Update on gout: new therapeutic strategies and options

The identification of an integral membrane, cytochrome c urate oxidase completes the catalytic repertoire of a therapeutic enzyme

In living organisms, the conversion of urate into allantoin requires three consecutive enzymes. The pathway was lost in hominid, predisposing humans to hyperuricemia and gout. Among other species, the genomic distribution of the two last enzymes of the pathway is wider than that of urate oxidase (Uox), suggesting the presence of unknown genes encoding Uox. Here we combine gene network analysis with association rule learning to identify the missing urate oxidase. In contrast with the known soluble Uox, the identified gene (puuD) encodes a membrane protein with a C-terminal cytochrome c. The 8-helix transmembrane domain corresponds to DUF989, a family without similarity to known proteins. Gene deletion in a PuuD-encoding organism (Agrobacterium fabrum) abolished urate degradation capacity; the phenotype was fully restored by complementation with a cytosolic Uox from zebrafish. Consistent with H₂O₂ production by zfUox, urate oxidation in the complemented strain caused a four-fold increase of catalase. No increase was observed in the wild-type, suggesting that urate oxidation by PuuD proceeds through cytochrome c-mediated electron transfer. These findings identify a missing link in purine catabolism, assign a biochemical activity to a domain of unknown function (DUF989), and complete the catalytic repertoire of an enzyme useful for human therapy.

Uric Acid Produces an Inflammatory Response through Activation of NF-κB in the Hypothalamus: Implications for the Pathogenesis of Metabolic Disorders

Epidemiological studies have shown that an elevated uric acid (UA) level predicts the development of metabolic syndrome and diabetes; however, there is no direct evidence of this, and the underlying mechanism remains unclear. Here, we showed that a high-UA diet triggered the expression of pro-inflammatory cytokines, activated the NF-κB pathway, and increased gliosis in the hypothalamus. Intracerebroventricular injection of UA induced hypothalamic inflammation and reactive gliosis, whereas these effects were markedly ameliorated by the inhibition of NF-κB. Moreover, magnetic resonance imaging confirmed that hyperuricemia in rodents and humans was associated with gliosis in the mediobasal hypothalamus. Importantly, the rats administered UA exhibited dyslipidemia and glucose intolerance, which were probably mediated by hypothalamic inflammation and hypothalamic neuroendocrine alterations. These results suggest that UA can cause hypothalamic inflammation via NF-κB signaling. Our findings provide a potential therapeutic strategy for UA-induced metabolic disorders.

SLC transporters as therapeutic targets: emerging opportunities

Solute carrier (SLC) transporters - a family of more than 300 membrane-bound proteins that facilitate the transport of a wide array of substrates across biological membranes - have important roles in physiological processes ranging from the cellular uptake of nutrients to the absorption of drugs and other xenobiotics. Several classes of marketed drugs target well-known SLC transporters, such as neurotransmitter transporters, and human genetic studies have provided powerful insight into the roles of more-recently characterized SLC transporters in both rare and common diseases, indicating a wealth of new therapeutic opportunities. This Review summarizes knowledge on the roles of SLC transporters in human disease, describes strategies to target such transporters, and highlights current and investigational drugs that modulate SLC transporters, as well as promising drug targets.

The Association between Serum Uric Acid Levels and the Prevalence of Vulnerable Atherosclerotic Carotid Plaque: A Cross-sectional Study

Little is known about the associations between serum uric acid (SUA) levels and atherosclerotic carotid plaque vulnerability. The aim of this study was to assess the associations of SUA levels with the prevalence of vulnerable atherosclerotic carotid plaque in a community-based cohort. In the Asymptomatic Polyvascular Abnormalities Community (APAC) study, cross-sectional data from 2860 Chinese residents who underwent SUA measurement and ultrasonographic assessment of carotid plaque were analyzed. Multivariable logistic regression models were used to assess the associations of SUA levels with presence of vulnerable carotid plaque. After adjustment for potential confounders, SUA levels were significantly associated with the prevalence of vulnerable plaque amongst the middle-aged adults (odds ratio [OR] = 1.19, 95% confidence interval [CI]: 1.11-1.28). Compared to the lowest quartile, quartiles 2, 3 and 4 had a prevalence OR of 1.33 (1.02-1.74), 1.70 (1.27-2.27) and 2.05 (1.53-2.75), respectively, for the presence of vulnerable carotid plaque (p for trend across quartiles < 0.001). In the APAC study, elevated SUA levels were independently associated with the prevalence of vulnerable carotid plaque in middle-aged adults.

Practical method for the rapid screening of xanthine oxidase inhibitors in herbal extracts by high-performance liquid chromatography based on on-line precolumn enzymatic reaction

A high-performance liquid chromatography method with on-line precolumn enzymatic reaction for the screening of xanthine oxidase inhibitors in natural extracts was developed. In this method, the enzymatic reaction occurred at the capillary inlet during a predetermined waiting period, after which the reaction product, uric acid, was separated and detected by liquid chromatography using ultraviolet absorption at 295 nm. Enzyme inhibition can be read out directly from the reduced peak area of uric acid in comparison to a reference chromatogram obtained in the absence of any inhibitor. In the present study, the availability of on-line precolumn enzymatic reaction with ultraviolet detection was firstly evaluated by determining the inhibitory mechanism and IC50 values of allopurinol, a commercially available positive drug. Then, the newly developed method was applied to screening of ten natural extracts from traditional Chinese medicine and as a result, the extract of Epimedium sagittatum (Sieb. et Zucc.) Maxim was found to be most positive for xanthine oxidase inhibition. The results obtained were compared with those obtained by offline enzyme assay and the effectiveness of the present method was confirmed. A rapid, low-cost, and fully automated method for xanthine oxidase inhibitor screening was proposed.

Rising burden of gout in the UK but continuing suboptimal management: a nationwide population study

OBJECTIVES

To describe trends in the epidemiology of gout and patterns of urate-lowering treatment (ULT) in the UK general population from 1997 to 2012.

METHODS

We used the Clinical Practice Research Datalink to estimate the prevalence and incidence of gout for each calendar year from 1997 to 2012. We also investigated the pattern of gout management for both prevalent and incident gout patients.

