Activity of xanthine oxidase in plasma correlates with indices of insulin resistance and liver dysfunction in patients with type 2 diabetes mellitus and metabolic syndrome: A pilot exploratory study

Origin tracing and adulteration identification of bird's nest by high- and low-field NMR combined with pattern recognition

Edible bird's nest (EBN) is a high-value health food with various nutrients and bioactive components. With increasing demand for EBN, they are often adulterated with cheaper ingredients or falsely labeled by the origin information, thus harming consumer interests. In this study, high- and low-field nuclear magnetic resonance (HF/LF-NMR) technology combined with multivariate statistical analysis was used to identify the geographical marker of EBN from different origins and authenticate the adulterated EBN with various adulterants at different adulteration rates. Authentic EBN samples from Malaysia were used to simulate adulteration using gelatin (GL), agar (AG) and starch (ST) at 10 %, 20 %, 40 %, 60 %, 80 %, and 100 % w/w, respectively. The results showed significant differences in composition among EBN from different origins, with isocaproate and citric acid serving as geographical markers for Malaysia and Vietnam, respectively. Leucine, glutamic acid, and N-acetylglycoprotein serving as geographical markers for Indonesia. In addition, PLS model further verified the accuracy of origin identification of EBN. The LF-NMR results of adulteration EBN showed a linear correlation between the transverse relaxation (T2, S2) and the adulterated ratio. The OPLS-DA based on T2 spectra could accurately identify authentic EBN from adulterated with GL, AG and ST at 40 %, 20 %, and 20 %, respectively. Fisher discrimination model was able to differentiate at 20 %, 20 %, and 40 %, respectively. These results show that the 1H NMR combined with multivariate statistical analysis method could be a potential tool for the detection of origin and adulteration of EBN.

Urate-lowering drugs for chronic kidney disease with asymptomatic hyperuricemia and hypertension: a randomized trial

INTRODUCTION

Xanthine oxidase (XO) inhibitors may slow down chronic kidney disease (CKD) progression. The comparative effectiveness of the different urate-lowering drugs is unknown. The aim of this study was to determine whether urate-lowering therapy with an XO inhibitor (febuxostat) and that with a uricosuric drug (benzbromarone) are comparable in slowing renal function decline in patients with CKD complicated with hypertension and hyperuricemia.

METHODS

This study was an open-label randomized parallel-group clinical trial of 95 patients with stage G3 CKD in Japan. The patients had hypertension and hyperuricemia without a history of gout. They were randomized to receive febuxostat ( n  = 47; febuxostat group) or benzbromarone ( n  = 48; benzbromarone group) and titrated to reduce their serum urate level to <6.0 mg/dl. The primary end-point was change in estimated glomerular filtration rate (eGFR) from baseline to 52 weeks. The secondary end-points included changes in uric acid level, blood pressure, urinary albumin-to-creatinine ratio, and XO activity.

RESULTS

Of the 95 patients, 88 (92.6%) completed the trial. There were no significant differences in change in eGFR (in ml/min/1.73 m 2 ) between the febuxostat [-0.23, 95% confidence interval (CI), -2.00 to 1.55] and benzbromarone (-2.18, 95% CI, -3.84 to -0.52) groups (difference, 1.95; 95% CI, -0.48 to 4.38; P  = 0.115) nor in the secondary end-points, except for XO activity. Febuxostat significantly reduced XO activity ( P  = 0.010). There were no significant differences in primary and secondary outcomes between the groups. A decrease in eGFR was significantly less in the febuxostat group than that of the benzbromarone group in the CKDG3a, but not in CKDG3b, in the subgroup analysis. There were no adverse effects specific to either drug.

CONCLUSIONS

No significant differences were found in the effects of febuxostat and benzbromarone in renal function decline in stage G3 CKD complicated with hyperuricemia and hypertension.

Contributing Factors of Diabetes Mellitus among Patients with Gout (Results of the Long-Term Prospective Study)

