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Concept: Uricosuric

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Our goal was to establish a model for the evaluation of the effects of uricosuric agents and to clarify the underlying mechanism(s). The effects of a uricosuric agent co-treated with pyrazinamide, an anti-tubercular agent, on urate handling were examined in rats. Furthermore, the effects of uricosuric agents on urate uptake were evaluated using the vesicles of rat renal brush-border membrane. Treatment with probenecid, at a dose of 100 mg/kg, significantly increased the urinary urate to creatinine ratio (UUA/UCRE) in pyrazinamide-treated rats although the same treatment did not produce any uricosuric effects in intact rats. In this model, the urinary excretion of pyrazinecarboxylic acid (PZA), an active metabolite of pyrazinamide, was decreased by probenecid and indicated an inverse correlation between urinary excretion of urate and PZA. Furthermore, in the examination using FYU-981, a potent uricosuric agent, a more than 10-fold leftward shift of the dose-response relationship of the uricosuric effect was observed in pyrazinamide-treated rats when compared with intact rats. In the in vitro study, the treatment of the vesicles of rat renal brush-border membrane with PZA produced an increased urate uptake, which was inhibited by uricosuric agents. The pyrazinamide-treated model used in the present study seems to be valuable for the evaluation of uricosurics because of its higher sensitivity to these drugs when compared to intact rats, and this is probably due to the enhanced urate reabsorption accompanied with trans-stimulated PZA transport at the renal brush-border membrane.

Concepts: Hypouricemia, Hyperuricosuria, Probenecid, In vitro, Gout, Uricosuric, Pharmacology, Hyperuricemia

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Despite being regarded as an easily-treatable disease, gout diagnosis and management can be challenging. We discuss here current issues in gout management and propose some potential solutions. Gout diagnosis should be reached as early as possible and often requires specific tests, such as synovial fluid analysis or imaging techniques that are not available in most centers, leaving health care professionals to rely only on clinical presentations and their experience. In addition, gout management requires the evaluation of multiple aspects, such as monitoring of serum uric acid (sUA) level (which should be reduced to <6 mg/dL) to ensure adherence and efficacy of treatment, evaluation of patient's risk profile and comorbidities, and continuous assessments to manage clinical manifestations. An important premise in gout management is non-pharmacological interventions; however, pharmacological urate-lowering therapy is crucial for an optimal control of the disease. Available options include xanthine-oxidase inhibitors (XOI), targeting uric acid overproduction, and uricosuric agents which target the predominant cause of hyperuricemia (underexcretion). Among these, lesinurad is the novel uricosuric agent to be used in combination with XOI in patients with gout not adequately controlled with XOI alone, which can further contribute to the control of hyperuricemia in gout. Multidisciplinary management is crucial for the diagnosis and treatment of gout in order to ensure treatment continuity and improve management. We therefore advise that educational activities for General Practitioners and specialists should be implemented to help raise awareness on gout diagnosis, monitoring and treatment.

Concepts: Uricosuric, Synovial fluid, Hyperuricosuria, Hypouricemia, Uric acid, Hyperuricemia, Gout

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Dual-urate lowering therapy (ULT) with xanthine oxidase inhibitor and uricosuric medications is a treatment option for severe gout. Uricosurics can cause hyperuricosuria, a risk factor for nephrolithiasis and acute uric acid nephropathy. The aims of this study were to simulate the relation between suboptimal drug adherence and efficacy, and to quantify the risk of hyperuricosuria in gout patients receiving mono and dual-ULTs.

Concepts: Xanthine, Acute uric acid nephropathy, Uricosuric, Xanthine oxidase, Hyperuricemia, Hyperuricosuria, Uric acid, Gout