RESULTS

In 2012, the prevalence of gout was 2.49% (95% CI 2.48% to 2.51%) and the incidence was 1.77 (95% CI 1.73 to 1.81) per 1000 person-years. Prevalence and incidence both were significantly higher in 2012 than in 1997, with a 63.9% increase in prevalence and 29.6% increase in incidence over this period. Regions with highest prevalence and incidence were the North East and Wales. Among prevalent gout patients in 2012, only 48.48% (95% CI 48.08% to 48.89%) were being consulted specifically for gout or treated with ULT and of these 37.63% (95% CI 37.28% to 38.99%) received ULT. In addition, only 18.6% (95% CI 17.6% to 19.6%) of incident gout patients received ULT within 6 months and 27.3% (95% CI 26.1% to 28.5%) within 12 months of diagnosis. The management of prevalent and incident gout patients remained essentially the same during the study period, although the percentage of adherent patients improved from 28.28% (95% CI 27.33% to 29.26%) in 1997 to 39.66% (95% CI 39.11% to 40.22%) in 2012.

CONCLUSIONS

In recent years, both the prevalence and incidence of gout have increased significantly in the UK. Suboptimal use of ULT has not changed between 1997 and 2012. Patient adherence has improved during the study period, but it remains poor.

Efficacy and safety of a urate lowering regimen in primary gout

BACKGROUND AND OBJECTIVES

Pharmacologic urate lowering therapy (ULT), at full maintenance doses, has been associated with acute gout arthritis (in up to 80% of patients). The American College of Rheumatology has recently advocated gradually titrating the maintenance dose upward to chosen serum urate target. Few studies have examined the efficacy and safety of a ULT in primary gout.

PATIENTS AND METHODS

The ULT regimen examined included allopurinol (50 mg/day, with increases of 50 mg/month up to 300 mg/day) and colchicine, as prophylaxis to prevent acute gouty attacks. The efficacy and safety of this regimen was examined in 42 patients in whom allopurinol was withheld for ≥3 months and restarted after this assessment and followed up for 12 months. The efficacy and safety of the ULT regimen was related to the serum urate decrease and to the incidence of acute gout flares, respectively.

RESULTS

Fifty-nine patients (mean age 59 years, 56 men) with primary gout received the gradually titrated ULT regimen. Baseline serum urate was (mean±SD) 8.4±0.8 mg/dL. At 3, 6, 9, and 12 months serum urate fell by a mean of 1.8, 2.5, 2.7, and 2.5 mg/dL, respectively (p<0.001). A serum urate level<6.0 mg/dL was achieved by 38/59 (64%) patients. During the 12 months following the start of the ULT we documented 10 acute arthritis episodes (17% of patients).

CONCLUSIONS

A gradually titrated hypouricemic regimen for 6 months in patients with primary gout appears to be effective and safe.

A novel enzymatic approach in the production of food with low purine content using Arxula adeninivorans endogenous and recombinant purine degradative enzymes

The purine degradation pathway in humans ends with uric acid, which has low water solubility. When the production of uric acid is increased either by elevated purine intake or by impaired kidney function, uric acid will accumulate in the blood (hyperuricemia). This increases the risk of gout, a disease described in humans for at least 1000 years. Many lower organisms, such as the yeast Arxula adeninivorans, possess the enzyme, urate oxidase that converts uric acid to 5-hydroxyisourate, thus preventing uric acid accumulation. We have examined the complete purine degradation pathway in A. adeninivorans and analyzed enzymes involved. Recombinant adenine deaminase, guanine deaminase, urate oxidase and endogenous xanthine oxidoreductase have been investigated as potential additives to degrade purines in the food. Here, we review the current model of the purine degradation pathway of A. adeninivorans and present an overview of proposed enzyme system with perspectives for its further development.

Health-related quality of life and treatment satisfaction in patients with gout: results from a cross-sectional study in a managed care setting

BACKGROUND

Patient satisfaction with treatment directly impacts adherence to medication.

OBJECTIVE

The objective was to assess and compare treatment satisfaction with the Treatment Satisfaction Questionnaire for Medication (TSQM), gout-specific health-related quality of life (HRQoL) with the Gout Impact Scale (GIS), and generic HRQoL with the SF-12v2(®) Health Survey (SF-12) in patients with gout in a real-world practice setting.

METHODS

This cross-sectional mail survey included gout patients enrolled in a large commercial health plan in the US. Patients were ≥18 years with self-reported gout diagnosis, who filled ≥1 prescription for febuxostat during April 26, 2012 to July 26, 2012 and were not taking any other urate-lowering therapies. The survey included the TSQM version II (TSQM vII, score 0-100, higher scores indicate better satisfaction), GIS (score 0-100, higher scores indicate worse condition), and SF-12 (physical component summary and mental component summary). Patients were stratified by self-report of currently experiencing a gout attack or not to assess the discriminant ability of the questionnaires.

RESULTS

A total of 257 patients were included in the analysis (mean age, 54.9 years; 87% male). Patients with current gout attack (n=29, 11%) had worse scores than those without gout attack on most instrument scales. Mean differences between current attack and no current attack for the TSQM domains were: -20.6, effectiveness; -10.6, side effects; -12.1, global satisfaction (all P<0.05); and -6.1, convenience (NS). For the GIS, mean differences were: 30.5, gout overall concern; 14.6, gout medication side effects; 22.7, unmet gout treatment needs; 11.5, gout concern during attack (all P<0.05); and 7.9, well-being during attack (NS). Mean difference in SF-12 was -6.6 for physical component summary (P<0.05) and -2.9 for mental component summary (NS). Correlations between several TSQM and GIS scales were moderate.

CONCLUSION

The TSQM and GIS were complementary in evaluating the impact of gout flare on treatment satisfaction and HRQoL. Correlations between the two instruments supported the relationship between treatment satisfaction and HRQoL.

