Study of the paradoxical effects of salicylate in low, intermediate and high dosage on the renal mechanisms for excretion of urate in man

Managing Gout in Patients with Metabolic Syndrome

Gout is characterized by monosodium urate (MSU) crystal deposition secondary to hyperuricemia. Gout is associated with metabolic syndrome (MetS) and its related comorbid conditions such as cardiovascular disease (CVD). Major advances have been made in the comprehension of the link between MetS and gout. Despite observational studies suggesting an association between MetS-related conditions and hyperuricemia, there is no proof of causality. Most studies using Mendelian randomization did not find hyperuricemia as a causal factor for MetS-related conditions. In contrast, these conditions were found associated with hyperuricemia, which suggests a reverse causality. Among patients with gout, this high CVD risk profile implies the need for systematic screening for MetS-related conditions. Most international guidelines recommend systematic screening for and care of CVD and related risk factors in patients with gout. Some anti-hypertensive agents, such as losartan and calcium channel blockers, are able to decrease serum urate (SU) levels. However, there are potential interactions between gout management therapies and the treatment of metabolic diseases. Some data suggest that anti-inflammatory drugs used for gout flare treatment, such as colchicine or canakinumab, might have benefits for CVD. Regarding the impact of urate-lowering therapies on CVD risk, recent studies found a similar CVD safety profile for allopurinol and febuxostat. Finally, sodium-glucose cotransporter-2 inhibitors are promising for gout because of their ability to decrease SU levels and risk of recurrent flares. In this review, we focus on the clinical challenge of managing MetS in patients with gout, particularly older patients with co-medications.

Environmental Triggers of Hyperuricemia and Gout

Gout is the most prevalent type of inflammatory arthritis worldwide and environmental factors contribute to hyperuricemia and risk for gout flare. Causes of hyperuricemia include increased purine consumption from meat, alcohol, and high fructose corn syrup as well as medications such as cyclosporine, low-dose aspirin, or diuretics. Triggers for gout flares include increased purine consumption and medication use such as urate lowering therapy and diuretics. Environmental exposures including lead exposure, particulate matter exposure, temperature fluctuations, and physiologic stress have been found to trigger flares. In the right clinical scenario, these factors should be considered when treating gout patients.

Lowering and Raising Serum Urate Levels: Off-Label Effects of Commonly Used Medications

Drug-induced hyperuricemia and gout present an increasingly prevalent problem in clinical practice. Herein, we review the urate-lowering or urate-raising effects of commonly used agents. We performed a PubMed search using the terms gout, urate, and medication, along with the specific agents/classes described herein. Reports were reviewed until 2022, and original studies were considered if they primarily or secondarily reported the effects of 1 or more drugs on serum urate level. Previous reviews were assessed for references to additional studies that described urate-altering effects of medications. Urate-changing drugs are summarized regarding their magnitude of effect, mechanism of action, and clinical significance. Potentially urate-lowering drugs include angiotensin II receptor blockers, calcium channel blockers, high-dose aspirin and salicylates, some nonsalicylate nonsteroidal anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, sodium-glucose cotransporter 2 inhibitors, statins, and fenofibrate. Potentially urate-increasing drugs discussed include diuretics, β-blockers, insulin, pyrazinamide, ethambutol, calcineurin inhibitors, low-dose aspirin, testosterone, and lactate. In patients who have or are at risk for hyperuricemia or gout, an increased awareness of drugs that affect serum urate level may allow for prescribing that effectively treats the indicated problem while minimizing adverse effects on hyperuricemia and gout.

A brief review of urate transporter 1 (URAT1) inhibitors for the treatment of hyperuricemia and gout: Current therapeutic options and potential applications

Hyperuricemia is a common metabolic condition, cause by increased levels of serum urate (SUA). Reduced excretion of uric acid is reported as the key factor of primary hyperuricemia, accounting for approximately 90% of the cases. Urate transporter 1 (URAT1) is a major protein involved in uric acid reabsorption (about 90%). Therefore, URAT1 inhibitors are considered to be a highly effective and promising class of uricosuric agents for treating hyperuricemia. This review summarizes the development of URAT1 inhibitors for the treatment of hyperuricemia, including approved URAT1 inhibitors, URAT1 inhibitors under development in clinical trials, substances with URAT1 inhibitory effects from derivatives and natural products, and conventional drugs with new uses. This review provides new ideas regarding research on URAT1 inhibitors by introducing the structure, properties, and side effects of chemical drugs, as well as the sources and categories of natural drugs. We also discuss new mechanisms of classic drugs, which may provide guidance to many practicing clinicians. The research and discovery of new inhibitors remain in full swing, and tremendous developments are expected in the field.

Modulation of Urate Transport by Drugs

BACKGROUND

Serum urate (SU) levels in primates are extraordinarily high among mammals. Urate is a Janus-faced molecule that acts physiologically as a protective antioxidant but provokes inflammation and gout when it precipitates at high concentrations. Transporters play crucial roles in urate disposition, and drugs that interact with urate transporters either by intention or by accident may modulate SU levels. We examined whether in vitro transporter interaction studies may clarify and predict such effects.

METHODS

Transporter interaction profiles of clinically proven urate-lowering (uricosuric) and hyperuricemic drugs were compiled from the literature, and the predictive value of in vitro-derived cut-offs like C_max/IC₅₀ on the in vivo outcome (clinically relevant decrease or increase of SU) was assessed.

