Regulation of xanthine oxidoreductase by intracellular iron

Iron metabolism in rheumatic diseases

Iron is a crucial element for living organism in terms of oxygen transport, hematopoiesis, enzymatic activity, mitochondrial respiratory chain function and also immune system function. The human being has evolved a mechanism to regulate body iron. In some rheumatic diseases such as rheumatoid arthritis (RA), systemic lupus erythematous (SLE), systemic sclerosis (SSc), ankylosing spondylitis (AS), and gout, this balanced iron regulation is impaired. Altered iron homeostasis can contribute to disease progression through ROS production, fibrosis, inflammation, abnormal bone homeostasis, NETosis and cell senescence. In this review, we have focused on the iron metabolism in rheumatic disease and its role in disease progression.

Association between urinary metal concentrations and hyperuricemia in Chinese community-dwelling elderly: Exploring the mediating role of estimating glomerular filtration rate

BACKGROUND

It has been shown that multiple metals exposure is associated with hyperuricemia. However, previous studies on the association and interaction between multiple metals exposure and hyperuricemia have been controversial, and there has been little evaluation of the potential mediating role of estimating glomerular filtration rate (eGFR).

METHODS

In this study, levels of 12 metals in the urine of 3756 study participants were measured using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The associations between urinary metals and the hyperuricemia were analyzed by multivariable logistic regression model and restricted cubic spline (RCS). Weighted Quantile Sum (WQS) regression was used to explore the weight of each metal. Bayesian Kernel Machine Regression (BKMR) was used to explore the join effect of mixed metal exposure. Mediation analysis was used to explore the role of eGFR in relationship between urinary metal concentration and hyperuricemia.

RESULTS

In the multi-metal model, the multivariate-adjusted odds ratio (OR) and 95 % confidence interval (CI) of hyperuricemia were 0.89 (0.81,0.99) for Fe, 0.79 (0.70,0.89) for Se, 0.84 (0.75,0.93) for Cd, 0.87 (0.79,0.96) for Pb, 1.36 (1.23,1.51) for Zn (all P < 0.05). The RCS regression indicated signification nonlinear associations for Zn and Pb (all P-non-linear <0.05). The WQS regression model based on the negative fit showed that the maximum weight of Cd is 43.1 %. In the BKMR model, metal mixtures showed an overall negative association with the risk of developing hyperuricemia, and we also found interactions between Zn and Pb. Mediation analysis showed that eGFR mediated the association between Fe, Se, Cd, Pb and hyperuricemia with mediation ratios of 11.18 %, 12.10 %, 9.60 %, and 12.01 %, respectively.

CONCLUSIONS

The metal mixture in urine is negatively correlated with hyperuricemia, with Cd having the greatest impact. eGFR may play a partial role in association of Fe, Se, Cd and Pb exposure with hyperuricemia.

Association between serum iron status and gout: results from the NHANES and Mendelian randomization study

Aims. Previous observational studies have provided inconsistent evidence for the association between serum iron status and the risk of gout. Moreover, it remains uncertain whether the observed association is causal or due to confounding or reverse causality. This research aimed to investigate the association of serum iron status indicators with the risk of gout and to further examine the causal relationship by the Mendelian randomization (MR) method. Methods. We first conducted a cross-sectional study from the National Health and Nutrition Examination Survey 2017-2018, including a total of 4635 participants. The association of serum iron status indicators with gout risk was evaluated using a multivariable logistic regression model. Furthermore, a two-sample MR study using genetic data from large-scale genome-wide association studies of serum iron status indicators (246 139 individuals) and gout (discovery: 13 179 cases and 75 0634 controls; replication: 5292 cases and 368 788 controls; 2115 cases and 67 259 controls) was conducted to infer causality. Inverse-variance-weighting (IVW) was applied as the main method of MR analysis. A series of sensitivity analyses were used to evaluate the robustness of their relationship. Results. In the cross-sectional study, there was no significant relationship between serum iron status indicators and gout risk. However, IVW results showed that genetically predicted serum iron and transferrin saturation (TSAT) were significantly associated with the increased risk of gout in the discovery analysis [odds ratio (OR): 1.21; 95% confidence interval (CI): 1.10-1.32; P = 9.80 × 10-5 for serum iron and OR: 1.16; 95% CI: 1.08-1.25; P = 7.14 × 10-5 for TSAT]. The replication analysis provided similar results compared with the discovery analysis. Conclusion. Our study provides support for potential causal associations between serum iron and the altered risk of gout. Further investigations are warranted to elucidate the biological processes through which iron influences susceptibility to gout.