It is assumed that the risk of developing type 2 diabetes mellitus (T2DM) in patients with gout is influenced by both generally accepted risk factors and factors related to gout. The aim of the study was to evaluate the impact of various risk factors for T2DM in patients with gout. A total of 444 patients (49 women, 395 men) ≥18 years old with gout and without DM were included. The duration of observation was 5.66 [2.69; 7.64] years. To identify the factors associated with the risk of developing T2DM, multivariate logistic regression was used, which included sex; T2DM in relatives; insufficient physical activity; unbalanced diet; age  ≥ 45 years; ≥4 attacks per year; presence of tophi; BMI ≥30 kg/m2; allopurinol, febuxostat, glucocorticoids, diuretics, metformin, colchicine; GFR < 60 mL/min/1.73 m2; serum uric acid level (sUA) ≥ 420 µmol/L and  ≥ 480 µmol/L. T2DM developed in 108 (24.3%) patients. According to the multivariate model, the presence of ≥4 attacks of arthritis per year increased the risk of T2DM (OR = 5.23; 95% CI: 2.98-9.19; p = 0.0001); presence of tophi (OR = 2.61; 95% CI: 1.50-4.54; p = 0.001); sUA ≥ 480 µmol/L (OR = 2.26; 95% CI: 1.02-5.00; p = 0.144); diuretics (OR = 2.35; 95% CI: 1.19-4.64; p = 0.014). Febuxostat (OR = 0.31; 95% CI: 0.11-0.84; p = 0.022) and metformin (OR = 0.49; 95% CI: 0.21-1.16; p = 0.107) reduced the risk of developing T2DM. Risk of T2DM in patients with gout is associated with high incidence of arthritis attacks, MK ≥ 480 μmol/L, hypertension, diuretic use, and febuxostat and metformin reduces risk.

Drug repurposing: Metformin's effect against liver tissue damage in diabetes and prostate cancer model

Background

There are evidences linking diabetes to the pathogenesis and progression of various cancers. Metformin is a well-known antidiabetic drug that reduces the levels of circulating glucose and insulin in patients with both insulin resistance and hyperinsulinemia. Aim of the present study was to evaluate the effect of metformin on the liver of rats bearing prostate cancer, diabetes and prostate cancer + diabetes via histopathological and biochemical methods.

Methods

Male Copenhagen rats were divided into six groups. Control group, diabetic group, cancer group, diabetic + cancer group, diabetic + cancer + metformin group, cancer + metformin group. Diabetes was induced by injecting single dose of streptozotocin (65 mg/kg) to Copenhagen rats, cancer induced 2 × 104 Mat-LyLu cells. Metformin treatment was administered daily by gavage following inocculation of the Mat- Lylu cells to fifth and sixth group. The experiment was terminated on the 14th day following Mat-LyLu cell injection. At the end of the experimental period, the rats were sacrificed, and liver tissue was taken. Liver damage was scored. Biochemically, serum prostate-specific antigen level was determined by employing Enzyme Linked Immuno Sorbent Assay method. In addition, the activities of different enzyme and biochemical parameters were determined spectrophotometrically inform the hepatic tissue specimens.

Results

The findings of this study reveal that histopathological and biochemical damage in cancer and diabetic + cancer groups decreased significantly in the metformin treated groups.

Conclusion

These highlights that the antidiabetic drug metformin can be repositioned for attenuating liver tissue damage associated with prostate cancer and diabetes.

A Review of Fibraurea tinctoria and Its Component, Berberine, as an Antidiabetic and Antioxidant

Diabetes mellitus is a group of metabolic disorders characterized by hyperglycemia caused by resistance to insulin action, inadequate insulin secretion, or excessive glucagon production. Numerous studies have linked diabetes mellitus and oxidative stress. People with diabetes usually exhibit high oxidative stress due to persistent and chronic hyperglycemia, which impairs the activity of the antioxidant defense system and promotes the formation of free radicals. Recently, several studies have focused on exploring natural antioxidants to improve diabetes mellitus. Fibraurea tinctoria has long been known as the native Borneo used in traditional medicine to treat diabetes. Taxonomically, this plant is part of the Menispermaceae family, widely known for producing various alkaloids. Among them are protoberberine alkaloids such as berberine. Berberine is an isoquinoline alkaloid with many pharmacological activities. Berberine is receiving considerable interest because of its antidiabetic and antioxidant activities, which are based on many biochemical pathways. Therefore, this review explores the pharmacological effects of Fibraurea tinctoria and its active constituent, berberine, against oxidative stress and diabetes, emphasizing its mechanistic aspects. This review also summarizes the pharmacokinetics and toxicity of berberine and in silico studies of berberine in several diseases and its protein targets.

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.

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.

The prognostic impact of uric acid in acute heart failure according to coexistence of diabetes mellitus

BACKGROUND AND AIMS

Increased uric acid levels predict higher mortality in heart failure (HF) patients. Patients with diabetes mellitus (DM) appear to have increased xanthine oxidase activity. We aimed to study if the association between uric acid and mortality in acute HF was different according to the coexistence of DM.

