Xanthine oxidase and cardiovascular risk in obese children

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

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

Malondialdehyde as an independent predictor of body mass index in adolescent girls

Background

Given the fact that the studies that examined oxidative stress in relation to obesity that included late adolescents are scarce and show inconclusive results we aimed to investigate a wide spectrum of nitro-oxidative stress biomarkers i.e., malondialdehyde (MDA), xanthine oxidase (XO), xanthine oxidoreductase (XOD), xanthine dehydrogenase (XDH), advanced oxidation protein products (AOPP) and nitric oxide products (NOx), as well as an antioxidative enzyme, i.e., catalase (CAT) in relation with obesity in the cohort of adolescent girls ages between 16 and 19 years old.

Methods

A total of 59 teenage girls were included in this cross-sectional study. Binary logistic regression analysis was performed to examine possible associations between biochemical and nitro-oxidative stress markers and body mass index (BMI).

Results

There were not significant differences between oxidative stress markers between normal weight and overweight/obese girls (i.e., AOPP, XOD, XO, XDH) and CAT, except for MDA (p<0.001) and NOx (p=0.010) concentrations which were significantly higher in overweight/obese adolescent girls. Positive associations were evident between BMI and high sensitivity C-reactive protein (hsCRP) (OR=2.495), BMI and uric acid (OR=1.024) and BMI and MDA (OR=1.062). Multivariable binary regression analysis demonstrated significant independent associations of BMI and hsCRP (OR=2.150) and BMI and MDA (OR=1.105). Even 76.3% of the variation in BMI could be explained with this Model.

Conclusions

Inflammation (as measured with hsCRP) and oxidative stress (as determined with MDA) independently correlated with BMI in teenage girls.

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.

Assessment of the relationship between serum xanthine oxidase levels and type 2 diabetes: a cross-sectional study

Xanthine oxidase (XO) is an enzyme associated with purine metabolism. The relationship between XO levels and type 2 diabetes (T2D) is not clear yet or little is known so far. Therefore, we conducted a cross-sectional study to determine the association of XO levels with T2D in a Bangladeshi adult cohort. A total of 325 participants (234 males and 91 females) were enrolled in the study. The participants were divided into three groups; diabetic (n = 173), prediabetic (n = 35), and non-diabetic control (n = 117). Serum levels of XO were measured by enzyme-linked immunosorbent assay (ELISA) and other biochemical parameters including fasting blood glucose (FBG), serum uric acid (SUA), and lipid profile markers measured by colorimetric methods. Participants with T2D were confirmed according to the definition of the American Diabetic Association. The association between serum XO levels and T2D was determined by logistic regression models. The mean level of serum XO was significantly higher in females (6.0 ± 3.7 U/L) compared to male (4.0 ± 2.8 U/L) participants (p < 0.001). In contrast, males had a higher mean level of SUA (6.1 ± 1.9 mg/dL) than female (4.4 ± 1.9 mg/dL) participants (p < 0.001). The mean level of XO was significantly higher in the diabetic group (5.8 ± 3.6 U/L) compared to the prediabetic (3.7 ± 1.9 U/L) and control (2.9 ± 1.8 U/L) groups (p < 0.001). On the other hand, the mean SUA concentration was significantly lower in the diabetic group than in the other two groups (p < 0.001). A significant increasing trend was observed for FBG levels across the XO quartiles (p < 0.001). A decreasing trend was found for SUA levels in the XO quartiles (p < 0.001). Serum levels of XO and SUA showed a positive and negative correlation with FBG, respectively. In regression analysis, serum XO levels showed an independent association with T2D. In conclusion, this study reports a positive and independent association between XO levels and T2D in Bangladeshi adults. Monitoring serum levels of XO may be useful in reducing the risk of T2D. Further research is needed to determine the underlying mechanisms of the association between elevated XO levels and T2D.

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.

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.