RESULTS

Interaction with the major reabsorptive urate transporter URAT1 appears to be dominant over interactions with secretory transporters in determining the net effect of a drug on SU levels. In vitro inhibition interpreted using the recommended cut-offs is useful at predicting the clinical outcome.

CONCLUSIONS

In vitro safety assessments regarding urate transport should be done early in drug development to identify candidates at risk of causing major imbalances. Attention should be paid both to the inhibition of secretory transporters and inhibition or trans-stimulation of reabsorptive transporters, especially URAT1.

Pathophysiology of Gout

Multiple interacting checkpoints are involved in the pathophysiology of gout. Hyperuricemia is the key risk factor for gout and is considered a prerequisite for monosodium urate (MSU) crystal formation. Urate underexcretion through renal and gut mechanisms is the major mechanism for hyperuricemia in most people. Multiple genetic, environmental, and metabolic factors are associated with serum urate and alter urate transport or synthesis. Urate supersaturation is the most important factor for MSU crystal formation, and other factors such as temperature, pH, and connective tissue components also play a role. The nucleotide-binding oligomerization domain leucine-rich repeats and pyrin domain-containing protein 3 inflammasome plays a pivotal role in the inflammatory response to MSU crystals, and interleukin 1β is the key cytokine mediating the inflammatory cascade. Variations in the regulatory mechanisms of this inflammatory response may affect an individual's susceptibility to developing gout. Tophus formation is the cardinal feature of advanced gout, and both MSU crystals and the inflammatory tissue component of the tophus contribute to the development of structural joint damage owing to gout. In this article, we review the pathophysiologic mechanisms of hyperuricemia, MSU crystal formation and the associated inflammatory response, tophus formation, and structural joint damage in gout.

[Hyperuricemia, gout and high cardiovascular risk - how to manage them in clinical practice]

In recent years, the relationship of hyperuricemia and gout with a high risk of cardiovascular disease has been widely discussed. Therefore, it is important to systematically examine patients in order to diagnose comorbidities, among which cardiovascular disease and its complications occupy a leading place and consider mandatory treatment of patients with hyperuricemia and gout with high cardiovascular risk with lowering drugs, which fully reflects the provisions of the latest European recommendations for the management and treatment of patients with gout.

Gender impact on the correlations between Graves' hyperthyroidism and hyperuricemia in Chinese

OBJECTIVE

An increased level of serum uric acid (SUA) can be observed in patients with hypothyroidism. Nonetheless, data on the relationship between hyperuricemia and hyperthyroidism was still controversial. Thus, we aimed to analyze the association between Graves' hyperthyroidism and hyperuricemia in Chinese men and women.

METHODS

We recruited 103 male and 254 female patients with Graves' hyperthyroidism, as well as the same number of control subjects. Anthropometric measurements and fasting blood tests were collected and analyzed statistically by binary logistic regressions to determine the risk of developing hyperuricemia in hyperthyroidism.

RESULTS

SUA levels in males were significantly higher than that in females in both patients and controls. SUA levels were also significantly increased in hyperthyroid patients compared to in controls in both genders. The incidence of hyperuricemia rose significantly in subjects with hyperthyroidism with a higher prevalence in males than in females. SUA was negatively correlated with age and fasting glucose in male hyperthyroid patients, while it was positively correlated with body height, body weight, free triiodothyronine, and free thyroxine in female patients. Hyperthyroidism was a risk factor for hyperuricemia with an odd ratio of 4.536 for men and 2.730 for women.

CONCLUSIONS

For hyperuricemia, hyperthyroidism was an important risk factor that should not be neglected, especially for men.

Individualized treatment strategies for hyperuricemia informed by a semi-mechanistic exposure-response model of uric acid dynamics

To provide insight into pharmacological treatment of hyperuricemia we developed a semi-mechanistic, dynamical model of uric acid (UA) disposition in human. Our model represents the hyperuricemic state in terms of production of UA (rate, PUA), its renal filtration (glomerular filtration rate, GFR) and proximal tubular reabsorption (fractional excretion coefficient, FE). Model parameters were estimated using data from 9 Phase I studies of xanthine oxidase inhibitors (XOI) allopurinol and febuxostat and a novel uricosuric, the selective UA reabsorption inhibitor lesinurad, approved for use in combination with a XOI. The model was qualified for prediction of the effect of patients' GFR and FE on concentration of UA in serum (sUA) and UA excretion in urine and their response to drug treatment, using data from 2 Phase I and 4 Phase III studies of lesinurad. Percent reduction in sUA from baseline by a XOI is predicted to be independent of GFR, FE or PUA. Uricosurics are more effective in underexcreters of UA or patients with normal GFR. Co-administration of a XOI and an uricosuric agent should be considered for patients with high sUA first in the treatment algorithm of gout before uptitration of XOI. The XOI dose in combination with a uricosuric can be reduced compared to XOI alone for the same target sUA to the degree dependent on patient's GFR and FE. This exposure-response model of UA can be used to rationally select the best drug treatment option to lower elevated sUA in gout patients under differing pathophysiological situations.

