Clinical classification of hyperuricemia in patients with chronic kidney disease.

PURPOSE: Clinical classification of hyperuricemia (HUA) could help to guide therapy of HUA. Studies on the classification of HUA with chronic kidney disease (CKD) are rare. Therefore, we aimed to investigate the classification of HUA with CKD. METHODS: A cross-sectional study of 428 CKD patients was conducted, including 218 HUA patients. By correlation analysis, the association of 24-h urinary uric acid (24-h Uur), uric acid clearance rate (Cur), the urinary uric acid excretion per kilogram of weight per hour (Eur) and fractional excretion of uric acid (FEur) with estimated glomerular filtration rate (eGFR) was analyzed in the HUA and non-HUA groups. According to Eur combined with Cur and the 24-h Uur combined with FEur, HUA with CKD was classified into underexcretion, renal overload, combined and 'normal' types, which were also stratified by CKD stages. RESULTS: According to the Eur and Cur, in early CKD (eGFR ≥ 60 mL/min/1.73 m2), the underexcretion type accounted for 83.75%, and the renal overload type accounted for 2.5%. As the CKD stage increased, the proportion of the underexcretion type increased. According to the 24-h Uur and FEur, in early CKD, the underexcretion type accounted for 53.75%, and the renal overload type accounted for 15%. With increasing CKD stages, the proportion of the 'normal' type increased significantly. CONCLUSION: Different uses of Eur with Cur or 24-h Uur with FEur varied significantly in classifying HUA patients with CKD. Eur + Cur may be more applicable to the classification of HUA patients with CKD, and further research is needed.

A clinical pharmacology study of the novel, selective urate reabsorption inhibitor dotinurad in outpatients.

BACKGROUND: Dotinurad is a novel, selective urate reabsorption inhibitor (SURI), which reduces serum uric acid levels by selective inhibition of the urate transporter 1 (URAT1). The Japanese guideline for the management of hyperuricemia and gout recommends that drug selection should be based on classification of hyperuricemia as a fundamental principle. However, there may be some cases where this principle is not observed. We investigated the pharmacodynamics and safety of dotinurad in outpatients with uric acid overproduction or uric acid underexcretion type. METHODS: This was a multicenter, open-label, forced titration study. Patients were classified as uric acid overproduction or underexcretion type. Study treatment was initiated at 0.5 mg/day, followed by dose titration to the estimated maximum dose of 4 mg/day over 14 weeks. The primary endpoint was urinary uric acid excretion at each 24-h urine collection. RESULTS: A total of 26 hyperuricemic patients with or without gout were enrolled in the study and assigned to the uric acid overproduction group (overproduction group) or the uric acid underexcretion group (underexcretion group). Although urinary uric acid excretion, the primary endpoint, tended to be slightly greater in the overproduction group, no notable difference was noted between the two hyperuricemic types. Neither type had noteworthy safety concerns associated with dotinurad. CONCLUSION: The results of the study demonstrated no relevant differences between the hyperuricemic types in terms of pharmacodynamic action and safety of dotinurad.

Dotinurad versus benzbromarone in Japanese hyperuricemic patient with or without gout: a randomized, double-blind, parallel-group, phase 3 study.

BACKGROUND: Dotinurad is a novel selective urate reabsorption inhibitor that reduces serum urate levels in hyperuricemic patients with or without gout by selectively inhibiting urate transporter 1. This study was conducted to compare the efficacy and safety of dotinurad with those of benzbromarone. METHODS: In this 14-week, randomized, multicenter, double-blind, parallel-group, dose escalation, benzbromarone-controlled, phase 3 study, hyperuricemic patients with or without gout were randomized to two groups that received either dotinurad 2 mg or benzbromarone 50 mg. Dotinurad or benzbromarone was administered once a day for 14 weeks. The primary endpoint was the percent change in serum uric acid level from the baseline to the final visit. RESULTS: A total of 201 Japanese hyperuricemic patients with or without gout (dotinurad: 102, benzbromarone: 99) received at least one dose of the study drug. The mean percent change in serum uric acid level from the baseline to the final visit in the dotinurad and benzbromarone groups was 45.9% and 43.8%, respectively. Non-inferiority of dotinurad 2 mg to benzbromarone 50 mg in lowering serum uric acid was verified by the predefined non-inferiority margin (95% CI - 1.27 to 5.37%). The incidence of adverse events and adverse drug reactions was comparable between the two groups. CONCLUSION: Dotinurad 2 mg was verified to have a non-inferior serum uric acid lowering effect compared with benzbromarone 50 mg, in Japanese hyperuricemic patients with or without gout. CLINICALTRIALS. GOV IDENTIFIER: NCT03100318.