Influence of xanthine oxidoreductase inhibitor, topiroxostat, on body weight of diabetic obese mice

Plasma xanthine oxidoreductase (XOR) activity is high in metabolic disorders such as diabetic mellitus, obesity, or overweight. Thus, this study investigated whether the XOR inhibitor, topiroxostat, affected body weight. Male db/db mice were fed standard diets with or without topiroxostat for 4 weeks. Body weight and food intake were constantly monitored, along with monitoring plasma biochemical markers, including insulin and XOR activity. Additionally, hepatic hypoxanthine and XOR activity were also documented. Single regression analysis was performed to determine the mechanism. Topiroxostat treatment suppressed weight gain relative to the vehicle without any impact on food intake. However, the weight of fat pads and hepatic and muscle triglyceride content did not change. Topiroxostat decreased the plasma uric acid and increased hepatic hypoxanthine in response to the inhibition of XOR activity. Plasma ketone body and free fatty acid were also increased. Moreover, fat weight was weakly associated with plasma XOR activity in the diabetic state and was negatively associated with ketone body by topiroxostat. These results suggested that topiroxostat amplified the burning of lipids and the salvage pathway, resulting in predisposing the body toward catabolism. The inhibition of plasma XOR activity may contribute to weight loss.

Oxidative Stress and Vascular Damage in the Context of Obesity: The Hidden Guest

The vascular system plays a central role in the transport of cells, oxygen and nutrients between different regions of the body, depending on the needs, as well as of metabolic waste products for their elimination. While the structure of different components of the vascular system varies, these structures, especially those of main arteries and arterioles, can be affected by the presence of different cardiovascular risk factors, including obesity. This vascular remodeling is mainly characterized by a thickening of the media layer as a consequence of changes in smooth muscle cells or excessive fibrosis accumulation. These vascular changes associated with obesity can trigger functional alterations, with endothelial dysfunction and vascular stiffness being especially common features of obese vessels. These changes can also lead to impaired tissue perfusion that may affect multiple tissues and organs. In this review, we focus on the role played by perivascular adipose tissue, the activation of the renin-angiotensin-aldosterone system and endoplasmic reticulum stress in the vascular dysfunction associated with obesity. In addition, the participation of oxidative stress in this vascular damage, which can be produced in the perivascular adipose tissue as well as in other components of the vascular wall, is updated.

Hydrogen sulfide stimulates xanthine oxidoreductase conversion to nitrite reductase and formation of NO

Cardiovascular disease is the leading cause of death and disability worldwide with increased oxidative stress and reduced NO bioavailability serving as key risk factors. For decades, elevation in protein abundance and enzymatic activity of xanthine oxidoreductase (XOR) under hypoxic/inflammatory conditions has been associated with organ damage and vascular dysfunction. Recent reports have challenged this dogma by identifying a beneficial function for XOR, under similar hypoxic/acidic conditions, whereby XOR catalyzes the reduction of nitrite (NO2-) to nitric oxide (NO) through poorly defined mechanisms. We previously reported that hydrogen sulfide (H2S/sulfide) confers significant vascular benefit under these same conditions via NO2- mediated mechanisms independent of nitric oxide synthase (NOS). Here we report for the first time the convergence of H2S, XOR, and nitrite to form a concerted triad for NO generation. Specifically, hypoxic endothelial cells show a dose-dependent, sulfide and polysulfide (diallyl trisulfide (DATS)-induced, NOS-independent NO2- reduction to NO that is dependent upon the enzymatic activity of XOR. Interestingly, nitrite reduction to NO was found to be slower and more sustained with DATS compared to H2S. Capacity for sulfide/polysulfide to produce an XOR-dependent impact on NO generation translates to salutary actions in vivo as DATS administration in cystathionine-γ-lyase (CSE) knockout mice significantly improved hindlimb ischemia blood flow post ligation, while the XOR-specific inhibitor, febuxostat (Febx), abrogated this benefit. Moreover, flow-mediated vasodilation (FMD) in CSE knockout mice following administration of DATS resulted in greater than 4-fold enhancement in femoral artery dilation while co-treatment with Febx completely completely abrogated this effect. Together, these results identify XOR as a focal point of convergence between sulfide- and nitrite-mediated signaling, as well as affirm the critical need to reexamine current dogma regarding inhibition of XOR in the context of vascular dysfunction.

Body mass index is independently associated with xanthine oxidase activity in overweight/obese population

PURPOSE

The pathophysiological mechanism of the relationship between xanthine oxidase (XO) activity and obesity has not been completely elucidated. Since inflammation and oxidative stress are regarded as key determinants of enlarged adipose tissue, we aimed to investigate the association between oxidative stress (as measured with XO activity), inflammation [as measured with high-sensitivity C-reactive protein (hsCRP)] and obesity [as measured with body mass index (BMI)]. In addition, we wanted to examine whether hsCRP itself plays an independent role in XO activity increase or it is only mediated through obesity.