An expanding role for interleukin-1 blockade from gout to cancer

There is an expanding role for interleukin (IL)-1 in diseases from gout to cancer. More than any other cytokine family, the IL-1 family is closely linked to innate inflammatory and immune responses. This linkage is because the cytoplasmic segment of all members of the IL-1 family of receptors contains a domain, which is highly homologous to the cytoplasmic domains of all toll-like receptors (TLRs). This domain, termed "toll IL-1 receptor (TIR) domain," signals as does the IL-1 receptors; therefore, inflammation due to the TLR and the IL-1 families is nearly the same. Fundamental responses such as the induction of cyclo-oxygenase type 2, increased surface expression of cellular adhesion molecules and increased gene expression of a broad number of inflammatory molecules characterizes IL-1 signal transduction as it does for TLR agonists. IL-1β is the most studied member of the IL-1 family because of its role in mediating autoinflammatory disease. However, a role for IL-1α in disease is being validated because of the availability of a neutralizing monoclonal antibody to human IL-1α. There are presently three approved therapies for blocking IL-1 activity. Anakinra is a recombinant form of the naturally occurring IL-1 receptor antagonist, which binds to the IL-1 receptor and prevents the binding of IL-1β as well as IL-1α. Rilonacept is a soluble decoy receptor that neutralizes primarily IL-1β but also IL-1α. Canakinumab is a human monoclonal antibody that neutralizes only IL-1β. Thus, a causal or significant contributing role can be established for IL-1β and IL-1α in human disease.

Serum uric acid level, blood pressure, and vascular angiotensin II responsiveness in healthy men and women

Uric acid is associated with hypertension and increased renin-angiotensin system activity, although this relationship diminishes after chronic exposure to high levels. Uric acid is more strongly associated with poor outcomes in women compared to men, although whether this is due to a sex-specific uric acid-mediated pathophysiology or reflects sex differences in baseline uric acid levels remains unknown. We examined the association between uric acid and vascular measures at baseline and in response to angiotensin-II challenge in young healthy humans. Fifty-two subjects (17 men, 35 premenopausal women) were studied in high-salt balance. Serum uric acid levels were significantly higher in men compared to women (328 ± 14 μmol/L vs. 248 ± 10 μmol/L, P < 0.001), although all values were within normal sex-specific range. Men demonstrated no association between uric acid and blood pressure, either at baseline or in response to angiotensin-II. In stark contrast, a significant association was observed between uric acid and blood pressure at baseline (systolic blood pressure, P = 0.005; diastolic blood pressure, P = 0.02) and in response to angiotensin-II (systolic blood pressure, P = 0.035; diastolic blood pressure, P = 0.056) in women. However, this sex difference lost significance after adjustment for baseline uric acid. When all subjects were stratified according to high (>300 μmol/L) or low (≤300 μmol/L) uric acid levels, only the low uric acid group showed a positive association between uric acid and measures of vascular tone at baseline and in response to angiotensin-II. Differences in uric acid-mediated outcomes between men and women likely reflect differences in exposure to increased uric acid levels, rather than a sex-specific uric acid-mediated pathophysiology.

Urate lowering therapy with febuxostat in daily practice-a multicentre, open-label, prospective observational study

Introduction. Febuxostat, a novel xanthine oxidase inhibitor for the treatment of symptomatic hyperuricemia, showed superiority over allopurinol in the reduction of serum uric acid levels in pivotal studies. Whether this holds true the FORTE (febuxostat in the oral urate lowering treatment: effectiveness and safety) study was conducted to evaluate treatment with febuxostat under daily practice conditions. Materials/Methods. The multicentre, open-label, and prospective observational study was conducted in 1,690 German medical practices from 9/2010 to 5/2011. Safety and efficacy data were assessed at baseline and week 4. Results. Data from 5,592 gout patients (72.6% male, mean age 63.7 years) were collected. Under urate lowering treatment with febuxostat mean serum uric acid levels decreased significantly from 8.9 ± 1.9 mg/dL (534.0 ± 114.6 μmol/L) at baseline to 6.2 ± 2.5 mg/dL (372.0 ± 150.0 μmol/L) at week 4. 67% which reached the mean uric acid target (6.1 ± 1.0 mg/dL [366.0 ± 59.4 μmol/L]). Only 43.1% of patients received concomitant flare prophylaxis. A total of 178 adverse events (mostly gout flares) were reported in 152 patients (2.6%). Conclusion. Febuxostat lowers serum uric acid levels effectively in routine clinical practice. Overall, treatment with febuxostat in both available dosages (80 mg/120 mg) was safe and well tolerated.

Development, external validation, and comparative assessment of a new diagnostic score for hepatic steatosis

OBJECTIVES

We used data from population-based studies to determine the accuracy of the Fatty Liver Index (FLI) and the Hepatic Steatosis Index (HSI) in determining individual risk of hepatic steatosis. We also developed a new risk scoring system and validated all three indices using external data.

METHODS

We used data from the Study of Health in Pomerania (SHIP; n=4,222), conducted in North-eastern Germany, to validate the existing scoring systems and to develop our own index. Data from the South German Echinococcus Multilocularis and Internal Diseases in Leutkirch (EMIL) study (n=2,177) were used as an external validation data set. Diagnostic performance was evaluated in terms of discrimination (area under the receiver operating characteristic curve (AUC)) and calibration plots. We applied boosting for generalized linear models to select relevant diagnostic separators.

RESULTS

The FLI accurately discriminated patients with fatty liver disease from those without (AUC=0.817) but had poor calibration, in that predicted risks differed considerably from observed risks, based on SHIP data. The FLI performed well in discrimination and calibration in the analysis of EMIL data (AUC=0.890). The HSI performed worse than the FLI in analysis of both data sets (SHIP: AUC=0.782 and EMIL: AUC=0.841), showing an extremely skewed calibration. Our newly developed risk score had a good performance in the development data set (SHIP: AUC=0.860) and also good discrimination ability in the validation data (EMIL: AUC=0.876), but it had low calibration based on the validation data set.

CONCLUSIONS

We compared the ability of the FLI, HSI, and our own scoring system to determine the risk of hepatic steatosis using two population-based data sets (one for the development of our own system and one for validation). In the development and independent replication data set, all three indices discriminated well between patients with and without hepatic steatosis, but the predicted risks did not match well with the observed risks, when applied to external data. Scoring systems for fatty liver disease could depend on methodological standardization of ultrasound diagnosis and laboratory measurements.

A systematic review and meta-analysis on the safety and efficacy of febuxostat versus allopurinol in chronic gout

OBJECTIVE

To evaluate the safety and efficacy of febuxostat compared to allopurinol for the treatment of chronic gout.