METHODS AND RESULTS

We studied a cohort of patients hospitalized due to acute HF in 2009-2010. Patients with no uric acid measurement upon admission were excluded from the analysis.

FOLLOW-UP

2 years; endpoint: all-cause mortality. Patients with elevated uric acid (>80.0 mg/L) were compared with those with lower values. We used a multivariate Cox-regression analysis to assess the prognostic impact of uric acid (both continuous and categorical variable: cut-off 80.0 mg/L). The analysis was stratified according to coexistence of DM. We studied 569 acute HF patients, 44.6%male, mean age 76 years, 290 were diabetic. Median admission uric acid: 81.2 mg/L and 52.2%had uric acid >80.0 mg/L. Elevated uric acid predicted all-cause mortality in acute HF only in patients with DM. The multivariate-adjusted HR of 2-year mortality was 1.68 (95 % CI: 1.15-2.46) for diabetic HF patients with uric acid>80.0 mg/L compared to those with lower levels (p = 0.008) and 1.10 (95 % CI: 1.03-1.18) per each 10 mg/L increase in uric acid (p = 0.007). In non-diabetic HF patients, uric acid was not associated with mortality.

CONCLUSIONS

Increased uric acid predicts ominous outcome in acute HF patients with diabetes, however, it is not prognostic associated in non-diabetics. Uric acid may play a different role in acute HF depending on DM status.

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.

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.

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.

Comparing the Effects of Febuxostat and Allopurinol in an Animal Model of Metabolic Syndrome

INTRODUCTION

Recent studies highlighted the association of hyperuricemia and metabolic syndrome (MS). The aim of this study was to compare the beneficial effects of febuxostat versus allopurinol on the biochemical changes that occur in MS.

METHODS

Forty adult male Sprague Dawley albino rats were used in the study. Insulin resistance and MS were induced by administration of a high-fructose diet for 8 weeks. Follow-up of changes in weight, blood pressure, serum biochemical parameters, serum antioxidant catalase, and glutathione peroxidase activities was done. At the end of the study, animals were sacrificed, and the thoracic aorta was isolated for in vitro study of the endothelial integrity.

RESULTS

Allopurinol and febuxostat treatment induced significant reduction in body weight, systolic blood pressure, blood glucose, insulin, lipids, and improved kidney functions and endothelial integrity compared to nontreated rats. Febuxostat was more effective than allopurinol in normalizing serum fasting glucose, uric acid, catalase, and glutathione peroxidase activities.

CONCLUSION

Xanthine oxidase inhibitors ameliorated the effects of MS. Febuxostat was mildly superior to allopurinol in lowering serum fasting glucose, lipids, uric acid, and antioxidant enzyme activities.

Inhibitory effects of xanthine oxidase inhibitor, topiroxostat, on development of neuropathy in db/db mice

Inflammation and oxidative stress contribute to the pathophysiology of diabetic neuropathy. According to recent evidence, the modulation of macrophage polarization in peripheral nerves represents a potential therapeutic target for diabetic neuropathy. Xanthine oxidase, which is a form of xanthin oxidoreductase, is the rate-limiting enzyme that catalyzes the degradation of hypoxanthine and xanthine into uric acid. Activation of xanthine oxidase promotes oxidative stress and macrophage activation. A preclinical study reported the beneficial effects of xanthine oxidase inhibitors on peripheral nerve dysfunction in experimental models of diabetes. However, the detailed mechanisms remain unknown. In this study, we examined the effect of the xanthine oxidase inhibitor topiroxostat on macrophage polarization and peripheral neuropathy in an obese diabetic model, db/db mice. First, the effects of xanthine oxidase inhibitors on cultured macrophages and dorsal root ganglion neurons exposed to xanthine oxidase were assessed. Furthermore, five-week-old db/db mice were administered the xanthine oxidase inhibitors topiroxostat [1 mg/kg/day (dbT1) or 2 mg/kg/day (dbT2)] or febuxostat [1 mg/kg (dbF)]. Glucose metabolism and body weight were evaluated during the experimental period. At 4 and 8 weeks of treatment, peripheral nerve functions such as nerve conduction velocities, thermal thresholds and pathology of skin and sciatic nerves were evaluated. The mRNA expression of molecules related to inflammation and oxidative stress was also measured in sciatic nerves. Untreated db/db mice and the nondiabetic db strain (db/m) were studied for comparison. An in vitro study showed that topiroxostat suppressed macrophage activation and proinflammatory but not anti-inflammatory polarization, and prevented the reduction in neurite outgrowth from neurons exposed to xanthine oxidase. Neuropathic changes exemplified by delayed nerve conduction and reduced intraepidermal nerve fiber density developed in db/db mice. These deficits were significantly prevented in the treated group, most potently in dbT2. Protective effects were associated with the suppression of macrophage infiltration, cytokine expression, and oxidative stress in the sciatic nerve and decreased plasma xanthine oxidoreductase activity. Our results revealed the beneficial effects of the xanthine oxidase inhibitor topiroxostat on neuropathy development in a mouse model of type 2 diabetes. The suppression of proinflammatory macrophage activation and oxidative stress-induced damage were suggested to be involved in this process.