METHODS

A total of 118 overweight/obese volunteers (mean age 54.76 ± 15.13 years) were included in the current cross-sectional study. Anthropometric, biochemical parameters, and blood pressure were obtained.

RESULTS

Significant differences between age, BMI, waist circumference, concentrations of uric acid and hsCRP, as well as xanthine dehydrogenase (XDH) activities were evident among XO tertile groups. Multiple linear regression analysis revealed that BMI (beta = 0.241, p = 0.012) and XDH (beta = - 0.489, p < 0.001) are the independent predictors of XO activity (R²-adjusted = 0.333), whereas hsCRP lost its independent role in XO activity prediction.

CONCLUSION

Obesity (as determined with increased BMI) is an independent predictor of high XO activity in overweight/obese population.

LEVEL OF EVIDENCE

Level V: cross-sectional descriptive study.

Insulin Resistance Associated with Plasma Xanthine Oxidoreductase Activity Independent of Visceral Adiposity and Adiponectin Level: MedCity21 Health Examination Registry

BACKGROUND

Higher levels of uric acid production have been reported in individuals with visceral fat obesity, and obesity is known to enhance xanthine oxidoreductase (XOR) activity, although the precise mechanism remains unclear. We investigated the associations of visceral fat area (VFA), serum adiponectin level, and insulin resistance with plasma XOR activity using our novel highly sensitive assay based on [¹³C₂,¹⁵N₂] xanthine and liquid chromatography/triple quadrupole mass spectrometry.

METHODS

This cross-sectional study included 193 subjects (92 males and 101 females) registered in the MedCity21 health examination registry. Plasma XOR activity, serum adiponectin level, and VFA obtained by computed tomography were measured, and insulin resistance was determined based on the homeostasis model assessment (HOMA-IR) index.

RESULTS

The mean values for VFA, log HOMA-IR, and log plasma XOR activity were 76.8 ± 45.8 cm², 0.14 ± 0.30, and 1.50 ± 0.44 pmol/h/mL, respectively. Multiple regression analysis showed that HOMA-IR was significantly (p=0.020) associated with plasma XOR activity independent of other factors, including VFA and adiponectin level, as well as age, sex, alcohol drinking habit, smoking habit, alanine transaminase, HbA1c, and eGFR. The "sex∗HOMA - IR" interaction was not significant (p=0.020) associated with plasma XOR activity independent of other factors, including VFA and adiponectin level, as well as age, sex, alcohol drinking habit, smoking habit, alanine transaminase, HbA1c, and eGFR. The ".

CONCLUSIONS

Our results indicate that insulin resistance is associated with plasma XOR activity and that relationship is independent of visceral adiposity and adiponectin level, suggesting that the development of insulin resistance resulting from increased visceral adiposity and/or reduced serum adiponectin contributes to increased uric acid production by stimulating XOR activity.

Metabolic syndrome and cancer risk: The role of xanthine oxidoreductase

Obesity and related pathologies such as diabetes and metabolic syndrome are associated with chronic inflammation and cancer. The serum level of xanthine oxidoreductase (XOR) is correlated to obesity-associated metabolic disorders. XOR can play a role in the pathogenesis of both metabolic syndrome and cancer through the inflammatory response and the oxidative stress elicited by the products of its activity. The reactive oxygen and nitrogen species and the uric acid derived from XOR concur to the development of hypertension, dyslipidemia and insulin resistance and participate in both cell transformation and proliferation, as well as in the progression and metastasis process. Despite the availability of different drugs to inhibit in vivo XOR activity, the complexity of XOR inhibition effects should be carefully considered before clinical application, save in the case of symptomatic hyperuricemia.

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Metabolic syndrome (MS) increases the risk of cancer development.

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Xanthine oxidoreductase (XOR) plays a role in both MS and cancer.

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Uric acid, ROS and RNS produced by XOR cause inflammation and oxidative stress.

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Inflammation and oxidative stress contribute to the pathogenesis of MS and cancer.

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XOR activity can be pharmacologically controlled.