Autonomous Defense Based on Biogenic Nanoparticle Formation in Daunomycin-Producing Streptomyces

Daunomycin is a chemotherapeutic agent widely used for the treatment of leukemia, but its toxicity toward healthy dividing cells limits its clinical use and its production by fermentation. Herein, we describe the development of a specialized cultivation medium for daunomycin production, including a shift to oil rather than sugar as the primary carbon source. This achieved an almost threefold increase in daunomycin yields, reaching 5.5-6.0 g/L. Daunomycin produced in the oil-based medium was predominantly found in the solid sediment, whereas that produced in the sugar-based medium was mostly soluble. The oil-based medium thus induces an autonomous daunomycin-resistance mechanism involving biogenic nanoparticle formation. The characterization of the nanoparticles confirmed the incorporation of iron and daunomycin, indicating that this approach has the potential to mitigate cytotoxicity while improving yields. The presence of proteins associated with iron homeostasis and oxidative stress responses revealed the ability of the production strain to adapt to high iron concentrations. Our findings provide insight into the mechanisms of biogenic nanoparticle formation and the optimization of cultivation processes. Further investigation will help to refine microbial production systems for daunomycin and also broaden the application of similar strategies for the synthesis of other therapeutically important compounds.

Role of AMP deaminase in diabetic cardiomyopathy

Diabetes mellitus is one of the major causes of ischemic and nonischemic heart failure. While hypertension and coronary artery disease are frequent comorbidities in patients with diabetes, cardiac contractile dysfunction and remodeling occur in diabetic patients even without comorbidities, which is referred to as diabetic cardiomyopathy. Investigations in recent decades have demonstrated that the production of reactive oxygen species (ROS), impaired handling of intracellular Ca2+, and alterations in energy metabolism are involved in the development of diabetic cardiomyopathy. AMP deaminase (AMPD) directly regulates adenine nucleotide metabolism and energy transfer by adenylate kinase and indirectly modulates xanthine oxidoreductase-mediated pathways and AMP-activated protein kinase-mediated signaling. Upregulation of AMPD in diabetic hearts was first reported more than 30 years ago, and subsequent studies showed similar upregulation in the liver and skeletal muscle. Evidence for the roles of AMPD in diabetes-induced fatty liver, sarcopenia, and heart failure has been accumulating. A series of our recent studies showed that AMPD localizes in the mitochondria-associated endoplasmic reticulum membrane as well as the sarcoplasmic reticulum and cytosol and participates in the regulation of mitochondrial Ca2+ and suggested that upregulated AMPD contributes to contractile dysfunction in diabetic cardiomyopathy via increased generation of ROS, adenine nucleotide depletion, and impaired mitochondrial respiration. The detrimental effects of AMPD were manifested at times of increased cardiac workload by pressure loading. In this review, we briefly summarize the expression and functions of AMPD in the heart and discuss the roles of AMPD in diabetic cardiomyopathy, mainly focusing on contractile dysfunction caused by this disorder.

Ferroptosis in Arthritis: Driver of the Disease or Therapeutic Option?

Ferroptosis is a form of iron-dependent regulated cell death caused by the accumulation of lipid peroxides. In this review, we summarize research on the impact of ferroptosis on disease models and isolated cells in various types of arthritis. While most studies have focused on rheumatoid arthritis (RA) and osteoarthritis (OA), there is limited research on spondylarthritis and crystal arthropathies. The effects of inducing or inhibiting ferroptosis on the disease strongly depend on the studied cell type. In the search for new therapeutic targets, inhibiting ferroptosis in chondrocytes might have promising effects for any type of arthritis. On the other hand, ferroptosis induction may also lead to a desired decrease of synovial fibroblasts in RA. Thus, ferroptosis research must consider the cell-type-specific effects on arthritis. Further investigation is needed to clarify these complexities.