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.

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

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

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

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.

Association of Hyperuricemia With Immune Disorders and Intestinal Barrier Dysfunction

Background

More than 30–40% of uric acid is excreted via the intestine, and the dysfunction of intestinal epithelium disrupts uric acid excretion. The involvement of gut microbiota in hyperuricemia has been reported in previous studies, but the changes and mechanisms of intestinal immunity in hyperuricemia are still unknown.

Methods

This study developed a urate oxidase (Uox)-knockout (Uox–/–) mouse model for hyperuricemia using CRISPR/Cas9 technology. The lipometabolism was assessed by measuring changes in biochemical indicators. Furthermore, 4-kDa fluorescein isothiocyanate–labeled dextran was used to assess gut barrier function. Also, 16S rRNA sequencing was performed to examine the changes in gut microbiota in mouse feces. RNA sequencing, Western blot, Q-PCR, ELISA, and immunohistochemical analysis were used for measuring gene transcription, the number of immune cells, and the levels of cytokines in intestinal tissues, serum, kidney, liver, pancreas, and vascellum.

Results

This study showed that the abundance of inflammation-related microbiota increased in hyperuricemic mice. The microbial pattern recognition–associated Toll-like receptor pathway and inflammation-associated TNF and NF-kappa B signaling pathways were significantly enriched. The increased abundance of inflammation-related microbiota resulted in immune disorders and intestinal barrier dysfunction by upregulating TLR2/4/5 and promoting the release of IL-1β and TNF-α. The levels of epithelial tight junction proteins occludin and claudin-1 decreased. The expression of the pro-apoptotic gene Bax increased. The levels of LPS and TNF-α in systemic circulation increased in hyperuricemic mice. A positive correlation was observed between the increase in intestinal permeability and serum levels of uric acid.

Conclusion

Hyperuricemia was characterized by dysregulated intestinal immunity, compromised intestinal barrier, and systemic inflammation. These findings might serve as a basis for future novel therapeutic interventions for hyperuricemia.

Allopurinol use and type 2 diabetes incidence among patients with gout: A VA retrospective cohort study

To assess the impact of allopurinol on diabetes in a retrospective cohort of Veterans' Affairs patients with gout.The New York Harbor VA computerized patient record system was searched to identify patients with an ICD-9 code for gout meeting at least 4 modified 1977 American Rheumatology Association gout diagnostic criteria. Patients were divided into subgroups based on >30 continuous days of allopurinol, versus no allopurinol. New diagnoses of diabetes, defined according to American Diabetes Association diagnostic criteria or clinical documentation explicitly stating a new diagnosis of diabetes, were identified during an observation period from January 1, 2000 through December 31, 2015.Six hundred six gout patients used allopurinol >30 continuous days, and 478 patients never used allopurinol. Over an average 7.9 ± 4.8 years of follow-up, there was no significant difference in diabetes incidence between the allopurinol and non-allopurinol groups (11.7/1000 person-years vs 10.0/1000 person-years, P = .27). A lower diabetes incidence in the longest versus shortest quartiles of allopurinol use (6.3 per 1000 person-years vs 19.4 per 1000 person-years, P<.0001) was attributable to longer duration of medical follow-up.In this study, allopurinol use was not associated with decreased diabetes incidence. Prospective studies may further elucidate the relationship between hyperuricemia, gout, xanthine oxidase activity, and diabetes, and the potential impact of gout treatments on diabetes incidence.

Independent association of plasma xanthine oxidoreductase activity with serum uric acid level based on stable isotope-labeled xanthine and liquid chromatography/triple quadrupole mass spectrometry: MedCity21 health examination registry

Background

We developed a novel high-sensitive assay for plasma xanthine oxidoreductase (XOR) activity that is not affected by the original serum uric acid level. However, the association of plasma XOR activity with that level has not been fully examined.

