxygen species (ROS). Here, we investigated the effects and mechanism of action of topiroxostat, a xanthine oxidase inhibitor, on ROS using an animal model of type 1 diabetes with persistent hyperglycemia. Six-week-old male Sprague-Dawley rats were administered 50 mg/kg streptozotocin to induce diabetes; at 8 weeks of age, animals were administered topiroxostat (0.3, 1, or 3 mg/kg) for 2 weeks through mixed feeding after which the aorta was sampled. The production of superoxide, a type of ROS, was measured by chemiluminescence and dihydroethidium staining. Cytotoxicity was evaluated by nitrotyrosine staining. Topiroxostat at 3 mg/kg significantly decreased blood urea nitrogen, e-selectin, urinary malondialdehyde, and the urinary albumin/creatinine ratio compared with the streptozotocin group. Superoxide production by xanthine oxidase anchored to the cell membrane was significantly decreased by topiroxostat at both 1 mg/kg and 3 mg/kg compared with the streptozotocin group. Dihydroethidium staining revealed no significant effect of topiroxostat administration on superoxide production. The fluorescence intensity of nitrotyrosine staining was significantly suppressed by 3 mg/kg topiroxostat. Topiroxostat was found to inhibit the production of ROS in the thoracic aorta and suppress vascular endothelial damage. The antioxidant effect of topiroxostat appears to be exerted via the inhibition of anchored xanthine oxidase.

Association of serum xanthine oxidase levels with hypertension: a study on Bangladeshi adults

Xanthine oxidase (XO) is a metalloflavoenzyme associated with the uric acid formation in purine metabolism. Serum XO has been suggested to be associated with liver and kidney dysfunction, diabetes and cardiovascular diseases. However, there is limited information on the relationship between serum XO levels and hypertension. This study aimed to assess the relationship between serum XO levels and hypertension in Bangladeshi adults. In this study, fasting blood samples were collected from 312 participants (225 males and 87 females), aged ≥ 20 years. Serum levels of XO were determined by ELISA and other biochemical parameters including serum uric acid (SUA) were measured by colorimetric methods. Hypertension was defined as SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg or self-reported recent use of anti-hypertensive medications. Association between serum XO levels and hypertension was evaluated by multinomial logistic regression analysis. The mean level of XO was significantly higher (p < 0.001) in females (5.8 ± 3.2 U/L) than in males (3.9 ± 2.5 U/L). When the participants were divided by blood pressure levels, the mean level of serum XO was significantly higher (p < 0.01) in the hypertensive group (5.0 ± 2.7 U/L) compared to the normotensive control group (4.0 ± 2.7 U/L). An increasing trend for SBP and DBP levels was observed across the XO quartiles (at least p < 0.01 for both cases). A significant positive correlation was found for XO with SBP and DBP (p < 0.01). In regression analysis, the serum levels of XO showed a significant and independent association with hypertension prevalence. In conclusion, the mean level of serum XO was significantly higher in hypertensive individuals and XO was independently associated with the prevalence of hypertension. Our results indicate that XO may have a potential role in the pathophysiology of elevated blood pressure through generating of reactive oxygen species. Further large-scale longitudinal studies are needed to determine the underlying mechanisms between XO and hypertension.

The Role of Oxidative Stress in Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vascular system and is the leading cause of cardiovascular diseases worldwide. Excessive generation of reactive oxygen species (ROS) leads to a state of oxidative stress which is a major risk factor for the development and progression of atherosclerosis. ROS are important for maintaining vascular health through their potent signalling properties. However, ROS also activate pro-atherogenic processes such as inflammation, endothelial dysfunction and altered lipid metabolism. As such, considerable efforts have been made to identify and characterise sources of oxidative stress in blood vessels. Major enzymatic sources of vascular ROS include NADPH oxidases, xanthine oxidase, nitric oxide synthases and mitochondrial electron transport chains. The production of ROS is balanced by ROS-scavenging antioxidant systems which may become dysfunctional in disease, contributing to oxidative stress. Changes in the expression and function of ROS sources and antioxidants have been observed in human atherosclerosis while in vitro and in vivo animal models have provided mechanistic insight into their functions. There is considerable interest in utilising antioxidant molecules to balance vascular oxidative stress, yet clinical trials are yet to demonstrate any atheroprotective effects of these molecules. Here we will review the contribution of ROS and oxidative stress to atherosclerosis and will discuss potential strategies to ameliorate these aspects of the disease.

