Plasma Xanthine Oxidoreductase Activity Research Articles

Abstract 1119: Ultrafine Particle Inhalation Initiates Vascular Inflammation Via Hepatic-derived Xanthine Oxidoreductase-mediated Epigenetic Alterations

Introduction: Poor air quality has become a growing health concern. Ultrafine particles (UFP), a component of air pollution, has been associated with cardiovascular disease/ events, establishing a critical need to understand the cellular mechanisms involved. Using a model UFP we have shown elevated vascular oxidant production, and inflammation. However, the underlying mechanisms were unexplored. Xanthine oxidoreductase (XOR), increases in circulation following various insults, which we recently established is actively derived from hepatocytes. The binding of endothelial cells (EC) and the mechanisms by which EC bound XOR mediates impairment are not fully understood. Bound XOR produces almost exclusively H 2 O 2 , which can across the membrane and influence cellular signaling and gene expression. We hypothesize that UFP inhalation elevates hepatic XOR release into circulation and XOR binds to EC initiating redox signaling pathways leading to epigenetic-mediated inflammatory gene upregulation. Methods & Results: Male (M) and female (F) rats and mice (8 wk) were exposed to sham air or UFP for 3 days. Plasma XOR activity increased 5-fold M and 3-fold F exposed to UFP (both p<0.05). We then determined that UFP activation of PKC (rat liver 2.4-fold, mouse liver 2.3-fold, AML12 cells 1.7-fold, all p<0.05) leads to G9a-dependent upregulation and release of XOR in hepatocytes (Control 2± 0.3 vs PMA 8± 1 vs PMA G9a siRNA 2± 2 μU/ml, p<0.05). In arterioles, UFP arterioles showed greater XOR binding when perfused with Alexaflur tagged XOR (69±6 vs 51±4 AFU, p<0.05) and impaired dilation, which was prevented in hepatocyte XOR knockouts mice (KO) (max dilation sham 62± 3 vs UFP 35± 4 vs UFP KO 50± 4, p<0.05). In culture EC were treated with XOR for 1h (for binding) then washed with PBS and cultured for 24 h (XOR-EC). XOR-EC increased demethylase KDM4a expression (1.7-fold, p<0.05) and inflammatory markers ICAM, VCAM, TNF, and TLR4 (p<0.05), leading to enhanced leukocyte adhesion (~2-fold, p<0.05). KDM4a loss of function (iKDM4a) prevented ICAM expression (XOR-EC 8-fold vs iKDM4a 2-fold, p<0.05) and diminished leukocyte adhesion (p<0.05). Conclusion: These findings suggest that vascular inflammation caused by UFP inhalation is mediated in part by an EC bound XOR- KDM4a pathway.

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

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. 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. The median values for plasma XOR activity, serum uric acid, and FMD were 26.6pmol/h/mL, 5.4mg/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). These findings suggest the possibility that XOR contributes to the pathophysiology of impaired VEF through ROS but not uric acid production.

A Newly Developed Method-Based Xanthine Oxidoreductase Activities in Various Human Liver Diseases.

Studies evaluating xanthine oxidoreductase (XOR) activities in comprehensive liver diseases are scarce, and different etiologies have previously been combined in groups for comparison. To accurately evaluate XOR activities in liver diseases, the plasma XOR activities in etiology-based comprehensive liver diseases were measured using a novel, sensitive, and accurate assay that is a combination of liquid chromatography and triple quadrupole mass spectrometry to detect [13C2, 15N2]uric acid using [13C2, 15N2]xanthine as a substrate. We also mainly evaluated the association between the plasma XOR activities and parameters of liver tests, purine metabolism-associated markers, oxidative stress markers, and an inflammation marker. In total, 329 patients and 32 controls were enrolled in our study. Plasma XOR activities were generally increased in liver diseases, especially in the active phase, such as in patients with hepatitis C virus RNA positivity, those with abnormal alanine transaminase (ALT) levels in autoimmune liver diseases, and uncured hepatocellular carcinoma patients. Plasma XOR activities were numerically highest in patients with acute hepatitis B. Plasma XOR activities were closely correlated with parameters of liver tests, especially serum ALT levels, regardless of etiology and plasma xanthine levels. Our results indicated that plasma XOR activity might reflect the active phase in various liver diseases.

