Background:Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the formation of uric acid from hypoxanthine and xanthine, leading to an increase in superoxide and reactive oxygen species. ...Activation of XOR promotes oxidative stress-related tissue injury. We investigated the associations between metabolic parameters and plasma XOR activity measured by a sensitive and accurate assay using a combination of liquid chromatography and triple quadrupole mass spectrometry to detect 13C2,15N2-uric acid using 13C2,15N2-xanthine as a substrate.Methods and Results:A total of 627 Japanese subjects (M/F, 292/335) from the Tanno-Sobetsu Study, a population-based cohort, were recruited. Plasma XOR activity was significantly higher in males than in females, and habitual smoking was associated with elevation of activity. Plasma XOR activity was positively correlated with body mass index (BMI; r=0.323, P<0.001), waist circumference, blood pressure, and levels of liver enzymes including alanine transaminase (r=0.694, P<0.001), uric acid (r=0.249, P<0.001), triglycerides (r=0.312, P<0.001), hemoglobin A1c, fasting glucose, insulin and HOMA-R (r=0.238, P<0.001) as a marker of insulin resistance and was negatively correlated with high-density lipoprotein cholesterol level. On stepwise and multivariate regression analyses, BMI, smoking and levels of alanine transaminase, uric acid, triglycerides and HOMA-R were independent predictors of plasma XOR activity after adjustment for age and gender.Conclusions:Plasma XOR activity is a novel biomarker of metabolic disorders in a general population.
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.
•Plasma xanthine oxidoreductase (XOR) activity is elevated in various pathologies (82).•We present a 13C2,15N2 xanthine-LC/triple quadrupole MS method for XOR detection (84).•Linear 13C2,15N2UA ...product detection was observed over 4–4000nM (r2>0.995) (81).•Plasma XOR correlated with uric acid and alanine and aspartate transaminase levels (84).•LC/TQMS is more rapid with higher sensitivity and specificity than current methods (85).
Associations between elevated plasma xanthine oxidoreductase (XOR) activity and various pathologies have been widely reported. However, it has been difficult to accurately measure human plasma XOR activity because the XOR activity of humans is lower than that of animals such as mouse. We developed a highly sensitive assay for XOR activity utilizing a combination of 13C2,15N2 xanthine and liquid chromatography/triple quadrupole mass spectrometry. In the present study, we established and validated a novel human plasma XOR activity assay utilizing this technique. The calibration curve of 13C2,15N2uric acid showed linearity over the range of 4–4000nM (r2>0.995) with a lower limit of quantitation of 4nM which corresponds to an XOR activity of 6.67pmol/h/mL plasma. Intra- and inter-assay coefficients of variation of pooled human plasma XOR activity were 6.5% and 9.1%, respectively. Plasma XOR activities of 20 healthy volunteers ranged from 32.8 to 227pmol/h/mL (mean±SD=89.1±55.1, n=20), which correlated with alanine transaminase (r=0.827), aspartate transaminase (r=0.487), and uric acid (r=0.502). The established assay is expected to be useful for investigating the function of XOR and the effect of its inhibitors in various diseases.
Topiroxostat, a xanthine oxidoreductase (XOR) inhibitor, has been shown to decrease the urinary albumin-to-creatinine ratio compared with placebo in hyperuricemic patients with stage 3 chronic kidney ...disease. Thus, we aimed to ascertain the albuminuria-lowering effect of topiroxostat in diabetic mouse. Db/db mice were fed standard diets with or without topiroxostat (0.1, 0.3, 1, and 3mg/kg/day) and febuxostat (0.1, 0.3, and 1mg/kg/day) for four weeks. Urinary albumin and purine bodies levels, XOR activities, and drug concentrations in the liver, kidney, and plasma were measured. Moreover, the XOR inhibitory activity of each XOR inhibitor was evaluated with or without an exogenous protein in vitro. Topiroxostat decreased dose-dependently the urinary albumin excretion, but febuxostat did not show such a tendency. Treatment with topiroxostat inhibited plasma XOR activity with dose-dependent increase in plasma purine levels, which was not observed by febuxostat. Pharmacokinetic/pharmacodynamic analysis revealed that topiroxostat and febuxostat concentration in each tissue showed a good correlation with both the hypouricemic effect and plasma drug concentration, whereas the change in albuminuria correlated neither with the change in uric acid nor with drug concentration in plasma. However, the change in urinary albumin and plasma XOR activity showed good correlation in topiroxostat group. The 50% inhibitory concentration (IC50 value) of febuxostat against plasma XOR in vitro was 12-fold higher than that of topiroxostat, and increased by approximately 13-fold by interfering with an exogenous protein. Topiroxostat caused reduced urinary albumin excretion, in which potent inhibition of the plasma XOR activity might be involved.