Multi-omics profiling and biochemical assays reveal the acute toxicity of environmental related concentrations of Di-(2-ethylhexyl) phthalate (DEHP) on the gill of crucian carp (Carassius auratus)

Di-(2-ethylhexyl) phthalate (DEHP) is one of the most extensively utilized plasticizers in the plastic manufacturing process. It is widely used in various fields due to its low cost and excellent effect. Although there is evidence that DEHP is harmful to animal and human health, DEHP-induced gill toxicity in aquatic organisms is inconclusive, and its mechanism has not been fully elucidated. Here, we investigated the effects of DEHP acute exposure on crucian carp gills at environmentally relevant concentrations of 20, 100, and 500 μg/L. Multi-omics profiling and biochemical assays were employed to characterize the potential toxicological mechanisms. The results showed that acute exposure to 100 and 500 μg/L of DEHP leads to oxidative stress in gills, as evidenced by overproduction of reactive oxygen species (ROS), increased antioxidant enzyme activity, and the transformation of glutathione from reduced to oxidized form, resulting in lipid peroxidation. Integrative analysis of transcriptomics and metabolomics indicated that increased purine metabolism was the potential source of increased ROS. Moreover, lipid metabolism disorder, including arachidonic acid metabolism, induces inflammation. Further, DEHP causes the imbalance of the CYP enzyme system in the gill, and DEHP-induced gill toxicity in crucian carp was associated with interference with CYP450 homeostasis. Taken together, this study broadens the molecular understanding of the DEHP-induced gill toxicity in aquatic organisms and provides novel perspectives for assessing the effects of DEHP on target and non-target aquatic organisms in the environment.

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.

Serum urate and heart failure: a bidirectional Mendelian randomization study

AIMS

Observational studies indicate that serum urate level is associated with heart failure (HF). However, whether this association is causal remains controversial, due to confounding factors and reverse causality. We aim to evaluate the causal relationship of genetically predicted serum urate level with HF.

METHODS AND RESULTS

A bidirectional Mendelian randomization (MR) study was performed. Instrumental variables were obtained from the largest genome-wide association studies of serum urate (457 690 individuals) to date. We obtained summary statistics of HF from HERMES consortium (47 309 cases; 930 014 controls), the FinnGen study (13 087 cases; 195 091 controls), and the UK Biobank study (1088 cases; 360 106 controls). Inverse-variance-weighted method was applied to obtain MR estimates and other statistical methods were conducted in the sensitivity analyses. The reverse MR analysis was performed to evaluate the effect of HF on serum urate levels. Genetically determined serum urate level was associated with HF [odds ratio (OR), 1.07; 95% confidence interval (CI), 1.03-1.10; P = 8.6×10-5]. The main results kept robust in the most sensitivity analyses. The association pattern remained for the HF in FinnGen (OR, 1.10; 95% CI, 1.03-1.19; P = 0.008) and the combined results of three data sources (OR, 1.08; 95% CI, 1.04-1.13; P < 0.001). No consistent evidence was found for the causal effect of HF on serum urate levels.

CONCLUSION

We provide consistent evidence for the causal effect of genetically predicted serum urate level on HF, but not the reverse effect of HF. Urate-lowering therapy may be of cardiovascular benefit in the prevention of HF.

Chronic kidney disease: Which role for xanthine oxidoreductase activity and products?

The present review explores the role of xanthine oxidoreductase (XOR) in the development and progression of chronic kidney disease (CKD). Human XOR is a multi-level regulated enzyme, which has many physiological functions, but that is also implicated in several pathological processes. The main XOR activities are the purine catabolism, which generates uric acid, and the regulation of cell redox state and cell signaling, through the production of reactive oxygen species. XOR dysregulation may lead to hyperuricemia and oxidative stress, which could have a pathogenic role in the initial phases of CKD, by promoting cell injury, hypertension, chronic inflammation and metabolic derangements. Hypertension is common in CKD patients and many mechanisms inducing it (upregulation of renin-angiotensin-aldosterone system, endothelial dysfunction and atherosclerosis) may be influenced by XOR products. High XOR activity and hyperuricemia are also risk factors for obesity, insulin resistance, type 2 diabetes and metabolic syndrome that are frequent CKD causes. Moreover, CKD is common in patients with gout, which is characterized by hyperuricemia, and in patients with cardiovascular diseases, which are associated with hypertension, endothelial dysfunction and atherosclerosis. Although hyperuricemia is undoubtedly related to CKD, controversial findings have been hitherto reported in patients treated with urate-lowering therapies.

Serum uric acid in patients with ST-segment elevation myocardial infarction: An innocent bystander or leading actor?

Elevated serum uric acid (SUA) levels have been associated with several cardiovascular risk factors and the progression of coronary artery disease. In the setting of acute myocardial infarction, increasing evidence suggests that high SUA levels could be related to adverse outcomes. Interestingly elevated SUA levels have been linked to endothelial dysfunction, inflammation and oxidative stress. The aim of this review is to discuss the potential negative effects of SUA in patients with ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention, analyzing the possible underlying pathophysiological mechanisms.