Clinical efficacy and safety of dotinurad, a novel selective urate reabsorption inhibitor, in Japanese hyperuricemic patients with or without gout: randomized, multicenter, double-blind, placebo-controlled, parallel-group, confirmatory phase 2 study.

BACKGROUND: Dotinurad, a novel selective urate reabsorption inhibitor (SURI), reduces serum uric acid levels by selectively inhibiting urate transporter 1 (URAT1) for the treatment of hyperuricemia with or without gout. We confirmed the serum uric acid lowering effect and safety of dotinurad. METHODS: This was a confirmatory, 12-week, randomized, multicenter, double-blind, placebo-controlled, parallel-group, dose escalation, late phase 2 study. The study arms were dotinurad 0.5, 1, 2, or 4 mg and placebo. The primary endpoint was the percent change in serum uric acid level from the baseline to the final visit. The secondary endpoint was the percentage of patients achieving a serum uric acid level ≤ 6.0 mg/dL at the final visit. RESULTS: The study drugs were administered to 200 Japanese hyperuricemic patients with or without gout. The mean percent change in serum uric acid level from the baseline to the final visit in the dotinurad 0.5, 1, 2, and 4 mg groups and the placebo group was 21.81%, 33.77%, 42.66%, 61.09%, and - 2.83%, respectively. The percentage of patients achieving a serum uric acid level ≤ 6.0 mg/dL at the final visit in each group was 23.1%, 65.9%, 74.4%, 100%, and none, respectively. Regarding safety, the incidence of adverse events did not increase with dose escalation in the dotinurad groups. No significant differences were observed in the incidence of gouty arthritis in each group. CONCLUSION: The serum uric acid lowering effect and safety of dotinurad were confirmed in hyperuricemic patients with or without gout. CLINICALTRIALS. GOV IDENTIFIER: NCT02416167.

Open-label study of long-term administration of dotinurad in Japanese hyperuricemic patients with or without gout.

BACKGROUND: Dotinurad is a novel selective urate reabsorption inhibitor (SURI) which reduces serum uric acid levels by selectively inhibiting urate transporter 1 (URAT1). This study was intended to verify the efficacy and safety of dotinurad following treatment for 34 or 58 weeks in hyperuricemic patients with or without gout. METHODS: This long-term study had an open-label design with dose escalation. The dose of dotinurad started at 0.5 mg/day and was increased progressively to 2 mg/day. If the serum uric acid level of patients did not reach ≤ 6 mg/dL at week 14, the dose was increased to 4 mg/day. The primary endpoint was the percent change in serum uric acid level from the baseline to each visit. RESULTS: At a dose of 2 mg, serum uric acid levels at week 34 and 58 were reduced from the baseline by 46.73% and 47.17%, respectively; at 4 mg, the respective values were 54.92% and 57.35%. At week 34 and 58, the percentages of patients achieving a serum uric acid levels ≤ 6.0 mg/dL with 2-mg dose were 89.11% and 91.30%, respectively; with 4 mg, the respective rates were 97.50% and 100.00%. In addition, the incidences of adverse events and adverse drug reactions were 65.2% and 21.8%, respectively. CONCLUSION: Dotinurad at doses of 2-4-mg sufficiently reduced serum uric acid levels in hyperuricemic patients with or without gout, and its efficacy and safety were verified for long-term administration. ClinicalTrials.gov Identifier: NCT03006445.

The effect for hyperuricemia inpatient of uric acid overproduction type or in combination with topiroxostat on the pharmacokinetics, pharmacodynamics and safety of dotinurad, a selective urate reabsorption inhibitor.

BACKGROUND: Dotinurad, a novel selective urate reabsorption inhibitor (SURI), increases urinary uric acid excretion. The aim of this study is to examine the pharmacokinetics, pharmacodynamics, and safety of dotinurad according to the type of hyperuricemia, with or without concomitant use of xanthine oxidase inhibitor, in uric acid "overproduction type" patients. METHODS: This open-label clinical pharmacology study was conducted in a hospital. Dotinurad 1 mg was administered for 7 days to hyperuricemic patients with uric acid "overproduction type" (overproduction group, n = 6; and combination group, n = 6) and uric acid "underexcretion type" (underexcretion group, n = 6). In the combination group, topiroxostat 80 mg was used concomitantly. RESULTS: No significant differences were observed in pharmacokinetics and safety between overproduction group and underexcretion group, and the percent change in serum uric acid level and the amount of urinary uric acid excretion after administration were comparable. In "overproduction type" patients of combination group, the percent change in serum uric acid level significantly increased and the amount of urinary uric acid excretion significantly decreased compared to those of overproduction group. No clinically meaningful differences were observed in safety between the overproduction group and the combination group. CONCLUSION: In inpatients, differences in hyperuricemic type did not significantly influence the pharmacokinetics, pharmacodynamics, and safety of dotinurad. Moreover, in "overproduction type", the coadministration of dotinurad and topiroxostat had an add-on serum uric acid lowering effect and suppressed urinary uric acid excretion. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02837198.