Gout and Diet: A Comprehensive Review of Mechanisms and Management

Gout is well known as an inflammatory rheumatic disease presenting with arthritis and abnormal metabolism of uric acid. The recognition of diet-induced systemic metabolic pathways have provided new mechanistic insights and potential interventions on gout progression. However, the dietary recommendations for gouty patients generally focus on food categories, with few simultaneous considerations of nutritional factors and systemic metabolism. It is worthwhile to comprehensively review the mechanistic findings and potential interventions of diet-related nutrients against the development of gout, including purine metabolism, urate deposition, and gouty inflammation. Although piecemeal modifications of various nutrients often provide incomplete dietary recommendations, understanding the role of nutritional factors in gouty development can help patients choose their healthy diet based on personal preference and disease course. The combination of dietary management and medication may potentially achieve enhanced treatment effects, especially for severe patients. Therefore, the role of dietary and nutritional factors in the development of gout is systematically reviewed to propose dietary modification strategies for gout management by: (1) reducing nutritional risk factors against metabolic syndrome; (2) supplementing with beneficial nutrients to affect uric acid metabolism and gouty inflammation; and (3) considering nutritional modification combined with medication supplementation to decrease the frequency of gout flares.

Ferroptosis in inflammatory arthritis: A promising future

Ferroptosis is a kind of regulatory cell death (RCD) caused by iron accumulation and lipid peroxidation, which is characterized by mitochondrial morphological changes and has a complex regulatory network. Ferroptosis has been gradually emphasized in the pathogenesis of inflammatory arthritis. In this review, we summarized the relevant research on ferroptosis in various inflammatory arthritis including rheumatoid arthritis (RA), osteoarthritis, gout arthritis, and ankylosing spondylitis, and focused on the relationship between RA and ferroptosis. In patients with RA and animal models of RA, there was evidence of iron overload and lipid peroxidation, as well as mitochondrial dysfunction that may be associated with ferroptosis. Ferroptosis inducers have shown good application prospects in tumor therapy, and some anti-rheumatic drugs such as methotrexate and sulfasalazine have been shown to have ferroptosis modulating effects. These phenomena suggest that the role of ferroptosis in the pathogenesis of inflammatory arthritis will be worth further study. The development of therapeutic strategies targeting ferroptosis for patients with inflammatory arthritis may be a promising future.

Biomarkers of iron status in allopurinol-treated renal stone patients

Limited evidence exists on the effect of xanthine oxidase inhibitors in nephrolithiasis patients on iron status markers, beyond their effects on urate. The aim of this study was to investigate whether allopurinol therapy was associated with a significant impact on parameters related to iron status, in patients with renal stones. Allopurinol treatment was associated with a nonsignificant decline in serum uric acid. There were no significant differences in serum levels of transferrin and ferritin after treatment with allopurinol compared to pre-treatment levels. A non-significant fall in serum levels of haptoglobin was registered. The drug was associated with a significant rise in serum iron levels. Serum uric acid and iron did not show a significant correlation with any parameter in the study. Allopurinol exerted an overall non-significant effect on iron metabolism in nephrolithiasis patients, save for serum iron, this entails lack of untoward effects in populations with-iron related conditions.

Combined Associations of Serum Ferritin and Body Size Phenotypes With Cardiovascular Risk Profiles: A Chinese Population-Based Study