Association of Hyperuricemia with 10-Year Atherosclerotic Cardiovascular Disease Risk among Chinese Adults and Elders

The purpose of this cross-sectional study is to use a representative sample of the Chinese population and the atherosclerotic cardiovascular disease (ASCVD) risk assessment tool developed specifically for the Chinese to explore the prevalence of hyperuricemia (HUA) and the relationship between hyperuricemia and 10-year ASCVD risk in Chinese adults. Data was collected from the Chinese Physiological Constant and Health Condition survey. In this study, 12,988 subjects aged between 35 and 74 were selected by two-stage, cluster and random sampling. The sex-specific 10-year ASCVD risk scores equations, which were conducted by China-PAR project and specifically designed for Chinese adults, were used to assess the risk of developing ASCVD 10 years later. The ordinal regression model was used to explore the relationship between hyperuricemia and ASCVD risk. The total prevalence of hyperuricemia was 12.69%, and males’ prevalence was significantly higher than females (17.7% vs. 8.5%). Compared with people without hyperuricemia, the 10-year ASCVD risk scores of female with hyperuricemia increased significantly, but no significant increased happened in male. The ordinal regression model indicated that hyperuricemia subjects were 1.3 (males, 95% CI: 1.11–1.52) and 4.34 (females, 95% CI: 3.16–5.91) times more likely to increase their ASCVD risk levels than those without hyperuricemia. In conclusion, Hyperuricemia is prevalent among Chinese adults. In both genders, hyperuricemia was related with higher risk of 10-year ASCVD, and the relationship is much stronger in females than in males. Thus, sex-specific serum uric acid management and intervention strategies should be done in the prevention and control of cardiovascular events.

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

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

Sex-specific effect of serum urate levels on coronary heart disease and myocardial infarction prevention: A Mendelian randomization study

BACKGROUND AND AIMS

Observational studies have examined serum urate levels in relation to coronary heart disease (CHD) and myocardial infarction (MI). Whether these associations are causal remains controversial, due to confounding factors and reverse causality. We aim to investigate the causality of these associations using Mendelian randomization method.

METHODS AND RESULTS

Instrumental variables were obtained from the largest genome-wide association studies of serum urate (457,690 individuals) to date. Summary statistics were from CARDIoGRAMplusC4D consortium (60,801 CHD cases; 43,676 MI cases), FinnGen (21,012 CHD cases; 12,801 MI cases), UK Biobank (10,157 CHD cases; 7018 MI cases), and Biobank Japan (29,319 CHD cases). Inverse-variance weighted method was applied as the main results. Other statistical methods and reverse MR analysis were conducted in the supplementary analyses. Elevated genetically determined serum urate levels were associated with increased risks of CHD and MI. The association pattern remained for the datasets in FinnGen, the combined results of three independent data sources (CHD: odds ratio (OR), 1.10; 95%CI, 1.06-1.15; p = 4.2 × 10^-6; MI: OR, 1.12; 95%CI, 1.07-1.18; p = 2.7 × 10^-6), and East Asian population. Interestingly, sex-specific subgroup analyses revealed that these associations kept in men only, but not among women in individuals of European ancestry. No consistent evidence was found for the causal effect of CHD or MI on serum urate levels.

CONCLUSION

We provide consistent evidence for the causal effect of genetically predicted serum urate levels on CHD and MI, but not the reverse effect. Urate-lowering therapy may be of cardiovascular benefit in the prevention of CHD and MI, especially for men.

Oxidative Stress in Arterial Hypertension (HTN): The Nuclear Factor Erythroid Factor 2-Related Factor 2 (Nrf2) Pathway, Implications and Future Perspectives

Arterial hypertension (HTN) is one of the most prevalent entities globally, characterized by increased incidence and heterogeneous pathophysiology. Among possible etiologies, oxidative stress (OS) is currently extensively studied, with emerging evidence showing its involvement in endothelial dysfunction and in different cardiovascular diseases (CVD) such as HTN, as well as its potential as a therapeutic target. While there is a clear physiological equilibrium between reactive oxygen species (ROS) and antioxidants essential for many cellular functions, excessive levels of ROS lead to vascular cell impairment with decreased nitric oxide (NO) availability and vasoconstriction, which promotes HTN. On the other hand, transcription factors such as nuclear factor erythroid factor 2-related factor 2 (Nrf2) mediate antioxidant response pathways and maintain cellular reduction-oxidation homeostasis, exerting protective effects. In this review, we describe the relationship between OS and hypertension-induced endothelial dysfunction and the involvement and therapeutic potential of Nrf2 in HTN.

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.

A New Predictor of Mortality in ST-Elevation Myocardial Infarction: The Uric Acid Albumin Ratio

Several studies have shown that high uric acid (UA) and low serum albumin (SA) values increase the risk of cardiovascular disease and mortality in ST-elevation myocardial infarction (STEMI). We determined whether the uric acid/albumin ratio (UAR) is a predictor of mortality in STEMI patients. All patients who presented at our center with a diagnosis of STEMI and underwent percutaneous intervention from 2015 to 2020 were screened consecutively; 4599 patients were included. A Cox proportional hazards model was used to evaluate UAR, and adjusted predictors obtained from laboratory findings and clinical characteristics contributed to mortality. Also, a regression model was presented with a directed acyclic graph (DAG). The median age of the patients was 58 years (IQR [interquartile range]: 50–67); 3581 patients (77.9%) were male. The incidence of mortality in the entire patient group was 11.9%. Median follow-up duration of all groups was 42 months. Multivariate Cox proportional regression (model-1) analysis showed age (increase 50 to 67 years; HR [hazard ratio]: 1.34, 95% CI 1.18–1.52) and UAR (increase 1.15–1.73; HR: 1.33, 95% CI 1.16–1.52) were associated with mortality. UAR may be a prognostic factor for mortality in STEMI patients and an easily accessible parameter to identify high-risk patients.