Gout, Hyperuricaemia and Crystal-Associated Disease Network (G-CAN) consensus statement regarding labels and definitions of disease states of gout.

OBJECTIVE: There is a lack of standardisation in the terminology used to describe gout. The aim of this project was to develop a consensus statement describing the recommended nomenclature for disease states of gout. METHODS: A content analysis of gout-related articles from rheumatology and general internal medicine journals published over a 5-year period identified potential disease states and the labels commonly assigned to them. Based on these findings, experts in gout were invited to participate in a Delphi exercise and face-to-face consensus meeting to reach agreement on disease state labels and definitions. RESULTS: The content analysis identified 13 unique disease states and a total of 63 unique labels. The Delphi exercise (n=76 respondents) and face-to-face meeting (n=35 attendees) established consensus agreement for eight disease state labels and definitions. The agreed labels were as follows: 'asymptomatic hyperuricaemia', 'asymptomatic monosodium urate crystal deposition', 'asymptomatic hyperuricaemia with monosodium urate crystal deposition', 'gout', 'tophaceous gout', 'erosive gout', 'first gout flare' and 'recurrent gout flares'. There was consensus agreement that the label 'gout' should be restricted to current or prior clinically evident disease caused by monosodium urate crystal deposition (gout flare, chronic gouty arthritis or subcutaneous tophus). CONCLUSION: Consensus agreement has been established for the labels and definitions of eight gout disease states, including 'gout' itself. The Gout, Hyperuricaemia and Crystal-Associated Disease Network recommends the use of these labels when describing disease states of gout in research and clinical practice.

Gout, Hyperuricemia, and Crystal-Associated Disease Network Consensus Statement Regarding Labels and Definitions for Disease Elements in Gout.

OBJECTIVE: The language currently used to describe gout lacks standardization. The aim of this project was to develop a consensus statement on the labels and definitions used to describe the basic disease elements of gout. METHODS: Experts in gout (n = 130) were invited to participate in a Delphi exercise and face-to-face consensus meeting to reach consensus on the labeling and definitions for the basic disease elements of gout. Disease elements and labels in current use were derived from a content analysis of the contemporary medical literature, and the results of this analysis were used for item selection in the Delphi exercise and face-to-face consensus meeting. RESULTS: There were 51 respondents to the Delphi exercise and 30 attendees at the face-to-face meeting. Consensus agreement (≥80%) was achieved for the labels of 8 disease elements through the Delphi exercise; the remaining 3 labels reached consensus agreement through the face-to-face consensus meeting. The agreed labels were monosodium urate crystals, urate, hyperuric(a)emia, tophus, subcutaneous tophus, gout flare, intercritical gout, chronic gouty arthritis, imaging evidence of monosodium urate crystal deposition, gouty bone erosion, and podagra. Participants at the face-to-face meeting achieved consensus agreement for the definitions of all 11 elements and a recommendation that the label "chronic gout" should not be used. CONCLUSION: Consensus agreement was achieved for the labels and definitions of 11 elements representing the fundamental components of gout etiology, pathophysiology, and clinical presentation. The Gout, Hyperuricemia, and Crystal-Associated Disease Network recommends the use of these labels when describing the basic disease elements of gout.

Survey Definitions of Gout for Epidemiologic Studies: Comparison With Crystal Identification as the Gold Standard.