Methods

This cross-sectional study included 191 subjects (91 males, 100 females) registered in the MedCity21 health examination registry. Plasma XOR activity was determined using our assay for plasma XOR activity with [13C2,15N2] xanthine and liquid chromatography/triple quadrupole mass spectrometry. Serum levels of uric acid and adiponectin, and visceral fat area (VFA) obtained by computed tomography were measured, and insulin resistance was determined based on the homeostasis model assessment (HOMA-IR) index.

Results

The median values for uric acid and plasma XOR activity were 333 μmol/L and 26.1 pmol/h/mL, respectively. Multivariable linear regression analysis showed a significant and positive association of serum uric acid level (coefficient: 26.503; 95% confidence interval: 2.06, 50.945; p = 0.035) with plasma XOR activity independent of VFA and HOMA-IR, and also age, gender, alcohol drinking habit, systolic blood pressure, estimated glomerular filtration rate (eGFR), glycated hemoglobin A1c, triglyceride, and adiponectin levels. The “gender*XOR activity” interaction was not significant (p = 0.91), providing no evidence that gender modifies the relationship between plasma XOR activity and serum uric acid level.

Conclusions

Plasma XOR activity was found to be positively associated with serum uric acid level independent of other known confounding factors affecting that level, including gender difference, eGFR, adiponectin level, VFA, and HOMA-IR.

Uric acid increases IL-1β secretion and Caspase-1 activation in PBMCs of Behçet's disease patients: The in vitro immunomodulatory effect of xanthine oxidase inhibitor Allopurinol

Behçet's disease (BD) is a multisystem disease, which shares some features with other diseases belonging to the autoinflammatory disorders panel. Recent studies have postulated that IL-1β/Caspase-1 may play a cardinal role in autoinflammatory diseases. In this study, we aimed to (i) elucidate the mechanism underlying the involvement of xanthine oxidase (XO) and Uric Acid (UA) in BD (ii) study the direct effects of UA and XO inhibitor "Allopurinol" on nitric oxide (NO) and caspase-1-mediated IL-1β release in peripheral blood mononuclear cells (PBMCs) of BD patients. In this context, plasma of BD patients and healthy controls (HC) were used to measure XO activity, UA, advanced oxidized proteins products (AOPP) and NO levels. In Addition, PBMCs of BD patients and HC were treated or not with either UA or Allopurinol. Then we quantified NO and IL-1β levels, and Caspase-1 Activity in the supernatants and lysates of PBMCs, respectively. We showed that plasma levels of XO activity, UA, AOPP and NO are significantly increased in BD patients compared to those of HC. Interestingly, a significant positive correlation between XO and UA was observed in BD patients. Additionally, while UA has markedly increased NO, IL-1β, and Caspase-1 activity levels in PBMCs of BD patients, Allopurinol has exerted an immunomodulatory effect resulting in reduced NO, IL-1β and Caspase-1 levels in PBMCs of BD patients particularly during the active stages. Collectively, our results indicate a potential clinical use of XO as a tool for assessing BD activity, and suggest that the in-vitro immunomodulatory effect of Allopurinol may have a promising therapeutic value in BD management.

Plasma Xanthine Oxidoreductase (XOR) Activity in Cardiovascular Disease Outpatients

Background: The mechanisms of the increased plasma xanthine oxidoreductase (XOR) activity in outpatients with cardiovascular disease were unclear.

Methods and Results: A total of 372 outpatients were screened, and 301 outpatients with cardiovascular disease were prospectively analyzed. Blood samples were collected from patients who visited a daily cardiovascular outpatient clinic. Patients with diabetes mellitus (DM) were significantly more likely to be classified into the high-XOR group (≥100 pg/h/mL; 50%) than the low-XOR group (<100 pmol/h/mL; 28.7%). On multivariate logistic regression analysis, DM (OR, 2.683; 95% CI: 1.441–4.996) was independently associated with high plasma XOR activity in all cohorts. In the diabetic cardiovascular disease patients (n=100), median body mass index (BMI) in the high-XOR group (28.0 kg/m²; IQR, 25.2–29.4 kg/m², n=32) was significantly higher than in the low-XOR group (23.6 kg/m²; IQR, 21.2–25.7 kg/m², n=68), and BMI was independently associated with high plasma XOR activity (OR, 1.340; 95% CI: 1.149–1.540). Plasma hydrogen peroxide was significantly higher in DM patients with high plasma XOR activity and obesity (>22 kg/m²) than in other patients.