Translational Application of Fluorescent Molecular Probes for the Detection of Reactive Oxygen and Nitrogen Species Associated with Intestinal Reperfusion Injury

Acute mesenteric ischemia, caused by an abrupt interruption of blood flow in the mesenteric vessels, is associated with high mortality. When treated with surgical interventions or drugs to re-open the vascular lumen, the reperfusion process itself can inflict damage to the intestinal wall. Ischemia and reperfusion injury comprise complex mechanisms involving disarrangement of the splanchnic microcirculatory flow and impairment of the mitochondrial respiratory chain due to initial hypoxemia and subsequent oxidative stress during the reperfusion phase. This pathophysiologic process results in the production of large amounts of reactive oxygen (ROS) and nitrogen (RNS) species, which damage deoxyribonucleic acid, protein, lipids, and carbohydrates by autophagy, mitoptosis, necrosis, necroptosis, and apoptosis. Fluorescence-based systems using molecular probes have emerged as highly effective tools to monitor the concentrations and locations of these often short-lived ROS and RNS. The timely and accurate detection of both ROS and RNS by such an approach would help to identify early injury events associated with ischemia and reperfusion and increase overall clinical diagnostic sensitivity. This abstract describes the pathophysiology of intestinal ischemia and reperfusion and the early biological laboratory diagnosis using fluorescent molecular probes anticipating clinical decisions in the face of an extremely morbid disease.

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.

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

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

Uric Acid in Inflammation and the Pathogenesis of Atherosclerosis

Hyperuricemia is a common metabolic syndrome. Elevated uric acid levels are risk factors for gout, hypertension, and chronic kidney diseases. Furthermore, various epidemiological studies have also demonstrated an association between cardiovascular risks and hyperuricemia. In hyperuricemia, reactive oxygen species (ROS) are produced simultaneously with the formation of uric acid by xanthine oxidases. Intracellular uric acid has also been reported to promote the production of ROS. The ROS and the intracellular uric acid itself regulate several intracellular signaling pathways, and alterations in these pathways may result in the development of atherosclerotic lesions. In this review, we describe the effect of uric acid on various molecular signals and the potential mechanisms of atherosclerosis development in hyperuricemia. Furthermore, we discuss the efficacy of treatments for hyperuricemia to protect against the development of atherosclerosis.

C-reactive Protein, Free Fatty Acid, and Uric Acid as Predictors of Adverse Events after Endovascular Revascularization of Arterial Femoropopliteal Occlusion Lesions

OBJECTIVES

This study aimed to investigate the relationship between pre-procedure high-sensitivity C-reactive protein (hsCRP), free fatty acid (FFA), and uric acid (UA) levels and post-procedure mortality and morbidity of endovascular revascularization of arterial femoropopliteal occlusion lesions.

METHODS

This was a retrospective review of clinical data retrieved from a prospectively held database in Peking Union Medical College Hospital. A total of 71 Patients who underwent endovascular treatment (EVT) for femoropopliteal occlusive disease between January 1, 2014 and November 1, 2017, were included in this study. Endpoints were defined as major adverse limb events (MALE; target vessel revascularization, amputation, or disease progression) and major adverse cardiovascular events (MACE; stroke, myocardial infarction, or all-cause death) during the entire follow-up period. Univariate and multivariate Cox proportional hazards regression models were used to evaluate the relationship of elevated biomarker levels (hsCRP, FFA and UA, measured by immunoturbidimetry assay, enzymatic assay and enzymatic assay, respectively) to MALE and MACE outcomes.

RESULTS

Seventy-one patients (72 limbs) with sufficient follow-up information were included in the analysis. The mean age was 69.7 ± 8.6 years; 21.1% were female. The Rutherford class of target limbs were ≥ 3. The median follow-up was 36 (range 18-59 months). Univariate analyses revealed that patients with elevated hsCRP levels had an increased risk of MALE (hazard ratio [HR], 2.682; 95% confidence interval [CI], 1.281-5.617, P = 0.009). High FFA levels were associated with an increased risk of MALE (HR, 2.658; 95% CI, 1.075-6.573; P = 0.034). Multivariate analyses demonstrated that elevated hsCRP values (HR, 4.015; 95% CI, 1.628-10.551; P = 0.003) and FFA value (HR, 3.034; 95% CI, 1.102-8.354; P = 0.032) were both significantly associated with increased MALE. Elevated UA levels predicted MACE in the presence of confounders (HR, 11.446; 95% CI, 1.367-95.801 P = 0.023).