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Uric acid, generated from the metabolism of purines, has both proven and emerging roles in human disease. Serum uric acid in humans is determined by production and by the net balance of reabsorption and secretion in kidney and intestine. In the human kidney, epithelial reabsorption dominates over secretion, such that in normal subjects there is at least 90% net reabsorption of filtered urate resulting in a fractional excretion of <10%. Tranilast, an anti-inflammatory drug with pleiotropic effects, has a marked hypouricemic, uricosuric effect in humans. We report here that tranilast is a potent inhibitor of [(14)C]-urate transport mediated by the major reabsorptive urate transporters (URAT1, GLUT9, OAT4, and OAT10) in Xenopus oocytes; this provides an unequivocal molecular mechanism for the drug's uricosuric effect. Tranilast was found to inhibit urate transport mediated by URAT1 and GLUT9 in a fully reversible and noncompetitive (mixed) manner. In addition, tranilast inhibits the secretory urate transporters NPT1, OAT1, and OAT3 without affecting the secretory efflux pump ABCG2. Notably, while benzbromarone and probenecid inhibited urate as well as nicotinate transport, tranilast inhibited the urate transport function of URAT1, GLUT9, OAT4, OAT10, and NPT1, without significantly affecting nicotinate transport mediated by SMCT1 (IC 50 ~1.1 mmol/L), SMCT2 (IC 50 ~1.0 mmol/L), and URAT1 (IC 50 ~178 μmol/L). In summary, tranilast causes uricosuria by inhibiting all the major reabsorptive urate transporters, selectively affecting urate over nicotinate transport. These data have implications for the treatment of hyperuricemia and gout, the pharmacology of tranilast, and the structure-function analysis of urate transport.

Concepts: Inhibitor, Uricosuric, Enzyme inhibitor, Hypouricemia, Hyperuricosuria, Hyperuricemia, Gout, Uric acid

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Gout is caused by elevated serum urate levels, which can be treated using inhibitors of the uric acid transporter, URAT1. Here, we characterize verinurad (RDEA3170), which is currently under evaluation for gout therapy. Verinurad specifically inhibits URAT1 with a potency of 25 nM. High affinity inhibition of uric acid transport requires URAT1 residues Cys-32, Ser-35, Phe-365 and Ile-481. Unlike other available uricosuric agents, the requirement for Cys-32 is unique to verinurad. Two of these residues, Ser-35 and Phe-365, are also important for urate transport kinetics. A URAT1 binding assay using radiolabeled verinurad revealed that distinct URAT1 inhibitors benzbromarone, sulfinpyrazone and probenecid all inhibit verinurad binding via a competitive mechanism. However, mutations made within the predicted transporter substrate channel differentially altered the potency for individual URAT1 inhibitors. Overall, our results suggest that URAT1 inhibitors bind to a common site in the core of the transporter and sterically hinder the transit of uric acid through the substrate channel, albeit with vastly different potencies and with differential interactions with specific URAT1 amino acids.

Concepts: Enzyme inhibitor, Xanthine oxidase inhibitor, Inhibitor, Hypouricemia, Hyperuricemia, Uricosuric, Gout, Uric acid

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The Gnaphalium affine D. Don is used in China as a folk medicine to treat gout, anti-inflammatory, antitussive and expectorant activities. The aim of this study was to evaluate the potential of the extract of G. affine to treat hyperuricemia and acute gouty arthritis in animal model.

Concepts: Xanthine oxidase inhibitor, Hypouricemia, Arthritis, Rheumatology, Uricosuric, Hyperuricemia, Uric acid, Gout

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Urate-lowering therapy is indispensable for the treatment of gout, but available drugs do not control serum urate levels tightly enough. Although the uricosurics benzbromarone and probenecid inhibit a urate reabsorption transporter known as renal urate transporter 1 (URAT1) and thus lower serum urate levels, they also inhibit other transporters responsible for secretion of urate into urine, which suggests that inhibiting URAT1 selectively would lower serum urate more effectively. We identified a novel potent and selective URAT1 inhibitor, UR-1102, and compared its efficacy with benzbromarone in vitro and in vivo. In HEK293 cells over-expressing URAT1, organic anion transporter 1 (OAT1), and OAT3, benzbromarone inhibited all transporters similarly, whereas UR-1102 inhibited URAT1 comparably to benzbromarone, but inhibited OAT1 and OAT3 quite modestly. UR-1102 at 3-30 mg/kg or benzbromarone at 3-100 mg/kg was administered orally once a day for 3 consecutive days to tufted capuchin monkeys, whose low uricase activity causes a high plasma urate level. When compared with the same dosage of benzbromarone, UR-1102 showed a better PK profile, increased the fractional excretion of urinary uric acid, and reduced plasma uric acid more effectively. Moreover, the maximum efficacy of UR-1102 was twice that of benzbromarone, suggesting that selective inhibition of URAT1 is effective. Additionally UR-1102 showed lower in vitro potential for mechanisms causing the hepatotoxicity induced by benzbromarone. These results indicate that UR-1102 achieves strong uricosuric effects by selectively inhibiting URAT1 over OAT1 and OAT3 in monkeys, and could be a novel therapeutic option for patients with gout or hyperuricemia.