METHODS

We did a systematic review and meta-analysis of randomized and non-randomized controlled trials that compared oral febuxostat to oral allopurinol for treatment of chronic gout. Two reviewers independently selected studies, assessed study quality, and extracted data. Risk ratios (RR) were calculated with random effects and were reported with corresponding 95% confidence intervals (CI).

RESULTS

From 1076 potentially relevant citations, 7 studies and 25 associated publications met inclusion criteria; 5 studies were ultimately included in the analysis. Febuxostat did not reduce the risk of gout flares compared with allopurinol (RR = 1.16, 95% CI = 1.03-1.30, I(2) = 44%). Overall, the risk of any adverse event was lower in febuxostat recipients compared to allopurinol (RR = 0.94, 95% CI = 0.90-0.99, I(2) = 13%). Patients receiving febuxostat were more likely to achieve a serum uric acid of <6 mg/dl than allopurinol recipients (RR = 1.56, 95% CI = 1.22-2.00, I(2) = 92%). Subgroup analysis did not indicate any significant difference between high- and low-dose febuxostat on the risk of gout flares.

CONCLUSION

Although febuxostat was associated with higher likelihood of achieving a target serum uric acid level of <6 mg/dl, there was significant heterogeneity in the pooled results. There was no evidence that febuxostat is superior to allopurinol for clinically relevant outcomes. Given its higher cost, febuxostat should not be routinely used for chronic gout.

Tubular Urate Transporter Gene Polymorphisms Differentiate Patients with Gout Who Have Normal and Decreased Urinary Uric Acid Excretion

Objective.

Primary gout has been associated with single-nucleotide polymorphisms (SNP) in several tubular urate transporter genes. No study has assessed the association of reabsorption and secretion urate transporter gene SNP with gout in a single cohort of documented primary patients with gout carefully subclassified as normoexcretors or underexcretors.

Methods.

Three reabsorption SNP (SLC22A12/URAT1, SLC2A9/GLUT9, and SLC22A11/OAT4) and 2 secretion transporter SNP (SLC17A1/NPT1 and ABCG2/BRCP) were studied in 104 patients with primary gout and in 300 control subjects. The patients were subclassified into normoexcretors and underexcretors according to their serum and 24-h urinary uric acid levels under strict conditions of dietary control.

Results.

Compared with control subjects, patients with gout showed different allele distributions of the 5 SNP analyzed. However, the diagnosis of underexcretor was only positively associated with the presence of the T allele of URAT1 rs11231825, the G allele of GLUT9 rs16890979, and the A allele of ABCG2 rs2231142. The association of the A allele of ABCG2 rs2231142 in normoexcretors was 10 times higher than in underexcretors. The C allele of NPT1 rs1165196 was only significantly associated with gout in patients with normal uric acid excretion.

Conclusion.

Gout with uric acid underexcretion is associated with transporter gene SNP related mainly to tubular reabsorption, whereas uric acid normoexcretion is associated only with tubular secretion SNP. This finding supports the concept of distinctive mechanisms to account for hyperuricemia in patients with gout with reduced or normal uric acid excretion.

Ultrasound-detected musculoskeletal urate crystal deposition: which joints and what findings should be assessed for diagnosing gout?

OBJECTIVE

The primary objective of this prospective case-control study was to assess the diagnostic value of several intra-articular and periarticular ultrasound (US)-detected abnormalities in the upper and lower limbs in gout. The secondary objective was to test the concurrent validity of US abnormalities using as gold standard the microscopic demonstration of monosodium urate (MSU) crystals.

METHODS

Ninety-one men with gout and 42 age-matched controls were prospectively recruited. All patients with gout and controls underwent US assessment of several US abnormalities in 26 joints, six bursae, eight tendons, 20 tendon compartments, four ligaments, and 18 articular cartilages by experts in US blinded to the patients' group. Patients with gout and controls with US abnormalities were asked to undergo US-guided aspiration for microscopic identification of MSU crystals. Interobserver and intraobserver reliability of the US assessment was evaluated in a web-based exercise.

RESULTS

The assessment of one joint (ie, radiocarpal joint) for hyperechoic aggregates (HAGs), two tendons (ie, patellar tendon and triceps tendon) for HAGs and three articular cartilages (ie, first metatarsal, talar and second metacarpal/femoral) for double contour sign showed the best balance between sensitivity and specificity (84.6% and 83.3%, respectively). Intraobserver reliability was good (mean κ 0.75) and interobserver reliability was moderate (κ 0.52). The aspirated material from HAGs was positive for MSU crystals in 77.6% of patients with gout and negative in all controls.

CONCLUSIONS

Our results suggest that US bilateral assessment of one joint, three articular cartilages and two tendons may be valid for diagnosing gout with acceptable sensitivity and specificity.

TRPA1 receptor stimulation by hydrogen peroxide is critical to trigger hyperalgesia and inflammation in a model of acute gout

Acute gout attacks produce severe joint pain and inflammation associated with monosodium urate (MSU) crystals leading to oxidative stress production. The transient potential receptor ankyrin 1 (TRPA1) is expressed by a subpopulation of peptidergic nociceptors and, via its activation by endogenous reactive oxygen species, including hydrogen peroxide (H2O2), contributes to pain and neurogenic inflammation. The aim of this study was to investigate the role of TRPA1 in hyperalgesia and inflammation in a model of acute gout attack in rodents. Inflammatory parameters and mechanical hyperalgesia were measured in male Wistar rats and in wild-type (Trpa1(+/+)) or TRPA1-deficient (Trpa1(-/-)) male mice. Animals received intra-articular (ia, ankle) injection of MSU. The role of TRPA1 was assessed by receptor antagonism, gene deletion or expression, sensory fiber defunctionalization, and calcitonin gene-related peptide (CGRP) release. We found that nociceptor defunctionalization, TRPA1 antagonist treatment (via ia or oral administration), and Trpa1 gene ablation abated hyperalgesia and inflammatory responses (edema, H2O2 generation, interleukin-1β release, and neutrophil infiltration) induced by ia MSU injection. In addition, we showed that MSU evoked generation of H2O2 in synovial tissue, which stimulated TRPA1 producing CGRP release and plasma protein extravasation. The MSU-elicited responses were also reduced by the H2O2-detoxifying enzyme catalase and the reducing agent dithiothreitol. TRPA1 activation by MSU challenge-generated H2O2 mediates the entire inflammatory response in an acute gout attack rodent model, thus strengthening the role of the TRPA1 receptor and H2O2 production as potential targets for treatment of acute gout attacks.