CONCLUSION

Pre-procedure hsCRP and FFA levels could serve as predictors of adverse events after EVT in patients with arterial femoropopliteal occlusive disease. The role of UA in MACE may warrant further investigation, because the correlation is not as powerful as the other two in the study.

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 of Plasma Xanthine Oxidoreductase with Arterial Stiffness in Type 2 Diabetes with Liver Dysfunction

BACKGROUND

Type 2 diabetes is a risk factor for atherosclerosis. Oxidative stress, which is a causative factor in insulin resistance, leads to atherosclerosis in patients with diabetes. Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid and is related to oxidative stress. We aimed to examine the influence of plasma XOR activity on arterial stiffness in patients with type 2 diabetes.

METHODS

In total, 458 patients with type 2 diabetes not receiving antihyperuricemic agents were enrolled and their clinical parameters including plasma XOR activity and the cardio-ankle vascular index (CAVI) were measured. Patients were divided into the liver dysfunction and absence of liver dysfunction groups. Multiple regression analysis was performed.

RESULTS

The median plasma XOR activity level was 64.3 pmol/h/mL (33.3-147.3 pmol/h/mL). Plasma XOR activity was correlated significantly and positively with aspartate transaminase and alanine transaminase (ρ > 0.5). The level of plasma XOR activity in the liver dysfunction group was eight-fold higher than that in the absence of liver dysfunction group. A significant positive correlation was observed between plasma XOR activity and the CAVI only in the liver dysfunction group (ρ = 0.3968, P < 0.0043). Multiple regression models demonstrated that plasma XOR activity was an independent predictor of the CAVI in the liver dysfunction group (P = 0.0055).

CONCLUSIONS

Our results suggest that plasma XOR activity is associated with arterial stiffness and may have a role in atherosclerosis development in patients with type 2 diabetes and liver dysfunction.

Simple metabolic markers associated with tophaceous gout

INTRODUCTION

The relationship between tophaceous gout and metabolic markers is not well understood. The aim of this study was to compare the correlations between different metabolic markers and tophi and evaluate their potential predictive values for tophus.

METHOD

We analysed the data of gout patients in Beijing Jishuitan Hospital from 2013 to 2020. Ten laboratory indicators (UA, eGFR, underexcretion, GLU, TRIG, HDL-C, ALT, TBIL, γ-GT and UPH) were included to evaluate the relationship between tophaceous gout and metabolic markers.

RESULTS

Tophi was present in 14.7% (119/808) of gout patients. UA, eGFR, ALT and γ-GT were independently related to the development of tophi; UA and γ-GT were positively correlated. The γ-GT/ALT ratio and UA/eGFR ratio showed a positive correlation with tophi, with (rho, P) of (0.305, < 0.001) and (0.195, < 0.001), respectively. The γ-GT/ALT ratio showed the best classificatory performance (AUC = 0.749, P < 0.001) for tophi among the four positive correlation indicators. With increasing integer γ-GT/ALT ratio, the incidence of tophi (4.9%, 9.7%, 22.3% and 38.4%, P < 0.001), chronic kidney disease (2.5%, 5.2%, 12.3% and 19.2%, P < 0.001) and hyperuricemia over 10 years (6.6%, 10.7%, 18.5% and 26.4%, P < 0.001) showed a progressive increase. The γ-GT/ALT ratio was positively correlated with the number of tophi and duration of hyperuricemia, negatively correlated with eGFR.

CONCLUSIONS

UA, eGFR, γ-GT and ALT were independently associated with tophi. The γ-GT/ALT ratio may be used as a predictor or monitor of tophi.

Data-Driven Cluster Analysis of Oxidative Stress Indexes in relation to Vitamin D Level, Age, and Metabolic Control in Patients with Type 2 Diabetes on Metformin Therapy