Conclusions: DM with obesity is one of the mechanisms of XOR enhancement in cardiovascular disease. The increase of XOR is a possible pathway for the production of reactive oxygen species in obese cardiovascular disease patients with DM.

Xanthine oxidoreductase activity correlates with vascular endothelial dysfunction in patients with type 1 diabetes

AIMS

Xanthine oxidoreductase (XOR) is an enzyme regulating uric acid synthesis and generation of reactive oxygen species. Several studies suggested relationship between XOR and atherosclerotic diseases; however, few previous studies have directly examined the relationship between XOR and vascular endothelial dysfunction in patients with type 1 diabetes mellitus (T1DM). The aim of this study was to evaluate the relationship between XOR activity and vascular endothelial function in patients with T1DM.

METHODS

Seventy-one patients with T1DM participated in the study and underwent assessments, including plasma XOR activity and flow-mediated dilation (FMD), to measure vascular endothelial function.

RESULTS

The natural logarithm value of XOR activity (ln-XOR) was 3.03 ± 0.99 pmol/h/mL, and FMD was 5.5% ± 2.4%. FMD was inversely and significantly correlated with ln-XOR (correlation coefficient: r = - 0.396, P < 0.001), UA (r = - 0.252, P = 0.034), and asymmetric dimethylarginine (ADMA) (r = - 0.414, P < 0.001). ln-XOR showed positive correlation with HbA1c (r = 0.292, P = 0.013), ALT (r = 0.658, P < 0.001), and ADMA (r = 0.363, P = 0.002). Stepwise multiple regression analysis showed that ln-XOR (standard partial regression coefficient: β = - 0.254, P = 0.018) was an independent explanatory variable of FMD.

CONCLUSIONS

The results of this study showed for the first time that XOR activity is associated with glycemic control in patients with T1DM and that XOR activity is associated with vascular endothelial dysfunction.

A novel mechanism of vitamin D anti-inflammatory/antioxidative potential in type 2 diabetic patients on metformin therapy

INTRODUCTION

The performed study focused on determining the effect of vitamin D supplementation on enzymes involved in both inflammation and reactive oxygen species (ROS) production and ROS degradation in patients with type 2 diabetes mellitus (T2DM).

MATERIAL AND METHODS

The 6-month follow-up, randomized, controlled study included 140 patients with T2DM, ≥ 30 years old, with good metabolic control, treated with metformin and lifestyle advice only. All patients were randomly assigned to two groups (70 each). Patients from the first group (Intervention group) were assigned to receive vitamin D3 50 000 IU or 14 000 IU regarding their vitamin D baseline levels. Patients from the second (Metformin) group continued to receive only metformin during the 6-month study period.

RESULTS

After 6 months, the myeloperoxidase activity was significantly lower and gradually decreased in the Intervention group by about 40%, compared to the baseline measurement (p = 0.015) and compared to the Metformin group (p = 0.001). After 6 months, the xanthine oxidase (XO) activity decreased significantly in the Intervention group compared to the baseline and 3^rd month levels (p < 0.001). In the Metformin group there was also a significant decrease in XO after 6 months compared to baseline (p < 0.001) and the 3^rd month (p = 0.003). The catalase activity significantly increased within the Intervention group only when comparing the 3^rd and 6^th month (p = 0.027).

CONCLUSIONS

Our study showed that vitamin D may improve endothelial dysfunction in patients with T2DM on metformin therapy by influencing two important factors implicated in the pathogenesis of diabetic complications - ROS production and inflammation, which can additionally contribute to a stable metabolic control during metformin therapy.

Efficacy of xanthine oxidase inhibitor for chronic kidney disease patients with hyperuricemia

BACKGROUND

Hyperuricemia is a known risk factor for end-stage renal disease. Although xanthine oxidase (XO) inhibitors are expected to protect the kidney function, evidence to this end is insufficient at present.

METHODS

This study was a multi-center, open-labeled, randomized study conducted in Mie Prefecture in Japan. Patients were included if they were between 20 and 80 years old and had a serum uric acid (sUA) level ≥ 7.0 mg/dl with or without gout, estimated glomerular filtration rate (eGFR) of 15-60 ml/min/1.73 m², and urinary protein creatinine ratio (uPCR) of 0.15-3.5 g/gCr. Patients were randomly assigned to a Topiroxostat or Febuxostat group, and the treatment target for the sUA level was < 6.0 mg/dl. The primary outcome was the change in the uPCR after 24 weeks.