Concepts: Hyperuricosuria, Hypouricemia, Tufted Capuchin, Xanthine oxidase inhibitor, Hyperuricemia, Uricosuric, Gout, Uric acid

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To explore the effect of urate transporter 1 (URAT1) polymorphisms on the hypertensive patients with hyperuricemia and the uricosuric action of losartan therapy among hypertensive patients with hyperuricemia.

Concepts: Losartan, Hypouricemia, The Transporter, Uricosuric, Hyperuricosuria, Hyperuricemia, Gout, Uric acid

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The effects of tofisopam, a GABA-receptor agonist, following oral administration (300mg) with and without allopurinol pretreatment on the plasma concentration and renal transport of uric acid and oxypurinol were investigated in 5 healthy subjects. Fractional and urinary excretions of uric acid were both significantly increased at 2-3 hours after tofisopam administration (559% and 459%, respectively), while plasma uric acid concentration was significantly decreased (36%) at 2.5 hours, suggesting that tofisopam affects uric acid metabolism via the tubular transport system. The hypouricemic effect of tofisopam was comparable to or greater than that of losartan and/or fenofibrate, which also have uric acid-lowering activity. In addition, with prior administration of allopurinol, the fractional and urinary excretions of oxypurinol were increased at 2-3 hours after tofisopam administration (51% and 33%, respectively), while the plasma oxypurinol concentration was significantly decreased at 1.5 and 2.5 hours (15% and 21%, respectively). Accordingly, tofisopam may be an attractive compound for treatment of hyperuricemia and/or gout, especially in patients complicated with autonomic dysfunction symptoms, though it is possible that the uric acid-lowering effect of oxypurinol is attenuated by tofisopam.

Concepts: Urine, Uricosuric, Hypouricemia, Kidney stone, Xanthine oxidase, Hyperuricemia, Gout, Uric acid

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Allopurinol is the most widely used urate-lowering drug (ULD). Together with efficacy and cost, safety is an aspect that helps taking clinical decisions. This systematic review analyzes allopurinol safety. The literature search was performed in MEDLINE, EMBASE, and the Cochrane Library (January 2014). Selection criteria: (a) patients >18, (b) gout by the ACR criteria or evidence of urate crystal in synovial fluid, © comparator (placebo or other ULD), and (d) RCTs, cohorts, or meta-analysis. Primary outcomes: rate of adverse events and death. The quality was assessed with the Jadad’s scale. A meta-analysis with fixed effects was performed. From 544 studies, seven met the eligibility criteria and were included. All RCT presented a low power for safety. All RCTs included a mixed population of patients with gout and hyperuricemia. Allopurinol (300 mg) was compared to febuxostat (40-240 mg) in five RCTs, to benzbromarone and probenecid in two RCTs, and to placebo in one. In the RCTs comparing allopurinol with benzbromarone and probenecid, the highest discontinuation rate was with probenecid (26 %), followed by allopurinol (11 %) and benzbromarone (4 %). The incidence of adverse events was similar between allopurinol (range 38.6-85) and febuxostat (range 41.8-80). Six patients on febuxostat and three on allopurinol died during the studies; no deaths were judged related to drug. The combined risk of adverse events was RR = 1.04 (95 % CI 0.98, 1.11). Allopurinol is a safe option, slightly better than other ULDs. The grade of evidence is high, but further research is needed to evaluate higher doses and long-term safety.

Concepts: Synovial fluid, Randomized controlled trial, Uricosuric, MEDLINE, Systematic review, Cochrane Library, Evidence-based medicine, Gout