Impact of comorbidities on gout and hyperuricaemia: an update on prevalence and treatment options

Gout, the most prevalent inflammatory arthritis worldwide, is associated with cardiovascular and renal diseases, and is an independent predictor of premature death. The frequencies of obesity, chronic kidney disease (CKD), hypertension, type 2 diabetes, dyslipidaemias, cardiac diseases (including coronary heart disease, heart failure and atrial fibrillation), stroke and peripheral arterial disease have been repeatedly shown to be increased in gout. Therefore, the screening and care of these comorbidities as well as of cardiovascular risk factors are of outmost importance in patients with gout. Comorbidities, especially CKD, and drugs prescribed for their treatment, also impact gout management. Numerous epidemiological studies have shown the association of asymptomatic hyperuricaemia with the above-mentioned diseases and cardiovascular risk factors. Animal studies have also produced a mechanistic approach to the vascular toxicity of soluble urate. However, causality remains uncertain because confounders, reverse causality or common etiological factors might explain the epidemiological results. Additionally, these uncertainties remain unsolved despite recent studies using Mendelian randomisation or therapeutic approaches. Thus, large randomised placebo-controlled trials are still needed to assess the benefits of treating asymptomatic hyperuricaemia.

Identification of Febuxostat as a New Strong ABCG2 Inhibitor: Potential Applications and Risks in Clinical Situations

ATP-binding cassette transporter G2 (ABCG2) is a plasma membrane protein that regulates the pharmacokinetics of a variety of drugs and serum uric acid (SUA) levels in humans. Despite the pharmacological and physiological importance of this transporter, there is no clinically available drug that modulates ABCG2 function. Therefore, to identify such drugs, we investigated the effect of drugs that affect SUA levels on ABCG2 function. This strategy was based on the hypothesis that the changes of SUA levels might caused by interaction with ABCG2 since it is a physiologically important urate transporter. The results of the in vitro screening showed that 10 of 25 drugs investigated strongly inhibited the urate transport activity of ABCG2. Moreover, febuxostat was revealed to be the most promising candidate of all the potential ABCG2 inhibitors based on its potent inhibition at clinical concentrations; the half-maximal inhibitory concentration of febuxostat was lower than its maximum plasma unbound concentrations reported. Indeed, our in vivo study demonstrated that orally administered febuxostat inhibited the intestinal Abcg2 and, thereby, increased the intestinal absorption of an ABCG2 substrate sulfasalazine in wild-type mice, but not in Abcg2 knockout mice. These results suggest that febuxostat might inhibit human ABCG2 at a clinical dose. Furthermore, the results of this study lead to a proposed new application of febuxostat for enhancing the bioavailability of ABCG2 substrate drugs, named febuxostat-boosted therapy, and also imply the potential risk of adverse effects by drug-drug interactions that could occur between febuxostat and ABCG2 substrate drugs.

Gouty arthropathy: Review of clinico-pathologic and imaging features

Gout is a common inflammatory arthropathy in adults, with the prevalence increasing in males of older age. It occurs when monosodium urate (MSU) crystals are deposited in joints and connective tissue causing inflammation. The gold standard for the diagnosis of gout is the demonstration of negatively birefringent, needle-shaped MSU crystals through synovial fluid aspiration. However, this is an invasive technique and may not always be conclusive or feasible. Imaging techniques have been developed to aid in diagnosis of gout non-invasively. Radiography has a low utility in the early diagnosis of gout and demonstrates erosions in late stages. Ultrasound (US) has a high overall sensitivity in diagnosing gout with the 'double contour' sign having a high specificity. Magnetic resonance imaging is good at detecting tophi, bone marrow oedema and erosions, but has a limited role in diagnosis because of its high cost and limited availability. Conventional computed tomography (CT) has no role in the routine diagnosis of gout before development of erosions and tophi. A newer technology, dual-energy CT (DECT) has been shown to be able to detect MSU crystals burden with high accuracy. It has a higher specificity and lower sensitivity that US in gout diagnosis. However, because of radiation exposure and cost, it has a better utility in diagnosing clinically suspected gout complicated by other concurrent rheumatologic conditions or if radiography, US and synovial aspiration are inconclusive or not feasible. This paper will review the clinico-pathologic and imaging features of gouty arthropathy.

Epidemiology of gout

Gout is the most prevalent inflammatory arthritis in men. The findings of several epidemiologic studies from a diverse range of countries suggest that the prevalence of gout has risen over the past few decades. Although incidence data are scarce, data from the United States suggests that the incidence of gout is also rising. Evidence from prospective epidemiologic studies has confirmed dietary factors (animal purines, alcohol, and fructose), obesity, the metabolic syndrome, hypertension, diuretic use, and chronic kidney disease as clinically relevant risk factors for hyperuricemia and gout. Low-fat dairy products, coffee, and vitamin C seem to have a protective effect.

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.

Low-dose aspirin use and recurrent gout attacks

OBJECTIVE

To examine the association between cardioprotective use of low-dose aspirin and the risk of recurrent gout attacks among gout patients.

METHODS

We conducted an online case-crossover study of individuals with gout over 1 year. The following information was obtained during gout attacks: the onset dates, symptoms and signs, medications, and exposure to potential risk factors, including daily aspirin use and dosage, during the 2-day hazard period prior to the gout attacks. The same exposure information was also obtained over 2-day control periods.