Background: Serum ferritin (SF) has been correlated with one or more metabolic syndrome features associated with an increased risk for cardiovascular disease (CVD). This study explored the associations between SF and CVD risk factors among different body size phenotypes that were based on metabolic status and body mass index (BMI) categories. Methods: A cross-sectional study was performed using a cohort of 7,549 Chinese adults from the China Health and Nutrition Survey. Participants did not exhibit acute inflammation, were not underweight and were stratified based on their metabolic status and BMI categories. The metabolically at-risk status was defined as having two or more criteria of the Adult Treatment Panel-III metabolic syndrome definition, excluding waist circumference. Results: Compared with individuals without high SF, subjects with high SF had an increased risk of diabetes in the metabolically at-risk normal-weight (MANW) and metabolically at-risk overweight/obesity (MAO) groups. The multivariate-adjusted odds ratios (ORs) were 1.52 [95% confidence interval (Cls): 1.02, 2.28] and 1.63 (95% Cls: 1.27, 2.09), respectively. Adjusted ORs for hyperuricemia from high SF in metabolically healthy normal-weight (MHNW), metabolically healthy overweight/obesity (MHO), MANW, and MAO phenotypes were 1.78 (95% Cls: 1.26, 2.53), 1.42 (95% Cls: 1.03, 1.95), 1.66 (95% Cls: 1.17, 2.36), and 1.42 (95% Cls: 1.17, 1.73), respectively. Similarly, positive correlations of high SF with triglycerides, non-high-density lipoprotein cholesterol, and apolipoprotein B100 were observed in all phenotypes. No association between high SF and elevated low-density lipoprotein cholesterol were observed among participants who were metabolically at-risk, regardless of their BMI categories. However, the ORs for elevated low-density lipoprotein cholesterol from high SF were 1.64 (95% Cls: 1.29, 2.08) in the MHNW group and 1.52 (95% Cls:1.22, 1.91) in the MHO group, significantly. This study demonstrated that the highest ORs were in MAO with a high SF group for all unfavorable CVD risk factors except low-density lipoprotein cholesterol (all p < 0.001). Conclusions: The associations of high SF with the prevalence of CVD risk factors, including diabetes, dyslipidemia, and hyperuricemia, vary in individuals among different body size phenotypes. In the MAO group, subjects with high SF levels exhibited worse CVD risk profiles than individuals without high SF.

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

BACKGROUND

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Associations of serum iron and ferritin with hyperuricemia and serum uric acid

OBJECTIVES

To assess the serum iron and ferritin levels in relation to the prevalence of hyperuricemia (HU) and the serum uric acid (SUA) level.

METHODS

Serum iron and ferritin concentrations were detected by Ferene method and chemiluminescence method, respectively. SUA level was detected by uricase-PAP method. HU was defined as SUA ≥ 416 μmol/L for male and ≥ 357 μmol/L for female. Multivariable-adjusted logistic regressions were constructed to investigate the associations between serum iron/ferritin levels and prevalence of HU. Pearson correlation analysis and multivariable linear regression were performed to examine the correlations between serum iron/ferritin levels and SUA level.

RESULTS

A total of 2824 subjects (mean age 52.2 ± 7.2) were included. The overall prevalence of HU was 17.3%. Compared with the lowest quartile, the multivariable-adjusted odds ratios (OR) and its 95% confidence interval (CI) of HU were 1.33 (95%CI 0.97-1.82), 1.17 (95%CI 0.85-1.60), and 1.56 (95%CI 1.14-2.13) in the second, third, and fourth quartiles of serum iron, respectively (P for trend = 0.012), and were 1.29 (95%CI 0.89-1.88) in the second, 2.13 (95%CI 1.47-3.07) in the third, and 2.25 (95%CI 1.54-3.29) in the fourth quartile of serum ferritin (P for trend < 0.001). Pearson correlation coefficient indicated a weak positive correlation between serum iron (r = 0.2, P < 0.001) and ferritin (r = 0.3, P < 0.001) levels and SUA. Such positive correlations were further confirmed by multiple linear regression (serum iron: standardized β = 0.059, P < 0.001; serum ferritin: standardized β = 0.061, P = 0.001).

CONCLUSIONS

Both serum iron and ferritin showed a positive correlation with the prevalence of HU, and a weak positive correlation with SUA level. Key Points • Subjects with higher levels of serum iron or ferritin had higher prevalence of HU. • There was a weak positive correlation between serum iron/ferritin levels and SUA level.

Xanthine oxidase-mediated oxidative stress promotes cancer cell-specific apoptosis

The natural compound Alternol was shown to induce profound oxidative stress and apoptotic cell death preferentially in cancer cells. In this study, a comprehensive investigation was conducted to understand the mechanism for Alternol-induced ROS accumulation responsible for apoptotic cell death. Our data revealed that Alternol treatment moderately increased mitochondrial superoxide formation rate, but it was significantly lower than the total ROS positive cell population. Pre-treatment with mitochondria-specific anti-oxidant MitoQ, NOX or NOS specific inhibitors had no protective effect on Alternol-induced ROS accumulation and cell death. However, XDH/XO inhibition by specific small chemical inhibitors or gene silencing reduced total ROS levels and protected cells from apoptosis induced by Alternol. Further analysis revealed that Alternol treatment significantly enhanced XDH oxidative activity and induced a strong protein oxidation-related damage in malignant but not benign cells. Interestingly, benign cells exerted a strong spike in anti-oxidant SOD and catalase activities compared to malignant cells after Alternol treatment. Cell-based protein-ligand engagement and in-silicon docking analysis showed that Alternol interacts with XDH protein on the catalytic domain with two amino acid residues away from its substrate binding sites. Taken together, our data demonstrate that Alternol treatment enhances XDH oxidative activity, leading to ROS-dependent apoptotic cell death.