G-protein-coupled receptor regulation of de novo purine biosynthesis: a novel druggable mechanism

Spatial organization of metabolic enzymes may represent a general cellular mechanism to regulate metabolic flux. One recent example of this type of cellular phenomenon is the purinosome, a newly discovered multi-enzyme metabolic assembly that includes all of the enzymes within the de novo purine biosynthetic pathway. Our understanding of the components and regulation of purinosomes has significantly grown in recent years. This paper reviews the purine de novo biosynthesis pathway and its regulation, and presents the evidence supporting the purinosome assembly and disassembly processes under the control of G-protein-coupled receptor (GPCR) signaling. This paper also discusses the implications of purinosome and GPCR regulation in drug discovery.

Gout: joints and beyond, epidemiology, clinical features, treatment and co-morbidities

Gout is a common inflammatory arthritis precipitated by an inflammatory reaction to urate crystals in the joint. Gout is increasingly being recognised as a disease primarily of urate overload with arthritis being a consequence of this pathological accumulation. It is associated with a number of important co-morbidities including chronic kidney disease, obesity, diabetes and cardiovascular disease. The prevalence of gout is increasing around the world. Significant progress has been made in determining the genetic basis for both gout and hyperuricaemia. Environmental risk factors for gout have been identified as certain foods, alcohol and several medications. There is, however, little evidence that changing these environmental risks improves gout on an individual level. Treatment of gout encompasses two strategies: firstly treatment of inflammatory arthritis with non-steroidal anti-inflammatories, corticosteroids, colchicine or interleukin-1 inhibitors. The second and most important strategy is urate lowering, to a target of 0.36 mmol/L (6 mg/dL) or potentially lower in those with tophi (collections of crystalline urate subcutaneously). Along with urate lowering, adequate and prolonged gout flare prophylaxis is required to prevent the precipitation of acute attacks. Newer urate lowering agents are in development and have the potential to significantly expand the potential treatment options. Education of patients regarding the importance of life long urate lowering therapy and prophylaxis of acute attacks is critical to treatment success as adherence with medication is low in chronic diseases in general but especially in gout.

The role of thiopurine metabolite monitoring in inflammatory bowel disease

Thiopurines are the mainstay of medical management in inflammatory bowel disease (IBD), especially in the maintenance of disease remission. Given the limited IBD armamentarium it is important to optimize each therapy before switching to an alternative drug. Conventional weight based dosing of thiopurines in IBD leads to intolerance or inefficacy in many patients. More recently increased knowledge of their metabolism has allowed for dose optimization using thiopurine metabolite levels, namely 6-thioguanine nucleotides and 6-methylmercaptopurine, with the potential for improved outcomes in patients with IBD. This review will outline the current understanding of thiopurine metabolism and pharmacogenomics and will describe the clinical application of this knowledge in the optimization of thiopurines in individual patients.

Airway uric acid is a sensor of inhaled protease allergens and initiates type 2 immune responses in respiratory mucosa

Although type 2 immune responses to environmental Ags are thought to play pivotal roles in asthma and allergic airway diseases, the immunological mechanisms that initiate the responses are largely unknown. Many allergens have biologic activities, including enzymatic activities and abilities to engage innate pattern-recognition receptors such as TLR4. In this article, we report that IL-33 and thymic stromal lymphopoietin were produced quickly in the lungs of naive mice exposed to cysteine proteases, such as bromelain and papain, as a model for allergens. IL-33 and thymic stromal lymphopoietin sensitized naive animals to an innocuous airway Ag OVA, which resulted in production of type 2 cytokines and IgE Ab, and eosinophilic airway inflammation when mice were challenged with the same Ag. Importantly, upon exposure to proteases, uric acid (UA) was rapidly released into the airway lumen, and removal of this endogenous UA by uricase prevented type 2 immune responses. UA promoted secretion of IL-33 by airway epithelial cells in vitro, and administration of UA into the airways of naive animals induced extracellular release of IL-33, followed by both innate and adaptive type 2 immune responses in vivo. Finally, a potent UA synthesis inhibitor, febuxostat, mitigated asthma phenotypes that were caused by repeated exposure to natural airborne allergens. These findings provide mechanistic insights into the development of type 2 immunity to airborne allergens and recognize airway UA as a key player that regulates the process in respiratory mucosa.

A revised estimate of the burden of illness of gout

Background

Gout is a chronic, inflammatory arthritis characterized by painful and debilitating acute/episodic flares. Until recently, gout has been regarded as a minor medical problem, in part because the associated economic burden has not been appreciated. Previous literature on this subject focused on the costs associated with acute episodes of gout rather than on the long-term medical and economic implications of this chronic disorder.

Objective

Our aim was to estimate the current impact of gout in the United States with respect to disability and economic costs.

Methods

The following data sources were used: published data on the incremental economic burden of gout; statistics from the US Census Bureau and the US Bureau of Labor Statistics; and recent epidemiological and clinical literature concerning the course, treatment, and outcomes of the disease. Disability is expressed as days of lost productivity. Charges for gout-related treatments were used as direct cost inputs.

Results

Gout affects an estimated 8 million Americans, among whom those working have an average of almost 5 more absence days annually than workers without gout. On average, the incremental annual cost of care for a gout patient is estimated at >$3000 compared with a nongouty individual. Even though comorbidities common in gout patients account for a portion of this increased economic burden, the total annual cost attributable to gout patients in the United States is likely in the tens of billions of dollars and comparable to those of other major chronic disorders, such as migraine and Parkinson’s disease.