Antiradical and Xanthine Oxidase Inhibitory Activity Evaluations of Averrhoa bilimbi L. Leaves and Tentative Identification of Bioactive Constituents through LC-QTOF-MS/MS and Molecular Docking Approach

The objective of the present study was to investigate the antiradical and xanthine oxidase inhibitory effects of Averrhoa bilimbi leaves. Hence, crude methanolic leaves extract and its resultant fractions, namely hexane, chloroform, and n-butanol were evaluated for 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging effect and xanthine oxidase inhibitory activity. The active constituents were tentatively identified through LC-QTOF-MS/MS and molecular docking approaches. The n-butanol fraction of A. bilimbi crude methanolic leaves extract displayed significant DPPH radical scavenging effect with IC₅₀ (4.14 ± 0.21 μg/mL) (p < 0.05), as well as xanthine oxidase inhibitory activity with IC₅₀ (64.84 ± 3.93 μg/mL) (p < 0.05). Afzelechin 3-O-alpha-l-rhamnopyranoside and cucumerin A were tentatively identified as possible metabolites that contribute to the antioxidant activity of the n-butanol fraction.

Elevated Serum Xanthine Oxidase Activity Is Associated With the Development of Type 2 Diabetes: A Prospective Cohort Study

OBJECTIVE

We aimed to evaluate whether xanthine oxidase (XO), a key enzyme in uric acid (UA) metabolism and a major source of reactive oxygen species, plays a causal and important role in the development of type 2 diabetes mellitus (T2DM) in a large prospective cohort study.

RESEARCH DESIGN AND METHODS

A total of 4,412 diabetes-free adults (2,071 women and 2,341 men) aged 30-65 years at baseline in 2008 were involved. Participants were followed for incident change of glucose metabolism during an average of 4.7 years. At baseline, serum XO and UA, serum lipids, and glucose homeostasis indexes including fasting blood glucose (FBG), 2-h blood glucose (PBG), glycosylated hemoglobin A_1c (HbA_1c), and fasting insulin were tested for analysis.

RESULTS

During an average follow-up period of 4.7 years, 249 women and 360 men developed new-onset T2DM. Serum XO activity was positively associated with UA concentration (all P values <0.001). When XO activity and UA concentration were considered in the same model of the sex-specific analysis, only XO activity was significantly associated with the incidence of T2DM, with the hazard ratios from the bottom to the top quartile of XO activity being 1.00, 1.67 (95% CI 1.00-2.79), 1.86 (1.11-3.13), and 2.36 (1.43-3.90) in women and 1.00, 1.01 (0.68-1.52), 1.41 (0.98-2.03), and 1.90 (1.30-2.78) in men.

CONCLUSIONS

Elevated serum XO activity, but not UA concentration, was associated with an increased risk of developing T2DM in women and men with mutual adjustment for XO and UA. Further studies are needed to examine the underlying mechanisms.

Xanthine oxidase and uric acid as independent predictors of albuminuria in patients with diabetes mellitus type 2

Xanthine oxidase (XO) is an important enzyme responsible for conversion of purine bases to uric acid and represents the major source of reactive oxygen species (ROS) production in circulation. Since pathophysiological mechanism of the relationship between XO activity and urinary albumin excretion (UAE) rate is not well elucidated, we aimed to investigate this association in patients with diabetes mellitus type 2 (DM2). In addition, we wanted to examine whether uric acid itself plays an independent role in albuminuria onset and progression, or it is only mediated through XO activity. A total of 83 patients with DM2 (of them 56.6% females) were included in this cross-sectional study. Anthropometric, biochemical parameters and blood pressure were obtained. Multivariate logistic regression analysis showed that uric acid and XO were the independent predictors for albuminuria onset in patients with DM2 [odds ratio (OR) 1.015, 95% CI (1.008-1.028), p = 0.026 and OR 1.015, 95% CI (1.006-1.026), p = 0.040, respectively]. Rise in uric acid for 1 µmol/L enhanced the probability for albuminuria by 1.5%. Also, elevation in XO activity for 1 U/L increased the probability for albuminuria for 1.5%. A total of 66.7% of variation in UAE could be explained with this Model. Both XO and uric acid are independently associated with albuminuria in diabetes. Better understanding of pathophysiological relationship between oxidative stress and albuminuria could lead to discoveries of best pharmacological treatment of XO- and/or uric acid-induced ROS, in order to prevent albuminuria onset and progression.