Recent advances in vitamin D research indicate that patients with type 2 diabetes mellitus (T2DM) are suffering from vitamin D deficiency and increased oxidative stress to a variable extent, which could produce different health impacts for each individual. The novel multivariate statistical method applied in the present study allows metabolic phenotyping of T2DM individuals based on vitamin D status, metabolic control, and oxidative stress status in order to identify effectively different subtypes in our type 2 DM study population. Data-driven statistical cluster analysis was performed with 95 patients with T2DM, treated with metformin. Clusters were based on 12 variables-age, disease duration, vitamin D level, insulin, fasting glycemia (FG), glycated hemoglobin (HbA1c), high-density and low-density lipoprotein, total cholesterol (TC), triglycerides (TG), body mass index (BMI), and triglycerides/glucose index (TYG). The analysis revealed four unique clusters which differed significantly in terms of vitamin D status, with a mean 25 (OH) D level in cluster 1 (57.84 ± 11.46 nmol/L) and cluster 4 (53.78 ± 22.36 nmol/L), falling within the insufficiency range. Cluster 2 had the highest mean level of 25 (OH) D (84.55 ± 22.66 nmol/L), indicative of vitamin D sufficiency. Cluster 3 had a mean vitamin D level below 50 nmol/L (49.27 ± 16.95), which is considered deficient. Patients in the vitamin D sufficient cluster had a significantly better glycemic and metabolic control as well as a lower level of lipid peroxidation compared to other clusters. The patients from the vitamin D sufficient cluster also had a significantly higher level of vitamin D/MPO, vitamin D/XO, vitamin D/MDA, vitamin D/CAT, and vitamin D/TRC than that in the vitamin deficient and insufficient clusters. The vitamin D deficient cluster included significantly younger patients and had a significantly lower level of AOPP/TRC and albumin/TRC than the vitamin D sufficient cluster. The evidence from our cluster analysis in the context of separated T2DM demonstrates beneficial effects of optimal vitamin D status on metabolic control and oxidative stress in T2DM patients. Older T2DM patients require higher vitamin D levels in order to achieve good metabolic control and favorable antioxidant protection. Since protein damage is more pronounced in these patients, adding water-soluble antioxidant in addition to higher doses of vitamin D should be considered.

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.

Dysregulation of nitric oxide synthases during early and late pathophysiological conditions of diabetes mellitus leads to amassing of microvascular impedement

Diabetes is a major killer worldwide and its unprecedented rise poses a serious threat to mankind. According to recent estimation, 387 million people worldwide are affected from the disease with a prevalence rate of 8.3 and 46.3 % still remains undiagnosed. Important characteristics of diabetes are abnormalities of the physiological signalling functions of reactive oxygen species and reactive nitrogen species. Increased oxidative stress contributes to the activation of stress-sensitive intracellular signalling pathways and the development of gene products that trigger cellular damage and contribute to the vascular complications of diabetes. Growing evidence from studies into many diseases suggests that the pathogenesis of diabetes, obesity, cancer, ageing, inflammation, neurodegenerative disorders, hypertension, apoptosis, cardiovascular diseases, and heart failure are correlated with oxidative stress. This leads to cell metabolism and cell-cell homeostasis to be complexly dysregulated. This review focuses to investigate the status of oxidative stress, nitric oxide and reactive species in early and diabetes. Significance of nitric oxide synthases Evidences has accumulated indicating that the generation of reactive oxygen species (oxidative stress) may play an important role in the etiology of diabetic complications thus attention was given on the reactive oxygen and reactive nitrogen species and their potential role in pathogenesis. Additionally, the therapeutic advances in diabetes management are included. Nanotechnology, statins and stem cell technology are some techniques which can be considered to have a possible future in the treatment sector of diabetes.

Food-Derived Bioactive Peptides with Antioxidative Capacity, Xanthine Oxidase and Tyrosinase Inhibitory Activity

Bioactive peptides (BPs) released by proteases from different food protein sources are often served as antioxidants in food applications. This study aims to investigate 11 BPs derived from fish and egg white as potential natural antioxidants by antioxidant activity assays. The kinetic activity of the BPs against xanthine oxidase (XOD) and tyrosinase was also analyzed. The antioxidative capacity of the BPs indicated that VWWW (VW4, mackerel meat), followed by IRW (IW3, egg white) and VKAGFAWTANQQLS (VS14, tuna backbone protein), possessed the highest antioxidant activity in 1,1-diphenyl-2-picrylhydrazyl radical (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and reducing power (RP) assays. Both the free-radical scavenging score predicted from the AnOxPePred algorithm and the DPPH, ABTS and RP results indicated that VW4 was the best antioxidant. Furthermore, the XOD and tyrosinase inhibition by three selected peptides exhibited competitive patterns of effective inhibition. The half maximal inhibitory concentrations (IC50) of the peptides for XOD inhibition were 5.310, 3.935, and 1.804 mM for VW4, IW3, and VS14, respectively, and they could serve as competitive natural XOD inhibitors. The IC50 of the peptides for tyrosinase inhibition were 1.254, 2.895, and 0.595 mM for VW4, IW3, and VS14, respectively. Overall, VW4, IW3, and VS14 are potential antioxidants and natural XOD inhibitors for preventing milk-fat oxidation, and anti-browning sources for inhibiting food-derived tyrosinase oxidation.