Conclusions

The economic burden of gout is most readily assessable in patients whose acute arthritic flares result in emergency department visits, bedridden days, and episodic loss of productivity. Chronic progression of the disease can also result in long-term impairment of function and health-related quality of life, but the contribution of chronic gout to the economic burden is more difficult to quantitate because gout is frequently associated with serious cardiovascular, metabolic, and renal comorbidities. Recent demonstration that successful gout management can reverse functional deficits in many chronic gout patients, however, supports the views that chronic gout contributes substantially to the medical and thus economic costs of these patients and that early and aggressive efforts to improve gout outcomes are likely to reduce the associated economic burden.

Arxula adeninivorans recombinant guanine deaminase and its application in the production of food with low purine content

Purines of exogenous and endogenous sources are degraded to uric acid in human beings. Concentrations >6.8 mg uric acid/dl serum cause hyperuricemia and its symptoms. Pharmaceuticals and the reduction of the intake of purine-rich food are used to control uric acid levels. A novel approach to the latter proposition is the enzymatic reduction of the purine content of food by purine-degrading enzymes. Here we describe the production of recombinant guanine deaminase by the yeast Arxula adeninivorans LS3 and its application in food. In media supplemented with nitrogen sources hypoxanthine or adenine, guanine deaminase (AGDA) gene expression is induced and intracellular accumulation of guanine deaminase (Agdap) protein occurs. The characteristics of the guanine deaminase isolated from wild-type strain LS3 and a transgenic strain expressing the AGDA gene under control of the strong constitutive TEF1 promoter were determined and compared. Both enzymes were dimeric and had temperature optima of 55°C with high substrate specificity for guanine and localisation in both the cytoplasm and vacuole of yeast. The enzyme was demonstrated to reduce levels of guanine in food. A mixture of guanine deaminase and other purine degradation enzymes will allow the reduction of purines in purine-rich foods.

The effect of febuxostat to prevent a further reduction in renal function of patients with hyperuricemia who have never had gout and are complicated by chronic kidney disease stage 3: study protocol for a multicenter randomized controlled study

BACKGROUND

Hyperuricemia is a risk factor for the onset of chronic kidney disease (CKD) and is significantly associated with the progression of CKD. However, there is no sufficient evidence by interventional research supporting a cause-effect relationship. Hyperuricemic patients without gouty arthritis, whose serum urate (SUA) concentration is ≥8.0 mg/dL and who have a complication, are treated by pharmacotherapy in addition to lifestyle guidance. Nevertheless, there is no evidence that rationalizes pharmacotherapy for patients with hyperuricemia who have no complication and whose SUA concentration is below 9.0 mg/dL.

METHODS/DESIGN

The FEATHER (FEbuxostat versus placebo rAndomized controlled Trial regarding reduced renal function in patients with Hyperuricemia complicated by chRonic kidney disease stage 3) study is a prospective, multicenter, double-blind, randomized, placebo-controlled trial of febuxostat-a novel, nonpurine, selective, xanthine oxidase inhibitor. The present study will enroll, at 64 medical institutions in Japan, 400 Japanese patients aged 20 years or older who have hyperuricemia without gouty arthritis, who present CKD stage 3, and whose SUA concentration is 7.1-10.0 mg/dL. Patients are randomly assigned to either the febuxostat or the control group, in which febuxostat tablets and placebo are administered orally, respectively. The dosage of the study drugs should be one 10-mg tablet/day at weeks 1 to 4 after study initiation, increased to one 20-mg tablet/day at weeks 5 to 8, and elevated to one 40-mg tablet/day at week 9 and then maintained until week 108. The primary endpoint is estimated glomerular filtration rate (eGFR) slope. The secondary endpoints include the amount and percent rate of change in eGFR from baseline to week 108, the amount and percent rate of change in SUA concentration from baseline to week 108, the proportion of patients who achieved an SUA concentration≤6.0 mg/dL, and the incidence of renal function deterioration.

DISCUSSION

The present study aims to examine whether febuxostat prevents a further reduction in renal function as assessed with eGFR in subjects and will (1) provide evidence to indicate the inverse association between a reduction in SUA concentration and an improvement in renal function and (2) rationalize pharmacotherapy for subjects and clarify its clinical relevance.

TRIAL REGISTRATION

UMIN Identifier: UMIN000008343.

Treating inflammation by blocking interleukin-1 in humans

IL-1 is a master cytokine of local and systemic inflammation. With the availability of specific IL-1 targeting therapies, a broadening list of diseases has revealed the pathologic role of IL-1-mediated inflammation. Although IL-1, either IL-1α or IL-1β, was administered to patients in order to improve bone marrow function or increase host immune responses to cancer, these patients experienced unacceptable toxicity with fever, anorexia, myalgias, arthralgias, fatigue, gastrointestinal upset and sleep disturbances; frank hypotension occurred. Thus it was not unexpected that specific pharmacological blockade of IL-1 activity in inflammatory diseases would be beneficial. Monotherapy blocking IL-1 activity in a broad spectrum of inflammatory syndromes results in a rapid and sustained reduction in disease severity. In common conditions such as heart failure and gout arthritis, IL-1 blockade can be effective therapy. Three IL-1blockers have been approved: the IL-1 receptor antagonist, anakinra, blocks the IL-1 receptor and therefore reduces the activity of IL-1α and IL-1β. A soluble decoy receptor, rilonacept, and a neutralizing monoclonal anti-interleukin-1β antibody, canakinumab, are also approved. A monoclonal antibody directed against the IL-1 receptor and a neutralizing anti-IL-1α are in clinical trials. By specifically blocking IL-1, we have learned a great deal about the role of this cytokine in inflammation but equally important, reducing IL-1 activity has lifted the burden of disease for many patients.

Chronic hyperuricemia, uric acid deposit and cardiovascular risk

Hyperuricemia is commonly associated with traditional risk factors such as dysglicemia, dyslipidemia, central obesity and abnormal blood pressure, i.e. the metabolic syndrome. Concordantly, recent studies have revived the controversy over the role of circulating uric acid, hyperuricemia, and gout as an independent prognostic factor for cardiovascular morbidity and mortality. In this regard, different studies also evaluated the possible role of xanthine inhibitors in inducing blood pressure reduction, increment in flow-mediated dilation, and improved cardiovascular prognosis in various patient settings. The vast majority of these studies have been conducted with either allopurinol or its active metabolite oxypurinol, i.e. two purine-like non-selective inhibitors of xanthine oxidase. More recently, the role of uric acid as a risk factor for cardiovascular disease and the possible protective role exerted by reduction of hyperuricemia to normal level have been evaluated by the use of febuxostat, a selective, non purine-like xanthine oxidase inhibitor. In this review, we will report current evidence on hyperuricemia in cardiovascular disease. The value of uric acid as a biomarker and as a potential therapeutic target for tailored old and novel "cardiometabolic" treatments will be also discussed.