OBJECTIVE: To identify the best-performing survey definition of gout from items commonly available in epidemiologic studies. METHODS: Survey definitions of gout were identified from 34 epidemiologic studies contributing to the Global Urate Genetics Consortium (GUGC) genome-wide association study. Data from the Study for Updated Gout Classification Criteria (SUGAR) were randomly divided into development and test data sets. A data-driven case definition was formed using logistic regression in the development data set. This definition, along with definitions used in GUGC studies and the 2015 American College of Rheumatology (ACR)/European League Against Rheumatism (EULAR) gout classification criteria were applied to the test data set, using monosodium urate crystal identification as the gold standard. RESULTS: For all tested GUGC definitions, the simple definition of "self-report of gout or urate-lowering therapy use" had the best test performance characteristics (sensitivity 82%, specificity 72%). The simple definition had similar performance to a SUGAR data-driven case definition with 5 weighted items: self-report, self-report of doctor diagnosis, colchicine use, urate-lowering therapy use, and hyperuricemia (sensitivity 87%, specificity 70%). Both of these definitions performed better than the 1977 American Rheumatism Association survey criteria (sensitivity 82%, specificity 67%). Of all tested definitions, the 2015 ACR/EULAR criteria had the best performance (sensitivity 92%, specificity 89%). CONCLUSION: A simple definition of "self-report of gout or urate-lowering therapy use" has the best test performance characteristics of existing definitions that use routinely available data. A more complex combination of features is more sensitive, but still lacks good specificity. If a more accurate case definition is required for a particular study, the 2015 ACR/EULAR gout classification criteria should be considered.

Autosomal dominant tubulointerstitial kidney disease: diagnosis, classification, and management--A KDIGO consensus report.

Rare autosomal dominant tubulointerstitial kidney disease is caused by mutations in the genes encoding uromodulin (UMOD), hepatocyte nuclear factor-1ß (HNF1B), renin (REN), and mucin-1 (MUC1). Multiple names have been proposed for these disorders, including 'Medullary Cystic Kidney Disease (MCKD) type 2', 'Familial Juvenile Hyperuricemic Nephropathy (FJHN)', or 'Uromodulin-Associated Kidney Disease (UAKD)' for UMOD-related diseases and 'MCKD type 1' for the disease caused by MUC1 mutations. The multiplicity of these terms, and the fact that cysts are not pathognomonic, creates confusion. Kidney Disease: Improving Global Outcomes (KDIGO) proposes adoption of a new terminology for this group of diseases using the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' (ADTKD) appended by a gene-based subclassification, and suggests diagnostic criteria. Implementation of these recommendations is anticipated to facilitate recognition and characterization of these monogenic diseases. A better understanding of these rare disorders may be relevant for the tubulointerstitial fibrosis component in many forms of chronic kidney disease.

Uromodulin biology and pathophysiology--an update.

Uromodulin (UMOD) is a glycoprotein expressed on the luminal surface of the apical membrane of renal tubular epithelial cells forming the thick ascending limb of Henle. Here, UMOD forms filamentous structures probably ensuring water impermeability and the countercurrent gradient. The multidomain structure, cellular topology of UMOD and clinical consequences associated with UMOD dysfunction, however, suggest that it may be involved in other biological processes such as receptor-mediated endocytosis, mechanosensation of urinary flow, Wnt-signaling, cell cycle regulation and planar cell polarity. A specific, but as yet unidentified, protease(s) releases UMOD into the urine, where it probably contributes to colloid osmotic pressure, retards passage of positively charged electrolytes, prevents urinary tract infection and modulates formation of supersaturated salts and their crystals. UMOD expression, biosynthesis and excretion are regulated in a complex manner, and dysregulation is found in a wide range of pathological conditions. It is strongly reduced or absent in cases with mutations in UMOD, renin, HNF1B and other genetic disorders causing autosomal dominant hyperuricemic nephropathy. In contrast, elevated UMOD excretion may be associated with, and thus predictive of, chronic kidney disease. UMOD analysis is therefore of importance in all conditions with renal involvement and may be useful in the proper classification of renal diseases.

[Historical review of gout and hyperuricemia investigations].