Impact of Hyper- and Hypo-Uricemia on Kidney Function.

Uric acid (UA) forms monosodium urate (MSU) crystals to exert proinflammatory actions, thus causing gout arthritis, urolithiasis, kidney disease, and cardiovascular disease. UA is also one of the most potent antioxidants that suppresses oxidative stress. Hyper andhypouricemia are caused by genetic mutations or polymorphism. Hyperuricemia increases urinary UA concentration and is frequently associated with urolithiasis, which is augmented by low urinary pH. Renal hypouricemia (RHU) is associated with renal stones by increased level of urinary UA, which correlates with the impaired tubular reabsorption of UA. Hyperuricemia causes gout nephropathy, characterized by renal interstitium and tubular damage because MSU precipitates in the tubules. RHU is also frequently associated with tubular damage with elevated urinary beta2-microglobulin due to increased urinary UA concentration, which is related to impaired tubular UA reabsorption through URAT1. Hyperuricemia could induce renal arteriopathy and reduce renal blood flow, while increasing urinary albumin excretion, which is correlated with plasma xanthine oxidoreductase (XOR) activity. RHU is associated with exercise-induced kidney injury, since low levels of SUA could induce the vasoconstriction of the kidney and the enhanced urinary UA excretion could form intratubular precipitation. A U-shaped association of SUA with organ damage is observed in patients with kidney diseases related to impaired endothelial function. Under hyperuricemia, intracellular UA, MSU crystals, and XOR could reduce NO and activate several proinflammatory signals, impairing endothelial functions. Under hypouricemia, the genetic and pharmacological depletion of UA could impair the NO-dependent and independent endothelial functions, suggesting that RHU and secondary hypouricemia might be a risk factor for the loss of kidney functions. In order to protect kidney functions in hyperuricemic patients, the use of urate lowering agents could be recommended to target SUA below 6 mg/dL. In order to protect the kidney functions in RHU patients, hydration and urinary alkalization may be recommended, and in some cases an XOR inhibitor might be recommended in order to reduce oxidative stress.

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.

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.

The Effects of Topiroxostat, a Selective Xanthine Oxidoreductase Inhibitor, on Arterial Stiffness in Hyperuricemic Patients with Liver Dysfunction: A Sub-Analysis of the BEYOND-UA Study

The effects of uric acid (UA)-lowering therapy with xanthine oxidoreductase (XOR) inhibitors on the development of cardiovascular diseases remain controversial. Based on recent findings that plasma XOR activity increased in liver disease conditions, we conducted a sub-analysis of the BEYOND-UA study to examine the differential effects of topiroxostat on arterial stiffness based on liver function in hyperuricemic individuals with hypertension. Sixty-three subjects treated with topiroxostat were grouped according to baseline alanine aminotransferase (ALT) levels (above or below cut-off values of 22, 30, or 40 U/L). The primary endpoint was changes in the cardio-ankle vascular index (CAVI) from baseline to 24 weeks. Significant reductions in CAVI during topiroxostat therapy occurred in subjects with baseline ALT ≥30 U/L or ≥40 U/L, and significant between-group differences were detected. Brachial-ankle pulse wave velocity significantly decreased in the ALT-high groups at all cut-off values. Reductions in morning home blood pressure and serum UA were similar regardless of the baseline ALT level. For eleven subjects with available data, ALT-high groups showed high plasma XOR activity, which was significantly suppressed by topiroxostat. Topiroxostat improved arterial stiffness parameters in hyperuricemic patients with liver dysfunction, which might be related to its inhibitory effect on plasma XOR.

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

BackgroundXanthine 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. MethodsWe 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. ResultsHF-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. ConclusionsHF-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.

Systemic Endothelial Function, Plasma Xanthine Oxidoreductase Activity, and Blood Pressure Variability in Patients with Stable Coronary Artery Disease.