Arxula adeninivorans recombinant urate oxidase and its application in the production of food with low uric acid content

Hyperuricemia and its symptoms are becoming increasingly common worldwide. Elevated serum uric acid levels are caused by increased uric acid synthesis from food constituents and reduced renal excretion. Treatment in most cases involves reducing alcohol intake and consumption of meat and fish or treatment with pharmaceuticals. Another approach could be to reduce uric acid level in food, either during production or consumption. This work reports the production of recombinant urate oxidase by Arxula adeninivorans and its application to reduce uric acid in a food product. The A. adeninivorans urate oxidase amino acid sequence was found to be similar to urate oxidases from other fungi (61-65% identity). In media supplemented with adenine, hypoxanthine or uric acid, induction of the urate oxidase (AUOX) gene and intracellular accumulation of urate oxidase (Auoxp) was observed. The enzyme characteristics were analyzed from isolates of the wild-type strain A. adeninivorans LS3, as well as from those of transgenic strains expressing the AUOX gene under control of the strong constitutive TEF1 promoter or the inducible AYNI1 promoter. The enzyme showed high substrate specificity for uric acid, a broad temperature and pH range, high thermostability and the ability to reduce uric acid content in food.

Detection of HLA-B*58:01, the susceptible allele for allopurinol-induced hypersensitivity, by loop-mediated isothermal amplification

BACKGROUND

Allopurinol, a common medication for gout treatment, can cause rare but life-threatening severe cutaneous adverse reactions. A strong pharmacogenetic association of human leucocyte antigen (HLA)-B*58:01 with allopurinol-induced drug hypersensitivity has been reported, especially in the Han Chinese population.

OBJECTIVES

To develop a rapid and simple loop-mediated isothermal amplification (LAMP) assay of HLA-B*58:01 and evaluate its feasibility in predicting allopurinol-induced drug hypersensitivity.

METHODS

Two sets of LAMP primers targeting exons 2 and 3 of HLA-B*58:01 were designed. DNA extracted from 20 clinical blood samples of patients with gout was used to evaluate the effectiveness of the two LAMP primer sets for the detection of HLA-B*58:01.

RESULTS

The results were compared with routine clinical genotyping methods. All extracted DNA samples tested with the HLA-B*58:01 LAMP assay showed agreement with the routine genotyping results. No amplifications were observed when unextracted blood samples were tested.

CONCLUSIONS

The HLA-B*58:01 LAMP assay was confirmed to be simple, rapid and specific for the detection of HLA-B*58:01, and therefore of potential value in the diagnosis of allopurinol-induced hypersensitivity.

Mechanistic aspects of inflammation and clinical management of inflammation in acute gouty arthritis

It has been recently demonstrated that interleukin 1β (IL-1β) plays a central role in monosodium urate crystal-induced inflammation and that the NALP3 inflammasome plays a major role in IL-1β production. These discoveries have offered new insights into the pathogenesis of acute gouty arthritis. In this review, we discuss the molecular mechanisms by which monosodium urate crystals induce acute inflammation and examine the mechanisms of action (MOAs) of traditional anti-inflammatory drugs (e.g., nonsteroidal anti-inflammatory drugs, colchicine, and glucocorticoids) and biologic agents (e.g., the IL-1β antagonists anakinra, rilonacept, and canakinumab) to understand how their MOAs contribute to their safety profiles. Traditional anti-inflammatory agents may act on the IL-1β pathway at some level; however, their MOAs are broad-ranging, unspecific, and biologically complex. This lack of specificity may explain the range of systemic adverse effects associated with them. The therapeutic margins of nonsteroidal anti-inflammatory drugs, colchicine, and glucocorticoids are particularly low in elderly patients and in patients with cardiovascular, metabolic, or renal comorbidities that are frequently associated with gouty arthritis. In contrast, the IL-1β antagonists act on very specific targets of inflammation, which may decrease the potential for systemic adverse effects, although infrequent but serious adverse events (including infection and administration reactions) have been reported. Because these IL-1β antagonists target an early event immediately downstream from NALP3 inflammasome activation, they may provide effective alternatives to traditional agents with minimal systemic adverse effects. Results of ongoing trials of IL-1β antagonists will likely provide clarification of their potential role in the management of acute gouty arthritis.

Gout: a critical analysis of scientific development

In recent years, scientific efforts on the topic "gout" have focused on pathogenetic aspects. This has opened new strategies of anti-inflammatory therapy and has improved urate-lowering therapy. So far, a scientometric analysis of the topic "gout" has not been generated despite an increased need for it in times of modified evaluation criteria for academic personnel and a subsequent tendency to co-authorship and author self-citation. The study aims to evaluate quality and quantity of scientific research dealing with the topic "gout" and to contribute to distinguish relevant research output. The current study uses scientometric methods and large-scale data analysis to evaluate quality and quantity of scientific efforts in the field of "gout." Data were gained from PubMed and ISI-Web. In the last 22 years (1990–2012), 4,424 items were published by 71 countries, of which the USA have been the most productive supplier with 32 % of all publications, followed in considerable distance by the United Kingdom, Japan, Spain and Germany, respectively. The USA have established their position as center of international cooperation. The most prolific journals in the field of gout were "Arthritis and Rheumatism," "Annals of the Rheumatic diseases" and the "Journal of Rheumatology." Our analysis specifies the most productive authors and institutions engaged with the topic, the most successful international and national cooperation and the most prolific journals and subject areas. Nevertheless, scientometric indicators, such as h-index, citation rate and impact factor, commonly used for assessment of scientific quality, should be seen critically due to distortion by bias of self-citation and co-authorship.

Characteristics of ocular abnormalities in gout patients

AIM

To characterize the clinical features of ocular surface in gout patients in coastal area of Shandong Province in China.