The relationship between ferritin and urate levels and risk of gout

BACKGROUND

Ferritin positively associates with serum urate and an interventional study suggests that iron has a role in triggering gout flares. The objective of this study was to further explore the relationship between iron/ferritin and urate/gout.

METHODS

European (100 cases, 60 controls) and Polynesian (100 cases, 60 controls) New Zealand (NZ) males and 189 US male cases and 60 male controls participated. The 10,727 participants without gout were from the Jackson Heart (JHS; African American = 1260) and NHANES III (European = 5112; African American = 4355) studies. Regression analyses were adjusted for age, sex, body mass index and C-reactive protein. To test for a causal relationship between ferritin and urate, bidirectional two-sample Mendelian randomization analysis was performed.

RESULTS

Serum ferritin positively associated with gout in NZ Polynesian (OR (per 10 ng ml- 1 increase) = 1.03, p = 1.8E-03) and US (OR = 1.11, p = 7.4E-06) data sets but not in NZ European (OR = 1.00, p = 0.84) data sets. Ferritin positively associated with urate in NZ Polynesian (β (mg dl- 1) = 0.014, p = 2.5E-04), JHS (β = 0.009, p = 3.2E-05) and NHANES III (European β = 0.007, p = 5.1E-11; African American β = 0.011, p = 2.1E-16) data sets but not in NZ European (β = 0.009, p = 0.31) or US (β = 0.041, p = 0.15) gout data sets. Ferritin positively associated with the frequency of gout flares in two of the gout data sets. By Mendelian randomization analysis a one standard deviation unit increase in iron and ferritin was, respectively, associated with 0.11 (p = 8E-04) and 0.19 mg dl- 1 (p = 2E-04) increases in serum urate. There was no evidence for a causal effect of urate on iron/ferritin.

CONCLUSIONS

These data replicate the association of ferritin with serum urate. Increased ferritin levels associated with gout and flare frequency. There was evidence of a causal effect of iron and ferritin on urate.

Markers of Iron Status Are Associated with Risk of Hyperuricemia among Chinese Adults: Nationwide Population-Based Study

Background: Elevated serum uric acid (SUA) involved in iron metabolism, has been increasingly recognized as a risk factor for gout and cardiovascular diseases. The objective of this study was to examine the associations between markers of iron status with risk of hyperuricemia (HU) in Chinese adult population. Methods: Data were extracted from the 2009 wave of the China Health and Nutrition Survey, consisting of 7946 apparently healthy adults. Serum ferritin (SF), transferrin, soluble transferrin receptors (sTfR), hemoglobin (Hb), high-sensitivity C-reactive protein (hs-CRP), and SUA were measured. Diet was assessed with three consecutive 24 h recalls. Demographic characteristics, smoking status, alcohol consumption, and physical activities were investigated using a structured questionnaire. Multilevel mixed-effects models were constructed to estimate the associations of SF, transferrin, sTfR, and Hb with SUA and the risk of HU. Results: The crude prevalence of HU was 16.1%. SF, transferrin, and Hb levels were positively associated with SUA and the risk of HU after adjustment for cluster effects and potential confounders (all p-trend < 0.05). Compared with participants in the lowest quartile of SF, those in the highest quartile had significantly higher SUA concentrations (β = 0.899 mg/dL, 95% confidence interval (CI): 0.788, 1.010; p < 0.001) and higher risk of HU (odds ratio (OR) = 3.086, 95% CI: 2.450, 3.888; p < 0.001). Participants with the highest quartile of transferrin had significantly higher SUA concentrations (β = 0.488 mg/dL, 95% CI: 0.389, 0.587; p < 0.001) and higher risk of HU (OR: 1.900; 95% CI: 1.579, 2.286; p < 0.001) when compared with those with the lowest quartile. In male participants, those in the highest quartile of Hb had significantly higher risk of HU when compared to the reference group (OR: 1.401, 95% CI: 1.104, 1.777; p < 0.01); however, this association was not found in female participants (OR: 1.093; 95% CI: 0.821, 1.455; p = 0.544). Conclusion: SF, transferrin, and Hb levels were positively associated with the risk of HU, and additional studies are needed to confirm the findings, as well as to elucidate their underlying mechanisms.