Background and Objectives: Although previous studies showed that an activity of xanthine oxidoreductase (XOR), a rate-limiting enzyme in purine metabolism, beyond the serum uric acid level, was associated with the development of coronary artery disease (CAD), the underlying mechanisms are unclear. Because endothelial dysfunction and a greater blood pressure (BP) variability may play a role, we investigated the relations among the endothelial function, XOR, and BP variability. Materials and Methods: This was a post-hoc study using pooled data of patients with a stable CAD from two prospective investigations, in which the systemic endothelial function was assessed with the reactive hyperemia index (RHI) and the XOR activity was measured. The BP variability was evaluated using BP measurements during the three- and four-day hospitalization. Results: A total of 106 patients with a stable CAD undergoing a percutaneous coronary intervention were included. Of the 106 patients, 46 (43.4%) had a systemic endothelial dysfunction (RHI < 1.67). The multivariable analysis identified a higher body mass index (BMI), female gender, and diabetes as factors associated with an endothelial dysfunction. A higher BMI was also related to an elevated XOR activity, in addition to current smoking. No significant correlation was observed between the RHI and XOR activity. Similarly, the in-hospital BP variability was associated with neither the endothelial function nor XOR. Conclusions: Among patients with a stable CAD, several factors were identified as being associated with a systemic endothelial dysfunction or an elevated XOR activity. However, no direct relations between the endothelial function, XOR, and BP variability were found.

Xanthine oxidoreductase activity is correlated with hepatic steatosis

The enzyme xanthine oxidoreductase (XOR) catalyzes the synthesis of uric acid (UA) from hypoxanthine and xanthine, which are products of purine metabolism starting from ribose-5-phosphate. Several studies suggested a relationship between hyperuricemia and hepatic steatosis; however, few previous studies have directly examined the relationship between XOR activity and hepatic steatosis. A total of 223 subjects with one or more cardiovascular risk factors were enrolled. The liver-to-spleen (L/S) ratio on computed tomography and the hepatic steatosis index (HSI) were used to assess hepatic steatosis. We used a newly developed highly sensitive assay based on [13C2, 15N2] xanthine and liquid chromatography/triple quadrupole mass spectrometry to measure plasma XOR activity. Subjects with the L/S ratio of < 1.1 and the HSI of < 36 had increased XOR activity and serum UA levels. Independent of insulin resistance and serum UA levels, multivariate logistic regression analysis revealed that plasma XOR activity was associated with the risk of hepatic steatosis as assessed by the L/S ratio and HSI. According to the findings of this study, plasma XOR activity is associated with hepatic steatosis independent of insulin resistance and serum UA levels.

Possible role of insulin resistance in activation of plasma xanthine oxidoreductase in health check-up examinees

We previously found an association of insulin resistance (IR) with plasma xanthine oxidoreductase (XOR) activity in a cross-sectional study. However, whether IR induces increased XOR activity has not been elucidated. This retrospective longitudinal observational study included 347 participants (173 males, 174 females) who underwent annual health examinations and were medication naïve. Homeostasis model assessment of IR (HOMA-IR) index, and physical and laboratory measurements were determined at the baseline. At baseline and 12-month follow-up examinations, plasma XOR activity was determined using our novel assay based on [13C2,15N2] xanthine and liquid chromatography/triple quadrupole mass spectrometry. Subjects with IR, defined as HOMA-IR index ≥ 1.7 (n = 92), exhibited significantly (p < 0.001) higher plasma XOR activity levels than those without IR (n = 255), with an increase in that activity seen in 180 (51.9%) after 12 months. Multivariable linear and logistic regression analyses showed that IR, but not BMI or waist circumference, at baseline was significantly associated with plasma XOR activity (β = 0.094, p = 0.033) and increased plasma XOR activity over the 12-month period (odds ratio, 1.986; 95% confidence interval, 1.048–3.761; p = 0.035), after adjustments for various clinical parameters, including plasma XOR activity at baseline. These results suggest that IR induces increased plasma XOR activity in a manner independent of adiposity.