Relationship between plasma xanthine oxidoreductase activity and left ventricular ejection fraction and hypertrophy among cardiac patients

Background and purpose

Xanthine oxidoreductase (XOR), which catalyzes purine catabolism, has two interconvertible forms, xanthine dehydrogenase and xanthine oxidase, the latter of which produces superoxide during uric acid (UA) synthesis. An association between plasma XOR activity and cardiovascular and renal outcomes has been previously suggested. We investigated the potential association between cardiac parameters and plasma XOR activity among cardiology patients.

Methods and results

Plasma XOR activity was measured by [¹³C₂,¹⁵N₂]xanthine coupled with liquid chromatography/triplequadrupole mass spectrometry. Among 270 patients who were not taking UA-lowering drugs, XOR activity was associated with body mass index (BMI), alanine aminotransferase (ALT), HbA1c and renal function. Although XOR activity was not associated with serum UA overall, patients with chronic kidney disease (CKD), those with higher XOR activity had higher serum UA among patients without CKD. Compared with patients with the lowest XOR activity quartile, those with higher three XOR activity quartiles more frequently had left ventricular hypertrophy. In addition, plasma XOR activity showed a U-shaped association with low left ventricular ejection fraction (LVEF) and increased plasma B-type natriuretic peptide (BNP) levels, and these associations were independent of age, gender, BMI, ALT, HbA1C, serum UA, and CKD stages.

Conclusions

Among cardiac patients, left ventricular hypertrophy, low LVEF, and increased BNP were significantly associated with plasma XOR activity independent of various confounding factors. Whether pharmaceutical modification of plasma XOR activity might inhibit cardiac remodeling and improve cardiovascular outcome should be investigated in future studies.

Weight Loss, Xanthine Oxidase, and Serum Urate Levels: A Prospective Longitudinal Study of Obese Patients

OBJECTIVE

The mechanisms by which weight loss decreases serum uric acid (SUA) levels are poorly known. We aimed to investigate the role played by xanthine oxidase (XOD), metabolic status, and low-grade inflammation in decreased SUA levels induced by weight loss in obese patients.

METHODS

Data were from a series of consecutive patients with severe obesity involved in a bariatric surgery program. Measurements of body composition and biologic samples were obtained before surgery and 6 months after surgery.

RESULTS

Among the 154 patients (mean ± SD age 41.0 ± 12.3 years, body mass index [BMI] 47.8 ± 7.2 kg/m(2) , 81% female), the mean ± SD weight loss at 6 months was 31.3 ± 7.8 kg. Reduction in SUA levels was modest (-10%): 4.98 ± 1.21 mg/dl at 6 months versus 5.52 ± 1.33 mg/dl at baseline (P < 0.001). The decrease in SUA levels was greatest (-18%) in hyperuricemic patients (n = 48). In these patients, circulating XOD activity decreased with weight loss (P < 0.0001). Multiple linear regression analysis revealed decreased SUA levels associated with decreased triglyceride levels (P = 0.0001) and BMI (P = 0.02) but not XOD activity, adipokine levels (leptin and adiponectin), insulin resistance, or levels of inflammatory variables (interleukin 6, orosomucoid, fibrinogen, and high-sensitivity C-reactive protein).

CONCLUSION

In obese patients, weight loss was associated with a decrease in both SUA levels and XOD activity. Our findings suggest that reduced SUA levels are not mediated by decreased XOD activity or improved insulin resistance but could be partly due to a reduction in triglyceride levels.

Impact of single anaerobic exercise on delayed activation of endothelial xanthine oxidase in men and women

OBJECTIVES

The aim of the study was to evaluate the activity of xanthine oxidase (XO) in the blood of men and women during the first hour following a single anaerobic exercise (AN-EX), and after 24 hours of recovery, and to determine whether the changes in XO activity in the blood after AN-EX are dependent on anaerobic performance.

METHODS

Ten men and ten women performed a single AN-EX. Blood was collected before and five times after completion of the AN-EX. The activity of XO was determined.

RESULTS

In both groups, a significant (P < 0.05) increase in blood XO activity was found only 24 hours after the AN-EX. The increased activity of XO in men was significantly lower than in women (P < 0.05). Negative correlations were found between the increase in XO activity in the blood plasma 24 hours after the AN-EX and anaerobic power, the total work performed during the AN-EX and the power decrease.