METHODS

A total of 380 consecutive gout patients were examined from January 2011 to May 2011. According to the course of gout, patients were divided into group A (<5 years), B (5-10 years) and C (>10 years). Group D (control group) was consist of 50 healthy subjects. Eyelids, lateral canthus, medial canthus, palpebral conjunctiva, sclera and cornea, anterior chamber, lens, anterior vitreous were examined by slit lamp to find whether there were deposition of uric acid crystals, ocular vascular tortuosity, redness and subconjunctival hemorrhage. The ophthalmic exams of visual acuity, intraocular pressure, fundus were used to assess any gout-related eye disease.

RESULTS

Uric acid crystals were found in 3 patients and the positions of the deposite were in corneal stroma, corneal epithelium and superficial stroma, and sclera respectively. The incidence was 0.79%. Dilatated and tortuous blood vessels in conjunctiva and sclera surface were found in 38 (23.8%), 40 (44.0%), 58 (45.0%), 9 (18.0%) patients in groups A, B, C and D, respectively. The differences between group B and D, group C and D were statistically significant (P<0.01, P<0.01). Transparent vesicles with metal-like reflected light in subconjunctiva were seen in 26 (16.2 %), 29 (31.9%), 41 (31.8%), 2 (4.00%) patients in groups A, B, C and D, respectively. The differences between A and D, B and D, C and D were statistically significant (P<0.05, P<0.01, P<0.01). Subconjunctival hemorrhage was found in all groups, the difference among the four groups showed no statistically significance.

CONCLUSION

Gout can cause ocular surface abnormalities, such as tophi deposition, subconjunctival transparent vesicles and hemorrhage, and vascular changes. These features have important clinical significance in early detection of the gout and prevention of eye injury.

Chronic gout in the elderly

Gout is the most common cause of inflammatory arthritis in men over 40 years old; it is a debilitating disease and, if untreated, can result in a chronic progressive disease, including tophaceous gout. In the elderly it represents a special issue, with notable clinical and therapeutic differences from the classical form with a systemic involvement. The burden of the disease increases particularly in the very old people, in whom arthritis, impaired gait and eyesight problems may enhance the related disability. Chronic gout moreover could aggravate heart and kidney disease and increase overall mortality and organ-related damage. Early diagnosis and appropriate treatment are important goals for the clinician that should to rely on the cooperation of specialists working together through the methodology of comprehensive geriatric assessment. The aim of the present review was to analyze chronic gout in old people in terms of epidemiology, pathophysiology, risk factors, clinical approach, and current treatment.

Comparison of activity indexes for recognizing enzyme mutants of higher activity with uricase as model

Background

For screening a library of enzyme mutants, an efficient and cost-effective method for reliable assay of enzyme activity and a decision method for safe recognition of mutants of higher activity are needed. The comparison of activity concentrations of mutants in lysates of transformed Escherichia coli cells against a threshold is unsafe to recognize mutants of higher activity due to variations of both expression levels of mutant proteins and lysis efficiency of transformed cells. Hence, by a spectrophotometric method after verification to measure uricase activity, specific activity calculated from the level of total proteins in a lysate was tested for recognizing a mutant of higher activity.

Results

During uricase reaction, the intermediate 5-hydroxyisourate interferes with the assay of uric acid absorbance, but the measurement of absorbance at 293 nm in alkaline borate buffer was reliable for measuring uricase initial rates within a reasonable range. The level of total proteins in a lysate was determined by the Bradford assay. Polyacrylamide gel electrophoresis analysis supported different relative abundance of uricase mutant proteins in their lysates; activity concentrations of uricase in such lysates positively correlated with levels of total proteins. Receiver-operation-curve analysis of activity concentration or specific activity yielded area-under-the-curve close to 1.00 for recognizing a mutant with > 200% improvement of activity. For a mutant with just about 80% improvement of activity, receiver-operation-curve analysis of specific activity gave area-under-the-curve close to 1.00 while the analysis of activity concentration gave smaller area-under-the-curve. With the mean plus 1.4-fold of the standard deviation of specific activity of a starting material as the threshold, uricase mutants whose activities were improved by more than 80% were recognized with higher sensitivity and specificity.

Conclusion

Specific activity calculated from the level of total proteins is a favorable index for recognizing an enzyme mutant with small improvement of activity.

ALPK1 genetic regulation and risk in relation to gout

BACKGROUND

The present study investigated whether single nucleotide polymorphisms (SNPs) in the alpha-protein kinase 1 (ALPK1) gene are associated with gout in aboriginal and Han Chinese Taiwanese.

METHODS

A total of 1351 aborigines from the community (511 cases and 840 controls) and 511 Han people from hospital (104 cases and 407 controls) were recruited. SNPs in potentially functional regions of the 38 genes within 4q25 were identified and genotypes determined by direct sequencing. Quantitation of blood ALPK1 mRNA expression levels and luciferase assay of gout-associated rs231253 pGL3-SNP constructs cotransfected with hsa-miR-519e were examined.

RESULTS

We found that ALPK1 gene was the most determinant of gout. Three SNPs of rs11726117 M861T [C], rs231247 [G] and rs231253 [G] were most associated with gout risk [odd ratios (OR) ≥1.44, P ≤ 3.78 × 10(-6)) in aborigines. A replication set using Han people had risk at rs11726117 and rs231247 (OR ≥1.72, P ≤ 4.08 × 10(-3)). From pooled analysis (Breslow-Day test, P > 0.33) assuming an additive model, each increasing copy of the risk allele of rs11726117 [C], rs231247 [G] and rs231253 [G] showed significantly elevated OR for gout ≥1.42 (P ≥ 1.53 × 10(-6)). Consistently, the composite homozygous of linked 3 SNPs (versus wild-type, OR = 1.83, P = 8.21 × 10(-4)) had strong associations with ALPK1 mRNA expression. Luciferase showed reduced hybridization between hsa-miR-519e and construct carrying gout-associated rs231253 [G] than the wild-type [C] (P = 6.19 × 10(-4)).

CONCLUSIONS

Our study found that a newly identified ALPK1 gene can effectively interfere with microRNA target recognition and modulates the mRNA expression; and the varying distribution of the implicated SNPs among cases and controls in the two studied populations suggests a significant role in gout susceptibility.