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 yr) 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.NEW & NOTEWORTHY This study is the first to show marathon running transiently increases plasma XOR activity and levels of purine degradation products (hypoxanthine, xanthine, and uric acid), and further to demonstrate that activated plasma XOR may contribute to marathon-induced elevations in biomarkers of AKI. These findings significantly extend our prior knowledge of the purine metabolic pathway and several AKI biomarkers under strenuous exercise conditions.

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.

Association between Plasma Xanthine Oxidoreductase Activity and the Renal Function in a General Japanese Population: The Tohoku Medical Megabank Community-Based Cohort Study

Introduction: Xanthine oxidoreductase (XOR) has been identified as a critical source of reactive oxygen species in various pathophysiological conditions, including hypertension, endothelial dysfunction, and atherosclerosis. This study investigated the association between XOR and renal function in a general Japanese population. Methods: The Iwate Tohoku Medical Megabank Organization pooled individual participant data from a community-based cohort study in Iwate prefecture. Chronic kidney disease (CKD) was estimated using the estimated glomerular filtration rate of cystatin C (eGFRcys). Individuals with a history of hyperuricemia or severe renal dysfunction (eGFRcys <15 mL/min/1.73 m² or undergoing dialysis) were excluded from the study. We performed a multinominal multivariate logistic analysis adjusted for age, blood pressure, uric acid, glycated hemoglobin A1c, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol to associate XOR activity and renal function. Results: The present study included 4,248 participants (male/female: 1,373/2,875, age: 62.9 ± 11.7 years). When participants were divided according to XOR quartiles, blood pressure, body mass index, uric acid, low-density lipoprotein cholesterol, and glycated hemoglobin A1c were highest in the highest XOR quartile (all p < 0.001). The XOR activity was significantly higher in the subgroup with CKD stage G3 and G4 (G1 vs. G2 vs. G3-G4: 44.8 ± 40.5 vs. 52.0 ± 42.9 vs. 54.1 ± 43.9 pmol/h/mL, p = 0.02). The higher XOR activity was significantly associated with an increase of CKD stage: the odd ratios (95% confidence intervals) per 1 pmol/h/mL increase in XOR activity with CKD stage G1 as a reference were 1.37 (1.13–1.73) in G2 and 1.51 (1.30–1.84) in G3-G4. Conclusion: The present study concluded that high XOR activity was associated with the severity of CKD in a general Japanese population, suggesting that upregulated XOR activity may be involved in advanced renal dysfunction.

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.

Gender differences in the impact of plasma xanthine oxidoreductase activity on coronary artery spasm

Abstract Background It has been reported that decreased nitric oxide bioavailability due to increased reactive oxygen species (ROS) is one of the most important causes of coronary artery spasm (CAS). Xanthine oxidoreductase (XOR) is the rate-limiting enzyme for uric acid (UA) production and plays a pivotal role in generating ROS. It was reported that the gender differences exist in the impact of serum UA levels on cardiovascular risks. We previously demonstrated that increased plasma XOR activity is significantly associated with the incidence of CAS. However, the gender differences in the impact of plasma XOR activity on CAS remain unclear. Purpose The aim of this study was to examine the gender differences in the clinical impact of plasma XOR activity on CAS. Methods We investigated plasma XOR activity in 132 patients suspected for CAS (male, n=78; female, n=54), and underwent intracoronary acetylcholine provocation test. XOR activity assay was performed using stable isotope-labeled substrate and liquid chromatography-triple quadrupole mass spectrometry. Provoked CAS was defined as total or subtotal occlusion (≥90%) with accompanying symptoms of chest pain and/or ischemic ST-segment changes on the electrocardiogram. We excluded the patients who had significant coronary artery stenosis (≥50%) and/or were taking XOR inhibitors. Results Plasma XOR activity was significantly lower in female compared with male patients (30.3 pmol/h/mL, interquartile range (IQR) 22.8–42.7 vs. 51.7 pmol/h/mL, IQR 34.7–101.8; P&amp;lt;0.001). CAS was provoked in 36 male patients and 17 female patients, and they each had significantly higher plasma XOR activity compared with those without, respectively. Multivariate logistic regression analysis showed that plasma XOR activity was independently associated with the incidence of CAS in both genders after adjustment for confounding factors. The optimal cut-off values for predicting CAS were lower in female than those in male patients (52.3 vs. 91.6 pmol/h/mL). Multivariate analysis demonstrated that female patients with high XOR activity (≥52.3 pmol/h/mL; odds ratio [OR] 22.6, P&amp;lt;0.001) exhibited a higher incidence of CAS compared with that in male patients (≥91.6 pmol/h/mL; OR 8.2, P&amp;lt;0.001). Conclusions Plasma XOR activity was an independent predictor for the incidence of CAS in both genders. The impact of plasma XOR activity on CAS was stronger in female patients than in male patients. Funding Acknowledgement Type of funding sources: None. Figure 1Figure 2