Dietary Annatto-Extracted Tocotrienol Reduces Inflammation and Oxidative Stress, and Improves Macronutrient Metabolism in Obese Mice: A Metabolic Profiling Study

Obesity and its related complications are a world-wide health problem. Dietary tocotrienols (TT) have been shown to improve obesity-associated metabolic disorders, such as hypercholesterolemia, hyperglycemia, and gut dysbiosis. This study examined the hypothesis that the antioxidant capacity of TT alters metabolites of oxidative stress and improves systemic metabolism. C57BL/6J mice were fed either a high-fat diet (HFD control) or HFD supplemented with 800 mg annatto-extracted TT/kg (HFD+TT800) for 14 weeks. Sera from obese mice were examined by non-targeted metabolite analysis using UHPLC/MS. Compared to the HFD group, the HFD+TT800 group had higher levels of serum metabolites, essential amino acids (lysine and methionine), sphingomyelins, phosphatidylcholine, lysophospholipids, and vitamins (pantothenate, pyridoxamine, pyridoxal, and retinol). TT-treated mice had lowered levels of serum metabolites, dicarboxylic fatty acids, and inflammatory/oxidative stress markers (trimethylamine N-oxide, kynurenate, 12,13-DiHOME, and 13-HODE + 9-HODE) compared to the control. The results suggest that TT supplementation lowered inflammation and oxidative stress (oxidized glutathione and GSH/GSSH) and improved macronutrient metabolism (carbohydrates) in obese mice. Thus, TT actions on metabolites were beneficial in reducing obesity-associated hypercholesterolemia/hyperglycemia. The effects of a non-toxic dose of TT in mice support the potential for clinical applications in obesity and metabolic disease.

Uric acid shown to contribute to increased oxidative stress level independent of xanthine oxidoreductase activity in MedCity21 health examination registry

Uric acid has both antioxidant and pro-oxidant properties in vitro by scavenging and production of reactive oxygen species (ROS). This cross-sectional study examined whether uric acid possesses effects on oxidative stress under physiological conditions independent of xanthine oxidoreductase (XOR), which is involved in uric acid and ROS production. Serum uric acid level was measured, while plasma XOR activity was determined using our high-sensitive assay in 192 participants (91 males, 101 females) who underwent health examinations and were not taking an antihyperuricemic agent. For antioxidant potential and oxidative stress level, biological antioxidant potential (BAP) and derivative of reactive oxygen metabolites (d-ROMs) in serum, respectively, were measured. Median uric acid level and plasma XOR activity were 5.6 mg/dL and 26.1 pmol/h/mL, respectively, and BAP and d-ROMs levels were 2112.8 μmol/L and 305.5 Carr U, respectively. Multivariable regression analyses revealed no significant association of serum uric acid level with BAP level, whereas serum uric acid level showed a significant association with d-ROMs level independent of plasma XOR activity (p = 0.045), which was prominent in females (p = 0.036; p for interaction = 0.148). Uric acid might contribute to increased oxidative stress independent of XOR activity by increasing ROS production, without affecting ROS scavenging, especially in females.

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.

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.

Xanthine oxidoreductase-mediated injury is amplified by upregulated AMP deaminase in type 2 diabetic rat hearts under the condition of pressure overload

BACKGROUND

We previously reported that upregulated AMP deaminase (AMPD) contributes to diastolic ventricular dysfunction via depletion of the adenine nucleotide pool in a rat model of type 2 diabetes (T2DM), Otsuka Long-Evans-Tokushima Fatty rats (OLETF). Meanwhile, AMPD promotes the formation of substrates of xanthine oxidoreductase (XOR), which produces ROS as a byproduct. Here, we tested the hypothesis that a functional link between upregulated AMPD and XOR is involved in ventricular dysfunction in T2DM rats.

METHODS AND RESULTS

Pressure-volume loop analysis revealed that pressure overloading by phenylephrine infusion induced severer left ventricular diastolic dysfunction (tau: 14.7 ± 0.8 vs 12.5 ± 0.7 msec, left ventricular end-diastolic pressure: 18.3 ± 1.5 vs 12.2 ± 1.3 mmHg, p < 0.05) and ventricular-arterial uncoupling in OLETF than in LETO, non-diabetic rats, though the baseline parameters were comparable in the two groups. While the pressure overload did not affect AMPD activity, it increased XOR activity both in OLETF and LETO, with OLETF showing significantly higher XOR activity than that in LETO (347.2 ± 17.9 vs 243.2 ± 6.1 μg/min/mg). Under the condition of pressure overload, myocardial ATP level was lower, and levels of xanthine and uric acid were higher in OLETF than in LETO. Addition of exogenous inosine, a product of AMP deamination, to the heart homogenates augmented XOR activity. OLETF showed 68% higher tissue ROS levels and 47% reduction in mitochondrial state 3 respiration compared with those in LETO. Overexpression of AMPD3 in H9c2 cells elevated levels of hypoxanthine and ROS and reduced the level of ATP. Inhibition of XOR suppressed the production of tissue ROS and mitochondrial dysfunction and improved ventricular function under the condition of pressure overload in OLETF.

CONCLUSIONS

The results suggest that increases in the activity of XOR and the formation of XOR substrates by upregulated AMPD contribute to ROS-mediated diastolic ventricular dysfunction at the time of increased cardiac workload in diabetic hearts.