Hyperferritinemia increases the risk of hyperuricemia in HFE-hereditary hemochromatosis

OBJECTIVES

Hyperuricemia is becoming increasingly frequent in the population, and is known to be sometimes the cause of gout. The impact of uric acid is still not clearly understood, however. The iron metabolism may interact with the uric acid metabolism. The aim of this study was to examine the relationship between the serum uric acid and serum ferritin levels in a cohort of hemochromatosis patients who were homozygous for the HFE p.Cys282Tyr mutation.

METHODS

738 patients with the HFE gene mutation Cys282Tyr in the homozygous state were included in the study. The variables measured during the initial evaluation were compared in univariate analysis by Student's t test. In multivariate analysis, linear stepwise regression was used.

RESULTS

In the group of hyperuricemic patients, ferritinemia was significantly higher than in the group of non-hyperuricemic patients (1576.7±1387.4μg/l vs. 1095.63±1319.24μg/l, P<0.005). With multivariate analysis, only ferritin and BMI independently explained the uricemia (R²=0.258) after adjustment for age, glycemia and CRP. The correlation between uricemia and log(ferritin) with partial regression correlation coefficients was 0.307 (P<0.01).

CONCLUSIONS

The increase in uricemia is associated with the increase in ferritin in a population of patients who were homozygous for the HFE gene mutation p.Cys282Tyr and this independently of factors commonly associated with hyperuricemia. The increase in uric acid associated with hyperferritinemia, could be a response to the visceral toxicity of excess non-transferrin bound iron linked to oxidative stress via the antioxidant properties of uric acid.

Prolonged fasting increases purine recycling in post-weaned northern elephant seals

Northern elephant seals are naturally adapted to prolonged periods (1-2 months) of absolute food and water deprivation (fasting). In terrestrial mammals, food deprivation stimulates ATP degradation and decreases ATP synthesis, resulting in the accumulation of purines (ATP degradation byproducts). Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) salvages ATP by recycling the purine degradation products derived from xanthine oxidase (XO) metabolism, which also promotes oxidant production. The contributions of HGPRT to purine recycling during prolonged food deprivation in marine mammals are not well defined. In the present study we cloned and characterized the complete and partial cDNA sequences that encode for HGPRT and xanthine oxidoreductase (XOR) in northern elephant seals. We also measured XO protein expression and circulating activity, along with xanthine and hypoxanthine plasma content in fasting northern elephant seal pups. Blood, adipose and muscle tissue samples were collected from animals after 1, 3, 5 and 7 weeks of their natural post-weaning fast. The complete HGPRT and partial XOR cDNA sequences are 771 and 345 bp long and encode proteins of 218 and 115 amino acids, respectively, with conserved domains important for their function and regulation. XOR mRNA and XO protein expression increased 3-fold and 1.7-fold with fasting, respectively, whereas HGPRT mRNA (4-fold) and protein (2-fold) expression increased after 7 weeks in adipose tissue and muscle. Plasma xanthine (3-fold) and hypoxanthine (2.5-fold) levels, and XO (1.7- to 20-fold) and HGPRT (1.5- to 1.7-fold) activities increased during the last 2 weeks of fasting. Results suggest that prolonged fasting in elephant seal pups is associated with increased capacity to recycle purines, which may contribute to ameliorating oxidant production and enhancing the supply of ATP, both of which would be beneficial during prolonged food deprivation and appear to be adaptive in this species.