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

BackgroundType 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. MethodsIn 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. ResultsThe 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). ConclusionsOur 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.

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

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. 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. 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. 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.

Increased plasma XOR activity induced by NAFLD/NASH and its possible involvement in vascular neointimal proliferation

Xanthine oxidoreductase (XOR) is an enzyme that catalyzes hypoxanthine to xanthine and xanthine to uric acid, respectively. However, the underlying mechanisms of increased plasma XOR and its pathological roles in systemic diseases, such as atherosclerosis, are not fully understood. In this study, we found that changes in plasma XOR activity after bariatric surgery closely associated with those in liver enzymes, but not with those in BMI. In a mouse model of nonalcoholic fatty liver disease/steatohepatitis (NAFLD/NASH), plasma XOR activity markedly increased. Besides, purine catabolism was accelerated in the plasma per se of NASH mice and human patients with high XOR activity. In our NASH mice, we observed an increased vascular neointima formation consisting of dedifferentiated vascular smooth muscle cells (SMCs), which was significantly attenuated by topiroxostat, a selective XOR inhibitor. In vitro, human liver S9–derived XOR promoted proliferation of SMCs with phenotypic modulation and induced ROS production by catabolizing hypoxanthine released from human endothelial cells. Collectively, the results from human and mouse models suggest that increased plasma XOR activity, mainly explained by excess hepatic leakage, was involved in the pathogenesis of vascular injury, especially in NAFLD/NASH conditions.

Impact of Plasma Xanthine Oxidoreductase Activity on the Mechanisms of Distal Symmetric Polyneuropathy Development in Patients with Type 2 Diabetes.

To unravel associations between plasma xanthine oxidoreductase (XOR) and diabetic vascular complications, especially distal symmetric polyneuropathy (DSP), we investigated plasma XOR activities using a novel assay. Patients with type 2 diabetes mellitus (T2DM) with available nerve conduction study (NCS) data were analyzed. None were currently taking XOR inhibitors. XOR activity of fasting blood samples was assayed using a stable isotope-labeled substrate and LC-TQMS. JMP Clinical version 5.0. was used for analysis. We analyzed 54 patients. Mean age was 64.7 years, mean body mass index was 26.0 kg/m2, and mean glycated hemoglobin was 9.4%. The logarithmically transformed plasma XOR activity (ln-XOR) correlated positively with hypoxanthine, xanthine, visceral fatty area, and liver dysfunction but negatively with HDL cholesterol. ln-XOR correlated negatively with diabetes duration and maximum intima-media thickness. Stepwise multiple regression analysis revealed ln-XOR to be among selected explanatory factors for various NCS parameters. Receiver operating characteristic curves showed the discriminatory power of ln-XOR. Principal component analysis revealed a negative relationship of ln-XOR with F-waves as well as positive relationships of ln-XOR with hepatic steatosis and obesity-related disorders. Taken together, our results show plasma XOR activity to be among potential disease status predictors in T2DM patients. Plasma XOR activity measurements might reliably detect pre-symptomatic DSP.