DISCUSSION

In the first hour after the single AN-EX, XO activity in the blood of women and men did not change, but after 24 hours of recovery, it was significantly higher compared to baseline levels in both sexes. Single AN-EX causes a smaller increase in XO activity in people with higher anaerobic performance.

Weight Loss Mediated Reduction in Xanthine Oxidase Activity and Uric Acid Clearance in Adolescents with Severe Obesity

BACKGROUND

Increased xanthine oxidase (XO) activity and uric acid levels are known to be associated with obesity and hypertension; however, it is not known if obesity is directly responsible for these associations in youth. This study investigated the effect of weight loss on XO activity, uric acid, and their relationship to blood pressure change in obese youth to provide greater insight on how obesity increases cardiovascular risk.

METHODS

This was an ancillary study in which 16 adolescents (mean age 15 ± 2 years) received meal replacement therapy over a period of four weeks. Outcomes measured at baseline and after intervention included weight, blood pressure, XO activity, plasma uric acid, uric acid clearance, and creatinine clearance.

RESULTS

After the meal replacement intervention, participants experienced reductions in body weight (109.2 ± 16 kg vs. 105.2 ± 14 kg, p < 0.0001) and BMI (38.7 ± 4 kg vs. 37.4 ± 3 kg, p < 0.0001). Plasma XO activity was reduced by 9.8% (p = 0.016). Uric acid clearance was decreased by 39% (p = 0.006). SBP (systolic blood pressure) and plasma uric acid concentrations were reduced but did not achieve statistical significance (p = 0.34 and 0.38, respectively). DBP (diastolic blood pressure) was unchanged (p = 0.86). No significant relationships were found between changes in blood pressure and changes in either XO activity or plasma uric acid levels.

CONCLUSION

Weight loss led to decreases in uric acid production by lowering XO activity and decreases in uric acid clearance by reducing glomerular filtration (GF) and increasing reabsorption. Changes in XO activity and uric acid levels did not correlate with changes in blood pressure.

A rapid high throughput proteomic method based on profiling of proteolytic free peptides to assess post-delivery degradation of placental tissue

A rapid method to determine quality for placental proteomic studies is required due to varying lengths of time between delivery and sampling in routine protocols. We developed a rapid 10 min LC-MS based scanning method to profile free peptides liberated from natural proteolytic degradation. The assay was applied to placenta samples obtained following refrigeration for varying time periods post-delivery (12 h, +24 h, +48 h and +72 h). Analysis reveals time dependant overlapping profiles for groups <24 to +48 h with greatest variation in the +72 h group, indicating that significant proteolysis affects tissue integrity between 48 and 72 h.

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

Xanthine oxidoreductase (XOR), the molybdoflavin enzyme responsible for the terminal steps of purine degradation in humans, is also recognized as a significant source of reactive species contributory to inflammatory disease. In animal models and clinical studies, inhibition of XOR has resulted in diminution of symptoms and enhancement of function in a number of pathologies including heart failure, diabetes, sickle cell anemia, hypertension and ischemia-reperfusion injury. For decades, XOR involvement in pathologic processes has been established by salutary outcomes attained from treatment with the XOR inhibitor allopurinol. This has served to frame a working dogma that elevation of XOR-specific activity is associated with enhanced rates of reactive species generation that mediate negative outcomes. While adherence to this narrowly focused practice of designating elevated XOR activity to be "bad" has produced some benefit, it has also led to significant underdevelopment of the processes mediating XOR regulation, identification of alternative reactants and products as well as micro-environmental factors that alter enzymatic activity. This is exemplified by recent reports: (1) identifying XOR as a nitrite reductase and thus a source of beneficial nitric oxide ((•)NO) under in vivo conditions similar to those where XOR inhibition has been assumed an optimal treatment choice, (2) describing XOR-derived uric acid (UA) as a critical pro-inflammatory mediator in vascular and metabolic disease and (3) ascribing an antioxidant/protective role for XOR-derived UA. When taken together, these proposed and countervailing functions of XOR affirm the need for a more comprehensive evaluation of product formation as well as the factors that govern product identity. As such, this review will critically evaluate XOR-catalyzed oxidant, (•)NO and UA formation as well as identify factors that mediate their production, inhibition and the resultant impact on inflammatory disease.