Untargeted plasma metabolite profiling reveals the broad systemic consequences of xanthine oxidoreductase inactivation in mice

A major challenge in systems biology is integration of molecular findings for individual enzyme activities into a cohesive high-level understanding of cellular metabolism and physiology/pathophysiology. However, meaningful prediction for how a perturbed enzyme activity will globally impact metabolism in a cell, tissue or intact organisms is precluded by multiple unknowns, including in vivo enzymatic rates, subcellular distribution and pathway interactions. To address this challenge, metabolomics offers the potential to simultaneously survey changes in thousands of structurally diverse metabolites within complex biological matrices. The present study assessed the capability of untargeted plasma metabolite profiling to discover systemic changes arising from inactivation of xanthine oxidoreductase (XOR), an enzyme that catalyzes the final steps in purine degradation. Using LC-MS coupled with a multivariate statistical data analysis platform, we confidently surveyed >3,700 plasma metabolites (50-1,000 Da) for differential expression in XOR wildtype vs. mice with inactivated XOR, arising from gene deletion or pharmacological inhibition. Results confirmed the predicted derangements in purine metabolism, but also revealed unanticipated perturbations in metabolism of pyrimidines, nicotinamides, tryptophan, phospholipids, Krebs and urea cycles, and revealed kidney dysfunction biomarkers. Histochemical studies confirmed and characterized kidney failure in xor-nullizygous mice. These findings provide new insight into XOR functions and demonstrate the power of untargeted metabolite profiling for systemic discovery of direct and indirect consequences of gene mutations and drug treatments.

Xanthine oxidoreductase - clinical significance in colorectal cancer and in vitro expression of the protein in human colon cancer cells

Xanthine oxidoreductase (XOR) is a key enzyme in degradation of DNA and RNA, and has previously been shown to be decreased in aggressive breast and gastric cancer. In this study, XOR expression was assessed in tissue microarray specimens of 478 patients with colorectal cancer and related to clinical parameters. In addition, we performed in vitro studies of XOR activity, protein and mRNA in colon cancer cells (Caco-2). Results from the tissue expression analyses show that XOR was decreased in 62% and undetectable in 22% of the tumours as compared to normal tissue. Loss of XOR was associated with poor grade of differentiation (p=0.006) and advanced Dukes stage (p=0.03). In multivariate survival analysis, XOR was a prognostic factor (p=0.008), independent of Dukes stage, histological grade, age and tumour location. The in vitro analyses show that XOR is not measurable in undifferentiated Caco-2 cells, but appears and increases with differentiation. We conclude that XOR expression is associated with histological grade of differentiation and extent of disease in colorectal cancer, and it provides significant prognostic information independently of established factors.

The prophylactic protective effect of sesamol against ferric-nitrilotriacetate-induced acute renal injury in mice

The aim of this study was to examine the prophylactic protective effects of 3,4-methylenedioxyphenol (sesamol) on ferric-nitrilotriacetate (Fe-NTA)-induced acute renal damage in mice. We induced acute renal injury in mice by treating them with 4 mg/kg of Fe-NTA for 3h. We used blood biochemistry, creatinine clearance, and histological examinations to assess renal function. With a high-performance chemiluminescence analyzer, we also determined the hydroxyl radical and superoxide anion levels (free radicals) generated. Renal xanthine oxidase activities were also assessed. Sesamol inhibited Fe-NTA-induced acute renal injury, renal lipid peroxidation, the levels of renal hydroxyl radical and superoxide anion generated, and the activity of xanthine oxidase in mice. Therefore, we concluded that sesamol protected mice against Fe-NTA-induced oxidative-stress-associated acute renal injury by at least partially inhibiting the production of reactive oxygen species.

Post-transcriptional regulation of plasminogen activator inhibitor-1 by intracellular iron in cultured human lung fibroblasts--interaction of an 81-kDa nuclear protein with the 3'-UTR

The proteinase inhibitor, type-1 plasminogen activator inhibitor (PAI-1), is a major regulator of the plasminogen activator system involved in plasmin formation and fibrinolysis. The present study explores the effects of intracellular iron on the expression of PAI-1 and associated cell-surface plasmin activity in human lung fibroblasts; and reports the presence of a novel iron-responsive protein. ELISA revealed a dose-dependent increase in PAI-1 antigen levels expressed in the conditioned medium of cells treated with deferoxamine, in the three cell lines studied. A concomitant increase in mRNA levels was also observed by Northern analyses. Presaturation with ferric citrate quenched the effect of deferoxamine. Experiments with transcription and translation inhibitors on TIG 3-20 cells demonstrated that intracellular iron modulated PAI-1 expression at the post-transcriptional level with the requirement of de-novo protein synthesis. Electrophoretic mobility shift assay and UV crosslinking assays revealed the presence of an approximately 81-kDa nuclear protein that interacted with the 3'-UTR of PAI-1 mRNA in an iron-sensitive manner. Finally, we demonstrated that the increased PAI-1 is functional in suppressing cell-surface plasmin activity, a process that can affect wound healing and tissue remodeling.