RESULTS

Of the 724 participants analysed, 40.5% took aspirin ≤325 mg/day during either a hazard or a control period. Compared with no aspirin use, the adjusted OR of gout attacks increased by 81% (OR=1.81, 95% CI 1.30 to 2.51) for ≤325 mg/day of aspirin use on two consecutive days. The corresponding ORs were stronger with lower doses (eg, OR=1.91 for ≤100 mg, 95% CI 1.32 to 2.85). These associations persisted across subgroups by sex, age, body mass index categories and renal insufficiency status. Concomitant use of allopurinol nullified the detrimental effect of aspirin.

CONCLUSIONS

Our findings suggest that the use of low-dose aspirin on two consecutive days is associated with an increased risk of recurrent gout attacks. Recommended serum urate monitoring with concomitant use and dose adjustment of a urate-lowering therapy among patients with gout may be especially important to help avoid the risk of gout attacks associated with low-dose aspirin.

Functional cooperation of URAT1 (SLC22A12) and URATv1 (SLC2A9) in renal reabsorption of urate

BACKGROUND

Serum urate (SUA) level is affected by alteration in urinary reabsorption caused by clinically important drugs; however, there are no experimental models suitable to assess their effect on renal reabsorption. We, therefore, aimed to establish an experimental system co-expressing the urate transporters URAT1 (SLC22A12) and URATv1 (SLC2A9) (designated UUv cells) at the apical and basolateral membranes, respectively.

METHODS

Apical uptake and vectorial transport of [(14)C]urate in the apical-to-basolateral direction in UUv cells were measured in the presence or absence of uricosuric benzbromarone or anti-uricosuric trans-stimulators.

RESULTS

The urate permeability in the apical-to-basolateral direction remarkably increased by 7.0-fold in UUv cells, compared with non-transfected mock cells. The apical-to-basolateral transport was cis-inhibited by benzbromarone, but trans-stimulated by pyrazinecarboxylic acid and monocarboxylates such as nicotinate and lactate. Furthermore, salicylate showed both trans-stimulation and cis-inhibition in the urate transport at low and high concentrations, respectively. Finally, coexpression of URAT1 and URATv1 in human kidney epithelial cells was exhibited immunohistochemically.

CONCLUSIONS

It is demonstrated that functional cooperation of URAT1 and URATv1 is essential for renal reabsorption of urate, and in the established system influence of drugs on SUA is reflected in the alteration of urate permeability across the renal tubular epithelial cells.

Extra-renal elimination of uric acid via intestinal efflux transporter BCRP/ABCG2

Urinary excretion accounts for two-thirds of total elimination of uric acid and the remainder is excreted in feces. However, the mechanism of extra-renal elimination is poorly understood. In the present study, we aimed to clarify the mechanism and the extent of elimination of uric acid through liver and intestine using oxonate-treated rats and Caco-2 cells as a model of human intestinal epithelium. In oxonate-treated rats, significant amounts of externally administered and endogenous uric acid were recovered in the intestinal lumen, while biliary excretion was minimal. Accordingly, direct intestinal secretion was thought to be a substantial contributor to extra-renal elimination of uric acid. Since human efflux transporter BCRP/ABCG2 accepts uric acid as a substrate and genetic polymorphism causing a decrease of BCRP activity is known to be associated with hyperuricemia and gout, the contribution of rBcrp to intestinal secretion was examined. rBcrp was confirmed to transport uric acid in a membrane vesicle study, and intestinal regional differences of expression of rBcrp mRNA were well correlated with uric acid secretory activity into the intestinal lumen. Bcrp1 knockout mice exhibited significantly decreased intestinal secretion and an increased plasma concentration of uric acid. Furthermore, a Bcrp inhibitor, elacridar, caused a decrease of intestinal secretion of uric acid. In Caco-2 cells, uric acid showed a polarized flux from the basolateral to apical side, and this flux was almost abolished in the presence of elacridar. These results demonstrate that BCRP contributes at least in part to the intestinal excretion of uric acid as extra-renal elimination pathway in humans and rats.

The 2010 nephrology quiz and questionnaire: part 1

Presentation of the Nephrology Quiz and Questionnaire (NQQ) has become an annual "tradition" at the meetings of the American Society of Nephrology. It is a very popular session judged by consistently large attendance. Members of the audience test their knowledge and judgment on a series of case-oriented questions prepared and discussed by experts. They can also compare their answers in real time, using audience response devices, to those of program directors of nephrology training programs in the United States, acquired through an Internet-based questionnaire. As in the past, the topics covered were transplantation, fluid and electrolyte disorders, end-stage renal disease and dialysis, and glomerular disorders. Two challenging cases representing each of these categories along with single best answer questions were prepared by a panel of experts (Drs. Hricik, Palmer, Bargman, and Fervenza, respectively). The "correct" and "incorrect" answers then were briefly discussed, after the audience responses and the results of the questionnaire were displayed. The 2010 version of the NQQ was exceptionally challenging, and the audience, for the first time, gained a better overall correct answer score than the program directors, but the margin was small. In this issue we present the transplantation and fluid and electrolyte cases; the remaining end-stage renal disease and dialysis, and glomerular disorder cases will be presented next month. These articles try to recapitulate the session and reproduce its educational value for a larger audience--the readers of the Clinical Journal of the American Society of Nephrology. Have fun.