Historical development of gout and hyperuricemia investigations was reviewed. Gout has been a recognized disease since the fifth century B.C. In 1683, Sydenham described the detailed clinical features of the disease based on his own condition. Leeuwenhoek (1679) first described crystals in a gouty tophus, which were identified as uric acid by Wollaston (1797). Since uric acid clearance of hyperuricemia was markedly lower than that in normal controls, early investigators considered that the main cause of hyperuricemia was urate underexcretion. However, in the 1940s, studies on uric acid metabolism using isotope tracer techniques demonstrated that a part of hyperuricemia resulted from urate overproduction, which was detected in approximately one-third of all gouty patients. In the 1970s, micropuncture, microinjection and microperfusion methods as well as stop-flow methods demonstrated that uric acid transports in nephron were suspected to consist of four steps, that were glomerular filtration, reabsorption, secretion and postsecretory reabsorption. The majority of filtrated uric acid was almost completely reabsorbed, followed by secretion and postsecretory reabsorption at a proximal site in the tubulus. Each proportion of transports to the glomerular filtration(100%) was estimated approximately 99%, 50% and 40%, respectively. Subsequently, about 10% of the filtrate was excreted in the urine. The authors (1999) suggested that the secretion rate of hyperuricemic patients was significantly lower than that of normal controls but postsecretory reabsorption was not. Therefore, the decrease in the secretion rate was suspected to be the main cause of underexcretion. Dunkan (1960) reported a family demonstrating hyperuricemia associated with severe renal damage that progressed rapidely. Currently, this disease is called familial juvenile hyperuricemic nephropathy (FJHN), and was recently found to be the result of a variation in uromodulin. Enomoto (2002) found a number of urate transporters in the cell surface of the tubulus, among which URAT1 was the most effective in reabsorbing urate from the tubulus lumen to the cells. The urate was released to the blood vessel side by the other transporter OAT. Therefore, URAT1 was suspected to be a cause of underexcretion. As the mechanism underlying overproduction of uric acid, de novo purine nucleotide synthesis has been shown to be increased. In some cases, the increase in de novo synthesis is the result of gene mutation in purine nucleotide synthesis enzymes, such as PRPP synthetase (Sperling, 1973) as well as hypoxanthine guanine phosphoribosylpyrophosphate synthetase (Seegmiller, 1967). However, the mechanism in majority of the overproduction has not yet been clarified and is currently under investigation.

[Definition and classification of hyperuricemia].

Hyperuricemia (serum urate level >7 mg/dL) is caused by accelerated generation of uric acid and/or impaired excretion in the kidney. It is classified into three types (overproduction, underexcretion and mixed types). The typical cases with the type of uric acid overproduction are hypoxanthine guanine phosphoribosyl transferase deficiency due to HPRT gene abnormality, excessive consumption of purine-rich diet, and cytolysis induced by chemotherapy for blood neoplasm, those with the type of underexcretion are familial juvenile hyperuricemic nephropathy due to uromodulin gene abnormality and abrupt body weight loss due to low calorie diet, and those with the mixed type are glucose 6-phosphatase deficiency due to glucose 6-phosphatase gene abnormality and excessive consumption of alcohol beverages.

[Primary hyperuricemia due to decreased renal uric acid excretion].

Hyperuricemia reflects extracellular fluid supersaturation for uric acid. Although dietary, genetic, or disease-related excesses in urate production underlie hyperuricemia in some cases, impaired renal excretion of uric acid is the dominant cause of hyperuricemia. This type of hyperuricemia may be primary (idiopathic) and unassociated with an identifiable disorder. Two important candidates that may affect renal urate excretion were identified recently. One is an organic anion transporter (OAT) family member called urate transporter (URAT) 1. URAT1 has highly specific urate transport activity, exchanging this anion with others including most of the endogenous organic anions and drug anions that are known to affect renal uric acid transport. Another is uromodulin (UMOD), which is the key protein for the pathogenesis of familial juvenile hyperuricemic nephropathy that is characterized by early onset of hyperuricemia and renal failure. The role of these proteins in the cause of hyperuricemia is under investigation.

[Pathophysiology and treatment of secondary hyperuricemia].

Hyperuricemia caused secondly from acquired disorders which affect production or excretion of uric acid is defined as secondary hyperuricemia. Many conditions are associated with this type of hyperuricemia and are classified into three types according to the underlying pathophysiology, including accelerated purine nucleotide degradation, ATP breakdown and purine de novo biosynthesis as overproductive type, use of drugs affecting renal urate handling and renal insufficiency as underexcretion type, or overintake of alcohol or fructose as mixed type. Determining uric acid clearance and urate excretion is important for pointing out original disorder; however, sometimes the result from correcting causal factor should be waited for to fix up a final diagnosis. Anti-hyperuricemia agents are used according to the pathophysiology.

[Uricosuric agent].

Urate lowering treatment is indicated in patients with recurrent acute attacks, tophi, gouty arthropathy, radiographic changes of gout, multiple joint involvement, or associated uric acid nephrolithiasis. Uricosuric agents like benzbromarone and probenecid are very useful to treat hyperuricemia as well as allopurinol (xanthine oxidase inhibitor). Uricosuric agents act the urate lowering effect through blocking the URAT1, an urate transporter, in brush border of renal proximal tubular cells. In order to avoid the nephrotoxicity and urolithiasis due to increasing of urinary urate excretion by using uricosuric agents, the proper urinary tract management (enough urine volume and correction of aciduria) should be performed.