Background
Constipation is frequently observed in patients with chronic kidney disease (CKD). Lactulose is expected to improve the intestinal environment by stimulating bowel movements as a ...disaccharide laxative and prebiotic. We studied the effect of lactulose on renal function in adenine-induced CKD rats and monitored uremic toxins and gut microbiota.
Methods
Wistar/ST male rats (10-week-old) were fed 0.75% adenine-containing diet for 3 weeks to induce CKD. Then, they were divided into three groups and fed as follows: control, normal diet; and 3.0- and 7.5-Lac, 3.0% and 7.5% lactulose-containing diets, respectively, for 4 weeks. Normal diet group was fed normal diet for 7 weeks. The rats were observed for parameters including renal function, uremic toxins, and gut microbiota.
Results
The control group showed significantly higher serum creatinine (sCr) and blood urea nitrogen (BUN) 3 weeks after adenine feeding than at baseline, with a 8.5-fold increase in serum indoxyl sulfate (IS). After switching to 4 weeks of normal diet following adenine feeding, the sCr and BUN in control group remained high with a further increase in serum IS. In addition, tubulointerstitial fibrosis area was increased in control group. On the other hand, 3.0- and 7.5-Lac groups improved sCr and BUN levels, and suppressed tubulointerstitial fibrosis, suggesting preventing of CKD progression by lactulose. Lac groups also lowered level of serum IS and proportions of gut microbiota producing IS precursor.
Conclusion
Lactulose modifies gut microbiota and ameliorates CKD progression by suppressing uremic toxin production.
Xanthine oxidoreductase (XOR) catalyzes the oxidation of hypoxanthine to xanthine, and of xanthine to uric acid. XOR also enhances the production of reactive oxygen species and causes endothelial ...dysfunction. In this study, we evaluated the association of XOR and its substrate with the vascular complications in 94 Japanese inpatients with type 2 diabetes (T2DM). The plasma XOR activity and plasma xanthine levels were positively correlated with the body mass index, aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-GTP, fasting plasma insulin, and the homeostasis model of assessment of insulin resistance (HOMA-IR), and negatively correlated with the high density lipoprotein cholesterol. The plasma XOR activity also showed a positive correlation with the serum triglyceride. Multivariate analyses identified AST, ALT, fasting plasma insulin and HOMA-IR as being independently associated with the plasma XOR activity. The plasma XOR activity negatively correlated with the duration of diabetes, and positively correlated with the coefficient of variation of the R-R interval and sensory nerve conduction velocity. Furthermore, the plasma XOR activity was significantly decreased in patients with coronary artery disease. Thus, the plasma XOR activity might be a surrogate marker for the development of vascular complications, as well as liver dysfunction and insulin resistance, in T2DM.Trial registration: This study is registered at the UMIN Clinical Trials Registry (UMIN000029970; https://www.umin.ac.jp/ctr/index-j.htm ). The study was conducted from Nov 15, 2017.
Xanthine 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.
Aims/Introduction
Uric acid is synthesized by oxidation of hypoxanthine and xanthine using a catalyzing enzyme, xanthine oxidoreductase (XOR), which can be a source of reactive oxygen species. Plasma ...XOR activity is a metabolic biomarker associated with obesity, hyperuricemia, liver dysfunction and insulin resistance. However, it has recently been reported that XOR activity in fat tissue is low in humans, unlike in rodents, and that hypoxanthine is secreted from human fat tissue.
Materials and Methods
The associations of obesity with hypoxanthine, xanthine and plasma XOR activity were investigated in 484 participants (men/women: 224/260) of the Tanno‐Sobetsu Study.
Results
Levels of hypoxanthine, xanthine and plasma XOR activity were significantly higher in men than in women. In 59 participants with hyperuricemia, 11 (men/women: 11/0) participants were being treated with an XOR inhibitor and had a significantly higher level of xanthine, but not hypoxanthine, than that in participants without treatment. In all of the participants, hypoxanthine concentration in smokers was significantly higher than that in non‐smokers. Stepwise and multivariate regression analyses showed that body mass index, smoking habit and xanthine were independent predictors of hypoxanthine after adjustment of age, sex and use of antihyperuricemic drugs. Whereas, alanine transaminase, hypoxanthine and plasma XOR activity were independent predictors for xanthine, and alanine transaminase, triglycerides and xanthine were independent predictors for plasma XOR activity.