2011 recommendations for the diagnosis and management of gout and hyperuricemia

Gout is a major health problem in the United States; it affects 8.3 million people, which is approximately 4% of the adult population. Gout is most often diagnosed and managed in primary care practices; thus, primary care physicians have a significant opportunity to improve patient outcomes. Following publication of the 2006 European League Against Rheumatism (EULAR) gout guidelines, significant new evidence has accumulated, and new treatments for patients with gout have become available. It is the objective of these 2011 recommendations to update the 2006 EULAR guidelines, paying special attention to the needs of primary care physicians. The revised 2011 recommendations are based on the Grading of Recommendations Assessment, Development, and Evaluation approach as an evidence-based strategy for rating quality of evidence and grading the strength of recommendation formulated for use in clinical practice. A total of 26 key recommendations, 10 for diagnosis and 16 for management, of patients with gout were evaluated, resulting in important updates for patient care. The presence of monosodium urate crystals and/or tophus and response to colchicine have the highest clinical diagnostic value. The key aspect of effective management of an acute gout attack is initiation of treatment within hours of symptom onset. Low-dose colchicine is better tolerated and is as effective as a high dose. When urate-lowering therapy (ULT) is indicated, the xanthine oxidase inhibitors allopurinol and febuxostat are the options of choice. Febuxostat can be prescribed at unchanged doses for patients with mild-to-moderate renal or hepatic impairment. The target of ULT should be a serum uric acid level that is ≤ 6 mg/dL. For patients with refractory and tophaceous gout, intravenous pegloticase is a new treatment option. This article is a summary of the 2011 clinical guidelines published in Postgraduate Medicine. This article provides a streamlined, accessible overview intended for quick review by primary care physicians, with the full guidelines being a resource for those seeking additional background information and expanded discussion.

Effect of oral vitamin C supplementation on serum uric acid: a meta-analysis of randomized controlled trials

OBJECTIVE

To assess the effect of vitamin C supplementation on serum uric acid (SUA) by pooling the findings from published randomized controlled trials (RCTs).

METHODS

A total of 2,082 publications identified through systematic search were subjected to the following inclusion criteria: 1) RCTs conducted on human subjects, 2) reported end-trial SUA means and variance, 3) study design with oral vitamin C supplementation and concurrent control groups, and 4) trial duration of at least 1 week. Trials that enrolled children or patients receiving dialysis were excluded. Two investigators independently abstracted trial and participant characteristics. SUA effects were pooled by random-effects models and weighted by inverse variance.

RESULTS

Thirteen RCTs were identified in the Medline, EMBase, and Cochrane Central Register of Controlled Trials databases. The total number of participants was 556, the median dosage of vitamin C was 500 mg/day, trial size ranged from 8-184 participants, and the median study duration was 30 days. Pretreatment SUA values ranged from 2.9-7.0 mg/dl (Système International d'Unités [SI units]: 172.5-416.4 μmoles/liter). The combined effect of these trials was a significant reduction in SUA of -0.35 mg/dl (95% confidence interval -0.66, -0.03 [P = 0.032]; SI units: -20.8 μmoles/liter). Trial heterogeneity was significant (I(2) = 77%, P < 0.01). Subgroup analyses based on trial characteristics indicated larger reductions in uric acid in trials that were placebo controlled.

CONCLUSIONS

In aggregate, vitamin C supplementation significantly lowered SUA. Future trials are needed to determine whether vitamin C supplementation can reduce hyperuricemia or prevent incident and recurrent gout.

Risk factors for gout and prevention: a systematic review of the literature

PURPOSE OF REVIEW

Our objective was to perform a systematic review of risk factors and prevention of gout. We searched Medline for fully published reports in English using keywords including but not limited to 'gout', 'epidemiology', 'primary prevention', 'secondary prevention', 'risk factors'. Data from relevant articles meeting inclusion criteria were extracted using standardized forms.

RECENT FINDINGS

Of the 751 titles and abstracts, 53 studies met the criteria and were included in the review. Several risk factors were studied. Alcohol consumption increased the risk of incident gout, especially beer and hard liquor. Several dietary factors increased the risk of incident gout, including meat intake, seafood intake, sugar sweetened soft drinks, and consumption of foods high in fructose. Diary intake, folate intake, and coffee consumption were each associated with a lower risk of incident gout and in some cases a lower rate of gout flares. Thiazide and loop diuretics were associated with higher risk of incident gout and higher rate of gout flares. Hypertension, renal insufficiency, hypertriglyceridemia, hypercholesterolemia, hyperuricemia, diabetes, obesity, and early menopause were each associated with a higher risk of incident gout and/or gout flares.

SUMMARY

Several dietary risk factors for incident gout and gout flares are modifiable. Prevention and optimal management of comorbidities are likely to decreased risk of gout. Research in preventive strategies for the treatment of gout is needed.

Lack of effect of hydrochlorothiazide and low-dose aspirin on the renal clearance of urate and oxypurinol after a single dose of allopurinol in normal volunteers

AIMS

To determine whether low-dose aspirin and hydrochlorothiazide (HCTZ) affect the renal clearance of oxypurinol and/or urate.