Vascular physiology and pathology of circulating xanthine oxidoreductase: from nucleotide sequence to functional enzyme

The evolutionarily conserved, cofactor-dependent, enzyme xanthine oxidoreductase exists in both cell-associated and circulatory forms. The exact role of the circulating form is not known; however, several putative physiological and pathological functions have been suggested that range from purine catabolism to a mediator of acute respiratory distress syndrome. Regulation of gene expression, cofactor synthesis and insertion, post-translational conversion, entry into the circulation, and putative physiological and pathological roles for human circulating xanthine oxidoreductase are discussed.

Renal xanthine oxidoreductase activity during development of hypertension in spontaneously hypertensive rats

BACKGROUND

Hyperuricaemia and reactive oxygen species have recently been associated with essential hypertension. Xanthine oxidoreductase (XOR) produces urate and, in its oxidase isoform, reactive oxygen species also. Our previous studies indicated that hypertension-prone rat strains have greater renal XOR activity than their normotensive counterparts, and that dietary sodium modifies renal XOR activity.

OBJECTIVE

To clarify whether renal XOR induction precedes or follows the development of hypertension.

METHODS

Five-week-old spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats were kept for 3-8 weeks on low sodium (0.3% salt w/w) or high sodium (6.0% salt w/w) intakes, with or without allopurinol, an inhibitor of XOR, to study the possible pathogenetic role of XOR in hypertension. Systolic blood pressure (SBP), renal XOR activity and mRNA expression were measured.

RESULTS

Regardless of sodium intake, renal XOR activity increased twofold during growth in SHRs, but not in WKY rats. SBP increased from 122 +/- 4 to 241 +/- 13 mmHg in SHRs kept on the high-sodium diet and to 204 +/- 11 mmHg in those on the low-sodium diet. At the end of the experiment, renal XOR activity correlated with SBP in SHRs. Allopurinol prevented hypertension-induced left ventricular and renal hypertrophy in SHRs, but had negligible effect on blood pressure.

CONCLUSION

Renal XOR induction in SHRs does not precede the development of hypertension, but progress concomitantly with an increase in SBP. The results indicate a role for locally synthesized XOR in the development of hypertension-associated end-organ damage, but no major role in the development of hypertension.

Posttranslational inactivation of human xanthine oxidoreductase by oxygen under standard cell culture conditions

Xanthine oxidoreductase (XOR) catalyzes the final reactions of purine catabolism and may account for cell damage by producing reactive oxygen metabolites in cells reoxygenated after hypoxia. We found a three- to eightfold higher XOR activity in cultured human bronchial epithelial cells exposed to hypoxia (0.5-3% O2) compared with cells grown in normoxia (21% O2) but no difference in XOR protein or mRNA. XOR promoter constructs failed to respond to hypoxia. The cellular XOR activity at 3% O2 returned to basal levels when the cells were returned to 21% O2, and hyperoxia (95% O2) abolished enzyme activity with no change in XOR protein. Our data suggest reversible enzyme inactivation by oxygen or its metabolites. NADH was normally oxidized by the oxygen-inactivated enzyme, which rules out damage to the flavin adenine dinucleotide cofactor. Hydrogen peroxide partially inactivated the molybdenum center of XOR, as shown by a parallel decrease in XOR-catalyzed xanthine oxidation and dichlorophenolindophenol reduction. We conclude that the transcription or translation of XOR is not influenced by hypoxia or hyperoxia. Instead, the molybdenum center of XOR is posttranslationally inactivated by oxygen metabolites in "normal" (21% O2) cell culture atmosphere. This inactivation is reversed in hypoxia and accounts for the apparent induction.