Conclusions
The concentration of hypoxanthine, but not that of xanthine, is independently associated with obesity and smoking habit, indicating differential regulation of hypoxanthine and xanthine in a general population.
In the present study, we investigated the associations of obesity with hypoxanthine, xanthine and plasma xanthine oxidoreductase activity in 484 participants from the general population. The concentration of hypoxanthine was independently associated with body mass index and smoking habit, whereas the level of xanthine was associated with parameters of mainly purine metabolism in the liver, including alanine transaminase, hypoxanthine and plasma xanthine oxidoreductase activity, indicating differential regulation of hypoxanthine and xanthine in a general population. In obesity, human adipose tissue would be a source of hypoxanthine as a substrate of xanthine oxidoreductase in the purine metabolism pathway.
Xanthine oxidoreductase (XOR) inhibitor administration reduces uric acid and reactive oxygen species (ROS) production, and also lowers blood pressure (BP). However, the associations of plasma XOR ...activity, uric acid level, and oxidative stress levels with BP remain unclear. This cross-sectional study included 156 subjects (68 males, 88 females) registered in the MedCity21 health examination registry without anti-hypertensive or anti-hyperuricemic agent administration. Plasma XOR activity was measured using our highly sensitive novel assay, which is unaffected by uric acid in the sample. BP was also determined, and serum uric acid and derivative of reactive oxygen metabolites (d-ROMs) levels were simultaneously measured. Median plasma XOR activity, serum uric acid, d-ROMs, and mean arterial pressure (MAP) values were 25.7 pmol/h/mL, 5.4 mg/dL, 305 Carr U, and 89.0 mmHg, respectively. Multiple regression analysis showed that plasma XOR activity (β = 0.211, p = 0.019), but not serum uric acid (β = 0.072, p = 0.502), was significantly associated with MAP. In subjects with lower but not higher d-ROMs level, an independent association of plasma XOR activity with MAP was observed (β = 0.428, p = 0.001 and β = 0.019, p = 0.891, respectively; p for interaction = 0.046). XOR may contribute to the pathophysiology of higher BP through ROS but not uric acid production, especially in patients with lower oxidative stress.
Aims/Introduction
Xanthine oxidoreductase (XOR) is a rate‐limiting enzyme that catalyzes uric acid formation in the purine metabolism, is involved in an increase in reactive oxygen species. Plasma ...XOR activity has been shown to be associated with obesity, smoking, liver dysfunction, hyperuricemia, dyslipidemia and insulin resistance.
Materials and Methods
The association between plasma XOR activity, measured by using liquid chromatography and mass spectrometry, and levels of adipokines, including adiponectin, fatty acid‐binding protein 4 (FABP4) and fibroblast growth factor 21 (FGF21), was investigated in 282 participants (male/female: 126/156) of the Tanno‐Sobetsu Study who were not taking medication.
Results
Women had lower plasma XOR activity than did men. Smoking habit was associated with increased activity. Plasma XOR activity was positively correlated with concentrations of FABP4 (r = 0.192, P < 0.001) and FGF21 (r = 0.208, P < 0.001), homeostasis model assessment of insulin resistance as an index of insulin resistance and uric acid, and was negatively correlated with adiponectin level (r = −0.243, P = 0.001). Multivariate regression analyses showed that levels of adiponectin, FABP4 and FGF21 were independent determinants of plasma XOR activity after adjusting age, sex, uric acid and homeostasis model assessment of insulin resistance. With additional adjustment of smoking habit, the level of FABP4, but not that of adiponectin or FGF21, remained as an independent predictor of plasma XOR activity.
Conclusions
Plasma XOR activity was independently associated with levels of adipokines in a general population of individuals not taking medication.
Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the formation of uric acid from hypoxanthine and xanthine, leading to an increase in reactive oxygen species. Plasma XOR activity was independently associated with several adipokines, including fatty acid‐binding protein 4 (FABP4), adiponectin and fibroblast growth factor 21 (FGF21), in a general population of individuals not taking medication.
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