METHODS

Healthy volunteers (n = 8) were treated with allopurinol (600 mg, control), and allopurinol (600 mg) co-administered with single doses of aspirin (100 mg) or HCTZ (25 mg) or a combination of the two.

RESULTS

Hydrochlorothiazide, low-dose aspirin or a combination of the two, when co-administered with allopurinol, did not significantly alter (P > 0.05) the renal clearance of oxypurinol or urate. In particular, aspirin and HCTZ, when taken together and with allopurinol, did not change (P > 0.05) oxypurinol fractional renal clearance (allopurinol alone: 0.217, 0.173-0.262; combined: 0.202, 0.155-0.250) or urate fractional renal clearance (allopurinol alone: 0.066, 0.032-0.099; combined: 0.058, 0.038-0.078).

CONCLUSIONS

A single, low-dose of aspirin or an anti-hypertensive dose of hydrochlorothiazide, when administered alone or together with allopurinol, are unlikely to alter the hypouricaemic effect of allopurinol. The effect of chronic aspirin and HCTZ dosing taken together upon the efficacy of chronic allopurinol therapy in patients with hyperuricaemia needs to be investigated.

Effect of hypouricaemic and hyperuricaemic drugs on the renal urate efflux transporter, multidrug resistance protein 4

BACKGROUND AND PURPOSE

The xanthine oxidase inhibitors allopurinol and oxypurinol are used to treat hyperuricaemia, whereas loop and thiazide diuretics can cause iatrogenic hyperuricaemia. Some uricosuric drugs and salicylate have a bimodal action on urate renal excretion. The mechanisms of action of these hypo- and hyperuricaemic drugs on the handling of urate in renal tubules have not been fully elucidated. Recently, we identified the multidrug resistance protein (MRP) 4 as a luminal efflux transporter for urate in the proximal tubule.

EXPERIMENTAL APPROACH

Here, we studied the effect of these drugs on [(14)C]urate transport using human embryonic kidney 293 cells overexpressing human MRP4 and in membrane vesicles isolated from these cells.

KEY RESULTS

Allopurinol stimulated MRP4-mediated cellular urate efflux and allopurinol and oxypurinol both markedly stimulated urate transport by MRP4 in membrane vesicles. Bumetanide and torasemide had no effect, whereas furosemide, chlorothiazide, hydrochlorothiazide, salicylate, benzbromarone and sulfinpyrazone inhibited urate transport, at concentrations ranging from nanomolar up to millimolar. Probenecid stimulated urate transport at 0.1 microM and inhibited transport at higher concentrations.

CONCLUSIONS AND IMPLICATIONS

These data suggest that inhibition of MRP4-mediated urate efflux by furosemide and thiazide diuretics could have an important function in their hyperuricaemic mechanisms. Furthermore, stimulation of MRP4-mediated renal urate efflux could be a new mechanism in the hypouricaemic action of allopurinol and oxypurinol. In conclusion, MRP4 may provide a potential target for drugs affecting urate homoeostasis, which needs to be further evaluated in vivo.

Serum uric acid is independently associated with hypertension in patients with rheumatoid arthritis

Hypertension (HT) is highly prevalent in rheumatoid arthritis (RA). Serum uric acid (SUA) has been associated with HT in the general population. The mutual exclusion of gout and RA, and the systemic inflammatory component of RA may alter this association in this patient population. We explored a potential association between SUA levels and HT in RA and evaluated whether this association is independent of HT risk factors, RA characteristics and relevant drugs. A total of 400 consecutive RA patients were assessed. SUA and complete biochemical profile were measured. Demographic, HT-related factors, RA characteristics and drugs were assessed as potential covariates. Results were analysed using binary logistic models to test the independence of the association between SUA and HT. SUA levels were higher in hypertensive compared to normotensive RA patients (5.44+/-1.6 mg dl(-1) (323.57+/-95.17 micromol l(-1)) vs 4.56+/-1.1 mg dl(-1) (271.23+/-65.43 micromol l(-1)), P<0.001). When adjusted for HT risk factors, renal function, RA characteristics, non-steroidal anti-inflammatory drugs, oral prednisolone, cyclosporine, leflunomide and low-dose aspirin, the odds of being a hypertensive RA patient per 1 mg dl(-1)(59.48 micromol l(-1)) SUA increase were significantly increased: OR=1.59 (95% CI: 1.21-2.1, P=0.001). This was also significant for the subgroup of patients who were not on diuretics (OR=1.5, 95% CI: 1.1-2.05; P=0.011). This cross-sectional study suggests that SUA levels are independently associated with HT in RA patients. Prospective longitudinal studies are needed to confirm and further explore the causes and implications of this association.