RESULTS

The change in the median uPCR after 24 weeks was not statistically significant after treatment in the Topiroxostat or Febuxostat group (0.05 g/gCr and - 0.04 g/gCr, respectively). However, the sUA levels decreased significantly in both groups (Topiroxostat group: 8.6 ± 1.1 at baseline to 6.0 ± 1.1 mg/dl at 24 weeks, Febuxostat group: 8.4 ± 1.1 mg/dl at baseline to 5.9 ± 1.3 mg/dl at 24 weeks). No significant change in the eGFR after 24 weeks was noted in either the Topiroxostat or Febuxostat group (- 0.04 ± 4.59 ml/min/1.73 m² and 0.31 ± 4.70 ml/min/1.73 m², respectively).

CONCLUSIONS

In this study, XO inhibitors did not significantly reduce the uPCR in chronic kidney disease stage 3 and 4 patients with hyperuricemia.

Annual change in plasma xanthine oxidoreductase activity is associated with changes in liver enzymes and body weight

Xanthine oxidoreductase (XOR), an enzyme of uric acid formation from hypoxanthine and xanthine, is recognized as a source of oxidative stress. Plasma activity of XOR has been reported to be a biomarker of metabolic disorders associated with obesity, liver dysfunction, insulin resistance, hyperuricemia and adipokines. We investigated longitudinal change in plasma XOR activity, which was determined by using mass spectrometry and liquid chromatography to detect [¹³C₂, ¹⁵N₂]-uric acid using [¹³C₂, ¹⁵N₂]-xanthine as a substrate, in 511 subjects (male/female: 244/267) of the Tanno-Sobetsu Study in the years 2016 and 2017. Plasma XOR activity in a basal state was significantly higher in men than in women, but no significant sex difference was observed in annual change in plasma XOR activity. Annual change in plasma activity of XOR was positively correlated with changes in each parameter, including body weight (r = 0.203, p < 0.001), body mass index, diastolic blood pressure, aspartate transaminase (AST) (r = 0.772, p < 0.001), alanine transaminase (r = 0.647, p < 0.001), γ-glutamyl transpeptidase, total cholesterol, triglycerides, uric acid, fasting glucose and HbA1c. Multivariate regression analysis demonstrated that change in AST and that in body weight were independent predictors of change in plasma XOR activity after adjustment of age, sex and changes in each variable with a significant correlation without multicollinearity. In conclusion, annual change in plasma XOR activity is independently associated with changes in liver enzymes and body weight in a general population. Improvement of liver function and reduction of body weight would decrease plasma XOR activity and its related oxidative stress as a therapeutic strategy.

Xanthine oxidase activity in type 2 diabetic Nigerians

AIM

This study evaluated the activity of xanthine oxidase in Nigerians with type 2 diabetic mellitus as well as its relationship with lipid peroxidation, inflammatory bio markers and glycemic control indices.

METHODS

Two hundred and thirty seven (237) subjects, comprising of one hundred and fifty seven (157) DM subjects and eighty (80) aged matched controls participated in this study. Blood samples were collected from the participants for the estimations of xanthine oxidase activity, uric acid, malon diadehyde (MDA), erythrocyte sedimentation rate (ESR), high sensitive c - reactive protein (hs CRP), glucose, fructosamine and glycosylated hemoglobin by standard methods.

RESULTS

The results of this study showed a significantly increased activity of xanthine oxidase in DM (0.044 ± 0.05μ/mg) compared with apparently healthy controls (0.028 ± 0.00 μ/mg). The mean plasma levels of MDA (42.40 ± 2.50μmol/l) and uric acid (7.22 ± 0.20 mg/dl) in DM were significantly higher (p ≤ 0.05) than healthy non DM group. The mean levels of hs CRP in DM (4.09 ± 0.91μg/ml) was significantly higher than controls (1.30 ± 0.50μg/ml, p = 0.009). While no association of xanthine oxidase was observed with glycemic control indices and hs CRP, a negative association of xanthine oxidase was observed with MDA (r = -0.514, p = 0.000).

CONCLUSION

Increased activity of xanthine oxidase in DM was associated with increased lipid peroxidation and could be a salient entity towards the onset on complications.