Xanthine oxidoreductase: One enzyme for multiple physiological tasks

Human xanthine oxidoreductase (XOR) is a multiple-level regulated enzyme, resulting from a complicated evolutionary process that assigned it many physiological roles. The main XOR activities are: (i) xanthine dehydrogenase (XDH) activity that performs the last two steps of purine catabolism, from hypoxanthine to uric acid; (ii) xanthine oxidase (XO) activity that, besides purine catabolism, produces reactive oxygen species (ROS); (iii) nitrite reductase activity that generates nitric oxide, contributing to vasodilation and regulation of blood pressure; (iv) NADH oxidase activity that produces ROS. All these XOR activities contribute also to metabolize various endogenous and exogenous compounds, including some drugs. About XOR products, it should be considered that (i) uric acid is not only a proinflammatory agent, but also a fundamental antioxidant molecule in serum and (ii) XOR-derived ROS are essential to the inflammatory defensive response. Although XOR has been the object of a large number of studies, most of them were focused on the pathological consequences of its activity and there is not a clear and schematic picture of XOR physiological roles. In this review, we try to fill this gap, reporting and graphically schematizing the main roles of XOR and its products.

Plasma xanthine oxidoreductase activity in Japanese patients with type 2 diabetes across hospitalized treatment

Aims/Introduction

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes hypoxanthine and xanthine to xanthine and uric acid, respectively. Plasma XOR activity has recently been measured in humans. However, limited information is known about plasma XOR activity in patients with type 2 diabetes mellitus, and its changes after short‐term glycemic control treatment.

Materials and Methods

We enrolled 28 Japanese patients (10 men/18 women) with type 2 diabetes mellitus who were hospitalized to undergo medical treatment for diabetes. Plasma XOR activity, quantified using triple quadrupole mass spectrometry and liquid chromatography, and other clinical parameters were examined at admission and 2 weeks after treatment during hospitalization. Changes in plasma XOR activity after treatment during hospitalization and associated clinical parameters were assessed.

Results

At the time of admission, the median plasma XOR activity was 83.1 pmol/h/mL, with a wide range of 14.4–1150 pmol/h/mL. Multiple regression analysis identified serum aspartate transaminase and alanine transaminase levels as significant and independent factors correlating with the baseline plasma XOR. Two weeks of treatment during hospitalization was associated with a significant decrease in plasma XOR activity. Changes in serum aspartate transaminase were also the only significant and independent factor correlating with changes in plasma XOR activity.

Conclusions

A close relationship was observed between plasma XOR activity and liver transaminases in patients with type 2 diabetes mellitus, cross‐sectionally, and also across treatment during hospitalization.

Metabolomic analysis of the hippocampus in a rat model of chronic mild unpredictable stress-induced depression based on a pathway crosstalk and network module approach

BACKGROUND

The molecular alterations underlying the pathogenesis of depression have not been systematically defined. Increasing evidence suggests that hippocampus metabolism is strongly involved in the pathogenesis of chronic mild unpredictable stress (CUMS)-induced depression. The principal objective of this study was to reveal important information concerning the pathogenesis of depression through a comprehensive analysis of metabolites in the hippocampus in a CUMS rat model.

METHODS

Metabolites related to metabolic changes in the hippocampus in the CUMS model were collected from a depression-specific database and published literature. Potential metabolite pathways were identified by the Omicsolution tool. Then, crosstalk analysis was carried out to investigate the relationship between different important pathways. In addition, MetaboAnalyst was used to analyze potential metabolites for drug-related metabolite enrichment analysis, which was used to study hippocampus metabolite-related drug pathways in a CUMS model. Then, a metabolite-protein interaction (MPI) network was constructed and analyzed to identify important metabolites and proteins. The functional modules were extracted using the CNM network decomposition algorithm. Finally, neurotransmitters in the hippocampus of rats with CUMS depression were detected to verify the important pathways.

RESULTS

In the current study, 53 significantly enriched pathways related to the 107 identified metabolites were selected, and the top ranked enriched pathways included arginine and proline metabolism, neuroactive ligand-receptor interaction, phenylalanine metabolism, bile secretion, and glutathione metabolism. Pathway crosstalk analysis showed that the significantly enriched pathways were divided into two interrelated modules, which were mainly involved in metabolism, signal transduction, neurotransmitters, and the endocrine system. Enrichment analysis of drug-related metabolic KEGG pathways identified the antibiotic pathways as the most important pathways. In the MPI network, the hub metabolites were phosphate, arachidonic acid, oxoglutaric acid, l-glutamic acid, and glutathione, and the hub proteins were Got1, Got2, Tat, Ccbl1, Ccbl2, Il4i1. A total of 16 functional modules were extracted from the MPI network by using the CNM algorithm. Finally, metabolites related to serotonergic synapses, dopaminergic synapses, and glutamatergic synapses were found to be involved in the pathology of depression.

CONCLUSION

We found that neurotransmitter pathways (serotonergic synapses, dopaminergic synapses and glutamatergic synapses) in the hippocampus play a crucial role in the underlying molecular mechanism of depression, which provides useful clues for identifying the detailed depression-associated metabolic profiles.

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.