Coexisting ankylosing spondylitis and gouty arthritis

The aim of this study was to investigate the clinical characteristics of patients with coexisting ankylosing spondylitis (AS) and gout. Between July 1987, and October 2004, sixty-five patients with coexisting AS and gout were enrolled. The clinical manifestations of both AS and gout in these patients were studied. Of the 65 patients included in the study, 61 were men and four were women (men-to-women ratio, 15.3:1). Sixty-three subjects were Han Chinese, and two were Atayal Aborigines. Mean ages at onset of AS and gout were 29.3 +/- 15.6 years (range 7-63) and 42.2 +/- 13.2 years (range 20-74), respectively. Fifty-six patients developed gout after (15.5 +/- 11.2 years; range, 1-51 years) onset of AS; nine patients developed gout before (average, 3.4 +/- 2.2 years; range. 1-7 years) onset of AS. Forty-four (67.7%) patients had chronic peripheral arthritis and all 65 (100%) patients had acute peripheral arthritis. Thirty-three (50.8%) cases had heel pain (enthesopathy), including 22 (33.9%) with chronic heel pain, seven (10.8%) with acute heel pain, and four (6.2%) with concurrent acute and chronic heel pain. Sixty-one (93.9%) subjects were HLA-B27 antigen positive. Medical conditions potentially associated with hyperuricemia or gout were urolithiasis (n = 17), hypertension (n = 21), diabetes mellitus (n = 8), hyperlipidemia (n = 34), congestive heart failure (n = 6), coronary heart disease (n = 5), and stroke (n = 3). The following drugs were prescribed: diuretics (n = 7), low-dose aspirin (n = 4), antituberculous drugs (n = 1), and sulphasalazine (n = 34). Six (6.2%) patients had iatrogenic Cushing syndrome with adrenal insufficiency. Patients with coexisting AS and gout are not rare. Distinguishing between peripheral arthritis or enthesopathies of AS and gout is essential, especially when the course of AS arthritis becomes acute or the course of gout becomes chronic.

Treatment of crystal arthropathy--history and advances

The history of gout and the many distinguished historical figures who have suffered the agonies of this crystal deposition disorder have claimed the attention of medical historians like no other disease. Its treatment with uric acid lowering drugs became a twentieth century paradigm for the successful management and prevention of a chronic rheumatic disease, but the colorful history of the treatment of gout and crystal deposition disorders stretches back over 4,000 years.

Renal Urate Transport

Serum uric acid is determined by a balance between production and renal excretion. Luminal reabsorption of urate by the proximal tubule from the glomerular ultrafiltrate involves coupling between sodium-anion cotransport and urate-anion exchange. Apical sodium-coupled cotransport of lactate, ketoacids, nicotinate, and pyrazinoate increases intracellular levels of these anions in proximal tubular cells, stimulating the apical absorption of luminal urate via anion exchange. Hyperuricemia occurs when plasma levels of these anions increase; for example, hyperuricemia is a well-recognized concomitant of lactic acidosis and ketoacidosis. Relevant developments in the molecular and renal physiology of urate homeostasis are reviewed.

A concise history of gout and hyperuricemia and their treatment

First identified by the Egyptians in 2640 BC, podagra (acute gout occurring in the first metatarsophalangeal joint) was later recognized by Hippocrates in the fifth century BC, who referred to it as 'the unwalkable disease'. The term is derived from the Latin word gutta (or 'drop'), and referred to the prevailing medieval belief that an excess of one of the four 'humors'--which in equilibrium were thought to maintain health--would, under certain circumstances, 'drop' or flow into a joint, causing pain and inflammation. Throughout history, gout has been associated with rich foods and excessive alcohol consumption. Because it is clearly associated with a lifestyle that, at least in the past, could only be afforded by the affluent, gout has been referred to as the 'disease of kings'. Although there is evidence that colchicine, an alkaloid derived from the autumn crocus (Colchicum autumnale), was used as a powerful purgative in ancient Greece more than 2000 years ago, its first use as a selective and specific treatment for gout is attributed to the Byzantine Christian physician Alexander of Tralles in the sixth century AD. Uricosuric agents were first used at the end of the 19th century. In the modern era, nonsteroidal anti-inflammatory drugs are usually the drugs of choice for treating acute gout. Perhaps the most important historical advance in the treatment of hyperuricemia was the development of xanthine oxidase inhibitors, which are effective in reducing plasma and urinary urate levels and have been shown to reverse the development of tophaceous deposits.

Epidemiology, risk factors, and lifestyle modifications for gout

Gout affects more than 1% of adults in the USA, and it is the most common form of inflammatory arthritis among men. Accumulating data support an increase in the prevalence of gout that is potentially attributable to recent shifts in diet and lifestyle, improved medical care, and increased longevity. There are both nonmodifiable and modifiable risk factors for hyperuricemia and gout. Nonmodifiable risk factors include age and sex. Gout prevalence increases in direct association with age; the increased longevity of populations in industrialized nations may contribute to a higher prevalence of gout through the disorder's association with aging-related diseases such as metabolic syndrome and hypertension, and treatments for these diseases such as thiazide diuretics for hypertension. Although gout is considered to be primarily a male disease, there is a more equal sex distribution among elderly patients. Modifiable risk factors for gout include obesity, the use of certain medications, high purine intake, and consumption of purine-rich alcoholic beverages. The increasing prevalence of gout worldwide indicates that there is an urgent need for improved efforts to identify patients with hyperuricemia early in the disease process, before the clinical manifestations of gout become apparent.

Early and late effects of low-dose aspirin on renal function in elderly patients

BACKGROUND

Although low-dose aspirin is used by many elderly patients, monitoring of renal function is currently not recommended. We recently reported transient retention of uric acid and creatinine caused by aspirin in doses of 75 to 325 mg/d. We therefore evaluated the renal effects of aspirin (100 mg/d), including post-treatment effects.