Brown rice-specific γ-oryzanol as a promising prophylactic avenue to protect against diabetes mellitus and obesity in humans

Chronic overconsumption of animal fats causes a variety of health problems, including diabetes mellitus and obesity. Underlying molecular mechanisms encompass leptin resistance, a decrease in rewarding effects of physical activities, xanthine oxidase-induced oxidative stress in vasculature and peripheral tissue, impaired activation of incretin signaling, deviation in food preference, and dysbiosis of gut microbiota. Based on our clinical observation that daily intake of brown rice effectively ameliorates bodyweight gain, impaired glucose tolerance/insulin resistance and dependence on fatty foods in obese, prediabetes men, a line of research on brown rice (rice bran)-derived γ-oryzanol in mice experiments, cultured cells and human clinical trials is underway in our laboratory. Our works in mice showed that γ-oryzanol, an ester mixture of ferulic acid and several kinds of phytosterols, acts as a molecular chaperone, thereby attenuating the strong preference for animal fats through suppression of endoplasmic reticulum stress in the hypothalamus. In pancreatic islets from both high-fat diet-induced and streptozotocin-induced diabetic mice, γ-oryzanol ameliorates endoplasmic reticulum stress and protects β-cells against apoptosis. Noticeably, γ-oryzanol also acts as a potent inhibitor against deoxyribonucleic acid methyltransferases in the brain reward system (striatum) in mice, thereby attenuating, at least partly, the preference for a high-fat diet through the epigenetic modulation of striatal dopamine D2 receptor. Because dopamine D2 receptor signaling in the brain reward system is considerably attenuated in obese humans and rodents, γ-oryzanol might represent a unique property to ameliorate both hedonic and metabolic dysregulation of feeding behavior, highlighting a promising prophylactic avenue to protect against metabolic derangement.

Unexpected high plasma xanthine oxidoreductase activity in female subjects with low levels of uric acid

Hypouricemia is a high-risk factor of exercise-induced acute kidney injury (EIAKI) probably through a lack of an antioxidant effect of uric acid. 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 has been proposed to promote oxidative stress-related tissue injury. We measured plasma XOR activity by a sensitive and accurate assay using a combination of liquid chromatography and triple quadrupole mass spectrometry in subjects with relatively low levels of uric acid (≤4.0 mg/dL) who were recruited from 627 subjects (male/female: 292/335) in the Tanno-Sobetsu Study, a population-based cohort. The numbers of subjects with uric acid ≤4.0 mg/dL, ≤3.0 mg/dL and ≤2.0 mg/dL were 72 (11.5%, male/female: 5/67), 13 (2.1%, all females) and 2 (0.3%, both females), respectively. Plasma XOR activities in 5 male subjects were below the median value of the 292 male subjects. In 12 (17.9%) of the 67 female subjects with uric acid ≤4.0 mg/dL, plasma XOR activities were above the upper quartile value of the 335 female subjects. Eleven of the 12 female subjects with high plasma XOR activity and a low uric acid level had liver dysfunction and/or insulin resistance. In conclusion, unexpected high plasma XOR activities were found in some female subjects with relatively low levels of uric acid. Measurement of plasma XOR activity may help to identify hypouricemic patients with a high risk for EIAKI.

Activity of xanthine oxidase in plasma correlates with indices of insulin resistance and liver dysfunction in patients with type 2 diabetes mellitus and metabolic syndrome: A pilot exploratory study

Aims/Introduction

There is controversy as to whether hyperuricemia is an independent risk factor for cardiometabolic diseases. The serum level of uric acid is affected by a wide variety of factors involved in its production and excretion. In contrast, evidence has accumulated that locally‐ and systemically‐activated xanthine oxidase (XO), a rate‐limiting enzyme for production of uric acid, is linked to metabolic derangement in humans and rodents. We therefore explored the clinical implication of plasma XO activity in patients with type 2 diabetes mellitus and metabolic syndrome (MetS).

Materials and Methods

We enrolled 60 patients with type 2 diabetes mellitus and MetS. MetS was defined according to the 2005 International Diabetes Federation guidelines. Plasma XO activity was measured by highly‐sensitive fluorometric assay measuring the conversion of pterin to isoxanthopterin, and explored associations between the value of plasma XO activity and metabolic parameters.

Results

The value of plasma XO activity was correlated with indices of insulin resistance and the level of circulating liver transaminases. In contrast, the level of serum uric acid was not correlated with indices of insulin resistance. The value of plasma XO activity was not correlated with the serum uric acid level.

Conclusions

Plasma XO activity correlates with indices of insulin resistance and liver dysfunction in Japanese patients with type 2 diabetes mellitus and MetS. Through assessing the plasma XO activity, patients showing normal levels of serum uric acid with higher activity of XO can be screened, thereby possibly providing a clue to uncovering metabolic risks in type 2 diabetes mellitus and MetS patients.