METHODS

We studied 83 stable geriatric patients in long-term care (aged 56 to 98 years) who were treated with low-dose aspirin (100 mg/d) for 2 weeks and 40 control patients. Other medications and diet were kept constant. Biochemical monitoring including blood samples and 24-hour urinary collections for creatinine and uric acid at baseline and weekly for a total of 5 weeks.

RESULTS

After 2 weeks on aspirin, urinary excretion of creatinine decreased in 60 (72%) and excretion of uric acid decreased in 54 (65%) of the 83 patients, and their mean clearances decreased; during the same period, serum blood urea nitrogen, creatinine, and uric acid levels increased (P <0.05 for all). Deterioration from baseline levels was significantly greater (and more prevalent) in the aspirin-treated group than in the 40 control patients (P = 0.001 to 0.09). After withdrawal of aspirin these parameters improved. However, 3 weeks after stopping aspirin, 48% (35 of the 73 in whom this measurement was available) had a persistent decline in creatinine clearance from baseline, as compared with only 8% (3/36) controls (P <0.001).

CONCLUSION

Short-term low-dose aspirin treatment may affect renal function in elderly patients. These effects persist 3 weeks after cessation of the drug in some of these patients.

Urate transport via human PAH transporter hOAT1 and its gene structure

BACKGROUND

We recently cloned the human organic anion transporter 1 (hOAT1) as a p-aminohippurate (PAH) transporter. Whether urate is transported by the PAH transporter in humans remains unclear. Familial juvenile gouty nephropathy (FJGN) is thought to develop as a result of an abnormality in the urate transporter.

METHODS

To determine if hOAT1 transported urate, the cellular uptakes of PAH and urate were determined, as were the inhibition profiles of inorganic anions, and uricosuric and antiuricosuric agents using a mouse S2 cell line expressing hOAT1. The hOAT1 gene was cloned from a genomic library using full-length hOAT1-1 cDNA as a probe. The coding regions of the hOAT1 genes of two sisters with FJGN were sequenced. Also, immunohistochemical fluorescence analysis of hOAT1 in the kidney of the younger sister with FJGN was performed.

RESULTS

The Km and Vmax values of urate transport via hOAT1 were 943 +/- 84 micromol/L and 1286 +/- 162 pmol/mg protein/min, respectively. The order of the IC50 of urate transport via hOAT1 was benzbromarone < probenecid < salicylate or pyrazine carboxylic acid. The 10.9 kb hOAT1 gene was found to be interrupted by nine introns. Mutations in the coding region of the hOAT1 gene from the two sisters with FJGN were undetectable. Immunohistochemical fluorescent staining showed that hOAT1 in the kidney of the younger sister was similar to that of control individuals.

CONCLUSIONS

Our data show that hOAT1 transports urate, and the inhibition profiles of uricosuric and antiuricosuric agents are defined. hOAT1 is not responsible for FJGN in the two sisters examined in this study.

Effect of Minidose Aspirin on Renal Function and Renal Uric Acid Handling in Healthy Young Adults

Minidose aspirin (60-325 mg/day) has been widely used in the prevention and treatment of cardiovascular and cerebrovascular diseases. However, studies on the effects of minidose aspirin on renal handling of uric acid and renal function are limited. We studied the effect of aspirin at 60 mg/day (n = 18) and 300 mg/day (n = 14) on uric acid handling and renal function in healthy subjects. The subjects were evaluated weekly during 2 weeks of aspirin therapy, and again 1 week after aspirin was discontinued. Aspirin at both dosages decreased the fractional excretion of uric acid. However, aspirin at 300 mg/day, but not 60 mg/day, significantly decreased uric acid clearance and creatinine clearance by the end of the second week of aspirin therapy. Despite these changes, serum uric acid and serum creatinine remained constant. The uric acid clearance, but not the creatinine clearance, returned to baseline value 1 week after aspirin therapy was discontinued. As aspirin at 60 mg/day showed no suppressive effect on renal function, it may be better for long-term use.

Part 1. Uric acid and losartan

PURPOSE OF REVIEW

To characterize the mechanism and clinical impact of the angiotensin-receptor blocker losartan on both renal uric acid handling and thereby serum uric acid.

RECENT FINDINGS

Losartan effect on serum uric acid has been demonstrated at various stages of renal failure including most recently observations obtained in end-stage renal disease patients. Other angiotensin-receptor blockers do not alter renal handling of uric acid. The uricosuria, which accompanies losartan administration, has not been associated with adverse renal consequences, in part, because of the increase in urinary pH that follows its administration.

SUMMARY

Hyperuricemia is closely linked to both hypertension and cardiovascular disease. The development of hyperuricemia and its persistence are clearly renal processes. Likewise, the correction of hyperuricemia is often accomplished by increasing its renal excretion. A number of medications, by way of varying mechanisms, can alter renal urate handling and thereby influence serum uric acid values. Most recently, the angiotensin-receptor blocker losartan has been shown to reduce serum uric acid. The mechanism of this process relates to losartan alone and does not involve the E-3174 metabolite of this compound. This probenecid-like effect of losartan occurs shortly after drug administration, and is both transient and dose-dependent. This property of losartan, touted by some as a meaningful pharmacological distinction among the angiotensin-receptor blockers, remains to be proved, since, to date, the hypothesis that a reduction in serum uric acid alters the natural history of cardiovascular disease has not been formally tested.